The ability of Osmium to mediate atom transfer radical polymerization (ATRP)) and stable free radical polymerization (SFRP) and to probe the potential interplay of these two radical polymerization mechanisms on a single metal catalysts was investigated. The polymers generated in reactions of bulk monomer at 100°C typically possessed molecular weights close to theoretical values based on conversion and were observed to follow first-order linear kinetics. Such observations indicated that the Os complex had mediated a controlled polymerization. The results show that polymerization could be mediated under directed ATRP conditions in DMF, but the solvent had an adverse effect on catalyst performance.