An equation that relates the glass transition temperature, T" and a binary interaction parameter, , for miscible binary polymer blends was derived. The equation including no adjustable parameters was based on a thermodynamic mixing formalism using enthalpy as the thermodynamic parameter. The enthalpy of mixing was written as a van Laar expression, and the Tt was formally treated as a second-order Ehrenfest transition. The equation satisfactorily predicts T,-composition curves for miscible binary polymer blends that exhibit either positive or negative deviation from a linear mixing rule, depending on the strength of the interaction. Good agreement was found between calculated and values experimentally determined by equilibrium melting point depression and inverse gem chromatography.

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Blends of a lightly sulfonated polystyrene (10.1 mol % sulfonation) neutralized with zinc (ZnSPS) and nylon-6 (N6) were found to be miscible over the entire compositional range. Miscibility was a consequence of transition metal complexation between the metal sulfonate and the amide groups. Melting point depression data gave a value for the polymer-polymer interaction parameter of = -1.3, which indicates very strong intermolecular interactions. FTIR and SAXS analyses indicated that the polyamide effectively solvated the ionic associations in the blends.

The block microstructure of a block copolymer ionomer, lightly sulfonated poly(6-styrene-6-(r-ethylene-co-r-butylene)-6-styrene) (S-SEBS), was investigated by small angle X-ray scattering. Sulfonation level was varied from 0 to 12 mol % of the polystyrene blocks and the sulfonic acid derivatives and Na and Zn salts were studied. Compression molded samples had a deformed spherical domain structure, and the extent of microphase separation was influenced by ionic aggregation that occurred in the sulfonated polystyrene domains. The extent of microphase separation decreased with increasing sulfonation level and with increasing strength of the ionic interactions, i.e., Na+ > Zn2+ > H+. Solution-cast samples exhibited a lamellar microstructure for the Zn salts and a spherical microstructure for the Na salts. Samples swollen with a paraffinic oil that plasticizes the rubber phase exhibited a spherical domain structure with a cubic arrangement of the domains. The development of microphase separation, however, decreased with increasing ionic strength of the ion dipoles.

Solid-state NMR was used to establish the specific intermolecular interactions responsible for the miscibility of blends of nylon 6 (PA6) and the zinc salt of lightly sulfonated polystyrene (Zn-SPS) and to characterize the scale of molecular mixing. 13C CP/MAS spectroscopy identified the interpolymer interaction as a complex between the Zn2+ cation of the ionomer and the amide nitrogen. Measurements of the spin-lattice relaxation times, TiH and 7\,H, indicated that mixing of the two polymers in the amorphous phase occurred at least down to a size scale of 2 nm. Ti"H measurements also revealed a microphase of >2.5-3.5 nm in the neat ionomer, which is consistent with the size of ionic domains inferred from previous small-angle X-ray (SAXS) measurements. Adding PA6 to Zn-SPS reduced the microheterogeneity in the ionomer as measured by Tlp.

Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the phase behavior and interactions of blends of the free acid derivative and lithium and sodium salts of lightly sulfonated polystyrene (MSPS) with Bisphenol A polycarbonate (PC). The blends exhibited upper critical solution temperature (UCST) phase behavior and a miscibility window with respect to the sulfonation level. At a fixed blend composition, a minimum in the cloud point temperature occurs at the sulfonation level marking the middle of the miscibility window. The miscibility window depended on the sulfonate cation used. No interactions involving either the carbonate carbonyl group or the sulfonate groups were detected for any of the blends. Miscibility was attributed to intramolecular repulsive interactions within the ionomer.

The morphology and phase behavior of blends of a lightly sulfonated styrenic block copolymer ionomer and poly(caprolactone) (PCL) were investigated by small-angle X-ray scattering and differential scanning calorimetry. Miscibility of PCL in the ionomeric microphase was enhanced due to exothermic interactions between the sulfonate groups and the polyester. In the blends, PCL exhibited unique crystallization behavior due to the effects of miscibility and the restriction imposed by the microdomains. The addition of PCL also changed the microstructure of the block copolymer from a less ordered, elongated spherical morphology to a well-defined lamellar arrangement.