Well-defined hyperbranched polystyrenes have been successfully prepared by polymerization of AB(2) macromonomer, polystyrene containing an azide group at its one end and two terminal propargyl groups at the other end via click reaction. For preparation of AB(2) macromonomers, an ATRP initiator, bispropargyl 2-bromosuccinate (BPBS) with two propargyl groups and one bromine group was synthesized by the successive bromination and esterification reaction of L-aspartic acid. The resulting BPBS initiated the ATRP of St, and subsequently, the terminal bromine groups of (CH C)(2)-PS-Brs were substituted by N-3 via the reaction with sodium azide resulting the AB(2) macromonomer, (CH C)(2)-PS-N-3 with various molecular weights. All intermediates and the resultant polymers were characterized by GPC, H-1 NMR, FTIR, and MALLS methods. The polymerization kinetics study showed fast increase of DP at the initial stage of polymerization and then slow increase of their DP. The final "HyperMacs" have high-molecular weight up to M-w,M-MALLS = 340,000 g/mol, their molecular weight distributions were moderately narrow (M-w/M-n = 1.47-1.65). The ratios Of [eta](H)/[eta](L) of the HyperMacs formed in the polymerization system increased with evolution of polymerization. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 454-462, 2010