The reversible addition-fragmentation chain transfer polymerization of methyl methacrylate mediated by 2-cyanoprop-2-yl dithiobenzoate (CPDB) in bulk (60 and 70 degrees C) and suspension (70 degrees C) was studied, and in both polymerization systems, a good control of the molecular weight and polydispersity was observed. Stable suspension polymerizations were carried out over a range of CPDB concentrations, and with increasing CPDB concentration, the particle size and polydispersity index of the produced polymer decreased. The former was ascribed to the lower viscosities of the monomer and polymer droplets at low conversions, which caused easier breakup with the applied shear stresses. Lower polydispersity indices at higher CPDB concentrations were probably caused by a diminished gel effect, which was observed at lower CPDB concentrations at high conversions, causing a broadening of the molecular weight distribution. The livingness of the polymers formed in suspension was proven by successful chain extensions with methyl methacrylate, styrene, and 2-hydroxyethyl methacrylate. (c) 2005 Wiley Periodicals, Inc.