An adaptive calorimetric method, coupled with state estimators for emulsion copolymerization, is shown to provide accurate, on-line information on the evolution of the composition and kinetics of an emulsion copolymerization. This method was evaluated for the emulsion copolymerization of methyl methacrylate-vinyl acetate (MMA-VAc) under nonisothermal conditions. In addition to providing on-line estimates of the number of moles of each polymerizing species in the reactor, the state estimator provides a value for a lumped kinetic parameter proportional to the product of (n) over bar N-p. This information can be combined with off-line measurements to study the evolution of polymerization kinetics and to explain the trends observed for the molecular weight distribution and glass transition temperatures. Values of (n) over bar were found to vary from 0.5 to 30 for the homopolymerization of MMA. However, the presence of VAc in the copolymerizing system drastically reduces (n) over bar. This can lead to a dramatic increase in the average molecular weight of the copolymer since it alters the ratio of propagation to termination in the polymerizing particles. (C) 2000 John Wiley & Sons, Inc.