A water-soluble or water-swellable polymer having a k value of 100 to 300, measured in 0.5% by weight solution in distilled water, containing a) 25 - 35 mol% of one or more recurrent structural units of the formula in which R 1, R 2 are hydrogen, methyl or ethyl, A is linear or branched C 1 -C 12 -alkylene, and Q + is H +, NH 4 +, Li +, Na +, K +, 1⁄2 Ca ++, 1⁄2 Mg ++, 1⁄2 Zn ++, 1/3 Al +++, organic ammonium ions of the formula [HNR 5 R 6 R 7] + where R 5, R 6 and R 7 may each independently be hydrogen, a linear or branched alkyl group having 1 to 22 carbon atoms, a linear or branched, mono- or polyunsaturated alkenyl group having 2 to 22 carbon atoms, a C 6 -C 22 -alkylamidopropyl group, a linear monohydroxyalkyl group having 2 to 10 carbon atoms or a linear or branched dihydroxyalkyl group having 3 to 10 carbon atoms, and where at least one of the R 5, R 6 and R 7 radicals is not hydrogen, or mixtures of these ions, b) 3 to 8 mol% of one or more recurrent structural units of the formula in which R 1 is hydrogen, methyl or ethyl, X + is H +, NH 4 -, Li +, Na +, K +, 1⁄2 Ca ++, 1⁄2 Mg ++, 1⁄2 Zn ++, 1⁄2 Al +++, organic ammonium ions of the formula [HNR 5 R 6 R 7] + where R 5, R 6 and R 7 may each independently be hydrogen, a linear or branched alkyl group having 1 to 22 carbon atoms, a linear or branched, mono- or polyunsaturated alkenyl group having 2 to 22 carbon atoms, a C 6 -C 22 -alkylamidopropyl group, a linear monohydroxyalkyl group having 2 to 10 carbon atoms or a linear or branched dihydroxyalkyl group having 3 to 10 carbon atoms, and where at least one of the R 5, R 6 and R 7 radicals is not hydrogen, or mixtures of these ions, B is a chemical bond, or a linear or branched alkylene group having 1 to 6 carbon atoms, and n is an integer from 0 to 5, and c) 57 to 72 mol% of one or more recurrent structural units of the formula in which R 1 is hydrogen, methyl or ethyl, and R 3 and R 4 are each independently hydrogen, methyl, ethyl, n-propyl, isopropyl or butyl. a) 25 - 35 mol% of one or more recurrent structural units of the formula in which R 1, R 2 are hydrogen, methyl or ethyl, A is linear or branched C 1 -C 12 -alkylene, and Q + is H +, NH 4 +, Li +, Na +, K +, 1⁄2 Ca ++, 1⁄2 Mg ++, 1⁄2 Zn ++, 1/3 Al +++, organic ammonium ions of the formula [HNR 5 R 6 R 7] + where R 5, R 6 and R 7 may each independently be hydrogen, a linear or branched alkyl group having 1 to 22 carbon atoms, a linear or branched, mono- or polyunsaturated alkenyl group having 2 to 22 carbon atoms, a C 6 -C 22 -alkylamidopropyl group, a linear monohydroxyalkyl group having 2 to 10 carbon atoms or a linear or branched dihydroxyalkyl group having 3 to 10 carbon atoms, and where at least one of the R 5, R 6 and R 7 radicals is not hydrogen, or mixtures of these ions, R 1, R 2 are hydrogen, methyl or ethyl, A is linear or branched C 1 -C 12 -alkylene, and Q + is H +, NH 4 +, Li +, Na +, K +, 1⁄2 Ca ++, 1⁄2 Mg ++, 1⁄2 Zn ++, 1/3 Al +++, organic ammonium ions of the formula [HNR 5 R 6 R 7] + where R 5, R 6 and R 7 may each independently be hydrogen, a linear or branched alkyl group having 1 to 22 carbon atoms, a linear or branched, mono- or polyunsaturated alkenyl group having 2 to 22 carbon atoms, a C 6 -C 22 -alkylamidopropyl group, a linear monohydroxyalkyl group having 2 to 10 carbon atoms or a linear or branched dihydroxyalkyl group having 3 to 10 carbon atoms, and where at least one of the R 5, R 6 and R 7 radicals is not hydrogen, or mixtures of these ions, b) 3 to 8 mol% of one or more recurrent structural units of the formula in which R 1 is hydrogen, methyl or ethyl, X + is H +, NH 4 -, Li +, Na +, K +, 1⁄2 Ca ++, 1⁄2 Mg ++, 1⁄2 Zn ++, 1⁄2 Al +++, organic ammonium ions of the formula [HNR 5 R 6 R 7] + where R 5, R 6 and R 7 may each independently be hydrogen, a linear or branched alkyl group having 1 to 22 carbon atoms, a linear or branched, mono- or polyunsaturated alkenyl group having 2 to 22 carbon atoms, a C 6 -C 22 -alkylamidopropyl group, a linear monohydroxyalkyl group having 2 to 10 carbon atoms or a linear or branched dihydroxyalkyl group having 3 to 10 carbon atoms, and where at least one of the R 5, R 6 and R 7 radicals is not hydrogen, or mixtures of these ions, B is a chemical bond, or a linear or branched alkylene group having 1 to 6 carbon atoms, and n is an integer from 0 to 5, and R 1 is hydrogen, methyl or ethyl, X + is H +, NH 4 -, Li +, Na +, K +, 1⁄2 Ca ++, 1⁄2 Mg ++, 1⁄2 Zn ++, 1⁄2 Al +++, organic ammonium ions of the formula [HNR 5 R 6 R 7] + where R 5, R 6 and R 7 may each independently be hydrogen, a linear or branched alkyl group having 1 to 22 carbon atoms, a linear or branched, mono- or polyunsaturated alkenyl group having 2 to 22 carbon atoms, a C 6 -C 22 -alkylamidopropyl group, a linear monohydroxyalkyl group having 2 to 10 carbon atoms or a linear or branched dihydroxyalkyl group having 3 to 10 carbon atoms, and where at least one of the R 5, R 6 and R 7 radicals is not hydrogen, or mixtures of these ions, B is a chemical bond, or a linear or branched alkylene group having 1 to 6 carbon atoms, and n is an integer from 0 to 5, c) 57 to 72 mol% of one or more recurrent structural units of the formula in which R 1 is hydrogen, methyl or ethyl, and R 3 and R 4 are each independently hydrogen, methyl, ethyl, n-propyl, isopropyl or butyl. R 1 is hydrogen, methyl or ethyl, and R 3 and R 4 are each independently hydrogen, methyl, ethyl, n-propyl, isopropyl or butyl.