AB(2) 3- and AB(4) 5-miktoarm star copolymers were prepared by combination of the anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D-3) and the TEMPO-mediated radical polymerization of styrene (St). Initially, two kinds of dendritic multifunctional initiators were prepared. One has a 4-bromobutoxy group and two TEMPO-based alkoxyamines and the other has a 4-bromobutoxy group and four TEMPO-based alkoxyamines. Treatment of the multifunctional initiators with tert-butyllithium gave the corresponding lithiobutoxy derivatives, and AROP of D-3 by the lithiobutoxy derivatives gave poly(D-3) with M-w/M-n of 1.07-1.12. Nitroxide-mediated radical polymerization of St by the poly(D-3)s at 120 degrees C gave AB(2) 3- and AB(4) 5-miktoarm star copolymers with M-w/M-n of 1.15-1.28. Their structures were analyzed by means of H-1 NMR and SEC measurements. (c) 2005 Elsevier Ltd. All rights reserved.