Studies On Synthesis, Characterization And Catalysis For Olefin Polymerization Of Novel Non-bridged Titanocene Catalysts

Group 4 metallocene-based catalysts have attracted extensive attention in the past decades, as homogeneous catalysts for olefin polymerization, since Kaminsky et al. discovered the highly active zirconocene dichloride/ methylaluminoxane (MAO) catalytic system for olefin polymerization in the early 1980's. Subsequently, research both academically and industrially has been focused on developing to develop new catalyst systems, which can provide high performance polyolefins, such as isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, high density polyethylene, linear low density polyethylene, syndiotactic polystyrene, and cyclo-olefin copolymer et al. Half-metallocene type catalysts have been widely studied in recent years, as one of the efficient catalyst precursors for olefin homopolymerization and copolymerization of ethylene withα-olefin. For example, this type of complex catalysts can be tuned by modification of cyclopentadienyl and/or ancillary anion aryloxide ligands with electronic and steric properties, thus displaying unique characteristics as the catalysts producing new polyolefins, including the copolymers of ethylene with cyclohexene, 2-methyl-1-pentene, and with vinylcyclohexane. In this dissertation, the preparation of a series of non-bridged titanocene complexes is described. And these titanium complexes are successfully used to catalyze the homopolymerization of ethylene/propylene and copolymerization of ethylene withα-olefin. Influences of the molecular structure of titanocene complexes and polymerization conditions on their catalytic performance were also studied.The bulky substituent on the cyclopentadienyl ring can construct a relatively crowded environment around the titanium center, thus could prevent the metallocene complex from dimerization through Cl and O atoms. And we modified cyclopentadienyl ligand with phenyl substituent with the special steric and electronic factors, and synthesized five aromatic substituted tetramethylcyclopentadienyl derivatives. Five aromatic substituted tetramethylcyclopentadienyl titanium trichloride derivatives were synthesized in similar way to the published procedure. Twenty non-bridged titanocenes, (1-R-2,3,4,5-tetramethyl-cyclopentadienyl) (aryloxo)titanium dichloride complexes, [R = 4-MeC6H4, 4-iPrC6H4, 4-tBuC6H4, 4-Me3SiC6H4, 3,5-(CF3)2C6H3; Ar = 2, 6-Me2C6H3, 2, 6-iPr2C6H3, 2, 6-tBu2C6H3, 2, 4,6-tBu3C6H2] had been synthesized by a direct procedure from the reaction of aromatic substituted tetramethylcyclopentadienyl titanium trichloride derivatives with the bulky lithium phenoxide. All titanium complexes have been characterized by elemental analysis, 1H and 13C NMR spectroscopy. The molecular structures of titanocene complexes were determined by single crystal X-ray diffraction analysis. During the course of study on the stability of these new compounds, it was found that these nonbridged titanocene complexes were air and moisture sensitive in both solution and the solid state. Two dimeric oxo-bridged complexes were obtained and characterized by 1H and 13C NMR spectroscopy, as well as single crystal X-ray diffraction analyses.The unbridged half- titanocene complexes can be tuned by modification of cyclopentadienyl and/or ancillary anion aryloxide ligands with electronic and steric properties. We have concentrated our efforts on designing a series of binuclear unbridged metallocenes linked by lithium biphenoxide. Considering steric and electric effects, two biphenol ( 3,3',5,5'-tetra-i-propyl biphenol, 3,3',5,5'-tetra-t-butyl biphenol) were synthesized in similar way to the published procedure. Eight binuclear non-bridged titanocenes had been synthesized by lithium salt elimination approach from the reaction of aromatic substituted tetramethylcyclopentadienyl titanium trichloride derivatives with the dilithio salts of biphenol. All titanium complexes have been characterized by elemental analysis, 1H and 13C NMR spectroscopy. The molecular structures of titanocene complexes were determined by single crystal X-ray diffraction analysis. It was found that the binuclear complexes can be easily hydrolysized in solution to produce dimeric oxo-bridged complexesThe catalytic performance for ethene polymerization of a series of unbridged mononuclear and binuclear titanocene were studied. Influences of the nature of substituents on cyclopentadienyl and aryloxide ligands of these complexes and polymerization conditions on their catalytic properties were investigated. When activated with iBu3Al and Ph3C+B(C6F5)4?, all titanium complexes exhibited reasonable catalytic activity, producing moderate molecular weight polyethylenes with high melting temperatures. The results showed that there is significant differences in catalytic activities of these titanocene with the different aryloxide ligand, and no significant differences in catalytic activities according to the substituent of phenyl groups of the cyclopentadienyl ligands, which construct a bulky environment in the front side of titanium atom. The steric effect of the substituent at the bulky substituent on of Cp ring had a significant effect on the molecular weight of resultant polymer. An influence of Ai/Ti ratio and temperature on the catalytic activity and molecular weight of the resultant polymer was investigated.A systematic study on the ethylene/1-hexene and ethylene/1-decene copolymerization behavior of a series of unbridged mononuclear and binuclear titanocene was carried out. Influences of both cyclopentadienyl and aryloxide ligands substituents of unbridged titanocenes activated with iBu3Al /Ph3C+B(C6F5)4? on their catalytic performance were investigated. All of our employed catalysts were active in copolymerization. The results showed that there is no significant differences in catalytic activities of these titanocene with the same aryloxide ligand, due to the substituents on the phenyl group attached to substituted tetramethyl cyclopentadienyl ligands of title titanocene analogues, and these results clearly indicated the catalytic activities were strongly influenced by ortho substituents in the aryloxide ligands. Comparison between results of our catalytic systems showed that the nature of substitents of catalysts precursor had a siganificant effect on the incorporation and sequence distribution of theα-olefin, as well as the molecular weight of resultant copolymer. In addition, it was found that polymerization conditions such as the polymerization temperature, Al/Ti molar ratio and B/Ti molar ratio had the similar influences on the catalytic activities to other common metallocene catalyst. By comparison with the ethylene homopolymerization, a positive comonomer effect on the catalytic activity under our employed conditions can be obviously observed with our copolymerization systems.The catalytic performance for propene polymerization of a series of unbridged mononuclear and binuclear titanocene were studied. Influences of the nature of substituents on cyclopentadienyl and aryloxide ligands of these complexes and polymerization conditions on their catalytic properties were investigated. When activated with iBu3Al and Ph3C+B(C6F5)4?, all titanocene exhibited high catalytic activity for propylene polymerization. Under the similar conditions, mononuclear titanocene catalysts system exhibited better catalytic activities than their corresponding binuclear ones, which could be explained by that the catalytic active species produced by mononuclear catalyst system were more stable than those of the corresponding binuclear system. An influence of Ai/Ti ratio and temperature on the catalytic activity and molecular weight of the resultant polymer was investigated. The results show that higher molecular weight of atactic polypropylene could be obtained at lower Al/Ti molar ratio and at practical temperature.