An anionic polysaccharide comprising carboxylic acid functional groups of formula I:in which: the polysaccharide may be either, synthetic or modified, i represents the degree of functionalization of the hydroxyls, j represents the degree of functionalization of the hydroxyls, L and Q represent an optionally branched and/or unsaturated chain comprising from 1 to 15 carbons, F is a functional group chosen from the group consisting of the carbamate functional group, the carbonyl being bonded to the Q radical, the ester functional group, the carbonyl being bonded to the Q radical, the amide functional group, the carbonyl being bonded to the Q radical, and the carboxylate functional group, and Grp is chosen from the group consisting of a mono- or divalent cation and of a chain comprising from 4 to 50 carbons.
