The present invention relates to the preparation of block copolymers, which can be used in particular as rheology agents, suitable, inter alia, for oil extraction, comprising a step of radical micellar polymerisation wherein the following are brought into contact in an aqueous medium: —hydrophilic monomers, dissolved or dispersed in the aqueous medium; —hydrophobic monomers in the form of a micellar solution, i.e. containing, in a dispersed state, micelles comprising these hydrophobic monomers; —at least one radical polymerisation initiator; and —at least one radical polymerisation control agent. The polymers obtained according to the invention can be used in particular for enhanced oil recovery (EOR).