This invention relates to copolymers of molecular mass of between 5,000 and 300,000, consisting of a hydrophilic central portion, for example a polyacrylamide chain, and of hydrophobic ends the hydrophobicity of which is comparable with that of alkyl groups containing 4-20 carbons. They are produced by polymerization of hydrophilic monomers with the aid of initiators, for example of azo type, the hydrophobic residues of which will constitute the hydrophobic ends of the final copolymer. These copolymers are useful for rheological control of aqueous and/or pigmented compositions, like paints.