The present invention relates to a process for preparing a polymer with a mass Mw of less than 300 000 g/mol (especially between 1000 and 300 000 g/mol), comprising a step (E) of controlled radical polymerization in which the following are placed in contact in an aqueous medium in which are dispersed surfactant micelles: ethylenically unsaturated hydrophilic monomers predominantly present in the aqueous medium; partially water-soluble ethylenically unsaturated hydrophobic monomers different from the preceding monomers, at least partly present in the surfactant micelles, and having a solubility in the aqueous medium at least equal to that of hexyl acrylate; at least one radical polymerization initiator; and at least one radical polymerization control agent.