The effects of additives such as methanol, water, and radical scavengers (TEMPO and galvinoxyl) were studied in the living polymerization of methyl methacrylate (MMA) with the PhCOCHCl2/RuCl2(PPh3)(3)/Al(OiPr)(3) initiating system in toluene at 80 degrees C. Upon addition of these additives at about 45% conversion, TEMPO and galvinoxyl completely terminated the polymerization, whereas methanol and water did not affect it at all in terms of rate, polymer molecular weight, and its narrow distribution. Living polymerization also occurred even in the presence of relatively high concentrations of methanol (40-1000 mM). The polymers that were recovered after quenching the living polymerization and subsequent purification under atmospheric conditions quantitatively possessed a carbon-chlorine terminal, and they served as a macroinitiator for the living polymerization of MMA in conjunction with RuCl2(PPh3)(3) and Al(OiPr)(3) to induce further molecular weight growth. These results indicate that the living polymerization proceeds via a radical pathway and that the polymer terminal is robust under atmospheric conditions and in the presence of protic compounds, though it readily generates an active end in the presence of the ruthenium and aluminum components.