Step II Chain propagation step The new free radical adds to another molecules of monomer to form a larger free radical .
Step III Chain termination step There are three ways of chain termination : Coupling reaction , disproportionation reaction , chain transfer reaction . One mode of termination of chain is shown as under :
( ii ) Cationic polymerisation It involves formation of carbocation which are generated by Lewis acids ( like BF3 , AICI3 , SnCI4 , etc .) and protonic acids such as H2SO4 , HF , etc .
Higher the stability of carbocation intermediate , more is the reactivity of monomers towards cationic addition polymerisation . It involves the following steps :
Step I . Initiation Step