Molecular Interpretation of Miscibility in Polyamide-6 Blends with Alkali Ionomers of Sulfonated Polystyrene.
Blends of polyamide-6 with lithium ionomers of 9.8 and 5.4 mole percent sulfonated polystyrene, formed by combining solutions of these polymers, are miscible over a wide compositional range, but those with the equivalent sodium ionomers are not. The molecular origin of this difference is addressed by studying the far infared and infrared spectra of the blends and pure materials to follow changes in the interactions between the cations and their surroundings, and changes in the interactions between functional groups. Based on analysis of these spectra, a molecular level interpretation of the blending is proposed. The initial step involves both the interaction of one amide carbonyl with an Li+ ion and simultaneous hydrogen bonding between an amide NH and a sulfonate group. This eventually leads to formation of an Li(>CO)+n(n ∼ 4) entity while the sulfonates are converted to the acid form through hydrogen bonding to the amide NH groups. The Na+ ion does not interact strongly enough with the amide groups to leave its sulfonate environment to a significant extent.