Poly(dimethylsiloxane)-containing diblock and triblock copolymers were prepared by the combination of anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D-3) and nitroxide-mediated radical polymerization (NMRP) of methyl acrylate (MA), isoprene (IP), and styrene (St). The first step was the preparation of a TlPNO-based alkoxyamine carrying a 4-bromophenyl group. The alkoxyamine was then treated with Li powder in ether, and AROP of D-3 was carried out using the resulting lithiophenyl alkoxyamine at room temperature, giving functional poly(D-3) with M-w/M-n, of 1.09-1.16. NMRPs of MA, St, and IP from the poly(D-3) at 120 degrees C gave poly(D-3-b-MA), poly(D-3-b-St), and poly(D-3-b-IP) diblock copolymers, and subsequent NMRPs of St from poly(D-3-b-MA) and poly(D-3-b-IP) at 120 degrees C gave poly(D-3-b-MA-b-St) and poly(D-3-b-IP-b-St) triblock copolymers. The poly(dimethylsiloxane)-containing diblock and triblock copolymers were analyzed by H-1 NMR and size exclusion chromatography. (c) 2005 Wiley Periodicals, Inc.