OXYGEN PERMEATION IN PERFLUORINATED IONOMERS BASED ON THE REACTION WITH THE METHYLVIOLOGEN CATION RADICAL - AN ESR AND OPTICAL STUDY

The methylviologen dication MV2+ was reduced photochemically to its cation radical in water and in perfluorinated membranes, in the presence of Ru(bpy)3(2+) as a sensitizer. The radical presence and concentration were determined from electron spin resonance (ESR) and optical spectra. The disappearance of the radical due to reaction with oxygen was used as a basis for the study of oxygen permeation through membranes swollen by water, methanol, and ethanol. The permeation coefficients for the swollen membranes are considerably larger than for polymers that do not contain ionic groups, indicating the importance of the solvent in the transport properties of the membranes. This result is an indirect proof for the connectivity of the ionic domains in the membranes. In membranes with long and short pendant chains the permeability coefficient is highest in membranes swollen by ethanol and lowest in membranes swollen by water. The enhanced permeability of oxygen in membranes swollen by the alcohols is related to the plasticizing effect of the solvent and is in agreement with recent F-19 NMR studies of dynamics in swollen membranes. The results also indicate that the major factors affecting oxygen transport are the presence and nature of the solvent and not the length of the pendant groups.