MORPHOLOGICAL-STUDIES OF A TRIBLOCK COPOLYMER IONOMER BY SMALL-ANGLE X-RAY-SCATTERING

The block microstructure of a block copolymer ionomer, lightly sulfonated poly(b-styrene-b-(r-ethylene-co-r-butylene)-b-styrene) (S-SEBS) was investigated by small angle X-ray scattering. Sulfonation level was varied from 0 to 12 mol% of the polystyrene blocks and the sulfonic acid derivatives and Na and Zn salts were studied. Compression molded samples had a deformed spherical domain structure, and the extent of microphase separation was influenced by ionic aggregation that occurred in the sulfonated polystyrene domains. The extent of microphase separation decreased with increasing sulfonation level and with increasing strength of the ionic interactions, i.e., Na+ > Zn2+ > H+. Solution-cast samples exhibited a lamellar microstructure for the Zn salts and a spherical microstructure for the Na salts. Samples swollen with a paraffinic oil that plasticizes the rubber phase exhibited a spherical domain structure with a cubic arrangement of the domains. The development of microphase separation, however, decreased with increasing ionic strength of the ion dipoles.