Synthesis and characterization of novel random copolyesters from trans-4-hydroxy-l-proline and functional cyclic esters

The melt polycondensation reaction of trans-4-hydroxy-N-benzyloxycarbonyl-l-proline (N-CBz-Hpr) and functional cyclic esters containing protected functional groups (carboxyl, and amino) at a wide range of molar fractions in the feed produced new degradable poly(N-CBz-Hpr-co-functional-ε-CL)s with stannous 2-ethylhexanoate (Sn(Oct)2) as a catalyst. The optimal reaction conditions for the synthesis of the copolymers were obtained with 1.5 wt% Sn(Oct)2 at 140 °C for 24 h. The copolymers obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), 1H NMR, differential scanning calorimetry, gel permeation chromatography, and Ubbelohde viscometry. The copolymers synthesized exhibited oligomeric molecular weights (3000–5000 g mol−1) with modestly narrow molecular weight distributions (1.11–1.37). The values of the glass-transition temperature (Tg) of the copolymers depend on the compositions, and the molar fractions of cyclic lactone. For the poly(N-CBz-Hpr-co-4-EtC-ε-CL) system, with a decrease in 4-EtC-ε-CL contents from 79 to 3 mol%, the Tg increased from −34 to 67 °C In vitro degradation of these copolymers was evaluated from weight-loss measurements.