What is polymerization?
• polymerization, any process in which relatively small molecules,
called monomers, combine chemically to produce a very large
chain like or network molecule, called a polymer.
Chain growth polymerization
• Chain growth polymer is also known as addition polymer.
• A chain-growth polymer is a polymer which is formed when
molecules of the same monomer or different monomers add
together on a large scale to form the polymer.
• Chain growth polymerization is mainly classified into 3 types:
1.Free radical addition polymerization
2.Cationic polymerization
3.Anionic polymerization

1.Free radical addition polymerization
• Free-radical polymerizations are chain reactions in which the addition of
a monomer molecule to an active chain-end regenerates the active site
at the chain-end.
• Free-radical polymerizations is always done in presence of heat or
sunlight.
• Free Radical Polymerization occurs in three steps, i.e.
(1) Initiation
(2) Propagation
(3)Termination.
(1) Initiation
• Initiation is the first step in the polymerization process.
• An active centre is generated in this process to begin polymerization.
• All the monomers are not liable for the initiation process.
• One or two radicals are created from the initiating molecules in the first
step.
• Radicals are transferred from the initiating molecules to the monomer
units in the second step.

• NOTE: If we want to start initiating step for polymerization then
we need any peroxide group (benzoyl peroxide, Acetyle peroxide,
di-oxide etc) that creates free radical for chain growth.

(2) Propagation
• A polymer spends most of its time expanding its chain length or
propagating. After initiation of free radical, it attacks another monomer
subunit.
• After initiation, the chain propagates until no monomer is left or
termination starts.

(3)Termination
• Termination is the final step in the polymerization process.

Applications of Free Radical Polymerization
• It is used in synthesizing polystyrene and elastomers.
• It is used in synthesizing chemical surfactants, lubricants.

Some Common Addition Polymers

2.Cationic polymerization
• Cationic polymerization is a type of chain growth polymerization in
which a cationic initiator transfers charge to a monomer which
then becomes reactive.(it initiated by Acid)
• For cationic polymerization, requires Strong Acids like H₂SO₄/Lewis
acids(AlCl₃).
• Suppose we take H₂SO₄ and in solution it gives H+ + HSO4
– ions.
(H₂SO₄ ------ > H+ + HSO4
– ) (As we know that H+ Requires
electrons so take ethylene as example.)

Example of Cationic polymerization
Polystyrene, poly isobutylene.
3.Anionic polymerization
• Cationic polymerization is a type of chain growth polymerization in which
an anionic initiator transfers charge to a monomer which then becomes reactive.(it
initiated by Base)
• For anionic polymerization,requires Strong Base like NaNH2(sodamite)/ R−Mg−X
(Grignard reagent)