Pre-Resonance Raman Characterization of Metal-Organic Films from Titanium Alkoxide Carboxylate Complexes
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PRE-RESONANCE RAMAN CHARACTERIZATION OF METAL-ORGANIC FILMS FROM TITANIUM ALKOXIDE CARBOXYLATE COMPLEXES CHARLES D. GAGLIARDI, DILUM DUNUWILA, AND KRIS A. BERGLUND Michigan State University, Department of Chemical Engineering and Center for Fundamental Materials Research, East Lansing, MI 48824.
ABSTRACT Metal-organic films were produced at ambient temperatures and pressures by the controlled hydrolysis of carboxylic acid and titanium isopropoxide mixtures. Pre-resonance Raman spectroscopy was used to study the effect of the organic acid chain length upon the nature of the resulting film. Propionic, butyric, valeric, hexanoic, and octanoic acids were studied, resulting in a proposed correlation between film quality and certain spectroscopic features of the alkoxide carboxylates. The choice of the carboxylic acid and the presence of an appropriate amount of water were shown to be critical in the development of a good film.
INTRODUCTION Coating materials produced from the controlled hydrolysis of titanium alkoxide carboxylates offer additional versatility and performance over standard sol-gel films. Two patents exist for the manufacturing of acyl-group-containing polymeric titanium compounds from titanium alkoxide and carboxylic acid precursors [1]. In the first of these patents [2], the alkoxide and carboxylic acid mixture is heated under reflux, followed by the removal of alcohol and alkyl ester by distillation. Under these conditions the only water present is that produced by the generation of the alkyl ester, and the resulting polymer is dependent upon the molar ratio (Ra) of alkoxide to acid [1,2]. Thus, [-0-Ti(OR)(OCOR']n, [-O-Ti(OR)(OCOR')-O-Ti(OCOR')2-]n, and [-O-Ti(OCOR')2-]n represent the polymeric structures resulting from Ra values of 2.0, 2.5, and 3.0, respectively. In the second patent [3], the alkoxide is first reacted with the carboxylic acid, and is then hydrolyzed with additional water. The byproducts of the reaction are removed by distillation as in the first patent, and the polymeric product is reported to have the structure [-O-Ti(OH) (OCOR')-]n. The materials produced by these methods have found wide application as highly refractive coatings for glass and other substrates, and water-resistant, protective films. The materials currently under investigation do not require refluxing at elevated temperatures or the removal of reaction byproducts by distillation; the procedure is thus more direct and cost effective. The resulting films are likewise optically transparent and water resistant. In the two patents previously referenced, longer chain length carboxylic acids are preferred. In the current work, relatively short chain length acids are the objects of study.
MATERIALS AND INSTRUMENTATION The titanium isopropoxide and the carboxylic acids (propionic, butyric, valeric, hexanoic, and octanoic) were obtained from the Aldrich Chemical Company and used without further purification. The microscope slides, which were used as substrates for the films, were standard, pre-cleaned slides manufactured by
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