AbstractThis paper extends our previous study of the morphology and properties of polyblends of a polycarbonate and poly(methyl methacrylate) to an investigation of the influence of small amounts of added graft copolymer. The results demonstrate that, in spite of the complexity of the molecular species involved, graft copolymers can act as effective surfactants in polymer blends. The dominant effect is to form finer dispersions of one component in the other, with commensurate increases in interfacial area. A preliminary investigation of the influence of molecular parameters in the graft copolymer is reported; in all cases the molecular weight of the poly(methyl methacrylate) in the copolymer was kept constant and greater than that of the homopolymer whereas the molecular weight of the polycarbonate was varied. Finer dispersions and greater modifications to the relaxation behaviour were found as the molecular weights of the polycarbonate blocks in the copolymer increased and became comparable with the molecular weight of the homopolymer, and as the copolymer content increased.