Novel, biodegradable, functional poly(ester-carbonate)s by copolymerization of trans-4-hydroxy-L-proline with cyclic carbonate bearing a pendent carboxylic group

Water-soluble poly(ester-carbonate) having pendent amino and carboxylic groups on the main-chain carbon is reported for the first time. This article describes the melt ring-opening/condensation reaction of trans-4-hydroxy-N- benzyloxycarbonyl-L-proline (N-CBz-Hpr) with 5-methyl-5-benzyloxycarbonyl-1,3- dioxan-2-one (MBC) at a wide range of molar fractions. The influence of reaction conditions such as catalyst concentration, polymerization time, and temperature on the number average molecular weight (M_n) and molecular weight distribution (M_w/M_n) of the copolymers was investigated. The polymerizations were carried out in bulk at 110°C with 3 wt % stannous octoate as a catalyst for 16 h. The poly(ester-carbonate)s obtained were characterized by Fourier transform infrared spectroscopy, ¹H NMR, differential scanning calorimetry, and gel permeation chromatography. The copolymers synthesized exhibited moderate molecular weights (M_n = 6000-14,700 g mol^-1) with reasonable molecular weight distributions (M_w/M_n = 1.11-2.23). The values of the glass-transition temperature (T_g) of the copolymers depended on the molar fractions of cyclic carbonate. When the MBC content decreased from 76 to 12 mol %, the T_g increased from 16 to 48°C. The relationship between the poly(N-CBz-Hpr-co-MBC) T_g and the compositions was in approximation with the Fox equation. In vitro degradation of these poly(N-CBz-Hpr-co-MBC)s was evaluated from weight-loss measurements and the change of M_n and M_w/M_n. Debenzylation of 3 by catalytic hydrogenation led to the corresponding linear poly(ester-carbonate), 4, with pendent amino and carboxylic groups.