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Small-angle X-ray scattering profiles of the ethylene and styrene ionomers were studied to clarify the structure of ionic aggregates as a functions of the nature of cations, acid content, and degree of neutralization. The ionic cluster peak was observed for the ionomers with a certain degree of neutralization. The scattering profile of the ionic cluster peak was analyzed by the modified hard-sphere model proposed by Yarusso and Cooper , and the size of ionic aggregates, closest approach distance between the aggregates, and average system volume per ionic aggregate were obtained. The size and distance of the ionic aggregates in the ionomers with monovalent cation, sodium and potassium cations, increased with the ion content (acid content × degree of neutralization), while those with divalent one, zinc and copper cations, and trivalent one, ferric cation, changed only slightly. The number of cations in an ionic aggregate was evaluated in an approximate manner by using the average system volume per ionic aggregate and the density of ionomer or the size of the ionic aggregate and the density of the ionic aggregate estimated by a simple additivity rule for each phase.

SynopsisThe annealing effect of ethylene ionomers annealed at various temperatures and for various periods was studied by differential scanning calorimetry. Two endothermic melting peaks were observed for all the ethylene ionomers annealed. The melting peak at the lower temperature, which was assigned to bundlelike crystal owing to a Hoffman-Weeks relationship, shifted to a higher temperature with the annealing temperature and period, indicative of recrystallization.There is physical cross-linking consisting of ionic aggregates, such as multiplets and clusters in ethylene ionomers. The crystallization kinetics of ethylene ionomers was fundamentally similar, but different from that of low-density polyethylene. Crystallization and recrystallization suggested a mobile ethylene chain in both amorphous regions and ionic aggregates even in the presence of cross-linking.