Crystallization kinetics of EMAA ionomers neutralized with zinc, and sodium cations

Random copolymers of ethylene and methacrylic acid (EMAA), in which some acid groups are partially neutralized with metal cations, form an important class of ionomers. Because of the strong energetic mismatch between the polar ionic groups and the nonpolar hydrocarbon backbone, these polymers generally exhibit microphase separation into ionic-rich domains. Prior calorimetric studies have demonstrated that both the cation type and the degree of neutralization have a strong impact on the crystallization behavior of EMAA ionomers. Long-term studies have also shown that, even after the main crystallization stage, secondary crystallization continues to progress for many years without reaching equilibrium. In this study, we use fast scanning calorimetry (FSC) to examine Zn- and Na-neutralized EMAA, enabling quantitative evaluation of their crystallization kinetics across six orders of magnitude in time. The FSC results allow us to derive a universal relationship describing the primary crystallization kinetics of these materials. Additionally, FSC uncovers the mechanism and rate of secondary crystallization, offering new understanding of the prolonged structural evolution in EMAA ionomers.