Fourier-transform infrared (FTIR) spectroscopy was used to examine specific interactions contributing to the partial miscibility in blends of styrene-sodium methacrylate copolymer (S-NaMA) and poly (ethylene oxide) (PEO). From the shifts of carboxylate ion and ether group stretching bands, an important specific interaction was found involving ion-dipole bonding between the ionic group in styrene ionomer and the ether group in PEO. The asymmetric stretching vibration frequency of the carboxylate ion group increases as the fractional amount of PEO in the blend is increased, while the symmetric stretching frequency is decreased. The transition value of the fraction of PEO, above which both vibration frequencies of the carboxylate ion mentioned above remained almost unchanged, increases as the concentration of ionic groups in ionomer is increased. The ether group stretching band shifts to higher frequencies as the PEO content in the ionomer/PEO blend is increased. From the differential scanning calorimetry (DSC) and FTIR studies, we find that the ion-dipole interaction is the important mechanism that determines the miscibility of S-NaMA/PEO blends. (C) 1994 John Wiley & Sons, Inc.