A new morphological model for random ionomers is proposed which incorporates the findings of recent dynamic mechanical and X-ray scattering studies. The model is based on the existence of multiplets, which reduce the mobility of the polymer chains in their vicinity. The thickness of the restricted mobility layer surrounding each multiplet is postulated to be of the order of the persistance length of the polymer. Isolated multiplets act as large cross-links, 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 behavior and are termed clusters. The model is in good agreement with a very wide range of experimentally observed phenomena, especially those based on dynamic mechanical and X-ray scattering techniques.

The mechanical properties of some random styrene ionomers are investigated in order to determine the effects of the type of the ionic groups and their position relative to the polymer backbone. Previous studies have shown that increasing the distance of the ion pairs from the polymer backbone leads to larger multiplets and greater intermultiplet spacings in random styrene ionomers. In this study, the position of the ion pairs relative to the polymer backbone is shown to have a profound influence on the mechanical properties of the material. This is attributed to differences in morphology resulting from different extents of steric hindrance to ion-pair aggregation in each ionomer. The strength of the electrostatic interactions between ionic groups is governed by the type of the ionic species. Strong electrostatic interactions between ion pairs tend to give rise to relatively stable multiplets which act as cross-links even at relatively high temperatures. The modulus of the material in the rubbery region remains constant while the multiplets are stable but decreases with the onset of ion hopping. This provides some insight into ion-hopping kinetics.

The high‐temperature dispersions occurring in some poly (styrene‐co‐alkali methacrylate) ionomers are investigated by dynamic mechanical thermal analysis as a function of ion content. The heights and areas of the loss modulus peaks associated with these dispersions suggest that the ionic “cluster” phase becomes the dominant and perhaps even continuous phase above an ion concentration of ca. 6 mol %. Apparent activation energies of these high‐temperature transitions support the phase‐separated cluster model and indicate that the dispersions are true glass transitions.

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A simple method is reported for the post‐polymerization partial p‐carboxylation of linear polystyrene without degradation or crosslinking of the polymer. The method is based on Friedel–Crafts acetylation of the polystyrene under mild conditions, followed by oxidation of the acetyl groups by means of a phase‐transfer‐catalyzed haloform reaction. The method is well suited for the synthesis of high molecular mass, monodisperse ionomers with p‐carboxylate groups situated randomly along the polystyrene chain. © 1993 John Wiley & Sons, Inc.