两性离子型单茂铬烯烃聚合催化剂的合成及性质研究

In recent years, we have developed a new type of mono-cyclopentadienylchromium complexes which show high catalytic activaty for ethylene polymerization reaction upon activation with a small amounts of trialkylaluminum and produce high molecular weight polyethylene without the use of methylaluminoxane (MAO) or highly fluorinated organoborate type of cocatalysts (JACS, 2007, 129(8), 2236; OM, 2011, 30(3), 433; OM, 2011, 30(4), 669; Dalton Trans, 2011, 40(39), 10184; New J Chem, 2010, 34(12), 2979). However, the neutral nature of these mono-cyclopentadienylchromium catalysts makes the coordination ability of α-olefins to the central metal of these catalysts being relatively low. As a result, these mono-cyclopentadienylchromium catalysts can not catalyze the copolymerization reaction of ethylene with α-olefins. A major application of the metallocene catalysts, especially the half-sandwich metallocene catalysts, is the production of linear low density polyethylene (LLDPE) by catalyzing the copolymerization of ethylene with α-olefins. So far, all the metallocene catalysts suitable for the copolymerization reaction have to be activated by MAO or the fluorinated organoborate cacatalysts. In this project, a series of new zwitterionic mono-cyclopentadienyl chromium complexes are going to be designed and synthesized. Their catalytic properties for the copolymerization of ethylene with α-olefins in the presence of a small amount of trialkylaluminum are going to be studied in detail. The effects of catalyst structure and polymerization conditions on the performance of catalysts will be examined for developing better catalysts and improving the polymerization reaction conditions. The zwitterionic catalysts, with their central metals carrying a positive charge, would enhance the coordination ability of α-olefins and therefore should be able to catalyze the copolymerization of ethylene with α-olefins. We hope that, by carrying out this research project, brand new type of alkylaluminum-activated metallocene catalysts for the production of LLDPE could be developed.

我们课题组近几年开发出一系列新型单茂铬催化剂，此类催化剂经少量烷基铝（25倍）活化即可催化乙烯聚合生成高分子量聚乙烯，无需使用MAO或五氟苯硼类助催化剂，且催化活性高，显示出良好的发展前景。然而，由于较大体积烯烃对此类中性催化剂的配位能力低，致使此类催化剂不能催化乙烯与α-烯烃共聚。合成两性离子型催化剂可使中心金属带正电荷，提高大体积烯烃的配位能力，进而可以催化乙烯与α-烯烃共聚。本项目拟在已有工作基础上，改进催化剂结构、合成两性离子型单茂铬催化剂，研究其在烷基铝活化下对乙烯与α-烯烃共聚反应的催化性能，探索此类催化剂结构与性能的关系，经过反复优化催化剂结构、催化体系和聚合反应条件，以期最终开发出对乙烯与α-烯烃共聚有良好催化性能的催化剂，使该类催化剂具有更广泛的应用。期望通过此项研究，开发出具有自主知识产权、可用烷基铝活化的生产线性低密度聚乙烯用新型茂金属催化剂。

在该项目资助下，合成了9类茂金属和非茂金属烯烃聚合催化剂，对所合成的新催化剂进行了必要的表征和组成分析，研究了其对乙烯、丙烯、1-己烯或异戊二烯均聚或工具反应的催化作用，获得了多种高性能催化剂体系。合成出一种含双水杨醛亚胺合锆结构单元的多孔配位聚合物催化剂，发现其对乙烯聚合具有优良的催化性能。合成出一种含亚胺基侧链的环戊二烯基钪配合物，用这种非手性钪配合物催化1-己烯聚合获得了高分子量等规聚己烯。合成出一种含胺基侧链的环戊二烯基钛配合物，这种钛配合物对乙烯/1-己烯共聚反应显示出良好的催化性能，具有催化剂热稳定性好、共单体插入率高、共聚物分子量高的优点。合成出NNNN-四齿胺-亚胺配体的钛、锆、铪配合物，这些配合物对乙烯聚合显示出良好的催化性能，所生产的聚乙烯具有超高分子量（粘均分子量达400万以上）。我们还开发出一种可催化异戊二烯高选择性顺-1,4-聚合的三齿钳式配体稀土催化剂。另外，开发出高效一锅煮脱HCl反应合成钛、锆、铪配合物的新方法和高效合成吖啶衍生物的新方法。项目执行期间，发表SCI检索论文15篇，获得授权中国发明专利6项。