Filamentous polymeric particles and process for the preparation of said particles by controlled free radical emulsion polymerization.

The invention relates to polymer particles in the form of filaments formed by block copolymers, as well as to the method for preparing same by means of controlled radical polymerization in emulsion in the presence of a specific living macroinitiator derived from a nitroxide. The invention is characterized in that the filamentous particles are obtained in a dispersed aqueous medium by means of the synthesis of said block copolymers, performed by heating the reaction medium at a temperature of 60 to 120° C., the final block copolymer containing between 10 and 50 mol. % of the macroinitiator which is water soluble and the hydrophobic monomer conversion rate being at least 50%. According to the invention, the weight ratio of hydrophilic fraction of the filamentous particles is less than 25 wt %.