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It is generally accepted that in random styrene ionomers the ion-pairs tend to associate to form small aggregates termed multiplets which are embedded in the polymer and act as crosslinks. At sufficiently high ion-contents, ion-rich regions termed clusters are believed to phase-separate from the polymer matrix. In this study, the dynamic mechanical properties of random styrene ionomers containing various concentrations of alkali-metal methacrylate groups were measured over a range of temperatures at several different frequencies. Two peaks are evident in the loss tangent (tan $ delta)$ vs. temperature curves, indicating that the materials are phase-separated, with each tan $ delta$ peak resulting from the glass transition (T$ sb{ rm g})$ of a separate phase. This hypothesis is supported by the magnitudes of the apparent activation energies determined in this study for each transition. The relative heights and areas of the tan $ delta$ peaks indicate that the cluster phase becomes dominant at ion contents above ca. 6 mol %, and that complete phase inversion occurs at relatively low ion-contents. This finding, together with the results of small-angle X-ray studies performed elsewhere, led to the development of a new model for the morphology of random styrene ionomers. The model is based on aggregation of ion-pairs to form multiplets. Each ion-pair in a multiplet effectively anchors the polymer chain to which it is attached, thereby forming a layer of polymer with restricted mobility surrounding the multiplet. Isolated multiplets act as large crosslinks, thus increasing the glass transition temperature of the material. As the ion content is increased, the regions of restricted mobility surrounding each multiplet overlap to form larger contiguous regions of restricted mobility. When these regions become sufficiently large, they exhibit phase-separated behaviour and are termed clusters. The model is in good agreement with a very wide range of experimentally observed p