The free-radical dispersion polymerization of methyl acrylate (MA) in isododecane was carried out in the presence of a poly(2-ethylhexyl acrylate) macromolecular RAFT (reversible addition-fragmentation chain transfer) agent bearing a trithiocarbonate reactive group in the middle of the chain (P2EHA-TTC). The presence of the trithiocarbonate function was crucial for the synthesis of monodisperse colloidal poly(methyl acrylate) (PMA) particles stabilized by the P2EHA segments. The hydrodynamic diameters ranged from 100 to 300 nm, using particularly low amounts of the macro(RAFT agent) (1-6 wt % vs. MA) in dispersion polymerizations carried out at 20 wt % solids content. As shown by 2D liquid chromatography, P2EHA-b-PMA or P2EHA-b-PMA-b-P2EHA block copolymers formed in situ at the early stage of the dispersion polymerization due to the reversible transfer process and played the role of particle stabilizer. The glass-transition temperature of the derived polymer films was not affected by the low amount of the chosen macromolecular stabilizer and the mechanical properties were mainly those of PMA, which makes the technique very attractive for coating applications. © 2010 American Chemical Society.