N-Bromosuccinimide (NBS) was used as the initiator in the atom transfer radical polymerizations of styrene (St) and methyl methacrylate (MMA). The NBS/ CuBr/bipyridine (bpy) system shows good controllability for both polymerizations and yields polymers with polydispersity indexes ranging from 1.18 to 1.25 for St and 1.14 to 1.41 for MMA, depending on the conditions used. The end-group analysis of poly(MMA) and polystyrene indicated the polymerization is initiated by the succinimidyl radicals formed from the redox reaction of NBS with CuBr/bpy. (C) 2004 Wiley Periodicals, Inc.