The graft copolymerization of n-butyl methacrylate monomer onto compounded poly(vinyl chloride) was carried out by melt-mixing process in a Brabender plasticorder (BPCR) using a free-radical initiator. The reaction conditions such as initiator and monomer concentration, shear rate (rpm), residence time, and temperature were optimized in the mixing head of BPCR attached to a torque rheometer. The graft copolymers were Soxhlet extracted with cyclohexane and were characterized by intrinsic viscosity, FTIR, and C-13-NMR spectroscopy. A maximum of 14% grafting was obtained. The graft copolymer showed significant improvement in processibility and both thermal and mechanical properties. Scale-up studies of the optimized recipe were carried out in a single-screw extruder for commercial trials /evaluation. (C) 2004 Wiley Periodicals, Inc.