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.
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.
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