Study On Olefin Polymerization Catalyzed By Novel Polystyrene-supported Zirconocene

Recently, the supported-metallocene catalysts, especial polymer-supported metallocene catalysts have attracted more attentions. However, some problem such as how to controlling the distribution of active sites on the carriers, the effect of carriers on the active sites, the mechanism of immobilization of metallocene catalyst and the mechanism of polymerization over supported metallocene still are unclear completely. It is of great theoretical significance and practical value to clear the above-mentioned problem.In this work, the linear polystyrene is prepared by suspension polymerization. Subsequently, the polystyrene is chloromethylated and cyclopentadienes are attached on the polystyrene. The cyclopentadienes attached on polystyrene react with BuLi for supporting CpZrCl₃ to form polystyrene-supported zirconocene catalyst. The two kinds of polystyrene-supported zirconocene catalysts with different Zr contents are synthesized and characterized by NMR. The polystyrene-supported zirconocene are employed as catalyst in a study of olefin polymerization in the presence of MAO cocatalyst. The influence of polymerization temperature, [Al]/[Zr] molar ratio, different comonomer on catalytic activities, (co)polymerization kinetics, the properties of resultant polyolefin have been investigated. The results show that the carriers have important effect on activities of those catalysts. The activities of the catalyst with lower cross-linked degree carriers are higher than those of catalysts with higher cross-linked degree carriers. The obvious "comonomer effect" is observed in the ethylene/α-olefin copolymerization catalyzed by the polystyrene-supported zirconocene catalysts.The polyoiefins obtained by the polystyrene-supported zirconocene catalysts are characterized with the techniques of DSC, GPC and ¹³C NMR. The results show that the melting temperature and crystallinity decrease markedly with the increase of comonomer in the ethylene/a-olefin copolymer. The microstructure of ethylene/1-hexene copolymer is investigated using ¹³C NMR. The results reveal that the content of comonomer in copolymer increases with increasing the concentration of comonomer in the feed. The composition of the ethylene/1-hexene copolymer obtained by the different catalysts is nearly same and the 1 -hexene units are distributed evenly in copolymer chains.The molecular-weight distribution(MWD) graphs of polyethylene obtained by polystyrene-supported zirconocene catalyst are fitted with Schulz-Flory "the most probable" distributions. The results show that it is possible there lie three kinds of active species in the catalytic system. According to the above-mentioned results, a novel kinetic model is presented. Simulating results using the model are consistent with experimental results. According to the theory of copolymerization and some assumption, a kinetic model of ethylene/1-hexene copolymerization isdeveloped. The model could fit the experimental results well, which suggests the model is reasonable.In this work, in the presence of Cp2ZrCl2, utilizing the Diels-Alder reaction of cyclopentadienes attached on the linear polystyrene to form the cross-linked polystyrene network, the Cp2ZrCl2 are encapsulated inside the cross-linked polystyrene network. The polystyrene-supported solid-homogeneous zirconocene catalyst is prepared. Using 4-oxo-2,2,6,6-tetramethyl -1-piperidinyloxy radicals as probe, the structure of cross-linked polystyrene network is investigated. The results show that the homogeneous microenvironment could form in the cross-linked polystyrene network.The olefin polymerization catalyzed by the polystyrene-supported solid-homogeneous zirconocene catalyst is studied in the presence of MAO cocataiyst. The results show that the fragmentation of carrier is the one of important reasons, which influence on the property of catalyst. The kinetic curves of ethylene polymerization catalyzed by the catalyst with low cross-linked degree carrier is stable and the polymerization rate of the catalyst with high cross-linked degree carrier decrease quickly. In addition, we find that polystyrene carrier could fragment and is distributed into polyethylene during ethylene polymerization. By the method, the polyethylene/polystyrene molecular composite membrane is prepared.The polyolefin obtained by the polystyrene-supported solid-homogeneous zirconocene catalyst are characterized by the techniques of DSC and GPC. The results show that the carrier has important effect on the molecular weight and molecular-weight distribution of polyethylene. The molecular-weight of polyethylene obtained by the catalyst with higher cross-linked density carrier is lower. The molecular-weight distribution(MWD) graphs of polyethylene obtained by polystyrene-supported solid-homogeneous zirconocene catalyst are fitted with Schulz-Flory "the most probable" distributions. The results show that it is possible there lie four kinds of active species in the catalytic system.