23Na nuclear magnetic resonance (NMR) is used to observe the sodium cations in sulfonated polystyrene ionomers (NaSPS). Three NMR peaks are detected, corresponding to isolated ion pairs, aggregated ions, and hydrated ions. Peak intensities vary with sample composition and treatment and provide insight into the effects of these variables on the morphology of the ionomer. Ion distributions are systematically influenced by hydration treatment, sulfonation level, and neutralization level. Fully dried NaSPS at low ion content shows isolated and aggregated sodium ions. Once humidified, the single peak at 0 ppm characteristic of fully hydrated sodium ions indicates that all sodium ions in NaSPS are available for hydration. As the sulfonation level increases, the fraction of sodium ions held in isolated ion pairs decreases while the fraction of ionic species in aggregates increases. This coincides with a shift in the peak position of the aggregated sodium ions to lower frequency, indicative of increased quadrupolar interactions. Finally, as the neutralization level increases at a constant 3.4% sulfonate content, the aggregate peak shifts to higher frequency due to incorporation of the neutralizing agent, NaOH, into the aggregates. At very high neutralization levels, a separate NMR peak characteristic of phase-separated NaOH appears.

23Na nuclear magnetic resonance (NMR) is used to study the local environment of sodium cations in lightly sulfonated polystyrene ionomers (NaSPS). Solution casting is shown to have a significant effect on the local morphology of NaSPS. NaSPS with 1.7% styrenesulfonate groups cast from solutions of DMF or THF/water at low concentrations showed more aggregated ions than those samples cast from relatively nonpolar solvents such as THF and THF/methanol mixtures. No changes due to sample history were seen for more highly sulfonated samples (4.2% styrenesulfonate groups). The changes in morphology due to solution casting were shown to have some reversible character.

Ion content and molecular weight have been shown to affect the 23Na NMR spectra of monodisperse sodium-neutralized sulfonated polystyrene ionomers (MNaSPS). A new NMR peak at −2.7 ppm appears at ionization levels above 1.2% and molecular weights of a least 35 000; this peak is not present in polydisperse NaSPS. The fraction of NMR intensity due to this peak is relatively constant above M n ∼ 100 000. It is proposed that this peak is due to a distorted version of an isolated site. Along with the new −2.7 ppm peak, the monodisperse materials also have far fewer isolated ions than the corresponding polydisperse ionomers. It is possible that the greater chain uniformity of the monodisperse ionomers eliminates plasticization of the aggregates by the low molecular weight components and steric hindrances from the high molecular weight components and permits more complete aggregation of the ionic groups. The new NMR peak can be removed by casting from a cosolvent of THF/water, but not by casting from THF/methanol. Blending of two or more monodisperse materials in solution followed by annealing resulted in an NMR spectrum similar to that of a polydisperse material; however, the behavior of the blend without annealing did not replicate that of polydisperse NaSPS.

Polyurethanes containing pendant pyridine units were blended with various metal acetates and studied by small‐angle x‐ray scattering (SAXS) and extended x‐ray absorption fine structure spectroscopy (EXAFS) to better understand the microscopic effect of blending on these materials. An earlier investigation found a dramatic enhancement in mechanical properties after blending, which suggests at least two pyridine units were coordinating to a single cation. This coordination would enable the cation to act as a cross‐linking site, which could then cause the observed changes in mechanical properties. To determine the effect of complexation on the microphase‐separated domain structure, small‐angle x‐ray scattering patterns were collected. Neutralization with a metal acetate increased the scattered intensity, which can be explained by an increase in electron density contrast but may also have been due to an improvement in phase separation. The distance between lamellar domains was basically unaffected by the addition of metal acetate, with the exception of nickel acetate. In this instance the distance decreased, which was caused by an improvement of packing inside the hard segments. EXAFS at the nickel and zinc edges indicated that the same qualitative changes occurred in the local environments around both cations after blending versus the unblended acetates. The magnitude of the first shell peak in the radial structure function (RSF) increased significantly upon blending, a result that is difficult to rationalize. The higher shell peaks exhibited significant changes in position and magnitude upon blending, which indicates substantial local rearrangement around the metal cation These fundamental changes in the EXAFS spectra may have been due to complexation between the cation and the pyridine group, but the results were not conclusive. © 1994 John Wiley & Sons, Inc.

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