Dendritic multifunctional macroinitiators having 12 TEMPO-based alkoxyamines were prepared by the reaction of a benzyl alcohol having 4 TEMPO-based alkoxyamines with 1,3,5-tris[(4-chlorocarbonyl)phenyl]benzene and 1,3,5-tris(4-isocyanatophenyl)benzene. Using the dodecafunctional macroinitiators, TEMPO-mediated radical polymerizations of styrene (St) were carried out at 120 degrees C, and 12-arm star polymers (star-12) with narrow polydispersities of M-w/M-n = 1.06-1.26 were obtained. To evaluate the livingness for the TEMPO-mediated radical polymerizations of St, hydrolysis of the ester bonds of the 12-arm star polymers and subsequent SEC measurements were carried out. Furthermore, using star-12 as the macroinitiator, TEMPO-mediated radical polymerization of 4-vinylpyridine (4-VP) was carried out, and well-defined poly(St)-b-poly(4-VP) 12-arm star diblock copolymers with M-w/M-m, = 1.18-1.19 were obtained. (c) 2005 Wiley Periodicals, Inc.