Water absorption effects on the thermal transition and stiffness of ethylene ionomers

Abstract

Abstract Changes in the thermal transition and stiffness of ionomers occuring during aging or water absorption were investigated. Ionomers used in this study are Na, K, Mg, and Zn salts of poly(ethylene‐ co ‐methacrylic acid) (EMAA), whose methacrylic acid unit is 5.4 mol %. It was found that ionomer stiffness is subject to water absorption and the effect differs with the neutralizing cations. Water absorption effects on the thermal transition, measured by differential scanning calorimetry (DSC), indicate that there are no significant changes in the higher‐temperature endotherm assigned to a melting of polyethylene (PE) crystallities. However, the lower‐temperature endotherm, which we attribute to an order‐disorder transition of ionic aggregates ( T i ), exhibits significant changes upon water absorption. The mechanism of the water absorption effects on the thermal transition and stiffness is described. © 1995 John Wiley & Sons, Inc.