CRITICAL ION CONCENTRATIONS FOR CLUSTERS IN SODIUM SULFONATED POLYSTYRENE IONOMERS

The critical ion concentration of sodium sulfonated polystyrene ionomer has been investigated by glass transition, NMR and viscosity measurements. It was found that the critical ion concentration was affected by the molecular weight. The critical ion concentration could be explained by using the linewidths and chemical shifts of Na-23+ NMR spectra. The Na-23+ linewidths of the ionomer solution increased with ion concentration, which could be explained in terms of a shift in the association-dissociation equilibrium between the Na+ and the counter-ion group of the polymer side chain. The reduced viscosity behavior also showed a consistent critical ion concentration.