Patent ID: 8216487

Claim:
Copolymer wherein its chain comprises: repeat units U(R) satisfying the formula: —O—CH 2 —CHR— in which R is H or CH 3 , in a molar proportion N(R); repeat units U(Li) satisfying the formula: —O—CH 2 —CH(—CH 2 —O—SO 3 − Li + )—, in a molar proportion N(Li); and repeat units U(R′) satisfying the formula: —O—CH 2 —CH(—CH 2 R′)— in which R′ is OH, in a molar proportion N(R′); wherein the molar proportions of units U(R), U(Li) and U(R′) are such that 70≦N(R)≦95 and 2.5≦N(Li)≦15 and 5≦N(R′)≦20 and the ratio O/Li=[N(R)+N(Li)+N(R′)]/N(Li) is less than 40, wherein O represents the number of solvating oxygen atoms and Li represents the number of Li atoms.