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 o f syndiotactic polystyrene dramatically inhibits crystallization from the m elt. However, small amounts of a surfactant, such as sodium dodecylbenzenes ulfonate (DBSNa) may be used to selectively plasticize the ionic domains of sulfonated polystyrene ionomers. On the basis of Na-23 SSNMR results and t he dynamic mechanical behavior of these ionomers, this preferential plastic ization 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 ch ain segments. With enhanced chain mobility, a higher degree of crystallinit y and an elevated rate of crystallization are observed. In contrast to the effect of DBSNa, the incorporation of phenyldodecane or sodium benzenesulfo nate (i.e., the separate nonpolar and polar components of DBSNa, respective ly) into the ionomer does not significantly affect the electrostatic networ k or enhance crystallization of sulfonated, syndiotactic polystyrene.