氮杂环卡宾稀土金属配合物催化α-烯烃立构规整性聚合

The development of efficient, stereoselective catalysts for olefin polymerization has been a long-standing research subject in coordination polymerization field. Rare-earth-metal catalyst system for olefinic polymerization has attracted considerable attention in recent decades, which has been reported to prepare a variety of stereospecific polymers (e.g. stereospecific poly(conjugated dienes) and polystyrene). However, only limited catalyst systems were found to be efficient in stereoselective polymerization of α-olefins, none of which could get the syndiotactic poly(α-olefins) unfortunately. Based on previous research and the theory of stereochemistry control, this project aims to develop a novel rare-earth-metal system for stereoregular polymerization of α-olefins. Two kinds of rare-earth-metal complexes, ligated by Cs- and C2-symmetric NHC ligands respectively, will be synthesized and used in stereoregular polymerization of α-olefins. The relationship between catalyst structures and catalytic properties in stereoselective polymerization of α-olefins will be systematically analyzed and expounded. What’s more, by modifying the structure, symmetry and steric hindrance of NHC ligands, the rare-earth-metal catalyst system will conduct syndiotactic polymerization of α-olefins successfully. The coordinated modes of the monomer, the routes of polymerization and the mechanisms of stereocontrol will also be investigated in details by means of isolation of intermediates, detection of polymer’s terminal groups and theoretical calculation method.

通过催化剂的结构设计实现聚合物的立体化学控制，一直是配位聚合领域的研究热点。稀土金属催化体系作为一类新兴的烯烃聚合体系，可以实现多种单体（如共轭二烯、苯乙烯等）的定向聚合，然而目前只有有限的稀土金属体系能够实现α-烯烃的立构规整性聚合，且仅能得到等规立构的聚α-烯烃。本项目拟在前期工作基础上，将催化剂空间对称性与聚合物微观结构的关系引入配体设计中，旨在发展一类稀土金属催化α-烯烃立构规整性聚合的新体系。研究在配有Cs和C2对称结构卡宾配体的稀土金属催化体系中，配体空间对称结构和取代基效应等对聚合反应立体选择性的影响，阐述卡宾稀土体系中配体结构与立体化学控制之间的关系；通过对配体结构的设计优化，实现稀土金属体系制备间规立构聚α-烯烃；通过对催化中间体的表征和聚合物结构的分析并辅以理论计算，探索卡宾稀土配合物催化α-烯烃聚合时的单体配位方式、聚合路径和立体化学控制机理。

聚烯烃是世界上用量最大的合成树脂品种，因此开发高效烯烃聚合催化体系一直是学术界和工业界的研究热点。本项目主要围绕稀土金属催化剂结构和聚合性能之间的关系，配位聚合反应机理的探索以及聚合物功能化改性方面进行研究。首先，开发了一类C2对称双噁唑啉卡宾配位的稀土金属催化剂，在有机硼盐活化下，该类Sc催化剂能够高活性催化α-烯烃聚合，得到中等分子量的聚合物；该体系还可以催化α-烯烃与α,ω-非共轭双烯的共聚，得到高环化程度的聚烯烃。中心金属的种类对聚合性能有决定性作用，该类Y和Lu催化剂对催化α-烯烃聚合没有活性，这可能是由于Sc离子具有较强的路易斯酸性造成的。其次，在聚合反应体系开发的基础上，对配位聚合反应机理也进行了探索。采用计算化学手段，研究了单茂钛配合物催化乙烯-苯乙烯共聚以及1,7-辛二烯聚合的反应机理。研究表明，单体的选择性插入主要是由于动力学控制，较低的插入能垒使得该类催体系选择性地得到孤立苯乙烯单元的乙烯-苯乙烯共聚物以及环化率较低的1,7-辛二烯聚合物。最后，通过对聚合物材料进行接枝改性来制备阴离子交换膜，特定离子传导基团的引入能够大幅度提高膜材料的化学稳定性和离子传导率。