SMALL-ANGLE X-RAY-SCATTERING INVESTIGATIONS OF IONOMERS WITH VARIABLE-LENGTH SIDE-CHAINS

Small-angle X-ray scattering was used to investigate the morphology of random, styrene-based ionomers that have ionic groups placed at the ends of variable-length side chains. The SAXS peaks were interpreted as arising from interparticle interferences, and the changes in peak position with increasing side-chain length were attributed to increasing distances between the scattering centers. The decrease in the width of the SAXS peaks with increasing side-chain length was attributed to an increased organization of the ionic domains for the long side-chain ionomers. The Bragg spacing was found to increase linearly both with increasing side-chain length and with increasing average separation distance between the ionic groups. Furthermore, the radii of the ionic aggregates were found to be independent of the ionic content and limited in size by the proximity of the bulky polystyrene backbone. Since previous SAXS data from copolymers of polystyrene with cesium methacrylate are in excellent agreement with the morphological trends observed in this study, it is suggested that a morphological continuity exists for styrene ionomers that have their ionic groups placed very close to the backbone of ionomers with large separations between their ionic groups. By extension, the morphological continuity is suggested to also include the halato telechelics.