Solution properties of ionomers. I. Counterion effect

Abstract The effect of counterions on the solution properties of two types of ionomers, one based on sulfonated polystyrene and the other based on styrene–methacrylic acid copolymer, was studied by viscosity and light scattering measurements. It was found that the order of counterion binding of ionomers in a polar solvent and the order of aggregation of ionomers in a low‐polarity solvent were the same for the same ionomer system. However, the order for the sulfonated ionomer was Li < Na < K < Cs, whereas that for the carboxylated ionomer was the opposite. This can be explained by a difference in desolvation during anion–cation interaction and by considering site‐binding in a polar solvent and the association of ion pairs in a low‐polarity solvent. These findings for ionomer systems are parallel to the association behavior of small ions in water, cation affinity in crosslinked resins, and counterion binding of polyelectrolytes in water.