Synthesis of Polylactide with Branched Structures and Control of Its Mechanical Property& Biodegradability

由于聚乳酸（PLA）具有良好的生物相容性、生物降解性和较高的机械强度，PLA已被临床用作可降解医用高分子材料。然而，已经指出，由于线性PLA的结晶度过高，其降解速率难以控制且弹性低。为了解决这些问题，本文首先合成了低糖基聚乳酸接枝多糖，并对其膜的力学性能、降解性能和功能性进行了初步研究;其次，以聚缩水甘油为大分子引发剂，通过本体聚合丙交酯，合成了不同接枝链长度的支链聚乳酸。通过热分析、拉伸试验等方法研究了支化PLLA和PDLA及其立体复合物的性能。与线性PLLA或PDLA膜相比，支化PLLA或PDLA膜表现出较低的玻璃化转变温度（Tg）、熔融温度（Tm）、结晶度、较低的杨氏模量和较高的断裂应变。立体复合物膜显示出高的最大应力和高的杨氏模量，保持其高的断裂应变。此外，支化PLLA或PDLA作为增塑剂的有用性进行了研究与1：9共混膜制备从支化PLLA或支化PDLA和线性PLLA。与线性PLLA膜相比，共混膜显示出更高的断裂应变。通过改变支化聚乳酸的分子量可以控制共混膜的性能

Since poly(L-lactide)(PLA) has a good biocompatibility, biodegradability and high mechanical strength, PLA has been clinically used as a degradable medical polymer material. However, it has been pointed out that the difficulty of control of degradation rate and low elasticity for linear PLA as a result of its too high crystallinity. In order to solve these problems, the introduction of branched atnicture into PLA were investigated.Firstly, PLA-grafted polysaccharides having low sugar unit contents were synthesized and mechanical properties, degradabilities and functionalites of films prepared from them were basically investigated.Secondly, branched PLAs with various lengths of graft chain were synthesized by bulk polymerization of lactide using polyglycidol as a macroinitiator. The properties of branched PLLA or PDLA and their stereocomplex were investigated through thermal analysis, tensile test. The branched PLLA or PDLA film exhibited a lower glass transition temperature (Tg), melting temperature (Tm), crystallinity, lower young's modulus, and higher strain at break compared to linear PLLAor PDLA film. The stereocomplex film showed high maximum stress and high Young's modulus keeping its high strain at break. Moreover, the usefulness of branched PLLAor PDLA as a plasticizer was investigated with 1:9 blend films prepared from the branched PLLA or branched PDLA and linear PLLA. The blend films showed higher strain at break compared with linear PLLA film. The properties of the blend films could be controlled by changing the molecular weight of branced PLA