Styrene/methyl methacrylate (75/25) monomer mixtures were copolymerized at 323 K in the presence of a polybutadiene seed latex using either a water soluble (potassium persulfate) or an oil soluble (cumene hydroperoxide) initiator. The polybutadiene seed latex was made via an emulsifier free emulsion polymerization process. The graft copolymerizations were performed over a range of emulsifier concentrations. The emulsifier free polymerization with cumene hydroperoxide shows a very high degree of grafting while neither secondary nucleation nor coagulation was observed. Furthermore, the graft polymers have been extensively studied in terms of intra- and intermolecular microstructure. For this purpose, the breaking of the polymer backbone by means of ozonolysis was necessary. The grafted styrene/methyl methacrylate copolymer is less rich in styrene than the free copolymer. The chemical composition distributions of the graft copolymer were broader than those of the free copolymer.