Reaction of Titanium Isopropoxide with Alkanolamines and Association of the Resultant Ti Species

A clear alcoholic solution of titanium alkoxide with an addition of various alkanolamines is suitable for a sol-gel coating of titania films. The reaction of titanium isopropoxide, Ti(OPr ⁱ )₄ (TIP), with alkanolamines, such as triethanolamine (TEAH₃), diethanolamine (DEAH₂), and N-ethyldiethanolamine (EDEAH₂), and an association of the Ti species in the resultant mixtures were examined via liquid-state nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and cryoscopy measurements. Regardless of the kinds of the alkanolamines used, the IR and NMR spectra showed that alcohol exchange reactions occurred between the alcoholic moieties in alkanolamines and the isopropoxy groups in TIP, and that the N atom in the alkanolamines might be datively bonded to Ti. In the DEAH₂ and EDEAH₂ systems with the molar ratio of amine/TIP = 1, the results of the NMR and cryoscopy measurements showed that an association degree of the formed Ti species increased with an increase in the concentration of TIP, according to the thermodynamical equilibriums of associations between various oligomers. The increase was larger in the DEAH₂ system than in the EDEAH₂ one, because of the larger equilibrium constants due to the smaller size of the DEA group. In the system of EDEAH₂/TIP = 2, the NMR spectra showed that only one kind of oligomer was formed as a Ti species, independent of the concentration of TIP. The oligomer may be a much more stable species than other species. The cryoscopy results showed that the oligomer had a tetrameric structure.