BACKGROUND: The reinforcement of elastomers by the addition of fillers is one of the most important aspects in rubber science and technology. In order to optimise the filler – polymer interface, innovative in situ generation of silica within isoprene rubber was carried out by means of a bottom-up approach through a sol – gel process starting from tetraethoxysilane as silica precursor. The main aim was the study of the effect of the silica concentration and of the presence of coupling agent on the morphology and the dynamic mechanical behaviour of the composites.RESULTS: The in situ generated silica particles were homogeneously dispersed in the vulcanised rubber with dimensions from a few nanometres to the submicrometre scale. In the presence of coupling agent a good polymer – filler adhesion was observed. The dynamic mechanical behaviour was nonlinear for silica contents higher than 20 wt%. In this range of compositions silica exerted a marked reinforcement on the low-amplitude storage modulus, which is related to the silica content according to the Huber–Vilgis model.CONCLUSION: Isoprene rubber can be effectively reinforced by the in situ generation of silica for silica contents higher than 20 wt%, and the interaction at the silica – rubber interface can be optimised by using suitable coupling agents.