This document discusses polymerization methods, including homogeneous and heterogeneous techniques. Homogeneous techniques involve a pure monomer or homogeneous monomer-polymer solution, and can be bulk or solution polymerization. Bulk polymerization produces high purity polymers but becomes difficult to control at high conversion due to increased viscosity. Solution polymerization uses a solvent to reduce viscosity and aid heat transfer. Heterogeneous techniques include suspension and emulsion polymerization, where the formed polymer is insoluble and precipitates out. Suspension uses an aqueous system to disperse the monomer phase, while emulsion polymerization employs an emulsifier and water to disperse the monomer and form polymer particles.

1. Muhammad Furqan
Roll No : 16103123-006

2.  A chemical reaction in which two or more
small molecules combine to form larger
molecules that contain repeating structural
units of the original molecules.

3.  Monomers may be polymerized by the
following methods:
 (1) Polymerization in homogeneous systems
 (2) Polymerization in heterogeneous systems

4.  The homogeneous polymerization techniques involve
pure monomer or homogeneous solutions of
monomer and polymer in a solvent.
 These techniques can be divided into two methods:
 (i) Bulk polymerization
 (ii) Solution polymerization

5.  Bulk polymerization is the simplest technique and
produces the highest-purity polymers.
 This method helps easy polymer recovery and
minimum contamination of product.
 The viscosity of the mixture is low initially to allow
readily mixing, heat transfer, and bubble elimination,
this method is used for the preparation of polyethene,
polystyrene, etc.

6.  Reaction medium becomes increasingly viscous as
reaction goes to higher conversion, making stirring,
heat removal and processing more difficult.
 Loss of monomer
 Near the end of polymerization, the viscosity is very
high and difficult to control the rate as the heat is
“trapped” inside.
 It leads to the auto acceleration process in which the
propagation rate is very higher than that of
termination rate, this method is seldom used in
commercial manufacture.

7.  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 auto acceleration.
 It requires the correct selection of the solvent. Both
the initiator and monomer be soluble in each other
and that the solvent are suitable for boiling points.

8.  It is often used to produce copolymers, this method is
used for the preparation of:
 polyvinyl acetate (C4H6O2)n
 poly (acrylic acid) (C3H4O2)n
 Polyacrylamide (C3H5NO)n

9.  Solvent has low viscosity, reaction mixture can be
stirred.
 Thermal control is easier than in the bulk.
 Aids in removal of heat of polymerization.

10.  Reduce monomer concentration which results in
decreasing the rate of the reaction and the degree of
polymerization.
 Difficult to remove solvent from final form, causing
degradation of bulk properties.
 Small production per reactor volume.
 Not suitable for dry polymers.

11.  Heterogeneous polymerization is a process that
begins initially as a homogeneous system in the
continuous phase, where the monomer and initiator
are completely soluble, but upon initiation the formed
polymer is insoluble and thus precipitates.

12.  Suspension polymerization consists of an aqueous
system with monomer as a dispersed phase and
results in polymer as a dispersed solid phase
 Monomer, initiator (must soluble in monomer) and
polymer must be insoluble in the suspension media.
 This method is used for the preparation of
polystyrene, polyvinyl chloride, polyvinyl acetate,
etc.

13.  An emulsion polymerization consists of
(a) Water (solvent or as the heat-transfer agent)
(b) Monomer
(c) Initiator (is soluble in water and insoluble in the
monomer)
(d) An emulsifier : It is a compound or substance that
acts as a stabilizer for emulsions preventing the
liquids from separating(such as sodium salt of
long-chain fatty acid).
 This method is used for the preparation of
polyvinyl acetate, butadiene/styrene/acrylonitrile
(C8H8·C4H6·C3H3N)n , polychloroprene copolymers
etc