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The microphase structure of noncrystalline poly(ethylene-co-13.3 mol % methacrylic acid) (E-0.133MAA) ionomers was investigated by using infrared (IR) spectroscopic, X-ray scattering, differential scanning calorimetric (DSC), and dielectric measurements. The noncrystallinity was confirmed by small-angle X-ray scattering (SAXS) and DSC studies, which has enabled a quantitative analysis of the SAXS ionic peak associated with ionic aggregates without being perturbed by the polyethylene lamellae peak. In 60% neutralized Na ionomer, it was revealed that almost 100% of MAA side groups including unneutralized COOH are incorporated into the ionic aggregates with an average ionic core radius (R 1 ) of ∼6 A. The dielectric relaxation studies showed that the ionic aggregates form a microphase-separated ionic cluster. Analysis of dielectric strengths indicated the most (∼90%) of the COONa groups are present in the ionic cluster. On the other hand, in the 60% neutralized Zn ionomer, both SAXS and dielectric studies indicated that the ionic aggregates with R 1 ∼ 4 A are almost isolated and dispersed in the matrix; the formation of ionic cluster was not recognized. Similarly to partly crystalline E-MAA ionomers, all noncrystalline E-0.133MAA ionomers exhibited an endothermic peak at 320-330 K (labeled T i ) on the first heating, depending on the aging time at room temperature. Several factors that would be critical for the DSC T i peak were discussed. It was concluded that the DSC T i peak is certainly associated with changes of the state of ionic aggregate region.

The structure of ionic aggregates in commercially important ethylene ionomers was studied by small-angle X-ray scattering (SAXS). The samples examined were sodium and zinc salts of poly(ethylene-co-13.3 mol % methacrylic acid) (EMAA) ionomers, which were found to be noncrystalline unlike commercially available EMAA ionomers with lower MAA contents. Not only the model fittings but also the correlation function analyses can be employed on those ionomers because of their noncrystallinity. The results clearly showed that the structure of ionic aggregate in both sodium and zinc salt ionomers can be described by Yarusso and Cooper's liquidlike model. The number of ions per aggregate was estimated on the basis of simple space-filling discussion using the data of low-molecular-mass model compounds, which reveals that the ionic core of the ionic aggregate contains anionic side groups as well as ions, and in the partially neutralized sodium salts, unneutralized COOH groups are also incorporated into the ionic aggre...