Study On Synthesis Of Flexible Bridged Dinuclear Metallocene Of Ti, Zr And Their Catalytic Behaviors In Ethylene Polymerization

Metallocnene catalyst, with high catalytic activity and the possibility of tailoring the polymer properties such as the molecular weight, the molecular wight distribution and the stereochemistry, have become the excellent catalyst for olefin polymerization after the Ziegler-Natta catalyst. However, the narrow molecular wight distribution of the polymer produced by metallocene catalyst causes difficulties in industrial procedure. In order to resolve the problems, scientific researchers used special polymerization procedure or different sturtures of metallocene catalysts to produce the polymers with broad molecular wight distribution. The dinuclear metallocene catalysts, which have two diffeent active sites in one molecule, should be able to produce polymer with broader or bimodal molecular weight distribution.Two asymmetric alkylidene bridged dinuclear titanocenium metallocene complexes (Cl and C2), two symmetric ethyl ether bridged dinuclear metallocene complexes (C4 and C5) and one asymmetric ethyl ether bridged dinuclear titanocenium metallocene complex (C3) have been synthesized and characterized by IR, ¹H-NMR and ¹³C-NMR.Homogenous ethylene polymerization by these complexes has been conducted systematically in the presence of metylaluminoxane (MAO). The influences of reaction parameters, such as catalyst concentration, [MAO]/[Cat] molar ratio, ethylene pressure, temperature and time have been studied in detail. The detail results showed as follow:1. Although the two asymmetric dinuclear complexes (Cl and C2) were different in only one [CH2] unit, the catalytic activity of C2 was somewhat twenty percents higher than that of Cl;however the molecular weight of polyethylene obtained by C2 was lower than that obtained from Cl. The molecular weight distribution. (MWD) of PE produced by these dinuclear complexes reached 6.9 and 7.3, respectively.2. The symmetric two ethyl ether bridged dinuclear metallocene complexes (C4and C5) were more active than the corresponding mononuclear catalysts (Cp2TiCl2 /MAO and Cp2ZrCl2/MAO), indicating that introduction of the hetero-atom oxygen into the bridges of C4 and C5 did not decrease the catalytic activity;on the contrary, it increases the polymerization activity. The molecular weight distributions of these dinuclear complexes are much wider than those of the corresponding mononuclear metallocenes (Cp2TiCl2 /MAO and Cp2ZrCl2/MAO).3. The asymmetric ethyl ether bridged dinuclear titanocenium metallocene complex (C3) produced polyethylene with broader molecular weight distribution (MWD=12.4). The melting points of the polyethylene produced ranged from 135-138 °C, indicating a high linearity and a high crystallinity.