Thesis Nitinart last version - Le Mans University

UCO2M−UMR CNRS n°6011 Université du Maine LCOM−Chimie des Polymères Faculté des Sciences et Techniques

THESE

Présentée en vue de l’obtention du grade de

DOCTEUR Spécialité: Chimie et Physicochimie des Polymères

par

Nitinart SAETUNG

Synthetic- and natural rubber-based telechelic polyisoprenes:

preparation and use for block copolymers via RAFT polymerization

Soutenue le 25 novembre 2010, devant le jury composé de:

Mme Pranee PHINYOCHEEP Assoc. Professeur, Mahidol University, Thaïlande Rapporteur M. Christophe BOISSON Directeur de Recherche-HDR CNRS, Université Lyon 1 Rapporteur Mme Sophie BISTAC Professeur, Université de Haute Alsace, Mulhouse Présidente M. Frédéric PERUCH Chargé de Recherche-HDR CNRS, Université de Bordeaux 1 Examinateur Mme Irène CAMPISTRON Ingénieur CNRS à l’Université du Maine Co-encadrante Mme Sagrario PASCUAL Maître de Conférences, Université du Maine Co-encadrante M. Laurent FONTAINE Professeur, Université du Maine Directeur M. Jean-François PILARD Professeur, Université du Maine Co-directeur

For my grandparents For my parents For my family members For my teachers

The present thesis is the result of my PhD research at the Université du Maine,

France. I will never forget this time in my life and, most importantly, the people I met here

and who helped me to create, develop and finish this thesis. First of all, I would like to

acknowledge the financial support from Prince of Songkla University, Thailand and from the

French Ministry of Education and Research. Taking this opportunity, I would like to express

my sincere gratitude to Assistance Professor Dr. Orasa PATARAPAIBOOLCHAI for her

advice and recommendation letter that brought me study for a Ph.D. at Université du Maine.

I would like to thank my advisor: Professor Laurent FONTAINE for giving me an

opportunity to do my PhD work within his group, as well as for his support and professional

guidance during my PhD period. Professor Laurent has been a wonderful advisor, providing

me with support, encouragement, patience and an endless source of ideas. His breadth of

knowledge and his enthusiasm for research inspires me. I thank him for the countless hours

he has spent with me, discussing everything from research to career choices, reading my

manuscript and correcting my presentation.

I would also like to thank Professor Jean-François PILARD, my Ph. D. co-advisor.

Professor Jean-François has been a great advisor. His enthusiasm for research and his vision

for the future have been an inspiration. He has given me support and encouragement and his

advice about my research have greatly enhanced the work. I thank him for his assistance and

for all the support provided to both me and to my husband, Anuwat SAETUNG.

I would like to express my sincere gratitude to Dr. Irène CAMPISTRON, whose

enthusiasm for the controlled oxidative and metathesis degradations of natural rubber and

her knowledge of the subject has helped me understand many aspects of controlled

degradation of natural rubber, especially the metathesis degradation that was foreign to me

beforehand, and for correcting my manuscript. Most importantly, I would like to thank her for

her encouragement, patience and also much assistance in my personal life for the past 4

years.

I am extremely grateful to Dr. Sagrario PASCUAL for the time spent discussing the

results related to living radical polymerization, especially RAFT polymerization that was new

to me at the start of this thesis. Most importantly, I would like to thank her for her

encouragement and for having confidence in me and my abilities and for finding the time to

read through the manuscripts and correct my manuscript.

Next, I would like to thank members of my thesis committee, Assoc. Professor Pranee

PHINYOCHEEP, Professor Sophie BISTAC, Dr. Christophe BOISSON and Dr. Frédéric

PERUCH who have been generous with their time and have assisted with the successful

completion of this work. I would especially like to thank to Professor Sophie BISTAC for her

help with preliminary wedge tests.

I am grateful to Dr. Jean-Claude SOUTIF for his assistance and useful discussions on

MALDI-TOF MS over the last year. Furthermore, I would especially like thank to Madame

Evette SOUTIF, his wife, for all the love, kindness and help offered to my family throughout,

in particular to my daughter, Alisa SAETUNG. Evette took care of my daughter like she was

her own granddaughter.

Many thanks to Mme Cécile CHAMIGNON and Mme Amélie DURAND for help

interpreting liquid 1H NMR spectra and 13C NMR spectra. I would also like to thank to Dr.

Monique BODY for the analysis of solid-state 13C NMR spectra of my samples.

I am greatly indebted to Dr.Véronique MONTEMBAULT, Dr. Michel THOMAS and

Dr. Charles COUGNON, Anita LOISEAU, Jean-Luc MONEGER and Aline LAMBERT for

their guidance and helpful in providing advice many times during my work here. I would

especially like thank to Dr. Fédéric GOHIER and his wife, Dr. Stephanie LEGOUPY, for

their kindness and support shown to my family throughout by lending me their baby clothes

and baby accessories for the past 4 years.

I am also grateful to Professor Jean-Claude BROSSE, Dr. Daniel DEROUET and

Dr. Albert LAGUERRE for their helpful, guidance and support for my study here.

Thank you all friends in LCOM laboratory, Chuanpit, Faten, Hoa, Sandie, Charles,

Dao, Ekasit, Ekkawit, Hien, Jean-Marc, Martin and Rachid for their friendship and good

atmosphere in laboratory. I would like to give special thanks to Martin for his helpful

discussions related to living radical polymerization and also for helping me to improve my,

English. I would also like to give special thanks to Chuanpit for her help in my personal life,

especially during my first year in France, and thanks to Faten for her help improving my

French.

Finally, I would like to thank my grandparents, my family for all their advice, support

and love. I am very lucky to have such wonderful family members. I especially thank my

wonderful husband, Anuwat SAETUNG who is my best friend and turn to ‘soul-mate’. He has

kept me happy and positive throughout the Ph.D. process, and I thank him for all his patience,

support, encouragement and love. I truly thank Anuwat for sticking by my side, even during

the difficult days. Most importantly, I am very lucky to have a wonderful daughter, Alisa

SAETUNG who was an inspiration during my graduate Ph. D. studies, and in future always

will be.

Synthetic- and natural rubber-based telechelic polyisoprenes: preparation and use for block copolymers via RAFT polymerization ABSTRACT: The aim of this research work is to develop new strategies to synthesize well-

defined block copolymers from natural rubber (NR) based telechelic polyisoprene (PI) by

reversible addition-fragmentation chain transfer (RAFT) polymerization. The tert-butyl

acrylate (t-BA) has been chosen as comonomer which is further modified to obtain acrylic

acid (AA) units. To target such block copolymers, two original synthetic routes have been

developed to target NR-based PIs which are further employed as macromolecular chain

transfer agents (macroCTAs) for the RAFT polymerization of t-BA.

In the first approach, a trithiocarbonate functionalized telechelic cis-1,4-PI was synthesized

via the oxidative degradation of NR followed by reductive amination and amidation. The

microstructure of the functionalized PI is strictly cis-1,4. The end-functionality was

determined by 1H-NMR spectroscopy and clearly demonstrated that telechelic cis-1,4-PI

chains carry the trithiocarbonate moiety. We demonstrated that the chain extension of the

trithiocarbonate functionalized cis-1,4-PI starting block resulted in an efficient block

copolymer formation. PI-b-P(t-BA) diblock copolymer presents an unimodal SEC trace and

polydispersity index equal to 1.76. The copolymer has a nM equal to 26,000 g.mol-1 as

determined by SEC and a nDP (PI) equal to 62 and a nDP (P(t-BA)) equal to 87 as

determined by 1H NMR spectroscopy.

In the second approach, a well-defined α,ω-bistrithiocarbonyl-end functionalized telechelic

cis-1,4-polyisoprene was synthesized via functional metathesis degradation from NR in the

presence of second generation Grubbs catalyst (GII) and a bistrithiocarbonyl-end

functionalized olefin as CTA. Formation of telechelic natural rubber occurs rapidly in a

single-step process. The nM was equal to 8,200 g. mol-1 as determined by SEC after 4h of

reaction at 25 °C. A perfectly bifunctional telechelic PI was obtained using a ratio of

[NR]0/[GII] 0/[CTA]0 to 100/1/2 at 25°C. Moreover, the difunctional telechelic PI has a strictly

cis-1,4-microstructure. It was successfully used as macroCTA for the RAFT polymerization

of t-BA to form well-defined P(t-BA)-b-PI-b-P(t-BA) triblock copolymer. The final

copolymer has a nM equal to 23,300 g.mol-1, PDI equal to 1.50 as determined by SEC and a

nDP (PI) equal to 80 and nDP (P(t-BA)) equal to 100 as determined by 1H NMR

spectroscopy.

Finally, the tert-butyl ester groups of the P(t-BA) blocks were chemically cleaved to acrylic

acid groups using iodotrimethylsilane at room temperature in order to get PI-b-PAA diblock

and PAA-b-PI-b-PAA triblock copolymers. The thermal properties of block copolymers

before and after dealkylation of tert-butyl ester groups have been investigated by DSC and

TGA analyses.

Keyword: natural rubber, polyisoprene, oxidative degradation, functional metathesis

degradation, telechelics, reversible addition-fragmentation chain transfer (RAFT)

polymerization.

List of abbreviations

AA Acrylic acid

ACVA Azobiscyanovaleric acid

AFM Atomic force microscopy

AIBN 2,2′-Azobis(2-methylpropionitrile)

AROP Anionic ring−opening polymerization

ATR Attenuated total reflectance

ATRP Atom transfer radical polymerization

BriBBr 2-Bromoisobutyryl bromide

CA Coupling agent

CNTs Carbon nanotubes

COSY 2D-correlation spectroscopy

CPDB 2-(2-Cyanopropyl)dithiobenzoate

CP-MAS Cross-polarisation combined with magic angle spining

CRP Controlled/living radical polymerization

CTA Chain transfer agent

D3 Hexamethylcyclotrisiloxane

DCP Dicumyl peroxide

DDAT S-1-Dodecyl-S’-(α,α’-dimethyl-α”-acetic acid)trithiocarbonate

DEPT Distortionless enhancement of polarisation transfer

DLS Dynamic light scattering

DMA N,N-Dimethylacrylamide

DPE Diphenylethylene

nDP Number-average degree of polymerization

DRC Dry rubber content

DSC Differential scanning calorimetry

DTG First derivative thermogravimetry

EO Ethylene oxide

ETSPE 2-Ethylsulfanylthiocarbonyl sulfanyl propionic acid ethyl ester

nf Average functionality

FTIR Fourier transform infrared spectroscopy

GII Second generation of Grubbs catalyst

HSQC Heteronuclear single-quantum correlation

I Isoprene


macroCTA Macromolecular chain transfer agent

MALDI-TOF Matrix-assisted laser desorption ionisation time-of-flight

m-CPBA meta-Chloroperbenzoic acid

MMA Methyl methacrylate

nM Number-average molecular weight

n,NMRM Number-average molecular weight determined by 1H NMR spectroscopy

SECnM , Number-average molecular weight determined by SEC

MPEB 1,4-Bis(4-methyl-1-phenylethyl)benzene

wM Weight-average molecular weight

NMP Nitroxide-mediated radical polymerization

NMR Nuclear magnetic resonance spectroscopy

NR Natural rubber

NVP N-Vinylpyrrolidinone

PAA Poly(acrylic acid)

PD3 Poly(hexamethylcyclotrisiloxane)

PDI Polydispersity index

PDMA Poly(N,N-dimethylacrylamide)

PEO Poly(ethylene oxide)

PI Polyisoprene

PLA Polylactide

PI-Li+ Polyisoprenyllithium

PMDETA N, N, N’, N’, N’’-Pentamethyldiethylenetriamine

PNVP Poly(N-vinylpyrrolidinone)

PS Polystyrene

PS-Li+ Polystyrenyllithium

P(t-BA) Poly(tert-butyl acrylate)

P(2-VP) Poly(2-vinylpyridine)

RAFT Reversible addition/fragmentation chain transfer

ROMP Ring-opening metathesis polymerization

rrPT Regioregular hydroxyl-functionalized poly(3-hexylthiophene)

SAXS Small angle X-ray scattering

s-BuLi sec-Butyllithium


SCK Shell-crosslinked

SEC Size exclusion chromatography

SLS Static light scatterting

t-BA tert-Butyl acrylate

t-bp tert-Butyl peroxide

t-BuP4 1-tert-Butyl-4,4,4-tris(dimethylamino)-2,2-bis-[tris(dimethylamino)-

phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene)]

Tg Glass transition temperature

TGA Thermogravimetric analysis

THF Tetrahydrofuran

TIPNO 2,2,5-Trimethyl-4-phenyl-3-azahexane-3-nitroxide

Tmax Maximum degradation temperature

TNR Telechelic cis-1,4-polyisoprene

TPC Terephthaloyl chloride

2-VP 2-Vinylpyridine

WAXS Wide-angle X-ray scattering

Table of contents

General introduction...…….......………………..………………………………..1

Chapter I : Literature on block copolymers based on PI

Introduction....................................................................................................................... ..........5

I. General strategies to synthesize block copolymers.................................................. ...........5 I.1 Synthesis of well-defined linear AB diblock copolymers...................................... ............6 I.2 Synthesis of well-defined ABA triblock copolymers............................................. ............8

II. Synthesis of block copolymers based on polyisoprene.......................................... ..........11 II.1 Using anionic polymerization.............................................................................. ..........11

II.1.1 Synthesis of AB diblock copolymers............................................................ ..........12 II.1.2 Synthesis of ABA triblock copolymers.......................................................... ..........19

II.2 Using controlled/living radical polymerizations................................................. ..........22 II.2.1 Nitroxide-Mediated Radical Polymerization (NMP)..................................... ..........23

II.2.1.1 Synthesis of AB diblock copolymers......................................................... ..........23 II.2.1.2 Synthesis of ABA triblock copolymers................................................... ..........30

II.2.2 Reversible Addition-Fragmentation Chain transfer Polymerization (RAFT).............32 II.3 Using a combination of various polymerizations................................................... ........36

II.3.1 Synthesis of AB diblock copolymers.............................................................. ........36 II.3.2 Synthesis of ABA triblock copolymers........................................................... ........39

Conclusion......................................................................................................................... ........41

References.......................................................................................................................... ........42

Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization

Introduction....................................................................................................................... .........45

I. Synthesis and characterization of polyisoprene........................................................ ........46

II. Synthesis and characterization of polyisoprene-b-poly(tert-butyl acrylate) block

copolymers....................................................................................................................

;........50

Conclusion......................................................................................................................... ........54

Experimental section...................................................................................................................55

References.......................................................................................................................... ........59

Table of contents

Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization

Introduction....................................................................................................................... .........61

I. Synthesis of αααα-trithiocarbonyl- ωωωω-carbonyl-cis-1,4-polyisoprene............................ ........63

II. Synthesis of PI-b-P(t-BA) diblock copolymer............................................................ ;........69

Conclusion......................................................................................................................... ........72


References.......................................................................................................................... ........77

Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization

Introduction....................................................................................................................... .........80

I. Functional Metathesis Degradation............................................................................ ........83

II. Synthesis of P(t-BA)-b-PI-b-(P(t-BA) triblock copolymers...................................... ;........93

Conclusion......................................................................................................................... ........97


References.......................................................................................................................... ........102

Chapter V : Thermal properties of block copolymers based on PI/P(P(t-BA) and PI/PAA

Introduction....................................................................................................................... ........104

I. Comparison between PI-macroCTA and block copolymers based on PI/P(t-BA) ........104

II. Influence of the PI microstructure............................................................................ ;......114

III. Deprotection of t-BA group and thermal stability of resulting block

copolymers based on PI/PAA.....................................................................................

......115

Conclusion......................................................................................................................... ........125


References.......................................................................................................................... ........128

General conclusion...............................................................................................129

General introduction


- 1 -

In the 20th century, natural polymers such as cellulose, cotton and rubber have attracted

considerable attention from polymer scientists. Increasing environmental consciousness

and demands of consumers have created significant opportunities for improved materials

and development of new preparation methods. Developing polymers from renewable

resources will support environmental request. The current challenge of polymers from

renewable resources is a growing area of reseach.1

Natural rubber (NR) is a polymer of great interest for use in producing new polymeric

materials as it is a polymer which comes form a renewable resource. Moreover, it is well

known that NR consists of a long sequence of cis-1,4-polyisoprene that provides the

material with unique and special properties, including good elastomeric properties, low

glass transition temperature, excellent flexibility, good “green” strength and building tack.2

Due to its excellent properties, polymer scientists have developed new synthetic routes to

obtain polyisoprene with very similar structure.3 The polymerization using Ziegler-Natta

catalysts leads to PIs with 98% of cis-1,4-polyisoprene units.4 However, these synthetic PIs

showed different properties from NR, especially in terms of processability. The living

anionic polymerization5 leads to PIs with 95% of cis-1,4-polyisoprene units, 1% of trans-

1,4-polyisoprene units and 4% of 3,4-polyisoprene units. The controlled/living radical

polymerizations (CRPs)6 of isoprene gave 80% of 1,4-polyisoprene, between 5% and 15%

of 3,4-polyisoprene and between 5% and 15% of 1,2-polyisoprene depending on the

reaction conditions. The microstructure influences the properties of the polyisoprene; for

example, the trans-1,4-polyisoprene has a higher degree of crystallinity and a higher glass

transition temperature than the cis-1,4-polyisoprene.7 Therefore, the synthesis of telechelic

strictly cis-1,4-polyisoprene from natural rubber (TNR) will give rise to original polymers

and copolymers with new potential applications. The most widely used methods to produce

TNR derivatives are controlled oxidative degradation8 or metathesis degradation.9

[1] Joseph, S.; John, M.; Pothen, L.; Thomas, S., Raw and Renewable Polymers. In Polymers-Opportunities and Risks II, Eyerer, P.;

Weller, M.; Hubner, C., Eds. Springer Berlin: Heidelberg, 2010; Vol. 12, p 55-80. [2] Morton, M., Rubber Technology. Van Nostrand Reinhold: New York, 1973. p 152. [3] Puskas, E. J.; Gautriaud, E.; Deffieux, A.; Kennedy, P. J., Prog. Polym. Sci. 2006, 31, 533-548. [4] Van Amerongen G, J., Transition Metal catalyst systems for polymerization Butadiene and Isoprene. In Elastomer Stereospecific

polymerization, Johnson, L. B.; Goodman, M., Eds. American chemical society: Washington, D.C., 1966; Vol. 52, p 136-152. [5] Young, N. R.; Quirk, R. P.; Fetters, J. L., Anionic Polymerizations of Non-Polar Monomers Involving Lithium. In Anionic

polymerization, Fetters, J. L.; Luston, J.; Quirk, R. P.; Vass, F.; Young, N. R., Eds. Springer-Verlag NewYork Heidelberg Berlin, 1984; Vol. 56, p 53.

[6] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [7] Kent, E. G.; Swinney, F. B., I&EC Product Research and Development 1966, 5, 134-138. [8] Nor, H. M.; Ebdon, J. R., Prog. Polym. Sci. 1998, 23, 143-177. [9] Ivin, K. J.; Mol, J. C., Olefin metathesis and metathesis polymerisation. Academic Press: London, 1997. p 375.


- 2 -

Oxidative degradation of NR has been widely used in our laboratory to develop precursors

for thermoplastic elastomers,10 biomaterials11 and polyurethane materials.12-15 In addition,

we have also developed a method for the preparation of TNR in a single-step process via

the metathesis degradation of cis-1,4-polyisoprene.16 Therefore, it is possible to prepare

functional TNR by combining chain cleavage reaction of NR with a post-functionalization

reaction to form original block copolymers with new potential applications. To best of our

knowledge, no work has been previously reported on the synthesis of telechelic cis-1,4-

polyisoprene from natural rubber as precursor for CRPs in order to obtain well-defined

block copolymers. Among CRP techniques, Reversible Addition/Fragmentation chain

transfer (RAFT) polymerization17 is recognized as one of the most versatile method for the

synthesis of block copolymers since it is effective for a wide range of monomers and thus

leads to a wide range of block copolymers.

The objective of this research work is to develop new strategies to synthesize well-defined

diblock copolymers and triblock copolymers from NR-based cis-1,4-PI by RAFT

polymerization in order to obtain new polymeric materials. In this work, the tert-butyl

acrylate (t-BA) has been chosen as a comonomer. To target such block copolymers, new

synthetic routes (Figure 1) are developed to prepare NR-based cis-1,4-PI which could

further be employed as macromolecular chain transfer agent (macroCTAs) for the RAFT

polymerization of t-BA. In the first approach, the PI-macroCTA was synthesized via the

oxidative degradation of NR followed by reductive amination and amidation. In the second

approach, the PI-macroCTA was synthesized via one-pot metathesis degradation from NR.

In order to compare the properties of final block copolymers, the preparation of synthetic

PI-macroCTAs has also been performed by RAFT polymerization.

[10] Derouet, D.; Nguyen, T. M. G.; Brosse, J.-C., J. Appl. Polym. Sci. 2007, 106, 2843-2858. [11] Kébir, N.; Campistron, I.; Laguerre, A.; Pilard, J.-F.; Bunel, C.; Jouenne, T., Biomaterials 2007, 28, 4200-4208. [12] Kébir, N.; Morandi, G.; Campistron, I.; Laguerre, A.; Pilard, J.-F., Polymer 2005, 46, 6844-6854. [13] Kébir, N.; Campistron, I.; Laguerre, A.; Pilard, J.-F.; Bunel, C.; Couvercelle, J.-P.; Gondard, C., Polymer 2005, 46, 6869-6877. [14] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.; Phinyocheep, P.; Pilard, J. F., J. Appl. Polym.

Sci. 2010, 117, 1279-1289. [15] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.; Phinyocheep, P.; Doutres, O.; Pilard, J.-F., J.

Appl. Polym. Sci. 2010, 117, 828-837. [16] Solanky, S. S.; Campistron, I.; Laguerre, A.; Pilard, J.-F., Macromol. Chem. Phys. 2005, 206, 1057-1063. [17] Moad, G.; Thang, S. H., Aust. J. Chem. 2009, 62, 1379-1381.


- 3 -

Natural Rubber

Degradation

= RAFT agent moiety

Oxidation

amination and amidation Metathesis

PI-b-P(t-BA) P( t-BA)-b-PI-b-P(t-BA)

RAFT polymerization RAFT polymerization

Figure 1. Synthetic routes to target block copolymers based on cis-1,4-PI from NR.

This PhD. manuscript is based on five chapters.

The first chapter is a literature survey about the synthesis and characterization of block

copolymers based on PI.

The second chapter describes the preparation of synthetic polyisoprene via RAFT

polymerization and then its use for the formation of PI-b-P(t-BA) diblock copolymer via

RAFT polymerization.

The third chapter describes the synthesis of a new trithiocarbonate functionalized NR-

based cis-1,4-polyisoprene via the oxidative degradation of natural rubber followed by

reductive amination and amidation. The well-defined α-trithiocarbonyl-ω-carbonyl-cis-

1,4-polyisoprene was used as a monofunctional macroCTA to mediate the RAFT

polymerization of t-BA to form well-defined PI-b-P(t-BA) diblock copolymers.


- 4 -

The fourth chapter describes the one-pot synthesis of a new α,ω-bistrithiocarbonyl-end

functionalized telechelic cis-1,4-polyisoprene via metathesis degradation from NR. The

new well-defined α,ω-bistrithiocarbonyl-end functionalized telechelic NR-based cis-1,4-

polyisoprene was used as macroCTA to mediate the RAFT polymerization of t-BA leading

to well-defined P(t-BA)-b-PI-b-P(t-BA) triblock copolymers.

The final chapter is devoted to thermal characterizations of PI-macroCTAs, PI-b-P(t-BA)

diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers and, to the study of

the thermal stability of block copolymers before and after dealkylation of tert-butyl ester

groups of the P(t-BA).

Chapter I

Literature on block copolymers

based on PI


- 5 -

Introduction

Block copolymers are a fascinating class of materials made by covalent bonding of two or

more chemically different polymeric chains (blocks) that, in most cases, are

thermodynamically incompatible giving rise to a rich variety of microstructures in bulk and

in solution. Therefore, they are materials with unique chemical and physical properties:

they combine the properties of individual blocks in one molecule.1 They have attracted a

great deal of attention both academically and industrially due to their wide range of

potential applications2-3.

Block copolymers which contain polyisoprene (PI) as a block have found applications as

nanofibers,4 thermoplastic elastomers,5 pressure sensitive adhesives,6-7 and biocompatible

materials.8-9 This is due to the fact that PI is of great interest for its low glass transition

temperature (Tg), for its double bond rich composition, for its 1,4-microstructure and

because it has been classified as a biopolymer.10

The objective of our research work is the synthesis of AB diblock copolymers and

symmetric ABA triblock copolymers based on PI block (A) and a polar poly(tert-butyl

acrylate) P(t-BA) block (B) in order to get novel polymeric materials. Therefore, in this

chapter, we report on the general strategies to synthesize block copolymers that lead to

well-defined linear AB and ABA block copolymers and focus on the preparation of

architecturally well-defined linear AB diblock and ABA triblock copolymers based on PI.

I. General strategies to synthesize block copolymers

Various architectures of linear block copolymers such as AB diblock, ABA and ABC

triblocks, (AB)n multiblock are shown in Figure I-1.


- 6 -

AB diblock (AB)n multiblock

ABA triblock ABC triblock

Figure I-1. Linear block copolymers architectures.

The use of controlled/living polymerization techniques are the most convenient and

efficient methodology to target well-defined block copolymers. In this section, the

synthetic strategies based on controlled/living polymerization techniques that lead to the

preparation of linear AB diblock and ABA triblock copolymers will be presented.

I.1 Synthesis of well-defined linear AB diblock copolymers

A summary of block copolymer synthesis techniques has been provided by Hillmyer11 and

Matyjaszewski.12 Four methods have been reported for the preparation of AB linear

diblock copolymers:

A) the sequential monomer addition,

B) site-transformation technique,

C) the use of a dual initiator and,

D) by coupling two well-defined telechelic polymers.


- 7 -

telechelic oligomer

n

telechelic oligomer

+ n

n

__ _ _ __ _

nn+

_n

_I

mechanism I Site transformation

n

mechanism IIm+n m

nn+ _I m

n

_ _m

YXn

n

mechanism IY

mechanism II

mn

_ _m

A)

B)

C)

D)

dual initiator

AB diblock copolymer

_

I : initiator; X and Y : initiator sites; : monomer A, and : monomer B




X Y

Y

coupling

Figure I-2. Schematic representation of synthetic strategies toward well-defined AB

diblock copolymers: A) sequential monomer addition using controlled/living

polymerizations, B) site-transformation technique, C) using a dual initiator, and D) by

coupling two well-defined telechelic polymers.

In the first case, sequential addition of monomer can be performed in a one-pot

polymerization reaction using controlled/living polymerizations (Figure I-2A).

Provided that termination and/or transfer reactions are negligible, after the consumption of

the first monomer A, the remaining functionality at the chain-end of polymer A must be

able to initiate the polymerization of the new incoming second monomer B. This crossover

reaction must proceed fast and quantitatively to prevent side reactions. In addition to well-

established living ionic polymerization,13-14 other living polymerization systems such as

controlled/living radical polymerizations,15-16 have been developed during the past years.

Well-defined block copolymers are prepared by these controlled/living systems, but the

sequential monomer addition technique excludes monomers that polymerize by different

mechanisms.17


- 8 -

The second process is the so-called site-transformation technique which is applied when

the involved monomers cannot undergo polymerization with the same type of active sites

(Figure I-2B). In this technique, the monomer A is polymerized by the mechanism I via

the active center X. The active center X is then transformed to the active center Y and

monomer B is polymerized by a second mechanism. Extensive reviews about the site-

transformation technique have been published1,18-22 and this technique was recently

updated by Hadjichristidis et al.23

The third route involves the use of a dual bifunctional initiator that is able to start

simultaneously two polymerizations with two monomers by different mechanisms (i.e.,

ring-opening metathesis polymerization (ROMP) and nitroxide-mediated polymerization

(NMP). The two active sites must be compatible and tolerate each other (Figure I-2C).

Recently, Du Prez et al.24 published a review about dual and heterofunctional initiator to

prepare well-defined block copolymers.

The fourth synthetic route relies on the coupling reaction of two different well-defined

telechelic homopolymers (Figure I-2D). This strategy involves that the different functions

at the chain-ends must be highly reactive.25 Recently, a lot of progress has been made in

this field by the application of “click chemistry”26 and metal-ligand couplings.27-28

I.2 Synthesis of well-defined ABA triblock copolymers

The synthesis of ABA triblock copolymers can be accomplished using one of the following

methods:

A) the use of a difunctional initiator and a two-step sequential addition of monomers,

B) two-step sequential addition of monomers followed by a coupling reaction,

C) three-step sequential addition of monomers and,

D) by site-transformation technique.


- 9 -

nn+ _I

XXn

nX

m

_

m

A)

B)

C)

D)

difunctionalinitiator ABA triblock copolymer

Xn

_

m

_m

m

n

coupling agent

_

mn

+

mn*

m n

CA

CA

nn+

_I _

m

m

n

n

nm

nn

_Y

mechanism Isite transformation

mechanism II

m

+

nXX

difunctionalmacroinitiator

XX

difunctionalinitiator

Y

n

_m

_m

I : initiator; X and Y: initiator sites; : monomer A and : monomer B

ABA triblock copolymer



n

Figure I-3. Schematic representation of synthetic strategies toward well-defined ABA

triblock copolymers: A) use of a difunctional initiator and a two-step sequential addition of

monomers, B) two-step sequential addition of monomers followed by a coupling reaction,

C) three-step sequential addition of monomers, and D) by site-transformation technique.


- 10 -

The most straightforward method and widely explored so far is the use of a difunctional

initiator. The middle block (Polymer A) is made first, bearing at both ends active sites

capable of initiating the polymerization of the second monomer B, which is added

sequentially in the reaction medium after the consumption of the first monomer A (Figure

I-3A) . This procedure can be performed in a one-pot reaction. Living ionic polymerization

techniques13-14 and controlled/living radical polymerizations15-16 have been successfully

used to synthesize ABA triblock copolymers using such strategy.

In the second method, a well-defined linear AB diblock copolymer is synthesized by

sequential addition of monomers A and B. This diblock copolymer is reacted in

stoichiometric amount with a difunctional coupling agent (CA) in order to form the ABA

triblock copolymers25 (Figure I-3B). Recently, “click chemistry” has been used for

coupling blocks together and, quantitative reactions of functional end-groups for the

construction of well-defined block copolymers have been obtained.29-31

The third method involves sequential monomers additions using a monofunctional

initiator. The first monomer A is polymerized followed by the polymerization of the

second one B. After complete consumption of the second monomer B, the first monomer A

is added to the reaction mixture resulting in an ABA triblock copolymer (Figure I-3C).

Finally, ABA can be prepared by a combination of polymerization techniques. This

procedure is needed when the two monomers A and B cannot be polymerized by the same

polymerization technique and have to carried out in a two-step reaction using a

difunctional initiator. The monomer A is polymerized by mechanism 1 via active centers

X. The active centers X are then transformed to active centers Y and the resulting

difunctional macroinitiator can be employed for the polymerization of monomer B by

mechanism II (Figure I-3D). This technique is extremely convenient for the formation of

mechanistically incompatible block copolymers.24


- 11 -

II. Synthesis of block copolymers based on polyisoprene

The general strategies to synthesize block copolymers presented in the section I of this

chapter are widely used for the synthesis of well-defined linear AB diblock and ABA

triblock copolymers based on polyisoprene (PI). PI is generally synthesized by anionic

polymerization, by Ziegler-Natta polymerization and by controlled/living radical

polymerization. It could also be obtained by ring-opening metathesis polymerization

(ROMP) and from natural rubber (NR). However, only anionic polymerization,

controlled/living radical polymerizations and a combination of various polymerizations

have been employed to synthesize block copolymers based on PI. Then, in this section, the

preparation of linear block copolymers based on polyisoprene by anionic polymerization,

controlled/living radical polymerizations and a combination of various polymerization

techniques is presented.

II.1 Using anionic polymerization

The anionic polymerization of isoprene has been widely reported.1,11,13,32 Anionic

polymerization proceeds efficiently via organometallic sites, carbanions (or oxanions) with

metallic counterions. Due to the fact that carbanions are nucleophiles, the monomers that

can undergo polymerization by anionic polymerization are those bearing an electron

withdrawing group at the polymerizable double bond. The most widely used initiators for

anionic polymerization are organolithiums.33 The primary reason for the employment of

these organometallic compounds as an anionic initiator is due to their rapid reaction with

the monomer at the initiation step of the polymerization reaction. With a rate of initiation

greater than that of the propagation step, the use of organometallic compounds leads to the

formation of the desired polymer with a narrow molecular weight distribution because all

active polymer chains start growing at almost the same time. Propagation proceeds through

the nucleophilic attack of a carbanionic site onto a monomer molecule with reformation of

the anionic active center. Under the appropriate experimental conditions, anionic

polymerization is associated with the absence of either spontaneous termination or chain

transfer reaction. Additionally, carbanions still remain active after the monomer is

completely consumed leading to well-defined block copolymers once a second monomer is

added to the reaction.


- 12 -

II.1.1 Synthesis of AB diblock copolymers

Two conditions are necessary in order to obtain well-defined diblock copolymers by

anionic polymerization:

a) the nucleophilicity of the macroanion A− must be high enough to initiate the

incoming monomer B without attacking its pendant groups (e.g., ester group of

acrylates);

b) the initiation of monomer A must be faster than the propagation rate of the

second monomer B. In general, sequential anionic polymerization requires the

following order of addition: dienes/styrene > vinylpyridines > (meth)acrylates >

oxiranes > siloxanes.13

The anionic polymerization of isoprene using sec-butyllithium (s-BuLi) as initiator in

hydrocarbon solvents at low temperature (−78 °C) is the most widely used and reported.

This is due to the fact that the use of hydrocarbon solvents and Li as counterion in the

initiator are essential for the production of polyisoprene having a high 1,4-microstructure

leading to a low Tg of the polymer and good elastomeric properties.

Various diblock copolymers based on isoprene and styrenic monomers or (meth)acrylic

monomers have been synthesized1,12-13 and used for many applications.34-38 Thus, the

synthesis of block copolymers containing an isoprenic block and other types of monomers

e.g. styrene, ethylene oxide (EO), 2-vinylpyridine (2-VP) and (meth)acrylic monomers

such as methyl methacrylate (MMA), tert-butyl acrylate (t-BA) will be studied in this part.

A wide variety of diblock copolymers of styrene and isoprene have been synthesized by

sequential addition of monomers.13,39 Polyisoprene was synthesized as the first block using

s-BuLi in benzene at low temperature (−78 °C) to form polyisoprenyllithium (PI−Li+)

active ion. The polymer was chain extended by the addition of styrene in the presence of a

small amount of a polar solvent (usually tetrahydrofuran (THF) (Scheme I-1A).

Alternatively, isoprene can be polymerized as the second block by generating

polystyrenyllithium (PS−Li +) active ion with s-BuLi in hydrocarbon solvent at low


- 13 -

temperature. Then, isoprene monomer was added to form a well-defined diblock

copolymer (Scheme I-1B). These reactions were terminated by the addition of methanol.

+ s BuLi Benzene78 °C

LiPITHF, LI78 °C

PI bCH3OH


LiPSBenzene,

LI78 °C CH3OH

A)

B)

PS

PS b PI

PI b PS

PS b PI

n

m

n

m

Scheme I-1. Synthesis of PI-b-PS via anionic polymerization: A) PI was synthesized as the

first block, and B) PI was synthesized as the second block.1.

The preparation of well-defined diblock copolymers based on isoprene and a polar

monomer (e.g. ethylene oxide, 2-vinylpyridine, and (meth)acrylates) is more complex than

that of the PI-b-PS or PS-b-PI diblock copolymers. Generally, the preparation of diblock

copolymers containing isoprene and ethylene oxide can be achieved in a two-steps

reaction1 (Scheme I-2A). First, isoprene monomer is polymerized in benzene with s-BuLi

as initiator at −78 °C. The living chain-end is then capped with one ethylene oxide unit.

After addition of ethanoic acid, an intermediate polymer containing hydroxyl group at the

chain-end (PI-OH) is obtained. Then, cumyl potassium was used to deprotonate the OH

group, leading to the macroinitiator PI-O−K+ which was further employed for the

polymerization of EO in THF at 50 °C. In this case K+ counterion has been used and not

Li+ because the strong ionic interaction between C-O− and Li+ leads to a low delocalization

of the negative charge on the oxygen and finally the insertion of monomers is

not possible.39-40 Förster et al.41 successfully used 1-tert-butyl-4,4,4-tris (dimethylamino)-

2,2-bis-[tris(dimethylamino)-phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene)]

(t-BuP4) with s-BuLi to prepare well-defined PI-b-PEO diblock copolymers in a one-pot

synthesis (Scheme I-2B). This strong phosphazene base can efficiently complex lithium

ions, thereby suppressing the strong ionic interaction between C-O− and Li+ facilitating the

polymerization of ethylene oxide. To synthesize this diblock copolymer, isoprene was first

polymerized, using s-BuLi/t-BuP4 system as the initiator in THF. Afterward, a small

amount of ethylene oxide is added at −40 °C to cap the living PI chain-end and the reaction


- 14 -

solution is heated to 40 °C to start chain propagation with EO. This reaction was finally

terminated by the addition of a carboxylic acid (Scheme I-2B).


LiPI PI

LI

O1.

2.CH3COOHOH

First step

PI OH

C

CH3

CH3

K

THFPI O K

THF, 50 °C

OCH3COOH

Second step

A)

+s BuLi/

78 °CLiPI PI

OO

THF,

OB)

BuP4tin hexane

40 °C 40 °C

N

P

N

NNP P

P

N(CH3)2

N(CH3)2

N(CH3)2

N(CH3)2N(CH3)2

N(CH3)2

(H3C)2Nt BuP4 :

Li BuP4t

PI b PEO PI b PEO

PI b PEO

n

m

nm

Scheme I-2. Synthesis of PI-b-PEO via anionic polymerization: A) in a two-step process,1

and B) in a one-pot reaction.41

In addition to the employment of ethylene oxide as a monomer, the use of 2-vinylpyridine

(2-VP) as monomer is also reported. For example, well-defined diblock copolymers

containing isoprene and 2-VP monomers were obtained by altering solvent from a non

polar to a polar solvent during the copolymerization.42 To make this diblock copolymer the

polyisoprenyl lithium was first synthesized in n-heptane at −78 °C and s-BuLi was used as

initiator. Afterward, the solvent was removed and the polar solvent (THF) was added for

the polymerization step of 2-VP. The reaction was quenched with methanol (Scheme I-

3A). Quirk et al.36 prepared well-defined PI-b-P(2-VP) diblock copolymers in benzene.

The PI block was synthesized in benzene at 45 °C using s-BuLi as initiator. LiCl was used


- 15 -

as cross-associator in benzene at 8 °C to reduce reactivity at the chain-end of well-defined

P(2-VP) from polymerization and then the reaction mixture was rapidly terminated by

adding acetic acid in methanol (Scheme I-3B).

N

+ s BuLi 78 °C LiPI LI

n-heptane THF, CH3OH

N

+ s BuLi, 45 °C

LiPI8 °C CH3CO2HBenzene Benzene,

CH3OHLiCl

LiCl,

78 °C

A)

B)

PI b P(2 VP) PI b P(2 VP)

PI b P(2 VP)LIPI b P(2 VP)

n

m

n

m

Scheme I-3. Synthesis of PI-b-P(2-VP) via anionic polymerization; A) by changing

solvents,42 and B) in benzene.36

The synthesis of block copolymers composed of polyisoprene and poly(meth)acrylates by

anionic polymerization has been reported. The anionic polymerization of (meth)acrylates

frequently produces side reactions due to the fact that the anionic propagating centers can

react with the carbonyl groups of the (meth)acrylate monomers. To avoid this problem,

the active site chain is usually modified to reduce the reactivity of the anion at the

chain-end.13,43-44

As our current investigation is concerned by the synthesis of block copolymers based on

polyisoprene and poly(tert-butyl acrylate), the anionic polymerization of block copolymers

involving PI and P(t-BA) was studied. Previously, Ünal et al.45 synthesized PI-b-P(t-BA)

by sequential addition of monomers by anionic polymerization using s-BuLi as the

initiator. The first block was synthesized by polymerization of isoprene using s-BuLi in

THF at 0°C. Then, the t-BA was added to the solution at –78°C. The reaction mixture was

stirred for a further 48 hours. The reaction was terminated by addition of methanol

(Scheme I-4). Characterization of block copolymers were carried out using size exclusion

chromatography (SEC) and elemental analysis (Table I-1).


- 16 -

+ s BuLi 0°C

LiPI LICH3OH 78 °CTHF

OO

bPI P(t BA)bPI P(t BA)n

m

Scheme I-4. Synthesis of PI-b-P(t-BA) by sequential addition of monomers via anionic

polymerization using s-BuLi as initiator.45

It was found that the block copolymers formed micelles consisting of a PI shell and a

P(t-BA) core in n-octane which is a poor solvent for the P(t-BA) block and a good solvent

for PI block. The micelle formation was studied by static light scattering (SLS). The light

scattering results showed that an increase of temperature led to a shift in the micelle/free-

chain equilibrium in favour of free-chains. Furthermore, the standard Gibbs energy of

micellization was evaluated and it was found that a large negative standard enthalpy of

micellization was obtained which is one of the important driving forces for micellization.

Table I-1. Characteristics of PI-b-P(t-BA) synthesized by sequential addition of monomer

using anionic polymerization.45

Polymer nM *

(g.mol-1) wM *

(g.mol-1) wM / nM * Weight (%) **

isoprene

COP3a 100 000 123 000 1.23 19.0±0.6

PI−3b 31 000 35 000 1.13 −

COP5a 70 000 77 000 1.09 35.0±1.1

PI−5b 36 000 42 000 1.15 −

*determined by SEC, ** determined by elemental analysis, aCOP for PI-b-P(t-BA) diblock copolymer, bPI for polyisoprene.

Wooley et al.46 use the advantages of micelle formation via diblock copolymer containing

polyisoprene unit to build nanocage structures. The polyisoprene-b-poly(acrylic acid)

(PI-b-PAA) block copolymer was prepared by the hydrolysis of PI-b-P(t-BA) copolymer

precursor. This precursor was synthesized by anionic polymerization of isoprene using s-

BuLi as initiator in hexane at room temperature, followed by addition of 1,1-

diphenylethylene (DPE) and then polymerization of t-BA in hexane/THF containing LiCl


- 17 -

at −78 °C (Scheme I-5). The copolymer composition of the amphiphilic diblock

copolymer PI-b-PAA was determined by 1H NMR spectroscopy ( nDP (PI) = 30 and

nDP (PAA) = 170). This copolymer formed micelles in aqueous solution consisting of a

hydrophobic core of PI and a hydrophilic shell of PAA. Chemical cross-linking of the PAA

segments with an α,ω-diaminopoly(ethylene oxide) led to the formation of shell cross-

linked particles. Interestingly, the double bonds moiety of the cis-1,4-polyisoprene

backbone contained within the micelle core were degraded by ozonolysis. Hollow

nanocages were obtained with different sizes that vary from 83 nm to 130 nm depending

the length of the α,ω-diaminopoly(ethylene oxide) cross-linker.

+ s BuLi LiPI

LICH3OH 78 °C

Hexane

RT PILi

Hexane/THF,

LiCl

bPI P(t BA) bPI P(t BA)

n

OO

m

Scheme I-5. Synthesis of PI-b-P(t-BA) via anionic polymerization using DPE and LiCl.46

Similarly, Terao et al.38 investigated the synthesis of PI-b-PAA via anionic polymerization.

The first block, polyisoprene was polymerized using the previous described procedure by

Wooley et al.46 and trimethylsilylacrylate monomer as second monomer was introduced at

−78 °C in THF. The trimethylsilyl groups were hydrolyzed using dilute hydrochloric acid.

The resulting copolymer was precipitated in methanol and washed with cyclohexane. The

polymer composition was determined by 1H NMR spectroscopy ( nDP (PI) = 40 and nDP

(PAA) = 40). Next, the PI40-b-PAA40 was dispersed into 0.3% aqueous solution to form

micelles; such nanoparticles were cross-linked by gamma-ray irradiation. The size

distribution of the core-shell nanoparticles was determined by dynamic light scattering

(DLS) and atomic force microscopy (AFM) and it was found that the size distribution was


- 18 -

very narrow. The average diameter of the particles decreased from 48 nm for the non-

irradiated micelles to 26 nm after irradiation with 30 kGy. The core size of this

nanostructure was determined by small angle X-ray scattering (SAXS) combined with

DLS and it was roughly constant of 10 nm, irrespective of irradiation dose. Whereas the

shell thickness of the micelles was twice as large as the core size and the size decreased

with increasing the irradiation dose.

Lu et al.47 reported the preparation of microspheres using PI-b-PAA as the surfactant to

disperse a solution of PI-b-P(t-BA) and a P(t-BA) homopolymer (hP(t-BA)) in

dichloromethane. The PI-b-P(t-BA) and the precursor of PI-b-PAA were prepared by

sequential anionic polymerization. A solution of t-BuP4 and s-BuLi at a molar ratio of

1.05/1.00 in hexane was used to initiate the polymerization of isoprene at −78 °C in THF.

After five hours DPE was added, followed by the addition of t-BA. The polymerization

was continued for a further three hours at −78 oC, where upon the reaction was terminated

by the addition of methanol (Scheme I-6). The PI-b-P(t-BA) had an average molecular

weight ( wM ) of 92,000 g.mol-1 as determined by light scattering (LS) and a PDI = 1.22

determined by SEC. The tert-butyl ester groups of the precursor of PI-b-PAA were

removed quantitatively under acidic hydrolysis by treatment with trifluoroacetic acid in dry

dichloromethane to form PI-b-PAA and then used as the surfactant. Permanent

microspheres were produced after PI domains were cross-linked with sulphur

monochloride (S2Cl2). Porous microspheres were produced after the hydrolysis of P(t-BA)

and extraction of the homopoly(acrylic acid) chains. The shape and connectivity of the

poly(acrylic acid)-lined pores could be adjusted by changing in the P(t-BA)/hP(t-BA)

content in precursor microspheres.


- 19 -

+ LiPI

LIP(tPICH3OH

BA) P(tPI BA)

PILi

THF, LiCl

BuP4/s

78 °C

THF, 78 °C

t BuLi

OO

m

n

Scheme I-6. Synthesis of PI-b-P(t-BA) by sequential addition of monomers via anionic

polymerization using t-BuP4/s-BuLi system as initiator.47

Bouropoulos and co-workers48 used the amphiphilic block copolymers (PI-b-PAA) to

modify the surface of muti-walled carbon nanotubes (CNTs) and the growth of calcium

carbonate on these modified CNTs was investigated. The amphiphilic block copolymers

were synthesized using the procedure previously described by Pipas.37 It was found that

wM = 42,400 g.mol-1, PDI = 1.16 determined by SEC and that the copolymer contains 10

wt % PI determined by 1H NMR spectroscopy. The morphology of calcite crystals on

CNTs treated with PI-b-PAA exhibited both a spherical and an ellipsoidal crystal while the

untreated CNTs were found only a rhombohedral calcite.

II.1.2 Synthesis of ABA triblock copolymers

The most reported methods to synthesize symmetric ABA triblock copolymer based on

polyisoprene by anionic polymerization are the use of a coupling agent and the use of a

difunctional initiator. These procedures were described in the section I.2 of this chapter.

PS-b-PI-b-PS triblock copolymer has been prepared by Morton and coworkers39 using a

coupling method that is developed for the preparation of PS-b-PI-b-PS thermoplastic

elastomers used in industries (Scheme I-7A). A PS block was firstly prepared in benzene

at −78 °C using s-BuLi as initiator, followed by the addition of isoprene. Then, an excess

of the living diblock is used for coupling with dichlorodimethylsilane (CH3)2SiCl2)


- 20 -

employed as the coupling agent to form PS-b-PI-Si(CH3)2-PI-b-PS triblock copolymer.

Recently, Li et al.49 have reported the synthesis of difunctional organolithium initiators for

the polymerization of the PS-b-PI-b-PS triblock copolymer in a non polar solvent. The

difunctional initiator (DiMPEBLi) (Scheme I-7B). was synthesized in cyclohexane by the

reaction between t-BuLi and 1,4-bis(4-methyl-1-phenylethenyl)benzene (MPEB). The

resulting compound is then employed as a difunctional initiator for the polymerization of

isoprene in cyclohexane. After that, styrene was added to continue the polymerization and

methanol was used to terminate the reaction.

+ s BuLiBenzene

78 °CLiPS LI

CH3OHSi

CH3

CH3

Cl Cl(excess)

+

Benzene

CH3CLi

CH2

CLi

CH2

CH3

Bu Bu

DiMPEBLi

+

CH3C

CH2

C

CH2

CH3

MPEB

t BuLi2

Cyclohexane

DiMPEBLiCyclohexane

PI LiLiCyclohexane

A)

B)

bPS PI b PS

bPS PI Si(CH3)2 PI b PS

bPS PI

LIbPS PI

m

n

m

n

Scheme I-7. Synthesis of PS-b-PI-b-PS triblock copolymers via anionic polymerization:

A) using dichlorodimethylsilane as the coupling agent,39 and B) using a difunctional

initiator.49

The synthesis of ABA triblock copolymers based on isoprene and EO50 were achieved

using sodium or potassium naphthalene as the difunctional initiator in which Na+ or K+

counterions were formed by electron transfer from the Na or K atom to the naphthalene

molecule. Isoprene was first polymerized in THF at −78 °C. Next, the difunctional

macroinitiator was employed for the polymerization of EO in THF at 50 °C and the

reaction was terminated by the addition of methanol (Scheme I-8). The molecular weight


- 21 -

distributions of the triblock copolymers were narrow and monomodal. Since Na or K

naphthalenide is soluble only in polar solvents (e.g. THF), the microstructure of PI

obtained was mostly 3,4 (approximately 80%) with remainder 1,2.

O

40 °C

K THFK

K 78 °CTHF,

K KCH3OH

PEO b b PEOPI PEO b b PEOPI

K KPI+ n

m

Scheme I-8. Synthesis of PEO-b-PI-b-PEO triblock copolymer via anionic polymerization

using a difunctional initiator.50

To the best of our knowledge, there are only a few reports about the synthesis of ABA

triblock copolymers with isoprene and t-BA monomers via anionic polymerization.

However, employment of general polydienes as the middle block (B) with

poly(meth)acrylates has been previously reported. In this part, the synthesis of triblock

copolymers based on polydienes and poly(tert-butyl acrylate) is particularly studied as it is

one of the topics of this PhD thesis project.

Varshney51 have successfully synthesized well-defined ABA triblock copolymer consisting

of PS or P(2-VP) or polydienes rich in 1,4-microstructure as the middle block and P(t-BA)

as the end block by using terephthaloyl chloride (TPC) as the coupling agent (Scheme I-9).

A PS-b-P(t-BA) diblock copolymer is first formed by the polymerization of styrene in THF

at −78 °C, followed by the addition of LiCl and t-BA. The living macroanion (PS-b-P(t-

BA)−Li+) was linked with TPC at −30 °C to form PS-b-P(t-BA)-b-PS triblock copolymers.

This procedure can be modified and used to synthesize of PI-b-P(t-BA)-b-PI triblock

copolymers by forming PI-b-P(t-BA) diblock copolymers first and their coupling with

TPC.


- 22 -

+ s BuLi LiPS

LI

78 °C

THFPS Li

LiCl

30 °CTPC

P(t BA) PS

DPE

TPC : Cl CO

CO

Cl

78 °CTHF,

78 °CTHF,

bPS P(t BA) bPS P(t BA) TPC

OO

m

n

Scheme I-9. Synthesis of PS-b-P(t-BA)-b-PS using TPC as coupling agent.51

II.2 Using controlled/living radical polymerizations

Living anionic polymerization is one synthetic technique that is widely employed to

produce well-defined block copolymers, however this technique has a number of

drawbacks. Firstly, there is a limitation on the types of monomers that may be polymerized

due to the incompatibility between the reactive centers and monomers. Secondly, living

anionic polymerization requires extremely stringent conditions. To overcome these

drawbacks, there has been considerable interest in polymerization processes that mimic

“living” systems with the versatility and ease of the radical process; moving toward a

controlled/living radical polymerization.15,52 These methods have emerged as powerful

tools for the preparation of block copolymers as they produce well-defined polymers with

a narrow molecular weight distribution and high chain-end functionality. Moreover, the

reactions may be adapted to a wide range of olefin monomers and are tolerant to traces of

impurities. Within the controlled/living radical polymerization, the nitroxide-mediated

radical polymerization (NMP)53 and the reversible addition-fragmentation chain transfer

(RAFT) polymerization54 are the most widely used to synthesize PI and PI-based block

copolymers. A preliminary study was performed on the atom transfer radical

polymerization (ATRP) of isoprene.55 In this study, it was shown that the ATRP of

isoprene proceeded to only 5% conversion, meaning that the reaction was unsuccessful.

The authors explained this result by suggesting that the Cu(I) active species necessary to

promote ATRP are low in the reaction medium due to a competitive chelation of the

copper catalyst by diene monomer units.


- 23 -

II.2.1 Nitroxide-Mediated Radical Polymerization (NMP)

A number of recent reports have described the preparation of PI and diblock copolymers

containing PI with a range of polar and non-polar monomers using NMP.53

II.2.1.1 Synthesis of AB diblock copolymers

Hawker and coworkers56 have developed a rod-coil block copolymer containing

polyisoprene via NMP. The formation of the rod-coil block copolymer was accomplished

by using a biphenyl ester oligomer (rod segment) as an alkoxyamine-terminated

macroinitiator (A, Scheme I-10) for the polymerization of isoprene in o-dichlorobenzene

as a solvent at 120 °C. The resulting block copolymer had a number-average molecular

weight ( nM ) of 3,100 g.mol−1 determined by 1H NMR spectroscopy and a polydispersity

index of 1.08 determined by SEC. The phase behaviour of the rod-coil block copolymer

was detected by wide-angle X-ray scattering (WAXS). The rod-coil block copolymer

containing 35 wt % polyisoprene coil segments did not show any crystallization at room

temperature and it exhibits a lamellar microstructure with short rigid domains.

O

OO

OO

OO

O ON

macroinitiator ( A)

n120 °C

o dichlorobenzene

n

O NA

Scheme I-10. Synthesis of rod-coil block copolymer containing a polyisoprene coil

segment via NMP.56


- 24 -

Grubbs et al.57 reported the synthesis of amphiphilic PEO-b-PI diblock copolymers via

NMP. First, PEO monomethyl ether (MeO-PEO, nM ≈ 5,200 g.mol-1) was functionalized

by esterification with 2-bromopropionyl bromide. Reaction with a copper bromide (I)

complexed and N, N, N’, N’, N’’-pentamethyldiethylenetriamine (PMDETA) abstracted the

bromine atom from bromoester that was subsequently trapped by 2,2,5-trimethyl-4-phenyl-

3-azahexane-3-nitroxide (TIPNO) at 80 °C to form a PEO macroinitiator (B, Scheme I-

11). The PEO macroinitiator (B) used to initiate the polymerization of isoprene in m-

xylene at 125 °C. The resulting PEO-b-PI diblock copolymer had a number-average

molecular weight ( nM ) of 11.4 kg.mol-1 and a low polydispersity index (PDI < 1.1) as

determined by SEC. Compositional analysis of the copolymer showed that it contained 54

wt % PI with approximately 90% of 1,4-microstructure as determined by 1H NMR

spectroscopy.

OHMeO

DMAP, CH2Cl2

OMeO

OBr

OMeO

OO N

PhEt3N,

BrCOCH(CH3)Br

0 °C to RT

CuBr, Cu(0), TIPNO

PMDETA,toluene, 80 °C

m-xylene, 125 °COMeO

O

O N

Phn

(B)

TIPNO : ON

n n

m

n

m

Scheme I-11. Synthesis of PEO-b-PI diblock copolymer via NMP 57

More recently the same group synthesized an efficient unimolecular initiator for

the polymerization of styrene, isoprene and n-butyl acrylate and their subsequent

block copolymers via NMP.58 An ester-functional alkoxyamine initiator (C, Scheme I-12)

was synthesized by the addition of 1-(4-(methoxycarbonyl)-phenyl)ethyl radicals to the

nitroso group of 2-methyl-2-nitrosopropane in high yield (85%). This alkoxyamine was

then used to initiate and mediate the polymerization of styrene in bulk at 125 °C. After the

polystyrene was purified by precipitation into methanol, it was used as a macroinitiator for

the polymerization of isoprene. The resulting diblock copolymer had a number-average

molecular weight ( nM ) of 10.1 kg.mol-1 and a PDI equal to 1.13 as determined by SEC. It


- 25 -

contains 58 wt % PI with approximately 89% of 1,4-microstructure as determined by 1H

NMR spectroscopy.

N

O

Br

CO2Me

+CuBr, Cu(0), PMDETA

toluene, N2, 60 °C, 85%

N OMeO2C

CO2Me(C)

N OMeO2C

CO2Me

125 °C

N OMeO2C

CO2Mem

n

m

125 °C

n

m

Scheme I-12. Synthesis of PS-b-PI diblock copolymer via NMP 58

McCullough et al.59 investigated conducting polymers by end-capping a regioregular

hydroxyl-functionalized poly(3-hexylthiophene) (rrPT)60 with 2,2,5-trimethyl-4-phenyl-3-

azahexane-3-nitroxide (TIPNO) (Scheme I-13). This polymer was then employed as a

macroinitiator for the polymerization of isoprene via NMP using previously reported

conditions.61 The polymerization reaction was performed at 110 °C in 50% v/v of toluene

The resulting rrPT-b-PI diblock copolymer had a number-average molecular weight ( nM )

of 20,300 g.mol-1 and a PDI equal to 1.8 as determined by SEC. The copolymer contained

65 wt % of PI with approximately 90% 1,4-microstructure as determined by 1H NMR

spectroscopy.


- 26 -

S

C6H13

OHBr

m

Br

O

Br1.

2. TIPNO S

C6H13

OBr m

OO N

Ph

50% toluene, 110 °C S

C6H13

OBr m

OO

n

nN

Ph

TIPNO : ON

Scheme I-13. Synthesis of rrPT-b-PI diblock copolymer via NMP.59

Moreover, the synthesis of PI-b-PS and PI-b-P(t-BA) block copolymers were investigated

and reported.61 For the preparation of PI-b-PS diblock copolymers, isoprene was

polymerized first using 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (I,

Scheme I-14A) as an unimolecular alkoxyamine initiator at 120 °C. After the reaction was

complete, polyisoprene was purified by precipitation into methanol and used as a PI-

macroinitiator for the polymerization of styrene in bulk at 120 °C under argon. The

characteristics of the PI-b-PS after purification showed a nM equal to

6,600 g.mol-1 and a PDI of 1.19 determined by SEC, with predominately 1,4-

microstructure as calculated by 1H NMR spectroscopy. Alternatively, a copolymer based

on PI and PS can be synthesized starting with the PS as the first block. In this case, styrene

was polymerized first, followed by the polymerization of isoprene in the same conditions

(Scheme I-14B). The polydispersity index of the PS-b-PI block copolymer is equal to 1.16.

In the case of P(t-BA)-b-PI block copolymer, the 2,2,5-trimethyl-3-(1-phenylethoxy)-4-

phenyl-3-azahexane (I, Scheme I-14C) and TIPNO were used to polymerize the t-BA at

125 °C under argon. The P(t-BA)-macroinitiator was purified by precipitation into

methanol and then used to initiate the polymerization of isoprene at 125 °C under argon.

The macromolecular characteristics of P(t-BA)-b-PI after purification were: nM = 9,700

g.mol-1 and PDI = 1.19 as determined by SEC, with predominantly a 1,4-microstucture as

calculated by 1H NMR spectroscopy. The authors showed that the PI-macroinitiatior is not


- 27 -

efficient for the polymerization of t-BA (Scheme I-14D) as incomplete initiation was

observed leading to a polydisperse sample.

I120 °C

ON

n

120 °C

120 °C

m ON

n m

A)

B)

m

ON

m m

ON

n120 °C

n

n

ON

n

x

I

ON

O O

x

n

125 °C

125 °C

ON

nO O

x

ON

n125 °C

ON

125 °C

C)

D)

I : initiator :

n

TIPNO : ON

+ TIPNO O O

OO

x

OO

x

Scheme I-14. Different strategies for the synthesis of AB diblock copolymers based on

polyisoprene via NMP: A) PI-b-PS diblock copolymer, B) PS-b-PI diblock copolymer,

C) P(t-BA)-b-PI diblock copolymer, and D) PI-b-P(t-BA) diblock copolymer.61


- 28 -

Wooley and co-workers62 have investigated the synthesis of amphiphilic shell-crosslinked

(SCK) nanoparticles consisting of a polyisoprene core and a poly(acrylic acid) shell from

block copolymers prepared via NMP, whereas previously this group used anionic

polymerization46,63 to prepare these structures (as mentioned in page 16 of this Chapter I).

Two amphiphilic diblock copolymers, one consisting of an unmodified PI block

(PAA-b-PI) and the other composed a hydrochlorinated PI block (PAA-b-PI(HCl)) were

prepared by the cleavage of the tert-butyl ester unit in P(t-BA)-b-PI block copolymer

precursors. The P(t-BA)-b-PI precursors were synthesized via NMP, using conditions

similar to that of Benoit.61 The P(t-BA) was polymerized first using an alkoxyamine (I,

Scheme I-14C) and TIPNO at 125 °C and then was used as a macroinitiator for the

polymerization of isoprene at 125 °C in bulk to form P(t-BA)-b-PI. The

copolymer composition was determined by 1H NMR spectroscopy ( nDP (PI) = 128, nDP

(P(t-BA)) = 64) and a number-average molecular weight and a polydispersity index

determined by SEC ( nM = 13 600 g.mol-1 and PDI = 1.18). The PI block contained

predominantly 86% of 1,4-microstructure.

The cleavage reaction of the tert-butyl ester unit was performed in toluene/acetic acid

using methanesulfonic acid as catalyst at 110 °C. This PAA-b-PI copolymer formed

micelles in aqueous solution and their micelle structure is based on a hydrophobic core of

PI and a hydrophilic shell of PAA. Chemical cross-linking of the PAA segments with an

α,ω-diaminopoly(ethylene oxide) led to the formation of shell cross-linked particles

increasing their rigidity and preventing their shape deformation when they are in contact

with substrates. An SCK containing a PI core untreated with HCl had a Tg of −63 °C, while

PI core treated with HCl had a Tg of 33 °C. These SCK showed little deformation from the

solution-state spherical shape upon deposition onto a mica substrate.

The same group64 further extended the synthesis of PI-b-P(t-BA) copolymers to the

synthesis of core-shell brush copolymers. A norbornene functional alkoxyamine (I,

Scheme 1-15) was first prepared. The norbornene group was polymerized via ring opening

metathesis (ROMP) using Grubbs catalyst to form a polynorbornene backbone with

pendant alkoxyamine functionalities. It was then used as a polyfunctional NMP

macroinitiator in the sequential polymerization of isoprene and t-BA in presence of TIPNO

to suppress biradical couplings.65 A brush copolymer consisting of a PI-b-P(t-BA) diblock

copolymer grafts and a polynorbornene backbone is obtained. The PI-b-P(t-BA) grafts


- 29 -

were characterized by 1H NMR spectroscopy ( nDP (PI) = 18 and nDP (P(t-BA)) = 41).

The P(t-BA) units are hydrolysed using HCl to form PAA units that were subsequently

crosslinked with 2,2-(ethylenedioxy)bis(ethylamine) to form a crosslinked brush

copolymer with hydrodynamic diameter of 17.2 nm as determined by DLS. Hollow

nanostructures were then formed by degradation of the PI core using ozonolysis.

O O

ON

198

10

O OO

N

198

10

18

n

(I)

ON

120 °C

x122 °C + TIPNO

+ TIPNO

ON

18O O

41

O O

198

10

TIPNO :

O OO

N10

ROMP Grubbs' catalyst

OO

Scheme I-15. Synthesis of brush copolymers based on PI-b-P(t-BA) grafts and on a

polynorbene backbone via NMP.64


- 30 -

II.2.1.2 Synthesis of ABA triblock copolymers

In addition to the synthesis of AB diblock copolymers via NMP, the synthesis of linear

ABA triblock copolymers based on polyisoprene has been reported recently.

Braslau et al.66 used the advantage of an unimolecular alkoxyamine to synthesize a

dialkoxyamine (I, Scheme I-16) used as an initiator to target a range of symmetrical ABA

triblock copolymers based on polyisoprene and poly(N,N-dimethylacrylamide) (PDMA)

(Scheme I-16A). The PI-macroinitiator was obtained using the bidirectional initiator at

123 °C under argon and then was employed for the polymerization of DMA to form

PDMA-b-PI-b-PDMA. The characteristics of PDMA-b-PI-b-PDMA triblock copolymer

were determined by SEC (nM = 7,000 g.mol-1, PDI = 1.23) and 1H NMR spectroscopy

( nM = 6,000 g.mol-1). In addition, the bidirectional initiator was used to prepare PI-b-P(t-

BA)-b-PI triblock copolymers. The polymerization of t-BA was performed first in bulk

with the bidirectional initiator and TIPNO at 125 °C under argon. Then the P(t-BA) with

the nitroxide cap at both chain-ends was used as a difunctional macroinitiator for the

polymerization of isoprene to form PI-b-P(t-BA)-b-PI triblock copolymers (Scheme I-

16B). nM of PI-b-P(t-BA)-b-PI after isolation was determined by SEC and it was found

equal to 29,800 g.mol-1 and PDI = 1.15. The polymer contained 10 wt% PI as determined

by 1H NMR spectroscopy.


- 31 -

ONPh nO

O NPh

NO

m m

124 °C

ONPh n

O NPh

ONm

I

n

124 °C

OOx

A)

125 °C

O

O O

x

ON

Ph

NPh

n

125 °C

O O

x

n

O NPhON

Ph n

B)

+ TIPNO

ON

TIPNO :

N

O NPh

ONPhI : initiator :

Scheme I-16. Synthesis of ABA triblock copolymers based on polyisoprene using a

bidirectional alkoxyamine initiator (I) via NMP; A) PDMA-b-PI-b-PDMA triblock

copolymer, and B) PI-b-P(t-BA)-b-PI triblock copolymer.66


- 32 -

II.2.2 Reversible Addition-Fragmentation Chain transfer (RAFT) Polymerization

The RAFT polymerization technique is recognized as one of the most versatile methods for

the synthesis of block copolymers since it is compatible with a wide range of unprotected

polar monomers54 including acrylic acid.67 The first successful polymerization of isoprene

via the RAFT process was reported by Jitchum and Perrier.68 The authors found the

optimum reaction conditions to synthesize well-defined polyisoprene homopolymers. In

this study, two different types of chain transfer agent (CTA) were investigated. The first

one was a dithiobenzoate derivative (2-(2-cyanopropyl)dithiobenzoate, CPDB).69 The

polymerization of isoprene mediated by CPDB at 60 °C and using 2,2′-azobis(2-

methylpropionitrile) (AIBN) as an initiator proceeded to low conversion (<15%).

Increasing the reaction temperature to 120 °C and using dicumyl peroxide (DCP) as an

initiator lead to an uncontrolled polymerization, shown by the broad polydispersity

(PDI = 4.07) of the product. It was proposed that the CPDB decomposed at this higher

temperature. By contrast the second trithiocarbonate derivative used as CTA, (2-

ethylsulfanylthiocarbonyl sulfanyl propionic acid ethyl ester, ETSPE)70 was able to control

the polymerization at 120 °C as ETSPE is stable at this reaction temperature. When a ratio

[ETSPE]0/[DCP]0 of 1/0.5 was used, a slightly broad polydispersity index (PDI ≈1.47-

1.67) was obtained, but reducing the [ETSPE]0/[DCP]0 ratio to 1/0.2 at 115 °C improved

the control and PDIs of less than 1.3 were obtained. (Scheme I-17A). Following this, the

optimized reaction conditions were used to produce AB diblock copolymers based on

polyisoprene using the RAFT process. Both P(t-BA) and PS were prepared and use as

macroCTA to mediate the polymerization of isoprene under previously mentioned

conditions (Scheme I-17B-C). The characteristics of PS-b-PI were determined by SEC and

found to be equal to nM = 44 300 g.mol-1, PDI = 1.19 and the copolymer contained 23

wt% PI as determined by 1H NMR spectroscopy. The characteristics of P(t-BA)-b-PI as

determined by SEC were found to be nM = 21 500 g.mol-1, PDI = 1.20 and the copolymer

contained 49 wt % PI. All of the PI blocks were found to feature a high proportion

(approximately 75%) of 1,4-microstructure products as determined by 1H NMR

spectroscopy.


- 33 -

S On S

S

S

ETSPE

115 °C

n

+

OOx

ETSPE

S

S

S

OOO

O

O

S

S

x

S

S

S

n

OO

O

O

x

O

O

n

m

S

S

S

n O

O

m

S

S

SO

O

m

DCP

DCP+

115 °C

115 °C

115 °CDCP,

n

115 °CDCP,

DCP+

A)

B)

C)

DCP : dicumyl peroxide

Scheme I-17. Synthesis of block copolymers based on polyisoprene using ETSPE as CTA

via RAFT process: A) synthesis of PI-macroCTA, B) synthesis of P(t-BA)-b-PI block

copolymer, and C) synthesis of PS-b-PI block copolymer.68

Wooley et al.71 have also prepared well-defined PI-b-PS diblock copolymers using the

RAFT process. In this synthesis, the polyisoprene block was obtained first using S-1-

dodecyl-S’-(α,α’-dimethyl-α”-acetic acid)trithiocarbonate72 (DDAT, Scheme I-18) as a

CTA and tert-butyl peroxide (t-bp) as an initiator at 125 °C under argon. The PI-

macroCTA was then chain extended by the addition of styrene in 1,4-dioxane using AIBN

as an initiator and a reaction temperature of 60 °C under argon. The copolymer was

recovered by precipitation in an excess of methanol. The characteristics of PI-b-PS were

determined by SEC ( nM = 15,590 g.mol-1, and PDI = 1.28). The final copolymer

contained 39 wt % PI with predominantly 1,4-microstructure as determined by 1H NMR

spectroscopy.


- 34 -

S

S

S

O

OH+ n125 °C

t-butyl peroxideS

S

S

n

O

OH

mAIBN, 60 °C

n

O

OHS

S

S

m

DDAT

C12H25 C12H25

C12H25

Scheme I-18. Synthesis of PI-b-PS block copolymer using DDAT as CTA via RAFT

process.71

Wooley et al. 73 also reported the preparation of P(t-BA)-b-PI via the RAFT process. The

P(t-BA) block was synthesized first using DDAT (Scheme I-19) as CTA at 80 °C using

AIBN as initiator. The polymer was recovered by precipitation into a cold 1:1 mixture of

water and methanol. The P(t-BA) was then used as a macroCTA for the polymerization of

isoprene in bulk performed at a reaction temperature of 125 °C to form P(t-BA)-b-PI

diblock copolymer. The characteristics of P(t-BA)-b-PI were determined by SEC to be

equal to nM = 34,500 g.mol-1 and PDI = 1.5. Analysis by 1H NMR spectroscopy revealed

that nM = 21,100 g.mol-1, nDP (P(t-BA)) = 53, nDP (PI) = 48 and that predominantly

1,4-microstructure for PI block is presented. Additionally, the synthesis of P(t-BA)-b-PI-b-

PS and P(t-BA)-b-PS-b-PI triblock copolymers were also reported.


- 35 -

S

S

S

O

OH +

125 °C

t-butyl peroxide

AIBN

60 °C

n

S

S

S

DDAT

OOx

S

S

S

OO

OH

O

x

n

OO

OH

O

x

C12H25

C12H25

C12H25

Scheme I-19. Synthesis of P(t-BA)-b-PI block copolymer using DDAT as CTA via RAFT

process.73

Recently, Wooley et al.74 used the RAFT process to form amphiphilic diblock copolymers

consisting of poly(N-vinylpyrrolidinone) (PNVP) and polyisoprene. The synthesis began

with the polymerization of NVP employing conditions similar to Gnanou75, using

azobiscyanovaleric acid (ACVA) as initiator and DDAT as CTA in 1,4-dioxane at 80 °C.

After precipitation, the PNVP-macroCTA was then employed to mediate the

polymerization of isoprene using tert-butyl peroxide as the initiator at 125 °C (Scheme I-

20). The conditions used were similar to those employed by Jichum and Perrier68 and

Wooley and Germack71. The molecular weight characteristics of PNVP-b-PI were

determined by SEC: wM = 226,000 g.mol-1, nM = 77,800 g.mol-1and PDI = 2.90. The

copolymer contained 30 wt % of PI. Analysis of the copolymer by 1H NMR spectroscopy

showed also that the 1,4-microstructure is predominant. These block copolymers were

cross-linked with sulphur monochloride (S2Cl2) to produce a complex amphiphilic

network.


- 36 -

S

S

S

O

OH +

125 °C

t-butyl peroxide

ACVA

1,4-dioxane, 60 °C

n

S

S

S

DDAT

Ny

S

S

SOH

O

y

n

NOH

O

y

O N O

O

C12H25

C12H25

C12H25

Scheme I-20. Synthesis of PNVP-b-PI block copolymer using DDAT as CTA via RAFT

process.74

II.3 Using a combination of various polymerizations

In each of the polymerization systems described above, the formation of block copolymers

requires the same polymerization mechanism for two (or more) monomers. In some cases,

the preparation of well-defined block copolymers cannot undergo polymerization with the

same method. The site-transformation technique as described in section I of this Chapter

allows to obtain well-defined block copolymers by the combination of various

polymerization mechanisms.

II.3.1 Synthesis of AB diblock copolymers

Only a few reports described the preparation of AB diblock copolymers containing

polyisoprene using the combination of various polymerizations.

Hilllmyer et al.76 investigated the synthesis of polyisoprene-b-polylactide (PI-b-PLA)

diblock copolymers by a combination of living anionic polymerization and controlled

coordination-insertion polymerization (Scheme I-21). To make these diblock copolymers,

the polyisoprenyl lithium was first synthesized in cyclohexane with s-BuLi as the initiator


- 37 -

at 40 °C. The living chain-end is then capped with one ethylene oxide unit. After the

addition of hydrochloric acid, an intermediate polymer containing hydroxyl group at the

chain-end (PI-OH) is obtained. Then, the PI-OH polymer was dissolved in toluene

followed by the addition of triethylaluminum (AlEt3) under an argon atmosphere at 70 °C

leading to the macroinitiator PI-OAlEt2 which was further employed for the

polymerization of D,L-lactide. This reaction was finally terminated by the addition of

hydrochloric acid. Characteristics of the copolymer were determined by 1H NMR

spectroscopy ( nM = 3,600 g.mol-1) and SEC (PDI = 1.26).

+ s BuLi40 °C

Cyclohexanen

n-1Li

1.

2. HClOH

n

OHn

AlEt3, toluene

70 °COAlEt2

n

+ C2H6

OAlEt2n

D,L lactide

O

2. HCl

toluene, 70 °C1.

On

O

O

O

O

m

Scheme I-21. Synthesis of PI-b-PLA block copolymer by the combination of living

anionic polymerization and controlled coordination-insertion polymerization.76

Recently, Carpentier and coworkers77 reported the synthesis of a well-defined PI-b-PLA

diblock copolymer by a combination of living anionic polymerization of isoprene and the

stereoselective ring-opening polymerization of rac-lactide. The copolymer was synthesized

by a two-step sequential procedure.76,78-79 The first step involves the living anionic

polymerization of isoprene, followed by addition of ethylene oxide to end-capped

polymers (PI-OH). In the second step, an aluminium (1, Scheme I-22A) or yttrium (2,

Scheme I-22B) organometallic moiety is grafted onto PI-OH to get PI-O-[Al] or PI-O-[Y]

macroinitiators. The polymerization of rac-lactide with the macroinitiator PI-O-[Y]

occurred under much milder conditions (THF, 20 °C, 1 h) than those required for

PI-O-[Al] (toluene, 70 °C, 96 h). Moreover, the PI-O-[Al] macroinitiator undergoes an

isotactic PLA block as the PI-O-[Y] macroinitiator undergoes a heterotactic PLA block.

The resulting PI-b-PLA copolymers with an isotactic or a heterotactic PLA segment have

nM ≈ 13,600 g.mol-1and polydispersity index of 1.19 determined by SEC.


- 38 -

A)

OH

n R-Y[X2]

Me-Al[X'2]

O

n

Y[X2]

O

n

Al[X'2]

O

n

O

O O

O

O

O

OO

H

m

O

n

O

O O

O

O

O

OO

H

m

1. D,L-lactide

2. H+

PI b (het D,L PLA)

THF

20 °C

PI b (iso D,L PLA)

1. D,L-lactide

2. H+

toluene

70 °C

p q

t-Bu O

t-Bu

N N

O t-Bu

t-Bu

Al

Me

t-Bu

t-Bu

N

O Y O

t-Bu

t-BuO

THF

RMe

R = N(SiHMe2)2

B)

1

2

1

2

Scheme I-22. Synthesis of PI-b-PLA block copolymers by a combination of living anionic

polymerization and controlled organometallic-insertion polymerization: A) using an

aluminium based organometallic, and B) using an yttrium based organometallic.77

Miura and Miyake80 investigated the synthesis of polydimethylsiloxane-b-polyisoprene

diblock copolymers by the combination of anionic ring-opening polymerization (AROP) of

hexamethylcyclotrisiloxane (D3) and NMP of isoprene (Scheme I-23). In the first step, an

alkoxyamine (A, Scheme I-23) was treated with Li powder in ether (B, Scheme I-23)

suitable for the AROP of D3. The resulting functional PD3 was employed for the

polymerization of isoprene in bulk at 120 °C in order to obtain PD3-b-PI diblock

copolymer. Characteristics of the copolymer were determined by SEC ( nM = 10,100

g.mol-1, PDI = 1.15) and 1H NMR spectroscopy ( nM = 13,000 g.mol-1). In addition, the

PD3-b-PI was also used as a macroinitiator to prepare PD3-b-PI-b-PS triblock copolymers.


- 39 -

BrO N

PhLi, ether

RTLi

O N

Ph(+ LiBr)

D3

O N

PhCH3

m

n

D3

O N

Ph

CH3m

D3, THF

RT

n120 °C

D3 :

(A) (B)

SiO

SiO

Si

O

m

Scheme I-23. Synthesis of PD3-b-PI block copolymer by combination of AROP and

NMP.80

II.3.2 Synthesis of ABA triblock copolymers

The synthesis of ABA triblock copolymers based on isoprene and styrene by a

combination of anionic polymerization and atom transfer radical polymerization81-82

(ATRP) has been described by Matyjaszewski et al.83. The macroinitiator, polystyrene-b-

polyisoprene containing a 2-bromoisobutyryl bromide (BriBBr) chain-end (PS-b-PI-Br)

(Scheme I-24A) was prepared by anionic polymerization. For that, styrene was first

polymerized in toluene at −30°C using BuLi as initiator in dry box. Afterward, isoprene

was added to the solution. The living PS-b-PI−Li+ was chain extended with styrene epoxide

and then terminated by addition of BriBBr (Scheme I-24B). The macromolecular

characteristics of PS-b-PI-Br were determined by SEC ( nM = 16,800 g.mol-1 and

PDI = 1.03). The copolymer composition was determined by 1H NMR spectroscopy ( nDP

(PS) = 58 and nDP (PI) = 160). The PS-b-PI-Br was then used to initiate the

polymerization of styrene by ATRP in bulk at 110 °C using copper bromide (I) complexed

with N, N, N’, N’, N’’-pentamethyldiethylenetriamine (PMDETA) as a catalytic system to

form PS-b-PI-b-PS triblock copolymer. The resulting triblock copolymer had a number-

average molecular weight nM = 32,800 g.mol-1 and a PDI of 1.20.


- 40 -

+ s BuLi30 °C

LiPSTHF,

LI30 °C

PS b PITHFH2C CH

O

LIPS b PI CH2 CH O BrPS b PI CH2 CH O C

OBrBr C

O

CuBr, PMDETA, 110 °CPS b PI b PS

A)

BrPS b PI CH2 CH O C

OB)

m

n

x

Scheme I-24. Synthesis of PS-b-PI-b-PS block copolymer by combination of anionic

polymerization and ATRP: A) PS-b-PI-Br diblock copolymer, and B) PS-b-PI-b-PS

triblock copolymers.83


- 41 -

Conclusion

Well-defined block copolymers based on polyisoprene and other polymers can be

synthesized either by anionic polymerization, controlled/living radical polymerization or a

combination of various polymerizations. Of these techniques, controlled/living radical

polymerization methods have numerous advantages over the anionic polymerization as the

reactions can be performed under less stringent conditions and they can be applied to a

wide range of functional monomers. These advantages drive us to use controlled/living

radical polymerization and more precisely the RAFT polymerization to synthesize block

copolymers based on polyisoprene as NMP necessitates high temperatures for some

monomers such as styrene and the challenging synthesis of difunctional initiators. The

polyisoprene block is often obtained starting from the isoprene monomer but it can also be

obtained from a biomacromolecule, cis-1,4-polyisoprene, or so called natural rubber (NR).

In this case, telechelics from natural rubber (TNR) are necessary to synthesize block

copolymers. The transformation of NR into TNR can be obtained by chain cleavage

reaction of NR with a functionalization.

In this work, we propose two strategies to prepare AB diblock copolymers based on PI

using the RAFT process:

− starting from synthetic isoprene monomer,

− starting with TNR obtained by oxidative chain cleavage of NR and then chemically

modified by coupling reaction with a RAFT agent.

These PIs are used as macromolecular chain transfer agents (macroCTAs), and then chain

extended with t-BA using RAFT polymerization to make AB diblock copolymers. In

addition, we will demonstrate the synthesis of ABA triblock copolymers based on PI

obtained from a functional metathesis degradation of NR. Such degradation leads to

difunctional PI-macroCTAs which were employed for the RAFT polymerization of t-BA

to form ABA triblock copolymers.


- 42 -

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Chapter II

Synthesis of block copolymers based

on PI by RAFT process


- 45 -

Introduction

As mentioned in the previous chapter, the successful polymerization of isoprene via the

RAFT process was reported by Perrier et al.1 and by Wooley et al.2-3 Moreover, these

groups demonstrated the ability of RAFT polymerization to prepare AB diblock

copolymers and ABC triblock copolymers. For instance, Perrier et al.1 have prepared well-

defined poly(tert-butyl acrylate)-b-polyisoprene (P(t-BA)-b-PI) and polystyrene-b-

polyisoprene (PS-b-PI) block copolymers. In this study,1 P(t-BA) or PS is first prepared

and then used as a molecular chain transfer agent (macroCTA) to chain extend with

isoprene in order to prepare P(t-BA)-b-PI or PS-b-PI block copolymers. Moreover,

Wooley et al.2 have reported the RAFT polymerization of isoprene to target PI and chain

extended the PI-macroCTA with styrene to form PI-b-PS diblock copolymer. The same

group3 also reported the preparation of P(t-BA)-b-PI-b-PS triblock copolymers via RAFT

polymerization. In this case, P(t-BA) is synthesized first followed by RAFT

polymerization of isoprene. The resulting P(t-BA)-b-PI is then used as a macroCTA for

the RAFT polymerization of styrene.

The aim of the research work described in this chapter is to develop synthetic routes to

obtain well-defined block copolymers based on PI and P(t-BA) via RAFT polymerization.

These copolymers may find applications as compatibilizers for polymer blends,4 surface

modifiers5 and adhesive applications when the tert-butyl group is cleaved in order to form

acrylic acid.

Herein, PI-b-P(t-BA) diblock copolymer was prepared via RAFT polymerization. The

method of synthesis differs from the work by Wooley. et al3 as the blocks are prepared in

the reverse order. In this work, well-defined polyisoprene is first synthesized by RAFT

polymerization using S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate6 (1,

Scheme II-1) as a chain transfer agent. The resulting PI was used as macroCTA to mediate

the RAFT polymerization of t-BA to form PI-b-P(t-BA) block copolymers.


- 46 -

I. Synthesis and characterization of polyisoprene

RAFT polymerization of isoprene was carried out using S-1-dodecyl-S’-(α-α’-dimethyl-

α’’-acetic acid) trithiocarbonate (1, Scheme II-1) and tert-butyl peroxide (t-bp) as initiator

at 125 °C for 25h. Monomer conversion was determined via gravimetry and calculated to

be 49 % conversion.

C12H25S

S

SOH

O

1

C12H25S

S

SO

OH

x y z

0.2 eq t-bp

125 °C, 25h

190 eq1 eq

+

2

Scheme II-1. Synthesis of polyisoprene via RAFT polymerization of isoprene in bulk at

125 °C ([I]0/([1]0/([t-bp]0=190/1/0.2).

The resulting polymer was characterized by 1H NMR spectroscopy and 13C NMR

spectroscopy (Figure II-1) . 1H NMR spectroscopy of a representative polymer (Figure II-

1A) revealed the presence of polyisoprene resonances arising from all three major repeat

unit isomers.7-8 Peaks at 5.84-5.67 ppm, at 5.12 ppm, 4.98-4.81 ppm and at 4.75-4.61 ppm

are corresponding to methine protons, 11 (1,2-polyisoprene, -HC=CH2), methine protons,

7 (1,4-polyisoprene, C(CH3)=CH ), methylene protons 12 (1,2-polyisoprene backbone, -

HC=CH2) and methylene protons 16 (3,4-polyisoprene backbone, (CH3)C=CH2),

respectively. The ratio of each isomer was calculated from integrals of the peaks of the 1,2-

polyisoprene at the range of 5.84-5.67 ppm, integrals the peaks of the 3,4-polyisoprene at

the range of 4.75-4.61 ppm and integrals of the 1,4-polyisoprene at 5.12 ppm by 1H NMR

spectroscopy. The polymer obtained had a ratio of 90% of 1,4-polyisoprene, 6% of 3,4-

polyisoprene and 4% of 1,2-polyisoprene. This ratio is essentially the same as previously

reported for polyisoprene prepared by NMP9-10 and RAFT1-3 which showed a

microstructure of predominately 1,4-addition units.

The arrangement of the internal trans and cis units can be determined by the 13C NMR

spectroscopy.11-14 Figure II-1 shows the 13C NMR spectrum (Figure II-1C) and the

DEPT-135 spectrum (Figure II-1B ) of polyisoprene. The signals at 125.11 and at 124.46

ppm are assigned to the methine carbon, 7 (-C(CH3)=CH-) of the trans and cis-1,4-

polyisoprene units, respectively. The signal at 40.03 ppm corresponds to the methylene


- 47 -

carbon (4, -CH2-(CH3)C=CH-) in the trans-1,4-polyisoprene and the signal at 32.26 ppm

corresponds to methylene carbon (4, -CH2-(CH3)C=CH-) in the cis-1,4-polyisoprene. In

addition, it was observed the signal at 23.36 ppm corresponding to methyl carbon in cis-

1,4-polyisoprene (6, -C(CH3)=CH-), while it appears at 16.00 ppm in trans-1,4-

polyisoprene. 13C NMR spectroscopy (Figure II-1C ) was used to estimate the relative

contents of the cis- and trans-1,4-polyisoprene. The signal at 23.36 ppm corresponds to the

methyl carbon (6, -C(CH3)=CH-) in the cis-1,4-polyisoprene and the signal at 16.00 ppm

corresponds to the methyl carbon (6, -C(CH3)=CH-) in the trans-1,4-polyisoprene. The

areas under those peaks at 23.36 ppm and at 16.00 ppm obtained by inverse gated

decoupling are used to estimate the ratio of the cis- and trans-1,4-polyisoprene. The area

ratio indicates that there is about 40% of the cis- and 60% of the trans-1,4-polyisoprene.


- 48 -

CH2

S

S

SO

OH

x y z

C10H20CH3

1

2

34

5

6

7

89

11

10

12

13 14

15

1617

1819

20 21

22

11 10 9 8 7 6 5 4 3 2 1 ppm

1

2

311

7

12 16 -CHSC(S)S

9

6(trans-), 17

6(cis-)

14

4, 8, 13, 18

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

1

2210,15

5 (trans-)

5 (cis-)

7 (cis-)

7 (trans-)

1216

CDCl3

1318

19

4 (trans-)

6 (trans-)6 (cis-)

17

8(cis-)

8(trans-)

3

4 (cis-)

-CH

-CH

3

2

-CH

Figure II-1. A) 1H NMR spectrum, B) DEPT-135 spectrum and C) 13C NMR spectrum of

polyisoprene synthesized by RAFT polymerization of isoprene in bulk at 125 °C

([I] 0/([1]0/([t-bp]0=190/1/0.2).

Confirmation of successful RAFT polymerization of isoprene was further provided by

FTIR spectroscopy (Figure II-2) . A band was observed at 1700 cm-1 corresponding to the

C=O stretching band of carbonyl group and a band was observed at 1070 cm-1

A)

B)

C)


- 49 -

corresponding to the stretching band of C=S trithiocarbonate group15-16 at the chain-end. A

strong band at 1664 cm-1 was observed which corresponds to the C=C double bonds in

polyisoprene.

4000 3500 3000 2500 2000 1500 1000 500

-20

0

20

40

60

80

100

120

C=S

1070-C=C-

1664

-C=O

1700

Tra

nsm

ittan

ce (

%)

Wavenumber (cm-1)

Figure II-2. FTIR spectrum of polyisoprene synthesized by RAFT polymerization of

isoprene in bulk at 125 °C ([I]0/[1]0/[t-bp]0=190/1/0.2).

The number-average degree of polymerization of PI is equal to 90 ( nM = 6,500 g. mol-1)

by comparing the integration of methylene protons of the chain-ends, 3 (Figure II-1A) at

3.32 ppm to the integrations of the methine protons of the 1,4-polyisoprene repeating unit,

7 (Figure II-1A) at 5.12 ppm, of the 1,2-polyisoprene repeating unit, 11 (Figure II-1A) at

5.84-5.67 ppm and of the methylene protons of the 3,4-polyisoprene repeating unit, 16

(Figure II-1A) at 4.98-4.81 ppm. A molecular weight of nM = 9,200 g. mol-1 and

polydispersity index (PDI) = 1.23 was determined by SEC.

The 1H NMR spectroscopy, 13C NMR spectroscopy, FT-IR and SEC data,

show that the RAFT polymerization of isoprene has been successful and leads to a well-

defined ω-trithiocarbonyl-polyisoprene which can further be used as a macroCTA to target

new well-defined block copolymers.


- 50 -

II. Synthesis and characterization of polyisoprene-b-poly(tert-butyl

acrylate) block copolymers

We investigated the synthesis of a PI-b-P(t-BA) diblock copolymer using a PI as a

macroCTA (2, Scheme II-2). The reaction was performed in bulk at 60 oC and AIBN was

used as an initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0=250/1/0.2). Monomer conversion was

determined by following the disappearance of the vinyl peaks of t-BA at the range of 6.40

to 5.60 ppm in comparison with methyl protons of anisole used as an internal standard at

3.75 ppm by 1H NMR spectroscopy.

CH2

S

S

SO

OH

81 4 5

C10H20CH3

CH2

S

S

SO

OH

81

C10H20CH3

O O

72

54

0.2 eq AIBN

60 °C, 2.5h

O O250 eq

90

90

2

3

Scheme II-2. Synthesis of PI-b-P(t-BA) via RAFT polymerization of t-BA in bulk at

60 °C ([t-BA] 0/[PI-macroCTA]0/[AIBN] 0=250/1/0.2).

After a polymerization time of 4h, the t-BA conversion reaches 48% (Table II-1). The

block copolymer had a number-average molecular weight of 24,400 g. mol-1 and a

polydispersity index of 1.55 as determined by SEC. The overlaid of the SEC traces of

copolymers obtained at different reaction times is presented in Figure II-3 . It shows a shift

of the SEC chromatograms toward earlier retention times corresponding to higher

molecular weights when the reaction time increases (Table II-1 and Figure II-3) .

However, a high molecular weight shoulder appeared on SEC traces (Figure II-3) when

the monomer conversion reaches 48%. This indicates that the level of control is slightly


- 51 -

deteriorated; this is confirmed by PDI values, which increase from 1.23 to 1.55. This

phenomenon could be explained by the presence of termination by combination between

growing radical chains. This feature has already been observed in RAFT polymerizations

of acrylates (e.g. methyl acrylate, butyl acrylate).17-18 Previous work has shown that the

shoulder became more pronounced with conversion and was most evident for higher

molecular weight polymers. The Table II-1 shows that the best result in terms of monomer

conversion, nM and PDI was obtained after 2.5h. The number-average molecular weights

determined experimentally using SEC (Table II-1) for the diblock copolymers are in good

agreement with the theoretical calculated values. This confirms that there is a good control

over molecular weights.

Table II-1. Synthesis of PI-b-P(t-BA) diblock copolymers via RAFT polymerization of

t-BA in bulk at 60°C ([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2).

Copolymer Reaction time

(h)

conv.a

(%)

bcalnM ,

(g. mol-1)

cSECnM ,

(g. mol-1)

PDId

S-0 0.00 0 9200 9200 1.23

S-1 1.50 8 11 760 12 000 1.26

S-2 2.50 22 16 240 16 000 1.40

S-3 3.25 37 21 040 21 000 1.55

S-4 4.00 48 24 560 24 000 1.55 aMonomer conversion determined using 1H NMR spectroscopy. bNumber-average molecular weight

calculated using: calnM , = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0,

MM and MmacroCTA are the initial concentration of t-BA monomer, the initial concentration of polyisoprene macroCTA, the molecular weight of t-BA monomer and the molecular weight of the polyisoprene macroCTA respectively. cNumber-average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards. dPolydispersity index measured by SEC.


- 52 -

9 10 11 12 13 14 15 16 17 18

Retention time (mins)

PI

PI-b-P(t-BA)_1.5h

PI-b-P(t-BA)_2.5h

PI-b-P(t-BA)_3.25h

PI-b-P(t-BA)_4h

Figure II-3. Overlaid SEC traces of PI-macroCTA and PI-b-P(t-BA) diblock

copolymers synthesized via RAFT polymerization of t-BA in bulk at 60 °C

([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2).

The molar composition of the diblock copolymer was determined by comparing the

integral of the ethylenic proton, 7 (Figure II-4A) , of the 1,4-polyisoprene backbone (set

equivalent to the degree of polymerization of 81) at resonance at 5.12 ppm to the methine

proton, 23 (Figure II-4A), of P(t-BA) resonances at 2.4-2.1 ppm on the 1H NMR spectrum

of the copolymer (Figure II-4A) . It was found that the diblock copolymer contains 47% of

P(t-BA) for 53% of 1,4-polyisoprene. Therefore, the number-average degree of

polymerization )DP( n of PI is equal to 90 and the nDP of P(t-BA) is equal to 72. Finally,

the molar composition of the diblock copolymer is equal to 55.5% of PI and 44.5% of

P(t-BA).


- 53 -

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm

1

2

3

4, 8, 13, 18

23

27

26

7

6 (trans-), 17

6 (cis-)

9

11 12 16

CH2

S

S

SO

OH

81

C10H20CH3

1

2

34

5

6

7

89

11

10

12

13 14

15

1617

1819

20 21

22

O O

72

54

2327

25

26

24

2626 90

A)

B)

Figure II-4. A) 1H NMR spectrum, and B) 13C NMR spectrum of PI-b-P(t-BA) diblock

copolymer (S-2, Table II-1) synthesized via RAFT polymerization of t-BA in bulk at

60 °C ([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2).

The copolymer structure was further confirmed by the 13C NMR spectrum, (Figure II-4B)

which showed the carbonyl carbon resonance at 174.16 ppm and the quaternary carbon at

80.41 ppm corresponding to P(t-BA) and also presented carbon resonances at 135.39,

135.22, 125.30, and 124.50 ppm, corresponding to those observed for polyisoprene earlier

in this chapter. The data obtained from SEC, 1H NMR spectroscopy and 13C NMR

spectroscopy provides additional evidence for the formation of the AB diblock copolymer.

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

5 (trans-)5 (cis-)

7 (cis-)

7 (trans-)

1

6 (trans-)

6 (cis-)

17

4 (trans-)

26

2524

23

4 (cis-)


- 54 -

Conclusion

We have demonstrated that the RAFT polymerization of isoprene leads to well-defined

polyisoprenes (PI) with 90% of 1,4-PI (60% trans and 40% cis), 4% of 1,2-PI and 6% of

3,4-PI as determined by 1H NMR spectroscopy and 13C NMR spectroscopy. The nM is

equal to 6,500 g. mol-1 and PDI to 1.23 as determined by SEC. The formation of block

copolymers PI-b-P(t-BA) via RAFT mediated polymerization using the resulting PI as

macroCTA, was investigated. We found that the used of [t-BA] 0/[macroCTA]0/[AIBN] 0

equal to 250/1/0.2 in bulk at 60°C for 2.5h leads to a block copolymer with a good control

over molecular weight and relatively low polydispersity index (1.40). The copolymer had a

nM equal to 16,000 g. mol-1 as determined by SEC and a nDP (PI) of 90 and a nDP

(P(t-BA)) of 72 as determined by 1H NMR spectroscopy.

The optimized conditions previously determined to produce PI-b-P(t-BA) block

copolymers were employed to produce original block copolymers from natural rubber and

P(t-BA). In that case, polyisoprene was obtained by oxidative chain cleavage of natural

rubber and then chemically modified by coupling reaction with a RAFT agent. The results

are described in Chapter III.


- 55 -

Experimental section

General Characterization. NMR spectra were recorded on a Bruker Avance 400

spectrometer for 1H NMR (400 MHz) and 13C NMR (100 MHz). Chemical shifts are

reported in ppm relative to the deuterated solvent resonances. Molecular weights and

molecular weight distributions were measured using size exclusion chromatography (SEC)

on a system equipped with a SpectraSYSTEM AS 1000 autosampler, with a Guard column

(Polymer Laboratories, PL gel 5 µm Guard column, 50 × 7.5 mm) followed by two

columns (Polymer Laboratories, 2 PL gel 5 µm MIXED-D columns, 2 × 300 × 7.5) and

with a SpectraSYSTEM RI-150 detector. The eluent used was tetrahydrofuran (THF) at a

flow rate of 1 mL min-1 at 35°C. Narrow molecular weight linear polystyrene standards

(ranging from 580 g. mol-1 to 4.83 × 105 g. mol-1) were used to calibrate the SEC. Infrared

spectra were recorded on a Nicolet Avatar 370 DTGS FT-IR spectrometer in the 4000–500

cm-1 range with KBr pellets and controlled by OMNIC software.

.

Materials. All chemicals were purchased from Aldrich unless otherwise noted. Isoprene

monomer (I, Acros, 99%), tert-butyl acrylate (t-BA), 99%) was purified by passing

through neutral alumina column to remove inhibitor. 2,2-Azobis(2-methylpropionitrile)

(AIBN, 98%) was recrystallized into methanol prior to use. Anisole (99%) were used as

received. Dichloromethane (99%+) and methanol (99%) were distilled over CaH2 prior to

use. The RAFT agent, S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate, (1,

Scheme II-1) was synthesized as described in an earlier publication.6

General method for the preparation of polyisoprene by RAFT polymerization. RAFT

polymerization of isoprene was conducted with S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic

acid) trithiocarbonate (1, Scheme II-1) as RAFT agent and tert-butyl peroxide (t-bp) as the

initiator in a manner similar to that previously reported,2-3 ([I] 0/[1]0/[t-bp]0 = 190/1/0.2).

Because of the high volatility of isoprene and the high temperatures employed in the

polymerization thereof, only thick-walled glass flasks, free of visible defects, were used for

these experiments, each conducted with at least 50% of the volume of the flask remaining

free. Briefly, a solution of 6 mL (59.9 mmol) of isoprene, 0.115 g (0.3158 mmol) of 1,

0.0115 mL (0.0615 mmol) of t-bp were deoxygenated by bubbling with argon for 15 min,

and then changed from a rubber septum to a Teflon screw cock. Polymerization was


- 56 -

initiated by immersion in oil bath at 125°C. After 25 h, the reaction mixture was removed

from the oil bath and cooled under cold running water for 15 min. The polymer was

isolated by removal of excess isoprene in vacuo to give a crude product (2.1279 g) as clear

yellow oil. The crude product was diluted with 10 mL CH2Cl2 and precipitated twice into

methanol and dried in vacuo to give the final product as viscous, clear yellow oil. It was

then analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy, FTIR spectroscopy and

SEC. The final product consisted of 1.7779 g (83% yield based on 49% conversion via

gravimetry).

1H-NMR (CDCl3): δ (ppm) 5.84-5.67 (m, 1,2-polyisoprene backbone, -HC=CH2), 5.12

(br, cis-1,4-polyisoprene backbone, -C(CH3)=CH), 4.98-4.81 (m, 1,2-polyisoprene

backbone, -HC=CH2), 4.75-4.61 (m, 3,4-polyisoprene backbone, (CH3)C=CH2), 4.1-4.0

(br, chain-end, (-CH-SC(S)-S-), 3.32 (t, chain-end, -C(S)-SCH2(CH2)10CH3), 2.42–1.93

(br, polyisoprene backbone, -CH2C(CH3)=CH-CH2), 1.87 (br, 3,4-polyisoprene backbone,

-CH2-CH-) 1.67 (t, cis-1,4-polyisoprene backbone, -C(CH3)=CH) 1.60 (t, trans-1,4 and

3,4-polyisoprene backbone, -C(CH3)=CH), 1.13-1.48 (m, chain-end, -C(S)-SCH2-(CH2)10-

CH3), 0.98 (1,2-polyisoprene backbone, -C(CH3)-CH2), 0.88 (t, chain-end, -C(S)-S-

(CH2)11CH3).

13C NMR (CDCl3): δ (ppm) 184.37 (chain-end, -C=O), 147.78 (3,4-polyisoprene

backbone, -C(CH3)=CH2), 147.69 (1,2-polyisoprene backbone, -CH=CH2), 135.39 (trans-

1,4-polyisoprene backbone, -C(CH3)=CH-), 135.22 (cis-1,4-polyisoprene backbone,

-C(CH3)=CH-), 125.11 (cis-1,4-polyisoprene, -C(CH3)=CH-), 124.46 (trans-1,4-

polyisoprene, -C(CH3)=CH-), 115.93 (1,2-polyisoprene, -CH=CH2), 111.30 (3,4-

polyisoprene backbone, C(CH3)=CH2), 51.83 (1,2-polyisoprene backbone, -CH2-C(CH3)-),

50.27 (3,4-polyisoprene backbone, -CH2-CH-), 42.21 (chain-end, -C(CH3)2-),

40.03 (trans-1,4-polyisoprene, -CH2-(CH3)C=CH-), 38.48 (3,4-polyisoprene,

-HC(C(CH3)=CH2)-CH2), 36.89 (chain-end, C(S)-SCH2CH2-), 32.26 (cis-1,4-polyisoprene,

-CH2C(CH3)=CH-), 31.92, 29.64, 29.63, 29.57, 29.46, 29.35, 29.12, 28.95, 27.86 (chain-

end, -SCH2(CH2)9CH2CH3), 26.71 (trans-1,4-polyisoprene backbone, -C(CH3)=CH-CH2-),

26.38 (cis-1,4-polyisoprene, -C(CH3)=CH-CH2-), 23.36 (cis-1,4-polyisoprene,

-C(CH3)=CH-), 22.87 (3,4-polyisoprene, C(CH3)=CH2), 22.70 (chain-end,

-S(CH2)9CH2CH3), 16.0 (trans-1,4-polyisoprene, ,-CH2-C(CH3)=CH-), 14.14 (chain-end,

-C(S)-S-(CH2)11-CH3).


- 57 -

FTIR: ν (cm-1) 3035 (H-C=C), 2900−2730 (CH2, CH3), 1700 (chain-end, -C=O),

1665 (polyisoprene backbone, -C=C-), 1448 (polyisoprene backbone, -CH2), 1376

(polyisoprene backbone, -CH2), 1070 (chain-end, C=S), 836 (polyisoprene backbone, -CH)

SEC: nM = 9,200 g. mol-1, wM = 11,200 g. mol-1, PDI =1.23

RAFT polymerization of tert-butyl acrylate using PI-macroCTA. A typical procedure

is given for the polymerization of tert-butyl acrylate (t-BA) mediated by polyisoprene (2,

Scheme II-1) used as macroCTA and using AIBN as initiator

([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2). A magnetic stir bar was charged to a

Schlenk tube together with the PI-macroCTA (0.3216 g, 0.0495 mmol), t-BA (1.5832 g,

12.37 mmol), AIBN (0.0016 g, 0.0098 mmol), and anisole (0.09 mL, 5% v/v). Then, the

reaction mixture was degassed by three cycles of freeze pump-thaw, back-filled with Ar,

and sealed. The polymerization was initiated (t = 0) by immersion in a thermostatted oil

bath at 60°C. Samples were withdrawn from the reaction mixture via a degassed syringe

for conversion monitoring (by 1H NMR spectroscopy) and molecular weight analysis (by

SEC). At the end of reaction, the polymer solution was concentrated under vacuum using

rotary evaporation and was purified by a series of precipitations from dichloromethane

(minimum volume) into an ice cold 1:1 mixture of water and methanol. The copolymer

was separated by filtration and dried under vacuum until constant weight. It was then

further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC. Yield: 78%.

1H NMR (CDCl3): δ (ppm) 5.84-5.67 (m, 1,2-polyisoprene, -HC=CH2), 5.12 (br, 1,4-

polyisoprene, -C(CH3)=CH), 4.98-4.81 (m, 1,2-polyisoprene, -HC=CH2), 4.75-4.61

(m, 3,4-polyisoprene, (CH3)C=CH2), 3.32 (t, chain-end, -C(S)-SCH2(CH2)10CH3), 2.40-

2.15 (br, P(t-BA), -CH2-CHC(O)-), 2.42–1.93 (br, polyisoprene, -CH2C(CH3)=CH-CH2),

1.90-1.70 (br, P(t-BA), -CH2-CHC(O)-), 1.67 (t, cis-1,4-polyisoprene, -C(CH3)=CH),

1.60 (t, trans-1,4 and 3,4-polyisoprene, -C(CH3)=CH), 1.48-1.38 (br, P(t-BA),

-OC(CH3)3), 1.35-1.25 (m, chain-end, -C(S)-S-CH2-(CH2)10CH3), 1.22 (m, 1,2-

polyisoprene -CH2-C(CH3)-, and 3,4-polyisoprene, -CH2-CH-), 0.98 (1,2-polyisoprene, -

C(CH3)-CH2), 0.88 (t, chain-end, -C(S)-S-(CH2)11CH3).


- 58 -

13C NMR (CDCl3): δ (ppm) 174.16 (P(t-BA) backbone, -C(O)-O-), 135.39 (trans-1,4-

polyisoprene backbone, -C(CH3)=CH-), 135.22 (cis-1,4-polyisoprene backbone,

-C(CH3)=CH-) 125.11 (cis-1,4-polyisoprene, -C(CH3)=CH-), 124.27 (trans-1,4-

polyisoprene, -C(CH3)=CH-), 80.41 (P(t-BA) backbone, -C(O)-O-C(CH3)3), 42.42

(P(t-BA) backbone, -CHC(O)-O-C(CH3)3), 38.78 (trans 1,4-polyisoprene,

-CH2-(CH3)C=CH-), 38.48 (3,4-polyisoprene, -HC(C(CH3)=CH2)-CH2), 36.89 (chain-end,

C(S)-SCH2CH2-), 32.26 (cis-1,4-polyisoprene, -CH2C(CH3)=CH-), 31.92, 29.64, 29.63,

29.57, 29.46, 29.35, 29.12, 28.95, 27.86 (chain-end, -SCH2(CH2)9CH2CH3), 28.10 (P(t-

BA) backbone, -O-C(CH3)3), 26.75 (cis- 1,4-polyisoprene backbone, -CH2C(CH3)=CH-),

23.47 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 22.87 (3,4-polyisoprene,

C(CH3)=CH2), 22.70 (chain-end, -S(CH2)9CH2CH3), 16.0 (trans-1,4-polyisoprene, -CH2-

C(CH3)=CH- ), 14.14 (chain-end, -C(S)-S-(CH2)11-CH3).

SEC: nM = 16,000 g. mol-1, wM = 22,000 g. mol-1, PDI =1.40


- 59 -

References [1] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [2] Germack, D. S.; Wooley, K. L., J. Polym. Sci., Part A: Polym. Chem. 2007, 45,

4100-4108. [3] Germack, D. S.; Wooley, K. L., Macromol. Chem. Phys. 2007, 208, 2481-2491. [4] Wootthikanokkhan, J.; Tongrubbai, B., J. Appl. Polym. Sci. 2003, 88, 921-927. [5] Lu, Z.; Liu, G.; Liu, F., J. Appl. Polym. Sci. 2003, 90, 2785-2793. [6] Lai, J. T.; Filla, D.; Shea, R., Macromolecules 2002, 35, 6754-6756. [7] Chen, H. Y., Anal. Chem. 1962, 34, 1134-1136. [8] Chen, H. Y., Anal. Chem. 1962, 34, 1793-1795. [9] Benoit, D.; Harth, E.; Fox, P.; Waymouth, R. M.; Hawker, C. J., Macromolecules

2000, 33, 363-370. [10] Wegrzyn, J. K.; Stephan, T.; Lau, R.; Grubbs, R. B., J. Polym. Sci., Part A: Polym.

Chem. 2005, 43, 2977-2984. [11] Tanaka, Y.; Sato, H.; Kageyu, A., Polymer 1982, 23, 1087-1090. [12] Tanaka, Y.; Takagi, M., Biochem. J 1979, 183, 163-165. [13] Tanaka, Y.; Sato, H.; Kageyu, A.; Tomita, T., Biochem. J 1987, 243, 481-485. [14] Dai, L., Macromol. Chem. Phys. 1997, 198, 1723-1738. [15] Whalley, E., Can. J. Chem. 1960, 38, 2105-2108. [16] You, Y. Z.; Hong, C. Y.; Pan, C. Y., Macromol. Rapid Commun. 2002, 23, 776-780. [17] Chong, Y. K.; Krstina, J.; Le, T. P. T.; Moad, G.; Postma, A.; Rizzardo, E.; Thang, S.

H., Macromolecules 2003, 36, 2256-2272. [18] Moad, G.; Mayadunne Roshan, T. A.; Rizzardo, E.; Skidmore, M.; Thang San, H.,

ACS Symp. Ser. 2003, 854, 520-535.

Chapter III

Synthesis of natural rubber-based

telechelic cis-1,4-polyisoprenes and

their use to prepare block copolymers

via RAFT polymerization


- 60 -

Synthesis of natural rubber-based telechelic cis-1,4 polyisoprenes and

their use to prepare block copolymers via RAFT polymerization

Nitinart Saetung, Irène Campistron, Sagrario Pascual, Jean-Claude Soutif, Jean-François Pilard* and Laurent Fontaine*

LCOM-Chimie des Polymères, UCO2M, UMR CNRS 6011, Université du Maine, Avenue Olivier. Messiaen, 72085 Le Mans Cedex 09, France.

Fax: (+33 (0)2 43 83 37 54)

E-mail: [email protected]; [email protected]

Publication accepted in European Polymer Journal, Ref. No. EUROPOL-D-10-01369R1

Graphical abstract

(COCl)2n

mCPBAH5IO6

C12H25S

S

S OH

O

NH4(OAc)

m

OC12H25

S

S

SO

NH

m

OH2N

m

OC12H25

S

S

SO

NH

O O

k

60 °C, toluene

AIBN, t-BA


- 61 -

ABSTRACT : A new trithiocarbonate functionalized cis-1,4-polyisoprene was obtained

from oxidative degradation of natural rubber followed by reductive amination and

amidation. The structure of the resulting functionalized cis-1,4-polyisoprene was

confirmed by a combination of 1H NMR spectroscopy, 13C NMR spectroscopy, MALDI-

TOF mass spectrometry and FTIR spectroscopy. 1H NMR spectroscopy showed that the

trithiocarbonate functionality was equal to 1. The well-defined trithiocarbonyl-end

functionalized cis-1,4-polyisoprene was used as a macromolecular chain transfer agent

(macroCTA) to mediate the RAFT polymerization of t-BA using AIBN as the initiator ([t-

BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2) in toluene at 60 °C. The resulting PI-b-P(t-BA)

diblock copolymer presents an unimodal SEC trace shifted toward higher molecular weight

in comparison with the SEC trace of the macroCTA, indicating that the polymerization of

the second block is effective. The characteristics of the copolymer were determined by

SEC nM( = 26,000 g.mol-1, PDI = 1.76) and 1H NMR spectroscopy ( nDP (PI) = 62 and

nDP (P(t-BA) = 87).

Keywords: natural rubber, cis-1,4-polyisoprene, oxidative degradation, telechelics,

reversible addition fragmentation chain transfer (RAFT).

Introduction

The synthesis of functional polymers from renewable resources1-2 has attracted

considerable attention from polymer scientists throughout the world because of

environmental problems. Natural rubber (NR) is interesting to use for producing new

polymeric materials because it can be recyclable or degradable when exposed to

sunlight3-4, ozone5, and long term heating6-9 due to the unsaturation of the carbon-carbon

double bonds within the isoprene backbone. NR is also interesting for its strictly cis-1,4-

microstructure that provides materials with unique and special properties including good

elastomeric properties. In order to enhance potential applications of NR, numerous new

telechelic oligoisoprenes from NR with high content in cis-1,4-structure with precise

chain-end functionalities have been developed10. Redox reaction11-12, photochemical

reaction13-14, chemical oxidation15-18, as well as ozonolysis19, have been widely exploited to

produce telechelic cis-1,4-polyisoprene from natural rubber. In this respect, our group has

developed a selective degradation of natural rubber leading to new carbonyl telechelic cis-


- 62 -

1,4-polyisoprene via a two-step procedure20-22. These carbonyl telechelic polyisoprenes are

useful functional materials used as precursors for thermoplastic elastomers23,

biomaterials24 and polyurethane materials.21-22,25-26 Moreover, telechelic polyisoprene

could be obtained from synthetic cis-1,4-polyisoprene either by oxidative degradation25,27

or by metathesis degradation28-29. Telechelic polyisoprene could also be synthesized via the

ring-opening metathesis polymerization of 1,5-dimethyl-1,5-cyclooctadiene30. However,

by this method Grubbs et al.30 showed that there is a formation of a random distribution of

the various isomeric units along the chain resulting from cis-1,4 and trans-1,4-addition. By

contrast, natural rubber features only the cis-1,4-microstructure. To the best of our

knowledge, no work has been reported yet to prepare telechelic cis-1,4-polyisoprene from

natural rubber as precursor for controlled/living radical polymerization (CRP) in order to

obtain well-defined block copolymers.

Amongst CRP techniques, Nitroxide Mediated Radical Polymerization (NMP)31, Atom

Transfer Radical Polymerization (ATRP)32 and Reversible Addition/Fragmentation chain

transfer (RAFT)33-34 polymerization have been intensively used during the last decades to

produce block copolymers. The RAFT polymerization is probably the most versatile of the

commonly used CRP techniques as it is effective for a wide range of monomers and then,

leads to a wide range of block copolymers. In the RAFT process, generally block

copolymers are synthesized in two steps35. The first block was synthesized using a chain

transfer agent to control the number-average molecular weight, the molecular weight

distribution and the chain-end functionality of the polymer. Then, this well-defined block

is used as a macromolecular chain transfer agent (macroCTA) to synthesize the second

block.

In the present work, we report an original strategy for the synthesis of α-trithiocarbonyl-ω-

carbonyl-cis-1,4-polyisoprene (4, Scheme III-1) suitable to be used as macroCTA for

RAFT polymerization. The functionalized cis-1,4-polyisoprene (4, Scheme III-1) is then

used as monofunctional macroCTA to mediate the RAFT polymerization of tert-

butylacrylate to form AB diblock copolymers. To the best of our knowledge, no previous

studies have been reported on the synthesis of telechelic cis-1,4-polyisoprene suitable to be

used as macroCTA for RAFT polymerization.


- 63 -

n n-mm

O

1

mCPBA

CH2Cl2

H5IO6

THF m

OO

2

NH4(OAC)/NaBH(OAC)3

CH2Cl2, 24h, 25°Cm

OH2N3

C12H25S

S

S OH

O

2. (COCl)2,

CH2Cl2, 24h, 25°C

1.

m

OHN

OSS

C12H25

S

4

Scheme III-1. Synthesis of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene.

I. Synthesis of αααα-trithiocarbonyl- ωωωω-carbonyl-cis-1,4-polyisoprene

Herein, α-amino-ω-carbonylpolyisoprene21,25,37 (2, Scheme III-1) was reacted with S-1-

dodecyl-S’-(α-α’-dimehyl-α’’-acetic acid) trithiocarbonate (3, Scheme III-1) in the

presence of oxalyl chloride in dichloromethane at 25 °C for 24h. The resulting

functionalized polyisoprene (4, Scheme III-1) was characterized by 1H NMR

spectroscopy, 2D HSQC (Heteronuclear Single-Quantum Correlation) experiment, 13C

NMR spectroscopy and MALDI TOF mass spectrometry. The 1H NMR spectroscopy

(Figure III-1) showed new signals at 3.05 ppm and at 2.80-2.70 ppm corresponding to

methylene protons 7 (-CH2NHC(O)) and proton 6 (-NHC(O)), respectively. This result

indicated that the amidation between the amino group of oligoisoprene (2, Scheme III-1)

and in situ formed carboxylic chloride of RAFT agent (3, Scheme III-1) occurred and the

α-trithiocarbonyl-ω-carbonylpolyisoprene (4, Scheme III-1) was formed. 2D HSQC

experiment was used to confirm the structure of the functionalized polyisoprene. The 2D

HSQC spectrum is shown in Figure III-1. The signal at 3.05 ppm corresponding to

methylene protons in the 1H NMR spectrum was reasonably correlated with the signal at

45.00 ppm in the 13C NMR spectrum. Thus, it was confirmed that a new functionalized α-

trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4, Scheme III-1) was formed. Moreover,

an intense signal at 5.12 ppm in 1H NMR spectrum (Figure III-1) corresponding to vinylic

protons (9,-(CH3)C=CHCH2-) was observed, indicating that the 1,4-microstructure is

prominent. The 13C NMR spectroscopy (Figure III-2) was used to identify the 1,4-

microstructure of telechelic polyisoprenes.38 The signals observed at 135.23 (10,


- 64 -

-C(CH3)=CH-), 125.28 (9, -C(CH3)=CH-), 32.13 ppm (8’, -CH2C(CH3)=CH-), 26.36 (8, -

C(CH3)=CHCH2-), and 23.36 ppm (11, -C(CH3)=CH-) correspond to cis-1,4-polyisoprene

units.39 There are no signals at 131.20 ppm (-C(CH3)=CH-), 124.27 (-C(CH3)=CH-), 40.02

ppm (-C(CH3)=CHCH2-), 16.00 (-C(CH3)=CH-) characteristics of trans-1,4-polyisoprene

units40. This result confirmed that α-triocarbonyl-ω-carbonylpolyisoprene has a cis-1,4-

microstructure.


- 65 -

m

OHN

O

SS

SCH2

CH2

(CH2)9

1

2 3

4

5

68'

7

8

914

13

12

5

10

11

H3C

2'

10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 ppm

2.62.83.03.23.4 ppm

2.04

2.00

1

2

36

9

11

12

8,8'

145

7 , 2’

ppm

8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm

140

130

120

110

100

90

80

70

60

50

40

30

20

10

1

1

3

3

7

12

12

7

Figure III-1. 1H NMR spectrum and 2D HSQC spectrum of α-trithiocarbonyl-ω-carbonyl-

cis-1,4-polyisoprene (4, Scheme III-1).


- 66 -

m

OHN

O

SS

SCH2

(CH2)10

CH3

1

2

3

4

5

68'

7

8

914

13

12

5

10

11

220 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

1

88'10 9

12

3

11

134

14

27

Figure III-2. 13C NMR spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4,

Scheme III-1).

The reaction between the in situ formed carboxylic chloride of the RAFT agent (3, Scheme

III-1) and the α-amino group of functionalized polyisoprene (2, Scheme III-1) was further

studied by MALDI-TOF MS analysis by using dithranol as matrix with silver

trifluoroacetate as added salt. Figure III-3 shows an enlargement from 800 to 1400 g mol-1

of the MALDI-TOF-MS spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene.

There are two sets of peaks separated by an identical peak-to-peak mass increment, which

is equal to the molecular weight of the isoprene repeating unit (68 Da). Here, the two sets

of molecular ions are labelled as A’ and B’ (Figure III-3) in ascending order of m/z

magnitude. Each peak of set A’ is higher in intensity than the corresponding peak of set B’,

separated by 16 in m/z corresponding to the presence of an epoxide unit in the main chain.

These epoxide units come from the uncomplete oxidative chain cleavage reaction used to

prepare the initial carbonyl telechelic cis-1,4-polyisoprene and have been previously

observed25,41. The fragment ion at m/z = 814.62 of series A’ (Figure III-2) corresponds to


- 67 -

a polymer chain consisting of n =9 isoprene units ionized by a hydrogen atom with a

sulfonium (EG1, Scheme III-2) at one chain-end and a ketone group (EG2, Scheme III-2)

at the other chain-end. The theoretical mass calculated with the equation (1) is 814.65 Da

(monisotopic peak) in good agreement with the experimental values of 814.62 Da,

confirming the formation of such a structure. The occurrence of fragmentation during

ionization in the MALDI-TOF analysis of dithiocarbamate-terminated polymers has

already been reported42-46. A fragmentation pathway involving the protonation of the

trithiocarbonyl group followed by the heterolytic cleavage of S-C(S)S group could

occurred (Scheme III-2). This cleavage leads to the formation of the sulfonium species

(EG1, Scheme III-2) and a neutral molecule (5, Scheme III-2). This is in a good

agreement with the analysis in negative mode, which did not show C12H25 nor

C12H25SCS species. Each peak value was calculated according to the following equation

(1):

Mcal = MEG + nMisoprene (1)

where MEG is the mass of the end groups (⊕S-C6H11NO, EG1 and C3H5O, EG2) with an

average molecular mass = 202.09,) in the telechelic cis-1,4-polymer, Misoprene is the mass of

isoprene unit (molecular mass = 68) and n is the number of repeating units.

m

ONHC12H25S

S

SO

m

ONHS

Ouν+ C13H26S2

EG1

19 kV

EG2H

4 4' 5

Scheme III-2. End groups observed during MALDI-TOF MS measurements.


- 68 -

Figure III-3. MALDI-TOF mass spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-

polyisoprene

The data obtained from 1H NMR spectroscopy and MALDI TOF mass spectrometry

provide evidence for the formation of the new α-trithiocarbonyl-ω-carbonyl-cis-1,4-

polyisoprene with a number-average molecular weight ( nM ) of 12,000 g mol-1and

polydispersity index of 1.60 as determined by SEC. The number-average degree of

polymerization equal to 62 ( nM = 4650 g mol-1) was calculated from 1H NMR spectrum

by comparing the integration of methylene protons of the chain-ends at 2.43 ppm (12,

Figure III-1) to the integration of the methine proton of the isoprene backbone at 5.12

ppm (9, Figure III-1) . The different nM values between SEC and 1H NMR spectroscopy

are attributed to the fact that polystyrene standards calibration was used to determine the

average molecular weights.

The average trithiocarbonyl functionality )( nf of α-trithiocarbonyl-ω-carbonyl-cis-1,4-

polyisoprene was determined by 1H NMR spectroscopy, by comparing the integration of


- 69 -

the methylene protons at 2.43 ppm (12, Figure III-1) with the one of the methylene

protons at 3.25 ppm (3, Figure III-1) . The integration of their respective peaks showed

complete trithiocarbonate functionality by 1H NMR spectroscopy (Figure III-1) that

agrees with a 1:1 theoretical ratio. Therefore, α-trithiocarbonyl-ω-carbonyl-cis-1,4-

polyisoprene can subsequently be used as a monofunctional macroCTA for the chain

extension reaction in order to form diblock copolymers.

II. Synthesis of PI-b-P(t-BA) diblock copolymer

We investigated the synthesis of a PI-b-P(t-BA) diblock copolymer using a purified α-

trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4, Scheme III-3) as a macromolecular

chain transfer agent (macroCTA). The reaction was performed in toluene at 60 oC and

AIBN was used as an initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2) (6, Scheme

III-3) . Monomer conversion was determined by following the disappearance of the vinyl

peaks of t-BA at the range of 6.40 to 5.60 ppm in comparison with methyl protons of

anisole used as an internal standard at 3.75 ppm by 1H NMR spectroscopy. Table III-1

shows that the t-BA conversion increases with time and reaches 39% after 5h. Moreover,

the number-average molecular weights of the block copolymer increase with t-BA

conversion. SEC traces in Figure III-4 shows a shift towards higher number-average

molecular weights indicating that the α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene

(4, Scheme III-3) was extended into a block copolymer. Moreover, the SEC traces of the

so obtained block copolymers are unimodals illustrating that the polymerization of the

second block underwent chain transfer quantitatively. The molar composition of block

copolymer (S-4, Table III-1) was analyzed by 1H-NMR spectroscopy. The number

average degree of polymerization )DP( n of PI was equal to 62 and that of P(t-BA) was

equal to 87 as calculated by comparing the integral of the ethylenic proton, (8, Figure III-

5) of the polyisoprene backbone at 5.12 ppm to the methine proton, (4, Figure III-5) of

P(t-BA) at 2.4-2.1 ppm on the 1H NMR spectrum of the copolymer (Figure III-5) . The

data obtained from SEC and 1H NMR spectroscopy provide additional evidence for the

formation of the AB diblock copolymer based on the cis-1,4-polyisoprene from natural

rubber.


- 70 -

m

OC12H25

S

S

SO

NH

4

60 °C, toluene

O O

0.2 eq. AIBN

m

OC12H25

S

S

SO

NH

O O

k

6

250 eq.

Scheme III-3. Synthesis of PI-b-P(t-BA) by RAFT polymerization using α-trithiocarbonyl-

ω-carbonyl-cis-1,4-polyisoprene as macroCTA.

Table III-1. Synthesis of AB diblock copolymers via RAFT polymerization of tert-butyl

acrylate (t-BA) using the PI as macroCTA and AIBN as initiator at 60°C in toluene.

Copolymer

Reaction time

(h)

conv.a

(%)

b,calnM

(g mol-1)

c,SECnM

(g mol-1)

PDId

S-1 1 2 12 640 13 000 1.55

S-2 2 4 13 280 13 500 1.55

S-3 4 21 18 720 19 000 1.55

S-4 5 39 24 480 26 000 1.76 aMonomer conversion determined using 1H NMR spectroscopy. bNumber average molecular weight

calculated using: calcnM , = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0, MM and MmacroCTA are the initial concentration of t-BA monomer, the initial concentration of ∝-trithicarbonyl-ω-carbonyl-cis-1,4-polyisoprene macroCTA, the molecular weight of t-BA monomer and the molecular weight of the ∝-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene macroCTA respectively. cNumber average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards. dPolydispersity index measured by SEC.


- 71 -

Figure III-4. Overlaid SEC traces using UV detection at a wavelength of 309 nm of PI

macroCTA and PI-b-P(t-BA) diblock copolymers.

1

2

3

4

6

7

895

62

OCH2

S

S

SO

NH

O O

87

(CH2)10

66

7' 10

11

H3C

1.01.52.02.53.03.54.04.55.05.56.0 ppm

3.33.43.5 ppm

3

9

4

5 1

2

1011

7,7' 6

8

Figure III-5. 1H NMR spectrum of PI-b-P(t-BA) diblock copolymer (S-4, Table III-1).


- 72 -

Conclusion

A new well-defined α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene was successfully

synthesized from α-amino-ω-carbonyl-cis-1,4-polyisoprene through coupling reaction with

S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate. The chain-end

functionality was confirmed by 1H NMR spectroscopy: the average trithiocarbonyl

functionality was equal to 1. The controlled chain extension of so obtained trithiocarbonyl-

functionalized-cis-1,4-polyisoprene with t-BA successfully formed PI-b-P(t-BA) diblock

copolymers through the RAFT polymerization process. This report is the first example of

diblock copolymer based on natural rubber-based polyisoprene, thus providing valuable

building blocks from a renewable raw material.

Acknowledgments: The authors wish to thank French Ministry of Education and Research

and Prince of Songkla University, Thailand, for their financial support.


- 73 -

Experimental Section


spectrometer for 1H NMR (400 MHz) and 13C NMR (100 MHz). Chemical shifts are

reported in ppm relative to the deuterated solvent resonances. Molecular weights and

molecular weight distributions were measured using size exclusion chromatography (SEC)

on a system equipped with a SpectraSYSTEM AS 1000 autosampler, with a Guard column

(Polymer Laboratories, PL gel 5 µm Guard column, 50 × 7.5 mm) followed by two

columns (Polymer Laboratories, 2 PL gel 5 µm MIXED-D columns, 2 × 300 × 7.5) and

with a SpectraSYSTEM RI-150 detector. The eluent used was tetrahydrofuran (THF) at a

flow rate of 1 mL min-1 at 35°C. Narrow molecular weight linear polystyrene standards

(ranging from 580 g mol-1 to 4.83 × 105 g mol-1) were used to calibrate the SEC. Infrared

spectra were recorded on a Nicolet Avatar 370 DTGS FT-IR spectrometer in the 4000-500

cm-1 range with KBr pellets and controlled by OMNIC software. Matrix-assisted laser

desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded on a

Bruker Biflex III equipped with a nitrogen laser (lZ337 nm). Solutions of dithranol (20

mg/ml), end-functional polymer (10 mg/ml), and silver trifluoroacetate (10 mg/ml) were

made in tetrahydrofuran. These solutions were mixed in the ratio matrix:cationizing

salt:polymer as for 10:1:2, and 1 ml of the solution was deposited on the sample holder. All

mass spectra were obtained in the linear mode with an acceleration voltage of 19 kV. The

delay time was 200 ns. Typically, 100 single-shot acquisitions were summed to give a

composite mass spectrum. All data were reprocessed using the Bruker XTOF software.

Materials. All chemicals were purchased from Aldrich unless otherwise noted. Toluene

(99%), 2-propanol (99%) (Fisher Scientific) and anisole (99%) were used as received.

Dichloromethane (99%+) and methanol (99%) were distilled over CaH2 prior to use. tert-

Butyl acrylate (t-BA, 99%) was purified by passing through neutral alumina column to

remove inhibitor. 2,2-Azobis(2-methylpropionitrile) (AIBN, 98%) was recrystallized into

methanol prior to use. The RAFT agent, S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid)

trithiocarbonate, (3, Scheme III-1) was synthesized as described in an earlier publication.36

The α-amino-ω-carbonyl-cis-1,4-polyisoprenes (2, Scheme III-1) were obtained from

initial carbonyl telechelic cis-1,4-polyisoprene (1, Scheme III-1) through reductive

amination according to procedure previously reported by our group.21,25,37


- 74 -

Synthesis of αααα-trithiocarbonyl- ωωωω-carbonyl-cis-1,4-polyisoprene. Under an argon

atmosphere, (COCl)2 (1.5 mL, 17 mmol) was added dropwise to S-1-dodecyl-S’-(α-α’-

dimehyl-α’’-acetic acid) trithiocarbonate (3, Scheme III-1) (0.57 g, 1.56 mmol) at 25°C

under a rapid stirring. After 4.5 h, the excess of (COCl)2 was removed under vacuum. A

solution of α-amino-ω-carbonyl cis-1,4-polyisoprene (2, Scheme III-1) (4.5 g, 1.05 mmol)

dissolved in 20 mL dichloromethane was added to the previous solution under an argon

atmosphere. The resulting solution was stirred at 25 °C for 24 h and then, concentrated

under vacuum. The polymer was precipitated twice by dissolving it in dichloromethane

(minimum volume) and precipitated into methanol (50 mL). The isolated polymer was

dried under vacuum to remove any traces of solvent. It was then analyzed by 1H NMR

spectroscopy, 13C NMR spectroscopy, FTIR spectroscopy and SEC. Yield: 76%.

1H-NMR (CDCl3): δ (ppm) 5.12 (br, polyisoprene backbone -(CH3)C=CHCH2), 3.25 (t,

chain-end, -SCH2CH2(CH2)9CH3), 3.05 (m, chain-end, -CH2NHC(O)) 2.80-2.70 (br, chain-

end, -NHC(O)), 2.43 (t, chain-end, CH3COCH2CH2), 2.25 (m, -C(O)CH2CH2), 2.13 (s,

chain-end, CH3COCH2), 2.04 (br, polyisoprene backbone, -CH2C(CH3)=CH-CH2 ), 1.75

(s, chain-end, -SC(CH3)2C(O)NH-), 1.70-1.60 (s, polyisoprene backbone, -C(CH3)=CH

and chain-end, -SCH2CH2(CH2)9CH3), 1.18-1.4 (m, chain-end, - SCH2CH2(CH2)9CH3),

0.88 (t, chain-end,(-CH2)10)CH3).

13C NMR (CDCl3): δ (ppm) 208.45 (chain-end, -(CH3)C(O)), 135.23 (cis-1,4-polyisoprene

backbone, -C(CH3)=CH-), 125.28 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 45.00

(chain-end, -CH2NHC(O)), 43.91 (chain-end, -(CH3)C(O)CH2), 37.41, (chain-end,

-SCH2CH2(CH2)9CH3), 32.13 (cis-1,4- isoprene backbone, -CH2C(CH3)=CH-), 31.85

(chain-end, -S(CH2)2CH2(CH2)8CH3), 29.77 (chain-end, -S(CH2)3CH2(CH2)7CH3), 29.57



(chain-end, -S(CH2)8CH2(CH2)2CH3), 28.86 (chain-end, -S(CH2)10CH2CH3), 27.92 (chain-

end, -SCH2CH2 (CH2)9CH3), 26.36 (cis-1,4-polyisoprene backbone, -C(CH3)=CHCH2-),

23.36 (1,4-cis-polyisoprene backbone -C(CH3)=CH-), 22.63 (chain-end, -

S(CH2)9CH2CH2CH3), 22.22 (chain-end, (CH3)C(O)-), 14.06 (chain-end, -CH3).


- 75 -

FTIR: ν (cm-1) 3400 (HN), 3035 (H-C=C), 2900-2730 (CH2, CH3), 1721 (chain-end, -

C=O), 1666 (polyisoprene backbone, -C=C-), 1448 (polyisoprene backbone, -CH2), 1376

(polyisoprene backbone, -CH2), 1075 (chain-end, -C-S), 836 (isoprene backbone, -CH),

SEC: nM = 12,000 g/mol-1, wM = 19,200 g/mol-1, PDI =1.60

A typical RAFT polymerization. A typical procedure is given for the polymerization of

tert-butyl acrylate (t-BA) mediated by the α-trithiocarbonyl-ω-carbonyl-cis-1,4-

polyisoprene. (4, Scheme III-1) used as macromolecular chain transfer agent (macroCTA)

and using AIBN as initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2). A magnetic stir

bar was charged to a Schlenk tube together with the macroCTA (0.4337 g, 0.093 mmol), t-

BA (2.976 g, 23.25 mmol), AIBN (0.0030 g, 0.018 mmol), toluene (0.8 mL, 20% v/v) and

anisole (0.17 mL, 5% v/v). Then, the reaction mixture was deoxygenated by bubbling with

argon for 15 min. The polymerization was initiated (t = 0) by immersion in a thermostated

oil bath at 60°C. Samples were withdrawn from the reaction mixture via a degassed

syringe for conversion monitoring (by 1H NMR spectroscopy) and molecular weight

analysis (by SEC). At the end of reaction, the polymer solution was concentrated under

vacuum using rotary evaporation and was purified by a series of precipitations from

dichloromethane (minimum volume) into an ice cold 1:1 mixture of water and methanol.

The copolymer was separated by filtration and dried under vacuum until constant weight. It

was then further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC. 1H NMR (CDCl3): δ (ppm) 5.12 (br, polyisoprene backbone -C(CH3)=CH), 3.25 (t, chain-

end, -SCH2CH2(CH2)9CH3), 2.43 (t, chain-end, CH3COCH2CH2), 2.40-2.15 (br, P(t-BA)

backbone -CH2-CHC(O)-), 2.13 (s, chain-end, CH3COCH2), 2.12-1.95 (br, polyisoprene

backbone, -CH2C(CH3)=CH- and -C(CH3)=CHCH2-), 1.90-1.75 (br, P(t-BA) backbone -

CH2-CHC(O)-), 1.72 (s, chain-end, -SC(CH3)2C(O)NH-), 1.70-1.60 (br, polyisoprene

backbone, -C(CH3)=CH-, and chain-end, -SCH2CH2(CH2)9CH3), 1.55-1.30 (br, P(t-BA)

backbone -OC(CH3)3), 1.20-1.40 (chain-end, -SCH2CH2(CH2)9CH3), 0.86 (chain-end,

S(CH2)11CH3).

13C NMR (CDCl3): δ(ppm) 174.16 (P(t-BA) backbone, -C(O)-O-), 135.23 (cis-1,4-

polyisoprene backbone, -C(CH3)=CH-), 125.28 (cis-1,4-polyisoprene backbone,

-C(CH3)=CH-) 80.20 (P(t-BA) backbone, -C(O)-O-C(CH3)3), 42.16 (P(t-BA) backbone,


- 76 -

-CHC(O)-O-C(CH3)3), 37.20, -SCH2CH2(CH2)9CH3), 32.03 (cis-1,4-polyisoprene

backbone, -CH2C(CH3)=CH-), 31.85 (chain-end, -S(CH2)2CH2(CH2)8CH3), 29.77 (chain-

end, -S(CH2)3CH2(CH2)7CH3), 29.57 (chain-end, -S(CH2)4CH2(CH2)6CH3), 29.46 (chain-



end, -S(CH2)10CH2CH3), 27.92 (chain-end, -SCH2CH2(CH2)9CH3), 26.36 (1,4-cis-

polyisoprene backbone -C(CH3)=CHCH2-), 23.44 (cis-1,4-polyisoprene backbone -

C(CH3)=CH-), 22.70 (chain-end, -S(CH2)9CH2CH2CH3), 22.22 (chain-end, (CH3)C(O)-),

14.14 (chain-end, -CH3).

SEC: : nM = 26,000 g.mol-1, wM = 45,800, PDI = 1.76


- 77 -

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Chapter IV

One-pot synthesis of natural rubber-

based telechelic cis-1,4-polyisoprene

and their use to prepare block

copolymers by RAFT polymerization


- 79 -

One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes

and their use to prepare block copolymers by RAFT polymerization.

Nitinart Saetung, Irène Campistron, Sagrario Pascual, Jean-Claude Soutif, Jean-François

Pilard* and Laurent Fontaine*

LCOM-Chimie des Polymères, UCO2M, UMR CNRS 6011, Université du Maine, Avenue

Olivier. Messiaen, 72085 Le Mans Cedex 09, France.

Fax: (+33 (0)2 43 83 37 54)

E-mail: [email protected]; [email protected]

Publication accepted in Macromolecules, DOI: 10.1021/ma102406w

Graphical abstract

n

C12H25S S

OS

O

OS S

C12H25

O

S

C12H25S S

S

S SC12H25

SqO O O O

m m

1) Grubbs II catalyst

2) t-butyl acrylate/ AIBN

+

P(t-BA)-b-PI-b-P(t-BA) triblock copolymer


- 80 -

ABSTRACT : We investigate the one-pot synthesis of a new α,ω-bistrithiocarbonyl-end

functionalized telechelic cis-1,4-polyisoprene (PIp) via metathesis degradation from

natural rubber (NR) in the presence of the Grubbs second generation catalyst (GII) and a

bistrithiocarbonyl-end functionalized olefin as a chain transfer agent (CTA). When the

metathesis degradation of the NR of 2x106 g mol-1 molecular weight is performed in

toluene at 25 °C using the ratio of [Ip]0/[GII] 0/[CTA] 0 = 100/1/1, a cis-1,4-polyisoprene of

14,000 g mol-1 after 4h is obtained. The functionality estimated by 1H NMR spectroscopy

is equal to 1.5±0.1. The structure of telechelic cis-1,4-polyisoprene was confirmed by

combination of 1H NMR, 13C NMR spectroscopy and FTIR. The influence of the CTA

concentration was investigated. It was found that using concentrations of catalyst

([Ip] 0/[GII] 0/[CTA] 0 of 100/1/2 and 100/1/5 lead to form a perfectly telechelic cis-1,4-

polyisoprene with a functionality of 2 with no significant difference in nM values

(approximately 6,400 g mol-1) and in polydispersity indices (∼1.70). The new well-defined

α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprenes were used

successfully as macromolecular chain transfer agents (macroCTA) to mediate the RAFT

polymerization of t-BA using AIBN as the initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 =

500/1/0.4) in toluene at 60 °C leading to well-defined P(t-BA)-b-PIp-b-P(t-BA) triblock

copolymers.

Keywords: natural rubber, cis-1,4-polyisoprene, metathesis degradation, telechelics,

triblock copolymers, RAFT polymerization.

Introduction

Telechelic unsaturated polymers are good candidates to obtain block copolymers with a

wide range of applications. For instance, block copolymers containing polyisoprene (PIp)

as a constituent have found applications as nanofibers1, thermoplastic elastomers,2 pressure

sensitive adhesives,3-4 and biocompatible materials.5-6 The PIp block is essentially

synthesized by living anionic polymerization of isoprene (Ip),7-16 by controlled/living

radical polymerization (CRP) of isoprene,17-27 or ring-opening metathesis polymerization

of 1,5-dimethyl-1,5-cyclooctadiene.28 The cis-1,4-polyisoprene block can be obtained from

natural rubber (NR) which is a biomacromolecule and a renewable resource. It is well

known that strictly cis-1,4-microstructure of NR provides unique and special properties,


- 81 -

including good elastomeric properties, very low glass transition temperature, excellent

flexibility, good “green” strength and building tack. Therefore, the synthesis of telechelic

cis-1,4-polyisoprene from NR (TNR) opens new synthetic routes to develop materials

based on a biopolymer from a renewable resource. The block copolymers obtained from

NR can lead to new materials with properties suitable for a number of potential

applications including microemulsion elastomers29 for the paint industry, adhesives3-4 and.

nanoporous materials.30 The transformation of NR into TNR can be obtained by combining

chain cleavage reaction of NR with a postfunctionalization reaction. The most widely used

methods to produce TNR derivatives are controlled oxidative degradation,

photodegradation or metathesis degradation.31 Our group has focused on selective

degradation of synthetic cis-1,4-polyisoprene using well-controlled oxidative chain

cleavage reaction leading to new carbonyl telechelic cis-1,4-polyisoprene32 and the

chemical modification of carbonyl end-groups has led to the development of new

hydroxyl6,33 and amino telechelic polyisoprenes.34 The hydroxyl telechelic polyisoprene

was engaged as a precursor in the synthesis of linear polyurethanes for biological

materials6 and foams applications.35-36 However, this technique requires several steps to

obtain the precursor of the desired products. Alternatively, we have also developed a

method for the preparation of acetoxy-telechelic polyisoprene in a single-step process via

the metathesis degradation of cis-1,4-polyisoprene.37-38 To the best of our knowledge, no

study has been reported on the single-step synthesis of telechelic cis-1,4-polyisoprene

suitable to be employed as precursors for controlled/living radical polymerizations (CRPs)

in order to obtain block copolymers. Among CRP techniques,39 Reversible

Addition/Fragmentation chain Transfer (RAFT) polymerization40 is recognized as one of

the most versatile method for the synthesis of block copolymers since it is compatible with

a wide range of unprotected polar monomers41 including acrylic acid.42 The most common

RAFT chain transfer agent (CTA) contains thiocarbonylthio groups that are easily removed

or modified by a variety of methods.43

Herein, we have investigated the one-pot synthesis of original telechelic cis-1,4-

polyisoprenes (PIp) through a metathesis degradation of NR using Grubbs second

generation catalyst and a bistrithiocarbonyl-end functionalized olefin as a CTA (2, Scheme

IV-1A ). The resulting PIp were used as difunctional macroCTAs to mediate the

polymerization of tert-butyl acrylate to form ABA triblock copolymers via the RAFT

process. To the best of our knowledge, no previous studies have been reported on the one-


- 82 -

pot synthesis of α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene

suitable to be used in RAFT polymerization.

n

[Ru]

+

[Ru]O

S SC12H25

O

S+

C12H25S S

OS

O

OS S

C12H25

O

S

p6

3

5'

4

5

B)

[Ru] [Ru]

m m'

C12H25S S

OS

O

n

p'6'

C12H25S S

OS

O

[Ru]

n'

+

7

C12H25S S

OS

O

OS S

C12H25

O

Sq

NN

Ru

PCy3

Ph

Cl

Cl

[Ru]Ph

:

[Ru]Ph

1. (COCl)2, 20 °C

HO OH1

2

C12H25S S

OHS

O

C12H25S S

OS

O

OS S

C12H25

O

S2.

Toluene, 25 °C

15 min.

A)

[Ru]O

S SC12H25

O

S33'

C12H25S S

OS

O Ph

+

Scheme IV-1. A) Synthesis of a bistrithiocarbonyl-end functionalized CTA and, B)

synthesis of α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene from

NR via metathesis degradation.


- 83 -

I. Functional Metathesis Degradation.

Herein, we investigated the synthesis of α,ω-bistrithiocarbonyl-end functionalized

telechelic cis-1,4-polyisoprene via metathesis degradation of NR using Grubbs second

generation catalyst (GII) and a bistrithiocarbonyl-end functionalized olefin (2) as the CTA

(Scheme IV-1). The difunctional CTA was reacted with Grubbs II catalyst in a

stoichiometrical ratio in toluene-d8 at 25 °C and the resulting product analyzed by 1H NMR

spectroscopy (Figure IV-1) and 2D-correlation spectroscopy (COSY) (Figure IV-2). New

peaks were observed in 1H NMR spectrum (Figure IV-1) at 5.35 ppm and 4.14 ppm that

are attributed to the olefinic proton, 1’([Ru]=CHCH2OC(O)-R) and to aliphatic proton, 2’

([Ru]=CHCH2OC(O)-R), respectively. In addition, new peaks were found at 4.36 ppm, at

5.87-5.80 ppm and at 6.15-6.10 ppm corresponding to 2’’ (Ph-CH=CHCH2OC(O)-R), to 4

(Ph-CH=CHCH2OC(O)-R), and to 4’ (Ph-CH=CHCH2OC(O)-R), respectively. COSY

two-dimensional NMR experiment was used to confirm these structures. In the COSY

spectrum (Figure IV-2), the signal at 4.14 ppm corresponding to aliphatic proton 2’ is

correlated with the signal centred at 5.35 ppm, corresponding to the olefinic proton, 1’. We

can also observe the correlation between the signals 6.15-6.10 ppm and 5.87-5.80 ppm,

corresponding to alkenes proton 4’ and 4, with the signal at 4.36 ppm, corresponding to

aliphatic proton 2” . Thus it was confirmed that the Grubbs II catalyst reacts with

difunctional CTA (2, Scheme IV-1A) to result in the new ruthenium carbene molecule (3,

Scheme IV-1A). This new catalyst (3, Scheme IV-1A) undergoes the metathesis

degradation at 25 °C with double bonds of NR (4, Scheme IV-1B) to form α,ω-

bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene (7, Scheme IV-1B).

Therefore, the one-pot degradation and functionalization reactions can continuously take

place in a catalytic fashion.


- 84 -

[Ru]

C12H25S

S

SO

O O

OS

S

SC12H25

O

OS

S

SC12H25

[Ru]

Ph

+

+

C12H25S

S

SO

O

Ph1

2

3

2'

2"

4

1'

4'

25 °C

Toluene-d8

4.55.05.56.06.57.07.5 ppm

4.55.05.56.06.57.07.5 ppm

4.55.05.56.06.57.07.5 ppm192021 ppm

192021 ppm

192021 ppm

1

1'

3

2

2'

2"44'

1'

Figure IV-1. 1H NMR spectra (toluene-d8), A) the resulting mixture solution between

CTA and Grubbs II catalyst, B) CTA, and C) Grubbs II catalyst.

A)

B)

C)


- 85 -

[Ru]

C12H25S

S

SO

O O

OS

S

SC12H25

O

OS

S

SC12H25

[Ru]

Ph

+

+

C12H25S

S

SO

O

Ph1

2

3

2'

2"

4

1'

4'

25 °C

Toluene-d8

ppm

4.04.55.05.56.06.57.0 ppm

4.0

4.5

5.0

5.5

6.0

6.5

7.0

2'

2"44'

1'

2'

2"

4

4'

1'

Figure IV-2. COSY spectrum (toluene-d8) of the resulting mixture solution between CTA

and Grubbs II catalyst.

A first attempt for the preparation of telechelic NR (entry A-2, Table IV-1) was

performed in toluene using Grubbs II catalyst and bistrithiocarbonyl-end functionalized

olefin (2, Scheme IV-1A) as the CTA. The reaction was carried out at room temperature

for 4h with a ratio [Ip]0/[GII] 0/[CTA] = 100/1/1. The resulting polymer was characterized

by 1H NMR spectroscopy (Figure IV-3) and 2D-correlation spectroscopy (COSY) (Figure

IV-4) . An intense signal corresponding to vinylic protons at 5.16 ppm (4,


- 86 -

-(CH3)C=CHCH2-) was observed in 1H NMR spectroscopy (Figure IV-3). This result

indicates that telechelic polyisoprenes with 1,4-microstructure are obtained. In addition,

new peeks were also observed at 5.86-5.70 ppm, at 5.60-5.50 ppm, at 5.38-5.28 ppm and at

4.72-4.50 ppm corresponding to 5 (cis -CH=CH), 5 (trans –CH=CH), 3 (-C(CH3)=CH)

and 2 (-C(CH3)=CH-CH2OC(O)-) or 6 (-CH=CH-CH2OC(O)-), respectively. COSY two-

dimensional NMR experiment was used to confirm these structures. In the COSY spectrum

(Figure IV-4), the signals centred at 5.78 ppm and at 5.55 ppm corresponding to cis- and

trans-ethylenic protons, 5, are correlated with the signal centred at 4.53 ppm corresponding

to aliphatic proton 6. We can also observe the correlation of the signal at 5.83 ppm, the

signal centred at 5.55 ppm and the signal centred at 5.34 ppm corresponding respectively

to cis- ethylenic proton, 5(cis-), trans- ethylenic proton, 5(trans-) and isoprenic proton, 3,

with the signal centred at 4.62 ppm corresponding to aliphatic protons, 6 and 2. In addition,

we can observe the correlation of the signal at 5.34 ppm corresponding to isoprenic proton,

3 with the signal centred at 4.68 ppm corresponding to aliphatic protons, 2. 13C NMR spectroscopy (Figure IV-5) was used to identify the 1,4-microstructure of

telechelic polyisoprenes. The signals observed at 135.21 (1, -C(CH3)=CH-), 125.02 (2,

-C(CH3)=CH-), 32.2 ppm (3, -CH2C(CH3)=CH-), 26.39 (5, -C(CH3)=CHCH2-), and 23.44

ppm (7, -C(CH3)=CH-) correspond to the cis-1,4- polyisoprene unit. There are no signals at

131.2 ppm (-C(CH3) =CH-), 124.27 (-C(CH3)=CH-), 40.02 ppm (-C(CH3)=CHCH2-),

16.00 (-C(CH3)=CH-) corresponding to the trans-1,4-polyisoprene unit.47 This result

confirmed that the telechelic polyisoprene is a strictly cis-1,4-polyisoprene. By contrast,

the synthesis of telechelic polyisoprene through anionic polymerization,48-49 NMP21 or

RAFT polymerization24-26 gives a mixture of 1,4-addition, 1,2-addition and 3,4-addition

products. On the other hand, the synthesis of telechelic polyisoprene via the Ring-Opening

Metathesis polymerization of 1,5-dimethyl-1,5-cyclooctadiene gives a mixture of telechelic

cis-1,4 and trans-1,4-polyisoprene.28

In order to determine the average functionality )( nf of telechelic cis-1,4-polyisoprene, the

number average polymerization degree (nDP ) of the oligomers determined by 1H NMR

spectroscopy was compared with the nDP determined by SEC. The nDP of cis-1,4-

polyisoprene from 1H NMR spectroscopy was calculated by comparing the relatives

integrations of the methylene protons (2 and 6, Figure IV-3) of the chain-ends at 4.72-

4.50 ppm, with those of the isoprenic protons (4, Figure IV-3) of polyisoprene backbone

at 5.16 ppm. The functionality was then calculated according to equation (1) which is an


- 87 -

adaptation of the equation used by Pham et al.50-51 for hydroxytelechelic polybutadiene

obtained by radical or anionic polymerization.

isopreneM

BSECnM

I

IInf

××

+++=

*,

4

62/)26( 2I (1)

with 2I corresponding to the relative integration of aliphatic protons 2 of isoprene chain-

end unit at 4.72-4.68 ppm (Figure IV-3);

26+I corresponding to the relative integration of aliphatic protons 6+2 of isoprene and

butadiene chain-ends unit at 4.68-4.56 ppm (Figure IV-3);

6I corresponding to the relative integration of aliphatic protons 6 of butadiene chain-end

unit at 4.56-4.50 ppm (Figure IV-3);

4I corresponding to the relative integration of vinylic protons 4 of isoprene backbone unit

at 5.16 ppm (Figure IV-3);

*,SECnM is the number average molecular weight of telechelic cis-1,4-polyisoprene

determined by SEC at 25 °C;

B is Benoît factor value52 of polyisoprene equal to 0.67;

Misoprene is the molar mass of isoprene unit equal to 68 g mol-1.

The resulting functionality for the cis-1,4-polyisoprene telechelic (entry A-2, Table IV-1)

was equal to 1.5±0.1. We believe that under these conditions the low concentration of CTA

gives rise to some active free ruthenium carbene (8, Scheme IV-2), which could be

involved in backbiting reactions leading to the formation of non-functional cyclic products

(8’, Scheme IV-2). Finally, ethyl vinyl ether used to stop the reaction leads to oligomer

vinylic chain-ends (8’’, Scheme IV-2). These reactions limit the functionality of the so-

obtained polyisoprenes.


- 88 -

+[Ru]

O

[Ru]O

+

8'

8''

Termination

Backbiting reaction

n

8

[Ru]

qC12H25

S SO

S

O

Scheme IV-2. The formation of non-functional chain-ends.

The evolution of number-average molecular weight of telechelic cis-1,4-polyisoprene with

reaction time is presented in Figure IV-6. It illustrates that metathesis degradation

proceeds in two relatively distinct steps. A very rapid decrease of the molecular weights of

the cis-1,4-polyisoprene, corresponding to a drop from 2×106 g mol-1 to 14,000 g mol-1, is

observed over the first two hours. In the initial stage of the reaction, an active ruthenium

carbene reacts rapidly with the double bonds of the cis-1,4-polyisoprene backbone leading

to a decrease of molecular weight. In addition, the active ruthenium carbene at the chain-

end can also react with the double bonds of cis-1,4-polyisoprene via intermolecular

metathesis reactions. Then, in a second period from 2h to 8h, the molecular weight of the

polymer decreases slowly but continually to form telechelic cis-1,4-polyisoprene with a

final molecular weight of approximately 5,800 g mol-1. This is also proved53-55 by the fact

that at very long reaction times intramolecular metathesis reactions can occur to form

cyclic oligomers. The resulting cyclic oligomers were confirmed by MALDI-TOF MS

analysis (Figure IV-7). The Ag+ ionized MALDI spectrum of oligomers isolated after

precipitation of the higher molecular weight fraction using 2-propranol reveals cyclic

polyisoprenic species. For example, the signal at m/z = 583 corresponds to a cyclic

polyisoprene consisting of n = 7 isoprene units ionized by Ag+ (Mcal = 107 + 7×68 = 583 g

mol-1; where 107 g mol-1 is the mass of silver atom and 68 g mol-1 is the mass of isoprene

unit) This experimental value is good agreement with the theoretical mass calculated (583

Da, monoisotopic peak), confirming the formation of cyclic oligomers via backbiting

reaction.


- 89 -

In order to obtain better control of the molecular weight and chain-end functionality of

telechelic cis-1,4-polyisoprene, the effect of changing the ratio of [Ip]0/[GII] 0/[CTA] 0

(entries A-1 to A-4, Table IV-1) was studied. When the ratio of [Ip]0/[GII] 0/[CTA] 0 is

equal to 200/1/1(entry A-1, Table IV-1), it was found that the evolution of the number-

average molecular weight of telechelic cis-1,4-polyisoprene with time followed a similar

two-step profile to that observed for sample A-2 (Table IV-1). During the first stage, a

period of two hours, the nM decreased rapidly from 2×106 g mol-1 to 34,000 g mol-1. After

2h, the nM decreased slowly to form telechelic cis-1,4-polyisoprene with a final

molecular weight of about 10,000 g mol-1 after a period of 8h (Figure IV-6). However, the

final telechelic cis-1,4-polyisoprene has a higher molecular weight corresponding to a

higher initial ratio of [Ip]0/[GII] 0/[CTA] 0. Moreover, the functionality of telechelic cis-1,4-

polyisoprene obtained was unaffected and remained less than 2. In order to form a

perfectly difunctional telechelic cis-1,4-polyisoprene, the influence of the CTA

concentration was investigated. The ratio of [GII]0/[CTA] 0 was set to 1/2 and 1/5, and the

ratio of [Ip]0/[GII] 0 was fixed at 100/1 (entries A-3 and A-4, Table IV-1). We observed

that ratios of [GII]0/[CTA] 0 of 1/2 and 1/5 formed polymers with a chain-end functionality

of 2 as shown by 1H NMR spectrum (Figure IV-3B) with no significant difference in

nM values and in polydispersity indices of the final telechelic cis-1,4-polyisoprene. This is

probably due to the fact that the CTA which have not reacted with the Grubbs II catalyst

may react with the ruthenium carbene at the chain-end (8, Scheme IV-3) leading to

difunctionalized cis-1,4-polyisoprene (7, Scheme IV-3).

[Ru]

qC12H25

S SO

S

O

C12H25S S

OS

O

OS S

C12H25

O

S

C12H25S S

OS

O

OS S

C12H25

O

Sq

8

7

difunctional CTA

Scheme IV-3. Formation of difunctionalized telechelic cis-1,4-polyisoprene.


- 90 -

Table IV-1. Metathesis degradation of NR using Grubbs II catalyst and difunctional chain

transfer agent in toluene at 25 °C after 4h.

Entry

[Ip] 0/[GII] 0/[CTA] 0 SECnM ,

a

(g mol-1)

NMRnM ,

b

(g mol-1)

Functionalityc

PDId

Yield

(%)

A-1 200/1/1 23 000 16 400 1.4±0.1 1.83 78

A-2 100/1/1 10 200e 7 200 1.5±0.1 1.76 76

A-3 100/1/2 8 200e 6 200 2.0±0.1 1.70 76

A-4 100/1/5 8 200 6 400 2.0±0.1 1.67 70 aExperimental number average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 35 °C, bDetermined by 1H NMR spectroscopy according to nM =

[(I4×68)/(I1/4)] + 848, cDetermined by 1H NMR spectroscopy and using equation (1). dPolydispersity index measured by SEC, eExperimental number average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 25 °C.

qO

O

S SCH2H2CS SO

OC11H23

12

345

6C11H23

1

5

S S7 7

8

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm

0.08

0.21

0.09

10.4

6

1

43

4.64.8 ppm5.45.65.86.0 ppm

5(cis-)

5(trans-)

2

2+66

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm

0.05

0.13

0.05

10.8

5

5.45.65.86.0 ppm 4.64.8 ppm

5(cis-)

5(trans-)

32

2+66

7 8

7 84

1

Figure IV-3. 1H NMR spectra of difunctional telechelic cis-1,4-polyisoprenes, A) entry

A-2, Table IV-1 and B) entry A-3, Table IV-1.

A)

B)

5.1=nf

0.2=nf


- 91 -

qO

O

S SCH2H2CS SO

OC11H23

12

345

6C11H23

1

5

S S

ppm

4.24.44.64.85.05.25.45.65.86.0 ppm

4.2

4.4

4.6

4.8

5.0

5.2

5.4

5.6

5.8

6.0

2

6+2

6

3

5(trans-)

5(cis-)

2+6

Figure IV-4. COSY spectrum of the difunctional telechelic cis-1,4-polyisoprene (entry A-

2, Table IV-1).


- 92 -

qO

O

S

S

S(CH2)11CH3

S

SO

O8

2

34

7

6

CH3(CH2)11S 15 4

6 6 6

7

8

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

1 2 3 5 7

4 6 8

Figure IV-5. 13C NMR spectrum of telechelic cis-1,4-polyisoprene (entry A-2, Table IV-

1).

0 2 4 6 800

10000

2000020000

30000

19000001900000

1950000

20000002000000

Mn

(g.m

ol-1)

Reaction time (hours)

A-1 A-2 A-3

Figure IV-6. Evolution of the telechelic cis-1,4-polyisoprene number-average molecular

weight as a function of reaction time (entries A-1 to A-3, Table IV-1).


- 93 -

573 578 583 588 593 598m/z

a.i.

Figure IV-7. MALDI-TOF mass spectrum of the cyclic polyisoprene oligomers obtained

via backbiting reaction. The insert shows the theoretical distribution at m/z 538.

II. Synthesis of P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.

We investigated the synthesis of ABA triblock copolymers containing polyisoprene as the

central block using a purified α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-

polyisoprene as macroCTA (7, Scheme IV-4). The P(t-BA)-b-PIp-b-P(t-BA) (9, Scheme

IV-4 ) was prepared from the RAFT polymerization of tert-butyl acrylate using the

difunctional telechelic cis-1,4-polyisoprene (A-3, Table IV-1) as a macroCTA. The

reaction was performed in toluene at 60 oC and AIBN was used as an initiator ([t-BA] 0/[

macroCTA]0/[AIBN] 0 = 500/1/0.4). Monomer conversion was determined by 1H NMR

spectroscopy by following the disappearance of the vinyl protons of t-BA at 6.40 to 5.60

ppm which were compared with methyl protons of anisole used as an internal standard at

3.75 ppm. The macromolecular characteristics of block copolymers were determined by

SEC.

580 650 720 m/z

1000

2000

3000

4000

5000

6000

7000

a.i.


- 94 -

After a polymerization time of 5h, the t-BA conversion reaches 26% (Table IV-2). The

block copolymer had a number-average molecular weight of 23,300 g mol-1 and a

polydispersity index of 1.50 by SEC. The SEC trace of the copolymer (Figure IV-8A )

showed the absence of a peak corresponding to the PIp-macroCTA and a unimodal curve,

illustrating that the polymerization of the second block underwent chain transfer

quantitatively. The number average degree of polymerization of the PIp block is equal to

80 and the one of P(t-BA) is equal to 100 as calculated by comparing the integral of the

ethylenic protons 4 of the polyisoprene backbone resonance at 5.14 ppm to the methine

protons 2 of P(t-BA) resonances at 2.4-2.1 ppm on the 1H NMR spectrum of the copolymer

(Figure IV-8B). The data obtained from SEC and 1H NMR spectroscopy provide

additional evidence for the formation of the ABA triblock copolymer based on the cis-1,4-

polyisoprene from NR with the desired topology.

Glass transition temperature (Tg) of PIp-macroCTA and P(t-BA)-b-PIp-b-P(t-BA) triblock

copolymer were investigated by thermal analysis by differential scanning calorimetry

(DSC) under nitrogen at 10 °C/min heating rate. A single Tg of PIp-macroCTA is observed

at −65 °C. Whereas, the P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers show two values of

Tg which the low temperature at −37 °C corresponds to the glass transition temperature of

PIp and the higher temperature at 32 °C corresponds to the glass transition temperature of

P(t-BA) as the Tg of P(t-BA) is equal to 48 °C.56 This is a supplementary proof of the

successful synthesis of P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.


- 95 -

Table IV-2. Synthesis of ABA triblock copolymers via RAFT polymerization of tert-butyl

acrylate (t-BA) using the macroCTA (A-3, Table IV-1) and AIBN as initiator at 60°C in

toluene.

Copolymer

Reaction time

(h)

conv.a

(%)

b,calnM

(g mol-1)

c,SECnM

(g mol-1)

PDId

S-1 2 2 9 080 8 200 1.75

S-2 4 15 17 400 16 000 1.50

S-3 4.5 21 21 240 20 000 1.50

S-4 5 26 24 440 23 300 1.50 aMonomer conversion determined using 1H NMR spectroscopy. bNumber average molecular weight calculated using: Mn,calc = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0, MM and MmacroCTA are the initial concentration of monomer, the initial concentration of difunctional telechelic cis-1,4-polyisoprene macroCTA, the molecular weight of monomer and the molecular weight of the difunctional telechelic cis-1,4-polyisoprene macroCTA respectively. cNumber average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 35°C. dPolydispersity index measured by SEC.

C12H25S S

OS

O

OS S

C12H25

O

S80

toluene, 60 °C, 5h O O0.4 eq. AIBN,

500 eq.

C12H25S S

S

S SC12H25

S80

O O O O

50 50

7

9

Scheme IV-4. Synthesis of P(t-BA)-b-PIp-b-P(t-BA) by RAFT polymerization using α,ω-

bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene as macroCTA.


- 96 -

A)

B)

1.01.52.02.53.03.54.04.55.05.56.0 ppm

3.33.43.5 ppm

1

4

2

3

Figure IV-8. A) Overlaid SEC traces of the telechelic cis-1,4-polyisoprene and of the P(t-

BA)-b-PIp-b-P(t-BA) triblock copolymers, and B) 1H NMR spectrum of P(t-BA)-b-PIp-b-

P(t-BA) triblock copolymers.

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Retention time (mins)

P(t-BA)-b-PI-b-P(t-BA)

PI

CH2S S

S

S SCH2

S80O O O O

50 50

C11H23C11H232

3 42

3

1 1


- 97 -

Conclusion

A new α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene was

successfully synthesized in one-pot reaction via metathesis degradation of NR using the

Grubbs II catalyst and a bistrithiocarbonyl-end functionalized olefin as a CTA. The

influence of the Grubbs II catalyst concentration and the CTA concentration were

investigated. The functionality of telechelic cis-1,4-polyisoprene reaches 2 when the ratio

of [GII] 0/[CTA] 0 is equal to 1/2 or/and 1/5 as demonstrated by 1H NMR spectroscopy. The

resulting α,ω-bistrithiocarbonyl-end functionalized telechlelic cis-1,4-polyisoprene was

successfully used as macroCTA for the RAFT polymerization of tert-butyl acrylate to form

P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers. This polymer precursor could be of great

interest in various block copolymers applications especially regarding adhesive properties

which are still in studies currently in our laboratory. This interest is also reinforced by the

fact that such functionalized oligomers are an alternative to few analogues coming from

petroleum origin.

Acknowledgments. The authors wish to thank French Ministry of education and research

and Prince of Songkla University, Thailand for their financial support. Thanks to Dr. Jean-

Claude Soutif for MALDI-TOF MS analysis.


- 98 -

Experimental Section


spectrometer for 1H NMR (400 MHz), 13C NMR (100 MHz). Chemical shifts are reported

in ppm down-field from tetramethylsilane (TMS). Molecular weights and molecular

weight distributions were measured using size exclusion chromatography (SEC) on a

system equipped with a SpectraSYSTEM AS 1000 autosampler, with a Guard column

(Polymer Laboratories, PL gel 5 µm Guard column, 50×7.5 mm) followed by two columns

(Polymer Laboratories, 2 PL gel 5 µm MIXED-D columns, 2×300×7.5) and with a

SpectraSYSTEM RI-150 detector. The eluent used was tetrahydrofuran (THF) at a flow

rate of 1 mL min-1 at 25 °C or 35°C. Narrow molecular weight linear polystyrene standards

(ranging from 580 g mol-1 to 4.83×105 g mol-1) were used to calibrate the SEC. Infrared

spectra were recorded on a Nicolet Avatar 370 DTGS FT-IR spectrometer in the 4000-500

cm-1 range with KBr pellets and controlled by OMNIC software. Matrix-assisted laser

desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded on a

Bruker Biflex III equipped with a nitrogen laser (lZ337 nm). All mass spectra were

obtained in the linear mode with an acceleration voltage of 19 kV. The delay time was 200

ns. Typically, 100 single-shot acquisitions were summed to give a composite mass

spectrum. All data were reprocessed using the Bruker XTOF software. Thermal transition

of samples was measured by DSC Q100 (TA Instrument) Differential Scanning

Calorimeter equipped with the cooling system that temperature can be decrease to −90°C.

Samples were put in the aluminium capsule and empty capsule was used as inert reference.

All experiments were carried out under nitrogen atmosphere at flow rate 50 mL/min with

weight of sample 5 to 10 mg. Two scans from −80 to 60°C were performed with a heating

and cooling rate of 10°C/min and the glass transition temperature was recorded.

Materials. All chemicals were purchased from Aldrich unless otherwise noted. Oxalyl

chloride (99%), cis-but-2-ene-1,4-diol (97%), toluene (99%), ethyl vinyl ether (99%),

tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene]

benzylidineruthenium (IV) dichloride (99%+) (Grubbs second generation catalyst, GII), 2-

propanol (99%) (Fisher Scientific) and anisole (99%) were used as received.

Dichloromethane (99%+) and methanol (99%) were distilled over CaH2 prior to use. tert-

butyl acrylate (t-BA, 99%) was purified by passing through neutral alumina column to


- 99 -

remove inhibitor. 2,2-Azobis(2-methylpropionitrile) (AIBN, 98%) was recrystallized into

methanol prior to use. NR latex was preserved with ammonia solution 0.7% (w/w) (Dry

rubber content, DRC = 60%, wM = 2×106 g mol-1, Pattani Industrial, Thailand) and non

rubber impurities were removed by urea treatment, nonionic surfactant washing and double

centrifugation followed by coagulation with methanol and dried.44 The RAFT agent, S-1-

dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate, (1, Scheme IV-1A) was

prepared according to a procedure reported in the literature.45 The bistrithiocarbonyl-end

functionalized olefin used as CTA (2, Scheme IV-1A) was synthesized as described

previously.46

Functional Metathesis Degradation Procedure. A general procedure for metathesis

degradation of NR to obtain difunctional telechelic cis-1,4-polyisoprene (7, Scheme IV-

1B) is described. A magnetic stirrer was charged to a dry Schlenk tube fitted with a rubber

septum. A degassed solution of purified NR (0.7 g, 0.0103 mol) dissolved in toluene (20

mL) was added. Separately, a solution of the difunctional CTA (2, Scheme IV-1A)

(0.1606 g, 0.2056 mmol) and Grubbs II catalyst (GII, 0.0873 g, 0.1028 mmol) in toluene (4

mL) was degassed by sparging with argon and stirred for 15 min. The resulting solution of

difunctional CTA and Grubbs II catalyst was transferred into the solution of NR using a

degassed syringe (defining t = 0) at 25 °C. Aliquots were withdrawn from the reaction

solution after 2, 4, 6 and 8 h. When this time had elapsed the metathesis reaction was

quenched by adding ethyl vinyl ether into the reaction solution under an argon atmosphere.

The resulting solution was concentrated under vacuum at room temperature and was

purified by a series of precipitations from dichloromethane (minimum volume) into 2-

propanol (100 mL) at room temperature. The isolated polymer was dried under vacuum to

remove any trace of solvent. It was then further analyzed by 1H NMR spectroscopy, 13C

NMR spectroscopy, FTIR spectroscopy and SEC. Yield: 76%.

1H NMR (CDCl3): δ (ppm) 5.86-5.70 (br, chain-end, cis -CH=CH), 5.60-5.50 (br, chain-

end, trans -CH=CH), 5.38-5.28 (br, chain-end; -C(CH3)=CH-), 5.14 (br, polyisoprene

backbone, -C(CH3)=CH), 4.72-4.65 (d, chain-end, -C(CH3)=CH-CH2OC(O)-), 4.65-4.56

(d, chain-end, -C(CH3)=CH-CH2OC(O)- and -CH=CH-CH2OC(O)-), 4.56-4.50 (d, chain-

end, -CH=CH-CH2OC(O)-), 3.25 (t, C(S)-SCH2CH2R), 2.12-1.95 (br, polyisoprene

backbone, -CH2C(CH3)=CH- and -C(CH3)=CHCH2), 1.70-1.60 (br, polyisoprene


- 100 -

backbone, -C(CH3)=CH, and chain-end -SC(CH3)2C(O)O-), 1.20-1.40 (br, chain-end, -

SCH2(CH2)10CH3), 0.86 (t, -S(CH2)11CH3).

13C NMR (CDCl3): δ(ppm) 135.21(cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 125.02

(cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 36.8 (chain-end, C(S)-SCH2CH2-), 32.2

(cis-1,4-polyisoprene backbone, -CH2C(CH3)=CH-), 31.92, 29.64, 29.63, 29.57, 29.46,

29.35, 29.12, 28.95, 27.86 (chain-end, -SCH2(CH2)9CH2CH3, 26.39 (cis-1,4-polyisoprene

backbone, -C(CH3)=CH-CH2-), 25.36 (chain-end, -SC(CH3)2C(O)O-), 23.44 (cis-1,4-

polyisoprene backbone -C(CH3)=CH-), 22.70 (chain-end, -SCH2(CH2)8CH2CH3), 14.14

(chain-end, -CH3)

FTIR: ν (cm-1) 3032 (H-C=C), 2962-2854 (CH2, CH3), 1735 (chain-end, -C=O), 1666

(polyisoprene backbone-C=C-), 1448 (polyisoprene backbone -CH2), 1376 (polyisoprene

backbone, -CH2), 1259 (chain-end, C-O-), 1082 (chain-end, -C-S), 836 (polyisoprene

backbone, -CH),

A typical RAFT polymerization. A typical procedure is given for the polymerization of

tert-butyl acrylate (t-BA) mediated by α,ω-bistrithiocarbonyl-end functionalized telechelic

cis-1,4-polyisoprene (7, Scheme IV-1B) used as macroCTA and using AIBN as the

initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 500/1/0.4). A magnetic stir bar was charged to a

Schlenk tube together with the CTA (0.3160 g, 0.051 mmol), t-BA (3.65 mL, 0.028 mol),

AIBN (0.0033 g, 0.020 mmol), toluene (1 mL, 20% v/v) and anisole (0.17 mL, 5% v/v).

Then, the reaction mixture was deoxygenated by bubbling with argon for 15 min. The

polymerization was initiated by immersion in a thermostatted oil bath at 60°C. Samples

were withdrawn from the reaction mixture via a degassed syringe for conversion

monitoring (by 1H NMR spectroscopy) and molecular weight analysis (by SEC). At the

end of reaction, the polymer solution was concentrated under vacuum using rotary

evaporation and was purified by a series of precipitations from dichloromethane (minimum

volume) into an ice cold 1:1 mixture of water and methanol. The copolymer was separated

by filtration and dried under vacuum until constant weight. It was then further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC.


- 101 -

1H NMR (CDCl3): δ (ppm) 5.86-5.70 (br, chain-end, cis -CH=CH-), 5.60-5.50 (br, chain-

end, trans-CH=CH-), 5.16 (br, polyisoprene backbone, -C(CH3)=CH), 4.72-4.65 (d, chain-

end, -C(CH3)=CH-CH2OC(O)-), 4.65-4.56 (d, chain-end, -C(CH3)=CH-CH2OC(O)- and -

CH=CH-CH2OC(O)-), 4.56-4.50 (d, chain-end, -CH=CH-CH2OC(O)-) 3.32 (t, C(S)-

SCH2CH2R), 2.40-2.15 (br, P(t-BA) backbone, -CH2-CHC(O)-), 2.12-1.95 (br,

polyisoprene backbone, -CH2C(CH3)=CH- and -C(CH3)=CHCH2-), 1.90-1.70 (br, P(t-BA)

backbone -CH2-CHC(O)-), 1.70-1.60 (br, polyisoprene backbone, -C(CH3)=CH-, and

chain-end -SC(CH3)2-C(O)O-), 1.55-1.30 (br, P(t-BA) backbone -OC(CH3)3), 1.20-1.40

(br, chain-end -SCH2CH2-(CH2)9CH3), 0.86 (t, S(CH2)11CH3).

13C NMR (CDCl3): δ(ppm) 174.16 (P(t-BA) backbone, -C(O)-O-), 135.21 (cis-1,4-

polyisoprene backbone, -C(CH3)=CH-), 125.02 (cis-1,4-polyisoprene backbone, -

C(CH3)=CH-), 80.41 (P(t-BA) backbone, -C(O)-O-C(CH3)3), 42.42 (P(t-BA) backbone, -

CHC(O)-O-C(CH3)3), 37.41, (chain-end, C(S)-SCH2CH2-), 32.20 (cis-1,4-polyisoprene

backbone, -CH2C(CH3)=CH-), 31.92, 29.64, 29.63, 29.57, 29.46, 29.35, 29.12, 28.95,

27.86 (chain-end, -SCH2(CH2)9CH2CH3, 28.14 (P(t-BA) backbone, -O-C(CH3)3), 26.39

(1,4-cis- polyisoprene backbone -C(CH3)=CH-CH2-), 23.44 (cis-1,4-polyisoprene

backbone -C(CH3)=CH-), 22.70 (chain-end, -S(CH2)9CH2CH3), 14.14 (chain-end, -CH3).


- 102 -

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2002, 43, 3173-3179.

Chapter V

Thermal properties of block

copolymers based on PI/P(t-BA) and

PI/PAA

Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA

- 104 -

Introduction

In order to have a better knowledge on the potential use of previously synthesized well-

defined block copolymers containing polyisoprene (PI) from synthetic- and natural rubber

(NR) with poly(tert-butyl acrylate) (P(t-BA)), the thermal properties of PI macromolecular

chain transfer agent (PI-macroCTAs), PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-

b-P(t-BA) triblock copolymers are studied in the first part. In the second part, the influence

of the PI microstructure on thermal properties was studied. The last part describes the

investigation on the cleavage reaction of the tert-butyl ester units of P(t-BA) to form

poly(acrylic acid) (PAA) and the determination of the thermal properties of resulting block

copolymers based on PI and PAA.

I. Comparison between PI-macroCTA and block copolymers based on

PI/P(t-BA)

In this section, the thermal properties of previous PI-macroCTAs, well-defined PI-b-P(t-

BA) diblock copolymers synthesized from successive RAFT polymerizations of isoprene

and t-BA (2, Scheme V-I) and from oxidative degradation of NR followed by reductive

amination, amidation and RAFT polymerization of t-BA (2’, Scheme V-I) are

investigated. Moreover, thermal analysis of well-defined P(t-BA)-b-PI-b-P(t-BA) triblock

copolymers (5, Scheme V-II) prepared via metathesis degradation of NR followed by the

RAFT polymerization of t-BA are carried out by differential scanning calorimetry (DSC)

and thermogravimetric analysis (TGA). The results are summarized in Table V-1.


- 105 -

A) B)

62

OC12H25

S

S

SO

NH

O O

87

C12H25

S

S

SO

OH

80O O

65

64

and

2 2'

C12H25

S

S

SO

OH

81 4 5

901

0.2 eq AIBN

60 °C, 2.5h250 eq t-BA

62

OC12H25

S

S

SO

NH

1'

62

OC12H25

S

S

SO

NH

O OH

87

iodotrimethylsilane25 °C, 4h

3'

0.2 eq AIBN

60 °C, 4h250 eq t-BA

C12H25

S

S

SO

OH

80O OH

6564

3

iodotrimethylsilane25 °C, 4h

CH2Cl2

CH2Cl2

Scheme V-1. Synthesis of PI-b-PAA diblock copolymers; A) PI block obtained by RAFT

polymerization of isoprene and B) PI block obtained by oxidative degradation of NR

followed by reductive amination and amidation.

80

50

OOOO

50

S

S

SC12H25

S

S

SC12H25

80

50

OHOOHO

50

S

S

SC12H25

S

S

SC12H25

25 °C, 4h

5

6

4

C12H25S S

OS

O

OS S

C12H25

O

S80

0.4 eq AIBN

60 °C, 5h500 eq t-BA

iodotrimethylsilane CH2Cl2

Scheme V-2. Synthesis of PAA-b-PI-b-PAA based on PI block obtained by metathesis

degradation of NR.


- 106 -

Table V-1. Thermal properties of PI-macroCTAs and block copolymers based on PI Glass transition Thermal degradation stage

Entry Sample temperature 1st stage 2nd stage 3rd stage Tg

1 Tg2 Tmax Weight

loss Tmax Weight

loss Tmax Weight

loss (°C) (°C) (°C) (%) (°C) (%) (°C) (%)

A-1 PI-macroCTA (1)a −60 - * 5.5 376 94.3 - -

A-2 PI-b-P(t-BA) (2) −35 37 181 34.5 272 14.3 425 42.4

A-3 PI-macroCTA (1’)b −64 - * 6.1 375 91.8 - -

A-4 PI-b-P(t-BA) (2) −40 30 240 38.0 264 9.0 380-434 46.5

A-5 PI-macroCTA (4)c −64 - * 9.7 375 87.7 - -

A-6 P(t-BA)-b-PI-b-

P(t-BA) (5)

−37 32 189 37.0 272 14.2 424 40.4

aPI-macroCTA obtained by polymerization of isoprene via RAFT polymerization, bPI-macroCTA obtained

by oxidative degradation of NR followed by reductive amination and amidation, cPI-macroCTA obtained by

metathesis degradation of NR. * Not determined (Thermal decomposition began ∼ 120 °C)

Glass transition temperature (Tg) of PI-macroCTAs, PI-b-P(t-BA) diblock copolymers and

P(t-BA)-b-PI-b-P(t-BA) triblock copolymers were investigated by DSC under nitrogen at

10 °C/min heating rate.

A single Tg is detected in all the DSC thermograms of PI-macroCTA except in block

copolymers that exhibit two glass transition temperatures. The DSC curve of PI-

macroCTA obtained by RAFT polymerization of isoprene (Figure V-1) shows a single

glass transition temperature (Tg) at −60 °C. This result confirms that the PI microstructure

is predominantly 1,4 as the Tg of cis-1,4-PI is equal to −73 °C1 and the one of trans-1,4-PI

is equal to −58 °C1 while the Tg of 3,4-PI is equal to 33 °C.2 The PI-b-P(t-BA) diblock

copolymer (entry A-2, Table V-1) shows two values of Tg, the low one at −35 °C

corresponding to the glass transition temperature of PI and the higher one at 37 °C

corresponding to the glass transition temperature of P(t-BA) as the Tg of P(t-BA) is equal

to 48 °C.3 The glass transition temperature assigned to the PI backbone is significantly

moved toward higher temperatures in the block copolymer compared to the PI-macroCTA.

This shift is expected since the introduction of rigid P(t-BA) reduces the mobility of the PI

backbone leading to an increase of the Tg value.


- 107 -

Similar results are seen in DSC curves (Figure V-2) of PI-macroCTA obtained by

oxidative degradation of NR followed by reductive amination and amidation (entry A-3,

Table V-1). A single Tg of PI-macroCTA is observed at −64 °C. Whereas, the PI-b-P(t-

BA) diblock copolymer (entry A-4, Table V-1) shows two values of Tg which the low

temperature at −40 °C corresponds to the glass transition temperature of PI and the higher

temperature at 30 °C corresponds to the glass transition temperature of P(t-BA).

In addition, similar curves could be observed on the DSC analysis (Figure V-3) of PI-

macroCTA obtained by metathesis degradation of NR (entry A-5, Table V-1) and P(t-

BA)-b-PI-b-P(t-BA) (entry A-6, Table V-1). We observe a single Tg of PI-macroCTA at

−64 °C and two values of Tg of P(t-BA)-b-PI-b-P(t-BA) triblock copolymers with the low

temperature at −37 °C corresponds to the glass transition temperature of PI and the higher

temperature at 32 °C corresponds to the glass transition temperature of P(t-BA).

This is a supplementary proof of the successful synthesis of PI-b-P(t-BA) diblock

copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers.

Figure V-1. DSC thermograms of PI-macroCTA (entry A-1, Table V-1) and PI-b-P(t-

BA) diblock copolymer (entry A-2, Table V-1).

PI-macroCTA --- PI-b-P(t-BA)


- 108 -

Figure V-2. DSC thermograms of PI-macroCTA (entry A-3, Table V-1) and PI-b-P(t-

BA) diblock copolymer (entry A-4, Table V-1).

Figure V-3. DSC thermograms of PI-macroCTA (entry A-5, Table V-1) and P(t-BA)-b-

PI-b-P(t-BA) diblock copolymer (entry A-6, Table V-1).

PI-macroCTA --- PI-b-P(t-BA)

PI-macroCTA --- P(t-BA)-b-PI-b-P(t-BA)


- 109 -

The thermal stability of PI-macroCTAs and block copolymers based on PI/P(t-BA) were

also studied using thermogravimetric analysis (TGA) under nitrogen at 10 °C/min heating

rate. The main TGA parameters are shown in Table V-1.

The thermogravimetric curve and its first derivative curve of PI-macroCTA obtained by

RAFT polymerization of isoprene is shown in Figure V-4. Results show that the thermal

decomposition starts at 120 °C with a weight loss of 5.5% and, then a weight loss of 94.3%

is obtained from 300 °C to 475 °C. The maximum temperature (Tmax) at 376 °C and a

shoulder at 420 °C were observed on the first derivative thermogravimetric curve. This

behaviour shows that the PI-macroCTA degradation involves many reactions. As

mentioned by Job et al.4 and Mattoso et al.5-6 during NR degradation, random scissions

occur with simultaneous crosslinkings and cycling reactions.

Similar behaviour were seen on thermogravimetric curve and its first derivative curve

(Figure V-5 and Figure V-6) of PI-macroCTA obtained from oxidative degradation of

NR followed by reductive amination and amidation (entry A-3, Table V-1) and PI-

macroCTA obtained by metathesis degradation of NR (entry A-5, Table V-1). The

thermal decomposition starts at 120 °C with a weight loss of 6.1% and of 9.7%,

respectively. A maximum temperature (Tmax) at 375 °C and a shoulder at 434 °C and at 420

°C with a weight loss of 91.8% and of 87.7% respectively, are attributed to the degradation

of polyisoprene part.

The thermogravimetric studies of block copolymers show that the PI-b-P(t-BA) diblock

copolymers (entry A-2, Table V-1) obtained from successive RAFT polymerizations of

isoprene and t-BA has a similar behaviour than the P(t-BA)-b-PI-b-P(t-BA) (entry A-6,

Table V-1). The first thermal degradation shows a Tmax at 180°C and at 189 °C with a

weight loss of 34.5% and of 37.0% respectively. This first stage is associated with the

elimination of tert-butyl ester group in P(t-BA) blocks3 (Scheme V-3). The second stage

has a Tmax at 272°C with a weight loss of 14.2% for both block copolymers. This is due to

the dehydration reactions between carboxylic groups to give six-member cyclic anhydride

structures3 (Scheme V-3). The final third stage is attributed to the degradation of

polyisoprene block with a Tmax at 425°C and a weight loss of 42.4% and of 40.4% for

diblock copolymer and triblock copolymer respectively.

The thermogravimetric curve of the PI-b-P(t-BA) diblock copolymers (entry A-4, Table

V-1) synthesized from the oxidative degradation of NR followed by reductive amination

and amidation and RAFT polymerization of t-BA shows a first degradation stage with a


- 110 -

Tmax at 240 °C and a weight loss of 38.0%. This Tmax is higher than the Tmax observed for

diblock copolymer issued from successive RAFT polymerization of isoprene and t-BA and

than Tmax observed for triblock copolymers. This is probably due to increasing intra- and

intermacromolecular interactions between the chains by hydrogen bonds between N-H

groups and C=O groups. At higher temperature that Tmax = 240 °C, the thermogravimetric

curve of the PI-b-P(t-BA) diblock copolymer (entry A-4, Table V-1) shows the thermal

degradations of P(t-BA) block and PI block as previously described.

O O O O

n

O OH O OH

n

O O O

n

+ H2O

+ 2

Scheme V-3. Mechanism of the first stage of P(t-BA) thermal degradation.3


- 111 -

Figure V-4. A) themogravimetric curves, B) first derivatives curve for PI-macroCTA

(entry A-1, Table V-1) and PI-b-P(t-BA) diblock copolymer (entry A-2, Table V-1)

under a nitrogen atmosphere, at a heating rate of 10 °C/min.

A)

B)


- 112 -


(entry A-3, Table V-1) and PI-b-P(t-BA) diblock copolymer (entry A-4, Table V-1)

under a nitrogen atmosphere, at a heating rate of 10 °C/min.

A)

B)


- 113 -


(entry A-5, Table V-1) and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (entry A-6,

Table V-1) under a nitrogen atmosphere, at a heating rate of 10 °C/min.

B)

A)


- 114 -

II. Influence of the PI microstructure

In this section, the influence of the PI microstructure on the thermal properties of PI-b-

P(t-BA) diblock copolymers is studied by comparing DSC curves and TGA curves

between PI-b-P(t-BA) diblock copolymer obtained from successive RAFT polymerizations

of isoprene and t-BA (2, Scheme V-1) and PI-b-P(t-BA) diblock copolymer obtained by

oxidative degradation of NR followed by reductive amination and amidation and RAFT

polymerization of t-BA (2’, Scheme V-1).

The Tg value of PI-macroCTA obtained by RAFT polymerization of isoprene (entry A-1,

Table V-1) was noted at −60°C that is a slightly higher than Tg noted (Tg= −64 °C) of PI-

macroCTA obtained by oxidative degradation of NR followed by reductive amination and

amidation (entry A-3, Table V-1). The PI-macroCTA (entry A-1, Table V-1) obtained by

RAFT polymerization of isoprene has a microstructure composed of 90% of 1,4-PI (60%

trans and 40% cis), 4% of 1,2-PI and 6% of 3,4-PI. By contrast, PI-macroCTA (entry A-3,

Table V-1) obtained by oxidative degradation of NR followed by reductive amination and

amidation leads to cis-1,4-PI units. It is well-known that the type of isomeric structures of

PI influences the degree of crystallinity and glass transition temperature of PI.7 Normally,

the Tg of cis-1,4-PI is lower than that of trans-1,4-PI and 3,4-PI due to the fact that the

lower the cis content, the less amount the crystallinity that the polymer can develop.8

However, the various PI microstructures in our work has no significant influence on their

thermal properties. This is probably due to the fact that the NR-based cis-1,4-PI obtained

after NR degradation have a low number-average molecular weight.

The Tg values assigned to the PI backbone of PI-b-P(t-BA) diblock copolymers (entry A-2

and entry A-4, Table V-1) increase from −60 °C to −35 °C and from −64 °C to −40 °C

respectively. This shift toward higher temperatures is expected since the introduction of

rigid P(t-BA) in the block copolymers reduces the mobility of the chains. This reduction of

mobility can also explained the thermal stability of PI-b-P(t-BA) diblock copolymers. It

can be observed that the Tmax (424 °C) in the second stage of PI-b-P(t-BA) diblock

copolymers from PI-macroCTA obtained by RAFT polymerization of isoprene (entry A-2,

Table V-1) is not different to the Tmax (425 °C) observed in the second stage of PI-b-P(t-

BA) diblock copolymers from PI-macroCTA obtained by oxidative degradation of NR


- 115 -

(entry A-4, Table V-1). Thus it can be concluded that the difference in microstructures of

low molecular weight PI has no effect on the thermal stability of the diblock copolymers.

III. Deprotection of t-BA group and thermal stability of resulting block

copolymers based PI/PAA

A number of recent reports have described the preparation of diblock copolymers

containing PI with poly(acrylic acid) (PAA) through the cleavage reaction of the tert-butyl

ester units to form PI-b-PAA. Wooley et al.9 have prepared PI-b-PAA by the hydrolysis of

PI-b-P(t-BA) copolymer precursor by heating the diblock polymers in 1,4-dioxane

containing concentrated HCl at reflux.

Lu et al.10 reported the preparation of microspheres using PI-b-PAA as the surfactant to

disperse a solution of PI-b-P(t-BA) and a P(t-BA) homopolymer (hP(t-BA)) in

dichloromethane. The PI-b-P(t-BA) and the precursor of PI-b-PAA were prepared by

sequential anionic polymerization. The tert-butyl ester groups of the precursor of PI-b-

PAA were removed quantitatively under acidic hydrolysis by treatment with trifluoroacetic

acid in dry dichloromethane to form PI-b-PAA and then used as the surfactant. More

recently Wooley and co-workers11 have investigated the synthesis of amphiphilic shell-

crosslinked (SCK) nanoparticles consisting of a PI core and a PAA shell from P(t-BA)-b-

PI block copolymers prepared via NMP. The cleavage reaction of the tert-butyl ester unit

was performed in toluene/acetic acid using methanesulfonic acid as catalyst at 110 °C. The

same group12 further extended the synthesis of PI-b-P(t-BA) copolymers to the synthesis of

core-shell brush copolymers. A brush copolymer consisting of a PI-b-P(t-BA) diblock

copolymer grafts and a polynorbornene backbone is obtained. The P(t-BA) units are

hydrolysed using HCl to form PAA units that were subsequently crosslinked with 2,2-

(ethylenedioxy)bis(ethylamine) to form a crosslinked brush. Full details of these

experiments were described in pages 15-28 of Chapter I.

Previous well-defined PI-b-P(t-BA) diblock copolymers synthesized from successive

RAFT polymerizations of isoprene and t-BA (2, Scheme V-I) and from oxidative

degradation of NR followed by reductive amination, amidation and RAFT polymerization

of t-BA (2’, Scheme V-I) were treated by iodotrimethylsilane at room temperature.13

After 4h, the excess solvent and reagent were removed and the copolymers were


- 116 -

redissolved in THF. The resulting solutions were dialyzed using nanopure water, followed

by lyophilisation to obtain the white solid product of PI-b-PAA diblock copolymers (3 and

3’, Scheme V-I). In addition, the previous P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (5,

Scheme V-II) prepared via metathesis degradation of NR followed from the RAFT

polymerization of t-BA were treated with iodotrimethylsilane to form PAA-b-PI-b-PAA

triblock copolymers (6, Scheme V-II) following the same conditions as for the preparation

of PI-b-PAA diblock copolymers (3 and 3’, Scheme V-I).

All solid products of PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA triblock

copolymers obtained after lyophilisation are difficult to solubilize in polar solvents

(DMSO (d-6), D2O, pyridine (d-5)) at 25 °C. Due to this problem, ATR-FTIR analysis and 13Carbon Cross-Polarisation (CP) combined with Magic Angle Spinning (MAS) (13C-CP-

MAS) solid-state NMR spectroscopy were used to observe the cleavage of the tert-butyl

groups. The modification of PI-b-P(t-BA) (2 and 2’, Scheme V-I) to PI-b-PAA (3 and 3’,

Scheme V-I) and P(t-BA)-b-PI-b-P(t-BA) (5, Scheme V-II) to PAA-b-PI-b-PAA (6,

Scheme V-II) were confirmed by ATR-FTIR analysis (Figures V-7-9). After deprotection

of the tert-butyl ester, the ATR-FTIR spectra show a broad peak in the region ~2900-3400

cm-1 corresponding to O-H bond stretching vibrations in acrylic acid groups, a broadening

of carbonyl band that shifts from 1730 to 1700 cm-1 and the disappearance of the bands at

1368 and 1392 cm-1 characteristics of the pendant methyl group of tert-butyl acrylate. This

indicates that the tert-butyl groups were successfully cleaved.

Similar results are seen in the ATR-FTIR spectrum of PAA-b-PI-b-PAA triblock

copolymers (Figure V-10). This result confirmed that tert-butyl groups were cleaved to

acrylic acid groups.


- 117 -

Figure V-7. ATR-FTIR spectra of PI-b-P(t-BA) diblock copolymer (2, Scheme V-1) and

PI-b-PAA diblock copolymer (3, Scheme V-1).

Figure V-8. ATR-FTIR spectra of PI-b-P(t-BA) diblock copolymer (2’, Scheme V-1) and

PI-b-PAA diblock copolymer (3’, Scheme V-1).

PI-b-P(t-BA)

412,7 429,0

471,5

750,9

844,5

1142,6

1255,1 1366,0

1392,0

1447,7

1723,8

2928,2

2963,

417,8

439,4

476,2

503,6 607,9 755,7

842,0

1052,9

1168,2

1251,8

1451,7

1704,2

2954,8

PI-b -PAA

Abs

orba

nce

500 1000 1500 2000 2500 3000 3500 4000 Wavenumber (cm-1)

751,4

845,8

1149,6

1256,8 1367,3

1392,3

1448,8

1728,4

2929,7

2976,7

599,9

780,9 804,5

1041,2 1158,3

1229,5

1413,8

1450,0

1703,2

1756,6 2934,0

Abs

orba

nce

1000 1500 2000 2500 3000 3500

Wave number (cm-1)

PI-b-PAA

PI-b-P(t-BA)


- 118 -

Figure V-9. ATR-FTIR spectra of P(t-BA)-b-PI-b-P(t-BA) triblock copolymer (5, Scheme

V-2) and PAA-b-PI-b-PAA triblock copolymer (6, Scheme V-2).

The PAA block was further confirmed by 13C solid-state NMR spectroscopy (performed by

Dr. Monique BODY, LPEC-UMR CNRS 6087, Université du Maine). The 13C solid-state

NMR spectroscopy was previously used by Mauritz, et al.14 who reported characteristics

of poly(tert-butyl acrylate)-b-polystyrene-b-poly(isobutylene)-b-polystyrene-b-poly(tert-

butyl acrylate) after tert-butyl ester deprotection to target acrylic acid end block

functionality by a thermal process.

A comparison between the 13C CP-MAS solid-state NMR spectrum of the PI-b-P(t-BA)

diblock copolymers (2’, Scheme V-1) and the 13C liquid NMR spectrum of the PI-b-PAA

is presented in Figure V-10. The 13C liquid NMR spectrum (Figure V-10B) shows the

carbonyl carbon at 174.16 ppm and the quaternary carbon at 80.41 ppm corresponding to

P(t-BA) and also presents carbon resonances at 135.90 and 127.15 ppm, corresponding to

polyisoprene. The cleavage of the tert-butyl acrylate to acrylic acid groups to form PI-b-

PAA diblock copolymers was confirmed by the 13C CP-MAS solid-state NMR

spectroscopy (Figure V-10A). We observe that the carbonyl carbon at 174.16 ppm shifts

to 180.00 ppm and the disappearance of the quaternary carbon of the tert-butyl group at

80.41 ppm. The result indicates that the tert-butyl ester group of P(t-BA) was successfully

cleaved to form PI-b-PAA. Similar results are seen in the 13C CP-MAS solid-state NMR

spectrum of PAA-b-PI-b-PAA triblock copolymers (Figure V-11). This result confirms

that tert-butyl ester groups were successfully cleaved.

751,7

844,4

1141,8

1254,8 1365,8

1446,1

1723,1

2977,4

401,1

411,0 792,3

1041,5

1160,5 1237,4

1413,9

1453,1

1698,5

1756,6 2848,4

2916,2 Abs

orba

nce

500 1000 1500 2000 2500 3000 3500

Wave number (cm-1)

PAA-b-PI-b-PAA

P(t-BA)-b-PI-b-P(t-BA)


- 119 -

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

1

1'

2

CDCl3

3

4

3' 4'

Figure V-10. A) 13C solid-state NMR spectrum of PI-b-PAA diblock copolymer (3’,

Scheme V-1) and B) 13C liquid NMR spectrum of PI-b-P(t-BA) diblock copolymer (2’,

Scheme V-1).

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm

1

1'

2

CDCl33 4

3' 4'

Figure V-11. A) 13C solid-state NMR spectrum of PAA-b-PI-b-PAA triblock copolymers

(6, Scheme V-2) and B) 13C liquid NMR spectrum of P(t-BA)-b-PI-b-P(t-BA) triblock

copolymers (5, Scheme V-2).

62

OC12H25

S

S

SO

NH

O O

87

1

2

3

4

62

OC12H25

S

S

SO

NH

O OH

87

1' 3'

4'

80

50OHO

OHO50

S

S

SC12H25

S

S

SC12H25

1'

3'

4'

1'

A)

A)

B)

B)

80

50

OOOO

50

S

S

SS

S

SC12H25

1

2

3

4

1

2

C12H25


- 120 -

The thermal properties of block copolymers before and after dealkylation of the t-BA units

of the block copolymers to form polar acrylic acid (AA) units have been investigated by

TGA. The main TGA parameters are shown in Table V-2.

Table V-2. Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA Thermal degradation stage Entry Sample 1st stage 2nd stage 3rd stage Tmax Weight

loss Tmax Weight

loss Tmax Weight

loss (°C) (%) (°C) (%) (°C) (%)

A-2 PI-b-P(t-BA) (2)a 181 34.5 272 14.3 425 42.4

B-2 PI-b-PAA (3) 242 20.3 432 48.4

A-4 PI-b-P(t-BA) (2’)b 240 38.0 261 9.0 380 46.5

B-4 PI-b-PAA (3’) 261 21.1 427 55.6

A-6 P(t-BA)-b-PI-b-P(t-BA) (5)c 189 37 272 14.2 424 40.4

B-6 PAA-b-PI-b-PAA (6) 266 22.9 429 51.0 - - aentry A-2, Table V-1, bentry A-4, Table V-1, centry A-6, Table V-1.

It can be observed that Tmax of PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA

triblock copolymers (entry B-2, entry B-4 and entry B-6, Table V-2) in the first stage are

shifted to higher temperatures in comparison with Tmax of PI-b-P(t-BA) diblock

copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (entry A-2, entry A-4 and

entry A-6, Table V-2). This result confirms the successful removing of the tert-butyl ester

groups. For the second step, Tmax of PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA

triblock copolymers (entry B-2, entry B-4 and entry B-6, Table V-2) is slightly shifted to

higher temperatures in comparison with Tmax of PI-b-P(t-BA) diblock copolymers and P(t-

BA)-b-PI-b-P(t-BA) triblock copolymers (entry A-2, entry A-4 and entry A-6, Table V-

2). This can be explained by hydrogen bonds interactions occurring between chains leading

to an increase of the thermal stability.

The thermogravimetric curve of the PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA

triblock copolymers (entry B-2, entry B-4 and entry B-6, Table V-2) show that the

thermal degradation takes place through two stages (Figure V-12, Figure V-13 and

Figure V-14). The first one is mainly associated with the dehydration and decarboxylation

reactions of carboxyl groups in PAA block copolymer15 (Scheme V-4) with a Tmax at

242°C, at 261 °C and at 266 °C with a weight loss of 20.3%, of 21.1% and of 22.9%

respectively. The second stage is associated with chain scissions of PAA15 (Scheme V-4)


- 121 -

and attributed to the degradation of polyisoprene part with a Tmax at 432°C, at 427°C and at

429 °C, with a weight loss of 48.4 %, of 55.6% and of 51.6% respectively.

O OH O OHn O O O

n

+ H2O

Dehydration

O O On

Decarboxylation

On O

O O O O OHn

n > 1

O O O O O O

O O O O OHn-1

O O O O O OO OH

or

homolysis

O O O O O O OH

+

+ oligomer or monomer

Chain scission

n

Scheme V-4. Mechanism of the first stage of PAA thermal degradation.15


- 122 -

Figure V-12. Themogravimetric curves for PI-b-P(t-BA) diblock copolymer (entry A-2,

Table V-2) and PI-b-PAA diblock copolymer (entry B-2, Table V-2) under a nitrogen

atmosphere, at a heating rate of 10 °C/min.

A)

B)


- 123 -

Figure V-13. Themogravimetric curves for PI-b-P(t-BA) diblock copolymer (entry A-4,

Table V-2) and PI-b-PAA diblock copolymer (entry B-4, Table V-2) under a nitrogen

atmosphere, at a heating rate of 10 °C/min.

A)

B)


- 124 -

Figure V-14. Themogravimetric curves for P(t-BA)-b-PI-b-P(t-BA) triblock copolymers

(entry A-6, Table V-2) and PAA-b-PI-b-PAA triblock copolymers (entry B-6, Table V-

2) under a nitrogen atmosphere, at a heating rate of 10 °C/min.

A)

B)


- 125 -

Conclusion

The thermal properties of PI-macroCTAs, PI-b-P(t-BA) diblock copolymers and P(t-BA)-

b-PI-b-P(t-BA) triblock copolymers were studied by DSC. The DSC results showed that a

single Tg of PI-macroCTA was observed between −64 °C and −60 °C. Moreover, the PI-b-

P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers exhibited

two values of Tg, one is attributed to the glass transition temperature of the PI block (Tg =

(−40 °C) to (−35 °C)), and the other is related to the glass transition temperature of the P(t-

BA) block (Tg = 37 °C).

The thermal stability of PI-macroCTAs, PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-

PI-b-P(t-BA) triblock copolymers were studied by TGA. The PI microstructures had no

effect on thermal stability of PI-macroCTAs and PI-b-P(t-BA) diblock copolymers. This is

probably due to the fact that the NR-based cis-1,4-polyisoprenes obtained after NR

degradation have low number-average molecular weights.

PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers exhibit

better thermal stability than PI-macroCTA by increasing the maximum degradation

temperature of PI block from 376 °C to 424 °C.

The polarity of P(t-BA) was improved though the cleavage reaction of the tert-butyl ester

units of P(t-BA) block to form PAA block. This leads to PI and PAA based block

copolymers with higher thermal stability than PI-b-P(t-BA) diblock copolymers and P(t-

BA)-b-PI-b-P(t-BA) triblock copolymers. Thus, block copolymers based on PI and

containing PAA blocks could be better suited for high temperature applications when

compared with PI-macroCTAs and PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-

P(t-BA) triblock copolymers.


- 126 -

Experimental section

General Characterization. Infrared spectra were recorded on a Nicolet Avatar 370 DTGS

FT-IR spectrometer in the 4000-500 cm-1 range with a diamond ATR device (attenuated

total reflection) and controlled by OMNIC software. NMR spectra were recorded on a

Bruker Avance 400 spectrometer for 13C liquid NMR (100 MHz). Chemical shifts are

reported in ppm relative to the deuterated solvent resonances. Solid-state 13C NMR spectra

were carried out at room temperature on a BRUKER AVANCE 300 MHz wide bore

spectrometer at 75.47 MHz using Cross-Polarisation (CP) combined with Magic Angle

Spinning (MAS). The spectra were recorded at spinning frequencies equal to 10 kHz.

Chemical shifts are referenced to tetramethylsilane (TMS). For CP-MAS experiments, we

chose the 1H radio frequency field strength such as the π/2 pulse duration was equal to 3.5

µs. The cross polarisation contact time was taken equal to 3.5 ms. A recycle delay of 3 s

between scans was used. A 1H decoupling field of 70 kHz was applied during acquisition.

Thermal transition of samples was measured by DSC Q100 (TA Instrument) Differential

Scanning Calorimeter equipped with the cooling system that temperature can be decrease

to −90°C. Samples were put in the aluminium capsule and empty capsule was used as inert

reference. All experiments were carried out under nitrogen atmosphere at flow rate 50

mL/min with weight of sample 5 to 10 mg. Two scans from −80 to 60°C were performed

with a heating and cooling rate of 10°C/min and the glass transition temperature was

recorded.

Thermogravimetric analysis (TGA) was performed on a TA Instruments (TGA Q 100)

with a heating rate of 10°C min-1 from room temperature to 600°C under nitrogen

atmosphere at a flow rate 90 mL min-1 using 10 mg of sample for analysis.

Materials. All chemicals were purchased from Aldrich unless otherwise noted.

Dichloromethane (99%+) was distilled over CaH2 prior to use. Tetrahydrofuran (99%) and

iodotrimethylsilane (97%) were used as received.

General procedure for deprotection of tert-butyl ester in block copolymers.

Synthesis of PI-b-PAA: The cleavage of the tert-butyl groups from PI-b-P(t-BA) (1,1’,

Scheme V-1) to PI-b-PAA (2, 2’ Scheme V-1) was performed according to a literature

method.13 A quantity of the diblock copolymer (0.2536 g, 0.013 mmol) was dissolved in


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50mL of dichloromethane and a solution of iodotrimethylsilane (0.4 mL, 28.1 mmol,

diluted by 10 mL CH2Cl2) was added. The reaction was stirred at room temperature for 4h,

followed by the removal of the excess solvent and reagents under reduced pressure. The

residue was redissolved in THF. The solution was then dialyzed against nanopure water for

5 days, followed by lyophilisation to afford the final product. White solid polymer was

obtained in a 60% yield.

13C-CP-MAS solid-state NMR : δ (ppm) 180.00 (poly(acrylic acid) backbone, -C=O),

135.90 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 127.15 (cis-1,4-polyisoprene,

-C(CH3)=CH-) and the large board between 16.00 ppm and 55.00 ppm corresponding to

aliphatic carbon of the PI-chain, P(t-BA)-chain and the chain-end.

FTIR: ν(cm-1) 3400-2900 (-OH acid), 1704 (-C=O), 1451 (-CH2), 1168 (C-O), 842 (-CH)

Synthesis of PAA-b-PI-b-PAA: The tert-butyl groups of P(t-BA)-b-PI-b-P(t-BA) triblock

copolymer (1, Scheme V-2) were removed to yield poly(acrylic acid)-b-PI-b-poly(acrylic

acid) (PAA-b-PI-b-PAA) (2, Scheme V-2) following the same procedure as for PI-b-P(t-

BA) diblock copolymer. The P(t-BA)-b-PI-b-P(t-BA) triblock copolymer (0.1536 g,

0.0080 mmol) was dissolved in 50mL of dichloromethane and a solution of

iodotrimethylsilane (0.4 mL, 28.1 mmol, diluted by 10 mL CH2Cl2) was added. The

reaction was stirred at room temperature for 4h, followed by the removal of the excess

solvent and reagents under reduced pressure. The residue was redissolved in THF. The

solution was then dialyzed against nanopure water for 5 days, followed by lyophilisation to

afford the final product. White solid polymer was obtained in a 60% yield.

13C-CP-MAS solid-state NMR : δ (ppm) 180.20 (poly(acrylic acid) backbone, -C=O),

135.90 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 126.40 (cis-1,4-polyisoprene,

-C(CH3)=CH-) and the large board between 16.00 ppm and 55.00 ppm corresponding to

aliphatic carbon of the PI-chain, P(t-BA)-chain and the chain-end.

FTIR: ν(cm-1) 3400-2900 (-OH acid), 1698 (-C=O), 1453 (-CH2), 1160 (C-O), 792 (-CH)


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References

[1] Brandrup, J. I., Edmund H.; Grulke, Eric A.; Abe, Akihiro; Bloch, Daniel R. , Polymer Handbook. 4th ed.; John Wiley & Sons New York, 2005. p V/208.

[2] Zhang, L.; Luo, Y.; Hou, Z., J. Am. Chem. Soc. 2005, 127, 14562-14563. [3] Fernández-García, M.; Fuente, J. L. d. l.; Cerrada, M. L.; Madruga, E. L., Polymer

2002, 43, 3173-3179. [4] Agostini, S. L. D.; Constantino, L. J. C.; Job, E. A., J. Therm. Anal. Calorim. 2008,

91, 703-707. [5] Moreno, R. M. B.; De Medeiros, E. S.; Ferreira, F. C.; Alves, N.; Goncalves, S. P.;

Mattoso, L. H. C., Plastics, Rubber and Composites 2006, 35, 15-21. [6] Medeiros, E.; Galiani, P.; Moreno, R.; Mattoso, L.; Malmonge, J., J. Therm. Anal.

Calorim. 2010, 100, 1045-1050. [7] Kent, E. G.; Swinney, F. B., I&EC Product Research and Development 1966, 5, 134-

138. [8] Brydson, J. A., Plastic Materials. 5th ed.; Butterworths: London, 1989. p 272. [9] Huang, H.; Remsen, E. E.; Kowalewski, T.; Wooley, K. L., J. Am. Chem. Soc. 1999,

121, 3805-3806. [10] Lu, Z.; Liu, G.; Liu, F., J. Appl. Polym. Sci. 2003, 90, 2785-2793. [11] Murthy, K. S.; Ma, Q.; Remsen, E. E.; Tomasz, K.; Wooley, L. K., J. Mater. Chem.

2003, 13, 2785. [12] Cheng, C.; Qi, K.; Khoshdel, E.; Wooley, K. L., J. Am. Chem. Soc. 2006, 128, 6808-

6809. [13] Li, Z.; Ma, J.; Cheng, C.; Zhang, K.; Wooley, K. L., Macromolecules 2010, 43,

1182-1184. [14] Kopchick, J. G.; Storey, R. F.; Jarrett, W. L.; Mauritz, K. A., Polymer 2008, 49,

5045-5052. [15] McNeill, C. I.; Sadeghi, T. M., Polym. Degrad. Stab. 1990, 29, 233-246.

General conclusion

General conclusion

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The objective of our research work was the synthesis of well-defined diblock copolymers and

triblock copolymers based on a polyisoprene (PI) block obtained from natural rubber via

Reversible Addition-Fragmentation chain transfer (RAFT) polymerization. The PI block was

used as a macromolecular chain transfer agent (macroCTA) to perform the RAFT

polymerization of tert-butyl acrylate. Then, the synthesis of well-defined trithiocarbonate

functionalized telechelic PIs was developed using two different strategies. The first one is based

on the oxidative degradation of natural rubber followed by reductive amination and amidation,

and the second one is based on the functional metathesis degradation of NR. It is interesting to

observe that no previous studies have been reported on the synthesis of NR-based block

copolymers by RAFT polymerization.

In order to compare final thermal properties of block copolymers taking into account the PI

microstructure, we first synthesized block copolymers via successive RAFT polymerization of

isoprene and t-BA. Well-defined PI (PDI = 1.23) with a mixture of microstructures was

obtained via RAFT polymerization. The microstructures consist of 90% of 1,4-PI (60% trans

and 40% cis), 5% of 1,2-PI and 6% of 3,4-PI. We found that the use of PI as macroCTA to

mediate the RAFT polymerization of t-BA using AIBN as initiator ([t-BA] 0/[PI-

macroCTA]0/[AIBN] 0 = 250/1/0.2) at 60 °C for 2.5h leads to well-defined PI-b-P(t-BA) that

presents unimodal molecular weight distribution and low polydispersity index (1.40). The

copolymer has a nM equal to 16,000 g.mol-1 as determined by SEC and a nDP (PI) equal to

90 and a nDP P(t-BA) equal to 72 as determined by 1H NMR spectroscopy.

A new trithiocarbonate functionalized telechelic cis-1,4-polyisoprene was synthesized via the

oxidative degradation of natural rubber followed by reductive amination and amidation. The

microstructure of the functionalized PI is strictly cis-1,4. The end-functionality was determined

by 1H-NMR spectroscopy and clearly demonstrated that telechelic cis-1,4-polyisoprene chains

carry the trithiocarbonate moiety. We demonstrated that the chain extension of the

trithiocarbonate functionalized cis-1,4-PI starting block resulted in an efficient block copolymer

formation. PI-b-P(t-BA) diblock copolymer presents an unimodal SEC trace and polydispersity

index equal to 1.76. The copolymer has a nM equal to 26,000 g.mol-1 as determined by SEC

and a nDP (PI) equal to 62 and nDP (P(t-BA)) equal to 87 as determined by 1H NMR

spectroscopy.

General conclusion

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In addition, a new α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene was

also prepared via functional metathesis degradation from NR in the presence of second

generation Grubbs catalyst (GII) and a bistrithiocarbonyl-end functionalized olefin as CTA.

Formation of telechelic natural rubber occurs rapidly in a single-step process. The nM was

equal to 8,200 g. mol-1 as determined by SEC after 4h of reaction at 25 °C. A perfectly

bifunctional telechelic PI was obtained using a ratio of [NR]0/[GII] 0/[CTA)] 0 to 100/1/2 at 25°C.

Moreover, the difunctional telechelic PI has a strictly cis-1,4-microstructure. It was successfully

used as macroCTA for the RAFT polymerization of t-BA to form well-defined P(t-BA)-b-PI-b-

P(t-BA) triblock copolymer. The final copolymer has a nM equal to 23,300 g.mol-1, PDI equal

to 1.50 as determined by SEC and a nDP (PI) equal to 80 and nDP (P(t-BA)) equal to 100 as

determined by 1H NMR spectroscopy.

A comparison can be made between the PI-macroCTAs obtained using the three different

techniques: RAFT polymerization of isoprene, oxidative degradation of natural rubber followed

by reductive amination/amidation and metathesis degradation from NR. All three techniques

produce PI with well-defined trithiocarbonate end groups that can be chain extended with t-BA

to form block copolymers. The PI-macroCTA obtained from polymerization of isoprene has a

PDI of 1.23. However, the microstructure of PI-macroCTA is not well-defined and consists of a

mixture of 1,4-PI, of 1,2-PI and of 3,4-PI. By contrast the PI-macroCTAs obtained from the

degradation of NR by either oxidative degradation or metathesis degradation features a strictly

cis-1,4-microstructure. Oxidative degradation produces α-trithiocarbonyl-ω-carbonyl-cis-1,4-PI

whilst metathesis degradation leads to α, ω-bistrithiocarbonyl-cis-1,4-PI. The PDIs of these PI-

macroCTAs are broader (PDI ∼1.60-1.70) but after chain extension with t-BA, copolymers of

similar characteristics were obtained regardless of the preparation of the starting PI-macroCTA.

Finally, the thermal properties were studied by DSC and TGA. The DSC results showed that a

single Tg of PI-macroCTA was observed between −64 °C and −60 °C. Moreover, DSC results

showed that PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers

have two glass transition temperatures characteristic of each block, one at −35 °C corresponding

to PI block and the other at 37 °C corresponding to P(t-BA) block. This increase of Tg of PI

block copolymers is a supplementary proof of the successful synthesis of PI-b-P(t-BA) diblock

copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers.

General conclusion

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In this work, we have shown that block copolymers based on PI can be synthesized form NR as

a renewable raw material. These investigations show that PI-macroCTAs from NR can be used

successfully for the formation of well-defined block copolymers containing P(t-BA) by either

PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers. The

polarity of P(t-BA) block and PAA block improve the thermal stability of PI block copolymers,

with increased polarity of the second block leading to increased thermal stability by more

interactions between the chains.

A possible extension of this work is the study of the adhesive performance of block copolymers

based on PI/P(t-BA) and PI/PAA for adhesive application on polar substrate such as stainless

steel. This is because the polar groups can rearrange and there after, orients to the interface

between the adhesive and the polar substrate, so as to minimize interfacial free energy during

adhesion. At the same time, hydrogen bonds can form between the polar groups and those in the

substrate. In addition, block copolymers based on PI/P(t-BA) and based on PI/PAA showed a

higher thermal stability than PI that may be used for high temperature adhesive applications.

Moreover, the unsaturated repeating units of the polyisoprene block can be chemically modified

by epoxidation to improve adhesive strength via crosslinking reaction. In addition, polymers

containing epoxide groups, such as poly(glycidyl (meth)acrylate) suitable to be synthesized by

RAFT polymerization in a control way could be employed. The main interest in those polymers

is largely due to the ability of pendant epoxide groups to be crosslinked by amines such as

diethylenetriamine. These advantages led to its explosive use as adhesive in industries.

Another possible extension of this work can be the development of adhesives in form of

waterborne or dispersion adhesives. The dispersion adhesive form is interesting in many

industrial and research work due to the use of water which has no negative impact for the

environment. Moreover, it has many advantages such as a safe man-working, a save storage and

a save distribution. The PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA triblock

copolymers can be dispersed in aqueous medium to form micelle structures due to the

incorporation of two different block segments. The hydrophobic segment is a polyisoprene

block and the hydrophilic segment is a poly(acrylic acid) block.

General conclusion

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In conclusion, we have established a new methodology for the formation of trithiocarbonyl-end

functionalized telechelic cis-1,4-PI obtained from natural rubber. This technique involves the

functional metathesis degradation on NR. It is unique and powerful as the degradation and the

functionalization of NR occurs in a one-pot process. In addition, the reactive functional

precursors could be further chain extended with a wide range of monomers by RAFT

polymerization. Such controlled/living radical polymerization is a powerful process to prepare

well-defined block copolymers containing a cis-1,4-PI issued from NR which has a great

interest as it is a renewable resource. Then, our results bring new synthetic routes to develop

materials based on a biopolymer which is a renewable resource.

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Thesis Nitinart last version - Le Mans University