生物基聚(乳酸-蓖麻油酸)的合成与立构复合及改性聚乳酸

Polylactide (PLA) is a biodegradable and bio-based polymer, which has been used as biomedical and environment-friendly materials.Broader implementation of the materials is limited due to its inherent deficiencies, such as slow growth rate, low heat-resistant temperature, brittleness and bad shock resistance. It is reported that the vegrtable oil-based polymers can be used as modifiers for PLA resion, such as the rubbery poly(ricinolei acid) (PRA),of which its molecular weight of 10 000 g/mol has excellent toughness.PLLA stereocomplex can enhance crystallizaiton, heat-resistant temperature and mechanical strength of PLA.Tough PRA and PLA are strong segregated, more abundant microscopic structures and morphologies can be obtained in crystalline-rubbery PLA-PRA block copolymers without macroscopic separaiton. In the work, PLLA-b-PRA and PDLA-b-PRA with different molecular weight and componment ratio will be synthesized, and the influences of molecular weight, PRA/PLLA (PDLA) ratio, crystallization pathway, shear effect on crystallization and strucure of PLLA-b-PRA/PDLA-b-PRA blend,and heat-resistance and mechanical properties. The crystallization and structure of PLLA-b-PRA/PDLA-b-PRA blends, the relationship between the final strcture, internal factors of the blends, and the external factors including crystallization conditions,will be further infestigated, which are all of importance for the performance of PLA materials. The stereocomplex of PLLA/PDLA can be used as nucleating agent for PLLA homopolymer, of which the nucleation, the crystallization growth rate and crystalline strucutre will be enhanced. The heat-resistance temperature and strength of PLLA material can also be enhanced due to the foramtion of PLLA/PDLA stereocomplex. Furthermore, core-shell structures of Rubbery PRA and PLLA/PDLA stereocomplex can be obtained by self-assemble of the block copolymers and stereocomplex crystallization of PLLA/PDLA, and these microscale and nanoscale structures will enhance the toughness and strength of PLLA.The interfical interaction between PLLA and the rubbery PRA is increased by the addition of PLLA-b-PRA and PDLA-b-PRA block copolymers. Meanwhile, the long PLLA and PDLA chains and the microscale crystals of PLLA/PDLA stereocomplex enhance PLLA chain entanglements, which is favor for the enhancement of PLLA melt strength. The processing of PLLA melt can be improved by increasing the melt strength. Furthermore, core-shell structures of Rubbery PRA and PLLA/PDLA stereocomplex can be obtained by self-assemble of the block copolymers and stereocomplex crystallization of PLLA/PDLA, and these microscale and nanoscale structures will enhance the toughness and strength of PLLA.

聚乳酸是具有良好应用前景的生物基可降解型高分子材料，但其结晶速度慢，耐热温度不高，韧性和抗冲击强度差的缺点限制了其广泛应用。文献报道，植物油脂基聚合物具有良好的柔韧性，能有效改善聚乳酸的韧性和抗冲击性能。同时，聚乳酸立构复合体可以改善其结晶行为，提高耐热温度和力学强度。但植物油脂基聚合物与聚乳酸相容性差，而其嵌段共聚物可以消除宏观相分离，且具有丰富的微结构。本项目的重点在于设计合成不同分子形态结构的生物质聚(L-乳酸-蓖麻油酸)(PLLA-b-PRA)和聚(D-乳酸-蓖麻油酸)(PDLA-b-PRA)嵌段共聚物，并研究其分子量及其分布、链段比例、熔融历史、结晶路线、剪切作用等因素对PLLA-b-PRA/PDLA-b-PRA体系结晶规律和结构的影响，通过对共混体系结晶行为和结构的调控，制备结构可控的立构复合物和"壳-核"复合结构，探索其在改性聚乳酸中的应用，开发高性能化聚乳酸材料。

聚乳酸是一种重要的源于可再生资源、可完全生物降解的工业化热塑性高分子。它在环境友好材料和生物医用领域具有巨大的应用前景。然而，聚乳酸结晶速度慢、结晶度低、结晶行为和结构复杂、柔韧性能不足、熔体强度较差、较石油基通用塑料成本高的缺陷，限制了聚乳酸的应用和工业化发展。同时聚乳酸的结晶和结构一直未研究清楚，也影响了结构的精确调控和材料的高性能化设计。.基于化学方法，在分子层面上调控高分子的组成和结构，制备聚乳酸共聚物、支化和超支化反应性大分子；并通过物理共混的方法引入高效的增容组分、柔性组分，结合聚乳酸的结晶和立构复合技术，控制多元聚乳酸树脂的多尺度结构，实现聚乳酸的增强增韧。以蓖麻油、蓖麻油酸、L-丙交酯、D-丙交酯合成制备了聚L-乳酸-b-聚氨酯、聚D-乳酸-b-聚氨酯、具有聚乳酸长支链的聚乳酸-b-聚氨酯共聚物、蓖麻油基聚氨酯、聚蓖麻油酸及其共聚物、聚L-乳酸、聚D-乳酸、聚L/D-乳酸，研究了材料的结晶行为和结构及转变行为、加工外场因素的影响，多元体系的流变行为、多元树脂的相结构和力学性能、增强和高性能化技术。.研究发现，具有长支链的聚L-乳酸-b-蓖麻油基聚氨酯、聚D-乳酸-b-聚氨酯改性聚乳酸（PLLA），其中PLLA block的结晶、PDLA block/PLLA立构复合物都能够显著提高聚乳酸基体树脂的成核密度、加快聚乳酸的结晶、提高材料的熔体强度、结晶度（≥40%），保留树脂的高强度（≥40MPa）并将断裂伸长率高达200%，通过分子量、组成比例、加工条件的控制，可以实现结晶结构和力学性能的调控。.聚蓖麻油酸-b-聚乳酸可以提高聚乳酸树脂的韧性，对聚乳酸的均聚物结晶和立构复合结晶具有重要影响，但由于难以合成高分子量聚蓖麻油酸链段，导致材料的柔韧性提高的同时力学强度大幅降低，适合低强度、高韧性材料的应用。.研究发现，聚乳酸的分子链结构、分子链的构象对聚乳酸的结晶行为和结构具有很大影响。通过分子序列结构、热历史的调控，可以改变聚乳酸的结晶行为和结构特征。.通过外场条件的控制，可以改变聚乳酸的成核、晶型结构、取向结构，可用于聚乳酸制品的高性能化，以及调控制品的结构和性能。.本项目系统研究了聚乳酸的结晶与结构、聚乳酸/共聚物体系的增容与性能、外场对聚乳酸材料的结构和性能的影响等，实验结果可以指导高性能聚乳酸树脂的研发。