Studies On Synthesis, Characterization And Catalysis For Olefin Polymerization Of Constrained Geometry Metallocene Catalysts

Since 1980's, Kaminsky and Sinn firstly discovered the highly active zirconcene dichloride/methylaluminoxane (MAO) catalytic system for olefin polymerization intensive research work has been focused on developing new metallocene catalysts for improving catalytic activities and polymer properties. The olefins polymerization made its way into the era of using metallocene as homogenous catalyst. Compared with the conventional Ziegler-Natta Catalysts, the most outstanding advantage of metallocene as catalyst for olefins polymerization is that the modification of the cyclopentadienyl ligand is an effective mean of optimizing catalyst activity as well as polymer properties such as molecular weight, stereoregularity and microstructure. Up to now, various kinds of metallocene catalysts have been synthesized and widely studied both in industry and academy, developped enormous special products of polymer. The polyethylene demand is expected to increase from about 55 million metric tons in 2002 to 87 million in 2010 and the polypropylene demand is projected to increase from about 35 million metric tons to nearly 60 million in the same period. That is to say the polyolefin could be presented in multifarious manner of people's daily household items, it has been also applied in the industry, agriculture and architecture to replace common materials such as glass, metal, paper, and concrete. Therefore, the metallocene catalyst owns a broad prospect. Among the multi-various kinds of metallocene catalysts, the constrained geometry metallocene catalysts have attracted particular research attention because of their applications as catalysts in olefin polymerization. The structurally open nature of the catalyst active site could allow them incorporate other largerα-olefin, styrene, cyclopentadiene, norbornene copolymerized with ethylene or propylene to produce new polyolefin products. Furthermore, constrained-geometry metallocene catalysts made it possible to functionalize the polyolefins by incorporating"funcational group"into the polymers. The constrained geometry metallocene catalysts with a pendent nitrogen donor on the cyclopentadienyl ligand, such as Me₂Si(η⁵-Me₄C₅)(tBuN)MX₂ (I, M=Ti, Zr, Hf; X=Cl, Me, CH₂Ph) (I), have been widely studied in industry as well as academic institutions. In comparison with the CGC catalysts of type I, the catalysts with a pendent oxygen donor on the cyclopentadienyl ring received relatively less attention and have not been studied systematically. 1c We and other groups have developed a number of CGC catalysts of the type [η⁵:η¹-C₅R₄-ArO] TiCl₂ (II) and found that these catalysts produce ethylene/α-olefin copolymers with relatively low molecular weights due probably to their ligands are not bulky enough. 4c Similar catalysts with a formula of [η⁵:η¹-C₅H₄-CR₂-ArO] TiCl₂ (III) were also synthesized, but no study on ethylene/α-olefin copolymerization has been reported. Considering that the ligands of the complexes III have a longer linkage and thus are bulkier than those of the catalysts II, complexes III might be more suitable catalysts for producing ethylene/α-olefin copolymers with higher molecular weights. In chapter two we have synthesized a number of new half-sandwich titanium complexes [η⁵:η¹-2-C₅H₄CHPh-4-R¹- 6-R²C₆H₂O] TiCl₂ from the reaction of their corresponding trimethylsilyl substituted ligand precursors 2-Me₃SiC₅H₄CHPh-4-R¹-6-R²C₆H₂OSiMe₃ with TiCl₄. All new Ti complexes were characterized by means of 1H and 13C NMR spectroscopy and elemental analysis, and the structure of complexe [η⁵:η¹-2-C₅H₄CHPh-4-tBu- 6-tBuC₆H₂O] TiCl₂ were determined by single crystal X-ray crystallography. In chapter three, the catalytic performance for ethylene polymerization of the metallocenes complexes were investigated. Influences of the molecular structure of these complexes and polymerization conditions on their catalytic properties were studied. When activated with iBu3Al and Ph₃C⁺B(C₆F₅)₄^-, all complexes exhibited reasonable catalytic activity, producing polyethylenes with moderate molecular weights and melting temperatures. All the complexes show better catalytic activity at 90℃with the Al/Ti ratio of 150. The complexes with di-tert-butyl substituent exhibit the best catalytic activities while the complexes with methyl group show lower catalytic activities, which could be attributed to the both steric and electronic effects of the substituents on the phenolate. All the complexes were also tested for copolymerization of ethylene with 1-hexene. It can be seen that the copolymerization catalytic activity of these catalysts changes in the same order as that observed in the ethylene homopolymerization under similar conditions. 13C NMR analysis of the obtained copolymers indicates reasonable incorporation of 1-hexene into the polymer chains for all catalyst systems. The ethylene and 1-hexene reactivity ratios (rE and rH are the reactivity ratios of ethylene and 1-hexene, respectively) were calculated from Finemane-Ross plots. The value of reactivity ratio products rErH is close to 1, which demonstrates that the ethylene/1-hexene copolymerization proceeds in a random manner.In chapter four, we report the synthesis of two ligands 2-(3,4-diphenylcyclopentadienyl)-4-methylphenol and 2-(3,4-diphenylcyclopentadienyl)-4-tert-butylphenol. Three complexes were synthesized by alkane elimination. The catalytic performance for ethylene polymerization of the metallocenes complexes were investigated.