ESR OF SOLUBLE NAFION AND NAFION MEMBRANES SPIN-LABELED VIA THE IONICBOND

Soluble perfluorinated ionomers (Nafion) were spin-labeled via the ion ic interaction between the pendant sulfonic group of the polymer and t he quaternary nitrogen of the deuteriated polar spin label. o)-2,2,6,6 -tetramethylperdeuteriopiperidine-N-oxyl iodide. . Electron spin reson ance (ESR) spectra of spin-labeled Nafion were measured in water, etha nol, formamide, and N-methylformamide solutions. Spin-labeled Nafion m embranes saturated by water and aqueous solutions of spin-labeled poly (styrene sulfonic acid) as the sodium salt were also studied for refer ence. The ESR spectra suggest reduced mobility of the label in aqueous solutions of Nafion compared to that of the free spin label in the ne at solvent. A smaller effect was observed for ethanol as solvent and p ractically no effect in formamide and N-methylformamide solutions. The results were rationalized by considering the specific influence of ea ch solvent on the solvophobicity of the ionomer backbone and on the in teraction between ion pairs. We suggest that the driving force for the self-assembling of perfluorinated ionomers in polar solvents is the s olvophobicity of the ionomer chains.