Copolymer, comprising structural units of formula wherein R 30, R 31 and R 32 independently of each other represent a hydrogen atom, an alkyl group with 1 to 6 carbon atoms or COOM; X is NH, N(C 1 -C 4 alkyl) or O; R 33 is OH, NR 34 R 35, COOM, COOR 34, SO 3 M, SO 3 R 34, NO 2, C 1 -C 6 alkoxy or C 1 -C 6 alkyl; R 34 and R 35 independently of each other represent H, C 1 -C 6 alkyl, phenyl, C 1 -C 6 alkylphenyl or phenyl-C 1 -C 6 alkyl; t is 0, 1, 2, or 3; x is 0 or 1; n is 1, 2 or 3; y is 0 or 1; z is 0 or 1; and M is H or a cation equivalent; and structural units having free polyether side chains, wherein the structural units having free polyether side chains are selected from units of the formulae (IIa), (IIb), (IIc) and/or (IId): wherein R 10, R 11 and R 12 independently of one another are H or an unbranched or branched C 1 -C 4 alkyl group; Z is O or S; E is an unbranched or branched C 1 -C 6 alkylene group, a cyclohexylene group, CH 2 -C 6 H 10 (-CH 2 -cyclohexyl-), 1,2-phenylene, 1,3-phenylene or 1,4-phenylene; G is O, NH or CO-NH; or E and G together are a chemical bond; A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 CH(C 6 H 5); n is 0, 1, 2, 3, 4 or 5; a is an integer from 2 to 350; R 13 is H, an unbranched or branched C 1 -C 4 alkyl group, CO-NH 2 and/or COCH 3; in which R 16, R 17 and R 18 independently of one another are H or an unbranched or branched C 1 -C 4 alkyl group; E is an unbranched or branched C 1 -C 6 alkylene group, a cyclohexylene group, CH 2 -C 6 H 10 (-CH 2 -cyclohexyl-), 1,2-phenylene, 1,3-phenylene, or 1,4-phenylene, or is a chemical bond; A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 -CH(C 6 H 5); n is 0, 1, 2, 3, 4 and/or 5; L is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 -CH(C 6 H 5); a is an integer from 2 to 350; d is an integer from 1 to 350; R 19 is H or an unbranched or branched C 1 -C 4 alkyl group; R 20 is H or an unbranched C 1 -C 4 alkyl group; in which R 21, R 22 and R 23 independently of one another are H or an unbranched or branched C 1 -C 4 alkyl group or COOM; W is O, NR 25, or is N; V is 1 if W = O or NR 25, and is 2 if W = N; A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 -CH(C 6 H 5); a is an integer from 2 to 350; R 24 is H or an unbranched or branched C 1 -C 4 alkyl group; and R 25 is H or an unbranched or branched C 1 -C 4 alkyl group; in which R 6 is H or an unbranched or branched C 1 -C 4 alkyl group; Q is NR 10, N or O; V is 1 if Q = O or NR 10 and is 2 if Q = N; R 10 is H or an unbranched or branched C 1 -C 4 alkyl group; and A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 CH(C 6 H 5); R 24 is H or an unbranched or branched C 1 -C 4 alkyl group; M is H or a cation equivalent; and a is an integer from 2 to 350. R 30, R 31 and R 32 independently of each other represent a hydrogen atom, an alkyl group with 1 to 6 carbon atoms or COOM; X is NH, N(C 1 -C 4 alkyl) or O; R 33 is OH, NR 34 R 35, COOM, COOR 34, SO 3 M, SO 3 R 34, NO 2, C 1 -C 6 alkoxy or C 1 -C 6 alkyl; R 34 and R 35 independently of each other represent H, C 1 -C 6 alkyl, phenyl, C 1 -C 6 alkylphenyl or phenyl-C 1 -C 6 alkyl; t is 0, 1, 2, or 3; x is 0 or 1; n is 1, 2 or 3; y is 0 or 1; z is 0 or 1; and M is H or a cation equivalent; and R 10, R 11 and R 12 independently of one another are H or an unbranched or branched C 1 -C 4 alkyl group; Z is O or S; E is an unbranched or branched C 1 -C 6 alkylene group, a cyclohexylene group, CH 2 -C 6 H 10 (-CH 2 -cyclohexyl-), 1,2-phenylene, 1,3-phenylene or 1,4-phenylene; G is O, NH or CO-NH; or E and G together are a chemical bond; A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 CH(C 6 H 5); n is 0, 1, 2, 3, 4 or 5; a is an integer from 2 to 350; R 13 is H, an unbranched or branched C 1 -C 4 alkyl group, CO-NH 2 and/or COCH 3; R 16, R 17 and R 18 independently of one another are H or an unbranched or branched C 1 -C 4 alkyl group; E is an unbranched or branched C 1 -C 6 alkylene group, a cyclohexylene group, CH 2 -C 6 H 10 (-CH 2 -cyclohexyl-), 1,2-phenylene, 1,3-phenylene, or 1,4-phenylene, or is a chemical bond; A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 -CH(C 6 H 5); n is 0, 1, 2, 3, 4 and/or 5; L is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 -CH(C 6 H 5); a is an integer from 2 to 350; d is an integer from 1 to 350; R 19 is H or an unbranched or branched C 1 -C 4 alkyl group; R 20 is H or an unbranched C 1 -C 4 alkyl group; R 21, R 22 and R 23 independently of one another are H or an unbranched or branched C 1 -C 4 alkyl group or COOM; W is O, NR 25, or is N; V is 1 if W = O or NR 25, and is 2 if W = N; A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 -CH(C 6 H 5); a is an integer from 2 to 350; R 24 is H or an unbranched or branched C 1 -C 4 alkyl group; and R 25 is H or an unbranched or branched C 1 -C 4 alkyl group; R 6 is H or an unbranched or branched C 1 -C 4 alkyl group; Q is NR 10, N or O; V is 1 if Q = O or NR 10 and is 2 if Q = N; R 10 is H or an unbranched or branched C 1 -C 4 alkyl group; and A is C x H 2x with x = 2, 3, 4 or 5, or is CH 2 CH(C 6 H 5); R 24 is H or an unbranched or branched C 1 -C 4 alkyl group; M is H or a cation equivalent; and a is an integer from 2 to 350.