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

由于聚l -丙交酯（PLA）具有良好的生物相容性、生物可降解性和较高的机械强度，PLA作为一种可降解的医用高分子材料已被临床应用。然而，由于线性聚乳酸的结晶度过高，存在降解率难以控制和弹性低的问题。为了解决这些问题，研究了在聚乳酸中引入分支结构的方法。首先，合成了低糖单位含量的聚乳酸接枝多糖，并对其制备的薄膜的力学性能、降解性能和功能进行了初步研究。其次，以聚甘油为宏观引发剂，通过丙交酯本体聚合法制备了不同接枝链长度的支化pla。通过热分析、拉伸试验研究了支化聚乳酸或聚乳酸及其立体配合物的性能。与线性PLLAor PDLA膜相比，支化PLLA或PDLA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。该立体配合物薄膜具有较高的最大应力和杨氏模量，并保持了较高的断裂应变。此外，研究了支化plla1或支化PDLA作为增塑剂的有效性，并将支化plla2或支化PDLA与线性PLLA制备成1:9共混膜。与线性PLLA膜相比，共混膜具有更高的断裂应变。通过改变支链聚乳酸的分子量，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