In this study, the reaction kinetics of asymmetric polymer-polymer interface was experimentally and theoretically studied. A new theological method correlating the change of theological property of reactive system with the conversion of the in situ formed copolymers was applied to study the reaction kinetics of PBT/epoxy. reactive system. Then, the new method was proved to be useful by comparing its results with that obtained from the conventional endgroup determination method. Moreover, the conversion of PBT/epoxy reactive system from theological method could be well fitted by the numerical analysis, from which the kinetic constant and the diffusion constant of epoxy in PBT could be determined simultaneously. (c) 2005 Elsevier Ltd. All rights reserved.