Anionically modified copolymers obtainable by polymerization of monomers, and to obtain nonionic copolymers which have reactive terminal OH groups on the polyoxyalkylene side chains, and subsequent conversion of the terminal OH groups to anionic end groups, where the anionic end groups represent one of SO 3 M, CH 2 COOM and sulfosuccinate, where M represents H, a monovalent metal cation, a divalent metal cation, NH 4 +, a secondary, tertiary or quaternary ammonium ion or a combination thereof, is a monomer of formula where A represents C 2 -C 4 -alkylene, B represents a C 2 -C 4 -alkylene other than A, R represents hydrogen or methyl, m is from 1 to 500; n is from 1 to 500, and the sum total of m + n is from 2 to 1000; is an ethylenically unsaturated monomer which contains an aromatic group; and wherein the monomer is a compound of formula (IIa) or (IIb): where X a represents an aromatic or araliphatic radical having 3 to 30 carbon atoms which optionally contains one or more of the hetero atoms N, O and S, Z a represents H or (C 1 -C 4)-alkyl, Z b represents H or (C 1 -C 4)-alkyl, Z c represents H or (C 1 -C 4)-alkyl; where R 1 represents hydrogen or methyl, X b represents an aromatic or araliphatic radical having 3 to 30 carbon atoms which optionally contains one or more of the hetero atoms N, O und S, W a represents oxygen or an NH group, and is an ethylenically unsaturated monomer which contains an alkyl radical, and wherein the monomer is a compound of formula: where R 2 represents hydrogen or methyl, Y represents an aliphatic hydrocarbyl radical having 1 to 30 carbon atoms, which may be linear or branched or else cyclic, and may also be unsaturated, W b represents oxygen or an NH group. is a monomer of formula where A represents C 2 -C 4 -alkylene, B represents a C 2 -C 4 -alkylene other than A, R represents hydrogen or methyl, m is from 1 to 500; n is from 1 to 500, and the sum total of m + n is from 2 to 1000; A represents C 2 -C 4 -alkylene, B represents a C 2 -C 4 -alkylene other than A, R represents hydrogen or methyl, m is from 1 to 500; n is from 1 to 500, is an ethylenically unsaturated monomer which contains an aromatic group; and wherein the monomer is a compound of formula (IIa) or (IIb): where X a represents an aromatic or araliphatic radical having 3 to 30 carbon atoms which optionally contains one or more of the hetero atoms N, O and S, Z a represents H or (C 1 -C 4)-alkyl, Z b represents H or (C 1 -C 4)-alkyl, Z c represents H or (C 1 -C 4)-alkyl; where R 1 represents hydrogen or methyl, X b represents an aromatic or araliphatic radical having 3 to 30 carbon atoms which optionally contains one or more of the hetero atoms N, O und S, W a represents oxygen or an NH group, and is an ethylenically unsaturated monomer which contains an alkyl radical, and wherein the monomer is a compound of formula: where R 2 represents hydrogen or methyl, Y represents an aliphatic hydrocarbyl radical having 1 to 30 carbon atoms, which may be linear or branched or else cyclic, and may also be unsaturated, W b represents oxygen or an NH group. X a represents an aromatic or araliphatic radical having 3 to 30 carbon atoms which optionally contains one or more of the hetero atoms N, O and S, Z a represents H or (C 1 -C 4)-alkyl, Z b represents H or (C 1 -C 4)-alkyl, Z c represents H or (C 1 -C 4)-alkyl; R 1 represents hydrogen or methyl, X b represents an aromatic or araliphatic radical having 3 to 30 carbon atoms which optionally contains one or more of the hetero atoms N, O und S, W a represents oxygen or an NH group, and is an ethylenically unsaturated monomer which contains an alkyl radical, and wherein the monomer is a compound of formula: R 2 represents hydrogen or methyl, Y represents an aliphatic hydrocarbyl radical having 1 to 30 carbon atoms, which may be linear or branched or else cyclic, and may also be unsaturated, W b represents oxygen or an NH group.