Effect of preferential plasticization on the crystallization of lightly sulfonated syndiotactic polystyrene ionomers

The incorporation of 2.2 mol % sodium sulfonate groups along the backbone of syndiotactic polystyrene dramatically inhibits crystallization from the melt. However, small amounts of a surfactant, such as sodium dodecylbenzenesulfonate (DBSNa) may be used to selectively plasticize the ionic domains of sulfonated polystyrene ionomers. On the basis of Na-23 SSNMR results and the dynamic mechanical behavior of these ionomers, this preferential plasticization is postulated to perturb the electrostatic interactions within the ionic multiplets (i.e., electrostatic cross-links), destabilize the dynamic network, and thus increase the molecular mobility of the crystallizable chain segments. With enhanced chain mobility, a higher degree of crystallinity and an elevated rate of crystallization are observed. In contrast to the effect of DBSNa, the incorporation of phenyldodecane or sodium benzenesulfonate (i.e., the separate nonpolar and polar components of DBSNa, respectively) into the ionomer does not significantly affect the electrostatic network or enhance crystallization of sulfonated, syndiotactic polystyrene.