高分子量sb-PLA的合成及其sc-PLA材料结构与性能

The pre-polymer of poly(L-lactide (PLLA)) or of poly(D-lactide (PDLA)) will be synthesized by ring-opening polymerization (ROP) of the L(D)-lactide monomer using zinc lactate or Stannous octanoate (Sn(Oct)2) as a catalyst. The terminal hydroxyls of the pre-polymer will be activated by Sn(Oct)2. Then a series of high molecular weight poly(L-lactide)-poly(D-lactide) (PLLA-PDLA) stereoblock copolymers (sb-PLA) with various molar ratios of L-lactide and D-lactide will be synthesized by ROP of D-lactide monomer with PLLA-SnOct pre-polymer as a macroinitiator (or by ROP of L-lactide monomer with PDLA-SnOct pre-polymer as a macroinitiator). A stereocomplex type of PLA (Stereocomplex Polylactide, sc-PLA) is expected to form in the sb-PLAs. The mole mass of sb-PLA and its stereocomplex segment configuration will be optimized by the novel ROP procedures. The thermodynamic parameters, dynamics of crystallization and morphology of single or aggregation of sc-PLA crystals will be obtained by selective enzymic degradation process, which will allow a better understanding on the mechanisms of crystallization of sc-PLA. The goal of the study is to understand how the stereocomplex forms between the sb-PLA and in particular the influence of the stereocomplex structure on the microstructures and thermal properties of the sc-PLA. The star shape pre-polymer of PLLA or PDLA will be prepared by ROP of the L(D)-lactide monomer with 1,1,1-Tris(hydroxymethyl)ethane (TME) as an initiator. The terminal hydroxyls of the pre-polymer will be activated by Sn(Oct)2. Novel star shape PLLA-PDLA stereoblock copolymers will be synthesized by ROP of the D-lactide monomer with functioned PLLA-SnOct pre-polymer as a macroinitiator (or by ROP of L-lactide monomer with star shape PDLA-SnOct pre-polymer as a macroinitiator). The mechanisms of the formation of the tereocomplex structure and its dissolution and recovery processes will be studied by various complementary techniques. Crystallization behaviors, structures and morphology of the star shape sc-PLA and their effects on the properties of this material will be elucidated. This project will allow us obtaining the theoretical or experimental knowledge about sc-PLA material which is highly promising as a biodegradable heat-resistivity engineering material.

本项目拟以左旋或右旋乳酸为原料，开环聚合PLLA或PDLA预聚体。采用链端基活化技术，制备高分子量的PLLA-PDLA立构嵌段共聚物（sb-PLA）。研究合成条件对sb-PLA分子量及其分布、链序列结构的影响，发展sb-PLA合成技术的新方法。利用选择性酶降解法，富集sc-PLA单晶及聚集体，直接观测sc-PLA晶体结构，研究其结晶热力学、动力学及形貌，揭示sc-PLA结晶机制，阐明sc-PLA材料结构对性能的影响。在此基础上，以多官能团化合物为起始剂，制备高分子量的星型sb-PLA嵌段共聚物及其立构复合体材料。研究星型sc-PLA立构交联网络的生成、解离和再生成的机制，探讨星型sc-PLA的结晶热力学、动力学和形态，阐明材料的凝聚态及转变行为对性能的影响。为耐热可降解sc-PLA工程材料的研究提供理论与实验依据。

在优化的合成条件下，分别合成了线性或三枝化聚乳酸预聚体，采用预聚体链端基活化技术，制备高活性链端基预聚体。以其作为引发剂，与预聚体不同旋光性的丙交酯开环共聚合，制备数十万数均分子量、高立构规整度的sb-PLA嵌段共聚物。项目开发的制备sb-PLA技术具有合成的共聚物分子构型与链序列结构可控、分子量和立构规整度高的特点。.基于对sc-PLA熔体中立构复合结构的温度、时间转变效应的发现，提出sc-PLA立构复合熔体结构特征温度Tcr。研究了分子量、链段结构、温度和时间对sc-PLA立构复合体形成与解离的影响，揭示了sc-PLA的“结晶记忆”效应和熔体再结晶的“自成核”机理。基于此原理，研究了sc-PLA对PLLA同质异相诱导结晶机制及sc-PLA/PLLA材料。.研究了sb-PLA的分子量、序列结构对其sc-PLA结晶热力学、动力学的影响，理论分析和计算sc-PLA成核与晶体生长机理；阐明了sb-PLA分子结构对sc-PLA结晶成核密度、片晶和球晶的结构及尺寸的影响机制；揭示了三枝化sb-PLA熔体结晶仅生成熔点>200度的sc-PLA晶体的结构-性能特点。项目开发的高分子量sc-PLA材料的拉伸强度>100MPa，断裂伸长率>50%，杨氏模量约2.8GPa。此外，利用蛋白酶K对sb-PLA的选择性降解行为，对富集的sc-PLA晶体结构与形貌进行了详实探讨。基于对sb-PLA链结构、分子量、结晶及形态等对sc-PLA材料的降解行为的调控，利用相分离及微结构控制，探讨制备sc-PLA多孔膜材料技术。对sb-PLA/石墨烯纳米片（GNS）纳米复合材料进行了研究，从sc-PLA结晶行为与结构阐述GNS对sc-PLA异相成核作用及sc-PLA凝聚态转变机制。 .采用不同旋光性的聚乳酸与三亚甲基碳酸酯合成了线型PLA-TMC嵌段共聚物并制备了sc-PLA-TMC新材料。探讨TMC链段对sc-PLA-TMC结晶、结构与性能的影响。当TMC摩尔含量高于5 %时，sc-PLA-TMC材料仅生成熔点高于200度的sc-PLA晶体，开发出耐热性和韧性均优于通常的PLLA-PTMC的新材料。.基于sb-PLA嵌段共聚物的结构控制与其sc-PLA材料200度下仍具有良好的物理性能的优势，开发了环保型高挠性sc-PLA薄膜并研究了温敏型仿人工皮肤自感应电子器件。