Synthesis and Characterization of a Novel Biodegradable Material, Poly(Lactic Acid-co-Tryptophane)

Abstract

With cheap D,L-lactic acid (D,L-LA) and tryptophan (Try) as starting materials, a novel biodegradable material, poly(lactic acid-co-tryptophane) (P(LA-co-Try)), was synthesized via melt co-polycondensation. When the molar feed ratio LA/Try is 90:10, the influences of different conditions, including catalyst kinds and its dosage, co-polymerization time and temperature on the synthesis of the polymer are discussed. When SnCl2/ZnO (weight ratio 7:3) was used as catalyst at a dose of 0.7 wt% of the pre-polymer, 8 h direct-melt polycondensation at 160°C and absolute pressure of 70 Pa after pre-polymerization gave the co-polymer with a maximum intrinsic viscosity [η] of 0.73 dl/g. The structure of the co-polymer was characterized by FT-IR and 1H-NMR. According to the optimal synthetic conditions, co-polymers with different molar feed ratios were synthesized and systematically characterized by [η], FT-IR, 1H-NMR, GPC, DSC and XRD. The GPC results show that the maximum weight-average molecular weight (M w) of P(LA-co-Try) is 6500 when the molar feed ratio LA/Try is 98:2. With the increase of the molar feed ratio of Try, [η], M w and its polydispersity index (M w /M n) decrease gradually. Due to the introduction of Try with a big aromatic ring into the co-polymer, the glass-transition temperature (T g) increases gradually with the increasing feed charge of Try and all co-polymers are amorphous. Direct-melt co-polycondensation is a cheap and practical method for the synthesis of Try-modified poly(lactic acid), a potential biomedical material, especially when used as a drug-delivery carrier.