含非平面环生物可降解热塑弹性体的合成及其增韧聚乳酸研究

Poly(lactic acid)(PLA) is a biodegradable bioplastic with high modulus and strength. However, its application is largely limited because of its brittleness, low impact strength and tearing strength. Therefore, development of a fully biodegradable PLA composite with high toughness is of great importance in order to improve its potential applications in various fields. Currently, although many toughening systems have been developed and used for the toughening of PLA, such as plasticizers, inorganic/organic particles, thermoplastic elastomers and biodegradable plastics, none of these systems is able to result in PLA composite with high toughness and maintain full biodegradability as well as high modulus and strength simultaneously. In our previous study, we found that polyester with non-planar ring structure has excellent ductility and elasticity, while the mechanism remains unknown. Therefore, in this study, we propose to design and synthesize a series of polyesters with various non-planar ring structure contents, distribution as well as stereochemical structure, using 1,4-cyclohexanedicarboxylic acid as starting material, in order to develop novel biodegradable thermoplastic elastomer with high toughness and elasticity, and use it for the toughening of PLA. This study would provide us a great opportunity to not only investigate the relationship between non-planar ring structure and properties of the product, but also explore the influence of non-planar ring structure to the toughening of PLA and help us find out the possible mechanism of toughening. In addition, this study would pave the way for the development of fully biodegradable high-performance PLA composite.

聚乳酸（PLA）是一种具有高模量和强度的可降解生物基塑料，但PLA质脆、韧性差、抗冲击和抗撕裂强度低，对缺口敏感，因此实用价值受到极大限制，需要对其进行增韧改性。然而现有的增韧体系如增塑剂、无机/有机刚性粒子、热塑性弹性体和可降解塑料等，均难以在保持PLA模量、强度和可降解性能的前提下获得优异的增韧效果。申请人团队前期研究发现含非平面环聚酯材料表现出优异的韧性和弹性，然而其构效关系尚不明确。因此，本项目拟选择含非平面环结构的1,4-环己烷二甲酸为原料，设计合成一系列不同非平面环含量、分布和立体化学结构的聚酯材料，希望得到具有优异韧性和弹性的可降解热塑性弹性体并用于PLA增韧改性。通过本项研究，初步阐明非平面环结构赋予材料优异性能的原因和机理，总结非平面环立体化学结构变化对材料性能及PLA增韧效果的影响规律，阐明增韧机理。为设计合成全生物降解高性能PLA复合材料积累新的理论知识和技术基础。

针对生物基可降解材料聚乳酸性能缺陷，研究开发新的增韧改性体系并阐明其增韧机理，对促进聚乳酸材料的结构性能研究和应用具有重要的理论和实际意义。本项目提出以含非平面环结构的1,4-环己烷二甲酸（CHDA）为原料，设计合成一系列不同非平面环含量、分布和立体化学结构的聚酯材料，以便得到具有优异韧性和弹性的可降解热塑性弹性体并用于PLA增韧改性。首先，本项目通过调整CHDA含量及立体构型变化及共聚单体类型，设计制备了三类不同体系的聚酯和共聚酯体系，分别是CHDA引入传统聚醚酯得到的PBCT-PTMG体系，CHDA、丁二醇与己二酸的共聚酯体系PBAC，以及CHDA、丁二醇与月桂二酸的共聚酯体系PBLC，均具有较好的弹性性能。其次，结合带不同侧链结构的短链二元醇，设计合成了一系列具有不同空间位阻效应的聚酯，通过DMA研究其次级转变的变化规律，发现具有对称或长侧链结构的短链二元醇可以提高CHDA非平面环的构象转变运动能力。在此基础上，通过固定CHDA顺反比例，优选了BC单元含量为80%的PBAC，得到了对PLA增韧改性效果显著的新型热塑性弹性体。进一步研究不同CHDA顺反比例，我们发现，高含量反式CHDA的存在会促进结晶，使所得PBAC聚酯为塑性的半结晶性聚合物，用于增韧聚乳酸时可有效提高其拉伸韧性。而高顺式CHDA的存在会破坏结晶，使得所得PBAC聚酯为无定型弹性体，用于增韧聚乳酸时可有效提高其冲击韧性。