AbstractThe far‐infrared spectra of polystyrene methacrylic acid/(PSMA) ionomers have been investigated as a function of cation and ion‐site concentration to obtain spectroscopic evidence of domain formation. A far‐infrared band, due to the vibration of a higher‐order cluster, is found at 170 cm−1in Na+‐form PSMA. This band, which is observed in addition to the known cation‐motion bands, is assigned to the vibrations of aggregates involving many cations and anionic sites close together, and the results are discussed in light of ion aggre