Studies On Ethylene And Methyl Methacrylate Polymerization By Bridged Dinuclear Titanocene

Metallocnene catalyst, with high catalytic activity and the possibility of tailoring the polymer properties such as the molecular weight, the molecular weight distribution and the stereochemistry, have become the excellent catalyst for olefin polymerization after the Ziegler-Natta catalyst. However, the narrow molecular weight distribution of the polymer produced by metallocene catalyst causes difficulties in industrial processing. In order to resolve the problems, scientific researchers used special polymerization procedure or synthesized different strutures of metallocene catalysts to produce the polymers with broad molecular weight distribution. The dinuclear metallocene catalysts, which might produce two different active sites in one molecule, should be able to produce polymer with broader or bimodal molecular weight distribution.One symmetric ethyl sulfide bridged dinuclear titanocenium metallocene complex [(CpTiCl₂)₂(C₅H₄CH₂CH₂SCH₂CH₂C₅H₄)](C1), one symmetric ethyl ether bridged dinuclear titanocenium complex [(MeCpTiCl₂)₂(C₅H₄CH₂CH₂OCH₂CH₂C₅H₄](C2) and two asymmetric ethyl ether bridged dinuclear titanocenium metallocene complexes [(MeCpTiCl₂)₂(C₉H₆CH₂CH₂OCH₂CH₂C₅H₄] and [(MeCpTiCl₂)₂(C₉H₆ CH₂CH₂OCH₂CH₂C₅H₃CH₃)](C3 and C4) have been synthesized and characterized by ¹H-NMR.Homogenous ethylene polymerization by complex C1 has been conducted systematically in the presence of metylaluminoxane (MAO). Bulk and solution polymerization of methyl methacrylate by complexes C2, C3 and C4 have been conducted systematically in the presence of Al(i-Bu)₃, etc. The influences of reaction parameters, such as catalyst concentration, the molar ratio of cocatalyst and catalyst, temperature and time have been studied in detail. The detail results showed as follows:1. Both the highest activity (3.63×10⁵ g PE/(mol Cat. · hr)) and the highest viscosity average molecular weight (56.66×10⁴) of C1/MAO are higher than that of the symmetric ethyl ether bridged dinuclear titanocenium [(CpTiCl₂)₂(C₅H₄CH₂CH₂O CH₂CH₂C₅H₄)] (C5/MAO) obviously, which is because the electron gaining ability of Sulfide is weaker than that of Oxygen. The molecular weight distribution of polyethylene catalysed by C1/MAO under certain conditions is as high as 10.58.2. The MMA's conversion in bulk polymerization catalysed by symmetric ethyl ether bridged dinuclear titanocenium C2/Al(i-Bu)₃ are as high as 90%, and the solution polymerization are about 40%. The viscosity average molecular weight of bulk polymerization are higher obviously than that of the solution polymerization. The molecular weight distribution of PMMA range from 4.5 to 7.0, and the syndiotactic content are about 70%.3. Under the polymerization condition of nMMA/nCat.=1500, nAl(i-Bu)₃/nCat.=20, 60℃, 24 hr, the MMA' conversion of bulk polymerization catalysed by asymmetric ethyl ether bridged dinuclear titanocenium C3/Al(i-Bu)₃ and C4/Al(i-Bu)₃ systems are 71.66 % and 83.88 % respectively, and the viscosity average molecular weights are 85.58×10⁴ and 79.61 ×10⁴. Under certain conditions, the syndiotactic content of PMMA are about 71.0 % and 73.4 %.