The polymer peroxide surfactants obtained by copolymerization of a peroxide monomer with maleic anhydride were either physically or chemically sorbed on the dispersed-phase surfaces, for example, on mineral fillers and latex particles. Subsequent initiation of graft copolymerization from the surface resulted in the formation of interfacial compatibilizing polymer layers in water emulsions and dispersed-filled polyethylene. The morphology of the resulting filled polymer was characterized by scanning electron microscopy. (C) 2000 John Wiley & Sons, Inc.