Anomalous Small-Angle X-ray Scattering from Nickel-Neutralized Ionomers. 1. Amorphous Polymer Matrices

Nickel-neutralized sulfonated polystyrene ionomers were examined by anomalous small-angle X-ray scattering (ASAXS) at the nickel K-edge. The intensity of the ionomer peak in the difference patterns, formed from SAXS patterns at two different energies, was shown to scale with the real part of the anomalous dispersion factor (f') and the fluorescent background with the imaginary part (f''). No change in the shape of the scattering patterns with energy was discernible, and the single-energy and difference patterns were found to be superimposable with appropriate scaling. These observations prove that both the ionomer peak and the upturn near zero angle are due to an inhomogeneous distribution of ionic repeat units throughout the material and not to precipitated neutralizing agent or microvoids. Debye plots of the intensity near zero angle were concave downward in all cases, contrary to the prediction of core-shell models of ionomer morphology.