Living anionic polymerization of methyl methacrylate can be achieved at -40 degrees C in tetrahydrofuran (THF) and at -78 degrees C in toluene/THF (9/1 v/v) using (1,1-diphenylhexyl)lithium as the initiator in the presence of lithium perchlorate (LiC1O(4)) as the additive. Polymerization of tert-butyl acrylate also proceeds in a living manner at -78 degrees C in THF. Polymers with narrow molecular weight distributions and high initiator efficiencies can be obtained. The use of lithium perchlorate retards the rate of polymerization. The ratio of LiC1O(4) to initiator has a greater influence in determining the control of polymerization. The beneficial effect of lithium perchlorate is attributed to its efficient interaction with growing ester-enolate ion pairs.