Results of Monsanto rheometic studies and measurements of physical properties reveal that precipitated silica interacts chemically with epoxidized natural rubber (ENR) during high temperature (180 degrees C) molding and the extent of chemical interaction increases in the presence of silane coupling agent, namely N-3(N-vinyl benzyl amino) ethyl-gamma-amino propyl trimethoxy silane monohydrogen chloride. Fourier transform infrared spectroscopic studies show that silica is bonded to ENR through formation of Si-O-C bond, whereas in the presence of silane coupling agent, silica is bonded to the coupling agent through Si-O-Si bond, and ENR is bonded to the coupling agent through C-N-C bond formation.