A new route to elaborate organic-inorganic hybrid materials is presented. It is based upon two successive steps, the former is the crosslinking of polymer which contains pendant ester groups such as poly(ethylene-co-vinyl acetate) (EVA) through ester-alkoxysilane interchange reaction in molten state in the presence of dibutyltin oxide as catalyst. The latter is the hydrolysis-condensation reactions of available alkoxysilane groups in the polymer network leading to the silica network co-grafted onto the organic network. More particularly the hydrolysis-condensation reactions in solid state leading to the silica network grafted and confined in the organic network are addressed in the present work. The progress of the hydrolysis-condensation reactions was investigated by gas chromatography, FT-IR spectroscopy, Si-29 solid NMR, volume swelling degree at equilibrium and dynamic mechanical analysis. Two side reactions have been evidenced leading to alcohol groups grafted onto EVA. The silanols and these alcohol groups can participate to hydrogen bonds between ester and silica domains. The organic - inorganic hybrids elaborated according to this new chemical route exhibit improved mechanical and thermomechanical properties with respect to the EVA while having an elastomeric behavior with respect to the nanocomposite synthesized by in situ polymerization of tetraethoxysilane. (C) 2003 Elsevier Ltd. All rights reserved.