Why is cationic polymerisation preferred in case of Vinylic monomers containing electron donating groups?

in vinyl polymerisation the chain propogates with apositive charge on the active center in the cationic polymerisation process .if an electron donating group is present on the vinyl center at its active center it stabilises the positive charge by its +i effect and hence it is preferred to have electron donating group attached to vinyl polymers in cationic polymerisation