A stable free radical (2,2,6,6-tertamethylpiperidinyl-1-oxy, TEMPO) polymerization technique was applied to a graft polymerization of styrene (ST) to polypropylene (PP). PP peroxides produced by gamma -irradiation (7.2, 12, End 35 kGy) in air were used as macromolecular initiators for grafting. Grafted polystyrene (PS,,rt) was cleaved from the main PP chain by reaction with trifluoroacetic acid. The molecular weight (M-n) and polydispersity of the PSgraft and the free (nongrafted) polystyrene (PSfree) were determined by GPC. These PS's have almost the same M-n (nearly theoretical M-n) and narrow polydispersity. Nitroxide-terminated PS grafted to the PP was chain extended by sequential activation of the dormant chain ends in the presence of additional ST monomer. The polydispersity of the extended PSgraft remained narrow. A controlled random graft copolymer of PP with ST and n-butyl methacrylate was also synthesized using this technique.