Synthesis And Application Of Dinuclear Zirconocene Catalysts For Olefin Polymerization

Polyolefins are widely used due to their low cost and versatile properties in our daily life and industrial productions,and play an important role in our economic development.Therefore,studying of suitable catalysts is the heart to improve performance of polyolefin materials,which has important scientific significance and industrial value.Considering the advantages of high activity and selectivity,and highly defined microstructure,metallocene catalysts have become a research hotspot in the field of olefin polymerization.Based on the synthesis of bimetallic catalysts and the effects of polymerization conditions on the olefin polymerization,this thesis designs and synthesizes two types of metallocene catalysts.And the structures of the complexes were characterized by NMR,elemental analysis and X-ray single crystal diffraction.The main work of this thesis is summarized as follows:Two kinds of dinuclear metallocene catalysts C1-Zr2 and C6-Zr2 with different bridged chain lengths were synthesized.Their structures were characterized by nuclear magnetic resonance,elemental analysis and X-ray diffraction.Analysis of the X-ray single crystal diffraction results of C1-Zr2 shows that the complex exhibits a triclinic configuration,and the distance between two zirconium metal central atoms is 7.330 A.The catalytic performance of these dinuclear metallocene zirconium complexes for olefin polymerization was investigated.Under the performance of co-catalyst methylaluminoxane(MAO),these complexes can achieve homopolymerization and copolymerization of ethylene,1-octene and 1-hexane with high activity.Polymerization activity and properties vary with the catalyst structure and polymerization conditions.The experimental results show that temperature has great influence on the catalysis,the activity of C1-Zr2 gradually increases with increasing temperature,however,the molecular weight of the resulting polymer is in the opposite trend.Therefore,the optimal temperature is 50?.Pressure also have greater effect on catalytic activity.The amount of MAO also has significant effect on polymer molecular weight and activity.Al/Zr=1000 is the optimal amount of MAO.Under the conditions of Al/Zr=1000,50?,the smaller the metal spacing in the dinuclear metallocene catalyst,the higher the molecular weight and regularity of the polymer obtained.When it comes to the homopolymerization of ethylene with C1-Zr2,the molecular weight can reach 1182 kg/mol and Mw/Mn=2.2.By comparing the difference in polymerization activity between dinuclear zirconium complexes and mononuclear zirconium complex Zri,the cooperative effect of bimetallic catalysts was discussed.Under the same experimental conditions,the activity of C6-Zr2(12020 kg(PE)mol-1(Zr)h-1)is much higher than the mononuclear complex(8650 kg(PE)mol-1(Zr)h-1).