Biphasic polystyrene ionomers neutralized by bifunctional organic counterions

Abstract

The evidence for biphasic morphology in lightly sulfonated polystyrene (PS-SSA) ionomers neutralized by bifunctional organic cations (namely, 1,6-hexanediamine or HDA) is established by comparing their dynamic mechanical behavior, as a function of ion content and degree of neutralization, with that for metal-neutralized biphasic ionomers. The trends as a function of ion content regarding the transition temperatures and intensities of the HDA-neutralized ionomers parallel what is observed for metal-neutralized ionomers, in particular polystyrene-based ones. A small-angle X-ray scattering peak, identified as an “ionomer peak”, is observed in the PS-SSA-HDA ionomer of the highest ion content studied. Furthermore, it was observed that partial neutralization affects the cluster phase more strongly than the matrix phase. This can be explained by the contribution of the acid groups to the matrix T_g, and their ability, when present in large amounts, to affect the ionic interaction strength or facilitate ion hopping, which influences primarily the cluster T_g.