New Y-shaped (AB(2)-type) amphiphilic copolymers of poly(ethylene glycol) (PEG) with poly(trimethylene carbonate) (PTMC), PEG-b-(PTMC)(2), were successfully synthesized by the ring-opening polymerization (ROP) of TMC with bishydroxy-modified monomethoxy-PEG (mPEG). First, a bishydroxy functional ROP initiator was synthesized by esterification of acryloyl bromide with mPEG, followed by Michael addition using excess diethanolamine. A series of Y-shaped amphiphilic PEG(PTMC)(2) block copolymers were obtained via ROP of TMC using this PEG with bishydroxyl end groups as macroinitiator and ZnEt2 as catalyst. The amphiphilic block copolymers with different compositions were characterized by gel permeation chromatography (GPC) and H-1 NMR, and their molecular weight was measured by GPC. The results showed that the molecular weight of Y-shaped copolymers increased with the increase of the molar ratio of TMC to mPEG-(OH)(2) initiator in feed while the PEG chain length was kept constant. The Y-shaped copolymer mPEG-(PTMC)(2) could self-assemble into micelles in aqueous medium and the critical micelle concentration values of the micelles decrease with increase in hydrophobic PTMC block length of mPEG-(PTMC)(2). The in vitro cytotoxicity and controlled drug release properties of the Y-shaped amphiphilic block copolymers were also investigated. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8131-8140, 2008