多臂右旋聚乳酸嵌段共聚物与左旋聚乳酸共混材料的制备、结构与性能关系研究

Polylactide (PLA) is a biodegardable bio-plastic, the melting temperature of neat Poly(L-lactide) (PLLA) and Poly(D-lactide) (PDLA)is low. PLA stereocomplex formed after PLLA bended with PDLA, and its melting temperature is as high as 230 C. Because of the strong interaction between enantiomeric PLAs and the rigidity of PLA chain, the elongation at break of the stereocomplex is still low, which limit its appliaction. Introducing flexible chain segment into the rigid chain, it can not only keep the strength of materials, but also can endow flexibility with the material. This project will synthesize the multi-armed PDLA with end hydroxyl group at first, then change it to carboxyl group, the PBS and PBAT with end hydroxyl groups are coupled with the muti-armed end carboxyl gourps modified PDLA. A series of (PDLA-OH)n, (PDLA-b-PBS)n and (PDLA-b-PBAT)n polymers with specific structures are synethesized. These polymers with different strutures, different compositions will blend with PLLA to made blending materials. In these blends, the PLLA can stereocomplex with the PDLA segment, and the formed PLA stereocomplexes will accelerate the crystallization of PLLA. Moreover, the introducing of PBS and PBAT segment will afford better flexibility. And the addation of multi-armed copolymer will favor the moulding injection. both the crystallization ability and the flexibility of the blends expect to be enhanced, and they will set the stage for their applications.

聚乳酸（PLA）是一类可生物降解的生物基塑料，左旋聚乳酸（PLLA）或右旋聚乳酸（PDLA）熔点较低。PLLA与PDLA共混可形成立体复合物，熔点达230℃。但因分子间相互作用较强及分子链刚性，复合后的聚乳酸断裂伸长率仍较低，这限制了其应用。在刚性链中引入柔性链段，不仅可保持共聚物的强度，还可赋予材料一定的韧性。本项目拟首先合成带有端羟基的多臂PDLA，将其端羟基羧基化后，与带端羟基的PBS、PBAT偶合，得到线性及多臂(PDLA-b-PBS)n、(PDLA-PBAT)n嵌段共聚物，将所得多臂PDLA及其嵌段共聚物与PLLA共混制备共混材料。该共混材料中，PLLA与PDLA段的立体复合可提高共混物的熔点，立体复合物亦可加速PLLA结晶；PBS及PBAT柔性段的引入可增加韧性；多臂聚合物的加入也可为加工成型提供有利条件。共混后的材料预期可提高材料的结晶性能及韧性,为应用提供基础。

聚左旋乳酸(PLLA)和聚右旋乳酸(PDLA)能够形成聚乳酸立体复合物(PLA SC，熔点约为230°C)，在聚乳酸应用过程中具有重要意义。在本项目支持下，以双金属中心席夫碱乙基铝为催化剂，合成单分散(PDI<1.1)、高立构规整度(旋光纯度>99.5%)的PLLA和PDLA，能使PLA SC熔点达到254°C。进一步将柔性链段PEG与PLLA或者PDLA形成线型和四臂嵌段共聚物PEG-b-PLLA和PEG-b-PDLA，并通过溶液共混制备等比例的线型和四臂共混物，并系统性的研究了PLA SC的结晶行为和凝聚态结构与嵌段共聚物链段结构和组成之间的联系。柔性链段PEG的引入能够有效的抑制PLA HC的出现。由于支化结构带来的空间位阻和粘度的增加，四臂共混物中PLA SC和PEG的熔点与结晶度均低于线型共混物中PLA SC和PEG的熔点与结晶度。同时，以L-缬氨酸为原料，探索合成一种与聚乳酸化学结构非常相似的新型聚酯-聚(L-2-羟基-3-甲基丁酸)[P(L-2H3MB)]，其熔点能够达到230°C，具有生物相容性和生物可降解性，且与PLLA呈现较好的相容性。通过将高熔点的P(L-2H3MB)与PLLA共混，构建PLLA受限结晶体系，并初步研究其结晶行为和凝聚态结构。链段结构、化学结构以及受限环境变化对聚乳酸嵌段共聚物/共混物结晶行为和凝聚态结构的系统研究，能够为制备高性能聚乳酸材料提供理论和实验依据。在本项目支持下，共发表SCI论文17篇，专利4项，培养博士研究生4名，硕士研究生1名。