2,2,6,6-Tetramethyl piperidinoxy (TEMPO) activated with diethyl aluminum bromide was employed as an initiator system for methyl methacrylate polymerization. Effect of addition of Co(acac)(3) and VO(acac)(2) complexes to the initiators system on methyl methacrylate polymerization were studied in benzene solvent. Various reaction parameters such as Al/TEMPO, monomer concentration, reaction temperature and time applied to the polymerization were investigated. The polymer yields, molecular weight and molecular weight distributions can be controlled with the addition of Co(acac)(3) to the initiator system. PMMA's of molecular weight distributions, as low as 1.10 was obtained under relatively mild conditions, in the temperature range 40-60 degrees C in benzene solvent. However, Co and V complexes did not influence the micro structure of the PMMA's formed. (C) 2009 Wiley Periodicals, Lnc. J Appl Polym Sci 114: 3932-3938, 2009