Inorganic-organic hybrid materials have been synthesized by reaction of tetraethoxysilane (TEOS), titanium tetrabutoxide (TBT) and silanol-terminated polydimethylsiloxane (PDMS). The hydrolysis and polymerization reactions of TEOS and PDMS in presence of TBT have been followed by means of FT-IR spectroscopy. Hydrolysis reactions have been characterized by Si-O-C and Ti-O-C bonds and polymerization reactions by Si-O-Si, Si-O-Ti and Ti-O-Ti bonds. The instantaneous hydrolysis of TEOS, the condensation reactions between Si OH groups forming crosslinked and linear Si-O-Si structures and the copolimerization reactions between Si-OH groups and PDMS molecules have been observed. The reaction between Ti-OH and Si-OH groups or PDMS gives Si-O-Ti bonds. Si-O-Ti bonds are formed during the addition step of TBT and they show a decrease along the reaction time up to gelling. By another hand, the concentration of crosslinked and linear Si-O-Si structures depend on the TBT concentration. High TBT concentration favors the formation of crosslinked chains. TBT influences the hydrolysis and copolymerization reactions between hydrolyzed TEOS and PDMS molecules. (C) 2003 Kluwer Academic Publishers.