Synthesis And Ethylene Polymerization Study Of Novel Dinuclear Titanocenes

Due to high catalytic activity,single active site,good copolymerization and the possibility of tailoring the polymer properties such as stereochemistry,molecular weight(MW) and molecular weight distribution(MWD),metallocene catalysts have been becoming an excellent catalytic system for olefin polymerization after Ziegler-Natta catalysts.However, narrow molecular weight distribution of polymers produced by metallocene causes some difficulties in industrial processing.In order to solve these problems,researchers used special polymerization procedures or unusual structures of metallocene catalysts to produce polymers with broader or bimodal MWD.It has been proved than the dinuclear metallocene catalysts could be able to produce polymers with broader or bimodal MWD.The dinuclear metallocene catalysts therefore became an hot study field in metallocene catalysts.Two kinds of dinuclear titanocenes have been synthesized and used as catalysts for ethylene polymerization in the presence of MAO,respectively.(1) Dinuclear ansa-titanocene complexesμ-(CH₂)n[CR₁R₂(C₅H₃)(C₅H₄)TiCl₂]2[n=4,6; R₁=R₂=CH₃,(CH₂)₅)].The results of polymerization show that their catalytic activity,MW and MWD are higher than corresponding mononuclear titanocenes.This kind of titanocenes keeps moderate catalytic activity at very high temperature(95℃,2.63×10⁵g of PE / mol Ti hr).(2) 3-substituted dinuclear titanocene complexesμ-(CH₂)_n{[R₁R₂CH(C₅H₃)](C₅H₅) TiCl₂}₂[n=4,6;R₁=R₂=CH₃,(CH₂)₄,(CH₂)₅].The catalytic activity and MW of PE decreased gradually with increasing of steric effect of 3-substituted group(cyclohexyl＞cyclopentyl＞isopropyl). The broader MWD of PE was produced by dinuclear titanocenes with longer bridge. This kind of catalysts performs good behaviors in lower temperature and concentration,and could be able to get high MW of PE.