An anionic polyelectrolyte resulting from the polymerization: a) of a mass ratio greater than or equal to 80% and less than or equal to 99.5% of monomeric units from a monomer with a weak acid function; b) of a mass ratio greater than or equal to 0.5% and less than or equal to 20%, —Either of a monomer of formula (Ia): R—(CH2)3—Si(CH3)2—[O—Si(CH3)2—]nO—Si(CH3)2—(CH2)3—R (Ia), wherein R represents the monovalent radical: —(O—CH2—CH2-)x[O—CH2—CH(CH3)-]yO—C(═O)—CH═CH2, —Or of a monomer of formula (Ib): Si(CH3)3—[O—Si(CH3)2—]m[O—Si(CH3)[(CH2)3—R]—]pO—Si(CH2)3 (Ib), c) optionally of a mass ratio greater than 0% and less than or equal to 5% of monomeric units from at least one monomer of formula (II): R2—C(═O)—O—[(CH2—CH(R4)—O]m—R3 (II), d) optionally of a mass ratio greater than 0% and less than or equal to 5% of at least one monomer with diethylenic or polyethylenic cross-linking; method for the preparation thereof and use as a thickener in topical compositions.