Heterogenization of racemic ethylenebis(1-indenyl)zirconium dichloride on trimethylaluminum vapor modified silica surface

Abstract

Heterogeneous metallocene catalysts were prepared by adsorbing rac-Et(Ind) 2ZrCl 2 on a modified silica surface in solution. The modification of silica was conducted in gas phase with atomic layer chemical vapor deposition (ALCVD) technique, where the silica, preheated at either 350 or 600°C, was allowed to react with vaporized trimethylaluminum (TMA) at 250°C. Modified carriers and heterogeneous catalysts were characterized with FTIR, 1 H MAS (magic-angle spinning) NMR, 13 C , and 29 Si CP (cross-polarization) MAS NMR spectroscopies and elemental analyses. In the reaction of TMA with silica, a saturated surface was formed consisting of different (O) 4− n Si(CH 3) n ( n=1, 2 or 3) and AlCH 3 groups. The ratio of SiMe to AlMe groups was approximately 1.5 in the TMA/SiO 2 carriers. When the metallocene was adsorbed onto the carrier it seemed to react with the surface AlCH 3 groups and possibly ZrCH 3 groups were formed. Heterogeneous catalysts were tested in the polymerization of ethylene and propylene in the presence of methylalumoxane (MAO). And they produced similar polymer as the homogeneous rac-Et(Ind) 2ZrCl 2 catalyst, but with lower activity. A catalyst with the best activity was achieved from silica that was preheated at 600°C. Moreover, leaching of catalyst was examined whereupon a part of zirconium was observed to desorb from the carrier.