An aqueous composition comprising at least one copolymer, the polymolecularity index P I of which is less than 3, determined by Size Exclusion Chromatography, obtained by at least one radical polymerisation reaction in water and at a temperature ranging from 10 to 90°C: (a) of at least one anionic monomer comprising at least one polymerisable olefinic unsaturation and at least one carboxylic acid group and (b) of at least one monomer of formula: wherein: - R 1 and R 2, identical or different, independently represent H or CH 3, - L 1 independently represents a group chosen among CH 2, CH 2 -CH 2 and O-CH 2 -CH 2 -CH 2 -CH 2, - L 2 independently represents a group chosen among (CH 2 -CH 2 O) x, (CH 2 CH(CH 3)O) y, (CH(CH 3)CH 2 O) z and combinations thereof and - x, y and z, identical or different, independently represent an integer or decimal comprised between 0 and 150 and the sum of x+y+z is comprised between 10 and 150, in the presence: (i) of from 0.05 to 5% by weight, with respect to the amount of monomers, of at least one compound of formula: wherein: - X independently represents H, Na or K and - R independently represents a C 1 -C 5 alkyl group and (ii) of at least one radical-generating compound chosen among hydrogen peroxide, ammonium persulphate, an alkali metal persulphate, and mixtures or associations thereof with ammonium bisulphite, with an alkali metal bisulphite or with an ion chosen among Fe II, Fe III, Cu I, Cu II. (a) of at least one anionic monomer comprising at least one polymerisable olefinic unsaturation and at least one carboxylic acid group and (b) of at least one monomer of formula: wherein: - R 1 and R 2, identical or different, independently represent H or CH 3, - L 1 independently represents a group chosen among CH 2, CH 2 -CH 2 and O-CH 2 -CH 2 -CH 2 -CH 2, - L 2 independently represents a group chosen among (CH 2 -CH 2 O) x, (CH 2 CH(CH 3)O) y, (CH(CH 3)CH 2 O) z and combinations thereof and - x, y and z, identical or different, independently represent an integer or decimal comprised between 0 and 150 and the sum of x+y+z is comprised between 10 and 150, - R 1 and R 2, identical or different, independently represent H or CH 3, - L 1 independently represents a group chosen among CH 2, CH 2 -CH 2 and O-CH 2 -CH 2 -CH 2 -CH 2, - L 2 independently represents a group chosen among (CH 2 -CH 2 O) x, (CH 2 CH(CH 3)O) y, (CH(CH 3)CH 2 O) z and combinations thereof and - x, y and z, identical or different, independently represent an integer or decimal comprised between 0 and 150 and the sum of x+y+z is comprised between 10 and 150, (i) of from 0.05 to 5% by weight, with respect to the amount of monomers, of at least one compound of formula: wherein: - X independently represents H, Na or K and - R independently represents a C 1 -C 5 alkyl group and - X independently represents H, Na or K and - R independently represents a C 1 -C 5 alkyl group and (ii) of at least one radical-generating compound chosen among hydrogen peroxide, ammonium persulphate, an alkali metal persulphate, and mixtures or associations thereof with ammonium bisulphite, with an alkali metal bisulphite or with an ion chosen among Fe II, Fe III, Cu I, Cu II.