FT-IR Study of the Hydrolysis and Polymerization of Tetraethyl Orthosilicate and Polydimethyl Siloxane in the Presence of Tetrabutyl Orthotitanate

In this work, we have used FT-IR spectroscopy to study the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) and polydimethyl-siloxane (PDMS) in the presence of tetrabutyl orthotitanate (TBOT). These reactions are used for obtaining SiO₂-PDMS-TiO₂ organically modified silicates (Ormosils). In order to obtain semi-quantitative information about such reactions, a deconvolution procedure of the FT-IR spectra has been done by use of a computer program. Hydrolysis reactions have been characterized by Me-O-C (Me = Si, Ti) bonds, and polymerization reactions by Me-O-Me bonds. Instantaneous hydrolysis of TEOS has been observed, together with condensation reactions between Si-OH groups, which give crosslinked and linear Si-O-Si structures. The TBOT is also hydrolyzed, but the high acid concentration inhibits condensation reactions between Ti-OH groups. The PDMS also condenses mainly with Si-OH groups and probably with Ti-OH, finally forming Me-O-PDMS bonds. The formation of Si-O-Si crosslinked structures and also Me-O-PDMS structures continues until the end of reaction. The gelling time is dependent on TBOT concentration in the reaction medium and, therefore, polycondensation reactions are dependent on TBOT concentration.