Roles of mono- and di-functional organic salts as plasticizer and/or filler in styrene-based ionomers

The plasticization and/or filler effects of sodium salts of hexanoate (Na6), adipate (Na6Na), dodecanedioate (Na12Na), and dodecylbenzenesulfonate (Na12) on the dynamic mechanical properties of styrene-based ionomers were investigated. When a small amount of Na6, having one carboxylate ionic group at one end of alkyl chain, was added to a styrene-methacrylate ionomer, the salt acted as a very effective plasticizer for the ionomer cluster regions. With increasing salt contents, however, the salts became phase-separated and formed bilayer crystalline domains that acted as filler. In the case of the Na12Na and Na6Na salts, containing two carboxylate ionic groups, one at each end of alkyl chain, they formed phase-separated domains, acting as filler, in the methacrylate ionomers. Na12, possessing one sulfonate ionic group at only one end of a long alkyl chain, acted as a plasticizer in a sulfonated polystyrene ionomer. However, an excess amount of Na12 salt also formed phase-separated domains. It was also found that Na12 showed a filler effect only at much higher salt contents in comparison with Na6.