A Comparison of Sulfonate and Carboxylate Ionomers

A comparison of metal carboxylate and metal sulfonate ionomers based on identical polystyrene backbones was conducted, showing a substantial difference between these two ionomers. Sodium carboxylated and sodium sulfonated polystyrenes were synthesized containing 0.3-5.0 mol % ionic functionality. The softening behavior of the metal sulfonate ionomer suggests that strong ionic association persists to temperatures of 50°-100°C above that of the corresponding carboxylate ionomer. Similarly, the melt viscosities of the sulfonate ionomers at a given level of functionality are two to three orders of magnitude greater than those of the carboxylate analogues. Similar differences are observed in the solution behavior of these two ionomers. These results are attributable to greater polarization in the sulfonate ionomers, thereby providing stronger ionic association.