Synthesis and Degradation of Poly(Lactic Acid-co-L-Tyrosine)

Abstract

Based on the fact that the polylactic acid (PLA) has high crystallinity and poor hydrophilicity and its degradation products are known to induce inflammatory reactions, tyrosine could be introduced in the chain of polylactic acid to enhance its poperties. The new copolymers poly(lactic acid-co-L-tyrosine) (PLA-co-Tyr) were synthesized via direct melt polycondensation with lactic acid (D,L-LA) and L-tyrosine (Tyr) as raw materials and SnCl2 as catalyst, using the linear heating method. The copolymers were characterized by viscosity-average molecular weight, FT-IR, 1H-NMR, GPC, DSC, and XRD. The degradation experiment of PLA-co-Tyr was carried out in phosphate buffer solution (PBS) at 37°C using PLA as the control sample. Scanning electronic microscopy (SEM) was used to analyze the results of degradation.The results demonstrate that with reaction conditions of 170°C and 500 Pa and with 0.4 wt.% SnCl2, 10 h of polymerization gave the PLA-co-Tyr with the largest average molecular weight of 2900 g/mol, which appears to meet the requirements necessary for a drug delivery applications. Compared with PLA, it has lower Tg and lower crystallinity. The copolymer has good thermal stability and superior performance against degradation.