Stabilized thermoplastic moulding compositions

A stabilized thermoplastic moulding composition comprising a mixture of

• (1) from 10 to 90 parts by weight of a polycarbonate of an aromatic dihydroxy compound and
• (2) from 90 to 10 parts by weight of a mixture of
• (a) from 25 to 100 parts by weight of graft copolymer comprising styrene, methyl methacrylate or a mixture thereof as one constituent and acrylonitrile, methacrylonitrile or a mixture thereof as the other constituent polymerized on a rubber;
• (b) from 0 to 20 parts by weight of a butadiene polymer having a butadiene content of at least 5% by weight and
• (c) from 0 to 75 parts by weight of a copolymer of at least one monomer selected from the group consisting of styrene, .alpha.-methyl styrene and mixtures thereof and another monomer selected from the group consisting of methyl methacrylate, acrylonitrile, methacrylonitrile and mixtures thereof,
• said composition containing 0.01 to 3% by weight, based on the mixture of (1) and (2) of a phosphite of the formula ##STR18## wherein R.sup.3 is C.sub.1 -C.sub.9 alkyl, C.sub.5 -C.sub.6 cycloalkyl, C.sub.7 -C.sub.9 aralkyl or C.sub.6 -C.sub.10 aryl;
• R.sup.4 is benzyl, methylbenzyl, dimethyl benzyl, methyl, ethyl, isopropyl, tertiary butyl, tertiary amyl, isononyl, cyclopentyl or cyclohexyl and Y is S or HCR.sup.5 wherein R.sup.5 is hydrogen, C.sub.1 -C.sub.6 alkyl, cyclohexenyl or cyclohexyl.