光调控的Lewis酸碱对催化单体聚合

The area of macromolecular synthesis catalyzed by Lewis pair has attracted tremendous interests in recent years. It shows advantages of mild reaction conditions, high activity, and controlled polymerization process. Controlled synthesis of cyclic polymers and linear polymers can be achieved by modulating the Lewis pairs. However, at present, the synthesis of cyclic polymers has various disadvantages, such as, wide molecular weight distribution, limited polymerization methods, difficulty in synthesizing high molecular weight polymers, and especially highly dependence on the structure of monomers. It has shown excellent catalytic performance of N-heterocyclic olefin-based Lewis pairs in polymer synthesis. In the process of polymerization, N-heterocyclic olefin initiated the polymerization and subsequently transformed into imidazolium, and the other end group is in the form of an anion. Therefore, cyclic polymers and linear polymers can be controlled synthesized by regulating the activity of imidazolium. Optimize the structure of N-heterocyclic olefin to reversibly regulate the reactivity of imidazolium by the domination of light, which control the nucleophilic attack of the negative ions on the end of the polymer chain to the imidazolium cation, and achieve the purpose of controlling the topological structure of the polymer.

Lewis酸碱对催化聚合是近年兴起的高分子合成方法，展现出反应条件温和、高效和聚合过程可控等优点。通过对Lewis酸碱对进行调控可以实现环状聚合物和线性聚合物的可控合成。然而，目前环状聚合物的合成不同程度地出现分子量分布较宽、聚合方法单一、难以合成高分子量聚合物、尤其是对单体结构严重依赖等缺点。Lewis碱氮杂环烯烃与Lewis酸协同催化在高分子合成领域表现出卓越的催化性能。在聚合过程中，氮杂环烯烃引发聚合后转变为咪唑盐阳离子，活性链的另一端为阴离子，因此通过调控咪唑盐阳离子的活性可以实现环状聚合物和线性聚合物的可控合成。本项目通过精心设计氮杂环烯烃的结构，借助光调控的手段，来可逆调控咪唑盐的反应活性以控制聚合物链末端阴离子对咪唑阳离子的亲核进攻，达到控制聚合物的拓扑结构的目的。

光催化的可控自由基聚合，在精确合成具有不同结构和性能的聚合物方面展现出广阔的前景。然而，其基于外层电子转移的机理导致单体兼容性受限和催化活性低等问题。本项目合成了两性离子有机硼烷[L2B]+X–光催化剂，并通过离子对内层电子转移机制调控自由基聚合。该聚合的催化剂负载量低至ppb级，并表现出高催化活性、广泛的单体兼容性、在5mol%酚类抑制剂存在下展现出优异的耐受性，并实现超高分子量线形聚合物的合成。离子对内层电子转移机制在开发新的有机反应和聚合方法方面具有理论研究价值。