New organic-inorganic hybrid materials were prepared by the sol-gel process. Simultaneous polymerizations of methyl methacrylate (MMA) and an organically modified silicon alkoxide, 3-glycidyl oxypropyltrimethoxysi lane (GLYMO), with varying MMA/GLYMO molar ratios, were performed. Poly (oxypropylene)diamine was used as an epoxy opening agent, as basic catalyst for GLYMO condensation and as poly(methyl methacrylate) (PMMA) crosslinking agent. Chemical reactions and the structure of prepared hybrids were Studied by means of Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and by scanning electron microscopy (SEM). Depending on the ratios of organic and inorganic components hybrids showed either a discrete microstructure or interpenetrating polymer network (IPN) structure. Silsesquioxane (SSQO) structures formed as a result of GLYMO hydrolysis and condensation in the sol-gel process influence the glass-transition temperature of PMMA. The hybrids have much better thermal stability than PMMA, their surfaces are more hydrophilic than PMMA and they may have potential as damping materials. (C) 2009 Elsevier Ltd. All rights reserved.