自负载自活化烯烃聚合催化剂的研究

Recently, the immobilization of the homogeneous single-site catalysts for olefin polymerization have attracted considerable attention in both the academic and industry. Over the past decades，the immobilization of the catalyst have evolved from the simple adherence to surface of the inorganic particles or polymeric balls to the seeding in the pores of the mesoporous material. Generally, large amount of MAO were needed before or after the immobilization to maintain the activity of the catalyst.The borane and borate, important cocatalysts in olefin polymerization, were not suitable for the activation of the heterogeneous catalyst due to their low solubilities in nonpolar solvents. In this project, we intend to introduce the borane/borate unit and ligands units into the covalent organic frameworks, and the immobilized cationic catalysts precusors can be formed in-situ by complexations of the metal chlorides with ligands unit and subsequent reactions with the borate. The catalysts precursors, after alkylation with alkylaluminum, could be used to initiate the olefin polymerization. The influence of pore-size, which can be altered by changing the lengths of the arms in the cage, on the polymerization/copolymerization of olefin will be also investigated.

近年来，均相单中心阳离子烯烃聚合催化剂的负载化研究受到学术界和工业界的广泛关注。随着这个领域的发展，负载化研究已经从简单无机盐表面，聚合物微球，逐步发展到分子筛等三维材料的孔道。为保证催化剂的活性，催化剂负载前或负载后都需要用大量路易斯酸性的甲基铝氧烷（MAO）活化。有机硼是一种强路易斯酸，也是一种常用的烯烃聚合助催化剂，而且它的用量是等当量的。但有机硼盐在非极性溶剂中溶解度低，不适于与非均相催化剂复配。本项目旨在研究将有机硼盐单元和配体单元引入到有机笼状负载材料中，利用载体中的有机硼盐单元与金属盐在负载化过程中生成阳离子化的烯烃聚合催化剂前体，这种阳离子催化剂前体用少量烷基铝活化就有可能直接用于烯烃聚合。通过自负载材料单元臂长的调控实现孔洞大小的可调性；研究此类自负载、自活化催化体系催化乙烯、丙烯聚合或乙烯与其它烯烃共聚合；为自负载自活化烯烃聚合催化剂的研究提供实验和理论基础。

本项目周期为两年，目的是探索将有机硼盐、有机配体及金属中心构筑到一个笼状结构上。有机硼盐作为骨架的一部分，同时作为烯烃聚合阳离子化的助剂，实现催化剂的自负载自活化。同时，计划利用骨架孔道的限制作用，降低β-H消除的几率，得到超高分子量的聚烯烃。为烯烃聚合催化剂的设计提供新的思路和方向。项目执行周期中我们合成了多种硼盐骨架的笼状结构聚合物。我们对这些聚合物进行了表征。采用后负载的方法负载了过渡金属镍，钛，锆 并对它们的催化性能进行了研究。实验结果显示这些负载了金属的硼盐聚合物在烷基铝的活化下对乙烯聚合具有偏低的活性。采用硼盐-Salen骨架负载的锰催化剂能催化苯乙烯的环氧化反应，而且能重复利用，具有较高的活性和选择性。