DYNAMICS OF ION-EXCHANGE IN PARTIALLY SULFONATED POLYSTYRENE IONOMER SOLUTIONS AS MONITORED BY STOPPED-FLOW FLUORESCENCE MEASUREMENTS

Stopped-flow studies were used to investigate the transport of ionic materials in ionomers. The exchange of ionic materials in PS-1.7 ionomer solutions was approximated by a two-component, time-dependent diffusion model. This model is developed based on the shell - core structural model suggested by our prior work. The time-independent components were shown to be limited by the rates of ionomer and, hence, ion aggregate reorientations. The diffusion-limited, time-dependent components were interpreted as a consequence of the slow ion migration through the mantle of the aggregates. The invariance of exchange kinetics as ionomer concentrations were increased provides evidence to support the proposal that ion aggregates retain their intramolecular nature even at high concentrations where intermolecular forces dominate the rheological characteristics. The dynamics of polymer conformational adjustment was observed to be rapid upon the addition of a polar solvent, which acts to reduce binding forces in the ion aggregates. This rapid readjustment suggests a highly strained polymer backbone configuration in the aggregated state.