The Preparation And Characterization Of Poly(Lactic Acid-proline)

In recent years, PLA[ply(lactic acid)], a typical biodegradable polymer produced from renewable agricultural resources, has been extensively applied in the biomedical, industrial and agricultural fields due to its outstanding properties, such as good biodegradability, excellent biocompatibility and bioabsorbability. However, for specific applications, PLA homopolymer has some disadvantages, such as high crystallinity, slow and uncontrolled degradation speed, poor hydrophilicity, which limits the application scope of PLA. Currently, copolymerization of amino acid(AA) and lactic acid(LA) is a well-known method to modify the properties of PLA. Poly(LA-AA) could change properties of PLA, such as hydrophilicity, crystallinity or biodegradation rate, while keep the good biodegradability, excellent biocompatibility and bioabsorbability.However, the synthesis of poly(LA-alt-AA) has rarely been focused on ring-opening homopolymerization of morpholine-2,5-dione derivatives. Unfortunately, the synthesis of morpholine-2,5-dione derivatives was very complicated and the reactivity of the monomers was low. Moreover, few people have considered to introduce proline into PLA to modify PLA. In order to solve the two problems, poly(lactic acid-alt-proline)(PLAP) and poly(lactic acid-co-proline)(PLAPL) was prepared by homopolymerization of line dimer of lactic acid-proline(PL) and copolymerization of PL and LA. This thesis mainly includes:①The PL was prepared by methyl esterification of proline, acetylation of lactic acid, amidation and hydrolysis. At the same time, cyclic dimer of lactic acid-proline(POL) was obtained. PL and POL were characterized by FTIR、1-NMR.②The PLAP was synthetized by direct melt polycondensation, starting from the PL. The yield of PLAP is about20%and Mn=3700, PDI=1.08. The glass transition temperature of PLAP(64.2℃) is higher than PLA and the thermal degradation temperature is similar with PLA, whereas the neat PLAP exhibited almost amorphous state corresponding to no apparent crystallization peak. We tried the ring-opening polymerization of POL, but the yield was<10%.③The PLAPL was prepared via the direct melt polycondensation starting from the PL and LA or POL and LA with different molar feed. PLAPL was characterized by FTIR、1-NMR、DSC etc. The results show that with the increase of the molar feed ratio of PL or POL in the copolymerization, not only molecular weight decreased gradually, but also conversion had the trend of gradual decrease. The glass transition temperature of PLAPL increased gradually and PLAPL changed from crystalline to amorphous cuvres as the PL in the reaction mixture was increased.