Isobornyl methacrylate (IBMA), a bulky hydrophobic methacrylate, undergoes very fast polymerization, in bulk, with Cu(I)Br/N,N,N′,N″,N″- pentamethyldiethylenetriamine (PMDETA)/ethyl-2-bromoisobutyrate system, at ambient temperature. IBMA also undergoes a spontaneous initiator-free polymerization, at ambient temperature, with Cu(I)Br/PMDETA catalytic system in dimethyl sulfoxide-water mixtures. The rate of the polymerization is seen to increase with the water content up to 80 mol % of water. A possible intervention of air in initiation is proposed. The active Cu(0) formed by the disproportionation of Cu(I) species in aqueous medium probably plays a vital role for a possible air-initiation of IBMA via single electron transfer-living radical polymerization (SET-LRP) mechanism. A high tolerance level to water under SET-LRP conditions is demonstrated. The poly(IBMA) samples obtained exhibit low molecular weight distributions (1.1-1.3). Similar behavior was not observed with other common methacrylates such as methyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate. © 2011 Wiley Periodicals, Inc.