In situ rubber nanocomposites prepared via reactive batch mixing and via reactive extrusion were studied. Materials produced via reactive batch mixing showed a significantly higher silica content for a similar reaction time as compared to previously prepared in situ nanocomposites using a diffusion process under static conditions, but an approximately 10% lower modulus over the strain range investigated (0.5-1000%). While the microstructure of the nanocomposites using static conditions was homogeneous with monosized silica particles, the structure of the composites obtained via reactive batch mixing was significantly different, consisting not only of single silica particles but also of aggregates and densely packed silica regions. The nanocomposites obtained via reactive extrusion had a maximum loading of 3.2 wt% silica, possessed a uniform dispersion of silica particles and a similar modulus (approximate to 120 kPa) as conventional nanocomposites, prepared by mixing silica and rubber, containing 10 wt% silica and a coupling agent. (C) 2015 Published by Elsevier Ltd.