As produced reactor copolymer, obtained by in-reactor grafting polymerization technology is a two-phase rigid polymer, which combines the best attributes of semicrystalline polypropylene and those of amorphous polystyrene. In the process, the compatibilizer, PP-g-PS and the non-olefinic polymer component, PS are simultaneously generated from the monomer styrene. The reactor product which has higher modulus but lower impact resistance is further toughened by incorporation of EPR (ethylene propylene rubber) and SEBS (styrene-ethylene-butylene-styrene) triblock copolymer, via intensive melt-mixing in a downstream compounding operation.