Siloxy-substituted alumoxanes: synthesis from polydialkylsiloxanes and trimethylaluminium, and application as aluminosilicate precursors

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Abstract
The interaction of AlMe3 with the polydialkylsiloxanes (OSiRMe)x and (OSiPh2)3 for long periods at elevated temperatures leads to the rupture 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 results in the formation of oligomeric siloxy-substituted alumoxanes having 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, physical properties, and the ceramic yield of aluminosilicate upon their pyrolysis are highly dependent on the nature of the alkyl substituent, R, on silicon. The aluminium siloxides and siloxy-alumoxanes have been characterised by IR, 1H, 13C, 17O, 27Al and 29Si NMR spectroscopy, mass spectrometry, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray (EDX) analysis. The aluminosilicate has been characterised by scanning electron microscopy (SEM), EDX, XPS and X-ray diffraction (XRD).

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