A simple model to explain the complex kinetic behavior of epoxy/anhydride systems

A survey of the literature dealing with the kinetics of epoxy/anhydride polymerizations initiated by tertiary amines, shows inconsistencies in results reported by several authors. Both first-order and autocatalytic expressions have been used to fit experimental results. In the former case, significantly different values of apparent activation energies were found in isothermal and nonisothermal experiments. A simple kinetic model is proposed to explain these inconsistencies, based on the following steps: (a) a reversible reaction transforming an inactive initiator species into an active one, (b) a propagation step, and (c) a chain transfer step regenerating the active initiator (step not relevant to the kinetic analysis). The simple model explains both the first-order and autocatalytic behaviors reported in the literature. It also leads to the experimental values of the apparent activation energies obtained under different conditions. It is also shown that isoconversional methods should not be applied to obtain fundamental kinetic parameters in systems where the reaction rate depends on the concentration of an active species that varies independently of the conversion of functional groups.