29Si and 17 O NMR investigations on Si-O-Ti bonds in solutions of diphenylsilanediol and titanium-tetra-isopropoxide

Abstract

The structural units in diphenylsilanediol/titanium-isopropoxide solutions with molar ratio Si:Ti between 1:0.1 and 1:5 were examined by means of 29Si and 17O NMR. The main component in solutions with molar ratio Si/Ti = 1:0.1 is the chain-like octaphenyltetrasiloxanediol. With increasing Ti-isopropoxide content (1:0.25-1:0.5) Si - O - Ti units of the spirocyclic titanosiloxane Ti[O5Si4(C6H5)8)] 2 prevail in the solutions accompanied by the chain-like tetrasiloxanediol. The 29Si NMR spectra of 1:1 solutions indicate a lot of different Si containing building units with chemical shifts mainly between -40 and -46 ppm. The signals with a chemical shift between -40 and -46 ppm are probably caused by Si atoms which are connected via oxygen bridges directly (Si - O - Ti) or indirectly (Si - O - Si - O - Ti) with titanium. Contrary to the 1:1 solutions only one or two different species with Si - O - Ti units are present in high Ti-alkoxide containing solutions (1:5). 29Si and 17O NMR results reveal a quick hydrolysis of the Ti - O - Si bonds to titanium-oxo-hydroxo-polymers and phenylsiloxanediols or their isopropyl esters after the addition of water to the solutions. This separation into species only containing either Ti - O - Ti or Si - O - Si bonds can entail a decreased homogeneity of the reaction products on a molecular level.