Abstract: A thermoplastic polymer composition(a) 10 to 95 parts by weight of a block copolymer which comprises at least two polymer segments comprised primarily of a vinyl aromatic hydrocarbon and at least one polymer segment comprised primarily of a conjugated diene, in which:(i) the content of the vinyl aromatic hydrocarbon is more than 60% by weight and 95% by weight;(ii) the weight ratio of the vinyl aromatic hydrocarbon present in the copolymer as the vinyl aromatic hydrocarbon polymer block to the total vinyl aromatic hydrocarbons present in the copolymer is more than 0.75% to 0.98%; and(iii) the ratio of the weight average molecular weight to the number average molecular weight of the vinyl aromatic hydrocarbon polymer block in the copolymer is 1.2 to 2.0 and(b) 5 to 90% by weight of polyphenylene ether, and, optionally,(c) 3 to 400 parts by weight, based on 100 parts by weight of the total weight of said components (a) and (b), of polystyrene.