Abstract The radiation-induced polymerization of styrene was conducted under emulsion conditions in the presence of polybutadiene latex in an attempt to induce grafting and the results were compared with the corresponding chemically initiated system. The propagation rate constants, kp, for styrene estimated on the assumption of the Smith-Ewart theory and the activation energies derived from the temperature dependence were found to be in good agreement with the values reported in the literature. The grafting efficiency was also measured and the results are discussed in association with the molecular weight of the polystyrene chains on the basis of a simple model. This is presented to explain some aspects of the experimental results and to give clearer ideas of the reactions involved.