金属有机配位催化剂与活性链转移剂组合：原位合成立构规整的梯度、多嵌段和非线性拓扑结构聚合物的新策略

The synthesis of gradient, multi-block and topologic polymer materials having versatile morphologies and aggregation states as well as excellent physical and mechanical and rheological properties, has been the hot research topics and challenging projects in polymer science. The classical method to access such materials is the combination of living radical and anionic polymerizations with organic reactions such as “click reaction” and coupling reactions. In this project, the coordination polymerization will be employed to combine with chain transfer agents of protic compounds to establish catalytic systems, thus the stereoregulated such materials will be achieved facilely and efficiently in situ. First, the organometallic complexes with stereo selectivity will be synthesized, and the factors, such as the structures of the ligands and the match of Lewis acidity between the ligands and the chain transfer agents, the metal-σ-groups and their leaving ability, which influence the rapid-reversible exchange reaction between these complexes and alcohols or amines to access the “immortal” polymerization, will be studied. Two complexes of different selectivity towards polymerization of cycloesters under the action of the chain-shuttling agents to achieve the gradient and multiblock polymers, will be investigated. The effects of the catalytic activity of the added two complexes, the molar ratio of the chain shuttling agents with the monomers and the addition manner of the monomers on the block lengths and their distribution, will be addressed. Preparation synthon of the topological polymer materials taking the multi-functional chain transfer agents as the templates, or the concert effect of the ring-opening polymerization and immortal polymerization of the hydroxyl or amino modified cyclic esters, will be elucidated.

梯度、多嵌段及非线性拓扑结构高分子材料具有丰富的相态和聚集态及优异的物理性能，其合成与应用一直是高分子科学的研究热点。经典的合成方法是阴离子和活性自由基聚合与“点击”化学等偶联反应相结合。本项目将应用配位聚合机理，以质子化合物为链转移剂，构筑“不死聚合”体系，简单、高效、原位合成立构规整的这些材料。将设计与合成具有立体选择性的金属有机配合物，研究其与链转移剂（醇或胺化合物）进行可逆-快速交换反应的关键因素：配体的结构及与链转移剂之间的Lewis酸性匹配、金属σ-基团的种类和离去能力，对构筑“不死聚合”体系的影响。研究不同立体选择性的催化剂并联、借助质子化合物导向的“链穿梭”作用，制备梯度和多嵌段聚酯，揭示催化剂间相对活性、单体与链转移剂的比例和加入方式与嵌段长度及分布的规律。探索以多官能度链转移剂为模板，或羟基/胺基修饰的内酯开环聚合与“不死聚合”的协同作用，制备拓扑结构聚酯的途径。

制备梯度、多嵌段或拓扑结构高分子链结构，获得具有丰富的相态和聚集态及优异的物理机械和流体力学等性质的材料，一直是高分子科学的研究热点。聚丙交酯（PLA）具有良好的生物相容性和生物可降解性，低毒性等特点，广泛用于包装材料、医用缝合线、药物控释体系等方面，是当今最重要的人工合成的生物材料之一。然而，聚丙交酯具有疏水性，其单体也很难进行功能化，限制了其在某些方面的应用。因此，在实际应用中往往需要在PLA中引入亲水性的聚乙二醇（PEG）链段，尤其是功能化的聚碳酸酯（PMPC）链段，主要因为相比于丙交酯，含有各种取代基的环状碳酸酯单体合成容易，而聚碳酸酯又具有良好的生物相容性及生物可降解性。关键问题是，碳酸酯尤其是功能化的碳酸酯与丙交酯共聚合较为困难。.本项目是通过催化剂设计实现丙交酯与碳酸酯共聚；同时将重要的功能基团通过配位聚合方法加入到丙交酯聚合物链中而不引起本体性质的破坏。我们设计与合成了各种稀土金属、铝、锌等配位聚合催化剂，以质子化合物为链转移剂，构筑了“不死聚合”体系，催化合成了具有立体选择性的丙交酯和碳酸酯梯度、多嵌段共聚物。通过动力学研究表明，杂同选择性催化剂对外消旋丙交酯和旋光纯丙交酯分别与碳酸酯共聚合时的旋光选择性差异，导致聚合反应速度不同，进而控制了聚合物序列分布，决定了材料的性质和降解速度的差异。同时利用不死聚合原理，制备出链端含有聚集诱导发光基团、抗紫外线、阻燃等功能基团的聚乳酸，而聚乳酸的杂同和全同立构规整度仍然保持。此外，还发展了生物友好的镁、锌催化剂和非金属催化剂，制备出聚硅醚和来源于生物资源的聚苯并呋喃。这些研究成果丰富和发展了配位催化聚合理论，得到的聚合物是通过目前的方法很难制备的。