Synthesis of poly(D,L-lactic acid) modified by cholic acid via direct melt copolycondensation and its characterization

摘要

From D,L-lactic acid and the natural functional molecule cholic acid (CA), the biodegradable material poly(D,L-lactide-cholate) was synthesized via direct copolycondensation. For the CA/lactic acid (LA) molar feed ratio of 1/64, the optimal synthesis conditions were as follows: a prepolymerization time of 8 h, 0.3 wt SnO catalyst, and melt copolycondensation for 8 h at 160°C, which gave a novel star-shaped poly(D,L-lactic acid) (PDLLA) modified by CA with the maximum weight-average molecular weight of 5600 Da at a yield of 51.9. The copolymer poly(D,L-lactide-cholate) at different molar feed ratios was characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry, thermogravimetry, and X-ray diffraction. Decreasing the molar feed ratio of CA/LA from 1/15 to 1/128 reduced the average number of CA units embedded in the copolymer from 4 to 1. With 1/15 CA/LA, the copolymer was not a star-shaped polymer, and its weight-average molecular weight was the biggest (weight-average molecular weight = 12,700 Da, weight-average molecular weight/ number-average molecular weight = 1.68). With 1/32 CA/ LA, the copolymer with two CA units was not a starshaped polymer either. With 1/64, 1/100, and 1/128 CA/ LA, the copolymer mainly had one CA unit core embedded as a normal star-shaped PDLLA with four arms, and certain crystallinity could be detected. The novel direct copolycondensation method was simple and practical for the synthesis of the asymmetrical star-shaped PDLLA material, and it was advantageous for this PDLLA material embedded in the special bioactive molecule CA to be applied in the field of drug delivery and tissue engineering.