A novel approach for the compatibilization of heterogeneous polymer blends with interface-active high-molecular-weight peroxides is presented. This three-step approach includes the synthesis of an anchor peroxide copolymer, the preparation of an interface-active, peroxide-containing graft copolymer (precompatibilizer) on its basis, and the localization of the precompatibilizer at the interfaces of the polymer blends during reactive blending with the in situ formation of compatibilizer macromolecules. We found that the precompatibilizer incorporating polypropylene fragments compatibilized blends of polypropylene with polystyrene, polyethylene, and unsaturated polyester resin. This verified a certain universality of the approach proposed for the compatibilization of polymer blends. (C) 2005 Wiley Periodicals, Inc.