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

Heterogeneous metallocene catalysts were prepared by adsorbing rac-Et(Ind)( 2)ZrCl2 on a modified silica surface in solution. The modification of silic a was conducted in gas phase with atomic layer chemical vapor deposition (A LCVD) technique, where the silica, preheated at either 350 or 600 degrees C , was allowed to react with vaporized trimethylaluminum (TMA) at 250 degree s C, Modified carriers and heterogeneous catalysts were characterized with FTIR, H-1 MAS (magic-angle spinning) NMR, C-13, and Si-29 CP (cross-polariz ation) MAS NMR spectroscopies and elemental analyses. In the reaction of TM A with silica, a saturated surface was formed consisting of different (-O)( 4-n)Si(CH3)(n) (n = 1, 2 or 3) and -AlCH3 groups. The ratio of -SiMe to -Al Me groups was approximately 1.5 in the TMA/SiO2 carriers. When the metalloc ene was adsorbed onto the carrier it seemed to react with the surface -AlCH 3 groups and possibly -ZrCH3 groups were formed. Heterogeneous catalysts we re tested in the polymerization of ethylene and propylene in the presence o f methylalumoxane (MAO). And they produced similar polymer as the homogeneo us rac-Et(Ind)(2)ZrCl2 catalyst, but with lower activity. A catalyst with t he best activity was achieved from silica that was preheated at 600 degrees C. Moreover, leaching of catalyst was examined whereupon a part of zirconi um was observed to desorb from the carrier. (C) 2000 Elsevier Science B.V. All rights reserved.