Monodisperse tert-butyl acrylate (tBA) oligomers of several lengths, functionalized at one end by a tertiary amine, were ionically grafted to lightly sulfonated polystyrene. Despite the oligomers being immiscible with the polystyrene matrix, dynamic mechanical analysis of the blends indicates only a weak phase separation effect, and the polymer is plasticized moderately. However, the blends (studied up to 30 wt %) are translucent, suggesting phase separation on a larger scale. A possible explanation is given in terms of nonspherical tBA domains subject to a hard-wall effect coupled with interfacial ionic interactions as well as ester-acid interactions. Evidence for the latter was noted in the infrared spectra.