The star block copolymers with polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as side chains and hyperbranched polyglycerol (HPG) as core were synthesized by combination of atom transfer radical polymerization (ATRP) with the "atom transfer nitroxide radical coupling" ("ATNRC") reaction. The multiarm PS with bromide end groups originated from the HPG core (HPG-g-(PS-Br)(n)) was synthesized by ATRP first, and the heterofunctional PEO with alpha-2,2,6,6-tetramethylpiperidinyl-1-oxy group and omega-hydroxyl group (TEMPO-PEO) was prepared by anionic polymerization separately using 4-hydroxyl-2,2,6,6-tetramethylpiperidinyl-1-oxy (HTEMPO) as parents compound. Then ATNRC reaction was conducted between the TEMPO groups in PEO and bromide groups in HPG-g-(PS-Br)(n) in the presence of CuBr and pentamethyldiethylenetriamine (PMDETA). The obtained star block copolymers and intermediates were characterized by gel permeation chromatography,nuclear magnetic resonance spectroscopy, fourier transform-infrared in detail. Those results showed that the efficiency of ATNRC in the preparation of multiarm star polymers was satisfactory (> 90%) even if the density of coupling cites on HPG was high. (c) 2008 Wiley Periodicals, Inc.