This paper reports the first quantitative reconciliation of imaging and scattering data for poly(styreneran-styrenesulfonate) (P(S-SS x )) ionomers. We examined the morphology of solvent-cast and spin-cast P(S-SS 0.019 )-M ionomers using the combination of scanning transmission electron microscopy (STEM) and X-ray scattering, where the scattering data were fit with a liquidlike hard-sphere model. Both the ionic aggregate sizes (R 1 ) and the sample volume per ionic aggregate (V P ) as measured by both techniques were in good agreement. In addition, STEM found that P(S-SS 0.019 ) ionomers prepared by spin-casting exhibit nanometer spherical ionic aggregates that are indistinguishable in size, shape, and spatial distribution from the bulk solvent-cast ionomers. Six P(S-SS 0.019 )-M ionomers fully neutralized with various cations have ionic aggregate compositions that are predominately ionic, and the ionic aggregate radius (R 1 ) increases as the cation radii increases. Finally, the influence of copolymer type was studied by comparing P(S-SS 0.070 ) and P(S-MAA 0.072 ) ionomers. The ionic aggregates in P(S-SS 0.070 )-Cu are surrounded by a thicker region of limited mobility and are more ionic as compared with P(S-MAA 0.072 ) ionomers. Although STEM and X-ray scattering have been reconciled for these P(S-SS x ) ionomers, a broad application of the liquidlike hard-sphere scattering model is not recommended. However, when STEM and X-ray scattering are reconciled, detailed morphological information can be extracted from the scattering data, particularly regarding the composition of the ionic aggregates, which is important for understanding the mechanisms of ion transport.

The blend miscibilities of deuterated polystyrene (dPS) and sulfonated poly(styrene-ranstyrenesulfonate) (P(S-SS)) are examined by using forward recoil spectrometry (FRES) to probe the intermixing of bilayer films. This method directly determined the equilibrium coexistence compositions for dPS:P(S-SS x ) blends where the degree of sulfonation (x) ranged from 0.2 to 2.6 mol %. In the temperature range 150-190 °C, FRES profiles reveal full miscibility for x e 0.2 mol % and complete immiscibility for x g 2.6 mol %. Partial miscibility exists in dPS:P(S-SS x ) blends with x ) 0.7, 1.0, and 1.2 mol %, where between 150 and 190 °C the coexisting compositions show upper critical solution temperature (UCST) phase behavior. Blend interaction parameters, χ blend , are calculated using the Flory-Huggins theory and the coexisting compositions of the partially miscible bilayers. The copolymer blend theory estimates the styrene-styrenesulfonate segmental interaction parameter to be extraordinarily large, χ S/SS g 25. While the applicability of mean-field approaches is limited in this profoundly incompatible system, recent theories about random copolymers have established criteria for "selfdemixing" due to their inherent compositional variations. Our estimate of the monomer-monomer interaction parameter suggests the potential for demixing in P(S-SS x ) random copolymers that possess even a narrow distribution of compositions.

Elastic recoil detection (ERD) was used to characterize the phase behavior of blends involving neutralized poly(styrene-ran-styrenesulfonate) ionomers (P(S-SS x )-M) and deuterated polystyrene (dPS). The lightly sulfonated ionomers (acid mole fraction x ) 0.007) were neutralized with various cations (M): sodium (Na + ), barium (Ba 2+ ), and zinc (Zn 2+ ). The dPS:P(S-SS 0.007 )-M blends have a higher upper critical solution temperature (UCST) than the dPS:P(S-SS 0.007 ) blends, indicating that neutralizing the acid copolymer reduces blend miscibility. The UCST is higher when P(S-SS 0.007 ) is neutralized (125%) with divalent cations, Ba 2+ and Zn 2+ , rather than with a monovalent cation, Na + . In addition, as the level of neutralization increases from 25% to 125%, the miscibility in the dPS:P(S-SS 0.007 )-Zn blends decreases; this was not observed in the dPS:P(S-SS 0.007 )-Na blends. Complementary linear viscoelastic measurements were performed on a copolymer and ionomers with a higher acid content. Upon neutralization, the storage moduli at lower frequencies indicate slower polymer chain relaxations and the self-assembly of ionic functional groups. The specific interactions that produce these physical cross-links also impede blend miscibility.