Effects of additives (metal alkoxides and halides) were investigated in the RuCl2(PPh3)(3)-catalyzed living radical polymerization of methyl methacrylate (MMA) in toluene at 80 degrees C. While the MMA polymerization with the RuCl2(PPh3)(3)/CCl4 system (CCl4: initiator) is very slow and produces polymers with broad molecular weight distributions (MWDs), addition of metal alkoxides, such as Al(Oi-Pr)(3), Ti(Oi-Pr)(4), and Sn(Oi-Pr)(4), accelerated the polymerization to produce polymers with controlled molecular weights and narrow MWDs. Metal chlorides such as SnCl4 and TiCl4 were not effective additives. According to NMR and cyclic voltammetric analyses, Al(Oi-Pr)a does not interact with monomer or the polymer termini (similar to similar to similar to C-Cl and similar to similar to similar to C-. radicals) but interacts with the ruthenium complex, or more likely, its higher oxidation state Ru(III) species.