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Chapter 5:Polymerization Techniques

1. Bulk polymerization

2. Solution polymerization

3. Suspension polymerization

4. Emulsion polymerization

5. Interfacial condensation polymerization

6. Etc.

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1. Bulk Polymerization :

- Liquid monomer- Initiator- Inhibitors- Chain transfer agents

Homogeneous : polymer remains dissolved in monomers. Ex. PMMA

Heterogeneous : aka. Precipitation polymerization polymer is insoluble in its monomers. Ex. Polyacrylonitrile, PVC

Problem : heat transfer not good

Make objects with a desirable shape by polymerization in a mold.

In the reactor:-

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I

I

I

IInitiator

I

I

I

IInitiator

Monomer

Model of Batch Polymerization

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Pros & Cons of Bulk Polymerization

Advantage Disadvantage

- Obtain purest possible polymer

- Conveniently cast to shape

- Obtain highest polymer yield per reactor volume

- Difficult to control

- Reaction has to be run slowly

- Cannot get high rate and high MW at the same time

- Difficult to remove last traces of unreacted monomer

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Ex. 1 The maximum possible temperature rise in a polymerizing batch may be calculated by assuming that no heat is transferred from the system. Estimate the adiabatic temperature rise for the bulk polymerization of styrene, Hp = -16.4 kcal/mol, molecular weight = 104•Solution Hp for polymerization of styrene = 1640,0 cal/mol (assuming complete conversion ) meaning that polymerization of 1 mol styrene release heat in the amount of 16,400 calories.•In the absense of heat transfer, all this energy heats up the reaction mass.• To a reasonable approximation, the heat capacity of most liquid organic systems may be taken as 0.5 cal/g-oC From Q = mc T

max116, 400 315 (!)104 0.5

oocal mol g CT x x C

mol g cal

(Note that- Boiling point of styrene = 146 oC)

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Solution Polymerization : Monomer dissolved into inert- solvent / inhibitor

- Monomer- Initiator- CTA- Inert solvent

Use for :

Solvent helps controlling heat transfer from reaction.

- Thermosetting condensation polymer (stop before gel point)

- Ionic polymerization

- Ziegler-Natta solution process

2. Solution Polymerization

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Model of Solution Polymerization

I

I

I

I

IMonomer

Solvent

Initiator

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The effect of solvent solubility on the molecular weight of polyurethane produced by

solution methodSolvent Viscosity of

polymer solution

Precipitation of polymer out of

the solutionXylene

Chlorobenzene

Nitrobenzene

Dimethyl sulfoxide

0.060.170.360.69

Precipitate immediately

Precipitate immediately

Precipitate within 0.5 hr.

Polymer remain dissolved in solution

Viscosity of polymer MWpolymer

High viscosity = high molecular weight !

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- Rate [M] reduce rate, chain length xn

- Solvent waste - Need solvent separation & recovery- Have traces of solvent, monomer- Lower yield

-Solvent may not be really inert (May interfere w/ rxn.-act as CTA)

Advantage Disadvantagesolvent

- Reduces the tendency toward autoacceleration

- Increases heat capacity/heat- transfer

- Reduces viscosity

- Minimize runaway reaction

Pros & Cons of Solution Polymerization

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Ref: S.L. Rosen, John Wiley & Sons 1993

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Ex. 2 Estimate the adiabatic temperature rise for the polymerization of a 20% (by weight) solution of styrene in an inert organic solvent

Solution In 100 g of the reaction mass, there are 20 g of styrene,

so the energy liberated on its complete conversion to polymer is

• Temperature rise is calculated from Q = mc T

Therefore, the adiabatic temperature rise is thenmax

( ) 1(3150 ) 63(0.5 ) (100 )

oog CT cal C

cal g

(1 ) (16400 )(20 ) 3150(104 ) ( )mol calg calg mol

13Ref: S.L. Rosen, John Wiley & Sons 1993


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3. Suspension Polymerization :

Monomer into water, suspending agents (Ex.Ionic detergent, barium sulfate)

- Ex. Polyvinyl alcohol- Beads of polymer ( 10-1000 m)

Watermonomer

Water(Hydrophilic)

Initiator+

(Hydrophobic)

Suspending agent

Model of suspension polymerization

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Typical Composition:

Monomer (hydrophobic)Initiator (dissolved in monomer) Monomer phaseChain-transfer agent (dissolved in monomer)

Water – suspending medium Protective Colloid

Suspending agent Insoluble inorganic salt

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Pros & Cons of Suspension Polymerization

Advantage1. Easy heat removal

and control2. Obtain polymer in a

directly useful from

Disadvantage

1. Low yield / reactor volume

2. Traces of suspending agent on particle surfaces

3. Cannot run continuously

4. Cannot be used for

-condensation polymers

-ionic or Ziegler-Natta polymerization


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Emulsion Polymerization : Use emulsifier / soap

monomerWater

SoapInitiator

(Hydrophilic)

-Reaction occurs in water phase until polymer gets very hydrophobic and then dissolve back in the monomer region.

Ex. Latex - very very small particle stable in solution - particle size << 1 m - can generate very high MW. polymer

4. Emulsion Polymerization

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Emulsion Polymerization (cont.):

Typical ingredient

100 part (by wt.) monomer (water insoluble)180 part water2-5 parts acid soap0.1-0.5 part water-soluble initiator0-1 part CTA (monomer soluble)

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-growing polymer particle-Monomers inside the micelle decrease

Unreacted monomers in other micelles and in droplets diffuse through water to the growing particles

Reaction terminates when 2nd radical gets in reaction starts again for the 2nd chain when 3rd particle gets in.

Steps in Emulsion Polymeriztion

Water-soluble initiatorPolymer born in water

Monomer swollen micellePolymer moves to micelle



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Interfacial Polycondensation of Nylon 6/11water

CCl4

Advantage :

2622 NHCHNH

ClCCHCCl 82

o= o=

Monomer1 : Hexamethlyene diamine

Monomer2 : Sebacoyl chloride

HClCCHCNCHNClCCHCClNHCHNH 8262822622

o= o= o= o=H=H=

Polymer formed at interface

2622 NHCHNH

ClCCHCCl 82

o= o=

Commercial scale easier to stir the phases together

- Reaction rapid at room temperature (no need for high T., vacuum P.)

5. Interfacial Polycondensation

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การดึงเสน้ใยไนลอนจากผิวสมัผัสของสารละลาย

Experiment onInterfacial Polycondensation of Nylon 6/11

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Pros Cons

Bulk - easy- No contamination

- Difficult to control temp. and heat transfer- High viscosity

Solution -good heat transfer-easy to control reaction temp.-low viscosity-polymer produced may be used directly in the solution form

- Need to use solvent –adding cost -Difficult to eliminate solvent entirely -Solvents sometimes act as chain transfer agent leading to lower MW polymer

Suspension - Good heat transfer- easy to control reaction temp.- low viscosity- polymer produced may be used directly as polymeric suspension

-Need extra process in washing out suspending agent/contaminants and drying the polymer beads-Polymer beads may stick together and maybe contaminated with suspending agent -Good only for addition polymerization using hydrophobic free radical initiator.

Emulsion -- Good heat transfer- easy to control reaction temp.- low viscosity- polymer produced may be used directly as polymer latex

-Need extra process in washing out emulsifier/ contaminants and drying-Good only for addition polymerization using hydrophilic initiator.

Interfacial -Reaction is fast at room temp. and pressure. No need for high temp. like in normal polycondensation.-Can produce polymer in fiber form - Good heat transfer- low viscosity

-Limited to polycondensation where the two reactants are insoluble in each other ex. Acid chloride (quite expensive)- Need extra process in recovering solvent and excess reactants

Pros & Cons of some polymerization techniques

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conditions บลัค์(bulk)

สารละลาย(solution)

ระหวา่งผิว (interfacial)

Temp สงู จำากัดอยูท่ี่จุดหลอมเหลวและจุดเดือดของตัวทำาละลายโดยทัว่ไปทำาท่ีอุณหภมูหิอ้ง

Heat stabilization จำาเป็น ไมจ่ำาเป็น ไมจ่ำาเป็นKinetic of Reaction

สมดลุ เป็นขัน้ สมดลุ เป็นขัน้ บอ่ยครัง้ไม่สมดลุ คล้ายปฏิกิรยิาลกูโซ๋

Reaction time

1 ชัว่โมงถึงหลายวนั

หลายนาทีถึง 1ชัว่โมง

หลายนาทีถึง 1ชัว่โมง

Productivity

สงู ตำ่าถึงสงู ตำ่าถึงสงู

Equality of reactants

จำาเป็น ไมค่่อยจำาเป็น ไมจ่ำาเป็น

Purity of reactants

จำาเป็น ไมจ่ำาเป็น ไมจ่ำาเป็น

Equipment พเิศษ ระบบปิด ง่ายๆ ระบบเปิด

ง่ายๆ ระบบเปิด

Pressure สงู, ตำ่า บรรยากาศ บรรยากาศ

Comparing different techniques for Polycondensation

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6. Gas-Phase Olefin Polymerization :

- Use Zieler-Natta catalyst

- Moderate P (7-20 atm)

- Low temperature ( < 100 oC)

- Use fluidized bed reactor

Good Point :- No solvent

- Monomer separation is easy

- Low capital + operating cost

