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 obtai ned by hydrolysis and polycondensation of bisindenyldiethoxysilane (Ind(2)S i(OEt)(2)) and tetraethoxysilane, TEOS (Si(OEt)(4)) under two different con ditions. Chemical structure was investigated by ultraviolet spectroscopy (U V-VIS), transmittance (FT-IR) and diffuse-reflectance (DRIFTS) infrared spe ctroscopy, magic angle spin nuclear magnetic resonance (MAS-NMR) and X-ray photoelectron spectroscopy (XPS). Xerogel texture and structure were analys ed by nitrogen sorption based on the Brunauer-Emmett-Teller (BET) method, X -ray diffraction spectroscopy (XRD), and natural scanning electron microsco py (N-SEM). Under our experimental conditions, in alkaline milieu and 1:3 i ndenyl/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 (xero gel H). Xerogel II was used as support for heterogeneous metallocene cataly st 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 reser ved.