有机小分子催化的离子型开环聚合：环氧乙烷基高分子的设计与合成

Polymers based on ethylene oxide (EO) have been playing a more and more significant role in the realm of macromolecular and materials sciences. Nevertheless, the development of synthetic methodologies for such materials has been relatively retarded, probably due to the highly demanding experimental skills for the handling of gaseous EO monomer. In view of the drawbacks and limitations of the existing methods, there is an urgent need for more efforts to be put into this section of polymer chemistry. Therefore, in this plan, the applicant proposes to formulate a novel organocatalytic system, taking advantage of ion-specific effects which would endow bulky and stable organic counterions to the oxyanion and thus promote efficient anionic ring-opening polymerization of EO. The new system would also benefit from its economic, facile and “greener” character, as the catalysts are formed in situ and the precursors of the catalysts are non-air-sensitive and less toxic. Utilizing this new catalytic system as well as other small-molecule organocatalysts, we also plan to further develop a few synthetic routes toward novel macromolecular structures based on ionic ring-opening reactions of EO, such as the following. 1. Traditional alkali metal-based anionic polymerization will be combined with the new organocatalytic system mentioned above to perform sequential anionic polymerization of vinyl monomer and EO. 2. Attempts will be made to realize alternating ionic copolymerization of EO and non-polymerizable heterocyclic compounds (e.g. cyclic anhydrides, cyclic phenolic esters) by the aid of organocatalysts, so as to enrich the catalogue of heterochain polymers with controllable and tunable structures. 3. Organocatalytic statistical ionic copolymerization of EO and epicyanohydrin will be conducted aiming at random copolymers of the two monomers, after which the pendent cyanogroups will be subject to chemical modifications to achieve amino- and/or amide-functionalized polyethers. 4. Epoxidized polydienes will be used as multifunctional macromolecular chain-transfer agents to develop a “somersault” type graft polymerization of EO, which combines “grating onto” and “grafting from” techniques into a one-step model and thus will allow for facile synthesis of double-graft type macromolecular architectures. We believe the implementation of this plan will advance the strategies for the design, synthesis and modification of valuable EO-based polymeric materials.

环氧乙烷基聚合物在高分子材料领域中的重要性日益彰显。因实验技能要求高，相关合成方法学发展缓慢。本项目中，申请人计划利用离子特异性和抗衡离子效应构建经济、简便和环境友好的新型有机小分子催化体系，发展基于环氧乙烷离子型开环反应的高分子结构设计与合成新策略，包括：（1）将传统阴离子聚合与新催化体系结合，进行烯类单体与环氧乙烷的连续聚合；（2）将本不能自聚的环状化合物（如环酚酯、环状酸酐）与环氧乙烷在有机小分子催化下进行离子型交替共聚，发展结构可控的新型杂链聚合物；（3）将环氧乙烷与环氧化丙烯腈进行离子型开环共聚，通过共聚物中氰基的化学改造获得含有氨基、酰胺等功能基团的聚醚；（4）以环氧化聚二烯烃为链转移剂，进行环氧乙烷的“穿梭式”接枝聚合，合成单点双枝型接枝共聚物。本项目的实施将丰富高分子合成方法，为相关高分子的设计、合成、改性提供思路。

环氧乙烷是第二大乙烯衍生物，聚乙二醇等高分子材料是其主要下游产品种类之一，具有非常广泛而重要的用途。我国具有近千万吨的环氧乙烷产能，然而，由于合成方法和生产工艺发展较为滞后，环氧乙烷的聚合物仍很大程度上依赖进口。基于这一背景以及项目负责人的研究特长，本小组一直以环氧乙烷的聚合反应和环氧乙烷基高分子材料的合成方法为核心研究内容。自本项目立项以来，我们按照研究计划对有机小分子催化的环氧乙烷离子型聚合若干体系进行了系统研究，主要取得了以下三个方面的成果。1) 利用简单的有机小分子催化剂，实现环氧乙烷与苯酐的活性交替共聚，获得分子量高达20万且窄分散的交替型聚酯，并提出“自缓冲”催化机理，为环氧基聚酯材料的简便、可控合成提供了重要路径。2) 发展新型“催化转换”策略，成功地将环氧乙烷的链式开环聚合与聚乙二醇-二异氰酸酯的逐步加成聚合串联，实现结构复杂的环氧乙烷基两亲性、多嵌段聚氨酯的一锅法简便合成，并发现其具有可调控的微相分离性质，可用于构建蛋白吸附/抗吸附表面。3) 发展新型双组分有机催化剂，使环氧乙烷的开环聚合在效率、选择性、反应条件等方面突破传统强碱型单组分催化剂的局限，可在室温、本体条件下使环氧乙烷发生高效的开环聚合，分子量在几百到几十万间可控，催化剂具有优异的官能团耐受性，且残留物无细胞毒性。总之，本项目为环氧乙烷的离子型开环聚合发展了更加高效、可控、简便、经济、绿色化的新型有机小分子催化体系，开辟了若干嵌段、交替共聚和端基官能化方法，获得了新型环氧乙烷基高分子结构及一定的构性关系信息，为环氧基高分子合成方法和环氧乙烷基高分子材料的发展和优化提供了重要的思路，并为环氧乙烷有机催化聚合的工业化应用打下了重要基础。