The objective of our research is the development of an environmentally benign process for the fabrication of alumina-based ceramics. We have designed an alternative synthetic pathway to alumina ceramics that does not utilize toxic reagents or volatile organic chemicals (VOCs); the aqueous synthesis of "water-soluble" carboxylate-alumoxane precursors from inexpensive boehmite feed stock. Carboxylate-alumoxanes, [Al(O) x (OH) y (O 2 CR) z ] n , were synthesized by the reaction of boehmite, [Al(O)(OH)] n , with acetic acid (HO 2 CCH 3 ), methoxyacetic acid (HO 2 CCH 2 OCH 3 ), (methoxyethoxy)acetic acid (HO 2 CCH 2 OCH 2 CH 2 OCH 3 ) and [(methoxyethoxy)ethoxy]acetic acid [HO 2 CCH 2 (OCH 2 CH 2 ) 2 OCH 3 ]. Carboxylate-alumoxanes are infinitely stable at ambient conditions in solid and solution. In addition, they show no propensity to segregation or polymerization and are readily processed in aqueous or hydrocarbon medium. Upon thermolysis the carboxylate-alumoxanes are converted to alumina. The physical and spectroscopic properties of the carboxylate-alumoxanes have been determined, including particle size, molecular weight, hardness, refractive index and dielectric constants. The application of the carboxylate-alumoxanes as preceramic binders in traditional tape casting, and infiltration agents has been demonstrated. The potential environmental impact of the new alumoxane methodology as compared to traditional approaches will be discussed.

The reaction of Al(tBu)3 with ethylene glycol (HOCH2CH2OH) in hexane yields “alucone” polymers, [Al(tBu)2 x (OCH2CH2O)1.5 - x ] n (0.3 ≤ 2x ≤ 0.8), with the concurrent formation of [Al2(tBu)3(OCH2CH2O)(OCH2CH2OH)] (1). If the reaction is carried out in Et2O solution, then [Al3(tBu)5(OCH2CH2O)2] (2) may be isolated. The molecular structure of compound 1 consists of a dimer formed by the alkoxide termini of two ligands bridging the Al(tBu) and Al(tBu)2 units. The Al(tBu) moiety is chelated by the nonbridging oxygens of the glycolate ligands, one of which remains protonated. Compound 2 consists of two Al(tBu)2 units and two glycolate ligands forming a cryptand-like 10-membered heterocycle; the Al(tBu) unit is positioned capping the four oxygen atoms. As with the previously reported ethoxy-substituted alucone polymers, [Al(OR)2 x (OCH2CH2O)1.5 - x ] n , thermolysis of [Al(tBu)2 x (OCH2CH2O)1.5 - x ] n , results in the formation of η-alumina (η-Al2O3) as determined by XRD. This is in contrast to the formation of γ-Al2O3 from the thermolysis of alumoxanes, [Al(O)(OR) x (OH)1 - x ] n , and may be rationalized by the structural relationship of compounds 1 and 2, and hence the alucones, to Bayerite rather than the boehmite core observed for alumoxanes.