| abstract |
The invention relates to a copolymer containing 1. at temperatures above 150 ° C with polyvalent metal ions reversibly crosslinkable copolymers containing i) 80-90% by weight of one or more structural units of the formula A, wherein R 1 is hydrogen or methyl, R 2 is C 2 -C 10 -alkylene and Me + represents an ammonium or an alkali metal ion, ii) 1 to 10% by weight of one or more structural units of the formula B, in which R 3 and R 4, independently of one another, denote hydrogen, methyl or ethyl, iii) 1 to 10% by weight of one or more structural units of the formula C, where n is a number between 1 and 6, iv) from 0.1 to 5% by weight of structural units of the formula D, wherein X is hydrogen, an ammonium or an alkali metal ion, and optionally v) 0 to 10% by weight of one or more structural units of the formula E, wherein R 5 is hydrogen, methyl and / or ethyl, with the proviso that the content of the copolymers of structural units B) and C) is between 6 and 15% by weight. |