Supported Metallocene Catalysts for Propene Polymerization

Abstract

A series of silica supported ethylenebisindenylzirconium dichloride catalysts have been prepared using a number of different experimental procedures and using different types of silica also pretreated under differing conditions. The kinetic and activity behaviour of these catalysts when used with methylaluminoxane (MAO) cocatalyst have been investigated for the polymerization of propene at various MAO concentrations. The activities of these supported catalysts were shown to be affected significantly by their methods of preparation and by the thermal treatment of the silica supports. Higher catalyst activities were obtained by first pretreating dehydrated silica with MAO and then reacting the product either with the metallocene or with a precontacted mixture of the metallocene and MAO. The use of a lower dehydration temperature, 260 °C rather than 460 °C, increased the activity of the supported catalyst systems. The catalyst activities also initially increased with increase in the concentration of external MAO. The order of treatment used for the supported catalyst preparation affected the shapes of the rate-time profiles which were obtained. MAO pretreated silica catalysts were shown by SEM studies to yield polymer of good morphology and evidence for silica fragmentation was also obtained. Leaching experiments were performed using selected MAO pretreated catalysts and showed the significance of leaching processes in these polymerization systems. These results are discussed in terms of a pore restricted model for the polymerization process.