Ionomeric blends of poly(ethyl acrylate-co-4-vinylpyridine) with metal-neutralized sulfonated poly(ethylene terephthalate) .4. Effects of counterions

This is the fourth part in a series of studies on the ionomer blend system of poly(ethyl acrylate-co-4-vinylpyridine) with metal neutralized sulfonated poly(ethylene terephthalate). The focus of this work was to investigate the influence of counterions of the ionomers on the phase behavior and the ultimate mechanical properties of the blend system. The counterions examined included the group I and II metals Li+, Na+, and Ca2+ and the transition metals Co2+, Ni2+, CU2+, and Zn2+. Specific interactions between the different metal-neutralized sulfonate groups and the vinylpyridine groups were proven by FTIR spectroscopy to exist for the transition metal counterions. As a result of these specific intermolecular interactions, compatible blends were achieved with the transition metal counterions whereas the group I and II counterions showed total immiscibility as evidenced by the glass transition behavior probed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). In addition, the mechanical properties of the compatible blends were significantly better than those of the immiscible blends, probably due to the lack of interfacial adhesion in the latter. The modulus and tensile strength of the Ca2+-containing blend showed some enhancement compared to the group I metal-containing blends, and this could arise from the presence of some interfacial interactions in it. The degree of property enhancement was found to be a complex function of the nature, strength, and extent of the transition metal complexation between the polymeric components. The crystalline phase in terms of the crystallization kinetics and crystalline morphology of the PET ionomers was strongly influenced by the presence of different counterions and their interactions with the vinylpyridine-containing polymer. The observed modifications provide indirect evidence for the compatibility of the blend system.