压缩CO2调控聚乳酸结晶行为及凝聚态结构的研究

This project is proposed to study the role of compressed CO2 on inducing and regulating the crystallization behavior and its effect on the resulting crystalline superstructure of polylactides, which show weak crystallization ability. Firstly, the effect of compressed CO2 on the crystal nucleation in amorphous polylactides would be quantitatively probed by analysis of thermal crystallization behavior after the physical aging by low pressure CO2 pre-conditioning, using analytical techniques of microscopy, DSC, and spectroscopy. Meanwhile, the compressed CO2 pre-conditioning enhanced mesomorphic structure (or locally ordered structure) formation in the early stage of polylactide crystallization would also be explored. Accordingly, we would disclose the kinetics and/or mechanisms of nucleation of compressed CO2-induced crystallization in polylactides with different chain structural characteristics such as tacticity (optical purity), long-chain branching, and molecular weight. Secondly, the crystal growth, crystalline morphology as well as the overall kinetics of the compressed CO2-induced crystallization of polylactides would be studied. Especially, we pay attention to the formation and evolution of the crystalline phase structures including crystal phase, mobile-amorphous fraction (MAF), and rigid-amorphous fraction (RAF) during the crystallization of polylactides. On the basis of the results of above studies, we aim to reveal how compressed CO2 and macromolecular structures affect the crystallization behavior (including crystal nucleation and growth) as well as the formation and evolution of the superstructure of polylactides. The results obtained would be significant for understanding the nucleation/crystallization behavior and the superstructure of semicrystalline polymers. Moreover, this project aims to provide some new insights into the control of the crystalline superstructure and even the physical properties of polylactides.

本申请拟围绕“压缩CO2对结晶缓慢聚乳酸的结晶行为和凝聚态结构的调控作用”开展系统研究工作。首先，通过低压CO2预处理/结晶的方法，利用显微镜、DSC和光谱等分析技术，研究非晶态聚乳酸在压缩CO2气氛中的物理老化和晶体成核，探讨CO2预处理聚乳酸中结晶初期局部有序结构的形成，考察成核对随后结晶行为的影响，以此阐明压缩CO2作用下不同链结构（规整度、长链支化和分子量）聚乳酸结晶的成核动力学和成核机理；另外，研究CO2处理诱导聚乳酸结晶的晶体生长、结晶形态，讨论其总结晶动力学，探讨聚乳酸结晶过程的晶相、自由非晶相和受限非晶相等相结构的组成及其形成和演变规律。在此基础上，揭示聚乳酸结晶的成核和生长等结晶行为以及聚集态结构与压缩CO2条件、分子链结构之间的关系，为理解聚合物的结晶行为、聚集态结构等基础科学问题提供更多的实验证据，为调控聚乳酸的聚集态结构乃至物理特性提供重要的理论依据。

聚乳酸特别是当分子链中含有D-异构体时，其空间立构规整度较低，结晶速率非常缓慢。我们按计划较好地实现利用压缩CO2对结晶缓慢聚乳酸结晶行为和聚集态结构进行调控，基本完成项目内容包括，通过利用压缩及超临界CO2，对不同链结构聚乳酸的总结晶速率、结晶微观形态/形貌、以及结晶的相态结构等进行系统研究。获得的具体重要结果体现在：（1）低温低压CO2预处理大幅促进聚乳酸形成局部有序结构包括中间相，这些有序结构由于显著促进成核效率而进一步大大加快聚乳酸在后续常压高温结晶时的总结晶速率，并改变结晶晶体尺寸和微观形貌，同时晶型保持不变。（2）较低温度和较高压力条件CO2诱导具有高度链结构缺陷的聚乳酸直接从起始玻璃态形成具有左手螺旋片晶构成的环带球晶。（3）高压CO2有效调控不同链结构聚乳酸的自由非晶相、受限非晶相和结晶相等三相结构的形成。项目完成期间以第一/通讯作者共发表基金标注SCI论文4篇（含2篇Macromolecules）；所获得的创新性结果为理解和调控聚乳酸等高分子的结晶行为和聚集态结构提供新的知识和依据。