Supported Metallocene Catalysts And Their Performance In Catalytic Propylene Polymerization

In this dissertation, the different classes of metallocene catalysts have been synthesized and the corresponding supported metallocene catalysts were prepared. The performance of these catalysts in catalytic propylene homo- and copolymerization lias been investigated. The structure and properties of resulting polymers was characterized and analyzed. The mechanism of supporting process for metallocene catalysts was deduced, and the relationship between structure of metallocene catalysts and their catalytic performance in propylene polymerization was discussed.Firstly, the unbridged metallocene catalyst, (2,4,6-Me3lnd)2ZrCl2 (met- II) was synthesized, then (2,4,7-Me3Ind)2ZrCl2(met-I) and (met- II) were immobilized on silica to obtain supported metallocene catalysts met-III and met-IV, respectively. The influence of polymerization temperature (Tp), reaction time (tp) and [Al]/[Zr] ratio on the polymerization behavior of propylene was investigated. It is demonstrated that the molecular weight (Mw) of resulting polypropylene (PP) is higher than 103 at lower tp. It is also found that the PP produced by met- II has higher [mmmm] isotactic sequences than that of met-I. The stereoselectivity, melting temperature (Tm) and crystallinity of PP obtained with met-IV has been improved comparing with that of the corresponding homogeneous met- II system.By changing the position of the two methyl groups on the six-member ring of the indenyl ligand from 4,7 to 4, 6 (met-I and met- II), the stability of the "racemic-like" conformer of the unbridged zirconocenes can be sensibly changed. Using a mechanism based on statistical analysis, it was found that chain-end model was dominant for met-I. However, met-II obeys the concurrent two-sites model during polymerization, which can be attributed to the existence of "racemic-like" conformer in its system. According to the results of structure parameters of polymer chains and DSC analysis, it is concluded that the resulting PP has multi-stereoblock structure with many short isotactic blocks interrupted by atactic blocks along the chain.Secondly, the bridged metallocene rac-Me2Si(Ind)2ZrCl2 was synthesized by two routes: salt elimination and amine elimination, in which the yield of latter route is much more than that of former route. The supported metallocene catalyst wasprepared by immobilized on SiO2 with pre-contacted compounds of rac-Me2Si(Ind)2ZrCl2 and methylaluminoxane (MAO), and its activity for propylene isospecific polymerization reaches 106gPP/mol.Zr.h. The behavior of this catalyst was also compared with its corresponding homogeneous catalytic system. It was demonstrated that the active site of heterogeneous system was more stable, and the Mw of obtained polymer was apparently higher. The microstructure of iPP produced by the two types of catalysts was determined by I3C-NMR spectra and analyzed by DSC. It was found that the isotacticity, regioselectivity and Tm of iPP obtained by heterogeneous system were higher. Based on the GPC analysis of polymer and the UV/Vis spectra of catalysts system, it is proposed that the supported metallocene catalyst keeps the single site character, and propylene polymerization mainly took place on the carries.The copolymerization of propylene with 1-hexene, 1-octene, 1-decene and 1-dodecene was carried out using silica-supported raoMe2Si(Ind)2ZrCl2 as catalyst. The copolymerization activity of the homogeneous and the supported catalysts and the microstructure of resulting copolymers were compared. The results reveal that there exist some differences in the copolymerization behavior and the microstructure of the obtained copolymers between the homogeneous and the supported metallocenes. The copolymerization activity is greatly reduced when the metallocene was supported on silica. Increasing the comonomer concentration in the supported system caused stronger negative effect on catalyst activity than in the homogeneous system, while increasing comonomer size influenced the homogeneous system more than the supported one. The activit...