Aggregation of the ionic groups in blends of sulfonated polystyrene (SPS) with ethyl acrylate/4-vinylpyridine and styrene/4-vinylpyridine copolymers was investigated by dynamic mechanical thermal analysis (DMTA) and small-angle X-ray scattering (SAXS). Viscoelastic measurements show the existence of a high-temperature loss peak, similar to the peak observed in ionomers. However, the temperature of the transition is depressed relative to the parent ionomers due to internal plasticization. The presence of ionic aggregates was confirmed by calculating the average network functionalities and by the failure of frequency-temperature superposition. Activation energies for the high-temperature transition are related to the relative strengths of the interactions, which is consistent with the transition being due to motion of the ionic groups. SAXS measurements show that the "ionic peak" present in ionomers is destroyed upon blending. The data are discussed in terms of models for ionomer morphology.