Thermoplastic moulding compositions based on polysiloxane/polycarbonate block copolymers

Claim 1

A thermoplastic moulding composition consisting essentially of (a) 20-80 parts by weight of a polydiorganosiloxane polycarbonate block copolymer which has an average molecular weight M w of 10,000 to 200,000 and contains between about 75% by weight and 97.5% by weight of aromatic carbonate structural units and between 25% by weight and 2.5% by weight of polydiorganosiloxane structural units, the block copolymer being prepared by reacting polydiorganosiloxanes which contain α,ω-bis-hydroxyaryloxy terminal groups with diphenol and a chain terminator and have a degree of polymerization P n of 5-100, (b) 70-5 parts by weight of a graft polymer of an ethyleneically unsaturated monomer selected from styrene, a styrene derivative, methyl metharcrylate and a monomer mixture of 95-50% by weight of styrene, α-methylstyrene, methylmethacrylate or a mixture thereof and 5-50% by weight of acrylonitrile, methylmethacrylate, maleic anhydride or a mixture thereof, onto a rubber selected from polybutadiene, a butadiene/styrene copolymer containing up to 30% by weight of styrene as copolymerized units, a copolymer of butadiene and acrylonitrile containing up to 20% by weight of acrylontrile, a copolymer of butadiene containing up to 20% by weight of a lower alkyl ester of acrylic or methacrylic acid, and an alkyl acrylate rubber based on a C 1 -C 8 -alkyl acrylate, and (c) 5-60 parts by weight of a rubber-free thermoplastic copolymer consisting of 95-50% by weight of styrene, α-methylstyrene or a mixture thereof, with 5-50% by weight of acrylonitrile, methacrylonitrile, maleic anhydride or a mixture thereof, the sum of the number of parts by weight of components (a)+(b)+(c) being 100 parts by weight in each case.