Ionic Aggregates in Zn- and Na-neutralized Poly(ethylene-ran-methacrylic acid)

The morphology of ionic aggregates in semi-crystalline Zn- and Na-neutralized poly(ethylene-ran-methacrylic acid) (EMAA) ionomer blown films has been explored with scanning transmission electron microscopy (STEM) and small angle x-ray scattering (SAXS). The ionic aggregates of Zn-EMAA are spherical, monodisperse and uniformly-distributed in as-extruded pellets and blown films prepared at low and high blow-up ratio. Thus, although the biaxial stresses of film blowing are sufficient to alter the PE superstructure, the ionic aggregates in Zn-EMAA are unaffected. In contrast, the morphology of Na-EMAA as detected by STEM changes from featureless in the as-extruded pellets to a heterogeneous distribution of Na-rich aggregates in the blown films. This transformation in Na-EMAA morphology is consistent with our earlier study of quiescent annealing suggesting that the morphological change is the result of thermal processing rather than the biaxial stresses of film blowing.