The elastic properties of organically modified silicates prepared by ultrasonics aided polycondensation of Tetraethoxysilane (TEOS) and Polidimethylsiloxane (PDMS) is studied by means of high resolution Brillouin spectroscopy. Our results evidence the micro-separation of the organic and inorganic phases for the systems with high content of polymer. We propose a mechanical model that qualitatively explains the observed variation of the elastic constant c11 vs. molar fraction of dimethylsiloxano (DMS) in these vitreous materials and develop a structural model that accounts for the observed dynamical behaviour.
	