碱土金属配合物合成及其催化丙交酯Immortal聚合合成链末端功能化聚合物

Due to its biodegradability and excellent mechanical properties,polylactide which derivated from non-petroleum resource has been widely applied to medical field, agriculture and packaging materials. However, the poor hydrophilicity, compatibility, processability and the brittleness of polylactide and also without functional group often limit its application. Thus to prepare PLA-based block copolymers or PLA with tipological structures, as well as functionalizing PLA to improve its physical and chemical properties and processing ability to afford high-value-added product, has recently attracted considerable attention. Immortal polymerization exists rapid and reversible exchange reaction between catalysts precursor, and alcohol and each active center generates more polymer chains, and automatically end capped polymer chains with hydroxyl etc. functional groups, which has developed to be a new effective method to synthesize and functionalize polylactide in one-pot. The key of the immortal polymerization is to explore suitable catalytic system. This project proposes to adopt a series of steric and electronic feasible amidinate as ligand, employ biocompatible and nontoxic alkaline-earth metal as catalytic center, because alkaline-earth metal combines nucleophilic reactivity of group I metal compounds and Lewis acidity of group III metal reagents. However, syntheses of heavier alkaline-earth metal complexes are hindered by the electron positive nature and the large ionic radii of these metals, which easily deduce redistribution of the ligand. Thus we will study how to synthesize stable alkaline-metal based complexes,to gain a better understanding of the relation between the stability of the metal complex, and the steric and electronic of the ligand, how to select alcohols to build highly effiecient catalytic system, and finally to access polylictide and functionalized polylactide through immortal polymerization in one pot.

聚丙交酯源于非石油资源并因可生物降解及优良的力学性能在医药领域、农业生产及日常生活中得到应用。但聚丙交酯亲水性差、脆性大、无改性基团，与其它材料相容性差，加工性能不好，应用受到限制。故合成嵌段或拓扑结构聚乳酸或功能化聚乳酸，改善其物理化学和加工性能，获得高附加值成为新的研究热点。Immortal聚合体系中存在醇与活性中心的可逆与快速链转移，每个催化中心可以产生多个聚合物分子，尤其赋予聚合物链末端功能基团，是高效合成聚丙交酯及其功能化的新方法，其关键是催化体系的构筑。本项目拟采用立体效应和电子效应易于调节的脒基为配体，选择生物相容性好、无毒，且同时具有碱金属的亲和性和稀土金属的Lewis酸性的碱土金属为催化中心。由于碱土金属电正性高和离子半径大，其配合物易于歧化，故将研究配体的结构对配合物稳定性的影响；研究如何选择醇构筑高活性催化体系；探讨通过Immortal聚合同时实现丙交酯合成和功能化。

按照研究计划，本项目进行了以下几方面的研究：①设计合成了一系列脒基、杂蝎型配体。通过胺交换反应制备配合物时，我们发现当脒基配体中没有侧臂或氮原子上连接刚性侧臂时均不能有效抑制均配碱土金属配合物的生成；当侧臂连接在脒基的碳原子上或选用杂蝎型配体时，可有效防止碱土金属配合物歧化为均配配合物。②采用杂蝎型碱土金属配合物，首次实现了碱土金属配合物催化外消旋丙交酯全同选择性聚合。③脒基碱土金属配合物/苯酚组成的二元催化体系可高效催化丙交酯Immortal聚合，实现了采用亲核性较差的酚做为丙交酯Immortal开环聚合的链转移剂。选用三元胺做链转移剂合成了三臂星型聚丙交酯。上述结果拓宽了丙交酯Immortal聚合链转移剂选择的范围。④对金属钙氨基配合物/不同pKa值链转移剂组成的二元催化体系催化丙交酯聚合进行了详细研究，发现与pKa值较大的链转移剂组成的二元催化体系，可控性更好，所得聚合物的分子量与理论分子量更接近，分子量分布相对较窄，为丙交酯Immortal开环聚合催化体系的构筑提供了指导。⑤通过Immortal聚合的方法，缩小了丙交酯、-己内酯共聚时两种单体的竞聚率，得到了己内酯与丙交酯的无规共聚物，为制备己内酯/丙交酯无规共聚物提供了一种新思路。⑥选用催化苯甲醛和二乙基亚磷酸反应制备链转移剂-羟基磷酸酯，然后加入丙交酯进行聚合，一锅法从商业化原料得到了-羟基磷酸酯封端的聚丙交酯，其热失重5%时的温度比苄氧基封端聚丙交酯的提高了57 ºC，开创了一种集约化、原子经济效率高的制备高热稳定性聚丙交酯的方法。⑦通过含有功能基团的苯乙烯与苯乙烯共聚制备大分子链转移剂，引发丙交酯聚合制备了接枝密度和支链长度可调的接枝共聚物，经热退火处理及刻蚀处理后，得到了孔密度和孔径可调的多孔材料。⑧开展了碱土金属配合物催化醛、酮膦氢反应制备主链含磷原子聚合物的前期探索工作。在本项目的资助下，4篇SCI论文已发表，3篇正在整理中；培养博士研究生1名，硕士研究生1名。