AbstractAn approach for the estimation of kinetic parameters in emulsion copolymerization systems is presented. This approach is based on an algorithm for parameter estimation in differential equations and uses the time evolution of the conversions of the monomers in chemically initiated seeded emulsion copolymerizations. The approach is used to estimate the kinetic parameters of a mathematical model useful for predictive work. This mathematical model includes material balances for the monomers, population balances for particles containingiradicals and the free radical balance in the aqueous phase. Analysis of the variability of the parameters of the model during polymerization showed changes as large as 18% in the values of the parameters. These values were mainly due to changes in the particle size rather than to a shift in the composition of the reaction mixture. Combination of the present approach with methods for both parameter estimation in emulsion homopolymerization and estimation of reactivity ratios in emulsion copolymerization systems allows a reasonable good estimation of these varying kinetic parameters as constant parameters. Additionally, it was found that when the dependence of the parameters on the particle size was included in the estimation process, the parameters of the model were accurately estimated.