The graft copolymers formed in situ in the 75/25 (wt/wt) mono-carboxylated polystyrene [PS-mCOOH]/poly(methyl methacrylate-ranglycidyl methacrylate) [PMMA-GMA] blends depending upon the molecular weight and the number of the epoxy functional groups (f) in PMMA-GMA were characterized using proton nuclear magnetic resonance spectroscopy and gel permeation chromatography. The graft copolymers formed in a homogeneous blend of PS-mCOOH/poly(styrene-ran-glycidyl methacrylate) [PS-GMA] were compared with those formed in the heterogeneous blend of PS-mCOOH/PMMA-GMA. For the homogeneous blend, the number of chains (n) of PS-mCOOH grafted onto a PS-GMA in in situ formed graft copolymers was similar to4 although the maximum possible rt is similar to7. This is due to the steric hindrance by the already existing grafted chains. However, for the heterogeneous blends, n appeared not to be much affected by both f and the molecular weight of PMMA-GMA, and n was similar to1 because of the existence of an interface between PS and PMMA phases in addition to the steric hindrance. The weight fraction of graft copolymers in the blends, w(copolymer)(blend) was found to increase with f. However, the interfacial areal density of PMMA-g-PS was constant as similar to0.02 chains/nm(2) regardless of f and the molecular weights of initially added PMMA-GMA. (C) 2001 Published by Elsevier Science Ltd.