Thermally stable water-soluble polymer which is crosslinkable at high temperatures

1 2 210+3 4 5 The invention relates to a copolymer containing: i) 80-90% by weight of one or more structural units of the formula A, where Ris hydrogen or methyl, Ris C-C-alkylene, and Me is an ammonium or an alkali metal ion; ii) from 1 to 10% by weight of one or more structural units of the formula B where Rand Rare each independently hydrogen, methyl or ethyl; iii) from 1 to 10% by weight of one or more structural units of the formula C, where n is a number from 1 to 6; iv) from 0.1 to 5% by weight of structural units of the formula D where X is hydrogen, an ammonium ion or an alkali metal ion; and optionally, v) from 0 to 10% by weight of one or more structural units of the formula E, where Ris hydrogen, methyl and/or ethyl, with the proviso that the content in the copolymers of structural units B) and C) is from 6 to 15% by weight.