乙烯原位共聚复合催化剂制备及高性能支化聚乙烯结构调控

The binuclear complex catalysts for in-situ copolymerization of ethylene will be synthesized in this project, since the demand of well designed linear low-density polyethylene (LLDPE) with high performance is increasing greatly. LLDPE is mainly produced by copolymerization of ethylene with linear alpha-olefins. Among the many linear alpha-olefins, 1-octene is the most valuable co-monomers for copolymerization because of the excellent performance of the copolymer. However, most of the 1-octene for copolymerization are expensive and need to be imported. .The in situ copolymerization of ethylene is a novel method of synthesizing LLDPE with a single feed of ethylene and two catalysts in single reactor. .Constrained-geometry catalysts is an important type of catalyst for olefin polymerization. As a novel type of catalyst, the complex with clear structure could be synthesized in simple procedure. Using as catalyst for olefin polymerization, high activity is available and affording polymer with high molecular weight. And excellent copolymerization ability could be observed, and some of the obtained copolymers could not be produced by Ziegler-Natta catalyst and traditional metallocene catalyst systems. On the other hand, the bis(phosphine) amine (PNP) ligand/Cr(III) catalyst system shows high selectivity for ethylene tetramerization to produce 1-octene. They are complexed for in-situ copolymerization of ethylene to produce well designed LLDPE with high performance in this project..At the first, constrained-geometry catalysts with different steric and electronic ligands will be synthesized and complexed to generate the complex catalyst containing two active centers for ethylene tetramerization and copolymerization activated with the same cocatalyst. polymerization behavior and polymer structure could be adjusted through balancing the structures of ligands. .The relation between catalyst structure, reaction conditions and catalytic activity, polymer molecular weight and distribution of branched-chain will be investigated, to clarify the synergy catalytic mechanism of the two active centers, and screening suitable cocatalyst to replace the expensive methylaluminiumoxane(MAO). Then molecular tailored branched polyethylene with excellent performance could be produced by adjusting structure of catalyst and polymerization conditions, while the problems in the multi-nuclear catalyst system or complex catalysts system are solved, such as copolymeric ability is so poor and the distribution of product is too broad to be copolymerized, lead to difficult to control the structure of copolymer..If the catalysts could be supported successful and activated without expensive MAO,it will promote the innovation of catalytic theory and show good prospects for industrialization.

本课题围绕双活性中心乙烯原位共聚复合催化剂的制备展开。合成了含有不同位阻和电子效应结构的新型限定几何构型催化剂，与高选择性乙烯四聚PNP/Cr（III）系催化剂复配，生成含有乙烯四聚和共聚两种活性中心的复合催化剂。用一种助催化剂即可同时激活两种活性中心，催化乙烯原位共聚。考察乙烯原位聚合中，催化剂结构和反应条件对催化活性、聚合物分子量及支链分布的影响，阐明双活性中心协同作用的催化机理，并筛选合适的助催化剂。通过催化剂结构的调节, 实现支化聚乙烯的分子裁剪。最终解决现有分子内多核或复合催化体系中，齐聚产物分布过宽，共聚活性中心共聚能力不足，双活性中心难以协调，导致产物不易调控的缺陷，生成结构可控、性能优良的支化聚乙烯，推动乙烯原位共聚催化理论的创新，并通过负载化研究与新型助催化剂的筛选，为下一步的工业化应用打下基础。

我们采用乙烯原位共聚制备高性能支化聚乙烯进行了探索，筛选复配了复合催化体系，使乙烯在四聚催化剂的作用下高选择性生产1-辛烯和1-己烯，然后通过茂金属的催化与乙烯共聚，实现单一原料乙烯、单一反应器内催化乙烯聚合生产高性能支化聚乙烯。.研究了聚合工艺条件对催化活性和聚合物性能的影响规律。并对聚合产物的性能进行了分析、表征，发现现有的PNP配体铬系催化剂的齐聚产物分布过宽，造成共聚产物熔点较低，因此对齐聚条件进行了调整，加入氢气试图改变齐聚产物的碳数分布，结果发现PNP配体铬系催化剂的齐聚过程表现出不同的链增长机理，不能达到调控的目的。.于是对催化剂的结构进行了调整，合成了新型环状配体双核铬系催化剂和吡啶配体PNN结构催化剂，改变齐聚产物的碳数分布，在后期的原位共聚中提供短链烯烃，从而改变其耐热性能。通过优化聚合工艺条件，所得聚合物显示出良好的结晶能力、加工流变性，呈现出耐热聚乙烯良好的热性能及力学性能。.