Poly(styrene-co-acrylonitrile)-graft-polyacrylonitrile graft copolymers were prepared using a mixed (free-radical/anionic) mechanism technique. For this purpose, poly(styrene-co-acrylonitrile) random copolymers which contain different amounts of acrylonitrile segments were regarded as saturated high-molecular-weight nitrile compounds and were allowed to react with tetrakis(dimethylamino)titanium. By this treatment pendant nitrile groups were transformed to organometallic active sites. These active groups lead to the polymerization of acrylonitrile via an anionic insertion process. Polyacrylonitrile grafts were grown on the poly(styrene-co-acrylonitrile) backbone.