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

聚L-丙交酯具有良好的生物相容性、生物降解性和较高的机械强度，已作为可降解医用高分子材料应用于临床。但由于线型聚乳酸的结晶度过高，导致其降解速度难以控制，弹性较低。为了解决这些问题，我们研究了在聚乳酸中引入支化结构。首先，合成了低糖含量的聚乳酸接枝多糖，并对其制备的薄膜的力学性能、降解性和功能化进行了初步研究；其次，以聚缩水甘油为大分子引发剂，通过本体聚合，合成了不同接枝链长度的支化聚乳酸。通过热分析、拉伸实验研究了支化聚乳酸或聚乳酸及其立体络合物的性能。与线型PLLA或PDLA薄膜相比，支化的PLLA或PDLA薄膜具有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。立体复合膜表现出高的最大应力和高的杨氏模量，使其在断裂时保持高应变。以1：9的支化PLLA或支化PDLA与线型PLLA共混制得薄膜，考察了支化PLLA或PDLA作为增塑剂的用途。与线性PLLA膜相比，共混膜表现出更高的断裂应变。通过改变支化聚乳酸的相对分子质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