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 .