The structure-property behavior of two series of new ionomers derived from well-defined block copolymers was investigated. The two types of triblock systems were either poly(tBMA-b-BD-b-tBMA) or poly(tBMS-b-S-t-BD-t-S-b-tBMA) (tBMA = tert-butyl methacrylate; BD = butadiene; S styrene; t = taper). The materials have been examined in the tert-butyl ester forms and also hydrolyzed (carboxylic acid) and neutralized to the cesium carboxylate salt. The ester precursor exhibits a morphological transformation upon neutralization in the case of a 9 mol % tBMA-BD triblock, from unoriented rodlike domains in the ester precursor to ion-containing spheroids in the ionomer. This transformation was observed by transmission electron microscopy (TEM) and also supported by the dynamic mechanical behavior of the respective systems. The introduction of styrene into the butadiene center block results in an increase in the glass transition temperature, as anticipated. However, the tapered nature of the center block in the styrenic materials promotes greater phase mixing, as supporting TEM and dynamic mechanical analysis (DMA) indicate. The composition of the center block in these tapered materials also alters the glass transition, as shown by DMA. In the tapered SBS cesium ionomers, the temperature of the transition to flow occurs at higher temperatures as the length of the ionic end block increases.