A series of novel types of three-armed poly(trans-4-hydroxy-N-benzyloxycarbonyl-L-proline)-block-poly(epsilon-c aprolactone) (PHpr-b-PCL) copolymers were successfully synthesized via melt block copolymerization of trans-4-hydroxy-N-benzyloxycarbonyl-L-proline (N-CBz-Hpr) and epsilon-caprolactone (E-CL) with a trifunctional initiator trimethylolpropane (TMP) and stannous octoate (SnOct(2),) as a catalyst. For the homopolycondensation of N-CBz-Hpr with TMP initiator and SnOct(2), catalyst, the number-average molecular weight (M-n) of prepolymer increases from 530 to 3540 g mol(-1) with the molar ratio of monomer to initiator (3-30), and the molecular weight distribution (M-w/M-n) is between 1.25 to 1.32. These three-armed prepolymer PHpr were subsequently block copolymerized with epsilon-caprolactone (epsilon-CL) in the presence of SnOct(2) as a catalyst. The M-n of the copolymer increased from 2240 to 18,840 g mol(-1) with the molar ratio (0-60) of epsilon-Cl, to PHpr. These products were characterized by differential scanning calorimetry (DSC), H-1 NMR, and gel permeation chromatography. According to DSC, the glass-transition temperature (T-g) of the three-armed polymers depended on the molar ratio of monomer/initiator that were added. In vitro degradation of these copolymers was evaluated from weight-loss measurements and the change of M-n and M-w/M-n. (c) 2005 Wiley Periodicals, Inc.