Heteroarm H-shaped terpolymers, [(poly(L-lactide))(polystyrene)]poly(ethylene oxide)[(polystyrene)(poly(L-lactide))], [(PLLA)(PS)]PEO[(PS)(PLLA)], in which PEO acts as a main chain and PS and PLLA as side arms, have been successfully prepared via combination of reversible addition-fragmentation transfer (RAFT) polymerization and ring-opening polymerization (ROP). The first step is the synthesis of the PEO capped with one terminal dithiobenzoate group and one hydroxyl group at every chain end, [(HOCH2)(PhC(S)S)IPEO[(S(S)CPh)(CH2OH)I from the reaction of carboxylic acid with ethylene oxide. Then, the RAFT polymerization of styrene (St) was carried out using F(HOCH2)(PhC(S)S)IPEO[(S(S)CPh)(CH2OH)] as RAFT agent and AIBN as initiator, and the triblock copolymer, [(HOCH2)(PS)]PEO[(PS)(CH2OH)], was formed. Finally, the heteroarm H-shaped terpolymers, [(PLLA)(PS)]PEO[(PS)(PLLA)1, were produced by ROP of LLA, using triblock copolymer, [(HOCH2)(PS)]PEC[(PS)(CH2OH)1, as macroinitiator and Sn(Oct)(2) as catalyst. The target products and intermediates were characterized by H-1 NMR spectroscopy and gel permeation chromatography. (c) 2007 Wiley Periodicals, Inc.