Near infrared spectroscopy (NIR) was used to characterize the nature of specific interactions in blends of lightly sulfonated polystyrene ionomers (M-SPS where M = Zn+2, Mn+2, or Li+) and polycaprolactam (PA6). The assignments of the NIR overtone bands that arise due to the interactions between the cation of the ionomer, and the amide groups were made using spectra of model compounds. The relative populations of the different environments of the N-H groups were qualitatively determined by deconvoluting the NIR spectra into five absorbances representing hydrogen-bonded N-H in crystalline and amorphous phases and an ion-amide complex. The ion-amide complex was specific for the blends. The interpolymer interactions were sensitive to composition and temperature, but qualitatively the behavior was the same for all three ionomer salts investigated. (C) 2008 Wiley Periodicals, Inc.