Acrylic copolymer- and 5% acrylic acid (AA) modified terpolymer-silica hybrid nanocomposites were synthesized by free radical bulk polymerization of ethyl acrylate (EA), butyl acrylate (BA) and acrylic acid (AA) with simultaneous generation of silica from tetraethoxysilane by sol-gel reaction. The pure polymers were analyzed by using Fourier Transform infrared (FTIR) spectroscopy and solid state nuclear magnetic resonance (NMR) spectroscopy. The hybrid samples were characterized by scanning electron microscopy (SEM), FTIR spectroscopy, NMR spectroscopy, dynamic mechanical, mechanical and thermal properties. SEM images confirmed the presence of nanosilica particles within the polymer matrices, whose dispersion and particle size distribution and visual appearance were dependent on the relative polarity (hydrophilicity) of the polymer matrices and the concentration of the filler. There was no evidence of strong chemical interaction between the polymers and the dispersed silica phase, as confirmed from the FTIR results. Terpolymer-silica hybrids demonstrated superior mechanical properties compared to the copolymer-silica hybrids. They also showed higher dynamic storage modulus and positive shift in the loss tangent peaks. The thermal stability of the nanocomposites was marginally higher which was possibly due to the dipolar interaction at the organic-inorganic interface. (c) 2006 Springer Science + Business Media, Inc.