Methods of Free Radical PolymerizationMethods of Free Radical Polymerization

There are four commonly used methods for free radical polymerization

1. Bulk polymerization 2. Solution polymerization3. Suspension polymerization4. Emulsion polymerization

BULK POLYMERIZATIONBULK POLYMERIZATION

The simplest method of polymerization where the reaction mixture contains only the monomer and a monomer soluble initiator.

ExamplePMMA

ADVANTAGEADVANTAGE

Advantage of the high concentration of monomer result in

1. High rates of polymerization 2. High degree of polymerization 3. High purity of product 4. High molar mass polymer are produce

DISADVANTAGEDISADVANTAGE

Increase in the reaction viscosity with conversion. *difficulty in removing heat. *autoacceleration *if the polymer formed is insoluble in the

monomer (such as acrylonitrile, vinyl chloride) ==> precipitating of the polymer and we can not apply the kinetics.

SOLUTION POLYMERIZATIONSOLUTION POLYMERIZATION This method is used to solve the problems associated with the bulk

polymerization because the solvent is employed to lower the viscosity of the reaction, thus help in the heat transfer and reduce autoacceleration.

BUT The disadvantage of solvent presence is1. Reduce monomer concentration which results in decreasing

the rate of the reaction and the degree of polymerization.2. Solvent may cause chain transfer.3. Clean up the product with a non solvent or evaporation of

solvent.

SUSPENSION POLYMERIZATIONSUSPENSION POLYMERIZATION

This method is used also to solve the problem of heat transfer.

It is similar to bulk polymerization where the reaction mixture is suspended as droplets in an inert medium.

Monomer, initiator and polymer must be insoluble in the suspension media such as water.

EMULSION POLYMERIZATIONEMULSION POLYMERIZATION This is similar to suspension polymerization except that

the initiation is soluble in suspension media and insoluble in the monomer.

The reaction product is colloidally stable dispersion known as latex.

The polymer particles have diameter in the range of (0.05 - 1 m) smaller than suspension.

IONIC POLYMERIZATION IONIC POLYMERIZATION Chain polymerization of olefinic monomers which can occur

with charged radicals. For example styrene.

Cationic polymerization when the radical is positively charge. CH2-C+H X

Anionic polymerization when the radical is negatively charge CH2-C--H

X

This polymerization are more monomer specific than free radical polymerization and will proceed only with monomers that have substituent groups which can stabilize the active center.

For cationic polymerization the active center will proceed if X group is able to donate electrons or delocalize the positive charge.

For anionic polymerization the active center will proceed if X group is able to withdraw electrons or delocalize the negative charge.

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