Reverse atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) employing 2,2-azobisisobutyronitrile (AIBN)/CuCl2/bipyridine(bipy) as the initiating system was approached at 80degreesC in two ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate (C(4)mim] [BF4]) and 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C(12)mim [BF4]), respectively. The polymerization\ in [C(12)mim][BF4] proceeded in a well-controlled manner as evidenced by kinetic studies, end group analysis, chain extension, and block copolymerization results, but not in [C(4)mim][BF4] presumably due to poor solubility of PMMA in it. The kinetic study of reverse ATRP of MMA in recycled [C(12)mim][BF4] suggested that this ionic liquid could be re-used as reaction solvent after simple purification, without affecting the living nature of polymerization. (C) 2003 Elsevier Ltd. All rights reserved.