Patent ID: 6891009

Claim:
A water-soluble or water-swellable crosslinked copolymer consisting essentially of a1) 1 to 50% by weight of a repeating structural unit of formula (1) where n is an integer from 2 to 9, or a2) 1 to 50% by weight of a mixture of the repeating structural unit of the formula (1) and a repeating structural unit of formula (2) where R, R 1 and R 2 may be identical or different and are hydrogen or a linear or branched alkyl or alkenyl group having in each case 1 to 30 carbon atoms and b) 49.99 to 98.99% by weight of a repeating structural unit of formula (3) in which R 3 is hydrogen, methyl or ethyl, Z is C 1 -C 8 -alkylene, and X is an ammonium ion, and c) 0.01 to 8% by weight of crosslinking structures resulting from a monomer having at least two olefinic double bonds.