Cumyl dithiobenzoate (CDB) mediated methyl acrylate (MA) bulk polymerizations at 80 degrees C, using CDB concentrations between 1.5 X 10(-2) and 5.0 X 10(-2) mol L-1, were modeled via a novel Monte Carlo simulation procedure with respect to experimental time-dependent conversions, X, number average molecular weights, M-n, and weight average molecular weights, M-w, The simulations were based upon individual treatment of 5 X 108 discrete molecules in accordance to their actual reaction pathways. The kinetic scheme employed includes termination reactions of intermediate RAFT radicals with propagating radicals and reaction steps of the RAFT pre-equilibrium, which are different from those of the RAFT main equilibrium. The equilibrium constant of the main equilibrium of the CDB/MA system at 80 degrees C was found to be K= 1.2 X 10(4) L mol(-1), indicating a relatively stable intermediate radical. The concentration of the intermediate RAFT radical, although not employed as experimental input data for the modeling, was calculated by using the obtained set of kinetic parameters as being in excellent agreement with experimental electron spin resonance spectroscopic data. (c) 2005 Elsevier Ltd. All rights reserved.