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Ministegravere de lrsquoEnseignement Supeacuterieur et de la Recherche Scientifique
Universiteacute dOran
Faculteacute des Sciences
THEgraveSE DE DOCTORAT DETAT
Option Chimie Physique
Preacutesenteacutee par
LEBSIR Hayet neacutee BENDAIKHA
Intituleacutee
SYNTHESIS AND CHARACTERIZATION OF POLY (1 3 DIOXOLANE) AND ITS COPOLYMERS
STUDY OF THEIR COMPATIBILIZING EFFECT ON IMMISCIBLE BLENDS
Membres du Jury
Nom Preacutenom Grade Etablissement drsquoOrigine Qualiteacute
Krallafa Abdelghani Pr Universiteacute drsquoOran Preacutesident
Hacini Salih Pr Universiteacute drsquoOran Examinateur
Benachour Djafer Pr Universiteacute de Seacutetif Examinateur
Belhakem Mustapha Pr Universiteacute de Mostaganem Examinateur
Ould Kada Seghier Pr Universiteacute drsquoOran Directeur de Thegravese
Acknowledgements
I would like to thank my advisor Prof S OULD KADA for his help and to
express my sincere gratitude to Prof A KRALLAFA for providing continuous support
to this work His expertise guidance and understanding were a significant help
throughout my work
Very special thanks are extended to Prof Jeanne FRANCOIS for allowing me
to use instruments in her laboratory and for numerous discussions suggestions and
valuable advices which were important contribution to this research
Special thanks and deep appreciation go to Mr G CLISSON for his patience
and help with SEC and DSC measurements
I also owe my sincere appreciation to Mr A KHOUKH for his help with NMR
measurements and important comments considering NMR spectra
I want to thank gratefully Prof M BELBACHIR and Dr A TAYEB for
support and help to this work
I also owe my thanks to Prof Z BOUTIBA and Miss A HADJ BRAHIM for
optical microscopy measurements
I also owe my thanks to Dr MHAMHA and Miss S CHAOUI for Rheological
measurements
To Mr YOUSFI (ENPC-Chlef) I want to thank for Polymer supply
I acknowledge Prof S HACINI Prof D BENACHOUR and Prof M
BELHAKEM who honored me in participating in the jury of my thesis
Special gratitude to my husband FOUAD for being a continuous source of
encouragements For that I doubt I will ever be able to convey my appreciation fully
Special Thanks are also given to my mother father sisters and daughters for
moral support
TABLE OF CONTENTS ACKNOWLEDGEMENTS i SUMMARY hellipii
CHAPTER I LITERATURE REVIEW helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 1
11 Macromonomer Interest and Synthesis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 2
12 Ring-Opening Polymerization Overview helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 4
121 Polymerizability of Cyclic Compounds helliphelliphelliphelliphelliphelliphelliphelliphellip 4
122 Mechanisms of Ring-opening Polymerization helliphelliphelliphelliphelliphellip 6
123 Cationic Ring-Opening Polymerization of Heterocycles helliphellip 7
13 Cationic polymerization of cyclic acetals helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 9
14 Synthesis of functionalized poly (13-dioxolane) helliphelliphelliphelliphelliphelliphelliphelliphelliphellip 13
141 Reaction of 1 3-dioxolane and hydroxyl-containing compounds 13
142 Synthesis of Poly (13-dioxolane) macromonomers helliphelliphelliphellip 15
15 Amphiphilic Graft Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 16
151 Graft Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 16
152 Amphiphilic Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 20
16 Kinetics of Free Radical Polymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 22
161 Kinetics of free radical addition Homo and Copolymerization 22
17 Chain Growth Copolymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 31
171 Copolymerization Equations helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 31
172 Determination of Reactivity Ratios helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 37 18 Controlled Radical Polymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 42
181 Fundamentals of ControlledLiving
Radical Polymerization (CRP) helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 43
182 Typical Features of ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 44
183 Controlled Compositions by ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 46
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 49
CHAPTER II Synthesis and Characterization of Macromonomers 54
21 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 54
22 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
221 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
222 Synthesis of Poly (13-dioxolane) Macromonomers helliphelliphelliphellip 57
223 Synthesis of Poly (13-dioxolane) Hydrogel Network helliphelliphellip 57
23 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
231 Raman Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
232 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
233 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
234 Swelling Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
235 Rheological Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
24 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
241 Structural Characterization of Macromonomers helliphelliphelliphelliphellip 59
242 Molecular Weight Determination helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62
243 Swelling of Poly (13 Dioxolane) Hydrogel helliphelliphelliphelliphelliphelliphellip 63
244 Viscoelastic Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 64
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 67
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 68
CHAPTER III Synthesis and Characterization of Copolymers 69
31 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 69
32 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
321 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
322 Synthesis of Poly (Styrene-g-Poly (1 3-dioxolane)) helliphelliphelliphellip 71
323 Synthesis of Poly (Methyl Methacrylate-g-Poly (1 3-dioxolane))76
33 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
331 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
332 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
333 Diffraction Scanning Calorimetry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
34 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 78
341 Structural Characterization of the Copolymers helliphelliphelliphelliphellip 78
342 Molecular Weight Determination and Copolymer Composition 80
343 Determination of Monomer Reactivity Ratios helliphelliphelliphelliphelliphellip 84
344 Glass Transition Temperatures helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 89
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 93
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
41 Background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
411 Physical Blends helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
412 Equilibrium Phase Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
413 Compatibilization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 97
414 Incorporation of Copolymers for Compatibilization helliphelliphellip 98
415 The Effect of Compatibilizer on a Blend helliphelliphelliphelliphelliphelliphelliphellip 99
416 Methods of Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 100
42 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
421 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
422 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
43 Characterization Techniques for Compatibilization helliphelliphelliphelliphelliphelliphelliphellip 102
431 Dilute Solution Viscometric Measurements helliphelliphelliphelliphelliphelliphellip 102
432 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
433 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
44 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
441 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphellip 104
442 Study of Compatibilization by Dilute Solution Viscometry hellip 106
443 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 116
444 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 118
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 124
References helliphelliphelliphelliphelliphellip helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 125
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g- Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
51 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 127
52 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
521 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
522 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
53 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
531 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
532 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
533 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
54 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
541 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphelliphellip 129
542 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 131
543 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 136
544 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 137
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 144
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 145 CONCLUSIONS helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 146
SUMMARY
Research and development performed on synthetic polymers during the last century has led to
many classes of different polymers for specific applications New types of synthetic polymers
with tailor-made properties are still being introduced for new applications The challenge for
polymer chemists is to control and alter the polymerization conditions such that the final
product has a well-defined structure with desired properties The complex structure of
polymers requires continued analytical chemical efforts to understand the polymerisation
process and the relationships between the molecular structure and material properties
The central point of this thesis is the synthesis and the exploration of the benefits of graft
copolymers derived from poly (1 3 dioxolane) (PDXL) as compatibilizing agents via their
incorporation in immiscible polymer blends The enhancement of adhesion in the solid state
can be accomplished by introducing a compatibilizer that can act as an adhesive between two
polymers andor by control of morphology especially by inducing the phase co-continuity
Graft copolymers offer all Properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheological control i e it
leads to decreased melt viscosities which is an important advantage for processing Depending
on the nature of their backbone and side chains they can be used for a wide variety of
applications such as impact-resistant plastics thermoplastic elastomers polymeric
emulsifiers and even more exciting is the ability of these graft copolymers to function as
compatibilizersinterfacial agents to blends immiscible polymers
The state-of-the-art technique to synthesize graft copolymers is the copolymerization of
macromonomers with low molecular weight comonomers It allows the control of the
polymeric structure which is given by three parameters (i) chains length of the side chains
which can be controlled by the synthesis of macromonomers by living polymerization (ii)
chain length of the backbone which can be controlled in a living polymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular-weight monomer
i
New properties lower prices and reuse of polymers are needed to meet demands of todayrsquos
society and hence of the polymer industry Unfortunately the demands for many applications
need a set of properties that no polymers can fulfil One method to satisfy these demands is by
mixing two or more polymers Materials made from two polymers mixed are called blends In
recent years blending of polymers as a means of combining the useful properties of different
materials to meet new market applications with minimum development cost offers an
interesting route to improve a variety of specific properties of the thermoplastics This has
been increasingly used by the polymer industry
Much work has been done on the blending (mixing) of polymers by many authors A large
part of these studies deal with attempts to obtain a combination of properties of different
polymers Unfortunately these properties of the polymer blends are usually worse instead of
better for many combinations of polymers Significance for these properties is compatibility
between the different polymers which is frequently defined as miscibility on a molecular scale
of the blends components The incorporation of a dispersed phase into a matrix mostly leads
to the presence of stress concentrations and weak interfaces arising from poor mechanical
coupling between phases and therefore morphologies with coarseness commonly on
micrometer scale are obtained Improving mechanical and morphological properties of an
immiscible blend is often done by compatibilization which is a process of modification of the
interfacial properties in immiscible polymer blend resulting in reduction of the interfacial
tension coefficient formation and stabilisation of the desired morphology The use of graft or
block copolymers as compatibilizers for immiscible polymer blends has become an efficient
means for development of new high-performance polymer materials There have been
numerous techniques of studying the miscibility of the polymeric blends The most useful
techniques are viscosimetry measurementsiiiiii thermal analysisiv dynamic mechanical
analysisv refractive indexvi nuclear magnetic resonance methodvii scanning electronviii and
optical spectroscopyix
i Z Sun W Wang and Z Fung Eur Polym J 28 (1992) 1259 ii Aroguz AZ and Baysal BM Eur Polym J42 3 (2006) 11ndash5iii Zhang Y Qian J Ke Z Zhu X Bi H and Nie K Eur Polym J 38 (2002) 333ndash7 iv M Song and F Long Eur Polym J 27 (1991) 983 v Olabisi O Rebeson LM and Shaw MT Polymerndashpolymer miscibility New York Academic Press (1979) vi AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 vii EG Crispim ITA Schuquel AF Rubira and EC Muniz Polymer 41 (3) (2000) 933 viii Martin IG Roleister KH Rosenau R and Koningsveld RJ Polym Sci Part B Polym Phys24 (1986) 723 ix W Wu X Luo D Ma Eur Polym J 35 (1999) 985
ii
Well-known examples of commercial blends are high impact polystyrene (HIPS) and
acrylonitrile-butadiene-styrene (ABS) These blends are tough and have good processability
One of the most interesting examples of an amorphous polymer is polystyrene because of its
brittleness Adding a compatibilizer with the structure of a copolymer to
Polystyrenepolyethylene (PSPE) improves the toughness by a factor 3x Another example is
the use of poly (styrene-co-methacrylic acid) as a compatibilizer in immiscible (incompatible)
blends of PS and polyethylene (PEG)xi
It is of great interest to study miscibility and phase behaviour of two different commodity
immiscible polymer blend systems as PSPEG and polymethyl methacrylate polyethylene
glycol (PMMAPEG) by adding poly (styrene-g-PDXL) and poly (methyl methacrylate-
PDXL) copolymers as compatibilizers respectively Firstly these systems consist of a very
rigid amorphous component (styrene andor PMMA) and a very flexible low-melting point
PEG The extremely high difference of glass transition temperatures (Tg) between the
components motivates us to investigate the phase behaviour of the blends via
compatibilization with prepared grafted copolymers
The first part of the thesis is devoted to the synthesis and characterization of amphiphilic graft
copolymers which were prepared in solution by radical polymerization of hydrophilic poly (1
3 dioxolane) macromonomers as side chains and hydrophobic comonomers such as styrene
and methyl methacrylate as backbone The second part of the thesis describes the blends
preparation and the study of the compatibilization effect of the incorporated amphiphilic graft
copolymers on immiscible (incompatible) blends
The research work in this thesis is presented through several chapters described as follows
Chapter I is a bibliographic survey on polymerization reactions involved in the thesis
Literature concerning the poly (1 3 dioxolane) was included
Chapter II describes the synthesis of poly (1 3 dioxolane) macromonomers and their
characterization As an aside research poly (1 3 dioxolane) network was obtained and the
x E Kroeze thesisUniversity of Groningen (1997) xi Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polym Journal 37 (2001) 1837-1842
iii
swelling and rheological behaviours of this network were discussed and included in this
chapter
Chapter III deals with the synthesis of a series of amphiphilic graft copolymers based on
polystyrene and methyl methacrylate as backbone with poly (1 3 dioxolane) macromonomers
as grafts in this study Selection of proper reaction conditions in terms of overall monomer
concentration and monomer molar ratio were investigated in order to prevent crosslinking
reactions due to the presence of bis-functional poly (1 3 dioxolane) macromonomers
The structure and composition of the graft copolymers were determined by Size Exclusion
Chromatography (SEC) technique and Proton Nuclear Magnetic Resonance (1H-NMR)
analysis Also Modulated Temperature Differential Scanning Calorimeter (MTDSC) was used
for thermal analysis to study the influence of poly (1 3 dioxolane) content on the glass
transition temperature of the copolymers
Last but not the least Chapter IV and Chapter V deal with the most important part of the
thesis which is the study of the compatibilization effect of the prepared copolymers
incorporated in two different immiscible blend systems These two chapters describe first
the polymers used as blend components and also polyblends preparation was discussed The
phase behavior and compatibilization of these polyblends were studied at a composition
of 5050 for both PSPEG and PMMAPEG systems Various amounts of copolymers were
incorporated to the so-called blends for compatibilization The techniques used for this study
were optical microscopy (OM) to analyze their morphology and Fourier-Transform Infra-Red
(FTIR) spectroscopy used to detect the intermolecular interactions in the blends In addition
viscometric method which is a simple inexpensive and sensitive analytical technique and also
alternative to other methods was used The application of the dilute-solution viscosity (DSV)
method for the study of interactions and miscibility of the polymeric system has been
described in more details in these chapters
Conclusions have been made on copolymer characterizations in terms of mostly monomer
reactivity and indeed on compatibilizing effect of these copolymers on the selected polymer
blends This study provides interesting results which can be useful for the development
nanoporous materials
iv
REacuteSUMEacute
La recherche et le deacuteveloppement faits sur des polymegraveres syntheacutetiques pendant le dernier siegravecle
ont abouti agrave plusieurs types de polymegraveres pour des applications speacutecifiques Les nouveaux
polymegraveres syntheacutetiques avec des proprieacuteteacutes faites sur mesure sont toujours introduits pour de
nouvelles applications Le deacutefi pour les chimistes en polymegraveres est de controcircler et drsquoalteacuterer les
conditions de polymeacuterisation de telle sorte que le produit final ait une structure bien deacutefinie avec
des proprieacuteteacutes souhaiteacutees La structure complexe de polymegraveres exige des efforts continus en
chimie analytique pour comprendre le processus de polymeacuterisation et les relations entre la
structure moleacuteculaire et les proprieacuteteacutes des mateacuteriaux
Le centre drsquointeacuterecirct de cette thegravese est la synthegravese et lexploration des avantages des copolymegraveres
greffeacutes deacuteriveacutes agrave partir du poly (1 3 dioxolane) (PDXL) utiliseacutes comme agents compatibilisant
via leur incorporation dans des meacutelanges de polymegraveres non miscibles Lrsquoameacutelioration drsquoadheacutesion
agrave lrsquoeacutetat solide peut ecirctre accomplie en introduisant un compatibilisant qui peut agir comme un
adheacutesif entre deux polymegraveres et ou par le controcircle de la morphologie particuliegraverement en
incitant la co-continuiteacute des phases Les copolymegraveres greffeacutes offrent toutes les proprieacuteteacutes des
copolymegraveres en blocs mais sont toujours plus facile agrave syntheacutetiser De plus la structure ramifieacutee
offre des possibiliteacutes importantes dans le controcircle rheacuteologique cest-agrave-dire elle aide la
diminution de la viscositeacute qui est un avantage important pour la transformation Selon la nature
de la chaicircne principale et des chaicircnes lateacuterales ces copolymegraveres peuvent ecirctre employeacutes pour une
grande varieacuteteacute drsquoapplications comme plastiques reacutesistants au choc elastomers thermoplastiques
des polymegraveres eacutemulsifiants et mecircme plus inteacuteressant est la possibiliteacute de ces copolymegraveres greffeacutes
de fonctionner comme compatibilisant agents drsquointerface aux meacutelanges des polymegraveres non
miscibles
La technique la plus sophistiqueacutee pour syntheacutetiser les copolymegraveres greffeacutes est la
copolymeacuterisation de macromonomegraveres avec des comonomegraveres agrave faible masse moleacuteculaire Elle
permet le controcircle de la structure polymeacuterique par trois paramegravetres (i) la longueur des chaicircnes
lateacuterales qui peut ecirctre controcircleacutee par la synthegravese de macromonomegraveres par la polymeacuterisation
v
vivante (ii) la longueur de chaicircne principale qui peut ecirctre controcircleacutee dans une polymeacuterisation
vivante (iii) espacement moyen des chaicircnes lateacuterales qui est deacutetermineacute par le rapport molaire des
comonomegraveres et taux de reacuteactiviteacute du monomegravere agrave faible masse moleacuteculaire
De nouvelles proprieacuteteacutes des prix bas et la reacuteutilisation de polymegraveres sont neacutecessaires pour
reacutepondre aux demandes de la socieacuteteacute daujourdhui et agrave lindustrie de polymegraveres
Malheureusement ces demandes pour un grand nombre drsquoapplications ont besoin dun jeu de
proprieacuteteacutes quaucun polymegravere ne peut accomplir Une meacutethode de satisfaire ces demandes est en
meacutelangeant deux polymegraveres ou plus Les mateacuteriaux obtenus agrave partir de meacutelanges de deux
polymegraveres meacutelangeacutes sont appeleacutes meacutelanges (Blends) Ces derniegraveres anneacutees le meacutelange de
polymegraveres comme moyen de combiner les proprieacuteteacutes utiles de diffeacuterents mateacuteriaux pour
rencontrer un marcheacute de nouvelles applications agrave un coucirct minimal offre un itineacuteraire inteacuteressant
pour ameacuteliorer une varieacuteteacute des proprieacuteteacutes speacutecifiques des polymegraveres thermoplastiques Cela a eacuteteacute
de plus en plus employeacute par lindustrie des polymegraveres
Beaucoup de travaux ont eacuteteacute faits par plusieurs auteurs sur le meacutelange de polymegraveres Une grande
partie de ces eacutetudes sont dirigeacutees pour obtenir une combinaison des proprieacuteteacutes de diffeacuterents
polymegraveres Malheureusement ces proprieacuteteacutes des meacutelanges de polymegravere sont souvent plus
mauvaises que preacutevues pour la plupart des combinaisons de polymegraveres La signification de ces
proprieacuteteacutes est la compatibiliteacute entre les diffeacuterents polymegraveres qui est freacutequemment deacutefinie comme
la miscibiliteacute agrave lrsquoeacutechelle moleacuteculaire des composants du meacutelange Lincorporation dune phase
disperseacutee dans une matrice provoque surtout la preacutesence de contraintes et des interfaces faibles
qui reacutesultent du faible meacutelange meacutecanique entre les deux phases Lameacutelioration des proprieacuteteacutes
meacutecaniques et morphologiques dun meacutelange non miscible est souvent faite par compatibilisation
qui est un processus de modification des proprieacuteteacutes superficielle dans les meacutelanges de polymegraveres
non miscibles aboutissant agrave la reacuteduction du coefficient de tension superficielle la formation et
stabiliteacute de la morphologie deacutesireacutee Lutilisation des copolymegraveres greffeacutes ou agrave blocs comme
compatibilisant pour des meacutelanges de polymegraveres non miscibles est devenue un moyen efficace
pour le deacuteveloppement de nouveaux mateacuteriaux plus performant Il y a eu de nombreuses
techniques pour lrsquoeacutetude de la miscibiliteacute des meacutelanges polymeacuteriques Les techniques les plus
vi
utiles sont les mesures viscomeacutetriques analyses thermiques analyses meacutecaniques indice de
reacutefraction la reacutesonance magneacutetique nucleacuteaire microscopes optique et eacutelectroniques agrave balayage
Les exemples de meacutelanges commerciaux tregraves bien connus sont le polystyregravene choc (HIPS) et
acrylonitrile-butadiene-styrene (ABS) Ces meacutelanges sont durs et ont bon processability Un
exemple de polymegraveres amorphes le plus inteacuteressant est le polystyregravene agrave cause de sa fragiliteacute
Laddition dun compatibilisant ayant la structure dun copolymegravere au meacutelange de Polystyregravene
polyeacutethylegravene (PSPE) ameacuteliore la dureteacute par un facteur de 3 Un autre exemple est lutilisation du
poly (styrene-co-acide meacutethacrylique) comme compatibilisant dans les meacutelanges non miscibles
de PS et le poly (eacutethylegravene glycol)
Il est tregraves important drsquoeacutetudier la miscibiliteacute et le comportement des phases de deux diffeacuterents
meacutelanges de polymegraveres commerciaux non miscibles (incompatibles) comme le
polystyregravenepolyeacutethylegravene glycol (PSPEG) et le polymeacutethacrylate de meacutethylepolyeacutethylegravene glycol
(PMMAPEG) en incorporant des copolymegraveres tels que (styrene-g-PDXL) et de (meacutethacrylate de
meacutethyle-PDXL) comme compatibilisant respectivement Premiegraverement lrsquoun des composants de
ces systegravemes est amorphe et tregraves rigide (le styregravene etou PMMA) et lrsquoautre (PEG) est flexible et
mou ayant un point de fusion tregraves faible Vu lrsquoextrecircme eacutecart entre les deux tempeacuteratures de
transition vitreuse (Tg) des composants de ces meacutelanges cela nous a motiveacute pour eacutetudier le
comportement de ces meacutelanges via compatibilisation avec des copolymegraveres greffeacutes preacutepareacutes par
nous mecircme
La premiegravere partie de la thegravese est consacreacute agrave la synthegravese et agrave la caracteacuterisation de copolymegraveres
greffeacutes amphiphiles preacutepareacutes en solution par la polymeacuterisation radicale des macromonomers
(poly (1 3 dioxolane)) hydrophiles comme des chaicircnes lateacuterales (greffons) avec des
comonomegraveres hydrophobes comme le styregravene et le meacutethyle methacrylate comme chaicircne
principale La deuxiegraveme partie de la thegravese couvre la preacuteparation des meacutelanges et leacutetude de leffet
de compatibilisant des copolymegraveres greffeacutes amphiphiles sur les meacutelanges non miscibles
(incompatibles)
La recherche concernant cette thegravese est preacutesenteacute par plusieurs chapitres deacutecrits comme suit
vii
Le chapitre I est une recherche bibliographique sur les reacuteactions de polymeacuterisations impliqueacutees
dans la thegravese La Litteacuterature concernant le poly (1 3 dioxolane) est inclue
Le chapitre II deacutecrit la synthegravese des macromonomegraveres du poly (1 3 dioxolane) et leurs
caracteacuterisations Une recherche suppleacutementaire a eacuteteacute effectueacutee concernant la synthegravese drsquoun reacuteseau
tridimensionnel du poly (1 3 dioxolane) Une eacutetude sur les comportements gonflant et
rheacuteologique de ce reacuteseau ont eacuteteacute discuteacutes et inclus dans ce chapitre
Le chapitre III preacutesente la synthegravese dune seacuterie de copolymegraveres greffeacutes amphiphiles constitueacutes de
polystyregravene ou methacrylate de meacutethyle comme chaicircne principale et de macromonomers du poly
(1 3 dioxolane) comme greffons dans cette eacutetude Le choix de conditions de reacuteaction approprieacutees
en termes de concentration totale et le rapport molaire des monomegraveres ont eacuteteacute bien eacutetudieacutes pour
empecirccher les reacuteactions de reacuteticulation agrave cause de la preacutesence de macromonomegraveres bis-
fonctionnel de poly (1 3 dioxolane)
La structure et la composition des copolymegraveres greffeacutes ont eacuteteacute deacutetermineacutees par la technique de la
Chromatographie dExclusion steacuterique (CES) et la spectroscopie en Reacutesonance Magneacutetique
Nucleacuteaire de Proton (1H-NMR) Aussi la Calorimeacutetrie Diffeacuterentielle agrave balayage agrave Temperature
Moduleacutee Calorimeacutetrie (MTDSC) a eacuteteacute employeacute pour lanalyse thermique et pour eacutetudier
linfluence de la proportion du poly (1 3 dioxolane) dans les copolymegraveres sur leur tempeacuterature
de transition vitreuse
Derniers mais pas le moindre les deux Chapitre IV et le Chapitre V couvrent la partie la plus
importante de la thegravese qui est leacutetude de leffet de compatibilisant de ces copolymegraveres preacutepareacutes et
incorporeacutes dans deux diffeacuterents systegravemes de meacutelanges non miscibles (incompatibles) Ces deux
chapitres deacutecrivent dabord les polymegraveres employeacutes comme composants des meacutelanges agrave eacutetudier et
aussi la preacuteparation de ces meacutelanges a eacuteteacute deacutecrite Le comportement de phase et la
compatibilisation des meacutelanges de PSPEG et PMMAPEG agrave une composition de 5050 Des
quantiteacutes diffeacuterentes de copolymegraveres ont eacuteteacute incorporeacutees aux meacutelanges Les techniques
employeacutees pour cette eacutetude sont la microscopie optique (OM) pour analyser leur morphologie et
la spectroscopie agrave Transformeacutee de Fourier Infrarouge (FTIR) pour deacutetecter les interactions
viii
intermoleacuteculaires dans les meacutelanges De plus la meacutethode viscomeacutetrique qui est une technique
simple peu coucircteuse et tregraves sensible a eacuteteacute employeacutee Lrsquoutilisation de la meacutethode de la viscositeacute de
solution dilueacutee (DSV) pour leacutetude dinteractions et la miscibiliteacute du systegraveme polymegravere a eacuteteacute
deacutecrite plus en deacutetail dans ces chapitres
Les conclusions ont eacuteteacute faites sur la caracteacuterisation des copolymegraveres en termes de surtout de la
reacuteactiviteacute des monomegraveres et bien entendu sur leffet compatibilisant de ces copolymegraveres sur les
meacutelanges de polymegraveres qui ont choisis Cette eacutetude fournit des reacutesultats inteacuteressants qui peuvent
ecirctre utiles pour le deacuteveloppement des mateacuteriaux nanoporeux
ix
CHAPTER I Literature Review
11 Macromonomer Interest and Synthesis
Macromonomers bearing polymerizable end groups have received considerable interest
during the last two decades and become a useful tool for the preparation of a variety of graft
copolymers with well-defined structure and composition and polymer networks The
macromonomer method for preparing graft copolymers consists of preparing branches first
followed by the preparation of the grafted structure through the addition of the comonomer to
the macromonomer branch1 2
Therefore macromonomers become the side chains in the graft copolymer with well-defined
length and molecular weight As a sequence the molecular structure of the copolymer can be
determined depending on the amount of macromonomer incorporated and the reactivity of the
end groups
Macromonomers which are linear macromolecules carrying polymerizable functions at one or
two chain ends have been prepared by all polymerization mechanisms anionic cationic free-
radical polyaddition and polycondensation while the polymerizable end groups have been
introduced during the initiation termination or chain transfer steps or by modification of end
groups of telechelic oligomers3
Among the polymerization mechanisms mentioned above the ionic ones allow the best
control of molecular weight polydispersity and functionality of the macromonomers
However they require very demanding experimental conditions like high purity of monomers
and solvents complete absence of moisture and other acidic impurities inert atmosphere etc
Whereas free-radical methods which involve less severe working conditions are largely
used even though the control over the properties of the macromonomers is lower3 For
instance polymers of epoxides tetrahydofuran and cyclic siloxanes are commercially
produced by cationic ring-opening polymerization The history of ring-opening
polymerization of cyclic monomers is shorter than that of the vinyl polymerization and
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422
1
polycondensation With ring-opening functional groups can be introduced into the main chain
of the polymer This polymer cannot be prepared by vinyl polymerization4
Milkovich first developed synthesis of graft polymer with uniform grafts via macromonomer
technique5 Schulz and Milkovich6 reported the synthesis of polystyrene macromonmers
through termination of living PS anions with methacryloyl chloride and their
copolymerization with butyl acrylate and ethyl acrylate
Candau Rempp et al7 obtained PS-g-PEO by reaction between living monofunctional PEO
and partly chloromethacrylated PS backbone (scheme 1) Characterization of the products by
light scattering GPC UV and NMR spectroscopy showed a high degree of grafting
Scheme 1
Ito et al8 used a macromonomer technique to obtain graft copolymers with uniform side
chains They synthesized a graft copolymer of PS with uniform PEO side chains through
copolymerization of styrene and PEO macromonomer (scheme 2) They obtained PEO
macromonomers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-
vinyl benzyl chloride as terminating agent An apparent decrease in reactivities of both poly
(ethylene oxide) of macromonomers and comonomers was ascribed to the thermodynamic
repulsion between the macromonomer and the backbone9
4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348
2
Scheme 2
This type graft copolymers of styrene and ethylene oxide was also obtained by Xie et al10
through copolymerization of styrene with PEO macromonomer prepared by anionic
polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydofuran as
initiator followed by termination with methacryloyl chloride
The method of macromonomer synthesis developed by Xie et al11 has the advantage of
shorter reaction time and a larger range of molecular weight of the PEO macromonomer than
the usual method using potassium alcoholate as initiator PEO macromonomers with
molecular weight from 2 103 to 3 104 and MwMn = 107 ndash 112 can be obtained by this
method12
Only Xie and coworkers have published reports concerning the synthesis of copolymers with
uniform PS grafts obtained through copolymerization of epoxy ether terminated polystyrene
macromonomer with EO13 using a quaternary catalyst composed of triisobutyl-aluminium-
phosphoric acid-water-tertiary amine14 and epichlorohydrin (ECH)15
Free radical polymerization technique has also provided well-defined macromonomers of
poly (acrylic acid)16 vinyl benzyl-terminated polystyrene17 18 poly (t-butyl methacrylate)19
and poly (vinyl acetate)20
Recently Matyjaszewski et al21 employed atom-transfer radical polymerization (ATRP) to
prepare well-defined vinyl acetate terminated PS macromonomers Taking advantage of the
10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp (1985) 461 Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823
3
extremely low reactivity of polystyryl radical towards the vinyl acetate double bond they
used vinyl chloroacetate to initiate the polymerization of styrene to produce the desired
macromonomers This concept has been used similarly in the preparation of a vinyl acetate-
terminated PS macromonomers3 by conventional free-radical polymerization by employing
vinyl iodoacetate as a chain transfer agent possessing a double bond which does not
copolymerize with the monomer that forms the backbone of the macromonomer
12 Ring-Opening Polymerization Overview
Ring-opening polymerization (ROP) is a unique polymerization process in which a cyclic
monomer is opened to generate a linear polymer It is fundamentally different from a
condensation polymerization in that there is no small molecule by-product during the
polymerization Polymers with a wide variety of functional groups can be produced by ring-
opening polymerizations Ring-opening polymerization can proceed through a number of
different mechanisms depending on the type of monomer and catalyst involved Of the wide
range of polymers produced via ROP some have gained industrial significance for example
poly (caprolactam) and poly (ethylene oxide)22 ROP of cyclic esters such as ε-caprolactone
(CL) and L L-dilactide is gaining industrial interest due to their degradability23 The
mechanisms of interest in this work are coordination insertion and cationic
121 Polymerizability of Cyclic Compounds
The thermodynamic polymerizability of a cyclic monomer has been elegantly summarized by
Ivin24 Negative free energy change from monomer to polymer is the thermodynamic driving
force for the ring-opening
ΔG = ΔH ndash T ΔS
For small sized cyclic compounds the enthalpy term is negative and dominant The strains in
bond angles and bond lengths are released upon ring opening Such monomers can be almost
completely converted to polymers For medium sized cyclic monomers (5-7 membered rings)
the ring strain is small and the entropy is a small positive term Thus the overall driving force
(ΔG) is small and the extent of polymerization is little or no reaction For 8- 9- and 10-
22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991)
4
membered monomers the enthalpy term is dominant and negative while the TΔS term is
relatively small The strain is due to the non-bonded interactions between atoms Essentially
complete conversion to polymer is possible When the ring size is very large and there is
virtually no ring-strain (ΔH ne 0) the driving force for ring-opening polymerization is the
large increase of entropy The polymerization should be an athermal process
Why not make polyethylene
In principle one could synthesize polyethylene from cyclohexane
There are two good reasons why this reaction cannot be performed
bull (Kinetic) Cyclohexane lacks any reactive functionality to get hold of
bull (Thermodynamic) Simple six membered rings are extremely stable
Free Energy (ΔG) of Polymerization for Cycloalkanes
The thermodynamic considerations for ring opening are illustrated by this graph (scheme 3) of
free energy (hypothetical) of polymerization from cycloalkanes with various ring sizes to
polyethylene (The two membered ring actually shows the data for ethylene CH2 = CH2)
Scheme 3
5
Three and four membered rings are quite strained so ring opening to polyethylene is
favorable if a suitable reaction pathway existed (Unfortunately no such reaction is known)
Six membered rings are stable so they can rarely be polymerized by ring opening Five and
seven membered rings are borderline cases so sometimes these can be polymerized Larger
rings have transanular steric interactions that cause some strain so rings of 8 members or
more can usually be polymerized Of course this graph changes when substitutions are made
to the rings (for example the presence of heteroatoms like O S and N or the introduction of
double bonds) However the graph for the simplest possible rings illustrates the trends in
other systems reasonably well
Even if the ring opening reaction is thermodynamically favorable there must be reaction
chemistry to get there In most cases the initiators used for ring opening polymerization are
polar or ionic species so the monomers must have groups that can react The most common
monomers for ring opening polymerization contain some kind of heteroatom in the ring as in
the examples of cyclic ethers esters amines amides etc At one extreme there are examples
such as the cyclic phosphazene shown that contain no carbon or hydrogen at all At the other
extreme just a carbon-carbon double bond will suffice for ring opening metathesis
polymerization as illustrated by norbornene
122 Mechanisms of Ring-opening Polymerization
In addition to the thermodynamic criterion there must be a kinetic pathway for the ring to
open and undergo the polymerization reaction Therefore the kinetics of the ring-opening of
the monomer should also be considered Ring-opening polymerization (ROP) can proceed
through a number of different mechanisms depending on the type of monomer and catalyst
involved Of the wide range of polymers produced via ROP some have gained industrial
significance for example poly (caprolactam) and poly (ethylene oxide)24 25 A variety of
mechanisms operate for ring-opening polymerizations including anionic cationic metathesis
and free radical mechanisms Examples of various ring-opening polymerizations are shown in
scheme 4
25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984)
6
Scheme 4
123 Cationic Ring-Opening Polymerization of Heterocycles
A broad range of heterocyclic compounds can undergo cationic ring-opening polymerization
(CROP)26 CROP propagates either through an activated monomer or an activated chain end
mechanism In both cases the propagation involves the formation of a positively charged
species27 A major drawback of CROP is the occurrence of unwanted side reactions thus
limiting the molecular weight of the final product2829 The cationic ring-opening
polymerization of heterocycles has become of significant importance in polymer synthesis
due in part to the diverse variety of functionalized materials that can be prepared by this
method including natural andor biodegradable polymers30 31
Systematic studies of this type of polymerization started around the nineteen sixties Since
then several groups are involved in the kinetics reaction mechanisms and thermodynamics of
the ring-opening polymerization mostly of tetrahydofuran and dioxolane During the last
26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996) (b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993) (c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice (d) Mishra M K Ed Polymer Frontiers New York (1994) 391 31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159
7
years many papers on the synthesis and polymerization of several other cyclic ethers
monocyclic and bicyclic acetals have been published32 33
Examples of commercially important polymers which are synthesized via ring-opening
polymerization are summarized in scheme 5 include such common polymers as
polyoxyethylene (POE 4) poly (butylene oxide) (PBO 5) nylon 6 (6) and poly
(ethyleneimine) (7)
Scheme 5
The synthesis of ring-opened heterocycles is often mediated by compounds whose role is to
initiate the polymerization process This provides less opportunity to ldquotunerdquo polyheterocycle
properties through catalyst choice and has stimulated research to develop initiators which
function beyond the simple activation of polymerization such as living polymerization
initiators343536 chiral initiators3738 enzyme initiators39 and ring-opening insertion
systems4041 The cationic ring-opening polymerization involves the formation of a positively
32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N Macromolecules 26 (1993) 7134
8
charged species which is subsequently attacked by a monomer The attack results in a ring-
opening of the positively charged species Ethylene oxide can be polymerized by cationic
initiators as well (scheme 6)
Scheme 6
13 Cationic Polymerization of Cyclic Acetals
Acetal polymers also known as polyoxymethylene (POM) or polyacetal are formaldehyde-
based thermoplastics that have been commercially available for over 40 years
Polyformaldehyde is a thermally unstable material that decomposes on heating to yield
formaldehyde gas Two methods of stabilizing polyformaldehyde for use as an engineering
polymer were developed and introduced by DuPont in 1959 and Celanese in 1962
DuPonts route for polyacetal yields a homopolymer through the condensation reaction of
polyformaldehyde and acetic acid (or acetic anhydride)
The Celanese route for the production of polyacetal yields a more stable copolymer product
via the reaction of trioxane a cyclic trimer of formaldehyde and a cyclic ether (eg ethylene
oxide or 13 dioxolane)
9
The improved thermal and chemical stability of the copolymer versus the homopolymer is a
result of randomly distributed oxyethylene groups These groups offer stability to oxidative
thermal acidic and alkaline attack The raw copolymer is hydrolyzed to an oxyethylene end
cap to provide thermally stable polyacetal copolymer Polyacetals are subject to oxidative and
acidic degradation which leads to molecular weight deterioration Once the chain of the
homopolymer is ruptured by such an attack the exposed polyformaldehyde ends decompose
to formaldehyde and acetic acid Deterioration in the copolymer ceases however when one
of the randomly distributed oxyethylene linkages is reached42
Cationic polymerization of cyclic acetals exhibits some special features which makes this
system distinctly different from cationic polymerization of simple heterocyclic monomers for
instance cyclic ethers Linear acetals (including polyacetals) are more basic (nucleophilic)
than cyclic ones thus when polymer starts to form it does not constitute a neutral component
of the system but participates effectively in transacetalization reactions which lead to
redistribution of molecular weights and formation of a cyclic fraction These processes which
are usually described by the term ldquoscramblingrdquo have been studied by several authors43 44
Cationic polymerizations of heterocyclic monomers are initiated as in cationic
polymerization of vinylic monomers by electrophilic agents such as the protonic acids (HCl
H2SO4 HClO4 etc) Lewis acids which are electron acceptors by definition and compounds
capable of generating carbonium ions can also initiate polymerization Examples of Lewis
acids are AlCl3 SnCl4 BF3 TiCl4 AgClO4 and I2 Lewis acid initiators required a co-
initiator such as H2O or an organic halogen compound Initiation by Lewis acids either
requires or proceeds faster in the presence of either a proton donor (protogen) such as water
alcohol and organic acids or a cation donor (cationogen) such as t-butyl chloride or
triphenylmethyl fluoride
The polymerization of a heterocyclic monomer initiated by a protonic acid usually starts with
opening of the monomer ring via oxonium sites that are formed upon alkylation (or
protonation) of the monomer
42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144
10
Protonation
BF3 H2O H BF3 OH+ +O
O
Acylation
R CO SbF6 +
OR CO O SbF6
Alkylation
Et3O BF4 +
OC2H5 Et2O BF4O +
Hydrogen transfer
C SbF6 +O
C SbF6H O+
SbF6
O + O O+ H O SbF6
In general initiation step can be shown as
A+
R O++R A O
The mechanism of chain growth involves nucleophilic attack of the oxygen of an incoming
monomer onto a carbon atom in α-position with respect to the oxonium site whereby the
cycle opens and the site is reformed on the attacking unit
A+O
O(CH2)4
O
A+O(CH2)4
Growing chain terminates with nucleophilic species as shown below
O (CH2)4 O+[ ]n
A O (CH2)4[ ]n
AO ( CH2 )4
11
Triflic initiators like trifluoromethane sulfonic acid derivatives can also be employed as an
initiator in the cationic polymerization of heterocyclics in this case initiation step follows
alkylation mechanism
CF3 SO3CH3 +O
CH3 CF3SO3O
CH3 O
CF3SO3
+ O CH3O(CH2)4 O CF3SO3
Ion pairs are in equilibrium with the ester form
(CH2)4 O CF3SO3 (CH2)4 O(CH2)4 O SO2CF3
If instead of ester triflic anhydride is used as initiator the same reaction can occur at both
chain ends and anhydride behaves as a bifunctional initiator
CF3SO2OSO2CF3 nO
+ CF3SO2 O (CH2)4 O (CH2)4 O SO2CF3n-1
(CH2)4 O (CH2)4 n-3
O O CF3SO3 CF3SO3
In the case of living cationic polymerization the growing sites are long living provided the
reaction medium does not contain any transfer agents such as alcohols ethers amines or
acids The reaction mechanism then involves only initiation and propagation steps and the
polymers formed are living The active sites are deactivated by addition of an adequate
nucleophile such as excess water tertiary amines alkoxides phenolates or lithium bromide
12
O(CH2)4
SbF6
(CH2)4 O(CH2)4 OH H
NR3
++ H2O
SbF6
+(CH2)4 O(CH2)4 NR3 SbF6
ONa+(CH2)4 O(CH2)4 O + NaSbF6
+ LiBr
(CH2)4 O(CH2)4 Br LiSbF6+
However facts concerning the real mechanism are scarce In order to progress further in
understanding the cationic polymerization of heterocycles initiated with a Bronsted acid
kinetic studies of simple ring-opening reactions of heterocyclic monomer rings by acids in
nonpolar aprotic and nonbasic solvents (inert solvents) have been performed45
14 Synthesis of Functionalized Poly (1 3-Dioxolane)
1 3-Dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer ends ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The molecular weight of the linear polymers is governed by the
ratio of reacted monomer to transfer agent and is generally well controlled up to 10 000gmol
141 Reaction of 1 3-Dioxolane and Hydroxyl- Containing Compounds
Classical initiation induces polymerization through cyclic tertiary oxonium ions which are
responsible for the formation of an important quantity of cyclic oligomers48
45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon Press 3(1989) 787
13
In several preceding articles Franta et al have investigated the cationic polymerization of
cyclic acetals in the presence of a diol49 50 in particular polymerization of 13-dioxolane
(DXL) and 13-dioxepane (DXP) in the presence of an oligoether diol (αω-dihydroxy-poly
(tetrahydofuran)) or (αω-dihydroxy-poly(ethylene oxide)) In all cases a similar behavior was
observed Cyclic oligomers are present in quantities as in the case of polymerization of DXL
in the absence of hydroxyl containing compounds51
When substituted oxiranes such as propylene oxide or epichlorohydrin are polymerized
according to the ldquoActivated Monomerrdquo mechanism (AM) Cyclic oligomers can be
eliminated52 53 In the AM mechanism polymerization of ethylene oxide however the
reaction of a protonated monomer molecule with a polymer chain leads to side reactions
including cyclization by the Active Chain End (ACE) mechanism53 Thus it is not
unexpected that in the polymerization of cyclic acetals due to the higher nucleophilicity of
the linear acetals located on the chain reactions with the latter will take place
The addition of a protonated DXL onto a hydroxyl group-containing compound is
accompanied by transacetalization involving a monomer molecule
In order to shed some light on the reactions involved Franta et al54 used a monoalcohol
methanol instead of a diol The results confirmed the occurrence of the Active Monomer
mechanism but dimethoxymethane was observed evidence of transacetalization between
methanol and dioxolane
Thus in the DXL-ethylene glycol (EG) system the presence of unreacted EG is in fact due to
the following equilibria
This equation shows the stoichiometry of the reaction rather than its actual mechanism the
reaction certainly has to involve an addition product as a first step
49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154
14
In the next step transacetalization occurs
The products of transacetalization are formed fast as compared to the addition product54 This
indicates that the last reaction is not slower and probably faster than the previous one
Consequently it has been found that although polymerization of DXL in the presence of
hydroxyl group containing compounds proceeds initially by a stepwise addition of protonated
monomer to the hydroxyl terminated linear species in agreement with the AM mechanism but
already at this stage fast transacetalization proceeds leading to formation of O-CH2-O links
between two oligodiols and liberation of ethylene glycol
The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism When DXL is polymerized by strong protonic acids such as triflic acid in the
presence of a diol the PDXL chains are essentially linear and carry end-standing OH
functions Despite the occurrence of some side reactions this mechanism leads to α ω-
dihydroxy-PDXL the molecular weight of which is controlled by the molar ratio of DXL
consumed to diol introduced It has been shown that the polydispersity is on the order of 14
and that molar masses up to 10 000 gmol can be covered
142 Synthesis of Poly (1 3-Dioxolane) Macromonomers
Macromonomers are useful intermediates to prepare graft copolymers and have indeed been
used extensively In order to prepare PDXL macromonomers Franta and al54 have used p-
isopropenylbenzylic alcohol (IPA) as an initiator and triflic acid as a catalyst
The following polymeric species were identified
15
Scheme 7
A is the most abundant compound it corresponds to 50 to 60 weight-wise It is a
macromonomer
B corresponds to 20 to 25 weight-wise It carries two p-isopropenyl functions
C corresponds to 20 to 25 weight-wise It carries no p-isopropenyl function but two
hydroxyl groups
As a result preparation of PDXL macromonomers leads to the preparation of PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of transacetalization
reaction described above a mixture of products was obtained54
Kruumlger et al55 used similar method to prepare macromonomers and come out to the same
conclusions in terms of structure and claim that a clear distinction should be made between
the products obtained and the mechanism responsible for their formation
15 Amphiphilic Graft Copolymers
151 Graft Copolymers
The increasing complexity of polymer applications has required the production of materials
with varied properties Often homopolymers do not afford the scope of attributes necessary to
many applications Copolymerization allows the formulation of polymer materials with
properties characteristic of two homopolymers contained in a single copolymer material The
monomers within a copolymer can be distributed in various fashions random statistical
alternating segmented block or graft56
55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387
16
Scheme 8
Graft copolymers are similar to block copolymers in that they possess long sequences of
monomer units However graft copolymer architecture differs substantially from typical
block copolymers In graft copolymers monomer sequences are grafted or attached to points
along a main polymer chain Grafted chains generally possess molecular weights less than
that of the main chain
These side chains have constitutional or configurational features that differ from those in the
main chain57
The simplest case of a graft copolymer can be represented by A-graft-B or the arrangement
and the corresponding name is polyA-graft-polyB where the monomer named first (A in this
case) is that which supplied the backbone (main chain) units while that named second (B) is
in the side chain(s)
Typical syntheses of the grafts occur by polymerization initiated at some reactive point along
the backbone or by copolymerization of a macromonomer Polymerization from the polymer
backbone is possible via anionic cationic and radical techniques but all require some
functional unit capable of further reaction58
Well defined graft copolymers are most frequently prepared by either
a)ldquografting throughrdquo or b)ldquografting fromrdquo controlled polymerization process
57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991)
17
a) Grafting though the ldquografting throughrdquo method (or macromonomer method) is one of the
simplest ways to synthesize graft copolymers with well defined side chains
Scheme 9
Typically a low molecular weight monomer is radically copolymerized with a methacrylate
functionalized macromonomer This method permits incorporation of macromonomers
prepared by other controlled polymerization processes into a backbone prepared by a CRP
Macromonomers such as polyethylene59 60 poly (ethylene oxide)61 polysiloxanes62 poly
(lactic acid)63 and polycaprolactone64 have been incorporated into a polystyrene or poly
(methacrylate) backbone Moreover it is possible to design well-defined graft copolymers by
combining the ldquografting throughrdquo macromonomers prepared by any controlled polymerization
process and CRP65 This combination allows control of polydispersity functionality
copolymer composition backbone length branch length and branch spacing by consideration
of MM ratio in the feed and reactivity ratio Branches can be distributed homogeneously or
heterogeneously and this has a significant effect on the physical properties of the
materials6263
b) Grafting from the primary requirement for a successful grafting from reaction is a
preformed macromolecule with distributed initiating functionality
59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003) 6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778 63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998) 823-830
18
Scheme 10
Grafting-from reactions have been conducted from polyethylene66 67 polyvinylchloride68 69
and polyisobutylene70 71 The only requirement for an ATRP is distributed radically
transferable atoms along the polymer backbone The initiating sites can be incorporated by
copolymerization68 be inherent parts of the first polymer69 or incorporated in a post-
polymerization reaction70
Graft copolymers perform similar functions to block copolymers in that they contain moieties
with varying properties Compatibilization represents a major area of application for grafts
because the grafted chains can be used to solubilize a polymer blend system containing two
immiscible polymers Additionally graft copolymers offer unique solution mechanical and
morphological properties that make them ideal for utilization as viscosity modifiers and
thermoplastic elastomers72 The unique molecular architecture of graft copolymers leads to
peculiar morphological properties The chain lengths of the grafted arms and backbone block
dictate the morphology that arises in the polymer Changes in the composition of the graft
copolymer alter the resulting polymer morphology A variety of morphologies is possible
ranging from lamellar to cylindrical to spherical73
Graft copolymers offer all properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheology control
Depending on the nature of their backbone and side chains graft copolymers can be used for a
wide variety of applications such as impact-resistant plastics thermoplastic elastomers
66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996) 7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R Macromolecules 32 (1999) 1152-1158
19
compatibilizers viscosity index improvers and polymeric emulsifiers74 75 The state-of-the-
art technique to synthesize graft copolymers is the copolymerization of macromonomers
(MM) with low molecular weight monomers76 In most cases conventional radical
copolymerization has been used for this purpose Using living polymerizations for both the
synthesis of the macromonomers and for the copolymerization offers the highest possible
control of the polymer structure In all these copolymerizations beside the desired graft
copolymers with at least two side chains a number of unwanted products can be expected
unreacted macromonomer ungrafted backbone and backbone with only one graft (star
copolymer) The latter is undesirable for applications as thermoplastic elastomer
Conventional and controlled copolymerizations lead to different copolymer structures In
conventional radical copolymerization the polymers show a broad molecular weight
distribution (MWD) and chemical heterogeneity of first order
152 Amphiphilic Copolymers
A characteristic feature of an amphiphilic polymer is that it contains both hydrophilic and
hydrophobic groups This type of polymer associates in aqueous solution and exhibits several
interesting features and can be used in connection with many industrial and pharmaceutical
applications Usually there is only a few mol of the hydrophobic moieties in order to make
the polymer water-soluble Due to the hydrophobicity of the amphiphilic polymers they have
a tendency to form association structures in aqueous solution by mutual interaction andor
interaction with other cosolutes such as surfactants and colloid particles
In particular the grafting of hydrophilic species onto hydrophobic polymers is of great utility
Amphiphilic graft copolymers so prepared often display enhanced surface properties such as
improved resistance to the adsorption of oils and proteins biocompatibility and reduced static
charge buildup
The synthesis of graft copolymers based on commercial polymers is most commonly
accomplished free radically Free radicals are produced on the parent polymer chains by
exposure to ionizing radiation andor a free-radical initiator77 78 Alternatively peroxide
groups are introduced on the parent polymer by ozone treatment79 80 The resulting reactive
74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998) 696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507
20
sites serve as initiation sites for the free radical polymerization of the comonomer A
significant disadvantage of these free radical techniques is that homopolymerization of the
comonomer always occurs to some extent resulting in a product which is a mixture of graft
copolymer and homopolymer Moreover backbone degradation and gel formation can occur
as a result of uncontrolled free radical production often limiting the attainable grafting
density81 For example amphiphilic graft copolymers synthesized from PEO macromonomer
and hydrophobic comonomers82 83were found to form micellar aggregates in polar medium
such as water wateralcohol alcohol dimethylformamide These phase separation processes
take place also during polymerization and supposedly affect not only the polymerization
kinetics but also properties of resulting copolymers So far unanswered remains the question
of molecular characteristics of reaction products including homopolymers from
macromonomer or comonomer formed under both the homogeneous and heterogeneous
(micellar) reaction conditions Modern liquid chromatographic techniques allow
discrimination of polymeric constituents differing in their chemical structure andor physical
architecture Subsequently the molar mass and molar mass distribution of constituents can be
assessed Recently analyzed products of dispersion copolymerization of polyethylene oxide
methacrylate macromonomer with styrene contained rather large amount of polystyrene
homopolymer84
In the main application areas for amphiphilic polymers the solution properties are of
fundamental importance In many industrial applications association and adsorption
phenomena of the polymers in solution are design properties Consequently a deep
understanding of these phenomena is necessary for the development of new specific
chemicals and new processes The research goals are to clarify the relations between the
molecular structure of amphiphilic polymers and their properties in aqueous solution A
further goal is to develop theoretical models for the description of the behavior of amphiphilic
polymers in solution and at surfaces Several projects concern the self-assembly of
amphiphilic polymer molecules and the association behavior of surfactants and
hydrophobically modified hydrophilic polymers such as cellulose derivatives Studies of
amphiphilic model polymers such as ethylene oxide block and graft copolymers are carried
80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication
21
out in order to gain fundamental knowledge on the solution behavior of amphiphilic
polymers
16 Kinetics of Free Radical Polymerization
Free radical polymerization is the most widespread method of polymerization of vinylic
monomers Free radical polymerizations are chain reactions in which every polymer chain
grows by addition of a monomer to the terminal free radical reactive site called ldquoactive
centerrdquo The addition of the monomer to this site induces the transfer of the active center to
the newly created chain end Free radical polymerization is characterized by many attractive
features such as applicability for a wide range of polymerizable groups including styrenic
vinylic acrylic and methacrylic derivatives as well as tolerance to many solvents small
amounts of impurities and many functional groups present in the monomers
161 Kinetics of free radical addition Homo and Copolymerization
Understanding of chemical kinetics during homo- and copolymerization is crucial for
copolymer synthesis The discussion below will review the kinetics of free radical initiated
polymerizations and copolymerizations
The three main kinetic steps that occur during polymerization are (1) initiation (2)
propagation and (3) termination
1 Initiation
The initiation step is considered to involve two reactions creating the free radical active
center The first event is the production of free radicals Many methods can be used to initiate
free radical polymerizations such as thermal initiation without added initiator or high energy
radiation of the monomers However free radicals are usually generated by the addition of
initiators that form radicals when heated or irradiated Two common examples of such
compounds which afford free radicals are benzoyl peroxide (BPO) and azobisisobutyronitrile
(AIBN)
22
Figure 1 Generation of Free Radicals by Thermal Decomposition of Benzoyl Peroxide
Figure 2 Decomposition of Azobisisobutyronitrile to Form Free Radicals
Figure 1 depicts the thermal decomposition of BPO to form two oxy-radicals and Figure 2
depicts the decomposition of AIBN to form two nitrile stabilized carbon based radicals
(equation 1)
In equation 1 kd is the rate constant which describes the first order initiation process The
radical that is formed can now add to the double bond of the monomer and initiate
polymerization
The symbol M will represent the monomer and the rate constant for this process will be ki as
described in equation 2
23
Together these two reactions the radical generation and the monomer addition to the radical
form the process of initiation Usually the assumption that is taken into account is that the
first step is the rate determining step This means that the decomposition to form the radical
is much slower than the monomer addition to the free radical Therefore the equation for the
rate of radical formation ri is
The number 2 is obtained from the fact that a maximum of two radicals can be generated for
the initiation
But not all of the primary radicals produced by the decomposition of the initiator will
necessarily react with the monomer which means several other competing reactions may
occur85 Therefore in order to determine the rate of initiation the fraction of initially formed
radicals that actually start chain growth will be denoted by f and the rate of initiation equation
becomes
2 Propagation
Now the propagation of the reaction will proceed through the successive addition of
monomer to the radicals This type of process can be expressed in the following form
85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster PA (1997)
24
And further generalizing the reaction scheme gives
The assumption that the reactivity of the addition of each monomer is independent of the
chain length is evident in these two equations and was postulated by Flory 58 86 The use of
the rate constant kp for both of these equations imply that the rate constant is independent of
chain length The rate of the propagation rp of this polymerization or the rate of monomer
removal is thus given by
3 Termination
The termination of these growing radical chains occurs in principally two different ways The
first way is the formation of a new bond in between the two radicals this is called
combination Secondly the radical chains can terminate by disproportionation This is a
process where a hydrogen atom from one of the chains is transferred to the other and the chain
that the proton was removed from forms a double bond These reactions are represented as
follows
Figure 3 Termination by Combination
86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995)
25
Figure 4 Termination by Disproportionation
Schematically the reactions can be represented as follows
Where the rate constant of termination by combination is denoted by ktc and the rate constant
of termination by disproportionation is denoted by ktd Since both of these reactions use two
radical species and have the same kinetics the overall equation for the rate of termination is
written as
where kt = ktc + ktd and the number 2 imply there are two radicals that are terminated in
each termination reaction The monomer structure and the temperature are what determines
the type of termination that is most dominant in the reaction For most systems the amount of
one termination type far exceeds the other termination type
The further calculations for the rate of polymerization Rp and the degree of conversion as a
function of time can now be developed The assumption of the steady state concentration of
transient species must be used here where the transient species is the radical M For the
steady state approximation to hold true the rate at which initiation occurs ri must be equal to
the rate at which termination occurs rt or in other words radicals must be generated at the
same rate at which they are terminated This assumption gives the equation
26
This equation then gives an expression for the radical species
Experimentally this value would be difficult to measure in the laboratory and therefore this
equation must be used in the subsequent equations that follow By further substitution an
expression for the rate of polymerization Rp can be obtained because it equals the rate of
propagation
From this equation it can be deduced that the rate of polymerization is directly proportional
to the monomer concentration and to the initiator concentration to the one half power In
other words Rp is first order with regards to the monomer concentration and half order to the
initiator concentration
When the conversion is low the assumption that the initiator concentration is constant is
reasonable but the consumption of the initiator can be added into the calculations Therefore
Then integration can be performed
Finally the rate of polymerization becomes
27
This equation can be broken into three different parts
The second term indicates that the rate of polymerization is still proportional to the monomer
concentration to the first power and the initiator concentration to the one half power but the
initiator concentration is now the initial concentration Therefore by increasing the initial
concentration of an initiator in a solution polymerization the rate of the reaction should
increase proportionally to the square root of the amount of initiator added The third term
indicates that as the initiator is consumed the polymerization slows down exponentially with
time as well as its slowing down due to monomer depletion
The first term in the brackets suggests that the rate of polymerization is proportional to kp
kt12 When experiments are performed to probe the kinetics of reactions in solution the
expected first order dependence on monomer concentration is observed But when the
experiment is performed in concentrated solvents or even in the bulk the polymerization
kinetics accelerate The reason for this anomaly is that the viscosity increases as the
polymerization proceeds because the polymer has a higher viscosity than the monomers The
kp is not affected but the kt is
The degree of conversion can now be expressed as a function of time by knowing that
By substituting the earlier equation for Rp and integrating that equation one can obtain this
Furthermore ([M]0 ndash [M]) [M]0 is equal to the degree of conversion and is the fraction of
the monomer that has been reacted where [M] is the concentration of the monomer that has
been left after the reaction and [M]0 is the initial monomer concentration Therefore ([M]0 ndash
[M]) is the concentration of the monomer that has reacted The conversion can then be
expressed as
28
This can also be expressed as
As is always the case the conversion never quite reaches 100 value or a factor of 1 given by
the exponential term So if the time goes to infinity the expression that is obtained for
maximum conversion that is less than 1 by an amount that is dependent on the initial initiator
concentration is
If the steady state approximation for the initiator concentration had been carried through these
calculations and equations then the conversion would approach a value of 1 after a long
period of time
Distributions on the average distribution of chain lengths during and after a polymerization
are present in free radical polymerizations This is due to the naturally but statistically
random termination reactions that occur in the solution with regard to chain length The
kinetic chain length v is the rate of monomer addition to growing chains over the rate at
which chains are started by radicals which is the expression for the number average chain
length In other words it is the average number of monomer units per growing chain radical
at a certain instant87 Therefore the initiator radical efficiency in polymerizing the monomers
is
87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993)
29
When termination occurs mainly by combination the chain length for the polymer chains on
the average doubles in size assuming nearly equal length chains combine But if
disproportionation mainly occurs the growing chains do not undergo any change in chain
length during the process So the expressions are thus
A new term can be used to more generally express the average chain length of the growing
polymer chain xn This new term is the average number of dead chains produced per
termination ξ This value is equal to the rate of dead chain formation over the rate of the
termination reactions The equations take into account that in combination only one dead
chain is produced and in disproportionation reactions two dead chains are produced
Therefore
Furthermore the instantaneous number average chain length can be expressed in terms of the
rate of addition of the monomer units divided by the rate of dead polymers forming This is
shown as
30
From this equation82 one can clearly see that the rate of polymerization is proportional to the
initiator concentration to the one half power [I]12 and that the instantaneous number average
chain length xn is proportional to the inverse of the initiator concentration to the one half
power 1[I]12 Thus if the polymerization was accelerated by using more initiator the chains
will end up to be shorter which may not be desirable85
17 Chain Growth Copolymerization
171 Copolymerization Equations
Chain polymerizations can obviously be performed with mixtures of monomers rather than
with only one monomer For many free radical polymerizations for example acrylonitrile and
methyl acrylate two monomers are used in the process and the subsequent copolymer might
be expected to contain both of the structures in the chain This type of reaction that employs
two comonomers is a copolymerization The reactivity and the relative concentrations of the
two monomers should determine the concentration of each comonomer that is incorporated
into the copolymer The application of chain copolymerizations has produced much important
fundamental information Most of the knowledge of the reactivities of monomers via
carbocations free radicals and carbanions in chain polymerizations has been derived from
chain copolymerization studies The chemical structure of these monomers strongly
influences reactivity during copolymerization Furthermore from the technological viewpoint
copolymerization has been critical to the design of the copolymer product with a variety of
specifically desired properties As compared to homopolymers the synthesis of copolymers
can produce an unlimited number of different sequential arrangements where the changes in
relative amounts and chemical structures of the monomers produce materials of varying
chemical and physical properties
Several different types of copolymers are known and the process of copolymerization can
often be changed in order to obtain these structures A statistical or random copolymer may
obey some type of statistical law which relates to the distribution of each type of comonomer
that has been incorporated into the copolymer Thus for example it may follow zero- or first-
31
or second-order Markov statistics88 Copolymers that are formed via a zero-order Markov
process or Bernoullian contain two monomer structures that are randomly distributed and
could be termed random copolymers
ndashAABBBABABBAABAmdash
Alternating block and graft copolymers are the other three types of copolymer structures
Equimolar compositions with a regularly alternating distribution of monomer units are
alternating copolymers
ndashABABABABABABA--
A linear copolymer that contains one or more long uninterrupted sequences of each of the
comonomer species is a block copolymer
--AAAAAAAA-BBBBBBBBB--
A graft copolymer contains a linear chain of one type of monomer structure and one or more
side chains that consist of linear chains of another monomer structure
--AAAAAAAAAAAAAmdash
B B
B B
B B
B B
For this discussion the main focus will be on randomly distributed or statistical copolymers
Copolymer composition is usually different than the composition of the starting materials
charged into the system Therefore monomers have different tendencies to be incorporated
into the copolymer which also means that each type of comonomer reacts at different rates
with the two free radical species present Even in the early work by Staudinger89 it was
noted that the copolymer that was formed had almost no similar characteristics to these of the
homopolymers derived from each of the monomers
Furthermore the relative reactivities of monomers in a copolymerization were also quite
different from their reactivities in the homopolymerization Thus some monomers were more 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151
32
reactive while some were less reactive during copolymerization than during their
homopolymerizations Even more interesting was that some monomers that would not
polymerize at all during homopolymerization would copolymerize relatively well with a
second monomer to form copolymers It was concluded that the homopolymerization features
do not easily directly relate to those of the copolymerization
Alfrey (1944) Mayo and Lewis (1944) and Walling (1957)909192 demonstrated that the
copolymerization composition can be determined by the chemical reactivity of the free radical
propagating chain terminal unit during copolymerization Application of the first-order
Markov statistics was used and the terminal model of copolymerization was proposed The
use of two monomers M1 and M2 during copolymerization leads to two types of propagating
species The first of these species is a propagating chain that ends with a monomer of
structure M1 and the second species is a propagating chain that ends with a monomer structure
M2 For radically initiated copolymerizations the two structures can be represented by
M1 and M2 where the zig-zag lines represent the chain and the M
represents the radical at the growing end of the chain The assumption that the reactivity of
these propagating species only depends on the monomer unit at the end of the chain is called
the terminal unit model58 If this is so only four propagation reactions are possible for a two
monomer system The propagating chain that ends in M1 can either add a monomer of type
M1 or of type M2 Also the propagating chain that ends in M2 can add a monomer unit of
type M2 or of type M1 Therefore these equations can be written with the rate constants of
reactions93
90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953)
33
The rate constant for the reaction of the propagating chain that ends in M1 and adds another
M1 to the end of the chain is k11 and the rate constant for the reaction of the propagating
chain that ends in M2 and adds M1 to the end of the chain is k21 and so on
The term self-propagation refers to the addition of a monomer unit to the chain that ends with
the same monomer unit and the term cross-propagation refers to a monomer unit that is added
the end of a propagating chain that ends in the different monomer unit These (normally)
irreversible reactions can propagate by free radical anionic or cationic processes although
active lifetimes could be very different
As indicated by reactions 30 and 32 monomer M1 is consumed and as indicated by reactions
31 and 33 monomer M2 is consumed The rates of entry into the copolymer and the rates of
disappearance of the two monomers are given by
In order to find the rate at which the two monomers enter into the copolymer equation 34
is divided by equation 35 to give the copolymer composition equation
The low concentrations (eg 10-8 molesliter) of the radical chains in the systems are very
hard to experimentally determine So to remove these from the equation the steady state
approximation is normally employed Therefore a steady state concentration is assumed for
both of the species M1 and M2 separately The interconversion between the two
species must be equal in order for the concentrations of each to remain constant and hence the
rates of reactions 31 and 32 must be equal
34
Rearrangement of equation 37 and combination with equation 36 gives
This equation can be further simplified by dividing the right side and the top and bottom by
k21 [M2] [M1] The results are then combined with the parameters r1 and r2 which are
defined to be the reactivity ratios
The most familiar form of the copolymerization composition equation is then obtained as
The ratio of the rates of addition of each monomer can also be considered to be the ratio of the
molar concentrations of the two monomers incorporated in the copolymer which is denoted
by (m1m2) The copolymer composition equation can then be written as
The copolymer composition equation defines the molar ratios of the two monomers that are
incorporated into the copolymer d[M1] d[M2] As seen in the equation this term is directly
related to the concentration of the monomers that were in the feed [M1] and [M2] and also
the monomer reactivity ratios r1 and r2 The ratio of the rate constant for the addition of its
own type of monomer to the rate constant for the addition of the other type of monomer is
35
defined as the monomer reactivity ratio for each monomer in the system When M1
prefers to add the monomer M1 instead of monomer M2 the r1 value is greater than one
When M1 prefers to add monomer M2 instead of monomer M1 the r1 value is less than
one When the r1 value is equal to zero the monomer M1 is not capable of adding to itself
which means that homopolymerization is not possible
The copolymer composition equation can also be expressed in mole fractions instead of
concentrations which helps to make the equation more useful for experimental studies In
order to put the equation into these terms F1 and F2 are the mole fractions of M1 and M2 in the
copolymer and f1 and f2 are the mole fractions of monomers M1 and M2 in the feed
Therefore
and
Then combining equations 42 43 and 40 gives
This form of the copolymer equation gives the mole fraction of monomer M1 introduced into
the copolymer58
Different types of monomers show different types of copolymerization behavior Depending
on the reactivity ratios of the monomers the copolymer can incorporate the comonomers in
different ways
The three main types of behavior that copolymerizations tend to follow correspond to the
conditions where r1 and r2 are both equal to one when r1 r2 lt 1 and when r1 r2 gt 1
bull A perfectly random copolymerization is achieved when the r1 and r2 values are both
equal to one This type of copolymerization will occur when the two different types of
36
propagating species M1 and M2 show the exact same preference for the addition of
each type of monomer In other words the growing radical chains do not prefer to add one of
the monomers more than the other monomer which results in perfectly random incorporation
into the copolymer
bull An alternating copolymerization is defined as r1 = r2 = 0 The polymer product in
this type of copolymerization shows a non-random equimolar amount of each comonomer
that is incorporated into the copolymer This may occur because the growing radical chains
will not add to its own monomer Therefore the opposite monomer will have to be added to
produce a growing chain and a perfectly alternating chain
When r1 gt 1 and r2 gt 1 both of the monomers want to add to themselves and in theory could
produce block copolymers But in actuality because of the short lifetime of the propagating
radical the product of such copolymerizations produces very undesirable heterogeneous
products that include homopolymers Therefore macroscopic phase separation could occur
and desirable physical properties such as transparency would not be achieved
172 Determination of Reactivity Ratios
Many methods have been used to estimate reactivity ratios of a large number of
comonomers94 The copolymer composition may not be independent of conversion This
means the disappearance of monomer one may be faster than the disappearance of monomer
two if monomer one is being incorporated into the copolymer at a faster rate and therefore it
has a larger reactivity ratio than monomer two
The approximation method95 is the simplest of the methods that has been used to calculate the
reactivity ratios of copolymer systems The method is based on the fact that r1 the reactivity
ratio of component one is mainly dependent on the composition of monomer two m2 that
has been incorporated into the copolymer at low concentrations of monomer two in the feed
M2 The expression is thus
94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
37
The value of the reactivity ratio for component one can be easily determined by only one
experiment but the value is only an approximation and does not provide any validity of the
estimated r1 In order to determine the amount of the comonomer that has been incorporated
into the copolymer various analytical methods must be used Proton Nuclear Magnetic
Resonance Carbon 13 NMR and Fourier Transform Infrared Spectroscopy are three sensitive
instruments that can determine the copolymer composition The approximation method is
limited when the reactivity ratio of one of the components in the system has a value of less
than 01 or greater than a value of 10
However the method does give good insight into the reactivity ratio values for many
copolymer systems The approximation of reactivity ratios can be easy and quick when using
this method of evaluation
The Mayo-Lewis intersection method91 96 uses a linear form of the copolymerization equation where r1 and r2 are linearly related
By using the equations m1M 22 m2M12 and (M2 M1)[(m1 m2) ndash 1] for the slope and intercept
respectively a plot can be produced for a set of experiments after the copolymer composition
has been determined The straight lines that are produced on the plot for each experiment
where r1 represents the ordinate and r2 represents the abscissa intersect at a point on the r1 vs
r2 plot The point where these lines meet is taken to be r1 and r2 for the system in study The
main advantage of this method is that it gives a qualitative observation of the validity of the
intersection area Over the whole range of possible copolymer compositions that were tested
more compact intersections better define the data However the method requires a visual
check of the data and a quantitative estimation of the error is impossible Therefore
weighting of the data is needed to determine the most precise values of r1 and r2
The Fineman-Ross linearization method97 uses another form of the copolymer equation
Where
And
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259
38
For this method by plotting G versus H for all the experiments one will obtain a straight line
where the slope of the straight line is the value for r1 and the intercept of the line is the value
for r2 This type of reactivity ratio determination has the same advantages and disadvantages
of the method described above however this treatment is a linear least squares analysis
instead of a graphical analysis The validity is only qualitative and the estimates of r1 and r2
can change with each experimenter by weighting the data in different ways Furthermore the
high and low experimental composition data are unequally weighted which produces large
effects on the calculated values of r1 and r2 Therefore different values of r1 and r2 can be
produced depending on which monomer is chosen as M158
A refinement of the linearization method was introduced by Kelen and Tudos98 99 100 by
adding an arbitrary positive constant a into the Fineman and Ross equation 47 This technique
spreads the data more evenly over the entire composition range to produce equal weighting to
all the data58 The Kelen and Tudos refined form of the copolymer equation is as follows
η = [ r1 + r2 α ] ξ minus r2 α (50)
where
η = G ( α + H ) (51)
ξ = H ( α + H ) (52)
By plotting η versus ξ a straight line is produced that gives ndashr2α and r1 as the intercepts on
extrapolation to ξ=0 and ξ=1 respectively Distribution of the experimental data
symmetrically on the plot is performed by choosing the α value to be (HmHM)12 where Hm
and HM are the lowest and highest H values respectively Even with this more complicated
monomer reactivity ratio technique statistical limitations are inherent in these linearization
methods101 102
98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265
39
OrsquoDriscoll Reilly et al103 104 determined that the dependent variable does not truly have a
constant variance and the independent variable in any form of the linear copolymer equation
is not truly independent Therefore analyzing the composition data using a non-linear
method has come to be the most statistically sound technique
The non-linear or curve-fitting method90 is based on the copolymer composition equation in
the form
This equation is based on the assumptions that the monomer concentrations do not change
much throughout the reaction and the molecular weight of the resulting polymer is relatively
high In order to determine reactivity ratios from the experimental data a graph must be
generated for the observed comonomer amount that was incorporated into the copolymer m1
versus the feed comonomer amount M1 for the entire range of comonomer concentrations
Then a curve can be drawn through the points for selected r1 and r2 values and the validity of
the chosen reactivity ratio values can be checked by changing the r1 and r2 values until the
experimenter can demonstrate that the curve best fits the data points
The main advantage of the reactivity ratio determination methods discussed thus far is the
results can be visually and qualitatively checked Disadvantages include a direct dependence
of the composition on conversion for most polymer systems and therefore low conversion
(eg instantaneous composition) is needed to determine the reactivity ratios Furthermore
extensive calculations are required but only qualitative measurements of precision can be
obtained Finally weighting of the experimental data for the methods to determine precise
reactivity ratios is hard to reproduce from one experimenter to another
Therefore a technique that allows the rigorous application of statistical analysis for r1 and r2
was proposed by Mortimer and Tidwell which they called the nonlinear least squares
method95105106107This method can be considered to be a modification or extension of the
curve fitting method For selected values of r1 and r2 the sum of the squares of the differences
between the observed and the computed polymer compositions is minimized
103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772
40
Using this criterion for the nonlinear least squares method of analysis the values for the
reactivity ratios are unique for a given set of data where all investigators arrive at the same
values for r1 and r2 by following the calculations Recently a computer program published by
van Herck108 109 allows for the first time rapid data analysis of the nonlinear calculations It
also permits the calculations of the validity of the reactivity ratios in a quantitative fashion110
The computer program produces reactivity ratios for the monomers in the system with a 95
joint confidence limit determination
The joint confidence limit is a quantitative estimation of the validity of the results of the
experiments and the calculations performed This method of data analysis consists of
obtaining initial estimates of the reactivity ratios for the system and experimental data of
comonomer charge amounts and comonomer amounts that have been incorporated into the
copolymer both in mole fractions Many repeated sets of calculations are performed by the
computer which rapidly determines a pair of reactivity ratios that fit the criterion wherein the
value of the sum of the squares of the differences between the observed polymer composition
and the computed polymer composition is minimized111 112 This method uses a form of the
copolymer composition equation with mole fractions of the feed It amounts to determining
the mole fraction of the comonomer that should be incorporated into the copolymer during a
differential time interval
For this equation F2 represents the mole fraction of comonomer two that was calculated to be
incorporated into the copolymer and f1 and f2 represent the mole fractions of each comonomer
that were fed into the reaction mixture The use of the Gauss-Newton nonlinear least squares
procedure predicts the reactivity ratios for a given set of data after repeating the calculations
so that the difference between the experimental data points and the calculated data points on a
plot of mole fraction of comonomer incorporated versus comonomer in the feed is reduced to
the minimum value113 114
108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65
41
18 Controlled Radical Polymerization
The development of new controlledliving radical polymerization processes such as Atom
Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated
polymerization and degenerative transfer processes including RAFT opened the way to the
use of radical polymerization for the synthesis of well-defined complex functional
nanostructures The development of such nanostructures is primarily dependent on self-
assembly of well-defined segmented copolymers This section describes the fundamentals of
ATRP relevant to the synthesis of such systems115
The main goal of macromolecular engineering is to carry out the synthesis (polymerization) in
such a way that it results in well-defined macromolecular products One of the ways to
achieve full control of the macromolecule (length sequence and regio- and stereo- regularity)
would be to build it one monomer at a time with mechanisms in place facilitating selection of
an appropriate monomer and assuring its addition in proper orientation This of course has
been achieved in Nature in the process of protein synthesis through the use of sophisticated
macromolecular ldquonanomachineryrdquo (DNA RNA Most commonly used synthetic routes to
linear polymers are based on addition (chain) reactions which can be controlled only in
statistical terms through such parameters as initiatormonomer ratios monomerpolymer
reactivities monomer concentrations reaction medium etc The main strategy to achieve the
reasonable control of such reactionsrsquo products is through the synchronized growth of ldquolivingrdquo
chains ie chains which cease to grow only in the absence of a monomer Synchronization of
chain growth can be achieved fairly easily through rapid initiation Living chains grown in
such synchronized fashion exhibit relatively narrow molecular weight distributions (MWD)
their average molecular weights can be controlled simply by the duration of reaction Until
recently radical polymerization which covers the broadest range of monomers appeared to
be inherently uncontrollable due to the presence of fast chain termination of growing radicals
Thus although very useful in the synthesis of bulk commodity polymers where precise
control is not always essential radical polymerization has been hardly ever viewed as a tool to
precisely engineer macromolecules for well-defined functional nanostructures
114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16
42
This outlook shifted dramatically recently with the development of new controlledliving
radical polymerization processes such as Atom Transfer Radical Polymerization (ATRP)116
117 118 and other techniques such as nitroxide mediated polymerization119 and degenerative
transfer processes120 including reversible addition-fragmentation chain transfer (RAFT)121
With the availability of effective control mechanisms given its applicability to a broadest
range of monomers radical polymerization is now ready to assume the central role in
macromolecular engineering geared towards the development of well-defined functional
nanostructures
181 Fundamentals of ControlledLiving Radical Polymerization (CRP)
The great expectations for the controlledliving radical polymerization (CRP) have their
origins in the dominating position of the free radical technique by far the most common
method of making polymeric materials (nearly 50 of all polymers are made this
way)122123124This is due to the large number of available vinyl monomers (eg there are
nearly 300 different methacrylates available commercially) which can be easily
homopolymerized and copolymerized The advent of CRP enables preparation of many new
materials such as well-defined components of coatings (with narrow MWD precisely
controlled functionalities and reduced volatile organic compounds -VOCs) non ionic
surfactants polar thermoplastic elastomers entirely water soluble block copolymers
(potentially for crystal engineering) gels and hydrogels lubricants and additives surface
modifiers hybrids with natural and inorganic polymers various biomaterials and electronic
materials
The controlledliving reactions are quite similar to the conventional ones however the radical
formation is reversible Similar values for the equilibrium constants during initiation and
propagation ensure that the initiator is consumed at the early stages of the polymerization
116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002)
43
generating chains which slowly and continuously grow as in a living process There are a
number of critical differences between conventional and controlledliving radical reactions
bull Perhaps the most important difference between the two approaches is the lifetime of
the propagating chains which is extended from 1 s to more than 1 h
bull The second major difference is the very significant increase in the initiation rate
which enables simultaneous growth of all the polymer chains
bull Termination processes cannot be avoided in CRPs Thus CRP is generally less precise
than the anionic polymerization Termination is the most dangerous chain breaking
reaction in CRPs Since it is a bimolecular process increasing the polymerization rate
increases the concentration of radicals and enhances the termination process
Termination also becomes more significant for longer chains and at higher conversion
However this process is somehow self tuned since termination is chain length
dependent
The key feature of the controlledliving radical polymerization is the dynamic equilibration
between the active radicals and various types of dormant species Currently three systems
seem to be most efficient nitroxide mediated polymerization (NMP) atom transfer radical
polymerization (ATRP) and degenerative transfer processes such as RAFT123 Each of the
CRPs has some limitations and some special advantages and it is expected that each
technique may find special areas where it would be best suited synthetically For example
NMP carried out in the presence of bulky nitroxides cannot be applied to the polymerization
of methacrylates due to fast β-H abstraction ATRP cannot yet be used for the polymerization
of acidic monomers which can protonate the ligands and complex with copper RAFT is very
slow for the synthesis of low MW polymers due to retardation effects and may provide
branching due to trapping of growing radicals by the intermediate radicals At the same time
each technique has some special advantages Terminal alkoxyamines may act as additional
stabilizers for some polymers ATRP enables the synthesis of special block copolymers by
utilizing a halogen exchange and has an inexpensive halogen at the chain end125 RAFT can
be applied to the polymerization of many unreactive monomers such as vinyl acetate126
182 Typical Features of ATRP
A successful ATRP process should meet several requirements
125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035
44
bull Initiator should be consumed at the early stages of polymerization to form polymers
with degrees of polymerization predetermined by the ratio of the concentrations of
converted monomer to the introduced initiator (DP = Δ[M][I]o)
bull The number of monomer molecules added during one activation step should be small
resulting in polymers with low polydispersities
bull The contribution of chain breaking reactions (transfer and termination) should be
negligible to yield polymers with high degrees of end-functionalities and allow the
synthesis of block copolymers
In order to reach these three goals it is necessary to select appropriate reagents and
appropriate reaction conditions ATRP is based on the reversible transfer of an atom or group
from a dormant polymer chain (R-X) to a transition metal (M nt Ligand) to form a radical (R)
which can initiate the polymerization and a metal-halide whose oxidation state has increased
by one (X-M n+1t Ligand) the transferred atom or group is covalently bound to the transition
metal A catalytic system employing copper (I) halides (Mnt Ligand) complexed with
substituted 2 2rsquo- bipyridines (bpy) has proven to be quite robust successfully polymerizing
styrenes various methacrylates acrylonitrile and other monomers116127 Other metal centers
have been used such as ruthenium nickel and iron based systems117 118 Copper salts with
various anions and polydentate complexing ligands were used such as substituted bpy
pyridines and linear polyamines The rate constants of the exchange process propagation and
termination shown in Scheme 11 refer to styrene polymerization at 110 C
Scheme 11
According to this general ATRP scheme the rate of polymerization is given by the following
equation
127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901
45
Thus the rate of polymerization is internally first order in monomer externally first order
with respect to initiator and activator Cu(I) and negative first order with respect to
deactivator XCu(II) However the kinetics may be more complex due to the formation of
XCu(II) species via the persistent radical effect (PRE) The actual kinetics depend on many
factors including the solubility of activator and deactivator their possible interactions and
variations of their structures and reactivities with concentrations and composition of the
reaction medium It should be also noted that the contribution of PRE at the initial stages
might be affected by the mixing method crystallinity of the metal compound and ligand etc
One of the most important parameters in ATRP is the dynamics of exchange and especially
the relative rate of deactivation If the deactivation process is slow in comparison with
propagation then a classic redox initiation process operates leading to conventional and not
controlled radical polymerization Polydispersities in ATRP are defined by the following
equation when the contribution of chain breaking reactions is small and initiation is
complete
Thus polydispersities decrease with conversion p the rate constant of deactivation kd and
also the concentration of deactivator [XCu(II)] They however increase with the propagation
rate constant kp and the concentration of initiator [RX]o This means that more uniform
polymers are obtained at higher conversions when the concentration of deactivator in solution
is high and the concentration of initiator is low Also more uniform polymers are formed
when the deactivator is very reactive (eg copper(II) complexed by 2 2-bipyridine or
pentamethyldiethylenetriamine rather than by water) and monomer propagates slowly (styrene
rather than acrylate)
183 Controlled Compositions by ATRP
One of the driving forces for the development of a controlledldquo livingrdquo radical polymerization
is to allow for the copolymerization of two or more monomers128 This has been demonstrated
with ATRP by copolymerization of various combinations of styrene methyl or butyl acrylate
methyl or butyl methacrylate and acrylonitrile ATRP allows for the copolymerization of
these monomers using all feed compositions without loss of control of the polymerization 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
46
this is in contrast to the use of 2266-tetramethylpiperidine-1-oxyl radical (TEMPO) which
must contain a significant amount of styrene as comonomer to retain control of the
polymerization This restriction does not apply to polymerizations mediated by new
nitroxides119 The statistical copolymers prepared by living polymerizations are not the same
as those prepared by conventional radical polymerizations due to the differences in
polymerization mechanism
During a copolymerization one monomer is generally consumed faster than the other
resulting in a constantly changing monomer feed composition during the polymerization the
preference is dependent on the reactivity ratios of the two (or more) monomers In
conventional radical polymerization where the polymer chains are continuously initiated and
are irreversibly terminated the change in monomer feed is recorded in the individual polymer
chains whose composition will vary from chain to chain depending on when the chain was
formed ie at the beginning or near the end of the reaction However since ATRP is a
controlledldquolivingrdquo polymerization system the vast majority of polymer chains does not
irreversibly terminate but grow gradually throughout the polymerization The change in
monomer feed is recorded in the polymer chain itself and not from chain to chain The drifting
of composition along the polymer chain is expected to yield gradient copolymers with novel
properties129 Conventional free radical polymerization methods are generally not suitable for
synthesizing star shaped polymers due to the occurrence of undesirable radical coupling
reactions During a ldquocore-firstrdquo synthesis this would lead to coupling of the growing polymer
arms and ultimately result in a cross-linking of the star macromolecules
Block copolymers can be formed by addition of a second vinyl monomer to a macroinitiator
which contains halide groups that participate in the atom transfer process Most notably this
has been demonstrated by successive addition of a second monomer at the end of the
polymerization of a first monomer by ATRP In this manner AB and ABA block copolymers
have been prepared with various combinations of styrene acrylates methacrylates and
acrylonitrile It is very important to select the right order of monomer addition For example
polyacrylates can be efficiently initiated by the poly (methyl methacrylate)- BrCuBrL
system However the opposite is not true because concentration of radicals and overall
reactivity of acrylates is generally too low to efficiently initiate MMA polymerization
Halogen exchange comes to the rescue bromoterminated polyacrylate in the presence of
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775
47
CuClL is an efficient initiator for MMA polymerization due to reduced polymerization rate
of PMMA-Cl species which are predominantly formed after the exchange process130 131 132
Scheme 12
To conclude atom transfer radical polymerization is a robust method for preparing well-
defined polymers and novel materials with unique compositions and architectures Although
significant progress has been made in the past few years since the development of ATRP
continuous research on the better mechanistic understanding of ATRP and the preparation of
more efficient catalyst systems to yield more well-defined polymers and polymerize new
monomers is needed The syntheses of new materials need to be optimized and their
properties should be studied
It is anticipated that the new controlledliving techniques will help to provide many new well-
defined polymers via macromolecular engineering
130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
48
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Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823 22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991) 25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
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Macromolecules 26 (1993) 7134 42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
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Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon
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J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003)
6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778
50
63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998)
823-830 66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996)
7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R
Macromolecules 32 (1999) 1152-1158 74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998)
696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507 80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication 85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster
PA (1997) 86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995) 87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993) 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151 90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953) 94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
51
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259 98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265 103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772 108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65 114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16 116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002) 125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035 127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
52
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775 130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
53
CHAPTER II Synthesis and Characterization of
Macromonomers
21 Introduction
Cationic ring opening polymerization of DXL proposed by Franta and Reibel133 results in
linear polymeric chains thereby preventing formation cyclic oligomers through cationic
polymerization of cyclic acetals15 17In fact the reaction of DXL in the presence of an
unsaturated alcohol (2-HPMA) results in a functionalized linear PDXL macromonomer
carrying at one or both ends an unsaturated system supported by the methacryloyl group of
the alcohol The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism44 Franta et al have established that when DXL is polymerized by strong protonic
acids such as triflic acid in the presence of a diol the PDXL chains are essentially linear and
carry end-standing OH functions It has been shown that the amount of cyclic species formed
is negligible that the dispersity is on the order of 14 and that the molecular weight of the
linear polymers is governed by the ratio of reacted monomer to transfer agent and is generally
well controlled up to 10 000 gmol
De Clercq and Goethals have reported the preparation of poly (13dioxolane)
bismacromonomers by copolymerization with MMA and provided the possibility to prepare
polymer networks containing PDXL segments134 135 PDXL based hydrogels have been
obtained in most cases by free radical copolymerization with comonomers such as acrylic
acid acrylamide and N-isopropylacrylamide134 136 137 styrene and butyl acrylate138
Hydrogels have received increasing attention for biomedical applications such as drug
delivery immobilization of enzymes dewatering of protein solutions and contact lenses139
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002) 1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080
54
140 These materials and are widely used in areas like baby diapers solute separation soil for
agriculture and horticulture absorbent pads etc139 Hydrogels are defined as hydrophilic
polymer networks which have a high capacity to adsorb a substantial amount of water which
have been proposed as protein releasing matrices The high water content ensures a good
compatibility with entrapped proteins as well as with surrounding tissue141 Even though a
number of applications are currently being pursued using hydrogel very little is known about
the mechanical behavior that describes the various physical processes in hydrogels142 Over
the last decade most interests have been emphasized on the synthesis of polymers containing
polyacetal segments because of the ease of degradation of these polymers under mild
conditions by treatment with a trace of acid134 143 Poly (1 3 dioxolane) is a hydrophilic non-
ionic polymer which like poly (ethylene oxide) is appreciably soluble in water but much
more sensitive to acidic degradation because of the presence of acetal groups in the chains144
In this chapter we report the synthesis of the functionalized poly (13dioxolane)
macromonomers which have been used for the preparation of PDXL hydrogel and
amphiphilic graft copolymers In the second part of this chapter we have focused on a
detailed study of the properties of the resulting hydrogel in terms of swelling behavior in
different organic solvents and viscoelastic properties determined by rheological measurements
in both the steady shear and oscillatory experiments
22 Experimental
221 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922
55
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
bull Dichloromethane (CH2Cl2 MW 8493 bp 40degC d 1325)
Dichloromethane (Prolabo 999) was dried by stirring over CaH2 for 24 h and then
distilled under a N2 atmosphere to remove impurities Purified dichloromethane was
stored under nitrogen over molecular sieve
bull 2-hydroxypropyl methacrylate (2-HPMA) (MW 14417 bp 240degC d 1028)
2-HPMA of commercial grade was purchased from Acros stabilized with 200 ppm
hydroquinone monomethyl ether Then it was stored over molecular sieve
bull n-Hexane 99 (C6H14 MW 8618 bp 68-70degC d 0658-0662) Stored under
nitrogen over molecular sieve
bull Trifluoromethanesulfonic acid (triflic acid Aldrich) was used as received
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile (AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull 1 3 dioxolane (DXL) (MW 7408 bp 78degC d 106)
The monomer DXL of commercial grade was purchased from Acros DXL was kept
under KOH for two and up to three days to remove any peroxide and stabilizer traces
and then purified by distillation over CaH2 under a N2 atmosphere prior to
polymerization
All chemicals were kept over molecular sieve before use
222 Reaction apparatus
All polymerization experiments were performed with a clean 250 ml three neck round bottom
flask A condenser was used on one of the necks of the flask in order to condense any
monomers that might otherwise possibly escape A magnetic bar was used to stir the solution
at a constant speed in order to assure even distribution of monomer and initiator
concentrations throughout the entire volume of solution A rubber septum was used to cover
one of the three necks
In the case of free radical polymerization reactions a thermocouple was also fitted to the
reaction vessel to monitor the temperature of the reaction The thermocouple regulated the
56
temperature at a constant 70degC throughout the reaction
223 Synthesis of Poly (13-dioxolane) Macromonomers
Methacrylate-terminated PDXL macromonomers were synthesized by Cationic ring-opening
polymerization which was carried out in 10 ml dichloromethane with triflic acid as initiator at
room temperature under nitrogen for 24 h in the presence of 2-hydroxypropyl methacrylate
(2-HPMA) as transfer agent 20 ml of DXL monomer was added The feed molar ratios
[DXL] [2-HPMA] are reported in Table1 as well as the molecular characteristics of the
obtained macromonomers The amount of the acid used was 20 μl After reaction the
resulting solution is poured into THF Then the product is purified by re-precipitation from
THF solution with a large excess of hexane and the obtained polymer was dried under
vacuum at room temperature The yield was checked by gravimetric determination and found
to be about 80
224 Synthesis of Poly (13-dioxolane) Hydrogel Network
The functionalized PDXL macromonomer taken for the preparation of PDXL netwok was
(FPP2) macromonomer with a theoretical average molecular weight of Mnth =2000
The macromonomer (1g) was polymerized by free radical polymerization in 10 ml of THF
using 2 2-azobisisobutyronitrile (AIBN) (001g) as initiator under a nitrogen atmosphere
The polymerization was carried out at 70degC for 24h A piece of hydrogel was obtained The
product was extracted with ethanol to remove unreacted macromonomers and then dried
under vacuum
23 Characterization Techniques
231 Raman Spectroscopy
Raman spectroscopy is used to study and analyse the structure of the macromonomers
The experiments were performed on a Dilor XY 800 spectrophotometer The detector was a
charge-coupled device (CCD) An argon laser pump beam (power density of 100 mW) has
been focused onto the sample through a microscope The working wavelength was chosen as
λ = 5145 nm In our experiments we explored the spectral range between 200 and 3700 cm-1
with a spectral resolution of 2 cm-1
57
232 1H-NMR Spectroscopy
Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) was used for structural analysis
and molecular weight of polymers and macromonomers Proton NMR spectra were obtained
using a high field 400Mhz Advance Bruker spectrometer
All of the 1H NMR samples were dissolved in deuterated chloroformThe chloroform
reference peak at 724 ppm was to ensure accuracy of peak assignments The integrals of the
peaks were used for the calculations to determine the Mw of the macromonomers
233 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) represents a chromatographic method widely used in
the analysis of polymer average molecular weights and molecular weight distributions SEC
Measurements were performed at 40degC on a Waters 2690 instrument equipped with UV
detector (Waters 996 PDA) coupled with a Differential Refractometer (ERC - 7515 A) and
four Styragel columns (106 105 500 and 50degA) THF is employed as eluent with a flow rate
of 10 mlmin Polystyrene standard samples were used for calibration
234 Swelling Measurements
In order to investigate the swelling behavior the measurement of the swelling ratio of the
polymer network is obtained from a gravimetric method in which small pieces of hydrogel
were immersed solvents such as CH2Cl2 and THF for 24 hours at room temperature (23degC)
until swelling equilibrium was reached ie when the gel thickness became essentially
constant The samples were removed from the solvents and carefully weighed (Ws) Then the
samples let to deswell and weighed every 5 min during in order to determine the swelling
kinetics in the solvents The swelling equilibrium was reached after 5 hours Afterwards the
gel was left to dry for 24 hours at room temperature until constant weight was attained and the
dry weight (Wd) was determined and the swelling ratio was calculated from equation
SR = ( ) 100timesminusWd
WdWs (57)
Where SR is equilibrium swelling ratio Ws and Wd are the sample weights in swollen and dry
states respectively
58
235 Rheological Measurements
Steady shear and oscillatory measurements have been performed on a stress imposed
rheometer Rheo-Stress-100 (RS100) from Haake used with a coneplate geometry (20 mm
diameter an angle of 4deg gap 2 mm)The imposed stress of 100 Pa during 30 seconds and a
frequency of 1Hz were applied while the strain was monitored The measurements have been
performed on swollen and unswollen samples The elastic (G) and the loss (G) moduli are
measured in linear viscoelastic region In the oscillatory experiments the frequency
dependence of both Grsquo and G is obtained at a constant strain All rheological measurements
were carried out at room temperature (23 degC)
24 Results and Discussion
241 Structural Characterization of Macromonomers
1 3 dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer end ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The synthesis of α ω-dihydroxy-PDXL chains is based on the
activated monomer mechanism44 Franta et al have established that when DXL is polymerized
by strong protonic acids such as triflic acid in the presence of a diol the PDXL chains are
essentially linear and carry end-standing OH functions It has been shown that the amount of
cyclic species formed is negligible that the dispersity is on the order of 14 and that the
molecular weight of the linear polymers is governed by the ratio of reacted monomer to
transfer agent and is generally well controlled up to 10 000 gmol
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel44 133 using an unsaturated alcohol (2-
59
HPMA) as a transfer agent results in linear polymeric chains thereby preventing formation of
cyclic oligomers through cationic polymerisation of cyclic acetals15 17 They were all prepared
at the same reaction conditions The synthetic route of functionalized PDXL macromonomers
is shown in scheme13
Scheme 13 Structures of PDXL macromonomer species54
According to this mechanism it is possible to prepare macromonomers ie PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of the
transacetalization reactions a mixture of products is obtained
A is the most abundant compound it corresponds to 50 to 60 weight wise54 It is a
macromonomer
B corresponds to 20 to 25 weight wise It is a bis-macromonomer It carries two
methacryloyl functions corresponding to transacetalization of R-OH and DXL
C corresponds to 20 to 25 weight wise It carries no methacryloyl function but two
hydroxyl groups It is a α ω-dihydroxy-PDXL
These 3 species A B and C stem from scrambling reactions that are typical with cyclic
acetals54
The characterization of these materials is based on structure and molecular weight
determination For instance the PDXL macromonomers carried at one of their ends a double
bond afforded by the methacryloyl group The latter was checked by Raman and 1H-NMR
spectroscopy All macromonomers prepared displayed functionality close to unity which
makes them suitable for the synthesis of graft copolymers
60
Raman spectroscopy is used to study and analyse the structure of the macromonomers The
aim of this study is to check the formation of linear polymer chains as well as the termination
with methacryloyl groups The spectra obtained exhibit two intense Raman bands at 800 to
900 cmP
-1 and 2700 to 3000 cmP
-1 regions and a series of small other peaks for all samples as
shown in figure 1 The most intense band (2700 ndash 3000 cmP
-1) is assigned to the aliphatic
stretching vibration of CH in the polyacetal chain Symmetric COCOC stretching frequencies
of aliphatic acetals fall in typical regions of 1115-1080cmP
-1 and 870-800 cmP
-1 145 and are
responsible for intense Raman bands In the low frequency region there are three very
characteristic Raman bands in the 600 ndash 550 cmP
-1 540 ndash 450 cmP
-1 and 400 ndash 320 cmP
-1 ranges
which are assigned to COCOC deformations145 146 Also the acetals have strong multiple
bands in the region of 1160ndash1040 cmP
-1 as noticed on the Raman spectra involving the C-O
stretching modes In addition to this the O-CH-O group gives rise to a band at 1350 ndash1325
cmP
-1 for C-H deformation Other intense Raman bands are observed in the region of 3000 ndash
2700 cmP
-1 Below 3000 cmP
-1 the corresponding frequencies are assigned to the aliphatic C-H
stretching modes145 The methoxy group is detected in the region of 2835 ndash 2780 cmP
-1
Figure 1 Raman spectra of methacrylic-terminated PDXL macromonomers (FPP2 FPP15 and
FPP1)
145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The Handbook of IR
and Raman Characteristic Frequencies of Organic Molecules United Kingdom Ed by Academic Press Limited London (1991)
146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman Spectroscopy 3rd Edition AP Limited London (1964)
61
As far as the presence of the methacryloyl group in the polymeric chain is important bands
have been observed at 1640 cmP
-1 which corresponds to C=C bonds The carbonyl compounds
absorb strongly within 1900 ndash1550 cmP
-1 region145 146 the spectra show a C=O bond absorption
found at 1720 cmP
-1 In the region of 1340 ndash1250 cmP
-1 the methacrylate bands are observed
Broad absorption is found near 3500 cm -1 owing to stretching of the OH bonds OH
deformation bands are found at 1400 cmP
-1P and 1340 cmP
-1 This observation indicates that both
methacrylic and ndashOH groups are present and eventually the resulting product is a mixture of
the three species as shown in the scheme above
Typical 1H-NMR spectrum of PDXL macromonomer shown in figure 2 exhibits the expected
resonance assigned to the methoxy protons (477 ppm) and OCH2CH2O protons at (374
ppm) Two signals corresponding to =CH2 were observed at (612 ndash 614 ppm) and (557 ndash
559 ppm) Therefore the spectrum confirmed the chemical structure HO[CH2CH2OCH2O]nR
of methacryloyl- terminated PDXL macromonomer
Figure 2 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP2)
242 Molecular Weight Determination
Besides the structure 1H-NMR enables us to determine the number-average molecular weight
(Mn) In the calculation of the latter the methacryloyl end group was included The
62
polydispersity and index MwMn and the number-average molecular weight were obtained
from SEC measurements Table 1 summarizes these values It can be seen that Mn (SEC) and
Mn (NMR) are very close to each other for all macromonomer samples and are in agreement
with the theoretical values predicted from calculations Under our polymerization conditions
the polydispersity index is 16 for all samples
Table 1 Characteristics of PDXL macromonomers prepared at different degrees of
polymerization
Sample Dp Mnth MnSEC MnRMN MwMn f (a)
FPP1 135 1000 1120 1160 16 097
FPP15 2025 1500 1540 1550 16 099
FPP2 270 2000 2040 2100 16 097
Dp degree of polymerization = [DXL] [2HPMA]
a functionality of macromonomers (methacryloyl end groups molecule)
243 Swelling of Poly (13 Dioxolane) Hydrogel
The synthesized PDXL hydrogel has been studied in terms of swelling and rheological
behaviors The degree of swelling and the rate of swelling of the hydrogel are studied It is
known that hydrogel can swell in several solvents but at different degree of swell according to
many factors related to the nature of the solvents and the type of polymer-solvent interactions
It was found that the solubility parameter of the solvents (δ) had a great effect on swelling
degree For instance hydrogels can swell fast in CH2Cl2 (δ = 976 cal cm12 -32) and reached
equilibrium within no more than an hour However it will take about more than 20 h to reach
equilibrium in CH3 OH (δ = 145 cal cm12 -32) It was known that the polymer can reach
greatest swelling degree when the solubility parameter of the polymer is close to that of the
solvents The solubility parameter of PDXL is about 93 cal cm 12 -32 134 The swelling has been
examined in THF and CH2Cl2 for PDXL hydrogel It has been observed that the swelling
equilibrium is reached after almost 5 hours of swelling for all samples in both solvents The
results show that THF (δ = 952 cal cm12 -32)147 swells the hydrogel to the greatest degree
compared to CH2Cl2 as shown in figure 3 However CH2Cl2 molecules provide less swelling
147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983)
63
capacity than in THF On the basis of the experiment The PDXL hydrogel reached high
swelling degree due to its solubility parameter is much closer to that of THF
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
THF CH2Cl2
Swel
ling
degr
ee
Time (min)
Figure 3 Swelling kinetics of PDXL hydrogel in two different solvents CH2 Cl2 (solid
squares) and in THF (hollow squares)
244 Viscoelastic Behavior
Rheological measurements were performed on rheometer in the Cone and Plate geometry
Both steady shear and oscillatory experiments were carried out The dynamic storage and loss
moduli G and G were examined at room temperature (23 degC)
Many attempts have been carried to extend the elasticity theory to swollen gels148 149 Based
on this approach all measurements have been performed on both swollen and unswollen
hydrogel samples for the purpose of comparison so that to examine the mechanical properties
even in swollen state For instance Flory and Rehner recognized the swelling phenomenon
exhibited by cross-linked polymers when exposed to certain solvents and related the modulus
of elasticity of a swollen cross-linked polymer network to an unswollen network150 Figure 4
illustrates the strain dependence of G and G for swollen and unswollen samples
148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for Experimental
Mechanics SEM Annual Conference Proceedings (2002)
64
10-5 10-4 10-3 10-2 10-1 100 101 102101
102
103
104
Guns Guns Gs Gs
GG
(Pa
)
γ ()
Figure 4 Strain dependence of the elastic modulus Grsquo (circles) and of the viscous modulus
Grdquo(triangles) for two samples of unswollen hydrogel (solid symbols) and swollen hydrogel
(hollow symbols)
The moduli are measured as a function of strain at a constant frequency It appears that the
linear viscoelastic region is observed while the strain is increasing in either state which
indicates that the internal structure of the samples has not been disrupted when deformed
This leads to reveal that the gel is strain resistant in swollen and unswollen states and within a
large strain range the hydrogel retains its elasticity as shown in figure 4 where the linear
viscoelastic region extends to almost 02
The frequency dependence of G and G is shown in figure 5 similarly for swollen and
unswollen hydrogels The system behaves typically like a gel as it can be noticed that the
elastic component G (storage modulus) is far greater than the viscous component G (loss
modulus)151 Based on these results the hydrogel exhibits extreme elasticity at low
frequencies
151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure 554 (2000) 99-108
65
100 101
103
104
105
Gs Guns Gs GunsG
G(
Pa)
ω (rads)
Figure 5 Frequency dependence of Grsquo(circles) and Grdquo(triangles) for swollen hydrogel
(hollow symbols) and unswollen hydogel (solid symbols)
Finally figure 6 illustrates the complex viscosity profiles another parameter of
viscoelasticity which measures the magnitude of the total resistance to a dynamic shear
Again this property has not been affected by swelling since the results show similar behavior
for swollen and unswollen states It decreases sharply as frequency increases which
characterizes the samples degree of viscoelasticity at various time scales Therefore from the
results discussed above the hydrogel network is elastic and stable even in the swollen state
thereby possessing very good mechanical properties
100 101 102 103
102
103
104
105
η unswollen η swollen
ηlowast (P
a s)
ω (rads)
Figure 6 Frequency dependence of the complex viscosity η for unswollen hydrogel (solid
squares) and swollen hydrogel (hollow triangles)
66
Conclusion
The hydrogel properties were discussed in terms of swelling and viscoelastic
behaviors The hydrogel has combined special properties Its swelling behaviour in the
solvents was dependent on the solubility parameter of both solvents and hydrogel
Rheological measurements were successful when used in order to study the viscoelastic
behavior of the hydrogel of pure PDXL in swollen and unswollen states The Strain
dependence of G and G for both samples shows linear viscoelastic region and allows to
determine the yield stress Same conclusions can be given concerning the frequency
dependence of complex viscosity the swelling does not affect this property The results reveal
a perfect elastic and resistant hydrogel in other words the viscoelastic properties have not
been so much affected by swelling They may be particularly useful in the design of improved
microfluidic devices that utilise the relationship between swelling and strain This kind of
material can be potentially used in biosystems such as intelligent drug delivery systems
67
References
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-
174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002)
1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080 140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922 145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The
Handbook of IR and Raman Characteristic Frequencies of Organic Molecules United
Kingdom Ed by Academic Press Limited London (1991) 146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman
Spectroscopy 3rd Edition AP Limited London (1964) 147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983) 148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-
1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for
Experimental Mechanics SEM Annual Conference Proceedings (2002) 151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure
554 (2000) 99-108
68
CHAPTER III Synthesis and Characterization of Copolymers
31 Introduction
Amphiphilic block and graft copolymers consisting of hydrophilic and hydrophobic parts
have been subjects of numerous studies within which block and graft copolymers containing
hydrophilic polyoxyethylene segments and other hydrophobic segments have attracted much
attention because polyoxyethylene segments are not only hydrophilic but also nonanionic
and crystalline and can complex monovalent metallic cations Graft copolymers offer all
properties of block copolymers but are usually easier to synthesize Moreover the branched
structure leads to decreased melt viscosities which is an important advantage for processing
Depending on the nature of their backbone and side chains they give rise to special properties
in selective solvents at surfaces as well as in the bulk owing to microphase separation
morphologies12 They can be used for a wide variety of applications such as polymeric
surfactants electrostatic charge reducers compatibilizers in polymer blends polymeric
emulsifiers controlled wet ability and so on152 153 In order to prepare graft copolymers with
well-defined structure one can utilize the macromonomer technique (grafting through
technique) Well-defined structure graft copolymers are synthesized by copolymerization of
macromonomers with low molecular weight comonomers6 It allows the control of the
polymer structure which is given by three parameters (i) chain length of side chains which
can be controlled by the synthesis of the macromonomer by living polymerization (ii) chain
length of backbone which can be controlled in a living copolymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular weight monomer However the distribution of spacings
may not be very easy to control due to the incompatibility of the polymer backbone and the
macromonomers154 As pointed out in recent publication reviews155 there is a complex
interplay of factors that govern the reactivities in copolymerizations involving
macromonomers When different comonomers are copolymerized with the same it seems that
the degree of interpenetration between the macromonomer and the propagating copolymer 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305
69
backbone plays the major role in the measured reactivities Nevertheless the main properties
depend on both the average composition of the systems and the microstructural distribution of
the comonomer sequences along the macromolecular backbone which is determined by the
reactivity ratios of the macromonomer and the corresponding comonomer in the free radical
polymerization process156 157
In this chapter our work deals with the preparation and characterization of new organo-
soluble associative copolymers based on short hydro-soluble chains of poly (1 3 dioxolane)
(PDXL) Many reports have been published on PDXL macromonomers used to form
hydrogels136 137 158 159 160 161 162 however very few were on graft copolymers with PDXL
branches162 These macromonomers are used for the preparation of amphiphilic graft
copolymers by solution free radical copolymerization with a hydrophobic comonomer
styrene (St) and methyl methacrylate (MMA) Structural characterization of these
copolymers molecular weight determination reactivity ratios and the polymerizability of the
PDXL macromonomer have been discussed Finally their thermal properties are discussed
according to the weight content of PDXL in the copolymers
32 Experimental
321 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269
70
bull Ethanol (C2H6O MW 4607 bp 78degC d 081)
Ethanol (Prolabo 95-96) was purified by distillation with 5g of Magnesium and 05g of
iodine for 75ml of alcohol under a N2 atmosphere After discoloration of the mixture
solution a volume of Ethanol was added and then distilled normallyThen it was stored
over molecular sieve
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile(AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull Styrene (C6H5CH=CH2 MW 10416 bp 145degC d 091)
Styrene (Prolabo product) was purified by distillation over CaHB2 at reduced pressure
bull Methyl Methacrylate (MMA)(H2C=C(CH3)CO2CH3 MW 10012 bp 100degC d
0936)
Methyl Methacrylate (Prolabo product) was purified by distillation over CaHB2 at reduced
pressure
All chemicals were kept over molecular sieve before use
322 Synthesis of Poly (Styrene-co-Poly (13-dioxolane))
a) Conventional Free Radical Copolymerization
The reaction route for the conventional copolymerization of Styrene and PDXL
macromonomers using AIBN as the free radical initiator at 60degC is shown in scheme 14
71
Scheme 14
PDXL macromonomers of different molecular weights were copolymerized with St in THF at
60degC in the presence of 2 2rsquo-azobisisobutyronitrile AIBN (1 based on the total weight of
the monomers) as initiator under a nitrogen atmosphere using different feed molar fractions
of macromonomers The total monomer concentration for was 6 10-1 M in all cases The
copolymerization product is diluted with THF and then added dropwise to a large excess of
ethanol to remove unreacted PDXL macromonomers25 43 and precipitate the copolymers
Then they were finally dried over vacuum at 40degC to constant weight The yields of all
reactions are 70ndash 90 Table 2 indicates the amounts of comonomers initiator and solvent
employed in the copolymerization study
72
Table 2 Copolymerization of PDXL macromonomers (M1) with Styrene (M2)
Sample M1 M2M1 PDXL (g) (mol)
Styrene (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2SP2 FPP2 20 349 174510-4 364 349 10-2 007 60 0610 3SP2 FPP2 30 232 116 10-4 364 349 10-2 006 60 0601 5SP2 FPP2 50 14 69810-4 364 349 10-2 005 60 0593
2SP15 FPP15 20 262 174510-4 364 349 10-2 006 60 0610 3SP15 FPP15 30 174 116 10-4 364 349 10-2 006 60 0601 5SP15 FPP15 50 105 69810-4 364 349 10-2 005 60 0593
2SP1 FPP1 20 174 174510-4 364 349 10-2 006 60 0610 5SP1 FPP1 50 07 69810-4 364 349 10-2 005 60 0593 8SP1 FPP1 80 0436 43610-4 364 349 10-2 005 60 0589
b) Controlled Free Radical Copolymerization
The comb-structure copolymer of styrene and PDXL was obtained by grafting-from
mechanism through Nitroxide-Mediated Polymerization
Nitroxide mediated polymerization (NMP) is a controlled radical polymerization (CRP)
technique which already offers the ability to prepare a wide variety of well-defined polymer
architectures119 Despite the significant improvements brought to CRP techniques such as
NMP atom transfer radical polymerization (ATRP) or reversible addition fragmentation chain
transfer (RAFT) the preparation of complex architectures by CRP is restricted by the
exclusion of monomer systems that are polymerized by fundamentally different mechanisms
like lactides ethylenepropylene oxide The most promising approaches to extend the range of
polymer compositions are based on the use of heterofunctional initiators163 allowing the
combination of mechanistically distinct polymerization reactions without the need for
intermediate transformation and protection steps
In the field of NMP the development of multifunctional initiators was focused on TEMPO
and TIPNO which are examples of nitroxides (Scheme 15) It is worth to mention that in
NMP these are used as counter-radicals associated with a conventional azoic initiator so this
pair of initiators is known as a bimolecular system
163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671
73
Scheme 15 TEMPO and based alkoxyamines
Another initiator used for NMP is the commercially available alkoxyamine also called
MAMA-SG1164 (Scheme 16) known as a monomolecular system initiator which is
particularly convenient for functionalization of polymer chain ends164 165 MAMA-SG1 has
been developed by Didier Gigmes and co in collaboration with Arkema Company166 Thanks
to a particularly high dissociation rate constant value kd1 up to now this alkoxyamine has
proved to be one of the most potent alkoxyamines reported in the field of NMP167 168 This
initiator is used for polymerization of styrene and n-butyle acrylate allowing formation of
well-defined linear and star structures
Scheme 16
164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006) 5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219
74
Scheme 17 MAMA-SG1 structure and dissociation scheme
bull Multifunctionalization of Polystyrene (HO-PS)
MAMA-SG1 was used to run copolymerization of styrene at 90 mol with HEMA in order
to obtain functionalized polystyrene The monomers and alkoxyamine were introduced in a
250 mL two neck round-bottom flasks fitted with septum condenser and degassed for 15
min by nitrogen bubbling The reaction was performed in bulk at 120 degC under N2 with
vigorous stirring Targeted molecular weight and polydispersity were 30 000 g mol and 12
respectively
After polymerization the final polymer mixture was dissolved in a minimum THF and
precipitated in cold ethanol followed by drying under vacuum at 30degC
bull Synthesis of PS-g-PDXL
PDXL was copolymerized by cationic ring-opening polymerization which was carried out in
40 ml dichloromethane with triflic acid as initiator at room temperature under nitrogen for 24
h in the presence of OH-multifunctionalized PS (1g 3 10-5 mol) as transfer agent 20 ml
(0286 mole) of DXL monomer was added Table 6 gives the molecular characteristics of the
obtained copolymer The amount of the acid used was 20 μl After reaction the resulting
solution is poured into THF Then the product is purified by re-precipitation from THF
solution with a large excess of hexane and the obtained polymer was dried under vacuum at
room temperature The yield was checked by gravimetric determination and found to be about
75 The polymerization route is presented in the scheme below
75
Scheme 18
323 Synthesis of Poly (Methyl Methacrylate-co-Poly (13-dioxolane))
Same procedure has been used for the synthesis of Poly (Methyl Methacrylate-co-Poly (1 3-
dioxolane)) copolymers The yields of the reactions are in the range of 70ndash 90
Table 3 shows the amounts of comonomers initiator and solvent employed in the
copolymerization reactions
Table 3 Copolymerization of PDXL macromonomers (M1) with MMA (M2)
Sample M1 M2M1 PDXL (g) (mol)
MMA (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2MP2 FPP2 20 374 187 10-4 3744 374 10-2 008 65 0604 3MP2 FPP2 30 2 10 10-4 300 300 10-2 005 50 0620 5MP2 FPP2 50 15 748 10-4 3744 374 10-2 005 60 0636
2MP15 FPP15 20 2 133 10-4 28 280 10-2 005 25 100 3MP15 FPP15 30 187 125 10-4 3744 374 0-2
006 60 0644 5MP15 FPP15 50 112 748 10-4 3744 374 10-2 005 60 0636
2MP1 FPP1 20 2 20 10-4 400 4 10-2
006 50 0840 3MP1 FPP1 50 125 125 10-4 3744 374 10-2 005 64 0604 5MP1 FPP1 80 075 748 10-4 3744 374 10-2 005 60 0636
33 Characterization Techniques
331 1H-NMR Spectroscopy
1H NMR Spectroscopy was used for compositional and structural analysis of the copolymers
1H-NMR spectra of the copolymers were recorded on the high field 400Mhz Advance Bruker
spectrometer All of the 1H NMR samples were dissolved in deuterated chloroform The
integrals of the peaks of copolymer components were used for the calculations to determine
76
the molecular weights polydispersity indices and the amount of each comonomer that was
incorporated into the copolymer
332 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) was used in the charaterization of the copolymers to
determine average molecular weights and polydispersity indices SEC Measurements were
performed at 40degC on a Waters 2690 instrument equipped with UV detector (Waters 996
PDA) coupled with a Differential Refractometer (ERC - 7515 A) and four Styragel columns
(106 105 500 and 50degA) THF is employed as the mobile phase with a flow rate of 10
mlmin Polystyrene standard samples were used for calibration
333 Diffraction Scanning Calorimetry
Diffraction Scanning Calorimetry (DSC) measurements are performed on a Modulated
Temperature Differential Scanning Calorimeter Q100 TA instrument under nitrogen at 50
mlmin The samples are hermetically sealed in aluminium pans and they are subjected to a
heating program as follows
For Poly (Styrene-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 120degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -80degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to130degC
For Poly (Methyl Methacrylate-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 130degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -95degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to150degC
The thermograms obtained illustrate Glass Transition Temperatures (Tg) and Meltind Points
(Tm) of the copolymers
77
34 Results and Discussion
Methacryloyl-terminated PDXL macromonomers with the Mn range of 1000-2000 gmole
were copolymerized with vinyl and methacrylic monomers in order to obtain amphiphilic
graft copolymers with chemical structure of hydrophobic backbone and hydrophilic side
chains
341 Structural Characterization of the Copolymers
The structure of the copolymers was well defined by 1H-NMR analysis The copolymer 1H-
NMR spectra confirm the formation of copolymers see figures 7 8 and 9 The chemical
shifts of protons of polystyrene and PDXL can be clearly distinguished The following peaks
are assigned for OCHBB2BBO protons at 478 ppm and OCHBB2BBCHBB2BBO protons at 375 ppm (5H CBB6BB
HBB5BB) at 728 711 and 706 ppm as shown in Figure 8 The spectrum of PMMA-PDXL
copolymer is shown in Figure 9 where the chemical shifts of PMMA correspond to the proton
resonance as depicted in the figure the O-CH3 protons are observed at 361 ppm and clear
resonance assigned to the methyl group protons at 085-103 ppm and eventually we observe
the corresponding chemical shifts for OCHBB2BBCHBB2BBO protons (374 ppm) and OCHBB2BBO protons
(477 ppm) to confirm the incorporation of PDXL in the copolymer
Figure 7 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP1)
78
Figure 8 1H-NMR spectrum of Styrene-g-PDXL copolymer in CDCl3 (sample 3SP2)
79
Figure 9 1H-NMR spectrum of MMA-g-PDXL copolymer in CDCl3 (sample 2MP2)
342 Copolymer Molecular Weight and Composition
a) Conventional Free Radical Copolymerization
Copolymerization of PDXL macromonomers with MMA and ST in THF solution was studied
for different molar feed ratio of PDXL The amounts of monomeric units in the copolymers
were determined by elemental analysis The results are presented in Table 4 and 5 which
summarise the characteristics of the graft copolymers in terms of macromonomer feed ratio
(M2M1) and average Mn obtained from SEC as well as copolymer composition in weight and
mole percentages which is determined from 1H-NMR
80
Table 4 Characteristics of PDXL macromonomers (M1) copolymerized with Styrene (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2SP2 FPP2 20 49 476 4025 337 9200 162 2 3SP2 FPP2 30 39 322 303 221 8900 162 2 5SP2 FPP2 50 277 196 21 13 7200 159 1
2SP15 FPP15 20 418 476 34 34 9100 157 2 3SP15 FPP15 30 323 322 24 214 7000 161 2 5SP15 FPP15 50 224 196 152 12 6700 147 1
2SP1 FPP1 20 323 476 30 427 9200 178 3 5SP1 FPP1 50 16 196 1424 17 5800 158 1 8SP1 FPP1 80 107 123 85 095 11900 195 1
Table 5 Characteristics of PDXL macromonomers (M1) copolymerized with MMA (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2MP2 FPP2 20 50 476 35 26 21900 198 4 3MP2 FPP2 30 40 322 21 13 25900 157 3 5MP2 FPP2 50 286 196 13 07 87200 455 6 2MP15 FPP15 20 416 45 28 25 19800 193 4 3MP15 FPP15 30 333 322 22 18 15200 277 3 5MP15 FPP15 50 23 196 13 10 24700 16 2 2MP1 FPP1 20 333 476 26 34 21100 319 6 3MP1 FPP1 30 333 322 19 22 17100 197 3 5MP1 FPP1 50 20 196 10 11 13900 354 2
81
b) Controlled Free Radical Copolymerization
Multifunctionalization of Polystyrene and Synthesis of poly (S-g-PDXL) copolymer give
results which are shown in Table 6 These data have been obtained from the 1H-NMR and
SEC analyses illustrated in figures 10 and 11 The resonance shifts assigned to all components
(PDXL PS and HEMA) are very clear This enables us to make calculations to determine
composition of each copolymer in addition to obtain the average number of grafts and the
number average-molecular weight of a graft
It is observed that the multifunctionalized-PS is composed of 20 in mole of HEMA which
results in 58 grafts (Ng = 58) per molecular chain
After copolymerization multifunctionalized-PS with DXL the copolymer PS-g-PDXL
(DXPS) possesses the following characteristics which are presented in Table 6 It has a
number average-molecular weight of 83000 gmol with 80 of PDXL content The number
average-molecular weight of one graft has been calculated and found to be 1000 gmol
Table 6 Characteristics of functionalized Styrene (HO-PS) and PS-g-PDXL (DXPS)
copolymer
Strusture Sample MnSEC IP PDXL
w mol
PS
w mol
HEMA
w mol
Ng Graft
Mn
HO-PS
32 700
12
_ _
77 80
23 20
58
_
DXPS
83 000
24
71 80
17 13
12 75
58
1000
82
Figure 10 1H-NMR spectrum of Multifunctionalized of Polystyrene in CDCl3
Figure 11 1H-NMR spectrum of poly (S-g-PDXL) copolymer (DXPS) in CDCl3
83
341 Determination of Monomer Reactivity Ratios
The application of the classical treatment based on linearization of the copolymerization
equation of Mayo and Lewis91 or the non-linear least-squares approach suggested by Tidwell
and Mortimer95 requires working with high macromonomer concentrations (ie feed
compositions higher than 20-30 of macromonomer)156
The MayondashLewis equation (58) that relates the instantaneous compositions of the monomer
mixture to the copolymer composition is approximated to a simplified form (equation (59))
suggested by Jaacks169 when working with a large excess of one of the comonomers This is
the case of copolymerisation reactions between a conventional comonomer and a
macromonomer of relatively high molecular weight where using low molar concentrations of
macromonomer is mandatory due to its restricted solubility and the extremely viscous media
][ ][ ]
[ ][ ]
[ ] [[ ] [ ]221
211
2
1
2
1
MrMMMr
MM
MdMd
++
=
(58)
[ ][ ] 1
22
1
2
MMr
MdMd
=
(59)
According to equation (59) the copolymer composition or the frequency of branches is
essentially determined by the monomer composition and the monomer reactivity ratio of the
comonomer r2 (inversely proportional to the macromonomer reactivity) under the limit
condition of [M2][M1] gtgt1 In order to obtain reliable values it is frequently necessary to
run the copolymerisation at different conversions or to carry out several copolymerizations
with different initial monomer ratios170 In such cases an integrated form of equation (59) is
used
[ ] [ ][ ][ ] 01
12
02
2 lnlnMM
rMM tt =
(60)
169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046
84
where [Mi]t[Mi]0 is the ratio among the composition of monomer i at time t and the initial
feed composition A plot of ln ([M2]t[M2]0) versus ln ([M1]t[M1]0) should result in a straight
line with a slope that equals to r2 (the reactivity ratio of the comonomer)
Thus the monomer reactivity ratios between the PDXL macromonomers and the comonomers
were estimated with the data in tables 4 and 5 We can apply equation (60) to the estimation
where M1 and M2 are the PDXL macromonomer and copolymer respectively The monomer
reactivity ratios are determined for macromonomers of different Mn (degree of
polymerization) and summarized in Table 7
Table 7 Monomer reactivity ratios for copolymerization of PDXL macromonomers (M1)
with St and MMA (M2)
Sample M2 M1
macromer Mnth
r2 1r2
SP2 St FPP2 2000 012 plusmn 0006 833
SP15 St FPP15 1500 0042 plusmn 6 10-4 238
SP1 St FPP1 1000 0015 plusmn 3 10-4 6666
MP2 MMA FPP2 2000 002 plusmn 001 50
MP15 MMA FPP15 1500 007 plusmn 0 02 1428
MP1 MMA FPP1 1000 0018 plusmn 001 5555
In the case of copolymerization with Styrene and MMA the results suggest that the reactivity
of the methacrylic double bond in the prepared macromonomers is not affected in their
copolymerization with Styrene or MMA This point is confirmed when analysing the inverse
ratio 1r2 = k21k22 which is sometimes considered as the relative copolymerization reactivity
of a macromonomer171 This quantity is the ratio between the crosspropagation and
homopropagation rate constants of comonomer (2) which is directly proportional to the
reactivity of the macromonomer (1) and gives a clear idea of the relative reactivity of a
growing radical ending in a 2 unit towards the addition of monomer (1) in comparison to the
171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620
85
tendency for the homopropagation So we have a situation where r1 gtgt 1 gtgt r2 and it is
expected that the initially formed chains should contain more macromonomers and then more
comonomer segments are added These are only assumptions but they give an indication
about the probable composition drift of the graft copolymers obtained On the other hand in
the case of copolymerization of poly (13dioxolane) macromonomers with styrene (Figure
12) the results show that r2 increases with increasing PDXL side chain length (in terms of
average Mn) and this leads to say that the side macromonomer chain length affect the
reactivity of the comonomer Thus this indicates that a growing radical of macromonomer
with a shorter chain length (ie lower Mn ) attacks more frequently a monomer of the same
nature than it does a macromonomer with a longer length (ie higher Mn) as it can be noticed
from the results in Table 7
However the r2 values of the copolymerization with MMA as shown in Figure 13 give
unclear dependence on the side poly (13dioxolane) macromonomer chain length this may be
due to the resulting polydispersity of the copolymerization Mentioned behaviour may be
related with the reactive structure of comonomers vinyl in the case of Styrene or methacrylic
in the case of MMA in regard to the ending methacrylic double bond of macromonomers
besides the hydrophilic character of the macromonomers
86
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0015 plusmn 3 10-4 SP1
b
r2 = 0042 plusmn 6 10-4
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP15
c
r2= 012 plusmn 0006
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP2
Figure 12 Application of Jaacksrsquo treatment to the St-g-PDXL copolymerization systems
(a) SP1 (b) SP15 (c) SP2
87
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0018 plusmn 001 MP1
b
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 007 plusmn 002MP15
036788
c
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 002 plusmn 001 MP2
Figure 13 Application of Jaacksrsquo treatment to the MMA-PDXL copolymerization systems
(a) MP1 (b) MP15 (c) MP2
88
341 Glass Transition Temperatures
Thermal analysis of Styrene-g-PDXL copolymers allows to determine their glass transition
and melting temperatures In the first place the measurements were performed on a
conventional DSC from which the thermograms obtained show an overlapping of PS glass
temperature and PDXL melting point signals This has been observed for all samples A
different approach in the characterisation of these copolymers was by means of Modulated
Temperature Differential Scanning Calorimeter (MTDSC) which is an extension of
conventional DSC This approach combines high resolution with high sensitivity by use of a
sinusoidal temperature modulation superimposed on a constant temperature or linear
temperature program with a small underlying average heating rate172 173 In comparison to
conventional DSC the MTDSC analysis enables the simultaneous calculations of an
additional quantity the cyclic or modulus of heat capacity Cp (J g-1K-1 172)
ωT
HFp A
AC =
(61)
is the amplitude of the cyclic heat flow (Wg-1) and AWhere AHF Tω is the amplitude of cyclic
heating rate with AT the temperature modulation amplitude (K) ω the modulation angular
frequency (2πp) and p is the modulation period (s)172
In fact the MTDSC splits the overlapped signals into two distinct temperatures melting
temperature of the hydrophilic grafts and glass transition temperature of the hydrophobic
backbone as can be noticed in Figure 14 in which melting temperature appears to be 5626degC
which is closer to the glass transition temperature with a value of 5671degC From the results
obtained out of the thermogram it is clear that the measurements show very close values of
Tm and Tg for all copolymer samples where in conventional DSC these two temperatures
cannot be distinguished
172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
89
Figure 14 MTDSC thermogram of 5SP1 copolymer at heating rate of 2degCmin
Tg was taken at the midpoint of the transition region The results obtained are shown in
Tables 8 and 9 for copolymers with Styrene and MMA respectively Then a plot of the
copolymers Tg has been constructed against PDXL content in order to determine the effect of
the latter on Tgrsquos As it can be noticed in the Figure 15 Tg of the copolymers decreases
exponentially with increasing PDXL content and this may be due to the decrease in the
intermolecular interactions between the molecular chains and can be associated with higher
mobility and flexibility of the polymeric chains when PDXL is incorporated in the
copolymers The results clearly indicate that Tg values of the copolymers depend on the
composition of comonomers and a decrease with increasing PDXL content in the obtained
copolymers
90
Table 8Transition temperatures of Styrene-g-PDXL copolymers obtained by thermal
analysis (DSC) Sample PDXL content Tg wt () (degC) 8SP 85 7489 1
5SP 1424 5671 1
5SP 152 5590 15
21 6739 5SP 2
303 4480 3SP 2
34 2665 2SP15
4025 2SP 4060 2
Table 9Transition temperatures of MMA-g-PDXL copolymers obtained by thermal analysis
(DSC)
Sample PDXL content Tg
wt () (degC)
5MP 10 10545 1
5MP 13 8278 15
21 6576 3MP 2
22 7550 3MP 15
26 7013 2MP1
91
5 10 15 20 25 30 35 40 4520
30
40
50
60
70
80
a
SP COPOLYMERSTg
(degC)
PDXL content in wt()
10 15 20 2560
70
80
90
100
110
b
Tg (deg
C)
PDXL content in wt()
MP COPOLYMERS
Figure 15 Glass transition temperatures vs PDXL macromonomer content for copolymer
systems (a) Styrene-g-PDXL copolymers (b) MMA-g-PDXL copolymers
92
Conclusion
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers The macromonomer reactivity estimation suggests that the
length of the PDXL side chains does affect the reactivity of the methacrylic double bond of
the macromonomer when copolymerized with St However in the case of copolymerization
with MMA there is no dependence on the graft size Finally from DSC measurements the
values of Tg depend on the composition and the size of the PDXL grafts In all copolymers
the increase in amount of the incorporated PDXL macromonomer results in a substantial
decease in glass transition
93
References 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305 156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269 163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671 164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006)
5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219 169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620 172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly
(1 3 Dioxolane)) on Immiscible Polymer Blends
of Polystyrene and Poly (Ethylene Glycol)
41 Background
411 Physical Blends
Physical blending is defined as the simple mechanical mixing of two or more polymers either
in the melt or in solution174 At first glance this approach would seem to be ideal for
preparing hybrids as blending is considered a simple and economical procedure that is
commonly used to produce new products from existing materials175 However in polymer
science the effectiveness of blending is dependent upon the degree of compatibility of the
polymers involved176 At least three general types of materials can result from blending
depending on the mutual solubility and semi-crystallinity of the constituents
412 Equilibrium Phase Behavior
Mixing of two amorphous polymers can produce either a homogeneous mixture at the
molecular level or a heterogeneous phase-separated blend Demixing of polymer chains
produces two totally separated phases and hence leads to macrophase separation in polymer
blends Some specific types of organized structures may be formed in block copolymers due
to microphase separation of block chains within one block copolymer molecule
Two terms for blends are commonly used in literature miscible blend and compatible blend
The terminology recommended by Utracki177 will be used By the miscible polymer blend it
means a blend of two or more amorphous polymers homogeneous down to the molecular
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York (1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York (1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser Publishers Munich (1989)
95
level and fulfilling the thermodynamic conditions for a miscible multicomponent system An
immiscible polymer blend is the blend that does not comply with the thermodynamic
conditions of phase stability The term compatible polymer blend indicates a commercially
attractive polymer mixture that is visibly homogeneous frequently with improved physical
properties compared with the constituent polymers
Miscible blends occur spontaneously when the overall energy of mixing (ΔGmix) is negative
as defined by the Gibbs-Helmholtz free energy equation (Equation 62)
(62)
In the Gibbs-Helmholtz equation ΔHmix is the enthalpy of mixing and ΔSmix is the entropy of
mixing while T is the temperature of the blend Flory-Huggins178 and Scott179 have made
further correlation of enthalpy and entropy as a function of the polymer components and their
properties (Equation 63)
(63)
In Equation 63 χ is a measure of the polymer-polymer interaction energy V is the volume of
the system Φi is the volume fraction of polymer i R is the gas constant T is the temperature
of blending Vr is the reference volume of the monomers and χi is the degree of
polymerization
Examination of Equation 63 reveals that the entropy of mixing is highly dependent on the
molecular weight of the blended polymers while the enthalpy is much more dependent on the
level of interaction between the polymer types Additionally Scott showed that as molecular
weight increases to the level commonly found in commercially useful materials ΔS
approached zero (0) Therefore polymer blends of commercial importance are primarily
influenced by the rate of enthalpy However for polymers with weak interactions (as χ
approaches 1) eg as observed in most polymer pairs the enthalpy of mixing can be further
reduced according to Equation 64
178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279
96
(64)
In Equation 64 δi is the polymerrsquos solubility parameter (an estimation of its ability to be
dissolved in a range of solvents) derived from the square root of the cohesive energy density
pioneered by Hildebrand180 Thus most early work with polymer blends concentrated on
matching the solubility parameters of the component polymers
Unfortunately the theoretical maximum difference in solubility for a 5050 polymer blend is
only 01 (calcm3)12 This narrow margin is much smaller than the standard error among
methods used to determine solubility parameters181 The ability to predict miscibility of
polymer pairs with strong interactions such as donor-acceptor and hydrogen bonding which
can increase miscibility by creating an exothermic reaction upon mixing (ΔH lt0) have been
attempted for many years with varying degrees of success
The formation of miscible blends is dependent on several factors including molecular
structure average chain length tacticity of the polymers as well as the temperature of mixing
and the blending method If the blended polymers are miscible (ΔGmix lt 0) and thus
compatible the resulting material will display an amalgamation of properties which are
predictable using the same techniques as those used for random or statistical copolymers
Polymer blends account for a significant percentage of polymer production and are produced
either to reduce costs to aid in processing or to improve a variety of specific properties For
example polycarbonates have been blended with polybutylene terephthalates to increase
chemical resistance and to aid in processing while polyphenylene oxides are bended with
polystyrenes to improve toughness and increase glass transition temperatures182
413 Compatibilization
As it follows from thermodynamics the blends of immiscible polymers obtained by simple
mixing show a strong separation tendency leading to a coarse structure and low interfacial
180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999)
97
adhesion The final material then shows poor mechanical properties On the other hand the
immiscibility or limited miscibility of polymers enables formation of wide range structures
some of which if stabilized can impart excellent end-use properties to the final material To
obtain such a stabilized structure it is necessary to ensure proper phase dispersion by
decreasing interfacial tension to suppress phase separation and improve adhesion This can be
achieved by modification of the interface by the formation of bonds (physical or chemical)
between the polymers This procedure is known as compatibilization and the active
component creating the bonding as the compatibilizer174 177 183
The most popular method of compatibilization is by addition of a third component In most
cases such an additive is either a block or graft copolymer Since the key requirement is
miscibility it is not necessary for the copolymer to have identical chain segments as those of
the main polymers It suffices that the copolymer has segments having specific interactions
with the main polymeric components viz hydrogen bonding dipole-dipole dipole-ionic
Lewis acid-base etc
Addition of a block or graft copolymer reduces the interfacial tension and alters the molecular
structure at the interface Thus compatibilization by addition changes not only the interfacial
properties but it may affect the flow behavior (hence processability)
One of the disadvantages of the addition method is the tendency of the added copolymers to
form micelles These reduce the efficiency of the compatibilizer increase the blend viscosity
and may lessen the mechanical performance
414 Incorporation of Copolymers for Compatibilization
Block or graft copolymers with segments that are miscible with their respective polymer
components show a tendency to be localized at the interface between immiscible blend
phases Random copolymers sometimes also used as compatibilizers reduce interfacial
tension but their ability to stabilize the phase structure is limited184 Finer morphology and
higher adhesion of the blend lead to improved mechanical properties The morphology of the
resulting two-phase (multiphase) material and consequently its properties depend on a
number of factors such as copolymer architecture (type and molecular parameters of
segments) blend composition blending conditions
183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001)
98
In Scheme19 the conformation of different block graft or random copolymers at the
interface is schematically drawn
Scheme 19 Possible localization of A-B copolymer at the AB interface Schematic of
connecting chains at an interface a-diblock copolymers b-end-grafted chains c-triblock
copolymersdmultiply grafted chain and e-random copolymer
415 The Effect of Compatibilizer on a Blend
The presence of a compatibilizer at the interface substantially affects the development of the
phase structure of molten blends in the flow and quiescent state The position and width of the
concentration region related to co-continuous morphology are affected by two competing
mechanisms A decrease in interfacial tension caused by a compatibilizer favors the formation
and stability of co-continuous structures
The effect of a compatibilizer on fineness of the phase structure can be understood through its
effects on droplet breakup and coalescence A decrease in interfacial tension due to the
presence of a compatibilizer decreases the droplet radius R
Effect of the Compatibilizer Architecture
Compatibilization efficiency of various copolymers follows from their thermodynamic and
microrheological effects It has been generally accepted that the total molecular weight of the
copolymer molecular weight of its blocks and their number are the main structural
compatibilizer characteristics affecting the phase structure of the final blend
99
Effect of Compatibilizer Concentration
The compatibilizing efficiency of the copolymers is besides the architecture a function of
their concentration The effect of a compatibilizer concentration has been quantitatively
characterized by the emulsification curvemdashthe dependence of the average particle diameter of
the minor dispersed phase on copolymer concentration185 The particle diameter decreases
with increase of copolymer concentration until a constant value is obtained For most systems
this value is achieved if the copolymer amount is 15ndash25 of the dispersed phase
416 Methods of Blend Preparation
Five different methods are used for the preparation of polymer blends186 187 melt mixing
solution blending latex mixing partial block or graft copolymerization and preparation of
interpenetrating polymer networks It should be mentioned that due to high viscosity of
polymer melts one of these methods is required for size reduction of the components (to the
order of μm) even for miscible blends
bull Melt mixing is the most widespread method of polymer blend preparation in practice
The blend components are mixed in the molten state in extruders or batch mixers Advantages
of the method are well-defined components and universality of mixing devicesmdashthe same
extruders or batch mixers can be used for a wide range of polymer blends Disadvantages of
the method are high energy consumption and possible unfavorable chemical changes of blend
components This procedure has not been used so far in industrial practice because of large
energy consumption
bull Solution blending is frequently used for preparation of polymer blends on a laboratory
scale The blend components are dissolved in a common solvent and intensively stirred The
blend is separated by precipitation or evaporation of the solvent The phase structure formed
in the process is a function of blend composition interaction parameters of the blend
components type of the solvent and history of its separation Advantages of the process are
rapid mixing of the system without large energy consumption and the potential to avoid
185 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons Inc New York Chap 16 (2000) 186 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709 187 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458
100
unfavorable chemical reactions On the other hand the method is limited by the necessity to
find a common solvent for the blend components and in particular to remove huge amounts
of organic (frequently toxic) solvent Therefore in industry the method is used only for
preparation of thin membranes surface layers and paints
bull A blend with heterogeneities on the order of 10 μm can be prepared by mixing of
latexes without using organic solvents or large energy consumption Significant energy is
needed only for removing water and eventually achievement of finer dispersion by melt
mixing The whole energetic balance of the process is usually better than that for melt mixing
The necessity to have all components in latex form limits the use of the process Because this
is not the case for most synthetic polymers the application of the process in industrial practice
is limited
bull In partial block or graft copolymerization homopolymers are the primary product
But an amount of a copolymer sufficient for achieving good adhesion between immiscible
phases is formed188 In most cases materials with better properties are prepared by this
procedure than those formed by pure melt mixing of the corresponding homopolymers The
disadvantage of this process is the complicated and expensive start-up of the production in
comparison with other methods eg melt mixing
bull Another procedure for synthesis of polymer blends is by formation of interpenetrating
polymer networks A network of one polymer is swollen with the other monomer or
prepolymer after that the monomer or prepolymer is crosslinked189 In contrast to the
preceding methods used for thermoplastics and uncrosslinked elastomers blends of
reactoplastics are prepared by this method
188 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 189 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981)
101
42 Experimental
421 Materials
Polymers used in this research were PEG and PS PEG was purchased from MERCK
company General Purpose PS was obtained from ENPC TP1-Chlef Company Physical and
Structural characterizations of these materials were performed by SEC 1H-NMR and DSC
422 Blend Preparation
PSPEG blends of 5050 wt were prepared by solution casting from THF 40degC The
polymer solutions were stirred until complete miscibility and then cast onto glass dishes and
left to evaporate the solvent to the atmosphere To remove residual solvent after casting the
blends were dried in vacuum oven at 40degC for a weak Table 10 shows the quantities of the
copolymers used for compatibilization of the blends of PSPEG
Table 10 The quantities of the copolymers used for compatibilization of the blends of
PSPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
43 Characterization Techniques for Compatibilization
431 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
102
Relative viscosities of polymer solutions were calculated by dividing the flow times of
solutions by that of the pure solvent The data were plotted using the Huggins equation with
the intrinsic viscosity [η] (dlg-1) determined by extrapolation to infinite dilution
432 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
433 FTIR Analysis
FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
44 Results and Discussion Polyethylene glycol (PEG) is very interesting and important polymers PEG presents good
properties eg hydrophilicity solubility in water and in organic solvents nontoxicity and
absence of antigenicity and immunogenicity190It has attracted increasing attention due to its
potential applications as biomedical and environment friendly materials PEG has been
widely used as a modifier for biomedical surfaces to reduce the protein absorption and
improve their biocompatibility192 and as a stabilizer for emulsion and dispersion It has also
been used as a plasticizer for poly (lactide) (PLA) which is stiff and brittle as a
biodegradable packaging material193
On the other hand polystyrene shows excellent processability good appearance tensile
strength and thermal and electrical characteristics however its brittleness considerably limits
its use in high performance products
Both PS and PEG are widely used commodity polymers Detailed studies on their miscibility
may contribute to technological and environmental applications These polymers form an
interesting pair to study since they exhibit contrasting physical properties PS is a
190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689
103
hydrophobic polymer whereas PEG is hydrophilic PEG is a much softer material than PS
PSPEO blends have been reported as incompatible materials in the literature194 195
N Watanabe et al have reported compatibilization effect of poly (styrene-co-methacrylic
acid) on immiscible blends of this system196
441 Characterization of the Blend Components
Analysis by SEC provides number average-molecular weights and polydispersity indices of
all materials DSC measurements performed to determine their glass transition temperatures
as well as melting point and degree of crystallinity of PEG (See Figure16) 1HNMR spectroscopy analysis was performed on these polymers to determine essentially the
tacticity of PS and also to get information about end groups of PEG which was found to
possess an OH group at each end It has been also determined that the stereoregularity of PS
is Syndiotactic-Atactic (rather highly syndiotactic) (See Figures 17)
Physical characteristics of materials used are given in Table11
Table 11 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PS ENPC TP1-Chlef (from CHI MEI Corp)
105
128 000
1076
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam] Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842
104
Figure 16 1H-NMR spectrum of PEG (Merck) in CDCl3
105
Figure 17 1H-NMR spectrum of Commercial Styrene (ENPC TP1-Chlef) in CDCl3
442 Study of Compatibilization by Dilute Solution Viscometry
a) Introduction
Polymer blends are physical mixtures of structurally different polymers which interact
through secondary forces with no covalent bonding Blending of the polymers may result in a
reduction in the basic cost and improved processing and also may enable properties of
importance to be maximized The polymer blends often exhibit properties that are superior
compared to the properties of each individual component polymer197 198 199 200 The main
advantages of the blend systems are simplicity of preparation and ease of control of physical
properties by compositional change201 202 However the mechanical thermal rheological and
197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85
106
other properties of a polymer blend depend strongly on its state of miscibility on the
molecular scale203
There have been numerous techniques of studying the miscibility of the polymeric blend The
most useful techniques are dynamic mechanical thermal electron-microscopic IR
spectroscopic refractive index203 optical microsscopic204 and viscometric techniques 179 205
Because of its simplicity viscometry is an attractive and very useful method for studying the
compatibility of polymer blends Additional advantages ie that no sophisticated equipment
is necessary and that the crystallinity or the morphological states of the polymer blends do
affect the result206 make the viscometric method more convincing for characterizing polymer
mixtures The principle of using a dilute solution viscosimetry to measure the miscibility is
based on the fact that while in solution molecules of both component polymers may exist in
a molecularly dispersed state and undergo a mutual attraction or repulsion which will
influence the viscosity It is assumed that polymerndashpolymer interaction usually dominate over
polymerndashsolvent ones207 The presence of interactions between atoms or groups of atoms of
unlike polymers is essential to obtain a miscible polymer blend177 179
Estimation of the compatibility of different pairs of polymers based on dilute solution
viscosity for a ternary polymerpolymer-solvent system has been attempted by several
authors including Mikhailov and Zeilkman208 Bohmer and Florian209 Feldman and Rusu210
Krigbaum and Wall211 and Catsiff and Hewett212
The compatibilization of the blends in question has been characterized by viscosity technique
using the Krigbaum and Wall interaction parameter Δb The versatility of the viscometric
technique is not affected by the choice of the solvent as was shown by Kulshreshta et al213
In this section we discuss in details our investigation on the compatibilization of the two
polymer blend systems PSPEG and PMMAPEG 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191
107
b) Theoretical background
The main aspects of the application of dilute solution viscometry method for the study of
interactions and miscibility phenomena in dilute multicomponent polymer solutions were
described Only the most important features will be repeated here It is common to use
empirical relations such as Hugginsrsquo equation214
(65)
for the description of the concentration dependence of viscosity of polymer solutions This
relation is strictly valid only for binary polymer solutions However equations like that of
Krigbaum and Wall211
(66)
And of Catsiff and Hewett212
(67)
were proposed for ideal ternary polymer solutions of the polymer 1+ polymer 2+ solvent type
In previous relations ηsp denotes the specific viscosity [η] is the intrinsic viscosity (limiting
viscosity number) c stands for the mass concentration of polymer and kH is Hugginsrsquo
constant which may be related (in an empirical manner) to the thermodynamic quality of
solvent Relative mass fractions of dissolved polymers wi are used to describe the
composition dependence of viscosity in ternary systems Quantities b 12 and b12 are used to
define the ideal behavior of ternary polymer solutions These are calculated by
(68)
and
(69)
214 ML Huggins J Am Chem Soc 64 (1942) 116
108
respectively Here b denotes the slope of Hugginsrsquo equation for binary solutions
(70)
Moreover it has been shown215 that both the sign and the extent of the deviation of
experimental from theoretical b-values may be correlated to the interactions between
polymeric components of a system under consideration The quantities of interest (miscibility
criterion variables) are defined by
(71)
and
(72)
or can be written in another form
(73)
where m denotes the polymer mixtures Δb intermolecular interaction parameter between
polymer 1and 2 and is considered a good criterion to predict the polymer-polymer
compatibility209 216 217 Δb 0 indicates that the two polymers are compatible whereas
Δb0 indicates that they are incompatible
c) Discussion of the Results
Herein we discuss in detail the compatibilization of PSPEG blends with the synthesized graft
copolymers by viscometric technique The plot of reduced specific viscosity of polymers
versus total polymeric concentration yields a straight line and the intercept and slope
correspond to intrinsic viscosity [η] and molecular interaction coefficient b respectively The
viscosity data for the homopolymers and their blends are presented in Tables 12 and 13
Table 12 Interaction coefficient for binary solutions (polymersolvent) 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin (1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849
109
Polymer components PEG PS
b11 007327 minus
b22 minus 02117
b12 = (b11 b22)12 = 01245 (theo)
Table 13 Interactions parameters for PSPEG blends with poly (St-g-PDXL) copolymers
(2SP2 2SP1 and DXSP) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
DXSP b12 003511 01295 01680 01833 01947
Δb - 00894 00050 00435 00588 00702
2SP2 b12 003511 009826 01052 01314 01515
Δb - 00894 - 00262 - 00193 00069 00270
2SP1 b12 003511 minus minus minus 01262
Δb - 00894 minus minus minus 00017
For incompatible blends the incompatible molecules refuse to overlap thus they shrink in
size which leads to a decrease in hydrodynamic volumes As a matter of fact the crossover in
the reduced viscosity-concentration plot is observed
As far as we are concerned with the blend of PSPEG the results obtained present similar
situation Figure 18 shows the Huggins plots for the homopolymers and the (5050) blend of
PSPEG In this figure a crossover is observed and a decrease of slope occurs at about 05
gdl in the viscosity-concentration plot Above this concentration two incompatible polymers
PS and PEG undergo mutual repulsion in dilute solution the hydrodynamic volume of chains
is lower The reduction of the hydrodynamic volume will result in a decrease of the reduced
viscosity of solution correspondingly the slope of the plot suddenly declines
110
02 03 04 05 06 07 08 09 10 11
03
04
05
06
07
08PS PEG and PSPEG (5050)
PS PSPEG 0 PEG
Redu
ced
visc
osity
η sp
c
(ldl
)
C (dll)
Figure 18 Plots of reduced viscosity (ηspc) vs concentration for PS PEG and PSPEG
blend (0) in THF at 30degC
Figures 19 20 21 and 22 show the incorporation of various amounts of copolymers in the
immiscible blend As far as the amount of the compatibilizers increases the crossover of the
plots occurs at very low concentration or even it is not observed In addition the slope of the
plot increases with an increase of the amount of the compatibilizers introduced in the blend
This is due to the mutual attraction of the blend components which is enhanced by the
presence of the copolymers As a matter of fact the latter act as compatibilizing agents
allowing to the blends to exhibit miscibility
111
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07BLENDS WITH DXPS
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 19 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of DXPS copolymer
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLENDS WITH 2SP2
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 20 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of 2SP2 copolymer
112
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLEND WITH 2SP1 40
PSPEG 0 2SP1 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 21 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with 40 of the dispersed phase of 2SP1 copolymer
02 03 04 05 06 07 08 09 10 1100
01
02
03
04
05
06
07
08
DXPS 40 2SP2 40
2SP1 40
2SP1 40 2SP2 40 DXPS 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 22 comparison of plots of reduced viscosity (ηspc) vs concentration for PSPEG
blends in THF at 30degC with 40 of the dispersed phase of DXPS 2SPS2 and 2SP1
copolymer
113
Figure 22 compares the three copolymers used for compatibilization of PSPEG with respect
to 40 by weight of the dispersed phase addition to the blends
Krigbaum and Wall suggested that information about the interaction between two polymers
should be obtained from the difference of experimental b12 and theoretical b12 Δb A positive
difference between the experimental and theoretical interaction coefficients is evidence of a
compatible polymer pair The higher the value of Δb the higher the extent of compatibility
Negative values refer to repulsive interaction and incompatible mixes The values of Δb
according to equation 73 for different blends with compatibilizers are given in Table 13 and
Figure 23
0 10 20 30 40 5
-010
-005
000
005
010
0
PS PEG BLENDS
2SP2 DXPS
Δb
Amount of incorporated copolymer w ()
Figure 23 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (DXPS and 2SP2) used for compatibilization
It was observed as the amount of compatibilizers increases values of the interaction
parameter increase thereby increasing the compatibility between the two polymer
components of the blend Consequently this indicates that these copolymers act as
compatibilizing agents in the immiscible blends of PS and PEG Now in comparing these
copolymers in terms of structure (number of grafts) and PDXL content it can be noticed that
the results obtained DXPS ( 71 w of PDXL) copolymer show higher values of Δb than
2SP1(30 w of PDXL) and 2SPS2 (4025 w of PDXL) do This is due to the comb-
structure of the DXPS copolymer (synthesized by CRP) and therefore containing more grafts
114
(Ng = 58) than the other copolymers Besides the amount of PDXL in the copolymer PDXL
includes polar groups which provide associative interactions with one of the blend
components (PEG) and thus undergoes significant effects upon compatibilization In the
figure below it can be seen that addition of 10 by weight of the dispersed phase (47 of
total weight of the blend) of DXPS is sufficient to compatibilize the immiscible blend of
PSPEG (5050) Then a drastic increase of the interaction parameter with the addition of the
compatibilizer (DXPS) compared to the addition of either 2SP2 or 2SP1 (Table 13)
From the results shown in the graph miscibility of the blend can be achieved by incorporating
around 25 (11 of total weight of the blend) of 2SP2 copolymer However compatibibility
of the blend with 2SP1 copolymer is obtained at 40 by weight of the dispersed phase since
its interaction parameter (Δb) found to be 00017
It is worth to mention that the PDXL content of 2SP1 is 30 and the length of the grafts is
half that of 2SP2 copolymer For this reason these two copolymers have been chosen for the
purpose of comparison in terms of side chains length
An optimization of the amount of copolymer needed for compatibilization of PSPEG (5050)
blend has been made (corresponding to Δb = 0) as function of the PDXL content and shown
in Table 14
Table 14 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050) vs PDXL content
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
DXPS 0 9 43 71
2SP2 0 245 109 4025
2SP1 0 40 166 30
115
443 Optical Microscopy and Phase Morphology
PDXL is a perfect alternate copolymer of poly (ethylene oxide) (PEO) and poly (methylene
oxide) (PMO) that has the same curious combination properties as PEG So PDXL must be
at least miscible with PEG or adhere at the interface between PS and PEG and between
PMMA and PEG The compatibility between hydrophobic PS or PMMA and hydrophilic
PEG is very poor Compatibilization between components of the two sets of polymer blends is
studied by optical microscopy
The morphological characteristics of the blends by different compatibilizers are presented in
Figure 24 The optical microscopy micrographs of PSPEG blends without compatibilizers
show a poor dispersion for PS disperse phase and a ldquoball-and-socketrdquo topography due to the
poor interfacial adhesion between PEG matrix and the dispersed phase However with the
addition of compatibilizers the morphological characteristics of the polymer blends are
greatly altered It can be noticed that for these two different blends the particle size of PS
domains gets progressively much smaller and uniform in compatibilized blends than in
incompatibilized ones This may be explained by the significant increase of the phase
interfacial adhesion Consequently the domain size strongly depends upon the
compatibilizers used
116
a) PSPEG (5050) 0 (without compatibilizer)
DXPS 10 DXPS 20 DXPS 30 DXPS 40 b) Compatibilizing effect of DXPS copolymer
2SP2 10 2SP2 20 2SP2 30 2SP2 40 c) Compatibilizing effect of 2SP2 copolymer
2SP1 40
117
d) Compatibilizing effect of 2SP1copolymer at 40 addition
Figure 24 Optical micrographs showing phase structure in 5050 PSPEG blends
a) blends without compatibilizer b) with DXPS c) with 2SP2 d) with 40 of 2SP1
For instance the PSPEG blends with the incorporation of the copolymers DXPS 2SP2 and
2SP1 as compatibilizers (Figure 24) the morphology displays a very fine dispersion of PS
phase and strong interfacial adhesion with PEG Matrix The good compatibilizing effect
mainly that of DXPS can be explained by two mechanisms
First the PDXL units in the compatibilizer interact with PEG ether groups leading to a good
adhesion at interface between the components of the blend In addition hydrogen bonding
may also exist between PDXL and PEG further increasing compatibilization Second since
the compatibilizer also contains styrene blocks it contributes to provide a good compatibility
with PS Consequently the remarkable compatibilizing effect of PS-g-PDXL copolymers
induced a drastic decrease in interfacial tension and suppression of coalescence between the
originally immiscible polymer phases
As it can be noticed from the micrographs given in the figure above the compatibilizer
exhibits finer dispersion and homogeneous morphology of the blends as the amount of
compatibilizers increases
Eventually each compatibilizer has its own effect on the immiscible blends depending on the
amount of PDXL (side chains) and number of grafts present in the copolymers
By comparing micrographs shown in Figure 24 b and c the compatibilization effect of DXPS
copolymer which contains more grafts but shorter is different from that of the 2SP2
copolymer In the case of DXPS it is observed that the size of the dispersed droplets is
deceased significantly and results in finer dispersion morphology However 2SP2 copolymers
shows an improvement in compatibility of the blend after addition up to 30 wt of the
dispersed phase (13 total weight of the blend) exhibits homogeneous morphology This
may be related to length of the grafts In all cases these copolymers act as good
compatibilizers for the blend of 5050 wt PSPEG
444 FTIR Analysis
The FTIR technique is very important since it allows one to study the specific interactions
between the polymers The knowledge of the polymerndashpolymer interactions will be useful for
118
studies of the compatibility in polymer blends To verify the intermolecular interactions that
can play a role in miscibility the vibrational spectra of the blends studied in the present work
were obtained In polymeric systems where there are multiple interactions vibrational bands
such as ν (C=O) ν (COC) and ν (OH) present contributions of spectroscopic free and
associated forms
In order to elucidate the role played by intermolecular interactions in the miscibility of these
blends FTIR absorption of individual polymer components PS PEG and PMMA and
compared to that of the mixtures Figures 26 27 and 28 present the FTIR absorption spectra
from 4000 to 400 cm-1 for all samples
In the case of PS the high-frequency infrared spectra consist of seven absorption bands The
bands with peak locations at 3008 3026 3060 3082 and 3103 cm-1 are due to C-H stretching
of benzene ring CH groups on the PS side-chain The bands with peak positions of 2924 and
2850 cm-1 are due to the C-H stretching vibration of the CH2 and CH groups of the main PS
chain respectively PEG with molecule chemical structure of HO-[CH2-CH2-O]n-H exhibits
important absorption bands from FTIR spectroscopy measurements as shown in Figure 25 It
was verified contributions associated with CndashOndashC symmetric stretching of ether groups218-220
221 from 1050 to 1150 cm-1 with maximum peak at 1150 cm-1 Characteristics CH2-O
stretching modes from 2800-3000 cm-1 are observed214 At low frequency region peaks at 850
and 890 cm-1 are assigned to CndashOndashC stretching and at 500 cm-1 ascribed to CndashOndashC
deformation The presence of PDXL in the blends is detected by the intense frequency at 1140
cm-1 which is assigned for acetal groups In addition both PDXL and PEG contain ether
groups and the spectra show that the corresponding peaks are overlapped for the blends The
intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of PEG
crystallinity in the blends222
218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10 219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601
119
It can be observed also a typical large hydroxyl bands with two distinct contributions which
can be seen for all samples They are attributed to the spectroscopically free and bonded ndashOH
stretching forms at 3600-3800 cm-1 and 3200-3500 cm-1 respectively221 - 227
500 1000 1500 2000 2500 3000 3500 4000-05
00
05
10
15
20
25
30
35
PS and PEG PEG PS
Abs
orba
nce
Wave number (cm-1)
Figure 25 FTIR spectra of PS PEG over 4000-400 cm-1 range
227 Peppas NA Wright L Macromolecules 1996298798ndash804
120
500 1000 1500 2000 2500 3000 3500 4000
0
1DXPS IN PSPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 26 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS)
All these absorption bands for individual polymer were observed in the FTIR spectrum of the
5050 (ww) PSPEG in which they were combined to give superimposed bands in the regions
of 750-1500 cm-1 and 2700- 3100 cm-1
The hydroxyl vibrational frequency is discernible in the blend spectrum for PSPEG at 0
With the incorporation of the copolymers for compatibilization a number of bands showed
small shifts and changes in position and shape in the resulting spectra In Figures 28 29 and
30 as it can be noticed that in the hydroxyl absorption region a decrease in the fraction of
free OH groups is observed as the amount of copolymers is increased in the blend This can
be due to the flexibility of the PDXL graft chains on the other hand to the acetal and ether
groups of PDXL which are probably randomly distributed among an increasing number of
hydroxyl groups of PEG statistically favoring the formation of the PDXL and PEG hydrogen
bond interaction The results indicate that the intermolecular hydrogen bonding between the
ether oxygen of PDXL and the hydroxyl groups of PEG may be formed thereby reducing the
fraction of free OH which is consistent with the shifts observed in the region of hydroxyl
stretching Intermolecular hydrogen bondings are expected to occur among PDXL and PEG
chains due the high hydrophilic forces These interactions have replaced the intramolecular
121
interactions between COC and OH groups of PEG before addition of containing PDXL
copolymers It can be noticed a progressive shift of hydroxyl band from 3340 to 3420 cm-1
with DXPS and from 3340 to 3350 cm-1 when 2SP2 is added This shift can be attributed to
the decrease of intramolecular interactions among hydroxyl groups within PEG chains in
favor to intermolecular interactions between PDXL and PEG228
500 1000 1500 2000 2500 3000 3500 4000
0
1
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 27 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2)
228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
122
3200 3300 3400 3500 3600 3700 3800
00
01
DXPS IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 28 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS) in the hydroxyl absorption region
3200 3300 3400 3500 3600 3700 3800
00
02
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 29 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2) in the hydroxyl absorption region
123
3200 3300 3400 3500 3600 3700 3800
00
DXPS 40 2SP2 40 2SP1 40
Abs
orba
nce
Wave number (cm-1)
Figure 30 FTIR spectra comparison of PSPEG blends (5050) with different compatibilizers
in the hydroxyl absorption region
Conclusions An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends Again The PS blocks of the copolymer result in good
compatibility with PS component of the blends The compatibilization of PSPEG blends is
apparently associated with hydrogen bonding where groups of the acetal units in PDXL
interact with hydroxyl groups of PEG These form a stronger interface between the two
phases which leads to important modifications of the blend properties Apparently the FTIR
result is in good agreement with the miscibility criteria proposed by Krigbaum and Wall (Δb)
interaction parameter which results from dilute-solution viscometry (DSV) method It can be
concluded that by the addition of 20ndash40 wt of incorporated copolymer reveal a good
compatibilizing efficiency for the blend systems as it was observed from micrographs as well
124
References
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York
(1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York
(1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser
Publishers Munich (1989) 178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279 180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999) 183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001) 185 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709
125
186 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and
Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458 187 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 188 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981) 189 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons
Inc New York Chap 16 (2000) 190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689 194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam]
Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842 197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191 214 ML Huggins J Am Chem Soc 64 (1942) 116 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin
(1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849 218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10
126
219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601 227 Peppas NA Wright L Macromolecules 1996298798ndash804 228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
127
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g-
Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of
Polystyrene and Poly (Ethylene Glycol)
51 Introduction
PMMA is more than just plastics of paint Often lubricating oils and hydraulic fluids tend to
get really viscous and even gummy when they get cold This is a real pain when operating
heavy equipments in very cold weather When a little bit of PMMA is dissolved in these oils
and fluids they donrsquot get viscous in the cold and machines can be operated down to -100degC
PMMA can find a several applications namely adhesive optical coating medical packaging
applications and so forthhellip
In medical applications PMMA and its derivatives are used particularly for hard tissue repair
and regeneration229 PMMA beads have been developed to deliver aminoglucoside antibiotics
locally for the treatment of bone infections230 PMMA and PEG form an important and unique
pair of polymers in that they are chemically different In the present work this study may
shed light on the PMMA properties modifications induced by blending with PEG to overcome
the difficult processing of rigid PMMA
Several studies have been made on blends of poly (ethylene oxide) PEO and PMMA in the
last decades but very few on PMMAPEG blends231 232 233
Numerous works reported that the miscibility domain ranges between 10 and 30 of PEO by
weight depending on the PMMA tacticity or molecular weight No phase diagram is available
yet in the literature for PMMAPEO and neither it is for PMMAPEG234
229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703
127
52 Experimental
521 Materials
PEG and PMMA were used as blend components PMMA was obtained from ENPC TP1-
Chlef Company PEG was purchased from MERCK Company Physical and Structural
characterizations of these materials were performed by SEC 1H-NMR and DSC
522 Blend Preparation
Blends of PMMAPEG (5050) were prepared using the same procedure as described for the
blends discussed in the previous chapter Table 15 shows the quantities of the copolymers
used for compatibilization of the blends of PMMAPEG
Table 15 The quantities of the copolymers used for compatibilization of the blends of
PMMAPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
53 Characterization Techniques
531 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
532 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
128
533 FTIR FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
54 Results and Discussion
541 Characterization of the Homopolymers
The polymers have been analyzed by SEC to determine their number average-molecular
weights and polydispersity indices DSC measurements performed to determine their glass
transition temperatures as well as melting point of crystallinity of PEG 1HNMR spectroscopy analysis revealed the tacticity of PMMA It has been found that PMMA
is Syndiotactic-Atactic (highly syndiotactic) as shown in Figure 3 and 321
Physical characteristics of materials used are given in Table 16
Table 16 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PMMA ENPC TP1-Chlef (fromLG MMA Corp)
119
55 000
113
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
129
Figure 31 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in CDCl3
Figure 32 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in the methyl shifts
region in CDCl3
130
542 Dilute Solution Viscometry
Dilute solution viscometry has been utilized to evaluate miscibility of PMMAPEG blends
and the same approach discussed in the previous section has been followed The
experimental reduced viscosities of the polyblends are plotted against concentration in dilute
solution viscometry Eventually plots of pure polymers and polyblends of 5050 PMMAPEG
are first obtained Then their interaction coefficients are determined as shown in Table 17
Table 17 Interaction coefficient for binary solutions (polymersolvent)
Blend components PEG PMMA
b11 007327 minus
b22 minus 006561
b12 = (b11 b22)12 = 006933 (theo)
The compatibility of this system has been evaluated through the sign of Δb The values of the
latter according to equation 73 for different amounts of poly (MMA-g-PDXL) copolymers in
the blends are given in Table 18 It is observed that the blend of PMMAPEG at 5050 by
weight shows a negative value of Krigbaum and Wall parameter which indicates
incompatibility of the system as it is expected Similarly to PSPEG blend a crossover in the
reduced viscosity-concentration plot is observed and a decrease of slope arises in the range of
05 to 066 gdl in the viscosity-concentration plot as shown in Figure 33 This is attributed to
the repulsive intermolecular interactions between the polymer chains
Then the incorporation of the copolymers at various amounts presents positive values
progressively Curves of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in
THF at 30degC with various amounts of copolymer are given in Figures 34 35 and 36
131
Table 18 Interactions parameters for PMMAPEG blends with poly (MMA-g-PDXL)
copolymers (3MP2 2MP2 and 3MP1) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
3MP2 b12 00288 01308 01904 02373 02602
Δb - 004053 00615 01211 01680 01909
2MP2 b12 00288 01286 01690 01893 02296
Δb - 004053 00593 00997 01200 01603
3MP1 b12 00288 00868 01670 02010 02379
Δb - 004053 00175 00977 01317 01686
00 01 02 03 04 05 06 07 08 09 10 11020
025
030
035
040PMMAPEG (5050) 0
PEG PMMAPEG 0 PMMARe
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 33 Plots of reduced viscosity (ηspc) vs concentration for PMMA PEG and
PMMAPEG blend (0) in THF at 30degC
132
02 03 04 05 06 07 08 09 10 11000
005
010
015
020
025
030
035
040 BLENDS WITH 3MP1
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 34 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP1 copolymer
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040
045BLENDS WITH 3MP2
PMMAPEG 0 10 20 30 40
Redu
ced
visc
osity
η
spc
(d
lg)
C (gdl)
Figure 35 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP2 copolymer
133
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040BLENDS WITH 2MP2
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 36 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 2MP2 copolymer
From our viscosity data as the copolymer content increases in the blend the polymer blend
molecules will become disentangled more spaciously resulting in a greater interaction
between structurally similar component segments This suggests that there are attractive
forces that induce miscible behavior of the blends as it is observed in Figure 37
0 10 20 30 40 5-01
00
01
02
0
PMMA PEG BLENDS
3MP2 2MP2 3MP1
Δb
Amount of incorporated copolymer w ()
Figure 37 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (3MP2 2MP2 and 3MP1) used for compatibilization
134
The three copolymers (3MP2 2MP2 and 3MP1) involved in this study for compatibilization
are different from the point of view of the PDXL content and the graft length For instance
3MP2 and 2MP2 have similar and longer grafts since the theoretical number average-
molecular weight of the graft is 2000 gmol However they contain different amount of
PDXL In the case of 3MP1 this graft copolymer has a structure with shorter side chain length
(Mn = 1000 gmol) corresponding to the half of the graft size in the former copolymers From
the observations made out of the figure above 3MP2 copolymer (21 w of PDXL) provides
higher values of the interaction parameter and therefore greater extent of compatibility
compared to the other copolymers since it has long grafts which allows penetration into the
other phase
It can be concluded that all three copolymers show good results for compatibilization on the
basis of the Δb criterion of polymer-polymer miscibility determined by viscometry
Similarly the minimum amount of copolymer needed for compatibilization of PSPEG
(5050) blend has been determined corresponding to Δb = 0 as function of the PDXL content
and shown in Table 19
Table 19 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050)
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
2MP2 0 34 16 35
3MP2 0 37 18 21
3MP1 0 58 28 19
135
543 Optical Microscopy and Phase Morphology
a) PMMAPEG (5050) 0 (without compatibilizer)
b) Compatibilizing effect of 2MP2 copolymer
c) Compatibilizing effect of 3MP2 copolymer
d) Compatibilizing effect of 3MP1copolymer
Figure 38 Optical micrographs showing phase structure in 5050 PMMAPEG blends
a) blends without compatibilizer b) with 2MP2 c) with 3MP2 d) with 3MP1
136
Figure 38 presents microscopy images of PMMAPEG blends with varying amounts of
compatibilizers The morphological characteristics of the blends of PMMAPEG without
compatibilizers show a poor dispersion of PMMA as a dispersed phase The addition of
compatibilizers changes drastically the morphological topology of this system The
compatibilizers used are of different length of the side chains and also different PDXL
content By introducing progressively variable amounts of the compatibilizers they display
similarly the morphological characteristics to some extent It is observed that the phase
separated domains of PMMA in the blends are reduced with increasing amounts of the
compatibilizers This is due to the compatibility of PMMA of the copolymers with the
PMMA blend component and on the other hand to the interfacial interactions of the PDXL
of the copolymers and PEG component of the blends From these results it is revealed that
compatibilizing effect of 2MP2 copolymer on this system is great compared to the others Not
only causes the size of the dispersed droplets to decrease but also dispersed droplets become
homogeneous However 3MP1 copolymer which contains shortest grafts (about half length
of those of the other copolymers) and less amount of PDXL shows less reduction in the
droplet size compared to the other copolymers Therefore it can be concluded that the
compatibilization of this blend depends upon length and number of grafts
On the overall observations these compatibilizing copolymers are very effective and hence
influence and improve the compatibility of PMMAPEG blend at a composition of 5050 wt
544 FTIR Analysis
Same observations can be made for the blends of PEG with PMMA The FTIR spectrum of
this blend at 0 compatibilizer is shown in Figure 39 For pure PMMA the
spectroscopically free carbonyl group band is observed at 1730 cm-1 In the blend sample one
large vibrational band due to hydroxyl group stretches in pure PEG is observed with two
distinct contributions which can be seen for all samples They are attributed to the
spectroscopically free and associated hydroxyl forms at 3495 and 3600 cm-1 respectively
A large band in the wave number range of 1400-1500 cm-1 is assigned to the deformation
vibration of the methyl groups The bands with peaks locations at 2820 and 2990 cm-1 are due
to C-H symmetrical and asymmetrical stretching vibration of CH3 respectively Peaks at
2886 and 2950 cm-1are ascribed to C-H symmetrical and asymmetrical stretching vibration of
CH2 figures 40 and 41 The C-O band is observed in the range of 1150- 1210 cm-1
137
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 PMMAPEG 0 Blend
Abs
orba
nce
Wave number cm-1
Figure 39 FTIR spectra of PMMAPEG 0 over 4000-400 cm-1 range
2750 2800 2850 2900 2950 3000 3050 3100-05
00
05
10
15
20
Abs
orba
nce
PEG PMMAPEG 0
Wave number cm-1
Figure 40 FTIR spectra of PMMAPEG 0 and PEG over the 3100-2700 cm-1 range
138
2750 2800 2850 2900 2950 3000 3050 3100
00
05
10
152MP2 in PMMAPEG
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 41 FTIR spectra of PMMAPEG 0 blends with 2MP2 addition over the 3100-2700
cm-1 range
The incorporation of PMMA-g-PDXL copolymers in the blends makes some changes in the
resulting spectra as it can be noticed in Figures 42 - 44 In the hydroxyl absorption region
same phenomenon has occurred as in the PSPEG blends The fraction of free OH groups has
decreased as the amount of the copolymers increased as shown in figures 45 and 46 which
present the effect of different compatibilizers in the hydroxyl absorption region This can be
explained as discussed above by the fact that the PEG hydroxyl groups undergo other
intermolecular interactions essentially with PDXL chains of the copolymers A comparison of
the effect of the three copolymers involved in the compatibilization at the highest amount
added is given in figure 47 It can be noticed that 2MP2 shows very few fraction of free OH
groups compared to the others This copolymer contains more PDXL (35 wt with 4 grafts)
than the others do (21 wt with 3 grafts and 19 wt with 3 grafts in 3MP2 and 3MP1
respectively)
A crystalline PEG phase is confirmed by the presence of the triplet peak of the COC
stretching vibration at 1148 1110 and 1062 cm-1 with a maximum at 1110 cm-1235 236
Changes in the intensity shape and position of the COC stretching mode are associated with
235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115
139
the interaction between PEG and PMMA-g-PDXL In addition both polymers contain the
same ether group and the spectra show that the corresponding peaks are overlapped for the
blends The intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of
PEG crystallinity in the blends237
Therefore the presence of this interacting system is probably responsible for the miscibility
and low degree of crystallinity observed for these blends
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
202MP2 in PMMAPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 42 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (2MP2)
237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
140
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 43 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2)
500 1000 1500 2000 2500 3000 3500 4000
0
1
2 3MP1 IN PMMAPEG BLENDS 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 44 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1)
141
3500
00
05
3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 45 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2) in the hydroxyl absorption region
3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
-02
00
02
04
06
08
3MP1 IN PMMAPEG 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 46 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1) in the hydroxyl absorption region
142
3500
2MP2 40 3MP2 40 3MP1 40
Abs
orba
nce
Wave number cm-1
Figure 47 FTIR spectra comparison of PMMAPEG blends (5050) with different
compatibilizers in the hydroxyl absorption region
The results from FTIR spectra indicate the compatibility of these polymer blends with the
addition of the PDXL copolymers via hydrogen bonds is observed and confirmed mainly by
the shifts of bands of the hydroxyl stretching modes
143
Conclusions
From the observations made out from this study reveal that all three copolymers show good
results for compatibilization on the basis of the Δb criterion of polymer-polymer miscibility
determined by viscometry Therefore these copolymers act as good compatibilizers since it
was found that the minimum amount needed for compatibilizing is between 1 to 3 of the
total weight of the blend which corresponds to 3 to 6 of the dispersed phase This
compatibilization is due to the fact that the copolymers have constituents which present strong
interactions with both polymer components of the blends These results are in great agreement
with microscopy analyses which demonstrate that the phase separated domains of PMMA in
the blends are reduced with increasing amounts of the compatibilizers This is due to the
compatibility of PMMA of the copolymers with the PMMA blend component and on the
other hand to the interfacial interactions of the PDXL of the copolymers and PEG component
of the blends
From FTIR results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PMMA and relatively long PMMA backbone of PMMA-g-PDXL copolymers respectively
These compatibilizing copolymers are very effective and hence influence and improve the
compatibility of PMMAPEG blend at a composition of 5050 wt
144
References 229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703 235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115 237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
145
CONCLUSIONS
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel using an unsaturated alcohol (2-
HPMA) as a transfer agent results in linear polymeric chains in order to prevent formation of
cyclic oligomers through cationic polymerisation of cyclic acetals They were all prepared at
the same reaction conditions
The characterization of these macromonomers has been conducted using different methods of
analysis Structure and molecular weight determination were provided from SEC and Raman
and 1H-NMR spectroscopy
We were interested in obtaining a hydrogel based on fully PDXL segments and study its
swelling and viscoelastic behaviour The hydrogel has combined special properties The
results reveal a perfect elastic and resistant hydrogel with interesting viscoelastic properties
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers Structure composition and number of grafts of the
copolymers were determined by SEC and 1H-NMR spectroscopy Another approach for
copolymerization has been made in order to compare the copolymers obtained from different
types of polymerization reactions like Conventional Free Radical and Controlled Radical
Polymerizations In the latter the copolymer obtained possesses larger number of grafts than
those from the former
The macromonomer reactivity estimation suggests that the length of the PDXL side chains
does affect the reactivity of the methacrylic double bond of the macromonomer when
copolymerized with St However in the case of copolymerization with MMA there is no
dependence on the graft size Finally from DSC measurements the values of Tg depend on
the composition and the size of the PDXL grafts In all copolymers the increase in amount of
the incorporated PDXL macromonomer results in a substantial decease in glass transition
An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
146
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends
The compatibilization effect of the copolymers used in this study on the PSPEG and
PMMAPEG was demonstrated from the viscometric results The contribution of both PS or
PMMA and PDXL of the copolymers has played a big role in the compatibilization of these
two different systems of blends thereby resulting in good compatibility due the chemical
affinity between these components which leads to a drastic decrease in interfacial tension and
suppression coalescence between the blend constituents
It has been shown that the immiscible blends in question exhibit compatibility when small
amount of copolymers synthesized for this purpose are added except for one of them
Styrene-g-PDXL copolymers act as good compatibilizers for PSPEG blends since it was
found that the minimum amount needed for compatibilizing is less than 11 of the total
weight of the blend which corresponds to 25 of the dispersed phase This compatibilization
is due to the fact that the copolymers have constituents which present strong interactions with
both polymer components of the blends
Compared with PS-g-PDXL with DXPS content the DXPS is more effective binary polymer
blends compatibilizer in the PSPEG blends which is due to the high number of grafts and
high PDXL content This has led to good adhesion of PDXL chains with the PEG phase in the
blends Again The PS blocks of the copolymer result in good compatibility with PS
component of the blends The compatibilization of PSPEG blends is apparently associated
with hydrogen bonding where groups of the acetal units in PDXL interact with hydroxyl
groups of PEG These form a stronger interface between the two phases which leads to
important modifications of the blend properties
Similarly PMMA-g-PDXL copolymers act as good compatibilizers since it was found that
the minimum amount needed for compatibilizing is between 1 to 3 of the total weight of
the blend which corresponds to 3 to 6 of the dispersed phase This compatibilization is due
to the fact that the copolymers have constituents which present strong interactions with both
polymer components of the blends
These results are in great agreement with microscopy analyses which demonstrate that the
phase separated domains of PMMA and PS in their respective blends are reduced with
increasing amounts of the compatibilizers
147
Specific interactions between chemical groups of two blend components can play an
important role in polymer mixtures There is a range of such interactions of varying strengths
which has been identified in polymer blends and such interactions are generally defined for
small molecules It should be noted that the extension of this concept to polymers is not
always straightforward it is more difficult to identify interactions in polymers the
spectroscopy is more complex and molecular conformations are less certain This situation is
further complicated because researchers use different names and definitions to describe
similar interactions
FTIR investigation showed that these interactions have been observed through the changes in
IR absorption peaks of PS PEG and PMMA upon mixing with increasing amount of
compatibilizers in their blends which have given rise to a wide investigation
From these the results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PSPEG and PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PS or PMMA and relatively long PS or PMMA backbone of PS-g-PDXL and PMMA-g-
PDXL copolymers respectively
148
Acknowledgements
I would like to thank my advisor Prof S OULD KADA for his help and to
express my sincere gratitude to Prof A KRALLAFA for providing continuous support
to this work His expertise guidance and understanding were a significant help
throughout my work
Very special thanks are extended to Prof Jeanne FRANCOIS for allowing me
to use instruments in her laboratory and for numerous discussions suggestions and
valuable advices which were important contribution to this research
Special thanks and deep appreciation go to Mr G CLISSON for his patience
and help with SEC and DSC measurements
I also owe my sincere appreciation to Mr A KHOUKH for his help with NMR
measurements and important comments considering NMR spectra
I want to thank gratefully Prof M BELBACHIR and Dr A TAYEB for
support and help to this work
I also owe my thanks to Prof Z BOUTIBA and Miss A HADJ BRAHIM for
optical microscopy measurements
I also owe my thanks to Dr MHAMHA and Miss S CHAOUI for Rheological
measurements
To Mr YOUSFI (ENPC-Chlef) I want to thank for Polymer supply
I acknowledge Prof S HACINI Prof D BENACHOUR and Prof M
BELHAKEM who honored me in participating in the jury of my thesis
Special gratitude to my husband FOUAD for being a continuous source of
encouragements For that I doubt I will ever be able to convey my appreciation fully
Special Thanks are also given to my mother father sisters and daughters for
moral support
TABLE OF CONTENTS ACKNOWLEDGEMENTS i SUMMARY hellipii
CHAPTER I LITERATURE REVIEW helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 1
11 Macromonomer Interest and Synthesis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 2
12 Ring-Opening Polymerization Overview helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 4
121 Polymerizability of Cyclic Compounds helliphelliphelliphelliphelliphelliphelliphelliphellip 4
122 Mechanisms of Ring-opening Polymerization helliphelliphelliphelliphelliphellip 6
123 Cationic Ring-Opening Polymerization of Heterocycles helliphellip 7
13 Cationic polymerization of cyclic acetals helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 9
14 Synthesis of functionalized poly (13-dioxolane) helliphelliphelliphelliphelliphelliphelliphelliphelliphellip 13
141 Reaction of 1 3-dioxolane and hydroxyl-containing compounds 13
142 Synthesis of Poly (13-dioxolane) macromonomers helliphelliphelliphellip 15
15 Amphiphilic Graft Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 16
151 Graft Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 16
152 Amphiphilic Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 20
16 Kinetics of Free Radical Polymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 22
161 Kinetics of free radical addition Homo and Copolymerization 22
17 Chain Growth Copolymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 31
171 Copolymerization Equations helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 31
172 Determination of Reactivity Ratios helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 37 18 Controlled Radical Polymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 42
181 Fundamentals of ControlledLiving
Radical Polymerization (CRP) helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 43
182 Typical Features of ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 44
183 Controlled Compositions by ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 46
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 49
CHAPTER II Synthesis and Characterization of Macromonomers 54
21 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 54
22 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
221 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
222 Synthesis of Poly (13-dioxolane) Macromonomers helliphelliphelliphellip 57
223 Synthesis of Poly (13-dioxolane) Hydrogel Network helliphelliphellip 57
23 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
231 Raman Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
232 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
233 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
234 Swelling Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
235 Rheological Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
24 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
241 Structural Characterization of Macromonomers helliphelliphelliphelliphellip 59
242 Molecular Weight Determination helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62
243 Swelling of Poly (13 Dioxolane) Hydrogel helliphelliphelliphelliphelliphelliphellip 63
244 Viscoelastic Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 64
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 67
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 68
CHAPTER III Synthesis and Characterization of Copolymers 69
31 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 69
32 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
321 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
322 Synthesis of Poly (Styrene-g-Poly (1 3-dioxolane)) helliphelliphelliphellip 71
323 Synthesis of Poly (Methyl Methacrylate-g-Poly (1 3-dioxolane))76
33 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
331 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
332 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
333 Diffraction Scanning Calorimetry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
34 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 78
341 Structural Characterization of the Copolymers helliphelliphelliphelliphellip 78
342 Molecular Weight Determination and Copolymer Composition 80
343 Determination of Monomer Reactivity Ratios helliphelliphelliphelliphelliphellip 84
344 Glass Transition Temperatures helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 89
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 93
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
41 Background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
411 Physical Blends helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
412 Equilibrium Phase Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
413 Compatibilization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 97
414 Incorporation of Copolymers for Compatibilization helliphelliphellip 98
415 The Effect of Compatibilizer on a Blend helliphelliphelliphelliphelliphelliphelliphellip 99
416 Methods of Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 100
42 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
421 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
422 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
43 Characterization Techniques for Compatibilization helliphelliphelliphelliphelliphelliphelliphellip 102
431 Dilute Solution Viscometric Measurements helliphelliphelliphelliphelliphelliphellip 102
432 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
433 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
44 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
441 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphellip 104
442 Study of Compatibilization by Dilute Solution Viscometry hellip 106
443 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 116
444 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 118
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 124
References helliphelliphelliphelliphelliphellip helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 125
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g- Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
51 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 127
52 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
521 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
522 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
53 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
531 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
532 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
533 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
54 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
541 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphelliphellip 129
542 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 131
543 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 136
544 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 137
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 144
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 145 CONCLUSIONS helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 146
SUMMARY
Research and development performed on synthetic polymers during the last century has led to
many classes of different polymers for specific applications New types of synthetic polymers
with tailor-made properties are still being introduced for new applications The challenge for
polymer chemists is to control and alter the polymerization conditions such that the final
product has a well-defined structure with desired properties The complex structure of
polymers requires continued analytical chemical efforts to understand the polymerisation
process and the relationships between the molecular structure and material properties
The central point of this thesis is the synthesis and the exploration of the benefits of graft
copolymers derived from poly (1 3 dioxolane) (PDXL) as compatibilizing agents via their
incorporation in immiscible polymer blends The enhancement of adhesion in the solid state
can be accomplished by introducing a compatibilizer that can act as an adhesive between two
polymers andor by control of morphology especially by inducing the phase co-continuity
Graft copolymers offer all Properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheological control i e it
leads to decreased melt viscosities which is an important advantage for processing Depending
on the nature of their backbone and side chains they can be used for a wide variety of
applications such as impact-resistant plastics thermoplastic elastomers polymeric
emulsifiers and even more exciting is the ability of these graft copolymers to function as
compatibilizersinterfacial agents to blends immiscible polymers
The state-of-the-art technique to synthesize graft copolymers is the copolymerization of
macromonomers with low molecular weight comonomers It allows the control of the
polymeric structure which is given by three parameters (i) chains length of the side chains
which can be controlled by the synthesis of macromonomers by living polymerization (ii)
chain length of the backbone which can be controlled in a living polymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular-weight monomer
i
New properties lower prices and reuse of polymers are needed to meet demands of todayrsquos
society and hence of the polymer industry Unfortunately the demands for many applications
need a set of properties that no polymers can fulfil One method to satisfy these demands is by
mixing two or more polymers Materials made from two polymers mixed are called blends In
recent years blending of polymers as a means of combining the useful properties of different
materials to meet new market applications with minimum development cost offers an
interesting route to improve a variety of specific properties of the thermoplastics This has
been increasingly used by the polymer industry
Much work has been done on the blending (mixing) of polymers by many authors A large
part of these studies deal with attempts to obtain a combination of properties of different
polymers Unfortunately these properties of the polymer blends are usually worse instead of
better for many combinations of polymers Significance for these properties is compatibility
between the different polymers which is frequently defined as miscibility on a molecular scale
of the blends components The incorporation of a dispersed phase into a matrix mostly leads
to the presence of stress concentrations and weak interfaces arising from poor mechanical
coupling between phases and therefore morphologies with coarseness commonly on
micrometer scale are obtained Improving mechanical and morphological properties of an
immiscible blend is often done by compatibilization which is a process of modification of the
interfacial properties in immiscible polymer blend resulting in reduction of the interfacial
tension coefficient formation and stabilisation of the desired morphology The use of graft or
block copolymers as compatibilizers for immiscible polymer blends has become an efficient
means for development of new high-performance polymer materials There have been
numerous techniques of studying the miscibility of the polymeric blends The most useful
techniques are viscosimetry measurementsiiiiii thermal analysisiv dynamic mechanical
analysisv refractive indexvi nuclear magnetic resonance methodvii scanning electronviii and
optical spectroscopyix
i Z Sun W Wang and Z Fung Eur Polym J 28 (1992) 1259 ii Aroguz AZ and Baysal BM Eur Polym J42 3 (2006) 11ndash5iii Zhang Y Qian J Ke Z Zhu X Bi H and Nie K Eur Polym J 38 (2002) 333ndash7 iv M Song and F Long Eur Polym J 27 (1991) 983 v Olabisi O Rebeson LM and Shaw MT Polymerndashpolymer miscibility New York Academic Press (1979) vi AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 vii EG Crispim ITA Schuquel AF Rubira and EC Muniz Polymer 41 (3) (2000) 933 viii Martin IG Roleister KH Rosenau R and Koningsveld RJ Polym Sci Part B Polym Phys24 (1986) 723 ix W Wu X Luo D Ma Eur Polym J 35 (1999) 985
ii
Well-known examples of commercial blends are high impact polystyrene (HIPS) and
acrylonitrile-butadiene-styrene (ABS) These blends are tough and have good processability
One of the most interesting examples of an amorphous polymer is polystyrene because of its
brittleness Adding a compatibilizer with the structure of a copolymer to
Polystyrenepolyethylene (PSPE) improves the toughness by a factor 3x Another example is
the use of poly (styrene-co-methacrylic acid) as a compatibilizer in immiscible (incompatible)
blends of PS and polyethylene (PEG)xi
It is of great interest to study miscibility and phase behaviour of two different commodity
immiscible polymer blend systems as PSPEG and polymethyl methacrylate polyethylene
glycol (PMMAPEG) by adding poly (styrene-g-PDXL) and poly (methyl methacrylate-
PDXL) copolymers as compatibilizers respectively Firstly these systems consist of a very
rigid amorphous component (styrene andor PMMA) and a very flexible low-melting point
PEG The extremely high difference of glass transition temperatures (Tg) between the
components motivates us to investigate the phase behaviour of the blends via
compatibilization with prepared grafted copolymers
The first part of the thesis is devoted to the synthesis and characterization of amphiphilic graft
copolymers which were prepared in solution by radical polymerization of hydrophilic poly (1
3 dioxolane) macromonomers as side chains and hydrophobic comonomers such as styrene
and methyl methacrylate as backbone The second part of the thesis describes the blends
preparation and the study of the compatibilization effect of the incorporated amphiphilic graft
copolymers on immiscible (incompatible) blends
The research work in this thesis is presented through several chapters described as follows
Chapter I is a bibliographic survey on polymerization reactions involved in the thesis
Literature concerning the poly (1 3 dioxolane) was included
Chapter II describes the synthesis of poly (1 3 dioxolane) macromonomers and their
characterization As an aside research poly (1 3 dioxolane) network was obtained and the
x E Kroeze thesisUniversity of Groningen (1997) xi Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polym Journal 37 (2001) 1837-1842
iii
swelling and rheological behaviours of this network were discussed and included in this
chapter
Chapter III deals with the synthesis of a series of amphiphilic graft copolymers based on
polystyrene and methyl methacrylate as backbone with poly (1 3 dioxolane) macromonomers
as grafts in this study Selection of proper reaction conditions in terms of overall monomer
concentration and monomer molar ratio were investigated in order to prevent crosslinking
reactions due to the presence of bis-functional poly (1 3 dioxolane) macromonomers
The structure and composition of the graft copolymers were determined by Size Exclusion
Chromatography (SEC) technique and Proton Nuclear Magnetic Resonance (1H-NMR)
analysis Also Modulated Temperature Differential Scanning Calorimeter (MTDSC) was used
for thermal analysis to study the influence of poly (1 3 dioxolane) content on the glass
transition temperature of the copolymers
Last but not the least Chapter IV and Chapter V deal with the most important part of the
thesis which is the study of the compatibilization effect of the prepared copolymers
incorporated in two different immiscible blend systems These two chapters describe first
the polymers used as blend components and also polyblends preparation was discussed The
phase behavior and compatibilization of these polyblends were studied at a composition
of 5050 for both PSPEG and PMMAPEG systems Various amounts of copolymers were
incorporated to the so-called blends for compatibilization The techniques used for this study
were optical microscopy (OM) to analyze their morphology and Fourier-Transform Infra-Red
(FTIR) spectroscopy used to detect the intermolecular interactions in the blends In addition
viscometric method which is a simple inexpensive and sensitive analytical technique and also
alternative to other methods was used The application of the dilute-solution viscosity (DSV)
method for the study of interactions and miscibility of the polymeric system has been
described in more details in these chapters
Conclusions have been made on copolymer characterizations in terms of mostly monomer
reactivity and indeed on compatibilizing effect of these copolymers on the selected polymer
blends This study provides interesting results which can be useful for the development
nanoporous materials
iv
REacuteSUMEacute
La recherche et le deacuteveloppement faits sur des polymegraveres syntheacutetiques pendant le dernier siegravecle
ont abouti agrave plusieurs types de polymegraveres pour des applications speacutecifiques Les nouveaux
polymegraveres syntheacutetiques avec des proprieacuteteacutes faites sur mesure sont toujours introduits pour de
nouvelles applications Le deacutefi pour les chimistes en polymegraveres est de controcircler et drsquoalteacuterer les
conditions de polymeacuterisation de telle sorte que le produit final ait une structure bien deacutefinie avec
des proprieacuteteacutes souhaiteacutees La structure complexe de polymegraveres exige des efforts continus en
chimie analytique pour comprendre le processus de polymeacuterisation et les relations entre la
structure moleacuteculaire et les proprieacuteteacutes des mateacuteriaux
Le centre drsquointeacuterecirct de cette thegravese est la synthegravese et lexploration des avantages des copolymegraveres
greffeacutes deacuteriveacutes agrave partir du poly (1 3 dioxolane) (PDXL) utiliseacutes comme agents compatibilisant
via leur incorporation dans des meacutelanges de polymegraveres non miscibles Lrsquoameacutelioration drsquoadheacutesion
agrave lrsquoeacutetat solide peut ecirctre accomplie en introduisant un compatibilisant qui peut agir comme un
adheacutesif entre deux polymegraveres et ou par le controcircle de la morphologie particuliegraverement en
incitant la co-continuiteacute des phases Les copolymegraveres greffeacutes offrent toutes les proprieacuteteacutes des
copolymegraveres en blocs mais sont toujours plus facile agrave syntheacutetiser De plus la structure ramifieacutee
offre des possibiliteacutes importantes dans le controcircle rheacuteologique cest-agrave-dire elle aide la
diminution de la viscositeacute qui est un avantage important pour la transformation Selon la nature
de la chaicircne principale et des chaicircnes lateacuterales ces copolymegraveres peuvent ecirctre employeacutes pour une
grande varieacuteteacute drsquoapplications comme plastiques reacutesistants au choc elastomers thermoplastiques
des polymegraveres eacutemulsifiants et mecircme plus inteacuteressant est la possibiliteacute de ces copolymegraveres greffeacutes
de fonctionner comme compatibilisant agents drsquointerface aux meacutelanges des polymegraveres non
miscibles
La technique la plus sophistiqueacutee pour syntheacutetiser les copolymegraveres greffeacutes est la
copolymeacuterisation de macromonomegraveres avec des comonomegraveres agrave faible masse moleacuteculaire Elle
permet le controcircle de la structure polymeacuterique par trois paramegravetres (i) la longueur des chaicircnes
lateacuterales qui peut ecirctre controcircleacutee par la synthegravese de macromonomegraveres par la polymeacuterisation
v
vivante (ii) la longueur de chaicircne principale qui peut ecirctre controcircleacutee dans une polymeacuterisation
vivante (iii) espacement moyen des chaicircnes lateacuterales qui est deacutetermineacute par le rapport molaire des
comonomegraveres et taux de reacuteactiviteacute du monomegravere agrave faible masse moleacuteculaire
De nouvelles proprieacuteteacutes des prix bas et la reacuteutilisation de polymegraveres sont neacutecessaires pour
reacutepondre aux demandes de la socieacuteteacute daujourdhui et agrave lindustrie de polymegraveres
Malheureusement ces demandes pour un grand nombre drsquoapplications ont besoin dun jeu de
proprieacuteteacutes quaucun polymegravere ne peut accomplir Une meacutethode de satisfaire ces demandes est en
meacutelangeant deux polymegraveres ou plus Les mateacuteriaux obtenus agrave partir de meacutelanges de deux
polymegraveres meacutelangeacutes sont appeleacutes meacutelanges (Blends) Ces derniegraveres anneacutees le meacutelange de
polymegraveres comme moyen de combiner les proprieacuteteacutes utiles de diffeacuterents mateacuteriaux pour
rencontrer un marcheacute de nouvelles applications agrave un coucirct minimal offre un itineacuteraire inteacuteressant
pour ameacuteliorer une varieacuteteacute des proprieacuteteacutes speacutecifiques des polymegraveres thermoplastiques Cela a eacuteteacute
de plus en plus employeacute par lindustrie des polymegraveres
Beaucoup de travaux ont eacuteteacute faits par plusieurs auteurs sur le meacutelange de polymegraveres Une grande
partie de ces eacutetudes sont dirigeacutees pour obtenir une combinaison des proprieacuteteacutes de diffeacuterents
polymegraveres Malheureusement ces proprieacuteteacutes des meacutelanges de polymegravere sont souvent plus
mauvaises que preacutevues pour la plupart des combinaisons de polymegraveres La signification de ces
proprieacuteteacutes est la compatibiliteacute entre les diffeacuterents polymegraveres qui est freacutequemment deacutefinie comme
la miscibiliteacute agrave lrsquoeacutechelle moleacuteculaire des composants du meacutelange Lincorporation dune phase
disperseacutee dans une matrice provoque surtout la preacutesence de contraintes et des interfaces faibles
qui reacutesultent du faible meacutelange meacutecanique entre les deux phases Lameacutelioration des proprieacuteteacutes
meacutecaniques et morphologiques dun meacutelange non miscible est souvent faite par compatibilisation
qui est un processus de modification des proprieacuteteacutes superficielle dans les meacutelanges de polymegraveres
non miscibles aboutissant agrave la reacuteduction du coefficient de tension superficielle la formation et
stabiliteacute de la morphologie deacutesireacutee Lutilisation des copolymegraveres greffeacutes ou agrave blocs comme
compatibilisant pour des meacutelanges de polymegraveres non miscibles est devenue un moyen efficace
pour le deacuteveloppement de nouveaux mateacuteriaux plus performant Il y a eu de nombreuses
techniques pour lrsquoeacutetude de la miscibiliteacute des meacutelanges polymeacuteriques Les techniques les plus
vi
utiles sont les mesures viscomeacutetriques analyses thermiques analyses meacutecaniques indice de
reacutefraction la reacutesonance magneacutetique nucleacuteaire microscopes optique et eacutelectroniques agrave balayage
Les exemples de meacutelanges commerciaux tregraves bien connus sont le polystyregravene choc (HIPS) et
acrylonitrile-butadiene-styrene (ABS) Ces meacutelanges sont durs et ont bon processability Un
exemple de polymegraveres amorphes le plus inteacuteressant est le polystyregravene agrave cause de sa fragiliteacute
Laddition dun compatibilisant ayant la structure dun copolymegravere au meacutelange de Polystyregravene
polyeacutethylegravene (PSPE) ameacuteliore la dureteacute par un facteur de 3 Un autre exemple est lutilisation du
poly (styrene-co-acide meacutethacrylique) comme compatibilisant dans les meacutelanges non miscibles
de PS et le poly (eacutethylegravene glycol)
Il est tregraves important drsquoeacutetudier la miscibiliteacute et le comportement des phases de deux diffeacuterents
meacutelanges de polymegraveres commerciaux non miscibles (incompatibles) comme le
polystyregravenepolyeacutethylegravene glycol (PSPEG) et le polymeacutethacrylate de meacutethylepolyeacutethylegravene glycol
(PMMAPEG) en incorporant des copolymegraveres tels que (styrene-g-PDXL) et de (meacutethacrylate de
meacutethyle-PDXL) comme compatibilisant respectivement Premiegraverement lrsquoun des composants de
ces systegravemes est amorphe et tregraves rigide (le styregravene etou PMMA) et lrsquoautre (PEG) est flexible et
mou ayant un point de fusion tregraves faible Vu lrsquoextrecircme eacutecart entre les deux tempeacuteratures de
transition vitreuse (Tg) des composants de ces meacutelanges cela nous a motiveacute pour eacutetudier le
comportement de ces meacutelanges via compatibilisation avec des copolymegraveres greffeacutes preacutepareacutes par
nous mecircme
La premiegravere partie de la thegravese est consacreacute agrave la synthegravese et agrave la caracteacuterisation de copolymegraveres
greffeacutes amphiphiles preacutepareacutes en solution par la polymeacuterisation radicale des macromonomers
(poly (1 3 dioxolane)) hydrophiles comme des chaicircnes lateacuterales (greffons) avec des
comonomegraveres hydrophobes comme le styregravene et le meacutethyle methacrylate comme chaicircne
principale La deuxiegraveme partie de la thegravese couvre la preacuteparation des meacutelanges et leacutetude de leffet
de compatibilisant des copolymegraveres greffeacutes amphiphiles sur les meacutelanges non miscibles
(incompatibles)
La recherche concernant cette thegravese est preacutesenteacute par plusieurs chapitres deacutecrits comme suit
vii
Le chapitre I est une recherche bibliographique sur les reacuteactions de polymeacuterisations impliqueacutees
dans la thegravese La Litteacuterature concernant le poly (1 3 dioxolane) est inclue
Le chapitre II deacutecrit la synthegravese des macromonomegraveres du poly (1 3 dioxolane) et leurs
caracteacuterisations Une recherche suppleacutementaire a eacuteteacute effectueacutee concernant la synthegravese drsquoun reacuteseau
tridimensionnel du poly (1 3 dioxolane) Une eacutetude sur les comportements gonflant et
rheacuteologique de ce reacuteseau ont eacuteteacute discuteacutes et inclus dans ce chapitre
Le chapitre III preacutesente la synthegravese dune seacuterie de copolymegraveres greffeacutes amphiphiles constitueacutes de
polystyregravene ou methacrylate de meacutethyle comme chaicircne principale et de macromonomers du poly
(1 3 dioxolane) comme greffons dans cette eacutetude Le choix de conditions de reacuteaction approprieacutees
en termes de concentration totale et le rapport molaire des monomegraveres ont eacuteteacute bien eacutetudieacutes pour
empecirccher les reacuteactions de reacuteticulation agrave cause de la preacutesence de macromonomegraveres bis-
fonctionnel de poly (1 3 dioxolane)
La structure et la composition des copolymegraveres greffeacutes ont eacuteteacute deacutetermineacutees par la technique de la
Chromatographie dExclusion steacuterique (CES) et la spectroscopie en Reacutesonance Magneacutetique
Nucleacuteaire de Proton (1H-NMR) Aussi la Calorimeacutetrie Diffeacuterentielle agrave balayage agrave Temperature
Moduleacutee Calorimeacutetrie (MTDSC) a eacuteteacute employeacute pour lanalyse thermique et pour eacutetudier
linfluence de la proportion du poly (1 3 dioxolane) dans les copolymegraveres sur leur tempeacuterature
de transition vitreuse
Derniers mais pas le moindre les deux Chapitre IV et le Chapitre V couvrent la partie la plus
importante de la thegravese qui est leacutetude de leffet de compatibilisant de ces copolymegraveres preacutepareacutes et
incorporeacutes dans deux diffeacuterents systegravemes de meacutelanges non miscibles (incompatibles) Ces deux
chapitres deacutecrivent dabord les polymegraveres employeacutes comme composants des meacutelanges agrave eacutetudier et
aussi la preacuteparation de ces meacutelanges a eacuteteacute deacutecrite Le comportement de phase et la
compatibilisation des meacutelanges de PSPEG et PMMAPEG agrave une composition de 5050 Des
quantiteacutes diffeacuterentes de copolymegraveres ont eacuteteacute incorporeacutees aux meacutelanges Les techniques
employeacutees pour cette eacutetude sont la microscopie optique (OM) pour analyser leur morphologie et
la spectroscopie agrave Transformeacutee de Fourier Infrarouge (FTIR) pour deacutetecter les interactions
viii
intermoleacuteculaires dans les meacutelanges De plus la meacutethode viscomeacutetrique qui est une technique
simple peu coucircteuse et tregraves sensible a eacuteteacute employeacutee Lrsquoutilisation de la meacutethode de la viscositeacute de
solution dilueacutee (DSV) pour leacutetude dinteractions et la miscibiliteacute du systegraveme polymegravere a eacuteteacute
deacutecrite plus en deacutetail dans ces chapitres
Les conclusions ont eacuteteacute faites sur la caracteacuterisation des copolymegraveres en termes de surtout de la
reacuteactiviteacute des monomegraveres et bien entendu sur leffet compatibilisant de ces copolymegraveres sur les
meacutelanges de polymegraveres qui ont choisis Cette eacutetude fournit des reacutesultats inteacuteressants qui peuvent
ecirctre utiles pour le deacuteveloppement des mateacuteriaux nanoporeux
ix
CHAPTER I Literature Review
11 Macromonomer Interest and Synthesis
Macromonomers bearing polymerizable end groups have received considerable interest
during the last two decades and become a useful tool for the preparation of a variety of graft
copolymers with well-defined structure and composition and polymer networks The
macromonomer method for preparing graft copolymers consists of preparing branches first
followed by the preparation of the grafted structure through the addition of the comonomer to
the macromonomer branch1 2
Therefore macromonomers become the side chains in the graft copolymer with well-defined
length and molecular weight As a sequence the molecular structure of the copolymer can be
determined depending on the amount of macromonomer incorporated and the reactivity of the
end groups
Macromonomers which are linear macromolecules carrying polymerizable functions at one or
two chain ends have been prepared by all polymerization mechanisms anionic cationic free-
radical polyaddition and polycondensation while the polymerizable end groups have been
introduced during the initiation termination or chain transfer steps or by modification of end
groups of telechelic oligomers3
Among the polymerization mechanisms mentioned above the ionic ones allow the best
control of molecular weight polydispersity and functionality of the macromonomers
However they require very demanding experimental conditions like high purity of monomers
and solvents complete absence of moisture and other acidic impurities inert atmosphere etc
Whereas free-radical methods which involve less severe working conditions are largely
used even though the control over the properties of the macromonomers is lower3 For
instance polymers of epoxides tetrahydofuran and cyclic siloxanes are commercially
produced by cationic ring-opening polymerization The history of ring-opening
polymerization of cyclic monomers is shorter than that of the vinyl polymerization and
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422
1
polycondensation With ring-opening functional groups can be introduced into the main chain
of the polymer This polymer cannot be prepared by vinyl polymerization4
Milkovich first developed synthesis of graft polymer with uniform grafts via macromonomer
technique5 Schulz and Milkovich6 reported the synthesis of polystyrene macromonmers
through termination of living PS anions with methacryloyl chloride and their
copolymerization with butyl acrylate and ethyl acrylate
Candau Rempp et al7 obtained PS-g-PEO by reaction between living monofunctional PEO
and partly chloromethacrylated PS backbone (scheme 1) Characterization of the products by
light scattering GPC UV and NMR spectroscopy showed a high degree of grafting
Scheme 1
Ito et al8 used a macromonomer technique to obtain graft copolymers with uniform side
chains They synthesized a graft copolymer of PS with uniform PEO side chains through
copolymerization of styrene and PEO macromonomer (scheme 2) They obtained PEO
macromonomers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-
vinyl benzyl chloride as terminating agent An apparent decrease in reactivities of both poly
(ethylene oxide) of macromonomers and comonomers was ascribed to the thermodynamic
repulsion between the macromonomer and the backbone9
4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348
2
Scheme 2
This type graft copolymers of styrene and ethylene oxide was also obtained by Xie et al10
through copolymerization of styrene with PEO macromonomer prepared by anionic
polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydofuran as
initiator followed by termination with methacryloyl chloride
The method of macromonomer synthesis developed by Xie et al11 has the advantage of
shorter reaction time and a larger range of molecular weight of the PEO macromonomer than
the usual method using potassium alcoholate as initiator PEO macromonomers with
molecular weight from 2 103 to 3 104 and MwMn = 107 ndash 112 can be obtained by this
method12
Only Xie and coworkers have published reports concerning the synthesis of copolymers with
uniform PS grafts obtained through copolymerization of epoxy ether terminated polystyrene
macromonomer with EO13 using a quaternary catalyst composed of triisobutyl-aluminium-
phosphoric acid-water-tertiary amine14 and epichlorohydrin (ECH)15
Free radical polymerization technique has also provided well-defined macromonomers of
poly (acrylic acid)16 vinyl benzyl-terminated polystyrene17 18 poly (t-butyl methacrylate)19
and poly (vinyl acetate)20
Recently Matyjaszewski et al21 employed atom-transfer radical polymerization (ATRP) to
prepare well-defined vinyl acetate terminated PS macromonomers Taking advantage of the
10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp (1985) 461 Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823
3
extremely low reactivity of polystyryl radical towards the vinyl acetate double bond they
used vinyl chloroacetate to initiate the polymerization of styrene to produce the desired
macromonomers This concept has been used similarly in the preparation of a vinyl acetate-
terminated PS macromonomers3 by conventional free-radical polymerization by employing
vinyl iodoacetate as a chain transfer agent possessing a double bond which does not
copolymerize with the monomer that forms the backbone of the macromonomer
12 Ring-Opening Polymerization Overview
Ring-opening polymerization (ROP) is a unique polymerization process in which a cyclic
monomer is opened to generate a linear polymer It is fundamentally different from a
condensation polymerization in that there is no small molecule by-product during the
polymerization Polymers with a wide variety of functional groups can be produced by ring-
opening polymerizations Ring-opening polymerization can proceed through a number of
different mechanisms depending on the type of monomer and catalyst involved Of the wide
range of polymers produced via ROP some have gained industrial significance for example
poly (caprolactam) and poly (ethylene oxide)22 ROP of cyclic esters such as ε-caprolactone
(CL) and L L-dilactide is gaining industrial interest due to their degradability23 The
mechanisms of interest in this work are coordination insertion and cationic
121 Polymerizability of Cyclic Compounds
The thermodynamic polymerizability of a cyclic monomer has been elegantly summarized by
Ivin24 Negative free energy change from monomer to polymer is the thermodynamic driving
force for the ring-opening
ΔG = ΔH ndash T ΔS
For small sized cyclic compounds the enthalpy term is negative and dominant The strains in
bond angles and bond lengths are released upon ring opening Such monomers can be almost
completely converted to polymers For medium sized cyclic monomers (5-7 membered rings)
the ring strain is small and the entropy is a small positive term Thus the overall driving force
(ΔG) is small and the extent of polymerization is little or no reaction For 8- 9- and 10-
22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991)
4
membered monomers the enthalpy term is dominant and negative while the TΔS term is
relatively small The strain is due to the non-bonded interactions between atoms Essentially
complete conversion to polymer is possible When the ring size is very large and there is
virtually no ring-strain (ΔH ne 0) the driving force for ring-opening polymerization is the
large increase of entropy The polymerization should be an athermal process
Why not make polyethylene
In principle one could synthesize polyethylene from cyclohexane
There are two good reasons why this reaction cannot be performed
bull (Kinetic) Cyclohexane lacks any reactive functionality to get hold of
bull (Thermodynamic) Simple six membered rings are extremely stable
Free Energy (ΔG) of Polymerization for Cycloalkanes
The thermodynamic considerations for ring opening are illustrated by this graph (scheme 3) of
free energy (hypothetical) of polymerization from cycloalkanes with various ring sizes to
polyethylene (The two membered ring actually shows the data for ethylene CH2 = CH2)
Scheme 3
5
Three and four membered rings are quite strained so ring opening to polyethylene is
favorable if a suitable reaction pathway existed (Unfortunately no such reaction is known)
Six membered rings are stable so they can rarely be polymerized by ring opening Five and
seven membered rings are borderline cases so sometimes these can be polymerized Larger
rings have transanular steric interactions that cause some strain so rings of 8 members or
more can usually be polymerized Of course this graph changes when substitutions are made
to the rings (for example the presence of heteroatoms like O S and N or the introduction of
double bonds) However the graph for the simplest possible rings illustrates the trends in
other systems reasonably well
Even if the ring opening reaction is thermodynamically favorable there must be reaction
chemistry to get there In most cases the initiators used for ring opening polymerization are
polar or ionic species so the monomers must have groups that can react The most common
monomers for ring opening polymerization contain some kind of heteroatom in the ring as in
the examples of cyclic ethers esters amines amides etc At one extreme there are examples
such as the cyclic phosphazene shown that contain no carbon or hydrogen at all At the other
extreme just a carbon-carbon double bond will suffice for ring opening metathesis
polymerization as illustrated by norbornene
122 Mechanisms of Ring-opening Polymerization
In addition to the thermodynamic criterion there must be a kinetic pathway for the ring to
open and undergo the polymerization reaction Therefore the kinetics of the ring-opening of
the monomer should also be considered Ring-opening polymerization (ROP) can proceed
through a number of different mechanisms depending on the type of monomer and catalyst
involved Of the wide range of polymers produced via ROP some have gained industrial
significance for example poly (caprolactam) and poly (ethylene oxide)24 25 A variety of
mechanisms operate for ring-opening polymerizations including anionic cationic metathesis
and free radical mechanisms Examples of various ring-opening polymerizations are shown in
scheme 4
25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984)
6
Scheme 4
123 Cationic Ring-Opening Polymerization of Heterocycles
A broad range of heterocyclic compounds can undergo cationic ring-opening polymerization
(CROP)26 CROP propagates either through an activated monomer or an activated chain end
mechanism In both cases the propagation involves the formation of a positively charged
species27 A major drawback of CROP is the occurrence of unwanted side reactions thus
limiting the molecular weight of the final product2829 The cationic ring-opening
polymerization of heterocycles has become of significant importance in polymer synthesis
due in part to the diverse variety of functionalized materials that can be prepared by this
method including natural andor biodegradable polymers30 31
Systematic studies of this type of polymerization started around the nineteen sixties Since
then several groups are involved in the kinetics reaction mechanisms and thermodynamics of
the ring-opening polymerization mostly of tetrahydofuran and dioxolane During the last
26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996) (b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993) (c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice (d) Mishra M K Ed Polymer Frontiers New York (1994) 391 31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159
7
years many papers on the synthesis and polymerization of several other cyclic ethers
monocyclic and bicyclic acetals have been published32 33
Examples of commercially important polymers which are synthesized via ring-opening
polymerization are summarized in scheme 5 include such common polymers as
polyoxyethylene (POE 4) poly (butylene oxide) (PBO 5) nylon 6 (6) and poly
(ethyleneimine) (7)
Scheme 5
The synthesis of ring-opened heterocycles is often mediated by compounds whose role is to
initiate the polymerization process This provides less opportunity to ldquotunerdquo polyheterocycle
properties through catalyst choice and has stimulated research to develop initiators which
function beyond the simple activation of polymerization such as living polymerization
initiators343536 chiral initiators3738 enzyme initiators39 and ring-opening insertion
systems4041 The cationic ring-opening polymerization involves the formation of a positively
32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N Macromolecules 26 (1993) 7134
8
charged species which is subsequently attacked by a monomer The attack results in a ring-
opening of the positively charged species Ethylene oxide can be polymerized by cationic
initiators as well (scheme 6)
Scheme 6
13 Cationic Polymerization of Cyclic Acetals
Acetal polymers also known as polyoxymethylene (POM) or polyacetal are formaldehyde-
based thermoplastics that have been commercially available for over 40 years
Polyformaldehyde is a thermally unstable material that decomposes on heating to yield
formaldehyde gas Two methods of stabilizing polyformaldehyde for use as an engineering
polymer were developed and introduced by DuPont in 1959 and Celanese in 1962
DuPonts route for polyacetal yields a homopolymer through the condensation reaction of
polyformaldehyde and acetic acid (or acetic anhydride)
The Celanese route for the production of polyacetal yields a more stable copolymer product
via the reaction of trioxane a cyclic trimer of formaldehyde and a cyclic ether (eg ethylene
oxide or 13 dioxolane)
9
The improved thermal and chemical stability of the copolymer versus the homopolymer is a
result of randomly distributed oxyethylene groups These groups offer stability to oxidative
thermal acidic and alkaline attack The raw copolymer is hydrolyzed to an oxyethylene end
cap to provide thermally stable polyacetal copolymer Polyacetals are subject to oxidative and
acidic degradation which leads to molecular weight deterioration Once the chain of the
homopolymer is ruptured by such an attack the exposed polyformaldehyde ends decompose
to formaldehyde and acetic acid Deterioration in the copolymer ceases however when one
of the randomly distributed oxyethylene linkages is reached42
Cationic polymerization of cyclic acetals exhibits some special features which makes this
system distinctly different from cationic polymerization of simple heterocyclic monomers for
instance cyclic ethers Linear acetals (including polyacetals) are more basic (nucleophilic)
than cyclic ones thus when polymer starts to form it does not constitute a neutral component
of the system but participates effectively in transacetalization reactions which lead to
redistribution of molecular weights and formation of a cyclic fraction These processes which
are usually described by the term ldquoscramblingrdquo have been studied by several authors43 44
Cationic polymerizations of heterocyclic monomers are initiated as in cationic
polymerization of vinylic monomers by electrophilic agents such as the protonic acids (HCl
H2SO4 HClO4 etc) Lewis acids which are electron acceptors by definition and compounds
capable of generating carbonium ions can also initiate polymerization Examples of Lewis
acids are AlCl3 SnCl4 BF3 TiCl4 AgClO4 and I2 Lewis acid initiators required a co-
initiator such as H2O or an organic halogen compound Initiation by Lewis acids either
requires or proceeds faster in the presence of either a proton donor (protogen) such as water
alcohol and organic acids or a cation donor (cationogen) such as t-butyl chloride or
triphenylmethyl fluoride
The polymerization of a heterocyclic monomer initiated by a protonic acid usually starts with
opening of the monomer ring via oxonium sites that are formed upon alkylation (or
protonation) of the monomer
42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144
10
Protonation
BF3 H2O H BF3 OH+ +O
O
Acylation
R CO SbF6 +
OR CO O SbF6
Alkylation
Et3O BF4 +
OC2H5 Et2O BF4O +
Hydrogen transfer
C SbF6 +O
C SbF6H O+
SbF6
O + O O+ H O SbF6
In general initiation step can be shown as
A+
R O++R A O
The mechanism of chain growth involves nucleophilic attack of the oxygen of an incoming
monomer onto a carbon atom in α-position with respect to the oxonium site whereby the
cycle opens and the site is reformed on the attacking unit
A+O
O(CH2)4
O
A+O(CH2)4
Growing chain terminates with nucleophilic species as shown below
O (CH2)4 O+[ ]n
A O (CH2)4[ ]n
AO ( CH2 )4
11
Triflic initiators like trifluoromethane sulfonic acid derivatives can also be employed as an
initiator in the cationic polymerization of heterocyclics in this case initiation step follows
alkylation mechanism
CF3 SO3CH3 +O
CH3 CF3SO3O
CH3 O
CF3SO3
+ O CH3O(CH2)4 O CF3SO3
Ion pairs are in equilibrium with the ester form
(CH2)4 O CF3SO3 (CH2)4 O(CH2)4 O SO2CF3
If instead of ester triflic anhydride is used as initiator the same reaction can occur at both
chain ends and anhydride behaves as a bifunctional initiator
CF3SO2OSO2CF3 nO
+ CF3SO2 O (CH2)4 O (CH2)4 O SO2CF3n-1
(CH2)4 O (CH2)4 n-3
O O CF3SO3 CF3SO3
In the case of living cationic polymerization the growing sites are long living provided the
reaction medium does not contain any transfer agents such as alcohols ethers amines or
acids The reaction mechanism then involves only initiation and propagation steps and the
polymers formed are living The active sites are deactivated by addition of an adequate
nucleophile such as excess water tertiary amines alkoxides phenolates or lithium bromide
12
O(CH2)4
SbF6
(CH2)4 O(CH2)4 OH H
NR3
++ H2O
SbF6
+(CH2)4 O(CH2)4 NR3 SbF6
ONa+(CH2)4 O(CH2)4 O + NaSbF6
+ LiBr
(CH2)4 O(CH2)4 Br LiSbF6+
However facts concerning the real mechanism are scarce In order to progress further in
understanding the cationic polymerization of heterocycles initiated with a Bronsted acid
kinetic studies of simple ring-opening reactions of heterocyclic monomer rings by acids in
nonpolar aprotic and nonbasic solvents (inert solvents) have been performed45
14 Synthesis of Functionalized Poly (1 3-Dioxolane)
1 3-Dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer ends ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The molecular weight of the linear polymers is governed by the
ratio of reacted monomer to transfer agent and is generally well controlled up to 10 000gmol
141 Reaction of 1 3-Dioxolane and Hydroxyl- Containing Compounds
Classical initiation induces polymerization through cyclic tertiary oxonium ions which are
responsible for the formation of an important quantity of cyclic oligomers48
45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon Press 3(1989) 787
13
In several preceding articles Franta et al have investigated the cationic polymerization of
cyclic acetals in the presence of a diol49 50 in particular polymerization of 13-dioxolane
(DXL) and 13-dioxepane (DXP) in the presence of an oligoether diol (αω-dihydroxy-poly
(tetrahydofuran)) or (αω-dihydroxy-poly(ethylene oxide)) In all cases a similar behavior was
observed Cyclic oligomers are present in quantities as in the case of polymerization of DXL
in the absence of hydroxyl containing compounds51
When substituted oxiranes such as propylene oxide or epichlorohydrin are polymerized
according to the ldquoActivated Monomerrdquo mechanism (AM) Cyclic oligomers can be
eliminated52 53 In the AM mechanism polymerization of ethylene oxide however the
reaction of a protonated monomer molecule with a polymer chain leads to side reactions
including cyclization by the Active Chain End (ACE) mechanism53 Thus it is not
unexpected that in the polymerization of cyclic acetals due to the higher nucleophilicity of
the linear acetals located on the chain reactions with the latter will take place
The addition of a protonated DXL onto a hydroxyl group-containing compound is
accompanied by transacetalization involving a monomer molecule
In order to shed some light on the reactions involved Franta et al54 used a monoalcohol
methanol instead of a diol The results confirmed the occurrence of the Active Monomer
mechanism but dimethoxymethane was observed evidence of transacetalization between
methanol and dioxolane
Thus in the DXL-ethylene glycol (EG) system the presence of unreacted EG is in fact due to
the following equilibria
This equation shows the stoichiometry of the reaction rather than its actual mechanism the
reaction certainly has to involve an addition product as a first step
49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154
14
In the next step transacetalization occurs
The products of transacetalization are formed fast as compared to the addition product54 This
indicates that the last reaction is not slower and probably faster than the previous one
Consequently it has been found that although polymerization of DXL in the presence of
hydroxyl group containing compounds proceeds initially by a stepwise addition of protonated
monomer to the hydroxyl terminated linear species in agreement with the AM mechanism but
already at this stage fast transacetalization proceeds leading to formation of O-CH2-O links
between two oligodiols and liberation of ethylene glycol
The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism When DXL is polymerized by strong protonic acids such as triflic acid in the
presence of a diol the PDXL chains are essentially linear and carry end-standing OH
functions Despite the occurrence of some side reactions this mechanism leads to α ω-
dihydroxy-PDXL the molecular weight of which is controlled by the molar ratio of DXL
consumed to diol introduced It has been shown that the polydispersity is on the order of 14
and that molar masses up to 10 000 gmol can be covered
142 Synthesis of Poly (1 3-Dioxolane) Macromonomers
Macromonomers are useful intermediates to prepare graft copolymers and have indeed been
used extensively In order to prepare PDXL macromonomers Franta and al54 have used p-
isopropenylbenzylic alcohol (IPA) as an initiator and triflic acid as a catalyst
The following polymeric species were identified
15
Scheme 7
A is the most abundant compound it corresponds to 50 to 60 weight-wise It is a
macromonomer
B corresponds to 20 to 25 weight-wise It carries two p-isopropenyl functions
C corresponds to 20 to 25 weight-wise It carries no p-isopropenyl function but two
hydroxyl groups
As a result preparation of PDXL macromonomers leads to the preparation of PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of transacetalization
reaction described above a mixture of products was obtained54
Kruumlger et al55 used similar method to prepare macromonomers and come out to the same
conclusions in terms of structure and claim that a clear distinction should be made between
the products obtained and the mechanism responsible for their formation
15 Amphiphilic Graft Copolymers
151 Graft Copolymers
The increasing complexity of polymer applications has required the production of materials
with varied properties Often homopolymers do not afford the scope of attributes necessary to
many applications Copolymerization allows the formulation of polymer materials with
properties characteristic of two homopolymers contained in a single copolymer material The
monomers within a copolymer can be distributed in various fashions random statistical
alternating segmented block or graft56
55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387
16
Scheme 8
Graft copolymers are similar to block copolymers in that they possess long sequences of
monomer units However graft copolymer architecture differs substantially from typical
block copolymers In graft copolymers monomer sequences are grafted or attached to points
along a main polymer chain Grafted chains generally possess molecular weights less than
that of the main chain
These side chains have constitutional or configurational features that differ from those in the
main chain57
The simplest case of a graft copolymer can be represented by A-graft-B or the arrangement
and the corresponding name is polyA-graft-polyB where the monomer named first (A in this
case) is that which supplied the backbone (main chain) units while that named second (B) is
in the side chain(s)
Typical syntheses of the grafts occur by polymerization initiated at some reactive point along
the backbone or by copolymerization of a macromonomer Polymerization from the polymer
backbone is possible via anionic cationic and radical techniques but all require some
functional unit capable of further reaction58
Well defined graft copolymers are most frequently prepared by either
a)ldquografting throughrdquo or b)ldquografting fromrdquo controlled polymerization process
57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991)
17
a) Grafting though the ldquografting throughrdquo method (or macromonomer method) is one of the
simplest ways to synthesize graft copolymers with well defined side chains
Scheme 9
Typically a low molecular weight monomer is radically copolymerized with a methacrylate
functionalized macromonomer This method permits incorporation of macromonomers
prepared by other controlled polymerization processes into a backbone prepared by a CRP
Macromonomers such as polyethylene59 60 poly (ethylene oxide)61 polysiloxanes62 poly
(lactic acid)63 and polycaprolactone64 have been incorporated into a polystyrene or poly
(methacrylate) backbone Moreover it is possible to design well-defined graft copolymers by
combining the ldquografting throughrdquo macromonomers prepared by any controlled polymerization
process and CRP65 This combination allows control of polydispersity functionality
copolymer composition backbone length branch length and branch spacing by consideration
of MM ratio in the feed and reactivity ratio Branches can be distributed homogeneously or
heterogeneously and this has a significant effect on the physical properties of the
materials6263
b) Grafting from the primary requirement for a successful grafting from reaction is a
preformed macromolecule with distributed initiating functionality
59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003) 6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778 63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998) 823-830
18
Scheme 10
Grafting-from reactions have been conducted from polyethylene66 67 polyvinylchloride68 69
and polyisobutylene70 71 The only requirement for an ATRP is distributed radically
transferable atoms along the polymer backbone The initiating sites can be incorporated by
copolymerization68 be inherent parts of the first polymer69 or incorporated in a post-
polymerization reaction70
Graft copolymers perform similar functions to block copolymers in that they contain moieties
with varying properties Compatibilization represents a major area of application for grafts
because the grafted chains can be used to solubilize a polymer blend system containing two
immiscible polymers Additionally graft copolymers offer unique solution mechanical and
morphological properties that make them ideal for utilization as viscosity modifiers and
thermoplastic elastomers72 The unique molecular architecture of graft copolymers leads to
peculiar morphological properties The chain lengths of the grafted arms and backbone block
dictate the morphology that arises in the polymer Changes in the composition of the graft
copolymer alter the resulting polymer morphology A variety of morphologies is possible
ranging from lamellar to cylindrical to spherical73
Graft copolymers offer all properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheology control
Depending on the nature of their backbone and side chains graft copolymers can be used for a
wide variety of applications such as impact-resistant plastics thermoplastic elastomers
66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996) 7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R Macromolecules 32 (1999) 1152-1158
19
compatibilizers viscosity index improvers and polymeric emulsifiers74 75 The state-of-the-
art technique to synthesize graft copolymers is the copolymerization of macromonomers
(MM) with low molecular weight monomers76 In most cases conventional radical
copolymerization has been used for this purpose Using living polymerizations for both the
synthesis of the macromonomers and for the copolymerization offers the highest possible
control of the polymer structure In all these copolymerizations beside the desired graft
copolymers with at least two side chains a number of unwanted products can be expected
unreacted macromonomer ungrafted backbone and backbone with only one graft (star
copolymer) The latter is undesirable for applications as thermoplastic elastomer
Conventional and controlled copolymerizations lead to different copolymer structures In
conventional radical copolymerization the polymers show a broad molecular weight
distribution (MWD) and chemical heterogeneity of first order
152 Amphiphilic Copolymers
A characteristic feature of an amphiphilic polymer is that it contains both hydrophilic and
hydrophobic groups This type of polymer associates in aqueous solution and exhibits several
interesting features and can be used in connection with many industrial and pharmaceutical
applications Usually there is only a few mol of the hydrophobic moieties in order to make
the polymer water-soluble Due to the hydrophobicity of the amphiphilic polymers they have
a tendency to form association structures in aqueous solution by mutual interaction andor
interaction with other cosolutes such as surfactants and colloid particles
In particular the grafting of hydrophilic species onto hydrophobic polymers is of great utility
Amphiphilic graft copolymers so prepared often display enhanced surface properties such as
improved resistance to the adsorption of oils and proteins biocompatibility and reduced static
charge buildup
The synthesis of graft copolymers based on commercial polymers is most commonly
accomplished free radically Free radicals are produced on the parent polymer chains by
exposure to ionizing radiation andor a free-radical initiator77 78 Alternatively peroxide
groups are introduced on the parent polymer by ozone treatment79 80 The resulting reactive
74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998) 696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507
20
sites serve as initiation sites for the free radical polymerization of the comonomer A
significant disadvantage of these free radical techniques is that homopolymerization of the
comonomer always occurs to some extent resulting in a product which is a mixture of graft
copolymer and homopolymer Moreover backbone degradation and gel formation can occur
as a result of uncontrolled free radical production often limiting the attainable grafting
density81 For example amphiphilic graft copolymers synthesized from PEO macromonomer
and hydrophobic comonomers82 83were found to form micellar aggregates in polar medium
such as water wateralcohol alcohol dimethylformamide These phase separation processes
take place also during polymerization and supposedly affect not only the polymerization
kinetics but also properties of resulting copolymers So far unanswered remains the question
of molecular characteristics of reaction products including homopolymers from
macromonomer or comonomer formed under both the homogeneous and heterogeneous
(micellar) reaction conditions Modern liquid chromatographic techniques allow
discrimination of polymeric constituents differing in their chemical structure andor physical
architecture Subsequently the molar mass and molar mass distribution of constituents can be
assessed Recently analyzed products of dispersion copolymerization of polyethylene oxide
methacrylate macromonomer with styrene contained rather large amount of polystyrene
homopolymer84
In the main application areas for amphiphilic polymers the solution properties are of
fundamental importance In many industrial applications association and adsorption
phenomena of the polymers in solution are design properties Consequently a deep
understanding of these phenomena is necessary for the development of new specific
chemicals and new processes The research goals are to clarify the relations between the
molecular structure of amphiphilic polymers and their properties in aqueous solution A
further goal is to develop theoretical models for the description of the behavior of amphiphilic
polymers in solution and at surfaces Several projects concern the self-assembly of
amphiphilic polymer molecules and the association behavior of surfactants and
hydrophobically modified hydrophilic polymers such as cellulose derivatives Studies of
amphiphilic model polymers such as ethylene oxide block and graft copolymers are carried
80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication
21
out in order to gain fundamental knowledge on the solution behavior of amphiphilic
polymers
16 Kinetics of Free Radical Polymerization
Free radical polymerization is the most widespread method of polymerization of vinylic
monomers Free radical polymerizations are chain reactions in which every polymer chain
grows by addition of a monomer to the terminal free radical reactive site called ldquoactive
centerrdquo The addition of the monomer to this site induces the transfer of the active center to
the newly created chain end Free radical polymerization is characterized by many attractive
features such as applicability for a wide range of polymerizable groups including styrenic
vinylic acrylic and methacrylic derivatives as well as tolerance to many solvents small
amounts of impurities and many functional groups present in the monomers
161 Kinetics of free radical addition Homo and Copolymerization
Understanding of chemical kinetics during homo- and copolymerization is crucial for
copolymer synthesis The discussion below will review the kinetics of free radical initiated
polymerizations and copolymerizations
The three main kinetic steps that occur during polymerization are (1) initiation (2)
propagation and (3) termination
1 Initiation
The initiation step is considered to involve two reactions creating the free radical active
center The first event is the production of free radicals Many methods can be used to initiate
free radical polymerizations such as thermal initiation without added initiator or high energy
radiation of the monomers However free radicals are usually generated by the addition of
initiators that form radicals when heated or irradiated Two common examples of such
compounds which afford free radicals are benzoyl peroxide (BPO) and azobisisobutyronitrile
(AIBN)
22
Figure 1 Generation of Free Radicals by Thermal Decomposition of Benzoyl Peroxide
Figure 2 Decomposition of Azobisisobutyronitrile to Form Free Radicals
Figure 1 depicts the thermal decomposition of BPO to form two oxy-radicals and Figure 2
depicts the decomposition of AIBN to form two nitrile stabilized carbon based radicals
(equation 1)
In equation 1 kd is the rate constant which describes the first order initiation process The
radical that is formed can now add to the double bond of the monomer and initiate
polymerization
The symbol M will represent the monomer and the rate constant for this process will be ki as
described in equation 2
23
Together these two reactions the radical generation and the monomer addition to the radical
form the process of initiation Usually the assumption that is taken into account is that the
first step is the rate determining step This means that the decomposition to form the radical
is much slower than the monomer addition to the free radical Therefore the equation for the
rate of radical formation ri is
The number 2 is obtained from the fact that a maximum of two radicals can be generated for
the initiation
But not all of the primary radicals produced by the decomposition of the initiator will
necessarily react with the monomer which means several other competing reactions may
occur85 Therefore in order to determine the rate of initiation the fraction of initially formed
radicals that actually start chain growth will be denoted by f and the rate of initiation equation
becomes
2 Propagation
Now the propagation of the reaction will proceed through the successive addition of
monomer to the radicals This type of process can be expressed in the following form
85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster PA (1997)
24
And further generalizing the reaction scheme gives
The assumption that the reactivity of the addition of each monomer is independent of the
chain length is evident in these two equations and was postulated by Flory 58 86 The use of
the rate constant kp for both of these equations imply that the rate constant is independent of
chain length The rate of the propagation rp of this polymerization or the rate of monomer
removal is thus given by
3 Termination
The termination of these growing radical chains occurs in principally two different ways The
first way is the formation of a new bond in between the two radicals this is called
combination Secondly the radical chains can terminate by disproportionation This is a
process where a hydrogen atom from one of the chains is transferred to the other and the chain
that the proton was removed from forms a double bond These reactions are represented as
follows
Figure 3 Termination by Combination
86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995)
25
Figure 4 Termination by Disproportionation
Schematically the reactions can be represented as follows
Where the rate constant of termination by combination is denoted by ktc and the rate constant
of termination by disproportionation is denoted by ktd Since both of these reactions use two
radical species and have the same kinetics the overall equation for the rate of termination is
written as
where kt = ktc + ktd and the number 2 imply there are two radicals that are terminated in
each termination reaction The monomer structure and the temperature are what determines
the type of termination that is most dominant in the reaction For most systems the amount of
one termination type far exceeds the other termination type
The further calculations for the rate of polymerization Rp and the degree of conversion as a
function of time can now be developed The assumption of the steady state concentration of
transient species must be used here where the transient species is the radical M For the
steady state approximation to hold true the rate at which initiation occurs ri must be equal to
the rate at which termination occurs rt or in other words radicals must be generated at the
same rate at which they are terminated This assumption gives the equation
26
This equation then gives an expression for the radical species
Experimentally this value would be difficult to measure in the laboratory and therefore this
equation must be used in the subsequent equations that follow By further substitution an
expression for the rate of polymerization Rp can be obtained because it equals the rate of
propagation
From this equation it can be deduced that the rate of polymerization is directly proportional
to the monomer concentration and to the initiator concentration to the one half power In
other words Rp is first order with regards to the monomer concentration and half order to the
initiator concentration
When the conversion is low the assumption that the initiator concentration is constant is
reasonable but the consumption of the initiator can be added into the calculations Therefore
Then integration can be performed
Finally the rate of polymerization becomes
27
This equation can be broken into three different parts
The second term indicates that the rate of polymerization is still proportional to the monomer
concentration to the first power and the initiator concentration to the one half power but the
initiator concentration is now the initial concentration Therefore by increasing the initial
concentration of an initiator in a solution polymerization the rate of the reaction should
increase proportionally to the square root of the amount of initiator added The third term
indicates that as the initiator is consumed the polymerization slows down exponentially with
time as well as its slowing down due to monomer depletion
The first term in the brackets suggests that the rate of polymerization is proportional to kp
kt12 When experiments are performed to probe the kinetics of reactions in solution the
expected first order dependence on monomer concentration is observed But when the
experiment is performed in concentrated solvents or even in the bulk the polymerization
kinetics accelerate The reason for this anomaly is that the viscosity increases as the
polymerization proceeds because the polymer has a higher viscosity than the monomers The
kp is not affected but the kt is
The degree of conversion can now be expressed as a function of time by knowing that
By substituting the earlier equation for Rp and integrating that equation one can obtain this
Furthermore ([M]0 ndash [M]) [M]0 is equal to the degree of conversion and is the fraction of
the monomer that has been reacted where [M] is the concentration of the monomer that has
been left after the reaction and [M]0 is the initial monomer concentration Therefore ([M]0 ndash
[M]) is the concentration of the monomer that has reacted The conversion can then be
expressed as
28
This can also be expressed as
As is always the case the conversion never quite reaches 100 value or a factor of 1 given by
the exponential term So if the time goes to infinity the expression that is obtained for
maximum conversion that is less than 1 by an amount that is dependent on the initial initiator
concentration is
If the steady state approximation for the initiator concentration had been carried through these
calculations and equations then the conversion would approach a value of 1 after a long
period of time
Distributions on the average distribution of chain lengths during and after a polymerization
are present in free radical polymerizations This is due to the naturally but statistically
random termination reactions that occur in the solution with regard to chain length The
kinetic chain length v is the rate of monomer addition to growing chains over the rate at
which chains are started by radicals which is the expression for the number average chain
length In other words it is the average number of monomer units per growing chain radical
at a certain instant87 Therefore the initiator radical efficiency in polymerizing the monomers
is
87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993)
29
When termination occurs mainly by combination the chain length for the polymer chains on
the average doubles in size assuming nearly equal length chains combine But if
disproportionation mainly occurs the growing chains do not undergo any change in chain
length during the process So the expressions are thus
A new term can be used to more generally express the average chain length of the growing
polymer chain xn This new term is the average number of dead chains produced per
termination ξ This value is equal to the rate of dead chain formation over the rate of the
termination reactions The equations take into account that in combination only one dead
chain is produced and in disproportionation reactions two dead chains are produced
Therefore
Furthermore the instantaneous number average chain length can be expressed in terms of the
rate of addition of the monomer units divided by the rate of dead polymers forming This is
shown as
30
From this equation82 one can clearly see that the rate of polymerization is proportional to the
initiator concentration to the one half power [I]12 and that the instantaneous number average
chain length xn is proportional to the inverse of the initiator concentration to the one half
power 1[I]12 Thus if the polymerization was accelerated by using more initiator the chains
will end up to be shorter which may not be desirable85
17 Chain Growth Copolymerization
171 Copolymerization Equations
Chain polymerizations can obviously be performed with mixtures of monomers rather than
with only one monomer For many free radical polymerizations for example acrylonitrile and
methyl acrylate two monomers are used in the process and the subsequent copolymer might
be expected to contain both of the structures in the chain This type of reaction that employs
two comonomers is a copolymerization The reactivity and the relative concentrations of the
two monomers should determine the concentration of each comonomer that is incorporated
into the copolymer The application of chain copolymerizations has produced much important
fundamental information Most of the knowledge of the reactivities of monomers via
carbocations free radicals and carbanions in chain polymerizations has been derived from
chain copolymerization studies The chemical structure of these monomers strongly
influences reactivity during copolymerization Furthermore from the technological viewpoint
copolymerization has been critical to the design of the copolymer product with a variety of
specifically desired properties As compared to homopolymers the synthesis of copolymers
can produce an unlimited number of different sequential arrangements where the changes in
relative amounts and chemical structures of the monomers produce materials of varying
chemical and physical properties
Several different types of copolymers are known and the process of copolymerization can
often be changed in order to obtain these structures A statistical or random copolymer may
obey some type of statistical law which relates to the distribution of each type of comonomer
that has been incorporated into the copolymer Thus for example it may follow zero- or first-
31
or second-order Markov statistics88 Copolymers that are formed via a zero-order Markov
process or Bernoullian contain two monomer structures that are randomly distributed and
could be termed random copolymers
ndashAABBBABABBAABAmdash
Alternating block and graft copolymers are the other three types of copolymer structures
Equimolar compositions with a regularly alternating distribution of monomer units are
alternating copolymers
ndashABABABABABABA--
A linear copolymer that contains one or more long uninterrupted sequences of each of the
comonomer species is a block copolymer
--AAAAAAAA-BBBBBBBBB--
A graft copolymer contains a linear chain of one type of monomer structure and one or more
side chains that consist of linear chains of another monomer structure
--AAAAAAAAAAAAAmdash
B B
B B
B B
B B
For this discussion the main focus will be on randomly distributed or statistical copolymers
Copolymer composition is usually different than the composition of the starting materials
charged into the system Therefore monomers have different tendencies to be incorporated
into the copolymer which also means that each type of comonomer reacts at different rates
with the two free radical species present Even in the early work by Staudinger89 it was
noted that the copolymer that was formed had almost no similar characteristics to these of the
homopolymers derived from each of the monomers
Furthermore the relative reactivities of monomers in a copolymerization were also quite
different from their reactivities in the homopolymerization Thus some monomers were more 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151
32
reactive while some were less reactive during copolymerization than during their
homopolymerizations Even more interesting was that some monomers that would not
polymerize at all during homopolymerization would copolymerize relatively well with a
second monomer to form copolymers It was concluded that the homopolymerization features
do not easily directly relate to those of the copolymerization
Alfrey (1944) Mayo and Lewis (1944) and Walling (1957)909192 demonstrated that the
copolymerization composition can be determined by the chemical reactivity of the free radical
propagating chain terminal unit during copolymerization Application of the first-order
Markov statistics was used and the terminal model of copolymerization was proposed The
use of two monomers M1 and M2 during copolymerization leads to two types of propagating
species The first of these species is a propagating chain that ends with a monomer of
structure M1 and the second species is a propagating chain that ends with a monomer structure
M2 For radically initiated copolymerizations the two structures can be represented by
M1 and M2 where the zig-zag lines represent the chain and the M
represents the radical at the growing end of the chain The assumption that the reactivity of
these propagating species only depends on the monomer unit at the end of the chain is called
the terminal unit model58 If this is so only four propagation reactions are possible for a two
monomer system The propagating chain that ends in M1 can either add a monomer of type
M1 or of type M2 Also the propagating chain that ends in M2 can add a monomer unit of
type M2 or of type M1 Therefore these equations can be written with the rate constants of
reactions93
90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953)
33
The rate constant for the reaction of the propagating chain that ends in M1 and adds another
M1 to the end of the chain is k11 and the rate constant for the reaction of the propagating
chain that ends in M2 and adds M1 to the end of the chain is k21 and so on
The term self-propagation refers to the addition of a monomer unit to the chain that ends with
the same monomer unit and the term cross-propagation refers to a monomer unit that is added
the end of a propagating chain that ends in the different monomer unit These (normally)
irreversible reactions can propagate by free radical anionic or cationic processes although
active lifetimes could be very different
As indicated by reactions 30 and 32 monomer M1 is consumed and as indicated by reactions
31 and 33 monomer M2 is consumed The rates of entry into the copolymer and the rates of
disappearance of the two monomers are given by
In order to find the rate at which the two monomers enter into the copolymer equation 34
is divided by equation 35 to give the copolymer composition equation
The low concentrations (eg 10-8 molesliter) of the radical chains in the systems are very
hard to experimentally determine So to remove these from the equation the steady state
approximation is normally employed Therefore a steady state concentration is assumed for
both of the species M1 and M2 separately The interconversion between the two
species must be equal in order for the concentrations of each to remain constant and hence the
rates of reactions 31 and 32 must be equal
34
Rearrangement of equation 37 and combination with equation 36 gives
This equation can be further simplified by dividing the right side and the top and bottom by
k21 [M2] [M1] The results are then combined with the parameters r1 and r2 which are
defined to be the reactivity ratios
The most familiar form of the copolymerization composition equation is then obtained as
The ratio of the rates of addition of each monomer can also be considered to be the ratio of the
molar concentrations of the two monomers incorporated in the copolymer which is denoted
by (m1m2) The copolymer composition equation can then be written as
The copolymer composition equation defines the molar ratios of the two monomers that are
incorporated into the copolymer d[M1] d[M2] As seen in the equation this term is directly
related to the concentration of the monomers that were in the feed [M1] and [M2] and also
the monomer reactivity ratios r1 and r2 The ratio of the rate constant for the addition of its
own type of monomer to the rate constant for the addition of the other type of monomer is
35
defined as the monomer reactivity ratio for each monomer in the system When M1
prefers to add the monomer M1 instead of monomer M2 the r1 value is greater than one
When M1 prefers to add monomer M2 instead of monomer M1 the r1 value is less than
one When the r1 value is equal to zero the monomer M1 is not capable of adding to itself
which means that homopolymerization is not possible
The copolymer composition equation can also be expressed in mole fractions instead of
concentrations which helps to make the equation more useful for experimental studies In
order to put the equation into these terms F1 and F2 are the mole fractions of M1 and M2 in the
copolymer and f1 and f2 are the mole fractions of monomers M1 and M2 in the feed
Therefore
and
Then combining equations 42 43 and 40 gives
This form of the copolymer equation gives the mole fraction of monomer M1 introduced into
the copolymer58
Different types of monomers show different types of copolymerization behavior Depending
on the reactivity ratios of the monomers the copolymer can incorporate the comonomers in
different ways
The three main types of behavior that copolymerizations tend to follow correspond to the
conditions where r1 and r2 are both equal to one when r1 r2 lt 1 and when r1 r2 gt 1
bull A perfectly random copolymerization is achieved when the r1 and r2 values are both
equal to one This type of copolymerization will occur when the two different types of
36
propagating species M1 and M2 show the exact same preference for the addition of
each type of monomer In other words the growing radical chains do not prefer to add one of
the monomers more than the other monomer which results in perfectly random incorporation
into the copolymer
bull An alternating copolymerization is defined as r1 = r2 = 0 The polymer product in
this type of copolymerization shows a non-random equimolar amount of each comonomer
that is incorporated into the copolymer This may occur because the growing radical chains
will not add to its own monomer Therefore the opposite monomer will have to be added to
produce a growing chain and a perfectly alternating chain
When r1 gt 1 and r2 gt 1 both of the monomers want to add to themselves and in theory could
produce block copolymers But in actuality because of the short lifetime of the propagating
radical the product of such copolymerizations produces very undesirable heterogeneous
products that include homopolymers Therefore macroscopic phase separation could occur
and desirable physical properties such as transparency would not be achieved
172 Determination of Reactivity Ratios
Many methods have been used to estimate reactivity ratios of a large number of
comonomers94 The copolymer composition may not be independent of conversion This
means the disappearance of monomer one may be faster than the disappearance of monomer
two if monomer one is being incorporated into the copolymer at a faster rate and therefore it
has a larger reactivity ratio than monomer two
The approximation method95 is the simplest of the methods that has been used to calculate the
reactivity ratios of copolymer systems The method is based on the fact that r1 the reactivity
ratio of component one is mainly dependent on the composition of monomer two m2 that
has been incorporated into the copolymer at low concentrations of monomer two in the feed
M2 The expression is thus
94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
37
The value of the reactivity ratio for component one can be easily determined by only one
experiment but the value is only an approximation and does not provide any validity of the
estimated r1 In order to determine the amount of the comonomer that has been incorporated
into the copolymer various analytical methods must be used Proton Nuclear Magnetic
Resonance Carbon 13 NMR and Fourier Transform Infrared Spectroscopy are three sensitive
instruments that can determine the copolymer composition The approximation method is
limited when the reactivity ratio of one of the components in the system has a value of less
than 01 or greater than a value of 10
However the method does give good insight into the reactivity ratio values for many
copolymer systems The approximation of reactivity ratios can be easy and quick when using
this method of evaluation
The Mayo-Lewis intersection method91 96 uses a linear form of the copolymerization equation where r1 and r2 are linearly related
By using the equations m1M 22 m2M12 and (M2 M1)[(m1 m2) ndash 1] for the slope and intercept
respectively a plot can be produced for a set of experiments after the copolymer composition
has been determined The straight lines that are produced on the plot for each experiment
where r1 represents the ordinate and r2 represents the abscissa intersect at a point on the r1 vs
r2 plot The point where these lines meet is taken to be r1 and r2 for the system in study The
main advantage of this method is that it gives a qualitative observation of the validity of the
intersection area Over the whole range of possible copolymer compositions that were tested
more compact intersections better define the data However the method requires a visual
check of the data and a quantitative estimation of the error is impossible Therefore
weighting of the data is needed to determine the most precise values of r1 and r2
The Fineman-Ross linearization method97 uses another form of the copolymer equation
Where
And
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259
38
For this method by plotting G versus H for all the experiments one will obtain a straight line
where the slope of the straight line is the value for r1 and the intercept of the line is the value
for r2 This type of reactivity ratio determination has the same advantages and disadvantages
of the method described above however this treatment is a linear least squares analysis
instead of a graphical analysis The validity is only qualitative and the estimates of r1 and r2
can change with each experimenter by weighting the data in different ways Furthermore the
high and low experimental composition data are unequally weighted which produces large
effects on the calculated values of r1 and r2 Therefore different values of r1 and r2 can be
produced depending on which monomer is chosen as M158
A refinement of the linearization method was introduced by Kelen and Tudos98 99 100 by
adding an arbitrary positive constant a into the Fineman and Ross equation 47 This technique
spreads the data more evenly over the entire composition range to produce equal weighting to
all the data58 The Kelen and Tudos refined form of the copolymer equation is as follows
η = [ r1 + r2 α ] ξ minus r2 α (50)
where
η = G ( α + H ) (51)
ξ = H ( α + H ) (52)
By plotting η versus ξ a straight line is produced that gives ndashr2α and r1 as the intercepts on
extrapolation to ξ=0 and ξ=1 respectively Distribution of the experimental data
symmetrically on the plot is performed by choosing the α value to be (HmHM)12 where Hm
and HM are the lowest and highest H values respectively Even with this more complicated
monomer reactivity ratio technique statistical limitations are inherent in these linearization
methods101 102
98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265
39
OrsquoDriscoll Reilly et al103 104 determined that the dependent variable does not truly have a
constant variance and the independent variable in any form of the linear copolymer equation
is not truly independent Therefore analyzing the composition data using a non-linear
method has come to be the most statistically sound technique
The non-linear or curve-fitting method90 is based on the copolymer composition equation in
the form
This equation is based on the assumptions that the monomer concentrations do not change
much throughout the reaction and the molecular weight of the resulting polymer is relatively
high In order to determine reactivity ratios from the experimental data a graph must be
generated for the observed comonomer amount that was incorporated into the copolymer m1
versus the feed comonomer amount M1 for the entire range of comonomer concentrations
Then a curve can be drawn through the points for selected r1 and r2 values and the validity of
the chosen reactivity ratio values can be checked by changing the r1 and r2 values until the
experimenter can demonstrate that the curve best fits the data points
The main advantage of the reactivity ratio determination methods discussed thus far is the
results can be visually and qualitatively checked Disadvantages include a direct dependence
of the composition on conversion for most polymer systems and therefore low conversion
(eg instantaneous composition) is needed to determine the reactivity ratios Furthermore
extensive calculations are required but only qualitative measurements of precision can be
obtained Finally weighting of the experimental data for the methods to determine precise
reactivity ratios is hard to reproduce from one experimenter to another
Therefore a technique that allows the rigorous application of statistical analysis for r1 and r2
was proposed by Mortimer and Tidwell which they called the nonlinear least squares
method95105106107This method can be considered to be a modification or extension of the
curve fitting method For selected values of r1 and r2 the sum of the squares of the differences
between the observed and the computed polymer compositions is minimized
103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772
40
Using this criterion for the nonlinear least squares method of analysis the values for the
reactivity ratios are unique for a given set of data where all investigators arrive at the same
values for r1 and r2 by following the calculations Recently a computer program published by
van Herck108 109 allows for the first time rapid data analysis of the nonlinear calculations It
also permits the calculations of the validity of the reactivity ratios in a quantitative fashion110
The computer program produces reactivity ratios for the monomers in the system with a 95
joint confidence limit determination
The joint confidence limit is a quantitative estimation of the validity of the results of the
experiments and the calculations performed This method of data analysis consists of
obtaining initial estimates of the reactivity ratios for the system and experimental data of
comonomer charge amounts and comonomer amounts that have been incorporated into the
copolymer both in mole fractions Many repeated sets of calculations are performed by the
computer which rapidly determines a pair of reactivity ratios that fit the criterion wherein the
value of the sum of the squares of the differences between the observed polymer composition
and the computed polymer composition is minimized111 112 This method uses a form of the
copolymer composition equation with mole fractions of the feed It amounts to determining
the mole fraction of the comonomer that should be incorporated into the copolymer during a
differential time interval
For this equation F2 represents the mole fraction of comonomer two that was calculated to be
incorporated into the copolymer and f1 and f2 represent the mole fractions of each comonomer
that were fed into the reaction mixture The use of the Gauss-Newton nonlinear least squares
procedure predicts the reactivity ratios for a given set of data after repeating the calculations
so that the difference between the experimental data points and the calculated data points on a
plot of mole fraction of comonomer incorporated versus comonomer in the feed is reduced to
the minimum value113 114
108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65
41
18 Controlled Radical Polymerization
The development of new controlledliving radical polymerization processes such as Atom
Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated
polymerization and degenerative transfer processes including RAFT opened the way to the
use of radical polymerization for the synthesis of well-defined complex functional
nanostructures The development of such nanostructures is primarily dependent on self-
assembly of well-defined segmented copolymers This section describes the fundamentals of
ATRP relevant to the synthesis of such systems115
The main goal of macromolecular engineering is to carry out the synthesis (polymerization) in
such a way that it results in well-defined macromolecular products One of the ways to
achieve full control of the macromolecule (length sequence and regio- and stereo- regularity)
would be to build it one monomer at a time with mechanisms in place facilitating selection of
an appropriate monomer and assuring its addition in proper orientation This of course has
been achieved in Nature in the process of protein synthesis through the use of sophisticated
macromolecular ldquonanomachineryrdquo (DNA RNA Most commonly used synthetic routes to
linear polymers are based on addition (chain) reactions which can be controlled only in
statistical terms through such parameters as initiatormonomer ratios monomerpolymer
reactivities monomer concentrations reaction medium etc The main strategy to achieve the
reasonable control of such reactionsrsquo products is through the synchronized growth of ldquolivingrdquo
chains ie chains which cease to grow only in the absence of a monomer Synchronization of
chain growth can be achieved fairly easily through rapid initiation Living chains grown in
such synchronized fashion exhibit relatively narrow molecular weight distributions (MWD)
their average molecular weights can be controlled simply by the duration of reaction Until
recently radical polymerization which covers the broadest range of monomers appeared to
be inherently uncontrollable due to the presence of fast chain termination of growing radicals
Thus although very useful in the synthesis of bulk commodity polymers where precise
control is not always essential radical polymerization has been hardly ever viewed as a tool to
precisely engineer macromolecules for well-defined functional nanostructures
114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16
42
This outlook shifted dramatically recently with the development of new controlledliving
radical polymerization processes such as Atom Transfer Radical Polymerization (ATRP)116
117 118 and other techniques such as nitroxide mediated polymerization119 and degenerative
transfer processes120 including reversible addition-fragmentation chain transfer (RAFT)121
With the availability of effective control mechanisms given its applicability to a broadest
range of monomers radical polymerization is now ready to assume the central role in
macromolecular engineering geared towards the development of well-defined functional
nanostructures
181 Fundamentals of ControlledLiving Radical Polymerization (CRP)
The great expectations for the controlledliving radical polymerization (CRP) have their
origins in the dominating position of the free radical technique by far the most common
method of making polymeric materials (nearly 50 of all polymers are made this
way)122123124This is due to the large number of available vinyl monomers (eg there are
nearly 300 different methacrylates available commercially) which can be easily
homopolymerized and copolymerized The advent of CRP enables preparation of many new
materials such as well-defined components of coatings (with narrow MWD precisely
controlled functionalities and reduced volatile organic compounds -VOCs) non ionic
surfactants polar thermoplastic elastomers entirely water soluble block copolymers
(potentially for crystal engineering) gels and hydrogels lubricants and additives surface
modifiers hybrids with natural and inorganic polymers various biomaterials and electronic
materials
The controlledliving reactions are quite similar to the conventional ones however the radical
formation is reversible Similar values for the equilibrium constants during initiation and
propagation ensure that the initiator is consumed at the early stages of the polymerization
116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002)
43
generating chains which slowly and continuously grow as in a living process There are a
number of critical differences between conventional and controlledliving radical reactions
bull Perhaps the most important difference between the two approaches is the lifetime of
the propagating chains which is extended from 1 s to more than 1 h
bull The second major difference is the very significant increase in the initiation rate
which enables simultaneous growth of all the polymer chains
bull Termination processes cannot be avoided in CRPs Thus CRP is generally less precise
than the anionic polymerization Termination is the most dangerous chain breaking
reaction in CRPs Since it is a bimolecular process increasing the polymerization rate
increases the concentration of radicals and enhances the termination process
Termination also becomes more significant for longer chains and at higher conversion
However this process is somehow self tuned since termination is chain length
dependent
The key feature of the controlledliving radical polymerization is the dynamic equilibration
between the active radicals and various types of dormant species Currently three systems
seem to be most efficient nitroxide mediated polymerization (NMP) atom transfer radical
polymerization (ATRP) and degenerative transfer processes such as RAFT123 Each of the
CRPs has some limitations and some special advantages and it is expected that each
technique may find special areas where it would be best suited synthetically For example
NMP carried out in the presence of bulky nitroxides cannot be applied to the polymerization
of methacrylates due to fast β-H abstraction ATRP cannot yet be used for the polymerization
of acidic monomers which can protonate the ligands and complex with copper RAFT is very
slow for the synthesis of low MW polymers due to retardation effects and may provide
branching due to trapping of growing radicals by the intermediate radicals At the same time
each technique has some special advantages Terminal alkoxyamines may act as additional
stabilizers for some polymers ATRP enables the synthesis of special block copolymers by
utilizing a halogen exchange and has an inexpensive halogen at the chain end125 RAFT can
be applied to the polymerization of many unreactive monomers such as vinyl acetate126
182 Typical Features of ATRP
A successful ATRP process should meet several requirements
125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035
44
bull Initiator should be consumed at the early stages of polymerization to form polymers
with degrees of polymerization predetermined by the ratio of the concentrations of
converted monomer to the introduced initiator (DP = Δ[M][I]o)
bull The number of monomer molecules added during one activation step should be small
resulting in polymers with low polydispersities
bull The contribution of chain breaking reactions (transfer and termination) should be
negligible to yield polymers with high degrees of end-functionalities and allow the
synthesis of block copolymers
In order to reach these three goals it is necessary to select appropriate reagents and
appropriate reaction conditions ATRP is based on the reversible transfer of an atom or group
from a dormant polymer chain (R-X) to a transition metal (M nt Ligand) to form a radical (R)
which can initiate the polymerization and a metal-halide whose oxidation state has increased
by one (X-M n+1t Ligand) the transferred atom or group is covalently bound to the transition
metal A catalytic system employing copper (I) halides (Mnt Ligand) complexed with
substituted 2 2rsquo- bipyridines (bpy) has proven to be quite robust successfully polymerizing
styrenes various methacrylates acrylonitrile and other monomers116127 Other metal centers
have been used such as ruthenium nickel and iron based systems117 118 Copper salts with
various anions and polydentate complexing ligands were used such as substituted bpy
pyridines and linear polyamines The rate constants of the exchange process propagation and
termination shown in Scheme 11 refer to styrene polymerization at 110 C
Scheme 11
According to this general ATRP scheme the rate of polymerization is given by the following
equation
127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901
45
Thus the rate of polymerization is internally first order in monomer externally first order
with respect to initiator and activator Cu(I) and negative first order with respect to
deactivator XCu(II) However the kinetics may be more complex due to the formation of
XCu(II) species via the persistent radical effect (PRE) The actual kinetics depend on many
factors including the solubility of activator and deactivator their possible interactions and
variations of their structures and reactivities with concentrations and composition of the
reaction medium It should be also noted that the contribution of PRE at the initial stages
might be affected by the mixing method crystallinity of the metal compound and ligand etc
One of the most important parameters in ATRP is the dynamics of exchange and especially
the relative rate of deactivation If the deactivation process is slow in comparison with
propagation then a classic redox initiation process operates leading to conventional and not
controlled radical polymerization Polydispersities in ATRP are defined by the following
equation when the contribution of chain breaking reactions is small and initiation is
complete
Thus polydispersities decrease with conversion p the rate constant of deactivation kd and
also the concentration of deactivator [XCu(II)] They however increase with the propagation
rate constant kp and the concentration of initiator [RX]o This means that more uniform
polymers are obtained at higher conversions when the concentration of deactivator in solution
is high and the concentration of initiator is low Also more uniform polymers are formed
when the deactivator is very reactive (eg copper(II) complexed by 2 2-bipyridine or
pentamethyldiethylenetriamine rather than by water) and monomer propagates slowly (styrene
rather than acrylate)
183 Controlled Compositions by ATRP
One of the driving forces for the development of a controlledldquo livingrdquo radical polymerization
is to allow for the copolymerization of two or more monomers128 This has been demonstrated
with ATRP by copolymerization of various combinations of styrene methyl or butyl acrylate
methyl or butyl methacrylate and acrylonitrile ATRP allows for the copolymerization of
these monomers using all feed compositions without loss of control of the polymerization 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
46
this is in contrast to the use of 2266-tetramethylpiperidine-1-oxyl radical (TEMPO) which
must contain a significant amount of styrene as comonomer to retain control of the
polymerization This restriction does not apply to polymerizations mediated by new
nitroxides119 The statistical copolymers prepared by living polymerizations are not the same
as those prepared by conventional radical polymerizations due to the differences in
polymerization mechanism
During a copolymerization one monomer is generally consumed faster than the other
resulting in a constantly changing monomer feed composition during the polymerization the
preference is dependent on the reactivity ratios of the two (or more) monomers In
conventional radical polymerization where the polymer chains are continuously initiated and
are irreversibly terminated the change in monomer feed is recorded in the individual polymer
chains whose composition will vary from chain to chain depending on when the chain was
formed ie at the beginning or near the end of the reaction However since ATRP is a
controlledldquolivingrdquo polymerization system the vast majority of polymer chains does not
irreversibly terminate but grow gradually throughout the polymerization The change in
monomer feed is recorded in the polymer chain itself and not from chain to chain The drifting
of composition along the polymer chain is expected to yield gradient copolymers with novel
properties129 Conventional free radical polymerization methods are generally not suitable for
synthesizing star shaped polymers due to the occurrence of undesirable radical coupling
reactions During a ldquocore-firstrdquo synthesis this would lead to coupling of the growing polymer
arms and ultimately result in a cross-linking of the star macromolecules
Block copolymers can be formed by addition of a second vinyl monomer to a macroinitiator
which contains halide groups that participate in the atom transfer process Most notably this
has been demonstrated by successive addition of a second monomer at the end of the
polymerization of a first monomer by ATRP In this manner AB and ABA block copolymers
have been prepared with various combinations of styrene acrylates methacrylates and
acrylonitrile It is very important to select the right order of monomer addition For example
polyacrylates can be efficiently initiated by the poly (methyl methacrylate)- BrCuBrL
system However the opposite is not true because concentration of radicals and overall
reactivity of acrylates is generally too low to efficiently initiate MMA polymerization
Halogen exchange comes to the rescue bromoterminated polyacrylate in the presence of
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775
47
CuClL is an efficient initiator for MMA polymerization due to reduced polymerization rate
of PMMA-Cl species which are predominantly formed after the exchange process130 131 132
Scheme 12
To conclude atom transfer radical polymerization is a robust method for preparing well-
defined polymers and novel materials with unique compositions and architectures Although
significant progress has been made in the past few years since the development of ATRP
continuous research on the better mechanistic understanding of ATRP and the preparation of
more efficient catalyst systems to yield more well-defined polymers and polymerize new
monomers is needed The syntheses of new materials need to be optimized and their
properties should be studied
It is anticipated that the new controlledliving techniques will help to provide many new well-
defined polymers via macromolecular engineering
130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
48
References
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422 4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348 10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp
(1985) 461
Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823 22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991) 25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996)
(b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993)
(c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice
(d) Mishra M K Ed Polymer Frontiers New York (1994) 391
49
31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159 32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer
Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N
Macromolecules 26 (1993) 7134 42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144 45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon
Press 3(1989) 787 49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154 55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387 57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991) 59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M
J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003)
6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778
50
63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998)
823-830 66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996)
7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R
Macromolecules 32 (1999) 1152-1158 74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998)
696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507 80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication 85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster
PA (1997) 86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995) 87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993) 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151 90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953) 94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
51
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259 98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265 103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772 108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65 114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16 116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002) 125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035 127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
52
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775 130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
53
CHAPTER II Synthesis and Characterization of
Macromonomers
21 Introduction
Cationic ring opening polymerization of DXL proposed by Franta and Reibel133 results in
linear polymeric chains thereby preventing formation cyclic oligomers through cationic
polymerization of cyclic acetals15 17In fact the reaction of DXL in the presence of an
unsaturated alcohol (2-HPMA) results in a functionalized linear PDXL macromonomer
carrying at one or both ends an unsaturated system supported by the methacryloyl group of
the alcohol The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism44 Franta et al have established that when DXL is polymerized by strong protonic
acids such as triflic acid in the presence of a diol the PDXL chains are essentially linear and
carry end-standing OH functions It has been shown that the amount of cyclic species formed
is negligible that the dispersity is on the order of 14 and that the molecular weight of the
linear polymers is governed by the ratio of reacted monomer to transfer agent and is generally
well controlled up to 10 000 gmol
De Clercq and Goethals have reported the preparation of poly (13dioxolane)
bismacromonomers by copolymerization with MMA and provided the possibility to prepare
polymer networks containing PDXL segments134 135 PDXL based hydrogels have been
obtained in most cases by free radical copolymerization with comonomers such as acrylic
acid acrylamide and N-isopropylacrylamide134 136 137 styrene and butyl acrylate138
Hydrogels have received increasing attention for biomedical applications such as drug
delivery immobilization of enzymes dewatering of protein solutions and contact lenses139
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002) 1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080
54
140 These materials and are widely used in areas like baby diapers solute separation soil for
agriculture and horticulture absorbent pads etc139 Hydrogels are defined as hydrophilic
polymer networks which have a high capacity to adsorb a substantial amount of water which
have been proposed as protein releasing matrices The high water content ensures a good
compatibility with entrapped proteins as well as with surrounding tissue141 Even though a
number of applications are currently being pursued using hydrogel very little is known about
the mechanical behavior that describes the various physical processes in hydrogels142 Over
the last decade most interests have been emphasized on the synthesis of polymers containing
polyacetal segments because of the ease of degradation of these polymers under mild
conditions by treatment with a trace of acid134 143 Poly (1 3 dioxolane) is a hydrophilic non-
ionic polymer which like poly (ethylene oxide) is appreciably soluble in water but much
more sensitive to acidic degradation because of the presence of acetal groups in the chains144
In this chapter we report the synthesis of the functionalized poly (13dioxolane)
macromonomers which have been used for the preparation of PDXL hydrogel and
amphiphilic graft copolymers In the second part of this chapter we have focused on a
detailed study of the properties of the resulting hydrogel in terms of swelling behavior in
different organic solvents and viscoelastic properties determined by rheological measurements
in both the steady shear and oscillatory experiments
22 Experimental
221 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922
55
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
bull Dichloromethane (CH2Cl2 MW 8493 bp 40degC d 1325)
Dichloromethane (Prolabo 999) was dried by stirring over CaH2 for 24 h and then
distilled under a N2 atmosphere to remove impurities Purified dichloromethane was
stored under nitrogen over molecular sieve
bull 2-hydroxypropyl methacrylate (2-HPMA) (MW 14417 bp 240degC d 1028)
2-HPMA of commercial grade was purchased from Acros stabilized with 200 ppm
hydroquinone monomethyl ether Then it was stored over molecular sieve
bull n-Hexane 99 (C6H14 MW 8618 bp 68-70degC d 0658-0662) Stored under
nitrogen over molecular sieve
bull Trifluoromethanesulfonic acid (triflic acid Aldrich) was used as received
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile (AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull 1 3 dioxolane (DXL) (MW 7408 bp 78degC d 106)
The monomer DXL of commercial grade was purchased from Acros DXL was kept
under KOH for two and up to three days to remove any peroxide and stabilizer traces
and then purified by distillation over CaH2 under a N2 atmosphere prior to
polymerization
All chemicals were kept over molecular sieve before use
222 Reaction apparatus
All polymerization experiments were performed with a clean 250 ml three neck round bottom
flask A condenser was used on one of the necks of the flask in order to condense any
monomers that might otherwise possibly escape A magnetic bar was used to stir the solution
at a constant speed in order to assure even distribution of monomer and initiator
concentrations throughout the entire volume of solution A rubber septum was used to cover
one of the three necks
In the case of free radical polymerization reactions a thermocouple was also fitted to the
reaction vessel to monitor the temperature of the reaction The thermocouple regulated the
56
temperature at a constant 70degC throughout the reaction
223 Synthesis of Poly (13-dioxolane) Macromonomers
Methacrylate-terminated PDXL macromonomers were synthesized by Cationic ring-opening
polymerization which was carried out in 10 ml dichloromethane with triflic acid as initiator at
room temperature under nitrogen for 24 h in the presence of 2-hydroxypropyl methacrylate
(2-HPMA) as transfer agent 20 ml of DXL monomer was added The feed molar ratios
[DXL] [2-HPMA] are reported in Table1 as well as the molecular characteristics of the
obtained macromonomers The amount of the acid used was 20 μl After reaction the
resulting solution is poured into THF Then the product is purified by re-precipitation from
THF solution with a large excess of hexane and the obtained polymer was dried under
vacuum at room temperature The yield was checked by gravimetric determination and found
to be about 80
224 Synthesis of Poly (13-dioxolane) Hydrogel Network
The functionalized PDXL macromonomer taken for the preparation of PDXL netwok was
(FPP2) macromonomer with a theoretical average molecular weight of Mnth =2000
The macromonomer (1g) was polymerized by free radical polymerization in 10 ml of THF
using 2 2-azobisisobutyronitrile (AIBN) (001g) as initiator under a nitrogen atmosphere
The polymerization was carried out at 70degC for 24h A piece of hydrogel was obtained The
product was extracted with ethanol to remove unreacted macromonomers and then dried
under vacuum
23 Characterization Techniques
231 Raman Spectroscopy
Raman spectroscopy is used to study and analyse the structure of the macromonomers
The experiments were performed on a Dilor XY 800 spectrophotometer The detector was a
charge-coupled device (CCD) An argon laser pump beam (power density of 100 mW) has
been focused onto the sample through a microscope The working wavelength was chosen as
λ = 5145 nm In our experiments we explored the spectral range between 200 and 3700 cm-1
with a spectral resolution of 2 cm-1
57
232 1H-NMR Spectroscopy
Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) was used for structural analysis
and molecular weight of polymers and macromonomers Proton NMR spectra were obtained
using a high field 400Mhz Advance Bruker spectrometer
All of the 1H NMR samples were dissolved in deuterated chloroformThe chloroform
reference peak at 724 ppm was to ensure accuracy of peak assignments The integrals of the
peaks were used for the calculations to determine the Mw of the macromonomers
233 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) represents a chromatographic method widely used in
the analysis of polymer average molecular weights and molecular weight distributions SEC
Measurements were performed at 40degC on a Waters 2690 instrument equipped with UV
detector (Waters 996 PDA) coupled with a Differential Refractometer (ERC - 7515 A) and
four Styragel columns (106 105 500 and 50degA) THF is employed as eluent with a flow rate
of 10 mlmin Polystyrene standard samples were used for calibration
234 Swelling Measurements
In order to investigate the swelling behavior the measurement of the swelling ratio of the
polymer network is obtained from a gravimetric method in which small pieces of hydrogel
were immersed solvents such as CH2Cl2 and THF for 24 hours at room temperature (23degC)
until swelling equilibrium was reached ie when the gel thickness became essentially
constant The samples were removed from the solvents and carefully weighed (Ws) Then the
samples let to deswell and weighed every 5 min during in order to determine the swelling
kinetics in the solvents The swelling equilibrium was reached after 5 hours Afterwards the
gel was left to dry for 24 hours at room temperature until constant weight was attained and the
dry weight (Wd) was determined and the swelling ratio was calculated from equation
SR = ( ) 100timesminusWd
WdWs (57)
Where SR is equilibrium swelling ratio Ws and Wd are the sample weights in swollen and dry
states respectively
58
235 Rheological Measurements
Steady shear and oscillatory measurements have been performed on a stress imposed
rheometer Rheo-Stress-100 (RS100) from Haake used with a coneplate geometry (20 mm
diameter an angle of 4deg gap 2 mm)The imposed stress of 100 Pa during 30 seconds and a
frequency of 1Hz were applied while the strain was monitored The measurements have been
performed on swollen and unswollen samples The elastic (G) and the loss (G) moduli are
measured in linear viscoelastic region In the oscillatory experiments the frequency
dependence of both Grsquo and G is obtained at a constant strain All rheological measurements
were carried out at room temperature (23 degC)
24 Results and Discussion
241 Structural Characterization of Macromonomers
1 3 dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer end ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The synthesis of α ω-dihydroxy-PDXL chains is based on the
activated monomer mechanism44 Franta et al have established that when DXL is polymerized
by strong protonic acids such as triflic acid in the presence of a diol the PDXL chains are
essentially linear and carry end-standing OH functions It has been shown that the amount of
cyclic species formed is negligible that the dispersity is on the order of 14 and that the
molecular weight of the linear polymers is governed by the ratio of reacted monomer to
transfer agent and is generally well controlled up to 10 000 gmol
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel44 133 using an unsaturated alcohol (2-
59
HPMA) as a transfer agent results in linear polymeric chains thereby preventing formation of
cyclic oligomers through cationic polymerisation of cyclic acetals15 17 They were all prepared
at the same reaction conditions The synthetic route of functionalized PDXL macromonomers
is shown in scheme13
Scheme 13 Structures of PDXL macromonomer species54
According to this mechanism it is possible to prepare macromonomers ie PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of the
transacetalization reactions a mixture of products is obtained
A is the most abundant compound it corresponds to 50 to 60 weight wise54 It is a
macromonomer
B corresponds to 20 to 25 weight wise It is a bis-macromonomer It carries two
methacryloyl functions corresponding to transacetalization of R-OH and DXL
C corresponds to 20 to 25 weight wise It carries no methacryloyl function but two
hydroxyl groups It is a α ω-dihydroxy-PDXL
These 3 species A B and C stem from scrambling reactions that are typical with cyclic
acetals54
The characterization of these materials is based on structure and molecular weight
determination For instance the PDXL macromonomers carried at one of their ends a double
bond afforded by the methacryloyl group The latter was checked by Raman and 1H-NMR
spectroscopy All macromonomers prepared displayed functionality close to unity which
makes them suitable for the synthesis of graft copolymers
60
Raman spectroscopy is used to study and analyse the structure of the macromonomers The
aim of this study is to check the formation of linear polymer chains as well as the termination
with methacryloyl groups The spectra obtained exhibit two intense Raman bands at 800 to
900 cmP
-1 and 2700 to 3000 cmP
-1 regions and a series of small other peaks for all samples as
shown in figure 1 The most intense band (2700 ndash 3000 cmP
-1) is assigned to the aliphatic
stretching vibration of CH in the polyacetal chain Symmetric COCOC stretching frequencies
of aliphatic acetals fall in typical regions of 1115-1080cmP
-1 and 870-800 cmP
-1 145 and are
responsible for intense Raman bands In the low frequency region there are three very
characteristic Raman bands in the 600 ndash 550 cmP
-1 540 ndash 450 cmP
-1 and 400 ndash 320 cmP
-1 ranges
which are assigned to COCOC deformations145 146 Also the acetals have strong multiple
bands in the region of 1160ndash1040 cmP
-1 as noticed on the Raman spectra involving the C-O
stretching modes In addition to this the O-CH-O group gives rise to a band at 1350 ndash1325
cmP
-1 for C-H deformation Other intense Raman bands are observed in the region of 3000 ndash
2700 cmP
-1 Below 3000 cmP
-1 the corresponding frequencies are assigned to the aliphatic C-H
stretching modes145 The methoxy group is detected in the region of 2835 ndash 2780 cmP
-1
Figure 1 Raman spectra of methacrylic-terminated PDXL macromonomers (FPP2 FPP15 and
FPP1)
145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The Handbook of IR
and Raman Characteristic Frequencies of Organic Molecules United Kingdom Ed by Academic Press Limited London (1991)
146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman Spectroscopy 3rd Edition AP Limited London (1964)
61
As far as the presence of the methacryloyl group in the polymeric chain is important bands
have been observed at 1640 cmP
-1 which corresponds to C=C bonds The carbonyl compounds
absorb strongly within 1900 ndash1550 cmP
-1 region145 146 the spectra show a C=O bond absorption
found at 1720 cmP
-1 In the region of 1340 ndash1250 cmP
-1 the methacrylate bands are observed
Broad absorption is found near 3500 cm -1 owing to stretching of the OH bonds OH
deformation bands are found at 1400 cmP
-1P and 1340 cmP
-1 This observation indicates that both
methacrylic and ndashOH groups are present and eventually the resulting product is a mixture of
the three species as shown in the scheme above
Typical 1H-NMR spectrum of PDXL macromonomer shown in figure 2 exhibits the expected
resonance assigned to the methoxy protons (477 ppm) and OCH2CH2O protons at (374
ppm) Two signals corresponding to =CH2 were observed at (612 ndash 614 ppm) and (557 ndash
559 ppm) Therefore the spectrum confirmed the chemical structure HO[CH2CH2OCH2O]nR
of methacryloyl- terminated PDXL macromonomer
Figure 2 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP2)
242 Molecular Weight Determination
Besides the structure 1H-NMR enables us to determine the number-average molecular weight
(Mn) In the calculation of the latter the methacryloyl end group was included The
62
polydispersity and index MwMn and the number-average molecular weight were obtained
from SEC measurements Table 1 summarizes these values It can be seen that Mn (SEC) and
Mn (NMR) are very close to each other for all macromonomer samples and are in agreement
with the theoretical values predicted from calculations Under our polymerization conditions
the polydispersity index is 16 for all samples
Table 1 Characteristics of PDXL macromonomers prepared at different degrees of
polymerization
Sample Dp Mnth MnSEC MnRMN MwMn f (a)
FPP1 135 1000 1120 1160 16 097
FPP15 2025 1500 1540 1550 16 099
FPP2 270 2000 2040 2100 16 097
Dp degree of polymerization = [DXL] [2HPMA]
a functionality of macromonomers (methacryloyl end groups molecule)
243 Swelling of Poly (13 Dioxolane) Hydrogel
The synthesized PDXL hydrogel has been studied in terms of swelling and rheological
behaviors The degree of swelling and the rate of swelling of the hydrogel are studied It is
known that hydrogel can swell in several solvents but at different degree of swell according to
many factors related to the nature of the solvents and the type of polymer-solvent interactions
It was found that the solubility parameter of the solvents (δ) had a great effect on swelling
degree For instance hydrogels can swell fast in CH2Cl2 (δ = 976 cal cm12 -32) and reached
equilibrium within no more than an hour However it will take about more than 20 h to reach
equilibrium in CH3 OH (δ = 145 cal cm12 -32) It was known that the polymer can reach
greatest swelling degree when the solubility parameter of the polymer is close to that of the
solvents The solubility parameter of PDXL is about 93 cal cm 12 -32 134 The swelling has been
examined in THF and CH2Cl2 for PDXL hydrogel It has been observed that the swelling
equilibrium is reached after almost 5 hours of swelling for all samples in both solvents The
results show that THF (δ = 952 cal cm12 -32)147 swells the hydrogel to the greatest degree
compared to CH2Cl2 as shown in figure 3 However CH2Cl2 molecules provide less swelling
147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983)
63
capacity than in THF On the basis of the experiment The PDXL hydrogel reached high
swelling degree due to its solubility parameter is much closer to that of THF
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
THF CH2Cl2
Swel
ling
degr
ee
Time (min)
Figure 3 Swelling kinetics of PDXL hydrogel in two different solvents CH2 Cl2 (solid
squares) and in THF (hollow squares)
244 Viscoelastic Behavior
Rheological measurements were performed on rheometer in the Cone and Plate geometry
Both steady shear and oscillatory experiments were carried out The dynamic storage and loss
moduli G and G were examined at room temperature (23 degC)
Many attempts have been carried to extend the elasticity theory to swollen gels148 149 Based
on this approach all measurements have been performed on both swollen and unswollen
hydrogel samples for the purpose of comparison so that to examine the mechanical properties
even in swollen state For instance Flory and Rehner recognized the swelling phenomenon
exhibited by cross-linked polymers when exposed to certain solvents and related the modulus
of elasticity of a swollen cross-linked polymer network to an unswollen network150 Figure 4
illustrates the strain dependence of G and G for swollen and unswollen samples
148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for Experimental
Mechanics SEM Annual Conference Proceedings (2002)
64
10-5 10-4 10-3 10-2 10-1 100 101 102101
102
103
104
Guns Guns Gs Gs
GG
(Pa
)
γ ()
Figure 4 Strain dependence of the elastic modulus Grsquo (circles) and of the viscous modulus
Grdquo(triangles) for two samples of unswollen hydrogel (solid symbols) and swollen hydrogel
(hollow symbols)
The moduli are measured as a function of strain at a constant frequency It appears that the
linear viscoelastic region is observed while the strain is increasing in either state which
indicates that the internal structure of the samples has not been disrupted when deformed
This leads to reveal that the gel is strain resistant in swollen and unswollen states and within a
large strain range the hydrogel retains its elasticity as shown in figure 4 where the linear
viscoelastic region extends to almost 02
The frequency dependence of G and G is shown in figure 5 similarly for swollen and
unswollen hydrogels The system behaves typically like a gel as it can be noticed that the
elastic component G (storage modulus) is far greater than the viscous component G (loss
modulus)151 Based on these results the hydrogel exhibits extreme elasticity at low
frequencies
151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure 554 (2000) 99-108
65
100 101
103
104
105
Gs Guns Gs GunsG
G(
Pa)
ω (rads)
Figure 5 Frequency dependence of Grsquo(circles) and Grdquo(triangles) for swollen hydrogel
(hollow symbols) and unswollen hydogel (solid symbols)
Finally figure 6 illustrates the complex viscosity profiles another parameter of
viscoelasticity which measures the magnitude of the total resistance to a dynamic shear
Again this property has not been affected by swelling since the results show similar behavior
for swollen and unswollen states It decreases sharply as frequency increases which
characterizes the samples degree of viscoelasticity at various time scales Therefore from the
results discussed above the hydrogel network is elastic and stable even in the swollen state
thereby possessing very good mechanical properties
100 101 102 103
102
103
104
105
η unswollen η swollen
ηlowast (P
a s)
ω (rads)
Figure 6 Frequency dependence of the complex viscosity η for unswollen hydrogel (solid
squares) and swollen hydrogel (hollow triangles)
66
Conclusion
The hydrogel properties were discussed in terms of swelling and viscoelastic
behaviors The hydrogel has combined special properties Its swelling behaviour in the
solvents was dependent on the solubility parameter of both solvents and hydrogel
Rheological measurements were successful when used in order to study the viscoelastic
behavior of the hydrogel of pure PDXL in swollen and unswollen states The Strain
dependence of G and G for both samples shows linear viscoelastic region and allows to
determine the yield stress Same conclusions can be given concerning the frequency
dependence of complex viscosity the swelling does not affect this property The results reveal
a perfect elastic and resistant hydrogel in other words the viscoelastic properties have not
been so much affected by swelling They may be particularly useful in the design of improved
microfluidic devices that utilise the relationship between swelling and strain This kind of
material can be potentially used in biosystems such as intelligent drug delivery systems
67
References
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-
174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002)
1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080 140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922 145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The
Handbook of IR and Raman Characteristic Frequencies of Organic Molecules United
Kingdom Ed by Academic Press Limited London (1991) 146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman
Spectroscopy 3rd Edition AP Limited London (1964) 147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983) 148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-
1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for
Experimental Mechanics SEM Annual Conference Proceedings (2002) 151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure
554 (2000) 99-108
68
CHAPTER III Synthesis and Characterization of Copolymers
31 Introduction
Amphiphilic block and graft copolymers consisting of hydrophilic and hydrophobic parts
have been subjects of numerous studies within which block and graft copolymers containing
hydrophilic polyoxyethylene segments and other hydrophobic segments have attracted much
attention because polyoxyethylene segments are not only hydrophilic but also nonanionic
and crystalline and can complex monovalent metallic cations Graft copolymers offer all
properties of block copolymers but are usually easier to synthesize Moreover the branched
structure leads to decreased melt viscosities which is an important advantage for processing
Depending on the nature of their backbone and side chains they give rise to special properties
in selective solvents at surfaces as well as in the bulk owing to microphase separation
morphologies12 They can be used for a wide variety of applications such as polymeric
surfactants electrostatic charge reducers compatibilizers in polymer blends polymeric
emulsifiers controlled wet ability and so on152 153 In order to prepare graft copolymers with
well-defined structure one can utilize the macromonomer technique (grafting through
technique) Well-defined structure graft copolymers are synthesized by copolymerization of
macromonomers with low molecular weight comonomers6 It allows the control of the
polymer structure which is given by three parameters (i) chain length of side chains which
can be controlled by the synthesis of the macromonomer by living polymerization (ii) chain
length of backbone which can be controlled in a living copolymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular weight monomer However the distribution of spacings
may not be very easy to control due to the incompatibility of the polymer backbone and the
macromonomers154 As pointed out in recent publication reviews155 there is a complex
interplay of factors that govern the reactivities in copolymerizations involving
macromonomers When different comonomers are copolymerized with the same it seems that
the degree of interpenetration between the macromonomer and the propagating copolymer 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305
69
backbone plays the major role in the measured reactivities Nevertheless the main properties
depend on both the average composition of the systems and the microstructural distribution of
the comonomer sequences along the macromolecular backbone which is determined by the
reactivity ratios of the macromonomer and the corresponding comonomer in the free radical
polymerization process156 157
In this chapter our work deals with the preparation and characterization of new organo-
soluble associative copolymers based on short hydro-soluble chains of poly (1 3 dioxolane)
(PDXL) Many reports have been published on PDXL macromonomers used to form
hydrogels136 137 158 159 160 161 162 however very few were on graft copolymers with PDXL
branches162 These macromonomers are used for the preparation of amphiphilic graft
copolymers by solution free radical copolymerization with a hydrophobic comonomer
styrene (St) and methyl methacrylate (MMA) Structural characterization of these
copolymers molecular weight determination reactivity ratios and the polymerizability of the
PDXL macromonomer have been discussed Finally their thermal properties are discussed
according to the weight content of PDXL in the copolymers
32 Experimental
321 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269
70
bull Ethanol (C2H6O MW 4607 bp 78degC d 081)
Ethanol (Prolabo 95-96) was purified by distillation with 5g of Magnesium and 05g of
iodine for 75ml of alcohol under a N2 atmosphere After discoloration of the mixture
solution a volume of Ethanol was added and then distilled normallyThen it was stored
over molecular sieve
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile(AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull Styrene (C6H5CH=CH2 MW 10416 bp 145degC d 091)
Styrene (Prolabo product) was purified by distillation over CaHB2 at reduced pressure
bull Methyl Methacrylate (MMA)(H2C=C(CH3)CO2CH3 MW 10012 bp 100degC d
0936)
Methyl Methacrylate (Prolabo product) was purified by distillation over CaHB2 at reduced
pressure
All chemicals were kept over molecular sieve before use
322 Synthesis of Poly (Styrene-co-Poly (13-dioxolane))
a) Conventional Free Radical Copolymerization
The reaction route for the conventional copolymerization of Styrene and PDXL
macromonomers using AIBN as the free radical initiator at 60degC is shown in scheme 14
71
Scheme 14
PDXL macromonomers of different molecular weights were copolymerized with St in THF at
60degC in the presence of 2 2rsquo-azobisisobutyronitrile AIBN (1 based on the total weight of
the monomers) as initiator under a nitrogen atmosphere using different feed molar fractions
of macromonomers The total monomer concentration for was 6 10-1 M in all cases The
copolymerization product is diluted with THF and then added dropwise to a large excess of
ethanol to remove unreacted PDXL macromonomers25 43 and precipitate the copolymers
Then they were finally dried over vacuum at 40degC to constant weight The yields of all
reactions are 70ndash 90 Table 2 indicates the amounts of comonomers initiator and solvent
employed in the copolymerization study
72
Table 2 Copolymerization of PDXL macromonomers (M1) with Styrene (M2)
Sample M1 M2M1 PDXL (g) (mol)
Styrene (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2SP2 FPP2 20 349 174510-4 364 349 10-2 007 60 0610 3SP2 FPP2 30 232 116 10-4 364 349 10-2 006 60 0601 5SP2 FPP2 50 14 69810-4 364 349 10-2 005 60 0593
2SP15 FPP15 20 262 174510-4 364 349 10-2 006 60 0610 3SP15 FPP15 30 174 116 10-4 364 349 10-2 006 60 0601 5SP15 FPP15 50 105 69810-4 364 349 10-2 005 60 0593
2SP1 FPP1 20 174 174510-4 364 349 10-2 006 60 0610 5SP1 FPP1 50 07 69810-4 364 349 10-2 005 60 0593 8SP1 FPP1 80 0436 43610-4 364 349 10-2 005 60 0589
b) Controlled Free Radical Copolymerization
The comb-structure copolymer of styrene and PDXL was obtained by grafting-from
mechanism through Nitroxide-Mediated Polymerization
Nitroxide mediated polymerization (NMP) is a controlled radical polymerization (CRP)
technique which already offers the ability to prepare a wide variety of well-defined polymer
architectures119 Despite the significant improvements brought to CRP techniques such as
NMP atom transfer radical polymerization (ATRP) or reversible addition fragmentation chain
transfer (RAFT) the preparation of complex architectures by CRP is restricted by the
exclusion of monomer systems that are polymerized by fundamentally different mechanisms
like lactides ethylenepropylene oxide The most promising approaches to extend the range of
polymer compositions are based on the use of heterofunctional initiators163 allowing the
combination of mechanistically distinct polymerization reactions without the need for
intermediate transformation and protection steps
In the field of NMP the development of multifunctional initiators was focused on TEMPO
and TIPNO which are examples of nitroxides (Scheme 15) It is worth to mention that in
NMP these are used as counter-radicals associated with a conventional azoic initiator so this
pair of initiators is known as a bimolecular system
163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671
73
Scheme 15 TEMPO and based alkoxyamines
Another initiator used for NMP is the commercially available alkoxyamine also called
MAMA-SG1164 (Scheme 16) known as a monomolecular system initiator which is
particularly convenient for functionalization of polymer chain ends164 165 MAMA-SG1 has
been developed by Didier Gigmes and co in collaboration with Arkema Company166 Thanks
to a particularly high dissociation rate constant value kd1 up to now this alkoxyamine has
proved to be one of the most potent alkoxyamines reported in the field of NMP167 168 This
initiator is used for polymerization of styrene and n-butyle acrylate allowing formation of
well-defined linear and star structures
Scheme 16
164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006) 5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219
74
Scheme 17 MAMA-SG1 structure and dissociation scheme
bull Multifunctionalization of Polystyrene (HO-PS)
MAMA-SG1 was used to run copolymerization of styrene at 90 mol with HEMA in order
to obtain functionalized polystyrene The monomers and alkoxyamine were introduced in a
250 mL two neck round-bottom flasks fitted with septum condenser and degassed for 15
min by nitrogen bubbling The reaction was performed in bulk at 120 degC under N2 with
vigorous stirring Targeted molecular weight and polydispersity were 30 000 g mol and 12
respectively
After polymerization the final polymer mixture was dissolved in a minimum THF and
precipitated in cold ethanol followed by drying under vacuum at 30degC
bull Synthesis of PS-g-PDXL
PDXL was copolymerized by cationic ring-opening polymerization which was carried out in
40 ml dichloromethane with triflic acid as initiator at room temperature under nitrogen for 24
h in the presence of OH-multifunctionalized PS (1g 3 10-5 mol) as transfer agent 20 ml
(0286 mole) of DXL monomer was added Table 6 gives the molecular characteristics of the
obtained copolymer The amount of the acid used was 20 μl After reaction the resulting
solution is poured into THF Then the product is purified by re-precipitation from THF
solution with a large excess of hexane and the obtained polymer was dried under vacuum at
room temperature The yield was checked by gravimetric determination and found to be about
75 The polymerization route is presented in the scheme below
75
Scheme 18
323 Synthesis of Poly (Methyl Methacrylate-co-Poly (13-dioxolane))
Same procedure has been used for the synthesis of Poly (Methyl Methacrylate-co-Poly (1 3-
dioxolane)) copolymers The yields of the reactions are in the range of 70ndash 90
Table 3 shows the amounts of comonomers initiator and solvent employed in the
copolymerization reactions
Table 3 Copolymerization of PDXL macromonomers (M1) with MMA (M2)
Sample M1 M2M1 PDXL (g) (mol)
MMA (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2MP2 FPP2 20 374 187 10-4 3744 374 10-2 008 65 0604 3MP2 FPP2 30 2 10 10-4 300 300 10-2 005 50 0620 5MP2 FPP2 50 15 748 10-4 3744 374 10-2 005 60 0636
2MP15 FPP15 20 2 133 10-4 28 280 10-2 005 25 100 3MP15 FPP15 30 187 125 10-4 3744 374 0-2
006 60 0644 5MP15 FPP15 50 112 748 10-4 3744 374 10-2 005 60 0636
2MP1 FPP1 20 2 20 10-4 400 4 10-2
006 50 0840 3MP1 FPP1 50 125 125 10-4 3744 374 10-2 005 64 0604 5MP1 FPP1 80 075 748 10-4 3744 374 10-2 005 60 0636
33 Characterization Techniques
331 1H-NMR Spectroscopy
1H NMR Spectroscopy was used for compositional and structural analysis of the copolymers
1H-NMR spectra of the copolymers were recorded on the high field 400Mhz Advance Bruker
spectrometer All of the 1H NMR samples were dissolved in deuterated chloroform The
integrals of the peaks of copolymer components were used for the calculations to determine
76
the molecular weights polydispersity indices and the amount of each comonomer that was
incorporated into the copolymer
332 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) was used in the charaterization of the copolymers to
determine average molecular weights and polydispersity indices SEC Measurements were
performed at 40degC on a Waters 2690 instrument equipped with UV detector (Waters 996
PDA) coupled with a Differential Refractometer (ERC - 7515 A) and four Styragel columns
(106 105 500 and 50degA) THF is employed as the mobile phase with a flow rate of 10
mlmin Polystyrene standard samples were used for calibration
333 Diffraction Scanning Calorimetry
Diffraction Scanning Calorimetry (DSC) measurements are performed on a Modulated
Temperature Differential Scanning Calorimeter Q100 TA instrument under nitrogen at 50
mlmin The samples are hermetically sealed in aluminium pans and they are subjected to a
heating program as follows
For Poly (Styrene-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 120degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -80degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to130degC
For Poly (Methyl Methacrylate-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 130degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -95degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to150degC
The thermograms obtained illustrate Glass Transition Temperatures (Tg) and Meltind Points
(Tm) of the copolymers
77
34 Results and Discussion
Methacryloyl-terminated PDXL macromonomers with the Mn range of 1000-2000 gmole
were copolymerized with vinyl and methacrylic monomers in order to obtain amphiphilic
graft copolymers with chemical structure of hydrophobic backbone and hydrophilic side
chains
341 Structural Characterization of the Copolymers
The structure of the copolymers was well defined by 1H-NMR analysis The copolymer 1H-
NMR spectra confirm the formation of copolymers see figures 7 8 and 9 The chemical
shifts of protons of polystyrene and PDXL can be clearly distinguished The following peaks
are assigned for OCHBB2BBO protons at 478 ppm and OCHBB2BBCHBB2BBO protons at 375 ppm (5H CBB6BB
HBB5BB) at 728 711 and 706 ppm as shown in Figure 8 The spectrum of PMMA-PDXL
copolymer is shown in Figure 9 where the chemical shifts of PMMA correspond to the proton
resonance as depicted in the figure the O-CH3 protons are observed at 361 ppm and clear
resonance assigned to the methyl group protons at 085-103 ppm and eventually we observe
the corresponding chemical shifts for OCHBB2BBCHBB2BBO protons (374 ppm) and OCHBB2BBO protons
(477 ppm) to confirm the incorporation of PDXL in the copolymer
Figure 7 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP1)
78
Figure 8 1H-NMR spectrum of Styrene-g-PDXL copolymer in CDCl3 (sample 3SP2)
79
Figure 9 1H-NMR spectrum of MMA-g-PDXL copolymer in CDCl3 (sample 2MP2)
342 Copolymer Molecular Weight and Composition
a) Conventional Free Radical Copolymerization
Copolymerization of PDXL macromonomers with MMA and ST in THF solution was studied
for different molar feed ratio of PDXL The amounts of monomeric units in the copolymers
were determined by elemental analysis The results are presented in Table 4 and 5 which
summarise the characteristics of the graft copolymers in terms of macromonomer feed ratio
(M2M1) and average Mn obtained from SEC as well as copolymer composition in weight and
mole percentages which is determined from 1H-NMR
80
Table 4 Characteristics of PDXL macromonomers (M1) copolymerized with Styrene (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2SP2 FPP2 20 49 476 4025 337 9200 162 2 3SP2 FPP2 30 39 322 303 221 8900 162 2 5SP2 FPP2 50 277 196 21 13 7200 159 1
2SP15 FPP15 20 418 476 34 34 9100 157 2 3SP15 FPP15 30 323 322 24 214 7000 161 2 5SP15 FPP15 50 224 196 152 12 6700 147 1
2SP1 FPP1 20 323 476 30 427 9200 178 3 5SP1 FPP1 50 16 196 1424 17 5800 158 1 8SP1 FPP1 80 107 123 85 095 11900 195 1
Table 5 Characteristics of PDXL macromonomers (M1) copolymerized with MMA (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2MP2 FPP2 20 50 476 35 26 21900 198 4 3MP2 FPP2 30 40 322 21 13 25900 157 3 5MP2 FPP2 50 286 196 13 07 87200 455 6 2MP15 FPP15 20 416 45 28 25 19800 193 4 3MP15 FPP15 30 333 322 22 18 15200 277 3 5MP15 FPP15 50 23 196 13 10 24700 16 2 2MP1 FPP1 20 333 476 26 34 21100 319 6 3MP1 FPP1 30 333 322 19 22 17100 197 3 5MP1 FPP1 50 20 196 10 11 13900 354 2
81
b) Controlled Free Radical Copolymerization
Multifunctionalization of Polystyrene and Synthesis of poly (S-g-PDXL) copolymer give
results which are shown in Table 6 These data have been obtained from the 1H-NMR and
SEC analyses illustrated in figures 10 and 11 The resonance shifts assigned to all components
(PDXL PS and HEMA) are very clear This enables us to make calculations to determine
composition of each copolymer in addition to obtain the average number of grafts and the
number average-molecular weight of a graft
It is observed that the multifunctionalized-PS is composed of 20 in mole of HEMA which
results in 58 grafts (Ng = 58) per molecular chain
After copolymerization multifunctionalized-PS with DXL the copolymer PS-g-PDXL
(DXPS) possesses the following characteristics which are presented in Table 6 It has a
number average-molecular weight of 83000 gmol with 80 of PDXL content The number
average-molecular weight of one graft has been calculated and found to be 1000 gmol
Table 6 Characteristics of functionalized Styrene (HO-PS) and PS-g-PDXL (DXPS)
copolymer
Strusture Sample MnSEC IP PDXL
w mol
PS
w mol
HEMA
w mol
Ng Graft
Mn
HO-PS
32 700
12
_ _
77 80
23 20
58
_
DXPS
83 000
24
71 80
17 13
12 75
58
1000
82
Figure 10 1H-NMR spectrum of Multifunctionalized of Polystyrene in CDCl3
Figure 11 1H-NMR spectrum of poly (S-g-PDXL) copolymer (DXPS) in CDCl3
83
341 Determination of Monomer Reactivity Ratios
The application of the classical treatment based on linearization of the copolymerization
equation of Mayo and Lewis91 or the non-linear least-squares approach suggested by Tidwell
and Mortimer95 requires working with high macromonomer concentrations (ie feed
compositions higher than 20-30 of macromonomer)156
The MayondashLewis equation (58) that relates the instantaneous compositions of the monomer
mixture to the copolymer composition is approximated to a simplified form (equation (59))
suggested by Jaacks169 when working with a large excess of one of the comonomers This is
the case of copolymerisation reactions between a conventional comonomer and a
macromonomer of relatively high molecular weight where using low molar concentrations of
macromonomer is mandatory due to its restricted solubility and the extremely viscous media
][ ][ ]
[ ][ ]
[ ] [[ ] [ ]221
211
2
1
2
1
MrMMMr
MM
MdMd
++
=
(58)
[ ][ ] 1
22
1
2
MMr
MdMd
=
(59)
According to equation (59) the copolymer composition or the frequency of branches is
essentially determined by the monomer composition and the monomer reactivity ratio of the
comonomer r2 (inversely proportional to the macromonomer reactivity) under the limit
condition of [M2][M1] gtgt1 In order to obtain reliable values it is frequently necessary to
run the copolymerisation at different conversions or to carry out several copolymerizations
with different initial monomer ratios170 In such cases an integrated form of equation (59) is
used
[ ] [ ][ ][ ] 01
12
02
2 lnlnMM
rMM tt =
(60)
169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046
84
where [Mi]t[Mi]0 is the ratio among the composition of monomer i at time t and the initial
feed composition A plot of ln ([M2]t[M2]0) versus ln ([M1]t[M1]0) should result in a straight
line with a slope that equals to r2 (the reactivity ratio of the comonomer)
Thus the monomer reactivity ratios between the PDXL macromonomers and the comonomers
were estimated with the data in tables 4 and 5 We can apply equation (60) to the estimation
where M1 and M2 are the PDXL macromonomer and copolymer respectively The monomer
reactivity ratios are determined for macromonomers of different Mn (degree of
polymerization) and summarized in Table 7
Table 7 Monomer reactivity ratios for copolymerization of PDXL macromonomers (M1)
with St and MMA (M2)
Sample M2 M1
macromer Mnth
r2 1r2
SP2 St FPP2 2000 012 plusmn 0006 833
SP15 St FPP15 1500 0042 plusmn 6 10-4 238
SP1 St FPP1 1000 0015 plusmn 3 10-4 6666
MP2 MMA FPP2 2000 002 plusmn 001 50
MP15 MMA FPP15 1500 007 plusmn 0 02 1428
MP1 MMA FPP1 1000 0018 plusmn 001 5555
In the case of copolymerization with Styrene and MMA the results suggest that the reactivity
of the methacrylic double bond in the prepared macromonomers is not affected in their
copolymerization with Styrene or MMA This point is confirmed when analysing the inverse
ratio 1r2 = k21k22 which is sometimes considered as the relative copolymerization reactivity
of a macromonomer171 This quantity is the ratio between the crosspropagation and
homopropagation rate constants of comonomer (2) which is directly proportional to the
reactivity of the macromonomer (1) and gives a clear idea of the relative reactivity of a
growing radical ending in a 2 unit towards the addition of monomer (1) in comparison to the
171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620
85
tendency for the homopropagation So we have a situation where r1 gtgt 1 gtgt r2 and it is
expected that the initially formed chains should contain more macromonomers and then more
comonomer segments are added These are only assumptions but they give an indication
about the probable composition drift of the graft copolymers obtained On the other hand in
the case of copolymerization of poly (13dioxolane) macromonomers with styrene (Figure
12) the results show that r2 increases with increasing PDXL side chain length (in terms of
average Mn) and this leads to say that the side macromonomer chain length affect the
reactivity of the comonomer Thus this indicates that a growing radical of macromonomer
with a shorter chain length (ie lower Mn ) attacks more frequently a monomer of the same
nature than it does a macromonomer with a longer length (ie higher Mn) as it can be noticed
from the results in Table 7
However the r2 values of the copolymerization with MMA as shown in Figure 13 give
unclear dependence on the side poly (13dioxolane) macromonomer chain length this may be
due to the resulting polydispersity of the copolymerization Mentioned behaviour may be
related with the reactive structure of comonomers vinyl in the case of Styrene or methacrylic
in the case of MMA in regard to the ending methacrylic double bond of macromonomers
besides the hydrophilic character of the macromonomers
86
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0015 plusmn 3 10-4 SP1
b
r2 = 0042 plusmn 6 10-4
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP15
c
r2= 012 plusmn 0006
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP2
Figure 12 Application of Jaacksrsquo treatment to the St-g-PDXL copolymerization systems
(a) SP1 (b) SP15 (c) SP2
87
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0018 plusmn 001 MP1
b
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 007 plusmn 002MP15
036788
c
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 002 plusmn 001 MP2
Figure 13 Application of Jaacksrsquo treatment to the MMA-PDXL copolymerization systems
(a) MP1 (b) MP15 (c) MP2
88
341 Glass Transition Temperatures
Thermal analysis of Styrene-g-PDXL copolymers allows to determine their glass transition
and melting temperatures In the first place the measurements were performed on a
conventional DSC from which the thermograms obtained show an overlapping of PS glass
temperature and PDXL melting point signals This has been observed for all samples A
different approach in the characterisation of these copolymers was by means of Modulated
Temperature Differential Scanning Calorimeter (MTDSC) which is an extension of
conventional DSC This approach combines high resolution with high sensitivity by use of a
sinusoidal temperature modulation superimposed on a constant temperature or linear
temperature program with a small underlying average heating rate172 173 In comparison to
conventional DSC the MTDSC analysis enables the simultaneous calculations of an
additional quantity the cyclic or modulus of heat capacity Cp (J g-1K-1 172)
ωT
HFp A
AC =
(61)
is the amplitude of the cyclic heat flow (Wg-1) and AWhere AHF Tω is the amplitude of cyclic
heating rate with AT the temperature modulation amplitude (K) ω the modulation angular
frequency (2πp) and p is the modulation period (s)172
In fact the MTDSC splits the overlapped signals into two distinct temperatures melting
temperature of the hydrophilic grafts and glass transition temperature of the hydrophobic
backbone as can be noticed in Figure 14 in which melting temperature appears to be 5626degC
which is closer to the glass transition temperature with a value of 5671degC From the results
obtained out of the thermogram it is clear that the measurements show very close values of
Tm and Tg for all copolymer samples where in conventional DSC these two temperatures
cannot be distinguished
172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
89
Figure 14 MTDSC thermogram of 5SP1 copolymer at heating rate of 2degCmin
Tg was taken at the midpoint of the transition region The results obtained are shown in
Tables 8 and 9 for copolymers with Styrene and MMA respectively Then a plot of the
copolymers Tg has been constructed against PDXL content in order to determine the effect of
the latter on Tgrsquos As it can be noticed in the Figure 15 Tg of the copolymers decreases
exponentially with increasing PDXL content and this may be due to the decrease in the
intermolecular interactions between the molecular chains and can be associated with higher
mobility and flexibility of the polymeric chains when PDXL is incorporated in the
copolymers The results clearly indicate that Tg values of the copolymers depend on the
composition of comonomers and a decrease with increasing PDXL content in the obtained
copolymers
90
Table 8Transition temperatures of Styrene-g-PDXL copolymers obtained by thermal
analysis (DSC) Sample PDXL content Tg wt () (degC) 8SP 85 7489 1
5SP 1424 5671 1
5SP 152 5590 15
21 6739 5SP 2
303 4480 3SP 2
34 2665 2SP15
4025 2SP 4060 2
Table 9Transition temperatures of MMA-g-PDXL copolymers obtained by thermal analysis
(DSC)
Sample PDXL content Tg
wt () (degC)
5MP 10 10545 1
5MP 13 8278 15
21 6576 3MP 2
22 7550 3MP 15
26 7013 2MP1
91
5 10 15 20 25 30 35 40 4520
30
40
50
60
70
80
a
SP COPOLYMERSTg
(degC)
PDXL content in wt()
10 15 20 2560
70
80
90
100
110
b
Tg (deg
C)
PDXL content in wt()
MP COPOLYMERS
Figure 15 Glass transition temperatures vs PDXL macromonomer content for copolymer
systems (a) Styrene-g-PDXL copolymers (b) MMA-g-PDXL copolymers
92
Conclusion
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers The macromonomer reactivity estimation suggests that the
length of the PDXL side chains does affect the reactivity of the methacrylic double bond of
the macromonomer when copolymerized with St However in the case of copolymerization
with MMA there is no dependence on the graft size Finally from DSC measurements the
values of Tg depend on the composition and the size of the PDXL grafts In all copolymers
the increase in amount of the incorporated PDXL macromonomer results in a substantial
decease in glass transition
93
References 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305 156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269 163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671 164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006)
5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219 169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620 172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly
(1 3 Dioxolane)) on Immiscible Polymer Blends
of Polystyrene and Poly (Ethylene Glycol)
41 Background
411 Physical Blends
Physical blending is defined as the simple mechanical mixing of two or more polymers either
in the melt or in solution174 At first glance this approach would seem to be ideal for
preparing hybrids as blending is considered a simple and economical procedure that is
commonly used to produce new products from existing materials175 However in polymer
science the effectiveness of blending is dependent upon the degree of compatibility of the
polymers involved176 At least three general types of materials can result from blending
depending on the mutual solubility and semi-crystallinity of the constituents
412 Equilibrium Phase Behavior
Mixing of two amorphous polymers can produce either a homogeneous mixture at the
molecular level or a heterogeneous phase-separated blend Demixing of polymer chains
produces two totally separated phases and hence leads to macrophase separation in polymer
blends Some specific types of organized structures may be formed in block copolymers due
to microphase separation of block chains within one block copolymer molecule
Two terms for blends are commonly used in literature miscible blend and compatible blend
The terminology recommended by Utracki177 will be used By the miscible polymer blend it
means a blend of two or more amorphous polymers homogeneous down to the molecular
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York (1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York (1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser Publishers Munich (1989)
95
level and fulfilling the thermodynamic conditions for a miscible multicomponent system An
immiscible polymer blend is the blend that does not comply with the thermodynamic
conditions of phase stability The term compatible polymer blend indicates a commercially
attractive polymer mixture that is visibly homogeneous frequently with improved physical
properties compared with the constituent polymers
Miscible blends occur spontaneously when the overall energy of mixing (ΔGmix) is negative
as defined by the Gibbs-Helmholtz free energy equation (Equation 62)
(62)
In the Gibbs-Helmholtz equation ΔHmix is the enthalpy of mixing and ΔSmix is the entropy of
mixing while T is the temperature of the blend Flory-Huggins178 and Scott179 have made
further correlation of enthalpy and entropy as a function of the polymer components and their
properties (Equation 63)
(63)
In Equation 63 χ is a measure of the polymer-polymer interaction energy V is the volume of
the system Φi is the volume fraction of polymer i R is the gas constant T is the temperature
of blending Vr is the reference volume of the monomers and χi is the degree of
polymerization
Examination of Equation 63 reveals that the entropy of mixing is highly dependent on the
molecular weight of the blended polymers while the enthalpy is much more dependent on the
level of interaction between the polymer types Additionally Scott showed that as molecular
weight increases to the level commonly found in commercially useful materials ΔS
approached zero (0) Therefore polymer blends of commercial importance are primarily
influenced by the rate of enthalpy However for polymers with weak interactions (as χ
approaches 1) eg as observed in most polymer pairs the enthalpy of mixing can be further
reduced according to Equation 64
178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279
96
(64)
In Equation 64 δi is the polymerrsquos solubility parameter (an estimation of its ability to be
dissolved in a range of solvents) derived from the square root of the cohesive energy density
pioneered by Hildebrand180 Thus most early work with polymer blends concentrated on
matching the solubility parameters of the component polymers
Unfortunately the theoretical maximum difference in solubility for a 5050 polymer blend is
only 01 (calcm3)12 This narrow margin is much smaller than the standard error among
methods used to determine solubility parameters181 The ability to predict miscibility of
polymer pairs with strong interactions such as donor-acceptor and hydrogen bonding which
can increase miscibility by creating an exothermic reaction upon mixing (ΔH lt0) have been
attempted for many years with varying degrees of success
The formation of miscible blends is dependent on several factors including molecular
structure average chain length tacticity of the polymers as well as the temperature of mixing
and the blending method If the blended polymers are miscible (ΔGmix lt 0) and thus
compatible the resulting material will display an amalgamation of properties which are
predictable using the same techniques as those used for random or statistical copolymers
Polymer blends account for a significant percentage of polymer production and are produced
either to reduce costs to aid in processing or to improve a variety of specific properties For
example polycarbonates have been blended with polybutylene terephthalates to increase
chemical resistance and to aid in processing while polyphenylene oxides are bended with
polystyrenes to improve toughness and increase glass transition temperatures182
413 Compatibilization
As it follows from thermodynamics the blends of immiscible polymers obtained by simple
mixing show a strong separation tendency leading to a coarse structure and low interfacial
180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999)
97
adhesion The final material then shows poor mechanical properties On the other hand the
immiscibility or limited miscibility of polymers enables formation of wide range structures
some of which if stabilized can impart excellent end-use properties to the final material To
obtain such a stabilized structure it is necessary to ensure proper phase dispersion by
decreasing interfacial tension to suppress phase separation and improve adhesion This can be
achieved by modification of the interface by the formation of bonds (physical or chemical)
between the polymers This procedure is known as compatibilization and the active
component creating the bonding as the compatibilizer174 177 183
The most popular method of compatibilization is by addition of a third component In most
cases such an additive is either a block or graft copolymer Since the key requirement is
miscibility it is not necessary for the copolymer to have identical chain segments as those of
the main polymers It suffices that the copolymer has segments having specific interactions
with the main polymeric components viz hydrogen bonding dipole-dipole dipole-ionic
Lewis acid-base etc
Addition of a block or graft copolymer reduces the interfacial tension and alters the molecular
structure at the interface Thus compatibilization by addition changes not only the interfacial
properties but it may affect the flow behavior (hence processability)
One of the disadvantages of the addition method is the tendency of the added copolymers to
form micelles These reduce the efficiency of the compatibilizer increase the blend viscosity
and may lessen the mechanical performance
414 Incorporation of Copolymers for Compatibilization
Block or graft copolymers with segments that are miscible with their respective polymer
components show a tendency to be localized at the interface between immiscible blend
phases Random copolymers sometimes also used as compatibilizers reduce interfacial
tension but their ability to stabilize the phase structure is limited184 Finer morphology and
higher adhesion of the blend lead to improved mechanical properties The morphology of the
resulting two-phase (multiphase) material and consequently its properties depend on a
number of factors such as copolymer architecture (type and molecular parameters of
segments) blend composition blending conditions
183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001)
98
In Scheme19 the conformation of different block graft or random copolymers at the
interface is schematically drawn
Scheme 19 Possible localization of A-B copolymer at the AB interface Schematic of
connecting chains at an interface a-diblock copolymers b-end-grafted chains c-triblock
copolymersdmultiply grafted chain and e-random copolymer
415 The Effect of Compatibilizer on a Blend
The presence of a compatibilizer at the interface substantially affects the development of the
phase structure of molten blends in the flow and quiescent state The position and width of the
concentration region related to co-continuous morphology are affected by two competing
mechanisms A decrease in interfacial tension caused by a compatibilizer favors the formation
and stability of co-continuous structures
The effect of a compatibilizer on fineness of the phase structure can be understood through its
effects on droplet breakup and coalescence A decrease in interfacial tension due to the
presence of a compatibilizer decreases the droplet radius R
Effect of the Compatibilizer Architecture
Compatibilization efficiency of various copolymers follows from their thermodynamic and
microrheological effects It has been generally accepted that the total molecular weight of the
copolymer molecular weight of its blocks and their number are the main structural
compatibilizer characteristics affecting the phase structure of the final blend
99
Effect of Compatibilizer Concentration
The compatibilizing efficiency of the copolymers is besides the architecture a function of
their concentration The effect of a compatibilizer concentration has been quantitatively
characterized by the emulsification curvemdashthe dependence of the average particle diameter of
the minor dispersed phase on copolymer concentration185 The particle diameter decreases
with increase of copolymer concentration until a constant value is obtained For most systems
this value is achieved if the copolymer amount is 15ndash25 of the dispersed phase
416 Methods of Blend Preparation
Five different methods are used for the preparation of polymer blends186 187 melt mixing
solution blending latex mixing partial block or graft copolymerization and preparation of
interpenetrating polymer networks It should be mentioned that due to high viscosity of
polymer melts one of these methods is required for size reduction of the components (to the
order of μm) even for miscible blends
bull Melt mixing is the most widespread method of polymer blend preparation in practice
The blend components are mixed in the molten state in extruders or batch mixers Advantages
of the method are well-defined components and universality of mixing devicesmdashthe same
extruders or batch mixers can be used for a wide range of polymer blends Disadvantages of
the method are high energy consumption and possible unfavorable chemical changes of blend
components This procedure has not been used so far in industrial practice because of large
energy consumption
bull Solution blending is frequently used for preparation of polymer blends on a laboratory
scale The blend components are dissolved in a common solvent and intensively stirred The
blend is separated by precipitation or evaporation of the solvent The phase structure formed
in the process is a function of blend composition interaction parameters of the blend
components type of the solvent and history of its separation Advantages of the process are
rapid mixing of the system without large energy consumption and the potential to avoid
185 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons Inc New York Chap 16 (2000) 186 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709 187 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458
100
unfavorable chemical reactions On the other hand the method is limited by the necessity to
find a common solvent for the blend components and in particular to remove huge amounts
of organic (frequently toxic) solvent Therefore in industry the method is used only for
preparation of thin membranes surface layers and paints
bull A blend with heterogeneities on the order of 10 μm can be prepared by mixing of
latexes without using organic solvents or large energy consumption Significant energy is
needed only for removing water and eventually achievement of finer dispersion by melt
mixing The whole energetic balance of the process is usually better than that for melt mixing
The necessity to have all components in latex form limits the use of the process Because this
is not the case for most synthetic polymers the application of the process in industrial practice
is limited
bull In partial block or graft copolymerization homopolymers are the primary product
But an amount of a copolymer sufficient for achieving good adhesion between immiscible
phases is formed188 In most cases materials with better properties are prepared by this
procedure than those formed by pure melt mixing of the corresponding homopolymers The
disadvantage of this process is the complicated and expensive start-up of the production in
comparison with other methods eg melt mixing
bull Another procedure for synthesis of polymer blends is by formation of interpenetrating
polymer networks A network of one polymer is swollen with the other monomer or
prepolymer after that the monomer or prepolymer is crosslinked189 In contrast to the
preceding methods used for thermoplastics and uncrosslinked elastomers blends of
reactoplastics are prepared by this method
188 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 189 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981)
101
42 Experimental
421 Materials
Polymers used in this research were PEG and PS PEG was purchased from MERCK
company General Purpose PS was obtained from ENPC TP1-Chlef Company Physical and
Structural characterizations of these materials were performed by SEC 1H-NMR and DSC
422 Blend Preparation
PSPEG blends of 5050 wt were prepared by solution casting from THF 40degC The
polymer solutions were stirred until complete miscibility and then cast onto glass dishes and
left to evaporate the solvent to the atmosphere To remove residual solvent after casting the
blends were dried in vacuum oven at 40degC for a weak Table 10 shows the quantities of the
copolymers used for compatibilization of the blends of PSPEG
Table 10 The quantities of the copolymers used for compatibilization of the blends of
PSPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
43 Characterization Techniques for Compatibilization
431 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
102
Relative viscosities of polymer solutions were calculated by dividing the flow times of
solutions by that of the pure solvent The data were plotted using the Huggins equation with
the intrinsic viscosity [η] (dlg-1) determined by extrapolation to infinite dilution
432 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
433 FTIR Analysis
FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
44 Results and Discussion Polyethylene glycol (PEG) is very interesting and important polymers PEG presents good
properties eg hydrophilicity solubility in water and in organic solvents nontoxicity and
absence of antigenicity and immunogenicity190It has attracted increasing attention due to its
potential applications as biomedical and environment friendly materials PEG has been
widely used as a modifier for biomedical surfaces to reduce the protein absorption and
improve their biocompatibility192 and as a stabilizer for emulsion and dispersion It has also
been used as a plasticizer for poly (lactide) (PLA) which is stiff and brittle as a
biodegradable packaging material193
On the other hand polystyrene shows excellent processability good appearance tensile
strength and thermal and electrical characteristics however its brittleness considerably limits
its use in high performance products
Both PS and PEG are widely used commodity polymers Detailed studies on their miscibility
may contribute to technological and environmental applications These polymers form an
interesting pair to study since they exhibit contrasting physical properties PS is a
190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689
103
hydrophobic polymer whereas PEG is hydrophilic PEG is a much softer material than PS
PSPEO blends have been reported as incompatible materials in the literature194 195
N Watanabe et al have reported compatibilization effect of poly (styrene-co-methacrylic
acid) on immiscible blends of this system196
441 Characterization of the Blend Components
Analysis by SEC provides number average-molecular weights and polydispersity indices of
all materials DSC measurements performed to determine their glass transition temperatures
as well as melting point and degree of crystallinity of PEG (See Figure16) 1HNMR spectroscopy analysis was performed on these polymers to determine essentially the
tacticity of PS and also to get information about end groups of PEG which was found to
possess an OH group at each end It has been also determined that the stereoregularity of PS
is Syndiotactic-Atactic (rather highly syndiotactic) (See Figures 17)
Physical characteristics of materials used are given in Table11
Table 11 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PS ENPC TP1-Chlef (from CHI MEI Corp)
105
128 000
1076
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam] Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842
104
Figure 16 1H-NMR spectrum of PEG (Merck) in CDCl3
105
Figure 17 1H-NMR spectrum of Commercial Styrene (ENPC TP1-Chlef) in CDCl3
442 Study of Compatibilization by Dilute Solution Viscometry
a) Introduction
Polymer blends are physical mixtures of structurally different polymers which interact
through secondary forces with no covalent bonding Blending of the polymers may result in a
reduction in the basic cost and improved processing and also may enable properties of
importance to be maximized The polymer blends often exhibit properties that are superior
compared to the properties of each individual component polymer197 198 199 200 The main
advantages of the blend systems are simplicity of preparation and ease of control of physical
properties by compositional change201 202 However the mechanical thermal rheological and
197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85
106
other properties of a polymer blend depend strongly on its state of miscibility on the
molecular scale203
There have been numerous techniques of studying the miscibility of the polymeric blend The
most useful techniques are dynamic mechanical thermal electron-microscopic IR
spectroscopic refractive index203 optical microsscopic204 and viscometric techniques 179 205
Because of its simplicity viscometry is an attractive and very useful method for studying the
compatibility of polymer blends Additional advantages ie that no sophisticated equipment
is necessary and that the crystallinity or the morphological states of the polymer blends do
affect the result206 make the viscometric method more convincing for characterizing polymer
mixtures The principle of using a dilute solution viscosimetry to measure the miscibility is
based on the fact that while in solution molecules of both component polymers may exist in
a molecularly dispersed state and undergo a mutual attraction or repulsion which will
influence the viscosity It is assumed that polymerndashpolymer interaction usually dominate over
polymerndashsolvent ones207 The presence of interactions between atoms or groups of atoms of
unlike polymers is essential to obtain a miscible polymer blend177 179
Estimation of the compatibility of different pairs of polymers based on dilute solution
viscosity for a ternary polymerpolymer-solvent system has been attempted by several
authors including Mikhailov and Zeilkman208 Bohmer and Florian209 Feldman and Rusu210
Krigbaum and Wall211 and Catsiff and Hewett212
The compatibilization of the blends in question has been characterized by viscosity technique
using the Krigbaum and Wall interaction parameter Δb The versatility of the viscometric
technique is not affected by the choice of the solvent as was shown by Kulshreshta et al213
In this section we discuss in details our investigation on the compatibilization of the two
polymer blend systems PSPEG and PMMAPEG 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191
107
b) Theoretical background
The main aspects of the application of dilute solution viscometry method for the study of
interactions and miscibility phenomena in dilute multicomponent polymer solutions were
described Only the most important features will be repeated here It is common to use
empirical relations such as Hugginsrsquo equation214
(65)
for the description of the concentration dependence of viscosity of polymer solutions This
relation is strictly valid only for binary polymer solutions However equations like that of
Krigbaum and Wall211
(66)
And of Catsiff and Hewett212
(67)
were proposed for ideal ternary polymer solutions of the polymer 1+ polymer 2+ solvent type
In previous relations ηsp denotes the specific viscosity [η] is the intrinsic viscosity (limiting
viscosity number) c stands for the mass concentration of polymer and kH is Hugginsrsquo
constant which may be related (in an empirical manner) to the thermodynamic quality of
solvent Relative mass fractions of dissolved polymers wi are used to describe the
composition dependence of viscosity in ternary systems Quantities b 12 and b12 are used to
define the ideal behavior of ternary polymer solutions These are calculated by
(68)
and
(69)
214 ML Huggins J Am Chem Soc 64 (1942) 116
108
respectively Here b denotes the slope of Hugginsrsquo equation for binary solutions
(70)
Moreover it has been shown215 that both the sign and the extent of the deviation of
experimental from theoretical b-values may be correlated to the interactions between
polymeric components of a system under consideration The quantities of interest (miscibility
criterion variables) are defined by
(71)
and
(72)
or can be written in another form
(73)
where m denotes the polymer mixtures Δb intermolecular interaction parameter between
polymer 1and 2 and is considered a good criterion to predict the polymer-polymer
compatibility209 216 217 Δb 0 indicates that the two polymers are compatible whereas
Δb0 indicates that they are incompatible
c) Discussion of the Results
Herein we discuss in detail the compatibilization of PSPEG blends with the synthesized graft
copolymers by viscometric technique The plot of reduced specific viscosity of polymers
versus total polymeric concentration yields a straight line and the intercept and slope
correspond to intrinsic viscosity [η] and molecular interaction coefficient b respectively The
viscosity data for the homopolymers and their blends are presented in Tables 12 and 13
Table 12 Interaction coefficient for binary solutions (polymersolvent) 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin (1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849
109
Polymer components PEG PS
b11 007327 minus
b22 minus 02117
b12 = (b11 b22)12 = 01245 (theo)
Table 13 Interactions parameters for PSPEG blends with poly (St-g-PDXL) copolymers
(2SP2 2SP1 and DXSP) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
DXSP b12 003511 01295 01680 01833 01947
Δb - 00894 00050 00435 00588 00702
2SP2 b12 003511 009826 01052 01314 01515
Δb - 00894 - 00262 - 00193 00069 00270
2SP1 b12 003511 minus minus minus 01262
Δb - 00894 minus minus minus 00017
For incompatible blends the incompatible molecules refuse to overlap thus they shrink in
size which leads to a decrease in hydrodynamic volumes As a matter of fact the crossover in
the reduced viscosity-concentration plot is observed
As far as we are concerned with the blend of PSPEG the results obtained present similar
situation Figure 18 shows the Huggins plots for the homopolymers and the (5050) blend of
PSPEG In this figure a crossover is observed and a decrease of slope occurs at about 05
gdl in the viscosity-concentration plot Above this concentration two incompatible polymers
PS and PEG undergo mutual repulsion in dilute solution the hydrodynamic volume of chains
is lower The reduction of the hydrodynamic volume will result in a decrease of the reduced
viscosity of solution correspondingly the slope of the plot suddenly declines
110
02 03 04 05 06 07 08 09 10 11
03
04
05
06
07
08PS PEG and PSPEG (5050)
PS PSPEG 0 PEG
Redu
ced
visc
osity
η sp
c
(ldl
)
C (dll)
Figure 18 Plots of reduced viscosity (ηspc) vs concentration for PS PEG and PSPEG
blend (0) in THF at 30degC
Figures 19 20 21 and 22 show the incorporation of various amounts of copolymers in the
immiscible blend As far as the amount of the compatibilizers increases the crossover of the
plots occurs at very low concentration or even it is not observed In addition the slope of the
plot increases with an increase of the amount of the compatibilizers introduced in the blend
This is due to the mutual attraction of the blend components which is enhanced by the
presence of the copolymers As a matter of fact the latter act as compatibilizing agents
allowing to the blends to exhibit miscibility
111
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07BLENDS WITH DXPS
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 19 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of DXPS copolymer
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLENDS WITH 2SP2
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 20 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of 2SP2 copolymer
112
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLEND WITH 2SP1 40
PSPEG 0 2SP1 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 21 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with 40 of the dispersed phase of 2SP1 copolymer
02 03 04 05 06 07 08 09 10 1100
01
02
03
04
05
06
07
08
DXPS 40 2SP2 40
2SP1 40
2SP1 40 2SP2 40 DXPS 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 22 comparison of plots of reduced viscosity (ηspc) vs concentration for PSPEG
blends in THF at 30degC with 40 of the dispersed phase of DXPS 2SPS2 and 2SP1
copolymer
113
Figure 22 compares the three copolymers used for compatibilization of PSPEG with respect
to 40 by weight of the dispersed phase addition to the blends
Krigbaum and Wall suggested that information about the interaction between two polymers
should be obtained from the difference of experimental b12 and theoretical b12 Δb A positive
difference between the experimental and theoretical interaction coefficients is evidence of a
compatible polymer pair The higher the value of Δb the higher the extent of compatibility
Negative values refer to repulsive interaction and incompatible mixes The values of Δb
according to equation 73 for different blends with compatibilizers are given in Table 13 and
Figure 23
0 10 20 30 40 5
-010
-005
000
005
010
0
PS PEG BLENDS
2SP2 DXPS
Δb
Amount of incorporated copolymer w ()
Figure 23 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (DXPS and 2SP2) used for compatibilization
It was observed as the amount of compatibilizers increases values of the interaction
parameter increase thereby increasing the compatibility between the two polymer
components of the blend Consequently this indicates that these copolymers act as
compatibilizing agents in the immiscible blends of PS and PEG Now in comparing these
copolymers in terms of structure (number of grafts) and PDXL content it can be noticed that
the results obtained DXPS ( 71 w of PDXL) copolymer show higher values of Δb than
2SP1(30 w of PDXL) and 2SPS2 (4025 w of PDXL) do This is due to the comb-
structure of the DXPS copolymer (synthesized by CRP) and therefore containing more grafts
114
(Ng = 58) than the other copolymers Besides the amount of PDXL in the copolymer PDXL
includes polar groups which provide associative interactions with one of the blend
components (PEG) and thus undergoes significant effects upon compatibilization In the
figure below it can be seen that addition of 10 by weight of the dispersed phase (47 of
total weight of the blend) of DXPS is sufficient to compatibilize the immiscible blend of
PSPEG (5050) Then a drastic increase of the interaction parameter with the addition of the
compatibilizer (DXPS) compared to the addition of either 2SP2 or 2SP1 (Table 13)
From the results shown in the graph miscibility of the blend can be achieved by incorporating
around 25 (11 of total weight of the blend) of 2SP2 copolymer However compatibibility
of the blend with 2SP1 copolymer is obtained at 40 by weight of the dispersed phase since
its interaction parameter (Δb) found to be 00017
It is worth to mention that the PDXL content of 2SP1 is 30 and the length of the grafts is
half that of 2SP2 copolymer For this reason these two copolymers have been chosen for the
purpose of comparison in terms of side chains length
An optimization of the amount of copolymer needed for compatibilization of PSPEG (5050)
blend has been made (corresponding to Δb = 0) as function of the PDXL content and shown
in Table 14
Table 14 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050) vs PDXL content
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
DXPS 0 9 43 71
2SP2 0 245 109 4025
2SP1 0 40 166 30
115
443 Optical Microscopy and Phase Morphology
PDXL is a perfect alternate copolymer of poly (ethylene oxide) (PEO) and poly (methylene
oxide) (PMO) that has the same curious combination properties as PEG So PDXL must be
at least miscible with PEG or adhere at the interface between PS and PEG and between
PMMA and PEG The compatibility between hydrophobic PS or PMMA and hydrophilic
PEG is very poor Compatibilization between components of the two sets of polymer blends is
studied by optical microscopy
The morphological characteristics of the blends by different compatibilizers are presented in
Figure 24 The optical microscopy micrographs of PSPEG blends without compatibilizers
show a poor dispersion for PS disperse phase and a ldquoball-and-socketrdquo topography due to the
poor interfacial adhesion between PEG matrix and the dispersed phase However with the
addition of compatibilizers the morphological characteristics of the polymer blends are
greatly altered It can be noticed that for these two different blends the particle size of PS
domains gets progressively much smaller and uniform in compatibilized blends than in
incompatibilized ones This may be explained by the significant increase of the phase
interfacial adhesion Consequently the domain size strongly depends upon the
compatibilizers used
116
a) PSPEG (5050) 0 (without compatibilizer)
DXPS 10 DXPS 20 DXPS 30 DXPS 40 b) Compatibilizing effect of DXPS copolymer
2SP2 10 2SP2 20 2SP2 30 2SP2 40 c) Compatibilizing effect of 2SP2 copolymer
2SP1 40
117
d) Compatibilizing effect of 2SP1copolymer at 40 addition
Figure 24 Optical micrographs showing phase structure in 5050 PSPEG blends
a) blends without compatibilizer b) with DXPS c) with 2SP2 d) with 40 of 2SP1
For instance the PSPEG blends with the incorporation of the copolymers DXPS 2SP2 and
2SP1 as compatibilizers (Figure 24) the morphology displays a very fine dispersion of PS
phase and strong interfacial adhesion with PEG Matrix The good compatibilizing effect
mainly that of DXPS can be explained by two mechanisms
First the PDXL units in the compatibilizer interact with PEG ether groups leading to a good
adhesion at interface between the components of the blend In addition hydrogen bonding
may also exist between PDXL and PEG further increasing compatibilization Second since
the compatibilizer also contains styrene blocks it contributes to provide a good compatibility
with PS Consequently the remarkable compatibilizing effect of PS-g-PDXL copolymers
induced a drastic decrease in interfacial tension and suppression of coalescence between the
originally immiscible polymer phases
As it can be noticed from the micrographs given in the figure above the compatibilizer
exhibits finer dispersion and homogeneous morphology of the blends as the amount of
compatibilizers increases
Eventually each compatibilizer has its own effect on the immiscible blends depending on the
amount of PDXL (side chains) and number of grafts present in the copolymers
By comparing micrographs shown in Figure 24 b and c the compatibilization effect of DXPS
copolymer which contains more grafts but shorter is different from that of the 2SP2
copolymer In the case of DXPS it is observed that the size of the dispersed droplets is
deceased significantly and results in finer dispersion morphology However 2SP2 copolymers
shows an improvement in compatibility of the blend after addition up to 30 wt of the
dispersed phase (13 total weight of the blend) exhibits homogeneous morphology This
may be related to length of the grafts In all cases these copolymers act as good
compatibilizers for the blend of 5050 wt PSPEG
444 FTIR Analysis
The FTIR technique is very important since it allows one to study the specific interactions
between the polymers The knowledge of the polymerndashpolymer interactions will be useful for
118
studies of the compatibility in polymer blends To verify the intermolecular interactions that
can play a role in miscibility the vibrational spectra of the blends studied in the present work
were obtained In polymeric systems where there are multiple interactions vibrational bands
such as ν (C=O) ν (COC) and ν (OH) present contributions of spectroscopic free and
associated forms
In order to elucidate the role played by intermolecular interactions in the miscibility of these
blends FTIR absorption of individual polymer components PS PEG and PMMA and
compared to that of the mixtures Figures 26 27 and 28 present the FTIR absorption spectra
from 4000 to 400 cm-1 for all samples
In the case of PS the high-frequency infrared spectra consist of seven absorption bands The
bands with peak locations at 3008 3026 3060 3082 and 3103 cm-1 are due to C-H stretching
of benzene ring CH groups on the PS side-chain The bands with peak positions of 2924 and
2850 cm-1 are due to the C-H stretching vibration of the CH2 and CH groups of the main PS
chain respectively PEG with molecule chemical structure of HO-[CH2-CH2-O]n-H exhibits
important absorption bands from FTIR spectroscopy measurements as shown in Figure 25 It
was verified contributions associated with CndashOndashC symmetric stretching of ether groups218-220
221 from 1050 to 1150 cm-1 with maximum peak at 1150 cm-1 Characteristics CH2-O
stretching modes from 2800-3000 cm-1 are observed214 At low frequency region peaks at 850
and 890 cm-1 are assigned to CndashOndashC stretching and at 500 cm-1 ascribed to CndashOndashC
deformation The presence of PDXL in the blends is detected by the intense frequency at 1140
cm-1 which is assigned for acetal groups In addition both PDXL and PEG contain ether
groups and the spectra show that the corresponding peaks are overlapped for the blends The
intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of PEG
crystallinity in the blends222
218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10 219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601
119
It can be observed also a typical large hydroxyl bands with two distinct contributions which
can be seen for all samples They are attributed to the spectroscopically free and bonded ndashOH
stretching forms at 3600-3800 cm-1 and 3200-3500 cm-1 respectively221 - 227
500 1000 1500 2000 2500 3000 3500 4000-05
00
05
10
15
20
25
30
35
PS and PEG PEG PS
Abs
orba
nce
Wave number (cm-1)
Figure 25 FTIR spectra of PS PEG over 4000-400 cm-1 range
227 Peppas NA Wright L Macromolecules 1996298798ndash804
120
500 1000 1500 2000 2500 3000 3500 4000
0
1DXPS IN PSPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 26 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS)
All these absorption bands for individual polymer were observed in the FTIR spectrum of the
5050 (ww) PSPEG in which they were combined to give superimposed bands in the regions
of 750-1500 cm-1 and 2700- 3100 cm-1
The hydroxyl vibrational frequency is discernible in the blend spectrum for PSPEG at 0
With the incorporation of the copolymers for compatibilization a number of bands showed
small shifts and changes in position and shape in the resulting spectra In Figures 28 29 and
30 as it can be noticed that in the hydroxyl absorption region a decrease in the fraction of
free OH groups is observed as the amount of copolymers is increased in the blend This can
be due to the flexibility of the PDXL graft chains on the other hand to the acetal and ether
groups of PDXL which are probably randomly distributed among an increasing number of
hydroxyl groups of PEG statistically favoring the formation of the PDXL and PEG hydrogen
bond interaction The results indicate that the intermolecular hydrogen bonding between the
ether oxygen of PDXL and the hydroxyl groups of PEG may be formed thereby reducing the
fraction of free OH which is consistent with the shifts observed in the region of hydroxyl
stretching Intermolecular hydrogen bondings are expected to occur among PDXL and PEG
chains due the high hydrophilic forces These interactions have replaced the intramolecular
121
interactions between COC and OH groups of PEG before addition of containing PDXL
copolymers It can be noticed a progressive shift of hydroxyl band from 3340 to 3420 cm-1
with DXPS and from 3340 to 3350 cm-1 when 2SP2 is added This shift can be attributed to
the decrease of intramolecular interactions among hydroxyl groups within PEG chains in
favor to intermolecular interactions between PDXL and PEG228
500 1000 1500 2000 2500 3000 3500 4000
0
1
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 27 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2)
228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
122
3200 3300 3400 3500 3600 3700 3800
00
01
DXPS IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 28 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS) in the hydroxyl absorption region
3200 3300 3400 3500 3600 3700 3800
00
02
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 29 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2) in the hydroxyl absorption region
123
3200 3300 3400 3500 3600 3700 3800
00
DXPS 40 2SP2 40 2SP1 40
Abs
orba
nce
Wave number (cm-1)
Figure 30 FTIR spectra comparison of PSPEG blends (5050) with different compatibilizers
in the hydroxyl absorption region
Conclusions An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends Again The PS blocks of the copolymer result in good
compatibility with PS component of the blends The compatibilization of PSPEG blends is
apparently associated with hydrogen bonding where groups of the acetal units in PDXL
interact with hydroxyl groups of PEG These form a stronger interface between the two
phases which leads to important modifications of the blend properties Apparently the FTIR
result is in good agreement with the miscibility criteria proposed by Krigbaum and Wall (Δb)
interaction parameter which results from dilute-solution viscometry (DSV) method It can be
concluded that by the addition of 20ndash40 wt of incorporated copolymer reveal a good
compatibilizing efficiency for the blend systems as it was observed from micrographs as well
124
References
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York
(1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York
(1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser
Publishers Munich (1989) 178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279 180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999) 183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001) 185 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709
125
186 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and
Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458 187 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 188 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981) 189 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons
Inc New York Chap 16 (2000) 190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689 194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam]
Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842 197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191 214 ML Huggins J Am Chem Soc 64 (1942) 116 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin
(1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849 218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10
126
219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601 227 Peppas NA Wright L Macromolecules 1996298798ndash804 228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
127
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g-
Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of
Polystyrene and Poly (Ethylene Glycol)
51 Introduction
PMMA is more than just plastics of paint Often lubricating oils and hydraulic fluids tend to
get really viscous and even gummy when they get cold This is a real pain when operating
heavy equipments in very cold weather When a little bit of PMMA is dissolved in these oils
and fluids they donrsquot get viscous in the cold and machines can be operated down to -100degC
PMMA can find a several applications namely adhesive optical coating medical packaging
applications and so forthhellip
In medical applications PMMA and its derivatives are used particularly for hard tissue repair
and regeneration229 PMMA beads have been developed to deliver aminoglucoside antibiotics
locally for the treatment of bone infections230 PMMA and PEG form an important and unique
pair of polymers in that they are chemically different In the present work this study may
shed light on the PMMA properties modifications induced by blending with PEG to overcome
the difficult processing of rigid PMMA
Several studies have been made on blends of poly (ethylene oxide) PEO and PMMA in the
last decades but very few on PMMAPEG blends231 232 233
Numerous works reported that the miscibility domain ranges between 10 and 30 of PEO by
weight depending on the PMMA tacticity or molecular weight No phase diagram is available
yet in the literature for PMMAPEO and neither it is for PMMAPEG234
229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703
127
52 Experimental
521 Materials
PEG and PMMA were used as blend components PMMA was obtained from ENPC TP1-
Chlef Company PEG was purchased from MERCK Company Physical and Structural
characterizations of these materials were performed by SEC 1H-NMR and DSC
522 Blend Preparation
Blends of PMMAPEG (5050) were prepared using the same procedure as described for the
blends discussed in the previous chapter Table 15 shows the quantities of the copolymers
used for compatibilization of the blends of PMMAPEG
Table 15 The quantities of the copolymers used for compatibilization of the blends of
PMMAPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
53 Characterization Techniques
531 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
532 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
128
533 FTIR FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
54 Results and Discussion
541 Characterization of the Homopolymers
The polymers have been analyzed by SEC to determine their number average-molecular
weights and polydispersity indices DSC measurements performed to determine their glass
transition temperatures as well as melting point of crystallinity of PEG 1HNMR spectroscopy analysis revealed the tacticity of PMMA It has been found that PMMA
is Syndiotactic-Atactic (highly syndiotactic) as shown in Figure 3 and 321
Physical characteristics of materials used are given in Table 16
Table 16 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PMMA ENPC TP1-Chlef (fromLG MMA Corp)
119
55 000
113
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
129
Figure 31 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in CDCl3
Figure 32 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in the methyl shifts
region in CDCl3
130
542 Dilute Solution Viscometry
Dilute solution viscometry has been utilized to evaluate miscibility of PMMAPEG blends
and the same approach discussed in the previous section has been followed The
experimental reduced viscosities of the polyblends are plotted against concentration in dilute
solution viscometry Eventually plots of pure polymers and polyblends of 5050 PMMAPEG
are first obtained Then their interaction coefficients are determined as shown in Table 17
Table 17 Interaction coefficient for binary solutions (polymersolvent)
Blend components PEG PMMA
b11 007327 minus
b22 minus 006561
b12 = (b11 b22)12 = 006933 (theo)
The compatibility of this system has been evaluated through the sign of Δb The values of the
latter according to equation 73 for different amounts of poly (MMA-g-PDXL) copolymers in
the blends are given in Table 18 It is observed that the blend of PMMAPEG at 5050 by
weight shows a negative value of Krigbaum and Wall parameter which indicates
incompatibility of the system as it is expected Similarly to PSPEG blend a crossover in the
reduced viscosity-concentration plot is observed and a decrease of slope arises in the range of
05 to 066 gdl in the viscosity-concentration plot as shown in Figure 33 This is attributed to
the repulsive intermolecular interactions between the polymer chains
Then the incorporation of the copolymers at various amounts presents positive values
progressively Curves of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in
THF at 30degC with various amounts of copolymer are given in Figures 34 35 and 36
131
Table 18 Interactions parameters for PMMAPEG blends with poly (MMA-g-PDXL)
copolymers (3MP2 2MP2 and 3MP1) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
3MP2 b12 00288 01308 01904 02373 02602
Δb - 004053 00615 01211 01680 01909
2MP2 b12 00288 01286 01690 01893 02296
Δb - 004053 00593 00997 01200 01603
3MP1 b12 00288 00868 01670 02010 02379
Δb - 004053 00175 00977 01317 01686
00 01 02 03 04 05 06 07 08 09 10 11020
025
030
035
040PMMAPEG (5050) 0
PEG PMMAPEG 0 PMMARe
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 33 Plots of reduced viscosity (ηspc) vs concentration for PMMA PEG and
PMMAPEG blend (0) in THF at 30degC
132
02 03 04 05 06 07 08 09 10 11000
005
010
015
020
025
030
035
040 BLENDS WITH 3MP1
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 34 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP1 copolymer
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040
045BLENDS WITH 3MP2
PMMAPEG 0 10 20 30 40
Redu
ced
visc
osity
η
spc
(d
lg)
C (gdl)
Figure 35 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP2 copolymer
133
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040BLENDS WITH 2MP2
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 36 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 2MP2 copolymer
From our viscosity data as the copolymer content increases in the blend the polymer blend
molecules will become disentangled more spaciously resulting in a greater interaction
between structurally similar component segments This suggests that there are attractive
forces that induce miscible behavior of the blends as it is observed in Figure 37
0 10 20 30 40 5-01
00
01
02
0
PMMA PEG BLENDS
3MP2 2MP2 3MP1
Δb
Amount of incorporated copolymer w ()
Figure 37 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (3MP2 2MP2 and 3MP1) used for compatibilization
134
The three copolymers (3MP2 2MP2 and 3MP1) involved in this study for compatibilization
are different from the point of view of the PDXL content and the graft length For instance
3MP2 and 2MP2 have similar and longer grafts since the theoretical number average-
molecular weight of the graft is 2000 gmol However they contain different amount of
PDXL In the case of 3MP1 this graft copolymer has a structure with shorter side chain length
(Mn = 1000 gmol) corresponding to the half of the graft size in the former copolymers From
the observations made out of the figure above 3MP2 copolymer (21 w of PDXL) provides
higher values of the interaction parameter and therefore greater extent of compatibility
compared to the other copolymers since it has long grafts which allows penetration into the
other phase
It can be concluded that all three copolymers show good results for compatibilization on the
basis of the Δb criterion of polymer-polymer miscibility determined by viscometry
Similarly the minimum amount of copolymer needed for compatibilization of PSPEG
(5050) blend has been determined corresponding to Δb = 0 as function of the PDXL content
and shown in Table 19
Table 19 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050)
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
2MP2 0 34 16 35
3MP2 0 37 18 21
3MP1 0 58 28 19
135
543 Optical Microscopy and Phase Morphology
a) PMMAPEG (5050) 0 (without compatibilizer)
b) Compatibilizing effect of 2MP2 copolymer
c) Compatibilizing effect of 3MP2 copolymer
d) Compatibilizing effect of 3MP1copolymer
Figure 38 Optical micrographs showing phase structure in 5050 PMMAPEG blends
a) blends without compatibilizer b) with 2MP2 c) with 3MP2 d) with 3MP1
136
Figure 38 presents microscopy images of PMMAPEG blends with varying amounts of
compatibilizers The morphological characteristics of the blends of PMMAPEG without
compatibilizers show a poor dispersion of PMMA as a dispersed phase The addition of
compatibilizers changes drastically the morphological topology of this system The
compatibilizers used are of different length of the side chains and also different PDXL
content By introducing progressively variable amounts of the compatibilizers they display
similarly the morphological characteristics to some extent It is observed that the phase
separated domains of PMMA in the blends are reduced with increasing amounts of the
compatibilizers This is due to the compatibility of PMMA of the copolymers with the
PMMA blend component and on the other hand to the interfacial interactions of the PDXL
of the copolymers and PEG component of the blends From these results it is revealed that
compatibilizing effect of 2MP2 copolymer on this system is great compared to the others Not
only causes the size of the dispersed droplets to decrease but also dispersed droplets become
homogeneous However 3MP1 copolymer which contains shortest grafts (about half length
of those of the other copolymers) and less amount of PDXL shows less reduction in the
droplet size compared to the other copolymers Therefore it can be concluded that the
compatibilization of this blend depends upon length and number of grafts
On the overall observations these compatibilizing copolymers are very effective and hence
influence and improve the compatibility of PMMAPEG blend at a composition of 5050 wt
544 FTIR Analysis
Same observations can be made for the blends of PEG with PMMA The FTIR spectrum of
this blend at 0 compatibilizer is shown in Figure 39 For pure PMMA the
spectroscopically free carbonyl group band is observed at 1730 cm-1 In the blend sample one
large vibrational band due to hydroxyl group stretches in pure PEG is observed with two
distinct contributions which can be seen for all samples They are attributed to the
spectroscopically free and associated hydroxyl forms at 3495 and 3600 cm-1 respectively
A large band in the wave number range of 1400-1500 cm-1 is assigned to the deformation
vibration of the methyl groups The bands with peaks locations at 2820 and 2990 cm-1 are due
to C-H symmetrical and asymmetrical stretching vibration of CH3 respectively Peaks at
2886 and 2950 cm-1are ascribed to C-H symmetrical and asymmetrical stretching vibration of
CH2 figures 40 and 41 The C-O band is observed in the range of 1150- 1210 cm-1
137
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 PMMAPEG 0 Blend
Abs
orba
nce
Wave number cm-1
Figure 39 FTIR spectra of PMMAPEG 0 over 4000-400 cm-1 range
2750 2800 2850 2900 2950 3000 3050 3100-05
00
05
10
15
20
Abs
orba
nce
PEG PMMAPEG 0
Wave number cm-1
Figure 40 FTIR spectra of PMMAPEG 0 and PEG over the 3100-2700 cm-1 range
138
2750 2800 2850 2900 2950 3000 3050 3100
00
05
10
152MP2 in PMMAPEG
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 41 FTIR spectra of PMMAPEG 0 blends with 2MP2 addition over the 3100-2700
cm-1 range
The incorporation of PMMA-g-PDXL copolymers in the blends makes some changes in the
resulting spectra as it can be noticed in Figures 42 - 44 In the hydroxyl absorption region
same phenomenon has occurred as in the PSPEG blends The fraction of free OH groups has
decreased as the amount of the copolymers increased as shown in figures 45 and 46 which
present the effect of different compatibilizers in the hydroxyl absorption region This can be
explained as discussed above by the fact that the PEG hydroxyl groups undergo other
intermolecular interactions essentially with PDXL chains of the copolymers A comparison of
the effect of the three copolymers involved in the compatibilization at the highest amount
added is given in figure 47 It can be noticed that 2MP2 shows very few fraction of free OH
groups compared to the others This copolymer contains more PDXL (35 wt with 4 grafts)
than the others do (21 wt with 3 grafts and 19 wt with 3 grafts in 3MP2 and 3MP1
respectively)
A crystalline PEG phase is confirmed by the presence of the triplet peak of the COC
stretching vibration at 1148 1110 and 1062 cm-1 with a maximum at 1110 cm-1235 236
Changes in the intensity shape and position of the COC stretching mode are associated with
235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115
139
the interaction between PEG and PMMA-g-PDXL In addition both polymers contain the
same ether group and the spectra show that the corresponding peaks are overlapped for the
blends The intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of
PEG crystallinity in the blends237
Therefore the presence of this interacting system is probably responsible for the miscibility
and low degree of crystallinity observed for these blends
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
202MP2 in PMMAPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 42 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (2MP2)
237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
140
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 43 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2)
500 1000 1500 2000 2500 3000 3500 4000
0
1
2 3MP1 IN PMMAPEG BLENDS 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 44 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1)
141
3500
00
05
3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 45 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2) in the hydroxyl absorption region
3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
-02
00
02
04
06
08
3MP1 IN PMMAPEG 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 46 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1) in the hydroxyl absorption region
142
3500
2MP2 40 3MP2 40 3MP1 40
Abs
orba
nce
Wave number cm-1
Figure 47 FTIR spectra comparison of PMMAPEG blends (5050) with different
compatibilizers in the hydroxyl absorption region
The results from FTIR spectra indicate the compatibility of these polymer blends with the
addition of the PDXL copolymers via hydrogen bonds is observed and confirmed mainly by
the shifts of bands of the hydroxyl stretching modes
143
Conclusions
From the observations made out from this study reveal that all three copolymers show good
results for compatibilization on the basis of the Δb criterion of polymer-polymer miscibility
determined by viscometry Therefore these copolymers act as good compatibilizers since it
was found that the minimum amount needed for compatibilizing is between 1 to 3 of the
total weight of the blend which corresponds to 3 to 6 of the dispersed phase This
compatibilization is due to the fact that the copolymers have constituents which present strong
interactions with both polymer components of the blends These results are in great agreement
with microscopy analyses which demonstrate that the phase separated domains of PMMA in
the blends are reduced with increasing amounts of the compatibilizers This is due to the
compatibility of PMMA of the copolymers with the PMMA blend component and on the
other hand to the interfacial interactions of the PDXL of the copolymers and PEG component
of the blends
From FTIR results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PMMA and relatively long PMMA backbone of PMMA-g-PDXL copolymers respectively
These compatibilizing copolymers are very effective and hence influence and improve the
compatibility of PMMAPEG blend at a composition of 5050 wt
144
References 229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703 235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115 237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
145
CONCLUSIONS
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel using an unsaturated alcohol (2-
HPMA) as a transfer agent results in linear polymeric chains in order to prevent formation of
cyclic oligomers through cationic polymerisation of cyclic acetals They were all prepared at
the same reaction conditions
The characterization of these macromonomers has been conducted using different methods of
analysis Structure and molecular weight determination were provided from SEC and Raman
and 1H-NMR spectroscopy
We were interested in obtaining a hydrogel based on fully PDXL segments and study its
swelling and viscoelastic behaviour The hydrogel has combined special properties The
results reveal a perfect elastic and resistant hydrogel with interesting viscoelastic properties
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers Structure composition and number of grafts of the
copolymers were determined by SEC and 1H-NMR spectroscopy Another approach for
copolymerization has been made in order to compare the copolymers obtained from different
types of polymerization reactions like Conventional Free Radical and Controlled Radical
Polymerizations In the latter the copolymer obtained possesses larger number of grafts than
those from the former
The macromonomer reactivity estimation suggests that the length of the PDXL side chains
does affect the reactivity of the methacrylic double bond of the macromonomer when
copolymerized with St However in the case of copolymerization with MMA there is no
dependence on the graft size Finally from DSC measurements the values of Tg depend on
the composition and the size of the PDXL grafts In all copolymers the increase in amount of
the incorporated PDXL macromonomer results in a substantial decease in glass transition
An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
146
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends
The compatibilization effect of the copolymers used in this study on the PSPEG and
PMMAPEG was demonstrated from the viscometric results The contribution of both PS or
PMMA and PDXL of the copolymers has played a big role in the compatibilization of these
two different systems of blends thereby resulting in good compatibility due the chemical
affinity between these components which leads to a drastic decrease in interfacial tension and
suppression coalescence between the blend constituents
It has been shown that the immiscible blends in question exhibit compatibility when small
amount of copolymers synthesized for this purpose are added except for one of them
Styrene-g-PDXL copolymers act as good compatibilizers for PSPEG blends since it was
found that the minimum amount needed for compatibilizing is less than 11 of the total
weight of the blend which corresponds to 25 of the dispersed phase This compatibilization
is due to the fact that the copolymers have constituents which present strong interactions with
both polymer components of the blends
Compared with PS-g-PDXL with DXPS content the DXPS is more effective binary polymer
blends compatibilizer in the PSPEG blends which is due to the high number of grafts and
high PDXL content This has led to good adhesion of PDXL chains with the PEG phase in the
blends Again The PS blocks of the copolymer result in good compatibility with PS
component of the blends The compatibilization of PSPEG blends is apparently associated
with hydrogen bonding where groups of the acetal units in PDXL interact with hydroxyl
groups of PEG These form a stronger interface between the two phases which leads to
important modifications of the blend properties
Similarly PMMA-g-PDXL copolymers act as good compatibilizers since it was found that
the minimum amount needed for compatibilizing is between 1 to 3 of the total weight of
the blend which corresponds to 3 to 6 of the dispersed phase This compatibilization is due
to the fact that the copolymers have constituents which present strong interactions with both
polymer components of the blends
These results are in great agreement with microscopy analyses which demonstrate that the
phase separated domains of PMMA and PS in their respective blends are reduced with
increasing amounts of the compatibilizers
147
Specific interactions between chemical groups of two blend components can play an
important role in polymer mixtures There is a range of such interactions of varying strengths
which has been identified in polymer blends and such interactions are generally defined for
small molecules It should be noted that the extension of this concept to polymers is not
always straightforward it is more difficult to identify interactions in polymers the
spectroscopy is more complex and molecular conformations are less certain This situation is
further complicated because researchers use different names and definitions to describe
similar interactions
FTIR investigation showed that these interactions have been observed through the changes in
IR absorption peaks of PS PEG and PMMA upon mixing with increasing amount of
compatibilizers in their blends which have given rise to a wide investigation
From these the results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PSPEG and PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PS or PMMA and relatively long PS or PMMA backbone of PS-g-PDXL and PMMA-g-
PDXL copolymers respectively
148
TABLE OF CONTENTS ACKNOWLEDGEMENTS i SUMMARY hellipii
CHAPTER I LITERATURE REVIEW helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 1
11 Macromonomer Interest and Synthesis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 2
12 Ring-Opening Polymerization Overview helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 4
121 Polymerizability of Cyclic Compounds helliphelliphelliphelliphelliphelliphelliphelliphellip 4
122 Mechanisms of Ring-opening Polymerization helliphelliphelliphelliphelliphellip 6
123 Cationic Ring-Opening Polymerization of Heterocycles helliphellip 7
13 Cationic polymerization of cyclic acetals helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 9
14 Synthesis of functionalized poly (13-dioxolane) helliphelliphelliphelliphelliphelliphelliphelliphelliphellip 13
141 Reaction of 1 3-dioxolane and hydroxyl-containing compounds 13
142 Synthesis of Poly (13-dioxolane) macromonomers helliphelliphelliphellip 15
15 Amphiphilic Graft Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 16
151 Graft Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 16
152 Amphiphilic Copolymers helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 20
16 Kinetics of Free Radical Polymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 22
161 Kinetics of free radical addition Homo and Copolymerization 22
17 Chain Growth Copolymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 31
171 Copolymerization Equations helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 31
172 Determination of Reactivity Ratios helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 37 18 Controlled Radical Polymerization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 42
181 Fundamentals of ControlledLiving
Radical Polymerization (CRP) helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 43
182 Typical Features of ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 44
183 Controlled Compositions by ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 46
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 49
CHAPTER II Synthesis and Characterization of Macromonomers 54
21 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 54
22 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
221 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
222 Synthesis of Poly (13-dioxolane) Macromonomers helliphelliphelliphellip 57
223 Synthesis of Poly (13-dioxolane) Hydrogel Network helliphelliphellip 57
23 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
231 Raman Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
232 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
233 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
234 Swelling Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
235 Rheological Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
24 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
241 Structural Characterization of Macromonomers helliphelliphelliphelliphellip 59
242 Molecular Weight Determination helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62
243 Swelling of Poly (13 Dioxolane) Hydrogel helliphelliphelliphelliphelliphelliphellip 63
244 Viscoelastic Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 64
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 67
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 68
CHAPTER III Synthesis and Characterization of Copolymers 69
31 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 69
32 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
321 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
322 Synthesis of Poly (Styrene-g-Poly (1 3-dioxolane)) helliphelliphelliphellip 71
323 Synthesis of Poly (Methyl Methacrylate-g-Poly (1 3-dioxolane))76
33 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
331 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
332 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
333 Diffraction Scanning Calorimetry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
34 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 78
341 Structural Characterization of the Copolymers helliphelliphelliphelliphellip 78
342 Molecular Weight Determination and Copolymer Composition 80
343 Determination of Monomer Reactivity Ratios helliphelliphelliphelliphelliphellip 84
344 Glass Transition Temperatures helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 89
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 93
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
41 Background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
411 Physical Blends helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
412 Equilibrium Phase Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
413 Compatibilization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 97
414 Incorporation of Copolymers for Compatibilization helliphelliphellip 98
415 The Effect of Compatibilizer on a Blend helliphelliphelliphelliphelliphelliphelliphellip 99
416 Methods of Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 100
42 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
421 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
422 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
43 Characterization Techniques for Compatibilization helliphelliphelliphelliphelliphelliphelliphellip 102
431 Dilute Solution Viscometric Measurements helliphelliphelliphelliphelliphelliphellip 102
432 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
433 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
44 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
441 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphellip 104
442 Study of Compatibilization by Dilute Solution Viscometry hellip 106
443 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 116
444 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 118
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 124
References helliphelliphelliphelliphelliphellip helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 125
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g- Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
51 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 127
52 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
521 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
522 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
53 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
531 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
532 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
533 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
54 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
541 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphelliphellip 129
542 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 131
543 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 136
544 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 137
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 144
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 145 CONCLUSIONS helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 146
SUMMARY
Research and development performed on synthetic polymers during the last century has led to
many classes of different polymers for specific applications New types of synthetic polymers
with tailor-made properties are still being introduced for new applications The challenge for
polymer chemists is to control and alter the polymerization conditions such that the final
product has a well-defined structure with desired properties The complex structure of
polymers requires continued analytical chemical efforts to understand the polymerisation
process and the relationships between the molecular structure and material properties
The central point of this thesis is the synthesis and the exploration of the benefits of graft
copolymers derived from poly (1 3 dioxolane) (PDXL) as compatibilizing agents via their
incorporation in immiscible polymer blends The enhancement of adhesion in the solid state
can be accomplished by introducing a compatibilizer that can act as an adhesive between two
polymers andor by control of morphology especially by inducing the phase co-continuity
Graft copolymers offer all Properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheological control i e it
leads to decreased melt viscosities which is an important advantage for processing Depending
on the nature of their backbone and side chains they can be used for a wide variety of
applications such as impact-resistant plastics thermoplastic elastomers polymeric
emulsifiers and even more exciting is the ability of these graft copolymers to function as
compatibilizersinterfacial agents to blends immiscible polymers
The state-of-the-art technique to synthesize graft copolymers is the copolymerization of
macromonomers with low molecular weight comonomers It allows the control of the
polymeric structure which is given by three parameters (i) chains length of the side chains
which can be controlled by the synthesis of macromonomers by living polymerization (ii)
chain length of the backbone which can be controlled in a living polymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular-weight monomer
i
New properties lower prices and reuse of polymers are needed to meet demands of todayrsquos
society and hence of the polymer industry Unfortunately the demands for many applications
need a set of properties that no polymers can fulfil One method to satisfy these demands is by
mixing two or more polymers Materials made from two polymers mixed are called blends In
recent years blending of polymers as a means of combining the useful properties of different
materials to meet new market applications with minimum development cost offers an
interesting route to improve a variety of specific properties of the thermoplastics This has
been increasingly used by the polymer industry
Much work has been done on the blending (mixing) of polymers by many authors A large
part of these studies deal with attempts to obtain a combination of properties of different
polymers Unfortunately these properties of the polymer blends are usually worse instead of
better for many combinations of polymers Significance for these properties is compatibility
between the different polymers which is frequently defined as miscibility on a molecular scale
of the blends components The incorporation of a dispersed phase into a matrix mostly leads
to the presence of stress concentrations and weak interfaces arising from poor mechanical
coupling between phases and therefore morphologies with coarseness commonly on
micrometer scale are obtained Improving mechanical and morphological properties of an
immiscible blend is often done by compatibilization which is a process of modification of the
interfacial properties in immiscible polymer blend resulting in reduction of the interfacial
tension coefficient formation and stabilisation of the desired morphology The use of graft or
block copolymers as compatibilizers for immiscible polymer blends has become an efficient
means for development of new high-performance polymer materials There have been
numerous techniques of studying the miscibility of the polymeric blends The most useful
techniques are viscosimetry measurementsiiiiii thermal analysisiv dynamic mechanical
analysisv refractive indexvi nuclear magnetic resonance methodvii scanning electronviii and
optical spectroscopyix
i Z Sun W Wang and Z Fung Eur Polym J 28 (1992) 1259 ii Aroguz AZ and Baysal BM Eur Polym J42 3 (2006) 11ndash5iii Zhang Y Qian J Ke Z Zhu X Bi H and Nie K Eur Polym J 38 (2002) 333ndash7 iv M Song and F Long Eur Polym J 27 (1991) 983 v Olabisi O Rebeson LM and Shaw MT Polymerndashpolymer miscibility New York Academic Press (1979) vi AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 vii EG Crispim ITA Schuquel AF Rubira and EC Muniz Polymer 41 (3) (2000) 933 viii Martin IG Roleister KH Rosenau R and Koningsveld RJ Polym Sci Part B Polym Phys24 (1986) 723 ix W Wu X Luo D Ma Eur Polym J 35 (1999) 985
ii
Well-known examples of commercial blends are high impact polystyrene (HIPS) and
acrylonitrile-butadiene-styrene (ABS) These blends are tough and have good processability
One of the most interesting examples of an amorphous polymer is polystyrene because of its
brittleness Adding a compatibilizer with the structure of a copolymer to
Polystyrenepolyethylene (PSPE) improves the toughness by a factor 3x Another example is
the use of poly (styrene-co-methacrylic acid) as a compatibilizer in immiscible (incompatible)
blends of PS and polyethylene (PEG)xi
It is of great interest to study miscibility and phase behaviour of two different commodity
immiscible polymer blend systems as PSPEG and polymethyl methacrylate polyethylene
glycol (PMMAPEG) by adding poly (styrene-g-PDXL) and poly (methyl methacrylate-
PDXL) copolymers as compatibilizers respectively Firstly these systems consist of a very
rigid amorphous component (styrene andor PMMA) and a very flexible low-melting point
PEG The extremely high difference of glass transition temperatures (Tg) between the
components motivates us to investigate the phase behaviour of the blends via
compatibilization with prepared grafted copolymers
The first part of the thesis is devoted to the synthesis and characterization of amphiphilic graft
copolymers which were prepared in solution by radical polymerization of hydrophilic poly (1
3 dioxolane) macromonomers as side chains and hydrophobic comonomers such as styrene
and methyl methacrylate as backbone The second part of the thesis describes the blends
preparation and the study of the compatibilization effect of the incorporated amphiphilic graft
copolymers on immiscible (incompatible) blends
The research work in this thesis is presented through several chapters described as follows
Chapter I is a bibliographic survey on polymerization reactions involved in the thesis
Literature concerning the poly (1 3 dioxolane) was included
Chapter II describes the synthesis of poly (1 3 dioxolane) macromonomers and their
characterization As an aside research poly (1 3 dioxolane) network was obtained and the
x E Kroeze thesisUniversity of Groningen (1997) xi Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polym Journal 37 (2001) 1837-1842
iii
swelling and rheological behaviours of this network were discussed and included in this
chapter
Chapter III deals with the synthesis of a series of amphiphilic graft copolymers based on
polystyrene and methyl methacrylate as backbone with poly (1 3 dioxolane) macromonomers
as grafts in this study Selection of proper reaction conditions in terms of overall monomer
concentration and monomer molar ratio were investigated in order to prevent crosslinking
reactions due to the presence of bis-functional poly (1 3 dioxolane) macromonomers
The structure and composition of the graft copolymers were determined by Size Exclusion
Chromatography (SEC) technique and Proton Nuclear Magnetic Resonance (1H-NMR)
analysis Also Modulated Temperature Differential Scanning Calorimeter (MTDSC) was used
for thermal analysis to study the influence of poly (1 3 dioxolane) content on the glass
transition temperature of the copolymers
Last but not the least Chapter IV and Chapter V deal with the most important part of the
thesis which is the study of the compatibilization effect of the prepared copolymers
incorporated in two different immiscible blend systems These two chapters describe first
the polymers used as blend components and also polyblends preparation was discussed The
phase behavior and compatibilization of these polyblends were studied at a composition
of 5050 for both PSPEG and PMMAPEG systems Various amounts of copolymers were
incorporated to the so-called blends for compatibilization The techniques used for this study
were optical microscopy (OM) to analyze their morphology and Fourier-Transform Infra-Red
(FTIR) spectroscopy used to detect the intermolecular interactions in the blends In addition
viscometric method which is a simple inexpensive and sensitive analytical technique and also
alternative to other methods was used The application of the dilute-solution viscosity (DSV)
method for the study of interactions and miscibility of the polymeric system has been
described in more details in these chapters
Conclusions have been made on copolymer characterizations in terms of mostly monomer
reactivity and indeed on compatibilizing effect of these copolymers on the selected polymer
blends This study provides interesting results which can be useful for the development
nanoporous materials
iv
REacuteSUMEacute
La recherche et le deacuteveloppement faits sur des polymegraveres syntheacutetiques pendant le dernier siegravecle
ont abouti agrave plusieurs types de polymegraveres pour des applications speacutecifiques Les nouveaux
polymegraveres syntheacutetiques avec des proprieacuteteacutes faites sur mesure sont toujours introduits pour de
nouvelles applications Le deacutefi pour les chimistes en polymegraveres est de controcircler et drsquoalteacuterer les
conditions de polymeacuterisation de telle sorte que le produit final ait une structure bien deacutefinie avec
des proprieacuteteacutes souhaiteacutees La structure complexe de polymegraveres exige des efforts continus en
chimie analytique pour comprendre le processus de polymeacuterisation et les relations entre la
structure moleacuteculaire et les proprieacuteteacutes des mateacuteriaux
Le centre drsquointeacuterecirct de cette thegravese est la synthegravese et lexploration des avantages des copolymegraveres
greffeacutes deacuteriveacutes agrave partir du poly (1 3 dioxolane) (PDXL) utiliseacutes comme agents compatibilisant
via leur incorporation dans des meacutelanges de polymegraveres non miscibles Lrsquoameacutelioration drsquoadheacutesion
agrave lrsquoeacutetat solide peut ecirctre accomplie en introduisant un compatibilisant qui peut agir comme un
adheacutesif entre deux polymegraveres et ou par le controcircle de la morphologie particuliegraverement en
incitant la co-continuiteacute des phases Les copolymegraveres greffeacutes offrent toutes les proprieacuteteacutes des
copolymegraveres en blocs mais sont toujours plus facile agrave syntheacutetiser De plus la structure ramifieacutee
offre des possibiliteacutes importantes dans le controcircle rheacuteologique cest-agrave-dire elle aide la
diminution de la viscositeacute qui est un avantage important pour la transformation Selon la nature
de la chaicircne principale et des chaicircnes lateacuterales ces copolymegraveres peuvent ecirctre employeacutes pour une
grande varieacuteteacute drsquoapplications comme plastiques reacutesistants au choc elastomers thermoplastiques
des polymegraveres eacutemulsifiants et mecircme plus inteacuteressant est la possibiliteacute de ces copolymegraveres greffeacutes
de fonctionner comme compatibilisant agents drsquointerface aux meacutelanges des polymegraveres non
miscibles
La technique la plus sophistiqueacutee pour syntheacutetiser les copolymegraveres greffeacutes est la
copolymeacuterisation de macromonomegraveres avec des comonomegraveres agrave faible masse moleacuteculaire Elle
permet le controcircle de la structure polymeacuterique par trois paramegravetres (i) la longueur des chaicircnes
lateacuterales qui peut ecirctre controcircleacutee par la synthegravese de macromonomegraveres par la polymeacuterisation
v
vivante (ii) la longueur de chaicircne principale qui peut ecirctre controcircleacutee dans une polymeacuterisation
vivante (iii) espacement moyen des chaicircnes lateacuterales qui est deacutetermineacute par le rapport molaire des
comonomegraveres et taux de reacuteactiviteacute du monomegravere agrave faible masse moleacuteculaire
De nouvelles proprieacuteteacutes des prix bas et la reacuteutilisation de polymegraveres sont neacutecessaires pour
reacutepondre aux demandes de la socieacuteteacute daujourdhui et agrave lindustrie de polymegraveres
Malheureusement ces demandes pour un grand nombre drsquoapplications ont besoin dun jeu de
proprieacuteteacutes quaucun polymegravere ne peut accomplir Une meacutethode de satisfaire ces demandes est en
meacutelangeant deux polymegraveres ou plus Les mateacuteriaux obtenus agrave partir de meacutelanges de deux
polymegraveres meacutelangeacutes sont appeleacutes meacutelanges (Blends) Ces derniegraveres anneacutees le meacutelange de
polymegraveres comme moyen de combiner les proprieacuteteacutes utiles de diffeacuterents mateacuteriaux pour
rencontrer un marcheacute de nouvelles applications agrave un coucirct minimal offre un itineacuteraire inteacuteressant
pour ameacuteliorer une varieacuteteacute des proprieacuteteacutes speacutecifiques des polymegraveres thermoplastiques Cela a eacuteteacute
de plus en plus employeacute par lindustrie des polymegraveres
Beaucoup de travaux ont eacuteteacute faits par plusieurs auteurs sur le meacutelange de polymegraveres Une grande
partie de ces eacutetudes sont dirigeacutees pour obtenir une combinaison des proprieacuteteacutes de diffeacuterents
polymegraveres Malheureusement ces proprieacuteteacutes des meacutelanges de polymegravere sont souvent plus
mauvaises que preacutevues pour la plupart des combinaisons de polymegraveres La signification de ces
proprieacuteteacutes est la compatibiliteacute entre les diffeacuterents polymegraveres qui est freacutequemment deacutefinie comme
la miscibiliteacute agrave lrsquoeacutechelle moleacuteculaire des composants du meacutelange Lincorporation dune phase
disperseacutee dans une matrice provoque surtout la preacutesence de contraintes et des interfaces faibles
qui reacutesultent du faible meacutelange meacutecanique entre les deux phases Lameacutelioration des proprieacuteteacutes
meacutecaniques et morphologiques dun meacutelange non miscible est souvent faite par compatibilisation
qui est un processus de modification des proprieacuteteacutes superficielle dans les meacutelanges de polymegraveres
non miscibles aboutissant agrave la reacuteduction du coefficient de tension superficielle la formation et
stabiliteacute de la morphologie deacutesireacutee Lutilisation des copolymegraveres greffeacutes ou agrave blocs comme
compatibilisant pour des meacutelanges de polymegraveres non miscibles est devenue un moyen efficace
pour le deacuteveloppement de nouveaux mateacuteriaux plus performant Il y a eu de nombreuses
techniques pour lrsquoeacutetude de la miscibiliteacute des meacutelanges polymeacuteriques Les techniques les plus
vi
utiles sont les mesures viscomeacutetriques analyses thermiques analyses meacutecaniques indice de
reacutefraction la reacutesonance magneacutetique nucleacuteaire microscopes optique et eacutelectroniques agrave balayage
Les exemples de meacutelanges commerciaux tregraves bien connus sont le polystyregravene choc (HIPS) et
acrylonitrile-butadiene-styrene (ABS) Ces meacutelanges sont durs et ont bon processability Un
exemple de polymegraveres amorphes le plus inteacuteressant est le polystyregravene agrave cause de sa fragiliteacute
Laddition dun compatibilisant ayant la structure dun copolymegravere au meacutelange de Polystyregravene
polyeacutethylegravene (PSPE) ameacuteliore la dureteacute par un facteur de 3 Un autre exemple est lutilisation du
poly (styrene-co-acide meacutethacrylique) comme compatibilisant dans les meacutelanges non miscibles
de PS et le poly (eacutethylegravene glycol)
Il est tregraves important drsquoeacutetudier la miscibiliteacute et le comportement des phases de deux diffeacuterents
meacutelanges de polymegraveres commerciaux non miscibles (incompatibles) comme le
polystyregravenepolyeacutethylegravene glycol (PSPEG) et le polymeacutethacrylate de meacutethylepolyeacutethylegravene glycol
(PMMAPEG) en incorporant des copolymegraveres tels que (styrene-g-PDXL) et de (meacutethacrylate de
meacutethyle-PDXL) comme compatibilisant respectivement Premiegraverement lrsquoun des composants de
ces systegravemes est amorphe et tregraves rigide (le styregravene etou PMMA) et lrsquoautre (PEG) est flexible et
mou ayant un point de fusion tregraves faible Vu lrsquoextrecircme eacutecart entre les deux tempeacuteratures de
transition vitreuse (Tg) des composants de ces meacutelanges cela nous a motiveacute pour eacutetudier le
comportement de ces meacutelanges via compatibilisation avec des copolymegraveres greffeacutes preacutepareacutes par
nous mecircme
La premiegravere partie de la thegravese est consacreacute agrave la synthegravese et agrave la caracteacuterisation de copolymegraveres
greffeacutes amphiphiles preacutepareacutes en solution par la polymeacuterisation radicale des macromonomers
(poly (1 3 dioxolane)) hydrophiles comme des chaicircnes lateacuterales (greffons) avec des
comonomegraveres hydrophobes comme le styregravene et le meacutethyle methacrylate comme chaicircne
principale La deuxiegraveme partie de la thegravese couvre la preacuteparation des meacutelanges et leacutetude de leffet
de compatibilisant des copolymegraveres greffeacutes amphiphiles sur les meacutelanges non miscibles
(incompatibles)
La recherche concernant cette thegravese est preacutesenteacute par plusieurs chapitres deacutecrits comme suit
vii
Le chapitre I est une recherche bibliographique sur les reacuteactions de polymeacuterisations impliqueacutees
dans la thegravese La Litteacuterature concernant le poly (1 3 dioxolane) est inclue
Le chapitre II deacutecrit la synthegravese des macromonomegraveres du poly (1 3 dioxolane) et leurs
caracteacuterisations Une recherche suppleacutementaire a eacuteteacute effectueacutee concernant la synthegravese drsquoun reacuteseau
tridimensionnel du poly (1 3 dioxolane) Une eacutetude sur les comportements gonflant et
rheacuteologique de ce reacuteseau ont eacuteteacute discuteacutes et inclus dans ce chapitre
Le chapitre III preacutesente la synthegravese dune seacuterie de copolymegraveres greffeacutes amphiphiles constitueacutes de
polystyregravene ou methacrylate de meacutethyle comme chaicircne principale et de macromonomers du poly
(1 3 dioxolane) comme greffons dans cette eacutetude Le choix de conditions de reacuteaction approprieacutees
en termes de concentration totale et le rapport molaire des monomegraveres ont eacuteteacute bien eacutetudieacutes pour
empecirccher les reacuteactions de reacuteticulation agrave cause de la preacutesence de macromonomegraveres bis-
fonctionnel de poly (1 3 dioxolane)
La structure et la composition des copolymegraveres greffeacutes ont eacuteteacute deacutetermineacutees par la technique de la
Chromatographie dExclusion steacuterique (CES) et la spectroscopie en Reacutesonance Magneacutetique
Nucleacuteaire de Proton (1H-NMR) Aussi la Calorimeacutetrie Diffeacuterentielle agrave balayage agrave Temperature
Moduleacutee Calorimeacutetrie (MTDSC) a eacuteteacute employeacute pour lanalyse thermique et pour eacutetudier
linfluence de la proportion du poly (1 3 dioxolane) dans les copolymegraveres sur leur tempeacuterature
de transition vitreuse
Derniers mais pas le moindre les deux Chapitre IV et le Chapitre V couvrent la partie la plus
importante de la thegravese qui est leacutetude de leffet de compatibilisant de ces copolymegraveres preacutepareacutes et
incorporeacutes dans deux diffeacuterents systegravemes de meacutelanges non miscibles (incompatibles) Ces deux
chapitres deacutecrivent dabord les polymegraveres employeacutes comme composants des meacutelanges agrave eacutetudier et
aussi la preacuteparation de ces meacutelanges a eacuteteacute deacutecrite Le comportement de phase et la
compatibilisation des meacutelanges de PSPEG et PMMAPEG agrave une composition de 5050 Des
quantiteacutes diffeacuterentes de copolymegraveres ont eacuteteacute incorporeacutees aux meacutelanges Les techniques
employeacutees pour cette eacutetude sont la microscopie optique (OM) pour analyser leur morphologie et
la spectroscopie agrave Transformeacutee de Fourier Infrarouge (FTIR) pour deacutetecter les interactions
viii
intermoleacuteculaires dans les meacutelanges De plus la meacutethode viscomeacutetrique qui est une technique
simple peu coucircteuse et tregraves sensible a eacuteteacute employeacutee Lrsquoutilisation de la meacutethode de la viscositeacute de
solution dilueacutee (DSV) pour leacutetude dinteractions et la miscibiliteacute du systegraveme polymegravere a eacuteteacute
deacutecrite plus en deacutetail dans ces chapitres
Les conclusions ont eacuteteacute faites sur la caracteacuterisation des copolymegraveres en termes de surtout de la
reacuteactiviteacute des monomegraveres et bien entendu sur leffet compatibilisant de ces copolymegraveres sur les
meacutelanges de polymegraveres qui ont choisis Cette eacutetude fournit des reacutesultats inteacuteressants qui peuvent
ecirctre utiles pour le deacuteveloppement des mateacuteriaux nanoporeux
ix
CHAPTER I Literature Review
11 Macromonomer Interest and Synthesis
Macromonomers bearing polymerizable end groups have received considerable interest
during the last two decades and become a useful tool for the preparation of a variety of graft
copolymers with well-defined structure and composition and polymer networks The
macromonomer method for preparing graft copolymers consists of preparing branches first
followed by the preparation of the grafted structure through the addition of the comonomer to
the macromonomer branch1 2
Therefore macromonomers become the side chains in the graft copolymer with well-defined
length and molecular weight As a sequence the molecular structure of the copolymer can be
determined depending on the amount of macromonomer incorporated and the reactivity of the
end groups
Macromonomers which are linear macromolecules carrying polymerizable functions at one or
two chain ends have been prepared by all polymerization mechanisms anionic cationic free-
radical polyaddition and polycondensation while the polymerizable end groups have been
introduced during the initiation termination or chain transfer steps or by modification of end
groups of telechelic oligomers3
Among the polymerization mechanisms mentioned above the ionic ones allow the best
control of molecular weight polydispersity and functionality of the macromonomers
However they require very demanding experimental conditions like high purity of monomers
and solvents complete absence of moisture and other acidic impurities inert atmosphere etc
Whereas free-radical methods which involve less severe working conditions are largely
used even though the control over the properties of the macromonomers is lower3 For
instance polymers of epoxides tetrahydofuran and cyclic siloxanes are commercially
produced by cationic ring-opening polymerization The history of ring-opening
polymerization of cyclic monomers is shorter than that of the vinyl polymerization and
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422
1
polycondensation With ring-opening functional groups can be introduced into the main chain
of the polymer This polymer cannot be prepared by vinyl polymerization4
Milkovich first developed synthesis of graft polymer with uniform grafts via macromonomer
technique5 Schulz and Milkovich6 reported the synthesis of polystyrene macromonmers
through termination of living PS anions with methacryloyl chloride and their
copolymerization with butyl acrylate and ethyl acrylate
Candau Rempp et al7 obtained PS-g-PEO by reaction between living monofunctional PEO
and partly chloromethacrylated PS backbone (scheme 1) Characterization of the products by
light scattering GPC UV and NMR spectroscopy showed a high degree of grafting
Scheme 1
Ito et al8 used a macromonomer technique to obtain graft copolymers with uniform side
chains They synthesized a graft copolymer of PS with uniform PEO side chains through
copolymerization of styrene and PEO macromonomer (scheme 2) They obtained PEO
macromonomers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-
vinyl benzyl chloride as terminating agent An apparent decrease in reactivities of both poly
(ethylene oxide) of macromonomers and comonomers was ascribed to the thermodynamic
repulsion between the macromonomer and the backbone9
4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348
2
Scheme 2
This type graft copolymers of styrene and ethylene oxide was also obtained by Xie et al10
through copolymerization of styrene with PEO macromonomer prepared by anionic
polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydofuran as
initiator followed by termination with methacryloyl chloride
The method of macromonomer synthesis developed by Xie et al11 has the advantage of
shorter reaction time and a larger range of molecular weight of the PEO macromonomer than
the usual method using potassium alcoholate as initiator PEO macromonomers with
molecular weight from 2 103 to 3 104 and MwMn = 107 ndash 112 can be obtained by this
method12
Only Xie and coworkers have published reports concerning the synthesis of copolymers with
uniform PS grafts obtained through copolymerization of epoxy ether terminated polystyrene
macromonomer with EO13 using a quaternary catalyst composed of triisobutyl-aluminium-
phosphoric acid-water-tertiary amine14 and epichlorohydrin (ECH)15
Free radical polymerization technique has also provided well-defined macromonomers of
poly (acrylic acid)16 vinyl benzyl-terminated polystyrene17 18 poly (t-butyl methacrylate)19
and poly (vinyl acetate)20
Recently Matyjaszewski et al21 employed atom-transfer radical polymerization (ATRP) to
prepare well-defined vinyl acetate terminated PS macromonomers Taking advantage of the
10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp (1985) 461 Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823
3
extremely low reactivity of polystyryl radical towards the vinyl acetate double bond they
used vinyl chloroacetate to initiate the polymerization of styrene to produce the desired
macromonomers This concept has been used similarly in the preparation of a vinyl acetate-
terminated PS macromonomers3 by conventional free-radical polymerization by employing
vinyl iodoacetate as a chain transfer agent possessing a double bond which does not
copolymerize with the monomer that forms the backbone of the macromonomer
12 Ring-Opening Polymerization Overview
Ring-opening polymerization (ROP) is a unique polymerization process in which a cyclic
monomer is opened to generate a linear polymer It is fundamentally different from a
condensation polymerization in that there is no small molecule by-product during the
polymerization Polymers with a wide variety of functional groups can be produced by ring-
opening polymerizations Ring-opening polymerization can proceed through a number of
different mechanisms depending on the type of monomer and catalyst involved Of the wide
range of polymers produced via ROP some have gained industrial significance for example
poly (caprolactam) and poly (ethylene oxide)22 ROP of cyclic esters such as ε-caprolactone
(CL) and L L-dilactide is gaining industrial interest due to their degradability23 The
mechanisms of interest in this work are coordination insertion and cationic
121 Polymerizability of Cyclic Compounds
The thermodynamic polymerizability of a cyclic monomer has been elegantly summarized by
Ivin24 Negative free energy change from monomer to polymer is the thermodynamic driving
force for the ring-opening
ΔG = ΔH ndash T ΔS
For small sized cyclic compounds the enthalpy term is negative and dominant The strains in
bond angles and bond lengths are released upon ring opening Such monomers can be almost
completely converted to polymers For medium sized cyclic monomers (5-7 membered rings)
the ring strain is small and the entropy is a small positive term Thus the overall driving force
(ΔG) is small and the extent of polymerization is little or no reaction For 8- 9- and 10-
22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991)
4
membered monomers the enthalpy term is dominant and negative while the TΔS term is
relatively small The strain is due to the non-bonded interactions between atoms Essentially
complete conversion to polymer is possible When the ring size is very large and there is
virtually no ring-strain (ΔH ne 0) the driving force for ring-opening polymerization is the
large increase of entropy The polymerization should be an athermal process
Why not make polyethylene
In principle one could synthesize polyethylene from cyclohexane
There are two good reasons why this reaction cannot be performed
bull (Kinetic) Cyclohexane lacks any reactive functionality to get hold of
bull (Thermodynamic) Simple six membered rings are extremely stable
Free Energy (ΔG) of Polymerization for Cycloalkanes
The thermodynamic considerations for ring opening are illustrated by this graph (scheme 3) of
free energy (hypothetical) of polymerization from cycloalkanes with various ring sizes to
polyethylene (The two membered ring actually shows the data for ethylene CH2 = CH2)
Scheme 3
5
Three and four membered rings are quite strained so ring opening to polyethylene is
favorable if a suitable reaction pathway existed (Unfortunately no such reaction is known)
Six membered rings are stable so they can rarely be polymerized by ring opening Five and
seven membered rings are borderline cases so sometimes these can be polymerized Larger
rings have transanular steric interactions that cause some strain so rings of 8 members or
more can usually be polymerized Of course this graph changes when substitutions are made
to the rings (for example the presence of heteroatoms like O S and N or the introduction of
double bonds) However the graph for the simplest possible rings illustrates the trends in
other systems reasonably well
Even if the ring opening reaction is thermodynamically favorable there must be reaction
chemistry to get there In most cases the initiators used for ring opening polymerization are
polar or ionic species so the monomers must have groups that can react The most common
monomers for ring opening polymerization contain some kind of heteroatom in the ring as in
the examples of cyclic ethers esters amines amides etc At one extreme there are examples
such as the cyclic phosphazene shown that contain no carbon or hydrogen at all At the other
extreme just a carbon-carbon double bond will suffice for ring opening metathesis
polymerization as illustrated by norbornene
122 Mechanisms of Ring-opening Polymerization
In addition to the thermodynamic criterion there must be a kinetic pathway for the ring to
open and undergo the polymerization reaction Therefore the kinetics of the ring-opening of
the monomer should also be considered Ring-opening polymerization (ROP) can proceed
through a number of different mechanisms depending on the type of monomer and catalyst
involved Of the wide range of polymers produced via ROP some have gained industrial
significance for example poly (caprolactam) and poly (ethylene oxide)24 25 A variety of
mechanisms operate for ring-opening polymerizations including anionic cationic metathesis
and free radical mechanisms Examples of various ring-opening polymerizations are shown in
scheme 4
25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984)
6
Scheme 4
123 Cationic Ring-Opening Polymerization of Heterocycles
A broad range of heterocyclic compounds can undergo cationic ring-opening polymerization
(CROP)26 CROP propagates either through an activated monomer or an activated chain end
mechanism In both cases the propagation involves the formation of a positively charged
species27 A major drawback of CROP is the occurrence of unwanted side reactions thus
limiting the molecular weight of the final product2829 The cationic ring-opening
polymerization of heterocycles has become of significant importance in polymer synthesis
due in part to the diverse variety of functionalized materials that can be prepared by this
method including natural andor biodegradable polymers30 31
Systematic studies of this type of polymerization started around the nineteen sixties Since
then several groups are involved in the kinetics reaction mechanisms and thermodynamics of
the ring-opening polymerization mostly of tetrahydofuran and dioxolane During the last
26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996) (b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993) (c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice (d) Mishra M K Ed Polymer Frontiers New York (1994) 391 31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159
7
years many papers on the synthesis and polymerization of several other cyclic ethers
monocyclic and bicyclic acetals have been published32 33
Examples of commercially important polymers which are synthesized via ring-opening
polymerization are summarized in scheme 5 include such common polymers as
polyoxyethylene (POE 4) poly (butylene oxide) (PBO 5) nylon 6 (6) and poly
(ethyleneimine) (7)
Scheme 5
The synthesis of ring-opened heterocycles is often mediated by compounds whose role is to
initiate the polymerization process This provides less opportunity to ldquotunerdquo polyheterocycle
properties through catalyst choice and has stimulated research to develop initiators which
function beyond the simple activation of polymerization such as living polymerization
initiators343536 chiral initiators3738 enzyme initiators39 and ring-opening insertion
systems4041 The cationic ring-opening polymerization involves the formation of a positively
32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N Macromolecules 26 (1993) 7134
8
charged species which is subsequently attacked by a monomer The attack results in a ring-
opening of the positively charged species Ethylene oxide can be polymerized by cationic
initiators as well (scheme 6)
Scheme 6
13 Cationic Polymerization of Cyclic Acetals
Acetal polymers also known as polyoxymethylene (POM) or polyacetal are formaldehyde-
based thermoplastics that have been commercially available for over 40 years
Polyformaldehyde is a thermally unstable material that decomposes on heating to yield
formaldehyde gas Two methods of stabilizing polyformaldehyde for use as an engineering
polymer were developed and introduced by DuPont in 1959 and Celanese in 1962
DuPonts route for polyacetal yields a homopolymer through the condensation reaction of
polyformaldehyde and acetic acid (or acetic anhydride)
The Celanese route for the production of polyacetal yields a more stable copolymer product
via the reaction of trioxane a cyclic trimer of formaldehyde and a cyclic ether (eg ethylene
oxide or 13 dioxolane)
9
The improved thermal and chemical stability of the copolymer versus the homopolymer is a
result of randomly distributed oxyethylene groups These groups offer stability to oxidative
thermal acidic and alkaline attack The raw copolymer is hydrolyzed to an oxyethylene end
cap to provide thermally stable polyacetal copolymer Polyacetals are subject to oxidative and
acidic degradation which leads to molecular weight deterioration Once the chain of the
homopolymer is ruptured by such an attack the exposed polyformaldehyde ends decompose
to formaldehyde and acetic acid Deterioration in the copolymer ceases however when one
of the randomly distributed oxyethylene linkages is reached42
Cationic polymerization of cyclic acetals exhibits some special features which makes this
system distinctly different from cationic polymerization of simple heterocyclic monomers for
instance cyclic ethers Linear acetals (including polyacetals) are more basic (nucleophilic)
than cyclic ones thus when polymer starts to form it does not constitute a neutral component
of the system but participates effectively in transacetalization reactions which lead to
redistribution of molecular weights and formation of a cyclic fraction These processes which
are usually described by the term ldquoscramblingrdquo have been studied by several authors43 44
Cationic polymerizations of heterocyclic monomers are initiated as in cationic
polymerization of vinylic monomers by electrophilic agents such as the protonic acids (HCl
H2SO4 HClO4 etc) Lewis acids which are electron acceptors by definition and compounds
capable of generating carbonium ions can also initiate polymerization Examples of Lewis
acids are AlCl3 SnCl4 BF3 TiCl4 AgClO4 and I2 Lewis acid initiators required a co-
initiator such as H2O or an organic halogen compound Initiation by Lewis acids either
requires or proceeds faster in the presence of either a proton donor (protogen) such as water
alcohol and organic acids or a cation donor (cationogen) such as t-butyl chloride or
triphenylmethyl fluoride
The polymerization of a heterocyclic monomer initiated by a protonic acid usually starts with
opening of the monomer ring via oxonium sites that are formed upon alkylation (or
protonation) of the monomer
42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144
10
Protonation
BF3 H2O H BF3 OH+ +O
O
Acylation
R CO SbF6 +
OR CO O SbF6
Alkylation
Et3O BF4 +
OC2H5 Et2O BF4O +
Hydrogen transfer
C SbF6 +O
C SbF6H O+
SbF6
O + O O+ H O SbF6
In general initiation step can be shown as
A+
R O++R A O
The mechanism of chain growth involves nucleophilic attack of the oxygen of an incoming
monomer onto a carbon atom in α-position with respect to the oxonium site whereby the
cycle opens and the site is reformed on the attacking unit
A+O
O(CH2)4
O
A+O(CH2)4
Growing chain terminates with nucleophilic species as shown below
O (CH2)4 O+[ ]n
A O (CH2)4[ ]n
AO ( CH2 )4
11
Triflic initiators like trifluoromethane sulfonic acid derivatives can also be employed as an
initiator in the cationic polymerization of heterocyclics in this case initiation step follows
alkylation mechanism
CF3 SO3CH3 +O
CH3 CF3SO3O
CH3 O
CF3SO3
+ O CH3O(CH2)4 O CF3SO3
Ion pairs are in equilibrium with the ester form
(CH2)4 O CF3SO3 (CH2)4 O(CH2)4 O SO2CF3
If instead of ester triflic anhydride is used as initiator the same reaction can occur at both
chain ends and anhydride behaves as a bifunctional initiator
CF3SO2OSO2CF3 nO
+ CF3SO2 O (CH2)4 O (CH2)4 O SO2CF3n-1
(CH2)4 O (CH2)4 n-3
O O CF3SO3 CF3SO3
In the case of living cationic polymerization the growing sites are long living provided the
reaction medium does not contain any transfer agents such as alcohols ethers amines or
acids The reaction mechanism then involves only initiation and propagation steps and the
polymers formed are living The active sites are deactivated by addition of an adequate
nucleophile such as excess water tertiary amines alkoxides phenolates or lithium bromide
12
O(CH2)4
SbF6
(CH2)4 O(CH2)4 OH H
NR3
++ H2O
SbF6
+(CH2)4 O(CH2)4 NR3 SbF6
ONa+(CH2)4 O(CH2)4 O + NaSbF6
+ LiBr
(CH2)4 O(CH2)4 Br LiSbF6+
However facts concerning the real mechanism are scarce In order to progress further in
understanding the cationic polymerization of heterocycles initiated with a Bronsted acid
kinetic studies of simple ring-opening reactions of heterocyclic monomer rings by acids in
nonpolar aprotic and nonbasic solvents (inert solvents) have been performed45
14 Synthesis of Functionalized Poly (1 3-Dioxolane)
1 3-Dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer ends ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The molecular weight of the linear polymers is governed by the
ratio of reacted monomer to transfer agent and is generally well controlled up to 10 000gmol
141 Reaction of 1 3-Dioxolane and Hydroxyl- Containing Compounds
Classical initiation induces polymerization through cyclic tertiary oxonium ions which are
responsible for the formation of an important quantity of cyclic oligomers48
45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon Press 3(1989) 787
13
In several preceding articles Franta et al have investigated the cationic polymerization of
cyclic acetals in the presence of a diol49 50 in particular polymerization of 13-dioxolane
(DXL) and 13-dioxepane (DXP) in the presence of an oligoether diol (αω-dihydroxy-poly
(tetrahydofuran)) or (αω-dihydroxy-poly(ethylene oxide)) In all cases a similar behavior was
observed Cyclic oligomers are present in quantities as in the case of polymerization of DXL
in the absence of hydroxyl containing compounds51
When substituted oxiranes such as propylene oxide or epichlorohydrin are polymerized
according to the ldquoActivated Monomerrdquo mechanism (AM) Cyclic oligomers can be
eliminated52 53 In the AM mechanism polymerization of ethylene oxide however the
reaction of a protonated monomer molecule with a polymer chain leads to side reactions
including cyclization by the Active Chain End (ACE) mechanism53 Thus it is not
unexpected that in the polymerization of cyclic acetals due to the higher nucleophilicity of
the linear acetals located on the chain reactions with the latter will take place
The addition of a protonated DXL onto a hydroxyl group-containing compound is
accompanied by transacetalization involving a monomer molecule
In order to shed some light on the reactions involved Franta et al54 used a monoalcohol
methanol instead of a diol The results confirmed the occurrence of the Active Monomer
mechanism but dimethoxymethane was observed evidence of transacetalization between
methanol and dioxolane
Thus in the DXL-ethylene glycol (EG) system the presence of unreacted EG is in fact due to
the following equilibria
This equation shows the stoichiometry of the reaction rather than its actual mechanism the
reaction certainly has to involve an addition product as a first step
49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154
14
In the next step transacetalization occurs
The products of transacetalization are formed fast as compared to the addition product54 This
indicates that the last reaction is not slower and probably faster than the previous one
Consequently it has been found that although polymerization of DXL in the presence of
hydroxyl group containing compounds proceeds initially by a stepwise addition of protonated
monomer to the hydroxyl terminated linear species in agreement with the AM mechanism but
already at this stage fast transacetalization proceeds leading to formation of O-CH2-O links
between two oligodiols and liberation of ethylene glycol
The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism When DXL is polymerized by strong protonic acids such as triflic acid in the
presence of a diol the PDXL chains are essentially linear and carry end-standing OH
functions Despite the occurrence of some side reactions this mechanism leads to α ω-
dihydroxy-PDXL the molecular weight of which is controlled by the molar ratio of DXL
consumed to diol introduced It has been shown that the polydispersity is on the order of 14
and that molar masses up to 10 000 gmol can be covered
142 Synthesis of Poly (1 3-Dioxolane) Macromonomers
Macromonomers are useful intermediates to prepare graft copolymers and have indeed been
used extensively In order to prepare PDXL macromonomers Franta and al54 have used p-
isopropenylbenzylic alcohol (IPA) as an initiator and triflic acid as a catalyst
The following polymeric species were identified
15
Scheme 7
A is the most abundant compound it corresponds to 50 to 60 weight-wise It is a
macromonomer
B corresponds to 20 to 25 weight-wise It carries two p-isopropenyl functions
C corresponds to 20 to 25 weight-wise It carries no p-isopropenyl function but two
hydroxyl groups
As a result preparation of PDXL macromonomers leads to the preparation of PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of transacetalization
reaction described above a mixture of products was obtained54
Kruumlger et al55 used similar method to prepare macromonomers and come out to the same
conclusions in terms of structure and claim that a clear distinction should be made between
the products obtained and the mechanism responsible for their formation
15 Amphiphilic Graft Copolymers
151 Graft Copolymers
The increasing complexity of polymer applications has required the production of materials
with varied properties Often homopolymers do not afford the scope of attributes necessary to
many applications Copolymerization allows the formulation of polymer materials with
properties characteristic of two homopolymers contained in a single copolymer material The
monomers within a copolymer can be distributed in various fashions random statistical
alternating segmented block or graft56
55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387
16
Scheme 8
Graft copolymers are similar to block copolymers in that they possess long sequences of
monomer units However graft copolymer architecture differs substantially from typical
block copolymers In graft copolymers monomer sequences are grafted or attached to points
along a main polymer chain Grafted chains generally possess molecular weights less than
that of the main chain
These side chains have constitutional or configurational features that differ from those in the
main chain57
The simplest case of a graft copolymer can be represented by A-graft-B or the arrangement
and the corresponding name is polyA-graft-polyB where the monomer named first (A in this
case) is that which supplied the backbone (main chain) units while that named second (B) is
in the side chain(s)
Typical syntheses of the grafts occur by polymerization initiated at some reactive point along
the backbone or by copolymerization of a macromonomer Polymerization from the polymer
backbone is possible via anionic cationic and radical techniques but all require some
functional unit capable of further reaction58
Well defined graft copolymers are most frequently prepared by either
a)ldquografting throughrdquo or b)ldquografting fromrdquo controlled polymerization process
57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991)
17
a) Grafting though the ldquografting throughrdquo method (or macromonomer method) is one of the
simplest ways to synthesize graft copolymers with well defined side chains
Scheme 9
Typically a low molecular weight monomer is radically copolymerized with a methacrylate
functionalized macromonomer This method permits incorporation of macromonomers
prepared by other controlled polymerization processes into a backbone prepared by a CRP
Macromonomers such as polyethylene59 60 poly (ethylene oxide)61 polysiloxanes62 poly
(lactic acid)63 and polycaprolactone64 have been incorporated into a polystyrene or poly
(methacrylate) backbone Moreover it is possible to design well-defined graft copolymers by
combining the ldquografting throughrdquo macromonomers prepared by any controlled polymerization
process and CRP65 This combination allows control of polydispersity functionality
copolymer composition backbone length branch length and branch spacing by consideration
of MM ratio in the feed and reactivity ratio Branches can be distributed homogeneously or
heterogeneously and this has a significant effect on the physical properties of the
materials6263
b) Grafting from the primary requirement for a successful grafting from reaction is a
preformed macromolecule with distributed initiating functionality
59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003) 6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778 63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998) 823-830
18
Scheme 10
Grafting-from reactions have been conducted from polyethylene66 67 polyvinylchloride68 69
and polyisobutylene70 71 The only requirement for an ATRP is distributed radically
transferable atoms along the polymer backbone The initiating sites can be incorporated by
copolymerization68 be inherent parts of the first polymer69 or incorporated in a post-
polymerization reaction70
Graft copolymers perform similar functions to block copolymers in that they contain moieties
with varying properties Compatibilization represents a major area of application for grafts
because the grafted chains can be used to solubilize a polymer blend system containing two
immiscible polymers Additionally graft copolymers offer unique solution mechanical and
morphological properties that make them ideal for utilization as viscosity modifiers and
thermoplastic elastomers72 The unique molecular architecture of graft copolymers leads to
peculiar morphological properties The chain lengths of the grafted arms and backbone block
dictate the morphology that arises in the polymer Changes in the composition of the graft
copolymer alter the resulting polymer morphology A variety of morphologies is possible
ranging from lamellar to cylindrical to spherical73
Graft copolymers offer all properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheology control
Depending on the nature of their backbone and side chains graft copolymers can be used for a
wide variety of applications such as impact-resistant plastics thermoplastic elastomers
66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996) 7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R Macromolecules 32 (1999) 1152-1158
19
compatibilizers viscosity index improvers and polymeric emulsifiers74 75 The state-of-the-
art technique to synthesize graft copolymers is the copolymerization of macromonomers
(MM) with low molecular weight monomers76 In most cases conventional radical
copolymerization has been used for this purpose Using living polymerizations for both the
synthesis of the macromonomers and for the copolymerization offers the highest possible
control of the polymer structure In all these copolymerizations beside the desired graft
copolymers with at least two side chains a number of unwanted products can be expected
unreacted macromonomer ungrafted backbone and backbone with only one graft (star
copolymer) The latter is undesirable for applications as thermoplastic elastomer
Conventional and controlled copolymerizations lead to different copolymer structures In
conventional radical copolymerization the polymers show a broad molecular weight
distribution (MWD) and chemical heterogeneity of first order
152 Amphiphilic Copolymers
A characteristic feature of an amphiphilic polymer is that it contains both hydrophilic and
hydrophobic groups This type of polymer associates in aqueous solution and exhibits several
interesting features and can be used in connection with many industrial and pharmaceutical
applications Usually there is only a few mol of the hydrophobic moieties in order to make
the polymer water-soluble Due to the hydrophobicity of the amphiphilic polymers they have
a tendency to form association structures in aqueous solution by mutual interaction andor
interaction with other cosolutes such as surfactants and colloid particles
In particular the grafting of hydrophilic species onto hydrophobic polymers is of great utility
Amphiphilic graft copolymers so prepared often display enhanced surface properties such as
improved resistance to the adsorption of oils and proteins biocompatibility and reduced static
charge buildup
The synthesis of graft copolymers based on commercial polymers is most commonly
accomplished free radically Free radicals are produced on the parent polymer chains by
exposure to ionizing radiation andor a free-radical initiator77 78 Alternatively peroxide
groups are introduced on the parent polymer by ozone treatment79 80 The resulting reactive
74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998) 696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507
20
sites serve as initiation sites for the free radical polymerization of the comonomer A
significant disadvantage of these free radical techniques is that homopolymerization of the
comonomer always occurs to some extent resulting in a product which is a mixture of graft
copolymer and homopolymer Moreover backbone degradation and gel formation can occur
as a result of uncontrolled free radical production often limiting the attainable grafting
density81 For example amphiphilic graft copolymers synthesized from PEO macromonomer
and hydrophobic comonomers82 83were found to form micellar aggregates in polar medium
such as water wateralcohol alcohol dimethylformamide These phase separation processes
take place also during polymerization and supposedly affect not only the polymerization
kinetics but also properties of resulting copolymers So far unanswered remains the question
of molecular characteristics of reaction products including homopolymers from
macromonomer or comonomer formed under both the homogeneous and heterogeneous
(micellar) reaction conditions Modern liquid chromatographic techniques allow
discrimination of polymeric constituents differing in their chemical structure andor physical
architecture Subsequently the molar mass and molar mass distribution of constituents can be
assessed Recently analyzed products of dispersion copolymerization of polyethylene oxide
methacrylate macromonomer with styrene contained rather large amount of polystyrene
homopolymer84
In the main application areas for amphiphilic polymers the solution properties are of
fundamental importance In many industrial applications association and adsorption
phenomena of the polymers in solution are design properties Consequently a deep
understanding of these phenomena is necessary for the development of new specific
chemicals and new processes The research goals are to clarify the relations between the
molecular structure of amphiphilic polymers and their properties in aqueous solution A
further goal is to develop theoretical models for the description of the behavior of amphiphilic
polymers in solution and at surfaces Several projects concern the self-assembly of
amphiphilic polymer molecules and the association behavior of surfactants and
hydrophobically modified hydrophilic polymers such as cellulose derivatives Studies of
amphiphilic model polymers such as ethylene oxide block and graft copolymers are carried
80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication
21
out in order to gain fundamental knowledge on the solution behavior of amphiphilic
polymers
16 Kinetics of Free Radical Polymerization
Free radical polymerization is the most widespread method of polymerization of vinylic
monomers Free radical polymerizations are chain reactions in which every polymer chain
grows by addition of a monomer to the terminal free radical reactive site called ldquoactive
centerrdquo The addition of the monomer to this site induces the transfer of the active center to
the newly created chain end Free radical polymerization is characterized by many attractive
features such as applicability for a wide range of polymerizable groups including styrenic
vinylic acrylic and methacrylic derivatives as well as tolerance to many solvents small
amounts of impurities and many functional groups present in the monomers
161 Kinetics of free radical addition Homo and Copolymerization
Understanding of chemical kinetics during homo- and copolymerization is crucial for
copolymer synthesis The discussion below will review the kinetics of free radical initiated
polymerizations and copolymerizations
The three main kinetic steps that occur during polymerization are (1) initiation (2)
propagation and (3) termination
1 Initiation
The initiation step is considered to involve two reactions creating the free radical active
center The first event is the production of free radicals Many methods can be used to initiate
free radical polymerizations such as thermal initiation without added initiator or high energy
radiation of the monomers However free radicals are usually generated by the addition of
initiators that form radicals when heated or irradiated Two common examples of such
compounds which afford free radicals are benzoyl peroxide (BPO) and azobisisobutyronitrile
(AIBN)
22
Figure 1 Generation of Free Radicals by Thermal Decomposition of Benzoyl Peroxide
Figure 2 Decomposition of Azobisisobutyronitrile to Form Free Radicals
Figure 1 depicts the thermal decomposition of BPO to form two oxy-radicals and Figure 2
depicts the decomposition of AIBN to form two nitrile stabilized carbon based radicals
(equation 1)
In equation 1 kd is the rate constant which describes the first order initiation process The
radical that is formed can now add to the double bond of the monomer and initiate
polymerization
The symbol M will represent the monomer and the rate constant for this process will be ki as
described in equation 2
23
Together these two reactions the radical generation and the monomer addition to the radical
form the process of initiation Usually the assumption that is taken into account is that the
first step is the rate determining step This means that the decomposition to form the radical
is much slower than the monomer addition to the free radical Therefore the equation for the
rate of radical formation ri is
The number 2 is obtained from the fact that a maximum of two radicals can be generated for
the initiation
But not all of the primary radicals produced by the decomposition of the initiator will
necessarily react with the monomer which means several other competing reactions may
occur85 Therefore in order to determine the rate of initiation the fraction of initially formed
radicals that actually start chain growth will be denoted by f and the rate of initiation equation
becomes
2 Propagation
Now the propagation of the reaction will proceed through the successive addition of
monomer to the radicals This type of process can be expressed in the following form
85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster PA (1997)
24
And further generalizing the reaction scheme gives
The assumption that the reactivity of the addition of each monomer is independent of the
chain length is evident in these two equations and was postulated by Flory 58 86 The use of
the rate constant kp for both of these equations imply that the rate constant is independent of
chain length The rate of the propagation rp of this polymerization or the rate of monomer
removal is thus given by
3 Termination
The termination of these growing radical chains occurs in principally two different ways The
first way is the formation of a new bond in between the two radicals this is called
combination Secondly the radical chains can terminate by disproportionation This is a
process where a hydrogen atom from one of the chains is transferred to the other and the chain
that the proton was removed from forms a double bond These reactions are represented as
follows
Figure 3 Termination by Combination
86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995)
25
Figure 4 Termination by Disproportionation
Schematically the reactions can be represented as follows
Where the rate constant of termination by combination is denoted by ktc and the rate constant
of termination by disproportionation is denoted by ktd Since both of these reactions use two
radical species and have the same kinetics the overall equation for the rate of termination is
written as
where kt = ktc + ktd and the number 2 imply there are two radicals that are terminated in
each termination reaction The monomer structure and the temperature are what determines
the type of termination that is most dominant in the reaction For most systems the amount of
one termination type far exceeds the other termination type
The further calculations for the rate of polymerization Rp and the degree of conversion as a
function of time can now be developed The assumption of the steady state concentration of
transient species must be used here where the transient species is the radical M For the
steady state approximation to hold true the rate at which initiation occurs ri must be equal to
the rate at which termination occurs rt or in other words radicals must be generated at the
same rate at which they are terminated This assumption gives the equation
26
This equation then gives an expression for the radical species
Experimentally this value would be difficult to measure in the laboratory and therefore this
equation must be used in the subsequent equations that follow By further substitution an
expression for the rate of polymerization Rp can be obtained because it equals the rate of
propagation
From this equation it can be deduced that the rate of polymerization is directly proportional
to the monomer concentration and to the initiator concentration to the one half power In
other words Rp is first order with regards to the monomer concentration and half order to the
initiator concentration
When the conversion is low the assumption that the initiator concentration is constant is
reasonable but the consumption of the initiator can be added into the calculations Therefore
Then integration can be performed
Finally the rate of polymerization becomes
27
This equation can be broken into three different parts
The second term indicates that the rate of polymerization is still proportional to the monomer
concentration to the first power and the initiator concentration to the one half power but the
initiator concentration is now the initial concentration Therefore by increasing the initial
concentration of an initiator in a solution polymerization the rate of the reaction should
increase proportionally to the square root of the amount of initiator added The third term
indicates that as the initiator is consumed the polymerization slows down exponentially with
time as well as its slowing down due to monomer depletion
The first term in the brackets suggests that the rate of polymerization is proportional to kp
kt12 When experiments are performed to probe the kinetics of reactions in solution the
expected first order dependence on monomer concentration is observed But when the
experiment is performed in concentrated solvents or even in the bulk the polymerization
kinetics accelerate The reason for this anomaly is that the viscosity increases as the
polymerization proceeds because the polymer has a higher viscosity than the monomers The
kp is not affected but the kt is
The degree of conversion can now be expressed as a function of time by knowing that
By substituting the earlier equation for Rp and integrating that equation one can obtain this
Furthermore ([M]0 ndash [M]) [M]0 is equal to the degree of conversion and is the fraction of
the monomer that has been reacted where [M] is the concentration of the monomer that has
been left after the reaction and [M]0 is the initial monomer concentration Therefore ([M]0 ndash
[M]) is the concentration of the monomer that has reacted The conversion can then be
expressed as
28
This can also be expressed as
As is always the case the conversion never quite reaches 100 value or a factor of 1 given by
the exponential term So if the time goes to infinity the expression that is obtained for
maximum conversion that is less than 1 by an amount that is dependent on the initial initiator
concentration is
If the steady state approximation for the initiator concentration had been carried through these
calculations and equations then the conversion would approach a value of 1 after a long
period of time
Distributions on the average distribution of chain lengths during and after a polymerization
are present in free radical polymerizations This is due to the naturally but statistically
random termination reactions that occur in the solution with regard to chain length The
kinetic chain length v is the rate of monomer addition to growing chains over the rate at
which chains are started by radicals which is the expression for the number average chain
length In other words it is the average number of monomer units per growing chain radical
at a certain instant87 Therefore the initiator radical efficiency in polymerizing the monomers
is
87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993)
29
When termination occurs mainly by combination the chain length for the polymer chains on
the average doubles in size assuming nearly equal length chains combine But if
disproportionation mainly occurs the growing chains do not undergo any change in chain
length during the process So the expressions are thus
A new term can be used to more generally express the average chain length of the growing
polymer chain xn This new term is the average number of dead chains produced per
termination ξ This value is equal to the rate of dead chain formation over the rate of the
termination reactions The equations take into account that in combination only one dead
chain is produced and in disproportionation reactions two dead chains are produced
Therefore
Furthermore the instantaneous number average chain length can be expressed in terms of the
rate of addition of the monomer units divided by the rate of dead polymers forming This is
shown as
30
From this equation82 one can clearly see that the rate of polymerization is proportional to the
initiator concentration to the one half power [I]12 and that the instantaneous number average
chain length xn is proportional to the inverse of the initiator concentration to the one half
power 1[I]12 Thus if the polymerization was accelerated by using more initiator the chains
will end up to be shorter which may not be desirable85
17 Chain Growth Copolymerization
171 Copolymerization Equations
Chain polymerizations can obviously be performed with mixtures of monomers rather than
with only one monomer For many free radical polymerizations for example acrylonitrile and
methyl acrylate two monomers are used in the process and the subsequent copolymer might
be expected to contain both of the structures in the chain This type of reaction that employs
two comonomers is a copolymerization The reactivity and the relative concentrations of the
two monomers should determine the concentration of each comonomer that is incorporated
into the copolymer The application of chain copolymerizations has produced much important
fundamental information Most of the knowledge of the reactivities of monomers via
carbocations free radicals and carbanions in chain polymerizations has been derived from
chain copolymerization studies The chemical structure of these monomers strongly
influences reactivity during copolymerization Furthermore from the technological viewpoint
copolymerization has been critical to the design of the copolymer product with a variety of
specifically desired properties As compared to homopolymers the synthesis of copolymers
can produce an unlimited number of different sequential arrangements where the changes in
relative amounts and chemical structures of the monomers produce materials of varying
chemical and physical properties
Several different types of copolymers are known and the process of copolymerization can
often be changed in order to obtain these structures A statistical or random copolymer may
obey some type of statistical law which relates to the distribution of each type of comonomer
that has been incorporated into the copolymer Thus for example it may follow zero- or first-
31
or second-order Markov statistics88 Copolymers that are formed via a zero-order Markov
process or Bernoullian contain two monomer structures that are randomly distributed and
could be termed random copolymers
ndashAABBBABABBAABAmdash
Alternating block and graft copolymers are the other three types of copolymer structures
Equimolar compositions with a regularly alternating distribution of monomer units are
alternating copolymers
ndashABABABABABABA--
A linear copolymer that contains one or more long uninterrupted sequences of each of the
comonomer species is a block copolymer
--AAAAAAAA-BBBBBBBBB--
A graft copolymer contains a linear chain of one type of monomer structure and one or more
side chains that consist of linear chains of another monomer structure
--AAAAAAAAAAAAAmdash
B B
B B
B B
B B
For this discussion the main focus will be on randomly distributed or statistical copolymers
Copolymer composition is usually different than the composition of the starting materials
charged into the system Therefore monomers have different tendencies to be incorporated
into the copolymer which also means that each type of comonomer reacts at different rates
with the two free radical species present Even in the early work by Staudinger89 it was
noted that the copolymer that was formed had almost no similar characteristics to these of the
homopolymers derived from each of the monomers
Furthermore the relative reactivities of monomers in a copolymerization were also quite
different from their reactivities in the homopolymerization Thus some monomers were more 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151
32
reactive while some were less reactive during copolymerization than during their
homopolymerizations Even more interesting was that some monomers that would not
polymerize at all during homopolymerization would copolymerize relatively well with a
second monomer to form copolymers It was concluded that the homopolymerization features
do not easily directly relate to those of the copolymerization
Alfrey (1944) Mayo and Lewis (1944) and Walling (1957)909192 demonstrated that the
copolymerization composition can be determined by the chemical reactivity of the free radical
propagating chain terminal unit during copolymerization Application of the first-order
Markov statistics was used and the terminal model of copolymerization was proposed The
use of two monomers M1 and M2 during copolymerization leads to two types of propagating
species The first of these species is a propagating chain that ends with a monomer of
structure M1 and the second species is a propagating chain that ends with a monomer structure
M2 For radically initiated copolymerizations the two structures can be represented by
M1 and M2 where the zig-zag lines represent the chain and the M
represents the radical at the growing end of the chain The assumption that the reactivity of
these propagating species only depends on the monomer unit at the end of the chain is called
the terminal unit model58 If this is so only four propagation reactions are possible for a two
monomer system The propagating chain that ends in M1 can either add a monomer of type
M1 or of type M2 Also the propagating chain that ends in M2 can add a monomer unit of
type M2 or of type M1 Therefore these equations can be written with the rate constants of
reactions93
90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953)
33
The rate constant for the reaction of the propagating chain that ends in M1 and adds another
M1 to the end of the chain is k11 and the rate constant for the reaction of the propagating
chain that ends in M2 and adds M1 to the end of the chain is k21 and so on
The term self-propagation refers to the addition of a monomer unit to the chain that ends with
the same monomer unit and the term cross-propagation refers to a monomer unit that is added
the end of a propagating chain that ends in the different monomer unit These (normally)
irreversible reactions can propagate by free radical anionic or cationic processes although
active lifetimes could be very different
As indicated by reactions 30 and 32 monomer M1 is consumed and as indicated by reactions
31 and 33 monomer M2 is consumed The rates of entry into the copolymer and the rates of
disappearance of the two monomers are given by
In order to find the rate at which the two monomers enter into the copolymer equation 34
is divided by equation 35 to give the copolymer composition equation
The low concentrations (eg 10-8 molesliter) of the radical chains in the systems are very
hard to experimentally determine So to remove these from the equation the steady state
approximation is normally employed Therefore a steady state concentration is assumed for
both of the species M1 and M2 separately The interconversion between the two
species must be equal in order for the concentrations of each to remain constant and hence the
rates of reactions 31 and 32 must be equal
34
Rearrangement of equation 37 and combination with equation 36 gives
This equation can be further simplified by dividing the right side and the top and bottom by
k21 [M2] [M1] The results are then combined with the parameters r1 and r2 which are
defined to be the reactivity ratios
The most familiar form of the copolymerization composition equation is then obtained as
The ratio of the rates of addition of each monomer can also be considered to be the ratio of the
molar concentrations of the two monomers incorporated in the copolymer which is denoted
by (m1m2) The copolymer composition equation can then be written as
The copolymer composition equation defines the molar ratios of the two monomers that are
incorporated into the copolymer d[M1] d[M2] As seen in the equation this term is directly
related to the concentration of the monomers that were in the feed [M1] and [M2] and also
the monomer reactivity ratios r1 and r2 The ratio of the rate constant for the addition of its
own type of monomer to the rate constant for the addition of the other type of monomer is
35
defined as the monomer reactivity ratio for each monomer in the system When M1
prefers to add the monomer M1 instead of monomer M2 the r1 value is greater than one
When M1 prefers to add monomer M2 instead of monomer M1 the r1 value is less than
one When the r1 value is equal to zero the monomer M1 is not capable of adding to itself
which means that homopolymerization is not possible
The copolymer composition equation can also be expressed in mole fractions instead of
concentrations which helps to make the equation more useful for experimental studies In
order to put the equation into these terms F1 and F2 are the mole fractions of M1 and M2 in the
copolymer and f1 and f2 are the mole fractions of monomers M1 and M2 in the feed
Therefore
and
Then combining equations 42 43 and 40 gives
This form of the copolymer equation gives the mole fraction of monomer M1 introduced into
the copolymer58
Different types of monomers show different types of copolymerization behavior Depending
on the reactivity ratios of the monomers the copolymer can incorporate the comonomers in
different ways
The three main types of behavior that copolymerizations tend to follow correspond to the
conditions where r1 and r2 are both equal to one when r1 r2 lt 1 and when r1 r2 gt 1
bull A perfectly random copolymerization is achieved when the r1 and r2 values are both
equal to one This type of copolymerization will occur when the two different types of
36
propagating species M1 and M2 show the exact same preference for the addition of
each type of monomer In other words the growing radical chains do not prefer to add one of
the monomers more than the other monomer which results in perfectly random incorporation
into the copolymer
bull An alternating copolymerization is defined as r1 = r2 = 0 The polymer product in
this type of copolymerization shows a non-random equimolar amount of each comonomer
that is incorporated into the copolymer This may occur because the growing radical chains
will not add to its own monomer Therefore the opposite monomer will have to be added to
produce a growing chain and a perfectly alternating chain
When r1 gt 1 and r2 gt 1 both of the monomers want to add to themselves and in theory could
produce block copolymers But in actuality because of the short lifetime of the propagating
radical the product of such copolymerizations produces very undesirable heterogeneous
products that include homopolymers Therefore macroscopic phase separation could occur
and desirable physical properties such as transparency would not be achieved
172 Determination of Reactivity Ratios
Many methods have been used to estimate reactivity ratios of a large number of
comonomers94 The copolymer composition may not be independent of conversion This
means the disappearance of monomer one may be faster than the disappearance of monomer
two if monomer one is being incorporated into the copolymer at a faster rate and therefore it
has a larger reactivity ratio than monomer two
The approximation method95 is the simplest of the methods that has been used to calculate the
reactivity ratios of copolymer systems The method is based on the fact that r1 the reactivity
ratio of component one is mainly dependent on the composition of monomer two m2 that
has been incorporated into the copolymer at low concentrations of monomer two in the feed
M2 The expression is thus
94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
37
The value of the reactivity ratio for component one can be easily determined by only one
experiment but the value is only an approximation and does not provide any validity of the
estimated r1 In order to determine the amount of the comonomer that has been incorporated
into the copolymer various analytical methods must be used Proton Nuclear Magnetic
Resonance Carbon 13 NMR and Fourier Transform Infrared Spectroscopy are three sensitive
instruments that can determine the copolymer composition The approximation method is
limited when the reactivity ratio of one of the components in the system has a value of less
than 01 or greater than a value of 10
However the method does give good insight into the reactivity ratio values for many
copolymer systems The approximation of reactivity ratios can be easy and quick when using
this method of evaluation
The Mayo-Lewis intersection method91 96 uses a linear form of the copolymerization equation where r1 and r2 are linearly related
By using the equations m1M 22 m2M12 and (M2 M1)[(m1 m2) ndash 1] for the slope and intercept
respectively a plot can be produced for a set of experiments after the copolymer composition
has been determined The straight lines that are produced on the plot for each experiment
where r1 represents the ordinate and r2 represents the abscissa intersect at a point on the r1 vs
r2 plot The point where these lines meet is taken to be r1 and r2 for the system in study The
main advantage of this method is that it gives a qualitative observation of the validity of the
intersection area Over the whole range of possible copolymer compositions that were tested
more compact intersections better define the data However the method requires a visual
check of the data and a quantitative estimation of the error is impossible Therefore
weighting of the data is needed to determine the most precise values of r1 and r2
The Fineman-Ross linearization method97 uses another form of the copolymer equation
Where
And
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259
38
For this method by plotting G versus H for all the experiments one will obtain a straight line
where the slope of the straight line is the value for r1 and the intercept of the line is the value
for r2 This type of reactivity ratio determination has the same advantages and disadvantages
of the method described above however this treatment is a linear least squares analysis
instead of a graphical analysis The validity is only qualitative and the estimates of r1 and r2
can change with each experimenter by weighting the data in different ways Furthermore the
high and low experimental composition data are unequally weighted which produces large
effects on the calculated values of r1 and r2 Therefore different values of r1 and r2 can be
produced depending on which monomer is chosen as M158
A refinement of the linearization method was introduced by Kelen and Tudos98 99 100 by
adding an arbitrary positive constant a into the Fineman and Ross equation 47 This technique
spreads the data more evenly over the entire composition range to produce equal weighting to
all the data58 The Kelen and Tudos refined form of the copolymer equation is as follows
η = [ r1 + r2 α ] ξ minus r2 α (50)
where
η = G ( α + H ) (51)
ξ = H ( α + H ) (52)
By plotting η versus ξ a straight line is produced that gives ndashr2α and r1 as the intercepts on
extrapolation to ξ=0 and ξ=1 respectively Distribution of the experimental data
symmetrically on the plot is performed by choosing the α value to be (HmHM)12 where Hm
and HM are the lowest and highest H values respectively Even with this more complicated
monomer reactivity ratio technique statistical limitations are inherent in these linearization
methods101 102
98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265
39
OrsquoDriscoll Reilly et al103 104 determined that the dependent variable does not truly have a
constant variance and the independent variable in any form of the linear copolymer equation
is not truly independent Therefore analyzing the composition data using a non-linear
method has come to be the most statistically sound technique
The non-linear or curve-fitting method90 is based on the copolymer composition equation in
the form
This equation is based on the assumptions that the monomer concentrations do not change
much throughout the reaction and the molecular weight of the resulting polymer is relatively
high In order to determine reactivity ratios from the experimental data a graph must be
generated for the observed comonomer amount that was incorporated into the copolymer m1
versus the feed comonomer amount M1 for the entire range of comonomer concentrations
Then a curve can be drawn through the points for selected r1 and r2 values and the validity of
the chosen reactivity ratio values can be checked by changing the r1 and r2 values until the
experimenter can demonstrate that the curve best fits the data points
The main advantage of the reactivity ratio determination methods discussed thus far is the
results can be visually and qualitatively checked Disadvantages include a direct dependence
of the composition on conversion for most polymer systems and therefore low conversion
(eg instantaneous composition) is needed to determine the reactivity ratios Furthermore
extensive calculations are required but only qualitative measurements of precision can be
obtained Finally weighting of the experimental data for the methods to determine precise
reactivity ratios is hard to reproduce from one experimenter to another
Therefore a technique that allows the rigorous application of statistical analysis for r1 and r2
was proposed by Mortimer and Tidwell which they called the nonlinear least squares
method95105106107This method can be considered to be a modification or extension of the
curve fitting method For selected values of r1 and r2 the sum of the squares of the differences
between the observed and the computed polymer compositions is minimized
103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772
40
Using this criterion for the nonlinear least squares method of analysis the values for the
reactivity ratios are unique for a given set of data where all investigators arrive at the same
values for r1 and r2 by following the calculations Recently a computer program published by
van Herck108 109 allows for the first time rapid data analysis of the nonlinear calculations It
also permits the calculations of the validity of the reactivity ratios in a quantitative fashion110
The computer program produces reactivity ratios for the monomers in the system with a 95
joint confidence limit determination
The joint confidence limit is a quantitative estimation of the validity of the results of the
experiments and the calculations performed This method of data analysis consists of
obtaining initial estimates of the reactivity ratios for the system and experimental data of
comonomer charge amounts and comonomer amounts that have been incorporated into the
copolymer both in mole fractions Many repeated sets of calculations are performed by the
computer which rapidly determines a pair of reactivity ratios that fit the criterion wherein the
value of the sum of the squares of the differences between the observed polymer composition
and the computed polymer composition is minimized111 112 This method uses a form of the
copolymer composition equation with mole fractions of the feed It amounts to determining
the mole fraction of the comonomer that should be incorporated into the copolymer during a
differential time interval
For this equation F2 represents the mole fraction of comonomer two that was calculated to be
incorporated into the copolymer and f1 and f2 represent the mole fractions of each comonomer
that were fed into the reaction mixture The use of the Gauss-Newton nonlinear least squares
procedure predicts the reactivity ratios for a given set of data after repeating the calculations
so that the difference between the experimental data points and the calculated data points on a
plot of mole fraction of comonomer incorporated versus comonomer in the feed is reduced to
the minimum value113 114
108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65
41
18 Controlled Radical Polymerization
The development of new controlledliving radical polymerization processes such as Atom
Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated
polymerization and degenerative transfer processes including RAFT opened the way to the
use of radical polymerization for the synthesis of well-defined complex functional
nanostructures The development of such nanostructures is primarily dependent on self-
assembly of well-defined segmented copolymers This section describes the fundamentals of
ATRP relevant to the synthesis of such systems115
The main goal of macromolecular engineering is to carry out the synthesis (polymerization) in
such a way that it results in well-defined macromolecular products One of the ways to
achieve full control of the macromolecule (length sequence and regio- and stereo- regularity)
would be to build it one monomer at a time with mechanisms in place facilitating selection of
an appropriate monomer and assuring its addition in proper orientation This of course has
been achieved in Nature in the process of protein synthesis through the use of sophisticated
macromolecular ldquonanomachineryrdquo (DNA RNA Most commonly used synthetic routes to
linear polymers are based on addition (chain) reactions which can be controlled only in
statistical terms through such parameters as initiatormonomer ratios monomerpolymer
reactivities monomer concentrations reaction medium etc The main strategy to achieve the
reasonable control of such reactionsrsquo products is through the synchronized growth of ldquolivingrdquo
chains ie chains which cease to grow only in the absence of a monomer Synchronization of
chain growth can be achieved fairly easily through rapid initiation Living chains grown in
such synchronized fashion exhibit relatively narrow molecular weight distributions (MWD)
their average molecular weights can be controlled simply by the duration of reaction Until
recently radical polymerization which covers the broadest range of monomers appeared to
be inherently uncontrollable due to the presence of fast chain termination of growing radicals
Thus although very useful in the synthesis of bulk commodity polymers where precise
control is not always essential radical polymerization has been hardly ever viewed as a tool to
precisely engineer macromolecules for well-defined functional nanostructures
114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16
42
This outlook shifted dramatically recently with the development of new controlledliving
radical polymerization processes such as Atom Transfer Radical Polymerization (ATRP)116
117 118 and other techniques such as nitroxide mediated polymerization119 and degenerative
transfer processes120 including reversible addition-fragmentation chain transfer (RAFT)121
With the availability of effective control mechanisms given its applicability to a broadest
range of monomers radical polymerization is now ready to assume the central role in
macromolecular engineering geared towards the development of well-defined functional
nanostructures
181 Fundamentals of ControlledLiving Radical Polymerization (CRP)
The great expectations for the controlledliving radical polymerization (CRP) have their
origins in the dominating position of the free radical technique by far the most common
method of making polymeric materials (nearly 50 of all polymers are made this
way)122123124This is due to the large number of available vinyl monomers (eg there are
nearly 300 different methacrylates available commercially) which can be easily
homopolymerized and copolymerized The advent of CRP enables preparation of many new
materials such as well-defined components of coatings (with narrow MWD precisely
controlled functionalities and reduced volatile organic compounds -VOCs) non ionic
surfactants polar thermoplastic elastomers entirely water soluble block copolymers
(potentially for crystal engineering) gels and hydrogels lubricants and additives surface
modifiers hybrids with natural and inorganic polymers various biomaterials and electronic
materials
The controlledliving reactions are quite similar to the conventional ones however the radical
formation is reversible Similar values for the equilibrium constants during initiation and
propagation ensure that the initiator is consumed at the early stages of the polymerization
116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002)
43
generating chains which slowly and continuously grow as in a living process There are a
number of critical differences between conventional and controlledliving radical reactions
bull Perhaps the most important difference between the two approaches is the lifetime of
the propagating chains which is extended from 1 s to more than 1 h
bull The second major difference is the very significant increase in the initiation rate
which enables simultaneous growth of all the polymer chains
bull Termination processes cannot be avoided in CRPs Thus CRP is generally less precise
than the anionic polymerization Termination is the most dangerous chain breaking
reaction in CRPs Since it is a bimolecular process increasing the polymerization rate
increases the concentration of radicals and enhances the termination process
Termination also becomes more significant for longer chains and at higher conversion
However this process is somehow self tuned since termination is chain length
dependent
The key feature of the controlledliving radical polymerization is the dynamic equilibration
between the active radicals and various types of dormant species Currently three systems
seem to be most efficient nitroxide mediated polymerization (NMP) atom transfer radical
polymerization (ATRP) and degenerative transfer processes such as RAFT123 Each of the
CRPs has some limitations and some special advantages and it is expected that each
technique may find special areas where it would be best suited synthetically For example
NMP carried out in the presence of bulky nitroxides cannot be applied to the polymerization
of methacrylates due to fast β-H abstraction ATRP cannot yet be used for the polymerization
of acidic monomers which can protonate the ligands and complex with copper RAFT is very
slow for the synthesis of low MW polymers due to retardation effects and may provide
branching due to trapping of growing radicals by the intermediate radicals At the same time
each technique has some special advantages Terminal alkoxyamines may act as additional
stabilizers for some polymers ATRP enables the synthesis of special block copolymers by
utilizing a halogen exchange and has an inexpensive halogen at the chain end125 RAFT can
be applied to the polymerization of many unreactive monomers such as vinyl acetate126
182 Typical Features of ATRP
A successful ATRP process should meet several requirements
125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035
44
bull Initiator should be consumed at the early stages of polymerization to form polymers
with degrees of polymerization predetermined by the ratio of the concentrations of
converted monomer to the introduced initiator (DP = Δ[M][I]o)
bull The number of monomer molecules added during one activation step should be small
resulting in polymers with low polydispersities
bull The contribution of chain breaking reactions (transfer and termination) should be
negligible to yield polymers with high degrees of end-functionalities and allow the
synthesis of block copolymers
In order to reach these three goals it is necessary to select appropriate reagents and
appropriate reaction conditions ATRP is based on the reversible transfer of an atom or group
from a dormant polymer chain (R-X) to a transition metal (M nt Ligand) to form a radical (R)
which can initiate the polymerization and a metal-halide whose oxidation state has increased
by one (X-M n+1t Ligand) the transferred atom or group is covalently bound to the transition
metal A catalytic system employing copper (I) halides (Mnt Ligand) complexed with
substituted 2 2rsquo- bipyridines (bpy) has proven to be quite robust successfully polymerizing
styrenes various methacrylates acrylonitrile and other monomers116127 Other metal centers
have been used such as ruthenium nickel and iron based systems117 118 Copper salts with
various anions and polydentate complexing ligands were used such as substituted bpy
pyridines and linear polyamines The rate constants of the exchange process propagation and
termination shown in Scheme 11 refer to styrene polymerization at 110 C
Scheme 11
According to this general ATRP scheme the rate of polymerization is given by the following
equation
127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901
45
Thus the rate of polymerization is internally first order in monomer externally first order
with respect to initiator and activator Cu(I) and negative first order with respect to
deactivator XCu(II) However the kinetics may be more complex due to the formation of
XCu(II) species via the persistent radical effect (PRE) The actual kinetics depend on many
factors including the solubility of activator and deactivator their possible interactions and
variations of their structures and reactivities with concentrations and composition of the
reaction medium It should be also noted that the contribution of PRE at the initial stages
might be affected by the mixing method crystallinity of the metal compound and ligand etc
One of the most important parameters in ATRP is the dynamics of exchange and especially
the relative rate of deactivation If the deactivation process is slow in comparison with
propagation then a classic redox initiation process operates leading to conventional and not
controlled radical polymerization Polydispersities in ATRP are defined by the following
equation when the contribution of chain breaking reactions is small and initiation is
complete
Thus polydispersities decrease with conversion p the rate constant of deactivation kd and
also the concentration of deactivator [XCu(II)] They however increase with the propagation
rate constant kp and the concentration of initiator [RX]o This means that more uniform
polymers are obtained at higher conversions when the concentration of deactivator in solution
is high and the concentration of initiator is low Also more uniform polymers are formed
when the deactivator is very reactive (eg copper(II) complexed by 2 2-bipyridine or
pentamethyldiethylenetriamine rather than by water) and monomer propagates slowly (styrene
rather than acrylate)
183 Controlled Compositions by ATRP
One of the driving forces for the development of a controlledldquo livingrdquo radical polymerization
is to allow for the copolymerization of two or more monomers128 This has been demonstrated
with ATRP by copolymerization of various combinations of styrene methyl or butyl acrylate
methyl or butyl methacrylate and acrylonitrile ATRP allows for the copolymerization of
these monomers using all feed compositions without loss of control of the polymerization 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
46
this is in contrast to the use of 2266-tetramethylpiperidine-1-oxyl radical (TEMPO) which
must contain a significant amount of styrene as comonomer to retain control of the
polymerization This restriction does not apply to polymerizations mediated by new
nitroxides119 The statistical copolymers prepared by living polymerizations are not the same
as those prepared by conventional radical polymerizations due to the differences in
polymerization mechanism
During a copolymerization one monomer is generally consumed faster than the other
resulting in a constantly changing monomer feed composition during the polymerization the
preference is dependent on the reactivity ratios of the two (or more) monomers In
conventional radical polymerization where the polymer chains are continuously initiated and
are irreversibly terminated the change in monomer feed is recorded in the individual polymer
chains whose composition will vary from chain to chain depending on when the chain was
formed ie at the beginning or near the end of the reaction However since ATRP is a
controlledldquolivingrdquo polymerization system the vast majority of polymer chains does not
irreversibly terminate but grow gradually throughout the polymerization The change in
monomer feed is recorded in the polymer chain itself and not from chain to chain The drifting
of composition along the polymer chain is expected to yield gradient copolymers with novel
properties129 Conventional free radical polymerization methods are generally not suitable for
synthesizing star shaped polymers due to the occurrence of undesirable radical coupling
reactions During a ldquocore-firstrdquo synthesis this would lead to coupling of the growing polymer
arms and ultimately result in a cross-linking of the star macromolecules
Block copolymers can be formed by addition of a second vinyl monomer to a macroinitiator
which contains halide groups that participate in the atom transfer process Most notably this
has been demonstrated by successive addition of a second monomer at the end of the
polymerization of a first monomer by ATRP In this manner AB and ABA block copolymers
have been prepared with various combinations of styrene acrylates methacrylates and
acrylonitrile It is very important to select the right order of monomer addition For example
polyacrylates can be efficiently initiated by the poly (methyl methacrylate)- BrCuBrL
system However the opposite is not true because concentration of radicals and overall
reactivity of acrylates is generally too low to efficiently initiate MMA polymerization
Halogen exchange comes to the rescue bromoterminated polyacrylate in the presence of
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775
47
CuClL is an efficient initiator for MMA polymerization due to reduced polymerization rate
of PMMA-Cl species which are predominantly formed after the exchange process130 131 132
Scheme 12
To conclude atom transfer radical polymerization is a robust method for preparing well-
defined polymers and novel materials with unique compositions and architectures Although
significant progress has been made in the past few years since the development of ATRP
continuous research on the better mechanistic understanding of ATRP and the preparation of
more efficient catalyst systems to yield more well-defined polymers and polymerize new
monomers is needed The syntheses of new materials need to be optimized and their
properties should be studied
It is anticipated that the new controlledliving techniques will help to provide many new well-
defined polymers via macromolecular engineering
130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
48
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PA (1997) 86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995) 87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993) 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151 90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953) 94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
51
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259 98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265 103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772 108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65 114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16 116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002) 125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035 127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
52
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775 130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
53
CHAPTER II Synthesis and Characterization of
Macromonomers
21 Introduction
Cationic ring opening polymerization of DXL proposed by Franta and Reibel133 results in
linear polymeric chains thereby preventing formation cyclic oligomers through cationic
polymerization of cyclic acetals15 17In fact the reaction of DXL in the presence of an
unsaturated alcohol (2-HPMA) results in a functionalized linear PDXL macromonomer
carrying at one or both ends an unsaturated system supported by the methacryloyl group of
the alcohol The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism44 Franta et al have established that when DXL is polymerized by strong protonic
acids such as triflic acid in the presence of a diol the PDXL chains are essentially linear and
carry end-standing OH functions It has been shown that the amount of cyclic species formed
is negligible that the dispersity is on the order of 14 and that the molecular weight of the
linear polymers is governed by the ratio of reacted monomer to transfer agent and is generally
well controlled up to 10 000 gmol
De Clercq and Goethals have reported the preparation of poly (13dioxolane)
bismacromonomers by copolymerization with MMA and provided the possibility to prepare
polymer networks containing PDXL segments134 135 PDXL based hydrogels have been
obtained in most cases by free radical copolymerization with comonomers such as acrylic
acid acrylamide and N-isopropylacrylamide134 136 137 styrene and butyl acrylate138
Hydrogels have received increasing attention for biomedical applications such as drug
delivery immobilization of enzymes dewatering of protein solutions and contact lenses139
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002) 1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080
54
140 These materials and are widely used in areas like baby diapers solute separation soil for
agriculture and horticulture absorbent pads etc139 Hydrogels are defined as hydrophilic
polymer networks which have a high capacity to adsorb a substantial amount of water which
have been proposed as protein releasing matrices The high water content ensures a good
compatibility with entrapped proteins as well as with surrounding tissue141 Even though a
number of applications are currently being pursued using hydrogel very little is known about
the mechanical behavior that describes the various physical processes in hydrogels142 Over
the last decade most interests have been emphasized on the synthesis of polymers containing
polyacetal segments because of the ease of degradation of these polymers under mild
conditions by treatment with a trace of acid134 143 Poly (1 3 dioxolane) is a hydrophilic non-
ionic polymer which like poly (ethylene oxide) is appreciably soluble in water but much
more sensitive to acidic degradation because of the presence of acetal groups in the chains144
In this chapter we report the synthesis of the functionalized poly (13dioxolane)
macromonomers which have been used for the preparation of PDXL hydrogel and
amphiphilic graft copolymers In the second part of this chapter we have focused on a
detailed study of the properties of the resulting hydrogel in terms of swelling behavior in
different organic solvents and viscoelastic properties determined by rheological measurements
in both the steady shear and oscillatory experiments
22 Experimental
221 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922
55
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
bull Dichloromethane (CH2Cl2 MW 8493 bp 40degC d 1325)
Dichloromethane (Prolabo 999) was dried by stirring over CaH2 for 24 h and then
distilled under a N2 atmosphere to remove impurities Purified dichloromethane was
stored under nitrogen over molecular sieve
bull 2-hydroxypropyl methacrylate (2-HPMA) (MW 14417 bp 240degC d 1028)
2-HPMA of commercial grade was purchased from Acros stabilized with 200 ppm
hydroquinone monomethyl ether Then it was stored over molecular sieve
bull n-Hexane 99 (C6H14 MW 8618 bp 68-70degC d 0658-0662) Stored under
nitrogen over molecular sieve
bull Trifluoromethanesulfonic acid (triflic acid Aldrich) was used as received
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile (AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull 1 3 dioxolane (DXL) (MW 7408 bp 78degC d 106)
The monomer DXL of commercial grade was purchased from Acros DXL was kept
under KOH for two and up to three days to remove any peroxide and stabilizer traces
and then purified by distillation over CaH2 under a N2 atmosphere prior to
polymerization
All chemicals were kept over molecular sieve before use
222 Reaction apparatus
All polymerization experiments were performed with a clean 250 ml three neck round bottom
flask A condenser was used on one of the necks of the flask in order to condense any
monomers that might otherwise possibly escape A magnetic bar was used to stir the solution
at a constant speed in order to assure even distribution of monomer and initiator
concentrations throughout the entire volume of solution A rubber septum was used to cover
one of the three necks
In the case of free radical polymerization reactions a thermocouple was also fitted to the
reaction vessel to monitor the temperature of the reaction The thermocouple regulated the
56
temperature at a constant 70degC throughout the reaction
223 Synthesis of Poly (13-dioxolane) Macromonomers
Methacrylate-terminated PDXL macromonomers were synthesized by Cationic ring-opening
polymerization which was carried out in 10 ml dichloromethane with triflic acid as initiator at
room temperature under nitrogen for 24 h in the presence of 2-hydroxypropyl methacrylate
(2-HPMA) as transfer agent 20 ml of DXL monomer was added The feed molar ratios
[DXL] [2-HPMA] are reported in Table1 as well as the molecular characteristics of the
obtained macromonomers The amount of the acid used was 20 μl After reaction the
resulting solution is poured into THF Then the product is purified by re-precipitation from
THF solution with a large excess of hexane and the obtained polymer was dried under
vacuum at room temperature The yield was checked by gravimetric determination and found
to be about 80
224 Synthesis of Poly (13-dioxolane) Hydrogel Network
The functionalized PDXL macromonomer taken for the preparation of PDXL netwok was
(FPP2) macromonomer with a theoretical average molecular weight of Mnth =2000
The macromonomer (1g) was polymerized by free radical polymerization in 10 ml of THF
using 2 2-azobisisobutyronitrile (AIBN) (001g) as initiator under a nitrogen atmosphere
The polymerization was carried out at 70degC for 24h A piece of hydrogel was obtained The
product was extracted with ethanol to remove unreacted macromonomers and then dried
under vacuum
23 Characterization Techniques
231 Raman Spectroscopy
Raman spectroscopy is used to study and analyse the structure of the macromonomers
The experiments were performed on a Dilor XY 800 spectrophotometer The detector was a
charge-coupled device (CCD) An argon laser pump beam (power density of 100 mW) has
been focused onto the sample through a microscope The working wavelength was chosen as
λ = 5145 nm In our experiments we explored the spectral range between 200 and 3700 cm-1
with a spectral resolution of 2 cm-1
57
232 1H-NMR Spectroscopy
Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) was used for structural analysis
and molecular weight of polymers and macromonomers Proton NMR spectra were obtained
using a high field 400Mhz Advance Bruker spectrometer
All of the 1H NMR samples were dissolved in deuterated chloroformThe chloroform
reference peak at 724 ppm was to ensure accuracy of peak assignments The integrals of the
peaks were used for the calculations to determine the Mw of the macromonomers
233 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) represents a chromatographic method widely used in
the analysis of polymer average molecular weights and molecular weight distributions SEC
Measurements were performed at 40degC on a Waters 2690 instrument equipped with UV
detector (Waters 996 PDA) coupled with a Differential Refractometer (ERC - 7515 A) and
four Styragel columns (106 105 500 and 50degA) THF is employed as eluent with a flow rate
of 10 mlmin Polystyrene standard samples were used for calibration
234 Swelling Measurements
In order to investigate the swelling behavior the measurement of the swelling ratio of the
polymer network is obtained from a gravimetric method in which small pieces of hydrogel
were immersed solvents such as CH2Cl2 and THF for 24 hours at room temperature (23degC)
until swelling equilibrium was reached ie when the gel thickness became essentially
constant The samples were removed from the solvents and carefully weighed (Ws) Then the
samples let to deswell and weighed every 5 min during in order to determine the swelling
kinetics in the solvents The swelling equilibrium was reached after 5 hours Afterwards the
gel was left to dry for 24 hours at room temperature until constant weight was attained and the
dry weight (Wd) was determined and the swelling ratio was calculated from equation
SR = ( ) 100timesminusWd
WdWs (57)
Where SR is equilibrium swelling ratio Ws and Wd are the sample weights in swollen and dry
states respectively
58
235 Rheological Measurements
Steady shear and oscillatory measurements have been performed on a stress imposed
rheometer Rheo-Stress-100 (RS100) from Haake used with a coneplate geometry (20 mm
diameter an angle of 4deg gap 2 mm)The imposed stress of 100 Pa during 30 seconds and a
frequency of 1Hz were applied while the strain was monitored The measurements have been
performed on swollen and unswollen samples The elastic (G) and the loss (G) moduli are
measured in linear viscoelastic region In the oscillatory experiments the frequency
dependence of both Grsquo and G is obtained at a constant strain All rheological measurements
were carried out at room temperature (23 degC)
24 Results and Discussion
241 Structural Characterization of Macromonomers
1 3 dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer end ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The synthesis of α ω-dihydroxy-PDXL chains is based on the
activated monomer mechanism44 Franta et al have established that when DXL is polymerized
by strong protonic acids such as triflic acid in the presence of a diol the PDXL chains are
essentially linear and carry end-standing OH functions It has been shown that the amount of
cyclic species formed is negligible that the dispersity is on the order of 14 and that the
molecular weight of the linear polymers is governed by the ratio of reacted monomer to
transfer agent and is generally well controlled up to 10 000 gmol
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel44 133 using an unsaturated alcohol (2-
59
HPMA) as a transfer agent results in linear polymeric chains thereby preventing formation of
cyclic oligomers through cationic polymerisation of cyclic acetals15 17 They were all prepared
at the same reaction conditions The synthetic route of functionalized PDXL macromonomers
is shown in scheme13
Scheme 13 Structures of PDXL macromonomer species54
According to this mechanism it is possible to prepare macromonomers ie PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of the
transacetalization reactions a mixture of products is obtained
A is the most abundant compound it corresponds to 50 to 60 weight wise54 It is a
macromonomer
B corresponds to 20 to 25 weight wise It is a bis-macromonomer It carries two
methacryloyl functions corresponding to transacetalization of R-OH and DXL
C corresponds to 20 to 25 weight wise It carries no methacryloyl function but two
hydroxyl groups It is a α ω-dihydroxy-PDXL
These 3 species A B and C stem from scrambling reactions that are typical with cyclic
acetals54
The characterization of these materials is based on structure and molecular weight
determination For instance the PDXL macromonomers carried at one of their ends a double
bond afforded by the methacryloyl group The latter was checked by Raman and 1H-NMR
spectroscopy All macromonomers prepared displayed functionality close to unity which
makes them suitable for the synthesis of graft copolymers
60
Raman spectroscopy is used to study and analyse the structure of the macromonomers The
aim of this study is to check the formation of linear polymer chains as well as the termination
with methacryloyl groups The spectra obtained exhibit two intense Raman bands at 800 to
900 cmP
-1 and 2700 to 3000 cmP
-1 regions and a series of small other peaks for all samples as
shown in figure 1 The most intense band (2700 ndash 3000 cmP
-1) is assigned to the aliphatic
stretching vibration of CH in the polyacetal chain Symmetric COCOC stretching frequencies
of aliphatic acetals fall in typical regions of 1115-1080cmP
-1 and 870-800 cmP
-1 145 and are
responsible for intense Raman bands In the low frequency region there are three very
characteristic Raman bands in the 600 ndash 550 cmP
-1 540 ndash 450 cmP
-1 and 400 ndash 320 cmP
-1 ranges
which are assigned to COCOC deformations145 146 Also the acetals have strong multiple
bands in the region of 1160ndash1040 cmP
-1 as noticed on the Raman spectra involving the C-O
stretching modes In addition to this the O-CH-O group gives rise to a band at 1350 ndash1325
cmP
-1 for C-H deformation Other intense Raman bands are observed in the region of 3000 ndash
2700 cmP
-1 Below 3000 cmP
-1 the corresponding frequencies are assigned to the aliphatic C-H
stretching modes145 The methoxy group is detected in the region of 2835 ndash 2780 cmP
-1
Figure 1 Raman spectra of methacrylic-terminated PDXL macromonomers (FPP2 FPP15 and
FPP1)
145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The Handbook of IR
and Raman Characteristic Frequencies of Organic Molecules United Kingdom Ed by Academic Press Limited London (1991)
146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman Spectroscopy 3rd Edition AP Limited London (1964)
61
As far as the presence of the methacryloyl group in the polymeric chain is important bands
have been observed at 1640 cmP
-1 which corresponds to C=C bonds The carbonyl compounds
absorb strongly within 1900 ndash1550 cmP
-1 region145 146 the spectra show a C=O bond absorption
found at 1720 cmP
-1 In the region of 1340 ndash1250 cmP
-1 the methacrylate bands are observed
Broad absorption is found near 3500 cm -1 owing to stretching of the OH bonds OH
deformation bands are found at 1400 cmP
-1P and 1340 cmP
-1 This observation indicates that both
methacrylic and ndashOH groups are present and eventually the resulting product is a mixture of
the three species as shown in the scheme above
Typical 1H-NMR spectrum of PDXL macromonomer shown in figure 2 exhibits the expected
resonance assigned to the methoxy protons (477 ppm) and OCH2CH2O protons at (374
ppm) Two signals corresponding to =CH2 were observed at (612 ndash 614 ppm) and (557 ndash
559 ppm) Therefore the spectrum confirmed the chemical structure HO[CH2CH2OCH2O]nR
of methacryloyl- terminated PDXL macromonomer
Figure 2 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP2)
242 Molecular Weight Determination
Besides the structure 1H-NMR enables us to determine the number-average molecular weight
(Mn) In the calculation of the latter the methacryloyl end group was included The
62
polydispersity and index MwMn and the number-average molecular weight were obtained
from SEC measurements Table 1 summarizes these values It can be seen that Mn (SEC) and
Mn (NMR) are very close to each other for all macromonomer samples and are in agreement
with the theoretical values predicted from calculations Under our polymerization conditions
the polydispersity index is 16 for all samples
Table 1 Characteristics of PDXL macromonomers prepared at different degrees of
polymerization
Sample Dp Mnth MnSEC MnRMN MwMn f (a)
FPP1 135 1000 1120 1160 16 097
FPP15 2025 1500 1540 1550 16 099
FPP2 270 2000 2040 2100 16 097
Dp degree of polymerization = [DXL] [2HPMA]
a functionality of macromonomers (methacryloyl end groups molecule)
243 Swelling of Poly (13 Dioxolane) Hydrogel
The synthesized PDXL hydrogel has been studied in terms of swelling and rheological
behaviors The degree of swelling and the rate of swelling of the hydrogel are studied It is
known that hydrogel can swell in several solvents but at different degree of swell according to
many factors related to the nature of the solvents and the type of polymer-solvent interactions
It was found that the solubility parameter of the solvents (δ) had a great effect on swelling
degree For instance hydrogels can swell fast in CH2Cl2 (δ = 976 cal cm12 -32) and reached
equilibrium within no more than an hour However it will take about more than 20 h to reach
equilibrium in CH3 OH (δ = 145 cal cm12 -32) It was known that the polymer can reach
greatest swelling degree when the solubility parameter of the polymer is close to that of the
solvents The solubility parameter of PDXL is about 93 cal cm 12 -32 134 The swelling has been
examined in THF and CH2Cl2 for PDXL hydrogel It has been observed that the swelling
equilibrium is reached after almost 5 hours of swelling for all samples in both solvents The
results show that THF (δ = 952 cal cm12 -32)147 swells the hydrogel to the greatest degree
compared to CH2Cl2 as shown in figure 3 However CH2Cl2 molecules provide less swelling
147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983)
63
capacity than in THF On the basis of the experiment The PDXL hydrogel reached high
swelling degree due to its solubility parameter is much closer to that of THF
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
THF CH2Cl2
Swel
ling
degr
ee
Time (min)
Figure 3 Swelling kinetics of PDXL hydrogel in two different solvents CH2 Cl2 (solid
squares) and in THF (hollow squares)
244 Viscoelastic Behavior
Rheological measurements were performed on rheometer in the Cone and Plate geometry
Both steady shear and oscillatory experiments were carried out The dynamic storage and loss
moduli G and G were examined at room temperature (23 degC)
Many attempts have been carried to extend the elasticity theory to swollen gels148 149 Based
on this approach all measurements have been performed on both swollen and unswollen
hydrogel samples for the purpose of comparison so that to examine the mechanical properties
even in swollen state For instance Flory and Rehner recognized the swelling phenomenon
exhibited by cross-linked polymers when exposed to certain solvents and related the modulus
of elasticity of a swollen cross-linked polymer network to an unswollen network150 Figure 4
illustrates the strain dependence of G and G for swollen and unswollen samples
148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for Experimental
Mechanics SEM Annual Conference Proceedings (2002)
64
10-5 10-4 10-3 10-2 10-1 100 101 102101
102
103
104
Guns Guns Gs Gs
GG
(Pa
)
γ ()
Figure 4 Strain dependence of the elastic modulus Grsquo (circles) and of the viscous modulus
Grdquo(triangles) for two samples of unswollen hydrogel (solid symbols) and swollen hydrogel
(hollow symbols)
The moduli are measured as a function of strain at a constant frequency It appears that the
linear viscoelastic region is observed while the strain is increasing in either state which
indicates that the internal structure of the samples has not been disrupted when deformed
This leads to reveal that the gel is strain resistant in swollen and unswollen states and within a
large strain range the hydrogel retains its elasticity as shown in figure 4 where the linear
viscoelastic region extends to almost 02
The frequency dependence of G and G is shown in figure 5 similarly for swollen and
unswollen hydrogels The system behaves typically like a gel as it can be noticed that the
elastic component G (storage modulus) is far greater than the viscous component G (loss
modulus)151 Based on these results the hydrogel exhibits extreme elasticity at low
frequencies
151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure 554 (2000) 99-108
65
100 101
103
104
105
Gs Guns Gs GunsG
G(
Pa)
ω (rads)
Figure 5 Frequency dependence of Grsquo(circles) and Grdquo(triangles) for swollen hydrogel
(hollow symbols) and unswollen hydogel (solid symbols)
Finally figure 6 illustrates the complex viscosity profiles another parameter of
viscoelasticity which measures the magnitude of the total resistance to a dynamic shear
Again this property has not been affected by swelling since the results show similar behavior
for swollen and unswollen states It decreases sharply as frequency increases which
characterizes the samples degree of viscoelasticity at various time scales Therefore from the
results discussed above the hydrogel network is elastic and stable even in the swollen state
thereby possessing very good mechanical properties
100 101 102 103
102
103
104
105
η unswollen η swollen
ηlowast (P
a s)
ω (rads)
Figure 6 Frequency dependence of the complex viscosity η for unswollen hydrogel (solid
squares) and swollen hydrogel (hollow triangles)
66
Conclusion
The hydrogel properties were discussed in terms of swelling and viscoelastic
behaviors The hydrogel has combined special properties Its swelling behaviour in the
solvents was dependent on the solubility parameter of both solvents and hydrogel
Rheological measurements were successful when used in order to study the viscoelastic
behavior of the hydrogel of pure PDXL in swollen and unswollen states The Strain
dependence of G and G for both samples shows linear viscoelastic region and allows to
determine the yield stress Same conclusions can be given concerning the frequency
dependence of complex viscosity the swelling does not affect this property The results reveal
a perfect elastic and resistant hydrogel in other words the viscoelastic properties have not
been so much affected by swelling They may be particularly useful in the design of improved
microfluidic devices that utilise the relationship between swelling and strain This kind of
material can be potentially used in biosystems such as intelligent drug delivery systems
67
References
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-
174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002)
1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080 140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922 145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The
Handbook of IR and Raman Characteristic Frequencies of Organic Molecules United
Kingdom Ed by Academic Press Limited London (1991) 146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman
Spectroscopy 3rd Edition AP Limited London (1964) 147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983) 148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-
1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for
Experimental Mechanics SEM Annual Conference Proceedings (2002) 151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure
554 (2000) 99-108
68
CHAPTER III Synthesis and Characterization of Copolymers
31 Introduction
Amphiphilic block and graft copolymers consisting of hydrophilic and hydrophobic parts
have been subjects of numerous studies within which block and graft copolymers containing
hydrophilic polyoxyethylene segments and other hydrophobic segments have attracted much
attention because polyoxyethylene segments are not only hydrophilic but also nonanionic
and crystalline and can complex monovalent metallic cations Graft copolymers offer all
properties of block copolymers but are usually easier to synthesize Moreover the branched
structure leads to decreased melt viscosities which is an important advantage for processing
Depending on the nature of their backbone and side chains they give rise to special properties
in selective solvents at surfaces as well as in the bulk owing to microphase separation
morphologies12 They can be used for a wide variety of applications such as polymeric
surfactants electrostatic charge reducers compatibilizers in polymer blends polymeric
emulsifiers controlled wet ability and so on152 153 In order to prepare graft copolymers with
well-defined structure one can utilize the macromonomer technique (grafting through
technique) Well-defined structure graft copolymers are synthesized by copolymerization of
macromonomers with low molecular weight comonomers6 It allows the control of the
polymer structure which is given by three parameters (i) chain length of side chains which
can be controlled by the synthesis of the macromonomer by living polymerization (ii) chain
length of backbone which can be controlled in a living copolymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular weight monomer However the distribution of spacings
may not be very easy to control due to the incompatibility of the polymer backbone and the
macromonomers154 As pointed out in recent publication reviews155 there is a complex
interplay of factors that govern the reactivities in copolymerizations involving
macromonomers When different comonomers are copolymerized with the same it seems that
the degree of interpenetration between the macromonomer and the propagating copolymer 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305
69
backbone plays the major role in the measured reactivities Nevertheless the main properties
depend on both the average composition of the systems and the microstructural distribution of
the comonomer sequences along the macromolecular backbone which is determined by the
reactivity ratios of the macromonomer and the corresponding comonomer in the free radical
polymerization process156 157
In this chapter our work deals with the preparation and characterization of new organo-
soluble associative copolymers based on short hydro-soluble chains of poly (1 3 dioxolane)
(PDXL) Many reports have been published on PDXL macromonomers used to form
hydrogels136 137 158 159 160 161 162 however very few were on graft copolymers with PDXL
branches162 These macromonomers are used for the preparation of amphiphilic graft
copolymers by solution free radical copolymerization with a hydrophobic comonomer
styrene (St) and methyl methacrylate (MMA) Structural characterization of these
copolymers molecular weight determination reactivity ratios and the polymerizability of the
PDXL macromonomer have been discussed Finally their thermal properties are discussed
according to the weight content of PDXL in the copolymers
32 Experimental
321 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269
70
bull Ethanol (C2H6O MW 4607 bp 78degC d 081)
Ethanol (Prolabo 95-96) was purified by distillation with 5g of Magnesium and 05g of
iodine for 75ml of alcohol under a N2 atmosphere After discoloration of the mixture
solution a volume of Ethanol was added and then distilled normallyThen it was stored
over molecular sieve
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile(AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull Styrene (C6H5CH=CH2 MW 10416 bp 145degC d 091)
Styrene (Prolabo product) was purified by distillation over CaHB2 at reduced pressure
bull Methyl Methacrylate (MMA)(H2C=C(CH3)CO2CH3 MW 10012 bp 100degC d
0936)
Methyl Methacrylate (Prolabo product) was purified by distillation over CaHB2 at reduced
pressure
All chemicals were kept over molecular sieve before use
322 Synthesis of Poly (Styrene-co-Poly (13-dioxolane))
a) Conventional Free Radical Copolymerization
The reaction route for the conventional copolymerization of Styrene and PDXL
macromonomers using AIBN as the free radical initiator at 60degC is shown in scheme 14
71
Scheme 14
PDXL macromonomers of different molecular weights were copolymerized with St in THF at
60degC in the presence of 2 2rsquo-azobisisobutyronitrile AIBN (1 based on the total weight of
the monomers) as initiator under a nitrogen atmosphere using different feed molar fractions
of macromonomers The total monomer concentration for was 6 10-1 M in all cases The
copolymerization product is diluted with THF and then added dropwise to a large excess of
ethanol to remove unreacted PDXL macromonomers25 43 and precipitate the copolymers
Then they were finally dried over vacuum at 40degC to constant weight The yields of all
reactions are 70ndash 90 Table 2 indicates the amounts of comonomers initiator and solvent
employed in the copolymerization study
72
Table 2 Copolymerization of PDXL macromonomers (M1) with Styrene (M2)
Sample M1 M2M1 PDXL (g) (mol)
Styrene (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2SP2 FPP2 20 349 174510-4 364 349 10-2 007 60 0610 3SP2 FPP2 30 232 116 10-4 364 349 10-2 006 60 0601 5SP2 FPP2 50 14 69810-4 364 349 10-2 005 60 0593
2SP15 FPP15 20 262 174510-4 364 349 10-2 006 60 0610 3SP15 FPP15 30 174 116 10-4 364 349 10-2 006 60 0601 5SP15 FPP15 50 105 69810-4 364 349 10-2 005 60 0593
2SP1 FPP1 20 174 174510-4 364 349 10-2 006 60 0610 5SP1 FPP1 50 07 69810-4 364 349 10-2 005 60 0593 8SP1 FPP1 80 0436 43610-4 364 349 10-2 005 60 0589
b) Controlled Free Radical Copolymerization
The comb-structure copolymer of styrene and PDXL was obtained by grafting-from
mechanism through Nitroxide-Mediated Polymerization
Nitroxide mediated polymerization (NMP) is a controlled radical polymerization (CRP)
technique which already offers the ability to prepare a wide variety of well-defined polymer
architectures119 Despite the significant improvements brought to CRP techniques such as
NMP atom transfer radical polymerization (ATRP) or reversible addition fragmentation chain
transfer (RAFT) the preparation of complex architectures by CRP is restricted by the
exclusion of monomer systems that are polymerized by fundamentally different mechanisms
like lactides ethylenepropylene oxide The most promising approaches to extend the range of
polymer compositions are based on the use of heterofunctional initiators163 allowing the
combination of mechanistically distinct polymerization reactions without the need for
intermediate transformation and protection steps
In the field of NMP the development of multifunctional initiators was focused on TEMPO
and TIPNO which are examples of nitroxides (Scheme 15) It is worth to mention that in
NMP these are used as counter-radicals associated with a conventional azoic initiator so this
pair of initiators is known as a bimolecular system
163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671
73
Scheme 15 TEMPO and based alkoxyamines
Another initiator used for NMP is the commercially available alkoxyamine also called
MAMA-SG1164 (Scheme 16) known as a monomolecular system initiator which is
particularly convenient for functionalization of polymer chain ends164 165 MAMA-SG1 has
been developed by Didier Gigmes and co in collaboration with Arkema Company166 Thanks
to a particularly high dissociation rate constant value kd1 up to now this alkoxyamine has
proved to be one of the most potent alkoxyamines reported in the field of NMP167 168 This
initiator is used for polymerization of styrene and n-butyle acrylate allowing formation of
well-defined linear and star structures
Scheme 16
164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006) 5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219
74
Scheme 17 MAMA-SG1 structure and dissociation scheme
bull Multifunctionalization of Polystyrene (HO-PS)
MAMA-SG1 was used to run copolymerization of styrene at 90 mol with HEMA in order
to obtain functionalized polystyrene The monomers and alkoxyamine were introduced in a
250 mL two neck round-bottom flasks fitted with septum condenser and degassed for 15
min by nitrogen bubbling The reaction was performed in bulk at 120 degC under N2 with
vigorous stirring Targeted molecular weight and polydispersity were 30 000 g mol and 12
respectively
After polymerization the final polymer mixture was dissolved in a minimum THF and
precipitated in cold ethanol followed by drying under vacuum at 30degC
bull Synthesis of PS-g-PDXL
PDXL was copolymerized by cationic ring-opening polymerization which was carried out in
40 ml dichloromethane with triflic acid as initiator at room temperature under nitrogen for 24
h in the presence of OH-multifunctionalized PS (1g 3 10-5 mol) as transfer agent 20 ml
(0286 mole) of DXL monomer was added Table 6 gives the molecular characteristics of the
obtained copolymer The amount of the acid used was 20 μl After reaction the resulting
solution is poured into THF Then the product is purified by re-precipitation from THF
solution with a large excess of hexane and the obtained polymer was dried under vacuum at
room temperature The yield was checked by gravimetric determination and found to be about
75 The polymerization route is presented in the scheme below
75
Scheme 18
323 Synthesis of Poly (Methyl Methacrylate-co-Poly (13-dioxolane))
Same procedure has been used for the synthesis of Poly (Methyl Methacrylate-co-Poly (1 3-
dioxolane)) copolymers The yields of the reactions are in the range of 70ndash 90
Table 3 shows the amounts of comonomers initiator and solvent employed in the
copolymerization reactions
Table 3 Copolymerization of PDXL macromonomers (M1) with MMA (M2)
Sample M1 M2M1 PDXL (g) (mol)
MMA (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2MP2 FPP2 20 374 187 10-4 3744 374 10-2 008 65 0604 3MP2 FPP2 30 2 10 10-4 300 300 10-2 005 50 0620 5MP2 FPP2 50 15 748 10-4 3744 374 10-2 005 60 0636
2MP15 FPP15 20 2 133 10-4 28 280 10-2 005 25 100 3MP15 FPP15 30 187 125 10-4 3744 374 0-2
006 60 0644 5MP15 FPP15 50 112 748 10-4 3744 374 10-2 005 60 0636
2MP1 FPP1 20 2 20 10-4 400 4 10-2
006 50 0840 3MP1 FPP1 50 125 125 10-4 3744 374 10-2 005 64 0604 5MP1 FPP1 80 075 748 10-4 3744 374 10-2 005 60 0636
33 Characterization Techniques
331 1H-NMR Spectroscopy
1H NMR Spectroscopy was used for compositional and structural analysis of the copolymers
1H-NMR spectra of the copolymers were recorded on the high field 400Mhz Advance Bruker
spectrometer All of the 1H NMR samples were dissolved in deuterated chloroform The
integrals of the peaks of copolymer components were used for the calculations to determine
76
the molecular weights polydispersity indices and the amount of each comonomer that was
incorporated into the copolymer
332 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) was used in the charaterization of the copolymers to
determine average molecular weights and polydispersity indices SEC Measurements were
performed at 40degC on a Waters 2690 instrument equipped with UV detector (Waters 996
PDA) coupled with a Differential Refractometer (ERC - 7515 A) and four Styragel columns
(106 105 500 and 50degA) THF is employed as the mobile phase with a flow rate of 10
mlmin Polystyrene standard samples were used for calibration
333 Diffraction Scanning Calorimetry
Diffraction Scanning Calorimetry (DSC) measurements are performed on a Modulated
Temperature Differential Scanning Calorimeter Q100 TA instrument under nitrogen at 50
mlmin The samples are hermetically sealed in aluminium pans and they are subjected to a
heating program as follows
For Poly (Styrene-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 120degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -80degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to130degC
For Poly (Methyl Methacrylate-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 130degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -95degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to150degC
The thermograms obtained illustrate Glass Transition Temperatures (Tg) and Meltind Points
(Tm) of the copolymers
77
34 Results and Discussion
Methacryloyl-terminated PDXL macromonomers with the Mn range of 1000-2000 gmole
were copolymerized with vinyl and methacrylic monomers in order to obtain amphiphilic
graft copolymers with chemical structure of hydrophobic backbone and hydrophilic side
chains
341 Structural Characterization of the Copolymers
The structure of the copolymers was well defined by 1H-NMR analysis The copolymer 1H-
NMR spectra confirm the formation of copolymers see figures 7 8 and 9 The chemical
shifts of protons of polystyrene and PDXL can be clearly distinguished The following peaks
are assigned for OCHBB2BBO protons at 478 ppm and OCHBB2BBCHBB2BBO protons at 375 ppm (5H CBB6BB
HBB5BB) at 728 711 and 706 ppm as shown in Figure 8 The spectrum of PMMA-PDXL
copolymer is shown in Figure 9 where the chemical shifts of PMMA correspond to the proton
resonance as depicted in the figure the O-CH3 protons are observed at 361 ppm and clear
resonance assigned to the methyl group protons at 085-103 ppm and eventually we observe
the corresponding chemical shifts for OCHBB2BBCHBB2BBO protons (374 ppm) and OCHBB2BBO protons
(477 ppm) to confirm the incorporation of PDXL in the copolymer
Figure 7 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP1)
78
Figure 8 1H-NMR spectrum of Styrene-g-PDXL copolymer in CDCl3 (sample 3SP2)
79
Figure 9 1H-NMR spectrum of MMA-g-PDXL copolymer in CDCl3 (sample 2MP2)
342 Copolymer Molecular Weight and Composition
a) Conventional Free Radical Copolymerization
Copolymerization of PDXL macromonomers with MMA and ST in THF solution was studied
for different molar feed ratio of PDXL The amounts of monomeric units in the copolymers
were determined by elemental analysis The results are presented in Table 4 and 5 which
summarise the characteristics of the graft copolymers in terms of macromonomer feed ratio
(M2M1) and average Mn obtained from SEC as well as copolymer composition in weight and
mole percentages which is determined from 1H-NMR
80
Table 4 Characteristics of PDXL macromonomers (M1) copolymerized with Styrene (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2SP2 FPP2 20 49 476 4025 337 9200 162 2 3SP2 FPP2 30 39 322 303 221 8900 162 2 5SP2 FPP2 50 277 196 21 13 7200 159 1
2SP15 FPP15 20 418 476 34 34 9100 157 2 3SP15 FPP15 30 323 322 24 214 7000 161 2 5SP15 FPP15 50 224 196 152 12 6700 147 1
2SP1 FPP1 20 323 476 30 427 9200 178 3 5SP1 FPP1 50 16 196 1424 17 5800 158 1 8SP1 FPP1 80 107 123 85 095 11900 195 1
Table 5 Characteristics of PDXL macromonomers (M1) copolymerized with MMA (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2MP2 FPP2 20 50 476 35 26 21900 198 4 3MP2 FPP2 30 40 322 21 13 25900 157 3 5MP2 FPP2 50 286 196 13 07 87200 455 6 2MP15 FPP15 20 416 45 28 25 19800 193 4 3MP15 FPP15 30 333 322 22 18 15200 277 3 5MP15 FPP15 50 23 196 13 10 24700 16 2 2MP1 FPP1 20 333 476 26 34 21100 319 6 3MP1 FPP1 30 333 322 19 22 17100 197 3 5MP1 FPP1 50 20 196 10 11 13900 354 2
81
b) Controlled Free Radical Copolymerization
Multifunctionalization of Polystyrene and Synthesis of poly (S-g-PDXL) copolymer give
results which are shown in Table 6 These data have been obtained from the 1H-NMR and
SEC analyses illustrated in figures 10 and 11 The resonance shifts assigned to all components
(PDXL PS and HEMA) are very clear This enables us to make calculations to determine
composition of each copolymer in addition to obtain the average number of grafts and the
number average-molecular weight of a graft
It is observed that the multifunctionalized-PS is composed of 20 in mole of HEMA which
results in 58 grafts (Ng = 58) per molecular chain
After copolymerization multifunctionalized-PS with DXL the copolymer PS-g-PDXL
(DXPS) possesses the following characteristics which are presented in Table 6 It has a
number average-molecular weight of 83000 gmol with 80 of PDXL content The number
average-molecular weight of one graft has been calculated and found to be 1000 gmol
Table 6 Characteristics of functionalized Styrene (HO-PS) and PS-g-PDXL (DXPS)
copolymer
Strusture Sample MnSEC IP PDXL
w mol
PS
w mol
HEMA
w mol
Ng Graft
Mn
HO-PS
32 700
12
_ _
77 80
23 20
58
_
DXPS
83 000
24
71 80
17 13
12 75
58
1000
82
Figure 10 1H-NMR spectrum of Multifunctionalized of Polystyrene in CDCl3
Figure 11 1H-NMR spectrum of poly (S-g-PDXL) copolymer (DXPS) in CDCl3
83
341 Determination of Monomer Reactivity Ratios
The application of the classical treatment based on linearization of the copolymerization
equation of Mayo and Lewis91 or the non-linear least-squares approach suggested by Tidwell
and Mortimer95 requires working with high macromonomer concentrations (ie feed
compositions higher than 20-30 of macromonomer)156
The MayondashLewis equation (58) that relates the instantaneous compositions of the monomer
mixture to the copolymer composition is approximated to a simplified form (equation (59))
suggested by Jaacks169 when working with a large excess of one of the comonomers This is
the case of copolymerisation reactions between a conventional comonomer and a
macromonomer of relatively high molecular weight where using low molar concentrations of
macromonomer is mandatory due to its restricted solubility and the extremely viscous media
][ ][ ]
[ ][ ]
[ ] [[ ] [ ]221
211
2
1
2
1
MrMMMr
MM
MdMd
++
=
(58)
[ ][ ] 1
22
1
2
MMr
MdMd
=
(59)
According to equation (59) the copolymer composition or the frequency of branches is
essentially determined by the monomer composition and the monomer reactivity ratio of the
comonomer r2 (inversely proportional to the macromonomer reactivity) under the limit
condition of [M2][M1] gtgt1 In order to obtain reliable values it is frequently necessary to
run the copolymerisation at different conversions or to carry out several copolymerizations
with different initial monomer ratios170 In such cases an integrated form of equation (59) is
used
[ ] [ ][ ][ ] 01
12
02
2 lnlnMM
rMM tt =
(60)
169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046
84
where [Mi]t[Mi]0 is the ratio among the composition of monomer i at time t and the initial
feed composition A plot of ln ([M2]t[M2]0) versus ln ([M1]t[M1]0) should result in a straight
line with a slope that equals to r2 (the reactivity ratio of the comonomer)
Thus the monomer reactivity ratios between the PDXL macromonomers and the comonomers
were estimated with the data in tables 4 and 5 We can apply equation (60) to the estimation
where M1 and M2 are the PDXL macromonomer and copolymer respectively The monomer
reactivity ratios are determined for macromonomers of different Mn (degree of
polymerization) and summarized in Table 7
Table 7 Monomer reactivity ratios for copolymerization of PDXL macromonomers (M1)
with St and MMA (M2)
Sample M2 M1
macromer Mnth
r2 1r2
SP2 St FPP2 2000 012 plusmn 0006 833
SP15 St FPP15 1500 0042 plusmn 6 10-4 238
SP1 St FPP1 1000 0015 plusmn 3 10-4 6666
MP2 MMA FPP2 2000 002 plusmn 001 50
MP15 MMA FPP15 1500 007 plusmn 0 02 1428
MP1 MMA FPP1 1000 0018 plusmn 001 5555
In the case of copolymerization with Styrene and MMA the results suggest that the reactivity
of the methacrylic double bond in the prepared macromonomers is not affected in their
copolymerization with Styrene or MMA This point is confirmed when analysing the inverse
ratio 1r2 = k21k22 which is sometimes considered as the relative copolymerization reactivity
of a macromonomer171 This quantity is the ratio between the crosspropagation and
homopropagation rate constants of comonomer (2) which is directly proportional to the
reactivity of the macromonomer (1) and gives a clear idea of the relative reactivity of a
growing radical ending in a 2 unit towards the addition of monomer (1) in comparison to the
171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620
85
tendency for the homopropagation So we have a situation where r1 gtgt 1 gtgt r2 and it is
expected that the initially formed chains should contain more macromonomers and then more
comonomer segments are added These are only assumptions but they give an indication
about the probable composition drift of the graft copolymers obtained On the other hand in
the case of copolymerization of poly (13dioxolane) macromonomers with styrene (Figure
12) the results show that r2 increases with increasing PDXL side chain length (in terms of
average Mn) and this leads to say that the side macromonomer chain length affect the
reactivity of the comonomer Thus this indicates that a growing radical of macromonomer
with a shorter chain length (ie lower Mn ) attacks more frequently a monomer of the same
nature than it does a macromonomer with a longer length (ie higher Mn) as it can be noticed
from the results in Table 7
However the r2 values of the copolymerization with MMA as shown in Figure 13 give
unclear dependence on the side poly (13dioxolane) macromonomer chain length this may be
due to the resulting polydispersity of the copolymerization Mentioned behaviour may be
related with the reactive structure of comonomers vinyl in the case of Styrene or methacrylic
in the case of MMA in regard to the ending methacrylic double bond of macromonomers
besides the hydrophilic character of the macromonomers
86
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0015 plusmn 3 10-4 SP1
b
r2 = 0042 plusmn 6 10-4
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP15
c
r2= 012 plusmn 0006
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP2
Figure 12 Application of Jaacksrsquo treatment to the St-g-PDXL copolymerization systems
(a) SP1 (b) SP15 (c) SP2
87
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0018 plusmn 001 MP1
b
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 007 plusmn 002MP15
036788
c
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 002 plusmn 001 MP2
Figure 13 Application of Jaacksrsquo treatment to the MMA-PDXL copolymerization systems
(a) MP1 (b) MP15 (c) MP2
88
341 Glass Transition Temperatures
Thermal analysis of Styrene-g-PDXL copolymers allows to determine their glass transition
and melting temperatures In the first place the measurements were performed on a
conventional DSC from which the thermograms obtained show an overlapping of PS glass
temperature and PDXL melting point signals This has been observed for all samples A
different approach in the characterisation of these copolymers was by means of Modulated
Temperature Differential Scanning Calorimeter (MTDSC) which is an extension of
conventional DSC This approach combines high resolution with high sensitivity by use of a
sinusoidal temperature modulation superimposed on a constant temperature or linear
temperature program with a small underlying average heating rate172 173 In comparison to
conventional DSC the MTDSC analysis enables the simultaneous calculations of an
additional quantity the cyclic or modulus of heat capacity Cp (J g-1K-1 172)
ωT
HFp A
AC =
(61)
is the amplitude of the cyclic heat flow (Wg-1) and AWhere AHF Tω is the amplitude of cyclic
heating rate with AT the temperature modulation amplitude (K) ω the modulation angular
frequency (2πp) and p is the modulation period (s)172
In fact the MTDSC splits the overlapped signals into two distinct temperatures melting
temperature of the hydrophilic grafts and glass transition temperature of the hydrophobic
backbone as can be noticed in Figure 14 in which melting temperature appears to be 5626degC
which is closer to the glass transition temperature with a value of 5671degC From the results
obtained out of the thermogram it is clear that the measurements show very close values of
Tm and Tg for all copolymer samples where in conventional DSC these two temperatures
cannot be distinguished
172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
89
Figure 14 MTDSC thermogram of 5SP1 copolymer at heating rate of 2degCmin
Tg was taken at the midpoint of the transition region The results obtained are shown in
Tables 8 and 9 for copolymers with Styrene and MMA respectively Then a plot of the
copolymers Tg has been constructed against PDXL content in order to determine the effect of
the latter on Tgrsquos As it can be noticed in the Figure 15 Tg of the copolymers decreases
exponentially with increasing PDXL content and this may be due to the decrease in the
intermolecular interactions between the molecular chains and can be associated with higher
mobility and flexibility of the polymeric chains when PDXL is incorporated in the
copolymers The results clearly indicate that Tg values of the copolymers depend on the
composition of comonomers and a decrease with increasing PDXL content in the obtained
copolymers
90
Table 8Transition temperatures of Styrene-g-PDXL copolymers obtained by thermal
analysis (DSC) Sample PDXL content Tg wt () (degC) 8SP 85 7489 1
5SP 1424 5671 1
5SP 152 5590 15
21 6739 5SP 2
303 4480 3SP 2
34 2665 2SP15
4025 2SP 4060 2
Table 9Transition temperatures of MMA-g-PDXL copolymers obtained by thermal analysis
(DSC)
Sample PDXL content Tg
wt () (degC)
5MP 10 10545 1
5MP 13 8278 15
21 6576 3MP 2
22 7550 3MP 15
26 7013 2MP1
91
5 10 15 20 25 30 35 40 4520
30
40
50
60
70
80
a
SP COPOLYMERSTg
(degC)
PDXL content in wt()
10 15 20 2560
70
80
90
100
110
b
Tg (deg
C)
PDXL content in wt()
MP COPOLYMERS
Figure 15 Glass transition temperatures vs PDXL macromonomer content for copolymer
systems (a) Styrene-g-PDXL copolymers (b) MMA-g-PDXL copolymers
92
Conclusion
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers The macromonomer reactivity estimation suggests that the
length of the PDXL side chains does affect the reactivity of the methacrylic double bond of
the macromonomer when copolymerized with St However in the case of copolymerization
with MMA there is no dependence on the graft size Finally from DSC measurements the
values of Tg depend on the composition and the size of the PDXL grafts In all copolymers
the increase in amount of the incorporated PDXL macromonomer results in a substantial
decease in glass transition
93
References 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305 156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269 163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671 164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006)
5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219 169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620 172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly
(1 3 Dioxolane)) on Immiscible Polymer Blends
of Polystyrene and Poly (Ethylene Glycol)
41 Background
411 Physical Blends
Physical blending is defined as the simple mechanical mixing of two or more polymers either
in the melt or in solution174 At first glance this approach would seem to be ideal for
preparing hybrids as blending is considered a simple and economical procedure that is
commonly used to produce new products from existing materials175 However in polymer
science the effectiveness of blending is dependent upon the degree of compatibility of the
polymers involved176 At least three general types of materials can result from blending
depending on the mutual solubility and semi-crystallinity of the constituents
412 Equilibrium Phase Behavior
Mixing of two amorphous polymers can produce either a homogeneous mixture at the
molecular level or a heterogeneous phase-separated blend Demixing of polymer chains
produces two totally separated phases and hence leads to macrophase separation in polymer
blends Some specific types of organized structures may be formed in block copolymers due
to microphase separation of block chains within one block copolymer molecule
Two terms for blends are commonly used in literature miscible blend and compatible blend
The terminology recommended by Utracki177 will be used By the miscible polymer blend it
means a blend of two or more amorphous polymers homogeneous down to the molecular
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York (1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York (1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser Publishers Munich (1989)
95
level and fulfilling the thermodynamic conditions for a miscible multicomponent system An
immiscible polymer blend is the blend that does not comply with the thermodynamic
conditions of phase stability The term compatible polymer blend indicates a commercially
attractive polymer mixture that is visibly homogeneous frequently with improved physical
properties compared with the constituent polymers
Miscible blends occur spontaneously when the overall energy of mixing (ΔGmix) is negative
as defined by the Gibbs-Helmholtz free energy equation (Equation 62)
(62)
In the Gibbs-Helmholtz equation ΔHmix is the enthalpy of mixing and ΔSmix is the entropy of
mixing while T is the temperature of the blend Flory-Huggins178 and Scott179 have made
further correlation of enthalpy and entropy as a function of the polymer components and their
properties (Equation 63)
(63)
In Equation 63 χ is a measure of the polymer-polymer interaction energy V is the volume of
the system Φi is the volume fraction of polymer i R is the gas constant T is the temperature
of blending Vr is the reference volume of the monomers and χi is the degree of
polymerization
Examination of Equation 63 reveals that the entropy of mixing is highly dependent on the
molecular weight of the blended polymers while the enthalpy is much more dependent on the
level of interaction between the polymer types Additionally Scott showed that as molecular
weight increases to the level commonly found in commercially useful materials ΔS
approached zero (0) Therefore polymer blends of commercial importance are primarily
influenced by the rate of enthalpy However for polymers with weak interactions (as χ
approaches 1) eg as observed in most polymer pairs the enthalpy of mixing can be further
reduced according to Equation 64
178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279
96
(64)
In Equation 64 δi is the polymerrsquos solubility parameter (an estimation of its ability to be
dissolved in a range of solvents) derived from the square root of the cohesive energy density
pioneered by Hildebrand180 Thus most early work with polymer blends concentrated on
matching the solubility parameters of the component polymers
Unfortunately the theoretical maximum difference in solubility for a 5050 polymer blend is
only 01 (calcm3)12 This narrow margin is much smaller than the standard error among
methods used to determine solubility parameters181 The ability to predict miscibility of
polymer pairs with strong interactions such as donor-acceptor and hydrogen bonding which
can increase miscibility by creating an exothermic reaction upon mixing (ΔH lt0) have been
attempted for many years with varying degrees of success
The formation of miscible blends is dependent on several factors including molecular
structure average chain length tacticity of the polymers as well as the temperature of mixing
and the blending method If the blended polymers are miscible (ΔGmix lt 0) and thus
compatible the resulting material will display an amalgamation of properties which are
predictable using the same techniques as those used for random or statistical copolymers
Polymer blends account for a significant percentage of polymer production and are produced
either to reduce costs to aid in processing or to improve a variety of specific properties For
example polycarbonates have been blended with polybutylene terephthalates to increase
chemical resistance and to aid in processing while polyphenylene oxides are bended with
polystyrenes to improve toughness and increase glass transition temperatures182
413 Compatibilization
As it follows from thermodynamics the blends of immiscible polymers obtained by simple
mixing show a strong separation tendency leading to a coarse structure and low interfacial
180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999)
97
adhesion The final material then shows poor mechanical properties On the other hand the
immiscibility or limited miscibility of polymers enables formation of wide range structures
some of which if stabilized can impart excellent end-use properties to the final material To
obtain such a stabilized structure it is necessary to ensure proper phase dispersion by
decreasing interfacial tension to suppress phase separation and improve adhesion This can be
achieved by modification of the interface by the formation of bonds (physical or chemical)
between the polymers This procedure is known as compatibilization and the active
component creating the bonding as the compatibilizer174 177 183
The most popular method of compatibilization is by addition of a third component In most
cases such an additive is either a block or graft copolymer Since the key requirement is
miscibility it is not necessary for the copolymer to have identical chain segments as those of
the main polymers It suffices that the copolymer has segments having specific interactions
with the main polymeric components viz hydrogen bonding dipole-dipole dipole-ionic
Lewis acid-base etc
Addition of a block or graft copolymer reduces the interfacial tension and alters the molecular
structure at the interface Thus compatibilization by addition changes not only the interfacial
properties but it may affect the flow behavior (hence processability)
One of the disadvantages of the addition method is the tendency of the added copolymers to
form micelles These reduce the efficiency of the compatibilizer increase the blend viscosity
and may lessen the mechanical performance
414 Incorporation of Copolymers for Compatibilization
Block or graft copolymers with segments that are miscible with their respective polymer
components show a tendency to be localized at the interface between immiscible blend
phases Random copolymers sometimes also used as compatibilizers reduce interfacial
tension but their ability to stabilize the phase structure is limited184 Finer morphology and
higher adhesion of the blend lead to improved mechanical properties The morphology of the
resulting two-phase (multiphase) material and consequently its properties depend on a
number of factors such as copolymer architecture (type and molecular parameters of
segments) blend composition blending conditions
183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001)
98
In Scheme19 the conformation of different block graft or random copolymers at the
interface is schematically drawn
Scheme 19 Possible localization of A-B copolymer at the AB interface Schematic of
connecting chains at an interface a-diblock copolymers b-end-grafted chains c-triblock
copolymersdmultiply grafted chain and e-random copolymer
415 The Effect of Compatibilizer on a Blend
The presence of a compatibilizer at the interface substantially affects the development of the
phase structure of molten blends in the flow and quiescent state The position and width of the
concentration region related to co-continuous morphology are affected by two competing
mechanisms A decrease in interfacial tension caused by a compatibilizer favors the formation
and stability of co-continuous structures
The effect of a compatibilizer on fineness of the phase structure can be understood through its
effects on droplet breakup and coalescence A decrease in interfacial tension due to the
presence of a compatibilizer decreases the droplet radius R
Effect of the Compatibilizer Architecture
Compatibilization efficiency of various copolymers follows from their thermodynamic and
microrheological effects It has been generally accepted that the total molecular weight of the
copolymer molecular weight of its blocks and their number are the main structural
compatibilizer characteristics affecting the phase structure of the final blend
99
Effect of Compatibilizer Concentration
The compatibilizing efficiency of the copolymers is besides the architecture a function of
their concentration The effect of a compatibilizer concentration has been quantitatively
characterized by the emulsification curvemdashthe dependence of the average particle diameter of
the minor dispersed phase on copolymer concentration185 The particle diameter decreases
with increase of copolymer concentration until a constant value is obtained For most systems
this value is achieved if the copolymer amount is 15ndash25 of the dispersed phase
416 Methods of Blend Preparation
Five different methods are used for the preparation of polymer blends186 187 melt mixing
solution blending latex mixing partial block or graft copolymerization and preparation of
interpenetrating polymer networks It should be mentioned that due to high viscosity of
polymer melts one of these methods is required for size reduction of the components (to the
order of μm) even for miscible blends
bull Melt mixing is the most widespread method of polymer blend preparation in practice
The blend components are mixed in the molten state in extruders or batch mixers Advantages
of the method are well-defined components and universality of mixing devicesmdashthe same
extruders or batch mixers can be used for a wide range of polymer blends Disadvantages of
the method are high energy consumption and possible unfavorable chemical changes of blend
components This procedure has not been used so far in industrial practice because of large
energy consumption
bull Solution blending is frequently used for preparation of polymer blends on a laboratory
scale The blend components are dissolved in a common solvent and intensively stirred The
blend is separated by precipitation or evaporation of the solvent The phase structure formed
in the process is a function of blend composition interaction parameters of the blend
components type of the solvent and history of its separation Advantages of the process are
rapid mixing of the system without large energy consumption and the potential to avoid
185 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons Inc New York Chap 16 (2000) 186 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709 187 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458
100
unfavorable chemical reactions On the other hand the method is limited by the necessity to
find a common solvent for the blend components and in particular to remove huge amounts
of organic (frequently toxic) solvent Therefore in industry the method is used only for
preparation of thin membranes surface layers and paints
bull A blend with heterogeneities on the order of 10 μm can be prepared by mixing of
latexes without using organic solvents or large energy consumption Significant energy is
needed only for removing water and eventually achievement of finer dispersion by melt
mixing The whole energetic balance of the process is usually better than that for melt mixing
The necessity to have all components in latex form limits the use of the process Because this
is not the case for most synthetic polymers the application of the process in industrial practice
is limited
bull In partial block or graft copolymerization homopolymers are the primary product
But an amount of a copolymer sufficient for achieving good adhesion between immiscible
phases is formed188 In most cases materials with better properties are prepared by this
procedure than those formed by pure melt mixing of the corresponding homopolymers The
disadvantage of this process is the complicated and expensive start-up of the production in
comparison with other methods eg melt mixing
bull Another procedure for synthesis of polymer blends is by formation of interpenetrating
polymer networks A network of one polymer is swollen with the other monomer or
prepolymer after that the monomer or prepolymer is crosslinked189 In contrast to the
preceding methods used for thermoplastics and uncrosslinked elastomers blends of
reactoplastics are prepared by this method
188 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 189 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981)
101
42 Experimental
421 Materials
Polymers used in this research were PEG and PS PEG was purchased from MERCK
company General Purpose PS was obtained from ENPC TP1-Chlef Company Physical and
Structural characterizations of these materials were performed by SEC 1H-NMR and DSC
422 Blend Preparation
PSPEG blends of 5050 wt were prepared by solution casting from THF 40degC The
polymer solutions were stirred until complete miscibility and then cast onto glass dishes and
left to evaporate the solvent to the atmosphere To remove residual solvent after casting the
blends were dried in vacuum oven at 40degC for a weak Table 10 shows the quantities of the
copolymers used for compatibilization of the blends of PSPEG
Table 10 The quantities of the copolymers used for compatibilization of the blends of
PSPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
43 Characterization Techniques for Compatibilization
431 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
102
Relative viscosities of polymer solutions were calculated by dividing the flow times of
solutions by that of the pure solvent The data were plotted using the Huggins equation with
the intrinsic viscosity [η] (dlg-1) determined by extrapolation to infinite dilution
432 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
433 FTIR Analysis
FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
44 Results and Discussion Polyethylene glycol (PEG) is very interesting and important polymers PEG presents good
properties eg hydrophilicity solubility in water and in organic solvents nontoxicity and
absence of antigenicity and immunogenicity190It has attracted increasing attention due to its
potential applications as biomedical and environment friendly materials PEG has been
widely used as a modifier for biomedical surfaces to reduce the protein absorption and
improve their biocompatibility192 and as a stabilizer for emulsion and dispersion It has also
been used as a plasticizer for poly (lactide) (PLA) which is stiff and brittle as a
biodegradable packaging material193
On the other hand polystyrene shows excellent processability good appearance tensile
strength and thermal and electrical characteristics however its brittleness considerably limits
its use in high performance products
Both PS and PEG are widely used commodity polymers Detailed studies on their miscibility
may contribute to technological and environmental applications These polymers form an
interesting pair to study since they exhibit contrasting physical properties PS is a
190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689
103
hydrophobic polymer whereas PEG is hydrophilic PEG is a much softer material than PS
PSPEO blends have been reported as incompatible materials in the literature194 195
N Watanabe et al have reported compatibilization effect of poly (styrene-co-methacrylic
acid) on immiscible blends of this system196
441 Characterization of the Blend Components
Analysis by SEC provides number average-molecular weights and polydispersity indices of
all materials DSC measurements performed to determine their glass transition temperatures
as well as melting point and degree of crystallinity of PEG (See Figure16) 1HNMR spectroscopy analysis was performed on these polymers to determine essentially the
tacticity of PS and also to get information about end groups of PEG which was found to
possess an OH group at each end It has been also determined that the stereoregularity of PS
is Syndiotactic-Atactic (rather highly syndiotactic) (See Figures 17)
Physical characteristics of materials used are given in Table11
Table 11 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PS ENPC TP1-Chlef (from CHI MEI Corp)
105
128 000
1076
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam] Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842
104
Figure 16 1H-NMR spectrum of PEG (Merck) in CDCl3
105
Figure 17 1H-NMR spectrum of Commercial Styrene (ENPC TP1-Chlef) in CDCl3
442 Study of Compatibilization by Dilute Solution Viscometry
a) Introduction
Polymer blends are physical mixtures of structurally different polymers which interact
through secondary forces with no covalent bonding Blending of the polymers may result in a
reduction in the basic cost and improved processing and also may enable properties of
importance to be maximized The polymer blends often exhibit properties that are superior
compared to the properties of each individual component polymer197 198 199 200 The main
advantages of the blend systems are simplicity of preparation and ease of control of physical
properties by compositional change201 202 However the mechanical thermal rheological and
197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85
106
other properties of a polymer blend depend strongly on its state of miscibility on the
molecular scale203
There have been numerous techniques of studying the miscibility of the polymeric blend The
most useful techniques are dynamic mechanical thermal electron-microscopic IR
spectroscopic refractive index203 optical microsscopic204 and viscometric techniques 179 205
Because of its simplicity viscometry is an attractive and very useful method for studying the
compatibility of polymer blends Additional advantages ie that no sophisticated equipment
is necessary and that the crystallinity or the morphological states of the polymer blends do
affect the result206 make the viscometric method more convincing for characterizing polymer
mixtures The principle of using a dilute solution viscosimetry to measure the miscibility is
based on the fact that while in solution molecules of both component polymers may exist in
a molecularly dispersed state and undergo a mutual attraction or repulsion which will
influence the viscosity It is assumed that polymerndashpolymer interaction usually dominate over
polymerndashsolvent ones207 The presence of interactions between atoms or groups of atoms of
unlike polymers is essential to obtain a miscible polymer blend177 179
Estimation of the compatibility of different pairs of polymers based on dilute solution
viscosity for a ternary polymerpolymer-solvent system has been attempted by several
authors including Mikhailov and Zeilkman208 Bohmer and Florian209 Feldman and Rusu210
Krigbaum and Wall211 and Catsiff and Hewett212
The compatibilization of the blends in question has been characterized by viscosity technique
using the Krigbaum and Wall interaction parameter Δb The versatility of the viscometric
technique is not affected by the choice of the solvent as was shown by Kulshreshta et al213
In this section we discuss in details our investigation on the compatibilization of the two
polymer blend systems PSPEG and PMMAPEG 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191
107
b) Theoretical background
The main aspects of the application of dilute solution viscometry method for the study of
interactions and miscibility phenomena in dilute multicomponent polymer solutions were
described Only the most important features will be repeated here It is common to use
empirical relations such as Hugginsrsquo equation214
(65)
for the description of the concentration dependence of viscosity of polymer solutions This
relation is strictly valid only for binary polymer solutions However equations like that of
Krigbaum and Wall211
(66)
And of Catsiff and Hewett212
(67)
were proposed for ideal ternary polymer solutions of the polymer 1+ polymer 2+ solvent type
In previous relations ηsp denotes the specific viscosity [η] is the intrinsic viscosity (limiting
viscosity number) c stands for the mass concentration of polymer and kH is Hugginsrsquo
constant which may be related (in an empirical manner) to the thermodynamic quality of
solvent Relative mass fractions of dissolved polymers wi are used to describe the
composition dependence of viscosity in ternary systems Quantities b 12 and b12 are used to
define the ideal behavior of ternary polymer solutions These are calculated by
(68)
and
(69)
214 ML Huggins J Am Chem Soc 64 (1942) 116
108
respectively Here b denotes the slope of Hugginsrsquo equation for binary solutions
(70)
Moreover it has been shown215 that both the sign and the extent of the deviation of
experimental from theoretical b-values may be correlated to the interactions between
polymeric components of a system under consideration The quantities of interest (miscibility
criterion variables) are defined by
(71)
and
(72)
or can be written in another form
(73)
where m denotes the polymer mixtures Δb intermolecular interaction parameter between
polymer 1and 2 and is considered a good criterion to predict the polymer-polymer
compatibility209 216 217 Δb 0 indicates that the two polymers are compatible whereas
Δb0 indicates that they are incompatible
c) Discussion of the Results
Herein we discuss in detail the compatibilization of PSPEG blends with the synthesized graft
copolymers by viscometric technique The plot of reduced specific viscosity of polymers
versus total polymeric concentration yields a straight line and the intercept and slope
correspond to intrinsic viscosity [η] and molecular interaction coefficient b respectively The
viscosity data for the homopolymers and their blends are presented in Tables 12 and 13
Table 12 Interaction coefficient for binary solutions (polymersolvent) 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin (1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849
109
Polymer components PEG PS
b11 007327 minus
b22 minus 02117
b12 = (b11 b22)12 = 01245 (theo)
Table 13 Interactions parameters for PSPEG blends with poly (St-g-PDXL) copolymers
(2SP2 2SP1 and DXSP) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
DXSP b12 003511 01295 01680 01833 01947
Δb - 00894 00050 00435 00588 00702
2SP2 b12 003511 009826 01052 01314 01515
Δb - 00894 - 00262 - 00193 00069 00270
2SP1 b12 003511 minus minus minus 01262
Δb - 00894 minus minus minus 00017
For incompatible blends the incompatible molecules refuse to overlap thus they shrink in
size which leads to a decrease in hydrodynamic volumes As a matter of fact the crossover in
the reduced viscosity-concentration plot is observed
As far as we are concerned with the blend of PSPEG the results obtained present similar
situation Figure 18 shows the Huggins plots for the homopolymers and the (5050) blend of
PSPEG In this figure a crossover is observed and a decrease of slope occurs at about 05
gdl in the viscosity-concentration plot Above this concentration two incompatible polymers
PS and PEG undergo mutual repulsion in dilute solution the hydrodynamic volume of chains
is lower The reduction of the hydrodynamic volume will result in a decrease of the reduced
viscosity of solution correspondingly the slope of the plot suddenly declines
110
02 03 04 05 06 07 08 09 10 11
03
04
05
06
07
08PS PEG and PSPEG (5050)
PS PSPEG 0 PEG
Redu
ced
visc
osity
η sp
c
(ldl
)
C (dll)
Figure 18 Plots of reduced viscosity (ηspc) vs concentration for PS PEG and PSPEG
blend (0) in THF at 30degC
Figures 19 20 21 and 22 show the incorporation of various amounts of copolymers in the
immiscible blend As far as the amount of the compatibilizers increases the crossover of the
plots occurs at very low concentration or even it is not observed In addition the slope of the
plot increases with an increase of the amount of the compatibilizers introduced in the blend
This is due to the mutual attraction of the blend components which is enhanced by the
presence of the copolymers As a matter of fact the latter act as compatibilizing agents
allowing to the blends to exhibit miscibility
111
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07BLENDS WITH DXPS
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 19 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of DXPS copolymer
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLENDS WITH 2SP2
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 20 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of 2SP2 copolymer
112
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLEND WITH 2SP1 40
PSPEG 0 2SP1 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 21 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with 40 of the dispersed phase of 2SP1 copolymer
02 03 04 05 06 07 08 09 10 1100
01
02
03
04
05
06
07
08
DXPS 40 2SP2 40
2SP1 40
2SP1 40 2SP2 40 DXPS 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 22 comparison of plots of reduced viscosity (ηspc) vs concentration for PSPEG
blends in THF at 30degC with 40 of the dispersed phase of DXPS 2SPS2 and 2SP1
copolymer
113
Figure 22 compares the three copolymers used for compatibilization of PSPEG with respect
to 40 by weight of the dispersed phase addition to the blends
Krigbaum and Wall suggested that information about the interaction between two polymers
should be obtained from the difference of experimental b12 and theoretical b12 Δb A positive
difference between the experimental and theoretical interaction coefficients is evidence of a
compatible polymer pair The higher the value of Δb the higher the extent of compatibility
Negative values refer to repulsive interaction and incompatible mixes The values of Δb
according to equation 73 for different blends with compatibilizers are given in Table 13 and
Figure 23
0 10 20 30 40 5
-010
-005
000
005
010
0
PS PEG BLENDS
2SP2 DXPS
Δb
Amount of incorporated copolymer w ()
Figure 23 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (DXPS and 2SP2) used for compatibilization
It was observed as the amount of compatibilizers increases values of the interaction
parameter increase thereby increasing the compatibility between the two polymer
components of the blend Consequently this indicates that these copolymers act as
compatibilizing agents in the immiscible blends of PS and PEG Now in comparing these
copolymers in terms of structure (number of grafts) and PDXL content it can be noticed that
the results obtained DXPS ( 71 w of PDXL) copolymer show higher values of Δb than
2SP1(30 w of PDXL) and 2SPS2 (4025 w of PDXL) do This is due to the comb-
structure of the DXPS copolymer (synthesized by CRP) and therefore containing more grafts
114
(Ng = 58) than the other copolymers Besides the amount of PDXL in the copolymer PDXL
includes polar groups which provide associative interactions with one of the blend
components (PEG) and thus undergoes significant effects upon compatibilization In the
figure below it can be seen that addition of 10 by weight of the dispersed phase (47 of
total weight of the blend) of DXPS is sufficient to compatibilize the immiscible blend of
PSPEG (5050) Then a drastic increase of the interaction parameter with the addition of the
compatibilizer (DXPS) compared to the addition of either 2SP2 or 2SP1 (Table 13)
From the results shown in the graph miscibility of the blend can be achieved by incorporating
around 25 (11 of total weight of the blend) of 2SP2 copolymer However compatibibility
of the blend with 2SP1 copolymer is obtained at 40 by weight of the dispersed phase since
its interaction parameter (Δb) found to be 00017
It is worth to mention that the PDXL content of 2SP1 is 30 and the length of the grafts is
half that of 2SP2 copolymer For this reason these two copolymers have been chosen for the
purpose of comparison in terms of side chains length
An optimization of the amount of copolymer needed for compatibilization of PSPEG (5050)
blend has been made (corresponding to Δb = 0) as function of the PDXL content and shown
in Table 14
Table 14 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050) vs PDXL content
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
DXPS 0 9 43 71
2SP2 0 245 109 4025
2SP1 0 40 166 30
115
443 Optical Microscopy and Phase Morphology
PDXL is a perfect alternate copolymer of poly (ethylene oxide) (PEO) and poly (methylene
oxide) (PMO) that has the same curious combination properties as PEG So PDXL must be
at least miscible with PEG or adhere at the interface between PS and PEG and between
PMMA and PEG The compatibility between hydrophobic PS or PMMA and hydrophilic
PEG is very poor Compatibilization between components of the two sets of polymer blends is
studied by optical microscopy
The morphological characteristics of the blends by different compatibilizers are presented in
Figure 24 The optical microscopy micrographs of PSPEG blends without compatibilizers
show a poor dispersion for PS disperse phase and a ldquoball-and-socketrdquo topography due to the
poor interfacial adhesion between PEG matrix and the dispersed phase However with the
addition of compatibilizers the morphological characteristics of the polymer blends are
greatly altered It can be noticed that for these two different blends the particle size of PS
domains gets progressively much smaller and uniform in compatibilized blends than in
incompatibilized ones This may be explained by the significant increase of the phase
interfacial adhesion Consequently the domain size strongly depends upon the
compatibilizers used
116
a) PSPEG (5050) 0 (without compatibilizer)
DXPS 10 DXPS 20 DXPS 30 DXPS 40 b) Compatibilizing effect of DXPS copolymer
2SP2 10 2SP2 20 2SP2 30 2SP2 40 c) Compatibilizing effect of 2SP2 copolymer
2SP1 40
117
d) Compatibilizing effect of 2SP1copolymer at 40 addition
Figure 24 Optical micrographs showing phase structure in 5050 PSPEG blends
a) blends without compatibilizer b) with DXPS c) with 2SP2 d) with 40 of 2SP1
For instance the PSPEG blends with the incorporation of the copolymers DXPS 2SP2 and
2SP1 as compatibilizers (Figure 24) the morphology displays a very fine dispersion of PS
phase and strong interfacial adhesion with PEG Matrix The good compatibilizing effect
mainly that of DXPS can be explained by two mechanisms
First the PDXL units in the compatibilizer interact with PEG ether groups leading to a good
adhesion at interface between the components of the blend In addition hydrogen bonding
may also exist between PDXL and PEG further increasing compatibilization Second since
the compatibilizer also contains styrene blocks it contributes to provide a good compatibility
with PS Consequently the remarkable compatibilizing effect of PS-g-PDXL copolymers
induced a drastic decrease in interfacial tension and suppression of coalescence between the
originally immiscible polymer phases
As it can be noticed from the micrographs given in the figure above the compatibilizer
exhibits finer dispersion and homogeneous morphology of the blends as the amount of
compatibilizers increases
Eventually each compatibilizer has its own effect on the immiscible blends depending on the
amount of PDXL (side chains) and number of grafts present in the copolymers
By comparing micrographs shown in Figure 24 b and c the compatibilization effect of DXPS
copolymer which contains more grafts but shorter is different from that of the 2SP2
copolymer In the case of DXPS it is observed that the size of the dispersed droplets is
deceased significantly and results in finer dispersion morphology However 2SP2 copolymers
shows an improvement in compatibility of the blend after addition up to 30 wt of the
dispersed phase (13 total weight of the blend) exhibits homogeneous morphology This
may be related to length of the grafts In all cases these copolymers act as good
compatibilizers for the blend of 5050 wt PSPEG
444 FTIR Analysis
The FTIR technique is very important since it allows one to study the specific interactions
between the polymers The knowledge of the polymerndashpolymer interactions will be useful for
118
studies of the compatibility in polymer blends To verify the intermolecular interactions that
can play a role in miscibility the vibrational spectra of the blends studied in the present work
were obtained In polymeric systems where there are multiple interactions vibrational bands
such as ν (C=O) ν (COC) and ν (OH) present contributions of spectroscopic free and
associated forms
In order to elucidate the role played by intermolecular interactions in the miscibility of these
blends FTIR absorption of individual polymer components PS PEG and PMMA and
compared to that of the mixtures Figures 26 27 and 28 present the FTIR absorption spectra
from 4000 to 400 cm-1 for all samples
In the case of PS the high-frequency infrared spectra consist of seven absorption bands The
bands with peak locations at 3008 3026 3060 3082 and 3103 cm-1 are due to C-H stretching
of benzene ring CH groups on the PS side-chain The bands with peak positions of 2924 and
2850 cm-1 are due to the C-H stretching vibration of the CH2 and CH groups of the main PS
chain respectively PEG with molecule chemical structure of HO-[CH2-CH2-O]n-H exhibits
important absorption bands from FTIR spectroscopy measurements as shown in Figure 25 It
was verified contributions associated with CndashOndashC symmetric stretching of ether groups218-220
221 from 1050 to 1150 cm-1 with maximum peak at 1150 cm-1 Characteristics CH2-O
stretching modes from 2800-3000 cm-1 are observed214 At low frequency region peaks at 850
and 890 cm-1 are assigned to CndashOndashC stretching and at 500 cm-1 ascribed to CndashOndashC
deformation The presence of PDXL in the blends is detected by the intense frequency at 1140
cm-1 which is assigned for acetal groups In addition both PDXL and PEG contain ether
groups and the spectra show that the corresponding peaks are overlapped for the blends The
intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of PEG
crystallinity in the blends222
218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10 219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601
119
It can be observed also a typical large hydroxyl bands with two distinct contributions which
can be seen for all samples They are attributed to the spectroscopically free and bonded ndashOH
stretching forms at 3600-3800 cm-1 and 3200-3500 cm-1 respectively221 - 227
500 1000 1500 2000 2500 3000 3500 4000-05
00
05
10
15
20
25
30
35
PS and PEG PEG PS
Abs
orba
nce
Wave number (cm-1)
Figure 25 FTIR spectra of PS PEG over 4000-400 cm-1 range
227 Peppas NA Wright L Macromolecules 1996298798ndash804
120
500 1000 1500 2000 2500 3000 3500 4000
0
1DXPS IN PSPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 26 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS)
All these absorption bands for individual polymer were observed in the FTIR spectrum of the
5050 (ww) PSPEG in which they were combined to give superimposed bands in the regions
of 750-1500 cm-1 and 2700- 3100 cm-1
The hydroxyl vibrational frequency is discernible in the blend spectrum for PSPEG at 0
With the incorporation of the copolymers for compatibilization a number of bands showed
small shifts and changes in position and shape in the resulting spectra In Figures 28 29 and
30 as it can be noticed that in the hydroxyl absorption region a decrease in the fraction of
free OH groups is observed as the amount of copolymers is increased in the blend This can
be due to the flexibility of the PDXL graft chains on the other hand to the acetal and ether
groups of PDXL which are probably randomly distributed among an increasing number of
hydroxyl groups of PEG statistically favoring the formation of the PDXL and PEG hydrogen
bond interaction The results indicate that the intermolecular hydrogen bonding between the
ether oxygen of PDXL and the hydroxyl groups of PEG may be formed thereby reducing the
fraction of free OH which is consistent with the shifts observed in the region of hydroxyl
stretching Intermolecular hydrogen bondings are expected to occur among PDXL and PEG
chains due the high hydrophilic forces These interactions have replaced the intramolecular
121
interactions between COC and OH groups of PEG before addition of containing PDXL
copolymers It can be noticed a progressive shift of hydroxyl band from 3340 to 3420 cm-1
with DXPS and from 3340 to 3350 cm-1 when 2SP2 is added This shift can be attributed to
the decrease of intramolecular interactions among hydroxyl groups within PEG chains in
favor to intermolecular interactions between PDXL and PEG228
500 1000 1500 2000 2500 3000 3500 4000
0
1
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 27 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2)
228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
122
3200 3300 3400 3500 3600 3700 3800
00
01
DXPS IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 28 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS) in the hydroxyl absorption region
3200 3300 3400 3500 3600 3700 3800
00
02
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 29 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2) in the hydroxyl absorption region
123
3200 3300 3400 3500 3600 3700 3800
00
DXPS 40 2SP2 40 2SP1 40
Abs
orba
nce
Wave number (cm-1)
Figure 30 FTIR spectra comparison of PSPEG blends (5050) with different compatibilizers
in the hydroxyl absorption region
Conclusions An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends Again The PS blocks of the copolymer result in good
compatibility with PS component of the blends The compatibilization of PSPEG blends is
apparently associated with hydrogen bonding where groups of the acetal units in PDXL
interact with hydroxyl groups of PEG These form a stronger interface between the two
phases which leads to important modifications of the blend properties Apparently the FTIR
result is in good agreement with the miscibility criteria proposed by Krigbaum and Wall (Δb)
interaction parameter which results from dilute-solution viscometry (DSV) method It can be
concluded that by the addition of 20ndash40 wt of incorporated copolymer reveal a good
compatibilizing efficiency for the blend systems as it was observed from micrographs as well
124
References
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York
(1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York
(1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser
Publishers Munich (1989) 178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279 180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999) 183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001) 185 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709
125
186 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and
Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458 187 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 188 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981) 189 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons
Inc New York Chap 16 (2000) 190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689 194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam]
Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842 197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191 214 ML Huggins J Am Chem Soc 64 (1942) 116 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin
(1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849 218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10
126
219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601 227 Peppas NA Wright L Macromolecules 1996298798ndash804 228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
127
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g-
Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of
Polystyrene and Poly (Ethylene Glycol)
51 Introduction
PMMA is more than just plastics of paint Often lubricating oils and hydraulic fluids tend to
get really viscous and even gummy when they get cold This is a real pain when operating
heavy equipments in very cold weather When a little bit of PMMA is dissolved in these oils
and fluids they donrsquot get viscous in the cold and machines can be operated down to -100degC
PMMA can find a several applications namely adhesive optical coating medical packaging
applications and so forthhellip
In medical applications PMMA and its derivatives are used particularly for hard tissue repair
and regeneration229 PMMA beads have been developed to deliver aminoglucoside antibiotics
locally for the treatment of bone infections230 PMMA and PEG form an important and unique
pair of polymers in that they are chemically different In the present work this study may
shed light on the PMMA properties modifications induced by blending with PEG to overcome
the difficult processing of rigid PMMA
Several studies have been made on blends of poly (ethylene oxide) PEO and PMMA in the
last decades but very few on PMMAPEG blends231 232 233
Numerous works reported that the miscibility domain ranges between 10 and 30 of PEO by
weight depending on the PMMA tacticity or molecular weight No phase diagram is available
yet in the literature for PMMAPEO and neither it is for PMMAPEG234
229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703
127
52 Experimental
521 Materials
PEG and PMMA were used as blend components PMMA was obtained from ENPC TP1-
Chlef Company PEG was purchased from MERCK Company Physical and Structural
characterizations of these materials were performed by SEC 1H-NMR and DSC
522 Blend Preparation
Blends of PMMAPEG (5050) were prepared using the same procedure as described for the
blends discussed in the previous chapter Table 15 shows the quantities of the copolymers
used for compatibilization of the blends of PMMAPEG
Table 15 The quantities of the copolymers used for compatibilization of the blends of
PMMAPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
53 Characterization Techniques
531 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
532 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
128
533 FTIR FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
54 Results and Discussion
541 Characterization of the Homopolymers
The polymers have been analyzed by SEC to determine their number average-molecular
weights and polydispersity indices DSC measurements performed to determine their glass
transition temperatures as well as melting point of crystallinity of PEG 1HNMR spectroscopy analysis revealed the tacticity of PMMA It has been found that PMMA
is Syndiotactic-Atactic (highly syndiotactic) as shown in Figure 3 and 321
Physical characteristics of materials used are given in Table 16
Table 16 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PMMA ENPC TP1-Chlef (fromLG MMA Corp)
119
55 000
113
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
129
Figure 31 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in CDCl3
Figure 32 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in the methyl shifts
region in CDCl3
130
542 Dilute Solution Viscometry
Dilute solution viscometry has been utilized to evaluate miscibility of PMMAPEG blends
and the same approach discussed in the previous section has been followed The
experimental reduced viscosities of the polyblends are plotted against concentration in dilute
solution viscometry Eventually plots of pure polymers and polyblends of 5050 PMMAPEG
are first obtained Then their interaction coefficients are determined as shown in Table 17
Table 17 Interaction coefficient for binary solutions (polymersolvent)
Blend components PEG PMMA
b11 007327 minus
b22 minus 006561
b12 = (b11 b22)12 = 006933 (theo)
The compatibility of this system has been evaluated through the sign of Δb The values of the
latter according to equation 73 for different amounts of poly (MMA-g-PDXL) copolymers in
the blends are given in Table 18 It is observed that the blend of PMMAPEG at 5050 by
weight shows a negative value of Krigbaum and Wall parameter which indicates
incompatibility of the system as it is expected Similarly to PSPEG blend a crossover in the
reduced viscosity-concentration plot is observed and a decrease of slope arises in the range of
05 to 066 gdl in the viscosity-concentration plot as shown in Figure 33 This is attributed to
the repulsive intermolecular interactions between the polymer chains
Then the incorporation of the copolymers at various amounts presents positive values
progressively Curves of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in
THF at 30degC with various amounts of copolymer are given in Figures 34 35 and 36
131
Table 18 Interactions parameters for PMMAPEG blends with poly (MMA-g-PDXL)
copolymers (3MP2 2MP2 and 3MP1) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
3MP2 b12 00288 01308 01904 02373 02602
Δb - 004053 00615 01211 01680 01909
2MP2 b12 00288 01286 01690 01893 02296
Δb - 004053 00593 00997 01200 01603
3MP1 b12 00288 00868 01670 02010 02379
Δb - 004053 00175 00977 01317 01686
00 01 02 03 04 05 06 07 08 09 10 11020
025
030
035
040PMMAPEG (5050) 0
PEG PMMAPEG 0 PMMARe
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 33 Plots of reduced viscosity (ηspc) vs concentration for PMMA PEG and
PMMAPEG blend (0) in THF at 30degC
132
02 03 04 05 06 07 08 09 10 11000
005
010
015
020
025
030
035
040 BLENDS WITH 3MP1
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 34 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP1 copolymer
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040
045BLENDS WITH 3MP2
PMMAPEG 0 10 20 30 40
Redu
ced
visc
osity
η
spc
(d
lg)
C (gdl)
Figure 35 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP2 copolymer
133
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040BLENDS WITH 2MP2
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 36 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 2MP2 copolymer
From our viscosity data as the copolymer content increases in the blend the polymer blend
molecules will become disentangled more spaciously resulting in a greater interaction
between structurally similar component segments This suggests that there are attractive
forces that induce miscible behavior of the blends as it is observed in Figure 37
0 10 20 30 40 5-01
00
01
02
0
PMMA PEG BLENDS
3MP2 2MP2 3MP1
Δb
Amount of incorporated copolymer w ()
Figure 37 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (3MP2 2MP2 and 3MP1) used for compatibilization
134
The three copolymers (3MP2 2MP2 and 3MP1) involved in this study for compatibilization
are different from the point of view of the PDXL content and the graft length For instance
3MP2 and 2MP2 have similar and longer grafts since the theoretical number average-
molecular weight of the graft is 2000 gmol However they contain different amount of
PDXL In the case of 3MP1 this graft copolymer has a structure with shorter side chain length
(Mn = 1000 gmol) corresponding to the half of the graft size in the former copolymers From
the observations made out of the figure above 3MP2 copolymer (21 w of PDXL) provides
higher values of the interaction parameter and therefore greater extent of compatibility
compared to the other copolymers since it has long grafts which allows penetration into the
other phase
It can be concluded that all three copolymers show good results for compatibilization on the
basis of the Δb criterion of polymer-polymer miscibility determined by viscometry
Similarly the minimum amount of copolymer needed for compatibilization of PSPEG
(5050) blend has been determined corresponding to Δb = 0 as function of the PDXL content
and shown in Table 19
Table 19 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050)
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
2MP2 0 34 16 35
3MP2 0 37 18 21
3MP1 0 58 28 19
135
543 Optical Microscopy and Phase Morphology
a) PMMAPEG (5050) 0 (without compatibilizer)
b) Compatibilizing effect of 2MP2 copolymer
c) Compatibilizing effect of 3MP2 copolymer
d) Compatibilizing effect of 3MP1copolymer
Figure 38 Optical micrographs showing phase structure in 5050 PMMAPEG blends
a) blends without compatibilizer b) with 2MP2 c) with 3MP2 d) with 3MP1
136
Figure 38 presents microscopy images of PMMAPEG blends with varying amounts of
compatibilizers The morphological characteristics of the blends of PMMAPEG without
compatibilizers show a poor dispersion of PMMA as a dispersed phase The addition of
compatibilizers changes drastically the morphological topology of this system The
compatibilizers used are of different length of the side chains and also different PDXL
content By introducing progressively variable amounts of the compatibilizers they display
similarly the morphological characteristics to some extent It is observed that the phase
separated domains of PMMA in the blends are reduced with increasing amounts of the
compatibilizers This is due to the compatibility of PMMA of the copolymers with the
PMMA blend component and on the other hand to the interfacial interactions of the PDXL
of the copolymers and PEG component of the blends From these results it is revealed that
compatibilizing effect of 2MP2 copolymer on this system is great compared to the others Not
only causes the size of the dispersed droplets to decrease but also dispersed droplets become
homogeneous However 3MP1 copolymer which contains shortest grafts (about half length
of those of the other copolymers) and less amount of PDXL shows less reduction in the
droplet size compared to the other copolymers Therefore it can be concluded that the
compatibilization of this blend depends upon length and number of grafts
On the overall observations these compatibilizing copolymers are very effective and hence
influence and improve the compatibility of PMMAPEG blend at a composition of 5050 wt
544 FTIR Analysis
Same observations can be made for the blends of PEG with PMMA The FTIR spectrum of
this blend at 0 compatibilizer is shown in Figure 39 For pure PMMA the
spectroscopically free carbonyl group band is observed at 1730 cm-1 In the blend sample one
large vibrational band due to hydroxyl group stretches in pure PEG is observed with two
distinct contributions which can be seen for all samples They are attributed to the
spectroscopically free and associated hydroxyl forms at 3495 and 3600 cm-1 respectively
A large band in the wave number range of 1400-1500 cm-1 is assigned to the deformation
vibration of the methyl groups The bands with peaks locations at 2820 and 2990 cm-1 are due
to C-H symmetrical and asymmetrical stretching vibration of CH3 respectively Peaks at
2886 and 2950 cm-1are ascribed to C-H symmetrical and asymmetrical stretching vibration of
CH2 figures 40 and 41 The C-O band is observed in the range of 1150- 1210 cm-1
137
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 PMMAPEG 0 Blend
Abs
orba
nce
Wave number cm-1
Figure 39 FTIR spectra of PMMAPEG 0 over 4000-400 cm-1 range
2750 2800 2850 2900 2950 3000 3050 3100-05
00
05
10
15
20
Abs
orba
nce
PEG PMMAPEG 0
Wave number cm-1
Figure 40 FTIR spectra of PMMAPEG 0 and PEG over the 3100-2700 cm-1 range
138
2750 2800 2850 2900 2950 3000 3050 3100
00
05
10
152MP2 in PMMAPEG
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 41 FTIR spectra of PMMAPEG 0 blends with 2MP2 addition over the 3100-2700
cm-1 range
The incorporation of PMMA-g-PDXL copolymers in the blends makes some changes in the
resulting spectra as it can be noticed in Figures 42 - 44 In the hydroxyl absorption region
same phenomenon has occurred as in the PSPEG blends The fraction of free OH groups has
decreased as the amount of the copolymers increased as shown in figures 45 and 46 which
present the effect of different compatibilizers in the hydroxyl absorption region This can be
explained as discussed above by the fact that the PEG hydroxyl groups undergo other
intermolecular interactions essentially with PDXL chains of the copolymers A comparison of
the effect of the three copolymers involved in the compatibilization at the highest amount
added is given in figure 47 It can be noticed that 2MP2 shows very few fraction of free OH
groups compared to the others This copolymer contains more PDXL (35 wt with 4 grafts)
than the others do (21 wt with 3 grafts and 19 wt with 3 grafts in 3MP2 and 3MP1
respectively)
A crystalline PEG phase is confirmed by the presence of the triplet peak of the COC
stretching vibration at 1148 1110 and 1062 cm-1 with a maximum at 1110 cm-1235 236
Changes in the intensity shape and position of the COC stretching mode are associated with
235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115
139
the interaction between PEG and PMMA-g-PDXL In addition both polymers contain the
same ether group and the spectra show that the corresponding peaks are overlapped for the
blends The intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of
PEG crystallinity in the blends237
Therefore the presence of this interacting system is probably responsible for the miscibility
and low degree of crystallinity observed for these blends
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
202MP2 in PMMAPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 42 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (2MP2)
237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
140
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 43 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2)
500 1000 1500 2000 2500 3000 3500 4000
0
1
2 3MP1 IN PMMAPEG BLENDS 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 44 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1)
141
3500
00
05
3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 45 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2) in the hydroxyl absorption region
3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
-02
00
02
04
06
08
3MP1 IN PMMAPEG 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 46 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1) in the hydroxyl absorption region
142
3500
2MP2 40 3MP2 40 3MP1 40
Abs
orba
nce
Wave number cm-1
Figure 47 FTIR spectra comparison of PMMAPEG blends (5050) with different
compatibilizers in the hydroxyl absorption region
The results from FTIR spectra indicate the compatibility of these polymer blends with the
addition of the PDXL copolymers via hydrogen bonds is observed and confirmed mainly by
the shifts of bands of the hydroxyl stretching modes
143
Conclusions
From the observations made out from this study reveal that all three copolymers show good
results for compatibilization on the basis of the Δb criterion of polymer-polymer miscibility
determined by viscometry Therefore these copolymers act as good compatibilizers since it
was found that the minimum amount needed for compatibilizing is between 1 to 3 of the
total weight of the blend which corresponds to 3 to 6 of the dispersed phase This
compatibilization is due to the fact that the copolymers have constituents which present strong
interactions with both polymer components of the blends These results are in great agreement
with microscopy analyses which demonstrate that the phase separated domains of PMMA in
the blends are reduced with increasing amounts of the compatibilizers This is due to the
compatibility of PMMA of the copolymers with the PMMA blend component and on the
other hand to the interfacial interactions of the PDXL of the copolymers and PEG component
of the blends
From FTIR results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PMMA and relatively long PMMA backbone of PMMA-g-PDXL copolymers respectively
These compatibilizing copolymers are very effective and hence influence and improve the
compatibility of PMMAPEG blend at a composition of 5050 wt
144
References 229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703 235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115 237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
145
CONCLUSIONS
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel using an unsaturated alcohol (2-
HPMA) as a transfer agent results in linear polymeric chains in order to prevent formation of
cyclic oligomers through cationic polymerisation of cyclic acetals They were all prepared at
the same reaction conditions
The characterization of these macromonomers has been conducted using different methods of
analysis Structure and molecular weight determination were provided from SEC and Raman
and 1H-NMR spectroscopy
We were interested in obtaining a hydrogel based on fully PDXL segments and study its
swelling and viscoelastic behaviour The hydrogel has combined special properties The
results reveal a perfect elastic and resistant hydrogel with interesting viscoelastic properties
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers Structure composition and number of grafts of the
copolymers were determined by SEC and 1H-NMR spectroscopy Another approach for
copolymerization has been made in order to compare the copolymers obtained from different
types of polymerization reactions like Conventional Free Radical and Controlled Radical
Polymerizations In the latter the copolymer obtained possesses larger number of grafts than
those from the former
The macromonomer reactivity estimation suggests that the length of the PDXL side chains
does affect the reactivity of the methacrylic double bond of the macromonomer when
copolymerized with St However in the case of copolymerization with MMA there is no
dependence on the graft size Finally from DSC measurements the values of Tg depend on
the composition and the size of the PDXL grafts In all copolymers the increase in amount of
the incorporated PDXL macromonomer results in a substantial decease in glass transition
An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
146
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends
The compatibilization effect of the copolymers used in this study on the PSPEG and
PMMAPEG was demonstrated from the viscometric results The contribution of both PS or
PMMA and PDXL of the copolymers has played a big role in the compatibilization of these
two different systems of blends thereby resulting in good compatibility due the chemical
affinity between these components which leads to a drastic decrease in interfacial tension and
suppression coalescence between the blend constituents
It has been shown that the immiscible blends in question exhibit compatibility when small
amount of copolymers synthesized for this purpose are added except for one of them
Styrene-g-PDXL copolymers act as good compatibilizers for PSPEG blends since it was
found that the minimum amount needed for compatibilizing is less than 11 of the total
weight of the blend which corresponds to 25 of the dispersed phase This compatibilization
is due to the fact that the copolymers have constituents which present strong interactions with
both polymer components of the blends
Compared with PS-g-PDXL with DXPS content the DXPS is more effective binary polymer
blends compatibilizer in the PSPEG blends which is due to the high number of grafts and
high PDXL content This has led to good adhesion of PDXL chains with the PEG phase in the
blends Again The PS blocks of the copolymer result in good compatibility with PS
component of the blends The compatibilization of PSPEG blends is apparently associated
with hydrogen bonding where groups of the acetal units in PDXL interact with hydroxyl
groups of PEG These form a stronger interface between the two phases which leads to
important modifications of the blend properties
Similarly PMMA-g-PDXL copolymers act as good compatibilizers since it was found that
the minimum amount needed for compatibilizing is between 1 to 3 of the total weight of
the blend which corresponds to 3 to 6 of the dispersed phase This compatibilization is due
to the fact that the copolymers have constituents which present strong interactions with both
polymer components of the blends
These results are in great agreement with microscopy analyses which demonstrate that the
phase separated domains of PMMA and PS in their respective blends are reduced with
increasing amounts of the compatibilizers
147
Specific interactions between chemical groups of two blend components can play an
important role in polymer mixtures There is a range of such interactions of varying strengths
which has been identified in polymer blends and such interactions are generally defined for
small molecules It should be noted that the extension of this concept to polymers is not
always straightforward it is more difficult to identify interactions in polymers the
spectroscopy is more complex and molecular conformations are less certain This situation is
further complicated because researchers use different names and definitions to describe
similar interactions
FTIR investigation showed that these interactions have been observed through the changes in
IR absorption peaks of PS PEG and PMMA upon mixing with increasing amount of
compatibilizers in their blends which have given rise to a wide investigation
From these the results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PSPEG and PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PS or PMMA and relatively long PS or PMMA backbone of PS-g-PDXL and PMMA-g-
PDXL copolymers respectively
148
182 Typical Features of ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 44
183 Controlled Compositions by ATRP helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 46
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 49
CHAPTER II Synthesis and Characterization of Macromonomers 54
21 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 54
22 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
221 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 55
222 Synthesis of Poly (13-dioxolane) Macromonomers helliphelliphelliphellip 57
223 Synthesis of Poly (13-dioxolane) Hydrogel Network helliphelliphellip 57
23 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
231 Raman Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 57
232 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
233 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
234 Swelling Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 58
235 Rheological Measurements helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
24 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 59
241 Structural Characterization of Macromonomers helliphelliphelliphelliphellip 59
242 Molecular Weight Determination helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 62
243 Swelling of Poly (13 Dioxolane) Hydrogel helliphelliphelliphelliphelliphelliphellip 63
244 Viscoelastic Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 64
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 67
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 68
CHAPTER III Synthesis and Characterization of Copolymers 69
31 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 69
32 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
321 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
322 Synthesis of Poly (Styrene-g-Poly (1 3-dioxolane)) helliphelliphelliphellip 71
323 Synthesis of Poly (Methyl Methacrylate-g-Poly (1 3-dioxolane))76
33 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
331 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
332 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
333 Diffraction Scanning Calorimetry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
34 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 78
341 Structural Characterization of the Copolymers helliphelliphelliphelliphellip 78
342 Molecular Weight Determination and Copolymer Composition 80
343 Determination of Monomer Reactivity Ratios helliphelliphelliphelliphelliphellip 84
344 Glass Transition Temperatures helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 89
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 93
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
41 Background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
411 Physical Blends helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
412 Equilibrium Phase Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
413 Compatibilization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 97
414 Incorporation of Copolymers for Compatibilization helliphelliphellip 98
415 The Effect of Compatibilizer on a Blend helliphelliphelliphelliphelliphelliphelliphellip 99
416 Methods of Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 100
42 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
421 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
422 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
43 Characterization Techniques for Compatibilization helliphelliphelliphelliphelliphelliphelliphellip 102
431 Dilute Solution Viscometric Measurements helliphelliphelliphelliphelliphelliphellip 102
432 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
433 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
44 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
441 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphellip 104
442 Study of Compatibilization by Dilute Solution Viscometry hellip 106
443 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 116
444 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 118
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 124
References helliphelliphelliphelliphelliphellip helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 125
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g- Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
51 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 127
52 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
521 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
522 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
53 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
531 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
532 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
533 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
54 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
541 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphelliphellip 129
542 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 131
543 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 136
544 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 137
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 144
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 145 CONCLUSIONS helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 146
SUMMARY
Research and development performed on synthetic polymers during the last century has led to
many classes of different polymers for specific applications New types of synthetic polymers
with tailor-made properties are still being introduced for new applications The challenge for
polymer chemists is to control and alter the polymerization conditions such that the final
product has a well-defined structure with desired properties The complex structure of
polymers requires continued analytical chemical efforts to understand the polymerisation
process and the relationships between the molecular structure and material properties
The central point of this thesis is the synthesis and the exploration of the benefits of graft
copolymers derived from poly (1 3 dioxolane) (PDXL) as compatibilizing agents via their
incorporation in immiscible polymer blends The enhancement of adhesion in the solid state
can be accomplished by introducing a compatibilizer that can act as an adhesive between two
polymers andor by control of morphology especially by inducing the phase co-continuity
Graft copolymers offer all Properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheological control i e it
leads to decreased melt viscosities which is an important advantage for processing Depending
on the nature of their backbone and side chains they can be used for a wide variety of
applications such as impact-resistant plastics thermoplastic elastomers polymeric
emulsifiers and even more exciting is the ability of these graft copolymers to function as
compatibilizersinterfacial agents to blends immiscible polymers
The state-of-the-art technique to synthesize graft copolymers is the copolymerization of
macromonomers with low molecular weight comonomers It allows the control of the
polymeric structure which is given by three parameters (i) chains length of the side chains
which can be controlled by the synthesis of macromonomers by living polymerization (ii)
chain length of the backbone which can be controlled in a living polymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular-weight monomer
i
New properties lower prices and reuse of polymers are needed to meet demands of todayrsquos
society and hence of the polymer industry Unfortunately the demands for many applications
need a set of properties that no polymers can fulfil One method to satisfy these demands is by
mixing two or more polymers Materials made from two polymers mixed are called blends In
recent years blending of polymers as a means of combining the useful properties of different
materials to meet new market applications with minimum development cost offers an
interesting route to improve a variety of specific properties of the thermoplastics This has
been increasingly used by the polymer industry
Much work has been done on the blending (mixing) of polymers by many authors A large
part of these studies deal with attempts to obtain a combination of properties of different
polymers Unfortunately these properties of the polymer blends are usually worse instead of
better for many combinations of polymers Significance for these properties is compatibility
between the different polymers which is frequently defined as miscibility on a molecular scale
of the blends components The incorporation of a dispersed phase into a matrix mostly leads
to the presence of stress concentrations and weak interfaces arising from poor mechanical
coupling between phases and therefore morphologies with coarseness commonly on
micrometer scale are obtained Improving mechanical and morphological properties of an
immiscible blend is often done by compatibilization which is a process of modification of the
interfacial properties in immiscible polymer blend resulting in reduction of the interfacial
tension coefficient formation and stabilisation of the desired morphology The use of graft or
block copolymers as compatibilizers for immiscible polymer blends has become an efficient
means for development of new high-performance polymer materials There have been
numerous techniques of studying the miscibility of the polymeric blends The most useful
techniques are viscosimetry measurementsiiiiii thermal analysisiv dynamic mechanical
analysisv refractive indexvi nuclear magnetic resonance methodvii scanning electronviii and
optical spectroscopyix
i Z Sun W Wang and Z Fung Eur Polym J 28 (1992) 1259 ii Aroguz AZ and Baysal BM Eur Polym J42 3 (2006) 11ndash5iii Zhang Y Qian J Ke Z Zhu X Bi H and Nie K Eur Polym J 38 (2002) 333ndash7 iv M Song and F Long Eur Polym J 27 (1991) 983 v Olabisi O Rebeson LM and Shaw MT Polymerndashpolymer miscibility New York Academic Press (1979) vi AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 vii EG Crispim ITA Schuquel AF Rubira and EC Muniz Polymer 41 (3) (2000) 933 viii Martin IG Roleister KH Rosenau R and Koningsveld RJ Polym Sci Part B Polym Phys24 (1986) 723 ix W Wu X Luo D Ma Eur Polym J 35 (1999) 985
ii
Well-known examples of commercial blends are high impact polystyrene (HIPS) and
acrylonitrile-butadiene-styrene (ABS) These blends are tough and have good processability
One of the most interesting examples of an amorphous polymer is polystyrene because of its
brittleness Adding a compatibilizer with the structure of a copolymer to
Polystyrenepolyethylene (PSPE) improves the toughness by a factor 3x Another example is
the use of poly (styrene-co-methacrylic acid) as a compatibilizer in immiscible (incompatible)
blends of PS and polyethylene (PEG)xi
It is of great interest to study miscibility and phase behaviour of two different commodity
immiscible polymer blend systems as PSPEG and polymethyl methacrylate polyethylene
glycol (PMMAPEG) by adding poly (styrene-g-PDXL) and poly (methyl methacrylate-
PDXL) copolymers as compatibilizers respectively Firstly these systems consist of a very
rigid amorphous component (styrene andor PMMA) and a very flexible low-melting point
PEG The extremely high difference of glass transition temperatures (Tg) between the
components motivates us to investigate the phase behaviour of the blends via
compatibilization with prepared grafted copolymers
The first part of the thesis is devoted to the synthesis and characterization of amphiphilic graft
copolymers which were prepared in solution by radical polymerization of hydrophilic poly (1
3 dioxolane) macromonomers as side chains and hydrophobic comonomers such as styrene
and methyl methacrylate as backbone The second part of the thesis describes the blends
preparation and the study of the compatibilization effect of the incorporated amphiphilic graft
copolymers on immiscible (incompatible) blends
The research work in this thesis is presented through several chapters described as follows
Chapter I is a bibliographic survey on polymerization reactions involved in the thesis
Literature concerning the poly (1 3 dioxolane) was included
Chapter II describes the synthesis of poly (1 3 dioxolane) macromonomers and their
characterization As an aside research poly (1 3 dioxolane) network was obtained and the
x E Kroeze thesisUniversity of Groningen (1997) xi Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polym Journal 37 (2001) 1837-1842
iii
swelling and rheological behaviours of this network were discussed and included in this
chapter
Chapter III deals with the synthesis of a series of amphiphilic graft copolymers based on
polystyrene and methyl methacrylate as backbone with poly (1 3 dioxolane) macromonomers
as grafts in this study Selection of proper reaction conditions in terms of overall monomer
concentration and monomer molar ratio were investigated in order to prevent crosslinking
reactions due to the presence of bis-functional poly (1 3 dioxolane) macromonomers
The structure and composition of the graft copolymers were determined by Size Exclusion
Chromatography (SEC) technique and Proton Nuclear Magnetic Resonance (1H-NMR)
analysis Also Modulated Temperature Differential Scanning Calorimeter (MTDSC) was used
for thermal analysis to study the influence of poly (1 3 dioxolane) content on the glass
transition temperature of the copolymers
Last but not the least Chapter IV and Chapter V deal with the most important part of the
thesis which is the study of the compatibilization effect of the prepared copolymers
incorporated in two different immiscible blend systems These two chapters describe first
the polymers used as blend components and also polyblends preparation was discussed The
phase behavior and compatibilization of these polyblends were studied at a composition
of 5050 for both PSPEG and PMMAPEG systems Various amounts of copolymers were
incorporated to the so-called blends for compatibilization The techniques used for this study
were optical microscopy (OM) to analyze their morphology and Fourier-Transform Infra-Red
(FTIR) spectroscopy used to detect the intermolecular interactions in the blends In addition
viscometric method which is a simple inexpensive and sensitive analytical technique and also
alternative to other methods was used The application of the dilute-solution viscosity (DSV)
method for the study of interactions and miscibility of the polymeric system has been
described in more details in these chapters
Conclusions have been made on copolymer characterizations in terms of mostly monomer
reactivity and indeed on compatibilizing effect of these copolymers on the selected polymer
blends This study provides interesting results which can be useful for the development
nanoporous materials
iv
REacuteSUMEacute
La recherche et le deacuteveloppement faits sur des polymegraveres syntheacutetiques pendant le dernier siegravecle
ont abouti agrave plusieurs types de polymegraveres pour des applications speacutecifiques Les nouveaux
polymegraveres syntheacutetiques avec des proprieacuteteacutes faites sur mesure sont toujours introduits pour de
nouvelles applications Le deacutefi pour les chimistes en polymegraveres est de controcircler et drsquoalteacuterer les
conditions de polymeacuterisation de telle sorte que le produit final ait une structure bien deacutefinie avec
des proprieacuteteacutes souhaiteacutees La structure complexe de polymegraveres exige des efforts continus en
chimie analytique pour comprendre le processus de polymeacuterisation et les relations entre la
structure moleacuteculaire et les proprieacuteteacutes des mateacuteriaux
Le centre drsquointeacuterecirct de cette thegravese est la synthegravese et lexploration des avantages des copolymegraveres
greffeacutes deacuteriveacutes agrave partir du poly (1 3 dioxolane) (PDXL) utiliseacutes comme agents compatibilisant
via leur incorporation dans des meacutelanges de polymegraveres non miscibles Lrsquoameacutelioration drsquoadheacutesion
agrave lrsquoeacutetat solide peut ecirctre accomplie en introduisant un compatibilisant qui peut agir comme un
adheacutesif entre deux polymegraveres et ou par le controcircle de la morphologie particuliegraverement en
incitant la co-continuiteacute des phases Les copolymegraveres greffeacutes offrent toutes les proprieacuteteacutes des
copolymegraveres en blocs mais sont toujours plus facile agrave syntheacutetiser De plus la structure ramifieacutee
offre des possibiliteacutes importantes dans le controcircle rheacuteologique cest-agrave-dire elle aide la
diminution de la viscositeacute qui est un avantage important pour la transformation Selon la nature
de la chaicircne principale et des chaicircnes lateacuterales ces copolymegraveres peuvent ecirctre employeacutes pour une
grande varieacuteteacute drsquoapplications comme plastiques reacutesistants au choc elastomers thermoplastiques
des polymegraveres eacutemulsifiants et mecircme plus inteacuteressant est la possibiliteacute de ces copolymegraveres greffeacutes
de fonctionner comme compatibilisant agents drsquointerface aux meacutelanges des polymegraveres non
miscibles
La technique la plus sophistiqueacutee pour syntheacutetiser les copolymegraveres greffeacutes est la
copolymeacuterisation de macromonomegraveres avec des comonomegraveres agrave faible masse moleacuteculaire Elle
permet le controcircle de la structure polymeacuterique par trois paramegravetres (i) la longueur des chaicircnes
lateacuterales qui peut ecirctre controcircleacutee par la synthegravese de macromonomegraveres par la polymeacuterisation
v
vivante (ii) la longueur de chaicircne principale qui peut ecirctre controcircleacutee dans une polymeacuterisation
vivante (iii) espacement moyen des chaicircnes lateacuterales qui est deacutetermineacute par le rapport molaire des
comonomegraveres et taux de reacuteactiviteacute du monomegravere agrave faible masse moleacuteculaire
De nouvelles proprieacuteteacutes des prix bas et la reacuteutilisation de polymegraveres sont neacutecessaires pour
reacutepondre aux demandes de la socieacuteteacute daujourdhui et agrave lindustrie de polymegraveres
Malheureusement ces demandes pour un grand nombre drsquoapplications ont besoin dun jeu de
proprieacuteteacutes quaucun polymegravere ne peut accomplir Une meacutethode de satisfaire ces demandes est en
meacutelangeant deux polymegraveres ou plus Les mateacuteriaux obtenus agrave partir de meacutelanges de deux
polymegraveres meacutelangeacutes sont appeleacutes meacutelanges (Blends) Ces derniegraveres anneacutees le meacutelange de
polymegraveres comme moyen de combiner les proprieacuteteacutes utiles de diffeacuterents mateacuteriaux pour
rencontrer un marcheacute de nouvelles applications agrave un coucirct minimal offre un itineacuteraire inteacuteressant
pour ameacuteliorer une varieacuteteacute des proprieacuteteacutes speacutecifiques des polymegraveres thermoplastiques Cela a eacuteteacute
de plus en plus employeacute par lindustrie des polymegraveres
Beaucoup de travaux ont eacuteteacute faits par plusieurs auteurs sur le meacutelange de polymegraveres Une grande
partie de ces eacutetudes sont dirigeacutees pour obtenir une combinaison des proprieacuteteacutes de diffeacuterents
polymegraveres Malheureusement ces proprieacuteteacutes des meacutelanges de polymegravere sont souvent plus
mauvaises que preacutevues pour la plupart des combinaisons de polymegraveres La signification de ces
proprieacuteteacutes est la compatibiliteacute entre les diffeacuterents polymegraveres qui est freacutequemment deacutefinie comme
la miscibiliteacute agrave lrsquoeacutechelle moleacuteculaire des composants du meacutelange Lincorporation dune phase
disperseacutee dans une matrice provoque surtout la preacutesence de contraintes et des interfaces faibles
qui reacutesultent du faible meacutelange meacutecanique entre les deux phases Lameacutelioration des proprieacuteteacutes
meacutecaniques et morphologiques dun meacutelange non miscible est souvent faite par compatibilisation
qui est un processus de modification des proprieacuteteacutes superficielle dans les meacutelanges de polymegraveres
non miscibles aboutissant agrave la reacuteduction du coefficient de tension superficielle la formation et
stabiliteacute de la morphologie deacutesireacutee Lutilisation des copolymegraveres greffeacutes ou agrave blocs comme
compatibilisant pour des meacutelanges de polymegraveres non miscibles est devenue un moyen efficace
pour le deacuteveloppement de nouveaux mateacuteriaux plus performant Il y a eu de nombreuses
techniques pour lrsquoeacutetude de la miscibiliteacute des meacutelanges polymeacuteriques Les techniques les plus
vi
utiles sont les mesures viscomeacutetriques analyses thermiques analyses meacutecaniques indice de
reacutefraction la reacutesonance magneacutetique nucleacuteaire microscopes optique et eacutelectroniques agrave balayage
Les exemples de meacutelanges commerciaux tregraves bien connus sont le polystyregravene choc (HIPS) et
acrylonitrile-butadiene-styrene (ABS) Ces meacutelanges sont durs et ont bon processability Un
exemple de polymegraveres amorphes le plus inteacuteressant est le polystyregravene agrave cause de sa fragiliteacute
Laddition dun compatibilisant ayant la structure dun copolymegravere au meacutelange de Polystyregravene
polyeacutethylegravene (PSPE) ameacuteliore la dureteacute par un facteur de 3 Un autre exemple est lutilisation du
poly (styrene-co-acide meacutethacrylique) comme compatibilisant dans les meacutelanges non miscibles
de PS et le poly (eacutethylegravene glycol)
Il est tregraves important drsquoeacutetudier la miscibiliteacute et le comportement des phases de deux diffeacuterents
meacutelanges de polymegraveres commerciaux non miscibles (incompatibles) comme le
polystyregravenepolyeacutethylegravene glycol (PSPEG) et le polymeacutethacrylate de meacutethylepolyeacutethylegravene glycol
(PMMAPEG) en incorporant des copolymegraveres tels que (styrene-g-PDXL) et de (meacutethacrylate de
meacutethyle-PDXL) comme compatibilisant respectivement Premiegraverement lrsquoun des composants de
ces systegravemes est amorphe et tregraves rigide (le styregravene etou PMMA) et lrsquoautre (PEG) est flexible et
mou ayant un point de fusion tregraves faible Vu lrsquoextrecircme eacutecart entre les deux tempeacuteratures de
transition vitreuse (Tg) des composants de ces meacutelanges cela nous a motiveacute pour eacutetudier le
comportement de ces meacutelanges via compatibilisation avec des copolymegraveres greffeacutes preacutepareacutes par
nous mecircme
La premiegravere partie de la thegravese est consacreacute agrave la synthegravese et agrave la caracteacuterisation de copolymegraveres
greffeacutes amphiphiles preacutepareacutes en solution par la polymeacuterisation radicale des macromonomers
(poly (1 3 dioxolane)) hydrophiles comme des chaicircnes lateacuterales (greffons) avec des
comonomegraveres hydrophobes comme le styregravene et le meacutethyle methacrylate comme chaicircne
principale La deuxiegraveme partie de la thegravese couvre la preacuteparation des meacutelanges et leacutetude de leffet
de compatibilisant des copolymegraveres greffeacutes amphiphiles sur les meacutelanges non miscibles
(incompatibles)
La recherche concernant cette thegravese est preacutesenteacute par plusieurs chapitres deacutecrits comme suit
vii
Le chapitre I est une recherche bibliographique sur les reacuteactions de polymeacuterisations impliqueacutees
dans la thegravese La Litteacuterature concernant le poly (1 3 dioxolane) est inclue
Le chapitre II deacutecrit la synthegravese des macromonomegraveres du poly (1 3 dioxolane) et leurs
caracteacuterisations Une recherche suppleacutementaire a eacuteteacute effectueacutee concernant la synthegravese drsquoun reacuteseau
tridimensionnel du poly (1 3 dioxolane) Une eacutetude sur les comportements gonflant et
rheacuteologique de ce reacuteseau ont eacuteteacute discuteacutes et inclus dans ce chapitre
Le chapitre III preacutesente la synthegravese dune seacuterie de copolymegraveres greffeacutes amphiphiles constitueacutes de
polystyregravene ou methacrylate de meacutethyle comme chaicircne principale et de macromonomers du poly
(1 3 dioxolane) comme greffons dans cette eacutetude Le choix de conditions de reacuteaction approprieacutees
en termes de concentration totale et le rapport molaire des monomegraveres ont eacuteteacute bien eacutetudieacutes pour
empecirccher les reacuteactions de reacuteticulation agrave cause de la preacutesence de macromonomegraveres bis-
fonctionnel de poly (1 3 dioxolane)
La structure et la composition des copolymegraveres greffeacutes ont eacuteteacute deacutetermineacutees par la technique de la
Chromatographie dExclusion steacuterique (CES) et la spectroscopie en Reacutesonance Magneacutetique
Nucleacuteaire de Proton (1H-NMR) Aussi la Calorimeacutetrie Diffeacuterentielle agrave balayage agrave Temperature
Moduleacutee Calorimeacutetrie (MTDSC) a eacuteteacute employeacute pour lanalyse thermique et pour eacutetudier
linfluence de la proportion du poly (1 3 dioxolane) dans les copolymegraveres sur leur tempeacuterature
de transition vitreuse
Derniers mais pas le moindre les deux Chapitre IV et le Chapitre V couvrent la partie la plus
importante de la thegravese qui est leacutetude de leffet de compatibilisant de ces copolymegraveres preacutepareacutes et
incorporeacutes dans deux diffeacuterents systegravemes de meacutelanges non miscibles (incompatibles) Ces deux
chapitres deacutecrivent dabord les polymegraveres employeacutes comme composants des meacutelanges agrave eacutetudier et
aussi la preacuteparation de ces meacutelanges a eacuteteacute deacutecrite Le comportement de phase et la
compatibilisation des meacutelanges de PSPEG et PMMAPEG agrave une composition de 5050 Des
quantiteacutes diffeacuterentes de copolymegraveres ont eacuteteacute incorporeacutees aux meacutelanges Les techniques
employeacutees pour cette eacutetude sont la microscopie optique (OM) pour analyser leur morphologie et
la spectroscopie agrave Transformeacutee de Fourier Infrarouge (FTIR) pour deacutetecter les interactions
viii
intermoleacuteculaires dans les meacutelanges De plus la meacutethode viscomeacutetrique qui est une technique
simple peu coucircteuse et tregraves sensible a eacuteteacute employeacutee Lrsquoutilisation de la meacutethode de la viscositeacute de
solution dilueacutee (DSV) pour leacutetude dinteractions et la miscibiliteacute du systegraveme polymegravere a eacuteteacute
deacutecrite plus en deacutetail dans ces chapitres
Les conclusions ont eacuteteacute faites sur la caracteacuterisation des copolymegraveres en termes de surtout de la
reacuteactiviteacute des monomegraveres et bien entendu sur leffet compatibilisant de ces copolymegraveres sur les
meacutelanges de polymegraveres qui ont choisis Cette eacutetude fournit des reacutesultats inteacuteressants qui peuvent
ecirctre utiles pour le deacuteveloppement des mateacuteriaux nanoporeux
ix
CHAPTER I Literature Review
11 Macromonomer Interest and Synthesis
Macromonomers bearing polymerizable end groups have received considerable interest
during the last two decades and become a useful tool for the preparation of a variety of graft
copolymers with well-defined structure and composition and polymer networks The
macromonomer method for preparing graft copolymers consists of preparing branches first
followed by the preparation of the grafted structure through the addition of the comonomer to
the macromonomer branch1 2
Therefore macromonomers become the side chains in the graft copolymer with well-defined
length and molecular weight As a sequence the molecular structure of the copolymer can be
determined depending on the amount of macromonomer incorporated and the reactivity of the
end groups
Macromonomers which are linear macromolecules carrying polymerizable functions at one or
two chain ends have been prepared by all polymerization mechanisms anionic cationic free-
radical polyaddition and polycondensation while the polymerizable end groups have been
introduced during the initiation termination or chain transfer steps or by modification of end
groups of telechelic oligomers3
Among the polymerization mechanisms mentioned above the ionic ones allow the best
control of molecular weight polydispersity and functionality of the macromonomers
However they require very demanding experimental conditions like high purity of monomers
and solvents complete absence of moisture and other acidic impurities inert atmosphere etc
Whereas free-radical methods which involve less severe working conditions are largely
used even though the control over the properties of the macromonomers is lower3 For
instance polymers of epoxides tetrahydofuran and cyclic siloxanes are commercially
produced by cationic ring-opening polymerization The history of ring-opening
polymerization of cyclic monomers is shorter than that of the vinyl polymerization and
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422
1
polycondensation With ring-opening functional groups can be introduced into the main chain
of the polymer This polymer cannot be prepared by vinyl polymerization4
Milkovich first developed synthesis of graft polymer with uniform grafts via macromonomer
technique5 Schulz and Milkovich6 reported the synthesis of polystyrene macromonmers
through termination of living PS anions with methacryloyl chloride and their
copolymerization with butyl acrylate and ethyl acrylate
Candau Rempp et al7 obtained PS-g-PEO by reaction between living monofunctional PEO
and partly chloromethacrylated PS backbone (scheme 1) Characterization of the products by
light scattering GPC UV and NMR spectroscopy showed a high degree of grafting
Scheme 1
Ito et al8 used a macromonomer technique to obtain graft copolymers with uniform side
chains They synthesized a graft copolymer of PS with uniform PEO side chains through
copolymerization of styrene and PEO macromonomer (scheme 2) They obtained PEO
macromonomers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-
vinyl benzyl chloride as terminating agent An apparent decrease in reactivities of both poly
(ethylene oxide) of macromonomers and comonomers was ascribed to the thermodynamic
repulsion between the macromonomer and the backbone9
4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348
2
Scheme 2
This type graft copolymers of styrene and ethylene oxide was also obtained by Xie et al10
through copolymerization of styrene with PEO macromonomer prepared by anionic
polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydofuran as
initiator followed by termination with methacryloyl chloride
The method of macromonomer synthesis developed by Xie et al11 has the advantage of
shorter reaction time and a larger range of molecular weight of the PEO macromonomer than
the usual method using potassium alcoholate as initiator PEO macromonomers with
molecular weight from 2 103 to 3 104 and MwMn = 107 ndash 112 can be obtained by this
method12
Only Xie and coworkers have published reports concerning the synthesis of copolymers with
uniform PS grafts obtained through copolymerization of epoxy ether terminated polystyrene
macromonomer with EO13 using a quaternary catalyst composed of triisobutyl-aluminium-
phosphoric acid-water-tertiary amine14 and epichlorohydrin (ECH)15
Free radical polymerization technique has also provided well-defined macromonomers of
poly (acrylic acid)16 vinyl benzyl-terminated polystyrene17 18 poly (t-butyl methacrylate)19
and poly (vinyl acetate)20
Recently Matyjaszewski et al21 employed atom-transfer radical polymerization (ATRP) to
prepare well-defined vinyl acetate terminated PS macromonomers Taking advantage of the
10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp (1985) 461 Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823
3
extremely low reactivity of polystyryl radical towards the vinyl acetate double bond they
used vinyl chloroacetate to initiate the polymerization of styrene to produce the desired
macromonomers This concept has been used similarly in the preparation of a vinyl acetate-
terminated PS macromonomers3 by conventional free-radical polymerization by employing
vinyl iodoacetate as a chain transfer agent possessing a double bond which does not
copolymerize with the monomer that forms the backbone of the macromonomer
12 Ring-Opening Polymerization Overview
Ring-opening polymerization (ROP) is a unique polymerization process in which a cyclic
monomer is opened to generate a linear polymer It is fundamentally different from a
condensation polymerization in that there is no small molecule by-product during the
polymerization Polymers with a wide variety of functional groups can be produced by ring-
opening polymerizations Ring-opening polymerization can proceed through a number of
different mechanisms depending on the type of monomer and catalyst involved Of the wide
range of polymers produced via ROP some have gained industrial significance for example
poly (caprolactam) and poly (ethylene oxide)22 ROP of cyclic esters such as ε-caprolactone
(CL) and L L-dilactide is gaining industrial interest due to their degradability23 The
mechanisms of interest in this work are coordination insertion and cationic
121 Polymerizability of Cyclic Compounds
The thermodynamic polymerizability of a cyclic monomer has been elegantly summarized by
Ivin24 Negative free energy change from monomer to polymer is the thermodynamic driving
force for the ring-opening
ΔG = ΔH ndash T ΔS
For small sized cyclic compounds the enthalpy term is negative and dominant The strains in
bond angles and bond lengths are released upon ring opening Such monomers can be almost
completely converted to polymers For medium sized cyclic monomers (5-7 membered rings)
the ring strain is small and the entropy is a small positive term Thus the overall driving force
(ΔG) is small and the extent of polymerization is little or no reaction For 8- 9- and 10-
22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991)
4
membered monomers the enthalpy term is dominant and negative while the TΔS term is
relatively small The strain is due to the non-bonded interactions between atoms Essentially
complete conversion to polymer is possible When the ring size is very large and there is
virtually no ring-strain (ΔH ne 0) the driving force for ring-opening polymerization is the
large increase of entropy The polymerization should be an athermal process
Why not make polyethylene
In principle one could synthesize polyethylene from cyclohexane
There are two good reasons why this reaction cannot be performed
bull (Kinetic) Cyclohexane lacks any reactive functionality to get hold of
bull (Thermodynamic) Simple six membered rings are extremely stable
Free Energy (ΔG) of Polymerization for Cycloalkanes
The thermodynamic considerations for ring opening are illustrated by this graph (scheme 3) of
free energy (hypothetical) of polymerization from cycloalkanes with various ring sizes to
polyethylene (The two membered ring actually shows the data for ethylene CH2 = CH2)
Scheme 3
5
Three and four membered rings are quite strained so ring opening to polyethylene is
favorable if a suitable reaction pathway existed (Unfortunately no such reaction is known)
Six membered rings are stable so they can rarely be polymerized by ring opening Five and
seven membered rings are borderline cases so sometimes these can be polymerized Larger
rings have transanular steric interactions that cause some strain so rings of 8 members or
more can usually be polymerized Of course this graph changes when substitutions are made
to the rings (for example the presence of heteroatoms like O S and N or the introduction of
double bonds) However the graph for the simplest possible rings illustrates the trends in
other systems reasonably well
Even if the ring opening reaction is thermodynamically favorable there must be reaction
chemistry to get there In most cases the initiators used for ring opening polymerization are
polar or ionic species so the monomers must have groups that can react The most common
monomers for ring opening polymerization contain some kind of heteroatom in the ring as in
the examples of cyclic ethers esters amines amides etc At one extreme there are examples
such as the cyclic phosphazene shown that contain no carbon or hydrogen at all At the other
extreme just a carbon-carbon double bond will suffice for ring opening metathesis
polymerization as illustrated by norbornene
122 Mechanisms of Ring-opening Polymerization
In addition to the thermodynamic criterion there must be a kinetic pathway for the ring to
open and undergo the polymerization reaction Therefore the kinetics of the ring-opening of
the monomer should also be considered Ring-opening polymerization (ROP) can proceed
through a number of different mechanisms depending on the type of monomer and catalyst
involved Of the wide range of polymers produced via ROP some have gained industrial
significance for example poly (caprolactam) and poly (ethylene oxide)24 25 A variety of
mechanisms operate for ring-opening polymerizations including anionic cationic metathesis
and free radical mechanisms Examples of various ring-opening polymerizations are shown in
scheme 4
25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984)
6
Scheme 4
123 Cationic Ring-Opening Polymerization of Heterocycles
A broad range of heterocyclic compounds can undergo cationic ring-opening polymerization
(CROP)26 CROP propagates either through an activated monomer or an activated chain end
mechanism In both cases the propagation involves the formation of a positively charged
species27 A major drawback of CROP is the occurrence of unwanted side reactions thus
limiting the molecular weight of the final product2829 The cationic ring-opening
polymerization of heterocycles has become of significant importance in polymer synthesis
due in part to the diverse variety of functionalized materials that can be prepared by this
method including natural andor biodegradable polymers30 31
Systematic studies of this type of polymerization started around the nineteen sixties Since
then several groups are involved in the kinetics reaction mechanisms and thermodynamics of
the ring-opening polymerization mostly of tetrahydofuran and dioxolane During the last
26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996) (b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993) (c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice (d) Mishra M K Ed Polymer Frontiers New York (1994) 391 31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159
7
years many papers on the synthesis and polymerization of several other cyclic ethers
monocyclic and bicyclic acetals have been published32 33
Examples of commercially important polymers which are synthesized via ring-opening
polymerization are summarized in scheme 5 include such common polymers as
polyoxyethylene (POE 4) poly (butylene oxide) (PBO 5) nylon 6 (6) and poly
(ethyleneimine) (7)
Scheme 5
The synthesis of ring-opened heterocycles is often mediated by compounds whose role is to
initiate the polymerization process This provides less opportunity to ldquotunerdquo polyheterocycle
properties through catalyst choice and has stimulated research to develop initiators which
function beyond the simple activation of polymerization such as living polymerization
initiators343536 chiral initiators3738 enzyme initiators39 and ring-opening insertion
systems4041 The cationic ring-opening polymerization involves the formation of a positively
32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N Macromolecules 26 (1993) 7134
8
charged species which is subsequently attacked by a monomer The attack results in a ring-
opening of the positively charged species Ethylene oxide can be polymerized by cationic
initiators as well (scheme 6)
Scheme 6
13 Cationic Polymerization of Cyclic Acetals
Acetal polymers also known as polyoxymethylene (POM) or polyacetal are formaldehyde-
based thermoplastics that have been commercially available for over 40 years
Polyformaldehyde is a thermally unstable material that decomposes on heating to yield
formaldehyde gas Two methods of stabilizing polyformaldehyde for use as an engineering
polymer were developed and introduced by DuPont in 1959 and Celanese in 1962
DuPonts route for polyacetal yields a homopolymer through the condensation reaction of
polyformaldehyde and acetic acid (or acetic anhydride)
The Celanese route for the production of polyacetal yields a more stable copolymer product
via the reaction of trioxane a cyclic trimer of formaldehyde and a cyclic ether (eg ethylene
oxide or 13 dioxolane)
9
The improved thermal and chemical stability of the copolymer versus the homopolymer is a
result of randomly distributed oxyethylene groups These groups offer stability to oxidative
thermal acidic and alkaline attack The raw copolymer is hydrolyzed to an oxyethylene end
cap to provide thermally stable polyacetal copolymer Polyacetals are subject to oxidative and
acidic degradation which leads to molecular weight deterioration Once the chain of the
homopolymer is ruptured by such an attack the exposed polyformaldehyde ends decompose
to formaldehyde and acetic acid Deterioration in the copolymer ceases however when one
of the randomly distributed oxyethylene linkages is reached42
Cationic polymerization of cyclic acetals exhibits some special features which makes this
system distinctly different from cationic polymerization of simple heterocyclic monomers for
instance cyclic ethers Linear acetals (including polyacetals) are more basic (nucleophilic)
than cyclic ones thus when polymer starts to form it does not constitute a neutral component
of the system but participates effectively in transacetalization reactions which lead to
redistribution of molecular weights and formation of a cyclic fraction These processes which
are usually described by the term ldquoscramblingrdquo have been studied by several authors43 44
Cationic polymerizations of heterocyclic monomers are initiated as in cationic
polymerization of vinylic monomers by electrophilic agents such as the protonic acids (HCl
H2SO4 HClO4 etc) Lewis acids which are electron acceptors by definition and compounds
capable of generating carbonium ions can also initiate polymerization Examples of Lewis
acids are AlCl3 SnCl4 BF3 TiCl4 AgClO4 and I2 Lewis acid initiators required a co-
initiator such as H2O or an organic halogen compound Initiation by Lewis acids either
requires or proceeds faster in the presence of either a proton donor (protogen) such as water
alcohol and organic acids or a cation donor (cationogen) such as t-butyl chloride or
triphenylmethyl fluoride
The polymerization of a heterocyclic monomer initiated by a protonic acid usually starts with
opening of the monomer ring via oxonium sites that are formed upon alkylation (or
protonation) of the monomer
42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144
10
Protonation
BF3 H2O H BF3 OH+ +O
O
Acylation
R CO SbF6 +
OR CO O SbF6
Alkylation
Et3O BF4 +
OC2H5 Et2O BF4O +
Hydrogen transfer
C SbF6 +O
C SbF6H O+
SbF6
O + O O+ H O SbF6
In general initiation step can be shown as
A+
R O++R A O
The mechanism of chain growth involves nucleophilic attack of the oxygen of an incoming
monomer onto a carbon atom in α-position with respect to the oxonium site whereby the
cycle opens and the site is reformed on the attacking unit
A+O
O(CH2)4
O
A+O(CH2)4
Growing chain terminates with nucleophilic species as shown below
O (CH2)4 O+[ ]n
A O (CH2)4[ ]n
AO ( CH2 )4
11
Triflic initiators like trifluoromethane sulfonic acid derivatives can also be employed as an
initiator in the cationic polymerization of heterocyclics in this case initiation step follows
alkylation mechanism
CF3 SO3CH3 +O
CH3 CF3SO3O
CH3 O
CF3SO3
+ O CH3O(CH2)4 O CF3SO3
Ion pairs are in equilibrium with the ester form
(CH2)4 O CF3SO3 (CH2)4 O(CH2)4 O SO2CF3
If instead of ester triflic anhydride is used as initiator the same reaction can occur at both
chain ends and anhydride behaves as a bifunctional initiator
CF3SO2OSO2CF3 nO
+ CF3SO2 O (CH2)4 O (CH2)4 O SO2CF3n-1
(CH2)4 O (CH2)4 n-3
O O CF3SO3 CF3SO3
In the case of living cationic polymerization the growing sites are long living provided the
reaction medium does not contain any transfer agents such as alcohols ethers amines or
acids The reaction mechanism then involves only initiation and propagation steps and the
polymers formed are living The active sites are deactivated by addition of an adequate
nucleophile such as excess water tertiary amines alkoxides phenolates or lithium bromide
12
O(CH2)4
SbF6
(CH2)4 O(CH2)4 OH H
NR3
++ H2O
SbF6
+(CH2)4 O(CH2)4 NR3 SbF6
ONa+(CH2)4 O(CH2)4 O + NaSbF6
+ LiBr
(CH2)4 O(CH2)4 Br LiSbF6+
However facts concerning the real mechanism are scarce In order to progress further in
understanding the cationic polymerization of heterocycles initiated with a Bronsted acid
kinetic studies of simple ring-opening reactions of heterocyclic monomer rings by acids in
nonpolar aprotic and nonbasic solvents (inert solvents) have been performed45
14 Synthesis of Functionalized Poly (1 3-Dioxolane)
1 3-Dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer ends ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The molecular weight of the linear polymers is governed by the
ratio of reacted monomer to transfer agent and is generally well controlled up to 10 000gmol
141 Reaction of 1 3-Dioxolane and Hydroxyl- Containing Compounds
Classical initiation induces polymerization through cyclic tertiary oxonium ions which are
responsible for the formation of an important quantity of cyclic oligomers48
45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon Press 3(1989) 787
13
In several preceding articles Franta et al have investigated the cationic polymerization of
cyclic acetals in the presence of a diol49 50 in particular polymerization of 13-dioxolane
(DXL) and 13-dioxepane (DXP) in the presence of an oligoether diol (αω-dihydroxy-poly
(tetrahydofuran)) or (αω-dihydroxy-poly(ethylene oxide)) In all cases a similar behavior was
observed Cyclic oligomers are present in quantities as in the case of polymerization of DXL
in the absence of hydroxyl containing compounds51
When substituted oxiranes such as propylene oxide or epichlorohydrin are polymerized
according to the ldquoActivated Monomerrdquo mechanism (AM) Cyclic oligomers can be
eliminated52 53 In the AM mechanism polymerization of ethylene oxide however the
reaction of a protonated monomer molecule with a polymer chain leads to side reactions
including cyclization by the Active Chain End (ACE) mechanism53 Thus it is not
unexpected that in the polymerization of cyclic acetals due to the higher nucleophilicity of
the linear acetals located on the chain reactions with the latter will take place
The addition of a protonated DXL onto a hydroxyl group-containing compound is
accompanied by transacetalization involving a monomer molecule
In order to shed some light on the reactions involved Franta et al54 used a monoalcohol
methanol instead of a diol The results confirmed the occurrence of the Active Monomer
mechanism but dimethoxymethane was observed evidence of transacetalization between
methanol and dioxolane
Thus in the DXL-ethylene glycol (EG) system the presence of unreacted EG is in fact due to
the following equilibria
This equation shows the stoichiometry of the reaction rather than its actual mechanism the
reaction certainly has to involve an addition product as a first step
49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154
14
In the next step transacetalization occurs
The products of transacetalization are formed fast as compared to the addition product54 This
indicates that the last reaction is not slower and probably faster than the previous one
Consequently it has been found that although polymerization of DXL in the presence of
hydroxyl group containing compounds proceeds initially by a stepwise addition of protonated
monomer to the hydroxyl terminated linear species in agreement with the AM mechanism but
already at this stage fast transacetalization proceeds leading to formation of O-CH2-O links
between two oligodiols and liberation of ethylene glycol
The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism When DXL is polymerized by strong protonic acids such as triflic acid in the
presence of a diol the PDXL chains are essentially linear and carry end-standing OH
functions Despite the occurrence of some side reactions this mechanism leads to α ω-
dihydroxy-PDXL the molecular weight of which is controlled by the molar ratio of DXL
consumed to diol introduced It has been shown that the polydispersity is on the order of 14
and that molar masses up to 10 000 gmol can be covered
142 Synthesis of Poly (1 3-Dioxolane) Macromonomers
Macromonomers are useful intermediates to prepare graft copolymers and have indeed been
used extensively In order to prepare PDXL macromonomers Franta and al54 have used p-
isopropenylbenzylic alcohol (IPA) as an initiator and triflic acid as a catalyst
The following polymeric species were identified
15
Scheme 7
A is the most abundant compound it corresponds to 50 to 60 weight-wise It is a
macromonomer
B corresponds to 20 to 25 weight-wise It carries two p-isopropenyl functions
C corresponds to 20 to 25 weight-wise It carries no p-isopropenyl function but two
hydroxyl groups
As a result preparation of PDXL macromonomers leads to the preparation of PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of transacetalization
reaction described above a mixture of products was obtained54
Kruumlger et al55 used similar method to prepare macromonomers and come out to the same
conclusions in terms of structure and claim that a clear distinction should be made between
the products obtained and the mechanism responsible for their formation
15 Amphiphilic Graft Copolymers
151 Graft Copolymers
The increasing complexity of polymer applications has required the production of materials
with varied properties Often homopolymers do not afford the scope of attributes necessary to
many applications Copolymerization allows the formulation of polymer materials with
properties characteristic of two homopolymers contained in a single copolymer material The
monomers within a copolymer can be distributed in various fashions random statistical
alternating segmented block or graft56
55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387
16
Scheme 8
Graft copolymers are similar to block copolymers in that they possess long sequences of
monomer units However graft copolymer architecture differs substantially from typical
block copolymers In graft copolymers monomer sequences are grafted or attached to points
along a main polymer chain Grafted chains generally possess molecular weights less than
that of the main chain
These side chains have constitutional or configurational features that differ from those in the
main chain57
The simplest case of a graft copolymer can be represented by A-graft-B or the arrangement
and the corresponding name is polyA-graft-polyB where the monomer named first (A in this
case) is that which supplied the backbone (main chain) units while that named second (B) is
in the side chain(s)
Typical syntheses of the grafts occur by polymerization initiated at some reactive point along
the backbone or by copolymerization of a macromonomer Polymerization from the polymer
backbone is possible via anionic cationic and radical techniques but all require some
functional unit capable of further reaction58
Well defined graft copolymers are most frequently prepared by either
a)ldquografting throughrdquo or b)ldquografting fromrdquo controlled polymerization process
57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991)
17
a) Grafting though the ldquografting throughrdquo method (or macromonomer method) is one of the
simplest ways to synthesize graft copolymers with well defined side chains
Scheme 9
Typically a low molecular weight monomer is radically copolymerized with a methacrylate
functionalized macromonomer This method permits incorporation of macromonomers
prepared by other controlled polymerization processes into a backbone prepared by a CRP
Macromonomers such as polyethylene59 60 poly (ethylene oxide)61 polysiloxanes62 poly
(lactic acid)63 and polycaprolactone64 have been incorporated into a polystyrene or poly
(methacrylate) backbone Moreover it is possible to design well-defined graft copolymers by
combining the ldquografting throughrdquo macromonomers prepared by any controlled polymerization
process and CRP65 This combination allows control of polydispersity functionality
copolymer composition backbone length branch length and branch spacing by consideration
of MM ratio in the feed and reactivity ratio Branches can be distributed homogeneously or
heterogeneously and this has a significant effect on the physical properties of the
materials6263
b) Grafting from the primary requirement for a successful grafting from reaction is a
preformed macromolecule with distributed initiating functionality
59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003) 6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778 63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998) 823-830
18
Scheme 10
Grafting-from reactions have been conducted from polyethylene66 67 polyvinylchloride68 69
and polyisobutylene70 71 The only requirement for an ATRP is distributed radically
transferable atoms along the polymer backbone The initiating sites can be incorporated by
copolymerization68 be inherent parts of the first polymer69 or incorporated in a post-
polymerization reaction70
Graft copolymers perform similar functions to block copolymers in that they contain moieties
with varying properties Compatibilization represents a major area of application for grafts
because the grafted chains can be used to solubilize a polymer blend system containing two
immiscible polymers Additionally graft copolymers offer unique solution mechanical and
morphological properties that make them ideal for utilization as viscosity modifiers and
thermoplastic elastomers72 The unique molecular architecture of graft copolymers leads to
peculiar morphological properties The chain lengths of the grafted arms and backbone block
dictate the morphology that arises in the polymer Changes in the composition of the graft
copolymer alter the resulting polymer morphology A variety of morphologies is possible
ranging from lamellar to cylindrical to spherical73
Graft copolymers offer all properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheology control
Depending on the nature of their backbone and side chains graft copolymers can be used for a
wide variety of applications such as impact-resistant plastics thermoplastic elastomers
66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996) 7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R Macromolecules 32 (1999) 1152-1158
19
compatibilizers viscosity index improvers and polymeric emulsifiers74 75 The state-of-the-
art technique to synthesize graft copolymers is the copolymerization of macromonomers
(MM) with low molecular weight monomers76 In most cases conventional radical
copolymerization has been used for this purpose Using living polymerizations for both the
synthesis of the macromonomers and for the copolymerization offers the highest possible
control of the polymer structure In all these copolymerizations beside the desired graft
copolymers with at least two side chains a number of unwanted products can be expected
unreacted macromonomer ungrafted backbone and backbone with only one graft (star
copolymer) The latter is undesirable for applications as thermoplastic elastomer
Conventional and controlled copolymerizations lead to different copolymer structures In
conventional radical copolymerization the polymers show a broad molecular weight
distribution (MWD) and chemical heterogeneity of first order
152 Amphiphilic Copolymers
A characteristic feature of an amphiphilic polymer is that it contains both hydrophilic and
hydrophobic groups This type of polymer associates in aqueous solution and exhibits several
interesting features and can be used in connection with many industrial and pharmaceutical
applications Usually there is only a few mol of the hydrophobic moieties in order to make
the polymer water-soluble Due to the hydrophobicity of the amphiphilic polymers they have
a tendency to form association structures in aqueous solution by mutual interaction andor
interaction with other cosolutes such as surfactants and colloid particles
In particular the grafting of hydrophilic species onto hydrophobic polymers is of great utility
Amphiphilic graft copolymers so prepared often display enhanced surface properties such as
improved resistance to the adsorption of oils and proteins biocompatibility and reduced static
charge buildup
The synthesis of graft copolymers based on commercial polymers is most commonly
accomplished free radically Free radicals are produced on the parent polymer chains by
exposure to ionizing radiation andor a free-radical initiator77 78 Alternatively peroxide
groups are introduced on the parent polymer by ozone treatment79 80 The resulting reactive
74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998) 696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507
20
sites serve as initiation sites for the free radical polymerization of the comonomer A
significant disadvantage of these free radical techniques is that homopolymerization of the
comonomer always occurs to some extent resulting in a product which is a mixture of graft
copolymer and homopolymer Moreover backbone degradation and gel formation can occur
as a result of uncontrolled free radical production often limiting the attainable grafting
density81 For example amphiphilic graft copolymers synthesized from PEO macromonomer
and hydrophobic comonomers82 83were found to form micellar aggregates in polar medium
such as water wateralcohol alcohol dimethylformamide These phase separation processes
take place also during polymerization and supposedly affect not only the polymerization
kinetics but also properties of resulting copolymers So far unanswered remains the question
of molecular characteristics of reaction products including homopolymers from
macromonomer or comonomer formed under both the homogeneous and heterogeneous
(micellar) reaction conditions Modern liquid chromatographic techniques allow
discrimination of polymeric constituents differing in their chemical structure andor physical
architecture Subsequently the molar mass and molar mass distribution of constituents can be
assessed Recently analyzed products of dispersion copolymerization of polyethylene oxide
methacrylate macromonomer with styrene contained rather large amount of polystyrene
homopolymer84
In the main application areas for amphiphilic polymers the solution properties are of
fundamental importance In many industrial applications association and adsorption
phenomena of the polymers in solution are design properties Consequently a deep
understanding of these phenomena is necessary for the development of new specific
chemicals and new processes The research goals are to clarify the relations between the
molecular structure of amphiphilic polymers and their properties in aqueous solution A
further goal is to develop theoretical models for the description of the behavior of amphiphilic
polymers in solution and at surfaces Several projects concern the self-assembly of
amphiphilic polymer molecules and the association behavior of surfactants and
hydrophobically modified hydrophilic polymers such as cellulose derivatives Studies of
amphiphilic model polymers such as ethylene oxide block and graft copolymers are carried
80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication
21
out in order to gain fundamental knowledge on the solution behavior of amphiphilic
polymers
16 Kinetics of Free Radical Polymerization
Free radical polymerization is the most widespread method of polymerization of vinylic
monomers Free radical polymerizations are chain reactions in which every polymer chain
grows by addition of a monomer to the terminal free radical reactive site called ldquoactive
centerrdquo The addition of the monomer to this site induces the transfer of the active center to
the newly created chain end Free radical polymerization is characterized by many attractive
features such as applicability for a wide range of polymerizable groups including styrenic
vinylic acrylic and methacrylic derivatives as well as tolerance to many solvents small
amounts of impurities and many functional groups present in the monomers
161 Kinetics of free radical addition Homo and Copolymerization
Understanding of chemical kinetics during homo- and copolymerization is crucial for
copolymer synthesis The discussion below will review the kinetics of free radical initiated
polymerizations and copolymerizations
The three main kinetic steps that occur during polymerization are (1) initiation (2)
propagation and (3) termination
1 Initiation
The initiation step is considered to involve two reactions creating the free radical active
center The first event is the production of free radicals Many methods can be used to initiate
free radical polymerizations such as thermal initiation without added initiator or high energy
radiation of the monomers However free radicals are usually generated by the addition of
initiators that form radicals when heated or irradiated Two common examples of such
compounds which afford free radicals are benzoyl peroxide (BPO) and azobisisobutyronitrile
(AIBN)
22
Figure 1 Generation of Free Radicals by Thermal Decomposition of Benzoyl Peroxide
Figure 2 Decomposition of Azobisisobutyronitrile to Form Free Radicals
Figure 1 depicts the thermal decomposition of BPO to form two oxy-radicals and Figure 2
depicts the decomposition of AIBN to form two nitrile stabilized carbon based radicals
(equation 1)
In equation 1 kd is the rate constant which describes the first order initiation process The
radical that is formed can now add to the double bond of the monomer and initiate
polymerization
The symbol M will represent the monomer and the rate constant for this process will be ki as
described in equation 2
23
Together these two reactions the radical generation and the monomer addition to the radical
form the process of initiation Usually the assumption that is taken into account is that the
first step is the rate determining step This means that the decomposition to form the radical
is much slower than the monomer addition to the free radical Therefore the equation for the
rate of radical formation ri is
The number 2 is obtained from the fact that a maximum of two radicals can be generated for
the initiation
But not all of the primary radicals produced by the decomposition of the initiator will
necessarily react with the monomer which means several other competing reactions may
occur85 Therefore in order to determine the rate of initiation the fraction of initially formed
radicals that actually start chain growth will be denoted by f and the rate of initiation equation
becomes
2 Propagation
Now the propagation of the reaction will proceed through the successive addition of
monomer to the radicals This type of process can be expressed in the following form
85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster PA (1997)
24
And further generalizing the reaction scheme gives
The assumption that the reactivity of the addition of each monomer is independent of the
chain length is evident in these two equations and was postulated by Flory 58 86 The use of
the rate constant kp for both of these equations imply that the rate constant is independent of
chain length The rate of the propagation rp of this polymerization or the rate of monomer
removal is thus given by
3 Termination
The termination of these growing radical chains occurs in principally two different ways The
first way is the formation of a new bond in between the two radicals this is called
combination Secondly the radical chains can terminate by disproportionation This is a
process where a hydrogen atom from one of the chains is transferred to the other and the chain
that the proton was removed from forms a double bond These reactions are represented as
follows
Figure 3 Termination by Combination
86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995)
25
Figure 4 Termination by Disproportionation
Schematically the reactions can be represented as follows
Where the rate constant of termination by combination is denoted by ktc and the rate constant
of termination by disproportionation is denoted by ktd Since both of these reactions use two
radical species and have the same kinetics the overall equation for the rate of termination is
written as
where kt = ktc + ktd and the number 2 imply there are two radicals that are terminated in
each termination reaction The monomer structure and the temperature are what determines
the type of termination that is most dominant in the reaction For most systems the amount of
one termination type far exceeds the other termination type
The further calculations for the rate of polymerization Rp and the degree of conversion as a
function of time can now be developed The assumption of the steady state concentration of
transient species must be used here where the transient species is the radical M For the
steady state approximation to hold true the rate at which initiation occurs ri must be equal to
the rate at which termination occurs rt or in other words radicals must be generated at the
same rate at which they are terminated This assumption gives the equation
26
This equation then gives an expression for the radical species
Experimentally this value would be difficult to measure in the laboratory and therefore this
equation must be used in the subsequent equations that follow By further substitution an
expression for the rate of polymerization Rp can be obtained because it equals the rate of
propagation
From this equation it can be deduced that the rate of polymerization is directly proportional
to the monomer concentration and to the initiator concentration to the one half power In
other words Rp is first order with regards to the monomer concentration and half order to the
initiator concentration
When the conversion is low the assumption that the initiator concentration is constant is
reasonable but the consumption of the initiator can be added into the calculations Therefore
Then integration can be performed
Finally the rate of polymerization becomes
27
This equation can be broken into three different parts
The second term indicates that the rate of polymerization is still proportional to the monomer
concentration to the first power and the initiator concentration to the one half power but the
initiator concentration is now the initial concentration Therefore by increasing the initial
concentration of an initiator in a solution polymerization the rate of the reaction should
increase proportionally to the square root of the amount of initiator added The third term
indicates that as the initiator is consumed the polymerization slows down exponentially with
time as well as its slowing down due to monomer depletion
The first term in the brackets suggests that the rate of polymerization is proportional to kp
kt12 When experiments are performed to probe the kinetics of reactions in solution the
expected first order dependence on monomer concentration is observed But when the
experiment is performed in concentrated solvents or even in the bulk the polymerization
kinetics accelerate The reason for this anomaly is that the viscosity increases as the
polymerization proceeds because the polymer has a higher viscosity than the monomers The
kp is not affected but the kt is
The degree of conversion can now be expressed as a function of time by knowing that
By substituting the earlier equation for Rp and integrating that equation one can obtain this
Furthermore ([M]0 ndash [M]) [M]0 is equal to the degree of conversion and is the fraction of
the monomer that has been reacted where [M] is the concentration of the monomer that has
been left after the reaction and [M]0 is the initial monomer concentration Therefore ([M]0 ndash
[M]) is the concentration of the monomer that has reacted The conversion can then be
expressed as
28
This can also be expressed as
As is always the case the conversion never quite reaches 100 value or a factor of 1 given by
the exponential term So if the time goes to infinity the expression that is obtained for
maximum conversion that is less than 1 by an amount that is dependent on the initial initiator
concentration is
If the steady state approximation for the initiator concentration had been carried through these
calculations and equations then the conversion would approach a value of 1 after a long
period of time
Distributions on the average distribution of chain lengths during and after a polymerization
are present in free radical polymerizations This is due to the naturally but statistically
random termination reactions that occur in the solution with regard to chain length The
kinetic chain length v is the rate of monomer addition to growing chains over the rate at
which chains are started by radicals which is the expression for the number average chain
length In other words it is the average number of monomer units per growing chain radical
at a certain instant87 Therefore the initiator radical efficiency in polymerizing the monomers
is
87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993)
29
When termination occurs mainly by combination the chain length for the polymer chains on
the average doubles in size assuming nearly equal length chains combine But if
disproportionation mainly occurs the growing chains do not undergo any change in chain
length during the process So the expressions are thus
A new term can be used to more generally express the average chain length of the growing
polymer chain xn This new term is the average number of dead chains produced per
termination ξ This value is equal to the rate of dead chain formation over the rate of the
termination reactions The equations take into account that in combination only one dead
chain is produced and in disproportionation reactions two dead chains are produced
Therefore
Furthermore the instantaneous number average chain length can be expressed in terms of the
rate of addition of the monomer units divided by the rate of dead polymers forming This is
shown as
30
From this equation82 one can clearly see that the rate of polymerization is proportional to the
initiator concentration to the one half power [I]12 and that the instantaneous number average
chain length xn is proportional to the inverse of the initiator concentration to the one half
power 1[I]12 Thus if the polymerization was accelerated by using more initiator the chains
will end up to be shorter which may not be desirable85
17 Chain Growth Copolymerization
171 Copolymerization Equations
Chain polymerizations can obviously be performed with mixtures of monomers rather than
with only one monomer For many free radical polymerizations for example acrylonitrile and
methyl acrylate two monomers are used in the process and the subsequent copolymer might
be expected to contain both of the structures in the chain This type of reaction that employs
two comonomers is a copolymerization The reactivity and the relative concentrations of the
two monomers should determine the concentration of each comonomer that is incorporated
into the copolymer The application of chain copolymerizations has produced much important
fundamental information Most of the knowledge of the reactivities of monomers via
carbocations free radicals and carbanions in chain polymerizations has been derived from
chain copolymerization studies The chemical structure of these monomers strongly
influences reactivity during copolymerization Furthermore from the technological viewpoint
copolymerization has been critical to the design of the copolymer product with a variety of
specifically desired properties As compared to homopolymers the synthesis of copolymers
can produce an unlimited number of different sequential arrangements where the changes in
relative amounts and chemical structures of the monomers produce materials of varying
chemical and physical properties
Several different types of copolymers are known and the process of copolymerization can
often be changed in order to obtain these structures A statistical or random copolymer may
obey some type of statistical law which relates to the distribution of each type of comonomer
that has been incorporated into the copolymer Thus for example it may follow zero- or first-
31
or second-order Markov statistics88 Copolymers that are formed via a zero-order Markov
process or Bernoullian contain two monomer structures that are randomly distributed and
could be termed random copolymers
ndashAABBBABABBAABAmdash
Alternating block and graft copolymers are the other three types of copolymer structures
Equimolar compositions with a regularly alternating distribution of monomer units are
alternating copolymers
ndashABABABABABABA--
A linear copolymer that contains one or more long uninterrupted sequences of each of the
comonomer species is a block copolymer
--AAAAAAAA-BBBBBBBBB--
A graft copolymer contains a linear chain of one type of monomer structure and one or more
side chains that consist of linear chains of another monomer structure
--AAAAAAAAAAAAAmdash
B B
B B
B B
B B
For this discussion the main focus will be on randomly distributed or statistical copolymers
Copolymer composition is usually different than the composition of the starting materials
charged into the system Therefore monomers have different tendencies to be incorporated
into the copolymer which also means that each type of comonomer reacts at different rates
with the two free radical species present Even in the early work by Staudinger89 it was
noted that the copolymer that was formed had almost no similar characteristics to these of the
homopolymers derived from each of the monomers
Furthermore the relative reactivities of monomers in a copolymerization were also quite
different from their reactivities in the homopolymerization Thus some monomers were more 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151
32
reactive while some were less reactive during copolymerization than during their
homopolymerizations Even more interesting was that some monomers that would not
polymerize at all during homopolymerization would copolymerize relatively well with a
second monomer to form copolymers It was concluded that the homopolymerization features
do not easily directly relate to those of the copolymerization
Alfrey (1944) Mayo and Lewis (1944) and Walling (1957)909192 demonstrated that the
copolymerization composition can be determined by the chemical reactivity of the free radical
propagating chain terminal unit during copolymerization Application of the first-order
Markov statistics was used and the terminal model of copolymerization was proposed The
use of two monomers M1 and M2 during copolymerization leads to two types of propagating
species The first of these species is a propagating chain that ends with a monomer of
structure M1 and the second species is a propagating chain that ends with a monomer structure
M2 For radically initiated copolymerizations the two structures can be represented by
M1 and M2 where the zig-zag lines represent the chain and the M
represents the radical at the growing end of the chain The assumption that the reactivity of
these propagating species only depends on the monomer unit at the end of the chain is called
the terminal unit model58 If this is so only four propagation reactions are possible for a two
monomer system The propagating chain that ends in M1 can either add a monomer of type
M1 or of type M2 Also the propagating chain that ends in M2 can add a monomer unit of
type M2 or of type M1 Therefore these equations can be written with the rate constants of
reactions93
90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953)
33
The rate constant for the reaction of the propagating chain that ends in M1 and adds another
M1 to the end of the chain is k11 and the rate constant for the reaction of the propagating
chain that ends in M2 and adds M1 to the end of the chain is k21 and so on
The term self-propagation refers to the addition of a monomer unit to the chain that ends with
the same monomer unit and the term cross-propagation refers to a monomer unit that is added
the end of a propagating chain that ends in the different monomer unit These (normally)
irreversible reactions can propagate by free radical anionic or cationic processes although
active lifetimes could be very different
As indicated by reactions 30 and 32 monomer M1 is consumed and as indicated by reactions
31 and 33 monomer M2 is consumed The rates of entry into the copolymer and the rates of
disappearance of the two monomers are given by
In order to find the rate at which the two monomers enter into the copolymer equation 34
is divided by equation 35 to give the copolymer composition equation
The low concentrations (eg 10-8 molesliter) of the radical chains in the systems are very
hard to experimentally determine So to remove these from the equation the steady state
approximation is normally employed Therefore a steady state concentration is assumed for
both of the species M1 and M2 separately The interconversion between the two
species must be equal in order for the concentrations of each to remain constant and hence the
rates of reactions 31 and 32 must be equal
34
Rearrangement of equation 37 and combination with equation 36 gives
This equation can be further simplified by dividing the right side and the top and bottom by
k21 [M2] [M1] The results are then combined with the parameters r1 and r2 which are
defined to be the reactivity ratios
The most familiar form of the copolymerization composition equation is then obtained as
The ratio of the rates of addition of each monomer can also be considered to be the ratio of the
molar concentrations of the two monomers incorporated in the copolymer which is denoted
by (m1m2) The copolymer composition equation can then be written as
The copolymer composition equation defines the molar ratios of the two monomers that are
incorporated into the copolymer d[M1] d[M2] As seen in the equation this term is directly
related to the concentration of the monomers that were in the feed [M1] and [M2] and also
the monomer reactivity ratios r1 and r2 The ratio of the rate constant for the addition of its
own type of monomer to the rate constant for the addition of the other type of monomer is
35
defined as the monomer reactivity ratio for each monomer in the system When M1
prefers to add the monomer M1 instead of monomer M2 the r1 value is greater than one
When M1 prefers to add monomer M2 instead of monomer M1 the r1 value is less than
one When the r1 value is equal to zero the monomer M1 is not capable of adding to itself
which means that homopolymerization is not possible
The copolymer composition equation can also be expressed in mole fractions instead of
concentrations which helps to make the equation more useful for experimental studies In
order to put the equation into these terms F1 and F2 are the mole fractions of M1 and M2 in the
copolymer and f1 and f2 are the mole fractions of monomers M1 and M2 in the feed
Therefore
and
Then combining equations 42 43 and 40 gives
This form of the copolymer equation gives the mole fraction of monomer M1 introduced into
the copolymer58
Different types of monomers show different types of copolymerization behavior Depending
on the reactivity ratios of the monomers the copolymer can incorporate the comonomers in
different ways
The three main types of behavior that copolymerizations tend to follow correspond to the
conditions where r1 and r2 are both equal to one when r1 r2 lt 1 and when r1 r2 gt 1
bull A perfectly random copolymerization is achieved when the r1 and r2 values are both
equal to one This type of copolymerization will occur when the two different types of
36
propagating species M1 and M2 show the exact same preference for the addition of
each type of monomer In other words the growing radical chains do not prefer to add one of
the monomers more than the other monomer which results in perfectly random incorporation
into the copolymer
bull An alternating copolymerization is defined as r1 = r2 = 0 The polymer product in
this type of copolymerization shows a non-random equimolar amount of each comonomer
that is incorporated into the copolymer This may occur because the growing radical chains
will not add to its own monomer Therefore the opposite monomer will have to be added to
produce a growing chain and a perfectly alternating chain
When r1 gt 1 and r2 gt 1 both of the monomers want to add to themselves and in theory could
produce block copolymers But in actuality because of the short lifetime of the propagating
radical the product of such copolymerizations produces very undesirable heterogeneous
products that include homopolymers Therefore macroscopic phase separation could occur
and desirable physical properties such as transparency would not be achieved
172 Determination of Reactivity Ratios
Many methods have been used to estimate reactivity ratios of a large number of
comonomers94 The copolymer composition may not be independent of conversion This
means the disappearance of monomer one may be faster than the disappearance of monomer
two if monomer one is being incorporated into the copolymer at a faster rate and therefore it
has a larger reactivity ratio than monomer two
The approximation method95 is the simplest of the methods that has been used to calculate the
reactivity ratios of copolymer systems The method is based on the fact that r1 the reactivity
ratio of component one is mainly dependent on the composition of monomer two m2 that
has been incorporated into the copolymer at low concentrations of monomer two in the feed
M2 The expression is thus
94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
37
The value of the reactivity ratio for component one can be easily determined by only one
experiment but the value is only an approximation and does not provide any validity of the
estimated r1 In order to determine the amount of the comonomer that has been incorporated
into the copolymer various analytical methods must be used Proton Nuclear Magnetic
Resonance Carbon 13 NMR and Fourier Transform Infrared Spectroscopy are three sensitive
instruments that can determine the copolymer composition The approximation method is
limited when the reactivity ratio of one of the components in the system has a value of less
than 01 or greater than a value of 10
However the method does give good insight into the reactivity ratio values for many
copolymer systems The approximation of reactivity ratios can be easy and quick when using
this method of evaluation
The Mayo-Lewis intersection method91 96 uses a linear form of the copolymerization equation where r1 and r2 are linearly related
By using the equations m1M 22 m2M12 and (M2 M1)[(m1 m2) ndash 1] for the slope and intercept
respectively a plot can be produced for a set of experiments after the copolymer composition
has been determined The straight lines that are produced on the plot for each experiment
where r1 represents the ordinate and r2 represents the abscissa intersect at a point on the r1 vs
r2 plot The point where these lines meet is taken to be r1 and r2 for the system in study The
main advantage of this method is that it gives a qualitative observation of the validity of the
intersection area Over the whole range of possible copolymer compositions that were tested
more compact intersections better define the data However the method requires a visual
check of the data and a quantitative estimation of the error is impossible Therefore
weighting of the data is needed to determine the most precise values of r1 and r2
The Fineman-Ross linearization method97 uses another form of the copolymer equation
Where
And
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259
38
For this method by plotting G versus H for all the experiments one will obtain a straight line
where the slope of the straight line is the value for r1 and the intercept of the line is the value
for r2 This type of reactivity ratio determination has the same advantages and disadvantages
of the method described above however this treatment is a linear least squares analysis
instead of a graphical analysis The validity is only qualitative and the estimates of r1 and r2
can change with each experimenter by weighting the data in different ways Furthermore the
high and low experimental composition data are unequally weighted which produces large
effects on the calculated values of r1 and r2 Therefore different values of r1 and r2 can be
produced depending on which monomer is chosen as M158
A refinement of the linearization method was introduced by Kelen and Tudos98 99 100 by
adding an arbitrary positive constant a into the Fineman and Ross equation 47 This technique
spreads the data more evenly over the entire composition range to produce equal weighting to
all the data58 The Kelen and Tudos refined form of the copolymer equation is as follows
η = [ r1 + r2 α ] ξ minus r2 α (50)
where
η = G ( α + H ) (51)
ξ = H ( α + H ) (52)
By plotting η versus ξ a straight line is produced that gives ndashr2α and r1 as the intercepts on
extrapolation to ξ=0 and ξ=1 respectively Distribution of the experimental data
symmetrically on the plot is performed by choosing the α value to be (HmHM)12 where Hm
and HM are the lowest and highest H values respectively Even with this more complicated
monomer reactivity ratio technique statistical limitations are inherent in these linearization
methods101 102
98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265
39
OrsquoDriscoll Reilly et al103 104 determined that the dependent variable does not truly have a
constant variance and the independent variable in any form of the linear copolymer equation
is not truly independent Therefore analyzing the composition data using a non-linear
method has come to be the most statistically sound technique
The non-linear or curve-fitting method90 is based on the copolymer composition equation in
the form
This equation is based on the assumptions that the monomer concentrations do not change
much throughout the reaction and the molecular weight of the resulting polymer is relatively
high In order to determine reactivity ratios from the experimental data a graph must be
generated for the observed comonomer amount that was incorporated into the copolymer m1
versus the feed comonomer amount M1 for the entire range of comonomer concentrations
Then a curve can be drawn through the points for selected r1 and r2 values and the validity of
the chosen reactivity ratio values can be checked by changing the r1 and r2 values until the
experimenter can demonstrate that the curve best fits the data points
The main advantage of the reactivity ratio determination methods discussed thus far is the
results can be visually and qualitatively checked Disadvantages include a direct dependence
of the composition on conversion for most polymer systems and therefore low conversion
(eg instantaneous composition) is needed to determine the reactivity ratios Furthermore
extensive calculations are required but only qualitative measurements of precision can be
obtained Finally weighting of the experimental data for the methods to determine precise
reactivity ratios is hard to reproduce from one experimenter to another
Therefore a technique that allows the rigorous application of statistical analysis for r1 and r2
was proposed by Mortimer and Tidwell which they called the nonlinear least squares
method95105106107This method can be considered to be a modification or extension of the
curve fitting method For selected values of r1 and r2 the sum of the squares of the differences
between the observed and the computed polymer compositions is minimized
103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772
40
Using this criterion for the nonlinear least squares method of analysis the values for the
reactivity ratios are unique for a given set of data where all investigators arrive at the same
values for r1 and r2 by following the calculations Recently a computer program published by
van Herck108 109 allows for the first time rapid data analysis of the nonlinear calculations It
also permits the calculations of the validity of the reactivity ratios in a quantitative fashion110
The computer program produces reactivity ratios for the monomers in the system with a 95
joint confidence limit determination
The joint confidence limit is a quantitative estimation of the validity of the results of the
experiments and the calculations performed This method of data analysis consists of
obtaining initial estimates of the reactivity ratios for the system and experimental data of
comonomer charge amounts and comonomer amounts that have been incorporated into the
copolymer both in mole fractions Many repeated sets of calculations are performed by the
computer which rapidly determines a pair of reactivity ratios that fit the criterion wherein the
value of the sum of the squares of the differences between the observed polymer composition
and the computed polymer composition is minimized111 112 This method uses a form of the
copolymer composition equation with mole fractions of the feed It amounts to determining
the mole fraction of the comonomer that should be incorporated into the copolymer during a
differential time interval
For this equation F2 represents the mole fraction of comonomer two that was calculated to be
incorporated into the copolymer and f1 and f2 represent the mole fractions of each comonomer
that were fed into the reaction mixture The use of the Gauss-Newton nonlinear least squares
procedure predicts the reactivity ratios for a given set of data after repeating the calculations
so that the difference between the experimental data points and the calculated data points on a
plot of mole fraction of comonomer incorporated versus comonomer in the feed is reduced to
the minimum value113 114
108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65
41
18 Controlled Radical Polymerization
The development of new controlledliving radical polymerization processes such as Atom
Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated
polymerization and degenerative transfer processes including RAFT opened the way to the
use of radical polymerization for the synthesis of well-defined complex functional
nanostructures The development of such nanostructures is primarily dependent on self-
assembly of well-defined segmented copolymers This section describes the fundamentals of
ATRP relevant to the synthesis of such systems115
The main goal of macromolecular engineering is to carry out the synthesis (polymerization) in
such a way that it results in well-defined macromolecular products One of the ways to
achieve full control of the macromolecule (length sequence and regio- and stereo- regularity)
would be to build it one monomer at a time with mechanisms in place facilitating selection of
an appropriate monomer and assuring its addition in proper orientation This of course has
been achieved in Nature in the process of protein synthesis through the use of sophisticated
macromolecular ldquonanomachineryrdquo (DNA RNA Most commonly used synthetic routes to
linear polymers are based on addition (chain) reactions which can be controlled only in
statistical terms through such parameters as initiatormonomer ratios monomerpolymer
reactivities monomer concentrations reaction medium etc The main strategy to achieve the
reasonable control of such reactionsrsquo products is through the synchronized growth of ldquolivingrdquo
chains ie chains which cease to grow only in the absence of a monomer Synchronization of
chain growth can be achieved fairly easily through rapid initiation Living chains grown in
such synchronized fashion exhibit relatively narrow molecular weight distributions (MWD)
their average molecular weights can be controlled simply by the duration of reaction Until
recently radical polymerization which covers the broadest range of monomers appeared to
be inherently uncontrollable due to the presence of fast chain termination of growing radicals
Thus although very useful in the synthesis of bulk commodity polymers where precise
control is not always essential radical polymerization has been hardly ever viewed as a tool to
precisely engineer macromolecules for well-defined functional nanostructures
114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16
42
This outlook shifted dramatically recently with the development of new controlledliving
radical polymerization processes such as Atom Transfer Radical Polymerization (ATRP)116
117 118 and other techniques such as nitroxide mediated polymerization119 and degenerative
transfer processes120 including reversible addition-fragmentation chain transfer (RAFT)121
With the availability of effective control mechanisms given its applicability to a broadest
range of monomers radical polymerization is now ready to assume the central role in
macromolecular engineering geared towards the development of well-defined functional
nanostructures
181 Fundamentals of ControlledLiving Radical Polymerization (CRP)
The great expectations for the controlledliving radical polymerization (CRP) have their
origins in the dominating position of the free radical technique by far the most common
method of making polymeric materials (nearly 50 of all polymers are made this
way)122123124This is due to the large number of available vinyl monomers (eg there are
nearly 300 different methacrylates available commercially) which can be easily
homopolymerized and copolymerized The advent of CRP enables preparation of many new
materials such as well-defined components of coatings (with narrow MWD precisely
controlled functionalities and reduced volatile organic compounds -VOCs) non ionic
surfactants polar thermoplastic elastomers entirely water soluble block copolymers
(potentially for crystal engineering) gels and hydrogels lubricants and additives surface
modifiers hybrids with natural and inorganic polymers various biomaterials and electronic
materials
The controlledliving reactions are quite similar to the conventional ones however the radical
formation is reversible Similar values for the equilibrium constants during initiation and
propagation ensure that the initiator is consumed at the early stages of the polymerization
116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002)
43
generating chains which slowly and continuously grow as in a living process There are a
number of critical differences between conventional and controlledliving radical reactions
bull Perhaps the most important difference between the two approaches is the lifetime of
the propagating chains which is extended from 1 s to more than 1 h
bull The second major difference is the very significant increase in the initiation rate
which enables simultaneous growth of all the polymer chains
bull Termination processes cannot be avoided in CRPs Thus CRP is generally less precise
than the anionic polymerization Termination is the most dangerous chain breaking
reaction in CRPs Since it is a bimolecular process increasing the polymerization rate
increases the concentration of radicals and enhances the termination process
Termination also becomes more significant for longer chains and at higher conversion
However this process is somehow self tuned since termination is chain length
dependent
The key feature of the controlledliving radical polymerization is the dynamic equilibration
between the active radicals and various types of dormant species Currently three systems
seem to be most efficient nitroxide mediated polymerization (NMP) atom transfer radical
polymerization (ATRP) and degenerative transfer processes such as RAFT123 Each of the
CRPs has some limitations and some special advantages and it is expected that each
technique may find special areas where it would be best suited synthetically For example
NMP carried out in the presence of bulky nitroxides cannot be applied to the polymerization
of methacrylates due to fast β-H abstraction ATRP cannot yet be used for the polymerization
of acidic monomers which can protonate the ligands and complex with copper RAFT is very
slow for the synthesis of low MW polymers due to retardation effects and may provide
branching due to trapping of growing radicals by the intermediate radicals At the same time
each technique has some special advantages Terminal alkoxyamines may act as additional
stabilizers for some polymers ATRP enables the synthesis of special block copolymers by
utilizing a halogen exchange and has an inexpensive halogen at the chain end125 RAFT can
be applied to the polymerization of many unreactive monomers such as vinyl acetate126
182 Typical Features of ATRP
A successful ATRP process should meet several requirements
125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035
44
bull Initiator should be consumed at the early stages of polymerization to form polymers
with degrees of polymerization predetermined by the ratio of the concentrations of
converted monomer to the introduced initiator (DP = Δ[M][I]o)
bull The number of monomer molecules added during one activation step should be small
resulting in polymers with low polydispersities
bull The contribution of chain breaking reactions (transfer and termination) should be
negligible to yield polymers with high degrees of end-functionalities and allow the
synthesis of block copolymers
In order to reach these three goals it is necessary to select appropriate reagents and
appropriate reaction conditions ATRP is based on the reversible transfer of an atom or group
from a dormant polymer chain (R-X) to a transition metal (M nt Ligand) to form a radical (R)
which can initiate the polymerization and a metal-halide whose oxidation state has increased
by one (X-M n+1t Ligand) the transferred atom or group is covalently bound to the transition
metal A catalytic system employing copper (I) halides (Mnt Ligand) complexed with
substituted 2 2rsquo- bipyridines (bpy) has proven to be quite robust successfully polymerizing
styrenes various methacrylates acrylonitrile and other monomers116127 Other metal centers
have been used such as ruthenium nickel and iron based systems117 118 Copper salts with
various anions and polydentate complexing ligands were used such as substituted bpy
pyridines and linear polyamines The rate constants of the exchange process propagation and
termination shown in Scheme 11 refer to styrene polymerization at 110 C
Scheme 11
According to this general ATRP scheme the rate of polymerization is given by the following
equation
127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901
45
Thus the rate of polymerization is internally first order in monomer externally first order
with respect to initiator and activator Cu(I) and negative first order with respect to
deactivator XCu(II) However the kinetics may be more complex due to the formation of
XCu(II) species via the persistent radical effect (PRE) The actual kinetics depend on many
factors including the solubility of activator and deactivator their possible interactions and
variations of their structures and reactivities with concentrations and composition of the
reaction medium It should be also noted that the contribution of PRE at the initial stages
might be affected by the mixing method crystallinity of the metal compound and ligand etc
One of the most important parameters in ATRP is the dynamics of exchange and especially
the relative rate of deactivation If the deactivation process is slow in comparison with
propagation then a classic redox initiation process operates leading to conventional and not
controlled radical polymerization Polydispersities in ATRP are defined by the following
equation when the contribution of chain breaking reactions is small and initiation is
complete
Thus polydispersities decrease with conversion p the rate constant of deactivation kd and
also the concentration of deactivator [XCu(II)] They however increase with the propagation
rate constant kp and the concentration of initiator [RX]o This means that more uniform
polymers are obtained at higher conversions when the concentration of deactivator in solution
is high and the concentration of initiator is low Also more uniform polymers are formed
when the deactivator is very reactive (eg copper(II) complexed by 2 2-bipyridine or
pentamethyldiethylenetriamine rather than by water) and monomer propagates slowly (styrene
rather than acrylate)
183 Controlled Compositions by ATRP
One of the driving forces for the development of a controlledldquo livingrdquo radical polymerization
is to allow for the copolymerization of two or more monomers128 This has been demonstrated
with ATRP by copolymerization of various combinations of styrene methyl or butyl acrylate
methyl or butyl methacrylate and acrylonitrile ATRP allows for the copolymerization of
these monomers using all feed compositions without loss of control of the polymerization 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
46
this is in contrast to the use of 2266-tetramethylpiperidine-1-oxyl radical (TEMPO) which
must contain a significant amount of styrene as comonomer to retain control of the
polymerization This restriction does not apply to polymerizations mediated by new
nitroxides119 The statistical copolymers prepared by living polymerizations are not the same
as those prepared by conventional radical polymerizations due to the differences in
polymerization mechanism
During a copolymerization one monomer is generally consumed faster than the other
resulting in a constantly changing monomer feed composition during the polymerization the
preference is dependent on the reactivity ratios of the two (or more) monomers In
conventional radical polymerization where the polymer chains are continuously initiated and
are irreversibly terminated the change in monomer feed is recorded in the individual polymer
chains whose composition will vary from chain to chain depending on when the chain was
formed ie at the beginning or near the end of the reaction However since ATRP is a
controlledldquolivingrdquo polymerization system the vast majority of polymer chains does not
irreversibly terminate but grow gradually throughout the polymerization The change in
monomer feed is recorded in the polymer chain itself and not from chain to chain The drifting
of composition along the polymer chain is expected to yield gradient copolymers with novel
properties129 Conventional free radical polymerization methods are generally not suitable for
synthesizing star shaped polymers due to the occurrence of undesirable radical coupling
reactions During a ldquocore-firstrdquo synthesis this would lead to coupling of the growing polymer
arms and ultimately result in a cross-linking of the star macromolecules
Block copolymers can be formed by addition of a second vinyl monomer to a macroinitiator
which contains halide groups that participate in the atom transfer process Most notably this
has been demonstrated by successive addition of a second monomer at the end of the
polymerization of a first monomer by ATRP In this manner AB and ABA block copolymers
have been prepared with various combinations of styrene acrylates methacrylates and
acrylonitrile It is very important to select the right order of monomer addition For example
polyacrylates can be efficiently initiated by the poly (methyl methacrylate)- BrCuBrL
system However the opposite is not true because concentration of radicals and overall
reactivity of acrylates is generally too low to efficiently initiate MMA polymerization
Halogen exchange comes to the rescue bromoterminated polyacrylate in the presence of
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775
47
CuClL is an efficient initiator for MMA polymerization due to reduced polymerization rate
of PMMA-Cl species which are predominantly formed after the exchange process130 131 132
Scheme 12
To conclude atom transfer radical polymerization is a robust method for preparing well-
defined polymers and novel materials with unique compositions and architectures Although
significant progress has been made in the past few years since the development of ATRP
continuous research on the better mechanistic understanding of ATRP and the preparation of
more efficient catalyst systems to yield more well-defined polymers and polymerize new
monomers is needed The syntheses of new materials need to be optimized and their
properties should be studied
It is anticipated that the new controlledliving techniques will help to provide many new well-
defined polymers via macromolecular engineering
130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
48
References
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422 4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348 10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp
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31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
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Macromolecules 26 (1993) 7134 42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144 45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon
Press 3(1989) 787 49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154 55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387 57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991) 59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M
J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003)
6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778
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63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998)
823-830 66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996)
7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R
Macromolecules 32 (1999) 1152-1158 74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998)
696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507 80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication 85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster
PA (1997) 86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995) 87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993) 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151 90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953) 94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
51
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259 98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265 103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772 108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65 114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16 116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002) 125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035 127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
52
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775 130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
53
CHAPTER II Synthesis and Characterization of
Macromonomers
21 Introduction
Cationic ring opening polymerization of DXL proposed by Franta and Reibel133 results in
linear polymeric chains thereby preventing formation cyclic oligomers through cationic
polymerization of cyclic acetals15 17In fact the reaction of DXL in the presence of an
unsaturated alcohol (2-HPMA) results in a functionalized linear PDXL macromonomer
carrying at one or both ends an unsaturated system supported by the methacryloyl group of
the alcohol The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism44 Franta et al have established that when DXL is polymerized by strong protonic
acids such as triflic acid in the presence of a diol the PDXL chains are essentially linear and
carry end-standing OH functions It has been shown that the amount of cyclic species formed
is negligible that the dispersity is on the order of 14 and that the molecular weight of the
linear polymers is governed by the ratio of reacted monomer to transfer agent and is generally
well controlled up to 10 000 gmol
De Clercq and Goethals have reported the preparation of poly (13dioxolane)
bismacromonomers by copolymerization with MMA and provided the possibility to prepare
polymer networks containing PDXL segments134 135 PDXL based hydrogels have been
obtained in most cases by free radical copolymerization with comonomers such as acrylic
acid acrylamide and N-isopropylacrylamide134 136 137 styrene and butyl acrylate138
Hydrogels have received increasing attention for biomedical applications such as drug
delivery immobilization of enzymes dewatering of protein solutions and contact lenses139
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002) 1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080
54
140 These materials and are widely used in areas like baby diapers solute separation soil for
agriculture and horticulture absorbent pads etc139 Hydrogels are defined as hydrophilic
polymer networks which have a high capacity to adsorb a substantial amount of water which
have been proposed as protein releasing matrices The high water content ensures a good
compatibility with entrapped proteins as well as with surrounding tissue141 Even though a
number of applications are currently being pursued using hydrogel very little is known about
the mechanical behavior that describes the various physical processes in hydrogels142 Over
the last decade most interests have been emphasized on the synthesis of polymers containing
polyacetal segments because of the ease of degradation of these polymers under mild
conditions by treatment with a trace of acid134 143 Poly (1 3 dioxolane) is a hydrophilic non-
ionic polymer which like poly (ethylene oxide) is appreciably soluble in water but much
more sensitive to acidic degradation because of the presence of acetal groups in the chains144
In this chapter we report the synthesis of the functionalized poly (13dioxolane)
macromonomers which have been used for the preparation of PDXL hydrogel and
amphiphilic graft copolymers In the second part of this chapter we have focused on a
detailed study of the properties of the resulting hydrogel in terms of swelling behavior in
different organic solvents and viscoelastic properties determined by rheological measurements
in both the steady shear and oscillatory experiments
22 Experimental
221 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922
55
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
bull Dichloromethane (CH2Cl2 MW 8493 bp 40degC d 1325)
Dichloromethane (Prolabo 999) was dried by stirring over CaH2 for 24 h and then
distilled under a N2 atmosphere to remove impurities Purified dichloromethane was
stored under nitrogen over molecular sieve
bull 2-hydroxypropyl methacrylate (2-HPMA) (MW 14417 bp 240degC d 1028)
2-HPMA of commercial grade was purchased from Acros stabilized with 200 ppm
hydroquinone monomethyl ether Then it was stored over molecular sieve
bull n-Hexane 99 (C6H14 MW 8618 bp 68-70degC d 0658-0662) Stored under
nitrogen over molecular sieve
bull Trifluoromethanesulfonic acid (triflic acid Aldrich) was used as received
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile (AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull 1 3 dioxolane (DXL) (MW 7408 bp 78degC d 106)
The monomer DXL of commercial grade was purchased from Acros DXL was kept
under KOH for two and up to three days to remove any peroxide and stabilizer traces
and then purified by distillation over CaH2 under a N2 atmosphere prior to
polymerization
All chemicals were kept over molecular sieve before use
222 Reaction apparatus
All polymerization experiments were performed with a clean 250 ml three neck round bottom
flask A condenser was used on one of the necks of the flask in order to condense any
monomers that might otherwise possibly escape A magnetic bar was used to stir the solution
at a constant speed in order to assure even distribution of monomer and initiator
concentrations throughout the entire volume of solution A rubber septum was used to cover
one of the three necks
In the case of free radical polymerization reactions a thermocouple was also fitted to the
reaction vessel to monitor the temperature of the reaction The thermocouple regulated the
56
temperature at a constant 70degC throughout the reaction
223 Synthesis of Poly (13-dioxolane) Macromonomers
Methacrylate-terminated PDXL macromonomers were synthesized by Cationic ring-opening
polymerization which was carried out in 10 ml dichloromethane with triflic acid as initiator at
room temperature under nitrogen for 24 h in the presence of 2-hydroxypropyl methacrylate
(2-HPMA) as transfer agent 20 ml of DXL monomer was added The feed molar ratios
[DXL] [2-HPMA] are reported in Table1 as well as the molecular characteristics of the
obtained macromonomers The amount of the acid used was 20 μl After reaction the
resulting solution is poured into THF Then the product is purified by re-precipitation from
THF solution with a large excess of hexane and the obtained polymer was dried under
vacuum at room temperature The yield was checked by gravimetric determination and found
to be about 80
224 Synthesis of Poly (13-dioxolane) Hydrogel Network
The functionalized PDXL macromonomer taken for the preparation of PDXL netwok was
(FPP2) macromonomer with a theoretical average molecular weight of Mnth =2000
The macromonomer (1g) was polymerized by free radical polymerization in 10 ml of THF
using 2 2-azobisisobutyronitrile (AIBN) (001g) as initiator under a nitrogen atmosphere
The polymerization was carried out at 70degC for 24h A piece of hydrogel was obtained The
product was extracted with ethanol to remove unreacted macromonomers and then dried
under vacuum
23 Characterization Techniques
231 Raman Spectroscopy
Raman spectroscopy is used to study and analyse the structure of the macromonomers
The experiments were performed on a Dilor XY 800 spectrophotometer The detector was a
charge-coupled device (CCD) An argon laser pump beam (power density of 100 mW) has
been focused onto the sample through a microscope The working wavelength was chosen as
λ = 5145 nm In our experiments we explored the spectral range between 200 and 3700 cm-1
with a spectral resolution of 2 cm-1
57
232 1H-NMR Spectroscopy
Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) was used for structural analysis
and molecular weight of polymers and macromonomers Proton NMR spectra were obtained
using a high field 400Mhz Advance Bruker spectrometer
All of the 1H NMR samples were dissolved in deuterated chloroformThe chloroform
reference peak at 724 ppm was to ensure accuracy of peak assignments The integrals of the
peaks were used for the calculations to determine the Mw of the macromonomers
233 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) represents a chromatographic method widely used in
the analysis of polymer average molecular weights and molecular weight distributions SEC
Measurements were performed at 40degC on a Waters 2690 instrument equipped with UV
detector (Waters 996 PDA) coupled with a Differential Refractometer (ERC - 7515 A) and
four Styragel columns (106 105 500 and 50degA) THF is employed as eluent with a flow rate
of 10 mlmin Polystyrene standard samples were used for calibration
234 Swelling Measurements
In order to investigate the swelling behavior the measurement of the swelling ratio of the
polymer network is obtained from a gravimetric method in which small pieces of hydrogel
were immersed solvents such as CH2Cl2 and THF for 24 hours at room temperature (23degC)
until swelling equilibrium was reached ie when the gel thickness became essentially
constant The samples were removed from the solvents and carefully weighed (Ws) Then the
samples let to deswell and weighed every 5 min during in order to determine the swelling
kinetics in the solvents The swelling equilibrium was reached after 5 hours Afterwards the
gel was left to dry for 24 hours at room temperature until constant weight was attained and the
dry weight (Wd) was determined and the swelling ratio was calculated from equation
SR = ( ) 100timesminusWd
WdWs (57)
Where SR is equilibrium swelling ratio Ws and Wd are the sample weights in swollen and dry
states respectively
58
235 Rheological Measurements
Steady shear and oscillatory measurements have been performed on a stress imposed
rheometer Rheo-Stress-100 (RS100) from Haake used with a coneplate geometry (20 mm
diameter an angle of 4deg gap 2 mm)The imposed stress of 100 Pa during 30 seconds and a
frequency of 1Hz were applied while the strain was monitored The measurements have been
performed on swollen and unswollen samples The elastic (G) and the loss (G) moduli are
measured in linear viscoelastic region In the oscillatory experiments the frequency
dependence of both Grsquo and G is obtained at a constant strain All rheological measurements
were carried out at room temperature (23 degC)
24 Results and Discussion
241 Structural Characterization of Macromonomers
1 3 dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer end ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The synthesis of α ω-dihydroxy-PDXL chains is based on the
activated monomer mechanism44 Franta et al have established that when DXL is polymerized
by strong protonic acids such as triflic acid in the presence of a diol the PDXL chains are
essentially linear and carry end-standing OH functions It has been shown that the amount of
cyclic species formed is negligible that the dispersity is on the order of 14 and that the
molecular weight of the linear polymers is governed by the ratio of reacted monomer to
transfer agent and is generally well controlled up to 10 000 gmol
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel44 133 using an unsaturated alcohol (2-
59
HPMA) as a transfer agent results in linear polymeric chains thereby preventing formation of
cyclic oligomers through cationic polymerisation of cyclic acetals15 17 They were all prepared
at the same reaction conditions The synthetic route of functionalized PDXL macromonomers
is shown in scheme13
Scheme 13 Structures of PDXL macromonomer species54
According to this mechanism it is possible to prepare macromonomers ie PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of the
transacetalization reactions a mixture of products is obtained
A is the most abundant compound it corresponds to 50 to 60 weight wise54 It is a
macromonomer
B corresponds to 20 to 25 weight wise It is a bis-macromonomer It carries two
methacryloyl functions corresponding to transacetalization of R-OH and DXL
C corresponds to 20 to 25 weight wise It carries no methacryloyl function but two
hydroxyl groups It is a α ω-dihydroxy-PDXL
These 3 species A B and C stem from scrambling reactions that are typical with cyclic
acetals54
The characterization of these materials is based on structure and molecular weight
determination For instance the PDXL macromonomers carried at one of their ends a double
bond afforded by the methacryloyl group The latter was checked by Raman and 1H-NMR
spectroscopy All macromonomers prepared displayed functionality close to unity which
makes them suitable for the synthesis of graft copolymers
60
Raman spectroscopy is used to study and analyse the structure of the macromonomers The
aim of this study is to check the formation of linear polymer chains as well as the termination
with methacryloyl groups The spectra obtained exhibit two intense Raman bands at 800 to
900 cmP
-1 and 2700 to 3000 cmP
-1 regions and a series of small other peaks for all samples as
shown in figure 1 The most intense band (2700 ndash 3000 cmP
-1) is assigned to the aliphatic
stretching vibration of CH in the polyacetal chain Symmetric COCOC stretching frequencies
of aliphatic acetals fall in typical regions of 1115-1080cmP
-1 and 870-800 cmP
-1 145 and are
responsible for intense Raman bands In the low frequency region there are three very
characteristic Raman bands in the 600 ndash 550 cmP
-1 540 ndash 450 cmP
-1 and 400 ndash 320 cmP
-1 ranges
which are assigned to COCOC deformations145 146 Also the acetals have strong multiple
bands in the region of 1160ndash1040 cmP
-1 as noticed on the Raman spectra involving the C-O
stretching modes In addition to this the O-CH-O group gives rise to a band at 1350 ndash1325
cmP
-1 for C-H deformation Other intense Raman bands are observed in the region of 3000 ndash
2700 cmP
-1 Below 3000 cmP
-1 the corresponding frequencies are assigned to the aliphatic C-H
stretching modes145 The methoxy group is detected in the region of 2835 ndash 2780 cmP
-1
Figure 1 Raman spectra of methacrylic-terminated PDXL macromonomers (FPP2 FPP15 and
FPP1)
145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The Handbook of IR
and Raman Characteristic Frequencies of Organic Molecules United Kingdom Ed by Academic Press Limited London (1991)
146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman Spectroscopy 3rd Edition AP Limited London (1964)
61
As far as the presence of the methacryloyl group in the polymeric chain is important bands
have been observed at 1640 cmP
-1 which corresponds to C=C bonds The carbonyl compounds
absorb strongly within 1900 ndash1550 cmP
-1 region145 146 the spectra show a C=O bond absorption
found at 1720 cmP
-1 In the region of 1340 ndash1250 cmP
-1 the methacrylate bands are observed
Broad absorption is found near 3500 cm -1 owing to stretching of the OH bonds OH
deformation bands are found at 1400 cmP
-1P and 1340 cmP
-1 This observation indicates that both
methacrylic and ndashOH groups are present and eventually the resulting product is a mixture of
the three species as shown in the scheme above
Typical 1H-NMR spectrum of PDXL macromonomer shown in figure 2 exhibits the expected
resonance assigned to the methoxy protons (477 ppm) and OCH2CH2O protons at (374
ppm) Two signals corresponding to =CH2 were observed at (612 ndash 614 ppm) and (557 ndash
559 ppm) Therefore the spectrum confirmed the chemical structure HO[CH2CH2OCH2O]nR
of methacryloyl- terminated PDXL macromonomer
Figure 2 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP2)
242 Molecular Weight Determination
Besides the structure 1H-NMR enables us to determine the number-average molecular weight
(Mn) In the calculation of the latter the methacryloyl end group was included The
62
polydispersity and index MwMn and the number-average molecular weight were obtained
from SEC measurements Table 1 summarizes these values It can be seen that Mn (SEC) and
Mn (NMR) are very close to each other for all macromonomer samples and are in agreement
with the theoretical values predicted from calculations Under our polymerization conditions
the polydispersity index is 16 for all samples
Table 1 Characteristics of PDXL macromonomers prepared at different degrees of
polymerization
Sample Dp Mnth MnSEC MnRMN MwMn f (a)
FPP1 135 1000 1120 1160 16 097
FPP15 2025 1500 1540 1550 16 099
FPP2 270 2000 2040 2100 16 097
Dp degree of polymerization = [DXL] [2HPMA]
a functionality of macromonomers (methacryloyl end groups molecule)
243 Swelling of Poly (13 Dioxolane) Hydrogel
The synthesized PDXL hydrogel has been studied in terms of swelling and rheological
behaviors The degree of swelling and the rate of swelling of the hydrogel are studied It is
known that hydrogel can swell in several solvents but at different degree of swell according to
many factors related to the nature of the solvents and the type of polymer-solvent interactions
It was found that the solubility parameter of the solvents (δ) had a great effect on swelling
degree For instance hydrogels can swell fast in CH2Cl2 (δ = 976 cal cm12 -32) and reached
equilibrium within no more than an hour However it will take about more than 20 h to reach
equilibrium in CH3 OH (δ = 145 cal cm12 -32) It was known that the polymer can reach
greatest swelling degree when the solubility parameter of the polymer is close to that of the
solvents The solubility parameter of PDXL is about 93 cal cm 12 -32 134 The swelling has been
examined in THF and CH2Cl2 for PDXL hydrogel It has been observed that the swelling
equilibrium is reached after almost 5 hours of swelling for all samples in both solvents The
results show that THF (δ = 952 cal cm12 -32)147 swells the hydrogel to the greatest degree
compared to CH2Cl2 as shown in figure 3 However CH2Cl2 molecules provide less swelling
147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983)
63
capacity than in THF On the basis of the experiment The PDXL hydrogel reached high
swelling degree due to its solubility parameter is much closer to that of THF
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
THF CH2Cl2
Swel
ling
degr
ee
Time (min)
Figure 3 Swelling kinetics of PDXL hydrogel in two different solvents CH2 Cl2 (solid
squares) and in THF (hollow squares)
244 Viscoelastic Behavior
Rheological measurements were performed on rheometer in the Cone and Plate geometry
Both steady shear and oscillatory experiments were carried out The dynamic storage and loss
moduli G and G were examined at room temperature (23 degC)
Many attempts have been carried to extend the elasticity theory to swollen gels148 149 Based
on this approach all measurements have been performed on both swollen and unswollen
hydrogel samples for the purpose of comparison so that to examine the mechanical properties
even in swollen state For instance Flory and Rehner recognized the swelling phenomenon
exhibited by cross-linked polymers when exposed to certain solvents and related the modulus
of elasticity of a swollen cross-linked polymer network to an unswollen network150 Figure 4
illustrates the strain dependence of G and G for swollen and unswollen samples
148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for Experimental
Mechanics SEM Annual Conference Proceedings (2002)
64
10-5 10-4 10-3 10-2 10-1 100 101 102101
102
103
104
Guns Guns Gs Gs
GG
(Pa
)
γ ()
Figure 4 Strain dependence of the elastic modulus Grsquo (circles) and of the viscous modulus
Grdquo(triangles) for two samples of unswollen hydrogel (solid symbols) and swollen hydrogel
(hollow symbols)
The moduli are measured as a function of strain at a constant frequency It appears that the
linear viscoelastic region is observed while the strain is increasing in either state which
indicates that the internal structure of the samples has not been disrupted when deformed
This leads to reveal that the gel is strain resistant in swollen and unswollen states and within a
large strain range the hydrogel retains its elasticity as shown in figure 4 where the linear
viscoelastic region extends to almost 02
The frequency dependence of G and G is shown in figure 5 similarly for swollen and
unswollen hydrogels The system behaves typically like a gel as it can be noticed that the
elastic component G (storage modulus) is far greater than the viscous component G (loss
modulus)151 Based on these results the hydrogel exhibits extreme elasticity at low
frequencies
151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure 554 (2000) 99-108
65
100 101
103
104
105
Gs Guns Gs GunsG
G(
Pa)
ω (rads)
Figure 5 Frequency dependence of Grsquo(circles) and Grdquo(triangles) for swollen hydrogel
(hollow symbols) and unswollen hydogel (solid symbols)
Finally figure 6 illustrates the complex viscosity profiles another parameter of
viscoelasticity which measures the magnitude of the total resistance to a dynamic shear
Again this property has not been affected by swelling since the results show similar behavior
for swollen and unswollen states It decreases sharply as frequency increases which
characterizes the samples degree of viscoelasticity at various time scales Therefore from the
results discussed above the hydrogel network is elastic and stable even in the swollen state
thereby possessing very good mechanical properties
100 101 102 103
102
103
104
105
η unswollen η swollen
ηlowast (P
a s)
ω (rads)
Figure 6 Frequency dependence of the complex viscosity η for unswollen hydrogel (solid
squares) and swollen hydrogel (hollow triangles)
66
Conclusion
The hydrogel properties were discussed in terms of swelling and viscoelastic
behaviors The hydrogel has combined special properties Its swelling behaviour in the
solvents was dependent on the solubility parameter of both solvents and hydrogel
Rheological measurements were successful when used in order to study the viscoelastic
behavior of the hydrogel of pure PDXL in swollen and unswollen states The Strain
dependence of G and G for both samples shows linear viscoelastic region and allows to
determine the yield stress Same conclusions can be given concerning the frequency
dependence of complex viscosity the swelling does not affect this property The results reveal
a perfect elastic and resistant hydrogel in other words the viscoelastic properties have not
been so much affected by swelling They may be particularly useful in the design of improved
microfluidic devices that utilise the relationship between swelling and strain This kind of
material can be potentially used in biosystems such as intelligent drug delivery systems
67
References
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-
174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002)
1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080 140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922 145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The
Handbook of IR and Raman Characteristic Frequencies of Organic Molecules United
Kingdom Ed by Academic Press Limited London (1991) 146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman
Spectroscopy 3rd Edition AP Limited London (1964) 147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983) 148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-
1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for
Experimental Mechanics SEM Annual Conference Proceedings (2002) 151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure
554 (2000) 99-108
68
CHAPTER III Synthesis and Characterization of Copolymers
31 Introduction
Amphiphilic block and graft copolymers consisting of hydrophilic and hydrophobic parts
have been subjects of numerous studies within which block and graft copolymers containing
hydrophilic polyoxyethylene segments and other hydrophobic segments have attracted much
attention because polyoxyethylene segments are not only hydrophilic but also nonanionic
and crystalline and can complex monovalent metallic cations Graft copolymers offer all
properties of block copolymers but are usually easier to synthesize Moreover the branched
structure leads to decreased melt viscosities which is an important advantage for processing
Depending on the nature of their backbone and side chains they give rise to special properties
in selective solvents at surfaces as well as in the bulk owing to microphase separation
morphologies12 They can be used for a wide variety of applications such as polymeric
surfactants electrostatic charge reducers compatibilizers in polymer blends polymeric
emulsifiers controlled wet ability and so on152 153 In order to prepare graft copolymers with
well-defined structure one can utilize the macromonomer technique (grafting through
technique) Well-defined structure graft copolymers are synthesized by copolymerization of
macromonomers with low molecular weight comonomers6 It allows the control of the
polymer structure which is given by three parameters (i) chain length of side chains which
can be controlled by the synthesis of the macromonomer by living polymerization (ii) chain
length of backbone which can be controlled in a living copolymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular weight monomer However the distribution of spacings
may not be very easy to control due to the incompatibility of the polymer backbone and the
macromonomers154 As pointed out in recent publication reviews155 there is a complex
interplay of factors that govern the reactivities in copolymerizations involving
macromonomers When different comonomers are copolymerized with the same it seems that
the degree of interpenetration between the macromonomer and the propagating copolymer 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305
69
backbone plays the major role in the measured reactivities Nevertheless the main properties
depend on both the average composition of the systems and the microstructural distribution of
the comonomer sequences along the macromolecular backbone which is determined by the
reactivity ratios of the macromonomer and the corresponding comonomer in the free radical
polymerization process156 157
In this chapter our work deals with the preparation and characterization of new organo-
soluble associative copolymers based on short hydro-soluble chains of poly (1 3 dioxolane)
(PDXL) Many reports have been published on PDXL macromonomers used to form
hydrogels136 137 158 159 160 161 162 however very few were on graft copolymers with PDXL
branches162 These macromonomers are used for the preparation of amphiphilic graft
copolymers by solution free radical copolymerization with a hydrophobic comonomer
styrene (St) and methyl methacrylate (MMA) Structural characterization of these
copolymers molecular weight determination reactivity ratios and the polymerizability of the
PDXL macromonomer have been discussed Finally their thermal properties are discussed
according to the weight content of PDXL in the copolymers
32 Experimental
321 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269
70
bull Ethanol (C2H6O MW 4607 bp 78degC d 081)
Ethanol (Prolabo 95-96) was purified by distillation with 5g of Magnesium and 05g of
iodine for 75ml of alcohol under a N2 atmosphere After discoloration of the mixture
solution a volume of Ethanol was added and then distilled normallyThen it was stored
over molecular sieve
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile(AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull Styrene (C6H5CH=CH2 MW 10416 bp 145degC d 091)
Styrene (Prolabo product) was purified by distillation over CaHB2 at reduced pressure
bull Methyl Methacrylate (MMA)(H2C=C(CH3)CO2CH3 MW 10012 bp 100degC d
0936)
Methyl Methacrylate (Prolabo product) was purified by distillation over CaHB2 at reduced
pressure
All chemicals were kept over molecular sieve before use
322 Synthesis of Poly (Styrene-co-Poly (13-dioxolane))
a) Conventional Free Radical Copolymerization
The reaction route for the conventional copolymerization of Styrene and PDXL
macromonomers using AIBN as the free radical initiator at 60degC is shown in scheme 14
71
Scheme 14
PDXL macromonomers of different molecular weights were copolymerized with St in THF at
60degC in the presence of 2 2rsquo-azobisisobutyronitrile AIBN (1 based on the total weight of
the monomers) as initiator under a nitrogen atmosphere using different feed molar fractions
of macromonomers The total monomer concentration for was 6 10-1 M in all cases The
copolymerization product is diluted with THF and then added dropwise to a large excess of
ethanol to remove unreacted PDXL macromonomers25 43 and precipitate the copolymers
Then they were finally dried over vacuum at 40degC to constant weight The yields of all
reactions are 70ndash 90 Table 2 indicates the amounts of comonomers initiator and solvent
employed in the copolymerization study
72
Table 2 Copolymerization of PDXL macromonomers (M1) with Styrene (M2)
Sample M1 M2M1 PDXL (g) (mol)
Styrene (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2SP2 FPP2 20 349 174510-4 364 349 10-2 007 60 0610 3SP2 FPP2 30 232 116 10-4 364 349 10-2 006 60 0601 5SP2 FPP2 50 14 69810-4 364 349 10-2 005 60 0593
2SP15 FPP15 20 262 174510-4 364 349 10-2 006 60 0610 3SP15 FPP15 30 174 116 10-4 364 349 10-2 006 60 0601 5SP15 FPP15 50 105 69810-4 364 349 10-2 005 60 0593
2SP1 FPP1 20 174 174510-4 364 349 10-2 006 60 0610 5SP1 FPP1 50 07 69810-4 364 349 10-2 005 60 0593 8SP1 FPP1 80 0436 43610-4 364 349 10-2 005 60 0589
b) Controlled Free Radical Copolymerization
The comb-structure copolymer of styrene and PDXL was obtained by grafting-from
mechanism through Nitroxide-Mediated Polymerization
Nitroxide mediated polymerization (NMP) is a controlled radical polymerization (CRP)
technique which already offers the ability to prepare a wide variety of well-defined polymer
architectures119 Despite the significant improvements brought to CRP techniques such as
NMP atom transfer radical polymerization (ATRP) or reversible addition fragmentation chain
transfer (RAFT) the preparation of complex architectures by CRP is restricted by the
exclusion of monomer systems that are polymerized by fundamentally different mechanisms
like lactides ethylenepropylene oxide The most promising approaches to extend the range of
polymer compositions are based on the use of heterofunctional initiators163 allowing the
combination of mechanistically distinct polymerization reactions without the need for
intermediate transformation and protection steps
In the field of NMP the development of multifunctional initiators was focused on TEMPO
and TIPNO which are examples of nitroxides (Scheme 15) It is worth to mention that in
NMP these are used as counter-radicals associated with a conventional azoic initiator so this
pair of initiators is known as a bimolecular system
163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671
73
Scheme 15 TEMPO and based alkoxyamines
Another initiator used for NMP is the commercially available alkoxyamine also called
MAMA-SG1164 (Scheme 16) known as a monomolecular system initiator which is
particularly convenient for functionalization of polymer chain ends164 165 MAMA-SG1 has
been developed by Didier Gigmes and co in collaboration with Arkema Company166 Thanks
to a particularly high dissociation rate constant value kd1 up to now this alkoxyamine has
proved to be one of the most potent alkoxyamines reported in the field of NMP167 168 This
initiator is used for polymerization of styrene and n-butyle acrylate allowing formation of
well-defined linear and star structures
Scheme 16
164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006) 5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219
74
Scheme 17 MAMA-SG1 structure and dissociation scheme
bull Multifunctionalization of Polystyrene (HO-PS)
MAMA-SG1 was used to run copolymerization of styrene at 90 mol with HEMA in order
to obtain functionalized polystyrene The monomers and alkoxyamine were introduced in a
250 mL two neck round-bottom flasks fitted with septum condenser and degassed for 15
min by nitrogen bubbling The reaction was performed in bulk at 120 degC under N2 with
vigorous stirring Targeted molecular weight and polydispersity were 30 000 g mol and 12
respectively
After polymerization the final polymer mixture was dissolved in a minimum THF and
precipitated in cold ethanol followed by drying under vacuum at 30degC
bull Synthesis of PS-g-PDXL
PDXL was copolymerized by cationic ring-opening polymerization which was carried out in
40 ml dichloromethane with triflic acid as initiator at room temperature under nitrogen for 24
h in the presence of OH-multifunctionalized PS (1g 3 10-5 mol) as transfer agent 20 ml
(0286 mole) of DXL monomer was added Table 6 gives the molecular characteristics of the
obtained copolymer The amount of the acid used was 20 μl After reaction the resulting
solution is poured into THF Then the product is purified by re-precipitation from THF
solution with a large excess of hexane and the obtained polymer was dried under vacuum at
room temperature The yield was checked by gravimetric determination and found to be about
75 The polymerization route is presented in the scheme below
75
Scheme 18
323 Synthesis of Poly (Methyl Methacrylate-co-Poly (13-dioxolane))
Same procedure has been used for the synthesis of Poly (Methyl Methacrylate-co-Poly (1 3-
dioxolane)) copolymers The yields of the reactions are in the range of 70ndash 90
Table 3 shows the amounts of comonomers initiator and solvent employed in the
copolymerization reactions
Table 3 Copolymerization of PDXL macromonomers (M1) with MMA (M2)
Sample M1 M2M1 PDXL (g) (mol)
MMA (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2MP2 FPP2 20 374 187 10-4 3744 374 10-2 008 65 0604 3MP2 FPP2 30 2 10 10-4 300 300 10-2 005 50 0620 5MP2 FPP2 50 15 748 10-4 3744 374 10-2 005 60 0636
2MP15 FPP15 20 2 133 10-4 28 280 10-2 005 25 100 3MP15 FPP15 30 187 125 10-4 3744 374 0-2
006 60 0644 5MP15 FPP15 50 112 748 10-4 3744 374 10-2 005 60 0636
2MP1 FPP1 20 2 20 10-4 400 4 10-2
006 50 0840 3MP1 FPP1 50 125 125 10-4 3744 374 10-2 005 64 0604 5MP1 FPP1 80 075 748 10-4 3744 374 10-2 005 60 0636
33 Characterization Techniques
331 1H-NMR Spectroscopy
1H NMR Spectroscopy was used for compositional and structural analysis of the copolymers
1H-NMR spectra of the copolymers were recorded on the high field 400Mhz Advance Bruker
spectrometer All of the 1H NMR samples were dissolved in deuterated chloroform The
integrals of the peaks of copolymer components were used for the calculations to determine
76
the molecular weights polydispersity indices and the amount of each comonomer that was
incorporated into the copolymer
332 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) was used in the charaterization of the copolymers to
determine average molecular weights and polydispersity indices SEC Measurements were
performed at 40degC on a Waters 2690 instrument equipped with UV detector (Waters 996
PDA) coupled with a Differential Refractometer (ERC - 7515 A) and four Styragel columns
(106 105 500 and 50degA) THF is employed as the mobile phase with a flow rate of 10
mlmin Polystyrene standard samples were used for calibration
333 Diffraction Scanning Calorimetry
Diffraction Scanning Calorimetry (DSC) measurements are performed on a Modulated
Temperature Differential Scanning Calorimeter Q100 TA instrument under nitrogen at 50
mlmin The samples are hermetically sealed in aluminium pans and they are subjected to a
heating program as follows
For Poly (Styrene-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 120degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -80degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to130degC
For Poly (Methyl Methacrylate-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 130degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -95degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to150degC
The thermograms obtained illustrate Glass Transition Temperatures (Tg) and Meltind Points
(Tm) of the copolymers
77
34 Results and Discussion
Methacryloyl-terminated PDXL macromonomers with the Mn range of 1000-2000 gmole
were copolymerized with vinyl and methacrylic monomers in order to obtain amphiphilic
graft copolymers with chemical structure of hydrophobic backbone and hydrophilic side
chains
341 Structural Characterization of the Copolymers
The structure of the copolymers was well defined by 1H-NMR analysis The copolymer 1H-
NMR spectra confirm the formation of copolymers see figures 7 8 and 9 The chemical
shifts of protons of polystyrene and PDXL can be clearly distinguished The following peaks
are assigned for OCHBB2BBO protons at 478 ppm and OCHBB2BBCHBB2BBO protons at 375 ppm (5H CBB6BB
HBB5BB) at 728 711 and 706 ppm as shown in Figure 8 The spectrum of PMMA-PDXL
copolymer is shown in Figure 9 where the chemical shifts of PMMA correspond to the proton
resonance as depicted in the figure the O-CH3 protons are observed at 361 ppm and clear
resonance assigned to the methyl group protons at 085-103 ppm and eventually we observe
the corresponding chemical shifts for OCHBB2BBCHBB2BBO protons (374 ppm) and OCHBB2BBO protons
(477 ppm) to confirm the incorporation of PDXL in the copolymer
Figure 7 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP1)
78
Figure 8 1H-NMR spectrum of Styrene-g-PDXL copolymer in CDCl3 (sample 3SP2)
79
Figure 9 1H-NMR spectrum of MMA-g-PDXL copolymer in CDCl3 (sample 2MP2)
342 Copolymer Molecular Weight and Composition
a) Conventional Free Radical Copolymerization
Copolymerization of PDXL macromonomers with MMA and ST in THF solution was studied
for different molar feed ratio of PDXL The amounts of monomeric units in the copolymers
were determined by elemental analysis The results are presented in Table 4 and 5 which
summarise the characteristics of the graft copolymers in terms of macromonomer feed ratio
(M2M1) and average Mn obtained from SEC as well as copolymer composition in weight and
mole percentages which is determined from 1H-NMR
80
Table 4 Characteristics of PDXL macromonomers (M1) copolymerized with Styrene (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2SP2 FPP2 20 49 476 4025 337 9200 162 2 3SP2 FPP2 30 39 322 303 221 8900 162 2 5SP2 FPP2 50 277 196 21 13 7200 159 1
2SP15 FPP15 20 418 476 34 34 9100 157 2 3SP15 FPP15 30 323 322 24 214 7000 161 2 5SP15 FPP15 50 224 196 152 12 6700 147 1
2SP1 FPP1 20 323 476 30 427 9200 178 3 5SP1 FPP1 50 16 196 1424 17 5800 158 1 8SP1 FPP1 80 107 123 85 095 11900 195 1
Table 5 Characteristics of PDXL macromonomers (M1) copolymerized with MMA (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2MP2 FPP2 20 50 476 35 26 21900 198 4 3MP2 FPP2 30 40 322 21 13 25900 157 3 5MP2 FPP2 50 286 196 13 07 87200 455 6 2MP15 FPP15 20 416 45 28 25 19800 193 4 3MP15 FPP15 30 333 322 22 18 15200 277 3 5MP15 FPP15 50 23 196 13 10 24700 16 2 2MP1 FPP1 20 333 476 26 34 21100 319 6 3MP1 FPP1 30 333 322 19 22 17100 197 3 5MP1 FPP1 50 20 196 10 11 13900 354 2
81
b) Controlled Free Radical Copolymerization
Multifunctionalization of Polystyrene and Synthesis of poly (S-g-PDXL) copolymer give
results which are shown in Table 6 These data have been obtained from the 1H-NMR and
SEC analyses illustrated in figures 10 and 11 The resonance shifts assigned to all components
(PDXL PS and HEMA) are very clear This enables us to make calculations to determine
composition of each copolymer in addition to obtain the average number of grafts and the
number average-molecular weight of a graft
It is observed that the multifunctionalized-PS is composed of 20 in mole of HEMA which
results in 58 grafts (Ng = 58) per molecular chain
After copolymerization multifunctionalized-PS with DXL the copolymer PS-g-PDXL
(DXPS) possesses the following characteristics which are presented in Table 6 It has a
number average-molecular weight of 83000 gmol with 80 of PDXL content The number
average-molecular weight of one graft has been calculated and found to be 1000 gmol
Table 6 Characteristics of functionalized Styrene (HO-PS) and PS-g-PDXL (DXPS)
copolymer
Strusture Sample MnSEC IP PDXL
w mol
PS
w mol
HEMA
w mol
Ng Graft
Mn
HO-PS
32 700
12
_ _
77 80
23 20
58
_
DXPS
83 000
24
71 80
17 13
12 75
58
1000
82
Figure 10 1H-NMR spectrum of Multifunctionalized of Polystyrene in CDCl3
Figure 11 1H-NMR spectrum of poly (S-g-PDXL) copolymer (DXPS) in CDCl3
83
341 Determination of Monomer Reactivity Ratios
The application of the classical treatment based on linearization of the copolymerization
equation of Mayo and Lewis91 or the non-linear least-squares approach suggested by Tidwell
and Mortimer95 requires working with high macromonomer concentrations (ie feed
compositions higher than 20-30 of macromonomer)156
The MayondashLewis equation (58) that relates the instantaneous compositions of the monomer
mixture to the copolymer composition is approximated to a simplified form (equation (59))
suggested by Jaacks169 when working with a large excess of one of the comonomers This is
the case of copolymerisation reactions between a conventional comonomer and a
macromonomer of relatively high molecular weight where using low molar concentrations of
macromonomer is mandatory due to its restricted solubility and the extremely viscous media
][ ][ ]
[ ][ ]
[ ] [[ ] [ ]221
211
2
1
2
1
MrMMMr
MM
MdMd
++
=
(58)
[ ][ ] 1
22
1
2
MMr
MdMd
=
(59)
According to equation (59) the copolymer composition or the frequency of branches is
essentially determined by the monomer composition and the monomer reactivity ratio of the
comonomer r2 (inversely proportional to the macromonomer reactivity) under the limit
condition of [M2][M1] gtgt1 In order to obtain reliable values it is frequently necessary to
run the copolymerisation at different conversions or to carry out several copolymerizations
with different initial monomer ratios170 In such cases an integrated form of equation (59) is
used
[ ] [ ][ ][ ] 01
12
02
2 lnlnMM
rMM tt =
(60)
169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046
84
where [Mi]t[Mi]0 is the ratio among the composition of monomer i at time t and the initial
feed composition A plot of ln ([M2]t[M2]0) versus ln ([M1]t[M1]0) should result in a straight
line with a slope that equals to r2 (the reactivity ratio of the comonomer)
Thus the monomer reactivity ratios between the PDXL macromonomers and the comonomers
were estimated with the data in tables 4 and 5 We can apply equation (60) to the estimation
where M1 and M2 are the PDXL macromonomer and copolymer respectively The monomer
reactivity ratios are determined for macromonomers of different Mn (degree of
polymerization) and summarized in Table 7
Table 7 Monomer reactivity ratios for copolymerization of PDXL macromonomers (M1)
with St and MMA (M2)
Sample M2 M1
macromer Mnth
r2 1r2
SP2 St FPP2 2000 012 plusmn 0006 833
SP15 St FPP15 1500 0042 plusmn 6 10-4 238
SP1 St FPP1 1000 0015 plusmn 3 10-4 6666
MP2 MMA FPP2 2000 002 plusmn 001 50
MP15 MMA FPP15 1500 007 plusmn 0 02 1428
MP1 MMA FPP1 1000 0018 plusmn 001 5555
In the case of copolymerization with Styrene and MMA the results suggest that the reactivity
of the methacrylic double bond in the prepared macromonomers is not affected in their
copolymerization with Styrene or MMA This point is confirmed when analysing the inverse
ratio 1r2 = k21k22 which is sometimes considered as the relative copolymerization reactivity
of a macromonomer171 This quantity is the ratio between the crosspropagation and
homopropagation rate constants of comonomer (2) which is directly proportional to the
reactivity of the macromonomer (1) and gives a clear idea of the relative reactivity of a
growing radical ending in a 2 unit towards the addition of monomer (1) in comparison to the
171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620
85
tendency for the homopropagation So we have a situation where r1 gtgt 1 gtgt r2 and it is
expected that the initially formed chains should contain more macromonomers and then more
comonomer segments are added These are only assumptions but they give an indication
about the probable composition drift of the graft copolymers obtained On the other hand in
the case of copolymerization of poly (13dioxolane) macromonomers with styrene (Figure
12) the results show that r2 increases with increasing PDXL side chain length (in terms of
average Mn) and this leads to say that the side macromonomer chain length affect the
reactivity of the comonomer Thus this indicates that a growing radical of macromonomer
with a shorter chain length (ie lower Mn ) attacks more frequently a monomer of the same
nature than it does a macromonomer with a longer length (ie higher Mn) as it can be noticed
from the results in Table 7
However the r2 values of the copolymerization with MMA as shown in Figure 13 give
unclear dependence on the side poly (13dioxolane) macromonomer chain length this may be
due to the resulting polydispersity of the copolymerization Mentioned behaviour may be
related with the reactive structure of comonomers vinyl in the case of Styrene or methacrylic
in the case of MMA in regard to the ending methacrylic double bond of macromonomers
besides the hydrophilic character of the macromonomers
86
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0015 plusmn 3 10-4 SP1
b
r2 = 0042 plusmn 6 10-4
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP15
c
r2= 012 plusmn 0006
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP2
Figure 12 Application of Jaacksrsquo treatment to the St-g-PDXL copolymerization systems
(a) SP1 (b) SP15 (c) SP2
87
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0018 plusmn 001 MP1
b
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 007 plusmn 002MP15
036788
c
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 002 plusmn 001 MP2
Figure 13 Application of Jaacksrsquo treatment to the MMA-PDXL copolymerization systems
(a) MP1 (b) MP15 (c) MP2
88
341 Glass Transition Temperatures
Thermal analysis of Styrene-g-PDXL copolymers allows to determine their glass transition
and melting temperatures In the first place the measurements were performed on a
conventional DSC from which the thermograms obtained show an overlapping of PS glass
temperature and PDXL melting point signals This has been observed for all samples A
different approach in the characterisation of these copolymers was by means of Modulated
Temperature Differential Scanning Calorimeter (MTDSC) which is an extension of
conventional DSC This approach combines high resolution with high sensitivity by use of a
sinusoidal temperature modulation superimposed on a constant temperature or linear
temperature program with a small underlying average heating rate172 173 In comparison to
conventional DSC the MTDSC analysis enables the simultaneous calculations of an
additional quantity the cyclic or modulus of heat capacity Cp (J g-1K-1 172)
ωT
HFp A
AC =
(61)
is the amplitude of the cyclic heat flow (Wg-1) and AWhere AHF Tω is the amplitude of cyclic
heating rate with AT the temperature modulation amplitude (K) ω the modulation angular
frequency (2πp) and p is the modulation period (s)172
In fact the MTDSC splits the overlapped signals into two distinct temperatures melting
temperature of the hydrophilic grafts and glass transition temperature of the hydrophobic
backbone as can be noticed in Figure 14 in which melting temperature appears to be 5626degC
which is closer to the glass transition temperature with a value of 5671degC From the results
obtained out of the thermogram it is clear that the measurements show very close values of
Tm and Tg for all copolymer samples where in conventional DSC these two temperatures
cannot be distinguished
172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
89
Figure 14 MTDSC thermogram of 5SP1 copolymer at heating rate of 2degCmin
Tg was taken at the midpoint of the transition region The results obtained are shown in
Tables 8 and 9 for copolymers with Styrene and MMA respectively Then a plot of the
copolymers Tg has been constructed against PDXL content in order to determine the effect of
the latter on Tgrsquos As it can be noticed in the Figure 15 Tg of the copolymers decreases
exponentially with increasing PDXL content and this may be due to the decrease in the
intermolecular interactions between the molecular chains and can be associated with higher
mobility and flexibility of the polymeric chains when PDXL is incorporated in the
copolymers The results clearly indicate that Tg values of the copolymers depend on the
composition of comonomers and a decrease with increasing PDXL content in the obtained
copolymers
90
Table 8Transition temperatures of Styrene-g-PDXL copolymers obtained by thermal
analysis (DSC) Sample PDXL content Tg wt () (degC) 8SP 85 7489 1
5SP 1424 5671 1
5SP 152 5590 15
21 6739 5SP 2
303 4480 3SP 2
34 2665 2SP15
4025 2SP 4060 2
Table 9Transition temperatures of MMA-g-PDXL copolymers obtained by thermal analysis
(DSC)
Sample PDXL content Tg
wt () (degC)
5MP 10 10545 1
5MP 13 8278 15
21 6576 3MP 2
22 7550 3MP 15
26 7013 2MP1
91
5 10 15 20 25 30 35 40 4520
30
40
50
60
70
80
a
SP COPOLYMERSTg
(degC)
PDXL content in wt()
10 15 20 2560
70
80
90
100
110
b
Tg (deg
C)
PDXL content in wt()
MP COPOLYMERS
Figure 15 Glass transition temperatures vs PDXL macromonomer content for copolymer
systems (a) Styrene-g-PDXL copolymers (b) MMA-g-PDXL copolymers
92
Conclusion
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers The macromonomer reactivity estimation suggests that the
length of the PDXL side chains does affect the reactivity of the methacrylic double bond of
the macromonomer when copolymerized with St However in the case of copolymerization
with MMA there is no dependence on the graft size Finally from DSC measurements the
values of Tg depend on the composition and the size of the PDXL grafts In all copolymers
the increase in amount of the incorporated PDXL macromonomer results in a substantial
decease in glass transition
93
References 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305 156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269 163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671 164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006)
5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219 169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620 172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly
(1 3 Dioxolane)) on Immiscible Polymer Blends
of Polystyrene and Poly (Ethylene Glycol)
41 Background
411 Physical Blends
Physical blending is defined as the simple mechanical mixing of two or more polymers either
in the melt or in solution174 At first glance this approach would seem to be ideal for
preparing hybrids as blending is considered a simple and economical procedure that is
commonly used to produce new products from existing materials175 However in polymer
science the effectiveness of blending is dependent upon the degree of compatibility of the
polymers involved176 At least three general types of materials can result from blending
depending on the mutual solubility and semi-crystallinity of the constituents
412 Equilibrium Phase Behavior
Mixing of two amorphous polymers can produce either a homogeneous mixture at the
molecular level or a heterogeneous phase-separated blend Demixing of polymer chains
produces two totally separated phases and hence leads to macrophase separation in polymer
blends Some specific types of organized structures may be formed in block copolymers due
to microphase separation of block chains within one block copolymer molecule
Two terms for blends are commonly used in literature miscible blend and compatible blend
The terminology recommended by Utracki177 will be used By the miscible polymer blend it
means a blend of two or more amorphous polymers homogeneous down to the molecular
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York (1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York (1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser Publishers Munich (1989)
95
level and fulfilling the thermodynamic conditions for a miscible multicomponent system An
immiscible polymer blend is the blend that does not comply with the thermodynamic
conditions of phase stability The term compatible polymer blend indicates a commercially
attractive polymer mixture that is visibly homogeneous frequently with improved physical
properties compared with the constituent polymers
Miscible blends occur spontaneously when the overall energy of mixing (ΔGmix) is negative
as defined by the Gibbs-Helmholtz free energy equation (Equation 62)
(62)
In the Gibbs-Helmholtz equation ΔHmix is the enthalpy of mixing and ΔSmix is the entropy of
mixing while T is the temperature of the blend Flory-Huggins178 and Scott179 have made
further correlation of enthalpy and entropy as a function of the polymer components and their
properties (Equation 63)
(63)
In Equation 63 χ is a measure of the polymer-polymer interaction energy V is the volume of
the system Φi is the volume fraction of polymer i R is the gas constant T is the temperature
of blending Vr is the reference volume of the monomers and χi is the degree of
polymerization
Examination of Equation 63 reveals that the entropy of mixing is highly dependent on the
molecular weight of the blended polymers while the enthalpy is much more dependent on the
level of interaction between the polymer types Additionally Scott showed that as molecular
weight increases to the level commonly found in commercially useful materials ΔS
approached zero (0) Therefore polymer blends of commercial importance are primarily
influenced by the rate of enthalpy However for polymers with weak interactions (as χ
approaches 1) eg as observed in most polymer pairs the enthalpy of mixing can be further
reduced according to Equation 64
178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279
96
(64)
In Equation 64 δi is the polymerrsquos solubility parameter (an estimation of its ability to be
dissolved in a range of solvents) derived from the square root of the cohesive energy density
pioneered by Hildebrand180 Thus most early work with polymer blends concentrated on
matching the solubility parameters of the component polymers
Unfortunately the theoretical maximum difference in solubility for a 5050 polymer blend is
only 01 (calcm3)12 This narrow margin is much smaller than the standard error among
methods used to determine solubility parameters181 The ability to predict miscibility of
polymer pairs with strong interactions such as donor-acceptor and hydrogen bonding which
can increase miscibility by creating an exothermic reaction upon mixing (ΔH lt0) have been
attempted for many years with varying degrees of success
The formation of miscible blends is dependent on several factors including molecular
structure average chain length tacticity of the polymers as well as the temperature of mixing
and the blending method If the blended polymers are miscible (ΔGmix lt 0) and thus
compatible the resulting material will display an amalgamation of properties which are
predictable using the same techniques as those used for random or statistical copolymers
Polymer blends account for a significant percentage of polymer production and are produced
either to reduce costs to aid in processing or to improve a variety of specific properties For
example polycarbonates have been blended with polybutylene terephthalates to increase
chemical resistance and to aid in processing while polyphenylene oxides are bended with
polystyrenes to improve toughness and increase glass transition temperatures182
413 Compatibilization
As it follows from thermodynamics the blends of immiscible polymers obtained by simple
mixing show a strong separation tendency leading to a coarse structure and low interfacial
180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999)
97
adhesion The final material then shows poor mechanical properties On the other hand the
immiscibility or limited miscibility of polymers enables formation of wide range structures
some of which if stabilized can impart excellent end-use properties to the final material To
obtain such a stabilized structure it is necessary to ensure proper phase dispersion by
decreasing interfacial tension to suppress phase separation and improve adhesion This can be
achieved by modification of the interface by the formation of bonds (physical or chemical)
between the polymers This procedure is known as compatibilization and the active
component creating the bonding as the compatibilizer174 177 183
The most popular method of compatibilization is by addition of a third component In most
cases such an additive is either a block or graft copolymer Since the key requirement is
miscibility it is not necessary for the copolymer to have identical chain segments as those of
the main polymers It suffices that the copolymer has segments having specific interactions
with the main polymeric components viz hydrogen bonding dipole-dipole dipole-ionic
Lewis acid-base etc
Addition of a block or graft copolymer reduces the interfacial tension and alters the molecular
structure at the interface Thus compatibilization by addition changes not only the interfacial
properties but it may affect the flow behavior (hence processability)
One of the disadvantages of the addition method is the tendency of the added copolymers to
form micelles These reduce the efficiency of the compatibilizer increase the blend viscosity
and may lessen the mechanical performance
414 Incorporation of Copolymers for Compatibilization
Block or graft copolymers with segments that are miscible with their respective polymer
components show a tendency to be localized at the interface between immiscible blend
phases Random copolymers sometimes also used as compatibilizers reduce interfacial
tension but their ability to stabilize the phase structure is limited184 Finer morphology and
higher adhesion of the blend lead to improved mechanical properties The morphology of the
resulting two-phase (multiphase) material and consequently its properties depend on a
number of factors such as copolymer architecture (type and molecular parameters of
segments) blend composition blending conditions
183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001)
98
In Scheme19 the conformation of different block graft or random copolymers at the
interface is schematically drawn
Scheme 19 Possible localization of A-B copolymer at the AB interface Schematic of
connecting chains at an interface a-diblock copolymers b-end-grafted chains c-triblock
copolymersdmultiply grafted chain and e-random copolymer
415 The Effect of Compatibilizer on a Blend
The presence of a compatibilizer at the interface substantially affects the development of the
phase structure of molten blends in the flow and quiescent state The position and width of the
concentration region related to co-continuous morphology are affected by two competing
mechanisms A decrease in interfacial tension caused by a compatibilizer favors the formation
and stability of co-continuous structures
The effect of a compatibilizer on fineness of the phase structure can be understood through its
effects on droplet breakup and coalescence A decrease in interfacial tension due to the
presence of a compatibilizer decreases the droplet radius R
Effect of the Compatibilizer Architecture
Compatibilization efficiency of various copolymers follows from their thermodynamic and
microrheological effects It has been generally accepted that the total molecular weight of the
copolymer molecular weight of its blocks and their number are the main structural
compatibilizer characteristics affecting the phase structure of the final blend
99
Effect of Compatibilizer Concentration
The compatibilizing efficiency of the copolymers is besides the architecture a function of
their concentration The effect of a compatibilizer concentration has been quantitatively
characterized by the emulsification curvemdashthe dependence of the average particle diameter of
the minor dispersed phase on copolymer concentration185 The particle diameter decreases
with increase of copolymer concentration until a constant value is obtained For most systems
this value is achieved if the copolymer amount is 15ndash25 of the dispersed phase
416 Methods of Blend Preparation
Five different methods are used for the preparation of polymer blends186 187 melt mixing
solution blending latex mixing partial block or graft copolymerization and preparation of
interpenetrating polymer networks It should be mentioned that due to high viscosity of
polymer melts one of these methods is required for size reduction of the components (to the
order of μm) even for miscible blends
bull Melt mixing is the most widespread method of polymer blend preparation in practice
The blend components are mixed in the molten state in extruders or batch mixers Advantages
of the method are well-defined components and universality of mixing devicesmdashthe same
extruders or batch mixers can be used for a wide range of polymer blends Disadvantages of
the method are high energy consumption and possible unfavorable chemical changes of blend
components This procedure has not been used so far in industrial practice because of large
energy consumption
bull Solution blending is frequently used for preparation of polymer blends on a laboratory
scale The blend components are dissolved in a common solvent and intensively stirred The
blend is separated by precipitation or evaporation of the solvent The phase structure formed
in the process is a function of blend composition interaction parameters of the blend
components type of the solvent and history of its separation Advantages of the process are
rapid mixing of the system without large energy consumption and the potential to avoid
185 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons Inc New York Chap 16 (2000) 186 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709 187 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458
100
unfavorable chemical reactions On the other hand the method is limited by the necessity to
find a common solvent for the blend components and in particular to remove huge amounts
of organic (frequently toxic) solvent Therefore in industry the method is used only for
preparation of thin membranes surface layers and paints
bull A blend with heterogeneities on the order of 10 μm can be prepared by mixing of
latexes without using organic solvents or large energy consumption Significant energy is
needed only for removing water and eventually achievement of finer dispersion by melt
mixing The whole energetic balance of the process is usually better than that for melt mixing
The necessity to have all components in latex form limits the use of the process Because this
is not the case for most synthetic polymers the application of the process in industrial practice
is limited
bull In partial block or graft copolymerization homopolymers are the primary product
But an amount of a copolymer sufficient for achieving good adhesion between immiscible
phases is formed188 In most cases materials with better properties are prepared by this
procedure than those formed by pure melt mixing of the corresponding homopolymers The
disadvantage of this process is the complicated and expensive start-up of the production in
comparison with other methods eg melt mixing
bull Another procedure for synthesis of polymer blends is by formation of interpenetrating
polymer networks A network of one polymer is swollen with the other monomer or
prepolymer after that the monomer or prepolymer is crosslinked189 In contrast to the
preceding methods used for thermoplastics and uncrosslinked elastomers blends of
reactoplastics are prepared by this method
188 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 189 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981)
101
42 Experimental
421 Materials
Polymers used in this research were PEG and PS PEG was purchased from MERCK
company General Purpose PS was obtained from ENPC TP1-Chlef Company Physical and
Structural characterizations of these materials were performed by SEC 1H-NMR and DSC
422 Blend Preparation
PSPEG blends of 5050 wt were prepared by solution casting from THF 40degC The
polymer solutions were stirred until complete miscibility and then cast onto glass dishes and
left to evaporate the solvent to the atmosphere To remove residual solvent after casting the
blends were dried in vacuum oven at 40degC for a weak Table 10 shows the quantities of the
copolymers used for compatibilization of the blends of PSPEG
Table 10 The quantities of the copolymers used for compatibilization of the blends of
PSPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
43 Characterization Techniques for Compatibilization
431 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
102
Relative viscosities of polymer solutions were calculated by dividing the flow times of
solutions by that of the pure solvent The data were plotted using the Huggins equation with
the intrinsic viscosity [η] (dlg-1) determined by extrapolation to infinite dilution
432 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
433 FTIR Analysis
FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
44 Results and Discussion Polyethylene glycol (PEG) is very interesting and important polymers PEG presents good
properties eg hydrophilicity solubility in water and in organic solvents nontoxicity and
absence of antigenicity and immunogenicity190It has attracted increasing attention due to its
potential applications as biomedical and environment friendly materials PEG has been
widely used as a modifier for biomedical surfaces to reduce the protein absorption and
improve their biocompatibility192 and as a stabilizer for emulsion and dispersion It has also
been used as a plasticizer for poly (lactide) (PLA) which is stiff and brittle as a
biodegradable packaging material193
On the other hand polystyrene shows excellent processability good appearance tensile
strength and thermal and electrical characteristics however its brittleness considerably limits
its use in high performance products
Both PS and PEG are widely used commodity polymers Detailed studies on their miscibility
may contribute to technological and environmental applications These polymers form an
interesting pair to study since they exhibit contrasting physical properties PS is a
190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689
103
hydrophobic polymer whereas PEG is hydrophilic PEG is a much softer material than PS
PSPEO blends have been reported as incompatible materials in the literature194 195
N Watanabe et al have reported compatibilization effect of poly (styrene-co-methacrylic
acid) on immiscible blends of this system196
441 Characterization of the Blend Components
Analysis by SEC provides number average-molecular weights and polydispersity indices of
all materials DSC measurements performed to determine their glass transition temperatures
as well as melting point and degree of crystallinity of PEG (See Figure16) 1HNMR spectroscopy analysis was performed on these polymers to determine essentially the
tacticity of PS and also to get information about end groups of PEG which was found to
possess an OH group at each end It has been also determined that the stereoregularity of PS
is Syndiotactic-Atactic (rather highly syndiotactic) (See Figures 17)
Physical characteristics of materials used are given in Table11
Table 11 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PS ENPC TP1-Chlef (from CHI MEI Corp)
105
128 000
1076
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam] Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842
104
Figure 16 1H-NMR spectrum of PEG (Merck) in CDCl3
105
Figure 17 1H-NMR spectrum of Commercial Styrene (ENPC TP1-Chlef) in CDCl3
442 Study of Compatibilization by Dilute Solution Viscometry
a) Introduction
Polymer blends are physical mixtures of structurally different polymers which interact
through secondary forces with no covalent bonding Blending of the polymers may result in a
reduction in the basic cost and improved processing and also may enable properties of
importance to be maximized The polymer blends often exhibit properties that are superior
compared to the properties of each individual component polymer197 198 199 200 The main
advantages of the blend systems are simplicity of preparation and ease of control of physical
properties by compositional change201 202 However the mechanical thermal rheological and
197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85
106
other properties of a polymer blend depend strongly on its state of miscibility on the
molecular scale203
There have been numerous techniques of studying the miscibility of the polymeric blend The
most useful techniques are dynamic mechanical thermal electron-microscopic IR
spectroscopic refractive index203 optical microsscopic204 and viscometric techniques 179 205
Because of its simplicity viscometry is an attractive and very useful method for studying the
compatibility of polymer blends Additional advantages ie that no sophisticated equipment
is necessary and that the crystallinity or the morphological states of the polymer blends do
affect the result206 make the viscometric method more convincing for characterizing polymer
mixtures The principle of using a dilute solution viscosimetry to measure the miscibility is
based on the fact that while in solution molecules of both component polymers may exist in
a molecularly dispersed state and undergo a mutual attraction or repulsion which will
influence the viscosity It is assumed that polymerndashpolymer interaction usually dominate over
polymerndashsolvent ones207 The presence of interactions between atoms or groups of atoms of
unlike polymers is essential to obtain a miscible polymer blend177 179
Estimation of the compatibility of different pairs of polymers based on dilute solution
viscosity for a ternary polymerpolymer-solvent system has been attempted by several
authors including Mikhailov and Zeilkman208 Bohmer and Florian209 Feldman and Rusu210
Krigbaum and Wall211 and Catsiff and Hewett212
The compatibilization of the blends in question has been characterized by viscosity technique
using the Krigbaum and Wall interaction parameter Δb The versatility of the viscometric
technique is not affected by the choice of the solvent as was shown by Kulshreshta et al213
In this section we discuss in details our investigation on the compatibilization of the two
polymer blend systems PSPEG and PMMAPEG 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191
107
b) Theoretical background
The main aspects of the application of dilute solution viscometry method for the study of
interactions and miscibility phenomena in dilute multicomponent polymer solutions were
described Only the most important features will be repeated here It is common to use
empirical relations such as Hugginsrsquo equation214
(65)
for the description of the concentration dependence of viscosity of polymer solutions This
relation is strictly valid only for binary polymer solutions However equations like that of
Krigbaum and Wall211
(66)
And of Catsiff and Hewett212
(67)
were proposed for ideal ternary polymer solutions of the polymer 1+ polymer 2+ solvent type
In previous relations ηsp denotes the specific viscosity [η] is the intrinsic viscosity (limiting
viscosity number) c stands for the mass concentration of polymer and kH is Hugginsrsquo
constant which may be related (in an empirical manner) to the thermodynamic quality of
solvent Relative mass fractions of dissolved polymers wi are used to describe the
composition dependence of viscosity in ternary systems Quantities b 12 and b12 are used to
define the ideal behavior of ternary polymer solutions These are calculated by
(68)
and
(69)
214 ML Huggins J Am Chem Soc 64 (1942) 116
108
respectively Here b denotes the slope of Hugginsrsquo equation for binary solutions
(70)
Moreover it has been shown215 that both the sign and the extent of the deviation of
experimental from theoretical b-values may be correlated to the interactions between
polymeric components of a system under consideration The quantities of interest (miscibility
criterion variables) are defined by
(71)
and
(72)
or can be written in another form
(73)
where m denotes the polymer mixtures Δb intermolecular interaction parameter between
polymer 1and 2 and is considered a good criterion to predict the polymer-polymer
compatibility209 216 217 Δb 0 indicates that the two polymers are compatible whereas
Δb0 indicates that they are incompatible
c) Discussion of the Results
Herein we discuss in detail the compatibilization of PSPEG blends with the synthesized graft
copolymers by viscometric technique The plot of reduced specific viscosity of polymers
versus total polymeric concentration yields a straight line and the intercept and slope
correspond to intrinsic viscosity [η] and molecular interaction coefficient b respectively The
viscosity data for the homopolymers and their blends are presented in Tables 12 and 13
Table 12 Interaction coefficient for binary solutions (polymersolvent) 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin (1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849
109
Polymer components PEG PS
b11 007327 minus
b22 minus 02117
b12 = (b11 b22)12 = 01245 (theo)
Table 13 Interactions parameters for PSPEG blends with poly (St-g-PDXL) copolymers
(2SP2 2SP1 and DXSP) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
DXSP b12 003511 01295 01680 01833 01947
Δb - 00894 00050 00435 00588 00702
2SP2 b12 003511 009826 01052 01314 01515
Δb - 00894 - 00262 - 00193 00069 00270
2SP1 b12 003511 minus minus minus 01262
Δb - 00894 minus minus minus 00017
For incompatible blends the incompatible molecules refuse to overlap thus they shrink in
size which leads to a decrease in hydrodynamic volumes As a matter of fact the crossover in
the reduced viscosity-concentration plot is observed
As far as we are concerned with the blend of PSPEG the results obtained present similar
situation Figure 18 shows the Huggins plots for the homopolymers and the (5050) blend of
PSPEG In this figure a crossover is observed and a decrease of slope occurs at about 05
gdl in the viscosity-concentration plot Above this concentration two incompatible polymers
PS and PEG undergo mutual repulsion in dilute solution the hydrodynamic volume of chains
is lower The reduction of the hydrodynamic volume will result in a decrease of the reduced
viscosity of solution correspondingly the slope of the plot suddenly declines
110
02 03 04 05 06 07 08 09 10 11
03
04
05
06
07
08PS PEG and PSPEG (5050)
PS PSPEG 0 PEG
Redu
ced
visc
osity
η sp
c
(ldl
)
C (dll)
Figure 18 Plots of reduced viscosity (ηspc) vs concentration for PS PEG and PSPEG
blend (0) in THF at 30degC
Figures 19 20 21 and 22 show the incorporation of various amounts of copolymers in the
immiscible blend As far as the amount of the compatibilizers increases the crossover of the
plots occurs at very low concentration or even it is not observed In addition the slope of the
plot increases with an increase of the amount of the compatibilizers introduced in the blend
This is due to the mutual attraction of the blend components which is enhanced by the
presence of the copolymers As a matter of fact the latter act as compatibilizing agents
allowing to the blends to exhibit miscibility
111
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07BLENDS WITH DXPS
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 19 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of DXPS copolymer
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLENDS WITH 2SP2
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 20 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of 2SP2 copolymer
112
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLEND WITH 2SP1 40
PSPEG 0 2SP1 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 21 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with 40 of the dispersed phase of 2SP1 copolymer
02 03 04 05 06 07 08 09 10 1100
01
02
03
04
05
06
07
08
DXPS 40 2SP2 40
2SP1 40
2SP1 40 2SP2 40 DXPS 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 22 comparison of plots of reduced viscosity (ηspc) vs concentration for PSPEG
blends in THF at 30degC with 40 of the dispersed phase of DXPS 2SPS2 and 2SP1
copolymer
113
Figure 22 compares the three copolymers used for compatibilization of PSPEG with respect
to 40 by weight of the dispersed phase addition to the blends
Krigbaum and Wall suggested that information about the interaction between two polymers
should be obtained from the difference of experimental b12 and theoretical b12 Δb A positive
difference between the experimental and theoretical interaction coefficients is evidence of a
compatible polymer pair The higher the value of Δb the higher the extent of compatibility
Negative values refer to repulsive interaction and incompatible mixes The values of Δb
according to equation 73 for different blends with compatibilizers are given in Table 13 and
Figure 23
0 10 20 30 40 5
-010
-005
000
005
010
0
PS PEG BLENDS
2SP2 DXPS
Δb
Amount of incorporated copolymer w ()
Figure 23 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (DXPS and 2SP2) used for compatibilization
It was observed as the amount of compatibilizers increases values of the interaction
parameter increase thereby increasing the compatibility between the two polymer
components of the blend Consequently this indicates that these copolymers act as
compatibilizing agents in the immiscible blends of PS and PEG Now in comparing these
copolymers in terms of structure (number of grafts) and PDXL content it can be noticed that
the results obtained DXPS ( 71 w of PDXL) copolymer show higher values of Δb than
2SP1(30 w of PDXL) and 2SPS2 (4025 w of PDXL) do This is due to the comb-
structure of the DXPS copolymer (synthesized by CRP) and therefore containing more grafts
114
(Ng = 58) than the other copolymers Besides the amount of PDXL in the copolymer PDXL
includes polar groups which provide associative interactions with one of the blend
components (PEG) and thus undergoes significant effects upon compatibilization In the
figure below it can be seen that addition of 10 by weight of the dispersed phase (47 of
total weight of the blend) of DXPS is sufficient to compatibilize the immiscible blend of
PSPEG (5050) Then a drastic increase of the interaction parameter with the addition of the
compatibilizer (DXPS) compared to the addition of either 2SP2 or 2SP1 (Table 13)
From the results shown in the graph miscibility of the blend can be achieved by incorporating
around 25 (11 of total weight of the blend) of 2SP2 copolymer However compatibibility
of the blend with 2SP1 copolymer is obtained at 40 by weight of the dispersed phase since
its interaction parameter (Δb) found to be 00017
It is worth to mention that the PDXL content of 2SP1 is 30 and the length of the grafts is
half that of 2SP2 copolymer For this reason these two copolymers have been chosen for the
purpose of comparison in terms of side chains length
An optimization of the amount of copolymer needed for compatibilization of PSPEG (5050)
blend has been made (corresponding to Δb = 0) as function of the PDXL content and shown
in Table 14
Table 14 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050) vs PDXL content
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
DXPS 0 9 43 71
2SP2 0 245 109 4025
2SP1 0 40 166 30
115
443 Optical Microscopy and Phase Morphology
PDXL is a perfect alternate copolymer of poly (ethylene oxide) (PEO) and poly (methylene
oxide) (PMO) that has the same curious combination properties as PEG So PDXL must be
at least miscible with PEG or adhere at the interface between PS and PEG and between
PMMA and PEG The compatibility between hydrophobic PS or PMMA and hydrophilic
PEG is very poor Compatibilization between components of the two sets of polymer blends is
studied by optical microscopy
The morphological characteristics of the blends by different compatibilizers are presented in
Figure 24 The optical microscopy micrographs of PSPEG blends without compatibilizers
show a poor dispersion for PS disperse phase and a ldquoball-and-socketrdquo topography due to the
poor interfacial adhesion between PEG matrix and the dispersed phase However with the
addition of compatibilizers the morphological characteristics of the polymer blends are
greatly altered It can be noticed that for these two different blends the particle size of PS
domains gets progressively much smaller and uniform in compatibilized blends than in
incompatibilized ones This may be explained by the significant increase of the phase
interfacial adhesion Consequently the domain size strongly depends upon the
compatibilizers used
116
a) PSPEG (5050) 0 (without compatibilizer)
DXPS 10 DXPS 20 DXPS 30 DXPS 40 b) Compatibilizing effect of DXPS copolymer
2SP2 10 2SP2 20 2SP2 30 2SP2 40 c) Compatibilizing effect of 2SP2 copolymer
2SP1 40
117
d) Compatibilizing effect of 2SP1copolymer at 40 addition
Figure 24 Optical micrographs showing phase structure in 5050 PSPEG blends
a) blends without compatibilizer b) with DXPS c) with 2SP2 d) with 40 of 2SP1
For instance the PSPEG blends with the incorporation of the copolymers DXPS 2SP2 and
2SP1 as compatibilizers (Figure 24) the morphology displays a very fine dispersion of PS
phase and strong interfacial adhesion with PEG Matrix The good compatibilizing effect
mainly that of DXPS can be explained by two mechanisms
First the PDXL units in the compatibilizer interact with PEG ether groups leading to a good
adhesion at interface between the components of the blend In addition hydrogen bonding
may also exist between PDXL and PEG further increasing compatibilization Second since
the compatibilizer also contains styrene blocks it contributes to provide a good compatibility
with PS Consequently the remarkable compatibilizing effect of PS-g-PDXL copolymers
induced a drastic decrease in interfacial tension and suppression of coalescence between the
originally immiscible polymer phases
As it can be noticed from the micrographs given in the figure above the compatibilizer
exhibits finer dispersion and homogeneous morphology of the blends as the amount of
compatibilizers increases
Eventually each compatibilizer has its own effect on the immiscible blends depending on the
amount of PDXL (side chains) and number of grafts present in the copolymers
By comparing micrographs shown in Figure 24 b and c the compatibilization effect of DXPS
copolymer which contains more grafts but shorter is different from that of the 2SP2
copolymer In the case of DXPS it is observed that the size of the dispersed droplets is
deceased significantly and results in finer dispersion morphology However 2SP2 copolymers
shows an improvement in compatibility of the blend after addition up to 30 wt of the
dispersed phase (13 total weight of the blend) exhibits homogeneous morphology This
may be related to length of the grafts In all cases these copolymers act as good
compatibilizers for the blend of 5050 wt PSPEG
444 FTIR Analysis
The FTIR technique is very important since it allows one to study the specific interactions
between the polymers The knowledge of the polymerndashpolymer interactions will be useful for
118
studies of the compatibility in polymer blends To verify the intermolecular interactions that
can play a role in miscibility the vibrational spectra of the blends studied in the present work
were obtained In polymeric systems where there are multiple interactions vibrational bands
such as ν (C=O) ν (COC) and ν (OH) present contributions of spectroscopic free and
associated forms
In order to elucidate the role played by intermolecular interactions in the miscibility of these
blends FTIR absorption of individual polymer components PS PEG and PMMA and
compared to that of the mixtures Figures 26 27 and 28 present the FTIR absorption spectra
from 4000 to 400 cm-1 for all samples
In the case of PS the high-frequency infrared spectra consist of seven absorption bands The
bands with peak locations at 3008 3026 3060 3082 and 3103 cm-1 are due to C-H stretching
of benzene ring CH groups on the PS side-chain The bands with peak positions of 2924 and
2850 cm-1 are due to the C-H stretching vibration of the CH2 and CH groups of the main PS
chain respectively PEG with molecule chemical structure of HO-[CH2-CH2-O]n-H exhibits
important absorption bands from FTIR spectroscopy measurements as shown in Figure 25 It
was verified contributions associated with CndashOndashC symmetric stretching of ether groups218-220
221 from 1050 to 1150 cm-1 with maximum peak at 1150 cm-1 Characteristics CH2-O
stretching modes from 2800-3000 cm-1 are observed214 At low frequency region peaks at 850
and 890 cm-1 are assigned to CndashOndashC stretching and at 500 cm-1 ascribed to CndashOndashC
deformation The presence of PDXL in the blends is detected by the intense frequency at 1140
cm-1 which is assigned for acetal groups In addition both PDXL and PEG contain ether
groups and the spectra show that the corresponding peaks are overlapped for the blends The
intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of PEG
crystallinity in the blends222
218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10 219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601
119
It can be observed also a typical large hydroxyl bands with two distinct contributions which
can be seen for all samples They are attributed to the spectroscopically free and bonded ndashOH
stretching forms at 3600-3800 cm-1 and 3200-3500 cm-1 respectively221 - 227
500 1000 1500 2000 2500 3000 3500 4000-05
00
05
10
15
20
25
30
35
PS and PEG PEG PS
Abs
orba
nce
Wave number (cm-1)
Figure 25 FTIR spectra of PS PEG over 4000-400 cm-1 range
227 Peppas NA Wright L Macromolecules 1996298798ndash804
120
500 1000 1500 2000 2500 3000 3500 4000
0
1DXPS IN PSPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 26 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS)
All these absorption bands for individual polymer were observed in the FTIR spectrum of the
5050 (ww) PSPEG in which they were combined to give superimposed bands in the regions
of 750-1500 cm-1 and 2700- 3100 cm-1
The hydroxyl vibrational frequency is discernible in the blend spectrum for PSPEG at 0
With the incorporation of the copolymers for compatibilization a number of bands showed
small shifts and changes in position and shape in the resulting spectra In Figures 28 29 and
30 as it can be noticed that in the hydroxyl absorption region a decrease in the fraction of
free OH groups is observed as the amount of copolymers is increased in the blend This can
be due to the flexibility of the PDXL graft chains on the other hand to the acetal and ether
groups of PDXL which are probably randomly distributed among an increasing number of
hydroxyl groups of PEG statistically favoring the formation of the PDXL and PEG hydrogen
bond interaction The results indicate that the intermolecular hydrogen bonding between the
ether oxygen of PDXL and the hydroxyl groups of PEG may be formed thereby reducing the
fraction of free OH which is consistent with the shifts observed in the region of hydroxyl
stretching Intermolecular hydrogen bondings are expected to occur among PDXL and PEG
chains due the high hydrophilic forces These interactions have replaced the intramolecular
121
interactions between COC and OH groups of PEG before addition of containing PDXL
copolymers It can be noticed a progressive shift of hydroxyl band from 3340 to 3420 cm-1
with DXPS and from 3340 to 3350 cm-1 when 2SP2 is added This shift can be attributed to
the decrease of intramolecular interactions among hydroxyl groups within PEG chains in
favor to intermolecular interactions between PDXL and PEG228
500 1000 1500 2000 2500 3000 3500 4000
0
1
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 27 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2)
228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
122
3200 3300 3400 3500 3600 3700 3800
00
01
DXPS IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 28 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS) in the hydroxyl absorption region
3200 3300 3400 3500 3600 3700 3800
00
02
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 29 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2) in the hydroxyl absorption region
123
3200 3300 3400 3500 3600 3700 3800
00
DXPS 40 2SP2 40 2SP1 40
Abs
orba
nce
Wave number (cm-1)
Figure 30 FTIR spectra comparison of PSPEG blends (5050) with different compatibilizers
in the hydroxyl absorption region
Conclusions An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends Again The PS blocks of the copolymer result in good
compatibility with PS component of the blends The compatibilization of PSPEG blends is
apparently associated with hydrogen bonding where groups of the acetal units in PDXL
interact with hydroxyl groups of PEG These form a stronger interface between the two
phases which leads to important modifications of the blend properties Apparently the FTIR
result is in good agreement with the miscibility criteria proposed by Krigbaum and Wall (Δb)
interaction parameter which results from dilute-solution viscometry (DSV) method It can be
concluded that by the addition of 20ndash40 wt of incorporated copolymer reveal a good
compatibilizing efficiency for the blend systems as it was observed from micrographs as well
124
References
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York
(1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York
(1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser
Publishers Munich (1989) 178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279 180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999) 183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001) 185 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709
125
186 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and
Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458 187 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 188 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981) 189 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons
Inc New York Chap 16 (2000) 190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689 194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam]
Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842 197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191 214 ML Huggins J Am Chem Soc 64 (1942) 116 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin
(1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849 218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10
126
219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601 227 Peppas NA Wright L Macromolecules 1996298798ndash804 228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
127
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g-
Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of
Polystyrene and Poly (Ethylene Glycol)
51 Introduction
PMMA is more than just plastics of paint Often lubricating oils and hydraulic fluids tend to
get really viscous and even gummy when they get cold This is a real pain when operating
heavy equipments in very cold weather When a little bit of PMMA is dissolved in these oils
and fluids they donrsquot get viscous in the cold and machines can be operated down to -100degC
PMMA can find a several applications namely adhesive optical coating medical packaging
applications and so forthhellip
In medical applications PMMA and its derivatives are used particularly for hard tissue repair
and regeneration229 PMMA beads have been developed to deliver aminoglucoside antibiotics
locally for the treatment of bone infections230 PMMA and PEG form an important and unique
pair of polymers in that they are chemically different In the present work this study may
shed light on the PMMA properties modifications induced by blending with PEG to overcome
the difficult processing of rigid PMMA
Several studies have been made on blends of poly (ethylene oxide) PEO and PMMA in the
last decades but very few on PMMAPEG blends231 232 233
Numerous works reported that the miscibility domain ranges between 10 and 30 of PEO by
weight depending on the PMMA tacticity or molecular weight No phase diagram is available
yet in the literature for PMMAPEO and neither it is for PMMAPEG234
229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703
127
52 Experimental
521 Materials
PEG and PMMA were used as blend components PMMA was obtained from ENPC TP1-
Chlef Company PEG was purchased from MERCK Company Physical and Structural
characterizations of these materials were performed by SEC 1H-NMR and DSC
522 Blend Preparation
Blends of PMMAPEG (5050) were prepared using the same procedure as described for the
blends discussed in the previous chapter Table 15 shows the quantities of the copolymers
used for compatibilization of the blends of PMMAPEG
Table 15 The quantities of the copolymers used for compatibilization of the blends of
PMMAPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
53 Characterization Techniques
531 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
532 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
128
533 FTIR FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
54 Results and Discussion
541 Characterization of the Homopolymers
The polymers have been analyzed by SEC to determine their number average-molecular
weights and polydispersity indices DSC measurements performed to determine their glass
transition temperatures as well as melting point of crystallinity of PEG 1HNMR spectroscopy analysis revealed the tacticity of PMMA It has been found that PMMA
is Syndiotactic-Atactic (highly syndiotactic) as shown in Figure 3 and 321
Physical characteristics of materials used are given in Table 16
Table 16 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PMMA ENPC TP1-Chlef (fromLG MMA Corp)
119
55 000
113
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
129
Figure 31 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in CDCl3
Figure 32 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in the methyl shifts
region in CDCl3
130
542 Dilute Solution Viscometry
Dilute solution viscometry has been utilized to evaluate miscibility of PMMAPEG blends
and the same approach discussed in the previous section has been followed The
experimental reduced viscosities of the polyblends are plotted against concentration in dilute
solution viscometry Eventually plots of pure polymers and polyblends of 5050 PMMAPEG
are first obtained Then their interaction coefficients are determined as shown in Table 17
Table 17 Interaction coefficient for binary solutions (polymersolvent)
Blend components PEG PMMA
b11 007327 minus
b22 minus 006561
b12 = (b11 b22)12 = 006933 (theo)
The compatibility of this system has been evaluated through the sign of Δb The values of the
latter according to equation 73 for different amounts of poly (MMA-g-PDXL) copolymers in
the blends are given in Table 18 It is observed that the blend of PMMAPEG at 5050 by
weight shows a negative value of Krigbaum and Wall parameter which indicates
incompatibility of the system as it is expected Similarly to PSPEG blend a crossover in the
reduced viscosity-concentration plot is observed and a decrease of slope arises in the range of
05 to 066 gdl in the viscosity-concentration plot as shown in Figure 33 This is attributed to
the repulsive intermolecular interactions between the polymer chains
Then the incorporation of the copolymers at various amounts presents positive values
progressively Curves of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in
THF at 30degC with various amounts of copolymer are given in Figures 34 35 and 36
131
Table 18 Interactions parameters for PMMAPEG blends with poly (MMA-g-PDXL)
copolymers (3MP2 2MP2 and 3MP1) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
3MP2 b12 00288 01308 01904 02373 02602
Δb - 004053 00615 01211 01680 01909
2MP2 b12 00288 01286 01690 01893 02296
Δb - 004053 00593 00997 01200 01603
3MP1 b12 00288 00868 01670 02010 02379
Δb - 004053 00175 00977 01317 01686
00 01 02 03 04 05 06 07 08 09 10 11020
025
030
035
040PMMAPEG (5050) 0
PEG PMMAPEG 0 PMMARe
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 33 Plots of reduced viscosity (ηspc) vs concentration for PMMA PEG and
PMMAPEG blend (0) in THF at 30degC
132
02 03 04 05 06 07 08 09 10 11000
005
010
015
020
025
030
035
040 BLENDS WITH 3MP1
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 34 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP1 copolymer
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040
045BLENDS WITH 3MP2
PMMAPEG 0 10 20 30 40
Redu
ced
visc
osity
η
spc
(d
lg)
C (gdl)
Figure 35 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP2 copolymer
133
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040BLENDS WITH 2MP2
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 36 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 2MP2 copolymer
From our viscosity data as the copolymer content increases in the blend the polymer blend
molecules will become disentangled more spaciously resulting in a greater interaction
between structurally similar component segments This suggests that there are attractive
forces that induce miscible behavior of the blends as it is observed in Figure 37
0 10 20 30 40 5-01
00
01
02
0
PMMA PEG BLENDS
3MP2 2MP2 3MP1
Δb
Amount of incorporated copolymer w ()
Figure 37 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (3MP2 2MP2 and 3MP1) used for compatibilization
134
The three copolymers (3MP2 2MP2 and 3MP1) involved in this study for compatibilization
are different from the point of view of the PDXL content and the graft length For instance
3MP2 and 2MP2 have similar and longer grafts since the theoretical number average-
molecular weight of the graft is 2000 gmol However they contain different amount of
PDXL In the case of 3MP1 this graft copolymer has a structure with shorter side chain length
(Mn = 1000 gmol) corresponding to the half of the graft size in the former copolymers From
the observations made out of the figure above 3MP2 copolymer (21 w of PDXL) provides
higher values of the interaction parameter and therefore greater extent of compatibility
compared to the other copolymers since it has long grafts which allows penetration into the
other phase
It can be concluded that all three copolymers show good results for compatibilization on the
basis of the Δb criterion of polymer-polymer miscibility determined by viscometry
Similarly the minimum amount of copolymer needed for compatibilization of PSPEG
(5050) blend has been determined corresponding to Δb = 0 as function of the PDXL content
and shown in Table 19
Table 19 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050)
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
2MP2 0 34 16 35
3MP2 0 37 18 21
3MP1 0 58 28 19
135
543 Optical Microscopy and Phase Morphology
a) PMMAPEG (5050) 0 (without compatibilizer)
b) Compatibilizing effect of 2MP2 copolymer
c) Compatibilizing effect of 3MP2 copolymer
d) Compatibilizing effect of 3MP1copolymer
Figure 38 Optical micrographs showing phase structure in 5050 PMMAPEG blends
a) blends without compatibilizer b) with 2MP2 c) with 3MP2 d) with 3MP1
136
Figure 38 presents microscopy images of PMMAPEG blends with varying amounts of
compatibilizers The morphological characteristics of the blends of PMMAPEG without
compatibilizers show a poor dispersion of PMMA as a dispersed phase The addition of
compatibilizers changes drastically the morphological topology of this system The
compatibilizers used are of different length of the side chains and also different PDXL
content By introducing progressively variable amounts of the compatibilizers they display
similarly the morphological characteristics to some extent It is observed that the phase
separated domains of PMMA in the blends are reduced with increasing amounts of the
compatibilizers This is due to the compatibility of PMMA of the copolymers with the
PMMA blend component and on the other hand to the interfacial interactions of the PDXL
of the copolymers and PEG component of the blends From these results it is revealed that
compatibilizing effect of 2MP2 copolymer on this system is great compared to the others Not
only causes the size of the dispersed droplets to decrease but also dispersed droplets become
homogeneous However 3MP1 copolymer which contains shortest grafts (about half length
of those of the other copolymers) and less amount of PDXL shows less reduction in the
droplet size compared to the other copolymers Therefore it can be concluded that the
compatibilization of this blend depends upon length and number of grafts
On the overall observations these compatibilizing copolymers are very effective and hence
influence and improve the compatibility of PMMAPEG blend at a composition of 5050 wt
544 FTIR Analysis
Same observations can be made for the blends of PEG with PMMA The FTIR spectrum of
this blend at 0 compatibilizer is shown in Figure 39 For pure PMMA the
spectroscopically free carbonyl group band is observed at 1730 cm-1 In the blend sample one
large vibrational band due to hydroxyl group stretches in pure PEG is observed with two
distinct contributions which can be seen for all samples They are attributed to the
spectroscopically free and associated hydroxyl forms at 3495 and 3600 cm-1 respectively
A large band in the wave number range of 1400-1500 cm-1 is assigned to the deformation
vibration of the methyl groups The bands with peaks locations at 2820 and 2990 cm-1 are due
to C-H symmetrical and asymmetrical stretching vibration of CH3 respectively Peaks at
2886 and 2950 cm-1are ascribed to C-H symmetrical and asymmetrical stretching vibration of
CH2 figures 40 and 41 The C-O band is observed in the range of 1150- 1210 cm-1
137
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 PMMAPEG 0 Blend
Abs
orba
nce
Wave number cm-1
Figure 39 FTIR spectra of PMMAPEG 0 over 4000-400 cm-1 range
2750 2800 2850 2900 2950 3000 3050 3100-05
00
05
10
15
20
Abs
orba
nce
PEG PMMAPEG 0
Wave number cm-1
Figure 40 FTIR spectra of PMMAPEG 0 and PEG over the 3100-2700 cm-1 range
138
2750 2800 2850 2900 2950 3000 3050 3100
00
05
10
152MP2 in PMMAPEG
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 41 FTIR spectra of PMMAPEG 0 blends with 2MP2 addition over the 3100-2700
cm-1 range
The incorporation of PMMA-g-PDXL copolymers in the blends makes some changes in the
resulting spectra as it can be noticed in Figures 42 - 44 In the hydroxyl absorption region
same phenomenon has occurred as in the PSPEG blends The fraction of free OH groups has
decreased as the amount of the copolymers increased as shown in figures 45 and 46 which
present the effect of different compatibilizers in the hydroxyl absorption region This can be
explained as discussed above by the fact that the PEG hydroxyl groups undergo other
intermolecular interactions essentially with PDXL chains of the copolymers A comparison of
the effect of the three copolymers involved in the compatibilization at the highest amount
added is given in figure 47 It can be noticed that 2MP2 shows very few fraction of free OH
groups compared to the others This copolymer contains more PDXL (35 wt with 4 grafts)
than the others do (21 wt with 3 grafts and 19 wt with 3 grafts in 3MP2 and 3MP1
respectively)
A crystalline PEG phase is confirmed by the presence of the triplet peak of the COC
stretching vibration at 1148 1110 and 1062 cm-1 with a maximum at 1110 cm-1235 236
Changes in the intensity shape and position of the COC stretching mode are associated with
235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115
139
the interaction between PEG and PMMA-g-PDXL In addition both polymers contain the
same ether group and the spectra show that the corresponding peaks are overlapped for the
blends The intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of
PEG crystallinity in the blends237
Therefore the presence of this interacting system is probably responsible for the miscibility
and low degree of crystallinity observed for these blends
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
202MP2 in PMMAPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 42 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (2MP2)
237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
140
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 43 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2)
500 1000 1500 2000 2500 3000 3500 4000
0
1
2 3MP1 IN PMMAPEG BLENDS 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 44 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1)
141
3500
00
05
3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 45 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2) in the hydroxyl absorption region
3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
-02
00
02
04
06
08
3MP1 IN PMMAPEG 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 46 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1) in the hydroxyl absorption region
142
3500
2MP2 40 3MP2 40 3MP1 40
Abs
orba
nce
Wave number cm-1
Figure 47 FTIR spectra comparison of PMMAPEG blends (5050) with different
compatibilizers in the hydroxyl absorption region
The results from FTIR spectra indicate the compatibility of these polymer blends with the
addition of the PDXL copolymers via hydrogen bonds is observed and confirmed mainly by
the shifts of bands of the hydroxyl stretching modes
143
Conclusions
From the observations made out from this study reveal that all three copolymers show good
results for compatibilization on the basis of the Δb criterion of polymer-polymer miscibility
determined by viscometry Therefore these copolymers act as good compatibilizers since it
was found that the minimum amount needed for compatibilizing is between 1 to 3 of the
total weight of the blend which corresponds to 3 to 6 of the dispersed phase This
compatibilization is due to the fact that the copolymers have constituents which present strong
interactions with both polymer components of the blends These results are in great agreement
with microscopy analyses which demonstrate that the phase separated domains of PMMA in
the blends are reduced with increasing amounts of the compatibilizers This is due to the
compatibility of PMMA of the copolymers with the PMMA blend component and on the
other hand to the interfacial interactions of the PDXL of the copolymers and PEG component
of the blends
From FTIR results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PMMA and relatively long PMMA backbone of PMMA-g-PDXL copolymers respectively
These compatibilizing copolymers are very effective and hence influence and improve the
compatibility of PMMAPEG blend at a composition of 5050 wt
144
References 229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703 235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115 237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
145
CONCLUSIONS
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel using an unsaturated alcohol (2-
HPMA) as a transfer agent results in linear polymeric chains in order to prevent formation of
cyclic oligomers through cationic polymerisation of cyclic acetals They were all prepared at
the same reaction conditions
The characterization of these macromonomers has been conducted using different methods of
analysis Structure and molecular weight determination were provided from SEC and Raman
and 1H-NMR spectroscopy
We were interested in obtaining a hydrogel based on fully PDXL segments and study its
swelling and viscoelastic behaviour The hydrogel has combined special properties The
results reveal a perfect elastic and resistant hydrogel with interesting viscoelastic properties
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers Structure composition and number of grafts of the
copolymers were determined by SEC and 1H-NMR spectroscopy Another approach for
copolymerization has been made in order to compare the copolymers obtained from different
types of polymerization reactions like Conventional Free Radical and Controlled Radical
Polymerizations In the latter the copolymer obtained possesses larger number of grafts than
those from the former
The macromonomer reactivity estimation suggests that the length of the PDXL side chains
does affect the reactivity of the methacrylic double bond of the macromonomer when
copolymerized with St However in the case of copolymerization with MMA there is no
dependence on the graft size Finally from DSC measurements the values of Tg depend on
the composition and the size of the PDXL grafts In all copolymers the increase in amount of
the incorporated PDXL macromonomer results in a substantial decease in glass transition
An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
146
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends
The compatibilization effect of the copolymers used in this study on the PSPEG and
PMMAPEG was demonstrated from the viscometric results The contribution of both PS or
PMMA and PDXL of the copolymers has played a big role in the compatibilization of these
two different systems of blends thereby resulting in good compatibility due the chemical
affinity between these components which leads to a drastic decrease in interfacial tension and
suppression coalescence between the blend constituents
It has been shown that the immiscible blends in question exhibit compatibility when small
amount of copolymers synthesized for this purpose are added except for one of them
Styrene-g-PDXL copolymers act as good compatibilizers for PSPEG blends since it was
found that the minimum amount needed for compatibilizing is less than 11 of the total
weight of the blend which corresponds to 25 of the dispersed phase This compatibilization
is due to the fact that the copolymers have constituents which present strong interactions with
both polymer components of the blends
Compared with PS-g-PDXL with DXPS content the DXPS is more effective binary polymer
blends compatibilizer in the PSPEG blends which is due to the high number of grafts and
high PDXL content This has led to good adhesion of PDXL chains with the PEG phase in the
blends Again The PS blocks of the copolymer result in good compatibility with PS
component of the blends The compatibilization of PSPEG blends is apparently associated
with hydrogen bonding where groups of the acetal units in PDXL interact with hydroxyl
groups of PEG These form a stronger interface between the two phases which leads to
important modifications of the blend properties
Similarly PMMA-g-PDXL copolymers act as good compatibilizers since it was found that
the minimum amount needed for compatibilizing is between 1 to 3 of the total weight of
the blend which corresponds to 3 to 6 of the dispersed phase This compatibilization is due
to the fact that the copolymers have constituents which present strong interactions with both
polymer components of the blends
These results are in great agreement with microscopy analyses which demonstrate that the
phase separated domains of PMMA and PS in their respective blends are reduced with
increasing amounts of the compatibilizers
147
Specific interactions between chemical groups of two blend components can play an
important role in polymer mixtures There is a range of such interactions of varying strengths
which has been identified in polymer blends and such interactions are generally defined for
small molecules It should be noted that the extension of this concept to polymers is not
always straightforward it is more difficult to identify interactions in polymers the
spectroscopy is more complex and molecular conformations are less certain This situation is
further complicated because researchers use different names and definitions to describe
similar interactions
FTIR investigation showed that these interactions have been observed through the changes in
IR absorption peaks of PS PEG and PMMA upon mixing with increasing amount of
compatibilizers in their blends which have given rise to a wide investigation
From these the results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PSPEG and PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PS or PMMA and relatively long PS or PMMA backbone of PS-g-PDXL and PMMA-g-
PDXL copolymers respectively
148
CHAPTER III Synthesis and Characterization of Copolymers 69
31 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 69
32 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
321 Chemicals and Purification helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 70
322 Synthesis of Poly (Styrene-g-Poly (1 3-dioxolane)) helliphelliphelliphellip 71
323 Synthesis of Poly (Methyl Methacrylate-g-Poly (1 3-dioxolane))76
33 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
331 1H-NMR Spectroscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 76
332 Size Exclusion Chromatography helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
333 Diffraction Scanning Calorimetry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 77
34 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 78
341 Structural Characterization of the Copolymers helliphelliphelliphelliphellip 78
342 Molecular Weight Determination and Copolymer Composition 80
343 Determination of Monomer Reactivity Ratios helliphelliphelliphelliphelliphellip 84
344 Glass Transition Temperatures helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 89
Conclusion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 93
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
41 Background helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
411 Physical Blends helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
412 Equilibrium Phase Behavior helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 95
413 Compatibilization helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 97
414 Incorporation of Copolymers for Compatibilization helliphelliphellip 98
415 The Effect of Compatibilizer on a Blend helliphelliphelliphelliphelliphelliphelliphellip 99
416 Methods of Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 100
42 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
421 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
422 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
43 Characterization Techniques for Compatibilization helliphelliphelliphelliphelliphelliphelliphellip 102
431 Dilute Solution Viscometric Measurements helliphelliphelliphelliphelliphelliphellip 102
432 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
433 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
44 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
441 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphellip 104
442 Study of Compatibilization by Dilute Solution Viscometry hellip 106
443 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 116
444 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 118
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 124
References helliphelliphelliphelliphelliphellip helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 125
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g- Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
51 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 127
52 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
521 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
522 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
53 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
531 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
532 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
533 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
54 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
541 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphelliphellip 129
542 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 131
543 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 136
544 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 137
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 144
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 145 CONCLUSIONS helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 146
SUMMARY
Research and development performed on synthetic polymers during the last century has led to
many classes of different polymers for specific applications New types of synthetic polymers
with tailor-made properties are still being introduced for new applications The challenge for
polymer chemists is to control and alter the polymerization conditions such that the final
product has a well-defined structure with desired properties The complex structure of
polymers requires continued analytical chemical efforts to understand the polymerisation
process and the relationships between the molecular structure and material properties
The central point of this thesis is the synthesis and the exploration of the benefits of graft
copolymers derived from poly (1 3 dioxolane) (PDXL) as compatibilizing agents via their
incorporation in immiscible polymer blends The enhancement of adhesion in the solid state
can be accomplished by introducing a compatibilizer that can act as an adhesive between two
polymers andor by control of morphology especially by inducing the phase co-continuity
Graft copolymers offer all Properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheological control i e it
leads to decreased melt viscosities which is an important advantage for processing Depending
on the nature of their backbone and side chains they can be used for a wide variety of
applications such as impact-resistant plastics thermoplastic elastomers polymeric
emulsifiers and even more exciting is the ability of these graft copolymers to function as
compatibilizersinterfacial agents to blends immiscible polymers
The state-of-the-art technique to synthesize graft copolymers is the copolymerization of
macromonomers with low molecular weight comonomers It allows the control of the
polymeric structure which is given by three parameters (i) chains length of the side chains
which can be controlled by the synthesis of macromonomers by living polymerization (ii)
chain length of the backbone which can be controlled in a living polymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular-weight monomer
i
New properties lower prices and reuse of polymers are needed to meet demands of todayrsquos
society and hence of the polymer industry Unfortunately the demands for many applications
need a set of properties that no polymers can fulfil One method to satisfy these demands is by
mixing two or more polymers Materials made from two polymers mixed are called blends In
recent years blending of polymers as a means of combining the useful properties of different
materials to meet new market applications with minimum development cost offers an
interesting route to improve a variety of specific properties of the thermoplastics This has
been increasingly used by the polymer industry
Much work has been done on the blending (mixing) of polymers by many authors A large
part of these studies deal with attempts to obtain a combination of properties of different
polymers Unfortunately these properties of the polymer blends are usually worse instead of
better for many combinations of polymers Significance for these properties is compatibility
between the different polymers which is frequently defined as miscibility on a molecular scale
of the blends components The incorporation of a dispersed phase into a matrix mostly leads
to the presence of stress concentrations and weak interfaces arising from poor mechanical
coupling between phases and therefore morphologies with coarseness commonly on
micrometer scale are obtained Improving mechanical and morphological properties of an
immiscible blend is often done by compatibilization which is a process of modification of the
interfacial properties in immiscible polymer blend resulting in reduction of the interfacial
tension coefficient formation and stabilisation of the desired morphology The use of graft or
block copolymers as compatibilizers for immiscible polymer blends has become an efficient
means for development of new high-performance polymer materials There have been
numerous techniques of studying the miscibility of the polymeric blends The most useful
techniques are viscosimetry measurementsiiiiii thermal analysisiv dynamic mechanical
analysisv refractive indexvi nuclear magnetic resonance methodvii scanning electronviii and
optical spectroscopyix
i Z Sun W Wang and Z Fung Eur Polym J 28 (1992) 1259 ii Aroguz AZ and Baysal BM Eur Polym J42 3 (2006) 11ndash5iii Zhang Y Qian J Ke Z Zhu X Bi H and Nie K Eur Polym J 38 (2002) 333ndash7 iv M Song and F Long Eur Polym J 27 (1991) 983 v Olabisi O Rebeson LM and Shaw MT Polymerndashpolymer miscibility New York Academic Press (1979) vi AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 vii EG Crispim ITA Schuquel AF Rubira and EC Muniz Polymer 41 (3) (2000) 933 viii Martin IG Roleister KH Rosenau R and Koningsveld RJ Polym Sci Part B Polym Phys24 (1986) 723 ix W Wu X Luo D Ma Eur Polym J 35 (1999) 985
ii
Well-known examples of commercial blends are high impact polystyrene (HIPS) and
acrylonitrile-butadiene-styrene (ABS) These blends are tough and have good processability
One of the most interesting examples of an amorphous polymer is polystyrene because of its
brittleness Adding a compatibilizer with the structure of a copolymer to
Polystyrenepolyethylene (PSPE) improves the toughness by a factor 3x Another example is
the use of poly (styrene-co-methacrylic acid) as a compatibilizer in immiscible (incompatible)
blends of PS and polyethylene (PEG)xi
It is of great interest to study miscibility and phase behaviour of two different commodity
immiscible polymer blend systems as PSPEG and polymethyl methacrylate polyethylene
glycol (PMMAPEG) by adding poly (styrene-g-PDXL) and poly (methyl methacrylate-
PDXL) copolymers as compatibilizers respectively Firstly these systems consist of a very
rigid amorphous component (styrene andor PMMA) and a very flexible low-melting point
PEG The extremely high difference of glass transition temperatures (Tg) between the
components motivates us to investigate the phase behaviour of the blends via
compatibilization with prepared grafted copolymers
The first part of the thesis is devoted to the synthesis and characterization of amphiphilic graft
copolymers which were prepared in solution by radical polymerization of hydrophilic poly (1
3 dioxolane) macromonomers as side chains and hydrophobic comonomers such as styrene
and methyl methacrylate as backbone The second part of the thesis describes the blends
preparation and the study of the compatibilization effect of the incorporated amphiphilic graft
copolymers on immiscible (incompatible) blends
The research work in this thesis is presented through several chapters described as follows
Chapter I is a bibliographic survey on polymerization reactions involved in the thesis
Literature concerning the poly (1 3 dioxolane) was included
Chapter II describes the synthesis of poly (1 3 dioxolane) macromonomers and their
characterization As an aside research poly (1 3 dioxolane) network was obtained and the
x E Kroeze thesisUniversity of Groningen (1997) xi Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polym Journal 37 (2001) 1837-1842
iii
swelling and rheological behaviours of this network were discussed and included in this
chapter
Chapter III deals with the synthesis of a series of amphiphilic graft copolymers based on
polystyrene and methyl methacrylate as backbone with poly (1 3 dioxolane) macromonomers
as grafts in this study Selection of proper reaction conditions in terms of overall monomer
concentration and monomer molar ratio were investigated in order to prevent crosslinking
reactions due to the presence of bis-functional poly (1 3 dioxolane) macromonomers
The structure and composition of the graft copolymers were determined by Size Exclusion
Chromatography (SEC) technique and Proton Nuclear Magnetic Resonance (1H-NMR)
analysis Also Modulated Temperature Differential Scanning Calorimeter (MTDSC) was used
for thermal analysis to study the influence of poly (1 3 dioxolane) content on the glass
transition temperature of the copolymers
Last but not the least Chapter IV and Chapter V deal with the most important part of the
thesis which is the study of the compatibilization effect of the prepared copolymers
incorporated in two different immiscible blend systems These two chapters describe first
the polymers used as blend components and also polyblends preparation was discussed The
phase behavior and compatibilization of these polyblends were studied at a composition
of 5050 for both PSPEG and PMMAPEG systems Various amounts of copolymers were
incorporated to the so-called blends for compatibilization The techniques used for this study
were optical microscopy (OM) to analyze their morphology and Fourier-Transform Infra-Red
(FTIR) spectroscopy used to detect the intermolecular interactions in the blends In addition
viscometric method which is a simple inexpensive and sensitive analytical technique and also
alternative to other methods was used The application of the dilute-solution viscosity (DSV)
method for the study of interactions and miscibility of the polymeric system has been
described in more details in these chapters
Conclusions have been made on copolymer characterizations in terms of mostly monomer
reactivity and indeed on compatibilizing effect of these copolymers on the selected polymer
blends This study provides interesting results which can be useful for the development
nanoporous materials
iv
REacuteSUMEacute
La recherche et le deacuteveloppement faits sur des polymegraveres syntheacutetiques pendant le dernier siegravecle
ont abouti agrave plusieurs types de polymegraveres pour des applications speacutecifiques Les nouveaux
polymegraveres syntheacutetiques avec des proprieacuteteacutes faites sur mesure sont toujours introduits pour de
nouvelles applications Le deacutefi pour les chimistes en polymegraveres est de controcircler et drsquoalteacuterer les
conditions de polymeacuterisation de telle sorte que le produit final ait une structure bien deacutefinie avec
des proprieacuteteacutes souhaiteacutees La structure complexe de polymegraveres exige des efforts continus en
chimie analytique pour comprendre le processus de polymeacuterisation et les relations entre la
structure moleacuteculaire et les proprieacuteteacutes des mateacuteriaux
Le centre drsquointeacuterecirct de cette thegravese est la synthegravese et lexploration des avantages des copolymegraveres
greffeacutes deacuteriveacutes agrave partir du poly (1 3 dioxolane) (PDXL) utiliseacutes comme agents compatibilisant
via leur incorporation dans des meacutelanges de polymegraveres non miscibles Lrsquoameacutelioration drsquoadheacutesion
agrave lrsquoeacutetat solide peut ecirctre accomplie en introduisant un compatibilisant qui peut agir comme un
adheacutesif entre deux polymegraveres et ou par le controcircle de la morphologie particuliegraverement en
incitant la co-continuiteacute des phases Les copolymegraveres greffeacutes offrent toutes les proprieacuteteacutes des
copolymegraveres en blocs mais sont toujours plus facile agrave syntheacutetiser De plus la structure ramifieacutee
offre des possibiliteacutes importantes dans le controcircle rheacuteologique cest-agrave-dire elle aide la
diminution de la viscositeacute qui est un avantage important pour la transformation Selon la nature
de la chaicircne principale et des chaicircnes lateacuterales ces copolymegraveres peuvent ecirctre employeacutes pour une
grande varieacuteteacute drsquoapplications comme plastiques reacutesistants au choc elastomers thermoplastiques
des polymegraveres eacutemulsifiants et mecircme plus inteacuteressant est la possibiliteacute de ces copolymegraveres greffeacutes
de fonctionner comme compatibilisant agents drsquointerface aux meacutelanges des polymegraveres non
miscibles
La technique la plus sophistiqueacutee pour syntheacutetiser les copolymegraveres greffeacutes est la
copolymeacuterisation de macromonomegraveres avec des comonomegraveres agrave faible masse moleacuteculaire Elle
permet le controcircle de la structure polymeacuterique par trois paramegravetres (i) la longueur des chaicircnes
lateacuterales qui peut ecirctre controcircleacutee par la synthegravese de macromonomegraveres par la polymeacuterisation
v
vivante (ii) la longueur de chaicircne principale qui peut ecirctre controcircleacutee dans une polymeacuterisation
vivante (iii) espacement moyen des chaicircnes lateacuterales qui est deacutetermineacute par le rapport molaire des
comonomegraveres et taux de reacuteactiviteacute du monomegravere agrave faible masse moleacuteculaire
De nouvelles proprieacuteteacutes des prix bas et la reacuteutilisation de polymegraveres sont neacutecessaires pour
reacutepondre aux demandes de la socieacuteteacute daujourdhui et agrave lindustrie de polymegraveres
Malheureusement ces demandes pour un grand nombre drsquoapplications ont besoin dun jeu de
proprieacuteteacutes quaucun polymegravere ne peut accomplir Une meacutethode de satisfaire ces demandes est en
meacutelangeant deux polymegraveres ou plus Les mateacuteriaux obtenus agrave partir de meacutelanges de deux
polymegraveres meacutelangeacutes sont appeleacutes meacutelanges (Blends) Ces derniegraveres anneacutees le meacutelange de
polymegraveres comme moyen de combiner les proprieacuteteacutes utiles de diffeacuterents mateacuteriaux pour
rencontrer un marcheacute de nouvelles applications agrave un coucirct minimal offre un itineacuteraire inteacuteressant
pour ameacuteliorer une varieacuteteacute des proprieacuteteacutes speacutecifiques des polymegraveres thermoplastiques Cela a eacuteteacute
de plus en plus employeacute par lindustrie des polymegraveres
Beaucoup de travaux ont eacuteteacute faits par plusieurs auteurs sur le meacutelange de polymegraveres Une grande
partie de ces eacutetudes sont dirigeacutees pour obtenir une combinaison des proprieacuteteacutes de diffeacuterents
polymegraveres Malheureusement ces proprieacuteteacutes des meacutelanges de polymegravere sont souvent plus
mauvaises que preacutevues pour la plupart des combinaisons de polymegraveres La signification de ces
proprieacuteteacutes est la compatibiliteacute entre les diffeacuterents polymegraveres qui est freacutequemment deacutefinie comme
la miscibiliteacute agrave lrsquoeacutechelle moleacuteculaire des composants du meacutelange Lincorporation dune phase
disperseacutee dans une matrice provoque surtout la preacutesence de contraintes et des interfaces faibles
qui reacutesultent du faible meacutelange meacutecanique entre les deux phases Lameacutelioration des proprieacuteteacutes
meacutecaniques et morphologiques dun meacutelange non miscible est souvent faite par compatibilisation
qui est un processus de modification des proprieacuteteacutes superficielle dans les meacutelanges de polymegraveres
non miscibles aboutissant agrave la reacuteduction du coefficient de tension superficielle la formation et
stabiliteacute de la morphologie deacutesireacutee Lutilisation des copolymegraveres greffeacutes ou agrave blocs comme
compatibilisant pour des meacutelanges de polymegraveres non miscibles est devenue un moyen efficace
pour le deacuteveloppement de nouveaux mateacuteriaux plus performant Il y a eu de nombreuses
techniques pour lrsquoeacutetude de la miscibiliteacute des meacutelanges polymeacuteriques Les techniques les plus
vi
utiles sont les mesures viscomeacutetriques analyses thermiques analyses meacutecaniques indice de
reacutefraction la reacutesonance magneacutetique nucleacuteaire microscopes optique et eacutelectroniques agrave balayage
Les exemples de meacutelanges commerciaux tregraves bien connus sont le polystyregravene choc (HIPS) et
acrylonitrile-butadiene-styrene (ABS) Ces meacutelanges sont durs et ont bon processability Un
exemple de polymegraveres amorphes le plus inteacuteressant est le polystyregravene agrave cause de sa fragiliteacute
Laddition dun compatibilisant ayant la structure dun copolymegravere au meacutelange de Polystyregravene
polyeacutethylegravene (PSPE) ameacuteliore la dureteacute par un facteur de 3 Un autre exemple est lutilisation du
poly (styrene-co-acide meacutethacrylique) comme compatibilisant dans les meacutelanges non miscibles
de PS et le poly (eacutethylegravene glycol)
Il est tregraves important drsquoeacutetudier la miscibiliteacute et le comportement des phases de deux diffeacuterents
meacutelanges de polymegraveres commerciaux non miscibles (incompatibles) comme le
polystyregravenepolyeacutethylegravene glycol (PSPEG) et le polymeacutethacrylate de meacutethylepolyeacutethylegravene glycol
(PMMAPEG) en incorporant des copolymegraveres tels que (styrene-g-PDXL) et de (meacutethacrylate de
meacutethyle-PDXL) comme compatibilisant respectivement Premiegraverement lrsquoun des composants de
ces systegravemes est amorphe et tregraves rigide (le styregravene etou PMMA) et lrsquoautre (PEG) est flexible et
mou ayant un point de fusion tregraves faible Vu lrsquoextrecircme eacutecart entre les deux tempeacuteratures de
transition vitreuse (Tg) des composants de ces meacutelanges cela nous a motiveacute pour eacutetudier le
comportement de ces meacutelanges via compatibilisation avec des copolymegraveres greffeacutes preacutepareacutes par
nous mecircme
La premiegravere partie de la thegravese est consacreacute agrave la synthegravese et agrave la caracteacuterisation de copolymegraveres
greffeacutes amphiphiles preacutepareacutes en solution par la polymeacuterisation radicale des macromonomers
(poly (1 3 dioxolane)) hydrophiles comme des chaicircnes lateacuterales (greffons) avec des
comonomegraveres hydrophobes comme le styregravene et le meacutethyle methacrylate comme chaicircne
principale La deuxiegraveme partie de la thegravese couvre la preacuteparation des meacutelanges et leacutetude de leffet
de compatibilisant des copolymegraveres greffeacutes amphiphiles sur les meacutelanges non miscibles
(incompatibles)
La recherche concernant cette thegravese est preacutesenteacute par plusieurs chapitres deacutecrits comme suit
vii
Le chapitre I est une recherche bibliographique sur les reacuteactions de polymeacuterisations impliqueacutees
dans la thegravese La Litteacuterature concernant le poly (1 3 dioxolane) est inclue
Le chapitre II deacutecrit la synthegravese des macromonomegraveres du poly (1 3 dioxolane) et leurs
caracteacuterisations Une recherche suppleacutementaire a eacuteteacute effectueacutee concernant la synthegravese drsquoun reacuteseau
tridimensionnel du poly (1 3 dioxolane) Une eacutetude sur les comportements gonflant et
rheacuteologique de ce reacuteseau ont eacuteteacute discuteacutes et inclus dans ce chapitre
Le chapitre III preacutesente la synthegravese dune seacuterie de copolymegraveres greffeacutes amphiphiles constitueacutes de
polystyregravene ou methacrylate de meacutethyle comme chaicircne principale et de macromonomers du poly
(1 3 dioxolane) comme greffons dans cette eacutetude Le choix de conditions de reacuteaction approprieacutees
en termes de concentration totale et le rapport molaire des monomegraveres ont eacuteteacute bien eacutetudieacutes pour
empecirccher les reacuteactions de reacuteticulation agrave cause de la preacutesence de macromonomegraveres bis-
fonctionnel de poly (1 3 dioxolane)
La structure et la composition des copolymegraveres greffeacutes ont eacuteteacute deacutetermineacutees par la technique de la
Chromatographie dExclusion steacuterique (CES) et la spectroscopie en Reacutesonance Magneacutetique
Nucleacuteaire de Proton (1H-NMR) Aussi la Calorimeacutetrie Diffeacuterentielle agrave balayage agrave Temperature
Moduleacutee Calorimeacutetrie (MTDSC) a eacuteteacute employeacute pour lanalyse thermique et pour eacutetudier
linfluence de la proportion du poly (1 3 dioxolane) dans les copolymegraveres sur leur tempeacuterature
de transition vitreuse
Derniers mais pas le moindre les deux Chapitre IV et le Chapitre V couvrent la partie la plus
importante de la thegravese qui est leacutetude de leffet de compatibilisant de ces copolymegraveres preacutepareacutes et
incorporeacutes dans deux diffeacuterents systegravemes de meacutelanges non miscibles (incompatibles) Ces deux
chapitres deacutecrivent dabord les polymegraveres employeacutes comme composants des meacutelanges agrave eacutetudier et
aussi la preacuteparation de ces meacutelanges a eacuteteacute deacutecrite Le comportement de phase et la
compatibilisation des meacutelanges de PSPEG et PMMAPEG agrave une composition de 5050 Des
quantiteacutes diffeacuterentes de copolymegraveres ont eacuteteacute incorporeacutees aux meacutelanges Les techniques
employeacutees pour cette eacutetude sont la microscopie optique (OM) pour analyser leur morphologie et
la spectroscopie agrave Transformeacutee de Fourier Infrarouge (FTIR) pour deacutetecter les interactions
viii
intermoleacuteculaires dans les meacutelanges De plus la meacutethode viscomeacutetrique qui est une technique
simple peu coucircteuse et tregraves sensible a eacuteteacute employeacutee Lrsquoutilisation de la meacutethode de la viscositeacute de
solution dilueacutee (DSV) pour leacutetude dinteractions et la miscibiliteacute du systegraveme polymegravere a eacuteteacute
deacutecrite plus en deacutetail dans ces chapitres
Les conclusions ont eacuteteacute faites sur la caracteacuterisation des copolymegraveres en termes de surtout de la
reacuteactiviteacute des monomegraveres et bien entendu sur leffet compatibilisant de ces copolymegraveres sur les
meacutelanges de polymegraveres qui ont choisis Cette eacutetude fournit des reacutesultats inteacuteressants qui peuvent
ecirctre utiles pour le deacuteveloppement des mateacuteriaux nanoporeux
ix
CHAPTER I Literature Review
11 Macromonomer Interest and Synthesis
Macromonomers bearing polymerizable end groups have received considerable interest
during the last two decades and become a useful tool for the preparation of a variety of graft
copolymers with well-defined structure and composition and polymer networks The
macromonomer method for preparing graft copolymers consists of preparing branches first
followed by the preparation of the grafted structure through the addition of the comonomer to
the macromonomer branch1 2
Therefore macromonomers become the side chains in the graft copolymer with well-defined
length and molecular weight As a sequence the molecular structure of the copolymer can be
determined depending on the amount of macromonomer incorporated and the reactivity of the
end groups
Macromonomers which are linear macromolecules carrying polymerizable functions at one or
two chain ends have been prepared by all polymerization mechanisms anionic cationic free-
radical polyaddition and polycondensation while the polymerizable end groups have been
introduced during the initiation termination or chain transfer steps or by modification of end
groups of telechelic oligomers3
Among the polymerization mechanisms mentioned above the ionic ones allow the best
control of molecular weight polydispersity and functionality of the macromonomers
However they require very demanding experimental conditions like high purity of monomers
and solvents complete absence of moisture and other acidic impurities inert atmosphere etc
Whereas free-radical methods which involve less severe working conditions are largely
used even though the control over the properties of the macromonomers is lower3 For
instance polymers of epoxides tetrahydofuran and cyclic siloxanes are commercially
produced by cationic ring-opening polymerization The history of ring-opening
polymerization of cyclic monomers is shorter than that of the vinyl polymerization and
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422
1
polycondensation With ring-opening functional groups can be introduced into the main chain
of the polymer This polymer cannot be prepared by vinyl polymerization4
Milkovich first developed synthesis of graft polymer with uniform grafts via macromonomer
technique5 Schulz and Milkovich6 reported the synthesis of polystyrene macromonmers
through termination of living PS anions with methacryloyl chloride and their
copolymerization with butyl acrylate and ethyl acrylate
Candau Rempp et al7 obtained PS-g-PEO by reaction between living monofunctional PEO
and partly chloromethacrylated PS backbone (scheme 1) Characterization of the products by
light scattering GPC UV and NMR spectroscopy showed a high degree of grafting
Scheme 1
Ito et al8 used a macromonomer technique to obtain graft copolymers with uniform side
chains They synthesized a graft copolymer of PS with uniform PEO side chains through
copolymerization of styrene and PEO macromonomer (scheme 2) They obtained PEO
macromonomers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-
vinyl benzyl chloride as terminating agent An apparent decrease in reactivities of both poly
(ethylene oxide) of macromonomers and comonomers was ascribed to the thermodynamic
repulsion between the macromonomer and the backbone9
4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348
2
Scheme 2
This type graft copolymers of styrene and ethylene oxide was also obtained by Xie et al10
through copolymerization of styrene with PEO macromonomer prepared by anionic
polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydofuran as
initiator followed by termination with methacryloyl chloride
The method of macromonomer synthesis developed by Xie et al11 has the advantage of
shorter reaction time and a larger range of molecular weight of the PEO macromonomer than
the usual method using potassium alcoholate as initiator PEO macromonomers with
molecular weight from 2 103 to 3 104 and MwMn = 107 ndash 112 can be obtained by this
method12
Only Xie and coworkers have published reports concerning the synthesis of copolymers with
uniform PS grafts obtained through copolymerization of epoxy ether terminated polystyrene
macromonomer with EO13 using a quaternary catalyst composed of triisobutyl-aluminium-
phosphoric acid-water-tertiary amine14 and epichlorohydrin (ECH)15
Free radical polymerization technique has also provided well-defined macromonomers of
poly (acrylic acid)16 vinyl benzyl-terminated polystyrene17 18 poly (t-butyl methacrylate)19
and poly (vinyl acetate)20
Recently Matyjaszewski et al21 employed atom-transfer radical polymerization (ATRP) to
prepare well-defined vinyl acetate terminated PS macromonomers Taking advantage of the
10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp (1985) 461 Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823
3
extremely low reactivity of polystyryl radical towards the vinyl acetate double bond they
used vinyl chloroacetate to initiate the polymerization of styrene to produce the desired
macromonomers This concept has been used similarly in the preparation of a vinyl acetate-
terminated PS macromonomers3 by conventional free-radical polymerization by employing
vinyl iodoacetate as a chain transfer agent possessing a double bond which does not
copolymerize with the monomer that forms the backbone of the macromonomer
12 Ring-Opening Polymerization Overview
Ring-opening polymerization (ROP) is a unique polymerization process in which a cyclic
monomer is opened to generate a linear polymer It is fundamentally different from a
condensation polymerization in that there is no small molecule by-product during the
polymerization Polymers with a wide variety of functional groups can be produced by ring-
opening polymerizations Ring-opening polymerization can proceed through a number of
different mechanisms depending on the type of monomer and catalyst involved Of the wide
range of polymers produced via ROP some have gained industrial significance for example
poly (caprolactam) and poly (ethylene oxide)22 ROP of cyclic esters such as ε-caprolactone
(CL) and L L-dilactide is gaining industrial interest due to their degradability23 The
mechanisms of interest in this work are coordination insertion and cationic
121 Polymerizability of Cyclic Compounds
The thermodynamic polymerizability of a cyclic monomer has been elegantly summarized by
Ivin24 Negative free energy change from monomer to polymer is the thermodynamic driving
force for the ring-opening
ΔG = ΔH ndash T ΔS
For small sized cyclic compounds the enthalpy term is negative and dominant The strains in
bond angles and bond lengths are released upon ring opening Such monomers can be almost
completely converted to polymers For medium sized cyclic monomers (5-7 membered rings)
the ring strain is small and the entropy is a small positive term Thus the overall driving force
(ΔG) is small and the extent of polymerization is little or no reaction For 8- 9- and 10-
22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991)
4
membered monomers the enthalpy term is dominant and negative while the TΔS term is
relatively small The strain is due to the non-bonded interactions between atoms Essentially
complete conversion to polymer is possible When the ring size is very large and there is
virtually no ring-strain (ΔH ne 0) the driving force for ring-opening polymerization is the
large increase of entropy The polymerization should be an athermal process
Why not make polyethylene
In principle one could synthesize polyethylene from cyclohexane
There are two good reasons why this reaction cannot be performed
bull (Kinetic) Cyclohexane lacks any reactive functionality to get hold of
bull (Thermodynamic) Simple six membered rings are extremely stable
Free Energy (ΔG) of Polymerization for Cycloalkanes
The thermodynamic considerations for ring opening are illustrated by this graph (scheme 3) of
free energy (hypothetical) of polymerization from cycloalkanes with various ring sizes to
polyethylene (The two membered ring actually shows the data for ethylene CH2 = CH2)
Scheme 3
5
Three and four membered rings are quite strained so ring opening to polyethylene is
favorable if a suitable reaction pathway existed (Unfortunately no such reaction is known)
Six membered rings are stable so they can rarely be polymerized by ring opening Five and
seven membered rings are borderline cases so sometimes these can be polymerized Larger
rings have transanular steric interactions that cause some strain so rings of 8 members or
more can usually be polymerized Of course this graph changes when substitutions are made
to the rings (for example the presence of heteroatoms like O S and N or the introduction of
double bonds) However the graph for the simplest possible rings illustrates the trends in
other systems reasonably well
Even if the ring opening reaction is thermodynamically favorable there must be reaction
chemistry to get there In most cases the initiators used for ring opening polymerization are
polar or ionic species so the monomers must have groups that can react The most common
monomers for ring opening polymerization contain some kind of heteroatom in the ring as in
the examples of cyclic ethers esters amines amides etc At one extreme there are examples
such as the cyclic phosphazene shown that contain no carbon or hydrogen at all At the other
extreme just a carbon-carbon double bond will suffice for ring opening metathesis
polymerization as illustrated by norbornene
122 Mechanisms of Ring-opening Polymerization
In addition to the thermodynamic criterion there must be a kinetic pathway for the ring to
open and undergo the polymerization reaction Therefore the kinetics of the ring-opening of
the monomer should also be considered Ring-opening polymerization (ROP) can proceed
through a number of different mechanisms depending on the type of monomer and catalyst
involved Of the wide range of polymers produced via ROP some have gained industrial
significance for example poly (caprolactam) and poly (ethylene oxide)24 25 A variety of
mechanisms operate for ring-opening polymerizations including anionic cationic metathesis
and free radical mechanisms Examples of various ring-opening polymerizations are shown in
scheme 4
25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984)
6
Scheme 4
123 Cationic Ring-Opening Polymerization of Heterocycles
A broad range of heterocyclic compounds can undergo cationic ring-opening polymerization
(CROP)26 CROP propagates either through an activated monomer or an activated chain end
mechanism In both cases the propagation involves the formation of a positively charged
species27 A major drawback of CROP is the occurrence of unwanted side reactions thus
limiting the molecular weight of the final product2829 The cationic ring-opening
polymerization of heterocycles has become of significant importance in polymer synthesis
due in part to the diverse variety of functionalized materials that can be prepared by this
method including natural andor biodegradable polymers30 31
Systematic studies of this type of polymerization started around the nineteen sixties Since
then several groups are involved in the kinetics reaction mechanisms and thermodynamics of
the ring-opening polymerization mostly of tetrahydofuran and dioxolane During the last
26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996) (b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993) (c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice (d) Mishra M K Ed Polymer Frontiers New York (1994) 391 31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159
7
years many papers on the synthesis and polymerization of several other cyclic ethers
monocyclic and bicyclic acetals have been published32 33
Examples of commercially important polymers which are synthesized via ring-opening
polymerization are summarized in scheme 5 include such common polymers as
polyoxyethylene (POE 4) poly (butylene oxide) (PBO 5) nylon 6 (6) and poly
(ethyleneimine) (7)
Scheme 5
The synthesis of ring-opened heterocycles is often mediated by compounds whose role is to
initiate the polymerization process This provides less opportunity to ldquotunerdquo polyheterocycle
properties through catalyst choice and has stimulated research to develop initiators which
function beyond the simple activation of polymerization such as living polymerization
initiators343536 chiral initiators3738 enzyme initiators39 and ring-opening insertion
systems4041 The cationic ring-opening polymerization involves the formation of a positively
32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N Macromolecules 26 (1993) 7134
8
charged species which is subsequently attacked by a monomer The attack results in a ring-
opening of the positively charged species Ethylene oxide can be polymerized by cationic
initiators as well (scheme 6)
Scheme 6
13 Cationic Polymerization of Cyclic Acetals
Acetal polymers also known as polyoxymethylene (POM) or polyacetal are formaldehyde-
based thermoplastics that have been commercially available for over 40 years
Polyformaldehyde is a thermally unstable material that decomposes on heating to yield
formaldehyde gas Two methods of stabilizing polyformaldehyde for use as an engineering
polymer were developed and introduced by DuPont in 1959 and Celanese in 1962
DuPonts route for polyacetal yields a homopolymer through the condensation reaction of
polyformaldehyde and acetic acid (or acetic anhydride)
The Celanese route for the production of polyacetal yields a more stable copolymer product
via the reaction of trioxane a cyclic trimer of formaldehyde and a cyclic ether (eg ethylene
oxide or 13 dioxolane)
9
The improved thermal and chemical stability of the copolymer versus the homopolymer is a
result of randomly distributed oxyethylene groups These groups offer stability to oxidative
thermal acidic and alkaline attack The raw copolymer is hydrolyzed to an oxyethylene end
cap to provide thermally stable polyacetal copolymer Polyacetals are subject to oxidative and
acidic degradation which leads to molecular weight deterioration Once the chain of the
homopolymer is ruptured by such an attack the exposed polyformaldehyde ends decompose
to formaldehyde and acetic acid Deterioration in the copolymer ceases however when one
of the randomly distributed oxyethylene linkages is reached42
Cationic polymerization of cyclic acetals exhibits some special features which makes this
system distinctly different from cationic polymerization of simple heterocyclic monomers for
instance cyclic ethers Linear acetals (including polyacetals) are more basic (nucleophilic)
than cyclic ones thus when polymer starts to form it does not constitute a neutral component
of the system but participates effectively in transacetalization reactions which lead to
redistribution of molecular weights and formation of a cyclic fraction These processes which
are usually described by the term ldquoscramblingrdquo have been studied by several authors43 44
Cationic polymerizations of heterocyclic monomers are initiated as in cationic
polymerization of vinylic monomers by electrophilic agents such as the protonic acids (HCl
H2SO4 HClO4 etc) Lewis acids which are electron acceptors by definition and compounds
capable of generating carbonium ions can also initiate polymerization Examples of Lewis
acids are AlCl3 SnCl4 BF3 TiCl4 AgClO4 and I2 Lewis acid initiators required a co-
initiator such as H2O or an organic halogen compound Initiation by Lewis acids either
requires or proceeds faster in the presence of either a proton donor (protogen) such as water
alcohol and organic acids or a cation donor (cationogen) such as t-butyl chloride or
triphenylmethyl fluoride
The polymerization of a heterocyclic monomer initiated by a protonic acid usually starts with
opening of the monomer ring via oxonium sites that are formed upon alkylation (or
protonation) of the monomer
42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144
10
Protonation
BF3 H2O H BF3 OH+ +O
O
Acylation
R CO SbF6 +
OR CO O SbF6
Alkylation
Et3O BF4 +
OC2H5 Et2O BF4O +
Hydrogen transfer
C SbF6 +O
C SbF6H O+
SbF6
O + O O+ H O SbF6
In general initiation step can be shown as
A+
R O++R A O
The mechanism of chain growth involves nucleophilic attack of the oxygen of an incoming
monomer onto a carbon atom in α-position with respect to the oxonium site whereby the
cycle opens and the site is reformed on the attacking unit
A+O
O(CH2)4
O
A+O(CH2)4
Growing chain terminates with nucleophilic species as shown below
O (CH2)4 O+[ ]n
A O (CH2)4[ ]n
AO ( CH2 )4
11
Triflic initiators like trifluoromethane sulfonic acid derivatives can also be employed as an
initiator in the cationic polymerization of heterocyclics in this case initiation step follows
alkylation mechanism
CF3 SO3CH3 +O
CH3 CF3SO3O
CH3 O
CF3SO3
+ O CH3O(CH2)4 O CF3SO3
Ion pairs are in equilibrium with the ester form
(CH2)4 O CF3SO3 (CH2)4 O(CH2)4 O SO2CF3
If instead of ester triflic anhydride is used as initiator the same reaction can occur at both
chain ends and anhydride behaves as a bifunctional initiator
CF3SO2OSO2CF3 nO
+ CF3SO2 O (CH2)4 O (CH2)4 O SO2CF3n-1
(CH2)4 O (CH2)4 n-3
O O CF3SO3 CF3SO3
In the case of living cationic polymerization the growing sites are long living provided the
reaction medium does not contain any transfer agents such as alcohols ethers amines or
acids The reaction mechanism then involves only initiation and propagation steps and the
polymers formed are living The active sites are deactivated by addition of an adequate
nucleophile such as excess water tertiary amines alkoxides phenolates or lithium bromide
12
O(CH2)4
SbF6
(CH2)4 O(CH2)4 OH H
NR3
++ H2O
SbF6
+(CH2)4 O(CH2)4 NR3 SbF6
ONa+(CH2)4 O(CH2)4 O + NaSbF6
+ LiBr
(CH2)4 O(CH2)4 Br LiSbF6+
However facts concerning the real mechanism are scarce In order to progress further in
understanding the cationic polymerization of heterocycles initiated with a Bronsted acid
kinetic studies of simple ring-opening reactions of heterocyclic monomer rings by acids in
nonpolar aprotic and nonbasic solvents (inert solvents) have been performed45
14 Synthesis of Functionalized Poly (1 3-Dioxolane)
1 3-Dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer ends ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The molecular weight of the linear polymers is governed by the
ratio of reacted monomer to transfer agent and is generally well controlled up to 10 000gmol
141 Reaction of 1 3-Dioxolane and Hydroxyl- Containing Compounds
Classical initiation induces polymerization through cyclic tertiary oxonium ions which are
responsible for the formation of an important quantity of cyclic oligomers48
45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon Press 3(1989) 787
13
In several preceding articles Franta et al have investigated the cationic polymerization of
cyclic acetals in the presence of a diol49 50 in particular polymerization of 13-dioxolane
(DXL) and 13-dioxepane (DXP) in the presence of an oligoether diol (αω-dihydroxy-poly
(tetrahydofuran)) or (αω-dihydroxy-poly(ethylene oxide)) In all cases a similar behavior was
observed Cyclic oligomers are present in quantities as in the case of polymerization of DXL
in the absence of hydroxyl containing compounds51
When substituted oxiranes such as propylene oxide or epichlorohydrin are polymerized
according to the ldquoActivated Monomerrdquo mechanism (AM) Cyclic oligomers can be
eliminated52 53 In the AM mechanism polymerization of ethylene oxide however the
reaction of a protonated monomer molecule with a polymer chain leads to side reactions
including cyclization by the Active Chain End (ACE) mechanism53 Thus it is not
unexpected that in the polymerization of cyclic acetals due to the higher nucleophilicity of
the linear acetals located on the chain reactions with the latter will take place
The addition of a protonated DXL onto a hydroxyl group-containing compound is
accompanied by transacetalization involving a monomer molecule
In order to shed some light on the reactions involved Franta et al54 used a monoalcohol
methanol instead of a diol The results confirmed the occurrence of the Active Monomer
mechanism but dimethoxymethane was observed evidence of transacetalization between
methanol and dioxolane
Thus in the DXL-ethylene glycol (EG) system the presence of unreacted EG is in fact due to
the following equilibria
This equation shows the stoichiometry of the reaction rather than its actual mechanism the
reaction certainly has to involve an addition product as a first step
49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154
14
In the next step transacetalization occurs
The products of transacetalization are formed fast as compared to the addition product54 This
indicates that the last reaction is not slower and probably faster than the previous one
Consequently it has been found that although polymerization of DXL in the presence of
hydroxyl group containing compounds proceeds initially by a stepwise addition of protonated
monomer to the hydroxyl terminated linear species in agreement with the AM mechanism but
already at this stage fast transacetalization proceeds leading to formation of O-CH2-O links
between two oligodiols and liberation of ethylene glycol
The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism When DXL is polymerized by strong protonic acids such as triflic acid in the
presence of a diol the PDXL chains are essentially linear and carry end-standing OH
functions Despite the occurrence of some side reactions this mechanism leads to α ω-
dihydroxy-PDXL the molecular weight of which is controlled by the molar ratio of DXL
consumed to diol introduced It has been shown that the polydispersity is on the order of 14
and that molar masses up to 10 000 gmol can be covered
142 Synthesis of Poly (1 3-Dioxolane) Macromonomers
Macromonomers are useful intermediates to prepare graft copolymers and have indeed been
used extensively In order to prepare PDXL macromonomers Franta and al54 have used p-
isopropenylbenzylic alcohol (IPA) as an initiator and triflic acid as a catalyst
The following polymeric species were identified
15
Scheme 7
A is the most abundant compound it corresponds to 50 to 60 weight-wise It is a
macromonomer
B corresponds to 20 to 25 weight-wise It carries two p-isopropenyl functions
C corresponds to 20 to 25 weight-wise It carries no p-isopropenyl function but two
hydroxyl groups
As a result preparation of PDXL macromonomers leads to the preparation of PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of transacetalization
reaction described above a mixture of products was obtained54
Kruumlger et al55 used similar method to prepare macromonomers and come out to the same
conclusions in terms of structure and claim that a clear distinction should be made between
the products obtained and the mechanism responsible for their formation
15 Amphiphilic Graft Copolymers
151 Graft Copolymers
The increasing complexity of polymer applications has required the production of materials
with varied properties Often homopolymers do not afford the scope of attributes necessary to
many applications Copolymerization allows the formulation of polymer materials with
properties characteristic of two homopolymers contained in a single copolymer material The
monomers within a copolymer can be distributed in various fashions random statistical
alternating segmented block or graft56
55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387
16
Scheme 8
Graft copolymers are similar to block copolymers in that they possess long sequences of
monomer units However graft copolymer architecture differs substantially from typical
block copolymers In graft copolymers monomer sequences are grafted or attached to points
along a main polymer chain Grafted chains generally possess molecular weights less than
that of the main chain
These side chains have constitutional or configurational features that differ from those in the
main chain57
The simplest case of a graft copolymer can be represented by A-graft-B or the arrangement
and the corresponding name is polyA-graft-polyB where the monomer named first (A in this
case) is that which supplied the backbone (main chain) units while that named second (B) is
in the side chain(s)
Typical syntheses of the grafts occur by polymerization initiated at some reactive point along
the backbone or by copolymerization of a macromonomer Polymerization from the polymer
backbone is possible via anionic cationic and radical techniques but all require some
functional unit capable of further reaction58
Well defined graft copolymers are most frequently prepared by either
a)ldquografting throughrdquo or b)ldquografting fromrdquo controlled polymerization process
57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991)
17
a) Grafting though the ldquografting throughrdquo method (or macromonomer method) is one of the
simplest ways to synthesize graft copolymers with well defined side chains
Scheme 9
Typically a low molecular weight monomer is radically copolymerized with a methacrylate
functionalized macromonomer This method permits incorporation of macromonomers
prepared by other controlled polymerization processes into a backbone prepared by a CRP
Macromonomers such as polyethylene59 60 poly (ethylene oxide)61 polysiloxanes62 poly
(lactic acid)63 and polycaprolactone64 have been incorporated into a polystyrene or poly
(methacrylate) backbone Moreover it is possible to design well-defined graft copolymers by
combining the ldquografting throughrdquo macromonomers prepared by any controlled polymerization
process and CRP65 This combination allows control of polydispersity functionality
copolymer composition backbone length branch length and branch spacing by consideration
of MM ratio in the feed and reactivity ratio Branches can be distributed homogeneously or
heterogeneously and this has a significant effect on the physical properties of the
materials6263
b) Grafting from the primary requirement for a successful grafting from reaction is a
preformed macromolecule with distributed initiating functionality
59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003) 6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778 63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998) 823-830
18
Scheme 10
Grafting-from reactions have been conducted from polyethylene66 67 polyvinylchloride68 69
and polyisobutylene70 71 The only requirement for an ATRP is distributed radically
transferable atoms along the polymer backbone The initiating sites can be incorporated by
copolymerization68 be inherent parts of the first polymer69 or incorporated in a post-
polymerization reaction70
Graft copolymers perform similar functions to block copolymers in that they contain moieties
with varying properties Compatibilization represents a major area of application for grafts
because the grafted chains can be used to solubilize a polymer blend system containing two
immiscible polymers Additionally graft copolymers offer unique solution mechanical and
morphological properties that make them ideal for utilization as viscosity modifiers and
thermoplastic elastomers72 The unique molecular architecture of graft copolymers leads to
peculiar morphological properties The chain lengths of the grafted arms and backbone block
dictate the morphology that arises in the polymer Changes in the composition of the graft
copolymer alter the resulting polymer morphology A variety of morphologies is possible
ranging from lamellar to cylindrical to spherical73
Graft copolymers offer all properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheology control
Depending on the nature of their backbone and side chains graft copolymers can be used for a
wide variety of applications such as impact-resistant plastics thermoplastic elastomers
66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996) 7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R Macromolecules 32 (1999) 1152-1158
19
compatibilizers viscosity index improvers and polymeric emulsifiers74 75 The state-of-the-
art technique to synthesize graft copolymers is the copolymerization of macromonomers
(MM) with low molecular weight monomers76 In most cases conventional radical
copolymerization has been used for this purpose Using living polymerizations for both the
synthesis of the macromonomers and for the copolymerization offers the highest possible
control of the polymer structure In all these copolymerizations beside the desired graft
copolymers with at least two side chains a number of unwanted products can be expected
unreacted macromonomer ungrafted backbone and backbone with only one graft (star
copolymer) The latter is undesirable for applications as thermoplastic elastomer
Conventional and controlled copolymerizations lead to different copolymer structures In
conventional radical copolymerization the polymers show a broad molecular weight
distribution (MWD) and chemical heterogeneity of first order
152 Amphiphilic Copolymers
A characteristic feature of an amphiphilic polymer is that it contains both hydrophilic and
hydrophobic groups This type of polymer associates in aqueous solution and exhibits several
interesting features and can be used in connection with many industrial and pharmaceutical
applications Usually there is only a few mol of the hydrophobic moieties in order to make
the polymer water-soluble Due to the hydrophobicity of the amphiphilic polymers they have
a tendency to form association structures in aqueous solution by mutual interaction andor
interaction with other cosolutes such as surfactants and colloid particles
In particular the grafting of hydrophilic species onto hydrophobic polymers is of great utility
Amphiphilic graft copolymers so prepared often display enhanced surface properties such as
improved resistance to the adsorption of oils and proteins biocompatibility and reduced static
charge buildup
The synthesis of graft copolymers based on commercial polymers is most commonly
accomplished free radically Free radicals are produced on the parent polymer chains by
exposure to ionizing radiation andor a free-radical initiator77 78 Alternatively peroxide
groups are introduced on the parent polymer by ozone treatment79 80 The resulting reactive
74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998) 696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507
20
sites serve as initiation sites for the free radical polymerization of the comonomer A
significant disadvantage of these free radical techniques is that homopolymerization of the
comonomer always occurs to some extent resulting in a product which is a mixture of graft
copolymer and homopolymer Moreover backbone degradation and gel formation can occur
as a result of uncontrolled free radical production often limiting the attainable grafting
density81 For example amphiphilic graft copolymers synthesized from PEO macromonomer
and hydrophobic comonomers82 83were found to form micellar aggregates in polar medium
such as water wateralcohol alcohol dimethylformamide These phase separation processes
take place also during polymerization and supposedly affect not only the polymerization
kinetics but also properties of resulting copolymers So far unanswered remains the question
of molecular characteristics of reaction products including homopolymers from
macromonomer or comonomer formed under both the homogeneous and heterogeneous
(micellar) reaction conditions Modern liquid chromatographic techniques allow
discrimination of polymeric constituents differing in their chemical structure andor physical
architecture Subsequently the molar mass and molar mass distribution of constituents can be
assessed Recently analyzed products of dispersion copolymerization of polyethylene oxide
methacrylate macromonomer with styrene contained rather large amount of polystyrene
homopolymer84
In the main application areas for amphiphilic polymers the solution properties are of
fundamental importance In many industrial applications association and adsorption
phenomena of the polymers in solution are design properties Consequently a deep
understanding of these phenomena is necessary for the development of new specific
chemicals and new processes The research goals are to clarify the relations between the
molecular structure of amphiphilic polymers and their properties in aqueous solution A
further goal is to develop theoretical models for the description of the behavior of amphiphilic
polymers in solution and at surfaces Several projects concern the self-assembly of
amphiphilic polymer molecules and the association behavior of surfactants and
hydrophobically modified hydrophilic polymers such as cellulose derivatives Studies of
amphiphilic model polymers such as ethylene oxide block and graft copolymers are carried
80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication
21
out in order to gain fundamental knowledge on the solution behavior of amphiphilic
polymers
16 Kinetics of Free Radical Polymerization
Free radical polymerization is the most widespread method of polymerization of vinylic
monomers Free radical polymerizations are chain reactions in which every polymer chain
grows by addition of a monomer to the terminal free radical reactive site called ldquoactive
centerrdquo The addition of the monomer to this site induces the transfer of the active center to
the newly created chain end Free radical polymerization is characterized by many attractive
features such as applicability for a wide range of polymerizable groups including styrenic
vinylic acrylic and methacrylic derivatives as well as tolerance to many solvents small
amounts of impurities and many functional groups present in the monomers
161 Kinetics of free radical addition Homo and Copolymerization
Understanding of chemical kinetics during homo- and copolymerization is crucial for
copolymer synthesis The discussion below will review the kinetics of free radical initiated
polymerizations and copolymerizations
The three main kinetic steps that occur during polymerization are (1) initiation (2)
propagation and (3) termination
1 Initiation
The initiation step is considered to involve two reactions creating the free radical active
center The first event is the production of free radicals Many methods can be used to initiate
free radical polymerizations such as thermal initiation without added initiator or high energy
radiation of the monomers However free radicals are usually generated by the addition of
initiators that form radicals when heated or irradiated Two common examples of such
compounds which afford free radicals are benzoyl peroxide (BPO) and azobisisobutyronitrile
(AIBN)
22
Figure 1 Generation of Free Radicals by Thermal Decomposition of Benzoyl Peroxide
Figure 2 Decomposition of Azobisisobutyronitrile to Form Free Radicals
Figure 1 depicts the thermal decomposition of BPO to form two oxy-radicals and Figure 2
depicts the decomposition of AIBN to form two nitrile stabilized carbon based radicals
(equation 1)
In equation 1 kd is the rate constant which describes the first order initiation process The
radical that is formed can now add to the double bond of the monomer and initiate
polymerization
The symbol M will represent the monomer and the rate constant for this process will be ki as
described in equation 2
23
Together these two reactions the radical generation and the monomer addition to the radical
form the process of initiation Usually the assumption that is taken into account is that the
first step is the rate determining step This means that the decomposition to form the radical
is much slower than the monomer addition to the free radical Therefore the equation for the
rate of radical formation ri is
The number 2 is obtained from the fact that a maximum of two radicals can be generated for
the initiation
But not all of the primary radicals produced by the decomposition of the initiator will
necessarily react with the monomer which means several other competing reactions may
occur85 Therefore in order to determine the rate of initiation the fraction of initially formed
radicals that actually start chain growth will be denoted by f and the rate of initiation equation
becomes
2 Propagation
Now the propagation of the reaction will proceed through the successive addition of
monomer to the radicals This type of process can be expressed in the following form
85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster PA (1997)
24
And further generalizing the reaction scheme gives
The assumption that the reactivity of the addition of each monomer is independent of the
chain length is evident in these two equations and was postulated by Flory 58 86 The use of
the rate constant kp for both of these equations imply that the rate constant is independent of
chain length The rate of the propagation rp of this polymerization or the rate of monomer
removal is thus given by
3 Termination
The termination of these growing radical chains occurs in principally two different ways The
first way is the formation of a new bond in between the two radicals this is called
combination Secondly the radical chains can terminate by disproportionation This is a
process where a hydrogen atom from one of the chains is transferred to the other and the chain
that the proton was removed from forms a double bond These reactions are represented as
follows
Figure 3 Termination by Combination
86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995)
25
Figure 4 Termination by Disproportionation
Schematically the reactions can be represented as follows
Where the rate constant of termination by combination is denoted by ktc and the rate constant
of termination by disproportionation is denoted by ktd Since both of these reactions use two
radical species and have the same kinetics the overall equation for the rate of termination is
written as
where kt = ktc + ktd and the number 2 imply there are two radicals that are terminated in
each termination reaction The monomer structure and the temperature are what determines
the type of termination that is most dominant in the reaction For most systems the amount of
one termination type far exceeds the other termination type
The further calculations for the rate of polymerization Rp and the degree of conversion as a
function of time can now be developed The assumption of the steady state concentration of
transient species must be used here where the transient species is the radical M For the
steady state approximation to hold true the rate at which initiation occurs ri must be equal to
the rate at which termination occurs rt or in other words radicals must be generated at the
same rate at which they are terminated This assumption gives the equation
26
This equation then gives an expression for the radical species
Experimentally this value would be difficult to measure in the laboratory and therefore this
equation must be used in the subsequent equations that follow By further substitution an
expression for the rate of polymerization Rp can be obtained because it equals the rate of
propagation
From this equation it can be deduced that the rate of polymerization is directly proportional
to the monomer concentration and to the initiator concentration to the one half power In
other words Rp is first order with regards to the monomer concentration and half order to the
initiator concentration
When the conversion is low the assumption that the initiator concentration is constant is
reasonable but the consumption of the initiator can be added into the calculations Therefore
Then integration can be performed
Finally the rate of polymerization becomes
27
This equation can be broken into three different parts
The second term indicates that the rate of polymerization is still proportional to the monomer
concentration to the first power and the initiator concentration to the one half power but the
initiator concentration is now the initial concentration Therefore by increasing the initial
concentration of an initiator in a solution polymerization the rate of the reaction should
increase proportionally to the square root of the amount of initiator added The third term
indicates that as the initiator is consumed the polymerization slows down exponentially with
time as well as its slowing down due to monomer depletion
The first term in the brackets suggests that the rate of polymerization is proportional to kp
kt12 When experiments are performed to probe the kinetics of reactions in solution the
expected first order dependence on monomer concentration is observed But when the
experiment is performed in concentrated solvents or even in the bulk the polymerization
kinetics accelerate The reason for this anomaly is that the viscosity increases as the
polymerization proceeds because the polymer has a higher viscosity than the monomers The
kp is not affected but the kt is
The degree of conversion can now be expressed as a function of time by knowing that
By substituting the earlier equation for Rp and integrating that equation one can obtain this
Furthermore ([M]0 ndash [M]) [M]0 is equal to the degree of conversion and is the fraction of
the monomer that has been reacted where [M] is the concentration of the monomer that has
been left after the reaction and [M]0 is the initial monomer concentration Therefore ([M]0 ndash
[M]) is the concentration of the monomer that has reacted The conversion can then be
expressed as
28
This can also be expressed as
As is always the case the conversion never quite reaches 100 value or a factor of 1 given by
the exponential term So if the time goes to infinity the expression that is obtained for
maximum conversion that is less than 1 by an amount that is dependent on the initial initiator
concentration is
If the steady state approximation for the initiator concentration had been carried through these
calculations and equations then the conversion would approach a value of 1 after a long
period of time
Distributions on the average distribution of chain lengths during and after a polymerization
are present in free radical polymerizations This is due to the naturally but statistically
random termination reactions that occur in the solution with regard to chain length The
kinetic chain length v is the rate of monomer addition to growing chains over the rate at
which chains are started by radicals which is the expression for the number average chain
length In other words it is the average number of monomer units per growing chain radical
at a certain instant87 Therefore the initiator radical efficiency in polymerizing the monomers
is
87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993)
29
When termination occurs mainly by combination the chain length for the polymer chains on
the average doubles in size assuming nearly equal length chains combine But if
disproportionation mainly occurs the growing chains do not undergo any change in chain
length during the process So the expressions are thus
A new term can be used to more generally express the average chain length of the growing
polymer chain xn This new term is the average number of dead chains produced per
termination ξ This value is equal to the rate of dead chain formation over the rate of the
termination reactions The equations take into account that in combination only one dead
chain is produced and in disproportionation reactions two dead chains are produced
Therefore
Furthermore the instantaneous number average chain length can be expressed in terms of the
rate of addition of the monomer units divided by the rate of dead polymers forming This is
shown as
30
From this equation82 one can clearly see that the rate of polymerization is proportional to the
initiator concentration to the one half power [I]12 and that the instantaneous number average
chain length xn is proportional to the inverse of the initiator concentration to the one half
power 1[I]12 Thus if the polymerization was accelerated by using more initiator the chains
will end up to be shorter which may not be desirable85
17 Chain Growth Copolymerization
171 Copolymerization Equations
Chain polymerizations can obviously be performed with mixtures of monomers rather than
with only one monomer For many free radical polymerizations for example acrylonitrile and
methyl acrylate two monomers are used in the process and the subsequent copolymer might
be expected to contain both of the structures in the chain This type of reaction that employs
two comonomers is a copolymerization The reactivity and the relative concentrations of the
two monomers should determine the concentration of each comonomer that is incorporated
into the copolymer The application of chain copolymerizations has produced much important
fundamental information Most of the knowledge of the reactivities of monomers via
carbocations free radicals and carbanions in chain polymerizations has been derived from
chain copolymerization studies The chemical structure of these monomers strongly
influences reactivity during copolymerization Furthermore from the technological viewpoint
copolymerization has been critical to the design of the copolymer product with a variety of
specifically desired properties As compared to homopolymers the synthesis of copolymers
can produce an unlimited number of different sequential arrangements where the changes in
relative amounts and chemical structures of the monomers produce materials of varying
chemical and physical properties
Several different types of copolymers are known and the process of copolymerization can
often be changed in order to obtain these structures A statistical or random copolymer may
obey some type of statistical law which relates to the distribution of each type of comonomer
that has been incorporated into the copolymer Thus for example it may follow zero- or first-
31
or second-order Markov statistics88 Copolymers that are formed via a zero-order Markov
process or Bernoullian contain two monomer structures that are randomly distributed and
could be termed random copolymers
ndashAABBBABABBAABAmdash
Alternating block and graft copolymers are the other three types of copolymer structures
Equimolar compositions with a regularly alternating distribution of monomer units are
alternating copolymers
ndashABABABABABABA--
A linear copolymer that contains one or more long uninterrupted sequences of each of the
comonomer species is a block copolymer
--AAAAAAAA-BBBBBBBBB--
A graft copolymer contains a linear chain of one type of monomer structure and one or more
side chains that consist of linear chains of another monomer structure
--AAAAAAAAAAAAAmdash
B B
B B
B B
B B
For this discussion the main focus will be on randomly distributed or statistical copolymers
Copolymer composition is usually different than the composition of the starting materials
charged into the system Therefore monomers have different tendencies to be incorporated
into the copolymer which also means that each type of comonomer reacts at different rates
with the two free radical species present Even in the early work by Staudinger89 it was
noted that the copolymer that was formed had almost no similar characteristics to these of the
homopolymers derived from each of the monomers
Furthermore the relative reactivities of monomers in a copolymerization were also quite
different from their reactivities in the homopolymerization Thus some monomers were more 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151
32
reactive while some were less reactive during copolymerization than during their
homopolymerizations Even more interesting was that some monomers that would not
polymerize at all during homopolymerization would copolymerize relatively well with a
second monomer to form copolymers It was concluded that the homopolymerization features
do not easily directly relate to those of the copolymerization
Alfrey (1944) Mayo and Lewis (1944) and Walling (1957)909192 demonstrated that the
copolymerization composition can be determined by the chemical reactivity of the free radical
propagating chain terminal unit during copolymerization Application of the first-order
Markov statistics was used and the terminal model of copolymerization was proposed The
use of two monomers M1 and M2 during copolymerization leads to two types of propagating
species The first of these species is a propagating chain that ends with a monomer of
structure M1 and the second species is a propagating chain that ends with a monomer structure
M2 For radically initiated copolymerizations the two structures can be represented by
M1 and M2 where the zig-zag lines represent the chain and the M
represents the radical at the growing end of the chain The assumption that the reactivity of
these propagating species only depends on the monomer unit at the end of the chain is called
the terminal unit model58 If this is so only four propagation reactions are possible for a two
monomer system The propagating chain that ends in M1 can either add a monomer of type
M1 or of type M2 Also the propagating chain that ends in M2 can add a monomer unit of
type M2 or of type M1 Therefore these equations can be written with the rate constants of
reactions93
90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953)
33
The rate constant for the reaction of the propagating chain that ends in M1 and adds another
M1 to the end of the chain is k11 and the rate constant for the reaction of the propagating
chain that ends in M2 and adds M1 to the end of the chain is k21 and so on
The term self-propagation refers to the addition of a monomer unit to the chain that ends with
the same monomer unit and the term cross-propagation refers to a monomer unit that is added
the end of a propagating chain that ends in the different monomer unit These (normally)
irreversible reactions can propagate by free radical anionic or cationic processes although
active lifetimes could be very different
As indicated by reactions 30 and 32 monomer M1 is consumed and as indicated by reactions
31 and 33 monomer M2 is consumed The rates of entry into the copolymer and the rates of
disappearance of the two monomers are given by
In order to find the rate at which the two monomers enter into the copolymer equation 34
is divided by equation 35 to give the copolymer composition equation
The low concentrations (eg 10-8 molesliter) of the radical chains in the systems are very
hard to experimentally determine So to remove these from the equation the steady state
approximation is normally employed Therefore a steady state concentration is assumed for
both of the species M1 and M2 separately The interconversion between the two
species must be equal in order for the concentrations of each to remain constant and hence the
rates of reactions 31 and 32 must be equal
34
Rearrangement of equation 37 and combination with equation 36 gives
This equation can be further simplified by dividing the right side and the top and bottom by
k21 [M2] [M1] The results are then combined with the parameters r1 and r2 which are
defined to be the reactivity ratios
The most familiar form of the copolymerization composition equation is then obtained as
The ratio of the rates of addition of each monomer can also be considered to be the ratio of the
molar concentrations of the two monomers incorporated in the copolymer which is denoted
by (m1m2) The copolymer composition equation can then be written as
The copolymer composition equation defines the molar ratios of the two monomers that are
incorporated into the copolymer d[M1] d[M2] As seen in the equation this term is directly
related to the concentration of the monomers that were in the feed [M1] and [M2] and also
the monomer reactivity ratios r1 and r2 The ratio of the rate constant for the addition of its
own type of monomer to the rate constant for the addition of the other type of monomer is
35
defined as the monomer reactivity ratio for each monomer in the system When M1
prefers to add the monomer M1 instead of monomer M2 the r1 value is greater than one
When M1 prefers to add monomer M2 instead of monomer M1 the r1 value is less than
one When the r1 value is equal to zero the monomer M1 is not capable of adding to itself
which means that homopolymerization is not possible
The copolymer composition equation can also be expressed in mole fractions instead of
concentrations which helps to make the equation more useful for experimental studies In
order to put the equation into these terms F1 and F2 are the mole fractions of M1 and M2 in the
copolymer and f1 and f2 are the mole fractions of monomers M1 and M2 in the feed
Therefore
and
Then combining equations 42 43 and 40 gives
This form of the copolymer equation gives the mole fraction of monomer M1 introduced into
the copolymer58
Different types of monomers show different types of copolymerization behavior Depending
on the reactivity ratios of the monomers the copolymer can incorporate the comonomers in
different ways
The three main types of behavior that copolymerizations tend to follow correspond to the
conditions where r1 and r2 are both equal to one when r1 r2 lt 1 and when r1 r2 gt 1
bull A perfectly random copolymerization is achieved when the r1 and r2 values are both
equal to one This type of copolymerization will occur when the two different types of
36
propagating species M1 and M2 show the exact same preference for the addition of
each type of monomer In other words the growing radical chains do not prefer to add one of
the monomers more than the other monomer which results in perfectly random incorporation
into the copolymer
bull An alternating copolymerization is defined as r1 = r2 = 0 The polymer product in
this type of copolymerization shows a non-random equimolar amount of each comonomer
that is incorporated into the copolymer This may occur because the growing radical chains
will not add to its own monomer Therefore the opposite monomer will have to be added to
produce a growing chain and a perfectly alternating chain
When r1 gt 1 and r2 gt 1 both of the monomers want to add to themselves and in theory could
produce block copolymers But in actuality because of the short lifetime of the propagating
radical the product of such copolymerizations produces very undesirable heterogeneous
products that include homopolymers Therefore macroscopic phase separation could occur
and desirable physical properties such as transparency would not be achieved
172 Determination of Reactivity Ratios
Many methods have been used to estimate reactivity ratios of a large number of
comonomers94 The copolymer composition may not be independent of conversion This
means the disappearance of monomer one may be faster than the disappearance of monomer
two if monomer one is being incorporated into the copolymer at a faster rate and therefore it
has a larger reactivity ratio than monomer two
The approximation method95 is the simplest of the methods that has been used to calculate the
reactivity ratios of copolymer systems The method is based on the fact that r1 the reactivity
ratio of component one is mainly dependent on the composition of monomer two m2 that
has been incorporated into the copolymer at low concentrations of monomer two in the feed
M2 The expression is thus
94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
37
The value of the reactivity ratio for component one can be easily determined by only one
experiment but the value is only an approximation and does not provide any validity of the
estimated r1 In order to determine the amount of the comonomer that has been incorporated
into the copolymer various analytical methods must be used Proton Nuclear Magnetic
Resonance Carbon 13 NMR and Fourier Transform Infrared Spectroscopy are three sensitive
instruments that can determine the copolymer composition The approximation method is
limited when the reactivity ratio of one of the components in the system has a value of less
than 01 or greater than a value of 10
However the method does give good insight into the reactivity ratio values for many
copolymer systems The approximation of reactivity ratios can be easy and quick when using
this method of evaluation
The Mayo-Lewis intersection method91 96 uses a linear form of the copolymerization equation where r1 and r2 are linearly related
By using the equations m1M 22 m2M12 and (M2 M1)[(m1 m2) ndash 1] for the slope and intercept
respectively a plot can be produced for a set of experiments after the copolymer composition
has been determined The straight lines that are produced on the plot for each experiment
where r1 represents the ordinate and r2 represents the abscissa intersect at a point on the r1 vs
r2 plot The point where these lines meet is taken to be r1 and r2 for the system in study The
main advantage of this method is that it gives a qualitative observation of the validity of the
intersection area Over the whole range of possible copolymer compositions that were tested
more compact intersections better define the data However the method requires a visual
check of the data and a quantitative estimation of the error is impossible Therefore
weighting of the data is needed to determine the most precise values of r1 and r2
The Fineman-Ross linearization method97 uses another form of the copolymer equation
Where
And
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259
38
For this method by plotting G versus H for all the experiments one will obtain a straight line
where the slope of the straight line is the value for r1 and the intercept of the line is the value
for r2 This type of reactivity ratio determination has the same advantages and disadvantages
of the method described above however this treatment is a linear least squares analysis
instead of a graphical analysis The validity is only qualitative and the estimates of r1 and r2
can change with each experimenter by weighting the data in different ways Furthermore the
high and low experimental composition data are unequally weighted which produces large
effects on the calculated values of r1 and r2 Therefore different values of r1 and r2 can be
produced depending on which monomer is chosen as M158
A refinement of the linearization method was introduced by Kelen and Tudos98 99 100 by
adding an arbitrary positive constant a into the Fineman and Ross equation 47 This technique
spreads the data more evenly over the entire composition range to produce equal weighting to
all the data58 The Kelen and Tudos refined form of the copolymer equation is as follows
η = [ r1 + r2 α ] ξ minus r2 α (50)
where
η = G ( α + H ) (51)
ξ = H ( α + H ) (52)
By plotting η versus ξ a straight line is produced that gives ndashr2α and r1 as the intercepts on
extrapolation to ξ=0 and ξ=1 respectively Distribution of the experimental data
symmetrically on the plot is performed by choosing the α value to be (HmHM)12 where Hm
and HM are the lowest and highest H values respectively Even with this more complicated
monomer reactivity ratio technique statistical limitations are inherent in these linearization
methods101 102
98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265
39
OrsquoDriscoll Reilly et al103 104 determined that the dependent variable does not truly have a
constant variance and the independent variable in any form of the linear copolymer equation
is not truly independent Therefore analyzing the composition data using a non-linear
method has come to be the most statistically sound technique
The non-linear or curve-fitting method90 is based on the copolymer composition equation in
the form
This equation is based on the assumptions that the monomer concentrations do not change
much throughout the reaction and the molecular weight of the resulting polymer is relatively
high In order to determine reactivity ratios from the experimental data a graph must be
generated for the observed comonomer amount that was incorporated into the copolymer m1
versus the feed comonomer amount M1 for the entire range of comonomer concentrations
Then a curve can be drawn through the points for selected r1 and r2 values and the validity of
the chosen reactivity ratio values can be checked by changing the r1 and r2 values until the
experimenter can demonstrate that the curve best fits the data points
The main advantage of the reactivity ratio determination methods discussed thus far is the
results can be visually and qualitatively checked Disadvantages include a direct dependence
of the composition on conversion for most polymer systems and therefore low conversion
(eg instantaneous composition) is needed to determine the reactivity ratios Furthermore
extensive calculations are required but only qualitative measurements of precision can be
obtained Finally weighting of the experimental data for the methods to determine precise
reactivity ratios is hard to reproduce from one experimenter to another
Therefore a technique that allows the rigorous application of statistical analysis for r1 and r2
was proposed by Mortimer and Tidwell which they called the nonlinear least squares
method95105106107This method can be considered to be a modification or extension of the
curve fitting method For selected values of r1 and r2 the sum of the squares of the differences
between the observed and the computed polymer compositions is minimized
103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772
40
Using this criterion for the nonlinear least squares method of analysis the values for the
reactivity ratios are unique for a given set of data where all investigators arrive at the same
values for r1 and r2 by following the calculations Recently a computer program published by
van Herck108 109 allows for the first time rapid data analysis of the nonlinear calculations It
also permits the calculations of the validity of the reactivity ratios in a quantitative fashion110
The computer program produces reactivity ratios for the monomers in the system with a 95
joint confidence limit determination
The joint confidence limit is a quantitative estimation of the validity of the results of the
experiments and the calculations performed This method of data analysis consists of
obtaining initial estimates of the reactivity ratios for the system and experimental data of
comonomer charge amounts and comonomer amounts that have been incorporated into the
copolymer both in mole fractions Many repeated sets of calculations are performed by the
computer which rapidly determines a pair of reactivity ratios that fit the criterion wherein the
value of the sum of the squares of the differences between the observed polymer composition
and the computed polymer composition is minimized111 112 This method uses a form of the
copolymer composition equation with mole fractions of the feed It amounts to determining
the mole fraction of the comonomer that should be incorporated into the copolymer during a
differential time interval
For this equation F2 represents the mole fraction of comonomer two that was calculated to be
incorporated into the copolymer and f1 and f2 represent the mole fractions of each comonomer
that were fed into the reaction mixture The use of the Gauss-Newton nonlinear least squares
procedure predicts the reactivity ratios for a given set of data after repeating the calculations
so that the difference between the experimental data points and the calculated data points on a
plot of mole fraction of comonomer incorporated versus comonomer in the feed is reduced to
the minimum value113 114
108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65
41
18 Controlled Radical Polymerization
The development of new controlledliving radical polymerization processes such as Atom
Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated
polymerization and degenerative transfer processes including RAFT opened the way to the
use of radical polymerization for the synthesis of well-defined complex functional
nanostructures The development of such nanostructures is primarily dependent on self-
assembly of well-defined segmented copolymers This section describes the fundamentals of
ATRP relevant to the synthesis of such systems115
The main goal of macromolecular engineering is to carry out the synthesis (polymerization) in
such a way that it results in well-defined macromolecular products One of the ways to
achieve full control of the macromolecule (length sequence and regio- and stereo- regularity)
would be to build it one monomer at a time with mechanisms in place facilitating selection of
an appropriate monomer and assuring its addition in proper orientation This of course has
been achieved in Nature in the process of protein synthesis through the use of sophisticated
macromolecular ldquonanomachineryrdquo (DNA RNA Most commonly used synthetic routes to
linear polymers are based on addition (chain) reactions which can be controlled only in
statistical terms through such parameters as initiatormonomer ratios monomerpolymer
reactivities monomer concentrations reaction medium etc The main strategy to achieve the
reasonable control of such reactionsrsquo products is through the synchronized growth of ldquolivingrdquo
chains ie chains which cease to grow only in the absence of a monomer Synchronization of
chain growth can be achieved fairly easily through rapid initiation Living chains grown in
such synchronized fashion exhibit relatively narrow molecular weight distributions (MWD)
their average molecular weights can be controlled simply by the duration of reaction Until
recently radical polymerization which covers the broadest range of monomers appeared to
be inherently uncontrollable due to the presence of fast chain termination of growing radicals
Thus although very useful in the synthesis of bulk commodity polymers where precise
control is not always essential radical polymerization has been hardly ever viewed as a tool to
precisely engineer macromolecules for well-defined functional nanostructures
114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16
42
This outlook shifted dramatically recently with the development of new controlledliving
radical polymerization processes such as Atom Transfer Radical Polymerization (ATRP)116
117 118 and other techniques such as nitroxide mediated polymerization119 and degenerative
transfer processes120 including reversible addition-fragmentation chain transfer (RAFT)121
With the availability of effective control mechanisms given its applicability to a broadest
range of monomers radical polymerization is now ready to assume the central role in
macromolecular engineering geared towards the development of well-defined functional
nanostructures
181 Fundamentals of ControlledLiving Radical Polymerization (CRP)
The great expectations for the controlledliving radical polymerization (CRP) have their
origins in the dominating position of the free radical technique by far the most common
method of making polymeric materials (nearly 50 of all polymers are made this
way)122123124This is due to the large number of available vinyl monomers (eg there are
nearly 300 different methacrylates available commercially) which can be easily
homopolymerized and copolymerized The advent of CRP enables preparation of many new
materials such as well-defined components of coatings (with narrow MWD precisely
controlled functionalities and reduced volatile organic compounds -VOCs) non ionic
surfactants polar thermoplastic elastomers entirely water soluble block copolymers
(potentially for crystal engineering) gels and hydrogels lubricants and additives surface
modifiers hybrids with natural and inorganic polymers various biomaterials and electronic
materials
The controlledliving reactions are quite similar to the conventional ones however the radical
formation is reversible Similar values for the equilibrium constants during initiation and
propagation ensure that the initiator is consumed at the early stages of the polymerization
116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002)
43
generating chains which slowly and continuously grow as in a living process There are a
number of critical differences between conventional and controlledliving radical reactions
bull Perhaps the most important difference between the two approaches is the lifetime of
the propagating chains which is extended from 1 s to more than 1 h
bull The second major difference is the very significant increase in the initiation rate
which enables simultaneous growth of all the polymer chains
bull Termination processes cannot be avoided in CRPs Thus CRP is generally less precise
than the anionic polymerization Termination is the most dangerous chain breaking
reaction in CRPs Since it is a bimolecular process increasing the polymerization rate
increases the concentration of radicals and enhances the termination process
Termination also becomes more significant for longer chains and at higher conversion
However this process is somehow self tuned since termination is chain length
dependent
The key feature of the controlledliving radical polymerization is the dynamic equilibration
between the active radicals and various types of dormant species Currently three systems
seem to be most efficient nitroxide mediated polymerization (NMP) atom transfer radical
polymerization (ATRP) and degenerative transfer processes such as RAFT123 Each of the
CRPs has some limitations and some special advantages and it is expected that each
technique may find special areas where it would be best suited synthetically For example
NMP carried out in the presence of bulky nitroxides cannot be applied to the polymerization
of methacrylates due to fast β-H abstraction ATRP cannot yet be used for the polymerization
of acidic monomers which can protonate the ligands and complex with copper RAFT is very
slow for the synthesis of low MW polymers due to retardation effects and may provide
branching due to trapping of growing radicals by the intermediate radicals At the same time
each technique has some special advantages Terminal alkoxyamines may act as additional
stabilizers for some polymers ATRP enables the synthesis of special block copolymers by
utilizing a halogen exchange and has an inexpensive halogen at the chain end125 RAFT can
be applied to the polymerization of many unreactive monomers such as vinyl acetate126
182 Typical Features of ATRP
A successful ATRP process should meet several requirements
125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035
44
bull Initiator should be consumed at the early stages of polymerization to form polymers
with degrees of polymerization predetermined by the ratio of the concentrations of
converted monomer to the introduced initiator (DP = Δ[M][I]o)
bull The number of monomer molecules added during one activation step should be small
resulting in polymers with low polydispersities
bull The contribution of chain breaking reactions (transfer and termination) should be
negligible to yield polymers with high degrees of end-functionalities and allow the
synthesis of block copolymers
In order to reach these three goals it is necessary to select appropriate reagents and
appropriate reaction conditions ATRP is based on the reversible transfer of an atom or group
from a dormant polymer chain (R-X) to a transition metal (M nt Ligand) to form a radical (R)
which can initiate the polymerization and a metal-halide whose oxidation state has increased
by one (X-M n+1t Ligand) the transferred atom or group is covalently bound to the transition
metal A catalytic system employing copper (I) halides (Mnt Ligand) complexed with
substituted 2 2rsquo- bipyridines (bpy) has proven to be quite robust successfully polymerizing
styrenes various methacrylates acrylonitrile and other monomers116127 Other metal centers
have been used such as ruthenium nickel and iron based systems117 118 Copper salts with
various anions and polydentate complexing ligands were used such as substituted bpy
pyridines and linear polyamines The rate constants of the exchange process propagation and
termination shown in Scheme 11 refer to styrene polymerization at 110 C
Scheme 11
According to this general ATRP scheme the rate of polymerization is given by the following
equation
127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901
45
Thus the rate of polymerization is internally first order in monomer externally first order
with respect to initiator and activator Cu(I) and negative first order with respect to
deactivator XCu(II) However the kinetics may be more complex due to the formation of
XCu(II) species via the persistent radical effect (PRE) The actual kinetics depend on many
factors including the solubility of activator and deactivator their possible interactions and
variations of their structures and reactivities with concentrations and composition of the
reaction medium It should be also noted that the contribution of PRE at the initial stages
might be affected by the mixing method crystallinity of the metal compound and ligand etc
One of the most important parameters in ATRP is the dynamics of exchange and especially
the relative rate of deactivation If the deactivation process is slow in comparison with
propagation then a classic redox initiation process operates leading to conventional and not
controlled radical polymerization Polydispersities in ATRP are defined by the following
equation when the contribution of chain breaking reactions is small and initiation is
complete
Thus polydispersities decrease with conversion p the rate constant of deactivation kd and
also the concentration of deactivator [XCu(II)] They however increase with the propagation
rate constant kp and the concentration of initiator [RX]o This means that more uniform
polymers are obtained at higher conversions when the concentration of deactivator in solution
is high and the concentration of initiator is low Also more uniform polymers are formed
when the deactivator is very reactive (eg copper(II) complexed by 2 2-bipyridine or
pentamethyldiethylenetriamine rather than by water) and monomer propagates slowly (styrene
rather than acrylate)
183 Controlled Compositions by ATRP
One of the driving forces for the development of a controlledldquo livingrdquo radical polymerization
is to allow for the copolymerization of two or more monomers128 This has been demonstrated
with ATRP by copolymerization of various combinations of styrene methyl or butyl acrylate
methyl or butyl methacrylate and acrylonitrile ATRP allows for the copolymerization of
these monomers using all feed compositions without loss of control of the polymerization 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
46
this is in contrast to the use of 2266-tetramethylpiperidine-1-oxyl radical (TEMPO) which
must contain a significant amount of styrene as comonomer to retain control of the
polymerization This restriction does not apply to polymerizations mediated by new
nitroxides119 The statistical copolymers prepared by living polymerizations are not the same
as those prepared by conventional radical polymerizations due to the differences in
polymerization mechanism
During a copolymerization one monomer is generally consumed faster than the other
resulting in a constantly changing monomer feed composition during the polymerization the
preference is dependent on the reactivity ratios of the two (or more) monomers In
conventional radical polymerization where the polymer chains are continuously initiated and
are irreversibly terminated the change in monomer feed is recorded in the individual polymer
chains whose composition will vary from chain to chain depending on when the chain was
formed ie at the beginning or near the end of the reaction However since ATRP is a
controlledldquolivingrdquo polymerization system the vast majority of polymer chains does not
irreversibly terminate but grow gradually throughout the polymerization The change in
monomer feed is recorded in the polymer chain itself and not from chain to chain The drifting
of composition along the polymer chain is expected to yield gradient copolymers with novel
properties129 Conventional free radical polymerization methods are generally not suitable for
synthesizing star shaped polymers due to the occurrence of undesirable radical coupling
reactions During a ldquocore-firstrdquo synthesis this would lead to coupling of the growing polymer
arms and ultimately result in a cross-linking of the star macromolecules
Block copolymers can be formed by addition of a second vinyl monomer to a macroinitiator
which contains halide groups that participate in the atom transfer process Most notably this
has been demonstrated by successive addition of a second monomer at the end of the
polymerization of a first monomer by ATRP In this manner AB and ABA block copolymers
have been prepared with various combinations of styrene acrylates methacrylates and
acrylonitrile It is very important to select the right order of monomer addition For example
polyacrylates can be efficiently initiated by the poly (methyl methacrylate)- BrCuBrL
system However the opposite is not true because concentration of radicals and overall
reactivity of acrylates is generally too low to efficiently initiate MMA polymerization
Halogen exchange comes to the rescue bromoterminated polyacrylate in the presence of
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775
47
CuClL is an efficient initiator for MMA polymerization due to reduced polymerization rate
of PMMA-Cl species which are predominantly formed after the exchange process130 131 132
Scheme 12
To conclude atom transfer radical polymerization is a robust method for preparing well-
defined polymers and novel materials with unique compositions and architectures Although
significant progress has been made in the past few years since the development of ATRP
continuous research on the better mechanistic understanding of ATRP and the preparation of
more efficient catalyst systems to yield more well-defined polymers and polymerize new
monomers is needed The syntheses of new materials need to be optimized and their
properties should be studied
It is anticipated that the new controlledliving techniques will help to provide many new well-
defined polymers via macromolecular engineering
130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
48
References
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422 4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348 10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp
(1985) 461
Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823 22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991) 25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996)
(b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993)
(c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice
(d) Mishra M K Ed Polymer Frontiers New York (1994) 391
49
31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159 32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer
Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N
Macromolecules 26 (1993) 7134 42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144 45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon
Press 3(1989) 787 49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154 55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387 57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991) 59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M
J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003)
6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778
50
63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998)
823-830 66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996)
7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R
Macromolecules 32 (1999) 1152-1158 74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998)
696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507 80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication 85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster
PA (1997) 86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995) 87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993) 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151 90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953) 94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
51
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259 98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265 103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772 108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65 114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16 116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002) 125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035 127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
52
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775 130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
53
CHAPTER II Synthesis and Characterization of
Macromonomers
21 Introduction
Cationic ring opening polymerization of DXL proposed by Franta and Reibel133 results in
linear polymeric chains thereby preventing formation cyclic oligomers through cationic
polymerization of cyclic acetals15 17In fact the reaction of DXL in the presence of an
unsaturated alcohol (2-HPMA) results in a functionalized linear PDXL macromonomer
carrying at one or both ends an unsaturated system supported by the methacryloyl group of
the alcohol The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism44 Franta et al have established that when DXL is polymerized by strong protonic
acids such as triflic acid in the presence of a diol the PDXL chains are essentially linear and
carry end-standing OH functions It has been shown that the amount of cyclic species formed
is negligible that the dispersity is on the order of 14 and that the molecular weight of the
linear polymers is governed by the ratio of reacted monomer to transfer agent and is generally
well controlled up to 10 000 gmol
De Clercq and Goethals have reported the preparation of poly (13dioxolane)
bismacromonomers by copolymerization with MMA and provided the possibility to prepare
polymer networks containing PDXL segments134 135 PDXL based hydrogels have been
obtained in most cases by free radical copolymerization with comonomers such as acrylic
acid acrylamide and N-isopropylacrylamide134 136 137 styrene and butyl acrylate138
Hydrogels have received increasing attention for biomedical applications such as drug
delivery immobilization of enzymes dewatering of protein solutions and contact lenses139
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002) 1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080
54
140 These materials and are widely used in areas like baby diapers solute separation soil for
agriculture and horticulture absorbent pads etc139 Hydrogels are defined as hydrophilic
polymer networks which have a high capacity to adsorb a substantial amount of water which
have been proposed as protein releasing matrices The high water content ensures a good
compatibility with entrapped proteins as well as with surrounding tissue141 Even though a
number of applications are currently being pursued using hydrogel very little is known about
the mechanical behavior that describes the various physical processes in hydrogels142 Over
the last decade most interests have been emphasized on the synthesis of polymers containing
polyacetal segments because of the ease of degradation of these polymers under mild
conditions by treatment with a trace of acid134 143 Poly (1 3 dioxolane) is a hydrophilic non-
ionic polymer which like poly (ethylene oxide) is appreciably soluble in water but much
more sensitive to acidic degradation because of the presence of acetal groups in the chains144
In this chapter we report the synthesis of the functionalized poly (13dioxolane)
macromonomers which have been used for the preparation of PDXL hydrogel and
amphiphilic graft copolymers In the second part of this chapter we have focused on a
detailed study of the properties of the resulting hydrogel in terms of swelling behavior in
different organic solvents and viscoelastic properties determined by rheological measurements
in both the steady shear and oscillatory experiments
22 Experimental
221 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922
55
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
bull Dichloromethane (CH2Cl2 MW 8493 bp 40degC d 1325)
Dichloromethane (Prolabo 999) was dried by stirring over CaH2 for 24 h and then
distilled under a N2 atmosphere to remove impurities Purified dichloromethane was
stored under nitrogen over molecular sieve
bull 2-hydroxypropyl methacrylate (2-HPMA) (MW 14417 bp 240degC d 1028)
2-HPMA of commercial grade was purchased from Acros stabilized with 200 ppm
hydroquinone monomethyl ether Then it was stored over molecular sieve
bull n-Hexane 99 (C6H14 MW 8618 bp 68-70degC d 0658-0662) Stored under
nitrogen over molecular sieve
bull Trifluoromethanesulfonic acid (triflic acid Aldrich) was used as received
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile (AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull 1 3 dioxolane (DXL) (MW 7408 bp 78degC d 106)
The monomer DXL of commercial grade was purchased from Acros DXL was kept
under KOH for two and up to three days to remove any peroxide and stabilizer traces
and then purified by distillation over CaH2 under a N2 atmosphere prior to
polymerization
All chemicals were kept over molecular sieve before use
222 Reaction apparatus
All polymerization experiments were performed with a clean 250 ml three neck round bottom
flask A condenser was used on one of the necks of the flask in order to condense any
monomers that might otherwise possibly escape A magnetic bar was used to stir the solution
at a constant speed in order to assure even distribution of monomer and initiator
concentrations throughout the entire volume of solution A rubber septum was used to cover
one of the three necks
In the case of free radical polymerization reactions a thermocouple was also fitted to the
reaction vessel to monitor the temperature of the reaction The thermocouple regulated the
56
temperature at a constant 70degC throughout the reaction
223 Synthesis of Poly (13-dioxolane) Macromonomers
Methacrylate-terminated PDXL macromonomers were synthesized by Cationic ring-opening
polymerization which was carried out in 10 ml dichloromethane with triflic acid as initiator at
room temperature under nitrogen for 24 h in the presence of 2-hydroxypropyl methacrylate
(2-HPMA) as transfer agent 20 ml of DXL monomer was added The feed molar ratios
[DXL] [2-HPMA] are reported in Table1 as well as the molecular characteristics of the
obtained macromonomers The amount of the acid used was 20 μl After reaction the
resulting solution is poured into THF Then the product is purified by re-precipitation from
THF solution with a large excess of hexane and the obtained polymer was dried under
vacuum at room temperature The yield was checked by gravimetric determination and found
to be about 80
224 Synthesis of Poly (13-dioxolane) Hydrogel Network
The functionalized PDXL macromonomer taken for the preparation of PDXL netwok was
(FPP2) macromonomer with a theoretical average molecular weight of Mnth =2000
The macromonomer (1g) was polymerized by free radical polymerization in 10 ml of THF
using 2 2-azobisisobutyronitrile (AIBN) (001g) as initiator under a nitrogen atmosphere
The polymerization was carried out at 70degC for 24h A piece of hydrogel was obtained The
product was extracted with ethanol to remove unreacted macromonomers and then dried
under vacuum
23 Characterization Techniques
231 Raman Spectroscopy
Raman spectroscopy is used to study and analyse the structure of the macromonomers
The experiments were performed on a Dilor XY 800 spectrophotometer The detector was a
charge-coupled device (CCD) An argon laser pump beam (power density of 100 mW) has
been focused onto the sample through a microscope The working wavelength was chosen as
λ = 5145 nm In our experiments we explored the spectral range between 200 and 3700 cm-1
with a spectral resolution of 2 cm-1
57
232 1H-NMR Spectroscopy
Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) was used for structural analysis
and molecular weight of polymers and macromonomers Proton NMR spectra were obtained
using a high field 400Mhz Advance Bruker spectrometer
All of the 1H NMR samples were dissolved in deuterated chloroformThe chloroform
reference peak at 724 ppm was to ensure accuracy of peak assignments The integrals of the
peaks were used for the calculations to determine the Mw of the macromonomers
233 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) represents a chromatographic method widely used in
the analysis of polymer average molecular weights and molecular weight distributions SEC
Measurements were performed at 40degC on a Waters 2690 instrument equipped with UV
detector (Waters 996 PDA) coupled with a Differential Refractometer (ERC - 7515 A) and
four Styragel columns (106 105 500 and 50degA) THF is employed as eluent with a flow rate
of 10 mlmin Polystyrene standard samples were used for calibration
234 Swelling Measurements
In order to investigate the swelling behavior the measurement of the swelling ratio of the
polymer network is obtained from a gravimetric method in which small pieces of hydrogel
were immersed solvents such as CH2Cl2 and THF for 24 hours at room temperature (23degC)
until swelling equilibrium was reached ie when the gel thickness became essentially
constant The samples were removed from the solvents and carefully weighed (Ws) Then the
samples let to deswell and weighed every 5 min during in order to determine the swelling
kinetics in the solvents The swelling equilibrium was reached after 5 hours Afterwards the
gel was left to dry for 24 hours at room temperature until constant weight was attained and the
dry weight (Wd) was determined and the swelling ratio was calculated from equation
SR = ( ) 100timesminusWd
WdWs (57)
Where SR is equilibrium swelling ratio Ws and Wd are the sample weights in swollen and dry
states respectively
58
235 Rheological Measurements
Steady shear and oscillatory measurements have been performed on a stress imposed
rheometer Rheo-Stress-100 (RS100) from Haake used with a coneplate geometry (20 mm
diameter an angle of 4deg gap 2 mm)The imposed stress of 100 Pa during 30 seconds and a
frequency of 1Hz were applied while the strain was monitored The measurements have been
performed on swollen and unswollen samples The elastic (G) and the loss (G) moduli are
measured in linear viscoelastic region In the oscillatory experiments the frequency
dependence of both Grsquo and G is obtained at a constant strain All rheological measurements
were carried out at room temperature (23 degC)
24 Results and Discussion
241 Structural Characterization of Macromonomers
1 3 dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer end ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The synthesis of α ω-dihydroxy-PDXL chains is based on the
activated monomer mechanism44 Franta et al have established that when DXL is polymerized
by strong protonic acids such as triflic acid in the presence of a diol the PDXL chains are
essentially linear and carry end-standing OH functions It has been shown that the amount of
cyclic species formed is negligible that the dispersity is on the order of 14 and that the
molecular weight of the linear polymers is governed by the ratio of reacted monomer to
transfer agent and is generally well controlled up to 10 000 gmol
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel44 133 using an unsaturated alcohol (2-
59
HPMA) as a transfer agent results in linear polymeric chains thereby preventing formation of
cyclic oligomers through cationic polymerisation of cyclic acetals15 17 They were all prepared
at the same reaction conditions The synthetic route of functionalized PDXL macromonomers
is shown in scheme13
Scheme 13 Structures of PDXL macromonomer species54
According to this mechanism it is possible to prepare macromonomers ie PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of the
transacetalization reactions a mixture of products is obtained
A is the most abundant compound it corresponds to 50 to 60 weight wise54 It is a
macromonomer
B corresponds to 20 to 25 weight wise It is a bis-macromonomer It carries two
methacryloyl functions corresponding to transacetalization of R-OH and DXL
C corresponds to 20 to 25 weight wise It carries no methacryloyl function but two
hydroxyl groups It is a α ω-dihydroxy-PDXL
These 3 species A B and C stem from scrambling reactions that are typical with cyclic
acetals54
The characterization of these materials is based on structure and molecular weight
determination For instance the PDXL macromonomers carried at one of their ends a double
bond afforded by the methacryloyl group The latter was checked by Raman and 1H-NMR
spectroscopy All macromonomers prepared displayed functionality close to unity which
makes them suitable for the synthesis of graft copolymers
60
Raman spectroscopy is used to study and analyse the structure of the macromonomers The
aim of this study is to check the formation of linear polymer chains as well as the termination
with methacryloyl groups The spectra obtained exhibit two intense Raman bands at 800 to
900 cmP
-1 and 2700 to 3000 cmP
-1 regions and a series of small other peaks for all samples as
shown in figure 1 The most intense band (2700 ndash 3000 cmP
-1) is assigned to the aliphatic
stretching vibration of CH in the polyacetal chain Symmetric COCOC stretching frequencies
of aliphatic acetals fall in typical regions of 1115-1080cmP
-1 and 870-800 cmP
-1 145 and are
responsible for intense Raman bands In the low frequency region there are three very
characteristic Raman bands in the 600 ndash 550 cmP
-1 540 ndash 450 cmP
-1 and 400 ndash 320 cmP
-1 ranges
which are assigned to COCOC deformations145 146 Also the acetals have strong multiple
bands in the region of 1160ndash1040 cmP
-1 as noticed on the Raman spectra involving the C-O
stretching modes In addition to this the O-CH-O group gives rise to a band at 1350 ndash1325
cmP
-1 for C-H deformation Other intense Raman bands are observed in the region of 3000 ndash
2700 cmP
-1 Below 3000 cmP
-1 the corresponding frequencies are assigned to the aliphatic C-H
stretching modes145 The methoxy group is detected in the region of 2835 ndash 2780 cmP
-1
Figure 1 Raman spectra of methacrylic-terminated PDXL macromonomers (FPP2 FPP15 and
FPP1)
145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The Handbook of IR
and Raman Characteristic Frequencies of Organic Molecules United Kingdom Ed by Academic Press Limited London (1991)
146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman Spectroscopy 3rd Edition AP Limited London (1964)
61
As far as the presence of the methacryloyl group in the polymeric chain is important bands
have been observed at 1640 cmP
-1 which corresponds to C=C bonds The carbonyl compounds
absorb strongly within 1900 ndash1550 cmP
-1 region145 146 the spectra show a C=O bond absorption
found at 1720 cmP
-1 In the region of 1340 ndash1250 cmP
-1 the methacrylate bands are observed
Broad absorption is found near 3500 cm -1 owing to stretching of the OH bonds OH
deformation bands are found at 1400 cmP
-1P and 1340 cmP
-1 This observation indicates that both
methacrylic and ndashOH groups are present and eventually the resulting product is a mixture of
the three species as shown in the scheme above
Typical 1H-NMR spectrum of PDXL macromonomer shown in figure 2 exhibits the expected
resonance assigned to the methoxy protons (477 ppm) and OCH2CH2O protons at (374
ppm) Two signals corresponding to =CH2 were observed at (612 ndash 614 ppm) and (557 ndash
559 ppm) Therefore the spectrum confirmed the chemical structure HO[CH2CH2OCH2O]nR
of methacryloyl- terminated PDXL macromonomer
Figure 2 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP2)
242 Molecular Weight Determination
Besides the structure 1H-NMR enables us to determine the number-average molecular weight
(Mn) In the calculation of the latter the methacryloyl end group was included The
62
polydispersity and index MwMn and the number-average molecular weight were obtained
from SEC measurements Table 1 summarizes these values It can be seen that Mn (SEC) and
Mn (NMR) are very close to each other for all macromonomer samples and are in agreement
with the theoretical values predicted from calculations Under our polymerization conditions
the polydispersity index is 16 for all samples
Table 1 Characteristics of PDXL macromonomers prepared at different degrees of
polymerization
Sample Dp Mnth MnSEC MnRMN MwMn f (a)
FPP1 135 1000 1120 1160 16 097
FPP15 2025 1500 1540 1550 16 099
FPP2 270 2000 2040 2100 16 097
Dp degree of polymerization = [DXL] [2HPMA]
a functionality of macromonomers (methacryloyl end groups molecule)
243 Swelling of Poly (13 Dioxolane) Hydrogel
The synthesized PDXL hydrogel has been studied in terms of swelling and rheological
behaviors The degree of swelling and the rate of swelling of the hydrogel are studied It is
known that hydrogel can swell in several solvents but at different degree of swell according to
many factors related to the nature of the solvents and the type of polymer-solvent interactions
It was found that the solubility parameter of the solvents (δ) had a great effect on swelling
degree For instance hydrogels can swell fast in CH2Cl2 (δ = 976 cal cm12 -32) and reached
equilibrium within no more than an hour However it will take about more than 20 h to reach
equilibrium in CH3 OH (δ = 145 cal cm12 -32) It was known that the polymer can reach
greatest swelling degree when the solubility parameter of the polymer is close to that of the
solvents The solubility parameter of PDXL is about 93 cal cm 12 -32 134 The swelling has been
examined in THF and CH2Cl2 for PDXL hydrogel It has been observed that the swelling
equilibrium is reached after almost 5 hours of swelling for all samples in both solvents The
results show that THF (δ = 952 cal cm12 -32)147 swells the hydrogel to the greatest degree
compared to CH2Cl2 as shown in figure 3 However CH2Cl2 molecules provide less swelling
147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983)
63
capacity than in THF On the basis of the experiment The PDXL hydrogel reached high
swelling degree due to its solubility parameter is much closer to that of THF
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
THF CH2Cl2
Swel
ling
degr
ee
Time (min)
Figure 3 Swelling kinetics of PDXL hydrogel in two different solvents CH2 Cl2 (solid
squares) and in THF (hollow squares)
244 Viscoelastic Behavior
Rheological measurements were performed on rheometer in the Cone and Plate geometry
Both steady shear and oscillatory experiments were carried out The dynamic storage and loss
moduli G and G were examined at room temperature (23 degC)
Many attempts have been carried to extend the elasticity theory to swollen gels148 149 Based
on this approach all measurements have been performed on both swollen and unswollen
hydrogel samples for the purpose of comparison so that to examine the mechanical properties
even in swollen state For instance Flory and Rehner recognized the swelling phenomenon
exhibited by cross-linked polymers when exposed to certain solvents and related the modulus
of elasticity of a swollen cross-linked polymer network to an unswollen network150 Figure 4
illustrates the strain dependence of G and G for swollen and unswollen samples
148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for Experimental
Mechanics SEM Annual Conference Proceedings (2002)
64
10-5 10-4 10-3 10-2 10-1 100 101 102101
102
103
104
Guns Guns Gs Gs
GG
(Pa
)
γ ()
Figure 4 Strain dependence of the elastic modulus Grsquo (circles) and of the viscous modulus
Grdquo(triangles) for two samples of unswollen hydrogel (solid symbols) and swollen hydrogel
(hollow symbols)
The moduli are measured as a function of strain at a constant frequency It appears that the
linear viscoelastic region is observed while the strain is increasing in either state which
indicates that the internal structure of the samples has not been disrupted when deformed
This leads to reveal that the gel is strain resistant in swollen and unswollen states and within a
large strain range the hydrogel retains its elasticity as shown in figure 4 where the linear
viscoelastic region extends to almost 02
The frequency dependence of G and G is shown in figure 5 similarly for swollen and
unswollen hydrogels The system behaves typically like a gel as it can be noticed that the
elastic component G (storage modulus) is far greater than the viscous component G (loss
modulus)151 Based on these results the hydrogel exhibits extreme elasticity at low
frequencies
151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure 554 (2000) 99-108
65
100 101
103
104
105
Gs Guns Gs GunsG
G(
Pa)
ω (rads)
Figure 5 Frequency dependence of Grsquo(circles) and Grdquo(triangles) for swollen hydrogel
(hollow symbols) and unswollen hydogel (solid symbols)
Finally figure 6 illustrates the complex viscosity profiles another parameter of
viscoelasticity which measures the magnitude of the total resistance to a dynamic shear
Again this property has not been affected by swelling since the results show similar behavior
for swollen and unswollen states It decreases sharply as frequency increases which
characterizes the samples degree of viscoelasticity at various time scales Therefore from the
results discussed above the hydrogel network is elastic and stable even in the swollen state
thereby possessing very good mechanical properties
100 101 102 103
102
103
104
105
η unswollen η swollen
ηlowast (P
a s)
ω (rads)
Figure 6 Frequency dependence of the complex viscosity η for unswollen hydrogel (solid
squares) and swollen hydrogel (hollow triangles)
66
Conclusion
The hydrogel properties were discussed in terms of swelling and viscoelastic
behaviors The hydrogel has combined special properties Its swelling behaviour in the
solvents was dependent on the solubility parameter of both solvents and hydrogel
Rheological measurements were successful when used in order to study the viscoelastic
behavior of the hydrogel of pure PDXL in swollen and unswollen states The Strain
dependence of G and G for both samples shows linear viscoelastic region and allows to
determine the yield stress Same conclusions can be given concerning the frequency
dependence of complex viscosity the swelling does not affect this property The results reveal
a perfect elastic and resistant hydrogel in other words the viscoelastic properties have not
been so much affected by swelling They may be particularly useful in the design of improved
microfluidic devices that utilise the relationship between swelling and strain This kind of
material can be potentially used in biosystems such as intelligent drug delivery systems
67
References
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-
174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002)
1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080 140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922 145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The
Handbook of IR and Raman Characteristic Frequencies of Organic Molecules United
Kingdom Ed by Academic Press Limited London (1991) 146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman
Spectroscopy 3rd Edition AP Limited London (1964) 147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983) 148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-
1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for
Experimental Mechanics SEM Annual Conference Proceedings (2002) 151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure
554 (2000) 99-108
68
CHAPTER III Synthesis and Characterization of Copolymers
31 Introduction
Amphiphilic block and graft copolymers consisting of hydrophilic and hydrophobic parts
have been subjects of numerous studies within which block and graft copolymers containing
hydrophilic polyoxyethylene segments and other hydrophobic segments have attracted much
attention because polyoxyethylene segments are not only hydrophilic but also nonanionic
and crystalline and can complex monovalent metallic cations Graft copolymers offer all
properties of block copolymers but are usually easier to synthesize Moreover the branched
structure leads to decreased melt viscosities which is an important advantage for processing
Depending on the nature of their backbone and side chains they give rise to special properties
in selective solvents at surfaces as well as in the bulk owing to microphase separation
morphologies12 They can be used for a wide variety of applications such as polymeric
surfactants electrostatic charge reducers compatibilizers in polymer blends polymeric
emulsifiers controlled wet ability and so on152 153 In order to prepare graft copolymers with
well-defined structure one can utilize the macromonomer technique (grafting through
technique) Well-defined structure graft copolymers are synthesized by copolymerization of
macromonomers with low molecular weight comonomers6 It allows the control of the
polymer structure which is given by three parameters (i) chain length of side chains which
can be controlled by the synthesis of the macromonomer by living polymerization (ii) chain
length of backbone which can be controlled in a living copolymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular weight monomer However the distribution of spacings
may not be very easy to control due to the incompatibility of the polymer backbone and the
macromonomers154 As pointed out in recent publication reviews155 there is a complex
interplay of factors that govern the reactivities in copolymerizations involving
macromonomers When different comonomers are copolymerized with the same it seems that
the degree of interpenetration between the macromonomer and the propagating copolymer 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305
69
backbone plays the major role in the measured reactivities Nevertheless the main properties
depend on both the average composition of the systems and the microstructural distribution of
the comonomer sequences along the macromolecular backbone which is determined by the
reactivity ratios of the macromonomer and the corresponding comonomer in the free radical
polymerization process156 157
In this chapter our work deals with the preparation and characterization of new organo-
soluble associative copolymers based on short hydro-soluble chains of poly (1 3 dioxolane)
(PDXL) Many reports have been published on PDXL macromonomers used to form
hydrogels136 137 158 159 160 161 162 however very few were on graft copolymers with PDXL
branches162 These macromonomers are used for the preparation of amphiphilic graft
copolymers by solution free radical copolymerization with a hydrophobic comonomer
styrene (St) and methyl methacrylate (MMA) Structural characterization of these
copolymers molecular weight determination reactivity ratios and the polymerizability of the
PDXL macromonomer have been discussed Finally their thermal properties are discussed
according to the weight content of PDXL in the copolymers
32 Experimental
321 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269
70
bull Ethanol (C2H6O MW 4607 bp 78degC d 081)
Ethanol (Prolabo 95-96) was purified by distillation with 5g of Magnesium and 05g of
iodine for 75ml of alcohol under a N2 atmosphere After discoloration of the mixture
solution a volume of Ethanol was added and then distilled normallyThen it was stored
over molecular sieve
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile(AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull Styrene (C6H5CH=CH2 MW 10416 bp 145degC d 091)
Styrene (Prolabo product) was purified by distillation over CaHB2 at reduced pressure
bull Methyl Methacrylate (MMA)(H2C=C(CH3)CO2CH3 MW 10012 bp 100degC d
0936)
Methyl Methacrylate (Prolabo product) was purified by distillation over CaHB2 at reduced
pressure
All chemicals were kept over molecular sieve before use
322 Synthesis of Poly (Styrene-co-Poly (13-dioxolane))
a) Conventional Free Radical Copolymerization
The reaction route for the conventional copolymerization of Styrene and PDXL
macromonomers using AIBN as the free radical initiator at 60degC is shown in scheme 14
71
Scheme 14
PDXL macromonomers of different molecular weights were copolymerized with St in THF at
60degC in the presence of 2 2rsquo-azobisisobutyronitrile AIBN (1 based on the total weight of
the monomers) as initiator under a nitrogen atmosphere using different feed molar fractions
of macromonomers The total monomer concentration for was 6 10-1 M in all cases The
copolymerization product is diluted with THF and then added dropwise to a large excess of
ethanol to remove unreacted PDXL macromonomers25 43 and precipitate the copolymers
Then they were finally dried over vacuum at 40degC to constant weight The yields of all
reactions are 70ndash 90 Table 2 indicates the amounts of comonomers initiator and solvent
employed in the copolymerization study
72
Table 2 Copolymerization of PDXL macromonomers (M1) with Styrene (M2)
Sample M1 M2M1 PDXL (g) (mol)
Styrene (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2SP2 FPP2 20 349 174510-4 364 349 10-2 007 60 0610 3SP2 FPP2 30 232 116 10-4 364 349 10-2 006 60 0601 5SP2 FPP2 50 14 69810-4 364 349 10-2 005 60 0593
2SP15 FPP15 20 262 174510-4 364 349 10-2 006 60 0610 3SP15 FPP15 30 174 116 10-4 364 349 10-2 006 60 0601 5SP15 FPP15 50 105 69810-4 364 349 10-2 005 60 0593
2SP1 FPP1 20 174 174510-4 364 349 10-2 006 60 0610 5SP1 FPP1 50 07 69810-4 364 349 10-2 005 60 0593 8SP1 FPP1 80 0436 43610-4 364 349 10-2 005 60 0589
b) Controlled Free Radical Copolymerization
The comb-structure copolymer of styrene and PDXL was obtained by grafting-from
mechanism through Nitroxide-Mediated Polymerization
Nitroxide mediated polymerization (NMP) is a controlled radical polymerization (CRP)
technique which already offers the ability to prepare a wide variety of well-defined polymer
architectures119 Despite the significant improvements brought to CRP techniques such as
NMP atom transfer radical polymerization (ATRP) or reversible addition fragmentation chain
transfer (RAFT) the preparation of complex architectures by CRP is restricted by the
exclusion of monomer systems that are polymerized by fundamentally different mechanisms
like lactides ethylenepropylene oxide The most promising approaches to extend the range of
polymer compositions are based on the use of heterofunctional initiators163 allowing the
combination of mechanistically distinct polymerization reactions without the need for
intermediate transformation and protection steps
In the field of NMP the development of multifunctional initiators was focused on TEMPO
and TIPNO which are examples of nitroxides (Scheme 15) It is worth to mention that in
NMP these are used as counter-radicals associated with a conventional azoic initiator so this
pair of initiators is known as a bimolecular system
163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671
73
Scheme 15 TEMPO and based alkoxyamines
Another initiator used for NMP is the commercially available alkoxyamine also called
MAMA-SG1164 (Scheme 16) known as a monomolecular system initiator which is
particularly convenient for functionalization of polymer chain ends164 165 MAMA-SG1 has
been developed by Didier Gigmes and co in collaboration with Arkema Company166 Thanks
to a particularly high dissociation rate constant value kd1 up to now this alkoxyamine has
proved to be one of the most potent alkoxyamines reported in the field of NMP167 168 This
initiator is used for polymerization of styrene and n-butyle acrylate allowing formation of
well-defined linear and star structures
Scheme 16
164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006) 5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219
74
Scheme 17 MAMA-SG1 structure and dissociation scheme
bull Multifunctionalization of Polystyrene (HO-PS)
MAMA-SG1 was used to run copolymerization of styrene at 90 mol with HEMA in order
to obtain functionalized polystyrene The monomers and alkoxyamine were introduced in a
250 mL two neck round-bottom flasks fitted with septum condenser and degassed for 15
min by nitrogen bubbling The reaction was performed in bulk at 120 degC under N2 with
vigorous stirring Targeted molecular weight and polydispersity were 30 000 g mol and 12
respectively
After polymerization the final polymer mixture was dissolved in a minimum THF and
precipitated in cold ethanol followed by drying under vacuum at 30degC
bull Synthesis of PS-g-PDXL
PDXL was copolymerized by cationic ring-opening polymerization which was carried out in
40 ml dichloromethane with triflic acid as initiator at room temperature under nitrogen for 24
h in the presence of OH-multifunctionalized PS (1g 3 10-5 mol) as transfer agent 20 ml
(0286 mole) of DXL monomer was added Table 6 gives the molecular characteristics of the
obtained copolymer The amount of the acid used was 20 μl After reaction the resulting
solution is poured into THF Then the product is purified by re-precipitation from THF
solution with a large excess of hexane and the obtained polymer was dried under vacuum at
room temperature The yield was checked by gravimetric determination and found to be about
75 The polymerization route is presented in the scheme below
75
Scheme 18
323 Synthesis of Poly (Methyl Methacrylate-co-Poly (13-dioxolane))
Same procedure has been used for the synthesis of Poly (Methyl Methacrylate-co-Poly (1 3-
dioxolane)) copolymers The yields of the reactions are in the range of 70ndash 90
Table 3 shows the amounts of comonomers initiator and solvent employed in the
copolymerization reactions
Table 3 Copolymerization of PDXL macromonomers (M1) with MMA (M2)
Sample M1 M2M1 PDXL (g) (mol)
MMA (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2MP2 FPP2 20 374 187 10-4 3744 374 10-2 008 65 0604 3MP2 FPP2 30 2 10 10-4 300 300 10-2 005 50 0620 5MP2 FPP2 50 15 748 10-4 3744 374 10-2 005 60 0636
2MP15 FPP15 20 2 133 10-4 28 280 10-2 005 25 100 3MP15 FPP15 30 187 125 10-4 3744 374 0-2
006 60 0644 5MP15 FPP15 50 112 748 10-4 3744 374 10-2 005 60 0636
2MP1 FPP1 20 2 20 10-4 400 4 10-2
006 50 0840 3MP1 FPP1 50 125 125 10-4 3744 374 10-2 005 64 0604 5MP1 FPP1 80 075 748 10-4 3744 374 10-2 005 60 0636
33 Characterization Techniques
331 1H-NMR Spectroscopy
1H NMR Spectroscopy was used for compositional and structural analysis of the copolymers
1H-NMR spectra of the copolymers were recorded on the high field 400Mhz Advance Bruker
spectrometer All of the 1H NMR samples were dissolved in deuterated chloroform The
integrals of the peaks of copolymer components were used for the calculations to determine
76
the molecular weights polydispersity indices and the amount of each comonomer that was
incorporated into the copolymer
332 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) was used in the charaterization of the copolymers to
determine average molecular weights and polydispersity indices SEC Measurements were
performed at 40degC on a Waters 2690 instrument equipped with UV detector (Waters 996
PDA) coupled with a Differential Refractometer (ERC - 7515 A) and four Styragel columns
(106 105 500 and 50degA) THF is employed as the mobile phase with a flow rate of 10
mlmin Polystyrene standard samples were used for calibration
333 Diffraction Scanning Calorimetry
Diffraction Scanning Calorimetry (DSC) measurements are performed on a Modulated
Temperature Differential Scanning Calorimeter Q100 TA instrument under nitrogen at 50
mlmin The samples are hermetically sealed in aluminium pans and they are subjected to a
heating program as follows
For Poly (Styrene-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 120degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -80degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to130degC
For Poly (Methyl Methacrylate-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 130degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -95degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to150degC
The thermograms obtained illustrate Glass Transition Temperatures (Tg) and Meltind Points
(Tm) of the copolymers
77
34 Results and Discussion
Methacryloyl-terminated PDXL macromonomers with the Mn range of 1000-2000 gmole
were copolymerized with vinyl and methacrylic monomers in order to obtain amphiphilic
graft copolymers with chemical structure of hydrophobic backbone and hydrophilic side
chains
341 Structural Characterization of the Copolymers
The structure of the copolymers was well defined by 1H-NMR analysis The copolymer 1H-
NMR spectra confirm the formation of copolymers see figures 7 8 and 9 The chemical
shifts of protons of polystyrene and PDXL can be clearly distinguished The following peaks
are assigned for OCHBB2BBO protons at 478 ppm and OCHBB2BBCHBB2BBO protons at 375 ppm (5H CBB6BB
HBB5BB) at 728 711 and 706 ppm as shown in Figure 8 The spectrum of PMMA-PDXL
copolymer is shown in Figure 9 where the chemical shifts of PMMA correspond to the proton
resonance as depicted in the figure the O-CH3 protons are observed at 361 ppm and clear
resonance assigned to the methyl group protons at 085-103 ppm and eventually we observe
the corresponding chemical shifts for OCHBB2BBCHBB2BBO protons (374 ppm) and OCHBB2BBO protons
(477 ppm) to confirm the incorporation of PDXL in the copolymer
Figure 7 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP1)
78
Figure 8 1H-NMR spectrum of Styrene-g-PDXL copolymer in CDCl3 (sample 3SP2)
79
Figure 9 1H-NMR spectrum of MMA-g-PDXL copolymer in CDCl3 (sample 2MP2)
342 Copolymer Molecular Weight and Composition
a) Conventional Free Radical Copolymerization
Copolymerization of PDXL macromonomers with MMA and ST in THF solution was studied
for different molar feed ratio of PDXL The amounts of monomeric units in the copolymers
were determined by elemental analysis The results are presented in Table 4 and 5 which
summarise the characteristics of the graft copolymers in terms of macromonomer feed ratio
(M2M1) and average Mn obtained from SEC as well as copolymer composition in weight and
mole percentages which is determined from 1H-NMR
80
Table 4 Characteristics of PDXL macromonomers (M1) copolymerized with Styrene (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2SP2 FPP2 20 49 476 4025 337 9200 162 2 3SP2 FPP2 30 39 322 303 221 8900 162 2 5SP2 FPP2 50 277 196 21 13 7200 159 1
2SP15 FPP15 20 418 476 34 34 9100 157 2 3SP15 FPP15 30 323 322 24 214 7000 161 2 5SP15 FPP15 50 224 196 152 12 6700 147 1
2SP1 FPP1 20 323 476 30 427 9200 178 3 5SP1 FPP1 50 16 196 1424 17 5800 158 1 8SP1 FPP1 80 107 123 85 095 11900 195 1
Table 5 Characteristics of PDXL macromonomers (M1) copolymerized with MMA (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2MP2 FPP2 20 50 476 35 26 21900 198 4 3MP2 FPP2 30 40 322 21 13 25900 157 3 5MP2 FPP2 50 286 196 13 07 87200 455 6 2MP15 FPP15 20 416 45 28 25 19800 193 4 3MP15 FPP15 30 333 322 22 18 15200 277 3 5MP15 FPP15 50 23 196 13 10 24700 16 2 2MP1 FPP1 20 333 476 26 34 21100 319 6 3MP1 FPP1 30 333 322 19 22 17100 197 3 5MP1 FPP1 50 20 196 10 11 13900 354 2
81
b) Controlled Free Radical Copolymerization
Multifunctionalization of Polystyrene and Synthesis of poly (S-g-PDXL) copolymer give
results which are shown in Table 6 These data have been obtained from the 1H-NMR and
SEC analyses illustrated in figures 10 and 11 The resonance shifts assigned to all components
(PDXL PS and HEMA) are very clear This enables us to make calculations to determine
composition of each copolymer in addition to obtain the average number of grafts and the
number average-molecular weight of a graft
It is observed that the multifunctionalized-PS is composed of 20 in mole of HEMA which
results in 58 grafts (Ng = 58) per molecular chain
After copolymerization multifunctionalized-PS with DXL the copolymer PS-g-PDXL
(DXPS) possesses the following characteristics which are presented in Table 6 It has a
number average-molecular weight of 83000 gmol with 80 of PDXL content The number
average-molecular weight of one graft has been calculated and found to be 1000 gmol
Table 6 Characteristics of functionalized Styrene (HO-PS) and PS-g-PDXL (DXPS)
copolymer
Strusture Sample MnSEC IP PDXL
w mol
PS
w mol
HEMA
w mol
Ng Graft
Mn
HO-PS
32 700
12
_ _
77 80
23 20
58
_
DXPS
83 000
24
71 80
17 13
12 75
58
1000
82
Figure 10 1H-NMR spectrum of Multifunctionalized of Polystyrene in CDCl3
Figure 11 1H-NMR spectrum of poly (S-g-PDXL) copolymer (DXPS) in CDCl3
83
341 Determination of Monomer Reactivity Ratios
The application of the classical treatment based on linearization of the copolymerization
equation of Mayo and Lewis91 or the non-linear least-squares approach suggested by Tidwell
and Mortimer95 requires working with high macromonomer concentrations (ie feed
compositions higher than 20-30 of macromonomer)156
The MayondashLewis equation (58) that relates the instantaneous compositions of the monomer
mixture to the copolymer composition is approximated to a simplified form (equation (59))
suggested by Jaacks169 when working with a large excess of one of the comonomers This is
the case of copolymerisation reactions between a conventional comonomer and a
macromonomer of relatively high molecular weight where using low molar concentrations of
macromonomer is mandatory due to its restricted solubility and the extremely viscous media
][ ][ ]
[ ][ ]
[ ] [[ ] [ ]221
211
2
1
2
1
MrMMMr
MM
MdMd
++
=
(58)
[ ][ ] 1
22
1
2
MMr
MdMd
=
(59)
According to equation (59) the copolymer composition or the frequency of branches is
essentially determined by the monomer composition and the monomer reactivity ratio of the
comonomer r2 (inversely proportional to the macromonomer reactivity) under the limit
condition of [M2][M1] gtgt1 In order to obtain reliable values it is frequently necessary to
run the copolymerisation at different conversions or to carry out several copolymerizations
with different initial monomer ratios170 In such cases an integrated form of equation (59) is
used
[ ] [ ][ ][ ] 01
12
02
2 lnlnMM
rMM tt =
(60)
169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046
84
where [Mi]t[Mi]0 is the ratio among the composition of monomer i at time t and the initial
feed composition A plot of ln ([M2]t[M2]0) versus ln ([M1]t[M1]0) should result in a straight
line with a slope that equals to r2 (the reactivity ratio of the comonomer)
Thus the monomer reactivity ratios between the PDXL macromonomers and the comonomers
were estimated with the data in tables 4 and 5 We can apply equation (60) to the estimation
where M1 and M2 are the PDXL macromonomer and copolymer respectively The monomer
reactivity ratios are determined for macromonomers of different Mn (degree of
polymerization) and summarized in Table 7
Table 7 Monomer reactivity ratios for copolymerization of PDXL macromonomers (M1)
with St and MMA (M2)
Sample M2 M1
macromer Mnth
r2 1r2
SP2 St FPP2 2000 012 plusmn 0006 833
SP15 St FPP15 1500 0042 plusmn 6 10-4 238
SP1 St FPP1 1000 0015 plusmn 3 10-4 6666
MP2 MMA FPP2 2000 002 plusmn 001 50
MP15 MMA FPP15 1500 007 plusmn 0 02 1428
MP1 MMA FPP1 1000 0018 plusmn 001 5555
In the case of copolymerization with Styrene and MMA the results suggest that the reactivity
of the methacrylic double bond in the prepared macromonomers is not affected in their
copolymerization with Styrene or MMA This point is confirmed when analysing the inverse
ratio 1r2 = k21k22 which is sometimes considered as the relative copolymerization reactivity
of a macromonomer171 This quantity is the ratio between the crosspropagation and
homopropagation rate constants of comonomer (2) which is directly proportional to the
reactivity of the macromonomer (1) and gives a clear idea of the relative reactivity of a
growing radical ending in a 2 unit towards the addition of monomer (1) in comparison to the
171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620
85
tendency for the homopropagation So we have a situation where r1 gtgt 1 gtgt r2 and it is
expected that the initially formed chains should contain more macromonomers and then more
comonomer segments are added These are only assumptions but they give an indication
about the probable composition drift of the graft copolymers obtained On the other hand in
the case of copolymerization of poly (13dioxolane) macromonomers with styrene (Figure
12) the results show that r2 increases with increasing PDXL side chain length (in terms of
average Mn) and this leads to say that the side macromonomer chain length affect the
reactivity of the comonomer Thus this indicates that a growing radical of macromonomer
with a shorter chain length (ie lower Mn ) attacks more frequently a monomer of the same
nature than it does a macromonomer with a longer length (ie higher Mn) as it can be noticed
from the results in Table 7
However the r2 values of the copolymerization with MMA as shown in Figure 13 give
unclear dependence on the side poly (13dioxolane) macromonomer chain length this may be
due to the resulting polydispersity of the copolymerization Mentioned behaviour may be
related with the reactive structure of comonomers vinyl in the case of Styrene or methacrylic
in the case of MMA in regard to the ending methacrylic double bond of macromonomers
besides the hydrophilic character of the macromonomers
86
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0015 plusmn 3 10-4 SP1
b
r2 = 0042 plusmn 6 10-4
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP15
c
r2= 012 plusmn 0006
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP2
Figure 12 Application of Jaacksrsquo treatment to the St-g-PDXL copolymerization systems
(a) SP1 (b) SP15 (c) SP2
87
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0018 plusmn 001 MP1
b
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 007 plusmn 002MP15
036788
c
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 002 plusmn 001 MP2
Figure 13 Application of Jaacksrsquo treatment to the MMA-PDXL copolymerization systems
(a) MP1 (b) MP15 (c) MP2
88
341 Glass Transition Temperatures
Thermal analysis of Styrene-g-PDXL copolymers allows to determine their glass transition
and melting temperatures In the first place the measurements were performed on a
conventional DSC from which the thermograms obtained show an overlapping of PS glass
temperature and PDXL melting point signals This has been observed for all samples A
different approach in the characterisation of these copolymers was by means of Modulated
Temperature Differential Scanning Calorimeter (MTDSC) which is an extension of
conventional DSC This approach combines high resolution with high sensitivity by use of a
sinusoidal temperature modulation superimposed on a constant temperature or linear
temperature program with a small underlying average heating rate172 173 In comparison to
conventional DSC the MTDSC analysis enables the simultaneous calculations of an
additional quantity the cyclic or modulus of heat capacity Cp (J g-1K-1 172)
ωT
HFp A
AC =
(61)
is the amplitude of the cyclic heat flow (Wg-1) and AWhere AHF Tω is the amplitude of cyclic
heating rate with AT the temperature modulation amplitude (K) ω the modulation angular
frequency (2πp) and p is the modulation period (s)172
In fact the MTDSC splits the overlapped signals into two distinct temperatures melting
temperature of the hydrophilic grafts and glass transition temperature of the hydrophobic
backbone as can be noticed in Figure 14 in which melting temperature appears to be 5626degC
which is closer to the glass transition temperature with a value of 5671degC From the results
obtained out of the thermogram it is clear that the measurements show very close values of
Tm and Tg for all copolymer samples where in conventional DSC these two temperatures
cannot be distinguished
172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
89
Figure 14 MTDSC thermogram of 5SP1 copolymer at heating rate of 2degCmin
Tg was taken at the midpoint of the transition region The results obtained are shown in
Tables 8 and 9 for copolymers with Styrene and MMA respectively Then a plot of the
copolymers Tg has been constructed against PDXL content in order to determine the effect of
the latter on Tgrsquos As it can be noticed in the Figure 15 Tg of the copolymers decreases
exponentially with increasing PDXL content and this may be due to the decrease in the
intermolecular interactions between the molecular chains and can be associated with higher
mobility and flexibility of the polymeric chains when PDXL is incorporated in the
copolymers The results clearly indicate that Tg values of the copolymers depend on the
composition of comonomers and a decrease with increasing PDXL content in the obtained
copolymers
90
Table 8Transition temperatures of Styrene-g-PDXL copolymers obtained by thermal
analysis (DSC) Sample PDXL content Tg wt () (degC) 8SP 85 7489 1
5SP 1424 5671 1
5SP 152 5590 15
21 6739 5SP 2
303 4480 3SP 2
34 2665 2SP15
4025 2SP 4060 2
Table 9Transition temperatures of MMA-g-PDXL copolymers obtained by thermal analysis
(DSC)
Sample PDXL content Tg
wt () (degC)
5MP 10 10545 1
5MP 13 8278 15
21 6576 3MP 2
22 7550 3MP 15
26 7013 2MP1
91
5 10 15 20 25 30 35 40 4520
30
40
50
60
70
80
a
SP COPOLYMERSTg
(degC)
PDXL content in wt()
10 15 20 2560
70
80
90
100
110
b
Tg (deg
C)
PDXL content in wt()
MP COPOLYMERS
Figure 15 Glass transition temperatures vs PDXL macromonomer content for copolymer
systems (a) Styrene-g-PDXL copolymers (b) MMA-g-PDXL copolymers
92
Conclusion
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers The macromonomer reactivity estimation suggests that the
length of the PDXL side chains does affect the reactivity of the methacrylic double bond of
the macromonomer when copolymerized with St However in the case of copolymerization
with MMA there is no dependence on the graft size Finally from DSC measurements the
values of Tg depend on the composition and the size of the PDXL grafts In all copolymers
the increase in amount of the incorporated PDXL macromonomer results in a substantial
decease in glass transition
93
References 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305 156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269 163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671 164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006)
5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219 169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620 172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly
(1 3 Dioxolane)) on Immiscible Polymer Blends
of Polystyrene and Poly (Ethylene Glycol)
41 Background
411 Physical Blends
Physical blending is defined as the simple mechanical mixing of two or more polymers either
in the melt or in solution174 At first glance this approach would seem to be ideal for
preparing hybrids as blending is considered a simple and economical procedure that is
commonly used to produce new products from existing materials175 However in polymer
science the effectiveness of blending is dependent upon the degree of compatibility of the
polymers involved176 At least three general types of materials can result from blending
depending on the mutual solubility and semi-crystallinity of the constituents
412 Equilibrium Phase Behavior
Mixing of two amorphous polymers can produce either a homogeneous mixture at the
molecular level or a heterogeneous phase-separated blend Demixing of polymer chains
produces two totally separated phases and hence leads to macrophase separation in polymer
blends Some specific types of organized structures may be formed in block copolymers due
to microphase separation of block chains within one block copolymer molecule
Two terms for blends are commonly used in literature miscible blend and compatible blend
The terminology recommended by Utracki177 will be used By the miscible polymer blend it
means a blend of two or more amorphous polymers homogeneous down to the molecular
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York (1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York (1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser Publishers Munich (1989)
95
level and fulfilling the thermodynamic conditions for a miscible multicomponent system An
immiscible polymer blend is the blend that does not comply with the thermodynamic
conditions of phase stability The term compatible polymer blend indicates a commercially
attractive polymer mixture that is visibly homogeneous frequently with improved physical
properties compared with the constituent polymers
Miscible blends occur spontaneously when the overall energy of mixing (ΔGmix) is negative
as defined by the Gibbs-Helmholtz free energy equation (Equation 62)
(62)
In the Gibbs-Helmholtz equation ΔHmix is the enthalpy of mixing and ΔSmix is the entropy of
mixing while T is the temperature of the blend Flory-Huggins178 and Scott179 have made
further correlation of enthalpy and entropy as a function of the polymer components and their
properties (Equation 63)
(63)
In Equation 63 χ is a measure of the polymer-polymer interaction energy V is the volume of
the system Φi is the volume fraction of polymer i R is the gas constant T is the temperature
of blending Vr is the reference volume of the monomers and χi is the degree of
polymerization
Examination of Equation 63 reveals that the entropy of mixing is highly dependent on the
molecular weight of the blended polymers while the enthalpy is much more dependent on the
level of interaction between the polymer types Additionally Scott showed that as molecular
weight increases to the level commonly found in commercially useful materials ΔS
approached zero (0) Therefore polymer blends of commercial importance are primarily
influenced by the rate of enthalpy However for polymers with weak interactions (as χ
approaches 1) eg as observed in most polymer pairs the enthalpy of mixing can be further
reduced according to Equation 64
178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279
96
(64)
In Equation 64 δi is the polymerrsquos solubility parameter (an estimation of its ability to be
dissolved in a range of solvents) derived from the square root of the cohesive energy density
pioneered by Hildebrand180 Thus most early work with polymer blends concentrated on
matching the solubility parameters of the component polymers
Unfortunately the theoretical maximum difference in solubility for a 5050 polymer blend is
only 01 (calcm3)12 This narrow margin is much smaller than the standard error among
methods used to determine solubility parameters181 The ability to predict miscibility of
polymer pairs with strong interactions such as donor-acceptor and hydrogen bonding which
can increase miscibility by creating an exothermic reaction upon mixing (ΔH lt0) have been
attempted for many years with varying degrees of success
The formation of miscible blends is dependent on several factors including molecular
structure average chain length tacticity of the polymers as well as the temperature of mixing
and the blending method If the blended polymers are miscible (ΔGmix lt 0) and thus
compatible the resulting material will display an amalgamation of properties which are
predictable using the same techniques as those used for random or statistical copolymers
Polymer blends account for a significant percentage of polymer production and are produced
either to reduce costs to aid in processing or to improve a variety of specific properties For
example polycarbonates have been blended with polybutylene terephthalates to increase
chemical resistance and to aid in processing while polyphenylene oxides are bended with
polystyrenes to improve toughness and increase glass transition temperatures182
413 Compatibilization
As it follows from thermodynamics the blends of immiscible polymers obtained by simple
mixing show a strong separation tendency leading to a coarse structure and low interfacial
180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999)
97
adhesion The final material then shows poor mechanical properties On the other hand the
immiscibility or limited miscibility of polymers enables formation of wide range structures
some of which if stabilized can impart excellent end-use properties to the final material To
obtain such a stabilized structure it is necessary to ensure proper phase dispersion by
decreasing interfacial tension to suppress phase separation and improve adhesion This can be
achieved by modification of the interface by the formation of bonds (physical or chemical)
between the polymers This procedure is known as compatibilization and the active
component creating the bonding as the compatibilizer174 177 183
The most popular method of compatibilization is by addition of a third component In most
cases such an additive is either a block or graft copolymer Since the key requirement is
miscibility it is not necessary for the copolymer to have identical chain segments as those of
the main polymers It suffices that the copolymer has segments having specific interactions
with the main polymeric components viz hydrogen bonding dipole-dipole dipole-ionic
Lewis acid-base etc
Addition of a block or graft copolymer reduces the interfacial tension and alters the molecular
structure at the interface Thus compatibilization by addition changes not only the interfacial
properties but it may affect the flow behavior (hence processability)
One of the disadvantages of the addition method is the tendency of the added copolymers to
form micelles These reduce the efficiency of the compatibilizer increase the blend viscosity
and may lessen the mechanical performance
414 Incorporation of Copolymers for Compatibilization
Block or graft copolymers with segments that are miscible with their respective polymer
components show a tendency to be localized at the interface between immiscible blend
phases Random copolymers sometimes also used as compatibilizers reduce interfacial
tension but their ability to stabilize the phase structure is limited184 Finer morphology and
higher adhesion of the blend lead to improved mechanical properties The morphology of the
resulting two-phase (multiphase) material and consequently its properties depend on a
number of factors such as copolymer architecture (type and molecular parameters of
segments) blend composition blending conditions
183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001)
98
In Scheme19 the conformation of different block graft or random copolymers at the
interface is schematically drawn
Scheme 19 Possible localization of A-B copolymer at the AB interface Schematic of
connecting chains at an interface a-diblock copolymers b-end-grafted chains c-triblock
copolymersdmultiply grafted chain and e-random copolymer
415 The Effect of Compatibilizer on a Blend
The presence of a compatibilizer at the interface substantially affects the development of the
phase structure of molten blends in the flow and quiescent state The position and width of the
concentration region related to co-continuous morphology are affected by two competing
mechanisms A decrease in interfacial tension caused by a compatibilizer favors the formation
and stability of co-continuous structures
The effect of a compatibilizer on fineness of the phase structure can be understood through its
effects on droplet breakup and coalescence A decrease in interfacial tension due to the
presence of a compatibilizer decreases the droplet radius R
Effect of the Compatibilizer Architecture
Compatibilization efficiency of various copolymers follows from their thermodynamic and
microrheological effects It has been generally accepted that the total molecular weight of the
copolymer molecular weight of its blocks and their number are the main structural
compatibilizer characteristics affecting the phase structure of the final blend
99
Effect of Compatibilizer Concentration
The compatibilizing efficiency of the copolymers is besides the architecture a function of
their concentration The effect of a compatibilizer concentration has been quantitatively
characterized by the emulsification curvemdashthe dependence of the average particle diameter of
the minor dispersed phase on copolymer concentration185 The particle diameter decreases
with increase of copolymer concentration until a constant value is obtained For most systems
this value is achieved if the copolymer amount is 15ndash25 of the dispersed phase
416 Methods of Blend Preparation
Five different methods are used for the preparation of polymer blends186 187 melt mixing
solution blending latex mixing partial block or graft copolymerization and preparation of
interpenetrating polymer networks It should be mentioned that due to high viscosity of
polymer melts one of these methods is required for size reduction of the components (to the
order of μm) even for miscible blends
bull Melt mixing is the most widespread method of polymer blend preparation in practice
The blend components are mixed in the molten state in extruders or batch mixers Advantages
of the method are well-defined components and universality of mixing devicesmdashthe same
extruders or batch mixers can be used for a wide range of polymer blends Disadvantages of
the method are high energy consumption and possible unfavorable chemical changes of blend
components This procedure has not been used so far in industrial practice because of large
energy consumption
bull Solution blending is frequently used for preparation of polymer blends on a laboratory
scale The blend components are dissolved in a common solvent and intensively stirred The
blend is separated by precipitation or evaporation of the solvent The phase structure formed
in the process is a function of blend composition interaction parameters of the blend
components type of the solvent and history of its separation Advantages of the process are
rapid mixing of the system without large energy consumption and the potential to avoid
185 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons Inc New York Chap 16 (2000) 186 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709 187 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458
100
unfavorable chemical reactions On the other hand the method is limited by the necessity to
find a common solvent for the blend components and in particular to remove huge amounts
of organic (frequently toxic) solvent Therefore in industry the method is used only for
preparation of thin membranes surface layers and paints
bull A blend with heterogeneities on the order of 10 μm can be prepared by mixing of
latexes without using organic solvents or large energy consumption Significant energy is
needed only for removing water and eventually achievement of finer dispersion by melt
mixing The whole energetic balance of the process is usually better than that for melt mixing
The necessity to have all components in latex form limits the use of the process Because this
is not the case for most synthetic polymers the application of the process in industrial practice
is limited
bull In partial block or graft copolymerization homopolymers are the primary product
But an amount of a copolymer sufficient for achieving good adhesion between immiscible
phases is formed188 In most cases materials with better properties are prepared by this
procedure than those formed by pure melt mixing of the corresponding homopolymers The
disadvantage of this process is the complicated and expensive start-up of the production in
comparison with other methods eg melt mixing
bull Another procedure for synthesis of polymer blends is by formation of interpenetrating
polymer networks A network of one polymer is swollen with the other monomer or
prepolymer after that the monomer or prepolymer is crosslinked189 In contrast to the
preceding methods used for thermoplastics and uncrosslinked elastomers blends of
reactoplastics are prepared by this method
188 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 189 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981)
101
42 Experimental
421 Materials
Polymers used in this research were PEG and PS PEG was purchased from MERCK
company General Purpose PS was obtained from ENPC TP1-Chlef Company Physical and
Structural characterizations of these materials were performed by SEC 1H-NMR and DSC
422 Blend Preparation
PSPEG blends of 5050 wt were prepared by solution casting from THF 40degC The
polymer solutions were stirred until complete miscibility and then cast onto glass dishes and
left to evaporate the solvent to the atmosphere To remove residual solvent after casting the
blends were dried in vacuum oven at 40degC for a weak Table 10 shows the quantities of the
copolymers used for compatibilization of the blends of PSPEG
Table 10 The quantities of the copolymers used for compatibilization of the blends of
PSPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
43 Characterization Techniques for Compatibilization
431 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
102
Relative viscosities of polymer solutions were calculated by dividing the flow times of
solutions by that of the pure solvent The data were plotted using the Huggins equation with
the intrinsic viscosity [η] (dlg-1) determined by extrapolation to infinite dilution
432 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
433 FTIR Analysis
FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
44 Results and Discussion Polyethylene glycol (PEG) is very interesting and important polymers PEG presents good
properties eg hydrophilicity solubility in water and in organic solvents nontoxicity and
absence of antigenicity and immunogenicity190It has attracted increasing attention due to its
potential applications as biomedical and environment friendly materials PEG has been
widely used as a modifier for biomedical surfaces to reduce the protein absorption and
improve their biocompatibility192 and as a stabilizer for emulsion and dispersion It has also
been used as a plasticizer for poly (lactide) (PLA) which is stiff and brittle as a
biodegradable packaging material193
On the other hand polystyrene shows excellent processability good appearance tensile
strength and thermal and electrical characteristics however its brittleness considerably limits
its use in high performance products
Both PS and PEG are widely used commodity polymers Detailed studies on their miscibility
may contribute to technological and environmental applications These polymers form an
interesting pair to study since they exhibit contrasting physical properties PS is a
190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689
103
hydrophobic polymer whereas PEG is hydrophilic PEG is a much softer material than PS
PSPEO blends have been reported as incompatible materials in the literature194 195
N Watanabe et al have reported compatibilization effect of poly (styrene-co-methacrylic
acid) on immiscible blends of this system196
441 Characterization of the Blend Components
Analysis by SEC provides number average-molecular weights and polydispersity indices of
all materials DSC measurements performed to determine their glass transition temperatures
as well as melting point and degree of crystallinity of PEG (See Figure16) 1HNMR spectroscopy analysis was performed on these polymers to determine essentially the
tacticity of PS and also to get information about end groups of PEG which was found to
possess an OH group at each end It has been also determined that the stereoregularity of PS
is Syndiotactic-Atactic (rather highly syndiotactic) (See Figures 17)
Physical characteristics of materials used are given in Table11
Table 11 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PS ENPC TP1-Chlef (from CHI MEI Corp)
105
128 000
1076
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam] Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842
104
Figure 16 1H-NMR spectrum of PEG (Merck) in CDCl3
105
Figure 17 1H-NMR spectrum of Commercial Styrene (ENPC TP1-Chlef) in CDCl3
442 Study of Compatibilization by Dilute Solution Viscometry
a) Introduction
Polymer blends are physical mixtures of structurally different polymers which interact
through secondary forces with no covalent bonding Blending of the polymers may result in a
reduction in the basic cost and improved processing and also may enable properties of
importance to be maximized The polymer blends often exhibit properties that are superior
compared to the properties of each individual component polymer197 198 199 200 The main
advantages of the blend systems are simplicity of preparation and ease of control of physical
properties by compositional change201 202 However the mechanical thermal rheological and
197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85
106
other properties of a polymer blend depend strongly on its state of miscibility on the
molecular scale203
There have been numerous techniques of studying the miscibility of the polymeric blend The
most useful techniques are dynamic mechanical thermal electron-microscopic IR
spectroscopic refractive index203 optical microsscopic204 and viscometric techniques 179 205
Because of its simplicity viscometry is an attractive and very useful method for studying the
compatibility of polymer blends Additional advantages ie that no sophisticated equipment
is necessary and that the crystallinity or the morphological states of the polymer blends do
affect the result206 make the viscometric method more convincing for characterizing polymer
mixtures The principle of using a dilute solution viscosimetry to measure the miscibility is
based on the fact that while in solution molecules of both component polymers may exist in
a molecularly dispersed state and undergo a mutual attraction or repulsion which will
influence the viscosity It is assumed that polymerndashpolymer interaction usually dominate over
polymerndashsolvent ones207 The presence of interactions between atoms or groups of atoms of
unlike polymers is essential to obtain a miscible polymer blend177 179
Estimation of the compatibility of different pairs of polymers based on dilute solution
viscosity for a ternary polymerpolymer-solvent system has been attempted by several
authors including Mikhailov and Zeilkman208 Bohmer and Florian209 Feldman and Rusu210
Krigbaum and Wall211 and Catsiff and Hewett212
The compatibilization of the blends in question has been characterized by viscosity technique
using the Krigbaum and Wall interaction parameter Δb The versatility of the viscometric
technique is not affected by the choice of the solvent as was shown by Kulshreshta et al213
In this section we discuss in details our investigation on the compatibilization of the two
polymer blend systems PSPEG and PMMAPEG 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191
107
b) Theoretical background
The main aspects of the application of dilute solution viscometry method for the study of
interactions and miscibility phenomena in dilute multicomponent polymer solutions were
described Only the most important features will be repeated here It is common to use
empirical relations such as Hugginsrsquo equation214
(65)
for the description of the concentration dependence of viscosity of polymer solutions This
relation is strictly valid only for binary polymer solutions However equations like that of
Krigbaum and Wall211
(66)
And of Catsiff and Hewett212
(67)
were proposed for ideal ternary polymer solutions of the polymer 1+ polymer 2+ solvent type
In previous relations ηsp denotes the specific viscosity [η] is the intrinsic viscosity (limiting
viscosity number) c stands for the mass concentration of polymer and kH is Hugginsrsquo
constant which may be related (in an empirical manner) to the thermodynamic quality of
solvent Relative mass fractions of dissolved polymers wi are used to describe the
composition dependence of viscosity in ternary systems Quantities b 12 and b12 are used to
define the ideal behavior of ternary polymer solutions These are calculated by
(68)
and
(69)
214 ML Huggins J Am Chem Soc 64 (1942) 116
108
respectively Here b denotes the slope of Hugginsrsquo equation for binary solutions
(70)
Moreover it has been shown215 that both the sign and the extent of the deviation of
experimental from theoretical b-values may be correlated to the interactions between
polymeric components of a system under consideration The quantities of interest (miscibility
criterion variables) are defined by
(71)
and
(72)
or can be written in another form
(73)
where m denotes the polymer mixtures Δb intermolecular interaction parameter between
polymer 1and 2 and is considered a good criterion to predict the polymer-polymer
compatibility209 216 217 Δb 0 indicates that the two polymers are compatible whereas
Δb0 indicates that they are incompatible
c) Discussion of the Results
Herein we discuss in detail the compatibilization of PSPEG blends with the synthesized graft
copolymers by viscometric technique The plot of reduced specific viscosity of polymers
versus total polymeric concentration yields a straight line and the intercept and slope
correspond to intrinsic viscosity [η] and molecular interaction coefficient b respectively The
viscosity data for the homopolymers and their blends are presented in Tables 12 and 13
Table 12 Interaction coefficient for binary solutions (polymersolvent) 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin (1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849
109
Polymer components PEG PS
b11 007327 minus
b22 minus 02117
b12 = (b11 b22)12 = 01245 (theo)
Table 13 Interactions parameters for PSPEG blends with poly (St-g-PDXL) copolymers
(2SP2 2SP1 and DXSP) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
DXSP b12 003511 01295 01680 01833 01947
Δb - 00894 00050 00435 00588 00702
2SP2 b12 003511 009826 01052 01314 01515
Δb - 00894 - 00262 - 00193 00069 00270
2SP1 b12 003511 minus minus minus 01262
Δb - 00894 minus minus minus 00017
For incompatible blends the incompatible molecules refuse to overlap thus they shrink in
size which leads to a decrease in hydrodynamic volumes As a matter of fact the crossover in
the reduced viscosity-concentration plot is observed
As far as we are concerned with the blend of PSPEG the results obtained present similar
situation Figure 18 shows the Huggins plots for the homopolymers and the (5050) blend of
PSPEG In this figure a crossover is observed and a decrease of slope occurs at about 05
gdl in the viscosity-concentration plot Above this concentration two incompatible polymers
PS and PEG undergo mutual repulsion in dilute solution the hydrodynamic volume of chains
is lower The reduction of the hydrodynamic volume will result in a decrease of the reduced
viscosity of solution correspondingly the slope of the plot suddenly declines
110
02 03 04 05 06 07 08 09 10 11
03
04
05
06
07
08PS PEG and PSPEG (5050)
PS PSPEG 0 PEG
Redu
ced
visc
osity
η sp
c
(ldl
)
C (dll)
Figure 18 Plots of reduced viscosity (ηspc) vs concentration for PS PEG and PSPEG
blend (0) in THF at 30degC
Figures 19 20 21 and 22 show the incorporation of various amounts of copolymers in the
immiscible blend As far as the amount of the compatibilizers increases the crossover of the
plots occurs at very low concentration or even it is not observed In addition the slope of the
plot increases with an increase of the amount of the compatibilizers introduced in the blend
This is due to the mutual attraction of the blend components which is enhanced by the
presence of the copolymers As a matter of fact the latter act as compatibilizing agents
allowing to the blends to exhibit miscibility
111
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07BLENDS WITH DXPS
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 19 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of DXPS copolymer
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLENDS WITH 2SP2
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 20 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of 2SP2 copolymer
112
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLEND WITH 2SP1 40
PSPEG 0 2SP1 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 21 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with 40 of the dispersed phase of 2SP1 copolymer
02 03 04 05 06 07 08 09 10 1100
01
02
03
04
05
06
07
08
DXPS 40 2SP2 40
2SP1 40
2SP1 40 2SP2 40 DXPS 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 22 comparison of plots of reduced viscosity (ηspc) vs concentration for PSPEG
blends in THF at 30degC with 40 of the dispersed phase of DXPS 2SPS2 and 2SP1
copolymer
113
Figure 22 compares the three copolymers used for compatibilization of PSPEG with respect
to 40 by weight of the dispersed phase addition to the blends
Krigbaum and Wall suggested that information about the interaction between two polymers
should be obtained from the difference of experimental b12 and theoretical b12 Δb A positive
difference between the experimental and theoretical interaction coefficients is evidence of a
compatible polymer pair The higher the value of Δb the higher the extent of compatibility
Negative values refer to repulsive interaction and incompatible mixes The values of Δb
according to equation 73 for different blends with compatibilizers are given in Table 13 and
Figure 23
0 10 20 30 40 5
-010
-005
000
005
010
0
PS PEG BLENDS
2SP2 DXPS
Δb
Amount of incorporated copolymer w ()
Figure 23 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (DXPS and 2SP2) used for compatibilization
It was observed as the amount of compatibilizers increases values of the interaction
parameter increase thereby increasing the compatibility between the two polymer
components of the blend Consequently this indicates that these copolymers act as
compatibilizing agents in the immiscible blends of PS and PEG Now in comparing these
copolymers in terms of structure (number of grafts) and PDXL content it can be noticed that
the results obtained DXPS ( 71 w of PDXL) copolymer show higher values of Δb than
2SP1(30 w of PDXL) and 2SPS2 (4025 w of PDXL) do This is due to the comb-
structure of the DXPS copolymer (synthesized by CRP) and therefore containing more grafts
114
(Ng = 58) than the other copolymers Besides the amount of PDXL in the copolymer PDXL
includes polar groups which provide associative interactions with one of the blend
components (PEG) and thus undergoes significant effects upon compatibilization In the
figure below it can be seen that addition of 10 by weight of the dispersed phase (47 of
total weight of the blend) of DXPS is sufficient to compatibilize the immiscible blend of
PSPEG (5050) Then a drastic increase of the interaction parameter with the addition of the
compatibilizer (DXPS) compared to the addition of either 2SP2 or 2SP1 (Table 13)
From the results shown in the graph miscibility of the blend can be achieved by incorporating
around 25 (11 of total weight of the blend) of 2SP2 copolymer However compatibibility
of the blend with 2SP1 copolymer is obtained at 40 by weight of the dispersed phase since
its interaction parameter (Δb) found to be 00017
It is worth to mention that the PDXL content of 2SP1 is 30 and the length of the grafts is
half that of 2SP2 copolymer For this reason these two copolymers have been chosen for the
purpose of comparison in terms of side chains length
An optimization of the amount of copolymer needed for compatibilization of PSPEG (5050)
blend has been made (corresponding to Δb = 0) as function of the PDXL content and shown
in Table 14
Table 14 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050) vs PDXL content
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
DXPS 0 9 43 71
2SP2 0 245 109 4025
2SP1 0 40 166 30
115
443 Optical Microscopy and Phase Morphology
PDXL is a perfect alternate copolymer of poly (ethylene oxide) (PEO) and poly (methylene
oxide) (PMO) that has the same curious combination properties as PEG So PDXL must be
at least miscible with PEG or adhere at the interface between PS and PEG and between
PMMA and PEG The compatibility between hydrophobic PS or PMMA and hydrophilic
PEG is very poor Compatibilization between components of the two sets of polymer blends is
studied by optical microscopy
The morphological characteristics of the blends by different compatibilizers are presented in
Figure 24 The optical microscopy micrographs of PSPEG blends without compatibilizers
show a poor dispersion for PS disperse phase and a ldquoball-and-socketrdquo topography due to the
poor interfacial adhesion between PEG matrix and the dispersed phase However with the
addition of compatibilizers the morphological characteristics of the polymer blends are
greatly altered It can be noticed that for these two different blends the particle size of PS
domains gets progressively much smaller and uniform in compatibilized blends than in
incompatibilized ones This may be explained by the significant increase of the phase
interfacial adhesion Consequently the domain size strongly depends upon the
compatibilizers used
116
a) PSPEG (5050) 0 (without compatibilizer)
DXPS 10 DXPS 20 DXPS 30 DXPS 40 b) Compatibilizing effect of DXPS copolymer
2SP2 10 2SP2 20 2SP2 30 2SP2 40 c) Compatibilizing effect of 2SP2 copolymer
2SP1 40
117
d) Compatibilizing effect of 2SP1copolymer at 40 addition
Figure 24 Optical micrographs showing phase structure in 5050 PSPEG blends
a) blends without compatibilizer b) with DXPS c) with 2SP2 d) with 40 of 2SP1
For instance the PSPEG blends with the incorporation of the copolymers DXPS 2SP2 and
2SP1 as compatibilizers (Figure 24) the morphology displays a very fine dispersion of PS
phase and strong interfacial adhesion with PEG Matrix The good compatibilizing effect
mainly that of DXPS can be explained by two mechanisms
First the PDXL units in the compatibilizer interact with PEG ether groups leading to a good
adhesion at interface between the components of the blend In addition hydrogen bonding
may also exist between PDXL and PEG further increasing compatibilization Second since
the compatibilizer also contains styrene blocks it contributes to provide a good compatibility
with PS Consequently the remarkable compatibilizing effect of PS-g-PDXL copolymers
induced a drastic decrease in interfacial tension and suppression of coalescence between the
originally immiscible polymer phases
As it can be noticed from the micrographs given in the figure above the compatibilizer
exhibits finer dispersion and homogeneous morphology of the blends as the amount of
compatibilizers increases
Eventually each compatibilizer has its own effect on the immiscible blends depending on the
amount of PDXL (side chains) and number of grafts present in the copolymers
By comparing micrographs shown in Figure 24 b and c the compatibilization effect of DXPS
copolymer which contains more grafts but shorter is different from that of the 2SP2
copolymer In the case of DXPS it is observed that the size of the dispersed droplets is
deceased significantly and results in finer dispersion morphology However 2SP2 copolymers
shows an improvement in compatibility of the blend after addition up to 30 wt of the
dispersed phase (13 total weight of the blend) exhibits homogeneous morphology This
may be related to length of the grafts In all cases these copolymers act as good
compatibilizers for the blend of 5050 wt PSPEG
444 FTIR Analysis
The FTIR technique is very important since it allows one to study the specific interactions
between the polymers The knowledge of the polymerndashpolymer interactions will be useful for
118
studies of the compatibility in polymer blends To verify the intermolecular interactions that
can play a role in miscibility the vibrational spectra of the blends studied in the present work
were obtained In polymeric systems where there are multiple interactions vibrational bands
such as ν (C=O) ν (COC) and ν (OH) present contributions of spectroscopic free and
associated forms
In order to elucidate the role played by intermolecular interactions in the miscibility of these
blends FTIR absorption of individual polymer components PS PEG and PMMA and
compared to that of the mixtures Figures 26 27 and 28 present the FTIR absorption spectra
from 4000 to 400 cm-1 for all samples
In the case of PS the high-frequency infrared spectra consist of seven absorption bands The
bands with peak locations at 3008 3026 3060 3082 and 3103 cm-1 are due to C-H stretching
of benzene ring CH groups on the PS side-chain The bands with peak positions of 2924 and
2850 cm-1 are due to the C-H stretching vibration of the CH2 and CH groups of the main PS
chain respectively PEG with molecule chemical structure of HO-[CH2-CH2-O]n-H exhibits
important absorption bands from FTIR spectroscopy measurements as shown in Figure 25 It
was verified contributions associated with CndashOndashC symmetric stretching of ether groups218-220
221 from 1050 to 1150 cm-1 with maximum peak at 1150 cm-1 Characteristics CH2-O
stretching modes from 2800-3000 cm-1 are observed214 At low frequency region peaks at 850
and 890 cm-1 are assigned to CndashOndashC stretching and at 500 cm-1 ascribed to CndashOndashC
deformation The presence of PDXL in the blends is detected by the intense frequency at 1140
cm-1 which is assigned for acetal groups In addition both PDXL and PEG contain ether
groups and the spectra show that the corresponding peaks are overlapped for the blends The
intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of PEG
crystallinity in the blends222
218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10 219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601
119
It can be observed also a typical large hydroxyl bands with two distinct contributions which
can be seen for all samples They are attributed to the spectroscopically free and bonded ndashOH
stretching forms at 3600-3800 cm-1 and 3200-3500 cm-1 respectively221 - 227
500 1000 1500 2000 2500 3000 3500 4000-05
00
05
10
15
20
25
30
35
PS and PEG PEG PS
Abs
orba
nce
Wave number (cm-1)
Figure 25 FTIR spectra of PS PEG over 4000-400 cm-1 range
227 Peppas NA Wright L Macromolecules 1996298798ndash804
120
500 1000 1500 2000 2500 3000 3500 4000
0
1DXPS IN PSPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 26 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS)
All these absorption bands for individual polymer were observed in the FTIR spectrum of the
5050 (ww) PSPEG in which they were combined to give superimposed bands in the regions
of 750-1500 cm-1 and 2700- 3100 cm-1
The hydroxyl vibrational frequency is discernible in the blend spectrum for PSPEG at 0
With the incorporation of the copolymers for compatibilization a number of bands showed
small shifts and changes in position and shape in the resulting spectra In Figures 28 29 and
30 as it can be noticed that in the hydroxyl absorption region a decrease in the fraction of
free OH groups is observed as the amount of copolymers is increased in the blend This can
be due to the flexibility of the PDXL graft chains on the other hand to the acetal and ether
groups of PDXL which are probably randomly distributed among an increasing number of
hydroxyl groups of PEG statistically favoring the formation of the PDXL and PEG hydrogen
bond interaction The results indicate that the intermolecular hydrogen bonding between the
ether oxygen of PDXL and the hydroxyl groups of PEG may be formed thereby reducing the
fraction of free OH which is consistent with the shifts observed in the region of hydroxyl
stretching Intermolecular hydrogen bondings are expected to occur among PDXL and PEG
chains due the high hydrophilic forces These interactions have replaced the intramolecular
121
interactions between COC and OH groups of PEG before addition of containing PDXL
copolymers It can be noticed a progressive shift of hydroxyl band from 3340 to 3420 cm-1
with DXPS and from 3340 to 3350 cm-1 when 2SP2 is added This shift can be attributed to
the decrease of intramolecular interactions among hydroxyl groups within PEG chains in
favor to intermolecular interactions between PDXL and PEG228
500 1000 1500 2000 2500 3000 3500 4000
0
1
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 27 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2)
228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
122
3200 3300 3400 3500 3600 3700 3800
00
01
DXPS IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 28 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS) in the hydroxyl absorption region
3200 3300 3400 3500 3600 3700 3800
00
02
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 29 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2) in the hydroxyl absorption region
123
3200 3300 3400 3500 3600 3700 3800
00
DXPS 40 2SP2 40 2SP1 40
Abs
orba
nce
Wave number (cm-1)
Figure 30 FTIR spectra comparison of PSPEG blends (5050) with different compatibilizers
in the hydroxyl absorption region
Conclusions An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends Again The PS blocks of the copolymer result in good
compatibility with PS component of the blends The compatibilization of PSPEG blends is
apparently associated with hydrogen bonding where groups of the acetal units in PDXL
interact with hydroxyl groups of PEG These form a stronger interface between the two
phases which leads to important modifications of the blend properties Apparently the FTIR
result is in good agreement with the miscibility criteria proposed by Krigbaum and Wall (Δb)
interaction parameter which results from dilute-solution viscometry (DSV) method It can be
concluded that by the addition of 20ndash40 wt of incorporated copolymer reveal a good
compatibilizing efficiency for the blend systems as it was observed from micrographs as well
124
References
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York
(1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York
(1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser
Publishers Munich (1989) 178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279 180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999) 183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001) 185 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709
125
186 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and
Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458 187 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 188 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981) 189 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons
Inc New York Chap 16 (2000) 190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689 194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam]
Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842 197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191 214 ML Huggins J Am Chem Soc 64 (1942) 116 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin
(1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849 218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10
126
219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601 227 Peppas NA Wright L Macromolecules 1996298798ndash804 228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
127
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g-
Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of
Polystyrene and Poly (Ethylene Glycol)
51 Introduction
PMMA is more than just plastics of paint Often lubricating oils and hydraulic fluids tend to
get really viscous and even gummy when they get cold This is a real pain when operating
heavy equipments in very cold weather When a little bit of PMMA is dissolved in these oils
and fluids they donrsquot get viscous in the cold and machines can be operated down to -100degC
PMMA can find a several applications namely adhesive optical coating medical packaging
applications and so forthhellip
In medical applications PMMA and its derivatives are used particularly for hard tissue repair
and regeneration229 PMMA beads have been developed to deliver aminoglucoside antibiotics
locally for the treatment of bone infections230 PMMA and PEG form an important and unique
pair of polymers in that they are chemically different In the present work this study may
shed light on the PMMA properties modifications induced by blending with PEG to overcome
the difficult processing of rigid PMMA
Several studies have been made on blends of poly (ethylene oxide) PEO and PMMA in the
last decades but very few on PMMAPEG blends231 232 233
Numerous works reported that the miscibility domain ranges between 10 and 30 of PEO by
weight depending on the PMMA tacticity or molecular weight No phase diagram is available
yet in the literature for PMMAPEO and neither it is for PMMAPEG234
229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703
127
52 Experimental
521 Materials
PEG and PMMA were used as blend components PMMA was obtained from ENPC TP1-
Chlef Company PEG was purchased from MERCK Company Physical and Structural
characterizations of these materials were performed by SEC 1H-NMR and DSC
522 Blend Preparation
Blends of PMMAPEG (5050) were prepared using the same procedure as described for the
blends discussed in the previous chapter Table 15 shows the quantities of the copolymers
used for compatibilization of the blends of PMMAPEG
Table 15 The quantities of the copolymers used for compatibilization of the blends of
PMMAPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
53 Characterization Techniques
531 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
532 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
128
533 FTIR FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
54 Results and Discussion
541 Characterization of the Homopolymers
The polymers have been analyzed by SEC to determine their number average-molecular
weights and polydispersity indices DSC measurements performed to determine their glass
transition temperatures as well as melting point of crystallinity of PEG 1HNMR spectroscopy analysis revealed the tacticity of PMMA It has been found that PMMA
is Syndiotactic-Atactic (highly syndiotactic) as shown in Figure 3 and 321
Physical characteristics of materials used are given in Table 16
Table 16 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PMMA ENPC TP1-Chlef (fromLG MMA Corp)
119
55 000
113
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
129
Figure 31 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in CDCl3
Figure 32 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in the methyl shifts
region in CDCl3
130
542 Dilute Solution Viscometry
Dilute solution viscometry has been utilized to evaluate miscibility of PMMAPEG blends
and the same approach discussed in the previous section has been followed The
experimental reduced viscosities of the polyblends are plotted against concentration in dilute
solution viscometry Eventually plots of pure polymers and polyblends of 5050 PMMAPEG
are first obtained Then their interaction coefficients are determined as shown in Table 17
Table 17 Interaction coefficient for binary solutions (polymersolvent)
Blend components PEG PMMA
b11 007327 minus
b22 minus 006561
b12 = (b11 b22)12 = 006933 (theo)
The compatibility of this system has been evaluated through the sign of Δb The values of the
latter according to equation 73 for different amounts of poly (MMA-g-PDXL) copolymers in
the blends are given in Table 18 It is observed that the blend of PMMAPEG at 5050 by
weight shows a negative value of Krigbaum and Wall parameter which indicates
incompatibility of the system as it is expected Similarly to PSPEG blend a crossover in the
reduced viscosity-concentration plot is observed and a decrease of slope arises in the range of
05 to 066 gdl in the viscosity-concentration plot as shown in Figure 33 This is attributed to
the repulsive intermolecular interactions between the polymer chains
Then the incorporation of the copolymers at various amounts presents positive values
progressively Curves of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in
THF at 30degC with various amounts of copolymer are given in Figures 34 35 and 36
131
Table 18 Interactions parameters for PMMAPEG blends with poly (MMA-g-PDXL)
copolymers (3MP2 2MP2 and 3MP1) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
3MP2 b12 00288 01308 01904 02373 02602
Δb - 004053 00615 01211 01680 01909
2MP2 b12 00288 01286 01690 01893 02296
Δb - 004053 00593 00997 01200 01603
3MP1 b12 00288 00868 01670 02010 02379
Δb - 004053 00175 00977 01317 01686
00 01 02 03 04 05 06 07 08 09 10 11020
025
030
035
040PMMAPEG (5050) 0
PEG PMMAPEG 0 PMMARe
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 33 Plots of reduced viscosity (ηspc) vs concentration for PMMA PEG and
PMMAPEG blend (0) in THF at 30degC
132
02 03 04 05 06 07 08 09 10 11000
005
010
015
020
025
030
035
040 BLENDS WITH 3MP1
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 34 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP1 copolymer
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040
045BLENDS WITH 3MP2
PMMAPEG 0 10 20 30 40
Redu
ced
visc
osity
η
spc
(d
lg)
C (gdl)
Figure 35 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP2 copolymer
133
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040BLENDS WITH 2MP2
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 36 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 2MP2 copolymer
From our viscosity data as the copolymer content increases in the blend the polymer blend
molecules will become disentangled more spaciously resulting in a greater interaction
between structurally similar component segments This suggests that there are attractive
forces that induce miscible behavior of the blends as it is observed in Figure 37
0 10 20 30 40 5-01
00
01
02
0
PMMA PEG BLENDS
3MP2 2MP2 3MP1
Δb
Amount of incorporated copolymer w ()
Figure 37 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (3MP2 2MP2 and 3MP1) used for compatibilization
134
The three copolymers (3MP2 2MP2 and 3MP1) involved in this study for compatibilization
are different from the point of view of the PDXL content and the graft length For instance
3MP2 and 2MP2 have similar and longer grafts since the theoretical number average-
molecular weight of the graft is 2000 gmol However they contain different amount of
PDXL In the case of 3MP1 this graft copolymer has a structure with shorter side chain length
(Mn = 1000 gmol) corresponding to the half of the graft size in the former copolymers From
the observations made out of the figure above 3MP2 copolymer (21 w of PDXL) provides
higher values of the interaction parameter and therefore greater extent of compatibility
compared to the other copolymers since it has long grafts which allows penetration into the
other phase
It can be concluded that all three copolymers show good results for compatibilization on the
basis of the Δb criterion of polymer-polymer miscibility determined by viscometry
Similarly the minimum amount of copolymer needed for compatibilization of PSPEG
(5050) blend has been determined corresponding to Δb = 0 as function of the PDXL content
and shown in Table 19
Table 19 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050)
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
2MP2 0 34 16 35
3MP2 0 37 18 21
3MP1 0 58 28 19
135
543 Optical Microscopy and Phase Morphology
a) PMMAPEG (5050) 0 (without compatibilizer)
b) Compatibilizing effect of 2MP2 copolymer
c) Compatibilizing effect of 3MP2 copolymer
d) Compatibilizing effect of 3MP1copolymer
Figure 38 Optical micrographs showing phase structure in 5050 PMMAPEG blends
a) blends without compatibilizer b) with 2MP2 c) with 3MP2 d) with 3MP1
136
Figure 38 presents microscopy images of PMMAPEG blends with varying amounts of
compatibilizers The morphological characteristics of the blends of PMMAPEG without
compatibilizers show a poor dispersion of PMMA as a dispersed phase The addition of
compatibilizers changes drastically the morphological topology of this system The
compatibilizers used are of different length of the side chains and also different PDXL
content By introducing progressively variable amounts of the compatibilizers they display
similarly the morphological characteristics to some extent It is observed that the phase
separated domains of PMMA in the blends are reduced with increasing amounts of the
compatibilizers This is due to the compatibility of PMMA of the copolymers with the
PMMA blend component and on the other hand to the interfacial interactions of the PDXL
of the copolymers and PEG component of the blends From these results it is revealed that
compatibilizing effect of 2MP2 copolymer on this system is great compared to the others Not
only causes the size of the dispersed droplets to decrease but also dispersed droplets become
homogeneous However 3MP1 copolymer which contains shortest grafts (about half length
of those of the other copolymers) and less amount of PDXL shows less reduction in the
droplet size compared to the other copolymers Therefore it can be concluded that the
compatibilization of this blend depends upon length and number of grafts
On the overall observations these compatibilizing copolymers are very effective and hence
influence and improve the compatibility of PMMAPEG blend at a composition of 5050 wt
544 FTIR Analysis
Same observations can be made for the blends of PEG with PMMA The FTIR spectrum of
this blend at 0 compatibilizer is shown in Figure 39 For pure PMMA the
spectroscopically free carbonyl group band is observed at 1730 cm-1 In the blend sample one
large vibrational band due to hydroxyl group stretches in pure PEG is observed with two
distinct contributions which can be seen for all samples They are attributed to the
spectroscopically free and associated hydroxyl forms at 3495 and 3600 cm-1 respectively
A large band in the wave number range of 1400-1500 cm-1 is assigned to the deformation
vibration of the methyl groups The bands with peaks locations at 2820 and 2990 cm-1 are due
to C-H symmetrical and asymmetrical stretching vibration of CH3 respectively Peaks at
2886 and 2950 cm-1are ascribed to C-H symmetrical and asymmetrical stretching vibration of
CH2 figures 40 and 41 The C-O band is observed in the range of 1150- 1210 cm-1
137
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 PMMAPEG 0 Blend
Abs
orba
nce
Wave number cm-1
Figure 39 FTIR spectra of PMMAPEG 0 over 4000-400 cm-1 range
2750 2800 2850 2900 2950 3000 3050 3100-05
00
05
10
15
20
Abs
orba
nce
PEG PMMAPEG 0
Wave number cm-1
Figure 40 FTIR spectra of PMMAPEG 0 and PEG over the 3100-2700 cm-1 range
138
2750 2800 2850 2900 2950 3000 3050 3100
00
05
10
152MP2 in PMMAPEG
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 41 FTIR spectra of PMMAPEG 0 blends with 2MP2 addition over the 3100-2700
cm-1 range
The incorporation of PMMA-g-PDXL copolymers in the blends makes some changes in the
resulting spectra as it can be noticed in Figures 42 - 44 In the hydroxyl absorption region
same phenomenon has occurred as in the PSPEG blends The fraction of free OH groups has
decreased as the amount of the copolymers increased as shown in figures 45 and 46 which
present the effect of different compatibilizers in the hydroxyl absorption region This can be
explained as discussed above by the fact that the PEG hydroxyl groups undergo other
intermolecular interactions essentially with PDXL chains of the copolymers A comparison of
the effect of the three copolymers involved in the compatibilization at the highest amount
added is given in figure 47 It can be noticed that 2MP2 shows very few fraction of free OH
groups compared to the others This copolymer contains more PDXL (35 wt with 4 grafts)
than the others do (21 wt with 3 grafts and 19 wt with 3 grafts in 3MP2 and 3MP1
respectively)
A crystalline PEG phase is confirmed by the presence of the triplet peak of the COC
stretching vibration at 1148 1110 and 1062 cm-1 with a maximum at 1110 cm-1235 236
Changes in the intensity shape and position of the COC stretching mode are associated with
235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115
139
the interaction between PEG and PMMA-g-PDXL In addition both polymers contain the
same ether group and the spectra show that the corresponding peaks are overlapped for the
blends The intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of
PEG crystallinity in the blends237
Therefore the presence of this interacting system is probably responsible for the miscibility
and low degree of crystallinity observed for these blends
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
202MP2 in PMMAPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 42 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (2MP2)
237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
140
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 43 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2)
500 1000 1500 2000 2500 3000 3500 4000
0
1
2 3MP1 IN PMMAPEG BLENDS 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 44 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1)
141
3500
00
05
3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 45 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2) in the hydroxyl absorption region
3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
-02
00
02
04
06
08
3MP1 IN PMMAPEG 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 46 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1) in the hydroxyl absorption region
142
3500
2MP2 40 3MP2 40 3MP1 40
Abs
orba
nce
Wave number cm-1
Figure 47 FTIR spectra comparison of PMMAPEG blends (5050) with different
compatibilizers in the hydroxyl absorption region
The results from FTIR spectra indicate the compatibility of these polymer blends with the
addition of the PDXL copolymers via hydrogen bonds is observed and confirmed mainly by
the shifts of bands of the hydroxyl stretching modes
143
Conclusions
From the observations made out from this study reveal that all three copolymers show good
results for compatibilization on the basis of the Δb criterion of polymer-polymer miscibility
determined by viscometry Therefore these copolymers act as good compatibilizers since it
was found that the minimum amount needed for compatibilizing is between 1 to 3 of the
total weight of the blend which corresponds to 3 to 6 of the dispersed phase This
compatibilization is due to the fact that the copolymers have constituents which present strong
interactions with both polymer components of the blends These results are in great agreement
with microscopy analyses which demonstrate that the phase separated domains of PMMA in
the blends are reduced with increasing amounts of the compatibilizers This is due to the
compatibility of PMMA of the copolymers with the PMMA blend component and on the
other hand to the interfacial interactions of the PDXL of the copolymers and PEG component
of the blends
From FTIR results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PMMA and relatively long PMMA backbone of PMMA-g-PDXL copolymers respectively
These compatibilizing copolymers are very effective and hence influence and improve the
compatibility of PMMAPEG blend at a composition of 5050 wt
144
References 229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703 235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115 237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
145
CONCLUSIONS
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel using an unsaturated alcohol (2-
HPMA) as a transfer agent results in linear polymeric chains in order to prevent formation of
cyclic oligomers through cationic polymerisation of cyclic acetals They were all prepared at
the same reaction conditions
The characterization of these macromonomers has been conducted using different methods of
analysis Structure and molecular weight determination were provided from SEC and Raman
and 1H-NMR spectroscopy
We were interested in obtaining a hydrogel based on fully PDXL segments and study its
swelling and viscoelastic behaviour The hydrogel has combined special properties The
results reveal a perfect elastic and resistant hydrogel with interesting viscoelastic properties
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers Structure composition and number of grafts of the
copolymers were determined by SEC and 1H-NMR spectroscopy Another approach for
copolymerization has been made in order to compare the copolymers obtained from different
types of polymerization reactions like Conventional Free Radical and Controlled Radical
Polymerizations In the latter the copolymer obtained possesses larger number of grafts than
those from the former
The macromonomer reactivity estimation suggests that the length of the PDXL side chains
does affect the reactivity of the methacrylic double bond of the macromonomer when
copolymerized with St However in the case of copolymerization with MMA there is no
dependence on the graft size Finally from DSC measurements the values of Tg depend on
the composition and the size of the PDXL grafts In all copolymers the increase in amount of
the incorporated PDXL macromonomer results in a substantial decease in glass transition
An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
146
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends
The compatibilization effect of the copolymers used in this study on the PSPEG and
PMMAPEG was demonstrated from the viscometric results The contribution of both PS or
PMMA and PDXL of the copolymers has played a big role in the compatibilization of these
two different systems of blends thereby resulting in good compatibility due the chemical
affinity between these components which leads to a drastic decrease in interfacial tension and
suppression coalescence between the blend constituents
It has been shown that the immiscible blends in question exhibit compatibility when small
amount of copolymers synthesized for this purpose are added except for one of them
Styrene-g-PDXL copolymers act as good compatibilizers for PSPEG blends since it was
found that the minimum amount needed for compatibilizing is less than 11 of the total
weight of the blend which corresponds to 25 of the dispersed phase This compatibilization
is due to the fact that the copolymers have constituents which present strong interactions with
both polymer components of the blends
Compared with PS-g-PDXL with DXPS content the DXPS is more effective binary polymer
blends compatibilizer in the PSPEG blends which is due to the high number of grafts and
high PDXL content This has led to good adhesion of PDXL chains with the PEG phase in the
blends Again The PS blocks of the copolymer result in good compatibility with PS
component of the blends The compatibilization of PSPEG blends is apparently associated
with hydrogen bonding where groups of the acetal units in PDXL interact with hydroxyl
groups of PEG These form a stronger interface between the two phases which leads to
important modifications of the blend properties
Similarly PMMA-g-PDXL copolymers act as good compatibilizers since it was found that
the minimum amount needed for compatibilizing is between 1 to 3 of the total weight of
the blend which corresponds to 3 to 6 of the dispersed phase This compatibilization is due
to the fact that the copolymers have constituents which present strong interactions with both
polymer components of the blends
These results are in great agreement with microscopy analyses which demonstrate that the
phase separated domains of PMMA and PS in their respective blends are reduced with
increasing amounts of the compatibilizers
147
Specific interactions between chemical groups of two blend components can play an
important role in polymer mixtures There is a range of such interactions of varying strengths
which has been identified in polymer blends and such interactions are generally defined for
small molecules It should be noted that the extension of this concept to polymers is not
always straightforward it is more difficult to identify interactions in polymers the
spectroscopy is more complex and molecular conformations are less certain This situation is
further complicated because researchers use different names and definitions to describe
similar interactions
FTIR investigation showed that these interactions have been observed through the changes in
IR absorption peaks of PS PEG and PMMA upon mixing with increasing amount of
compatibilizers in their blends which have given rise to a wide investigation
From these the results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PSPEG and PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PS or PMMA and relatively long PS or PMMA backbone of PS-g-PDXL and PMMA-g-
PDXL copolymers respectively
148
414 Incorporation of Copolymers for Compatibilization helliphelliphellip 98
415 The Effect of Compatibilizer on a Blend helliphelliphelliphelliphelliphelliphelliphellip 99
416 Methods of Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 100
42 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
421 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
422 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 102
43 Characterization Techniques for Compatibilization helliphelliphelliphelliphelliphelliphelliphellip 102
431 Dilute Solution Viscometric Measurements helliphelliphelliphelliphelliphelliphellip 102
432 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
433 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
44 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 103
441 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphellip 104
442 Study of Compatibilization by Dilute Solution Viscometry hellip 106
443 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 116
444 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 118
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 124
References helliphelliphelliphelliphelliphellip helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 125
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g- Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of Polystyrene and Poly (Ethylene Glycol)
51 Introduction helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 127
52 Experimental helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
521 Materials helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
522 Blend Preparation helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
53 Characterization Techniques helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
531 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
532 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
533 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
54 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
541 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphelliphellip 129
542 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 131
543 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 136
544 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 137
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 144
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 145 CONCLUSIONS helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 146
SUMMARY
Research and development performed on synthetic polymers during the last century has led to
many classes of different polymers for specific applications New types of synthetic polymers
with tailor-made properties are still being introduced for new applications The challenge for
polymer chemists is to control and alter the polymerization conditions such that the final
product has a well-defined structure with desired properties The complex structure of
polymers requires continued analytical chemical efforts to understand the polymerisation
process and the relationships between the molecular structure and material properties
The central point of this thesis is the synthesis and the exploration of the benefits of graft
copolymers derived from poly (1 3 dioxolane) (PDXL) as compatibilizing agents via their
incorporation in immiscible polymer blends The enhancement of adhesion in the solid state
can be accomplished by introducing a compatibilizer that can act as an adhesive between two
polymers andor by control of morphology especially by inducing the phase co-continuity
Graft copolymers offer all Properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheological control i e it
leads to decreased melt viscosities which is an important advantage for processing Depending
on the nature of their backbone and side chains they can be used for a wide variety of
applications such as impact-resistant plastics thermoplastic elastomers polymeric
emulsifiers and even more exciting is the ability of these graft copolymers to function as
compatibilizersinterfacial agents to blends immiscible polymers
The state-of-the-art technique to synthesize graft copolymers is the copolymerization of
macromonomers with low molecular weight comonomers It allows the control of the
polymeric structure which is given by three parameters (i) chains length of the side chains
which can be controlled by the synthesis of macromonomers by living polymerization (ii)
chain length of the backbone which can be controlled in a living polymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular-weight monomer
i
New properties lower prices and reuse of polymers are needed to meet demands of todayrsquos
society and hence of the polymer industry Unfortunately the demands for many applications
need a set of properties that no polymers can fulfil One method to satisfy these demands is by
mixing two or more polymers Materials made from two polymers mixed are called blends In
recent years blending of polymers as a means of combining the useful properties of different
materials to meet new market applications with minimum development cost offers an
interesting route to improve a variety of specific properties of the thermoplastics This has
been increasingly used by the polymer industry
Much work has been done on the blending (mixing) of polymers by many authors A large
part of these studies deal with attempts to obtain a combination of properties of different
polymers Unfortunately these properties of the polymer blends are usually worse instead of
better for many combinations of polymers Significance for these properties is compatibility
between the different polymers which is frequently defined as miscibility on a molecular scale
of the blends components The incorporation of a dispersed phase into a matrix mostly leads
to the presence of stress concentrations and weak interfaces arising from poor mechanical
coupling between phases and therefore morphologies with coarseness commonly on
micrometer scale are obtained Improving mechanical and morphological properties of an
immiscible blend is often done by compatibilization which is a process of modification of the
interfacial properties in immiscible polymer blend resulting in reduction of the interfacial
tension coefficient formation and stabilisation of the desired morphology The use of graft or
block copolymers as compatibilizers for immiscible polymer blends has become an efficient
means for development of new high-performance polymer materials There have been
numerous techniques of studying the miscibility of the polymeric blends The most useful
techniques are viscosimetry measurementsiiiiii thermal analysisiv dynamic mechanical
analysisv refractive indexvi nuclear magnetic resonance methodvii scanning electronviii and
optical spectroscopyix
i Z Sun W Wang and Z Fung Eur Polym J 28 (1992) 1259 ii Aroguz AZ and Baysal BM Eur Polym J42 3 (2006) 11ndash5iii Zhang Y Qian J Ke Z Zhu X Bi H and Nie K Eur Polym J 38 (2002) 333ndash7 iv M Song and F Long Eur Polym J 27 (1991) 983 v Olabisi O Rebeson LM and Shaw MT Polymerndashpolymer miscibility New York Academic Press (1979) vi AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 vii EG Crispim ITA Schuquel AF Rubira and EC Muniz Polymer 41 (3) (2000) 933 viii Martin IG Roleister KH Rosenau R and Koningsveld RJ Polym Sci Part B Polym Phys24 (1986) 723 ix W Wu X Luo D Ma Eur Polym J 35 (1999) 985
ii
Well-known examples of commercial blends are high impact polystyrene (HIPS) and
acrylonitrile-butadiene-styrene (ABS) These blends are tough and have good processability
One of the most interesting examples of an amorphous polymer is polystyrene because of its
brittleness Adding a compatibilizer with the structure of a copolymer to
Polystyrenepolyethylene (PSPE) improves the toughness by a factor 3x Another example is
the use of poly (styrene-co-methacrylic acid) as a compatibilizer in immiscible (incompatible)
blends of PS and polyethylene (PEG)xi
It is of great interest to study miscibility and phase behaviour of two different commodity
immiscible polymer blend systems as PSPEG and polymethyl methacrylate polyethylene
glycol (PMMAPEG) by adding poly (styrene-g-PDXL) and poly (methyl methacrylate-
PDXL) copolymers as compatibilizers respectively Firstly these systems consist of a very
rigid amorphous component (styrene andor PMMA) and a very flexible low-melting point
PEG The extremely high difference of glass transition temperatures (Tg) between the
components motivates us to investigate the phase behaviour of the blends via
compatibilization with prepared grafted copolymers
The first part of the thesis is devoted to the synthesis and characterization of amphiphilic graft
copolymers which were prepared in solution by radical polymerization of hydrophilic poly (1
3 dioxolane) macromonomers as side chains and hydrophobic comonomers such as styrene
and methyl methacrylate as backbone The second part of the thesis describes the blends
preparation and the study of the compatibilization effect of the incorporated amphiphilic graft
copolymers on immiscible (incompatible) blends
The research work in this thesis is presented through several chapters described as follows
Chapter I is a bibliographic survey on polymerization reactions involved in the thesis
Literature concerning the poly (1 3 dioxolane) was included
Chapter II describes the synthesis of poly (1 3 dioxolane) macromonomers and their
characterization As an aside research poly (1 3 dioxolane) network was obtained and the
x E Kroeze thesisUniversity of Groningen (1997) xi Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polym Journal 37 (2001) 1837-1842
iii
swelling and rheological behaviours of this network were discussed and included in this
chapter
Chapter III deals with the synthesis of a series of amphiphilic graft copolymers based on
polystyrene and methyl methacrylate as backbone with poly (1 3 dioxolane) macromonomers
as grafts in this study Selection of proper reaction conditions in terms of overall monomer
concentration and monomer molar ratio were investigated in order to prevent crosslinking
reactions due to the presence of bis-functional poly (1 3 dioxolane) macromonomers
The structure and composition of the graft copolymers were determined by Size Exclusion
Chromatography (SEC) technique and Proton Nuclear Magnetic Resonance (1H-NMR)
analysis Also Modulated Temperature Differential Scanning Calorimeter (MTDSC) was used
for thermal analysis to study the influence of poly (1 3 dioxolane) content on the glass
transition temperature of the copolymers
Last but not the least Chapter IV and Chapter V deal with the most important part of the
thesis which is the study of the compatibilization effect of the prepared copolymers
incorporated in two different immiscible blend systems These two chapters describe first
the polymers used as blend components and also polyblends preparation was discussed The
phase behavior and compatibilization of these polyblends were studied at a composition
of 5050 for both PSPEG and PMMAPEG systems Various amounts of copolymers were
incorporated to the so-called blends for compatibilization The techniques used for this study
were optical microscopy (OM) to analyze their morphology and Fourier-Transform Infra-Red
(FTIR) spectroscopy used to detect the intermolecular interactions in the blends In addition
viscometric method which is a simple inexpensive and sensitive analytical technique and also
alternative to other methods was used The application of the dilute-solution viscosity (DSV)
method for the study of interactions and miscibility of the polymeric system has been
described in more details in these chapters
Conclusions have been made on copolymer characterizations in terms of mostly monomer
reactivity and indeed on compatibilizing effect of these copolymers on the selected polymer
blends This study provides interesting results which can be useful for the development
nanoporous materials
iv
REacuteSUMEacute
La recherche et le deacuteveloppement faits sur des polymegraveres syntheacutetiques pendant le dernier siegravecle
ont abouti agrave plusieurs types de polymegraveres pour des applications speacutecifiques Les nouveaux
polymegraveres syntheacutetiques avec des proprieacuteteacutes faites sur mesure sont toujours introduits pour de
nouvelles applications Le deacutefi pour les chimistes en polymegraveres est de controcircler et drsquoalteacuterer les
conditions de polymeacuterisation de telle sorte que le produit final ait une structure bien deacutefinie avec
des proprieacuteteacutes souhaiteacutees La structure complexe de polymegraveres exige des efforts continus en
chimie analytique pour comprendre le processus de polymeacuterisation et les relations entre la
structure moleacuteculaire et les proprieacuteteacutes des mateacuteriaux
Le centre drsquointeacuterecirct de cette thegravese est la synthegravese et lexploration des avantages des copolymegraveres
greffeacutes deacuteriveacutes agrave partir du poly (1 3 dioxolane) (PDXL) utiliseacutes comme agents compatibilisant
via leur incorporation dans des meacutelanges de polymegraveres non miscibles Lrsquoameacutelioration drsquoadheacutesion
agrave lrsquoeacutetat solide peut ecirctre accomplie en introduisant un compatibilisant qui peut agir comme un
adheacutesif entre deux polymegraveres et ou par le controcircle de la morphologie particuliegraverement en
incitant la co-continuiteacute des phases Les copolymegraveres greffeacutes offrent toutes les proprieacuteteacutes des
copolymegraveres en blocs mais sont toujours plus facile agrave syntheacutetiser De plus la structure ramifieacutee
offre des possibiliteacutes importantes dans le controcircle rheacuteologique cest-agrave-dire elle aide la
diminution de la viscositeacute qui est un avantage important pour la transformation Selon la nature
de la chaicircne principale et des chaicircnes lateacuterales ces copolymegraveres peuvent ecirctre employeacutes pour une
grande varieacuteteacute drsquoapplications comme plastiques reacutesistants au choc elastomers thermoplastiques
des polymegraveres eacutemulsifiants et mecircme plus inteacuteressant est la possibiliteacute de ces copolymegraveres greffeacutes
de fonctionner comme compatibilisant agents drsquointerface aux meacutelanges des polymegraveres non
miscibles
La technique la plus sophistiqueacutee pour syntheacutetiser les copolymegraveres greffeacutes est la
copolymeacuterisation de macromonomegraveres avec des comonomegraveres agrave faible masse moleacuteculaire Elle
permet le controcircle de la structure polymeacuterique par trois paramegravetres (i) la longueur des chaicircnes
lateacuterales qui peut ecirctre controcircleacutee par la synthegravese de macromonomegraveres par la polymeacuterisation
v
vivante (ii) la longueur de chaicircne principale qui peut ecirctre controcircleacutee dans une polymeacuterisation
vivante (iii) espacement moyen des chaicircnes lateacuterales qui est deacutetermineacute par le rapport molaire des
comonomegraveres et taux de reacuteactiviteacute du monomegravere agrave faible masse moleacuteculaire
De nouvelles proprieacuteteacutes des prix bas et la reacuteutilisation de polymegraveres sont neacutecessaires pour
reacutepondre aux demandes de la socieacuteteacute daujourdhui et agrave lindustrie de polymegraveres
Malheureusement ces demandes pour un grand nombre drsquoapplications ont besoin dun jeu de
proprieacuteteacutes quaucun polymegravere ne peut accomplir Une meacutethode de satisfaire ces demandes est en
meacutelangeant deux polymegraveres ou plus Les mateacuteriaux obtenus agrave partir de meacutelanges de deux
polymegraveres meacutelangeacutes sont appeleacutes meacutelanges (Blends) Ces derniegraveres anneacutees le meacutelange de
polymegraveres comme moyen de combiner les proprieacuteteacutes utiles de diffeacuterents mateacuteriaux pour
rencontrer un marcheacute de nouvelles applications agrave un coucirct minimal offre un itineacuteraire inteacuteressant
pour ameacuteliorer une varieacuteteacute des proprieacuteteacutes speacutecifiques des polymegraveres thermoplastiques Cela a eacuteteacute
de plus en plus employeacute par lindustrie des polymegraveres
Beaucoup de travaux ont eacuteteacute faits par plusieurs auteurs sur le meacutelange de polymegraveres Une grande
partie de ces eacutetudes sont dirigeacutees pour obtenir une combinaison des proprieacuteteacutes de diffeacuterents
polymegraveres Malheureusement ces proprieacuteteacutes des meacutelanges de polymegravere sont souvent plus
mauvaises que preacutevues pour la plupart des combinaisons de polymegraveres La signification de ces
proprieacuteteacutes est la compatibiliteacute entre les diffeacuterents polymegraveres qui est freacutequemment deacutefinie comme
la miscibiliteacute agrave lrsquoeacutechelle moleacuteculaire des composants du meacutelange Lincorporation dune phase
disperseacutee dans une matrice provoque surtout la preacutesence de contraintes et des interfaces faibles
qui reacutesultent du faible meacutelange meacutecanique entre les deux phases Lameacutelioration des proprieacuteteacutes
meacutecaniques et morphologiques dun meacutelange non miscible est souvent faite par compatibilisation
qui est un processus de modification des proprieacuteteacutes superficielle dans les meacutelanges de polymegraveres
non miscibles aboutissant agrave la reacuteduction du coefficient de tension superficielle la formation et
stabiliteacute de la morphologie deacutesireacutee Lutilisation des copolymegraveres greffeacutes ou agrave blocs comme
compatibilisant pour des meacutelanges de polymegraveres non miscibles est devenue un moyen efficace
pour le deacuteveloppement de nouveaux mateacuteriaux plus performant Il y a eu de nombreuses
techniques pour lrsquoeacutetude de la miscibiliteacute des meacutelanges polymeacuteriques Les techniques les plus
vi
utiles sont les mesures viscomeacutetriques analyses thermiques analyses meacutecaniques indice de
reacutefraction la reacutesonance magneacutetique nucleacuteaire microscopes optique et eacutelectroniques agrave balayage
Les exemples de meacutelanges commerciaux tregraves bien connus sont le polystyregravene choc (HIPS) et
acrylonitrile-butadiene-styrene (ABS) Ces meacutelanges sont durs et ont bon processability Un
exemple de polymegraveres amorphes le plus inteacuteressant est le polystyregravene agrave cause de sa fragiliteacute
Laddition dun compatibilisant ayant la structure dun copolymegravere au meacutelange de Polystyregravene
polyeacutethylegravene (PSPE) ameacuteliore la dureteacute par un facteur de 3 Un autre exemple est lutilisation du
poly (styrene-co-acide meacutethacrylique) comme compatibilisant dans les meacutelanges non miscibles
de PS et le poly (eacutethylegravene glycol)
Il est tregraves important drsquoeacutetudier la miscibiliteacute et le comportement des phases de deux diffeacuterents
meacutelanges de polymegraveres commerciaux non miscibles (incompatibles) comme le
polystyregravenepolyeacutethylegravene glycol (PSPEG) et le polymeacutethacrylate de meacutethylepolyeacutethylegravene glycol
(PMMAPEG) en incorporant des copolymegraveres tels que (styrene-g-PDXL) et de (meacutethacrylate de
meacutethyle-PDXL) comme compatibilisant respectivement Premiegraverement lrsquoun des composants de
ces systegravemes est amorphe et tregraves rigide (le styregravene etou PMMA) et lrsquoautre (PEG) est flexible et
mou ayant un point de fusion tregraves faible Vu lrsquoextrecircme eacutecart entre les deux tempeacuteratures de
transition vitreuse (Tg) des composants de ces meacutelanges cela nous a motiveacute pour eacutetudier le
comportement de ces meacutelanges via compatibilisation avec des copolymegraveres greffeacutes preacutepareacutes par
nous mecircme
La premiegravere partie de la thegravese est consacreacute agrave la synthegravese et agrave la caracteacuterisation de copolymegraveres
greffeacutes amphiphiles preacutepareacutes en solution par la polymeacuterisation radicale des macromonomers
(poly (1 3 dioxolane)) hydrophiles comme des chaicircnes lateacuterales (greffons) avec des
comonomegraveres hydrophobes comme le styregravene et le meacutethyle methacrylate comme chaicircne
principale La deuxiegraveme partie de la thegravese couvre la preacuteparation des meacutelanges et leacutetude de leffet
de compatibilisant des copolymegraveres greffeacutes amphiphiles sur les meacutelanges non miscibles
(incompatibles)
La recherche concernant cette thegravese est preacutesenteacute par plusieurs chapitres deacutecrits comme suit
vii
Le chapitre I est une recherche bibliographique sur les reacuteactions de polymeacuterisations impliqueacutees
dans la thegravese La Litteacuterature concernant le poly (1 3 dioxolane) est inclue
Le chapitre II deacutecrit la synthegravese des macromonomegraveres du poly (1 3 dioxolane) et leurs
caracteacuterisations Une recherche suppleacutementaire a eacuteteacute effectueacutee concernant la synthegravese drsquoun reacuteseau
tridimensionnel du poly (1 3 dioxolane) Une eacutetude sur les comportements gonflant et
rheacuteologique de ce reacuteseau ont eacuteteacute discuteacutes et inclus dans ce chapitre
Le chapitre III preacutesente la synthegravese dune seacuterie de copolymegraveres greffeacutes amphiphiles constitueacutes de
polystyregravene ou methacrylate de meacutethyle comme chaicircne principale et de macromonomers du poly
(1 3 dioxolane) comme greffons dans cette eacutetude Le choix de conditions de reacuteaction approprieacutees
en termes de concentration totale et le rapport molaire des monomegraveres ont eacuteteacute bien eacutetudieacutes pour
empecirccher les reacuteactions de reacuteticulation agrave cause de la preacutesence de macromonomegraveres bis-
fonctionnel de poly (1 3 dioxolane)
La structure et la composition des copolymegraveres greffeacutes ont eacuteteacute deacutetermineacutees par la technique de la
Chromatographie dExclusion steacuterique (CES) et la spectroscopie en Reacutesonance Magneacutetique
Nucleacuteaire de Proton (1H-NMR) Aussi la Calorimeacutetrie Diffeacuterentielle agrave balayage agrave Temperature
Moduleacutee Calorimeacutetrie (MTDSC) a eacuteteacute employeacute pour lanalyse thermique et pour eacutetudier
linfluence de la proportion du poly (1 3 dioxolane) dans les copolymegraveres sur leur tempeacuterature
de transition vitreuse
Derniers mais pas le moindre les deux Chapitre IV et le Chapitre V couvrent la partie la plus
importante de la thegravese qui est leacutetude de leffet de compatibilisant de ces copolymegraveres preacutepareacutes et
incorporeacutes dans deux diffeacuterents systegravemes de meacutelanges non miscibles (incompatibles) Ces deux
chapitres deacutecrivent dabord les polymegraveres employeacutes comme composants des meacutelanges agrave eacutetudier et
aussi la preacuteparation de ces meacutelanges a eacuteteacute deacutecrite Le comportement de phase et la
compatibilisation des meacutelanges de PSPEG et PMMAPEG agrave une composition de 5050 Des
quantiteacutes diffeacuterentes de copolymegraveres ont eacuteteacute incorporeacutees aux meacutelanges Les techniques
employeacutees pour cette eacutetude sont la microscopie optique (OM) pour analyser leur morphologie et
la spectroscopie agrave Transformeacutee de Fourier Infrarouge (FTIR) pour deacutetecter les interactions
viii
intermoleacuteculaires dans les meacutelanges De plus la meacutethode viscomeacutetrique qui est une technique
simple peu coucircteuse et tregraves sensible a eacuteteacute employeacutee Lrsquoutilisation de la meacutethode de la viscositeacute de
solution dilueacutee (DSV) pour leacutetude dinteractions et la miscibiliteacute du systegraveme polymegravere a eacuteteacute
deacutecrite plus en deacutetail dans ces chapitres
Les conclusions ont eacuteteacute faites sur la caracteacuterisation des copolymegraveres en termes de surtout de la
reacuteactiviteacute des monomegraveres et bien entendu sur leffet compatibilisant de ces copolymegraveres sur les
meacutelanges de polymegraveres qui ont choisis Cette eacutetude fournit des reacutesultats inteacuteressants qui peuvent
ecirctre utiles pour le deacuteveloppement des mateacuteriaux nanoporeux
ix
CHAPTER I Literature Review
11 Macromonomer Interest and Synthesis
Macromonomers bearing polymerizable end groups have received considerable interest
during the last two decades and become a useful tool for the preparation of a variety of graft
copolymers with well-defined structure and composition and polymer networks The
macromonomer method for preparing graft copolymers consists of preparing branches first
followed by the preparation of the grafted structure through the addition of the comonomer to
the macromonomer branch1 2
Therefore macromonomers become the side chains in the graft copolymer with well-defined
length and molecular weight As a sequence the molecular structure of the copolymer can be
determined depending on the amount of macromonomer incorporated and the reactivity of the
end groups
Macromonomers which are linear macromolecules carrying polymerizable functions at one or
two chain ends have been prepared by all polymerization mechanisms anionic cationic free-
radical polyaddition and polycondensation while the polymerizable end groups have been
introduced during the initiation termination or chain transfer steps or by modification of end
groups of telechelic oligomers3
Among the polymerization mechanisms mentioned above the ionic ones allow the best
control of molecular weight polydispersity and functionality of the macromonomers
However they require very demanding experimental conditions like high purity of monomers
and solvents complete absence of moisture and other acidic impurities inert atmosphere etc
Whereas free-radical methods which involve less severe working conditions are largely
used even though the control over the properties of the macromonomers is lower3 For
instance polymers of epoxides tetrahydofuran and cyclic siloxanes are commercially
produced by cationic ring-opening polymerization The history of ring-opening
polymerization of cyclic monomers is shorter than that of the vinyl polymerization and
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422
1
polycondensation With ring-opening functional groups can be introduced into the main chain
of the polymer This polymer cannot be prepared by vinyl polymerization4
Milkovich first developed synthesis of graft polymer with uniform grafts via macromonomer
technique5 Schulz and Milkovich6 reported the synthesis of polystyrene macromonmers
through termination of living PS anions with methacryloyl chloride and their
copolymerization with butyl acrylate and ethyl acrylate
Candau Rempp et al7 obtained PS-g-PEO by reaction between living monofunctional PEO
and partly chloromethacrylated PS backbone (scheme 1) Characterization of the products by
light scattering GPC UV and NMR spectroscopy showed a high degree of grafting
Scheme 1
Ito et al8 used a macromonomer technique to obtain graft copolymers with uniform side
chains They synthesized a graft copolymer of PS with uniform PEO side chains through
copolymerization of styrene and PEO macromonomer (scheme 2) They obtained PEO
macromonomers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-
vinyl benzyl chloride as terminating agent An apparent decrease in reactivities of both poly
(ethylene oxide) of macromonomers and comonomers was ascribed to the thermodynamic
repulsion between the macromonomer and the backbone9
4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348
2
Scheme 2
This type graft copolymers of styrene and ethylene oxide was also obtained by Xie et al10
through copolymerization of styrene with PEO macromonomer prepared by anionic
polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydofuran as
initiator followed by termination with methacryloyl chloride
The method of macromonomer synthesis developed by Xie et al11 has the advantage of
shorter reaction time and a larger range of molecular weight of the PEO macromonomer than
the usual method using potassium alcoholate as initiator PEO macromonomers with
molecular weight from 2 103 to 3 104 and MwMn = 107 ndash 112 can be obtained by this
method12
Only Xie and coworkers have published reports concerning the synthesis of copolymers with
uniform PS grafts obtained through copolymerization of epoxy ether terminated polystyrene
macromonomer with EO13 using a quaternary catalyst composed of triisobutyl-aluminium-
phosphoric acid-water-tertiary amine14 and epichlorohydrin (ECH)15
Free radical polymerization technique has also provided well-defined macromonomers of
poly (acrylic acid)16 vinyl benzyl-terminated polystyrene17 18 poly (t-butyl methacrylate)19
and poly (vinyl acetate)20
Recently Matyjaszewski et al21 employed atom-transfer radical polymerization (ATRP) to
prepare well-defined vinyl acetate terminated PS macromonomers Taking advantage of the
10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp (1985) 461 Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823
3
extremely low reactivity of polystyryl radical towards the vinyl acetate double bond they
used vinyl chloroacetate to initiate the polymerization of styrene to produce the desired
macromonomers This concept has been used similarly in the preparation of a vinyl acetate-
terminated PS macromonomers3 by conventional free-radical polymerization by employing
vinyl iodoacetate as a chain transfer agent possessing a double bond which does not
copolymerize with the monomer that forms the backbone of the macromonomer
12 Ring-Opening Polymerization Overview
Ring-opening polymerization (ROP) is a unique polymerization process in which a cyclic
monomer is opened to generate a linear polymer It is fundamentally different from a
condensation polymerization in that there is no small molecule by-product during the
polymerization Polymers with a wide variety of functional groups can be produced by ring-
opening polymerizations Ring-opening polymerization can proceed through a number of
different mechanisms depending on the type of monomer and catalyst involved Of the wide
range of polymers produced via ROP some have gained industrial significance for example
poly (caprolactam) and poly (ethylene oxide)22 ROP of cyclic esters such as ε-caprolactone
(CL) and L L-dilactide is gaining industrial interest due to their degradability23 The
mechanisms of interest in this work are coordination insertion and cationic
121 Polymerizability of Cyclic Compounds
The thermodynamic polymerizability of a cyclic monomer has been elegantly summarized by
Ivin24 Negative free energy change from monomer to polymer is the thermodynamic driving
force for the ring-opening
ΔG = ΔH ndash T ΔS
For small sized cyclic compounds the enthalpy term is negative and dominant The strains in
bond angles and bond lengths are released upon ring opening Such monomers can be almost
completely converted to polymers For medium sized cyclic monomers (5-7 membered rings)
the ring strain is small and the entropy is a small positive term Thus the overall driving force
(ΔG) is small and the extent of polymerization is little or no reaction For 8- 9- and 10-
22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991)
4
membered monomers the enthalpy term is dominant and negative while the TΔS term is
relatively small The strain is due to the non-bonded interactions between atoms Essentially
complete conversion to polymer is possible When the ring size is very large and there is
virtually no ring-strain (ΔH ne 0) the driving force for ring-opening polymerization is the
large increase of entropy The polymerization should be an athermal process
Why not make polyethylene
In principle one could synthesize polyethylene from cyclohexane
There are two good reasons why this reaction cannot be performed
bull (Kinetic) Cyclohexane lacks any reactive functionality to get hold of
bull (Thermodynamic) Simple six membered rings are extremely stable
Free Energy (ΔG) of Polymerization for Cycloalkanes
The thermodynamic considerations for ring opening are illustrated by this graph (scheme 3) of
free energy (hypothetical) of polymerization from cycloalkanes with various ring sizes to
polyethylene (The two membered ring actually shows the data for ethylene CH2 = CH2)
Scheme 3
5
Three and four membered rings are quite strained so ring opening to polyethylene is
favorable if a suitable reaction pathway existed (Unfortunately no such reaction is known)
Six membered rings are stable so they can rarely be polymerized by ring opening Five and
seven membered rings are borderline cases so sometimes these can be polymerized Larger
rings have transanular steric interactions that cause some strain so rings of 8 members or
more can usually be polymerized Of course this graph changes when substitutions are made
to the rings (for example the presence of heteroatoms like O S and N or the introduction of
double bonds) However the graph for the simplest possible rings illustrates the trends in
other systems reasonably well
Even if the ring opening reaction is thermodynamically favorable there must be reaction
chemistry to get there In most cases the initiators used for ring opening polymerization are
polar or ionic species so the monomers must have groups that can react The most common
monomers for ring opening polymerization contain some kind of heteroatom in the ring as in
the examples of cyclic ethers esters amines amides etc At one extreme there are examples
such as the cyclic phosphazene shown that contain no carbon or hydrogen at all At the other
extreme just a carbon-carbon double bond will suffice for ring opening metathesis
polymerization as illustrated by norbornene
122 Mechanisms of Ring-opening Polymerization
In addition to the thermodynamic criterion there must be a kinetic pathway for the ring to
open and undergo the polymerization reaction Therefore the kinetics of the ring-opening of
the monomer should also be considered Ring-opening polymerization (ROP) can proceed
through a number of different mechanisms depending on the type of monomer and catalyst
involved Of the wide range of polymers produced via ROP some have gained industrial
significance for example poly (caprolactam) and poly (ethylene oxide)24 25 A variety of
mechanisms operate for ring-opening polymerizations including anionic cationic metathesis
and free radical mechanisms Examples of various ring-opening polymerizations are shown in
scheme 4
25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984)
6
Scheme 4
123 Cationic Ring-Opening Polymerization of Heterocycles
A broad range of heterocyclic compounds can undergo cationic ring-opening polymerization
(CROP)26 CROP propagates either through an activated monomer or an activated chain end
mechanism In both cases the propagation involves the formation of a positively charged
species27 A major drawback of CROP is the occurrence of unwanted side reactions thus
limiting the molecular weight of the final product2829 The cationic ring-opening
polymerization of heterocycles has become of significant importance in polymer synthesis
due in part to the diverse variety of functionalized materials that can be prepared by this
method including natural andor biodegradable polymers30 31
Systematic studies of this type of polymerization started around the nineteen sixties Since
then several groups are involved in the kinetics reaction mechanisms and thermodynamics of
the ring-opening polymerization mostly of tetrahydofuran and dioxolane During the last
26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996) (b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993) (c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice (d) Mishra M K Ed Polymer Frontiers New York (1994) 391 31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159
7
years many papers on the synthesis and polymerization of several other cyclic ethers
monocyclic and bicyclic acetals have been published32 33
Examples of commercially important polymers which are synthesized via ring-opening
polymerization are summarized in scheme 5 include such common polymers as
polyoxyethylene (POE 4) poly (butylene oxide) (PBO 5) nylon 6 (6) and poly
(ethyleneimine) (7)
Scheme 5
The synthesis of ring-opened heterocycles is often mediated by compounds whose role is to
initiate the polymerization process This provides less opportunity to ldquotunerdquo polyheterocycle
properties through catalyst choice and has stimulated research to develop initiators which
function beyond the simple activation of polymerization such as living polymerization
initiators343536 chiral initiators3738 enzyme initiators39 and ring-opening insertion
systems4041 The cationic ring-opening polymerization involves the formation of a positively
32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N Macromolecules 26 (1993) 7134
8
charged species which is subsequently attacked by a monomer The attack results in a ring-
opening of the positively charged species Ethylene oxide can be polymerized by cationic
initiators as well (scheme 6)
Scheme 6
13 Cationic Polymerization of Cyclic Acetals
Acetal polymers also known as polyoxymethylene (POM) or polyacetal are formaldehyde-
based thermoplastics that have been commercially available for over 40 years
Polyformaldehyde is a thermally unstable material that decomposes on heating to yield
formaldehyde gas Two methods of stabilizing polyformaldehyde for use as an engineering
polymer were developed and introduced by DuPont in 1959 and Celanese in 1962
DuPonts route for polyacetal yields a homopolymer through the condensation reaction of
polyformaldehyde and acetic acid (or acetic anhydride)
The Celanese route for the production of polyacetal yields a more stable copolymer product
via the reaction of trioxane a cyclic trimer of formaldehyde and a cyclic ether (eg ethylene
oxide or 13 dioxolane)
9
The improved thermal and chemical stability of the copolymer versus the homopolymer is a
result of randomly distributed oxyethylene groups These groups offer stability to oxidative
thermal acidic and alkaline attack The raw copolymer is hydrolyzed to an oxyethylene end
cap to provide thermally stable polyacetal copolymer Polyacetals are subject to oxidative and
acidic degradation which leads to molecular weight deterioration Once the chain of the
homopolymer is ruptured by such an attack the exposed polyformaldehyde ends decompose
to formaldehyde and acetic acid Deterioration in the copolymer ceases however when one
of the randomly distributed oxyethylene linkages is reached42
Cationic polymerization of cyclic acetals exhibits some special features which makes this
system distinctly different from cationic polymerization of simple heterocyclic monomers for
instance cyclic ethers Linear acetals (including polyacetals) are more basic (nucleophilic)
than cyclic ones thus when polymer starts to form it does not constitute a neutral component
of the system but participates effectively in transacetalization reactions which lead to
redistribution of molecular weights and formation of a cyclic fraction These processes which
are usually described by the term ldquoscramblingrdquo have been studied by several authors43 44
Cationic polymerizations of heterocyclic monomers are initiated as in cationic
polymerization of vinylic monomers by electrophilic agents such as the protonic acids (HCl
H2SO4 HClO4 etc) Lewis acids which are electron acceptors by definition and compounds
capable of generating carbonium ions can also initiate polymerization Examples of Lewis
acids are AlCl3 SnCl4 BF3 TiCl4 AgClO4 and I2 Lewis acid initiators required a co-
initiator such as H2O or an organic halogen compound Initiation by Lewis acids either
requires or proceeds faster in the presence of either a proton donor (protogen) such as water
alcohol and organic acids or a cation donor (cationogen) such as t-butyl chloride or
triphenylmethyl fluoride
The polymerization of a heterocyclic monomer initiated by a protonic acid usually starts with
opening of the monomer ring via oxonium sites that are formed upon alkylation (or
protonation) of the monomer
42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144
10
Protonation
BF3 H2O H BF3 OH+ +O
O
Acylation
R CO SbF6 +
OR CO O SbF6
Alkylation
Et3O BF4 +
OC2H5 Et2O BF4O +
Hydrogen transfer
C SbF6 +O
C SbF6H O+
SbF6
O + O O+ H O SbF6
In general initiation step can be shown as
A+
R O++R A O
The mechanism of chain growth involves nucleophilic attack of the oxygen of an incoming
monomer onto a carbon atom in α-position with respect to the oxonium site whereby the
cycle opens and the site is reformed on the attacking unit
A+O
O(CH2)4
O
A+O(CH2)4
Growing chain terminates with nucleophilic species as shown below
O (CH2)4 O+[ ]n
A O (CH2)4[ ]n
AO ( CH2 )4
11
Triflic initiators like trifluoromethane sulfonic acid derivatives can also be employed as an
initiator in the cationic polymerization of heterocyclics in this case initiation step follows
alkylation mechanism
CF3 SO3CH3 +O
CH3 CF3SO3O
CH3 O
CF3SO3
+ O CH3O(CH2)4 O CF3SO3
Ion pairs are in equilibrium with the ester form
(CH2)4 O CF3SO3 (CH2)4 O(CH2)4 O SO2CF3
If instead of ester triflic anhydride is used as initiator the same reaction can occur at both
chain ends and anhydride behaves as a bifunctional initiator
CF3SO2OSO2CF3 nO
+ CF3SO2 O (CH2)4 O (CH2)4 O SO2CF3n-1
(CH2)4 O (CH2)4 n-3
O O CF3SO3 CF3SO3
In the case of living cationic polymerization the growing sites are long living provided the
reaction medium does not contain any transfer agents such as alcohols ethers amines or
acids The reaction mechanism then involves only initiation and propagation steps and the
polymers formed are living The active sites are deactivated by addition of an adequate
nucleophile such as excess water tertiary amines alkoxides phenolates or lithium bromide
12
O(CH2)4
SbF6
(CH2)4 O(CH2)4 OH H
NR3
++ H2O
SbF6
+(CH2)4 O(CH2)4 NR3 SbF6
ONa+(CH2)4 O(CH2)4 O + NaSbF6
+ LiBr
(CH2)4 O(CH2)4 Br LiSbF6+
However facts concerning the real mechanism are scarce In order to progress further in
understanding the cationic polymerization of heterocycles initiated with a Bronsted acid
kinetic studies of simple ring-opening reactions of heterocyclic monomer rings by acids in
nonpolar aprotic and nonbasic solvents (inert solvents) have been performed45
14 Synthesis of Functionalized Poly (1 3-Dioxolane)
1 3-Dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer ends ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The molecular weight of the linear polymers is governed by the
ratio of reacted monomer to transfer agent and is generally well controlled up to 10 000gmol
141 Reaction of 1 3-Dioxolane and Hydroxyl- Containing Compounds
Classical initiation induces polymerization through cyclic tertiary oxonium ions which are
responsible for the formation of an important quantity of cyclic oligomers48
45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon Press 3(1989) 787
13
In several preceding articles Franta et al have investigated the cationic polymerization of
cyclic acetals in the presence of a diol49 50 in particular polymerization of 13-dioxolane
(DXL) and 13-dioxepane (DXP) in the presence of an oligoether diol (αω-dihydroxy-poly
(tetrahydofuran)) or (αω-dihydroxy-poly(ethylene oxide)) In all cases a similar behavior was
observed Cyclic oligomers are present in quantities as in the case of polymerization of DXL
in the absence of hydroxyl containing compounds51
When substituted oxiranes such as propylene oxide or epichlorohydrin are polymerized
according to the ldquoActivated Monomerrdquo mechanism (AM) Cyclic oligomers can be
eliminated52 53 In the AM mechanism polymerization of ethylene oxide however the
reaction of a protonated monomer molecule with a polymer chain leads to side reactions
including cyclization by the Active Chain End (ACE) mechanism53 Thus it is not
unexpected that in the polymerization of cyclic acetals due to the higher nucleophilicity of
the linear acetals located on the chain reactions with the latter will take place
The addition of a protonated DXL onto a hydroxyl group-containing compound is
accompanied by transacetalization involving a monomer molecule
In order to shed some light on the reactions involved Franta et al54 used a monoalcohol
methanol instead of a diol The results confirmed the occurrence of the Active Monomer
mechanism but dimethoxymethane was observed evidence of transacetalization between
methanol and dioxolane
Thus in the DXL-ethylene glycol (EG) system the presence of unreacted EG is in fact due to
the following equilibria
This equation shows the stoichiometry of the reaction rather than its actual mechanism the
reaction certainly has to involve an addition product as a first step
49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154
14
In the next step transacetalization occurs
The products of transacetalization are formed fast as compared to the addition product54 This
indicates that the last reaction is not slower and probably faster than the previous one
Consequently it has been found that although polymerization of DXL in the presence of
hydroxyl group containing compounds proceeds initially by a stepwise addition of protonated
monomer to the hydroxyl terminated linear species in agreement with the AM mechanism but
already at this stage fast transacetalization proceeds leading to formation of O-CH2-O links
between two oligodiols and liberation of ethylene glycol
The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism When DXL is polymerized by strong protonic acids such as triflic acid in the
presence of a diol the PDXL chains are essentially linear and carry end-standing OH
functions Despite the occurrence of some side reactions this mechanism leads to α ω-
dihydroxy-PDXL the molecular weight of which is controlled by the molar ratio of DXL
consumed to diol introduced It has been shown that the polydispersity is on the order of 14
and that molar masses up to 10 000 gmol can be covered
142 Synthesis of Poly (1 3-Dioxolane) Macromonomers
Macromonomers are useful intermediates to prepare graft copolymers and have indeed been
used extensively In order to prepare PDXL macromonomers Franta and al54 have used p-
isopropenylbenzylic alcohol (IPA) as an initiator and triflic acid as a catalyst
The following polymeric species were identified
15
Scheme 7
A is the most abundant compound it corresponds to 50 to 60 weight-wise It is a
macromonomer
B corresponds to 20 to 25 weight-wise It carries two p-isopropenyl functions
C corresponds to 20 to 25 weight-wise It carries no p-isopropenyl function but two
hydroxyl groups
As a result preparation of PDXL macromonomers leads to the preparation of PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of transacetalization
reaction described above a mixture of products was obtained54
Kruumlger et al55 used similar method to prepare macromonomers and come out to the same
conclusions in terms of structure and claim that a clear distinction should be made between
the products obtained and the mechanism responsible for their formation
15 Amphiphilic Graft Copolymers
151 Graft Copolymers
The increasing complexity of polymer applications has required the production of materials
with varied properties Often homopolymers do not afford the scope of attributes necessary to
many applications Copolymerization allows the formulation of polymer materials with
properties characteristic of two homopolymers contained in a single copolymer material The
monomers within a copolymer can be distributed in various fashions random statistical
alternating segmented block or graft56
55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387
16
Scheme 8
Graft copolymers are similar to block copolymers in that they possess long sequences of
monomer units However graft copolymer architecture differs substantially from typical
block copolymers In graft copolymers monomer sequences are grafted or attached to points
along a main polymer chain Grafted chains generally possess molecular weights less than
that of the main chain
These side chains have constitutional or configurational features that differ from those in the
main chain57
The simplest case of a graft copolymer can be represented by A-graft-B or the arrangement
and the corresponding name is polyA-graft-polyB where the monomer named first (A in this
case) is that which supplied the backbone (main chain) units while that named second (B) is
in the side chain(s)
Typical syntheses of the grafts occur by polymerization initiated at some reactive point along
the backbone or by copolymerization of a macromonomer Polymerization from the polymer
backbone is possible via anionic cationic and radical techniques but all require some
functional unit capable of further reaction58
Well defined graft copolymers are most frequently prepared by either
a)ldquografting throughrdquo or b)ldquografting fromrdquo controlled polymerization process
57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991)
17
a) Grafting though the ldquografting throughrdquo method (or macromonomer method) is one of the
simplest ways to synthesize graft copolymers with well defined side chains
Scheme 9
Typically a low molecular weight monomer is radically copolymerized with a methacrylate
functionalized macromonomer This method permits incorporation of macromonomers
prepared by other controlled polymerization processes into a backbone prepared by a CRP
Macromonomers such as polyethylene59 60 poly (ethylene oxide)61 polysiloxanes62 poly
(lactic acid)63 and polycaprolactone64 have been incorporated into a polystyrene or poly
(methacrylate) backbone Moreover it is possible to design well-defined graft copolymers by
combining the ldquografting throughrdquo macromonomers prepared by any controlled polymerization
process and CRP65 This combination allows control of polydispersity functionality
copolymer composition backbone length branch length and branch spacing by consideration
of MM ratio in the feed and reactivity ratio Branches can be distributed homogeneously or
heterogeneously and this has a significant effect on the physical properties of the
materials6263
b) Grafting from the primary requirement for a successful grafting from reaction is a
preformed macromolecule with distributed initiating functionality
59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003) 6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778 63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998) 823-830
18
Scheme 10
Grafting-from reactions have been conducted from polyethylene66 67 polyvinylchloride68 69
and polyisobutylene70 71 The only requirement for an ATRP is distributed radically
transferable atoms along the polymer backbone The initiating sites can be incorporated by
copolymerization68 be inherent parts of the first polymer69 or incorporated in a post-
polymerization reaction70
Graft copolymers perform similar functions to block copolymers in that they contain moieties
with varying properties Compatibilization represents a major area of application for grafts
because the grafted chains can be used to solubilize a polymer blend system containing two
immiscible polymers Additionally graft copolymers offer unique solution mechanical and
morphological properties that make them ideal for utilization as viscosity modifiers and
thermoplastic elastomers72 The unique molecular architecture of graft copolymers leads to
peculiar morphological properties The chain lengths of the grafted arms and backbone block
dictate the morphology that arises in the polymer Changes in the composition of the graft
copolymer alter the resulting polymer morphology A variety of morphologies is possible
ranging from lamellar to cylindrical to spherical73
Graft copolymers offer all properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheology control
Depending on the nature of their backbone and side chains graft copolymers can be used for a
wide variety of applications such as impact-resistant plastics thermoplastic elastomers
66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996) 7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R Macromolecules 32 (1999) 1152-1158
19
compatibilizers viscosity index improvers and polymeric emulsifiers74 75 The state-of-the-
art technique to synthesize graft copolymers is the copolymerization of macromonomers
(MM) with low molecular weight monomers76 In most cases conventional radical
copolymerization has been used for this purpose Using living polymerizations for both the
synthesis of the macromonomers and for the copolymerization offers the highest possible
control of the polymer structure In all these copolymerizations beside the desired graft
copolymers with at least two side chains a number of unwanted products can be expected
unreacted macromonomer ungrafted backbone and backbone with only one graft (star
copolymer) The latter is undesirable for applications as thermoplastic elastomer
Conventional and controlled copolymerizations lead to different copolymer structures In
conventional radical copolymerization the polymers show a broad molecular weight
distribution (MWD) and chemical heterogeneity of first order
152 Amphiphilic Copolymers
A characteristic feature of an amphiphilic polymer is that it contains both hydrophilic and
hydrophobic groups This type of polymer associates in aqueous solution and exhibits several
interesting features and can be used in connection with many industrial and pharmaceutical
applications Usually there is only a few mol of the hydrophobic moieties in order to make
the polymer water-soluble Due to the hydrophobicity of the amphiphilic polymers they have
a tendency to form association structures in aqueous solution by mutual interaction andor
interaction with other cosolutes such as surfactants and colloid particles
In particular the grafting of hydrophilic species onto hydrophobic polymers is of great utility
Amphiphilic graft copolymers so prepared often display enhanced surface properties such as
improved resistance to the adsorption of oils and proteins biocompatibility and reduced static
charge buildup
The synthesis of graft copolymers based on commercial polymers is most commonly
accomplished free radically Free radicals are produced on the parent polymer chains by
exposure to ionizing radiation andor a free-radical initiator77 78 Alternatively peroxide
groups are introduced on the parent polymer by ozone treatment79 80 The resulting reactive
74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998) 696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507
20
sites serve as initiation sites for the free radical polymerization of the comonomer A
significant disadvantage of these free radical techniques is that homopolymerization of the
comonomer always occurs to some extent resulting in a product which is a mixture of graft
copolymer and homopolymer Moreover backbone degradation and gel formation can occur
as a result of uncontrolled free radical production often limiting the attainable grafting
density81 For example amphiphilic graft copolymers synthesized from PEO macromonomer
and hydrophobic comonomers82 83were found to form micellar aggregates in polar medium
such as water wateralcohol alcohol dimethylformamide These phase separation processes
take place also during polymerization and supposedly affect not only the polymerization
kinetics but also properties of resulting copolymers So far unanswered remains the question
of molecular characteristics of reaction products including homopolymers from
macromonomer or comonomer formed under both the homogeneous and heterogeneous
(micellar) reaction conditions Modern liquid chromatographic techniques allow
discrimination of polymeric constituents differing in their chemical structure andor physical
architecture Subsequently the molar mass and molar mass distribution of constituents can be
assessed Recently analyzed products of dispersion copolymerization of polyethylene oxide
methacrylate macromonomer with styrene contained rather large amount of polystyrene
homopolymer84
In the main application areas for amphiphilic polymers the solution properties are of
fundamental importance In many industrial applications association and adsorption
phenomena of the polymers in solution are design properties Consequently a deep
understanding of these phenomena is necessary for the development of new specific
chemicals and new processes The research goals are to clarify the relations between the
molecular structure of amphiphilic polymers and their properties in aqueous solution A
further goal is to develop theoretical models for the description of the behavior of amphiphilic
polymers in solution and at surfaces Several projects concern the self-assembly of
amphiphilic polymer molecules and the association behavior of surfactants and
hydrophobically modified hydrophilic polymers such as cellulose derivatives Studies of
amphiphilic model polymers such as ethylene oxide block and graft copolymers are carried
80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication
21
out in order to gain fundamental knowledge on the solution behavior of amphiphilic
polymers
16 Kinetics of Free Radical Polymerization
Free radical polymerization is the most widespread method of polymerization of vinylic
monomers Free radical polymerizations are chain reactions in which every polymer chain
grows by addition of a monomer to the terminal free radical reactive site called ldquoactive
centerrdquo The addition of the monomer to this site induces the transfer of the active center to
the newly created chain end Free radical polymerization is characterized by many attractive
features such as applicability for a wide range of polymerizable groups including styrenic
vinylic acrylic and methacrylic derivatives as well as tolerance to many solvents small
amounts of impurities and many functional groups present in the monomers
161 Kinetics of free radical addition Homo and Copolymerization
Understanding of chemical kinetics during homo- and copolymerization is crucial for
copolymer synthesis The discussion below will review the kinetics of free radical initiated
polymerizations and copolymerizations
The three main kinetic steps that occur during polymerization are (1) initiation (2)
propagation and (3) termination
1 Initiation
The initiation step is considered to involve two reactions creating the free radical active
center The first event is the production of free radicals Many methods can be used to initiate
free radical polymerizations such as thermal initiation without added initiator or high energy
radiation of the monomers However free radicals are usually generated by the addition of
initiators that form radicals when heated or irradiated Two common examples of such
compounds which afford free radicals are benzoyl peroxide (BPO) and azobisisobutyronitrile
(AIBN)
22
Figure 1 Generation of Free Radicals by Thermal Decomposition of Benzoyl Peroxide
Figure 2 Decomposition of Azobisisobutyronitrile to Form Free Radicals
Figure 1 depicts the thermal decomposition of BPO to form two oxy-radicals and Figure 2
depicts the decomposition of AIBN to form two nitrile stabilized carbon based radicals
(equation 1)
In equation 1 kd is the rate constant which describes the first order initiation process The
radical that is formed can now add to the double bond of the monomer and initiate
polymerization
The symbol M will represent the monomer and the rate constant for this process will be ki as
described in equation 2
23
Together these two reactions the radical generation and the monomer addition to the radical
form the process of initiation Usually the assumption that is taken into account is that the
first step is the rate determining step This means that the decomposition to form the radical
is much slower than the monomer addition to the free radical Therefore the equation for the
rate of radical formation ri is
The number 2 is obtained from the fact that a maximum of two radicals can be generated for
the initiation
But not all of the primary radicals produced by the decomposition of the initiator will
necessarily react with the monomer which means several other competing reactions may
occur85 Therefore in order to determine the rate of initiation the fraction of initially formed
radicals that actually start chain growth will be denoted by f and the rate of initiation equation
becomes
2 Propagation
Now the propagation of the reaction will proceed through the successive addition of
monomer to the radicals This type of process can be expressed in the following form
85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster PA (1997)
24
And further generalizing the reaction scheme gives
The assumption that the reactivity of the addition of each monomer is independent of the
chain length is evident in these two equations and was postulated by Flory 58 86 The use of
the rate constant kp for both of these equations imply that the rate constant is independent of
chain length The rate of the propagation rp of this polymerization or the rate of monomer
removal is thus given by
3 Termination
The termination of these growing radical chains occurs in principally two different ways The
first way is the formation of a new bond in between the two radicals this is called
combination Secondly the radical chains can terminate by disproportionation This is a
process where a hydrogen atom from one of the chains is transferred to the other and the chain
that the proton was removed from forms a double bond These reactions are represented as
follows
Figure 3 Termination by Combination
86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995)
25
Figure 4 Termination by Disproportionation
Schematically the reactions can be represented as follows
Where the rate constant of termination by combination is denoted by ktc and the rate constant
of termination by disproportionation is denoted by ktd Since both of these reactions use two
radical species and have the same kinetics the overall equation for the rate of termination is
written as
where kt = ktc + ktd and the number 2 imply there are two radicals that are terminated in
each termination reaction The monomer structure and the temperature are what determines
the type of termination that is most dominant in the reaction For most systems the amount of
one termination type far exceeds the other termination type
The further calculations for the rate of polymerization Rp and the degree of conversion as a
function of time can now be developed The assumption of the steady state concentration of
transient species must be used here where the transient species is the radical M For the
steady state approximation to hold true the rate at which initiation occurs ri must be equal to
the rate at which termination occurs rt or in other words radicals must be generated at the
same rate at which they are terminated This assumption gives the equation
26
This equation then gives an expression for the radical species
Experimentally this value would be difficult to measure in the laboratory and therefore this
equation must be used in the subsequent equations that follow By further substitution an
expression for the rate of polymerization Rp can be obtained because it equals the rate of
propagation
From this equation it can be deduced that the rate of polymerization is directly proportional
to the monomer concentration and to the initiator concentration to the one half power In
other words Rp is first order with regards to the monomer concentration and half order to the
initiator concentration
When the conversion is low the assumption that the initiator concentration is constant is
reasonable but the consumption of the initiator can be added into the calculations Therefore
Then integration can be performed
Finally the rate of polymerization becomes
27
This equation can be broken into three different parts
The second term indicates that the rate of polymerization is still proportional to the monomer
concentration to the first power and the initiator concentration to the one half power but the
initiator concentration is now the initial concentration Therefore by increasing the initial
concentration of an initiator in a solution polymerization the rate of the reaction should
increase proportionally to the square root of the amount of initiator added The third term
indicates that as the initiator is consumed the polymerization slows down exponentially with
time as well as its slowing down due to monomer depletion
The first term in the brackets suggests that the rate of polymerization is proportional to kp
kt12 When experiments are performed to probe the kinetics of reactions in solution the
expected first order dependence on monomer concentration is observed But when the
experiment is performed in concentrated solvents or even in the bulk the polymerization
kinetics accelerate The reason for this anomaly is that the viscosity increases as the
polymerization proceeds because the polymer has a higher viscosity than the monomers The
kp is not affected but the kt is
The degree of conversion can now be expressed as a function of time by knowing that
By substituting the earlier equation for Rp and integrating that equation one can obtain this
Furthermore ([M]0 ndash [M]) [M]0 is equal to the degree of conversion and is the fraction of
the monomer that has been reacted where [M] is the concentration of the monomer that has
been left after the reaction and [M]0 is the initial monomer concentration Therefore ([M]0 ndash
[M]) is the concentration of the monomer that has reacted The conversion can then be
expressed as
28
This can also be expressed as
As is always the case the conversion never quite reaches 100 value or a factor of 1 given by
the exponential term So if the time goes to infinity the expression that is obtained for
maximum conversion that is less than 1 by an amount that is dependent on the initial initiator
concentration is
If the steady state approximation for the initiator concentration had been carried through these
calculations and equations then the conversion would approach a value of 1 after a long
period of time
Distributions on the average distribution of chain lengths during and after a polymerization
are present in free radical polymerizations This is due to the naturally but statistically
random termination reactions that occur in the solution with regard to chain length The
kinetic chain length v is the rate of monomer addition to growing chains over the rate at
which chains are started by radicals which is the expression for the number average chain
length In other words it is the average number of monomer units per growing chain radical
at a certain instant87 Therefore the initiator radical efficiency in polymerizing the monomers
is
87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993)
29
When termination occurs mainly by combination the chain length for the polymer chains on
the average doubles in size assuming nearly equal length chains combine But if
disproportionation mainly occurs the growing chains do not undergo any change in chain
length during the process So the expressions are thus
A new term can be used to more generally express the average chain length of the growing
polymer chain xn This new term is the average number of dead chains produced per
termination ξ This value is equal to the rate of dead chain formation over the rate of the
termination reactions The equations take into account that in combination only one dead
chain is produced and in disproportionation reactions two dead chains are produced
Therefore
Furthermore the instantaneous number average chain length can be expressed in terms of the
rate of addition of the monomer units divided by the rate of dead polymers forming This is
shown as
30
From this equation82 one can clearly see that the rate of polymerization is proportional to the
initiator concentration to the one half power [I]12 and that the instantaneous number average
chain length xn is proportional to the inverse of the initiator concentration to the one half
power 1[I]12 Thus if the polymerization was accelerated by using more initiator the chains
will end up to be shorter which may not be desirable85
17 Chain Growth Copolymerization
171 Copolymerization Equations
Chain polymerizations can obviously be performed with mixtures of monomers rather than
with only one monomer For many free radical polymerizations for example acrylonitrile and
methyl acrylate two monomers are used in the process and the subsequent copolymer might
be expected to contain both of the structures in the chain This type of reaction that employs
two comonomers is a copolymerization The reactivity and the relative concentrations of the
two monomers should determine the concentration of each comonomer that is incorporated
into the copolymer The application of chain copolymerizations has produced much important
fundamental information Most of the knowledge of the reactivities of monomers via
carbocations free radicals and carbanions in chain polymerizations has been derived from
chain copolymerization studies The chemical structure of these monomers strongly
influences reactivity during copolymerization Furthermore from the technological viewpoint
copolymerization has been critical to the design of the copolymer product with a variety of
specifically desired properties As compared to homopolymers the synthesis of copolymers
can produce an unlimited number of different sequential arrangements where the changes in
relative amounts and chemical structures of the monomers produce materials of varying
chemical and physical properties
Several different types of copolymers are known and the process of copolymerization can
often be changed in order to obtain these structures A statistical or random copolymer may
obey some type of statistical law which relates to the distribution of each type of comonomer
that has been incorporated into the copolymer Thus for example it may follow zero- or first-
31
or second-order Markov statistics88 Copolymers that are formed via a zero-order Markov
process or Bernoullian contain two monomer structures that are randomly distributed and
could be termed random copolymers
ndashAABBBABABBAABAmdash
Alternating block and graft copolymers are the other three types of copolymer structures
Equimolar compositions with a regularly alternating distribution of monomer units are
alternating copolymers
ndashABABABABABABA--
A linear copolymer that contains one or more long uninterrupted sequences of each of the
comonomer species is a block copolymer
--AAAAAAAA-BBBBBBBBB--
A graft copolymer contains a linear chain of one type of monomer structure and one or more
side chains that consist of linear chains of another monomer structure
--AAAAAAAAAAAAAmdash
B B
B B
B B
B B
For this discussion the main focus will be on randomly distributed or statistical copolymers
Copolymer composition is usually different than the composition of the starting materials
charged into the system Therefore monomers have different tendencies to be incorporated
into the copolymer which also means that each type of comonomer reacts at different rates
with the two free radical species present Even in the early work by Staudinger89 it was
noted that the copolymer that was formed had almost no similar characteristics to these of the
homopolymers derived from each of the monomers
Furthermore the relative reactivities of monomers in a copolymerization were also quite
different from their reactivities in the homopolymerization Thus some monomers were more 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151
32
reactive while some were less reactive during copolymerization than during their
homopolymerizations Even more interesting was that some monomers that would not
polymerize at all during homopolymerization would copolymerize relatively well with a
second monomer to form copolymers It was concluded that the homopolymerization features
do not easily directly relate to those of the copolymerization
Alfrey (1944) Mayo and Lewis (1944) and Walling (1957)909192 demonstrated that the
copolymerization composition can be determined by the chemical reactivity of the free radical
propagating chain terminal unit during copolymerization Application of the first-order
Markov statistics was used and the terminal model of copolymerization was proposed The
use of two monomers M1 and M2 during copolymerization leads to two types of propagating
species The first of these species is a propagating chain that ends with a monomer of
structure M1 and the second species is a propagating chain that ends with a monomer structure
M2 For radically initiated copolymerizations the two structures can be represented by
M1 and M2 where the zig-zag lines represent the chain and the M
represents the radical at the growing end of the chain The assumption that the reactivity of
these propagating species only depends on the monomer unit at the end of the chain is called
the terminal unit model58 If this is so only four propagation reactions are possible for a two
monomer system The propagating chain that ends in M1 can either add a monomer of type
M1 or of type M2 Also the propagating chain that ends in M2 can add a monomer unit of
type M2 or of type M1 Therefore these equations can be written with the rate constants of
reactions93
90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953)
33
The rate constant for the reaction of the propagating chain that ends in M1 and adds another
M1 to the end of the chain is k11 and the rate constant for the reaction of the propagating
chain that ends in M2 and adds M1 to the end of the chain is k21 and so on
The term self-propagation refers to the addition of a monomer unit to the chain that ends with
the same monomer unit and the term cross-propagation refers to a monomer unit that is added
the end of a propagating chain that ends in the different monomer unit These (normally)
irreversible reactions can propagate by free radical anionic or cationic processes although
active lifetimes could be very different
As indicated by reactions 30 and 32 monomer M1 is consumed and as indicated by reactions
31 and 33 monomer M2 is consumed The rates of entry into the copolymer and the rates of
disappearance of the two monomers are given by
In order to find the rate at which the two monomers enter into the copolymer equation 34
is divided by equation 35 to give the copolymer composition equation
The low concentrations (eg 10-8 molesliter) of the radical chains in the systems are very
hard to experimentally determine So to remove these from the equation the steady state
approximation is normally employed Therefore a steady state concentration is assumed for
both of the species M1 and M2 separately The interconversion between the two
species must be equal in order for the concentrations of each to remain constant and hence the
rates of reactions 31 and 32 must be equal
34
Rearrangement of equation 37 and combination with equation 36 gives
This equation can be further simplified by dividing the right side and the top and bottom by
k21 [M2] [M1] The results are then combined with the parameters r1 and r2 which are
defined to be the reactivity ratios
The most familiar form of the copolymerization composition equation is then obtained as
The ratio of the rates of addition of each monomer can also be considered to be the ratio of the
molar concentrations of the two monomers incorporated in the copolymer which is denoted
by (m1m2) The copolymer composition equation can then be written as
The copolymer composition equation defines the molar ratios of the two monomers that are
incorporated into the copolymer d[M1] d[M2] As seen in the equation this term is directly
related to the concentration of the monomers that were in the feed [M1] and [M2] and also
the monomer reactivity ratios r1 and r2 The ratio of the rate constant for the addition of its
own type of monomer to the rate constant for the addition of the other type of monomer is
35
defined as the monomer reactivity ratio for each monomer in the system When M1
prefers to add the monomer M1 instead of monomer M2 the r1 value is greater than one
When M1 prefers to add monomer M2 instead of monomer M1 the r1 value is less than
one When the r1 value is equal to zero the monomer M1 is not capable of adding to itself
which means that homopolymerization is not possible
The copolymer composition equation can also be expressed in mole fractions instead of
concentrations which helps to make the equation more useful for experimental studies In
order to put the equation into these terms F1 and F2 are the mole fractions of M1 and M2 in the
copolymer and f1 and f2 are the mole fractions of monomers M1 and M2 in the feed
Therefore
and
Then combining equations 42 43 and 40 gives
This form of the copolymer equation gives the mole fraction of monomer M1 introduced into
the copolymer58
Different types of monomers show different types of copolymerization behavior Depending
on the reactivity ratios of the monomers the copolymer can incorporate the comonomers in
different ways
The three main types of behavior that copolymerizations tend to follow correspond to the
conditions where r1 and r2 are both equal to one when r1 r2 lt 1 and when r1 r2 gt 1
bull A perfectly random copolymerization is achieved when the r1 and r2 values are both
equal to one This type of copolymerization will occur when the two different types of
36
propagating species M1 and M2 show the exact same preference for the addition of
each type of monomer In other words the growing radical chains do not prefer to add one of
the monomers more than the other monomer which results in perfectly random incorporation
into the copolymer
bull An alternating copolymerization is defined as r1 = r2 = 0 The polymer product in
this type of copolymerization shows a non-random equimolar amount of each comonomer
that is incorporated into the copolymer This may occur because the growing radical chains
will not add to its own monomer Therefore the opposite monomer will have to be added to
produce a growing chain and a perfectly alternating chain
When r1 gt 1 and r2 gt 1 both of the monomers want to add to themselves and in theory could
produce block copolymers But in actuality because of the short lifetime of the propagating
radical the product of such copolymerizations produces very undesirable heterogeneous
products that include homopolymers Therefore macroscopic phase separation could occur
and desirable physical properties such as transparency would not be achieved
172 Determination of Reactivity Ratios
Many methods have been used to estimate reactivity ratios of a large number of
comonomers94 The copolymer composition may not be independent of conversion This
means the disappearance of monomer one may be faster than the disappearance of monomer
two if monomer one is being incorporated into the copolymer at a faster rate and therefore it
has a larger reactivity ratio than monomer two
The approximation method95 is the simplest of the methods that has been used to calculate the
reactivity ratios of copolymer systems The method is based on the fact that r1 the reactivity
ratio of component one is mainly dependent on the composition of monomer two m2 that
has been incorporated into the copolymer at low concentrations of monomer two in the feed
M2 The expression is thus
94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
37
The value of the reactivity ratio for component one can be easily determined by only one
experiment but the value is only an approximation and does not provide any validity of the
estimated r1 In order to determine the amount of the comonomer that has been incorporated
into the copolymer various analytical methods must be used Proton Nuclear Magnetic
Resonance Carbon 13 NMR and Fourier Transform Infrared Spectroscopy are three sensitive
instruments that can determine the copolymer composition The approximation method is
limited when the reactivity ratio of one of the components in the system has a value of less
than 01 or greater than a value of 10
However the method does give good insight into the reactivity ratio values for many
copolymer systems The approximation of reactivity ratios can be easy and quick when using
this method of evaluation
The Mayo-Lewis intersection method91 96 uses a linear form of the copolymerization equation where r1 and r2 are linearly related
By using the equations m1M 22 m2M12 and (M2 M1)[(m1 m2) ndash 1] for the slope and intercept
respectively a plot can be produced for a set of experiments after the copolymer composition
has been determined The straight lines that are produced on the plot for each experiment
where r1 represents the ordinate and r2 represents the abscissa intersect at a point on the r1 vs
r2 plot The point where these lines meet is taken to be r1 and r2 for the system in study The
main advantage of this method is that it gives a qualitative observation of the validity of the
intersection area Over the whole range of possible copolymer compositions that were tested
more compact intersections better define the data However the method requires a visual
check of the data and a quantitative estimation of the error is impossible Therefore
weighting of the data is needed to determine the most precise values of r1 and r2
The Fineman-Ross linearization method97 uses another form of the copolymer equation
Where
And
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259
38
For this method by plotting G versus H for all the experiments one will obtain a straight line
where the slope of the straight line is the value for r1 and the intercept of the line is the value
for r2 This type of reactivity ratio determination has the same advantages and disadvantages
of the method described above however this treatment is a linear least squares analysis
instead of a graphical analysis The validity is only qualitative and the estimates of r1 and r2
can change with each experimenter by weighting the data in different ways Furthermore the
high and low experimental composition data are unequally weighted which produces large
effects on the calculated values of r1 and r2 Therefore different values of r1 and r2 can be
produced depending on which monomer is chosen as M158
A refinement of the linearization method was introduced by Kelen and Tudos98 99 100 by
adding an arbitrary positive constant a into the Fineman and Ross equation 47 This technique
spreads the data more evenly over the entire composition range to produce equal weighting to
all the data58 The Kelen and Tudos refined form of the copolymer equation is as follows
η = [ r1 + r2 α ] ξ minus r2 α (50)
where
η = G ( α + H ) (51)
ξ = H ( α + H ) (52)
By plotting η versus ξ a straight line is produced that gives ndashr2α and r1 as the intercepts on
extrapolation to ξ=0 and ξ=1 respectively Distribution of the experimental data
symmetrically on the plot is performed by choosing the α value to be (HmHM)12 where Hm
and HM are the lowest and highest H values respectively Even with this more complicated
monomer reactivity ratio technique statistical limitations are inherent in these linearization
methods101 102
98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265
39
OrsquoDriscoll Reilly et al103 104 determined that the dependent variable does not truly have a
constant variance and the independent variable in any form of the linear copolymer equation
is not truly independent Therefore analyzing the composition data using a non-linear
method has come to be the most statistically sound technique
The non-linear or curve-fitting method90 is based on the copolymer composition equation in
the form
This equation is based on the assumptions that the monomer concentrations do not change
much throughout the reaction and the molecular weight of the resulting polymer is relatively
high In order to determine reactivity ratios from the experimental data a graph must be
generated for the observed comonomer amount that was incorporated into the copolymer m1
versus the feed comonomer amount M1 for the entire range of comonomer concentrations
Then a curve can be drawn through the points for selected r1 and r2 values and the validity of
the chosen reactivity ratio values can be checked by changing the r1 and r2 values until the
experimenter can demonstrate that the curve best fits the data points
The main advantage of the reactivity ratio determination methods discussed thus far is the
results can be visually and qualitatively checked Disadvantages include a direct dependence
of the composition on conversion for most polymer systems and therefore low conversion
(eg instantaneous composition) is needed to determine the reactivity ratios Furthermore
extensive calculations are required but only qualitative measurements of precision can be
obtained Finally weighting of the experimental data for the methods to determine precise
reactivity ratios is hard to reproduce from one experimenter to another
Therefore a technique that allows the rigorous application of statistical analysis for r1 and r2
was proposed by Mortimer and Tidwell which they called the nonlinear least squares
method95105106107This method can be considered to be a modification or extension of the
curve fitting method For selected values of r1 and r2 the sum of the squares of the differences
between the observed and the computed polymer compositions is minimized
103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772
40
Using this criterion for the nonlinear least squares method of analysis the values for the
reactivity ratios are unique for a given set of data where all investigators arrive at the same
values for r1 and r2 by following the calculations Recently a computer program published by
van Herck108 109 allows for the first time rapid data analysis of the nonlinear calculations It
also permits the calculations of the validity of the reactivity ratios in a quantitative fashion110
The computer program produces reactivity ratios for the monomers in the system with a 95
joint confidence limit determination
The joint confidence limit is a quantitative estimation of the validity of the results of the
experiments and the calculations performed This method of data analysis consists of
obtaining initial estimates of the reactivity ratios for the system and experimental data of
comonomer charge amounts and comonomer amounts that have been incorporated into the
copolymer both in mole fractions Many repeated sets of calculations are performed by the
computer which rapidly determines a pair of reactivity ratios that fit the criterion wherein the
value of the sum of the squares of the differences between the observed polymer composition
and the computed polymer composition is minimized111 112 This method uses a form of the
copolymer composition equation with mole fractions of the feed It amounts to determining
the mole fraction of the comonomer that should be incorporated into the copolymer during a
differential time interval
For this equation F2 represents the mole fraction of comonomer two that was calculated to be
incorporated into the copolymer and f1 and f2 represent the mole fractions of each comonomer
that were fed into the reaction mixture The use of the Gauss-Newton nonlinear least squares
procedure predicts the reactivity ratios for a given set of data after repeating the calculations
so that the difference between the experimental data points and the calculated data points on a
plot of mole fraction of comonomer incorporated versus comonomer in the feed is reduced to
the minimum value113 114
108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65
41
18 Controlled Radical Polymerization
The development of new controlledliving radical polymerization processes such as Atom
Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated
polymerization and degenerative transfer processes including RAFT opened the way to the
use of radical polymerization for the synthesis of well-defined complex functional
nanostructures The development of such nanostructures is primarily dependent on self-
assembly of well-defined segmented copolymers This section describes the fundamentals of
ATRP relevant to the synthesis of such systems115
The main goal of macromolecular engineering is to carry out the synthesis (polymerization) in
such a way that it results in well-defined macromolecular products One of the ways to
achieve full control of the macromolecule (length sequence and regio- and stereo- regularity)
would be to build it one monomer at a time with mechanisms in place facilitating selection of
an appropriate monomer and assuring its addition in proper orientation This of course has
been achieved in Nature in the process of protein synthesis through the use of sophisticated
macromolecular ldquonanomachineryrdquo (DNA RNA Most commonly used synthetic routes to
linear polymers are based on addition (chain) reactions which can be controlled only in
statistical terms through such parameters as initiatormonomer ratios monomerpolymer
reactivities monomer concentrations reaction medium etc The main strategy to achieve the
reasonable control of such reactionsrsquo products is through the synchronized growth of ldquolivingrdquo
chains ie chains which cease to grow only in the absence of a monomer Synchronization of
chain growth can be achieved fairly easily through rapid initiation Living chains grown in
such synchronized fashion exhibit relatively narrow molecular weight distributions (MWD)
their average molecular weights can be controlled simply by the duration of reaction Until
recently radical polymerization which covers the broadest range of monomers appeared to
be inherently uncontrollable due to the presence of fast chain termination of growing radicals
Thus although very useful in the synthesis of bulk commodity polymers where precise
control is not always essential radical polymerization has been hardly ever viewed as a tool to
precisely engineer macromolecules for well-defined functional nanostructures
114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16
42
This outlook shifted dramatically recently with the development of new controlledliving
radical polymerization processes such as Atom Transfer Radical Polymerization (ATRP)116
117 118 and other techniques such as nitroxide mediated polymerization119 and degenerative
transfer processes120 including reversible addition-fragmentation chain transfer (RAFT)121
With the availability of effective control mechanisms given its applicability to a broadest
range of monomers radical polymerization is now ready to assume the central role in
macromolecular engineering geared towards the development of well-defined functional
nanostructures
181 Fundamentals of ControlledLiving Radical Polymerization (CRP)
The great expectations for the controlledliving radical polymerization (CRP) have their
origins in the dominating position of the free radical technique by far the most common
method of making polymeric materials (nearly 50 of all polymers are made this
way)122123124This is due to the large number of available vinyl monomers (eg there are
nearly 300 different methacrylates available commercially) which can be easily
homopolymerized and copolymerized The advent of CRP enables preparation of many new
materials such as well-defined components of coatings (with narrow MWD precisely
controlled functionalities and reduced volatile organic compounds -VOCs) non ionic
surfactants polar thermoplastic elastomers entirely water soluble block copolymers
(potentially for crystal engineering) gels and hydrogels lubricants and additives surface
modifiers hybrids with natural and inorganic polymers various biomaterials and electronic
materials
The controlledliving reactions are quite similar to the conventional ones however the radical
formation is reversible Similar values for the equilibrium constants during initiation and
propagation ensure that the initiator is consumed at the early stages of the polymerization
116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002)
43
generating chains which slowly and continuously grow as in a living process There are a
number of critical differences between conventional and controlledliving radical reactions
bull Perhaps the most important difference between the two approaches is the lifetime of
the propagating chains which is extended from 1 s to more than 1 h
bull The second major difference is the very significant increase in the initiation rate
which enables simultaneous growth of all the polymer chains
bull Termination processes cannot be avoided in CRPs Thus CRP is generally less precise
than the anionic polymerization Termination is the most dangerous chain breaking
reaction in CRPs Since it is a bimolecular process increasing the polymerization rate
increases the concentration of radicals and enhances the termination process
Termination also becomes more significant for longer chains and at higher conversion
However this process is somehow self tuned since termination is chain length
dependent
The key feature of the controlledliving radical polymerization is the dynamic equilibration
between the active radicals and various types of dormant species Currently three systems
seem to be most efficient nitroxide mediated polymerization (NMP) atom transfer radical
polymerization (ATRP) and degenerative transfer processes such as RAFT123 Each of the
CRPs has some limitations and some special advantages and it is expected that each
technique may find special areas where it would be best suited synthetically For example
NMP carried out in the presence of bulky nitroxides cannot be applied to the polymerization
of methacrylates due to fast β-H abstraction ATRP cannot yet be used for the polymerization
of acidic monomers which can protonate the ligands and complex with copper RAFT is very
slow for the synthesis of low MW polymers due to retardation effects and may provide
branching due to trapping of growing radicals by the intermediate radicals At the same time
each technique has some special advantages Terminal alkoxyamines may act as additional
stabilizers for some polymers ATRP enables the synthesis of special block copolymers by
utilizing a halogen exchange and has an inexpensive halogen at the chain end125 RAFT can
be applied to the polymerization of many unreactive monomers such as vinyl acetate126
182 Typical Features of ATRP
A successful ATRP process should meet several requirements
125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035
44
bull Initiator should be consumed at the early stages of polymerization to form polymers
with degrees of polymerization predetermined by the ratio of the concentrations of
converted monomer to the introduced initiator (DP = Δ[M][I]o)
bull The number of monomer molecules added during one activation step should be small
resulting in polymers with low polydispersities
bull The contribution of chain breaking reactions (transfer and termination) should be
negligible to yield polymers with high degrees of end-functionalities and allow the
synthesis of block copolymers
In order to reach these three goals it is necessary to select appropriate reagents and
appropriate reaction conditions ATRP is based on the reversible transfer of an atom or group
from a dormant polymer chain (R-X) to a transition metal (M nt Ligand) to form a radical (R)
which can initiate the polymerization and a metal-halide whose oxidation state has increased
by one (X-M n+1t Ligand) the transferred atom or group is covalently bound to the transition
metal A catalytic system employing copper (I) halides (Mnt Ligand) complexed with
substituted 2 2rsquo- bipyridines (bpy) has proven to be quite robust successfully polymerizing
styrenes various methacrylates acrylonitrile and other monomers116127 Other metal centers
have been used such as ruthenium nickel and iron based systems117 118 Copper salts with
various anions and polydentate complexing ligands were used such as substituted bpy
pyridines and linear polyamines The rate constants of the exchange process propagation and
termination shown in Scheme 11 refer to styrene polymerization at 110 C
Scheme 11
According to this general ATRP scheme the rate of polymerization is given by the following
equation
127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901
45
Thus the rate of polymerization is internally first order in monomer externally first order
with respect to initiator and activator Cu(I) and negative first order with respect to
deactivator XCu(II) However the kinetics may be more complex due to the formation of
XCu(II) species via the persistent radical effect (PRE) The actual kinetics depend on many
factors including the solubility of activator and deactivator their possible interactions and
variations of their structures and reactivities with concentrations and composition of the
reaction medium It should be also noted that the contribution of PRE at the initial stages
might be affected by the mixing method crystallinity of the metal compound and ligand etc
One of the most important parameters in ATRP is the dynamics of exchange and especially
the relative rate of deactivation If the deactivation process is slow in comparison with
propagation then a classic redox initiation process operates leading to conventional and not
controlled radical polymerization Polydispersities in ATRP are defined by the following
equation when the contribution of chain breaking reactions is small and initiation is
complete
Thus polydispersities decrease with conversion p the rate constant of deactivation kd and
also the concentration of deactivator [XCu(II)] They however increase with the propagation
rate constant kp and the concentration of initiator [RX]o This means that more uniform
polymers are obtained at higher conversions when the concentration of deactivator in solution
is high and the concentration of initiator is low Also more uniform polymers are formed
when the deactivator is very reactive (eg copper(II) complexed by 2 2-bipyridine or
pentamethyldiethylenetriamine rather than by water) and monomer propagates slowly (styrene
rather than acrylate)
183 Controlled Compositions by ATRP
One of the driving forces for the development of a controlledldquo livingrdquo radical polymerization
is to allow for the copolymerization of two or more monomers128 This has been demonstrated
with ATRP by copolymerization of various combinations of styrene methyl or butyl acrylate
methyl or butyl methacrylate and acrylonitrile ATRP allows for the copolymerization of
these monomers using all feed compositions without loss of control of the polymerization 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
46
this is in contrast to the use of 2266-tetramethylpiperidine-1-oxyl radical (TEMPO) which
must contain a significant amount of styrene as comonomer to retain control of the
polymerization This restriction does not apply to polymerizations mediated by new
nitroxides119 The statistical copolymers prepared by living polymerizations are not the same
as those prepared by conventional radical polymerizations due to the differences in
polymerization mechanism
During a copolymerization one monomer is generally consumed faster than the other
resulting in a constantly changing monomer feed composition during the polymerization the
preference is dependent on the reactivity ratios of the two (or more) monomers In
conventional radical polymerization where the polymer chains are continuously initiated and
are irreversibly terminated the change in monomer feed is recorded in the individual polymer
chains whose composition will vary from chain to chain depending on when the chain was
formed ie at the beginning or near the end of the reaction However since ATRP is a
controlledldquolivingrdquo polymerization system the vast majority of polymer chains does not
irreversibly terminate but grow gradually throughout the polymerization The change in
monomer feed is recorded in the polymer chain itself and not from chain to chain The drifting
of composition along the polymer chain is expected to yield gradient copolymers with novel
properties129 Conventional free radical polymerization methods are generally not suitable for
synthesizing star shaped polymers due to the occurrence of undesirable radical coupling
reactions During a ldquocore-firstrdquo synthesis this would lead to coupling of the growing polymer
arms and ultimately result in a cross-linking of the star macromolecules
Block copolymers can be formed by addition of a second vinyl monomer to a macroinitiator
which contains halide groups that participate in the atom transfer process Most notably this
has been demonstrated by successive addition of a second monomer at the end of the
polymerization of a first monomer by ATRP In this manner AB and ABA block copolymers
have been prepared with various combinations of styrene acrylates methacrylates and
acrylonitrile It is very important to select the right order of monomer addition For example
polyacrylates can be efficiently initiated by the poly (methyl methacrylate)- BrCuBrL
system However the opposite is not true because concentration of radicals and overall
reactivity of acrylates is generally too low to efficiently initiate MMA polymerization
Halogen exchange comes to the rescue bromoterminated polyacrylate in the presence of
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775
47
CuClL is an efficient initiator for MMA polymerization due to reduced polymerization rate
of PMMA-Cl species which are predominantly formed after the exchange process130 131 132
Scheme 12
To conclude atom transfer radical polymerization is a robust method for preparing well-
defined polymers and novel materials with unique compositions and architectures Although
significant progress has been made in the past few years since the development of ATRP
continuous research on the better mechanistic understanding of ATRP and the preparation of
more efficient catalyst systems to yield more well-defined polymers and polymerize new
monomers is needed The syntheses of new materials need to be optimized and their
properties should be studied
It is anticipated that the new controlledliving techniques will help to provide many new well-
defined polymers via macromolecular engineering
130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
48
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1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422 4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348 10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp
(1985) 461
Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823 22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991) 25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996)
(b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993)
(c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice
(d) Mishra M K Ed Polymer Frontiers New York (1994) 391
49
31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159 32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer
Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N
Macromolecules 26 (1993) 7134 42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144 45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon
Press 3(1989) 787 49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154 55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387 57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991) 59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M
J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003)
6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778
50
63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998)
823-830 66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996)
7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R
Macromolecules 32 (1999) 1152-1158 74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998)
696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507 80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication 85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster
PA (1997) 86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995) 87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993) 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151 90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953) 94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
51
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259 98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265 103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772 108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65 114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16 116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002) 125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035 127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
52
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775 130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
53
CHAPTER II Synthesis and Characterization of
Macromonomers
21 Introduction
Cationic ring opening polymerization of DXL proposed by Franta and Reibel133 results in
linear polymeric chains thereby preventing formation cyclic oligomers through cationic
polymerization of cyclic acetals15 17In fact the reaction of DXL in the presence of an
unsaturated alcohol (2-HPMA) results in a functionalized linear PDXL macromonomer
carrying at one or both ends an unsaturated system supported by the methacryloyl group of
the alcohol The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism44 Franta et al have established that when DXL is polymerized by strong protonic
acids such as triflic acid in the presence of a diol the PDXL chains are essentially linear and
carry end-standing OH functions It has been shown that the amount of cyclic species formed
is negligible that the dispersity is on the order of 14 and that the molecular weight of the
linear polymers is governed by the ratio of reacted monomer to transfer agent and is generally
well controlled up to 10 000 gmol
De Clercq and Goethals have reported the preparation of poly (13dioxolane)
bismacromonomers by copolymerization with MMA and provided the possibility to prepare
polymer networks containing PDXL segments134 135 PDXL based hydrogels have been
obtained in most cases by free radical copolymerization with comonomers such as acrylic
acid acrylamide and N-isopropylacrylamide134 136 137 styrene and butyl acrylate138
Hydrogels have received increasing attention for biomedical applications such as drug
delivery immobilization of enzymes dewatering of protein solutions and contact lenses139
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002) 1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080
54
140 These materials and are widely used in areas like baby diapers solute separation soil for
agriculture and horticulture absorbent pads etc139 Hydrogels are defined as hydrophilic
polymer networks which have a high capacity to adsorb a substantial amount of water which
have been proposed as protein releasing matrices The high water content ensures a good
compatibility with entrapped proteins as well as with surrounding tissue141 Even though a
number of applications are currently being pursued using hydrogel very little is known about
the mechanical behavior that describes the various physical processes in hydrogels142 Over
the last decade most interests have been emphasized on the synthesis of polymers containing
polyacetal segments because of the ease of degradation of these polymers under mild
conditions by treatment with a trace of acid134 143 Poly (1 3 dioxolane) is a hydrophilic non-
ionic polymer which like poly (ethylene oxide) is appreciably soluble in water but much
more sensitive to acidic degradation because of the presence of acetal groups in the chains144
In this chapter we report the synthesis of the functionalized poly (13dioxolane)
macromonomers which have been used for the preparation of PDXL hydrogel and
amphiphilic graft copolymers In the second part of this chapter we have focused on a
detailed study of the properties of the resulting hydrogel in terms of swelling behavior in
different organic solvents and viscoelastic properties determined by rheological measurements
in both the steady shear and oscillatory experiments
22 Experimental
221 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922
55
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
bull Dichloromethane (CH2Cl2 MW 8493 bp 40degC d 1325)
Dichloromethane (Prolabo 999) was dried by stirring over CaH2 for 24 h and then
distilled under a N2 atmosphere to remove impurities Purified dichloromethane was
stored under nitrogen over molecular sieve
bull 2-hydroxypropyl methacrylate (2-HPMA) (MW 14417 bp 240degC d 1028)
2-HPMA of commercial grade was purchased from Acros stabilized with 200 ppm
hydroquinone monomethyl ether Then it was stored over molecular sieve
bull n-Hexane 99 (C6H14 MW 8618 bp 68-70degC d 0658-0662) Stored under
nitrogen over molecular sieve
bull Trifluoromethanesulfonic acid (triflic acid Aldrich) was used as received
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile (AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull 1 3 dioxolane (DXL) (MW 7408 bp 78degC d 106)
The monomer DXL of commercial grade was purchased from Acros DXL was kept
under KOH for two and up to three days to remove any peroxide and stabilizer traces
and then purified by distillation over CaH2 under a N2 atmosphere prior to
polymerization
All chemicals were kept over molecular sieve before use
222 Reaction apparatus
All polymerization experiments were performed with a clean 250 ml three neck round bottom
flask A condenser was used on one of the necks of the flask in order to condense any
monomers that might otherwise possibly escape A magnetic bar was used to stir the solution
at a constant speed in order to assure even distribution of monomer and initiator
concentrations throughout the entire volume of solution A rubber septum was used to cover
one of the three necks
In the case of free radical polymerization reactions a thermocouple was also fitted to the
reaction vessel to monitor the temperature of the reaction The thermocouple regulated the
56
temperature at a constant 70degC throughout the reaction
223 Synthesis of Poly (13-dioxolane) Macromonomers
Methacrylate-terminated PDXL macromonomers were synthesized by Cationic ring-opening
polymerization which was carried out in 10 ml dichloromethane with triflic acid as initiator at
room temperature under nitrogen for 24 h in the presence of 2-hydroxypropyl methacrylate
(2-HPMA) as transfer agent 20 ml of DXL monomer was added The feed molar ratios
[DXL] [2-HPMA] are reported in Table1 as well as the molecular characteristics of the
obtained macromonomers The amount of the acid used was 20 μl After reaction the
resulting solution is poured into THF Then the product is purified by re-precipitation from
THF solution with a large excess of hexane and the obtained polymer was dried under
vacuum at room temperature The yield was checked by gravimetric determination and found
to be about 80
224 Synthesis of Poly (13-dioxolane) Hydrogel Network
The functionalized PDXL macromonomer taken for the preparation of PDXL netwok was
(FPP2) macromonomer with a theoretical average molecular weight of Mnth =2000
The macromonomer (1g) was polymerized by free radical polymerization in 10 ml of THF
using 2 2-azobisisobutyronitrile (AIBN) (001g) as initiator under a nitrogen atmosphere
The polymerization was carried out at 70degC for 24h A piece of hydrogel was obtained The
product was extracted with ethanol to remove unreacted macromonomers and then dried
under vacuum
23 Characterization Techniques
231 Raman Spectroscopy
Raman spectroscopy is used to study and analyse the structure of the macromonomers
The experiments were performed on a Dilor XY 800 spectrophotometer The detector was a
charge-coupled device (CCD) An argon laser pump beam (power density of 100 mW) has
been focused onto the sample through a microscope The working wavelength was chosen as
λ = 5145 nm In our experiments we explored the spectral range between 200 and 3700 cm-1
with a spectral resolution of 2 cm-1
57
232 1H-NMR Spectroscopy
Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) was used for structural analysis
and molecular weight of polymers and macromonomers Proton NMR spectra were obtained
using a high field 400Mhz Advance Bruker spectrometer
All of the 1H NMR samples were dissolved in deuterated chloroformThe chloroform
reference peak at 724 ppm was to ensure accuracy of peak assignments The integrals of the
peaks were used for the calculations to determine the Mw of the macromonomers
233 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) represents a chromatographic method widely used in
the analysis of polymer average molecular weights and molecular weight distributions SEC
Measurements were performed at 40degC on a Waters 2690 instrument equipped with UV
detector (Waters 996 PDA) coupled with a Differential Refractometer (ERC - 7515 A) and
four Styragel columns (106 105 500 and 50degA) THF is employed as eluent with a flow rate
of 10 mlmin Polystyrene standard samples were used for calibration
234 Swelling Measurements
In order to investigate the swelling behavior the measurement of the swelling ratio of the
polymer network is obtained from a gravimetric method in which small pieces of hydrogel
were immersed solvents such as CH2Cl2 and THF for 24 hours at room temperature (23degC)
until swelling equilibrium was reached ie when the gel thickness became essentially
constant The samples were removed from the solvents and carefully weighed (Ws) Then the
samples let to deswell and weighed every 5 min during in order to determine the swelling
kinetics in the solvents The swelling equilibrium was reached after 5 hours Afterwards the
gel was left to dry for 24 hours at room temperature until constant weight was attained and the
dry weight (Wd) was determined and the swelling ratio was calculated from equation
SR = ( ) 100timesminusWd
WdWs (57)
Where SR is equilibrium swelling ratio Ws and Wd are the sample weights in swollen and dry
states respectively
58
235 Rheological Measurements
Steady shear and oscillatory measurements have been performed on a stress imposed
rheometer Rheo-Stress-100 (RS100) from Haake used with a coneplate geometry (20 mm
diameter an angle of 4deg gap 2 mm)The imposed stress of 100 Pa during 30 seconds and a
frequency of 1Hz were applied while the strain was monitored The measurements have been
performed on swollen and unswollen samples The elastic (G) and the loss (G) moduli are
measured in linear viscoelastic region In the oscillatory experiments the frequency
dependence of both Grsquo and G is obtained at a constant strain All rheological measurements
were carried out at room temperature (23 degC)
24 Results and Discussion
241 Structural Characterization of Macromonomers
1 3 dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer end ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The synthesis of α ω-dihydroxy-PDXL chains is based on the
activated monomer mechanism44 Franta et al have established that when DXL is polymerized
by strong protonic acids such as triflic acid in the presence of a diol the PDXL chains are
essentially linear and carry end-standing OH functions It has been shown that the amount of
cyclic species formed is negligible that the dispersity is on the order of 14 and that the
molecular weight of the linear polymers is governed by the ratio of reacted monomer to
transfer agent and is generally well controlled up to 10 000 gmol
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel44 133 using an unsaturated alcohol (2-
59
HPMA) as a transfer agent results in linear polymeric chains thereby preventing formation of
cyclic oligomers through cationic polymerisation of cyclic acetals15 17 They were all prepared
at the same reaction conditions The synthetic route of functionalized PDXL macromonomers
is shown in scheme13
Scheme 13 Structures of PDXL macromonomer species54
According to this mechanism it is possible to prepare macromonomers ie PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of the
transacetalization reactions a mixture of products is obtained
A is the most abundant compound it corresponds to 50 to 60 weight wise54 It is a
macromonomer
B corresponds to 20 to 25 weight wise It is a bis-macromonomer It carries two
methacryloyl functions corresponding to transacetalization of R-OH and DXL
C corresponds to 20 to 25 weight wise It carries no methacryloyl function but two
hydroxyl groups It is a α ω-dihydroxy-PDXL
These 3 species A B and C stem from scrambling reactions that are typical with cyclic
acetals54
The characterization of these materials is based on structure and molecular weight
determination For instance the PDXL macromonomers carried at one of their ends a double
bond afforded by the methacryloyl group The latter was checked by Raman and 1H-NMR
spectroscopy All macromonomers prepared displayed functionality close to unity which
makes them suitable for the synthesis of graft copolymers
60
Raman spectroscopy is used to study and analyse the structure of the macromonomers The
aim of this study is to check the formation of linear polymer chains as well as the termination
with methacryloyl groups The spectra obtained exhibit two intense Raman bands at 800 to
900 cmP
-1 and 2700 to 3000 cmP
-1 regions and a series of small other peaks for all samples as
shown in figure 1 The most intense band (2700 ndash 3000 cmP
-1) is assigned to the aliphatic
stretching vibration of CH in the polyacetal chain Symmetric COCOC stretching frequencies
of aliphatic acetals fall in typical regions of 1115-1080cmP
-1 and 870-800 cmP
-1 145 and are
responsible for intense Raman bands In the low frequency region there are three very
characteristic Raman bands in the 600 ndash 550 cmP
-1 540 ndash 450 cmP
-1 and 400 ndash 320 cmP
-1 ranges
which are assigned to COCOC deformations145 146 Also the acetals have strong multiple
bands in the region of 1160ndash1040 cmP
-1 as noticed on the Raman spectra involving the C-O
stretching modes In addition to this the O-CH-O group gives rise to a band at 1350 ndash1325
cmP
-1 for C-H deformation Other intense Raman bands are observed in the region of 3000 ndash
2700 cmP
-1 Below 3000 cmP
-1 the corresponding frequencies are assigned to the aliphatic C-H
stretching modes145 The methoxy group is detected in the region of 2835 ndash 2780 cmP
-1
Figure 1 Raman spectra of methacrylic-terminated PDXL macromonomers (FPP2 FPP15 and
FPP1)
145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The Handbook of IR
and Raman Characteristic Frequencies of Organic Molecules United Kingdom Ed by Academic Press Limited London (1991)
146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman Spectroscopy 3rd Edition AP Limited London (1964)
61
As far as the presence of the methacryloyl group in the polymeric chain is important bands
have been observed at 1640 cmP
-1 which corresponds to C=C bonds The carbonyl compounds
absorb strongly within 1900 ndash1550 cmP
-1 region145 146 the spectra show a C=O bond absorption
found at 1720 cmP
-1 In the region of 1340 ndash1250 cmP
-1 the methacrylate bands are observed
Broad absorption is found near 3500 cm -1 owing to stretching of the OH bonds OH
deformation bands are found at 1400 cmP
-1P and 1340 cmP
-1 This observation indicates that both
methacrylic and ndashOH groups are present and eventually the resulting product is a mixture of
the three species as shown in the scheme above
Typical 1H-NMR spectrum of PDXL macromonomer shown in figure 2 exhibits the expected
resonance assigned to the methoxy protons (477 ppm) and OCH2CH2O protons at (374
ppm) Two signals corresponding to =CH2 were observed at (612 ndash 614 ppm) and (557 ndash
559 ppm) Therefore the spectrum confirmed the chemical structure HO[CH2CH2OCH2O]nR
of methacryloyl- terminated PDXL macromonomer
Figure 2 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP2)
242 Molecular Weight Determination
Besides the structure 1H-NMR enables us to determine the number-average molecular weight
(Mn) In the calculation of the latter the methacryloyl end group was included The
62
polydispersity and index MwMn and the number-average molecular weight were obtained
from SEC measurements Table 1 summarizes these values It can be seen that Mn (SEC) and
Mn (NMR) are very close to each other for all macromonomer samples and are in agreement
with the theoretical values predicted from calculations Under our polymerization conditions
the polydispersity index is 16 for all samples
Table 1 Characteristics of PDXL macromonomers prepared at different degrees of
polymerization
Sample Dp Mnth MnSEC MnRMN MwMn f (a)
FPP1 135 1000 1120 1160 16 097
FPP15 2025 1500 1540 1550 16 099
FPP2 270 2000 2040 2100 16 097
Dp degree of polymerization = [DXL] [2HPMA]
a functionality of macromonomers (methacryloyl end groups molecule)
243 Swelling of Poly (13 Dioxolane) Hydrogel
The synthesized PDXL hydrogel has been studied in terms of swelling and rheological
behaviors The degree of swelling and the rate of swelling of the hydrogel are studied It is
known that hydrogel can swell in several solvents but at different degree of swell according to
many factors related to the nature of the solvents and the type of polymer-solvent interactions
It was found that the solubility parameter of the solvents (δ) had a great effect on swelling
degree For instance hydrogels can swell fast in CH2Cl2 (δ = 976 cal cm12 -32) and reached
equilibrium within no more than an hour However it will take about more than 20 h to reach
equilibrium in CH3 OH (δ = 145 cal cm12 -32) It was known that the polymer can reach
greatest swelling degree when the solubility parameter of the polymer is close to that of the
solvents The solubility parameter of PDXL is about 93 cal cm 12 -32 134 The swelling has been
examined in THF and CH2Cl2 for PDXL hydrogel It has been observed that the swelling
equilibrium is reached after almost 5 hours of swelling for all samples in both solvents The
results show that THF (δ = 952 cal cm12 -32)147 swells the hydrogel to the greatest degree
compared to CH2Cl2 as shown in figure 3 However CH2Cl2 molecules provide less swelling
147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983)
63
capacity than in THF On the basis of the experiment The PDXL hydrogel reached high
swelling degree due to its solubility parameter is much closer to that of THF
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
THF CH2Cl2
Swel
ling
degr
ee
Time (min)
Figure 3 Swelling kinetics of PDXL hydrogel in two different solvents CH2 Cl2 (solid
squares) and in THF (hollow squares)
244 Viscoelastic Behavior
Rheological measurements were performed on rheometer in the Cone and Plate geometry
Both steady shear and oscillatory experiments were carried out The dynamic storage and loss
moduli G and G were examined at room temperature (23 degC)
Many attempts have been carried to extend the elasticity theory to swollen gels148 149 Based
on this approach all measurements have been performed on both swollen and unswollen
hydrogel samples for the purpose of comparison so that to examine the mechanical properties
even in swollen state For instance Flory and Rehner recognized the swelling phenomenon
exhibited by cross-linked polymers when exposed to certain solvents and related the modulus
of elasticity of a swollen cross-linked polymer network to an unswollen network150 Figure 4
illustrates the strain dependence of G and G for swollen and unswollen samples
148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for Experimental
Mechanics SEM Annual Conference Proceedings (2002)
64
10-5 10-4 10-3 10-2 10-1 100 101 102101
102
103
104
Guns Guns Gs Gs
GG
(Pa
)
γ ()
Figure 4 Strain dependence of the elastic modulus Grsquo (circles) and of the viscous modulus
Grdquo(triangles) for two samples of unswollen hydrogel (solid symbols) and swollen hydrogel
(hollow symbols)
The moduli are measured as a function of strain at a constant frequency It appears that the
linear viscoelastic region is observed while the strain is increasing in either state which
indicates that the internal structure of the samples has not been disrupted when deformed
This leads to reveal that the gel is strain resistant in swollen and unswollen states and within a
large strain range the hydrogel retains its elasticity as shown in figure 4 where the linear
viscoelastic region extends to almost 02
The frequency dependence of G and G is shown in figure 5 similarly for swollen and
unswollen hydrogels The system behaves typically like a gel as it can be noticed that the
elastic component G (storage modulus) is far greater than the viscous component G (loss
modulus)151 Based on these results the hydrogel exhibits extreme elasticity at low
frequencies
151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure 554 (2000) 99-108
65
100 101
103
104
105
Gs Guns Gs GunsG
G(
Pa)
ω (rads)
Figure 5 Frequency dependence of Grsquo(circles) and Grdquo(triangles) for swollen hydrogel
(hollow symbols) and unswollen hydogel (solid symbols)
Finally figure 6 illustrates the complex viscosity profiles another parameter of
viscoelasticity which measures the magnitude of the total resistance to a dynamic shear
Again this property has not been affected by swelling since the results show similar behavior
for swollen and unswollen states It decreases sharply as frequency increases which
characterizes the samples degree of viscoelasticity at various time scales Therefore from the
results discussed above the hydrogel network is elastic and stable even in the swollen state
thereby possessing very good mechanical properties
100 101 102 103
102
103
104
105
η unswollen η swollen
ηlowast (P
a s)
ω (rads)
Figure 6 Frequency dependence of the complex viscosity η for unswollen hydrogel (solid
squares) and swollen hydrogel (hollow triangles)
66
Conclusion
The hydrogel properties were discussed in terms of swelling and viscoelastic
behaviors The hydrogel has combined special properties Its swelling behaviour in the
solvents was dependent on the solubility parameter of both solvents and hydrogel
Rheological measurements were successful when used in order to study the viscoelastic
behavior of the hydrogel of pure PDXL in swollen and unswollen states The Strain
dependence of G and G for both samples shows linear viscoelastic region and allows to
determine the yield stress Same conclusions can be given concerning the frequency
dependence of complex viscosity the swelling does not affect this property The results reveal
a perfect elastic and resistant hydrogel in other words the viscoelastic properties have not
been so much affected by swelling They may be particularly useful in the design of improved
microfluidic devices that utilise the relationship between swelling and strain This kind of
material can be potentially used in biosystems such as intelligent drug delivery systems
67
References
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-
174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002)
1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080 140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922 145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The
Handbook of IR and Raman Characteristic Frequencies of Organic Molecules United
Kingdom Ed by Academic Press Limited London (1991) 146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman
Spectroscopy 3rd Edition AP Limited London (1964) 147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983) 148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-
1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for
Experimental Mechanics SEM Annual Conference Proceedings (2002) 151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure
554 (2000) 99-108
68
CHAPTER III Synthesis and Characterization of Copolymers
31 Introduction
Amphiphilic block and graft copolymers consisting of hydrophilic and hydrophobic parts
have been subjects of numerous studies within which block and graft copolymers containing
hydrophilic polyoxyethylene segments and other hydrophobic segments have attracted much
attention because polyoxyethylene segments are not only hydrophilic but also nonanionic
and crystalline and can complex monovalent metallic cations Graft copolymers offer all
properties of block copolymers but are usually easier to synthesize Moreover the branched
structure leads to decreased melt viscosities which is an important advantage for processing
Depending on the nature of their backbone and side chains they give rise to special properties
in selective solvents at surfaces as well as in the bulk owing to microphase separation
morphologies12 They can be used for a wide variety of applications such as polymeric
surfactants electrostatic charge reducers compatibilizers in polymer blends polymeric
emulsifiers controlled wet ability and so on152 153 In order to prepare graft copolymers with
well-defined structure one can utilize the macromonomer technique (grafting through
technique) Well-defined structure graft copolymers are synthesized by copolymerization of
macromonomers with low molecular weight comonomers6 It allows the control of the
polymer structure which is given by three parameters (i) chain length of side chains which
can be controlled by the synthesis of the macromonomer by living polymerization (ii) chain
length of backbone which can be controlled in a living copolymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular weight monomer However the distribution of spacings
may not be very easy to control due to the incompatibility of the polymer backbone and the
macromonomers154 As pointed out in recent publication reviews155 there is a complex
interplay of factors that govern the reactivities in copolymerizations involving
macromonomers When different comonomers are copolymerized with the same it seems that
the degree of interpenetration between the macromonomer and the propagating copolymer 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305
69
backbone plays the major role in the measured reactivities Nevertheless the main properties
depend on both the average composition of the systems and the microstructural distribution of
the comonomer sequences along the macromolecular backbone which is determined by the
reactivity ratios of the macromonomer and the corresponding comonomer in the free radical
polymerization process156 157
In this chapter our work deals with the preparation and characterization of new organo-
soluble associative copolymers based on short hydro-soluble chains of poly (1 3 dioxolane)
(PDXL) Many reports have been published on PDXL macromonomers used to form
hydrogels136 137 158 159 160 161 162 however very few were on graft copolymers with PDXL
branches162 These macromonomers are used for the preparation of amphiphilic graft
copolymers by solution free radical copolymerization with a hydrophobic comonomer
styrene (St) and methyl methacrylate (MMA) Structural characterization of these
copolymers molecular weight determination reactivity ratios and the polymerizability of the
PDXL macromonomer have been discussed Finally their thermal properties are discussed
according to the weight content of PDXL in the copolymers
32 Experimental
321 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269
70
bull Ethanol (C2H6O MW 4607 bp 78degC d 081)
Ethanol (Prolabo 95-96) was purified by distillation with 5g of Magnesium and 05g of
iodine for 75ml of alcohol under a N2 atmosphere After discoloration of the mixture
solution a volume of Ethanol was added and then distilled normallyThen it was stored
over molecular sieve
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile(AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull Styrene (C6H5CH=CH2 MW 10416 bp 145degC d 091)
Styrene (Prolabo product) was purified by distillation over CaHB2 at reduced pressure
bull Methyl Methacrylate (MMA)(H2C=C(CH3)CO2CH3 MW 10012 bp 100degC d
0936)
Methyl Methacrylate (Prolabo product) was purified by distillation over CaHB2 at reduced
pressure
All chemicals were kept over molecular sieve before use
322 Synthesis of Poly (Styrene-co-Poly (13-dioxolane))
a) Conventional Free Radical Copolymerization
The reaction route for the conventional copolymerization of Styrene and PDXL
macromonomers using AIBN as the free radical initiator at 60degC is shown in scheme 14
71
Scheme 14
PDXL macromonomers of different molecular weights were copolymerized with St in THF at
60degC in the presence of 2 2rsquo-azobisisobutyronitrile AIBN (1 based on the total weight of
the monomers) as initiator under a nitrogen atmosphere using different feed molar fractions
of macromonomers The total monomer concentration for was 6 10-1 M in all cases The
copolymerization product is diluted with THF and then added dropwise to a large excess of
ethanol to remove unreacted PDXL macromonomers25 43 and precipitate the copolymers
Then they were finally dried over vacuum at 40degC to constant weight The yields of all
reactions are 70ndash 90 Table 2 indicates the amounts of comonomers initiator and solvent
employed in the copolymerization study
72
Table 2 Copolymerization of PDXL macromonomers (M1) with Styrene (M2)
Sample M1 M2M1 PDXL (g) (mol)
Styrene (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2SP2 FPP2 20 349 174510-4 364 349 10-2 007 60 0610 3SP2 FPP2 30 232 116 10-4 364 349 10-2 006 60 0601 5SP2 FPP2 50 14 69810-4 364 349 10-2 005 60 0593
2SP15 FPP15 20 262 174510-4 364 349 10-2 006 60 0610 3SP15 FPP15 30 174 116 10-4 364 349 10-2 006 60 0601 5SP15 FPP15 50 105 69810-4 364 349 10-2 005 60 0593
2SP1 FPP1 20 174 174510-4 364 349 10-2 006 60 0610 5SP1 FPP1 50 07 69810-4 364 349 10-2 005 60 0593 8SP1 FPP1 80 0436 43610-4 364 349 10-2 005 60 0589
b) Controlled Free Radical Copolymerization
The comb-structure copolymer of styrene and PDXL was obtained by grafting-from
mechanism through Nitroxide-Mediated Polymerization
Nitroxide mediated polymerization (NMP) is a controlled radical polymerization (CRP)
technique which already offers the ability to prepare a wide variety of well-defined polymer
architectures119 Despite the significant improvements brought to CRP techniques such as
NMP atom transfer radical polymerization (ATRP) or reversible addition fragmentation chain
transfer (RAFT) the preparation of complex architectures by CRP is restricted by the
exclusion of monomer systems that are polymerized by fundamentally different mechanisms
like lactides ethylenepropylene oxide The most promising approaches to extend the range of
polymer compositions are based on the use of heterofunctional initiators163 allowing the
combination of mechanistically distinct polymerization reactions without the need for
intermediate transformation and protection steps
In the field of NMP the development of multifunctional initiators was focused on TEMPO
and TIPNO which are examples of nitroxides (Scheme 15) It is worth to mention that in
NMP these are used as counter-radicals associated with a conventional azoic initiator so this
pair of initiators is known as a bimolecular system
163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671
73
Scheme 15 TEMPO and based alkoxyamines
Another initiator used for NMP is the commercially available alkoxyamine also called
MAMA-SG1164 (Scheme 16) known as a monomolecular system initiator which is
particularly convenient for functionalization of polymer chain ends164 165 MAMA-SG1 has
been developed by Didier Gigmes and co in collaboration with Arkema Company166 Thanks
to a particularly high dissociation rate constant value kd1 up to now this alkoxyamine has
proved to be one of the most potent alkoxyamines reported in the field of NMP167 168 This
initiator is used for polymerization of styrene and n-butyle acrylate allowing formation of
well-defined linear and star structures
Scheme 16
164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006) 5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219
74
Scheme 17 MAMA-SG1 structure and dissociation scheme
bull Multifunctionalization of Polystyrene (HO-PS)
MAMA-SG1 was used to run copolymerization of styrene at 90 mol with HEMA in order
to obtain functionalized polystyrene The monomers and alkoxyamine were introduced in a
250 mL two neck round-bottom flasks fitted with septum condenser and degassed for 15
min by nitrogen bubbling The reaction was performed in bulk at 120 degC under N2 with
vigorous stirring Targeted molecular weight and polydispersity were 30 000 g mol and 12
respectively
After polymerization the final polymer mixture was dissolved in a minimum THF and
precipitated in cold ethanol followed by drying under vacuum at 30degC
bull Synthesis of PS-g-PDXL
PDXL was copolymerized by cationic ring-opening polymerization which was carried out in
40 ml dichloromethane with triflic acid as initiator at room temperature under nitrogen for 24
h in the presence of OH-multifunctionalized PS (1g 3 10-5 mol) as transfer agent 20 ml
(0286 mole) of DXL monomer was added Table 6 gives the molecular characteristics of the
obtained copolymer The amount of the acid used was 20 μl After reaction the resulting
solution is poured into THF Then the product is purified by re-precipitation from THF
solution with a large excess of hexane and the obtained polymer was dried under vacuum at
room temperature The yield was checked by gravimetric determination and found to be about
75 The polymerization route is presented in the scheme below
75
Scheme 18
323 Synthesis of Poly (Methyl Methacrylate-co-Poly (13-dioxolane))
Same procedure has been used for the synthesis of Poly (Methyl Methacrylate-co-Poly (1 3-
dioxolane)) copolymers The yields of the reactions are in the range of 70ndash 90
Table 3 shows the amounts of comonomers initiator and solvent employed in the
copolymerization reactions
Table 3 Copolymerization of PDXL macromonomers (M1) with MMA (M2)
Sample M1 M2M1 PDXL (g) (mol)
MMA (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2MP2 FPP2 20 374 187 10-4 3744 374 10-2 008 65 0604 3MP2 FPP2 30 2 10 10-4 300 300 10-2 005 50 0620 5MP2 FPP2 50 15 748 10-4 3744 374 10-2 005 60 0636
2MP15 FPP15 20 2 133 10-4 28 280 10-2 005 25 100 3MP15 FPP15 30 187 125 10-4 3744 374 0-2
006 60 0644 5MP15 FPP15 50 112 748 10-4 3744 374 10-2 005 60 0636
2MP1 FPP1 20 2 20 10-4 400 4 10-2
006 50 0840 3MP1 FPP1 50 125 125 10-4 3744 374 10-2 005 64 0604 5MP1 FPP1 80 075 748 10-4 3744 374 10-2 005 60 0636
33 Characterization Techniques
331 1H-NMR Spectroscopy
1H NMR Spectroscopy was used for compositional and structural analysis of the copolymers
1H-NMR spectra of the copolymers were recorded on the high field 400Mhz Advance Bruker
spectrometer All of the 1H NMR samples were dissolved in deuterated chloroform The
integrals of the peaks of copolymer components were used for the calculations to determine
76
the molecular weights polydispersity indices and the amount of each comonomer that was
incorporated into the copolymer
332 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) was used in the charaterization of the copolymers to
determine average molecular weights and polydispersity indices SEC Measurements were
performed at 40degC on a Waters 2690 instrument equipped with UV detector (Waters 996
PDA) coupled with a Differential Refractometer (ERC - 7515 A) and four Styragel columns
(106 105 500 and 50degA) THF is employed as the mobile phase with a flow rate of 10
mlmin Polystyrene standard samples were used for calibration
333 Diffraction Scanning Calorimetry
Diffraction Scanning Calorimetry (DSC) measurements are performed on a Modulated
Temperature Differential Scanning Calorimeter Q100 TA instrument under nitrogen at 50
mlmin The samples are hermetically sealed in aluminium pans and they are subjected to a
heating program as follows
For Poly (Styrene-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 120degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -80degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to130degC
For Poly (Methyl Methacrylate-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 130degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -95degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to150degC
The thermograms obtained illustrate Glass Transition Temperatures (Tg) and Meltind Points
(Tm) of the copolymers
77
34 Results and Discussion
Methacryloyl-terminated PDXL macromonomers with the Mn range of 1000-2000 gmole
were copolymerized with vinyl and methacrylic monomers in order to obtain amphiphilic
graft copolymers with chemical structure of hydrophobic backbone and hydrophilic side
chains
341 Structural Characterization of the Copolymers
The structure of the copolymers was well defined by 1H-NMR analysis The copolymer 1H-
NMR spectra confirm the formation of copolymers see figures 7 8 and 9 The chemical
shifts of protons of polystyrene and PDXL can be clearly distinguished The following peaks
are assigned for OCHBB2BBO protons at 478 ppm and OCHBB2BBCHBB2BBO protons at 375 ppm (5H CBB6BB
HBB5BB) at 728 711 and 706 ppm as shown in Figure 8 The spectrum of PMMA-PDXL
copolymer is shown in Figure 9 where the chemical shifts of PMMA correspond to the proton
resonance as depicted in the figure the O-CH3 protons are observed at 361 ppm and clear
resonance assigned to the methyl group protons at 085-103 ppm and eventually we observe
the corresponding chemical shifts for OCHBB2BBCHBB2BBO protons (374 ppm) and OCHBB2BBO protons
(477 ppm) to confirm the incorporation of PDXL in the copolymer
Figure 7 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP1)
78
Figure 8 1H-NMR spectrum of Styrene-g-PDXL copolymer in CDCl3 (sample 3SP2)
79
Figure 9 1H-NMR spectrum of MMA-g-PDXL copolymer in CDCl3 (sample 2MP2)
342 Copolymer Molecular Weight and Composition
a) Conventional Free Radical Copolymerization
Copolymerization of PDXL macromonomers with MMA and ST in THF solution was studied
for different molar feed ratio of PDXL The amounts of monomeric units in the copolymers
were determined by elemental analysis The results are presented in Table 4 and 5 which
summarise the characteristics of the graft copolymers in terms of macromonomer feed ratio
(M2M1) and average Mn obtained from SEC as well as copolymer composition in weight and
mole percentages which is determined from 1H-NMR
80
Table 4 Characteristics of PDXL macromonomers (M1) copolymerized with Styrene (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2SP2 FPP2 20 49 476 4025 337 9200 162 2 3SP2 FPP2 30 39 322 303 221 8900 162 2 5SP2 FPP2 50 277 196 21 13 7200 159 1
2SP15 FPP15 20 418 476 34 34 9100 157 2 3SP15 FPP15 30 323 322 24 214 7000 161 2 5SP15 FPP15 50 224 196 152 12 6700 147 1
2SP1 FPP1 20 323 476 30 427 9200 178 3 5SP1 FPP1 50 16 196 1424 17 5800 158 1 8SP1 FPP1 80 107 123 85 095 11900 195 1
Table 5 Characteristics of PDXL macromonomers (M1) copolymerized with MMA (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2MP2 FPP2 20 50 476 35 26 21900 198 4 3MP2 FPP2 30 40 322 21 13 25900 157 3 5MP2 FPP2 50 286 196 13 07 87200 455 6 2MP15 FPP15 20 416 45 28 25 19800 193 4 3MP15 FPP15 30 333 322 22 18 15200 277 3 5MP15 FPP15 50 23 196 13 10 24700 16 2 2MP1 FPP1 20 333 476 26 34 21100 319 6 3MP1 FPP1 30 333 322 19 22 17100 197 3 5MP1 FPP1 50 20 196 10 11 13900 354 2
81
b) Controlled Free Radical Copolymerization
Multifunctionalization of Polystyrene and Synthesis of poly (S-g-PDXL) copolymer give
results which are shown in Table 6 These data have been obtained from the 1H-NMR and
SEC analyses illustrated in figures 10 and 11 The resonance shifts assigned to all components
(PDXL PS and HEMA) are very clear This enables us to make calculations to determine
composition of each copolymer in addition to obtain the average number of grafts and the
number average-molecular weight of a graft
It is observed that the multifunctionalized-PS is composed of 20 in mole of HEMA which
results in 58 grafts (Ng = 58) per molecular chain
After copolymerization multifunctionalized-PS with DXL the copolymer PS-g-PDXL
(DXPS) possesses the following characteristics which are presented in Table 6 It has a
number average-molecular weight of 83000 gmol with 80 of PDXL content The number
average-molecular weight of one graft has been calculated and found to be 1000 gmol
Table 6 Characteristics of functionalized Styrene (HO-PS) and PS-g-PDXL (DXPS)
copolymer
Strusture Sample MnSEC IP PDXL
w mol
PS
w mol
HEMA
w mol
Ng Graft
Mn
HO-PS
32 700
12
_ _
77 80
23 20
58
_
DXPS
83 000
24
71 80
17 13
12 75
58
1000
82
Figure 10 1H-NMR spectrum of Multifunctionalized of Polystyrene in CDCl3
Figure 11 1H-NMR spectrum of poly (S-g-PDXL) copolymer (DXPS) in CDCl3
83
341 Determination of Monomer Reactivity Ratios
The application of the classical treatment based on linearization of the copolymerization
equation of Mayo and Lewis91 or the non-linear least-squares approach suggested by Tidwell
and Mortimer95 requires working with high macromonomer concentrations (ie feed
compositions higher than 20-30 of macromonomer)156
The MayondashLewis equation (58) that relates the instantaneous compositions of the monomer
mixture to the copolymer composition is approximated to a simplified form (equation (59))
suggested by Jaacks169 when working with a large excess of one of the comonomers This is
the case of copolymerisation reactions between a conventional comonomer and a
macromonomer of relatively high molecular weight where using low molar concentrations of
macromonomer is mandatory due to its restricted solubility and the extremely viscous media
][ ][ ]
[ ][ ]
[ ] [[ ] [ ]221
211
2
1
2
1
MrMMMr
MM
MdMd
++
=
(58)
[ ][ ] 1
22
1
2
MMr
MdMd
=
(59)
According to equation (59) the copolymer composition or the frequency of branches is
essentially determined by the monomer composition and the monomer reactivity ratio of the
comonomer r2 (inversely proportional to the macromonomer reactivity) under the limit
condition of [M2][M1] gtgt1 In order to obtain reliable values it is frequently necessary to
run the copolymerisation at different conversions or to carry out several copolymerizations
with different initial monomer ratios170 In such cases an integrated form of equation (59) is
used
[ ] [ ][ ][ ] 01
12
02
2 lnlnMM
rMM tt =
(60)
169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046
84
where [Mi]t[Mi]0 is the ratio among the composition of monomer i at time t and the initial
feed composition A plot of ln ([M2]t[M2]0) versus ln ([M1]t[M1]0) should result in a straight
line with a slope that equals to r2 (the reactivity ratio of the comonomer)
Thus the monomer reactivity ratios between the PDXL macromonomers and the comonomers
were estimated with the data in tables 4 and 5 We can apply equation (60) to the estimation
where M1 and M2 are the PDXL macromonomer and copolymer respectively The monomer
reactivity ratios are determined for macromonomers of different Mn (degree of
polymerization) and summarized in Table 7
Table 7 Monomer reactivity ratios for copolymerization of PDXL macromonomers (M1)
with St and MMA (M2)
Sample M2 M1
macromer Mnth
r2 1r2
SP2 St FPP2 2000 012 plusmn 0006 833
SP15 St FPP15 1500 0042 plusmn 6 10-4 238
SP1 St FPP1 1000 0015 plusmn 3 10-4 6666
MP2 MMA FPP2 2000 002 plusmn 001 50
MP15 MMA FPP15 1500 007 plusmn 0 02 1428
MP1 MMA FPP1 1000 0018 plusmn 001 5555
In the case of copolymerization with Styrene and MMA the results suggest that the reactivity
of the methacrylic double bond in the prepared macromonomers is not affected in their
copolymerization with Styrene or MMA This point is confirmed when analysing the inverse
ratio 1r2 = k21k22 which is sometimes considered as the relative copolymerization reactivity
of a macromonomer171 This quantity is the ratio between the crosspropagation and
homopropagation rate constants of comonomer (2) which is directly proportional to the
reactivity of the macromonomer (1) and gives a clear idea of the relative reactivity of a
growing radical ending in a 2 unit towards the addition of monomer (1) in comparison to the
171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620
85
tendency for the homopropagation So we have a situation where r1 gtgt 1 gtgt r2 and it is
expected that the initially formed chains should contain more macromonomers and then more
comonomer segments are added These are only assumptions but they give an indication
about the probable composition drift of the graft copolymers obtained On the other hand in
the case of copolymerization of poly (13dioxolane) macromonomers with styrene (Figure
12) the results show that r2 increases with increasing PDXL side chain length (in terms of
average Mn) and this leads to say that the side macromonomer chain length affect the
reactivity of the comonomer Thus this indicates that a growing radical of macromonomer
with a shorter chain length (ie lower Mn ) attacks more frequently a monomer of the same
nature than it does a macromonomer with a longer length (ie higher Mn) as it can be noticed
from the results in Table 7
However the r2 values of the copolymerization with MMA as shown in Figure 13 give
unclear dependence on the side poly (13dioxolane) macromonomer chain length this may be
due to the resulting polydispersity of the copolymerization Mentioned behaviour may be
related with the reactive structure of comonomers vinyl in the case of Styrene or methacrylic
in the case of MMA in regard to the ending methacrylic double bond of macromonomers
besides the hydrophilic character of the macromonomers
86
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0015 plusmn 3 10-4 SP1
b
r2 = 0042 plusmn 6 10-4
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP15
c
r2= 012 plusmn 0006
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP2
Figure 12 Application of Jaacksrsquo treatment to the St-g-PDXL copolymerization systems
(a) SP1 (b) SP15 (c) SP2
87
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0018 plusmn 001 MP1
b
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 007 plusmn 002MP15
036788
c
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 002 plusmn 001 MP2
Figure 13 Application of Jaacksrsquo treatment to the MMA-PDXL copolymerization systems
(a) MP1 (b) MP15 (c) MP2
88
341 Glass Transition Temperatures
Thermal analysis of Styrene-g-PDXL copolymers allows to determine their glass transition
and melting temperatures In the first place the measurements were performed on a
conventional DSC from which the thermograms obtained show an overlapping of PS glass
temperature and PDXL melting point signals This has been observed for all samples A
different approach in the characterisation of these copolymers was by means of Modulated
Temperature Differential Scanning Calorimeter (MTDSC) which is an extension of
conventional DSC This approach combines high resolution with high sensitivity by use of a
sinusoidal temperature modulation superimposed on a constant temperature or linear
temperature program with a small underlying average heating rate172 173 In comparison to
conventional DSC the MTDSC analysis enables the simultaneous calculations of an
additional quantity the cyclic or modulus of heat capacity Cp (J g-1K-1 172)
ωT
HFp A
AC =
(61)
is the amplitude of the cyclic heat flow (Wg-1) and AWhere AHF Tω is the amplitude of cyclic
heating rate with AT the temperature modulation amplitude (K) ω the modulation angular
frequency (2πp) and p is the modulation period (s)172
In fact the MTDSC splits the overlapped signals into two distinct temperatures melting
temperature of the hydrophilic grafts and glass transition temperature of the hydrophobic
backbone as can be noticed in Figure 14 in which melting temperature appears to be 5626degC
which is closer to the glass transition temperature with a value of 5671degC From the results
obtained out of the thermogram it is clear that the measurements show very close values of
Tm and Tg for all copolymer samples where in conventional DSC these two temperatures
cannot be distinguished
172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
89
Figure 14 MTDSC thermogram of 5SP1 copolymer at heating rate of 2degCmin
Tg was taken at the midpoint of the transition region The results obtained are shown in
Tables 8 and 9 for copolymers with Styrene and MMA respectively Then a plot of the
copolymers Tg has been constructed against PDXL content in order to determine the effect of
the latter on Tgrsquos As it can be noticed in the Figure 15 Tg of the copolymers decreases
exponentially with increasing PDXL content and this may be due to the decrease in the
intermolecular interactions between the molecular chains and can be associated with higher
mobility and flexibility of the polymeric chains when PDXL is incorporated in the
copolymers The results clearly indicate that Tg values of the copolymers depend on the
composition of comonomers and a decrease with increasing PDXL content in the obtained
copolymers
90
Table 8Transition temperatures of Styrene-g-PDXL copolymers obtained by thermal
analysis (DSC) Sample PDXL content Tg wt () (degC) 8SP 85 7489 1
5SP 1424 5671 1
5SP 152 5590 15
21 6739 5SP 2
303 4480 3SP 2
34 2665 2SP15
4025 2SP 4060 2
Table 9Transition temperatures of MMA-g-PDXL copolymers obtained by thermal analysis
(DSC)
Sample PDXL content Tg
wt () (degC)
5MP 10 10545 1
5MP 13 8278 15
21 6576 3MP 2
22 7550 3MP 15
26 7013 2MP1
91
5 10 15 20 25 30 35 40 4520
30
40
50
60
70
80
a
SP COPOLYMERSTg
(degC)
PDXL content in wt()
10 15 20 2560
70
80
90
100
110
b
Tg (deg
C)
PDXL content in wt()
MP COPOLYMERS
Figure 15 Glass transition temperatures vs PDXL macromonomer content for copolymer
systems (a) Styrene-g-PDXL copolymers (b) MMA-g-PDXL copolymers
92
Conclusion
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers The macromonomer reactivity estimation suggests that the
length of the PDXL side chains does affect the reactivity of the methacrylic double bond of
the macromonomer when copolymerized with St However in the case of copolymerization
with MMA there is no dependence on the graft size Finally from DSC measurements the
values of Tg depend on the composition and the size of the PDXL grafts In all copolymers
the increase in amount of the incorporated PDXL macromonomer results in a substantial
decease in glass transition
93
References 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305 156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269 163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671 164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006)
5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219 169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620 172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly
(1 3 Dioxolane)) on Immiscible Polymer Blends
of Polystyrene and Poly (Ethylene Glycol)
41 Background
411 Physical Blends
Physical blending is defined as the simple mechanical mixing of two or more polymers either
in the melt or in solution174 At first glance this approach would seem to be ideal for
preparing hybrids as blending is considered a simple and economical procedure that is
commonly used to produce new products from existing materials175 However in polymer
science the effectiveness of blending is dependent upon the degree of compatibility of the
polymers involved176 At least three general types of materials can result from blending
depending on the mutual solubility and semi-crystallinity of the constituents
412 Equilibrium Phase Behavior
Mixing of two amorphous polymers can produce either a homogeneous mixture at the
molecular level or a heterogeneous phase-separated blend Demixing of polymer chains
produces two totally separated phases and hence leads to macrophase separation in polymer
blends Some specific types of organized structures may be formed in block copolymers due
to microphase separation of block chains within one block copolymer molecule
Two terms for blends are commonly used in literature miscible blend and compatible blend
The terminology recommended by Utracki177 will be used By the miscible polymer blend it
means a blend of two or more amorphous polymers homogeneous down to the molecular
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York (1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York (1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser Publishers Munich (1989)
95
level and fulfilling the thermodynamic conditions for a miscible multicomponent system An
immiscible polymer blend is the blend that does not comply with the thermodynamic
conditions of phase stability The term compatible polymer blend indicates a commercially
attractive polymer mixture that is visibly homogeneous frequently with improved physical
properties compared with the constituent polymers
Miscible blends occur spontaneously when the overall energy of mixing (ΔGmix) is negative
as defined by the Gibbs-Helmholtz free energy equation (Equation 62)
(62)
In the Gibbs-Helmholtz equation ΔHmix is the enthalpy of mixing and ΔSmix is the entropy of
mixing while T is the temperature of the blend Flory-Huggins178 and Scott179 have made
further correlation of enthalpy and entropy as a function of the polymer components and their
properties (Equation 63)
(63)
In Equation 63 χ is a measure of the polymer-polymer interaction energy V is the volume of
the system Φi is the volume fraction of polymer i R is the gas constant T is the temperature
of blending Vr is the reference volume of the monomers and χi is the degree of
polymerization
Examination of Equation 63 reveals that the entropy of mixing is highly dependent on the
molecular weight of the blended polymers while the enthalpy is much more dependent on the
level of interaction between the polymer types Additionally Scott showed that as molecular
weight increases to the level commonly found in commercially useful materials ΔS
approached zero (0) Therefore polymer blends of commercial importance are primarily
influenced by the rate of enthalpy However for polymers with weak interactions (as χ
approaches 1) eg as observed in most polymer pairs the enthalpy of mixing can be further
reduced according to Equation 64
178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279
96
(64)
In Equation 64 δi is the polymerrsquos solubility parameter (an estimation of its ability to be
dissolved in a range of solvents) derived from the square root of the cohesive energy density
pioneered by Hildebrand180 Thus most early work with polymer blends concentrated on
matching the solubility parameters of the component polymers
Unfortunately the theoretical maximum difference in solubility for a 5050 polymer blend is
only 01 (calcm3)12 This narrow margin is much smaller than the standard error among
methods used to determine solubility parameters181 The ability to predict miscibility of
polymer pairs with strong interactions such as donor-acceptor and hydrogen bonding which
can increase miscibility by creating an exothermic reaction upon mixing (ΔH lt0) have been
attempted for many years with varying degrees of success
The formation of miscible blends is dependent on several factors including molecular
structure average chain length tacticity of the polymers as well as the temperature of mixing
and the blending method If the blended polymers are miscible (ΔGmix lt 0) and thus
compatible the resulting material will display an amalgamation of properties which are
predictable using the same techniques as those used for random or statistical copolymers
Polymer blends account for a significant percentage of polymer production and are produced
either to reduce costs to aid in processing or to improve a variety of specific properties For
example polycarbonates have been blended with polybutylene terephthalates to increase
chemical resistance and to aid in processing while polyphenylene oxides are bended with
polystyrenes to improve toughness and increase glass transition temperatures182
413 Compatibilization
As it follows from thermodynamics the blends of immiscible polymers obtained by simple
mixing show a strong separation tendency leading to a coarse structure and low interfacial
180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999)
97
adhesion The final material then shows poor mechanical properties On the other hand the
immiscibility or limited miscibility of polymers enables formation of wide range structures
some of which if stabilized can impart excellent end-use properties to the final material To
obtain such a stabilized structure it is necessary to ensure proper phase dispersion by
decreasing interfacial tension to suppress phase separation and improve adhesion This can be
achieved by modification of the interface by the formation of bonds (physical or chemical)
between the polymers This procedure is known as compatibilization and the active
component creating the bonding as the compatibilizer174 177 183
The most popular method of compatibilization is by addition of a third component In most
cases such an additive is either a block or graft copolymer Since the key requirement is
miscibility it is not necessary for the copolymer to have identical chain segments as those of
the main polymers It suffices that the copolymer has segments having specific interactions
with the main polymeric components viz hydrogen bonding dipole-dipole dipole-ionic
Lewis acid-base etc
Addition of a block or graft copolymer reduces the interfacial tension and alters the molecular
structure at the interface Thus compatibilization by addition changes not only the interfacial
properties but it may affect the flow behavior (hence processability)
One of the disadvantages of the addition method is the tendency of the added copolymers to
form micelles These reduce the efficiency of the compatibilizer increase the blend viscosity
and may lessen the mechanical performance
414 Incorporation of Copolymers for Compatibilization
Block or graft copolymers with segments that are miscible with their respective polymer
components show a tendency to be localized at the interface between immiscible blend
phases Random copolymers sometimes also used as compatibilizers reduce interfacial
tension but their ability to stabilize the phase structure is limited184 Finer morphology and
higher adhesion of the blend lead to improved mechanical properties The morphology of the
resulting two-phase (multiphase) material and consequently its properties depend on a
number of factors such as copolymer architecture (type and molecular parameters of
segments) blend composition blending conditions
183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001)
98
In Scheme19 the conformation of different block graft or random copolymers at the
interface is schematically drawn
Scheme 19 Possible localization of A-B copolymer at the AB interface Schematic of
connecting chains at an interface a-diblock copolymers b-end-grafted chains c-triblock
copolymersdmultiply grafted chain and e-random copolymer
415 The Effect of Compatibilizer on a Blend
The presence of a compatibilizer at the interface substantially affects the development of the
phase structure of molten blends in the flow and quiescent state The position and width of the
concentration region related to co-continuous morphology are affected by two competing
mechanisms A decrease in interfacial tension caused by a compatibilizer favors the formation
and stability of co-continuous structures
The effect of a compatibilizer on fineness of the phase structure can be understood through its
effects on droplet breakup and coalescence A decrease in interfacial tension due to the
presence of a compatibilizer decreases the droplet radius R
Effect of the Compatibilizer Architecture
Compatibilization efficiency of various copolymers follows from their thermodynamic and
microrheological effects It has been generally accepted that the total molecular weight of the
copolymer molecular weight of its blocks and their number are the main structural
compatibilizer characteristics affecting the phase structure of the final blend
99
Effect of Compatibilizer Concentration
The compatibilizing efficiency of the copolymers is besides the architecture a function of
their concentration The effect of a compatibilizer concentration has been quantitatively
characterized by the emulsification curvemdashthe dependence of the average particle diameter of
the minor dispersed phase on copolymer concentration185 The particle diameter decreases
with increase of copolymer concentration until a constant value is obtained For most systems
this value is achieved if the copolymer amount is 15ndash25 of the dispersed phase
416 Methods of Blend Preparation
Five different methods are used for the preparation of polymer blends186 187 melt mixing
solution blending latex mixing partial block or graft copolymerization and preparation of
interpenetrating polymer networks It should be mentioned that due to high viscosity of
polymer melts one of these methods is required for size reduction of the components (to the
order of μm) even for miscible blends
bull Melt mixing is the most widespread method of polymer blend preparation in practice
The blend components are mixed in the molten state in extruders or batch mixers Advantages
of the method are well-defined components and universality of mixing devicesmdashthe same
extruders or batch mixers can be used for a wide range of polymer blends Disadvantages of
the method are high energy consumption and possible unfavorable chemical changes of blend
components This procedure has not been used so far in industrial practice because of large
energy consumption
bull Solution blending is frequently used for preparation of polymer blends on a laboratory
scale The blend components are dissolved in a common solvent and intensively stirred The
blend is separated by precipitation or evaporation of the solvent The phase structure formed
in the process is a function of blend composition interaction parameters of the blend
components type of the solvent and history of its separation Advantages of the process are
rapid mixing of the system without large energy consumption and the potential to avoid
185 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons Inc New York Chap 16 (2000) 186 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709 187 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458
100
unfavorable chemical reactions On the other hand the method is limited by the necessity to
find a common solvent for the blend components and in particular to remove huge amounts
of organic (frequently toxic) solvent Therefore in industry the method is used only for
preparation of thin membranes surface layers and paints
bull A blend with heterogeneities on the order of 10 μm can be prepared by mixing of
latexes without using organic solvents or large energy consumption Significant energy is
needed only for removing water and eventually achievement of finer dispersion by melt
mixing The whole energetic balance of the process is usually better than that for melt mixing
The necessity to have all components in latex form limits the use of the process Because this
is not the case for most synthetic polymers the application of the process in industrial practice
is limited
bull In partial block or graft copolymerization homopolymers are the primary product
But an amount of a copolymer sufficient for achieving good adhesion between immiscible
phases is formed188 In most cases materials with better properties are prepared by this
procedure than those formed by pure melt mixing of the corresponding homopolymers The
disadvantage of this process is the complicated and expensive start-up of the production in
comparison with other methods eg melt mixing
bull Another procedure for synthesis of polymer blends is by formation of interpenetrating
polymer networks A network of one polymer is swollen with the other monomer or
prepolymer after that the monomer or prepolymer is crosslinked189 In contrast to the
preceding methods used for thermoplastics and uncrosslinked elastomers blends of
reactoplastics are prepared by this method
188 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 189 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981)
101
42 Experimental
421 Materials
Polymers used in this research were PEG and PS PEG was purchased from MERCK
company General Purpose PS was obtained from ENPC TP1-Chlef Company Physical and
Structural characterizations of these materials were performed by SEC 1H-NMR and DSC
422 Blend Preparation
PSPEG blends of 5050 wt were prepared by solution casting from THF 40degC The
polymer solutions were stirred until complete miscibility and then cast onto glass dishes and
left to evaporate the solvent to the atmosphere To remove residual solvent after casting the
blends were dried in vacuum oven at 40degC for a weak Table 10 shows the quantities of the
copolymers used for compatibilization of the blends of PSPEG
Table 10 The quantities of the copolymers used for compatibilization of the blends of
PSPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
43 Characterization Techniques for Compatibilization
431 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
102
Relative viscosities of polymer solutions were calculated by dividing the flow times of
solutions by that of the pure solvent The data were plotted using the Huggins equation with
the intrinsic viscosity [η] (dlg-1) determined by extrapolation to infinite dilution
432 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
433 FTIR Analysis
FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
44 Results and Discussion Polyethylene glycol (PEG) is very interesting and important polymers PEG presents good
properties eg hydrophilicity solubility in water and in organic solvents nontoxicity and
absence of antigenicity and immunogenicity190It has attracted increasing attention due to its
potential applications as biomedical and environment friendly materials PEG has been
widely used as a modifier for biomedical surfaces to reduce the protein absorption and
improve their biocompatibility192 and as a stabilizer for emulsion and dispersion It has also
been used as a plasticizer for poly (lactide) (PLA) which is stiff and brittle as a
biodegradable packaging material193
On the other hand polystyrene shows excellent processability good appearance tensile
strength and thermal and electrical characteristics however its brittleness considerably limits
its use in high performance products
Both PS and PEG are widely used commodity polymers Detailed studies on their miscibility
may contribute to technological and environmental applications These polymers form an
interesting pair to study since they exhibit contrasting physical properties PS is a
190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689
103
hydrophobic polymer whereas PEG is hydrophilic PEG is a much softer material than PS
PSPEO blends have been reported as incompatible materials in the literature194 195
N Watanabe et al have reported compatibilization effect of poly (styrene-co-methacrylic
acid) on immiscible blends of this system196
441 Characterization of the Blend Components
Analysis by SEC provides number average-molecular weights and polydispersity indices of
all materials DSC measurements performed to determine their glass transition temperatures
as well as melting point and degree of crystallinity of PEG (See Figure16) 1HNMR spectroscopy analysis was performed on these polymers to determine essentially the
tacticity of PS and also to get information about end groups of PEG which was found to
possess an OH group at each end It has been also determined that the stereoregularity of PS
is Syndiotactic-Atactic (rather highly syndiotactic) (See Figures 17)
Physical characteristics of materials used are given in Table11
Table 11 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PS ENPC TP1-Chlef (from CHI MEI Corp)
105
128 000
1076
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam] Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842
104
Figure 16 1H-NMR spectrum of PEG (Merck) in CDCl3
105
Figure 17 1H-NMR spectrum of Commercial Styrene (ENPC TP1-Chlef) in CDCl3
442 Study of Compatibilization by Dilute Solution Viscometry
a) Introduction
Polymer blends are physical mixtures of structurally different polymers which interact
through secondary forces with no covalent bonding Blending of the polymers may result in a
reduction in the basic cost and improved processing and also may enable properties of
importance to be maximized The polymer blends often exhibit properties that are superior
compared to the properties of each individual component polymer197 198 199 200 The main
advantages of the blend systems are simplicity of preparation and ease of control of physical
properties by compositional change201 202 However the mechanical thermal rheological and
197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85
106
other properties of a polymer blend depend strongly on its state of miscibility on the
molecular scale203
There have been numerous techniques of studying the miscibility of the polymeric blend The
most useful techniques are dynamic mechanical thermal electron-microscopic IR
spectroscopic refractive index203 optical microsscopic204 and viscometric techniques 179 205
Because of its simplicity viscometry is an attractive and very useful method for studying the
compatibility of polymer blends Additional advantages ie that no sophisticated equipment
is necessary and that the crystallinity or the morphological states of the polymer blends do
affect the result206 make the viscometric method more convincing for characterizing polymer
mixtures The principle of using a dilute solution viscosimetry to measure the miscibility is
based on the fact that while in solution molecules of both component polymers may exist in
a molecularly dispersed state and undergo a mutual attraction or repulsion which will
influence the viscosity It is assumed that polymerndashpolymer interaction usually dominate over
polymerndashsolvent ones207 The presence of interactions between atoms or groups of atoms of
unlike polymers is essential to obtain a miscible polymer blend177 179
Estimation of the compatibility of different pairs of polymers based on dilute solution
viscosity for a ternary polymerpolymer-solvent system has been attempted by several
authors including Mikhailov and Zeilkman208 Bohmer and Florian209 Feldman and Rusu210
Krigbaum and Wall211 and Catsiff and Hewett212
The compatibilization of the blends in question has been characterized by viscosity technique
using the Krigbaum and Wall interaction parameter Δb The versatility of the viscometric
technique is not affected by the choice of the solvent as was shown by Kulshreshta et al213
In this section we discuss in details our investigation on the compatibilization of the two
polymer blend systems PSPEG and PMMAPEG 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191
107
b) Theoretical background
The main aspects of the application of dilute solution viscometry method for the study of
interactions and miscibility phenomena in dilute multicomponent polymer solutions were
described Only the most important features will be repeated here It is common to use
empirical relations such as Hugginsrsquo equation214
(65)
for the description of the concentration dependence of viscosity of polymer solutions This
relation is strictly valid only for binary polymer solutions However equations like that of
Krigbaum and Wall211
(66)
And of Catsiff and Hewett212
(67)
were proposed for ideal ternary polymer solutions of the polymer 1+ polymer 2+ solvent type
In previous relations ηsp denotes the specific viscosity [η] is the intrinsic viscosity (limiting
viscosity number) c stands for the mass concentration of polymer and kH is Hugginsrsquo
constant which may be related (in an empirical manner) to the thermodynamic quality of
solvent Relative mass fractions of dissolved polymers wi are used to describe the
composition dependence of viscosity in ternary systems Quantities b 12 and b12 are used to
define the ideal behavior of ternary polymer solutions These are calculated by
(68)
and
(69)
214 ML Huggins J Am Chem Soc 64 (1942) 116
108
respectively Here b denotes the slope of Hugginsrsquo equation for binary solutions
(70)
Moreover it has been shown215 that both the sign and the extent of the deviation of
experimental from theoretical b-values may be correlated to the interactions between
polymeric components of a system under consideration The quantities of interest (miscibility
criterion variables) are defined by
(71)
and
(72)
or can be written in another form
(73)
where m denotes the polymer mixtures Δb intermolecular interaction parameter between
polymer 1and 2 and is considered a good criterion to predict the polymer-polymer
compatibility209 216 217 Δb 0 indicates that the two polymers are compatible whereas
Δb0 indicates that they are incompatible
c) Discussion of the Results
Herein we discuss in detail the compatibilization of PSPEG blends with the synthesized graft
copolymers by viscometric technique The plot of reduced specific viscosity of polymers
versus total polymeric concentration yields a straight line and the intercept and slope
correspond to intrinsic viscosity [η] and molecular interaction coefficient b respectively The
viscosity data for the homopolymers and their blends are presented in Tables 12 and 13
Table 12 Interaction coefficient for binary solutions (polymersolvent) 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin (1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849
109
Polymer components PEG PS
b11 007327 minus
b22 minus 02117
b12 = (b11 b22)12 = 01245 (theo)
Table 13 Interactions parameters for PSPEG blends with poly (St-g-PDXL) copolymers
(2SP2 2SP1 and DXSP) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
DXSP b12 003511 01295 01680 01833 01947
Δb - 00894 00050 00435 00588 00702
2SP2 b12 003511 009826 01052 01314 01515
Δb - 00894 - 00262 - 00193 00069 00270
2SP1 b12 003511 minus minus minus 01262
Δb - 00894 minus minus minus 00017
For incompatible blends the incompatible molecules refuse to overlap thus they shrink in
size which leads to a decrease in hydrodynamic volumes As a matter of fact the crossover in
the reduced viscosity-concentration plot is observed
As far as we are concerned with the blend of PSPEG the results obtained present similar
situation Figure 18 shows the Huggins plots for the homopolymers and the (5050) blend of
PSPEG In this figure a crossover is observed and a decrease of slope occurs at about 05
gdl in the viscosity-concentration plot Above this concentration two incompatible polymers
PS and PEG undergo mutual repulsion in dilute solution the hydrodynamic volume of chains
is lower The reduction of the hydrodynamic volume will result in a decrease of the reduced
viscosity of solution correspondingly the slope of the plot suddenly declines
110
02 03 04 05 06 07 08 09 10 11
03
04
05
06
07
08PS PEG and PSPEG (5050)
PS PSPEG 0 PEG
Redu
ced
visc
osity
η sp
c
(ldl
)
C (dll)
Figure 18 Plots of reduced viscosity (ηspc) vs concentration for PS PEG and PSPEG
blend (0) in THF at 30degC
Figures 19 20 21 and 22 show the incorporation of various amounts of copolymers in the
immiscible blend As far as the amount of the compatibilizers increases the crossover of the
plots occurs at very low concentration or even it is not observed In addition the slope of the
plot increases with an increase of the amount of the compatibilizers introduced in the blend
This is due to the mutual attraction of the blend components which is enhanced by the
presence of the copolymers As a matter of fact the latter act as compatibilizing agents
allowing to the blends to exhibit miscibility
111
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07BLENDS WITH DXPS
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 19 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of DXPS copolymer
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLENDS WITH 2SP2
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 20 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of 2SP2 copolymer
112
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLEND WITH 2SP1 40
PSPEG 0 2SP1 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 21 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with 40 of the dispersed phase of 2SP1 copolymer
02 03 04 05 06 07 08 09 10 1100
01
02
03
04
05
06
07
08
DXPS 40 2SP2 40
2SP1 40
2SP1 40 2SP2 40 DXPS 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 22 comparison of plots of reduced viscosity (ηspc) vs concentration for PSPEG
blends in THF at 30degC with 40 of the dispersed phase of DXPS 2SPS2 and 2SP1
copolymer
113
Figure 22 compares the three copolymers used for compatibilization of PSPEG with respect
to 40 by weight of the dispersed phase addition to the blends
Krigbaum and Wall suggested that information about the interaction between two polymers
should be obtained from the difference of experimental b12 and theoretical b12 Δb A positive
difference between the experimental and theoretical interaction coefficients is evidence of a
compatible polymer pair The higher the value of Δb the higher the extent of compatibility
Negative values refer to repulsive interaction and incompatible mixes The values of Δb
according to equation 73 for different blends with compatibilizers are given in Table 13 and
Figure 23
0 10 20 30 40 5
-010
-005
000
005
010
0
PS PEG BLENDS
2SP2 DXPS
Δb
Amount of incorporated copolymer w ()
Figure 23 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (DXPS and 2SP2) used for compatibilization
It was observed as the amount of compatibilizers increases values of the interaction
parameter increase thereby increasing the compatibility between the two polymer
components of the blend Consequently this indicates that these copolymers act as
compatibilizing agents in the immiscible blends of PS and PEG Now in comparing these
copolymers in terms of structure (number of grafts) and PDXL content it can be noticed that
the results obtained DXPS ( 71 w of PDXL) copolymer show higher values of Δb than
2SP1(30 w of PDXL) and 2SPS2 (4025 w of PDXL) do This is due to the comb-
structure of the DXPS copolymer (synthesized by CRP) and therefore containing more grafts
114
(Ng = 58) than the other copolymers Besides the amount of PDXL in the copolymer PDXL
includes polar groups which provide associative interactions with one of the blend
components (PEG) and thus undergoes significant effects upon compatibilization In the
figure below it can be seen that addition of 10 by weight of the dispersed phase (47 of
total weight of the blend) of DXPS is sufficient to compatibilize the immiscible blend of
PSPEG (5050) Then a drastic increase of the interaction parameter with the addition of the
compatibilizer (DXPS) compared to the addition of either 2SP2 or 2SP1 (Table 13)
From the results shown in the graph miscibility of the blend can be achieved by incorporating
around 25 (11 of total weight of the blend) of 2SP2 copolymer However compatibibility
of the blend with 2SP1 copolymer is obtained at 40 by weight of the dispersed phase since
its interaction parameter (Δb) found to be 00017
It is worth to mention that the PDXL content of 2SP1 is 30 and the length of the grafts is
half that of 2SP2 copolymer For this reason these two copolymers have been chosen for the
purpose of comparison in terms of side chains length
An optimization of the amount of copolymer needed for compatibilization of PSPEG (5050)
blend has been made (corresponding to Δb = 0) as function of the PDXL content and shown
in Table 14
Table 14 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050) vs PDXL content
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
DXPS 0 9 43 71
2SP2 0 245 109 4025
2SP1 0 40 166 30
115
443 Optical Microscopy and Phase Morphology
PDXL is a perfect alternate copolymer of poly (ethylene oxide) (PEO) and poly (methylene
oxide) (PMO) that has the same curious combination properties as PEG So PDXL must be
at least miscible with PEG or adhere at the interface between PS and PEG and between
PMMA and PEG The compatibility between hydrophobic PS or PMMA and hydrophilic
PEG is very poor Compatibilization between components of the two sets of polymer blends is
studied by optical microscopy
The morphological characteristics of the blends by different compatibilizers are presented in
Figure 24 The optical microscopy micrographs of PSPEG blends without compatibilizers
show a poor dispersion for PS disperse phase and a ldquoball-and-socketrdquo topography due to the
poor interfacial adhesion between PEG matrix and the dispersed phase However with the
addition of compatibilizers the morphological characteristics of the polymer blends are
greatly altered It can be noticed that for these two different blends the particle size of PS
domains gets progressively much smaller and uniform in compatibilized blends than in
incompatibilized ones This may be explained by the significant increase of the phase
interfacial adhesion Consequently the domain size strongly depends upon the
compatibilizers used
116
a) PSPEG (5050) 0 (without compatibilizer)
DXPS 10 DXPS 20 DXPS 30 DXPS 40 b) Compatibilizing effect of DXPS copolymer
2SP2 10 2SP2 20 2SP2 30 2SP2 40 c) Compatibilizing effect of 2SP2 copolymer
2SP1 40
117
d) Compatibilizing effect of 2SP1copolymer at 40 addition
Figure 24 Optical micrographs showing phase structure in 5050 PSPEG blends
a) blends without compatibilizer b) with DXPS c) with 2SP2 d) with 40 of 2SP1
For instance the PSPEG blends with the incorporation of the copolymers DXPS 2SP2 and
2SP1 as compatibilizers (Figure 24) the morphology displays a very fine dispersion of PS
phase and strong interfacial adhesion with PEG Matrix The good compatibilizing effect
mainly that of DXPS can be explained by two mechanisms
First the PDXL units in the compatibilizer interact with PEG ether groups leading to a good
adhesion at interface between the components of the blend In addition hydrogen bonding
may also exist between PDXL and PEG further increasing compatibilization Second since
the compatibilizer also contains styrene blocks it contributes to provide a good compatibility
with PS Consequently the remarkable compatibilizing effect of PS-g-PDXL copolymers
induced a drastic decrease in interfacial tension and suppression of coalescence between the
originally immiscible polymer phases
As it can be noticed from the micrographs given in the figure above the compatibilizer
exhibits finer dispersion and homogeneous morphology of the blends as the amount of
compatibilizers increases
Eventually each compatibilizer has its own effect on the immiscible blends depending on the
amount of PDXL (side chains) and number of grafts present in the copolymers
By comparing micrographs shown in Figure 24 b and c the compatibilization effect of DXPS
copolymer which contains more grafts but shorter is different from that of the 2SP2
copolymer In the case of DXPS it is observed that the size of the dispersed droplets is
deceased significantly and results in finer dispersion morphology However 2SP2 copolymers
shows an improvement in compatibility of the blend after addition up to 30 wt of the
dispersed phase (13 total weight of the blend) exhibits homogeneous morphology This
may be related to length of the grafts In all cases these copolymers act as good
compatibilizers for the blend of 5050 wt PSPEG
444 FTIR Analysis
The FTIR technique is very important since it allows one to study the specific interactions
between the polymers The knowledge of the polymerndashpolymer interactions will be useful for
118
studies of the compatibility in polymer blends To verify the intermolecular interactions that
can play a role in miscibility the vibrational spectra of the blends studied in the present work
were obtained In polymeric systems where there are multiple interactions vibrational bands
such as ν (C=O) ν (COC) and ν (OH) present contributions of spectroscopic free and
associated forms
In order to elucidate the role played by intermolecular interactions in the miscibility of these
blends FTIR absorption of individual polymer components PS PEG and PMMA and
compared to that of the mixtures Figures 26 27 and 28 present the FTIR absorption spectra
from 4000 to 400 cm-1 for all samples
In the case of PS the high-frequency infrared spectra consist of seven absorption bands The
bands with peak locations at 3008 3026 3060 3082 and 3103 cm-1 are due to C-H stretching
of benzene ring CH groups on the PS side-chain The bands with peak positions of 2924 and
2850 cm-1 are due to the C-H stretching vibration of the CH2 and CH groups of the main PS
chain respectively PEG with molecule chemical structure of HO-[CH2-CH2-O]n-H exhibits
important absorption bands from FTIR spectroscopy measurements as shown in Figure 25 It
was verified contributions associated with CndashOndashC symmetric stretching of ether groups218-220
221 from 1050 to 1150 cm-1 with maximum peak at 1150 cm-1 Characteristics CH2-O
stretching modes from 2800-3000 cm-1 are observed214 At low frequency region peaks at 850
and 890 cm-1 are assigned to CndashOndashC stretching and at 500 cm-1 ascribed to CndashOndashC
deformation The presence of PDXL in the blends is detected by the intense frequency at 1140
cm-1 which is assigned for acetal groups In addition both PDXL and PEG contain ether
groups and the spectra show that the corresponding peaks are overlapped for the blends The
intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of PEG
crystallinity in the blends222
218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10 219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601
119
It can be observed also a typical large hydroxyl bands with two distinct contributions which
can be seen for all samples They are attributed to the spectroscopically free and bonded ndashOH
stretching forms at 3600-3800 cm-1 and 3200-3500 cm-1 respectively221 - 227
500 1000 1500 2000 2500 3000 3500 4000-05
00
05
10
15
20
25
30
35
PS and PEG PEG PS
Abs
orba
nce
Wave number (cm-1)
Figure 25 FTIR spectra of PS PEG over 4000-400 cm-1 range
227 Peppas NA Wright L Macromolecules 1996298798ndash804
120
500 1000 1500 2000 2500 3000 3500 4000
0
1DXPS IN PSPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 26 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS)
All these absorption bands for individual polymer were observed in the FTIR spectrum of the
5050 (ww) PSPEG in which they were combined to give superimposed bands in the regions
of 750-1500 cm-1 and 2700- 3100 cm-1
The hydroxyl vibrational frequency is discernible in the blend spectrum for PSPEG at 0
With the incorporation of the copolymers for compatibilization a number of bands showed
small shifts and changes in position and shape in the resulting spectra In Figures 28 29 and
30 as it can be noticed that in the hydroxyl absorption region a decrease in the fraction of
free OH groups is observed as the amount of copolymers is increased in the blend This can
be due to the flexibility of the PDXL graft chains on the other hand to the acetal and ether
groups of PDXL which are probably randomly distributed among an increasing number of
hydroxyl groups of PEG statistically favoring the formation of the PDXL and PEG hydrogen
bond interaction The results indicate that the intermolecular hydrogen bonding between the
ether oxygen of PDXL and the hydroxyl groups of PEG may be formed thereby reducing the
fraction of free OH which is consistent with the shifts observed in the region of hydroxyl
stretching Intermolecular hydrogen bondings are expected to occur among PDXL and PEG
chains due the high hydrophilic forces These interactions have replaced the intramolecular
121
interactions between COC and OH groups of PEG before addition of containing PDXL
copolymers It can be noticed a progressive shift of hydroxyl band from 3340 to 3420 cm-1
with DXPS and from 3340 to 3350 cm-1 when 2SP2 is added This shift can be attributed to
the decrease of intramolecular interactions among hydroxyl groups within PEG chains in
favor to intermolecular interactions between PDXL and PEG228
500 1000 1500 2000 2500 3000 3500 4000
0
1
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 27 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2)
228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
122
3200 3300 3400 3500 3600 3700 3800
00
01
DXPS IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 28 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS) in the hydroxyl absorption region
3200 3300 3400 3500 3600 3700 3800
00
02
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 29 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2) in the hydroxyl absorption region
123
3200 3300 3400 3500 3600 3700 3800
00
DXPS 40 2SP2 40 2SP1 40
Abs
orba
nce
Wave number (cm-1)
Figure 30 FTIR spectra comparison of PSPEG blends (5050) with different compatibilizers
in the hydroxyl absorption region
Conclusions An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends Again The PS blocks of the copolymer result in good
compatibility with PS component of the blends The compatibilization of PSPEG blends is
apparently associated with hydrogen bonding where groups of the acetal units in PDXL
interact with hydroxyl groups of PEG These form a stronger interface between the two
phases which leads to important modifications of the blend properties Apparently the FTIR
result is in good agreement with the miscibility criteria proposed by Krigbaum and Wall (Δb)
interaction parameter which results from dilute-solution viscometry (DSV) method It can be
concluded that by the addition of 20ndash40 wt of incorporated copolymer reveal a good
compatibilizing efficiency for the blend systems as it was observed from micrographs as well
124
References
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York
(1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York
(1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser
Publishers Munich (1989) 178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279 180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999) 183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001) 185 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709
125
186 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and
Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458 187 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 188 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981) 189 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons
Inc New York Chap 16 (2000) 190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689 194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam]
Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842 197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191 214 ML Huggins J Am Chem Soc 64 (1942) 116 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin
(1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849 218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10
126
219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601 227 Peppas NA Wright L Macromolecules 1996298798ndash804 228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
127
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g-
Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of
Polystyrene and Poly (Ethylene Glycol)
51 Introduction
PMMA is more than just plastics of paint Often lubricating oils and hydraulic fluids tend to
get really viscous and even gummy when they get cold This is a real pain when operating
heavy equipments in very cold weather When a little bit of PMMA is dissolved in these oils
and fluids they donrsquot get viscous in the cold and machines can be operated down to -100degC
PMMA can find a several applications namely adhesive optical coating medical packaging
applications and so forthhellip
In medical applications PMMA and its derivatives are used particularly for hard tissue repair
and regeneration229 PMMA beads have been developed to deliver aminoglucoside antibiotics
locally for the treatment of bone infections230 PMMA and PEG form an important and unique
pair of polymers in that they are chemically different In the present work this study may
shed light on the PMMA properties modifications induced by blending with PEG to overcome
the difficult processing of rigid PMMA
Several studies have been made on blends of poly (ethylene oxide) PEO and PMMA in the
last decades but very few on PMMAPEG blends231 232 233
Numerous works reported that the miscibility domain ranges between 10 and 30 of PEO by
weight depending on the PMMA tacticity or molecular weight No phase diagram is available
yet in the literature for PMMAPEO and neither it is for PMMAPEG234
229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703
127
52 Experimental
521 Materials
PEG and PMMA were used as blend components PMMA was obtained from ENPC TP1-
Chlef Company PEG was purchased from MERCK Company Physical and Structural
characterizations of these materials were performed by SEC 1H-NMR and DSC
522 Blend Preparation
Blends of PMMAPEG (5050) were prepared using the same procedure as described for the
blends discussed in the previous chapter Table 15 shows the quantities of the copolymers
used for compatibilization of the blends of PMMAPEG
Table 15 The quantities of the copolymers used for compatibilization of the blends of
PMMAPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
53 Characterization Techniques
531 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
532 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
128
533 FTIR FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
54 Results and Discussion
541 Characterization of the Homopolymers
The polymers have been analyzed by SEC to determine their number average-molecular
weights and polydispersity indices DSC measurements performed to determine their glass
transition temperatures as well as melting point of crystallinity of PEG 1HNMR spectroscopy analysis revealed the tacticity of PMMA It has been found that PMMA
is Syndiotactic-Atactic (highly syndiotactic) as shown in Figure 3 and 321
Physical characteristics of materials used are given in Table 16
Table 16 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PMMA ENPC TP1-Chlef (fromLG MMA Corp)
119
55 000
113
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
129
Figure 31 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in CDCl3
Figure 32 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in the methyl shifts
region in CDCl3
130
542 Dilute Solution Viscometry
Dilute solution viscometry has been utilized to evaluate miscibility of PMMAPEG blends
and the same approach discussed in the previous section has been followed The
experimental reduced viscosities of the polyblends are plotted against concentration in dilute
solution viscometry Eventually plots of pure polymers and polyblends of 5050 PMMAPEG
are first obtained Then their interaction coefficients are determined as shown in Table 17
Table 17 Interaction coefficient for binary solutions (polymersolvent)
Blend components PEG PMMA
b11 007327 minus
b22 minus 006561
b12 = (b11 b22)12 = 006933 (theo)
The compatibility of this system has been evaluated through the sign of Δb The values of the
latter according to equation 73 for different amounts of poly (MMA-g-PDXL) copolymers in
the blends are given in Table 18 It is observed that the blend of PMMAPEG at 5050 by
weight shows a negative value of Krigbaum and Wall parameter which indicates
incompatibility of the system as it is expected Similarly to PSPEG blend a crossover in the
reduced viscosity-concentration plot is observed and a decrease of slope arises in the range of
05 to 066 gdl in the viscosity-concentration plot as shown in Figure 33 This is attributed to
the repulsive intermolecular interactions between the polymer chains
Then the incorporation of the copolymers at various amounts presents positive values
progressively Curves of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in
THF at 30degC with various amounts of copolymer are given in Figures 34 35 and 36
131
Table 18 Interactions parameters for PMMAPEG blends with poly (MMA-g-PDXL)
copolymers (3MP2 2MP2 and 3MP1) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
3MP2 b12 00288 01308 01904 02373 02602
Δb - 004053 00615 01211 01680 01909
2MP2 b12 00288 01286 01690 01893 02296
Δb - 004053 00593 00997 01200 01603
3MP1 b12 00288 00868 01670 02010 02379
Δb - 004053 00175 00977 01317 01686
00 01 02 03 04 05 06 07 08 09 10 11020
025
030
035
040PMMAPEG (5050) 0
PEG PMMAPEG 0 PMMARe
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 33 Plots of reduced viscosity (ηspc) vs concentration for PMMA PEG and
PMMAPEG blend (0) in THF at 30degC
132
02 03 04 05 06 07 08 09 10 11000
005
010
015
020
025
030
035
040 BLENDS WITH 3MP1
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 34 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP1 copolymer
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040
045BLENDS WITH 3MP2
PMMAPEG 0 10 20 30 40
Redu
ced
visc
osity
η
spc
(d
lg)
C (gdl)
Figure 35 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP2 copolymer
133
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040BLENDS WITH 2MP2
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 36 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 2MP2 copolymer
From our viscosity data as the copolymer content increases in the blend the polymer blend
molecules will become disentangled more spaciously resulting in a greater interaction
between structurally similar component segments This suggests that there are attractive
forces that induce miscible behavior of the blends as it is observed in Figure 37
0 10 20 30 40 5-01
00
01
02
0
PMMA PEG BLENDS
3MP2 2MP2 3MP1
Δb
Amount of incorporated copolymer w ()
Figure 37 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (3MP2 2MP2 and 3MP1) used for compatibilization
134
The three copolymers (3MP2 2MP2 and 3MP1) involved in this study for compatibilization
are different from the point of view of the PDXL content and the graft length For instance
3MP2 and 2MP2 have similar and longer grafts since the theoretical number average-
molecular weight of the graft is 2000 gmol However they contain different amount of
PDXL In the case of 3MP1 this graft copolymer has a structure with shorter side chain length
(Mn = 1000 gmol) corresponding to the half of the graft size in the former copolymers From
the observations made out of the figure above 3MP2 copolymer (21 w of PDXL) provides
higher values of the interaction parameter and therefore greater extent of compatibility
compared to the other copolymers since it has long grafts which allows penetration into the
other phase
It can be concluded that all three copolymers show good results for compatibilization on the
basis of the Δb criterion of polymer-polymer miscibility determined by viscometry
Similarly the minimum amount of copolymer needed for compatibilization of PSPEG
(5050) blend has been determined corresponding to Δb = 0 as function of the PDXL content
and shown in Table 19
Table 19 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050)
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
2MP2 0 34 16 35
3MP2 0 37 18 21
3MP1 0 58 28 19
135
543 Optical Microscopy and Phase Morphology
a) PMMAPEG (5050) 0 (without compatibilizer)
b) Compatibilizing effect of 2MP2 copolymer
c) Compatibilizing effect of 3MP2 copolymer
d) Compatibilizing effect of 3MP1copolymer
Figure 38 Optical micrographs showing phase structure in 5050 PMMAPEG blends
a) blends without compatibilizer b) with 2MP2 c) with 3MP2 d) with 3MP1
136
Figure 38 presents microscopy images of PMMAPEG blends with varying amounts of
compatibilizers The morphological characteristics of the blends of PMMAPEG without
compatibilizers show a poor dispersion of PMMA as a dispersed phase The addition of
compatibilizers changes drastically the morphological topology of this system The
compatibilizers used are of different length of the side chains and also different PDXL
content By introducing progressively variable amounts of the compatibilizers they display
similarly the morphological characteristics to some extent It is observed that the phase
separated domains of PMMA in the blends are reduced with increasing amounts of the
compatibilizers This is due to the compatibility of PMMA of the copolymers with the
PMMA blend component and on the other hand to the interfacial interactions of the PDXL
of the copolymers and PEG component of the blends From these results it is revealed that
compatibilizing effect of 2MP2 copolymer on this system is great compared to the others Not
only causes the size of the dispersed droplets to decrease but also dispersed droplets become
homogeneous However 3MP1 copolymer which contains shortest grafts (about half length
of those of the other copolymers) and less amount of PDXL shows less reduction in the
droplet size compared to the other copolymers Therefore it can be concluded that the
compatibilization of this blend depends upon length and number of grafts
On the overall observations these compatibilizing copolymers are very effective and hence
influence and improve the compatibility of PMMAPEG blend at a composition of 5050 wt
544 FTIR Analysis
Same observations can be made for the blends of PEG with PMMA The FTIR spectrum of
this blend at 0 compatibilizer is shown in Figure 39 For pure PMMA the
spectroscopically free carbonyl group band is observed at 1730 cm-1 In the blend sample one
large vibrational band due to hydroxyl group stretches in pure PEG is observed with two
distinct contributions which can be seen for all samples They are attributed to the
spectroscopically free and associated hydroxyl forms at 3495 and 3600 cm-1 respectively
A large band in the wave number range of 1400-1500 cm-1 is assigned to the deformation
vibration of the methyl groups The bands with peaks locations at 2820 and 2990 cm-1 are due
to C-H symmetrical and asymmetrical stretching vibration of CH3 respectively Peaks at
2886 and 2950 cm-1are ascribed to C-H symmetrical and asymmetrical stretching vibration of
CH2 figures 40 and 41 The C-O band is observed in the range of 1150- 1210 cm-1
137
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 PMMAPEG 0 Blend
Abs
orba
nce
Wave number cm-1
Figure 39 FTIR spectra of PMMAPEG 0 over 4000-400 cm-1 range
2750 2800 2850 2900 2950 3000 3050 3100-05
00
05
10
15
20
Abs
orba
nce
PEG PMMAPEG 0
Wave number cm-1
Figure 40 FTIR spectra of PMMAPEG 0 and PEG over the 3100-2700 cm-1 range
138
2750 2800 2850 2900 2950 3000 3050 3100
00
05
10
152MP2 in PMMAPEG
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 41 FTIR spectra of PMMAPEG 0 blends with 2MP2 addition over the 3100-2700
cm-1 range
The incorporation of PMMA-g-PDXL copolymers in the blends makes some changes in the
resulting spectra as it can be noticed in Figures 42 - 44 In the hydroxyl absorption region
same phenomenon has occurred as in the PSPEG blends The fraction of free OH groups has
decreased as the amount of the copolymers increased as shown in figures 45 and 46 which
present the effect of different compatibilizers in the hydroxyl absorption region This can be
explained as discussed above by the fact that the PEG hydroxyl groups undergo other
intermolecular interactions essentially with PDXL chains of the copolymers A comparison of
the effect of the three copolymers involved in the compatibilization at the highest amount
added is given in figure 47 It can be noticed that 2MP2 shows very few fraction of free OH
groups compared to the others This copolymer contains more PDXL (35 wt with 4 grafts)
than the others do (21 wt with 3 grafts and 19 wt with 3 grafts in 3MP2 and 3MP1
respectively)
A crystalline PEG phase is confirmed by the presence of the triplet peak of the COC
stretching vibration at 1148 1110 and 1062 cm-1 with a maximum at 1110 cm-1235 236
Changes in the intensity shape and position of the COC stretching mode are associated with
235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115
139
the interaction between PEG and PMMA-g-PDXL In addition both polymers contain the
same ether group and the spectra show that the corresponding peaks are overlapped for the
blends The intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of
PEG crystallinity in the blends237
Therefore the presence of this interacting system is probably responsible for the miscibility
and low degree of crystallinity observed for these blends
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
202MP2 in PMMAPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 42 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (2MP2)
237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
140
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 43 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2)
500 1000 1500 2000 2500 3000 3500 4000
0
1
2 3MP1 IN PMMAPEG BLENDS 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 44 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1)
141
3500
00
05
3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 45 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2) in the hydroxyl absorption region
3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
-02
00
02
04
06
08
3MP1 IN PMMAPEG 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 46 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1) in the hydroxyl absorption region
142
3500
2MP2 40 3MP2 40 3MP1 40
Abs
orba
nce
Wave number cm-1
Figure 47 FTIR spectra comparison of PMMAPEG blends (5050) with different
compatibilizers in the hydroxyl absorption region
The results from FTIR spectra indicate the compatibility of these polymer blends with the
addition of the PDXL copolymers via hydrogen bonds is observed and confirmed mainly by
the shifts of bands of the hydroxyl stretching modes
143
Conclusions
From the observations made out from this study reveal that all three copolymers show good
results for compatibilization on the basis of the Δb criterion of polymer-polymer miscibility
determined by viscometry Therefore these copolymers act as good compatibilizers since it
was found that the minimum amount needed for compatibilizing is between 1 to 3 of the
total weight of the blend which corresponds to 3 to 6 of the dispersed phase This
compatibilization is due to the fact that the copolymers have constituents which present strong
interactions with both polymer components of the blends These results are in great agreement
with microscopy analyses which demonstrate that the phase separated domains of PMMA in
the blends are reduced with increasing amounts of the compatibilizers This is due to the
compatibility of PMMA of the copolymers with the PMMA blend component and on the
other hand to the interfacial interactions of the PDXL of the copolymers and PEG component
of the blends
From FTIR results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PMMA and relatively long PMMA backbone of PMMA-g-PDXL copolymers respectively
These compatibilizing copolymers are very effective and hence influence and improve the
compatibility of PMMAPEG blend at a composition of 5050 wt
144
References 229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703 235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115 237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
145
CONCLUSIONS
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel using an unsaturated alcohol (2-
HPMA) as a transfer agent results in linear polymeric chains in order to prevent formation of
cyclic oligomers through cationic polymerisation of cyclic acetals They were all prepared at
the same reaction conditions
The characterization of these macromonomers has been conducted using different methods of
analysis Structure and molecular weight determination were provided from SEC and Raman
and 1H-NMR spectroscopy
We were interested in obtaining a hydrogel based on fully PDXL segments and study its
swelling and viscoelastic behaviour The hydrogel has combined special properties The
results reveal a perfect elastic and resistant hydrogel with interesting viscoelastic properties
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers Structure composition and number of grafts of the
copolymers were determined by SEC and 1H-NMR spectroscopy Another approach for
copolymerization has been made in order to compare the copolymers obtained from different
types of polymerization reactions like Conventional Free Radical and Controlled Radical
Polymerizations In the latter the copolymer obtained possesses larger number of grafts than
those from the former
The macromonomer reactivity estimation suggests that the length of the PDXL side chains
does affect the reactivity of the methacrylic double bond of the macromonomer when
copolymerized with St However in the case of copolymerization with MMA there is no
dependence on the graft size Finally from DSC measurements the values of Tg depend on
the composition and the size of the PDXL grafts In all copolymers the increase in amount of
the incorporated PDXL macromonomer results in a substantial decease in glass transition
An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
146
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends
The compatibilization effect of the copolymers used in this study on the PSPEG and
PMMAPEG was demonstrated from the viscometric results The contribution of both PS or
PMMA and PDXL of the copolymers has played a big role in the compatibilization of these
two different systems of blends thereby resulting in good compatibility due the chemical
affinity between these components which leads to a drastic decrease in interfacial tension and
suppression coalescence between the blend constituents
It has been shown that the immiscible blends in question exhibit compatibility when small
amount of copolymers synthesized for this purpose are added except for one of them
Styrene-g-PDXL copolymers act as good compatibilizers for PSPEG blends since it was
found that the minimum amount needed for compatibilizing is less than 11 of the total
weight of the blend which corresponds to 25 of the dispersed phase This compatibilization
is due to the fact that the copolymers have constituents which present strong interactions with
both polymer components of the blends
Compared with PS-g-PDXL with DXPS content the DXPS is more effective binary polymer
blends compatibilizer in the PSPEG blends which is due to the high number of grafts and
high PDXL content This has led to good adhesion of PDXL chains with the PEG phase in the
blends Again The PS blocks of the copolymer result in good compatibility with PS
component of the blends The compatibilization of PSPEG blends is apparently associated
with hydrogen bonding where groups of the acetal units in PDXL interact with hydroxyl
groups of PEG These form a stronger interface between the two phases which leads to
important modifications of the blend properties
Similarly PMMA-g-PDXL copolymers act as good compatibilizers since it was found that
the minimum amount needed for compatibilizing is between 1 to 3 of the total weight of
the blend which corresponds to 3 to 6 of the dispersed phase This compatibilization is due
to the fact that the copolymers have constituents which present strong interactions with both
polymer components of the blends
These results are in great agreement with microscopy analyses which demonstrate that the
phase separated domains of PMMA and PS in their respective blends are reduced with
increasing amounts of the compatibilizers
147
Specific interactions between chemical groups of two blend components can play an
important role in polymer mixtures There is a range of such interactions of varying strengths
which has been identified in polymer blends and such interactions are generally defined for
small molecules It should be noted that the extension of this concept to polymers is not
always straightforward it is more difficult to identify interactions in polymers the
spectroscopy is more complex and molecular conformations are less certain This situation is
further complicated because researchers use different names and definitions to describe
similar interactions
FTIR investigation showed that these interactions have been observed through the changes in
IR absorption peaks of PS PEG and PMMA upon mixing with increasing amount of
compatibilizers in their blends which have given rise to a wide investigation
From these the results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PSPEG and PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PS or PMMA and relatively long PS or PMMA backbone of PS-g-PDXL and PMMA-g-
PDXL copolymers respectively
148
532 Optical Microscopy helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 128
533 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
54 Results and Discussion helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 129
541 Characterization of the Homopolymers helliphelliphelliphelliphelliphelliphelliphelliphellip 129
542 Dilute Solution Viscometry helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 131
543 Optical Microscopy and Phase Morphology helliphelliphelliphelliphelliphelliphellip 136
544 FTIR Analysis helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 137
Conclusions helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 144
References helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 145 CONCLUSIONS helliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip 146
SUMMARY
Research and development performed on synthetic polymers during the last century has led to
many classes of different polymers for specific applications New types of synthetic polymers
with tailor-made properties are still being introduced for new applications The challenge for
polymer chemists is to control and alter the polymerization conditions such that the final
product has a well-defined structure with desired properties The complex structure of
polymers requires continued analytical chemical efforts to understand the polymerisation
process and the relationships between the molecular structure and material properties
The central point of this thesis is the synthesis and the exploration of the benefits of graft
copolymers derived from poly (1 3 dioxolane) (PDXL) as compatibilizing agents via their
incorporation in immiscible polymer blends The enhancement of adhesion in the solid state
can be accomplished by introducing a compatibilizer that can act as an adhesive between two
polymers andor by control of morphology especially by inducing the phase co-continuity
Graft copolymers offer all Properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheological control i e it
leads to decreased melt viscosities which is an important advantage for processing Depending
on the nature of their backbone and side chains they can be used for a wide variety of
applications such as impact-resistant plastics thermoplastic elastomers polymeric
emulsifiers and even more exciting is the ability of these graft copolymers to function as
compatibilizersinterfacial agents to blends immiscible polymers
The state-of-the-art technique to synthesize graft copolymers is the copolymerization of
macromonomers with low molecular weight comonomers It allows the control of the
polymeric structure which is given by three parameters (i) chains length of the side chains
which can be controlled by the synthesis of macromonomers by living polymerization (ii)
chain length of the backbone which can be controlled in a living polymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular-weight monomer
i
New properties lower prices and reuse of polymers are needed to meet demands of todayrsquos
society and hence of the polymer industry Unfortunately the demands for many applications
need a set of properties that no polymers can fulfil One method to satisfy these demands is by
mixing two or more polymers Materials made from two polymers mixed are called blends In
recent years blending of polymers as a means of combining the useful properties of different
materials to meet new market applications with minimum development cost offers an
interesting route to improve a variety of specific properties of the thermoplastics This has
been increasingly used by the polymer industry
Much work has been done on the blending (mixing) of polymers by many authors A large
part of these studies deal with attempts to obtain a combination of properties of different
polymers Unfortunately these properties of the polymer blends are usually worse instead of
better for many combinations of polymers Significance for these properties is compatibility
between the different polymers which is frequently defined as miscibility on a molecular scale
of the blends components The incorporation of a dispersed phase into a matrix mostly leads
to the presence of stress concentrations and weak interfaces arising from poor mechanical
coupling between phases and therefore morphologies with coarseness commonly on
micrometer scale are obtained Improving mechanical and morphological properties of an
immiscible blend is often done by compatibilization which is a process of modification of the
interfacial properties in immiscible polymer blend resulting in reduction of the interfacial
tension coefficient formation and stabilisation of the desired morphology The use of graft or
block copolymers as compatibilizers for immiscible polymer blends has become an efficient
means for development of new high-performance polymer materials There have been
numerous techniques of studying the miscibility of the polymeric blends The most useful
techniques are viscosimetry measurementsiiiiii thermal analysisiv dynamic mechanical
analysisv refractive indexvi nuclear magnetic resonance methodvii scanning electronviii and
optical spectroscopyix
i Z Sun W Wang and Z Fung Eur Polym J 28 (1992) 1259 ii Aroguz AZ and Baysal BM Eur Polym J42 3 (2006) 11ndash5iii Zhang Y Qian J Ke Z Zhu X Bi H and Nie K Eur Polym J 38 (2002) 333ndash7 iv M Song and F Long Eur Polym J 27 (1991) 983 v Olabisi O Rebeson LM and Shaw MT Polymerndashpolymer miscibility New York Academic Press (1979) vi AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 vii EG Crispim ITA Schuquel AF Rubira and EC Muniz Polymer 41 (3) (2000) 933 viii Martin IG Roleister KH Rosenau R and Koningsveld RJ Polym Sci Part B Polym Phys24 (1986) 723 ix W Wu X Luo D Ma Eur Polym J 35 (1999) 985
ii
Well-known examples of commercial blends are high impact polystyrene (HIPS) and
acrylonitrile-butadiene-styrene (ABS) These blends are tough and have good processability
One of the most interesting examples of an amorphous polymer is polystyrene because of its
brittleness Adding a compatibilizer with the structure of a copolymer to
Polystyrenepolyethylene (PSPE) improves the toughness by a factor 3x Another example is
the use of poly (styrene-co-methacrylic acid) as a compatibilizer in immiscible (incompatible)
blends of PS and polyethylene (PEG)xi
It is of great interest to study miscibility and phase behaviour of two different commodity
immiscible polymer blend systems as PSPEG and polymethyl methacrylate polyethylene
glycol (PMMAPEG) by adding poly (styrene-g-PDXL) and poly (methyl methacrylate-
PDXL) copolymers as compatibilizers respectively Firstly these systems consist of a very
rigid amorphous component (styrene andor PMMA) and a very flexible low-melting point
PEG The extremely high difference of glass transition temperatures (Tg) between the
components motivates us to investigate the phase behaviour of the blends via
compatibilization with prepared grafted copolymers
The first part of the thesis is devoted to the synthesis and characterization of amphiphilic graft
copolymers which were prepared in solution by radical polymerization of hydrophilic poly (1
3 dioxolane) macromonomers as side chains and hydrophobic comonomers such as styrene
and methyl methacrylate as backbone The second part of the thesis describes the blends
preparation and the study of the compatibilization effect of the incorporated amphiphilic graft
copolymers on immiscible (incompatible) blends
The research work in this thesis is presented through several chapters described as follows
Chapter I is a bibliographic survey on polymerization reactions involved in the thesis
Literature concerning the poly (1 3 dioxolane) was included
Chapter II describes the synthesis of poly (1 3 dioxolane) macromonomers and their
characterization As an aside research poly (1 3 dioxolane) network was obtained and the
x E Kroeze thesisUniversity of Groningen (1997) xi Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polym Journal 37 (2001) 1837-1842
iii
swelling and rheological behaviours of this network were discussed and included in this
chapter
Chapter III deals with the synthesis of a series of amphiphilic graft copolymers based on
polystyrene and methyl methacrylate as backbone with poly (1 3 dioxolane) macromonomers
as grafts in this study Selection of proper reaction conditions in terms of overall monomer
concentration and monomer molar ratio were investigated in order to prevent crosslinking
reactions due to the presence of bis-functional poly (1 3 dioxolane) macromonomers
The structure and composition of the graft copolymers were determined by Size Exclusion
Chromatography (SEC) technique and Proton Nuclear Magnetic Resonance (1H-NMR)
analysis Also Modulated Temperature Differential Scanning Calorimeter (MTDSC) was used
for thermal analysis to study the influence of poly (1 3 dioxolane) content on the glass
transition temperature of the copolymers
Last but not the least Chapter IV and Chapter V deal with the most important part of the
thesis which is the study of the compatibilization effect of the prepared copolymers
incorporated in two different immiscible blend systems These two chapters describe first
the polymers used as blend components and also polyblends preparation was discussed The
phase behavior and compatibilization of these polyblends were studied at a composition
of 5050 for both PSPEG and PMMAPEG systems Various amounts of copolymers were
incorporated to the so-called blends for compatibilization The techniques used for this study
were optical microscopy (OM) to analyze their morphology and Fourier-Transform Infra-Red
(FTIR) spectroscopy used to detect the intermolecular interactions in the blends In addition
viscometric method which is a simple inexpensive and sensitive analytical technique and also
alternative to other methods was used The application of the dilute-solution viscosity (DSV)
method for the study of interactions and miscibility of the polymeric system has been
described in more details in these chapters
Conclusions have been made on copolymer characterizations in terms of mostly monomer
reactivity and indeed on compatibilizing effect of these copolymers on the selected polymer
blends This study provides interesting results which can be useful for the development
nanoporous materials
iv
REacuteSUMEacute
La recherche et le deacuteveloppement faits sur des polymegraveres syntheacutetiques pendant le dernier siegravecle
ont abouti agrave plusieurs types de polymegraveres pour des applications speacutecifiques Les nouveaux
polymegraveres syntheacutetiques avec des proprieacuteteacutes faites sur mesure sont toujours introduits pour de
nouvelles applications Le deacutefi pour les chimistes en polymegraveres est de controcircler et drsquoalteacuterer les
conditions de polymeacuterisation de telle sorte que le produit final ait une structure bien deacutefinie avec
des proprieacuteteacutes souhaiteacutees La structure complexe de polymegraveres exige des efforts continus en
chimie analytique pour comprendre le processus de polymeacuterisation et les relations entre la
structure moleacuteculaire et les proprieacuteteacutes des mateacuteriaux
Le centre drsquointeacuterecirct de cette thegravese est la synthegravese et lexploration des avantages des copolymegraveres
greffeacutes deacuteriveacutes agrave partir du poly (1 3 dioxolane) (PDXL) utiliseacutes comme agents compatibilisant
via leur incorporation dans des meacutelanges de polymegraveres non miscibles Lrsquoameacutelioration drsquoadheacutesion
agrave lrsquoeacutetat solide peut ecirctre accomplie en introduisant un compatibilisant qui peut agir comme un
adheacutesif entre deux polymegraveres et ou par le controcircle de la morphologie particuliegraverement en
incitant la co-continuiteacute des phases Les copolymegraveres greffeacutes offrent toutes les proprieacuteteacutes des
copolymegraveres en blocs mais sont toujours plus facile agrave syntheacutetiser De plus la structure ramifieacutee
offre des possibiliteacutes importantes dans le controcircle rheacuteologique cest-agrave-dire elle aide la
diminution de la viscositeacute qui est un avantage important pour la transformation Selon la nature
de la chaicircne principale et des chaicircnes lateacuterales ces copolymegraveres peuvent ecirctre employeacutes pour une
grande varieacuteteacute drsquoapplications comme plastiques reacutesistants au choc elastomers thermoplastiques
des polymegraveres eacutemulsifiants et mecircme plus inteacuteressant est la possibiliteacute de ces copolymegraveres greffeacutes
de fonctionner comme compatibilisant agents drsquointerface aux meacutelanges des polymegraveres non
miscibles
La technique la plus sophistiqueacutee pour syntheacutetiser les copolymegraveres greffeacutes est la
copolymeacuterisation de macromonomegraveres avec des comonomegraveres agrave faible masse moleacuteculaire Elle
permet le controcircle de la structure polymeacuterique par trois paramegravetres (i) la longueur des chaicircnes
lateacuterales qui peut ecirctre controcircleacutee par la synthegravese de macromonomegraveres par la polymeacuterisation
v
vivante (ii) la longueur de chaicircne principale qui peut ecirctre controcircleacutee dans une polymeacuterisation
vivante (iii) espacement moyen des chaicircnes lateacuterales qui est deacutetermineacute par le rapport molaire des
comonomegraveres et taux de reacuteactiviteacute du monomegravere agrave faible masse moleacuteculaire
De nouvelles proprieacuteteacutes des prix bas et la reacuteutilisation de polymegraveres sont neacutecessaires pour
reacutepondre aux demandes de la socieacuteteacute daujourdhui et agrave lindustrie de polymegraveres
Malheureusement ces demandes pour un grand nombre drsquoapplications ont besoin dun jeu de
proprieacuteteacutes quaucun polymegravere ne peut accomplir Une meacutethode de satisfaire ces demandes est en
meacutelangeant deux polymegraveres ou plus Les mateacuteriaux obtenus agrave partir de meacutelanges de deux
polymegraveres meacutelangeacutes sont appeleacutes meacutelanges (Blends) Ces derniegraveres anneacutees le meacutelange de
polymegraveres comme moyen de combiner les proprieacuteteacutes utiles de diffeacuterents mateacuteriaux pour
rencontrer un marcheacute de nouvelles applications agrave un coucirct minimal offre un itineacuteraire inteacuteressant
pour ameacuteliorer une varieacuteteacute des proprieacuteteacutes speacutecifiques des polymegraveres thermoplastiques Cela a eacuteteacute
de plus en plus employeacute par lindustrie des polymegraveres
Beaucoup de travaux ont eacuteteacute faits par plusieurs auteurs sur le meacutelange de polymegraveres Une grande
partie de ces eacutetudes sont dirigeacutees pour obtenir une combinaison des proprieacuteteacutes de diffeacuterents
polymegraveres Malheureusement ces proprieacuteteacutes des meacutelanges de polymegravere sont souvent plus
mauvaises que preacutevues pour la plupart des combinaisons de polymegraveres La signification de ces
proprieacuteteacutes est la compatibiliteacute entre les diffeacuterents polymegraveres qui est freacutequemment deacutefinie comme
la miscibiliteacute agrave lrsquoeacutechelle moleacuteculaire des composants du meacutelange Lincorporation dune phase
disperseacutee dans une matrice provoque surtout la preacutesence de contraintes et des interfaces faibles
qui reacutesultent du faible meacutelange meacutecanique entre les deux phases Lameacutelioration des proprieacuteteacutes
meacutecaniques et morphologiques dun meacutelange non miscible est souvent faite par compatibilisation
qui est un processus de modification des proprieacuteteacutes superficielle dans les meacutelanges de polymegraveres
non miscibles aboutissant agrave la reacuteduction du coefficient de tension superficielle la formation et
stabiliteacute de la morphologie deacutesireacutee Lutilisation des copolymegraveres greffeacutes ou agrave blocs comme
compatibilisant pour des meacutelanges de polymegraveres non miscibles est devenue un moyen efficace
pour le deacuteveloppement de nouveaux mateacuteriaux plus performant Il y a eu de nombreuses
techniques pour lrsquoeacutetude de la miscibiliteacute des meacutelanges polymeacuteriques Les techniques les plus
vi
utiles sont les mesures viscomeacutetriques analyses thermiques analyses meacutecaniques indice de
reacutefraction la reacutesonance magneacutetique nucleacuteaire microscopes optique et eacutelectroniques agrave balayage
Les exemples de meacutelanges commerciaux tregraves bien connus sont le polystyregravene choc (HIPS) et
acrylonitrile-butadiene-styrene (ABS) Ces meacutelanges sont durs et ont bon processability Un
exemple de polymegraveres amorphes le plus inteacuteressant est le polystyregravene agrave cause de sa fragiliteacute
Laddition dun compatibilisant ayant la structure dun copolymegravere au meacutelange de Polystyregravene
polyeacutethylegravene (PSPE) ameacuteliore la dureteacute par un facteur de 3 Un autre exemple est lutilisation du
poly (styrene-co-acide meacutethacrylique) comme compatibilisant dans les meacutelanges non miscibles
de PS et le poly (eacutethylegravene glycol)
Il est tregraves important drsquoeacutetudier la miscibiliteacute et le comportement des phases de deux diffeacuterents
meacutelanges de polymegraveres commerciaux non miscibles (incompatibles) comme le
polystyregravenepolyeacutethylegravene glycol (PSPEG) et le polymeacutethacrylate de meacutethylepolyeacutethylegravene glycol
(PMMAPEG) en incorporant des copolymegraveres tels que (styrene-g-PDXL) et de (meacutethacrylate de
meacutethyle-PDXL) comme compatibilisant respectivement Premiegraverement lrsquoun des composants de
ces systegravemes est amorphe et tregraves rigide (le styregravene etou PMMA) et lrsquoautre (PEG) est flexible et
mou ayant un point de fusion tregraves faible Vu lrsquoextrecircme eacutecart entre les deux tempeacuteratures de
transition vitreuse (Tg) des composants de ces meacutelanges cela nous a motiveacute pour eacutetudier le
comportement de ces meacutelanges via compatibilisation avec des copolymegraveres greffeacutes preacutepareacutes par
nous mecircme
La premiegravere partie de la thegravese est consacreacute agrave la synthegravese et agrave la caracteacuterisation de copolymegraveres
greffeacutes amphiphiles preacutepareacutes en solution par la polymeacuterisation radicale des macromonomers
(poly (1 3 dioxolane)) hydrophiles comme des chaicircnes lateacuterales (greffons) avec des
comonomegraveres hydrophobes comme le styregravene et le meacutethyle methacrylate comme chaicircne
principale La deuxiegraveme partie de la thegravese couvre la preacuteparation des meacutelanges et leacutetude de leffet
de compatibilisant des copolymegraveres greffeacutes amphiphiles sur les meacutelanges non miscibles
(incompatibles)
La recherche concernant cette thegravese est preacutesenteacute par plusieurs chapitres deacutecrits comme suit
vii
Le chapitre I est une recherche bibliographique sur les reacuteactions de polymeacuterisations impliqueacutees
dans la thegravese La Litteacuterature concernant le poly (1 3 dioxolane) est inclue
Le chapitre II deacutecrit la synthegravese des macromonomegraveres du poly (1 3 dioxolane) et leurs
caracteacuterisations Une recherche suppleacutementaire a eacuteteacute effectueacutee concernant la synthegravese drsquoun reacuteseau
tridimensionnel du poly (1 3 dioxolane) Une eacutetude sur les comportements gonflant et
rheacuteologique de ce reacuteseau ont eacuteteacute discuteacutes et inclus dans ce chapitre
Le chapitre III preacutesente la synthegravese dune seacuterie de copolymegraveres greffeacutes amphiphiles constitueacutes de
polystyregravene ou methacrylate de meacutethyle comme chaicircne principale et de macromonomers du poly
(1 3 dioxolane) comme greffons dans cette eacutetude Le choix de conditions de reacuteaction approprieacutees
en termes de concentration totale et le rapport molaire des monomegraveres ont eacuteteacute bien eacutetudieacutes pour
empecirccher les reacuteactions de reacuteticulation agrave cause de la preacutesence de macromonomegraveres bis-
fonctionnel de poly (1 3 dioxolane)
La structure et la composition des copolymegraveres greffeacutes ont eacuteteacute deacutetermineacutees par la technique de la
Chromatographie dExclusion steacuterique (CES) et la spectroscopie en Reacutesonance Magneacutetique
Nucleacuteaire de Proton (1H-NMR) Aussi la Calorimeacutetrie Diffeacuterentielle agrave balayage agrave Temperature
Moduleacutee Calorimeacutetrie (MTDSC) a eacuteteacute employeacute pour lanalyse thermique et pour eacutetudier
linfluence de la proportion du poly (1 3 dioxolane) dans les copolymegraveres sur leur tempeacuterature
de transition vitreuse
Derniers mais pas le moindre les deux Chapitre IV et le Chapitre V couvrent la partie la plus
importante de la thegravese qui est leacutetude de leffet de compatibilisant de ces copolymegraveres preacutepareacutes et
incorporeacutes dans deux diffeacuterents systegravemes de meacutelanges non miscibles (incompatibles) Ces deux
chapitres deacutecrivent dabord les polymegraveres employeacutes comme composants des meacutelanges agrave eacutetudier et
aussi la preacuteparation de ces meacutelanges a eacuteteacute deacutecrite Le comportement de phase et la
compatibilisation des meacutelanges de PSPEG et PMMAPEG agrave une composition de 5050 Des
quantiteacutes diffeacuterentes de copolymegraveres ont eacuteteacute incorporeacutees aux meacutelanges Les techniques
employeacutees pour cette eacutetude sont la microscopie optique (OM) pour analyser leur morphologie et
la spectroscopie agrave Transformeacutee de Fourier Infrarouge (FTIR) pour deacutetecter les interactions
viii
intermoleacuteculaires dans les meacutelanges De plus la meacutethode viscomeacutetrique qui est une technique
simple peu coucircteuse et tregraves sensible a eacuteteacute employeacutee Lrsquoutilisation de la meacutethode de la viscositeacute de
solution dilueacutee (DSV) pour leacutetude dinteractions et la miscibiliteacute du systegraveme polymegravere a eacuteteacute
deacutecrite plus en deacutetail dans ces chapitres
Les conclusions ont eacuteteacute faites sur la caracteacuterisation des copolymegraveres en termes de surtout de la
reacuteactiviteacute des monomegraveres et bien entendu sur leffet compatibilisant de ces copolymegraveres sur les
meacutelanges de polymegraveres qui ont choisis Cette eacutetude fournit des reacutesultats inteacuteressants qui peuvent
ecirctre utiles pour le deacuteveloppement des mateacuteriaux nanoporeux
ix
CHAPTER I Literature Review
11 Macromonomer Interest and Synthesis
Macromonomers bearing polymerizable end groups have received considerable interest
during the last two decades and become a useful tool for the preparation of a variety of graft
copolymers with well-defined structure and composition and polymer networks The
macromonomer method for preparing graft copolymers consists of preparing branches first
followed by the preparation of the grafted structure through the addition of the comonomer to
the macromonomer branch1 2
Therefore macromonomers become the side chains in the graft copolymer with well-defined
length and molecular weight As a sequence the molecular structure of the copolymer can be
determined depending on the amount of macromonomer incorporated and the reactivity of the
end groups
Macromonomers which are linear macromolecules carrying polymerizable functions at one or
two chain ends have been prepared by all polymerization mechanisms anionic cationic free-
radical polyaddition and polycondensation while the polymerizable end groups have been
introduced during the initiation termination or chain transfer steps or by modification of end
groups of telechelic oligomers3
Among the polymerization mechanisms mentioned above the ionic ones allow the best
control of molecular weight polydispersity and functionality of the macromonomers
However they require very demanding experimental conditions like high purity of monomers
and solvents complete absence of moisture and other acidic impurities inert atmosphere etc
Whereas free-radical methods which involve less severe working conditions are largely
used even though the control over the properties of the macromonomers is lower3 For
instance polymers of epoxides tetrahydofuran and cyclic siloxanes are commercially
produced by cationic ring-opening polymerization The history of ring-opening
polymerization of cyclic monomers is shorter than that of the vinyl polymerization and
1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422
1
polycondensation With ring-opening functional groups can be introduced into the main chain
of the polymer This polymer cannot be prepared by vinyl polymerization4
Milkovich first developed synthesis of graft polymer with uniform grafts via macromonomer
technique5 Schulz and Milkovich6 reported the synthesis of polystyrene macromonmers
through termination of living PS anions with methacryloyl chloride and their
copolymerization with butyl acrylate and ethyl acrylate
Candau Rempp et al7 obtained PS-g-PEO by reaction between living monofunctional PEO
and partly chloromethacrylated PS backbone (scheme 1) Characterization of the products by
light scattering GPC UV and NMR spectroscopy showed a high degree of grafting
Scheme 1
Ito et al8 used a macromonomer technique to obtain graft copolymers with uniform side
chains They synthesized a graft copolymer of PS with uniform PEO side chains through
copolymerization of styrene and PEO macromonomer (scheme 2) They obtained PEO
macromonomers using potassium tertiary butoxide as initiator and methacryloyl chloride or p-
vinyl benzyl chloride as terminating agent An apparent decrease in reactivities of both poly
(ethylene oxide) of macromonomers and comonomers was ascribed to the thermodynamic
repulsion between the macromonomer and the backbone9
4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348
2
Scheme 2
This type graft copolymers of styrene and ethylene oxide was also obtained by Xie et al10
through copolymerization of styrene with PEO macromonomer prepared by anionic
polymerization of EO in dimethylsulfoxide using potassium naphthalene in tetrahydofuran as
initiator followed by termination with methacryloyl chloride
The method of macromonomer synthesis developed by Xie et al11 has the advantage of
shorter reaction time and a larger range of molecular weight of the PEO macromonomer than
the usual method using potassium alcoholate as initiator PEO macromonomers with
molecular weight from 2 103 to 3 104 and MwMn = 107 ndash 112 can be obtained by this
method12
Only Xie and coworkers have published reports concerning the synthesis of copolymers with
uniform PS grafts obtained through copolymerization of epoxy ether terminated polystyrene
macromonomer with EO13 using a quaternary catalyst composed of triisobutyl-aluminium-
phosphoric acid-water-tertiary amine14 and epichlorohydrin (ECH)15
Free radical polymerization technique has also provided well-defined macromonomers of
poly (acrylic acid)16 vinyl benzyl-terminated polystyrene17 18 poly (t-butyl methacrylate)19
and poly (vinyl acetate)20
Recently Matyjaszewski et al21 employed atom-transfer radical polymerization (ATRP) to
prepare well-defined vinyl acetate terminated PS macromonomers Taking advantage of the
10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp (1985) 461 Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823
3
extremely low reactivity of polystyryl radical towards the vinyl acetate double bond they
used vinyl chloroacetate to initiate the polymerization of styrene to produce the desired
macromonomers This concept has been used similarly in the preparation of a vinyl acetate-
terminated PS macromonomers3 by conventional free-radical polymerization by employing
vinyl iodoacetate as a chain transfer agent possessing a double bond which does not
copolymerize with the monomer that forms the backbone of the macromonomer
12 Ring-Opening Polymerization Overview
Ring-opening polymerization (ROP) is a unique polymerization process in which a cyclic
monomer is opened to generate a linear polymer It is fundamentally different from a
condensation polymerization in that there is no small molecule by-product during the
polymerization Polymers with a wide variety of functional groups can be produced by ring-
opening polymerizations Ring-opening polymerization can proceed through a number of
different mechanisms depending on the type of monomer and catalyst involved Of the wide
range of polymers produced via ROP some have gained industrial significance for example
poly (caprolactam) and poly (ethylene oxide)22 ROP of cyclic esters such as ε-caprolactone
(CL) and L L-dilactide is gaining industrial interest due to their degradability23 The
mechanisms of interest in this work are coordination insertion and cationic
121 Polymerizability of Cyclic Compounds
The thermodynamic polymerizability of a cyclic monomer has been elegantly summarized by
Ivin24 Negative free energy change from monomer to polymer is the thermodynamic driving
force for the ring-opening
ΔG = ΔH ndash T ΔS
For small sized cyclic compounds the enthalpy term is negative and dominant The strains in
bond angles and bond lengths are released upon ring opening Such monomers can be almost
completely converted to polymers For medium sized cyclic monomers (5-7 membered rings)
the ring strain is small and the entropy is a small positive term Thus the overall driving force
(ΔG) is small and the extent of polymerization is little or no reaction For 8- 9- and 10-
22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991)
4
membered monomers the enthalpy term is dominant and negative while the TΔS term is
relatively small The strain is due to the non-bonded interactions between atoms Essentially
complete conversion to polymer is possible When the ring size is very large and there is
virtually no ring-strain (ΔH ne 0) the driving force for ring-opening polymerization is the
large increase of entropy The polymerization should be an athermal process
Why not make polyethylene
In principle one could synthesize polyethylene from cyclohexane
There are two good reasons why this reaction cannot be performed
bull (Kinetic) Cyclohexane lacks any reactive functionality to get hold of
bull (Thermodynamic) Simple six membered rings are extremely stable
Free Energy (ΔG) of Polymerization for Cycloalkanes
The thermodynamic considerations for ring opening are illustrated by this graph (scheme 3) of
free energy (hypothetical) of polymerization from cycloalkanes with various ring sizes to
polyethylene (The two membered ring actually shows the data for ethylene CH2 = CH2)
Scheme 3
5
Three and four membered rings are quite strained so ring opening to polyethylene is
favorable if a suitable reaction pathway existed (Unfortunately no such reaction is known)
Six membered rings are stable so they can rarely be polymerized by ring opening Five and
seven membered rings are borderline cases so sometimes these can be polymerized Larger
rings have transanular steric interactions that cause some strain so rings of 8 members or
more can usually be polymerized Of course this graph changes when substitutions are made
to the rings (for example the presence of heteroatoms like O S and N or the introduction of
double bonds) However the graph for the simplest possible rings illustrates the trends in
other systems reasonably well
Even if the ring opening reaction is thermodynamically favorable there must be reaction
chemistry to get there In most cases the initiators used for ring opening polymerization are
polar or ionic species so the monomers must have groups that can react The most common
monomers for ring opening polymerization contain some kind of heteroatom in the ring as in
the examples of cyclic ethers esters amines amides etc At one extreme there are examples
such as the cyclic phosphazene shown that contain no carbon or hydrogen at all At the other
extreme just a carbon-carbon double bond will suffice for ring opening metathesis
polymerization as illustrated by norbornene
122 Mechanisms of Ring-opening Polymerization
In addition to the thermodynamic criterion there must be a kinetic pathway for the ring to
open and undergo the polymerization reaction Therefore the kinetics of the ring-opening of
the monomer should also be considered Ring-opening polymerization (ROP) can proceed
through a number of different mechanisms depending on the type of monomer and catalyst
involved Of the wide range of polymers produced via ROP some have gained industrial
significance for example poly (caprolactam) and poly (ethylene oxide)24 25 A variety of
mechanisms operate for ring-opening polymerizations including anionic cationic metathesis
and free radical mechanisms Examples of various ring-opening polymerizations are shown in
scheme 4
25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984)
6
Scheme 4
123 Cationic Ring-Opening Polymerization of Heterocycles
A broad range of heterocyclic compounds can undergo cationic ring-opening polymerization
(CROP)26 CROP propagates either through an activated monomer or an activated chain end
mechanism In both cases the propagation involves the formation of a positively charged
species27 A major drawback of CROP is the occurrence of unwanted side reactions thus
limiting the molecular weight of the final product2829 The cationic ring-opening
polymerization of heterocycles has become of significant importance in polymer synthesis
due in part to the diverse variety of functionalized materials that can be prepared by this
method including natural andor biodegradable polymers30 31
Systematic studies of this type of polymerization started around the nineteen sixties Since
then several groups are involved in the kinetics reaction mechanisms and thermodynamics of
the ring-opening polymerization mostly of tetrahydofuran and dioxolane During the last
26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996) (b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993) (c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice (d) Mishra M K Ed Polymer Frontiers New York (1994) 391 31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159
7
years many papers on the synthesis and polymerization of several other cyclic ethers
monocyclic and bicyclic acetals have been published32 33
Examples of commercially important polymers which are synthesized via ring-opening
polymerization are summarized in scheme 5 include such common polymers as
polyoxyethylene (POE 4) poly (butylene oxide) (PBO 5) nylon 6 (6) and poly
(ethyleneimine) (7)
Scheme 5
The synthesis of ring-opened heterocycles is often mediated by compounds whose role is to
initiate the polymerization process This provides less opportunity to ldquotunerdquo polyheterocycle
properties through catalyst choice and has stimulated research to develop initiators which
function beyond the simple activation of polymerization such as living polymerization
initiators343536 chiral initiators3738 enzyme initiators39 and ring-opening insertion
systems4041 The cationic ring-opening polymerization involves the formation of a positively
32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N Macromolecules 26 (1993) 7134
8
charged species which is subsequently attacked by a monomer The attack results in a ring-
opening of the positively charged species Ethylene oxide can be polymerized by cationic
initiators as well (scheme 6)
Scheme 6
13 Cationic Polymerization of Cyclic Acetals
Acetal polymers also known as polyoxymethylene (POM) or polyacetal are formaldehyde-
based thermoplastics that have been commercially available for over 40 years
Polyformaldehyde is a thermally unstable material that decomposes on heating to yield
formaldehyde gas Two methods of stabilizing polyformaldehyde for use as an engineering
polymer were developed and introduced by DuPont in 1959 and Celanese in 1962
DuPonts route for polyacetal yields a homopolymer through the condensation reaction of
polyformaldehyde and acetic acid (or acetic anhydride)
The Celanese route for the production of polyacetal yields a more stable copolymer product
via the reaction of trioxane a cyclic trimer of formaldehyde and a cyclic ether (eg ethylene
oxide or 13 dioxolane)
9
The improved thermal and chemical stability of the copolymer versus the homopolymer is a
result of randomly distributed oxyethylene groups These groups offer stability to oxidative
thermal acidic and alkaline attack The raw copolymer is hydrolyzed to an oxyethylene end
cap to provide thermally stable polyacetal copolymer Polyacetals are subject to oxidative and
acidic degradation which leads to molecular weight deterioration Once the chain of the
homopolymer is ruptured by such an attack the exposed polyformaldehyde ends decompose
to formaldehyde and acetic acid Deterioration in the copolymer ceases however when one
of the randomly distributed oxyethylene linkages is reached42
Cationic polymerization of cyclic acetals exhibits some special features which makes this
system distinctly different from cationic polymerization of simple heterocyclic monomers for
instance cyclic ethers Linear acetals (including polyacetals) are more basic (nucleophilic)
than cyclic ones thus when polymer starts to form it does not constitute a neutral component
of the system but participates effectively in transacetalization reactions which lead to
redistribution of molecular weights and formation of a cyclic fraction These processes which
are usually described by the term ldquoscramblingrdquo have been studied by several authors43 44
Cationic polymerizations of heterocyclic monomers are initiated as in cationic
polymerization of vinylic monomers by electrophilic agents such as the protonic acids (HCl
H2SO4 HClO4 etc) Lewis acids which are electron acceptors by definition and compounds
capable of generating carbonium ions can also initiate polymerization Examples of Lewis
acids are AlCl3 SnCl4 BF3 TiCl4 AgClO4 and I2 Lewis acid initiators required a co-
initiator such as H2O or an organic halogen compound Initiation by Lewis acids either
requires or proceeds faster in the presence of either a proton donor (protogen) such as water
alcohol and organic acids or a cation donor (cationogen) such as t-butyl chloride or
triphenylmethyl fluoride
The polymerization of a heterocyclic monomer initiated by a protonic acid usually starts with
opening of the monomer ring via oxonium sites that are formed upon alkylation (or
protonation) of the monomer
42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144
10
Protonation
BF3 H2O H BF3 OH+ +O
O
Acylation
R CO SbF6 +
OR CO O SbF6
Alkylation
Et3O BF4 +
OC2H5 Et2O BF4O +
Hydrogen transfer
C SbF6 +O
C SbF6H O+
SbF6
O + O O+ H O SbF6
In general initiation step can be shown as
A+
R O++R A O
The mechanism of chain growth involves nucleophilic attack of the oxygen of an incoming
monomer onto a carbon atom in α-position with respect to the oxonium site whereby the
cycle opens and the site is reformed on the attacking unit
A+O
O(CH2)4
O
A+O(CH2)4
Growing chain terminates with nucleophilic species as shown below
O (CH2)4 O+[ ]n
A O (CH2)4[ ]n
AO ( CH2 )4
11
Triflic initiators like trifluoromethane sulfonic acid derivatives can also be employed as an
initiator in the cationic polymerization of heterocyclics in this case initiation step follows
alkylation mechanism
CF3 SO3CH3 +O
CH3 CF3SO3O
CH3 O
CF3SO3
+ O CH3O(CH2)4 O CF3SO3
Ion pairs are in equilibrium with the ester form
(CH2)4 O CF3SO3 (CH2)4 O(CH2)4 O SO2CF3
If instead of ester triflic anhydride is used as initiator the same reaction can occur at both
chain ends and anhydride behaves as a bifunctional initiator
CF3SO2OSO2CF3 nO
+ CF3SO2 O (CH2)4 O (CH2)4 O SO2CF3n-1
(CH2)4 O (CH2)4 n-3
O O CF3SO3 CF3SO3
In the case of living cationic polymerization the growing sites are long living provided the
reaction medium does not contain any transfer agents such as alcohols ethers amines or
acids The reaction mechanism then involves only initiation and propagation steps and the
polymers formed are living The active sites are deactivated by addition of an adequate
nucleophile such as excess water tertiary amines alkoxides phenolates or lithium bromide
12
O(CH2)4
SbF6
(CH2)4 O(CH2)4 OH H
NR3
++ H2O
SbF6
+(CH2)4 O(CH2)4 NR3 SbF6
ONa+(CH2)4 O(CH2)4 O + NaSbF6
+ LiBr
(CH2)4 O(CH2)4 Br LiSbF6+
However facts concerning the real mechanism are scarce In order to progress further in
understanding the cationic polymerization of heterocycles initiated with a Bronsted acid
kinetic studies of simple ring-opening reactions of heterocyclic monomer rings by acids in
nonpolar aprotic and nonbasic solvents (inert solvents) have been performed45
14 Synthesis of Functionalized Poly (1 3-Dioxolane)
1 3-Dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer ends ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The molecular weight of the linear polymers is governed by the
ratio of reacted monomer to transfer agent and is generally well controlled up to 10 000gmol
141 Reaction of 1 3-Dioxolane and Hydroxyl- Containing Compounds
Classical initiation induces polymerization through cyclic tertiary oxonium ions which are
responsible for the formation of an important quantity of cyclic oligomers48
45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon Press 3(1989) 787
13
In several preceding articles Franta et al have investigated the cationic polymerization of
cyclic acetals in the presence of a diol49 50 in particular polymerization of 13-dioxolane
(DXL) and 13-dioxepane (DXP) in the presence of an oligoether diol (αω-dihydroxy-poly
(tetrahydofuran)) or (αω-dihydroxy-poly(ethylene oxide)) In all cases a similar behavior was
observed Cyclic oligomers are present in quantities as in the case of polymerization of DXL
in the absence of hydroxyl containing compounds51
When substituted oxiranes such as propylene oxide or epichlorohydrin are polymerized
according to the ldquoActivated Monomerrdquo mechanism (AM) Cyclic oligomers can be
eliminated52 53 In the AM mechanism polymerization of ethylene oxide however the
reaction of a protonated monomer molecule with a polymer chain leads to side reactions
including cyclization by the Active Chain End (ACE) mechanism53 Thus it is not
unexpected that in the polymerization of cyclic acetals due to the higher nucleophilicity of
the linear acetals located on the chain reactions with the latter will take place
The addition of a protonated DXL onto a hydroxyl group-containing compound is
accompanied by transacetalization involving a monomer molecule
In order to shed some light on the reactions involved Franta et al54 used a monoalcohol
methanol instead of a diol The results confirmed the occurrence of the Active Monomer
mechanism but dimethoxymethane was observed evidence of transacetalization between
methanol and dioxolane
Thus in the DXL-ethylene glycol (EG) system the presence of unreacted EG is in fact due to
the following equilibria
This equation shows the stoichiometry of the reaction rather than its actual mechanism the
reaction certainly has to involve an addition product as a first step
49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154
14
In the next step transacetalization occurs
The products of transacetalization are formed fast as compared to the addition product54 This
indicates that the last reaction is not slower and probably faster than the previous one
Consequently it has been found that although polymerization of DXL in the presence of
hydroxyl group containing compounds proceeds initially by a stepwise addition of protonated
monomer to the hydroxyl terminated linear species in agreement with the AM mechanism but
already at this stage fast transacetalization proceeds leading to formation of O-CH2-O links
between two oligodiols and liberation of ethylene glycol
The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism When DXL is polymerized by strong protonic acids such as triflic acid in the
presence of a diol the PDXL chains are essentially linear and carry end-standing OH
functions Despite the occurrence of some side reactions this mechanism leads to α ω-
dihydroxy-PDXL the molecular weight of which is controlled by the molar ratio of DXL
consumed to diol introduced It has been shown that the polydispersity is on the order of 14
and that molar masses up to 10 000 gmol can be covered
142 Synthesis of Poly (1 3-Dioxolane) Macromonomers
Macromonomers are useful intermediates to prepare graft copolymers and have indeed been
used extensively In order to prepare PDXL macromonomers Franta and al54 have used p-
isopropenylbenzylic alcohol (IPA) as an initiator and triflic acid as a catalyst
The following polymeric species were identified
15
Scheme 7
A is the most abundant compound it corresponds to 50 to 60 weight-wise It is a
macromonomer
B corresponds to 20 to 25 weight-wise It carries two p-isopropenyl functions
C corresponds to 20 to 25 weight-wise It carries no p-isopropenyl function but two
hydroxyl groups
As a result preparation of PDXL macromonomers leads to the preparation of PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of transacetalization
reaction described above a mixture of products was obtained54
Kruumlger et al55 used similar method to prepare macromonomers and come out to the same
conclusions in terms of structure and claim that a clear distinction should be made between
the products obtained and the mechanism responsible for their formation
15 Amphiphilic Graft Copolymers
151 Graft Copolymers
The increasing complexity of polymer applications has required the production of materials
with varied properties Often homopolymers do not afford the scope of attributes necessary to
many applications Copolymerization allows the formulation of polymer materials with
properties characteristic of two homopolymers contained in a single copolymer material The
monomers within a copolymer can be distributed in various fashions random statistical
alternating segmented block or graft56
55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387
16
Scheme 8
Graft copolymers are similar to block copolymers in that they possess long sequences of
monomer units However graft copolymer architecture differs substantially from typical
block copolymers In graft copolymers monomer sequences are grafted or attached to points
along a main polymer chain Grafted chains generally possess molecular weights less than
that of the main chain
These side chains have constitutional or configurational features that differ from those in the
main chain57
The simplest case of a graft copolymer can be represented by A-graft-B or the arrangement
and the corresponding name is polyA-graft-polyB where the monomer named first (A in this
case) is that which supplied the backbone (main chain) units while that named second (B) is
in the side chain(s)
Typical syntheses of the grafts occur by polymerization initiated at some reactive point along
the backbone or by copolymerization of a macromonomer Polymerization from the polymer
backbone is possible via anionic cationic and radical techniques but all require some
functional unit capable of further reaction58
Well defined graft copolymers are most frequently prepared by either
a)ldquografting throughrdquo or b)ldquografting fromrdquo controlled polymerization process
57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991)
17
a) Grafting though the ldquografting throughrdquo method (or macromonomer method) is one of the
simplest ways to synthesize graft copolymers with well defined side chains
Scheme 9
Typically a low molecular weight monomer is radically copolymerized with a methacrylate
functionalized macromonomer This method permits incorporation of macromonomers
prepared by other controlled polymerization processes into a backbone prepared by a CRP
Macromonomers such as polyethylene59 60 poly (ethylene oxide)61 polysiloxanes62 poly
(lactic acid)63 and polycaprolactone64 have been incorporated into a polystyrene or poly
(methacrylate) backbone Moreover it is possible to design well-defined graft copolymers by
combining the ldquografting throughrdquo macromonomers prepared by any controlled polymerization
process and CRP65 This combination allows control of polydispersity functionality
copolymer composition backbone length branch length and branch spacing by consideration
of MM ratio in the feed and reactivity ratio Branches can be distributed homogeneously or
heterogeneously and this has a significant effect on the physical properties of the
materials6263
b) Grafting from the primary requirement for a successful grafting from reaction is a
preformed macromolecule with distributed initiating functionality
59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003) 6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778 63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998) 823-830
18
Scheme 10
Grafting-from reactions have been conducted from polyethylene66 67 polyvinylchloride68 69
and polyisobutylene70 71 The only requirement for an ATRP is distributed radically
transferable atoms along the polymer backbone The initiating sites can be incorporated by
copolymerization68 be inherent parts of the first polymer69 or incorporated in a post-
polymerization reaction70
Graft copolymers perform similar functions to block copolymers in that they contain moieties
with varying properties Compatibilization represents a major area of application for grafts
because the grafted chains can be used to solubilize a polymer blend system containing two
immiscible polymers Additionally graft copolymers offer unique solution mechanical and
morphological properties that make them ideal for utilization as viscosity modifiers and
thermoplastic elastomers72 The unique molecular architecture of graft copolymers leads to
peculiar morphological properties The chain lengths of the grafted arms and backbone block
dictate the morphology that arises in the polymer Changes in the composition of the graft
copolymer alter the resulting polymer morphology A variety of morphologies is possible
ranging from lamellar to cylindrical to spherical73
Graft copolymers offer all properties of block copolymers but are usually easier to synthesize
Moreover the branched structure offers important possibilities of rheology control
Depending on the nature of their backbone and side chains graft copolymers can be used for a
wide variety of applications such as impact-resistant plastics thermoplastic elastomers
66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996) 7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R Macromolecules 32 (1999) 1152-1158
19
compatibilizers viscosity index improvers and polymeric emulsifiers74 75 The state-of-the-
art technique to synthesize graft copolymers is the copolymerization of macromonomers
(MM) with low molecular weight monomers76 In most cases conventional radical
copolymerization has been used for this purpose Using living polymerizations for both the
synthesis of the macromonomers and for the copolymerization offers the highest possible
control of the polymer structure In all these copolymerizations beside the desired graft
copolymers with at least two side chains a number of unwanted products can be expected
unreacted macromonomer ungrafted backbone and backbone with only one graft (star
copolymer) The latter is undesirable for applications as thermoplastic elastomer
Conventional and controlled copolymerizations lead to different copolymer structures In
conventional radical copolymerization the polymers show a broad molecular weight
distribution (MWD) and chemical heterogeneity of first order
152 Amphiphilic Copolymers
A characteristic feature of an amphiphilic polymer is that it contains both hydrophilic and
hydrophobic groups This type of polymer associates in aqueous solution and exhibits several
interesting features and can be used in connection with many industrial and pharmaceutical
applications Usually there is only a few mol of the hydrophobic moieties in order to make
the polymer water-soluble Due to the hydrophobicity of the amphiphilic polymers they have
a tendency to form association structures in aqueous solution by mutual interaction andor
interaction with other cosolutes such as surfactants and colloid particles
In particular the grafting of hydrophilic species onto hydrophobic polymers is of great utility
Amphiphilic graft copolymers so prepared often display enhanced surface properties such as
improved resistance to the adsorption of oils and proteins biocompatibility and reduced static
charge buildup
The synthesis of graft copolymers based on commercial polymers is most commonly
accomplished free radically Free radicals are produced on the parent polymer chains by
exposure to ionizing radiation andor a free-radical initiator77 78 Alternatively peroxide
groups are introduced on the parent polymer by ozone treatment79 80 The resulting reactive
74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998) 696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507
20
sites serve as initiation sites for the free radical polymerization of the comonomer A
significant disadvantage of these free radical techniques is that homopolymerization of the
comonomer always occurs to some extent resulting in a product which is a mixture of graft
copolymer and homopolymer Moreover backbone degradation and gel formation can occur
as a result of uncontrolled free radical production often limiting the attainable grafting
density81 For example amphiphilic graft copolymers synthesized from PEO macromonomer
and hydrophobic comonomers82 83were found to form micellar aggregates in polar medium
such as water wateralcohol alcohol dimethylformamide These phase separation processes
take place also during polymerization and supposedly affect not only the polymerization
kinetics but also properties of resulting copolymers So far unanswered remains the question
of molecular characteristics of reaction products including homopolymers from
macromonomer or comonomer formed under both the homogeneous and heterogeneous
(micellar) reaction conditions Modern liquid chromatographic techniques allow
discrimination of polymeric constituents differing in their chemical structure andor physical
architecture Subsequently the molar mass and molar mass distribution of constituents can be
assessed Recently analyzed products of dispersion copolymerization of polyethylene oxide
methacrylate macromonomer with styrene contained rather large amount of polystyrene
homopolymer84
In the main application areas for amphiphilic polymers the solution properties are of
fundamental importance In many industrial applications association and adsorption
phenomena of the polymers in solution are design properties Consequently a deep
understanding of these phenomena is necessary for the development of new specific
chemicals and new processes The research goals are to clarify the relations between the
molecular structure of amphiphilic polymers and their properties in aqueous solution A
further goal is to develop theoretical models for the description of the behavior of amphiphilic
polymers in solution and at surfaces Several projects concern the self-assembly of
amphiphilic polymer molecules and the association behavior of surfactants and
hydrophobically modified hydrophilic polymers such as cellulose derivatives Studies of
amphiphilic model polymers such as ethylene oxide block and graft copolymers are carried
80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication
21
out in order to gain fundamental knowledge on the solution behavior of amphiphilic
polymers
16 Kinetics of Free Radical Polymerization
Free radical polymerization is the most widespread method of polymerization of vinylic
monomers Free radical polymerizations are chain reactions in which every polymer chain
grows by addition of a monomer to the terminal free radical reactive site called ldquoactive
centerrdquo The addition of the monomer to this site induces the transfer of the active center to
the newly created chain end Free radical polymerization is characterized by many attractive
features such as applicability for a wide range of polymerizable groups including styrenic
vinylic acrylic and methacrylic derivatives as well as tolerance to many solvents small
amounts of impurities and many functional groups present in the monomers
161 Kinetics of free radical addition Homo and Copolymerization
Understanding of chemical kinetics during homo- and copolymerization is crucial for
copolymer synthesis The discussion below will review the kinetics of free radical initiated
polymerizations and copolymerizations
The three main kinetic steps that occur during polymerization are (1) initiation (2)
propagation and (3) termination
1 Initiation
The initiation step is considered to involve two reactions creating the free radical active
center The first event is the production of free radicals Many methods can be used to initiate
free radical polymerizations such as thermal initiation without added initiator or high energy
radiation of the monomers However free radicals are usually generated by the addition of
initiators that form radicals when heated or irradiated Two common examples of such
compounds which afford free radicals are benzoyl peroxide (BPO) and azobisisobutyronitrile
(AIBN)
22
Figure 1 Generation of Free Radicals by Thermal Decomposition of Benzoyl Peroxide
Figure 2 Decomposition of Azobisisobutyronitrile to Form Free Radicals
Figure 1 depicts the thermal decomposition of BPO to form two oxy-radicals and Figure 2
depicts the decomposition of AIBN to form two nitrile stabilized carbon based radicals
(equation 1)
In equation 1 kd is the rate constant which describes the first order initiation process The
radical that is formed can now add to the double bond of the monomer and initiate
polymerization
The symbol M will represent the monomer and the rate constant for this process will be ki as
described in equation 2
23
Together these two reactions the radical generation and the monomer addition to the radical
form the process of initiation Usually the assumption that is taken into account is that the
first step is the rate determining step This means that the decomposition to form the radical
is much slower than the monomer addition to the free radical Therefore the equation for the
rate of radical formation ri is
The number 2 is obtained from the fact that a maximum of two radicals can be generated for
the initiation
But not all of the primary radicals produced by the decomposition of the initiator will
necessarily react with the monomer which means several other competing reactions may
occur85 Therefore in order to determine the rate of initiation the fraction of initially formed
radicals that actually start chain growth will be denoted by f and the rate of initiation equation
becomes
2 Propagation
Now the propagation of the reaction will proceed through the successive addition of
monomer to the radicals This type of process can be expressed in the following form
85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster PA (1997)
24
And further generalizing the reaction scheme gives
The assumption that the reactivity of the addition of each monomer is independent of the
chain length is evident in these two equations and was postulated by Flory 58 86 The use of
the rate constant kp for both of these equations imply that the rate constant is independent of
chain length The rate of the propagation rp of this polymerization or the rate of monomer
removal is thus given by
3 Termination
The termination of these growing radical chains occurs in principally two different ways The
first way is the formation of a new bond in between the two radicals this is called
combination Secondly the radical chains can terminate by disproportionation This is a
process where a hydrogen atom from one of the chains is transferred to the other and the chain
that the proton was removed from forms a double bond These reactions are represented as
follows
Figure 3 Termination by Combination
86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995)
25
Figure 4 Termination by Disproportionation
Schematically the reactions can be represented as follows
Where the rate constant of termination by combination is denoted by ktc and the rate constant
of termination by disproportionation is denoted by ktd Since both of these reactions use two
radical species and have the same kinetics the overall equation for the rate of termination is
written as
where kt = ktc + ktd and the number 2 imply there are two radicals that are terminated in
each termination reaction The monomer structure and the temperature are what determines
the type of termination that is most dominant in the reaction For most systems the amount of
one termination type far exceeds the other termination type
The further calculations for the rate of polymerization Rp and the degree of conversion as a
function of time can now be developed The assumption of the steady state concentration of
transient species must be used here where the transient species is the radical M For the
steady state approximation to hold true the rate at which initiation occurs ri must be equal to
the rate at which termination occurs rt or in other words radicals must be generated at the
same rate at which they are terminated This assumption gives the equation
26
This equation then gives an expression for the radical species
Experimentally this value would be difficult to measure in the laboratory and therefore this
equation must be used in the subsequent equations that follow By further substitution an
expression for the rate of polymerization Rp can be obtained because it equals the rate of
propagation
From this equation it can be deduced that the rate of polymerization is directly proportional
to the monomer concentration and to the initiator concentration to the one half power In
other words Rp is first order with regards to the monomer concentration and half order to the
initiator concentration
When the conversion is low the assumption that the initiator concentration is constant is
reasonable but the consumption of the initiator can be added into the calculations Therefore
Then integration can be performed
Finally the rate of polymerization becomes
27
This equation can be broken into three different parts
The second term indicates that the rate of polymerization is still proportional to the monomer
concentration to the first power and the initiator concentration to the one half power but the
initiator concentration is now the initial concentration Therefore by increasing the initial
concentration of an initiator in a solution polymerization the rate of the reaction should
increase proportionally to the square root of the amount of initiator added The third term
indicates that as the initiator is consumed the polymerization slows down exponentially with
time as well as its slowing down due to monomer depletion
The first term in the brackets suggests that the rate of polymerization is proportional to kp
kt12 When experiments are performed to probe the kinetics of reactions in solution the
expected first order dependence on monomer concentration is observed But when the
experiment is performed in concentrated solvents or even in the bulk the polymerization
kinetics accelerate The reason for this anomaly is that the viscosity increases as the
polymerization proceeds because the polymer has a higher viscosity than the monomers The
kp is not affected but the kt is
The degree of conversion can now be expressed as a function of time by knowing that
By substituting the earlier equation for Rp and integrating that equation one can obtain this
Furthermore ([M]0 ndash [M]) [M]0 is equal to the degree of conversion and is the fraction of
the monomer that has been reacted where [M] is the concentration of the monomer that has
been left after the reaction and [M]0 is the initial monomer concentration Therefore ([M]0 ndash
[M]) is the concentration of the monomer that has reacted The conversion can then be
expressed as
28
This can also be expressed as
As is always the case the conversion never quite reaches 100 value or a factor of 1 given by
the exponential term So if the time goes to infinity the expression that is obtained for
maximum conversion that is less than 1 by an amount that is dependent on the initial initiator
concentration is
If the steady state approximation for the initiator concentration had been carried through these
calculations and equations then the conversion would approach a value of 1 after a long
period of time
Distributions on the average distribution of chain lengths during and after a polymerization
are present in free radical polymerizations This is due to the naturally but statistically
random termination reactions that occur in the solution with regard to chain length The
kinetic chain length v is the rate of monomer addition to growing chains over the rate at
which chains are started by radicals which is the expression for the number average chain
length In other words it is the average number of monomer units per growing chain radical
at a certain instant87 Therefore the initiator radical efficiency in polymerizing the monomers
is
87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993)
29
When termination occurs mainly by combination the chain length for the polymer chains on
the average doubles in size assuming nearly equal length chains combine But if
disproportionation mainly occurs the growing chains do not undergo any change in chain
length during the process So the expressions are thus
A new term can be used to more generally express the average chain length of the growing
polymer chain xn This new term is the average number of dead chains produced per
termination ξ This value is equal to the rate of dead chain formation over the rate of the
termination reactions The equations take into account that in combination only one dead
chain is produced and in disproportionation reactions two dead chains are produced
Therefore
Furthermore the instantaneous number average chain length can be expressed in terms of the
rate of addition of the monomer units divided by the rate of dead polymers forming This is
shown as
30
From this equation82 one can clearly see that the rate of polymerization is proportional to the
initiator concentration to the one half power [I]12 and that the instantaneous number average
chain length xn is proportional to the inverse of the initiator concentration to the one half
power 1[I]12 Thus if the polymerization was accelerated by using more initiator the chains
will end up to be shorter which may not be desirable85
17 Chain Growth Copolymerization
171 Copolymerization Equations
Chain polymerizations can obviously be performed with mixtures of monomers rather than
with only one monomer For many free radical polymerizations for example acrylonitrile and
methyl acrylate two monomers are used in the process and the subsequent copolymer might
be expected to contain both of the structures in the chain This type of reaction that employs
two comonomers is a copolymerization The reactivity and the relative concentrations of the
two monomers should determine the concentration of each comonomer that is incorporated
into the copolymer The application of chain copolymerizations has produced much important
fundamental information Most of the knowledge of the reactivities of monomers via
carbocations free radicals and carbanions in chain polymerizations has been derived from
chain copolymerization studies The chemical structure of these monomers strongly
influences reactivity during copolymerization Furthermore from the technological viewpoint
copolymerization has been critical to the design of the copolymer product with a variety of
specifically desired properties As compared to homopolymers the synthesis of copolymers
can produce an unlimited number of different sequential arrangements where the changes in
relative amounts and chemical structures of the monomers produce materials of varying
chemical and physical properties
Several different types of copolymers are known and the process of copolymerization can
often be changed in order to obtain these structures A statistical or random copolymer may
obey some type of statistical law which relates to the distribution of each type of comonomer
that has been incorporated into the copolymer Thus for example it may follow zero- or first-
31
or second-order Markov statistics88 Copolymers that are formed via a zero-order Markov
process or Bernoullian contain two monomer structures that are randomly distributed and
could be termed random copolymers
ndashAABBBABABBAABAmdash
Alternating block and graft copolymers are the other three types of copolymer structures
Equimolar compositions with a regularly alternating distribution of monomer units are
alternating copolymers
ndashABABABABABABA--
A linear copolymer that contains one or more long uninterrupted sequences of each of the
comonomer species is a block copolymer
--AAAAAAAA-BBBBBBBBB--
A graft copolymer contains a linear chain of one type of monomer structure and one or more
side chains that consist of linear chains of another monomer structure
--AAAAAAAAAAAAAmdash
B B
B B
B B
B B
For this discussion the main focus will be on randomly distributed or statistical copolymers
Copolymer composition is usually different than the composition of the starting materials
charged into the system Therefore monomers have different tendencies to be incorporated
into the copolymer which also means that each type of comonomer reacts at different rates
with the two free radical species present Even in the early work by Staudinger89 it was
noted that the copolymer that was formed had almost no similar characteristics to these of the
homopolymers derived from each of the monomers
Furthermore the relative reactivities of monomers in a copolymerization were also quite
different from their reactivities in the homopolymerization Thus some monomers were more 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151
32
reactive while some were less reactive during copolymerization than during their
homopolymerizations Even more interesting was that some monomers that would not
polymerize at all during homopolymerization would copolymerize relatively well with a
second monomer to form copolymers It was concluded that the homopolymerization features
do not easily directly relate to those of the copolymerization
Alfrey (1944) Mayo and Lewis (1944) and Walling (1957)909192 demonstrated that the
copolymerization composition can be determined by the chemical reactivity of the free radical
propagating chain terminal unit during copolymerization Application of the first-order
Markov statistics was used and the terminal model of copolymerization was proposed The
use of two monomers M1 and M2 during copolymerization leads to two types of propagating
species The first of these species is a propagating chain that ends with a monomer of
structure M1 and the second species is a propagating chain that ends with a monomer structure
M2 For radically initiated copolymerizations the two structures can be represented by
M1 and M2 where the zig-zag lines represent the chain and the M
represents the radical at the growing end of the chain The assumption that the reactivity of
these propagating species only depends on the monomer unit at the end of the chain is called
the terminal unit model58 If this is so only four propagation reactions are possible for a two
monomer system The propagating chain that ends in M1 can either add a monomer of type
M1 or of type M2 Also the propagating chain that ends in M2 can add a monomer unit of
type M2 or of type M1 Therefore these equations can be written with the rate constants of
reactions93
90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953)
33
The rate constant for the reaction of the propagating chain that ends in M1 and adds another
M1 to the end of the chain is k11 and the rate constant for the reaction of the propagating
chain that ends in M2 and adds M1 to the end of the chain is k21 and so on
The term self-propagation refers to the addition of a monomer unit to the chain that ends with
the same monomer unit and the term cross-propagation refers to a monomer unit that is added
the end of a propagating chain that ends in the different monomer unit These (normally)
irreversible reactions can propagate by free radical anionic or cationic processes although
active lifetimes could be very different
As indicated by reactions 30 and 32 monomer M1 is consumed and as indicated by reactions
31 and 33 monomer M2 is consumed The rates of entry into the copolymer and the rates of
disappearance of the two monomers are given by
In order to find the rate at which the two monomers enter into the copolymer equation 34
is divided by equation 35 to give the copolymer composition equation
The low concentrations (eg 10-8 molesliter) of the radical chains in the systems are very
hard to experimentally determine So to remove these from the equation the steady state
approximation is normally employed Therefore a steady state concentration is assumed for
both of the species M1 and M2 separately The interconversion between the two
species must be equal in order for the concentrations of each to remain constant and hence the
rates of reactions 31 and 32 must be equal
34
Rearrangement of equation 37 and combination with equation 36 gives
This equation can be further simplified by dividing the right side and the top and bottom by
k21 [M2] [M1] The results are then combined with the parameters r1 and r2 which are
defined to be the reactivity ratios
The most familiar form of the copolymerization composition equation is then obtained as
The ratio of the rates of addition of each monomer can also be considered to be the ratio of the
molar concentrations of the two monomers incorporated in the copolymer which is denoted
by (m1m2) The copolymer composition equation can then be written as
The copolymer composition equation defines the molar ratios of the two monomers that are
incorporated into the copolymer d[M1] d[M2] As seen in the equation this term is directly
related to the concentration of the monomers that were in the feed [M1] and [M2] and also
the monomer reactivity ratios r1 and r2 The ratio of the rate constant for the addition of its
own type of monomer to the rate constant for the addition of the other type of monomer is
35
defined as the monomer reactivity ratio for each monomer in the system When M1
prefers to add the monomer M1 instead of monomer M2 the r1 value is greater than one
When M1 prefers to add monomer M2 instead of monomer M1 the r1 value is less than
one When the r1 value is equal to zero the monomer M1 is not capable of adding to itself
which means that homopolymerization is not possible
The copolymer composition equation can also be expressed in mole fractions instead of
concentrations which helps to make the equation more useful for experimental studies In
order to put the equation into these terms F1 and F2 are the mole fractions of M1 and M2 in the
copolymer and f1 and f2 are the mole fractions of monomers M1 and M2 in the feed
Therefore
and
Then combining equations 42 43 and 40 gives
This form of the copolymer equation gives the mole fraction of monomer M1 introduced into
the copolymer58
Different types of monomers show different types of copolymerization behavior Depending
on the reactivity ratios of the monomers the copolymer can incorporate the comonomers in
different ways
The three main types of behavior that copolymerizations tend to follow correspond to the
conditions where r1 and r2 are both equal to one when r1 r2 lt 1 and when r1 r2 gt 1
bull A perfectly random copolymerization is achieved when the r1 and r2 values are both
equal to one This type of copolymerization will occur when the two different types of
36
propagating species M1 and M2 show the exact same preference for the addition of
each type of monomer In other words the growing radical chains do not prefer to add one of
the monomers more than the other monomer which results in perfectly random incorporation
into the copolymer
bull An alternating copolymerization is defined as r1 = r2 = 0 The polymer product in
this type of copolymerization shows a non-random equimolar amount of each comonomer
that is incorporated into the copolymer This may occur because the growing radical chains
will not add to its own monomer Therefore the opposite monomer will have to be added to
produce a growing chain and a perfectly alternating chain
When r1 gt 1 and r2 gt 1 both of the monomers want to add to themselves and in theory could
produce block copolymers But in actuality because of the short lifetime of the propagating
radical the product of such copolymerizations produces very undesirable heterogeneous
products that include homopolymers Therefore macroscopic phase separation could occur
and desirable physical properties such as transparency would not be achieved
172 Determination of Reactivity Ratios
Many methods have been used to estimate reactivity ratios of a large number of
comonomers94 The copolymer composition may not be independent of conversion This
means the disappearance of monomer one may be faster than the disappearance of monomer
two if monomer one is being incorporated into the copolymer at a faster rate and therefore it
has a larger reactivity ratio than monomer two
The approximation method95 is the simplest of the methods that has been used to calculate the
reactivity ratios of copolymer systems The method is based on the fact that r1 the reactivity
ratio of component one is mainly dependent on the composition of monomer two m2 that
has been incorporated into the copolymer at low concentrations of monomer two in the feed
M2 The expression is thus
94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
37
The value of the reactivity ratio for component one can be easily determined by only one
experiment but the value is only an approximation and does not provide any validity of the
estimated r1 In order to determine the amount of the comonomer that has been incorporated
into the copolymer various analytical methods must be used Proton Nuclear Magnetic
Resonance Carbon 13 NMR and Fourier Transform Infrared Spectroscopy are three sensitive
instruments that can determine the copolymer composition The approximation method is
limited when the reactivity ratio of one of the components in the system has a value of less
than 01 or greater than a value of 10
However the method does give good insight into the reactivity ratio values for many
copolymer systems The approximation of reactivity ratios can be easy and quick when using
this method of evaluation
The Mayo-Lewis intersection method91 96 uses a linear form of the copolymerization equation where r1 and r2 are linearly related
By using the equations m1M 22 m2M12 and (M2 M1)[(m1 m2) ndash 1] for the slope and intercept
respectively a plot can be produced for a set of experiments after the copolymer composition
has been determined The straight lines that are produced on the plot for each experiment
where r1 represents the ordinate and r2 represents the abscissa intersect at a point on the r1 vs
r2 plot The point where these lines meet is taken to be r1 and r2 for the system in study The
main advantage of this method is that it gives a qualitative observation of the validity of the
intersection area Over the whole range of possible copolymer compositions that were tested
more compact intersections better define the data However the method requires a visual
check of the data and a quantitative estimation of the error is impossible Therefore
weighting of the data is needed to determine the most precise values of r1 and r2
The Fineman-Ross linearization method97 uses another form of the copolymer equation
Where
And
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259
38
For this method by plotting G versus H for all the experiments one will obtain a straight line
where the slope of the straight line is the value for r1 and the intercept of the line is the value
for r2 This type of reactivity ratio determination has the same advantages and disadvantages
of the method described above however this treatment is a linear least squares analysis
instead of a graphical analysis The validity is only qualitative and the estimates of r1 and r2
can change with each experimenter by weighting the data in different ways Furthermore the
high and low experimental composition data are unequally weighted which produces large
effects on the calculated values of r1 and r2 Therefore different values of r1 and r2 can be
produced depending on which monomer is chosen as M158
A refinement of the linearization method was introduced by Kelen and Tudos98 99 100 by
adding an arbitrary positive constant a into the Fineman and Ross equation 47 This technique
spreads the data more evenly over the entire composition range to produce equal weighting to
all the data58 The Kelen and Tudos refined form of the copolymer equation is as follows
η = [ r1 + r2 α ] ξ minus r2 α (50)
where
η = G ( α + H ) (51)
ξ = H ( α + H ) (52)
By plotting η versus ξ a straight line is produced that gives ndashr2α and r1 as the intercepts on
extrapolation to ξ=0 and ξ=1 respectively Distribution of the experimental data
symmetrically on the plot is performed by choosing the α value to be (HmHM)12 where Hm
and HM are the lowest and highest H values respectively Even with this more complicated
monomer reactivity ratio technique statistical limitations are inherent in these linearization
methods101 102
98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265
39
OrsquoDriscoll Reilly et al103 104 determined that the dependent variable does not truly have a
constant variance and the independent variable in any form of the linear copolymer equation
is not truly independent Therefore analyzing the composition data using a non-linear
method has come to be the most statistically sound technique
The non-linear or curve-fitting method90 is based on the copolymer composition equation in
the form
This equation is based on the assumptions that the monomer concentrations do not change
much throughout the reaction and the molecular weight of the resulting polymer is relatively
high In order to determine reactivity ratios from the experimental data a graph must be
generated for the observed comonomer amount that was incorporated into the copolymer m1
versus the feed comonomer amount M1 for the entire range of comonomer concentrations
Then a curve can be drawn through the points for selected r1 and r2 values and the validity of
the chosen reactivity ratio values can be checked by changing the r1 and r2 values until the
experimenter can demonstrate that the curve best fits the data points
The main advantage of the reactivity ratio determination methods discussed thus far is the
results can be visually and qualitatively checked Disadvantages include a direct dependence
of the composition on conversion for most polymer systems and therefore low conversion
(eg instantaneous composition) is needed to determine the reactivity ratios Furthermore
extensive calculations are required but only qualitative measurements of precision can be
obtained Finally weighting of the experimental data for the methods to determine precise
reactivity ratios is hard to reproduce from one experimenter to another
Therefore a technique that allows the rigorous application of statistical analysis for r1 and r2
was proposed by Mortimer and Tidwell which they called the nonlinear least squares
method95105106107This method can be considered to be a modification or extension of the
curve fitting method For selected values of r1 and r2 the sum of the squares of the differences
between the observed and the computed polymer compositions is minimized
103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772
40
Using this criterion for the nonlinear least squares method of analysis the values for the
reactivity ratios are unique for a given set of data where all investigators arrive at the same
values for r1 and r2 by following the calculations Recently a computer program published by
van Herck108 109 allows for the first time rapid data analysis of the nonlinear calculations It
also permits the calculations of the validity of the reactivity ratios in a quantitative fashion110
The computer program produces reactivity ratios for the monomers in the system with a 95
joint confidence limit determination
The joint confidence limit is a quantitative estimation of the validity of the results of the
experiments and the calculations performed This method of data analysis consists of
obtaining initial estimates of the reactivity ratios for the system and experimental data of
comonomer charge amounts and comonomer amounts that have been incorporated into the
copolymer both in mole fractions Many repeated sets of calculations are performed by the
computer which rapidly determines a pair of reactivity ratios that fit the criterion wherein the
value of the sum of the squares of the differences between the observed polymer composition
and the computed polymer composition is minimized111 112 This method uses a form of the
copolymer composition equation with mole fractions of the feed It amounts to determining
the mole fraction of the comonomer that should be incorporated into the copolymer during a
differential time interval
For this equation F2 represents the mole fraction of comonomer two that was calculated to be
incorporated into the copolymer and f1 and f2 represent the mole fractions of each comonomer
that were fed into the reaction mixture The use of the Gauss-Newton nonlinear least squares
procedure predicts the reactivity ratios for a given set of data after repeating the calculations
so that the difference between the experimental data points and the calculated data points on a
plot of mole fraction of comonomer incorporated versus comonomer in the feed is reduced to
the minimum value113 114
108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65
41
18 Controlled Radical Polymerization
The development of new controlledliving radical polymerization processes such as Atom
Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated
polymerization and degenerative transfer processes including RAFT opened the way to the
use of radical polymerization for the synthesis of well-defined complex functional
nanostructures The development of such nanostructures is primarily dependent on self-
assembly of well-defined segmented copolymers This section describes the fundamentals of
ATRP relevant to the synthesis of such systems115
The main goal of macromolecular engineering is to carry out the synthesis (polymerization) in
such a way that it results in well-defined macromolecular products One of the ways to
achieve full control of the macromolecule (length sequence and regio- and stereo- regularity)
would be to build it one monomer at a time with mechanisms in place facilitating selection of
an appropriate monomer and assuring its addition in proper orientation This of course has
been achieved in Nature in the process of protein synthesis through the use of sophisticated
macromolecular ldquonanomachineryrdquo (DNA RNA Most commonly used synthetic routes to
linear polymers are based on addition (chain) reactions which can be controlled only in
statistical terms through such parameters as initiatormonomer ratios monomerpolymer
reactivities monomer concentrations reaction medium etc The main strategy to achieve the
reasonable control of such reactionsrsquo products is through the synchronized growth of ldquolivingrdquo
chains ie chains which cease to grow only in the absence of a monomer Synchronization of
chain growth can be achieved fairly easily through rapid initiation Living chains grown in
such synchronized fashion exhibit relatively narrow molecular weight distributions (MWD)
their average molecular weights can be controlled simply by the duration of reaction Until
recently radical polymerization which covers the broadest range of monomers appeared to
be inherently uncontrollable due to the presence of fast chain termination of growing radicals
Thus although very useful in the synthesis of bulk commodity polymers where precise
control is not always essential radical polymerization has been hardly ever viewed as a tool to
precisely engineer macromolecules for well-defined functional nanostructures
114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16
42
This outlook shifted dramatically recently with the development of new controlledliving
radical polymerization processes such as Atom Transfer Radical Polymerization (ATRP)116
117 118 and other techniques such as nitroxide mediated polymerization119 and degenerative
transfer processes120 including reversible addition-fragmentation chain transfer (RAFT)121
With the availability of effective control mechanisms given its applicability to a broadest
range of monomers radical polymerization is now ready to assume the central role in
macromolecular engineering geared towards the development of well-defined functional
nanostructures
181 Fundamentals of ControlledLiving Radical Polymerization (CRP)
The great expectations for the controlledliving radical polymerization (CRP) have their
origins in the dominating position of the free radical technique by far the most common
method of making polymeric materials (nearly 50 of all polymers are made this
way)122123124This is due to the large number of available vinyl monomers (eg there are
nearly 300 different methacrylates available commercially) which can be easily
homopolymerized and copolymerized The advent of CRP enables preparation of many new
materials such as well-defined components of coatings (with narrow MWD precisely
controlled functionalities and reduced volatile organic compounds -VOCs) non ionic
surfactants polar thermoplastic elastomers entirely water soluble block copolymers
(potentially for crystal engineering) gels and hydrogels lubricants and additives surface
modifiers hybrids with natural and inorganic polymers various biomaterials and electronic
materials
The controlledliving reactions are quite similar to the conventional ones however the radical
formation is reversible Similar values for the equilibrium constants during initiation and
propagation ensure that the initiator is consumed at the early stages of the polymerization
116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002)
43
generating chains which slowly and continuously grow as in a living process There are a
number of critical differences between conventional and controlledliving radical reactions
bull Perhaps the most important difference between the two approaches is the lifetime of
the propagating chains which is extended from 1 s to more than 1 h
bull The second major difference is the very significant increase in the initiation rate
which enables simultaneous growth of all the polymer chains
bull Termination processes cannot be avoided in CRPs Thus CRP is generally less precise
than the anionic polymerization Termination is the most dangerous chain breaking
reaction in CRPs Since it is a bimolecular process increasing the polymerization rate
increases the concentration of radicals and enhances the termination process
Termination also becomes more significant for longer chains and at higher conversion
However this process is somehow self tuned since termination is chain length
dependent
The key feature of the controlledliving radical polymerization is the dynamic equilibration
between the active radicals and various types of dormant species Currently three systems
seem to be most efficient nitroxide mediated polymerization (NMP) atom transfer radical
polymerization (ATRP) and degenerative transfer processes such as RAFT123 Each of the
CRPs has some limitations and some special advantages and it is expected that each
technique may find special areas where it would be best suited synthetically For example
NMP carried out in the presence of bulky nitroxides cannot be applied to the polymerization
of methacrylates due to fast β-H abstraction ATRP cannot yet be used for the polymerization
of acidic monomers which can protonate the ligands and complex with copper RAFT is very
slow for the synthesis of low MW polymers due to retardation effects and may provide
branching due to trapping of growing radicals by the intermediate radicals At the same time
each technique has some special advantages Terminal alkoxyamines may act as additional
stabilizers for some polymers ATRP enables the synthesis of special block copolymers by
utilizing a halogen exchange and has an inexpensive halogen at the chain end125 RAFT can
be applied to the polymerization of many unreactive monomers such as vinyl acetate126
182 Typical Features of ATRP
A successful ATRP process should meet several requirements
125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035
44
bull Initiator should be consumed at the early stages of polymerization to form polymers
with degrees of polymerization predetermined by the ratio of the concentrations of
converted monomer to the introduced initiator (DP = Δ[M][I]o)
bull The number of monomer molecules added during one activation step should be small
resulting in polymers with low polydispersities
bull The contribution of chain breaking reactions (transfer and termination) should be
negligible to yield polymers with high degrees of end-functionalities and allow the
synthesis of block copolymers
In order to reach these three goals it is necessary to select appropriate reagents and
appropriate reaction conditions ATRP is based on the reversible transfer of an atom or group
from a dormant polymer chain (R-X) to a transition metal (M nt Ligand) to form a radical (R)
which can initiate the polymerization and a metal-halide whose oxidation state has increased
by one (X-M n+1t Ligand) the transferred atom or group is covalently bound to the transition
metal A catalytic system employing copper (I) halides (Mnt Ligand) complexed with
substituted 2 2rsquo- bipyridines (bpy) has proven to be quite robust successfully polymerizing
styrenes various methacrylates acrylonitrile and other monomers116127 Other metal centers
have been used such as ruthenium nickel and iron based systems117 118 Copper salts with
various anions and polydentate complexing ligands were used such as substituted bpy
pyridines and linear polyamines The rate constants of the exchange process propagation and
termination shown in Scheme 11 refer to styrene polymerization at 110 C
Scheme 11
According to this general ATRP scheme the rate of polymerization is given by the following
equation
127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901
45
Thus the rate of polymerization is internally first order in monomer externally first order
with respect to initiator and activator Cu(I) and negative first order with respect to
deactivator XCu(II) However the kinetics may be more complex due to the formation of
XCu(II) species via the persistent radical effect (PRE) The actual kinetics depend on many
factors including the solubility of activator and deactivator their possible interactions and
variations of their structures and reactivities with concentrations and composition of the
reaction medium It should be also noted that the contribution of PRE at the initial stages
might be affected by the mixing method crystallinity of the metal compound and ligand etc
One of the most important parameters in ATRP is the dynamics of exchange and especially
the relative rate of deactivation If the deactivation process is slow in comparison with
propagation then a classic redox initiation process operates leading to conventional and not
controlled radical polymerization Polydispersities in ATRP are defined by the following
equation when the contribution of chain breaking reactions is small and initiation is
complete
Thus polydispersities decrease with conversion p the rate constant of deactivation kd and
also the concentration of deactivator [XCu(II)] They however increase with the propagation
rate constant kp and the concentration of initiator [RX]o This means that more uniform
polymers are obtained at higher conversions when the concentration of deactivator in solution
is high and the concentration of initiator is low Also more uniform polymers are formed
when the deactivator is very reactive (eg copper(II) complexed by 2 2-bipyridine or
pentamethyldiethylenetriamine rather than by water) and monomer propagates slowly (styrene
rather than acrylate)
183 Controlled Compositions by ATRP
One of the driving forces for the development of a controlledldquo livingrdquo radical polymerization
is to allow for the copolymerization of two or more monomers128 This has been demonstrated
with ATRP by copolymerization of various combinations of styrene methyl or butyl acrylate
methyl or butyl methacrylate and acrylonitrile ATRP allows for the copolymerization of
these monomers using all feed compositions without loss of control of the polymerization 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
46
this is in contrast to the use of 2266-tetramethylpiperidine-1-oxyl radical (TEMPO) which
must contain a significant amount of styrene as comonomer to retain control of the
polymerization This restriction does not apply to polymerizations mediated by new
nitroxides119 The statistical copolymers prepared by living polymerizations are not the same
as those prepared by conventional radical polymerizations due to the differences in
polymerization mechanism
During a copolymerization one monomer is generally consumed faster than the other
resulting in a constantly changing monomer feed composition during the polymerization the
preference is dependent on the reactivity ratios of the two (or more) monomers In
conventional radical polymerization where the polymer chains are continuously initiated and
are irreversibly terminated the change in monomer feed is recorded in the individual polymer
chains whose composition will vary from chain to chain depending on when the chain was
formed ie at the beginning or near the end of the reaction However since ATRP is a
controlledldquolivingrdquo polymerization system the vast majority of polymer chains does not
irreversibly terminate but grow gradually throughout the polymerization The change in
monomer feed is recorded in the polymer chain itself and not from chain to chain The drifting
of composition along the polymer chain is expected to yield gradient copolymers with novel
properties129 Conventional free radical polymerization methods are generally not suitable for
synthesizing star shaped polymers due to the occurrence of undesirable radical coupling
reactions During a ldquocore-firstrdquo synthesis this would lead to coupling of the growing polymer
arms and ultimately result in a cross-linking of the star macromolecules
Block copolymers can be formed by addition of a second vinyl monomer to a macroinitiator
which contains halide groups that participate in the atom transfer process Most notably this
has been demonstrated by successive addition of a second monomer at the end of the
polymerization of a first monomer by ATRP In this manner AB and ABA block copolymers
have been prepared with various combinations of styrene acrylates methacrylates and
acrylonitrile It is very important to select the right order of monomer addition For example
polyacrylates can be efficiently initiated by the poly (methyl methacrylate)- BrCuBrL
system However the opposite is not true because concentration of radicals and overall
reactivity of acrylates is generally too low to efficiently initiate MMA polymerization
Halogen exchange comes to the rescue bromoterminated polyacrylate in the presence of
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775
47
CuClL is an efficient initiator for MMA polymerization due to reduced polymerization rate
of PMMA-Cl species which are predominantly formed after the exchange process130 131 132
Scheme 12
To conclude atom transfer radical polymerization is a robust method for preparing well-
defined polymers and novel materials with unique compositions and architectures Although
significant progress has been made in the past few years since the development of ATRP
continuous research on the better mechanistic understanding of ATRP and the preparation of
more efficient catalyst systems to yield more well-defined polymers and polymerize new
monomers is needed The syntheses of new materials need to be optimized and their
properties should be studied
It is anticipated that the new controlledliving techniques will help to provide many new well-
defined polymers via macromolecular engineering
130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
48
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1 G Carrot J Hilborn and DM Knauss Polymer 38 26 (1997) 6401-6407 2 P Rempp and E Franta Adv Polym Sci 58 1 (1984) 3 M Teodorescu European Polymer Journal 37 (2001) 1417-1422 4 Nagatsuta-cho Midori-ku Die Angewandte Makromolekulare Chemie 240 (1996) 171-180 5 R Milkovich USP 3 786 (1974) 116 6 G O Schulz R Milkovich J Appl PolymSci 27 (1982) 4773 7 Candau F Afchar F Taromi F Rempp P Polymer 18 (1977) 1253 8 Ito K Tsuchinda H Kitano T Yanada E Matsumoto T Polym J 17 (1985) 827 9 Ito K Tanak K Tanak H Imai G Kawaguchi S Itsumo S Macromolecules 24 (1991) 2348 10 Xie H Q Liu J Xie D Eur Polym J 25 11 (1989) 1119 11 Xie HQ Liu J Li H J Macromol Sci Chem A 27 6 (1990) 725 12 Hong-Quan Xie and Dong Xie Prog Polym Sci 24 (1999) 275-313 13 HQ Xie WB Sun Polym Sci Technol Ser Vol 31 Advances in polymer synthesis Plenum Publ Corp
(1985) 461
Polym Prepr 25 2 (1984) 67 14 HQ Xie JS Guo GQ Yu J Zu J Appl Polym Sci 80 2446 (2001) 15 HQ Xie SB Pan JS Guo European Polymer Journal 39 (2003) 715-724 16 K Ishizu M Yamashita A Ichimura Polymer 38 No21 (1997) 5471-5474 17 K Ishizu X X Shen Polymer 40 (1999) 3251-3254 18 K Ishizu T Ono T Fukutomi and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 131 19 K Ishizu and K Mitsutani J Polym Sci Polym Lett Edn 26 (1988) 511 20 T Fukutomi K Ishizu and K Shiraki J Polym Sci Polym Lett Edn 25 (1987) 175 21 Matyjaszewski K Beers K L Kern A Gaynor SG J Polym Sci Part A Polym Chem 36 (1998) 823 22 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 23 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 24 Ivin K J Makromol Chem Macromol Symp 4243 1 (1991) 25 KJ Ivin and T Saegusa Ring-opening polymerization Vol1 Ed Elsevier NY (1984) 26 MH Hartmann Biopolymers from Renewable Resources Ed DL Kaplan Springer Berlin (1998) 27 T Endo Y Shibasaki F Sanda Journal of Polymer Science 40 (2002) 2190 28 CJ Hawker Dendrimers and Other Dendritic Polymers Ed JMJ Freacutechet DA Tomalia Wiley NY
(2001) 29 S Penczek Makroloekulare Chemie 134 (1970) 299 30 (a) Matyjaszewski K Ed Marcel Dekker Cationic Polymerization New York (1996)
(b) Brunelle D J Ring-Opening Polymerization Ed Hanser Munich (1993)
(c) Yagci Y and Mishra M K In Macromolecular Design Concept and Practice
(d) Mishra M K Ed Polymer Frontiers New York (1994) 391
49
31 J Furukawa KTada in Kinetics and Mechanisms of Polymerization (EditKCFrisch SLReegen) 2 M
Dekker NY (1969) 159 32 HSumitomo MOkada Advanced PolymSci 28 (1978) 47 33 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 34 Matyjaszewski K Ed Marcel Dekker New York (1996) 35 Brunelle D J Ed Hanser Munich (1993) 36 Yagci Y Mishra M K Macromolecular Design Concept and Practice Mishra M K Ed Polymer
Frontiers New York (1994) 391 37 NakanoT Okamoto Y and Hatada K JAm Chem Soc114 (1992) 1318 38 Novak B M Goodwin A A Patten T E and Deming T J Polym Prepr37 (1996) 446 39 Bisht K S Deng F Gross R A Kaplan D L and Swift G J Am Chem Soc 120 (1998)1363 40 AidaT and Inoue S J Am Chem Soc 107 (1985) 1358 41 Yasuda H Tamamoto H Yamashita MYokota K Nakamura A Miyake S Kai Y and Kanehisa N
Macromolecules 26 (1993) 7134 42 Chem Systemrsquos Process Evaluation Research Planning Program PERP report Polyacetal October (2002) 43 S Penczek P Kubisa and K Matyjaszewski Adv Polym Sci 37 (1980) 44 E Franta P Kubisa J Refai S Ould Kada and L Reibel Makromol Chem Makromol Symp 1314
(1988) 127-144 45 L Wilczek and J Chojnowski Macromolecules 14 (1981) 9-17 46 PH Plesch and PH Westermann Polymer10 (1969)105 47 K Matyaszewski M Zielinski P Kubisa S Slomokowski J Chojnowski and S Penczek Makromol
Chem 181 (1980) 1469 48 S Penczek and P Kubisa Comprehensive Polymer Sci Ed by G Allen and JC Bevington Pergamon
Press 3(1989) 787 49 L Reibel H Zouine and E Franta Makromol Chem Makromol Symp 3 (1986) 221 50 E Franta P Kubisa J Refai S Ould Kada and L Reibel ACS Polymer Prepr 29 1 (1988) 83 51 J A Semlyen and J M Andrews Polymer 13 (1972) 142 52 M Wojtania P Kubisa and S Penczek Makromol Chem Makromol Symp 6 (1986) 201 53 P Kubisa Makromol Chem Makromol Symp 1314 (1988) 203 54 E Franta Kubisa S Ould Kada and L Reibel Makromol Chem Makromol Symp 60 (1992) 145-154 55 H Kruumlger H Much G Schulz and C Wehrstedt Makromol Chem 191 (1990) 907 56 Tidwell P W and Mortimer G A J Polymer Sci Pt A 3 (1965) 369-387 57 IUPAC Pure Appl Chem 40 (1974) 477-491 58 G Odian Principles of Polymerization 3rd ed New York John Wiley and Sons Inc (1991) 59 Hong S C Jia S Teodorescu M Kowalewski T Matyjaszewski K Gottfried A C and Brookhart M
J Polym Sci Polym Chem Ed 40 (2002) 2736-2749 60 Kaneyoshi H Inoue Y and Matyjaszewski K Macromolecules 38 (2005) 5425-5435 61 Neugebauer D Zhang Y Pakula T Sheiko S S and Matyjaszewski K Macromolecules 36 (2003)
6746-6755 62 Shinoda H Matyjaszewski K Okrasa L Mierzwa M and Pakula T Macromolecules 36 (2003) 4772-4778
50
63 Shinoda H and Matyjaszewski K Macromolecules 34 (2001) 6243-6248 64 Hawker C J et al Macromol Chem Phys 198 (1997) 155-166 65 Beers K L Kern A Gaynor S G and Matyjaszewski K J Polym Sci Part A Polym Chem 36 (1998)
823-830 66 Inoue Y Matsugi T Kashiwa N and Matyjaszewski K Macromolecules 37 (2004) 3651-3658 67 Kaneyoshi H et al Polymeric Materials Science and Engineering 91 (2004) 41-42 68 Paik H J Gaynor S G and Matyjaszewski K Macromol Rapid Commun 19 (1998) 47-52 69 Percec V and Asgarzadeh F J Polym Sci Part A Polym Chem 39 (2001) 1120-1135 70 Hong S C et al Polymeric Materials Science and Engineering 84 (2001) 767-768 71 Matyjaszewski K et al In PCT Int Appl (CMU USA) WO 9840415 (1998) 230 72 Gido S P Lee C Pochan D J Pispas S Mays J W and Hadjichristidis N Macromolecules 29 (1996)
7022-7028 73 Ruokolainen J Saariaho M Ikkala O ten Brinke G Thomas E L Torkkeli M and Serimaa R
Macromolecules 32 (1999) 1152-1158 74 Dreyfuss P Quirk R P Encyclopedia of Polymer Science amp TechnologyVol 7 Wiley New York (1987)
551 75 Roos S Muumlller A H E Kaufmann M Siol W and Auschra C Quirk R P Ed ACS Symp Ser (1998)
696-208 76 Schulz G O and Milkovich R Journal of Appl Polym Sci 27 (1982) 4773 77 Xu G X and Lin S G Journal of Macromol SciRev Macromol Chem Phys C34 (1994) 555-606 78 Mukherjee A K and Gupta B D J Journal of Macromol Sci Chem A19 (1983) 1069-1099 79 Boutevin B Robin J J and Serdani A Eur Polym Journal 28 (1992) 1507 80 Liu Y Lee J Y Kang E T Wang P and Tan K L React Funct Polym 47 (2001) 201-213 81 Wang X-S Luo N Ying S-K Polymer 40 (1999) 4515-4520 82 Furuhashi H Kawaguchi S Itsuno S and Ito K Colloid Polym Sci 227 (1997) 275 83 Capek I Adv Polym Sci 1 (1999) 145 84 Nguyen SH Berek D Capek I J Polym Sci submitted for publication 85 Painter P C and Coleman M M Fundamentals of Polymer Science Technomic Publishing Inc Lancaster
PA (1997) 86 Moad G Solomon D H The Chemistry of Free Radical Polymerization Pergamon Press New York (1995) 87 Rosen S L Fundamental Principles of Polymeric Materials John Wiley and Sons New York (1993) 88 Mark H F Bikales N M Overberger C G and Menges G Eds Wiley-Interscience New York Vol 4
(1986) 192-233 89 Staudinger H Schneiders J Ann Chim 541 (1939) 151 90 Alfrey T Bohrer J Jand Mark H Copolymerization Interscience New York (1952) 91 Mayo F R and Lewis F M J Am Chem Soc 66 (1944) 4594 92 Walling C Free Radicals in Solution Wiley New York Chap 4 (1957) 93 Flory P J Principles of Polymer Chemistry Cornell University Press Ithaca (1953) 94 Polic A L Duever T A and Penlidis A J Polym Sci Part A 36 (1998) 813 95 Tidwell P W and Mortimer G A Journal of Polym Sci Part A 3 (1965) 369
51
96 Davis T P Journal of Polym Sci Part A 39 (2001) 597 97 Fineman M and Ross S D Journal of Polymer Sci 5 (1950) 259 98 Kelen T Tudos F and Turcsanyi B Polymer Bull 2 (1980) 71-76 99 Tudos F Kelen T Foldes-Berezsnich T and Turcsanyi B J Macromol SciPart A 10 (1976) 1513-1540 100 Tudos F and Kelen T J Macromol Sci Part A 16 (1981) 1283 101 Greenley R Z In Polymer Handbook 4th Edition Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1999) 102 Greenley R Z In Polymer Handbook Part II 3rd Ed Brandup J Immergut E H and Grulke E Eds John
Wiley New York (1989) 153-265 103 ODriscoll K F and Reilly P M Makromol Chem Makromol Symp 1011 (1987) 355 104 ODriscoll K F Kale L T Garcia-Rubio L H and Reilly P M J Polym Sci Polym Chem Ed 22
(1984) 2777 105 Hill D J T and ODonnell J H Makromol Chem Makromol Symp 1011 (1987) 375 106 Hill D J T Lang A P ODonnell J H and OSullivan P W Eur Polym J 25 (1989) 911 107 Hill D J T Lang A P and ODonnell J H Eur Polym J 27 (1991) 765-772 108 van Herck A M J Chem Ed 72 (1995) 138 109 van Herck A M Manders B G Smulders W and Aerdts A Macromolecules 30 (1997) 322-323 110 Mott G Brendlein W and Braun D Eur Polym J 9 (1973) 1007-1012 111 Davis T P ODriscoll K F Piton M C and Winnik M A J Polym Sci Part C Polym Lett 27 (1989)
181 112 Davis T P ODriscoll K F Piton M C Winnik M A Macromolecules 23 (1990) 2113 113 Davis T P ODriscoll K F Piton M C and Winnik M A Polym Int 24 (1991) 65 114 Ghi P Y Hill D J T ODonnell J H Pomeroy P J and Whittaker A K Polymer Gels and Networks 4
(1996) 253 115 T Kowalewski RD McCullough and K Matyjaszewski Eur Phys J E 10 (2003) 5ndash16 116 J-S Wang and K Matyjaszewski J Am Chem Soc 117 (1995) 5614 117 K Matyjaszewski and J Xia Chem Rev 101 (2001) 2921 118 M Kamigaito T Ando and M Sawamoto Chem Rev 101 (2001) 3689 119 CJ Hawker AW Bosman and E Harth Chem Rev 101 (2001) 3661 120 SG Gaynor J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 8051 121 RTA Mayadunne E Rizzardo J Chiefari YK Chong G Moad and SH Thang Macromolecules 32
(1999) 6977 122 K Matyjaszewski Ed ACS Symposium Series (2000) 685 123 K Matyjaszewski Ed ACS Symposium Series 2 (2000) 768 124 K Matyjaszewski and TP Davis Eds Handbook of radicalPolymerizationWiley-Interscience Hoboken
(2002) 125 K Matyjaszewski DA Shipp J-L Wang T Grimaud and TE Patten Macromolecules 31 (1998) 6836 126 M Destarac D Charmot and X Franck ZSZ Macromol Rapid Comm 21 (2000) 1035 127 J-S Wang and K Matyjaszewski Macromolecules 28 (1995) 7901 128 KD Davis K Matyjaszewski Adv Pol Sci 159 (2002) 1
52
129 K Matyjaszewski MJ Ziegler SV Arehart D Greszta and T Pakula J Phys Org Chem 13 (2000) 775 130 DA Shipp J-L Wang K Matyjaszewski Macromolecules 31 (1998) 8005 131 K Matyjaszewski DA Shipp GP McMurtry SG Gaynor T Pakula J Polym Sci A 38 (2000) 2023 132 Braunecker WA and Matyjaszewski K Prog Polym Sci (2007) 3293
53
CHAPTER II Synthesis and Characterization of
Macromonomers
21 Introduction
Cationic ring opening polymerization of DXL proposed by Franta and Reibel133 results in
linear polymeric chains thereby preventing formation cyclic oligomers through cationic
polymerization of cyclic acetals15 17In fact the reaction of DXL in the presence of an
unsaturated alcohol (2-HPMA) results in a functionalized linear PDXL macromonomer
carrying at one or both ends an unsaturated system supported by the methacryloyl group of
the alcohol The synthesis of α ω-dihydroxy-PDXL chains is based on the activated monomer
mechanism44 Franta et al have established that when DXL is polymerized by strong protonic
acids such as triflic acid in the presence of a diol the PDXL chains are essentially linear and
carry end-standing OH functions It has been shown that the amount of cyclic species formed
is negligible that the dispersity is on the order of 14 and that the molecular weight of the
linear polymers is governed by the ratio of reacted monomer to transfer agent and is generally
well controlled up to 10 000 gmol
De Clercq and Goethals have reported the preparation of poly (13dioxolane)
bismacromonomers by copolymerization with MMA and provided the possibility to prepare
polymer networks containing PDXL segments134 135 PDXL based hydrogels have been
obtained in most cases by free radical copolymerization with comonomers such as acrylic
acid acrylamide and N-isopropylacrylamide134 136 137 styrene and butyl acrylate138
Hydrogels have received increasing attention for biomedical applications such as drug
delivery immobilization of enzymes dewatering of protein solutions and contact lenses139
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002) 1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080
54
140 These materials and are widely used in areas like baby diapers solute separation soil for
agriculture and horticulture absorbent pads etc139 Hydrogels are defined as hydrophilic
polymer networks which have a high capacity to adsorb a substantial amount of water which
have been proposed as protein releasing matrices The high water content ensures a good
compatibility with entrapped proteins as well as with surrounding tissue141 Even though a
number of applications are currently being pursued using hydrogel very little is known about
the mechanical behavior that describes the various physical processes in hydrogels142 Over
the last decade most interests have been emphasized on the synthesis of polymers containing
polyacetal segments because of the ease of degradation of these polymers under mild
conditions by treatment with a trace of acid134 143 Poly (1 3 dioxolane) is a hydrophilic non-
ionic polymer which like poly (ethylene oxide) is appreciably soluble in water but much
more sensitive to acidic degradation because of the presence of acetal groups in the chains144
In this chapter we report the synthesis of the functionalized poly (13dioxolane)
macromonomers which have been used for the preparation of PDXL hydrogel and
amphiphilic graft copolymers In the second part of this chapter we have focused on a
detailed study of the properties of the resulting hydrogel in terms of swelling behavior in
different organic solvents and viscoelastic properties determined by rheological measurements
in both the steady shear and oscillatory experiments
22 Experimental
221 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922
55
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
bull Dichloromethane (CH2Cl2 MW 8493 bp 40degC d 1325)
Dichloromethane (Prolabo 999) was dried by stirring over CaH2 for 24 h and then
distilled under a N2 atmosphere to remove impurities Purified dichloromethane was
stored under nitrogen over molecular sieve
bull 2-hydroxypropyl methacrylate (2-HPMA) (MW 14417 bp 240degC d 1028)
2-HPMA of commercial grade was purchased from Acros stabilized with 200 ppm
hydroquinone monomethyl ether Then it was stored over molecular sieve
bull n-Hexane 99 (C6H14 MW 8618 bp 68-70degC d 0658-0662) Stored under
nitrogen over molecular sieve
bull Trifluoromethanesulfonic acid (triflic acid Aldrich) was used as received
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile (AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull 1 3 dioxolane (DXL) (MW 7408 bp 78degC d 106)
The monomer DXL of commercial grade was purchased from Acros DXL was kept
under KOH for two and up to three days to remove any peroxide and stabilizer traces
and then purified by distillation over CaH2 under a N2 atmosphere prior to
polymerization
All chemicals were kept over molecular sieve before use
222 Reaction apparatus
All polymerization experiments were performed with a clean 250 ml three neck round bottom
flask A condenser was used on one of the necks of the flask in order to condense any
monomers that might otherwise possibly escape A magnetic bar was used to stir the solution
at a constant speed in order to assure even distribution of monomer and initiator
concentrations throughout the entire volume of solution A rubber septum was used to cover
one of the three necks
In the case of free radical polymerization reactions a thermocouple was also fitted to the
reaction vessel to monitor the temperature of the reaction The thermocouple regulated the
56
temperature at a constant 70degC throughout the reaction
223 Synthesis of Poly (13-dioxolane) Macromonomers
Methacrylate-terminated PDXL macromonomers were synthesized by Cationic ring-opening
polymerization which was carried out in 10 ml dichloromethane with triflic acid as initiator at
room temperature under nitrogen for 24 h in the presence of 2-hydroxypropyl methacrylate
(2-HPMA) as transfer agent 20 ml of DXL monomer was added The feed molar ratios
[DXL] [2-HPMA] are reported in Table1 as well as the molecular characteristics of the
obtained macromonomers The amount of the acid used was 20 μl After reaction the
resulting solution is poured into THF Then the product is purified by re-precipitation from
THF solution with a large excess of hexane and the obtained polymer was dried under
vacuum at room temperature The yield was checked by gravimetric determination and found
to be about 80
224 Synthesis of Poly (13-dioxolane) Hydrogel Network
The functionalized PDXL macromonomer taken for the preparation of PDXL netwok was
(FPP2) macromonomer with a theoretical average molecular weight of Mnth =2000
The macromonomer (1g) was polymerized by free radical polymerization in 10 ml of THF
using 2 2-azobisisobutyronitrile (AIBN) (001g) as initiator under a nitrogen atmosphere
The polymerization was carried out at 70degC for 24h A piece of hydrogel was obtained The
product was extracted with ethanol to remove unreacted macromonomers and then dried
under vacuum
23 Characterization Techniques
231 Raman Spectroscopy
Raman spectroscopy is used to study and analyse the structure of the macromonomers
The experiments were performed on a Dilor XY 800 spectrophotometer The detector was a
charge-coupled device (CCD) An argon laser pump beam (power density of 100 mW) has
been focused onto the sample through a microscope The working wavelength was chosen as
λ = 5145 nm In our experiments we explored the spectral range between 200 and 3700 cm-1
with a spectral resolution of 2 cm-1
57
232 1H-NMR Spectroscopy
Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) was used for structural analysis
and molecular weight of polymers and macromonomers Proton NMR spectra were obtained
using a high field 400Mhz Advance Bruker spectrometer
All of the 1H NMR samples were dissolved in deuterated chloroformThe chloroform
reference peak at 724 ppm was to ensure accuracy of peak assignments The integrals of the
peaks were used for the calculations to determine the Mw of the macromonomers
233 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) represents a chromatographic method widely used in
the analysis of polymer average molecular weights and molecular weight distributions SEC
Measurements were performed at 40degC on a Waters 2690 instrument equipped with UV
detector (Waters 996 PDA) coupled with a Differential Refractometer (ERC - 7515 A) and
four Styragel columns (106 105 500 and 50degA) THF is employed as eluent with a flow rate
of 10 mlmin Polystyrene standard samples were used for calibration
234 Swelling Measurements
In order to investigate the swelling behavior the measurement of the swelling ratio of the
polymer network is obtained from a gravimetric method in which small pieces of hydrogel
were immersed solvents such as CH2Cl2 and THF for 24 hours at room temperature (23degC)
until swelling equilibrium was reached ie when the gel thickness became essentially
constant The samples were removed from the solvents and carefully weighed (Ws) Then the
samples let to deswell and weighed every 5 min during in order to determine the swelling
kinetics in the solvents The swelling equilibrium was reached after 5 hours Afterwards the
gel was left to dry for 24 hours at room temperature until constant weight was attained and the
dry weight (Wd) was determined and the swelling ratio was calculated from equation
SR = ( ) 100timesminusWd
WdWs (57)
Where SR is equilibrium swelling ratio Ws and Wd are the sample weights in swollen and dry
states respectively
58
235 Rheological Measurements
Steady shear and oscillatory measurements have been performed on a stress imposed
rheometer Rheo-Stress-100 (RS100) from Haake used with a coneplate geometry (20 mm
diameter an angle of 4deg gap 2 mm)The imposed stress of 100 Pa during 30 seconds and a
frequency of 1Hz were applied while the strain was monitored The measurements have been
performed on swollen and unswollen samples The elastic (G) and the loss (G) moduli are
measured in linear viscoelastic region In the oscillatory experiments the frequency
dependence of both Grsquo and G is obtained at a constant strain All rheological measurements
were carried out at room temperature (23 degC)
24 Results and Discussion
241 Structural Characterization of Macromonomers
1 3 dioxolane (DXL) belongs to the class of heterocyclic monomers containing acetal
functions that only polymerize cationically46 A specific characteristic of DXL is its lower
nucleophilicity as compared to that of the acetal functions in PDXL Thus in competition
with the propagation reaction the active sites at the growing polymer end ie cyclic
dioxolenium cations will also be involved in a reaction with the acetal functions in the
polymer chains25 43 This continuous transacetalization process results in a broadening of the
molecular weight distribution and in the formation of cyclic structures47 It has been shown
that these intermolecular transfer reactions can be applied to introduce reactive end groups on
both chain ends of PDXL by the addition of a low molar mass formal as chain transfer agent
during the polymerization The synthesis of α ω-dihydroxy-PDXL chains is based on the
activated monomer mechanism44 Franta et al have established that when DXL is polymerized
by strong protonic acids such as triflic acid in the presence of a diol the PDXL chains are
essentially linear and carry end-standing OH functions It has been shown that the amount of
cyclic species formed is negligible that the dispersity is on the order of 14 and that the
molecular weight of the linear polymers is governed by the ratio of reacted monomer to
transfer agent and is generally well controlled up to 10 000 gmol
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel44 133 using an unsaturated alcohol (2-
59
HPMA) as a transfer agent results in linear polymeric chains thereby preventing formation of
cyclic oligomers through cationic polymerisation of cyclic acetals15 17 They were all prepared
at the same reaction conditions The synthetic route of functionalized PDXL macromonomers
is shown in scheme13
Scheme 13 Structures of PDXL macromonomer species54
According to this mechanism it is possible to prepare macromonomers ie PDXL chains
carrying polymerizable double bonds at their ends Nevertheless because of the
transacetalization reactions a mixture of products is obtained
A is the most abundant compound it corresponds to 50 to 60 weight wise54 It is a
macromonomer
B corresponds to 20 to 25 weight wise It is a bis-macromonomer It carries two
methacryloyl functions corresponding to transacetalization of R-OH and DXL
C corresponds to 20 to 25 weight wise It carries no methacryloyl function but two
hydroxyl groups It is a α ω-dihydroxy-PDXL
These 3 species A B and C stem from scrambling reactions that are typical with cyclic
acetals54
The characterization of these materials is based on structure and molecular weight
determination For instance the PDXL macromonomers carried at one of their ends a double
bond afforded by the methacryloyl group The latter was checked by Raman and 1H-NMR
spectroscopy All macromonomers prepared displayed functionality close to unity which
makes them suitable for the synthesis of graft copolymers
60
Raman spectroscopy is used to study and analyse the structure of the macromonomers The
aim of this study is to check the formation of linear polymer chains as well as the termination
with methacryloyl groups The spectra obtained exhibit two intense Raman bands at 800 to
900 cmP
-1 and 2700 to 3000 cmP
-1 regions and a series of small other peaks for all samples as
shown in figure 1 The most intense band (2700 ndash 3000 cmP
-1) is assigned to the aliphatic
stretching vibration of CH in the polyacetal chain Symmetric COCOC stretching frequencies
of aliphatic acetals fall in typical regions of 1115-1080cmP
-1 and 870-800 cmP
-1 145 and are
responsible for intense Raman bands In the low frequency region there are three very
characteristic Raman bands in the 600 ndash 550 cmP
-1 540 ndash 450 cmP
-1 and 400 ndash 320 cmP
-1 ranges
which are assigned to COCOC deformations145 146 Also the acetals have strong multiple
bands in the region of 1160ndash1040 cmP
-1 as noticed on the Raman spectra involving the C-O
stretching modes In addition to this the O-CH-O group gives rise to a band at 1350 ndash1325
cmP
-1 for C-H deformation Other intense Raman bands are observed in the region of 3000 ndash
2700 cmP
-1 Below 3000 cmP
-1 the corresponding frequencies are assigned to the aliphatic C-H
stretching modes145 The methoxy group is detected in the region of 2835 ndash 2780 cmP
-1
Figure 1 Raman spectra of methacrylic-terminated PDXL macromonomers (FPP2 FPP15 and
FPP1)
145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The Handbook of IR
and Raman Characteristic Frequencies of Organic Molecules United Kingdom Ed by Academic Press Limited London (1991)
146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman Spectroscopy 3rd Edition AP Limited London (1964)
61
As far as the presence of the methacryloyl group in the polymeric chain is important bands
have been observed at 1640 cmP
-1 which corresponds to C=C bonds The carbonyl compounds
absorb strongly within 1900 ndash1550 cmP
-1 region145 146 the spectra show a C=O bond absorption
found at 1720 cmP
-1 In the region of 1340 ndash1250 cmP
-1 the methacrylate bands are observed
Broad absorption is found near 3500 cm -1 owing to stretching of the OH bonds OH
deformation bands are found at 1400 cmP
-1P and 1340 cmP
-1 This observation indicates that both
methacrylic and ndashOH groups are present and eventually the resulting product is a mixture of
the three species as shown in the scheme above
Typical 1H-NMR spectrum of PDXL macromonomer shown in figure 2 exhibits the expected
resonance assigned to the methoxy protons (477 ppm) and OCH2CH2O protons at (374
ppm) Two signals corresponding to =CH2 were observed at (612 ndash 614 ppm) and (557 ndash
559 ppm) Therefore the spectrum confirmed the chemical structure HO[CH2CH2OCH2O]nR
of methacryloyl- terminated PDXL macromonomer
Figure 2 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP2)
242 Molecular Weight Determination
Besides the structure 1H-NMR enables us to determine the number-average molecular weight
(Mn) In the calculation of the latter the methacryloyl end group was included The
62
polydispersity and index MwMn and the number-average molecular weight were obtained
from SEC measurements Table 1 summarizes these values It can be seen that Mn (SEC) and
Mn (NMR) are very close to each other for all macromonomer samples and are in agreement
with the theoretical values predicted from calculations Under our polymerization conditions
the polydispersity index is 16 for all samples
Table 1 Characteristics of PDXL macromonomers prepared at different degrees of
polymerization
Sample Dp Mnth MnSEC MnRMN MwMn f (a)
FPP1 135 1000 1120 1160 16 097
FPP15 2025 1500 1540 1550 16 099
FPP2 270 2000 2040 2100 16 097
Dp degree of polymerization = [DXL] [2HPMA]
a functionality of macromonomers (methacryloyl end groups molecule)
243 Swelling of Poly (13 Dioxolane) Hydrogel
The synthesized PDXL hydrogel has been studied in terms of swelling and rheological
behaviors The degree of swelling and the rate of swelling of the hydrogel are studied It is
known that hydrogel can swell in several solvents but at different degree of swell according to
many factors related to the nature of the solvents and the type of polymer-solvent interactions
It was found that the solubility parameter of the solvents (δ) had a great effect on swelling
degree For instance hydrogels can swell fast in CH2Cl2 (δ = 976 cal cm12 -32) and reached
equilibrium within no more than an hour However it will take about more than 20 h to reach
equilibrium in CH3 OH (δ = 145 cal cm12 -32) It was known that the polymer can reach
greatest swelling degree when the solubility parameter of the polymer is close to that of the
solvents The solubility parameter of PDXL is about 93 cal cm 12 -32 134 The swelling has been
examined in THF and CH2Cl2 for PDXL hydrogel It has been observed that the swelling
equilibrium is reached after almost 5 hours of swelling for all samples in both solvents The
results show that THF (δ = 952 cal cm12 -32)147 swells the hydrogel to the greatest degree
compared to CH2Cl2 as shown in figure 3 However CH2Cl2 molecules provide less swelling
147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983)
63
capacity than in THF On the basis of the experiment The PDXL hydrogel reached high
swelling degree due to its solubility parameter is much closer to that of THF
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
THF CH2Cl2
Swel
ling
degr
ee
Time (min)
Figure 3 Swelling kinetics of PDXL hydrogel in two different solvents CH2 Cl2 (solid
squares) and in THF (hollow squares)
244 Viscoelastic Behavior
Rheological measurements were performed on rheometer in the Cone and Plate geometry
Both steady shear and oscillatory experiments were carried out The dynamic storage and loss
moduli G and G were examined at room temperature (23 degC)
Many attempts have been carried to extend the elasticity theory to swollen gels148 149 Based
on this approach all measurements have been performed on both swollen and unswollen
hydrogel samples for the purpose of comparison so that to examine the mechanical properties
even in swollen state For instance Flory and Rehner recognized the swelling phenomenon
exhibited by cross-linked polymers when exposed to certain solvents and related the modulus
of elasticity of a swollen cross-linked polymer network to an unswollen network150 Figure 4
illustrates the strain dependence of G and G for swollen and unswollen samples
148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for Experimental
Mechanics SEM Annual Conference Proceedings (2002)
64
10-5 10-4 10-3 10-2 10-1 100 101 102101
102
103
104
Guns Guns Gs Gs
GG
(Pa
)
γ ()
Figure 4 Strain dependence of the elastic modulus Grsquo (circles) and of the viscous modulus
Grdquo(triangles) for two samples of unswollen hydrogel (solid symbols) and swollen hydrogel
(hollow symbols)
The moduli are measured as a function of strain at a constant frequency It appears that the
linear viscoelastic region is observed while the strain is increasing in either state which
indicates that the internal structure of the samples has not been disrupted when deformed
This leads to reveal that the gel is strain resistant in swollen and unswollen states and within a
large strain range the hydrogel retains its elasticity as shown in figure 4 where the linear
viscoelastic region extends to almost 02
The frequency dependence of G and G is shown in figure 5 similarly for swollen and
unswollen hydrogels The system behaves typically like a gel as it can be noticed that the
elastic component G (storage modulus) is far greater than the viscous component G (loss
modulus)151 Based on these results the hydrogel exhibits extreme elasticity at low
frequencies
151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure 554 (2000) 99-108
65
100 101
103
104
105
Gs Guns Gs GunsG
G(
Pa)
ω (rads)
Figure 5 Frequency dependence of Grsquo(circles) and Grdquo(triangles) for swollen hydrogel
(hollow symbols) and unswollen hydogel (solid symbols)
Finally figure 6 illustrates the complex viscosity profiles another parameter of
viscoelasticity which measures the magnitude of the total resistance to a dynamic shear
Again this property has not been affected by swelling since the results show similar behavior
for swollen and unswollen states It decreases sharply as frequency increases which
characterizes the samples degree of viscoelasticity at various time scales Therefore from the
results discussed above the hydrogel network is elastic and stable even in the swollen state
thereby possessing very good mechanical properties
100 101 102 103
102
103
104
105
η unswollen η swollen
ηlowast (P
a s)
ω (rads)
Figure 6 Frequency dependence of the complex viscosity η for unswollen hydrogel (solid
squares) and swollen hydrogel (hollow triangles)
66
Conclusion
The hydrogel properties were discussed in terms of swelling and viscoelastic
behaviors The hydrogel has combined special properties Its swelling behaviour in the
solvents was dependent on the solubility parameter of both solvents and hydrogel
Rheological measurements were successful when used in order to study the viscoelastic
behavior of the hydrogel of pure PDXL in swollen and unswollen states The Strain
dependence of G and G for both samples shows linear viscoelastic region and allows to
determine the yield stress Same conclusions can be given concerning the frequency
dependence of complex viscosity the swelling does not affect this property The results reveal
a perfect elastic and resistant hydrogel in other words the viscoelastic properties have not
been so much affected by swelling They may be particularly useful in the design of improved
microfluidic devices that utilise the relationship between swelling and strain This kind of
material can be potentially used in biosystems such as intelligent drug delivery systems
67
References
133 EFranta JRefai CDurand LReibel MakromolChem Makromol Symp32 (1990) 169-
174 134 J Du X Ding Z Zheng Y Peng European Polymer Journal 38 (2002) 1033-1037 135 EJ Goethals and al Makromol Chem Makromol Symp 48 (1991) 427-429 136 Juan Du Yuxing Peng Xiaobin Ding Colloid Polym Sci 281 (2003) 90-95 137 J Du YPeng T Zhang X Ding Z Zheng Journal of Applied Polym Sci 83 (2002)
1678-1682 138 RR De Clercq EJ Goethals Macromolecules 25 (1992) 1109-1113 139 Caihua Ni Xiao-Xia Zhu European Polymer Journal 40 (2004)1075-1080 140 B Yildiz B Isik M Kis Reactive amp Functional Polymers 52 (2002) 3-10 141 SJde Jong and al Journal of controlled release 72 (2001) 47-56 142 S K De and al Journal of Micro electromechanical Systems 11 (2002) 544-554 143 A Benkhira E Franta J Franccedilois Macromolecules 25 (1992) 5697-5704 144 K Naragui N Sahli M Belbachir E Franta PJ Lutz Polymer Int 51 (2002) 912-922 145 Daimay Lin-Vien Norman B Colthup William G Fateley and Jeanette G Grasselli The
Handbook of IR and Raman Characteristic Frequencies of Organic Molecules United
Kingdom Ed by Academic Press Limited London (1991) 146 Norman B Colthup and Stephen E Wilberly Introduction to Infrared and Raman
Spectroscopy 3rd Edition AP Limited London (1964) 147 Allan F M Barton ldquoHandbook of Solubility Parametersrdquo CRC Press (1983) 148 N W Taylor and E B Bagley Journal of Polym Sci Polymer Physics 13 (1975) 1133-
1144 149 H N Nae and W W Reichert Reologica Acta 31 (1992) 351-360 150 BD Johnson DJ Niedermaier WC Crone J Moorthy and DJ Beebe Society for
Experimental Mechanics SEM Annual Conference Proceedings (2002) 151 C Chassenieux J Fundin G Ducouret and I Iliopoulos Journal of Molecular Structure
554 (2000) 99-108
68
CHAPTER III Synthesis and Characterization of Copolymers
31 Introduction
Amphiphilic block and graft copolymers consisting of hydrophilic and hydrophobic parts
have been subjects of numerous studies within which block and graft copolymers containing
hydrophilic polyoxyethylene segments and other hydrophobic segments have attracted much
attention because polyoxyethylene segments are not only hydrophilic but also nonanionic
and crystalline and can complex monovalent metallic cations Graft copolymers offer all
properties of block copolymers but are usually easier to synthesize Moreover the branched
structure leads to decreased melt viscosities which is an important advantage for processing
Depending on the nature of their backbone and side chains they give rise to special properties
in selective solvents at surfaces as well as in the bulk owing to microphase separation
morphologies12 They can be used for a wide variety of applications such as polymeric
surfactants electrostatic charge reducers compatibilizers in polymer blends polymeric
emulsifiers controlled wet ability and so on152 153 In order to prepare graft copolymers with
well-defined structure one can utilize the macromonomer technique (grafting through
technique) Well-defined structure graft copolymers are synthesized by copolymerization of
macromonomers with low molecular weight comonomers6 It allows the control of the
polymer structure which is given by three parameters (i) chain length of side chains which
can be controlled by the synthesis of the macromonomer by living polymerization (ii) chain
length of backbone which can be controlled in a living copolymerization (iii) average
spacing of the side chains which is determined by the molar ratio of the comonomers and the
reactivity ratio of the low-molecular weight monomer However the distribution of spacings
may not be very easy to control due to the incompatibility of the polymer backbone and the
macromonomers154 As pointed out in recent publication reviews155 there is a complex
interplay of factors that govern the reactivities in copolymerizations involving
macromonomers When different comonomers are copolymerized with the same it seems that
the degree of interpenetration between the macromonomer and the propagating copolymer 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305
69
backbone plays the major role in the measured reactivities Nevertheless the main properties
depend on both the average composition of the systems and the microstructural distribution of
the comonomer sequences along the macromolecular backbone which is determined by the
reactivity ratios of the macromonomer and the corresponding comonomer in the free radical
polymerization process156 157
In this chapter our work deals with the preparation and characterization of new organo-
soluble associative copolymers based on short hydro-soluble chains of poly (1 3 dioxolane)
(PDXL) Many reports have been published on PDXL macromonomers used to form
hydrogels136 137 158 159 160 161 162 however very few were on graft copolymers with PDXL
branches162 These macromonomers are used for the preparation of amphiphilic graft
copolymers by solution free radical copolymerization with a hydrophobic comonomer
styrene (St) and methyl methacrylate (MMA) Structural characterization of these
copolymers molecular weight determination reactivity ratios and the polymerizability of the
PDXL macromonomer have been discussed Finally their thermal properties are discussed
according to the weight content of PDXL in the copolymers
32 Experimental
321 Chemicals and Purification
a) Solvents and Reagents
bull Tetrahydrofuran (THF C4H8O MW 7211 bp 65-67degC d 0885-0890)
Major impurities in THF include inhibitors peroxides and water To remove these
impurities commercial THF (Prolabo product) was refluxed over a small amount of
sodium (Aldrich 40 wt in paraffin) and benzophenone (Aldrich 99) under a nitrogen
atmosphere at 66degC The anhydrous state of THF was indicated by a deep purple
complex formed from sodium and benzophenone Pure THF was distilled from this deep
purple solution immediately prior to use
156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269
70
bull Ethanol (C2H6O MW 4607 bp 78degC d 081)
Ethanol (Prolabo 95-96) was purified by distillation with 5g of Magnesium and 05g of
iodine for 75ml of alcohol under a N2 atmosphere After discoloration of the mixture
solution a volume of Ethanol was added and then distilled normallyThen it was stored
over molecular sieve
bull 22-azobis(2-methylpropioyonitrile(IUPAC-name)Azobisisobutyronitrile(AIBN)
((CH3)2C(CN)N=NC(CH3)2CN) (MW 16421 mp 104degC)
The free radical initiator AIBN was obtained from Aldrich Chemicals AIBN is a white
powder was purified by recrystallization from methanol
b) Monomer
bull Styrene (C6H5CH=CH2 MW 10416 bp 145degC d 091)
Styrene (Prolabo product) was purified by distillation over CaHB2 at reduced pressure
bull Methyl Methacrylate (MMA)(H2C=C(CH3)CO2CH3 MW 10012 bp 100degC d
0936)
Methyl Methacrylate (Prolabo product) was purified by distillation over CaHB2 at reduced
pressure
All chemicals were kept over molecular sieve before use
322 Synthesis of Poly (Styrene-co-Poly (13-dioxolane))
a) Conventional Free Radical Copolymerization
The reaction route for the conventional copolymerization of Styrene and PDXL
macromonomers using AIBN as the free radical initiator at 60degC is shown in scheme 14
71
Scheme 14
PDXL macromonomers of different molecular weights were copolymerized with St in THF at
60degC in the presence of 2 2rsquo-azobisisobutyronitrile AIBN (1 based on the total weight of
the monomers) as initiator under a nitrogen atmosphere using different feed molar fractions
of macromonomers The total monomer concentration for was 6 10-1 M in all cases The
copolymerization product is diluted with THF and then added dropwise to a large excess of
ethanol to remove unreacted PDXL macromonomers25 43 and precipitate the copolymers
Then they were finally dried over vacuum at 40degC to constant weight The yields of all
reactions are 70ndash 90 Table 2 indicates the amounts of comonomers initiator and solvent
employed in the copolymerization study
72
Table 2 Copolymerization of PDXL macromonomers (M1) with Styrene (M2)
Sample M1 M2M1 PDXL (g) (mol)
Styrene (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2SP2 FPP2 20 349 174510-4 364 349 10-2 007 60 0610 3SP2 FPP2 30 232 116 10-4 364 349 10-2 006 60 0601 5SP2 FPP2 50 14 69810-4 364 349 10-2 005 60 0593
2SP15 FPP15 20 262 174510-4 364 349 10-2 006 60 0610 3SP15 FPP15 30 174 116 10-4 364 349 10-2 006 60 0601 5SP15 FPP15 50 105 69810-4 364 349 10-2 005 60 0593
2SP1 FPP1 20 174 174510-4 364 349 10-2 006 60 0610 5SP1 FPP1 50 07 69810-4 364 349 10-2 005 60 0593 8SP1 FPP1 80 0436 43610-4 364 349 10-2 005 60 0589
b) Controlled Free Radical Copolymerization
The comb-structure copolymer of styrene and PDXL was obtained by grafting-from
mechanism through Nitroxide-Mediated Polymerization
Nitroxide mediated polymerization (NMP) is a controlled radical polymerization (CRP)
technique which already offers the ability to prepare a wide variety of well-defined polymer
architectures119 Despite the significant improvements brought to CRP techniques such as
NMP atom transfer radical polymerization (ATRP) or reversible addition fragmentation chain
transfer (RAFT) the preparation of complex architectures by CRP is restricted by the
exclusion of monomer systems that are polymerized by fundamentally different mechanisms
like lactides ethylenepropylene oxide The most promising approaches to extend the range of
polymer compositions are based on the use of heterofunctional initiators163 allowing the
combination of mechanistically distinct polymerization reactions without the need for
intermediate transformation and protection steps
In the field of NMP the development of multifunctional initiators was focused on TEMPO
and TIPNO which are examples of nitroxides (Scheme 15) It is worth to mention that in
NMP these are used as counter-radicals associated with a conventional azoic initiator so this
pair of initiators is known as a bimolecular system
163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671
73
Scheme 15 TEMPO and based alkoxyamines
Another initiator used for NMP is the commercially available alkoxyamine also called
MAMA-SG1164 (Scheme 16) known as a monomolecular system initiator which is
particularly convenient for functionalization of polymer chain ends164 165 MAMA-SG1 has
been developed by Didier Gigmes and co in collaboration with Arkema Company166 Thanks
to a particularly high dissociation rate constant value kd1 up to now this alkoxyamine has
proved to be one of the most potent alkoxyamines reported in the field of NMP167 168 This
initiator is used for polymerization of styrene and n-butyle acrylate allowing formation of
well-defined linear and star structures
Scheme 16
164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006) 5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219
74
Scheme 17 MAMA-SG1 structure and dissociation scheme
bull Multifunctionalization of Polystyrene (HO-PS)
MAMA-SG1 was used to run copolymerization of styrene at 90 mol with HEMA in order
to obtain functionalized polystyrene The monomers and alkoxyamine were introduced in a
250 mL two neck round-bottom flasks fitted with septum condenser and degassed for 15
min by nitrogen bubbling The reaction was performed in bulk at 120 degC under N2 with
vigorous stirring Targeted molecular weight and polydispersity were 30 000 g mol and 12
respectively
After polymerization the final polymer mixture was dissolved in a minimum THF and
precipitated in cold ethanol followed by drying under vacuum at 30degC
bull Synthesis of PS-g-PDXL
PDXL was copolymerized by cationic ring-opening polymerization which was carried out in
40 ml dichloromethane with triflic acid as initiator at room temperature under nitrogen for 24
h in the presence of OH-multifunctionalized PS (1g 3 10-5 mol) as transfer agent 20 ml
(0286 mole) of DXL monomer was added Table 6 gives the molecular characteristics of the
obtained copolymer The amount of the acid used was 20 μl After reaction the resulting
solution is poured into THF Then the product is purified by re-precipitation from THF
solution with a large excess of hexane and the obtained polymer was dried under vacuum at
room temperature The yield was checked by gravimetric determination and found to be about
75 The polymerization route is presented in the scheme below
75
Scheme 18
323 Synthesis of Poly (Methyl Methacrylate-co-Poly (13-dioxolane))
Same procedure has been used for the synthesis of Poly (Methyl Methacrylate-co-Poly (1 3-
dioxolane)) copolymers The yields of the reactions are in the range of 70ndash 90
Table 3 shows the amounts of comonomers initiator and solvent employed in the
copolymerization reactions
Table 3 Copolymerization of PDXL macromonomers (M1) with MMA (M2)
Sample M1 M2M1 PDXL (g) (mol)
MMA (g) (mol)
AIBN (g)
THF (ml)
Conc (moll)
2MP2 FPP2 20 374 187 10-4 3744 374 10-2 008 65 0604 3MP2 FPP2 30 2 10 10-4 300 300 10-2 005 50 0620 5MP2 FPP2 50 15 748 10-4 3744 374 10-2 005 60 0636
2MP15 FPP15 20 2 133 10-4 28 280 10-2 005 25 100 3MP15 FPP15 30 187 125 10-4 3744 374 0-2
006 60 0644 5MP15 FPP15 50 112 748 10-4 3744 374 10-2 005 60 0636
2MP1 FPP1 20 2 20 10-4 400 4 10-2
006 50 0840 3MP1 FPP1 50 125 125 10-4 3744 374 10-2 005 64 0604 5MP1 FPP1 80 075 748 10-4 3744 374 10-2 005 60 0636
33 Characterization Techniques
331 1H-NMR Spectroscopy
1H NMR Spectroscopy was used for compositional and structural analysis of the copolymers
1H-NMR spectra of the copolymers were recorded on the high field 400Mhz Advance Bruker
spectrometer All of the 1H NMR samples were dissolved in deuterated chloroform The
integrals of the peaks of copolymer components were used for the calculations to determine
76
the molecular weights polydispersity indices and the amount of each comonomer that was
incorporated into the copolymer
332 Size Exclusion Chromatography
Size Exclusion Chromatography (SEC) was used in the charaterization of the copolymers to
determine average molecular weights and polydispersity indices SEC Measurements were
performed at 40degC on a Waters 2690 instrument equipped with UV detector (Waters 996
PDA) coupled with a Differential Refractometer (ERC - 7515 A) and four Styragel columns
(106 105 500 and 50degA) THF is employed as the mobile phase with a flow rate of 10
mlmin Polystyrene standard samples were used for calibration
333 Diffraction Scanning Calorimetry
Diffraction Scanning Calorimetry (DSC) measurements are performed on a Modulated
Temperature Differential Scanning Calorimeter Q100 TA instrument under nitrogen at 50
mlmin The samples are hermetically sealed in aluminium pans and they are subjected to a
heating program as follows
For Poly (Styrene-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 120degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -80degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to130degC
For Poly (Methyl Methacrylate-co-Poly (13-dioxolane)) copolymers
- Ramp of 5degCmin to 130degC (Heat flow on conventional DSC)
- Ramp of 2degCmin to -95degC
- Then an isothermal for 5 min
- Modulate +- 060 degC every 60 seconds
- Ramp of 2degCmin to150degC
The thermograms obtained illustrate Glass Transition Temperatures (Tg) and Meltind Points
(Tm) of the copolymers
77
34 Results and Discussion
Methacryloyl-terminated PDXL macromonomers with the Mn range of 1000-2000 gmole
were copolymerized with vinyl and methacrylic monomers in order to obtain amphiphilic
graft copolymers with chemical structure of hydrophobic backbone and hydrophilic side
chains
341 Structural Characterization of the Copolymers
The structure of the copolymers was well defined by 1H-NMR analysis The copolymer 1H-
NMR spectra confirm the formation of copolymers see figures 7 8 and 9 The chemical
shifts of protons of polystyrene and PDXL can be clearly distinguished The following peaks
are assigned for OCHBB2BBO protons at 478 ppm and OCHBB2BBCHBB2BBO protons at 375 ppm (5H CBB6BB
HBB5BB) at 728 711 and 706 ppm as shown in Figure 8 The spectrum of PMMA-PDXL
copolymer is shown in Figure 9 where the chemical shifts of PMMA correspond to the proton
resonance as depicted in the figure the O-CH3 protons are observed at 361 ppm and clear
resonance assigned to the methyl group protons at 085-103 ppm and eventually we observe
the corresponding chemical shifts for OCHBB2BBCHBB2BBO protons (374 ppm) and OCHBB2BBO protons
(477 ppm) to confirm the incorporation of PDXL in the copolymer
Figure 7 1H-NMR spectrum of PDXL macromonomer CDCl3 (sample FPP1)
78
Figure 8 1H-NMR spectrum of Styrene-g-PDXL copolymer in CDCl3 (sample 3SP2)
79
Figure 9 1H-NMR spectrum of MMA-g-PDXL copolymer in CDCl3 (sample 2MP2)
342 Copolymer Molecular Weight and Composition
a) Conventional Free Radical Copolymerization
Copolymerization of PDXL macromonomers with MMA and ST in THF solution was studied
for different molar feed ratio of PDXL The amounts of monomeric units in the copolymers
were determined by elemental analysis The results are presented in Table 4 and 5 which
summarise the characteristics of the graft copolymers in terms of macromonomer feed ratio
(M2M1) and average Mn obtained from SEC as well as copolymer composition in weight and
mole percentages which is determined from 1H-NMR
80
Table 4 Characteristics of PDXL macromonomers (M1) copolymerized with Styrene (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2SP2 FPP2 20 49 476 4025 337 9200 162 2 3SP2 FPP2 30 39 322 303 221 8900 162 2 5SP2 FPP2 50 277 196 21 13 7200 159 1
2SP15 FPP15 20 418 476 34 34 9100 157 2 3SP15 FPP15 30 323 322 24 214 7000 161 2 5SP15 FPP15 50 224 196 152 12 6700 147 1
2SP1 FPP1 20 323 476 30 427 9200 178 3 5SP1 FPP1 50 16 196 1424 17 5800 158 1 8SP1 FPP1 80 107 123 85 095 11900 195 1
Table 5 Characteristics of PDXL macromonomers (M1) copolymerized with MMA (M2)
Sample
M1
M2M1
M1 in the feed
wt() mol()
M1 in the copolymer
wt() mol()
Mn SEC
Mw Mn
Ng
2MP2 FPP2 20 50 476 35 26 21900 198 4 3MP2 FPP2 30 40 322 21 13 25900 157 3 5MP2 FPP2 50 286 196 13 07 87200 455 6 2MP15 FPP15 20 416 45 28 25 19800 193 4 3MP15 FPP15 30 333 322 22 18 15200 277 3 5MP15 FPP15 50 23 196 13 10 24700 16 2 2MP1 FPP1 20 333 476 26 34 21100 319 6 3MP1 FPP1 30 333 322 19 22 17100 197 3 5MP1 FPP1 50 20 196 10 11 13900 354 2
81
b) Controlled Free Radical Copolymerization
Multifunctionalization of Polystyrene and Synthesis of poly (S-g-PDXL) copolymer give
results which are shown in Table 6 These data have been obtained from the 1H-NMR and
SEC analyses illustrated in figures 10 and 11 The resonance shifts assigned to all components
(PDXL PS and HEMA) are very clear This enables us to make calculations to determine
composition of each copolymer in addition to obtain the average number of grafts and the
number average-molecular weight of a graft
It is observed that the multifunctionalized-PS is composed of 20 in mole of HEMA which
results in 58 grafts (Ng = 58) per molecular chain
After copolymerization multifunctionalized-PS with DXL the copolymer PS-g-PDXL
(DXPS) possesses the following characteristics which are presented in Table 6 It has a
number average-molecular weight of 83000 gmol with 80 of PDXL content The number
average-molecular weight of one graft has been calculated and found to be 1000 gmol
Table 6 Characteristics of functionalized Styrene (HO-PS) and PS-g-PDXL (DXPS)
copolymer
Strusture Sample MnSEC IP PDXL
w mol
PS
w mol
HEMA
w mol
Ng Graft
Mn
HO-PS
32 700
12
_ _
77 80
23 20
58
_
DXPS
83 000
24
71 80
17 13
12 75
58
1000
82
Figure 10 1H-NMR spectrum of Multifunctionalized of Polystyrene in CDCl3
Figure 11 1H-NMR spectrum of poly (S-g-PDXL) copolymer (DXPS) in CDCl3
83
341 Determination of Monomer Reactivity Ratios
The application of the classical treatment based on linearization of the copolymerization
equation of Mayo and Lewis91 or the non-linear least-squares approach suggested by Tidwell
and Mortimer95 requires working with high macromonomer concentrations (ie feed
compositions higher than 20-30 of macromonomer)156
The MayondashLewis equation (58) that relates the instantaneous compositions of the monomer
mixture to the copolymer composition is approximated to a simplified form (equation (59))
suggested by Jaacks169 when working with a large excess of one of the comonomers This is
the case of copolymerisation reactions between a conventional comonomer and a
macromonomer of relatively high molecular weight where using low molar concentrations of
macromonomer is mandatory due to its restricted solubility and the extremely viscous media
][ ][ ]
[ ][ ]
[ ] [[ ] [ ]221
211
2
1
2
1
MrMMMr
MM
MdMd
++
=
(58)
[ ][ ] 1
22
1
2
MMr
MdMd
=
(59)
According to equation (59) the copolymer composition or the frequency of branches is
essentially determined by the monomer composition and the monomer reactivity ratio of the
comonomer r2 (inversely proportional to the macromonomer reactivity) under the limit
condition of [M2][M1] gtgt1 In order to obtain reliable values it is frequently necessary to
run the copolymerisation at different conversions or to carry out several copolymerizations
with different initial monomer ratios170 In such cases an integrated form of equation (59) is
used
[ ] [ ][ ][ ] 01
12
02
2 lnlnMM
rMM tt =
(60)
169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046
84
where [Mi]t[Mi]0 is the ratio among the composition of monomer i at time t and the initial
feed composition A plot of ln ([M2]t[M2]0) versus ln ([M1]t[M1]0) should result in a straight
line with a slope that equals to r2 (the reactivity ratio of the comonomer)
Thus the monomer reactivity ratios between the PDXL macromonomers and the comonomers
were estimated with the data in tables 4 and 5 We can apply equation (60) to the estimation
where M1 and M2 are the PDXL macromonomer and copolymer respectively The monomer
reactivity ratios are determined for macromonomers of different Mn (degree of
polymerization) and summarized in Table 7
Table 7 Monomer reactivity ratios for copolymerization of PDXL macromonomers (M1)
with St and MMA (M2)
Sample M2 M1
macromer Mnth
r2 1r2
SP2 St FPP2 2000 012 plusmn 0006 833
SP15 St FPP15 1500 0042 plusmn 6 10-4 238
SP1 St FPP1 1000 0015 plusmn 3 10-4 6666
MP2 MMA FPP2 2000 002 plusmn 001 50
MP15 MMA FPP15 1500 007 plusmn 0 02 1428
MP1 MMA FPP1 1000 0018 plusmn 001 5555
In the case of copolymerization with Styrene and MMA the results suggest that the reactivity
of the methacrylic double bond in the prepared macromonomers is not affected in their
copolymerization with Styrene or MMA This point is confirmed when analysing the inverse
ratio 1r2 = k21k22 which is sometimes considered as the relative copolymerization reactivity
of a macromonomer171 This quantity is the ratio between the crosspropagation and
homopropagation rate constants of comonomer (2) which is directly proportional to the
reactivity of the macromonomer (1) and gives a clear idea of the relative reactivity of a
growing radical ending in a 2 unit towards the addition of monomer (1) in comparison to the
171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620
85
tendency for the homopropagation So we have a situation where r1 gtgt 1 gtgt r2 and it is
expected that the initially formed chains should contain more macromonomers and then more
comonomer segments are added These are only assumptions but they give an indication
about the probable composition drift of the graft copolymers obtained On the other hand in
the case of copolymerization of poly (13dioxolane) macromonomers with styrene (Figure
12) the results show that r2 increases with increasing PDXL side chain length (in terms of
average Mn) and this leads to say that the side macromonomer chain length affect the
reactivity of the comonomer Thus this indicates that a growing radical of macromonomer
with a shorter chain length (ie lower Mn ) attacks more frequently a monomer of the same
nature than it does a macromonomer with a longer length (ie higher Mn) as it can be noticed
from the results in Table 7
However the r2 values of the copolymerization with MMA as shown in Figure 13 give
unclear dependence on the side poly (13dioxolane) macromonomer chain length this may be
due to the resulting polydispersity of the copolymerization Mentioned behaviour may be
related with the reactive structure of comonomers vinyl in the case of Styrene or methacrylic
in the case of MMA in regard to the ending methacrylic double bond of macromonomers
besides the hydrophilic character of the macromonomers
86
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0015 plusmn 3 10-4 SP1
b
r2 = 0042 plusmn 6 10-4
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP15
c
r2= 012 plusmn 0006
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
SP2
Figure 12 Application of Jaacksrsquo treatment to the St-g-PDXL copolymerization systems
(a) SP1 (b) SP15 (c) SP2
87
a
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 0018 plusmn 001 MP1
b
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 007 plusmn 002MP15
036788
c
ln[M
2] t[M
2] 0
ln[M1]tln[M1]0
r2 = 002 plusmn 001 MP2
Figure 13 Application of Jaacksrsquo treatment to the MMA-PDXL copolymerization systems
(a) MP1 (b) MP15 (c) MP2
88
341 Glass Transition Temperatures
Thermal analysis of Styrene-g-PDXL copolymers allows to determine their glass transition
and melting temperatures In the first place the measurements were performed on a
conventional DSC from which the thermograms obtained show an overlapping of PS glass
temperature and PDXL melting point signals This has been observed for all samples A
different approach in the characterisation of these copolymers was by means of Modulated
Temperature Differential Scanning Calorimeter (MTDSC) which is an extension of
conventional DSC This approach combines high resolution with high sensitivity by use of a
sinusoidal temperature modulation superimposed on a constant temperature or linear
temperature program with a small underlying average heating rate172 173 In comparison to
conventional DSC the MTDSC analysis enables the simultaneous calculations of an
additional quantity the cyclic or modulus of heat capacity Cp (J g-1K-1 172)
ωT
HFp A
AC =
(61)
is the amplitude of the cyclic heat flow (Wg-1) and AWhere AHF Tω is the amplitude of cyclic
heating rate with AT the temperature modulation amplitude (K) ω the modulation angular
frequency (2πp) and p is the modulation period (s)172
In fact the MTDSC splits the overlapped signals into two distinct temperatures melting
temperature of the hydrophilic grafts and glass transition temperature of the hydrophobic
backbone as can be noticed in Figure 14 in which melting temperature appears to be 5626degC
which is closer to the glass transition temperature with a value of 5671degC From the results
obtained out of the thermogram it is clear that the measurements show very close values of
Tm and Tg for all copolymer samples where in conventional DSC these two temperatures
cannot be distinguished
172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
89
Figure 14 MTDSC thermogram of 5SP1 copolymer at heating rate of 2degCmin
Tg was taken at the midpoint of the transition region The results obtained are shown in
Tables 8 and 9 for copolymers with Styrene and MMA respectively Then a plot of the
copolymers Tg has been constructed against PDXL content in order to determine the effect of
the latter on Tgrsquos As it can be noticed in the Figure 15 Tg of the copolymers decreases
exponentially with increasing PDXL content and this may be due to the decrease in the
intermolecular interactions between the molecular chains and can be associated with higher
mobility and flexibility of the polymeric chains when PDXL is incorporated in the
copolymers The results clearly indicate that Tg values of the copolymers depend on the
composition of comonomers and a decrease with increasing PDXL content in the obtained
copolymers
90
Table 8Transition temperatures of Styrene-g-PDXL copolymers obtained by thermal
analysis (DSC) Sample PDXL content Tg wt () (degC) 8SP 85 7489 1
5SP 1424 5671 1
5SP 152 5590 15
21 6739 5SP 2
303 4480 3SP 2
34 2665 2SP15
4025 2SP 4060 2
Table 9Transition temperatures of MMA-g-PDXL copolymers obtained by thermal analysis
(DSC)
Sample PDXL content Tg
wt () (degC)
5MP 10 10545 1
5MP 13 8278 15
21 6576 3MP 2
22 7550 3MP 15
26 7013 2MP1
91
5 10 15 20 25 30 35 40 4520
30
40
50
60
70
80
a
SP COPOLYMERSTg
(degC)
PDXL content in wt()
10 15 20 2560
70
80
90
100
110
b
Tg (deg
C)
PDXL content in wt()
MP COPOLYMERS
Figure 15 Glass transition temperatures vs PDXL macromonomer content for copolymer
systems (a) Styrene-g-PDXL copolymers (b) MMA-g-PDXL copolymers
92
Conclusion
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers The macromonomer reactivity estimation suggests that the
length of the PDXL side chains does affect the reactivity of the methacrylic double bond of
the macromonomer when copolymerized with St However in the case of copolymerization
with MMA there is no dependence on the graft size Finally from DSC measurements the
values of Tg depend on the composition and the size of the PDXL grafts In all copolymers
the increase in amount of the incorporated PDXL macromonomer results in a substantial
decease in glass transition
93
References 152 Fernandez-Garcia M Luis de la Fuente J Cerrada ML and Madruga EL Polymer 43 (2002) 3173-3179 153 Hou SS and Kuo PL Polymer 42 (2001) 2387-2394 154 Roos SG Muller Axel H E and K Matyjaszewski Macromolecules 32 (1999) 8331-8335 155 Meijs F and Rizzardo E JMacromol Sci Rev Macromol ChemPhys 33 (C30) (1990) 305 156 Eguiburu J L Fernandez-Berridi MJ and San Roman J Polymer 37 (16) (1996) 3615-3622 157 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 158 Adriaensens P Storme L Carleer R Gelan J and Du Prez F E Macromolecules 35 (2002) 3965-3970 159 Naraghi K Sahli N Belbachir M Franta E and Lutz PJ Polym Inter 51 (2002) 912-922 160 Reguieg F Sahli N Belbachir M and Lutz P J Journal of Applied Polymer Science 99 (2006) 3147-3152 161 Lutz Pierre J Polymer Bulletin (2006) 162 Reibel LC Durand CP and Franta E Can J ChemRev Can Chim 63 (1985) 264-269 163 Bernaerts KV Du Prez FE Prog Polym Sci 31 (2006) 671 164 Bruno Grassi Geacuterald Clisson Abdel Khoukh Laurent Billon European Polymer Journal 44 (2008) 50ndash58 165 Jerome Vinas Nelly Chagneux Didier Gigmes Thomas Trimaille Arnaud Favier and Denis Bertin Polymer
49 (2008) 3639-3647 166 Gigmes D Bertin D Guerret O Marque SRA Tordo P Chauvin F et al PCT WO 014926 13 February
2004 167 Chauvin F Dufils PE Gigmes D Guillaneuf Y Marque SRA and Tordo P Macromolecules 39 (2006)
5238 168 Dufils PE Chagneux N Gigmes D Trimaille T Marque SRA and Bertin D Polymer 48 (2007) 5219 169 Jaacks V Makromol Chem 161 (1972) 161ndash72 170 Larraz E Elvira C Gallardo A and San Romaacuten J Polymer 46 (2005) 2040ndash2046 171 Ito K Progr Polym Sci 23 (4) (1998) 581ndash620 172 Dreezen G Groeninckx G Swier S and Van Mele B Polymer 42 (2001) 1449-1459 173 Reading M Elliot D and Hill VL J Thermal Anal 40 (1993) 949-955
94
CHAPTER IV Compatibilization Effect of Poly (Styrene-g-Poly
(1 3 Dioxolane)) on Immiscible Polymer Blends
of Polystyrene and Poly (Ethylene Glycol)
41 Background
411 Physical Blends
Physical blending is defined as the simple mechanical mixing of two or more polymers either
in the melt or in solution174 At first glance this approach would seem to be ideal for
preparing hybrids as blending is considered a simple and economical procedure that is
commonly used to produce new products from existing materials175 However in polymer
science the effectiveness of blending is dependent upon the degree of compatibility of the
polymers involved176 At least three general types of materials can result from blending
depending on the mutual solubility and semi-crystallinity of the constituents
412 Equilibrium Phase Behavior
Mixing of two amorphous polymers can produce either a homogeneous mixture at the
molecular level or a heterogeneous phase-separated blend Demixing of polymer chains
produces two totally separated phases and hence leads to macrophase separation in polymer
blends Some specific types of organized structures may be formed in block copolymers due
to microphase separation of block chains within one block copolymer molecule
Two terms for blends are commonly used in literature miscible blend and compatible blend
The terminology recommended by Utracki177 will be used By the miscible polymer blend it
means a blend of two or more amorphous polymers homogeneous down to the molecular
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York (1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York (1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser Publishers Munich (1989)
95
level and fulfilling the thermodynamic conditions for a miscible multicomponent system An
immiscible polymer blend is the blend that does not comply with the thermodynamic
conditions of phase stability The term compatible polymer blend indicates a commercially
attractive polymer mixture that is visibly homogeneous frequently with improved physical
properties compared with the constituent polymers
Miscible blends occur spontaneously when the overall energy of mixing (ΔGmix) is negative
as defined by the Gibbs-Helmholtz free energy equation (Equation 62)
(62)
In the Gibbs-Helmholtz equation ΔHmix is the enthalpy of mixing and ΔSmix is the entropy of
mixing while T is the temperature of the blend Flory-Huggins178 and Scott179 have made
further correlation of enthalpy and entropy as a function of the polymer components and their
properties (Equation 63)
(63)
In Equation 63 χ is a measure of the polymer-polymer interaction energy V is the volume of
the system Φi is the volume fraction of polymer i R is the gas constant T is the temperature
of blending Vr is the reference volume of the monomers and χi is the degree of
polymerization
Examination of Equation 63 reveals that the entropy of mixing is highly dependent on the
molecular weight of the blended polymers while the enthalpy is much more dependent on the
level of interaction between the polymer types Additionally Scott showed that as molecular
weight increases to the level commonly found in commercially useful materials ΔS
approached zero (0) Therefore polymer blends of commercial importance are primarily
influenced by the rate of enthalpy However for polymers with weak interactions (as χ
approaches 1) eg as observed in most polymer pairs the enthalpy of mixing can be further
reduced according to Equation 64
178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279
96
(64)
In Equation 64 δi is the polymerrsquos solubility parameter (an estimation of its ability to be
dissolved in a range of solvents) derived from the square root of the cohesive energy density
pioneered by Hildebrand180 Thus most early work with polymer blends concentrated on
matching the solubility parameters of the component polymers
Unfortunately the theoretical maximum difference in solubility for a 5050 polymer blend is
only 01 (calcm3)12 This narrow margin is much smaller than the standard error among
methods used to determine solubility parameters181 The ability to predict miscibility of
polymer pairs with strong interactions such as donor-acceptor and hydrogen bonding which
can increase miscibility by creating an exothermic reaction upon mixing (ΔH lt0) have been
attempted for many years with varying degrees of success
The formation of miscible blends is dependent on several factors including molecular
structure average chain length tacticity of the polymers as well as the temperature of mixing
and the blending method If the blended polymers are miscible (ΔGmix lt 0) and thus
compatible the resulting material will display an amalgamation of properties which are
predictable using the same techniques as those used for random or statistical copolymers
Polymer blends account for a significant percentage of polymer production and are produced
either to reduce costs to aid in processing or to improve a variety of specific properties For
example polycarbonates have been blended with polybutylene terephthalates to increase
chemical resistance and to aid in processing while polyphenylene oxides are bended with
polystyrenes to improve toughness and increase glass transition temperatures182
413 Compatibilization
As it follows from thermodynamics the blends of immiscible polymers obtained by simple
mixing show a strong separation tendency leading to a coarse structure and low interfacial
180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999)
97
adhesion The final material then shows poor mechanical properties On the other hand the
immiscibility or limited miscibility of polymers enables formation of wide range structures
some of which if stabilized can impart excellent end-use properties to the final material To
obtain such a stabilized structure it is necessary to ensure proper phase dispersion by
decreasing interfacial tension to suppress phase separation and improve adhesion This can be
achieved by modification of the interface by the formation of bonds (physical or chemical)
between the polymers This procedure is known as compatibilization and the active
component creating the bonding as the compatibilizer174 177 183
The most popular method of compatibilization is by addition of a third component In most
cases such an additive is either a block or graft copolymer Since the key requirement is
miscibility it is not necessary for the copolymer to have identical chain segments as those of
the main polymers It suffices that the copolymer has segments having specific interactions
with the main polymeric components viz hydrogen bonding dipole-dipole dipole-ionic
Lewis acid-base etc
Addition of a block or graft copolymer reduces the interfacial tension and alters the molecular
structure at the interface Thus compatibilization by addition changes not only the interfacial
properties but it may affect the flow behavior (hence processability)
One of the disadvantages of the addition method is the tendency of the added copolymers to
form micelles These reduce the efficiency of the compatibilizer increase the blend viscosity
and may lessen the mechanical performance
414 Incorporation of Copolymers for Compatibilization
Block or graft copolymers with segments that are miscible with their respective polymer
components show a tendency to be localized at the interface between immiscible blend
phases Random copolymers sometimes also used as compatibilizers reduce interfacial
tension but their ability to stabilize the phase structure is limited184 Finer morphology and
higher adhesion of the blend lead to improved mechanical properties The morphology of the
resulting two-phase (multiphase) material and consequently its properties depend on a
number of factors such as copolymer architecture (type and molecular parameters of
segments) blend composition blending conditions
183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001)
98
In Scheme19 the conformation of different block graft or random copolymers at the
interface is schematically drawn
Scheme 19 Possible localization of A-B copolymer at the AB interface Schematic of
connecting chains at an interface a-diblock copolymers b-end-grafted chains c-triblock
copolymersdmultiply grafted chain and e-random copolymer
415 The Effect of Compatibilizer on a Blend
The presence of a compatibilizer at the interface substantially affects the development of the
phase structure of molten blends in the flow and quiescent state The position and width of the
concentration region related to co-continuous morphology are affected by two competing
mechanisms A decrease in interfacial tension caused by a compatibilizer favors the formation
and stability of co-continuous structures
The effect of a compatibilizer on fineness of the phase structure can be understood through its
effects on droplet breakup and coalescence A decrease in interfacial tension due to the
presence of a compatibilizer decreases the droplet radius R
Effect of the Compatibilizer Architecture
Compatibilization efficiency of various copolymers follows from their thermodynamic and
microrheological effects It has been generally accepted that the total molecular weight of the
copolymer molecular weight of its blocks and their number are the main structural
compatibilizer characteristics affecting the phase structure of the final blend
99
Effect of Compatibilizer Concentration
The compatibilizing efficiency of the copolymers is besides the architecture a function of
their concentration The effect of a compatibilizer concentration has been quantitatively
characterized by the emulsification curvemdashthe dependence of the average particle diameter of
the minor dispersed phase on copolymer concentration185 The particle diameter decreases
with increase of copolymer concentration until a constant value is obtained For most systems
this value is achieved if the copolymer amount is 15ndash25 of the dispersed phase
416 Methods of Blend Preparation
Five different methods are used for the preparation of polymer blends186 187 melt mixing
solution blending latex mixing partial block or graft copolymerization and preparation of
interpenetrating polymer networks It should be mentioned that due to high viscosity of
polymer melts one of these methods is required for size reduction of the components (to the
order of μm) even for miscible blends
bull Melt mixing is the most widespread method of polymer blend preparation in practice
The blend components are mixed in the molten state in extruders or batch mixers Advantages
of the method are well-defined components and universality of mixing devicesmdashthe same
extruders or batch mixers can be used for a wide range of polymer blends Disadvantages of
the method are high energy consumption and possible unfavorable chemical changes of blend
components This procedure has not been used so far in industrial practice because of large
energy consumption
bull Solution blending is frequently used for preparation of polymer blends on a laboratory
scale The blend components are dissolved in a common solvent and intensively stirred The
blend is separated by precipitation or evaporation of the solvent The phase structure formed
in the process is a function of blend composition interaction parameters of the blend
components type of the solvent and history of its separation Advantages of the process are
rapid mixing of the system without large energy consumption and the potential to avoid
185 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons Inc New York Chap 16 (2000) 186 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709 187 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458
100
unfavorable chemical reactions On the other hand the method is limited by the necessity to
find a common solvent for the blend components and in particular to remove huge amounts
of organic (frequently toxic) solvent Therefore in industry the method is used only for
preparation of thin membranes surface layers and paints
bull A blend with heterogeneities on the order of 10 μm can be prepared by mixing of
latexes without using organic solvents or large energy consumption Significant energy is
needed only for removing water and eventually achievement of finer dispersion by melt
mixing The whole energetic balance of the process is usually better than that for melt mixing
The necessity to have all components in latex form limits the use of the process Because this
is not the case for most synthetic polymers the application of the process in industrial practice
is limited
bull In partial block or graft copolymerization homopolymers are the primary product
But an amount of a copolymer sufficient for achieving good adhesion between immiscible
phases is formed188 In most cases materials with better properties are prepared by this
procedure than those formed by pure melt mixing of the corresponding homopolymers The
disadvantage of this process is the complicated and expensive start-up of the production in
comparison with other methods eg melt mixing
bull Another procedure for synthesis of polymer blends is by formation of interpenetrating
polymer networks A network of one polymer is swollen with the other monomer or
prepolymer after that the monomer or prepolymer is crosslinked189 In contrast to the
preceding methods used for thermoplastics and uncrosslinked elastomers blends of
reactoplastics are prepared by this method
188 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 189 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981)
101
42 Experimental
421 Materials
Polymers used in this research were PEG and PS PEG was purchased from MERCK
company General Purpose PS was obtained from ENPC TP1-Chlef Company Physical and
Structural characterizations of these materials were performed by SEC 1H-NMR and DSC
422 Blend Preparation
PSPEG blends of 5050 wt were prepared by solution casting from THF 40degC The
polymer solutions were stirred until complete miscibility and then cast onto glass dishes and
left to evaporate the solvent to the atmosphere To remove residual solvent after casting the
blends were dried in vacuum oven at 40degC for a weak Table 10 shows the quantities of the
copolymers used for compatibilization of the blends of PSPEG
Table 10 The quantities of the copolymers used for compatibilization of the blends of
PSPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
43 Characterization Techniques for Compatibilization
431 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
102
Relative viscosities of polymer solutions were calculated by dividing the flow times of
solutions by that of the pure solvent The data were plotted using the Huggins equation with
the intrinsic viscosity [η] (dlg-1) determined by extrapolation to infinite dilution
432 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
433 FTIR Analysis
FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
44 Results and Discussion Polyethylene glycol (PEG) is very interesting and important polymers PEG presents good
properties eg hydrophilicity solubility in water and in organic solvents nontoxicity and
absence of antigenicity and immunogenicity190It has attracted increasing attention due to its
potential applications as biomedical and environment friendly materials PEG has been
widely used as a modifier for biomedical surfaces to reduce the protein absorption and
improve their biocompatibility192 and as a stabilizer for emulsion and dispersion It has also
been used as a plasticizer for poly (lactide) (PLA) which is stiff and brittle as a
biodegradable packaging material193
On the other hand polystyrene shows excellent processability good appearance tensile
strength and thermal and electrical characteristics however its brittleness considerably limits
its use in high performance products
Both PS and PEG are widely used commodity polymers Detailed studies on their miscibility
may contribute to technological and environmental applications These polymers form an
interesting pair to study since they exhibit contrasting physical properties PS is a
190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689
103
hydrophobic polymer whereas PEG is hydrophilic PEG is a much softer material than PS
PSPEO blends have been reported as incompatible materials in the literature194 195
N Watanabe et al have reported compatibilization effect of poly (styrene-co-methacrylic
acid) on immiscible blends of this system196
441 Characterization of the Blend Components
Analysis by SEC provides number average-molecular weights and polydispersity indices of
all materials DSC measurements performed to determine their glass transition temperatures
as well as melting point and degree of crystallinity of PEG (See Figure16) 1HNMR spectroscopy analysis was performed on these polymers to determine essentially the
tacticity of PS and also to get information about end groups of PEG which was found to
possess an OH group at each end It has been also determined that the stereoregularity of PS
is Syndiotactic-Atactic (rather highly syndiotactic) (See Figures 17)
Physical characteristics of materials used are given in Table11
Table 11 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PS ENPC TP1-Chlef (from CHI MEI Corp)
105
128 000
1076
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam] Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842
104
Figure 16 1H-NMR spectrum of PEG (Merck) in CDCl3
105
Figure 17 1H-NMR spectrum of Commercial Styrene (ENPC TP1-Chlef) in CDCl3
442 Study of Compatibilization by Dilute Solution Viscometry
a) Introduction
Polymer blends are physical mixtures of structurally different polymers which interact
through secondary forces with no covalent bonding Blending of the polymers may result in a
reduction in the basic cost and improved processing and also may enable properties of
importance to be maximized The polymer blends often exhibit properties that are superior
compared to the properties of each individual component polymer197 198 199 200 The main
advantages of the blend systems are simplicity of preparation and ease of control of physical
properties by compositional change201 202 However the mechanical thermal rheological and
197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85
106
other properties of a polymer blend depend strongly on its state of miscibility on the
molecular scale203
There have been numerous techniques of studying the miscibility of the polymeric blend The
most useful techniques are dynamic mechanical thermal electron-microscopic IR
spectroscopic refractive index203 optical microsscopic204 and viscometric techniques 179 205
Because of its simplicity viscometry is an attractive and very useful method for studying the
compatibility of polymer blends Additional advantages ie that no sophisticated equipment
is necessary and that the crystallinity or the morphological states of the polymer blends do
affect the result206 make the viscometric method more convincing for characterizing polymer
mixtures The principle of using a dilute solution viscosimetry to measure the miscibility is
based on the fact that while in solution molecules of both component polymers may exist in
a molecularly dispersed state and undergo a mutual attraction or repulsion which will
influence the viscosity It is assumed that polymerndashpolymer interaction usually dominate over
polymerndashsolvent ones207 The presence of interactions between atoms or groups of atoms of
unlike polymers is essential to obtain a miscible polymer blend177 179
Estimation of the compatibility of different pairs of polymers based on dilute solution
viscosity for a ternary polymerpolymer-solvent system has been attempted by several
authors including Mikhailov and Zeilkman208 Bohmer and Florian209 Feldman and Rusu210
Krigbaum and Wall211 and Catsiff and Hewett212
The compatibilization of the blends in question has been characterized by viscosity technique
using the Krigbaum and Wall interaction parameter Δb The versatility of the viscometric
technique is not affected by the choice of the solvent as was shown by Kulshreshta et al213
In this section we discuss in details our investigation on the compatibilization of the two
polymer blend systems PSPEG and PMMAPEG 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191
107
b) Theoretical background
The main aspects of the application of dilute solution viscometry method for the study of
interactions and miscibility phenomena in dilute multicomponent polymer solutions were
described Only the most important features will be repeated here It is common to use
empirical relations such as Hugginsrsquo equation214
(65)
for the description of the concentration dependence of viscosity of polymer solutions This
relation is strictly valid only for binary polymer solutions However equations like that of
Krigbaum and Wall211
(66)
And of Catsiff and Hewett212
(67)
were proposed for ideal ternary polymer solutions of the polymer 1+ polymer 2+ solvent type
In previous relations ηsp denotes the specific viscosity [η] is the intrinsic viscosity (limiting
viscosity number) c stands for the mass concentration of polymer and kH is Hugginsrsquo
constant which may be related (in an empirical manner) to the thermodynamic quality of
solvent Relative mass fractions of dissolved polymers wi are used to describe the
composition dependence of viscosity in ternary systems Quantities b 12 and b12 are used to
define the ideal behavior of ternary polymer solutions These are calculated by
(68)
and
(69)
214 ML Huggins J Am Chem Soc 64 (1942) 116
108
respectively Here b denotes the slope of Hugginsrsquo equation for binary solutions
(70)
Moreover it has been shown215 that both the sign and the extent of the deviation of
experimental from theoretical b-values may be correlated to the interactions between
polymeric components of a system under consideration The quantities of interest (miscibility
criterion variables) are defined by
(71)
and
(72)
or can be written in another form
(73)
where m denotes the polymer mixtures Δb intermolecular interaction parameter between
polymer 1and 2 and is considered a good criterion to predict the polymer-polymer
compatibility209 216 217 Δb 0 indicates that the two polymers are compatible whereas
Δb0 indicates that they are incompatible
c) Discussion of the Results
Herein we discuss in detail the compatibilization of PSPEG blends with the synthesized graft
copolymers by viscometric technique The plot of reduced specific viscosity of polymers
versus total polymeric concentration yields a straight line and the intercept and slope
correspond to intrinsic viscosity [η] and molecular interaction coefficient b respectively The
viscosity data for the homopolymers and their blends are presented in Tables 12 and 13
Table 12 Interaction coefficient for binary solutions (polymersolvent) 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin (1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849
109
Polymer components PEG PS
b11 007327 minus
b22 minus 02117
b12 = (b11 b22)12 = 01245 (theo)
Table 13 Interactions parameters for PSPEG blends with poly (St-g-PDXL) copolymers
(2SP2 2SP1 and DXSP) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
DXSP b12 003511 01295 01680 01833 01947
Δb - 00894 00050 00435 00588 00702
2SP2 b12 003511 009826 01052 01314 01515
Δb - 00894 - 00262 - 00193 00069 00270
2SP1 b12 003511 minus minus minus 01262
Δb - 00894 minus minus minus 00017
For incompatible blends the incompatible molecules refuse to overlap thus they shrink in
size which leads to a decrease in hydrodynamic volumes As a matter of fact the crossover in
the reduced viscosity-concentration plot is observed
As far as we are concerned with the blend of PSPEG the results obtained present similar
situation Figure 18 shows the Huggins plots for the homopolymers and the (5050) blend of
PSPEG In this figure a crossover is observed and a decrease of slope occurs at about 05
gdl in the viscosity-concentration plot Above this concentration two incompatible polymers
PS and PEG undergo mutual repulsion in dilute solution the hydrodynamic volume of chains
is lower The reduction of the hydrodynamic volume will result in a decrease of the reduced
viscosity of solution correspondingly the slope of the plot suddenly declines
110
02 03 04 05 06 07 08 09 10 11
03
04
05
06
07
08PS PEG and PSPEG (5050)
PS PSPEG 0 PEG
Redu
ced
visc
osity
η sp
c
(ldl
)
C (dll)
Figure 18 Plots of reduced viscosity (ηspc) vs concentration for PS PEG and PSPEG
blend (0) in THF at 30degC
Figures 19 20 21 and 22 show the incorporation of various amounts of copolymers in the
immiscible blend As far as the amount of the compatibilizers increases the crossover of the
plots occurs at very low concentration or even it is not observed In addition the slope of the
plot increases with an increase of the amount of the compatibilizers introduced in the blend
This is due to the mutual attraction of the blend components which is enhanced by the
presence of the copolymers As a matter of fact the latter act as compatibilizing agents
allowing to the blends to exhibit miscibility
111
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07BLENDS WITH DXPS
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 19 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of DXPS copolymer
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLENDS WITH 2SP2
PSPEG 0 10 20 30 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 20 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with various amounts of 2SP2 copolymer
112
02 03 04 05 06 07 08 09 10 1101
02
03
04
05
06
07
08BLEND WITH 2SP1 40
PSPEG 0 2SP1 40 Re
duce
d vi
scos
ity η sp
c (
dlg-1
)
C (gdl)
Figure 21 Plots of reduced viscosity (ηspc) vs concentration for PSPEG blends in THF at
30degC with 40 of the dispersed phase of 2SP1 copolymer
02 03 04 05 06 07 08 09 10 1100
01
02
03
04
05
06
07
08
DXPS 40 2SP2 40
2SP1 40
2SP1 40 2SP2 40 DXPS 40 Re
duce
d vi
scos
ity η
spc
(dl
g-1)
C (gdl)
Figure 22 comparison of plots of reduced viscosity (ηspc) vs concentration for PSPEG
blends in THF at 30degC with 40 of the dispersed phase of DXPS 2SPS2 and 2SP1
copolymer
113
Figure 22 compares the three copolymers used for compatibilization of PSPEG with respect
to 40 by weight of the dispersed phase addition to the blends
Krigbaum and Wall suggested that information about the interaction between two polymers
should be obtained from the difference of experimental b12 and theoretical b12 Δb A positive
difference between the experimental and theoretical interaction coefficients is evidence of a
compatible polymer pair The higher the value of Δb the higher the extent of compatibility
Negative values refer to repulsive interaction and incompatible mixes The values of Δb
according to equation 73 for different blends with compatibilizers are given in Table 13 and
Figure 23
0 10 20 30 40 5
-010
-005
000
005
010
0
PS PEG BLENDS
2SP2 DXPS
Δb
Amount of incorporated copolymer w ()
Figure 23 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (DXPS and 2SP2) used for compatibilization
It was observed as the amount of compatibilizers increases values of the interaction
parameter increase thereby increasing the compatibility between the two polymer
components of the blend Consequently this indicates that these copolymers act as
compatibilizing agents in the immiscible blends of PS and PEG Now in comparing these
copolymers in terms of structure (number of grafts) and PDXL content it can be noticed that
the results obtained DXPS ( 71 w of PDXL) copolymer show higher values of Δb than
2SP1(30 w of PDXL) and 2SPS2 (4025 w of PDXL) do This is due to the comb-
structure of the DXPS copolymer (synthesized by CRP) and therefore containing more grafts
114
(Ng = 58) than the other copolymers Besides the amount of PDXL in the copolymer PDXL
includes polar groups which provide associative interactions with one of the blend
components (PEG) and thus undergoes significant effects upon compatibilization In the
figure below it can be seen that addition of 10 by weight of the dispersed phase (47 of
total weight of the blend) of DXPS is sufficient to compatibilize the immiscible blend of
PSPEG (5050) Then a drastic increase of the interaction parameter with the addition of the
compatibilizer (DXPS) compared to the addition of either 2SP2 or 2SP1 (Table 13)
From the results shown in the graph miscibility of the blend can be achieved by incorporating
around 25 (11 of total weight of the blend) of 2SP2 copolymer However compatibibility
of the blend with 2SP1 copolymer is obtained at 40 by weight of the dispersed phase since
its interaction parameter (Δb) found to be 00017
It is worth to mention that the PDXL content of 2SP1 is 30 and the length of the grafts is
half that of 2SP2 copolymer For this reason these two copolymers have been chosen for the
purpose of comparison in terms of side chains length
An optimization of the amount of copolymer needed for compatibilization of PSPEG (5050)
blend has been made (corresponding to Δb = 0) as function of the PDXL content and shown
in Table 14
Table 14 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050) vs PDXL content
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
DXPS 0 9 43 71
2SP2 0 245 109 4025
2SP1 0 40 166 30
115
443 Optical Microscopy and Phase Morphology
PDXL is a perfect alternate copolymer of poly (ethylene oxide) (PEO) and poly (methylene
oxide) (PMO) that has the same curious combination properties as PEG So PDXL must be
at least miscible with PEG or adhere at the interface between PS and PEG and between
PMMA and PEG The compatibility between hydrophobic PS or PMMA and hydrophilic
PEG is very poor Compatibilization between components of the two sets of polymer blends is
studied by optical microscopy
The morphological characteristics of the blends by different compatibilizers are presented in
Figure 24 The optical microscopy micrographs of PSPEG blends without compatibilizers
show a poor dispersion for PS disperse phase and a ldquoball-and-socketrdquo topography due to the
poor interfacial adhesion between PEG matrix and the dispersed phase However with the
addition of compatibilizers the morphological characteristics of the polymer blends are
greatly altered It can be noticed that for these two different blends the particle size of PS
domains gets progressively much smaller and uniform in compatibilized blends than in
incompatibilized ones This may be explained by the significant increase of the phase
interfacial adhesion Consequently the domain size strongly depends upon the
compatibilizers used
116
a) PSPEG (5050) 0 (without compatibilizer)
DXPS 10 DXPS 20 DXPS 30 DXPS 40 b) Compatibilizing effect of DXPS copolymer
2SP2 10 2SP2 20 2SP2 30 2SP2 40 c) Compatibilizing effect of 2SP2 copolymer
2SP1 40
117
d) Compatibilizing effect of 2SP1copolymer at 40 addition
Figure 24 Optical micrographs showing phase structure in 5050 PSPEG blends
a) blends without compatibilizer b) with DXPS c) with 2SP2 d) with 40 of 2SP1
For instance the PSPEG blends with the incorporation of the copolymers DXPS 2SP2 and
2SP1 as compatibilizers (Figure 24) the morphology displays a very fine dispersion of PS
phase and strong interfacial adhesion with PEG Matrix The good compatibilizing effect
mainly that of DXPS can be explained by two mechanisms
First the PDXL units in the compatibilizer interact with PEG ether groups leading to a good
adhesion at interface between the components of the blend In addition hydrogen bonding
may also exist between PDXL and PEG further increasing compatibilization Second since
the compatibilizer also contains styrene blocks it contributes to provide a good compatibility
with PS Consequently the remarkable compatibilizing effect of PS-g-PDXL copolymers
induced a drastic decrease in interfacial tension and suppression of coalescence between the
originally immiscible polymer phases
As it can be noticed from the micrographs given in the figure above the compatibilizer
exhibits finer dispersion and homogeneous morphology of the blends as the amount of
compatibilizers increases
Eventually each compatibilizer has its own effect on the immiscible blends depending on the
amount of PDXL (side chains) and number of grafts present in the copolymers
By comparing micrographs shown in Figure 24 b and c the compatibilization effect of DXPS
copolymer which contains more grafts but shorter is different from that of the 2SP2
copolymer In the case of DXPS it is observed that the size of the dispersed droplets is
deceased significantly and results in finer dispersion morphology However 2SP2 copolymers
shows an improvement in compatibility of the blend after addition up to 30 wt of the
dispersed phase (13 total weight of the blend) exhibits homogeneous morphology This
may be related to length of the grafts In all cases these copolymers act as good
compatibilizers for the blend of 5050 wt PSPEG
444 FTIR Analysis
The FTIR technique is very important since it allows one to study the specific interactions
between the polymers The knowledge of the polymerndashpolymer interactions will be useful for
118
studies of the compatibility in polymer blends To verify the intermolecular interactions that
can play a role in miscibility the vibrational spectra of the blends studied in the present work
were obtained In polymeric systems where there are multiple interactions vibrational bands
such as ν (C=O) ν (COC) and ν (OH) present contributions of spectroscopic free and
associated forms
In order to elucidate the role played by intermolecular interactions in the miscibility of these
blends FTIR absorption of individual polymer components PS PEG and PMMA and
compared to that of the mixtures Figures 26 27 and 28 present the FTIR absorption spectra
from 4000 to 400 cm-1 for all samples
In the case of PS the high-frequency infrared spectra consist of seven absorption bands The
bands with peak locations at 3008 3026 3060 3082 and 3103 cm-1 are due to C-H stretching
of benzene ring CH groups on the PS side-chain The bands with peak positions of 2924 and
2850 cm-1 are due to the C-H stretching vibration of the CH2 and CH groups of the main PS
chain respectively PEG with molecule chemical structure of HO-[CH2-CH2-O]n-H exhibits
important absorption bands from FTIR spectroscopy measurements as shown in Figure 25 It
was verified contributions associated with CndashOndashC symmetric stretching of ether groups218-220
221 from 1050 to 1150 cm-1 with maximum peak at 1150 cm-1 Characteristics CH2-O
stretching modes from 2800-3000 cm-1 are observed214 At low frequency region peaks at 850
and 890 cm-1 are assigned to CndashOndashC stretching and at 500 cm-1 ascribed to CndashOndashC
deformation The presence of PDXL in the blends is detected by the intense frequency at 1140
cm-1 which is assigned for acetal groups In addition both PDXL and PEG contain ether
groups and the spectra show that the corresponding peaks are overlapped for the blends The
intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of PEG
crystallinity in the blends222
218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10 219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601
119
It can be observed also a typical large hydroxyl bands with two distinct contributions which
can be seen for all samples They are attributed to the spectroscopically free and bonded ndashOH
stretching forms at 3600-3800 cm-1 and 3200-3500 cm-1 respectively221 - 227
500 1000 1500 2000 2500 3000 3500 4000-05
00
05
10
15
20
25
30
35
PS and PEG PEG PS
Abs
orba
nce
Wave number (cm-1)
Figure 25 FTIR spectra of PS PEG over 4000-400 cm-1 range
227 Peppas NA Wright L Macromolecules 1996298798ndash804
120
500 1000 1500 2000 2500 3000 3500 4000
0
1DXPS IN PSPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 26 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS)
All these absorption bands for individual polymer were observed in the FTIR spectrum of the
5050 (ww) PSPEG in which they were combined to give superimposed bands in the regions
of 750-1500 cm-1 and 2700- 3100 cm-1
The hydroxyl vibrational frequency is discernible in the blend spectrum for PSPEG at 0
With the incorporation of the copolymers for compatibilization a number of bands showed
small shifts and changes in position and shape in the resulting spectra In Figures 28 29 and
30 as it can be noticed that in the hydroxyl absorption region a decrease in the fraction of
free OH groups is observed as the amount of copolymers is increased in the blend This can
be due to the flexibility of the PDXL graft chains on the other hand to the acetal and ether
groups of PDXL which are probably randomly distributed among an increasing number of
hydroxyl groups of PEG statistically favoring the formation of the PDXL and PEG hydrogen
bond interaction The results indicate that the intermolecular hydrogen bonding between the
ether oxygen of PDXL and the hydroxyl groups of PEG may be formed thereby reducing the
fraction of free OH which is consistent with the shifts observed in the region of hydroxyl
stretching Intermolecular hydrogen bondings are expected to occur among PDXL and PEG
chains due the high hydrophilic forces These interactions have replaced the intramolecular
121
interactions between COC and OH groups of PEG before addition of containing PDXL
copolymers It can be noticed a progressive shift of hydroxyl band from 3340 to 3420 cm-1
with DXPS and from 3340 to 3350 cm-1 when 2SP2 is added This shift can be attributed to
the decrease of intramolecular interactions among hydroxyl groups within PEG chains in
favor to intermolecular interactions between PDXL and PEG228
500 1000 1500 2000 2500 3000 3500 4000
0
1
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 27 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2)
228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
122
3200 3300 3400 3500 3600 3700 3800
00
01
DXPS IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number (cm-1)
Figure 28 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(DXPS) in the hydroxyl absorption region
3200 3300 3400 3500 3600 3700 3800
00
02
2SP2 IN PSPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 29 FTIR spectra of PSPEG blends (5050) with different amounts of compatibilizer
(2SP2) in the hydroxyl absorption region
123
3200 3300 3400 3500 3600 3700 3800
00
DXPS 40 2SP2 40 2SP1 40
Abs
orba
nce
Wave number (cm-1)
Figure 30 FTIR spectra comparison of PSPEG blends (5050) with different compatibilizers
in the hydroxyl absorption region
Conclusions An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends Again The PS blocks of the copolymer result in good
compatibility with PS component of the blends The compatibilization of PSPEG blends is
apparently associated with hydrogen bonding where groups of the acetal units in PDXL
interact with hydroxyl groups of PEG These form a stronger interface between the two
phases which leads to important modifications of the blend properties Apparently the FTIR
result is in good agreement with the miscibility criteria proposed by Krigbaum and Wall (Δb)
interaction parameter which results from dilute-solution viscometry (DSV) method It can be
concluded that by the addition of 20ndash40 wt of incorporated copolymer reveal a good
compatibilizing efficiency for the blend systems as it was observed from micrographs as well
124
References
174 Paul D R and Newman S Eds ldquoPolymer Blendsrdquo Academic Press New York Vol I-II (1979) 175 Noshay A and McGrath J E ldquoBlock Copolymers-Overview and Surveyrdquo Academic Press New York
(1977) 176 Olabisi O Robeson L M and Shaw M ldquoPolymer-Polymer Miscibilityrdquo Academic Press New York
(1979) 177 L A Utracki ldquoPolymer Alloys and Blends Thermodynamic and Rheologyrdquo Hanser
Publishers Munich (1989) 178 Flory P J Principles of Polymer Chemistry Cornell Ithaca NY (1953) 179 Scott R L J Chem Phys 17 (1949) 279 180 Hildebrand J H and Scott R L ldquoThe Solubility of Non-electrolytesrdquo 3rd ed Reinhold Publishing Corp
New York (1950) 181 Paul D R and Barlow J W ldquoIn Multiphase Polymersrdquo Advances in Chemistry Series no176 Cooper S
L Estes G 182 Paul D R Bucknall C B ldquoPolymer Blendsrdquo Wiley New York (1999) 183 D R Paul J W Barlow and H Keskula in J I Kroschwitz ed-in-ch ldquoEncyclopedia of Polymer Science
and Engineeringrdquo 2nd ed Wiley-Interscience New York (1985) 184 G P Hellmann and M Dietz Macromol Symp 170 (2001) 185 60 B D Gesner ldquoEncyclopedia of Polymer Science and Technologyrdquo Interscience New York Vol 10
(1969) 694ndash709
125
186 R D Deanin in H F Mark N G Gaylord and N M Bikales eds ldquoEncyclopedia of Polymer Science and
Technologyrdquo Suppl Wiley-Interscience New York Vol 2 (1977) 458 187 J Schies and D B Priddy eds ldquoModern Styrenic Polymers Polystyrene and Styrenic Copolymersrdquo John
Wiley amp Sons Chichester UK (2003) 188 L H Sperling ldquoInterpenetrating Polymer Networks and Related Materialsrdquo Plenum Press New York
(1981) 189 BD Favis in D R Paul and C B Bucknall eds Polymer Blends Vol 1 Formulations John Wiley amp Sons
Inc New York Chap 16 (2000) 190 Herold CB Keil K Bruns DE Biochem Pharmacol 38 (1989) 73 192 CChorng-Shyan Cheng-kang Lee and Kuan-chaung Lin Journal of Polymer Research 13 (2006) 247-254 193 Y Hua YS Hua V Topolkaraevb A Hiltnera E Baera Polymer 44 (2003) 5681ndash5689 194 S P Timg B J Bulkin and E M Pearce J Polym Ser Polym Chem 19 (1981) 451 195 T Suzuki Y Murakami T lnm and Y Takenam]
Poljmer J 13 1027 (1981) 196 Norimasa Watanabe Isamu Akiba and Saburo Akiyama Europ Polymer Journal 37 (2001) 1837-1842 197 HJ Rhoo HT Kim JK Park TS Hwang Electrochim Acta 42 (1997) 1571 198 B Oh YR Kim Solid State Ionics 124 (1ndash2) (1999) 83 199 K Pielichowski Eur Polym J 35 (1999) 27 200 AM Stephen TP Kumar NG Renganathan S Pitchumani R Thirunakaran and N Muniyandi J Power
Sources 89 (2000)80 201 JL Acosta E Morales Solid State Ionics 85 (1996) 85 202 AM Rocco RP Pereira MI Felisberti Polymer 42 (2001)5199 203 AV Rajulu RL Reddy SM Raghavendra and SA Ahmed Eur Polym J 35 (6) (1999) 1183 204 W Wu X Luo D Ma Eur Polym J 35 (1999) 985 205 Krause S ldquoPolymer-polymer compatibilityrdquo in PolymerBlends Vol 1 ed D R Paul and S Newman
Academic Press NY (1978) 206 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 24 (1988) 29 207 Z Pingping Y Haiyang Z Yiming Eur Polym J 35 (1999) 915 208 Mikhailov NV and Zeilkman SG Kolloid Z 19 (1957) 465 209 Bohmer B Berek D and Florian S Eur Polym J 6 (1970) 471 210 Feldman D and Rusu M EurPolym J 6 (1970) 627 211 Krigbaum W R and Wall F J Journal of Polym Sci 5 (1950) 505 212 Catsiff E H and Hewett W A J Appl Polym Sci 6 (1962) 530 213 Kulshreshta AK Singh B P and Sharma Y N Eur Polym J 2 (1988) 191 214 ML Huggins J Am Chem Soc 64 (1942) 116 215 E Schroder G Muller and KF Arndt ldquoLeitfaden der PolymerCharakterisierungrdquo Akademie Verlag Berlin
(1982) 216 Garcia R Melad O Gomez C M Figueruelo J E and Campos A Eur Polym J 35 (1999) 4 217 Melad O Asian J of Chem 14 (2002) 849 218 Sahlin JJ and Peppas NA J Appl Polym Sci63 (1997) 103ndash10
126
219 Roberts MJ Bently MD and Harris J M Adv Drug Deliv Rev 54 (2002) 459ndash76 220 Chiavacci LA Dahmouche K Santilli CV Bermudez Z Carlos LD Briois V and Craievich AF J Appl
Cryst 36 (2003) 405ndash9 221 Coates J In Meyers RA editor ldquoEncyclopaedia of analytical chemistryrdquo Chichester Wiley (2000) 10815ndash
37 222 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123 223 JD Thomas MSc Thesis Sep 2001 Drexel University Novel associated PVAPVP hydrogels for nucleus
pulposus replacement Philadelphia PA USA 224 Hassan CM Peppas NA Adv Polym Sci 200015337ndash65 225 Peppas NA Polymer 197718403ndash8 226 Peppas NA Makromol Chem 1977178595ndash601 227 Peppas NA Wright L Macromolecules 1996298798ndash804 228 Daniliuc L David C and De Kesel C Eur Polym J 11 1992) 1365ndash71
127
CHAPTER V Compatibilization Effect of Poly (Methyl Methacrylate-g-
Poly (1 3 Dioxolane)) on Immiscible Polymer Blends of
Polystyrene and Poly (Ethylene Glycol)
51 Introduction
PMMA is more than just plastics of paint Often lubricating oils and hydraulic fluids tend to
get really viscous and even gummy when they get cold This is a real pain when operating
heavy equipments in very cold weather When a little bit of PMMA is dissolved in these oils
and fluids they donrsquot get viscous in the cold and machines can be operated down to -100degC
PMMA can find a several applications namely adhesive optical coating medical packaging
applications and so forthhellip
In medical applications PMMA and its derivatives are used particularly for hard tissue repair
and regeneration229 PMMA beads have been developed to deliver aminoglucoside antibiotics
locally for the treatment of bone infections230 PMMA and PEG form an important and unique
pair of polymers in that they are chemically different In the present work this study may
shed light on the PMMA properties modifications induced by blending with PEG to overcome
the difficult processing of rigid PMMA
Several studies have been made on blends of poly (ethylene oxide) PEO and PMMA in the
last decades but very few on PMMAPEG blends231 232 233
Numerous works reported that the miscibility domain ranges between 10 and 30 of PEO by
weight depending on the PMMA tacticity or molecular weight No phase diagram is available
yet in the literature for PMMAPEO and neither it is for PMMAPEG234
229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703
127
52 Experimental
521 Materials
PEG and PMMA were used as blend components PMMA was obtained from ENPC TP1-
Chlef Company PEG was purchased from MERCK Company Physical and Structural
characterizations of these materials were performed by SEC 1H-NMR and DSC
522 Blend Preparation
Blends of PMMAPEG (5050) were prepared using the same procedure as described for the
blends discussed in the previous chapter Table 15 shows the quantities of the copolymers
used for compatibilization of the blends of PMMAPEG
Table 15 The quantities of the copolymers used for compatibilization of the blends of
PMMAPEG
Weight of the dispersed phase
10 20 30 40
Weight of the total weight of the blend
47 9 13 166
53 Characterization Techniques
531 Dilute Solution Viscometric Measurements
Viscometric measurements were performed at 30 plusmn 002 degC using the Ubbelohde capillary
viscometer (Schott Gerte KPG-type) having a viscometer constant K = 003 It was
immersed in a constant temperature bath The samples were dissolved in THF filtered and
then added to the viscometer reservoir Dilutions were carried out progressively by adding
fresh solvent to the viscometer starting from 1gdl and allowing 10 min for the solution to
reach thermal equilibrium Six dilutions were made for each blend sample At least five
observations were made for each measurement
532 Optical Microscopy
The samples were observed under a binocular lens optical microscope MOTIC coupled with computer-controlled CCD camera
128
533 FTIR FTIR measurements were performed on a Bruker IFS 66S Fourier transform spectrometer at
room temperature The recorded wave number was in the range of 4000-400 cm-1 The spectra
were obtained at a resolution of 2 cm-1 and of 100 scans Samples for FTIR spectroscopic
characterization were prepared by grinding the blends with KBr (5 w ) and compressing the
mixtures to form sheets
54 Results and Discussion
541 Characterization of the Homopolymers
The polymers have been analyzed by SEC to determine their number average-molecular
weights and polydispersity indices DSC measurements performed to determine their glass
transition temperatures as well as melting point of crystallinity of PEG 1HNMR spectroscopy analysis revealed the tacticity of PMMA It has been found that PMMA
is Syndiotactic-Atactic (highly syndiotactic) as shown in Figure 3 and 321
Physical characteristics of materials used are given in Table 16
Table 16 Characteristics of PEG PS and PMMA used in this research
Materials
Source Specific gravity
Mw gmol
Tg
degC Tm range
degC Crystallinity
PMMA ENPC TP1-Chlef (fromLG MMA Corp)
119
55 000
113
_ _
PEG Merck
102
35 000
-50
60 ndash 65
80
129
Figure 31 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in CDCl3
Figure 32 1H-NMR spectrum of Commercial PMMA (ENPC TP1-Chlef) in the methyl shifts
region in CDCl3
130
542 Dilute Solution Viscometry
Dilute solution viscometry has been utilized to evaluate miscibility of PMMAPEG blends
and the same approach discussed in the previous section has been followed The
experimental reduced viscosities of the polyblends are plotted against concentration in dilute
solution viscometry Eventually plots of pure polymers and polyblends of 5050 PMMAPEG
are first obtained Then their interaction coefficients are determined as shown in Table 17
Table 17 Interaction coefficient for binary solutions (polymersolvent)
Blend components PEG PMMA
b11 007327 minus
b22 minus 006561
b12 = (b11 b22)12 = 006933 (theo)
The compatibility of this system has been evaluated through the sign of Δb The values of the
latter according to equation 73 for different amounts of poly (MMA-g-PDXL) copolymers in
the blends are given in Table 18 It is observed that the blend of PMMAPEG at 5050 by
weight shows a negative value of Krigbaum and Wall parameter which indicates
incompatibility of the system as it is expected Similarly to PSPEG blend a crossover in the
reduced viscosity-concentration plot is observed and a decrease of slope arises in the range of
05 to 066 gdl in the viscosity-concentration plot as shown in Figure 33 This is attributed to
the repulsive intermolecular interactions between the polymer chains
Then the incorporation of the copolymers at various amounts presents positive values
progressively Curves of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in
THF at 30degC with various amounts of copolymer are given in Figures 34 35 and 36
131
Table 18 Interactions parameters for PMMAPEG blends with poly (MMA-g-PDXL)
copolymers (3MP2 2MP2 and 3MP1) as compatibilizers
Copolymers (b12) and (Δb) Amount of incorporated copolymer in weight percent
0 10 20 30 40
3MP2 b12 00288 01308 01904 02373 02602
Δb - 004053 00615 01211 01680 01909
2MP2 b12 00288 01286 01690 01893 02296
Δb - 004053 00593 00997 01200 01603
3MP1 b12 00288 00868 01670 02010 02379
Δb - 004053 00175 00977 01317 01686
00 01 02 03 04 05 06 07 08 09 10 11020
025
030
035
040PMMAPEG (5050) 0
PEG PMMAPEG 0 PMMARe
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 33 Plots of reduced viscosity (ηspc) vs concentration for PMMA PEG and
PMMAPEG blend (0) in THF at 30degC
132
02 03 04 05 06 07 08 09 10 11000
005
010
015
020
025
030
035
040 BLENDS WITH 3MP1
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 34 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP1 copolymer
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040
045BLENDS WITH 3MP2
PMMAPEG 0 10 20 30 40
Redu
ced
visc
osity
η
spc
(d
lg)
C (gdl)
Figure 35 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 3MP2 copolymer
133
02 03 04 05 06 07 08 09 10 11010
015
020
025
030
035
040BLENDS WITH 2MP2
PMMAPEG 0 10 20 30 40 Re
duce
d vi
scos
ity
ηspc
(d
lg)
C (gdl)
Figure 36 Plots of reduced viscosity (ηspc) vs concentration for PMMAPEG blends in THF
at 30degC with various amounts of 2MP2 copolymer
From our viscosity data as the copolymer content increases in the blend the polymer blend
molecules will become disentangled more spaciously resulting in a greater interaction
between structurally similar component segments This suggests that there are attractive
forces that induce miscible behavior of the blends as it is observed in Figure 37
0 10 20 30 40 5-01
00
01
02
0
PMMA PEG BLENDS
3MP2 2MP2 3MP1
Δb
Amount of incorporated copolymer w ()
Figure 37 Dependence of viscometric interaction parameter (Δb) on the amount of
copolymers (3MP2 2MP2 and 3MP1) used for compatibilization
134
The three copolymers (3MP2 2MP2 and 3MP1) involved in this study for compatibilization
are different from the point of view of the PDXL content and the graft length For instance
3MP2 and 2MP2 have similar and longer grafts since the theoretical number average-
molecular weight of the graft is 2000 gmol However they contain different amount of
PDXL In the case of 3MP1 this graft copolymer has a structure with shorter side chain length
(Mn = 1000 gmol) corresponding to the half of the graft size in the former copolymers From
the observations made out of the figure above 3MP2 copolymer (21 w of PDXL) provides
higher values of the interaction parameter and therefore greater extent of compatibility
compared to the other copolymers since it has long grafts which allows penetration into the
other phase
It can be concluded that all three copolymers show good results for compatibilization on the
basis of the Δb criterion of polymer-polymer miscibility determined by viscometry
Similarly the minimum amount of copolymer needed for compatibilization of PSPEG
(5050) blend has been determined corresponding to Δb = 0 as function of the PDXL content
and shown in Table 19
Table 19 minimum amount of compatibilizer needed for compatibilization of PSPEG
(5050)
Compatibilizer Δb Minimum Amount Needed PDXL Content wt dispersed phase wt of total blend
(wt)
2MP2 0 34 16 35
3MP2 0 37 18 21
3MP1 0 58 28 19
135
543 Optical Microscopy and Phase Morphology
a) PMMAPEG (5050) 0 (without compatibilizer)
b) Compatibilizing effect of 2MP2 copolymer
c) Compatibilizing effect of 3MP2 copolymer
d) Compatibilizing effect of 3MP1copolymer
Figure 38 Optical micrographs showing phase structure in 5050 PMMAPEG blends
a) blends without compatibilizer b) with 2MP2 c) with 3MP2 d) with 3MP1
136
Figure 38 presents microscopy images of PMMAPEG blends with varying amounts of
compatibilizers The morphological characteristics of the blends of PMMAPEG without
compatibilizers show a poor dispersion of PMMA as a dispersed phase The addition of
compatibilizers changes drastically the morphological topology of this system The
compatibilizers used are of different length of the side chains and also different PDXL
content By introducing progressively variable amounts of the compatibilizers they display
similarly the morphological characteristics to some extent It is observed that the phase
separated domains of PMMA in the blends are reduced with increasing amounts of the
compatibilizers This is due to the compatibility of PMMA of the copolymers with the
PMMA blend component and on the other hand to the interfacial interactions of the PDXL
of the copolymers and PEG component of the blends From these results it is revealed that
compatibilizing effect of 2MP2 copolymer on this system is great compared to the others Not
only causes the size of the dispersed droplets to decrease but also dispersed droplets become
homogeneous However 3MP1 copolymer which contains shortest grafts (about half length
of those of the other copolymers) and less amount of PDXL shows less reduction in the
droplet size compared to the other copolymers Therefore it can be concluded that the
compatibilization of this blend depends upon length and number of grafts
On the overall observations these compatibilizing copolymers are very effective and hence
influence and improve the compatibility of PMMAPEG blend at a composition of 5050 wt
544 FTIR Analysis
Same observations can be made for the blends of PEG with PMMA The FTIR spectrum of
this blend at 0 compatibilizer is shown in Figure 39 For pure PMMA the
spectroscopically free carbonyl group band is observed at 1730 cm-1 In the blend sample one
large vibrational band due to hydroxyl group stretches in pure PEG is observed with two
distinct contributions which can be seen for all samples They are attributed to the
spectroscopically free and associated hydroxyl forms at 3495 and 3600 cm-1 respectively
A large band in the wave number range of 1400-1500 cm-1 is assigned to the deformation
vibration of the methyl groups The bands with peaks locations at 2820 and 2990 cm-1 are due
to C-H symmetrical and asymmetrical stretching vibration of CH3 respectively Peaks at
2886 and 2950 cm-1are ascribed to C-H symmetrical and asymmetrical stretching vibration of
CH2 figures 40 and 41 The C-O band is observed in the range of 1150- 1210 cm-1
137
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 PMMAPEG 0 Blend
Abs
orba
nce
Wave number cm-1
Figure 39 FTIR spectra of PMMAPEG 0 over 4000-400 cm-1 range
2750 2800 2850 2900 2950 3000 3050 3100-05
00
05
10
15
20
Abs
orba
nce
PEG PMMAPEG 0
Wave number cm-1
Figure 40 FTIR spectra of PMMAPEG 0 and PEG over the 3100-2700 cm-1 range
138
2750 2800 2850 2900 2950 3000 3050 3100
00
05
10
152MP2 in PMMAPEG
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 41 FTIR spectra of PMMAPEG 0 blends with 2MP2 addition over the 3100-2700
cm-1 range
The incorporation of PMMA-g-PDXL copolymers in the blends makes some changes in the
resulting spectra as it can be noticed in Figures 42 - 44 In the hydroxyl absorption region
same phenomenon has occurred as in the PSPEG blends The fraction of free OH groups has
decreased as the amount of the copolymers increased as shown in figures 45 and 46 which
present the effect of different compatibilizers in the hydroxyl absorption region This can be
explained as discussed above by the fact that the PEG hydroxyl groups undergo other
intermolecular interactions essentially with PDXL chains of the copolymers A comparison of
the effect of the three copolymers involved in the compatibilization at the highest amount
added is given in figure 47 It can be noticed that 2MP2 shows very few fraction of free OH
groups compared to the others This copolymer contains more PDXL (35 wt with 4 grafts)
than the others do (21 wt with 3 grafts and 19 wt with 3 grafts in 3MP2 and 3MP1
respectively)
A crystalline PEG phase is confirmed by the presence of the triplet peak of the COC
stretching vibration at 1148 1110 and 1062 cm-1 with a maximum at 1110 cm-1235 236
Changes in the intensity shape and position of the COC stretching mode are associated with
235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115
139
the interaction between PEG and PMMA-g-PDXL In addition both polymers contain the
same ether group and the spectra show that the corresponding peaks are overlapped for the
blends The intensity of the side bands at 1144 and 1062 cm-1 decreases due to the decrease of
PEG crystallinity in the blends237
Therefore the presence of this interacting system is probably responsible for the miscibility
and low degree of crystallinity observed for these blends
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
202MP2 in PMMAPEG BLENDS
0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 42 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (2MP2)
237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
140
500 1000 1500 2000 2500 3000 3500 4000
00
05
10
15
20 3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 43 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2)
500 1000 1500 2000 2500 3000 3500 4000
0
1
2 3MP1 IN PMMAPEG BLENDS 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 44 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1)
141
3500
00
05
3MP2 IN PMMAPEG BLENDS 0 10 20 30 40
Abs
orba
nce
Wave number cm-1
Figure 45 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP2) in the hydroxyl absorption region
3100 3150 3200 3250 3300 3350 3400 3450 3500 3550 3600 3650 3700 3750 3800
-02
00
02
04
06
08
3MP1 IN PMMAPEG 40 30 20 10 0
Abs
orba
nce
Wave number cm-1
Figure 46 FTIR spectra of PMMAPEG blends (5050) with different amounts of
compatibilizer (3MP1) in the hydroxyl absorption region
142
3500
2MP2 40 3MP2 40 3MP1 40
Abs
orba
nce
Wave number cm-1
Figure 47 FTIR spectra comparison of PMMAPEG blends (5050) with different
compatibilizers in the hydroxyl absorption region
The results from FTIR spectra indicate the compatibility of these polymer blends with the
addition of the PDXL copolymers via hydrogen bonds is observed and confirmed mainly by
the shifts of bands of the hydroxyl stretching modes
143
Conclusions
From the observations made out from this study reveal that all three copolymers show good
results for compatibilization on the basis of the Δb criterion of polymer-polymer miscibility
determined by viscometry Therefore these copolymers act as good compatibilizers since it
was found that the minimum amount needed for compatibilizing is between 1 to 3 of the
total weight of the blend which corresponds to 3 to 6 of the dispersed phase This
compatibilization is due to the fact that the copolymers have constituents which present strong
interactions with both polymer components of the blends These results are in great agreement
with microscopy analyses which demonstrate that the phase separated domains of PMMA in
the blends are reduced with increasing amounts of the compatibilizers This is due to the
compatibility of PMMA of the copolymers with the PMMA blend component and on the
other hand to the interfacial interactions of the PDXL of the copolymers and PEG component
of the blends
From FTIR results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PMMA and relatively long PMMA backbone of PMMA-g-PDXL copolymers respectively
These compatibilizing copolymers are very effective and hence influence and improve the
compatibility of PMMAPEG blend at a composition of 5050 wt
144
References 229 M Sivakumar KP Rao Reactive Funct Polym 46 (2000) 29 230 AJDomb Polymeric Site Specific Pharmacotherapy Wiley New York (1994) 243 231 Schants S Macromolecules 30 (1997) 1419 232 Chen X Yin J Alfonso G C Pedemonte E TurturroA And Gattiglia E Polymer 39 (1998) 4929 233 Parizel N Laupetre F and Monnerie L Polymer 30 (1997) 3719 234 L Hamon Y Grohens A Soldera and Y Holl Polymer 42 (2001) 9697-9703 235 Li X and Hsu SL J Polym Sci Polym Phys Ed22 (1984) 1331 236 Bailey JrF E and Koleske JV Poly (ethylene oxide) New York AcademicPress (1976) 115 237 Fox TG J Appl Bull Am Phys Soc 1 (1956) 123
145
CONCLUSIONS
The preparation of the methacryloyl-terminated PDXL macromonomers via Activated
Monomer mechanism proposed by Franta and Reibel using an unsaturated alcohol (2-
HPMA) as a transfer agent results in linear polymeric chains in order to prevent formation of
cyclic oligomers through cationic polymerisation of cyclic acetals They were all prepared at
the same reaction conditions
The characterization of these macromonomers has been conducted using different methods of
analysis Structure and molecular weight determination were provided from SEC and Raman
and 1H-NMR spectroscopy
We were interested in obtaining a hydrogel based on fully PDXL segments and study its
swelling and viscoelastic behaviour The hydrogel has combined special properties The
results reveal a perfect elastic and resistant hydrogel with interesting viscoelastic properties
Methacrylate-terminated PDXL macromonomers were copolymerized with St and MMA
using different feed molar ratios Both feed molar ratio and the size of the graft influence the
composition of the copolymers Structure composition and number of grafts of the
copolymers were determined by SEC and 1H-NMR spectroscopy Another approach for
copolymerization has been made in order to compare the copolymers obtained from different
types of polymerization reactions like Conventional Free Radical and Controlled Radical
Polymerizations In the latter the copolymer obtained possesses larger number of grafts than
those from the former
The macromonomer reactivity estimation suggests that the length of the PDXL side chains
does affect the reactivity of the methacrylic double bond of the macromonomer when
copolymerized with St However in the case of copolymerization with MMA there is no
dependence on the graft size Finally from DSC measurements the values of Tg depend on
the composition and the size of the PDXL grafts In all copolymers the increase in amount of
the incorporated PDXL macromonomer results in a substantial decease in glass transition
An effective strategy for compatibilization of two kinds of immiscible polymer blends has
been demonstrated Compared with PS-g-PDXL with DXPS content the DXPS is more
effective binary polymer blends compatibilizer in the PSPEG blends which is due to the high
146
number of grafts and high PDXL content This has led to good adhesion of PDXL chains with
the PEG phase in the blends
The compatibilization effect of the copolymers used in this study on the PSPEG and
PMMAPEG was demonstrated from the viscometric results The contribution of both PS or
PMMA and PDXL of the copolymers has played a big role in the compatibilization of these
two different systems of blends thereby resulting in good compatibility due the chemical
affinity between these components which leads to a drastic decrease in interfacial tension and
suppression coalescence between the blend constituents
It has been shown that the immiscible blends in question exhibit compatibility when small
amount of copolymers synthesized for this purpose are added except for one of them
Styrene-g-PDXL copolymers act as good compatibilizers for PSPEG blends since it was
found that the minimum amount needed for compatibilizing is less than 11 of the total
weight of the blend which corresponds to 25 of the dispersed phase This compatibilization
is due to the fact that the copolymers have constituents which present strong interactions with
both polymer components of the blends
Compared with PS-g-PDXL with DXPS content the DXPS is more effective binary polymer
blends compatibilizer in the PSPEG blends which is due to the high number of grafts and
high PDXL content This has led to good adhesion of PDXL chains with the PEG phase in the
blends Again The PS blocks of the copolymer result in good compatibility with PS
component of the blends The compatibilization of PSPEG blends is apparently associated
with hydrogen bonding where groups of the acetal units in PDXL interact with hydroxyl
groups of PEG These form a stronger interface between the two phases which leads to
important modifications of the blend properties
Similarly PMMA-g-PDXL copolymers act as good compatibilizers since it was found that
the minimum amount needed for compatibilizing is between 1 to 3 of the total weight of
the blend which corresponds to 3 to 6 of the dispersed phase This compatibilization is due
to the fact that the copolymers have constituents which present strong interactions with both
polymer components of the blends
These results are in great agreement with microscopy analyses which demonstrate that the
phase separated domains of PMMA and PS in their respective blends are reduced with
increasing amounts of the compatibilizers
147
Specific interactions between chemical groups of two blend components can play an
important role in polymer mixtures There is a range of such interactions of varying strengths
which has been identified in polymer blends and such interactions are generally defined for
small molecules It should be noted that the extension of this concept to polymers is not
always straightforward it is more difficult to identify interactions in polymers the
spectroscopy is more complex and molecular conformations are less certain This situation is
further complicated because researchers use different names and definitions to describe
similar interactions
FTIR investigation showed that these interactions have been observed through the changes in
IR absorption peaks of PS PEG and PMMA upon mixing with increasing amount of
compatibilizers in their blends which have given rise to a wide investigation
From these the results obtained in this work copolymers containing large amount of PDXL is
effective as compatibilizing agent for PSPEG and PMMAPEG blends It is pointed out that
compatibilizing effects of these copolymers are caused due to the associative interactions
between ether groups of PDXL grafts and hydroxyl groups of PEG and miscibility between
PS or PMMA and relatively long PS or PMMA backbone of PS-g-PDXL and PMMA-g-
PDXL copolymers respectively
148
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