Studies On Synthesis, Characterization And Catalytic Properties Of POPs-Supported Metallocene Chromium Catalysis

Polyolefin products as a kind of synthetic polymer materials are widely used in industry, agriculture, packaging and daily life. Polyethylene has the largest yield,fastest-growing and most active product development in the synthesis of polymer materials. In order to improve the yield and properties of polyethylene product,developing highly active catalysts for olefin polymerization is of great significance. In industry, homogeneous catalysts should be immobilized on suitable supports such as Si O2, Mg Cl2 or zeolite to meet production needs. The catalysts immobilized on supports can control polymer particle size and make the size distributions in a certain extent. However, in some cases the immobilization of olefin polymerization catalysts causes a remarkable decrease in catalytic activity and the polymers with broad distributions of molecular weight and chemical composition. Therefore, it is difficult to control the microstructure and properties of the polyolefin when using these multisite catalysts. The silica-supported heterogeneous Phillips Cr Ox/Si O2 catalysts have been widely used in production of high-density polyethylene in industry. This kind of catalyst is simple to prepare and it can be performed without any cocatalyst in the polymerization process. However, the research of the active center of the Phillips catalysts and the polymerization mechanism is still in the poimary stage.In recent years, it was found that a series of half-metallocene chromium(III)complexes bearing a salicylaldiminato ligand combined with small amount of alkylaluminium as cocatalyst, were highly active as homogeneous catalysts for the polymerization of ethylene to linear polyethylene. In order to make this kind of catalysts useful in industry application, the choice of suitable load carrier is very important. Porous organic polymers have excellent adsorption properties and high specific surface area. Since the different structures and functions can be designed and synthesized, and can be easily modified by tuning the ligands and substituent groups,the porous organic polymers become excellent catalyst carriers in the field of heterogeneous catalysis.In this paper, we have successfully designed and synthesized two novel porous organic polymers bearing salicylaldiminato ligands. By varying the reaction time and the reaction temperature, we receive a number of catalysts with different chromium content. The two ligands and these catalysts were characterized by elemental analysis,thermal gravimetric analysis, specific surface area and pore size distribution analysis and ICP-OES analyses. A series of chromium-based porous organic polymers(POPs)were constructed and utilized as stable and remarkably active catalysts for the ethylene polymerization. These half-metallocene chromium(III) POP catalysts were sufficient for ethylene polymerization upon activation with Al R3 and these catalysts exhibited long life times. The spherical or granular morphology of the original support had been retained and replicated throughout catalyst immobilization and polymerization.