The superior chemical stability of fluorine-carbon chemical bonds has been translated into the remarkable commercial success of the perfluoro sulfonate and carboxylate membranes such as Nafion, Flemion, etc. These and the more recent bilayer composites have revolutionized the energy-intensive chloralkali industry and made space-age fuel cells useful in orbit and feasible in electric automobiles. These materials are sufficiently good so that proposals to improve their performance must be viewed with alertness if not scepticism. The lack of permanent chemical crosslinks in these polymers limits the useful range of equivalent weight because the water uptake can be too high as the equivalent weight is decreased, or the electrical resistance can be too high as the equivalent weight is increased. The practical range has been 800 to 1500, with carboxylate on the cathode side of chloralkali cells. The new membrane will have independent control of swelling through the wide range of crosslink density available, and will permit the equivalent weight to be one-third to one-quarter of the figures cited above. Solvents and diluents may be used to influence the porosity and hence the flux rate. To prepare the membranes, selected monomers are copolymerized to form a precursor film of desired thickness, crosslink density, and functionality, and then the hydrogen atoms are replaced very carefully with fluorine atoms using F2 gas to retain the carbon skeleton as designed. The successful fluorination of films crosslinked with radiation and of elastoniers for geothermal and other severe enviornments has been previously reported.Anticipated Results/Potential Commercial Applications as described by the awardee:Higher ion exchange capacity and control of swelling by chemical crosslinks may substantially increase the energy efficiency of chloralkali cells and fuel cells and make new permselective devices practical. Vicinal carboxyl groups may increase selectivity of separations. Lower production costs should speed the development of automotive fuel cells. Nonionic versions of these materials may operate well above 120'C and thus allow membrane separations of corrosive industrial streams.
