Well-defined poly(methyl methacrylate) (PMMA) with an a-isobutyronitrile group and an omega-bromine atom as the end groups was synthesized by the microemulsion polymerization of methyl methacrylate (MMA) at 70 degrees C with a 2,2'-azobisisobutyronitrile/CuBr2/2,2'-bipyridine system. The conversion of the polymerization reached 81.9%, The viscosity-average molecular weight of PMMA was high (380,000), and the polydispersity index was 1.58. The polymerization of MMA exhibited some controlled radical polymerization characteristics. The mechanism of con-trolled polymerization was studied. The presence of hydrogen and bromine atoms as end groups of the obtained PMMA was determined by H-1-NMR spectroscopy. The shape and size of the final polymer particles were analyzed by scanning probe microscopy, and the diameters of the obtained particles were usually in the range of 60-100 nm. (c) 2006 Wiley Periodicals, Inc.