A poly(ethylene oxide)-based macromolecular agent for reversible addition-fragmentation chain transfer (PEO-RAFT, 2 000 g.mol(-1)) was synthesized and used as a stabilizer and a control agent in the miniemulsion polymerization of styrene. Using 2,2'-azobis(isobutyronitrile) as initiator, stable polystyrene (PS) particles sterically stabilized by the PEO segments were obtained with almost complete conversion after 22 h. Molar masses increased linearly with conversion although rather broad molar mass distributions were obtained due to the presence of several populations of PEO-b-PS block copolymers. However, dynamic light scattering analyses showed a significant increase in particle diameter with conversion and the ratio of the number of particles to the number of droplets (N-p/N-d) was thus lower than one indicating that the system did not follow a true miniemulsion process. Transmission electron microscopy additionally revealed the presence of holes inside the formed particles suggesting that block copolymer PEO-b-PS could be buried inside the particles during the polymerization. Varying the concentration and the nature of the initiator did not lead to an improvement of the molar mass distribution, while a decrease in polymerization temperature to 40 degrees C enabled to keep the particle size constant throughout the polymerization with values close to the starting droplet diameter as expected for a true miniemulsion.