Synthesis of Poly(D,L-lactic acid) Modified by Cholic Acid via Direct Melt Copolycondensation and Its Characterization

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 star-shaped 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. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1405-1415, 2010