基于高杂同催化剂的手性/非手性单体序列可控共聚合及机理研究

As a representational biodegradable polymer materials, polylactic acid (PLA) has been obtained a great attention and development. The deficiency of uncontrolled-degradation, poor hydrophilic property, uncomplicated function，etc. need to be improved by copolymerization method. However, as the different reactivity ratios of two comonomers, the achievement of the sequence-regulated polymerization with precise microstructure of polymer chain is crucial for resolving these problems. This program will share an advantages of high stereo-controlled capability originated by metal catalyst to a chiral/achiral monomers copolymerization and their sequence controlled research. A series of rare-earth metal based catalysts with various substituents on side arm together with a different structural cyclic esters will be designed and synthesized. Taking advantage of high chain-end control effect arising from the synergy between catalyst and chiral monomer, the related reactivity ratio of chiral and achiral comonomers will be controlled by the steric/electric effects of substituents on catalyst. The match of different structural comonomers will be researched and the effectual role for instructing the sequence controlled copolymerization will be established. The functional achiral monomers and distinctive monomers will be developed for building functional polymers or controlled-degradation materials, by means of the sequence controlled polymerization role. This project will provide a new method for sequence controlled ring-opening polymerization and present a solution for modified copolymerization and developed new materials.

聚乳酸是可生物降解高分子材料最重要的一类代表,但其自身存在脆性、降解不可控、功能单一等不足。通过共聚改性可丰富此类聚合物链结构，然而共聚单体聚合反应速率差异较大，聚合物链结构难以有效调节进而改善材料性能。如何实现此类共聚物微观结构的有效调控，是目前面临的关键问题。本项目拟将金属有机催化剂对手性丙交酯优异的立构控制能力拓展到手性/非手性单体共聚合及序列调控领域：设计侧臂具有不同空间/电子效应的一系列高杂同稀土金属有机催化剂，利用催化剂和手性单体协同产生的链端控制效应增大非手性单体的插入率，进一步通过催化剂侧臂的改变调节共聚单体的相对反应速率，实现共聚物序列结构的有效调控；研究不同结构手性/非手性单体适用范围，完善聚合物序列调控规律；发展功能化非手性单体及特色单体，结合调控规律制备新型功能高分子及可控降解新材料。本项目将为序列可控开环聚合提供新方法，为共聚改性及开发功能材料提供新手段。

基于本项目所要解决的关键问题（如何将立体选择性催化剂对手性单体聚合的立构控制能力转化为对非手性单体聚合的调控能力，并进一步实现对手性/非手性单体共聚合的序列控制能力），我们取得了一系列的成果：.1. 杂同催化剂催化旋光丙交酯L-LA与环状碳酸酯TMCR共聚时，非手性的TMCR相当于另一种光学纯的LA（D-LA）,使得kTL≈kLT>kTT，得到无规共聚物。当使用没有选择性的催化剂时相应的序列结构也消失。这开创了一种使用立体选择性催化剂催化不同手性单体与非手性单体共聚来调控共聚物序列的新方法。.2. 进一步分别选用高杂同选择性和高全同选择性的铝配合物催化丙交酯(LA)与功能化碳酸酯(MAC)的共聚合，成功制备了从无规到近似嵌段结构的4种具有不同微观结构的共聚物。当使用杂同选择性配合物催化L-LA与MAC共聚时，得到了无规共聚物（rL-LA = 0.217，rMAC = 0.578）及梯度共聚物(rrac-LA/rMAC = 0.584/2.478)。当使用全同选择性配合物催化L-LA和MAC共聚时，得到了近似嵌段的结构(rL-LA/rMAC = 2.035/0.112)及形成了楔形共聚物(rrac-LA/rMAC = 1.619/0.283)。共聚物的微观结构是由催化剂的选择性、活性和共聚单体的配位能力等因素共同决定的。.3.通过本项目开发的“立体选择性催化剂调控共聚物序列分布”方法，我们进一步成功制备了无规、锥形和两嵌段三种序列的丙交酯和官能化碳酸酯共聚物。我们发现降解速率与共聚物序列密切相关：无规共聚物poly(L-LA-ran-MCC) > 锥形共聚物poly(rac-LA-tap-MCC) > 两嵌段共聚物PLLA-b-PMCC，首次证明了共聚物的降解速率受主链中连接点的数量控制（L-C ≈ C-L > C-C > L-L）。降解产物为乳酸、2,2-二羟甲基丙酸和CO2，它们也是制备单体的原料。.利用本项目我们建立了序列结构-聚合物性能的有效关联；经由共聚物的微观序列结构调控拓展材料性能，制备先进材料。