Preparation from alumoxanes

The tricarboxylates are highly susceptible to hydrolysis, are nonvolatile, and thermally unstable. They lose one equivalent of acid anhydride upon heating to 200 °C to form carboxy-substituted alumoxanes, (RC02A10) . The latter compounds have been used as precursors for alumina fibers and films and are more conveniently prepared from the mixed aluminum alkoxide monocarboxylate (equation 40). 

All of the alumoxanes prepared from boehmite decompose between 180 and 385 °C to give AI2O3 in essentially quantitative yield. XRD spectra of the residues are consistent with their identity as y-alumina. Based on X-ray photoelectron spectroscopic (XPS) analysis, carbon incorporation is found to be very low if the pyrolysis is carried out in an oxidizing atmosphere. 

The DTA shows a small endotherm at 140 °C consistent with the boiling point of propanoic acid (141 C) however, the insignificant mass loss suggests that only traces of free acid remained in the sample. A second endotherm at 245 is accompanied by a sharp mass loss of 24 %. A third larger endothermic mass loss occurs at 330 °C. The carboxylate-alumoxanes prepared by Kimura et al (13) showed similar endothermic mass losses (220 - 260 and 300 - 500°C). However, in contrast to the carboxylate-alumoxanes prepared from boehmite the second endotherm occurred over a larger temperature range. The reasons for this difference are at present unclear. 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

The siloxides of aluminum can be prepared in the same manner as the alkoxides and exhibit similar structural features. Interest in these compounds arose from a desire for sol-gel or polymeric precursors for aluminosilicates. Unfortunately, these compounds extensively hydrolyze, losing most of the silicon as the silanol. However, the investigation of the hydrolysis of (Et3SiO)3Al has generated considerable insight into the structure and composition of alkoxy- and siloxy-substituted alumoxane polymers, (ROAIO) . These macromolecules are now believed to have a structure related to that of boehmite. 

Conventional MAO has very low solubility in aliphatic solvents as well as poor storage stability in solution, which considerably limits its utility. Other more soluble and commonly used aluminoxanes are ethylaluminoxane and isobutylaluminoxane, which are synthesized by the partial hydrolysis of triethyl-aluminum (TEA) and triisobutylaluminum (TIBA), respectively. However, these alkylaluminoxanes do not perform as well as MAO in metallocene-mediated olefin polymerization. " It was reported, however, that tetrakis(isooctyl) alumoxane [(i-octyl)2—O—Al-(i-octyl)2], prepared by reaction of Al(i-octyl)3 with 0.5 equiv of water, exhibits remarkable cocatalytic activity, comparable to or even greater than that obtained with MAO, for ethylene polymerization catalyzed by racemic an5a-bis(indenyl)-type zir-conocene dichlorides. Furthermore, commercial modified methylaluminoxanes (MMAO) available from... 

Recently, the sol-gel procedures for preparing alumoxane ceramics from car-boxylates of the general formula [Al(0)j (OH) ((X)CR)J , were analyzed. M(acac) complexes (M = Ca +, Mn +, etc.) can be incorporated into ceramics during the reaction. Metallic Co and Fe and their alloys, formed by hydrogen reduction of the corresponding nitrates, were dispersed in an aluminosilicate matrix. The matrix was synthesized from (BuO)2A10Si(OEt)3 by sol-gel reaction. This product possesses dielectric properties. Nanocomposites were formed that contain -20 nm particles and possess magnetic properties (Fig. 14). ... 

Furthermore, while some of the carboxylate-alumoxanes formed gels in THF only those with long chain substituents (e.g., dodecanoic acid) and hence low ceramic yield were melt-processable. It would thus be desirable not only to prepare alumoxane preceramics in a one-pot bench-top synthesis from readily available starting materials, but also to determine if lower hydrocarbon substituents could yield better processability. 

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