Synthesis of three‐armed poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐ L ‐proline)‐block‐poly(ε‐caprolactone) copolymers

A series of novel types of three‐armed poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L‐proline)‐block‐poly(ε‐caprolactone) (PHpr‐b‐PCL) copolymers were successfully synthesized via melt block copolymerization of trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L‐proline (N‐CBz‐Hpr) and ε‐caprolactone (ε‐CL) with a trifunctional initiator trimethylolpropane (TMP) and stannous octoate (SnOct2) as a catalyst. For the homopolycondensation of N‐CBz‐Hpr with TMP initiator and SnOct2 catalyst, the number‐average molecular weight (Mn) 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 (Mw/Mn) is between 1.25 to 1.32. These three‐armed prepolymer PHpr were subsequently block copolymerized with ε‐caprolactone (ε‐CL) in the presence of SnOct2 as a catalyst. The Mn of the copolymer increased from 2240 to 18,840 g mol−1 with the molar ratio (0–60) of ε‐CL to PHpr. These products were characterized by differential scanning calorimetry (DSC), 1H NMR, and gel permeation chromatography. According to DSC, the glass‐transition temperature (Tg) 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 Mn and Mw/Mn.