Indenyl-silica xerogels: new materials for supporting metallocene catalysts

Inorganic-organic hybrid xerogels bearing indenyl groups on their surfaces have been synthesised by the sol-gel method. The hybrid xerogels were obtained by hydrolysis and polycondensation of bisindenyldiethoxysilane (Ind(2)Si(OEt)(2)) and tetraethoxysilane, TEOS (Si(OEt)(4)) under two different conditions. Chemical structure was investigated by ultraviolet spectroscopy (UV-VIS), transmittance (FT-IR) and diffuse-reflectance (DRIFTS) infrared spectroscopy, magic angle spin nuclear magnetic resonance (MAS-NMR) and X-ray photoelectron spectroscopy (XPS). Xerogel texture and structure were analysed by nitrogen sorption based on the Brunauer-Emmett-Teller (BET) method, X-ray diffraction spectroscopy (XRD), and natural scanning electron microscopy (N-SEM). Under our experimental conditions, in alkaline milieu and 1:3 indenyl/TEOS ratio, a xerogel with higher indenyl content, but nonporous and showing agglomerate patterns was produced (xerogel 1). Spherical particles of diameter about 6-8 mum where obtained in the absence of catalyst, using 1:5 indenyl/TEOS ratio, higher temperature and shorter reaction time (xerogel H). Xerogel II was used as support for heterogeneous metallocene catalyst synthesis. The resulting catalyst presented high Zr content (0.68 m-mol Zr g(cat)(-1)) and high catalyst activity (40 x kg 10(3) mol(-1) Zr h(-1)) in ethylene polymerisation. (C) 2001 Elsevier Science B.V. All rights reserved.