The synthesis of a new macroinitiator for cationic polymerization via radical polymerization is presented. The macroinitiator, consisting of poly(methyl methacrylate)-block-poly[styrene-co-(4-chloromethylstyrene)], was synthesized by heating poly(methyl methacrylate), prepared in the presence of 1,1-diphenylethylene, in a mixture of styrene and 4-chloromethylstyrene to 85 degreesC without any additional initiator. The resulting macroinitiator could be used for the catonic polymerization of isobutylene yielding graft copolymers.