Ionic interactions have been shown to enhance polymer-polymer miscibility in several highly dissimilar blend systems. In some cases, the miscibility is due to proton transfer from an acidic site on one polymer to a basic site on another, which leads to ion-ion interactions. Studies that have focused on the formation of ionomer blends from highly dissimilar materials, such as fluorocarbons and hydrocarbons or aromatics and aliphatics of widely differing glass transitions, have shown that in the absence of ionic interactions, these materials are immiscible. In this study, we have used Fourier transform infrared (FTIR) spectroscopy techniques, both qualitatively and semiquantitatively, to evaluate the extent of the proton-transfer mechanism in the enhancement of miscibility in perfluorinated acid copolymer/poly(ethyl acrylate) blends. The perfluorinated acid copolymer contains sulfonic acid groups, whereas the poly(ethyl acrylate) has been modified by the introduction of various amounts of 4-vinyl pyridine groups as comonomers in the polymer chains. The proton-transfer mechanism in this case consists of the transfer of the proton on the sulfonic acid group to the nitrogen on the pyridine group, forming a pyridinium cation and a sulfonate anion pair. FTIR has been used to distinguish between the pyridine and pyridinium groups through their absorption bands at 1416 and 1642 cm(-1), respectively. The relative intensities of these bands, as a function of the molar concentration of the pyridine comonomers in the blend, provides a direct quantitative indication of the extent of proton transfer occurring in the system. (C) 2003 Wiley Periodicals, Inc.