The kinetics of radical polymerizations of methyl methacrylate initiated by methyl 2-[(4-diphenylmethylene)-2,5-cyclohexadienyl]-2-methyl-propanoate, a model for the growing chain end in ＇quasi-living＇ radical polymerizations of methyl methacrylate mediated by trityl radicals, conventionally generated from phenylazotriphenylmethane, have been investigated. It is shown that the polymerizations have many of the characteristics of living systems, including the ability for polymer chains recovered from the polymerizations to reinitiate polymerization when added to fresh monomer. However, molecular weight distributions of polymers broaden considerably with conversion, suggesting significant termination, probably via transfer to trityl radicals and/or conventional bimolecular termination. Also, the polymers recovered from reinitiation experiments have molecular weights which are too high to be consistent with simple reinitiation via regeneration of growing radicals; rather it seems probable that reinitiation occurs via breakdown of a peroxidic species introduced during work-up of the original polymer.