The biocompatible tadpole-shaped copolymers [cyclic-poly(ethylene oxide) (PEO)]-b-[linear poly(epsilon-caprolactone) (PCL)](2) [(c-PEO)-b-PCL2] with one PEO ring and two PCL tails were synthesized by combination of glaser coupling with ring-opening polymerization (ROP). First, a linear PEO precursor with two alkyne groups at the chain terminal and two hydroxyl groups at the chain middle was prepared by ROP of EO monomer and the following transformation of functional groups. Then, cyclic PEO with two hydroxyl groups at the same site was obtained by the "Glaser" cyclization. Finally, the hydroxyl groups on cyclic PEO directly initiated the ROP of epsilon-CL monomer to produce the target copolymers (c-PEO)-b-PCL2. The target copolymers and intermediates were all well characterized by GPC, MALDI-TOF MS, H-1 NMR and FT-IR. (C) 2012 Elsevier Ltd. All rights reserved.