金属手性锌、镁配合物催化外消旋丙交酯等规选择性聚合研究

Stereocomplexes of isotactic polylactides are known to possess enhanced mechanical and physical/chemical properties than homochiral poly(L-lactide). In view of the good biocompatibility of Zn and Mg elements, designing and synthesizing Zn and Mg based complexes on the molecular level to achieve efficient preparation of polylactide stereocomplexes via highly isoselective polymerization of rac-lactide would be of great importance for both theoretical studies and commodity applications.. This project intends to synthesize well-defined racemic zinc and magnesium complexes supported by achiral tridentate or tetradentate aminophenolate ligands with a pendant planar heterocyclic group. Four series of proligands with different framework will be used to complex with zinc and magnesium staring complexes, the influence of different ligand framework, the steric and electronic effects of substituents, and additional donor atoms introduced to the ligand itself on the stability of the formed complexes will be studied. The influence of the structure factors of these metal complexes, including the framework of the ancillary ligand and substituents thereon, the type of central metal, and the dentate number of the ligand itself, on the catalytic activity and stereoselectivity of the corresponding complexes toward the ROP of rac-lactide will be investigated in detail; the related stereocontrol mechanism on working during the stereoselective polymerization processes will be also studied. Based on the preliminary structure-performance relationship, further modification of the ligand structure will be carried out in order to obtain efficient zinc, and magnesium calcium catalysts for highly active and isoselective polymerization of rac-lactide to produce polylactide stereocomplexes of high performance in controlled manners.

外消旋丙交酯等规立体选择性聚合所得等规聚乳酸、等规嵌段聚乳酸立体复合物具有较常规聚L-乳酸更为优良的机械、理化性能。基于锌、镁金属元素的生物相容性，通过分子水平的锌、镁配合物催化剂设计来实现高性能聚乳酸立体复合物的合成具有重要的学术意义及显著的社会应用前景。. 本项目提出利用四个系列具悬垂平面杂环基团的非手性三齿或四齿胺基酚类配体构筑外消旋形式的单活性中心锌、镁配合物，研究配体骨架结构中不同电子因素杂环结构的引入、各取代基的电子和空间位阻因素以及配体不同的齿数对形成稳定配位环境锌、镁配合物的影响；并进而研究金属配合物中配体基本骨架结构、取代基类型、中心金属类型以及配体结构中额外配位原子的引入等对催化外消旋丙交酯开环聚合催化活性、立体选择性的影响，研究聚合过程中的立体控制机理。在此基础上调整配合物催化剂结构，以期催化外消旋丙交酯高活性、高等规立体选择性聚合，实现高性能聚乳酸立体复合物的可控性合成。

聚乳酸作为重要的生物可降解性高分子，其宏观物理性能与微观立体结构紧密相关；通过分子水平新型金属络合物催化剂设计有望对聚乳酸高分子链微观立体结构实现有效控制。锌、镁等金属的络合物不但活性高，且色浅，作为低毒性金属配位催化剂，催化外消旋丙交酯开环聚合实现高性能聚乳酸立体复合物的合成具有重要的学术意义及显著的社会应用前景。. 本项目设计合成了多个系列基于悬垂平面杂环结构的非手性三齿氨基酚类配体配位的锌、镁络合物100余个，均通过标准分析鉴定，典型络合物经X-ray单晶衍射确证空间配位构型。所有络合物对外消旋丙交酯开环聚合具有中等至高的催化活性，悬垂杂环结构、配体各取代基等显著影响所得聚乳酸微观立体结构。. 具悬垂苯并咪唑、苯并噻唑、噻唑、吡唑取代的氨基酚氧基锌络合物实现了中等至高活性、高等规选择性催化外消旋丙交酯开环聚合，可获得高等规度（Pm = 0.89-0.93）的聚丙交酯立体嵌段复合物，聚合物熔点达到186-193摄氏度，在锌络合物催化外消旋丙交酯等规立体选择性聚合方面取得了较好的突破。典型具悬垂咪唑取代的氨基酚氧基锌硅氨基络合物对外消旋丙交酯聚合具有高催化活性，室温下催化外消旋丙交酯聚合，TOF值高达23280/h，是目前对丙交酯聚合具有最高催化活性的锌络合物催化剂之一。. 爪型多齿氨基酚氧基锌氯化物以及苯并咪唑取代氨基酚氧基锌氯化合物对单体中杂质具有好的耐受性，可催化高达150000当量工业级丙交酯高效聚合得到环状聚丙交酯。苯并咪唑取代的氨基酚氧基锌氯化物实现催化工业级外消旋丙交酯聚合得到环状等规嵌段聚丙交酯，等规度最高达到Pm = 0.93。通过优化条件所得环状聚丙交酯的重均分子量最高达到110,000 g/mol。. 所合成高活性、高等规选择性络合物催化剂可有效催化取代丙交酯、取代乙交酯、1,3-二氧戊环-4-酮类单体的聚合，以及这些单体与丙交酯的共聚、丙交酯/epsilon-己内酯共聚、环氧化物/酸酐等交替共聚、三元共聚反应，获得了各种结构可控的生物降解型聚合物。.