Thermoplastic resin composition

Claim 1

A resin composition consisting essentially of polystyrene having a molecular weight of 150,000 to 500,000 and a styrene-butadiene block copolymer represented by the formula A 1 --B 1 --C--B 2 --A 2 , wherein A 1 and A 2 represent non-elastomeric blocks composed of polymeric styrene chains, B 1 and B 2 represent elastomeric blocks composed of random-copolymer chains containing styrene and butadiene units uniformly distributed therein, C represents an elastomeric block composed of a polymeric butadiene chain or a styrene-butadiene copolymer chain, the total amount of A 1 and A 2 is 40 to 80% by weight, the total amount of B 1 and B 2 is 10 to 60% by weight, the amount of C is 0 to 25% by weight provided that the amount of C is smaller than the total amount of B 1 and B 2 , the weight ratio of A 1 to A 2 is 2:8 to 8:2, the weight ratio of B 1 to B 2 is 0:10 to 10:0, the weight ratio of styrene to butadiene in B 1 and B 2 is 10:90 to 75:25, and the weight ratio of styrene to butadiene in C is 0:100 to 10:90, the total styrene content to said styrene-butadiene block copolymer being 65 to 90% by weight, the total butadiene content of said block copolymer being 10 to 35% by weight, and said block copolymer having an intrinsic viscosity of 0.35 to 1.8 dl/g, as measure in toluene at 30° C, said resin composition obtained by mixing said polystyrene and said block copolymer.