Is the kinetics of crosslinking polymerization the same on heating and cooling?

Abstract

Following our previous short communication, this study continues to explore the intriguing phenomenon of thermally initiated crosslinking polymerization (or curing) during continuous cooling. It is demonstrated that the polymerization on cooling can be successfully studied by using differential scanning calorimetry. Nonstoichiometric and stoichiometric reactions of diglycidyl ether of bisphenol A epoxy and m-phenylenediamine are chosen as examples of single- and multi-step kinetics. The differences in the kinetics are investigated by analyzing the activation energy, the preexponential factor, and the reaction model along with the glass transition temperatures. The analysis reveals that for the reaction in the nonstoichiometric system the kinetic parameters remain the same for heating and cooling as hypothesized for a single-step process. The multi-step stoichiometric polymerization demonstrates significantly different kinetic behavior for heating and cooling experiments. The obtained results accentuate the need of further kinetic studies of multi-step processes on cooling for the benefit of scientific and engineering communities.