In this study, a novel application of radical addition-coupling polymerization (RACP) for synthesis of hyperbranched polymers is reported. By Cu/PMDETA-mediated RACP of 2-methyl-2-nitrosopropane with trimethylolpropane tris(2-bromopropionate) or a bromo-ended 3-arm PS macromonomer, two types of hyperbranched polymers with high degree of polymerization are synthesized under mild conditions, respectively. The chemical structures of the hyperbranched polymers are carefully characterized. By selective degradations of the ester groups and weak bonds of NOC in the polymers, high degree of alternative connection of the two monomers in the synthesized polymers have been identified. Based on the experimental results, mechanism of formation of the hyperbranched polymer is proposed, which includes formation of carbon radicals from the tribromo monomer through single electron transfer, its capture by 2-methyl-2-nitrosopropane that results in nitroxide radical, and cross-coupling reaction of the nitroxide radical with other carbon radicals. Hyperbranched polymer can be formed in a step-growth mode after multiple steps of such reactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 904–913