Polymerization of ethylene using zirconocenes supported on swellable cation-exchanged fluorotetrasilicic mica

Abstract

Supported catalysts consisting of Cp 2ZrCl 2 and cation-exchanged fluorotetrasilicic mica (M n+ -mica, M n+ = Na +, Mg 2+, Fe 3+, Co 2+, Ni 2+, Cu 2+, Zn 2+) were prepared and employed in the ethylene polymerization or ethylene/1-hexene copolymerization in the presence of R 3Al. The catalysts consisting of swellable Mg 2+-mica and Zn 2+-mica (both calcined at 200 °C) and Cp 2ZrCl 2 displayed high activity for the polymerization reaction. By contrast, when Mg 2+-mica and Zn 2+-mica were calcined above 250 °C, the swellability was lost, and the activities of Cp 2ZrCl 2 supported on these non-swellable micas were significantly reduced. The relationship between the activity and swellability of mica was clearly observed both in ethylene polymerizations employing ( n-BuCp) 2ZrCl 2 in place of Cp 2ZrCl 2 and in ethylene/1-hexene copolymerizations using Cp 2ZrCl 2. The role of M n+ -mica for the activation of the metallocene complex was investigated by surface observation using a scanning electron microscope and by XRD measurements of the catalysts after polymerization of ethylene for a short time. The results of the surface observations indicated that polyethylene was produced on the edges of M n+ -mica lamellas at the initial stage of the polymerization. The XRD measurements show that the regularity of the stacked lamellas was immediately lost at this stage. The catalyst prepared by removing free Cp 2ZrCl 2 (i.e., unsupported Cp 2ZrCl 2, Cp 2ZrCl 2 dissolved into the catalyst slurry) showed extremely low activity, suggesting that the most of the active sites were formed through the reactions of M n+ -mica and free Cp 2ZrCl 2. These results indicate that the lamellas of M n+ -mica are peeled off at the initial stage of the polymerization and that exposed metal cations react with free-Cp 2ZrCl 2 to form additional active species. The swellability of M n+ -mica strongly affects the formation of additional active sites, and therefore the supported catalysts based on non-swellable M n+ -mica displayed only low activities.