Free Radical Polymerization
Free radical polymerization follows the same three steps mentiond in radical reactions:
- Initiation
- Propagation
- Termination
Initiation
The Initiation process in free radical polymerization reactions has two stages:
- Decomposition - and formation of free radicals.
- Addition - of a monomer molecule to free radical.
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Decomposition of initiator
The initiator is commonly a molecule with two mirror-images parts joined by a single or double bond. The bond is usually broken thermally ( thermal decomposition ) but it can also be broken by light ( photochemical decomposition ).
For example benzoyl peroxide
and 2,2-azobisisobutyronitrile ( called AIBN )
Addition of radical to monomer
Once the free radical is formed a monomer molecule
if we represent the free radical ( formed the initiator I ) as 
and the monomer molecule as 
, then the complete initiation process can be represented as folloes:
Mechanism
Propagation
The chain radical formed in the initiation setp is capable od adding successive monomers to propagate the chain ( make the chain longer ).
Termination
Termination of a polymerization reaction can occur by two mechanisms:
- Combination
- Disproportionation
Termination – By Combination
Termination – By Disproportionation
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