AUGUST 20 - 24, 2000
Barron Research Group
Posters and Talks

Synthetic mechanisms for the formation of Methyl Alumoxane Co-Catalysts, Stephen J. Obrey and Andrew R. Barron*, Department of Chemistry, Rice University, Houston, TX 77005

The reaction of aluminum alkyls (AlR3) with tertiary group 14 alcohols (Ph3MOH) produce synthetic intermediates for the production of alkyl alumoxanes. Two distinct reaction mechanisms are observed dependent on the basicity of the group 14 alcohol. Reaction of acidic alcohols with AlMe3 proceed via alkane elimination to form an intermediate dimeric aluminum alkoxide which may decompose to methyl alumoxane by a Lewis acid catalyzed reaction. The reaction of basic alcohols with AlMe3 proceed through an exchange mechanism where the first step is a hydroxide transfer followed by alkane elimination to form methyl alumoxane. The structural characteristics of these intermediate pathways as well as their relationships to traditional synthetic methods will be discussed.

Application of Carboxylate-Alumoxane Non-Particles as Post-Process Infiltration, Surface Repair, and Strengthening Agents for Ceramic Bodies, Kimberly A. DeFriend Varela and Andrew R. Barron, Department of Chemistry, Rice University, Houston, TX 77005

A major problem with traditional "green body" ceramic processing is the significant shrinkage and therefore porosity exists in the finished ceramic body. The porosity is essential for the formation of CMCFC's, ceramic matrix ceramic fiber composite, by infiltrating with a pre-ceramic binder. A second problem with ceramic composites processed through traditional routes is the formation of a rough surface due to micromachining and the sintering step. We have investigated the application of carboxylate-alumoxane nano-particles through post-process infiltration and re-sintering as a solution to these problems by strengthening the ceramic body.

Infiltration of porous Al2O3 ceramic bodies and carbon composites with aqueous solutions of aceto-alumoxane (A-A) has been investigated. The effects of solution concentration (2-12%wt), number of infiltration dips, and the smoothing of the surface has been determined. ESEM, AFM, and elemental microprobe results will be presented along with an outline of the optimum conditions.

Influence of hydrogen bonding on alkane elimination of aluminum and gallium alkyls, Stephen J. Obrey and Andrew R. Barron*, Department of Chemistry, Rice University, Houston, TX 77005

The reaction of aluminum and gallium with simple alcohols and amines usually proceed by alkane elimination forming dimeric alkoxides and amides, respectively. In the case of hydrogen bonded diols and diamines, the reactivity is altered. In the reaction of (tBu)3Al with 2,2-dimethyl-1,3-propanediamine (DMPA), the expected alkane elimination is not observed. Rather the adduct (tBu)3Al·DMPA is formed. Upon heating (tBu)3Al·DMPA, alkane elimination is observed forming a [Al3(tBu)5(DMPA)2] complex. The reactivity and structural characteristics of these compounds as well as the influence of transition metal halides on the products formed will be presented

Reaction of Group 13 Chlorides with Mercury Dichloride, Alexander S.Borovik (a), Simon G.Bott (b), and Andrew R.Barron (a)*, Department of Chemistry, Rice University (a), Houston, Texas and Department of Chemistry, University of Houston (b), TX

Novel Lewis acid-base mercury (II) complexes featuring strong aromatic coordination toward mercury atom have been prepared by the reaction of HgCl2 with MCl3 (M = Al, Ga) in a variety of aromatic solvents. These new materials were found to be extremely efficient activators of CArñH bonds. The catalytic proton-deuterium exchange and the olefin addition to the aromatic ring will be discussed. Toluene, methylbenzene and o-xylene mercury complexes were characterized by X-ray crystallography.

Cement Hydration Inhibition, Maximilienne Bishop (a), Simon G.Bott (b), and Andrew R.Barron* (a), Department of Chemistry, Rice University (a), Houston, Texas and Department of Chemistry, University of Houston (b), TX
Tartaric acid, sucrose, and organophosphonates are known to retard cement hydration. The effects of tartaric acid, sucrose, and a phosphonic acid on the hydration of the main components of Portland Cement and the formation of ettringite were investigated in order to gain insight into the different mechanisms of hydration inhibition. It was found that the organophosphonate initially accelerates the hydration of the aluminate phase and the formation of ettringite, then halts the reactions completely for several hours. In addition, nitrilotris(methylene)triphosphonic acid enhances the dissolution of calcium oxide and subsequently precipitates a layered calcium phosphonate polymer. The structure of this material and the dissolution-precipitation mechanism are discussed with regard to cement hydration inhibition. Tartaric acid was found to be most effective at stopping hydration of the aluminate phases and formation of ettringite, with no initial acceleration period observed. In contrast, sucrose accelerates the formation of crystalline ettringite. The different hydration inhibition mechanisms that may be at work are discussed with possible application to the development of new retarders.

Molecular coupling layers formed by reactions of epoxy resins with self-assembled monolayers grown on the native oxide of aluminum, Christopher L. Edwards, Cullen T. Vogelson, Andrea Keys, and Andrew R. Barron. Department of Chemistry, Rice University, Houston, TX 77005

In order to produce molecular coupling layers, epoxy resins cross-linked with self-assembled monolayers (SAMs) grown on the native oxide of aluminum have been investigated. Initially, SAMs have been formed by the attachment of carboxylic acids RCO2H [R=C17H35, CH3, C6H4-3-Br, C6H4-3-OH, and C(NH2)(CH2)4NH2] to the native oxides of aluminum thin films on silicon substrates. In order to investigate the cross-linking reaction between carboxylate monolayers and an epoxide, grown monolayers of p-hydroxybenzoate and lysine were reacted with a mono-epoxy resin, 1,2-epoxy-3-phenoxypropane. The SAM systems have been characterized by XPS, EDX analysis, and contact angle measurements. In addition to these surface materials, aluminum oxide surfaces supporting either lysine or p-hydroxybenzoate monolayers were reacted in pairs with a di-epoxide (DER 332) to form an adhesive layer between the two surfaces. Finally, this epoxy-SAM interaction is shown to form a "molecular glue" type interface which has been characterized by SEM.

Lewis base exchange reactions of a monomeric aluminum, Laura van Poppel and Andrew R. Barron. Department of Chemistry, Rice University, Houston, TX 77005

Tert-butyl aluminum has been reacted with hydroquinone in an uncoordinating solvent to give an oligomeric species, Al(tBu)2(C6H5O2)n. In order to characterize this oligomer, it has been reacted with three coordinating solvents, pyridine, THF, and acetonitrile. [(tBu)2Al(THF)]2(C6H5O2) and [(tBu)2Al(C6H5N)]2(C6H5O2) monomeric species have been isolated and characterized using single crystal x-ray diffraction and 1H NMR. The tert-butyl gallium analogs have also been made and characterized by 1H NMR.

Reactions of Group 13 alkyls with benzoic acid derivatives. Catherine S. Branch1, Andrew R. Barron1, and Janusz Lewinski2. (1) Department of Chemistry, Rice University, (2) Warsaw Institute of Technology

Reactions of MtBu3 (M=Al, Ga) with salicylic and anthranilic acids have been shown to form the dimeric structures [(tBu2)M(µ-O2CC6H4-2-OH)]2, and [(tBu2)M(µ-O2CC6H4-2-NH2)]2, respectively. These structures have been characterized by X-ray crystallography, IR, and multiuclear NMR spectroscopy. Variable-temperature NMR has also been performed to investigate the ACSintramolecular hydrogen bonding between the carboxylate oxygen and the salicylate OH or anthranilate NH2 groups.

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