Types of Polymerisation
1. Chain Growth Polymerisation or Addition Polymerisation
It involves formation of reactive intermediate such as free radical, a carbocation or a carbanion. For this polymerisation monomers used are unsaturated compounds like alkenes; alkadienes and their derivatives. Depending upon the nature of the reactive species involved. chain growth polymerisation occurs by the following mechanisms:
Free radical addition polymerisation Cationic polymerisation Anionic polymerisation
( i) Free radical addition polymerisation The monomers used are generally monosubstituted alkenes. The most commonly used catalysts are benzoyl peroxide, hydrogen peroxide or t- butyl peroxide etc.
Mechanism The reaction involves the following steps
Step I Chain initiation step In this step, peroxide undergoes homolytic fission, e. g., benzoyl peroxide on heating produces phenyl initiator free radical.