PREPARATION OF THIN PERFLUOROSULFONATE CATION-EXCHANGER FILMS BY PLASMA POLYMERIZATION

Perfluorinated, ultrathin polymer films containing sulfonic acid group s were prepared by plasma polymerization of trifluoromethanesulfonic a cid and hexafluoropropylene. Electron spectroscopy for chemical analys is and Fourier transform infrared spectroscopy measurements indicated that the sulfonic acid groups were fixed to the backbone chain of the perfluorinated polymer. The structure of the plasma polymer was strong ly dependent on the applied RF power. At high levels of applied RF pow er, the sulfonic acid groups of the starting material were easily deco mposed during plasma polymerization. The perfluorinated cation-exchang er films prepared at low applied RF power were about 1 mum thick and f ree from pinholes. The films showed high cation permselectivity, as co nfirmed by a K+ ion transference number of 0.99 in aqueous KCl solutio n.