SILOXY-SUBSTITUTED ALUMOXANES - SYNTHESIS FROM POLYDIALKYLSILOXANES AND TRIMETHYLALUMINUM, AND APPLICATION AS ALUMINOSILICATE PRECURSORS

The interaction of AlMe3 with the polydialkylsiloxanes (OSiRMe)x and ( OSiPh2)3 for long periods at elevated temperatures leads to the ruptur e of the silicon-oxygen framework and yields dimeric dimethylaluminium siloxides [Me2Al(OSiMe2R)]2, R = Me (1), n-C6H13 (2), n-C8H17 (3), n- C14H29 (4), n-C18H37 (5), -CH2CH2CF3 (6), Ph (7), and [Me2Al(OSiMePh2) ]2 (8), respectively. Hydrolysis of the dimethylaluminium siloxides re sults in the formation of oligomeric siloxy-substituted alumoxanes hav ing the composition [Al(O)(OH)x(OSiMe2R)1-x]n, R = Me (9), n-C6H13 (10 ), n-C8H17 (11), n-C14H29 (12), n-C18H37 (13), -CH2CH2CF3 (14), Ph (15 ), and [Al(O)(OH)x(OSiMePh2)1-x]n (16). The extent of hydrolysis, phys ical properties, and the ceramic yield of aluminosilicate upon their p yrolysis are highly dependent on the nature of the alkyl substituent, R, on silicon. The aluminium siloxides and siloxy-alumoxanes have been characterised by IR, H-1, C-13, O-17, Al-27 and Si-29 NMR spectroscop y, mass spectrometry, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray (EDX) analysis. The al uminosilicate has been characterised by scanning electron microscopy ( SEM), EDX, XPS and X-ray diffraction (XRD).