We present a comprehensive investigation of the controlled dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide (scCO(2)) utilizing reversible addition fragmentation chain transfer (RAFT) polymerization to produce living microparticles. These microparticles show controlled molecular weight evolution, low polydispersities (PDI < 1.20), and well-defined spherical morphology (diameter ca. 1.40 mu m). Four chain transfer agents are examined with modifications to both the stabilizing group (Z group) and leaving group (R group). We investigated their impact on molecular weight evolution and the morphology of the resulting polymer products in scCO(2). The rate retardation effect intrinsic to many RAFT reactions which provides good kinetic control Was shown to be much larger than that observed in analogous solution polymerizations performed in conventional organic media. This is believed to be due to the combination of the RAFT mechanism and the dispersion mechanism in scCO(2).