Polybutadiene-polystyrene graft copolymers were prepared by free radical coupling method at 80 degrees C. Oligo(adipoyl-5-peroxy-2,5-dimethyl n-hexyl peroxide) or oligo dodecandioyl peroxide were used in the polymerization of styrene at 60 or 80 degrees C to prepare active polystyrene samples having undecomposed peroxy groups in the main chain. Homogeneous mixtures of active polystyrene and polybutadiene gave graft copolymers at 80 degrees C under vacuum. Polystyrene-g-polybutadiene copolymers were separated from corresponding homopolymers by fractional precipitation. UV,IR,NMR and GPC techniques were used for analysis of pure graft copolymers formed in the yield range between 12% and 92%. DSC curves of graft copolymers exhibited a wide endotherm transition between 40 and 80 degrees C while the corresponding homopolymers showed only glass transitions.