Orientation and Relaxation Behavior of Ionomers.

Lightly sulfonated polystyrene with 6.1 mole percent sulfonate groups was studied using extended x-ray absorption fine structure spectroscopy (EXAFS) and small-angle x-ray scattering (SAXS). These materials, stoichiometrically neutralized with either zinc, nickel or cadmium, were also uniaxially stretched and changes in morphology were followed using these two techniques. Simulations of EXAFS patterns from the undrawn samples were consistent with a cation local coordination environment of sulfonate groups supplemented by a small number of water molecules, in contrast with results reported from previous studies. The oriented polymers showed distortions in the local environment for the nickel and zinc-neutralized materials, which was attributed to anisotropy of the ionic aggregates. The cadmium-neutralized material did not exhibit any change in the cation local environment with macroscopic elongation. SAXS patterns of the oriented zinc-neutralized materials were collected with the detection direction parallel to the draw direction. The interaggregate spacing did not change with draw ratio, which was extremely surprising. Yarusso model fits to the scattering patterns indicated that the aggregate radius was larger in the stretch direction versus the unstretched sample while the closest approach radius decreased slightly.