Polystyrene-based ionomers possessing sodium methacrylate (MA) and sodium styrenesulfonate (SS) units in each polymer chain [poly(styrene-co-methacrylate-co-styrenesulfonate) (PSMA-SS)] were synthesized. The dynamic mechanical properties of PSMA-SS ionomers were studied and compared with those of styrene ionomers containing only MA (PSMA ionomer) or SS (PSS ionomer) units. It was observed that the ionic moduli of PSMA-SS ionomers depended directly on the total ion content and that the ionic modulus was highest for the PSMA ionomer and lowest for the PSMA-SS ionomer. The matrix Tgs of the three ionomer systems were found to be similar to each other; the cluster Tg of PSMA-SS ionomer was higher than that of PSS ionomer at low SS contents but became closer to each other at high SS contents. In addition, the small-angle X-ray scattering study revealed that the multiplet size might be in the following order: PSMA-SS > PSS > PSMA. This implied that at the same ion content, the fractions of cluster regions were smallest for PSMA-SS ionomer in comparison with those of PSS or PSMA ionomers. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012