Raman spectroscopic studies of acid dissociation in sulfonated polystyrene resins

FT-Raman spectra of sulfonated polystyrene resins with varying levels of sulfonation from 9–97% have been recorded. Molecular markers of –SO3H and –SO3- moieties have been proposed and used to determine quantitatively the degree of dissociation of the acids as a function of total sulfonic acid and sulfonate concentrations. Comparison with the ethanesulfonic acid/water system has been made and it is concluded that the low-sulfonation and high-sulfonation resins closely resemble this molecular acid/water system, but that intermediate sulfonation specimens are dissociated some 18% less than the corresponding ethanesulfonic acid/water analogues. This is ascribed to the presence of hydrogen-bonded acid groups with water in the gel region of the resins which had been suggested in previous infrared spectroscopic measurements.