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钒系烯烃聚合催化剂在工业上有着不可替代的位置,它可用于制备高活性窄分布的聚合物、乙烯与α-烯烃共聚物和间规聚丙烯等.但由于实验手段难以确定钒催化剂活性物种的结构,进一步对催化机理的确认及催化剂结构的改进十分困难.本文运用密度泛函方法对水杨醛亚胺钒配合物催化乙烯聚合的活性物种结构进行了理论研究.对多种活性物种模型的比较研究结果表明,对此催化反应最有利的活性物种为中性双金属物种a1,a1结构中包含两个连接铝原子与钒中心的氯桥结构.研究同时表明,助催化剂Al Et2Cl的存在不仅加速了钒配合物前体的烷基化反应,同时其对活性物种a1结构中氯桥的形成至关重要.最后还研究了该催化体系的链终止反应机理.
Vanadium-based olefin polymerization catalyst has an irreplaceable position in the industry, it can be used for the preparation of highly active narrow distribution of polymers, ethylene and α-olefin copolymer and syndiotactic polypropylene, etc. However, due to experimental means it is difficult to determine the vanadium catalyst active species , The further confirmation of the catalytic mechanism and the improvement of the catalyst structure are very difficult.In this paper, the density functional theory method was used to study the structure of active species catalyzed by vanadyl salicylaldimine complex to ethylene polymerization.Comparison of various active species models The results show that the most favorable active species for this catalytic reaction are the neutral bimetallic species a1, which contains two chloralkali bridges linking the aluminum atom and the vanadium center.The study also shows that the presence of the promoter Al Et2Cl not only accelerates Alkylation of the vanadium complex precursors is crucial for the formation of chlorine bridges in the active species a1. Finally, the chain termination mechanism of the catalytic system is also studied.