| abstract |
There is disclosed a copolymer containing i) 80 - 90% by weight of one or more structural units of formula A wherein R 1 is hydrogen or methyl R 2 is C 2 -C 10 alkylene and Me + is an ammonium or an alkali metal ion ii) 1 to 10% by weight of one or more structural units of formula B wherein R3 and R4 independently represent hydrogen, methyl or ethyl, iii) 1 to 10% by weight of one or more structural units of formula C, wherein n is a number between 1 and 6, iv) 0.1 to 5% by weight of structural units of formula D wherein X represents hydrogen, an ammonium or alkali metal ion, and optionally v) 0 to 10% by weight of one or more structural units of formula E wherein R5 is for hydrogen, methyl and / or ethyl, provided that the content of copolymers of structural units B) and C) is between 6 and 15% by weight. |