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 pol ymerizations initiated by tertiary amines, shows inconsistencies in results reported by several authors. Both first-order and autocatalytic expression s have been used to fit experimental results. In the former case, significa ntly different values of apparent activation energies were found in isother mal and nonisothermal experiments. A simple kinetic model is proposed to ex plain 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 ex plains both the first-order and autocatalytic behaviors reported in the lit erature. It also leads to the experimental values of the apparent activatio n energies obtained under different conditions. It is also shown that isoco nversional methods should not be applied to obtain fundamental kinetic para meters in systems where the reaction rate depends on the concentration of a n active species that varies independently of the conversion of functional groups. (C) 1999 John Wiley & Sons, Inc.