The microphase structure of ionomers based on an amorphous, maleated ethylene-propylene copolymer was investigated by using small-angle X-ray scattering (SAXS) and solid-state NMR experiments. It was shown that in this kind of ionomers grafted maleic anhydride, its salts with Zn 2+ and a fraction of EPM chain fragments form immobilized, ion-rich aggregates. Three types of EPM chain units with different mobility were detected in the ionomers and in the ionomer precursor, which can be attributed to chain units with low mobility forming aggregates surrounded by an interfacial layer, EPM network chains interconnecting these aggregates, and network imperfections such as dangling ends and chain loops. When the the degree of neutralization is increased, the average dimension of the immobilized aggregate remains almost constant, while the thickness of the interfacial layer with restricted mobility slightly increases. The size of the aggregates in MAn-g-EPM ionomers is significantly larger compared to other ionomers, and as a consequence, the number of acid groups within an aggregate is also larger. At 50% neutralization, the number of aggregates suddenly decreases. The changes in some macroscopic properties, such as compression set and tensile properties, are related to the morphology of the ionomers as determined by SAXS and NMR. When the degree of neutralization is increased, the properties of the materials change due to strengthening of the ionic aggregates.

The thermoreversible nature of the ionic associations in aggregates makes ionomers with a low glass transition temperature interesting candidates for thermoplastic elastomers. In this paper, a low-T g ionomer based on low molecular weight ethylene−propylene copolymers modified by maleic anhydride (MAn-g-EPM) is introduced, and the morphology of a series of ionomers, neutralized with Cs+, Na+, K+, Li+, Zn2+, Ba2+, and Mg2+, was investigated with small-angle X-ray scattering (SAXS). To determine the size and composition of the ionic aggregates, the observed SAXS peak was interpreted with the help of the Yarusso−Cooper model, which describes the ionomer morphology by spherical aggregates of the ionic species with a high electron density surrounded by a layer with a restricted mobility. The results from the ionomer precursors suggest that there is a critical concentration above which aggregation of the polar groups in the apolar matrix occurs. Upon increasing degree of neutralization, the average dimension of the aggregate remains almost constant, while the restricted mobility layer increases. The size of the aggregates is much larger in comparison to other ionomer systems, and as a consequence, the number of acid groups within an aggregate is much larger. For low degrees of neutralization, it was shown that the aggregates contain a large fraction of EPM fragments of at least 60 vol %. For the ionomers neutralized with divalent cations, it was observed that the morphology changes drastically beyond degrees of neutralization of 50%; the number of the aggregates decreases, and the size increases. This was explained with the help of the coordination mechanism.