A series of polystyrene (PS)/SiO2 nanocomposites were prepared. Silica nanoparticles with an average diameter of 16 nm were used, and treated with dimethyldichlorosilane, while their weight fraction varied from 4 up to 10%. The viscoelastic-thermomechanical properties of the nanocomposites and their interrelation with the material's structure were studied with various experimental techniques. Scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, and tensile testing at three different temperatures were applied. The stress-strain curves at 85 degrees C, where the material's viscoplastic response is manifested, were simulated through a plasticity model, developed in previous works. The 4% weight fraction was found to be the optimum one for the enhancement of the thermornechanical properties. (c) 2007 Wiley Periodicals, Inc.