The properties of poly(styrene-co-itaconate) ionomers were studied dynamic mechanically. It was observed that ionic moduli increased as ion content increased and that the increased ionic modulus values were comparable to those of well-clustered polystyrene ionomers. It was also found that only a very weak cluster loss tangent peak was present and that the shoulder-like peak shifted to higher temperatures with increasing ion content. This implies that the itaconate ionomers are weakly clustered materials. Also, the cluster T-g of the itaconate ionomers was found to be much higher than that of the well-clustered poly(styrene-co-methacrylate) ionomers, From these results, it was postulated that in the present ionomer system the ion hopping of the ion pairs in multiplets played an important role in determining the mechanical properties of the ionomers. The SAXS study showed that as ion content increased more ionic groups formed not at the prevalent distances, but very randomly, inferring that the multiplets in the present system were not in line with those in the EHM model. In addition, it was discovered that nonpolar plasticization was effective for the formation of more clustering, while upon polar plasticization, interaction between ionic groups became weaker, and thus a more distinct cluster loss tangent peak due to ion hopping was observed at lower temperature.