A method to determine the recombination/disproportionation rate during the polymerization of styrene is described. In this method, a perfluorinated azo initiator used to prepare a perfluorinated polystyrene was first synthesized. Then, the recombination/disproportionation rate was calculated by comparing the number-average molecular weight (DP(n)) and the fluorine content in weight of this resulting polystyrene.