Miscibility enhancement of aliphatic polyamides with other polymers through ion-dipole interactions

Polystyrene (PS), functionalized with various ionic groups, was blended with polyamides (PA) in order to investigate the effect of ion-dipole interactions on the miscibility of PS/PA blends. Sulfonic acid groups interact strongly with amides, but catalyze the hydrolysis of the amide bonds of the PA. The neutralization of the sulfonic acid groups eliminates this reaction in the blends, and when the counterion is lithium, strong miscibility enhancement is seen between the lithium sulfonated polystyrene (LiSPS) and polyamides-6 (PA-6), $-$66, $-$610 and $-$11. This miscibility enhancement increases with the lithium sulfonate content of the LiSPS and the amide content of the PA, and is also dependent on the blend composition. An equilibrium thermodynamic approach is used to describe the miscibility behavior of the LiSPS blends with PA-6. When the ionic group is sodium sulfonate, lithium carboxylate or sodium carboxylate, the miscibility enhancement is negligible. As a possibly better alternative to the PS ionomers as a blend component with PAs, novel sulfonated poly(styrene-ethylene-butylene)random ionomers were synthesised and characterized