Differential scanning calorimetry (DSC) has been used to monitor the reaction between castor oil and isophorone diisocyanate (IPDI), using a non-isothermal method, at different heating rates. The NCO/OH ratio in these systems was 1, so that the concentration of NCO and OH groups could be considered equivalent during all the experiments. Despite the complexity of the system, in which different order kinetics are possible, as well as physically controlled diffusion processes, data were fitted to a simple kinetic model, of apparent order n, apparent activation energy EA, and apparent frequency factor A(0). The dependency of these parameters on heating rate was used to analyze kinetics of polymerization of these systems. (C) 2004 Elsevier B.V. All rights reserved.