Water-soluble, hydrophobic associating copolymers

A copolymer comprising

• (a) at least one monoethylenically unsaturated, water-soluble, surface-active monomer (a), and
• (b) at least one monoethylenically unsaturated, hydrophilic monomer (b) different from monomer (a),
• wherein the monomer (a) is at least one compound selected from the group consisting of formulae (I), (II) or (III)
• H2C═C(R1)—R4—O—(—CH2—CH2—O—)k—(—CH2—CH(R3)—O—)L—H (I)
• H2C═C(R1)—O—(—CH2—CH2—O—)k—R2 (II) and
• H2C═C(R1)—C═O)—O—(—CH2—CH2—O—)k—R2 (III),
• wherein the units —(—CH2—CH2—O—)k and —(—CH2—CH(R3)—O—)1 are arranged in block structure in the order shown in formula (I) and the radicals and indices are defined as follows:
• k is a number from 6 to 150,
• L is a number from 5 to 25,
• R1 is H or methyl,
• R2 is a hydrocarbon radical having 8 to 40 carbon atoms, wherein the hydrocarbon radical is at least one member selected from the group consisting of aliphatic, aromatic, straight-chain and branched,
• R3 is independently of one another, a hydrocarbon radical having at least 2 carbon atoms,
• R4 is a single bond or a divalent linking group selected from the group of —(CnH2n)—, —O—(Cn′H2′)— and —C(O)—O—(Cn″H2″)— where n, n′ and n″ is in each case a natural number from 1 to 6, and
• wherein during its synthesis, prior to the initiation of the polymerization reaction, at least one further, but nonpolymerizable surface-active compound has been used as further component (c), and wherein the copolymer is a water-soluble, hydrophobically associating copolymer.