A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4-(2-bromo-2-methylpropionyloxy)-2,2,6,6tetramethyl-l-piperidinyloxy (Br-TEMPO), was synthesized by the reaction of 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2-bromo-2-methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br-TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the omega-end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. (c) 2006 Wiley Periodicals, Inc.