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 SiO 2 -PDMS -TiO 2 organically modified silicates (Ormosils). In order to obtain semiquantitative information about such reactions, a deconvolution procedure ORDER REPRINTS of the FT-IR spectra has been done by use of a computer program. Hydrolysis reactions have been characterized by Me -O-C (Me ¼ 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.

Se han preparado materiales híbridos por medio de reacciones de hidrólisis y condensación de alcóxidos de Si y Ti (TEOS y TBT, respectivamente) y de reacciones de copolimerización de éstos con polidimetilsiloxano (PDMS). Se han estudiado las citadas reacciones mediante espectroscopia FT-IR, desde el mismo comienzo hasta la obtención del material final. La hidrólisis del TEOS así como la autocondensación del os grupos Si-OH generados tanto para formar cadenas entrecruzadas como lineales se han seguido mediante las bandas situadas a 880, 1180 y 1150 cm -1 , respectivamente. La policondensación de dichos grupos con PDMS se ha seguido por la banda a 850 cm -1 . Por otro lado, la hidrólisis del TBT y la autocondensación de grupos Ti-OH se han seguido por la banda situada a 1130 y por la variación de la absorbancia en la región espectral 770-510 cm -1 , respectivamente. La formación de enlaces Si-O-Ti por condensación de grupos Si-OH y Ti-OH se ha seguido mediante la banda a 936 cm -1 . Los resultados obtenidos han mostrado que las reacciones de hidrólisis y policondensación dependen de la concentración de TBT en el medio de reacción. La formación de estructuras entrecruzadas de enlaces Si-O-Si se ve favorecida por el TBT, si bien por el contrario éste impide la reacción de copolimerización TEOS-PDMS. La autocondensación de grupos Si-OH y Ti-OH es muy rápida dando lugar a enlaces Si-O-Si y Ti-O-Ti, respectivamente. También se forman enlaces Si-O-Ti en los comienzos de la reacción, sin embargo éstos tienden a desaparecer en el transcurso de la misma. Finalmente se ha estudiado la variación de la concentración de cadenas cíclicas y lineales de PDMS durante toda la reacción. Palabras Clave: Ormosil, sol-gel, hidrólisis, condensación, FT-IR. FT-IR spectroscopy study of the reaction of obtention of hybrid materialsHybrid materials have been prepared in this work through the reactions of Si and Ti alkoxides (TEOS and TBT, respectively) and polydimethil siloxane (PDMS). These reactions have been studied by means of FT-IR spectroscopy during the whole reaction time. The hydrolysis of TEOS molecule has been followed by the 880 cm -1 band, and the self-condensation reactions through the 1180 and 1150 cm -1 bands. Polycondesation reaction between Si-OH groups and PDMS molecules has been followed by the 850 cm -1 band. On the other hand, the hydrolysis reaction of TBT and the self-condensation of Ti-OH groups have been followed by the 1130 and 770-510 cm -1 bands, respectively. Finally the condensation reaction between Si-OH and Ti-OH groups have been studied by the 936 cm -1 band. Results have shown that hydrolysis and condensation reactions are depending on TBT concentration. The formation of Si-O-Si cross-linked structures increases with the TBT concentrations in the reaction. The selfcondensation reaction of Si-OH grups or Ti-OH grous is very reapid forming Si-O-Si and Ti-O-Ti bonds, respectively. However, the Si-O-Ti bonds which are formed during the first moments of reaction are also rapidly broken due to H 2 O molecules or...

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