The invention relates to anionically modified copolymers that can be obtained by the polymerization of monomers (A), (B), (C) and (D) in order to obtain non-ionic copolymers comprising reactive terminal OH groups, and subsequent reaction of the terminal OH groups to form anionic end groups, where A) is a monomer of formula (I) wherein A is C2-C4 alkylene and B is a C2-C4 alkylene different from A, and R is hydrogen or methyl; (B) is a monomer of formula (II) wherein D is C3 alkylene, R is hydrogen or methyl, and o is a number between 2 and 500; (C) is an ethylenically unsaturated monomer containing an aromatic group; and (D) is an ethylenically unsaturated monomer containing an alkyl radical.