Ionomers perfluorinated

There are a number of NMR reports on ion-exchange membranes of the Nafion type. In these ionomers, perfluorinated sulfonates are attached as pendant groups to PTFE backbones. Several of the publications [130-136]... 

Before discussing membrane chemical degradation in detail, the factors governing the degradation mechanism must be identified. Among three major types of membrane materials, hydrocarbon, partially fluorinated, and perfluorinated ionomers, perfluorinated sulfonic acid (PFSA) is the most widely used membrane material owing to its high chemical stability (Schiraldi 2006). 

The term chlor-alkali refers to those products obtained from the commercial electrolysis of aqueous sodium chloride. These are chlorine, sodium hydroxide, and sodium carbonate. The first two are produced simultaneously during the electrolysis while the latter is included because it is also produced in small quantities and shares many of the end uses of sodium hydroxide. Perfluorinated ionomer membranes are permeable to sodium ions but not the chloride ions, and hence they are useful for these electrolytic cells. The arrangement of a typical membrane cell is shown in Figure 10.2. 

Fujimura M., Hashimoto T., and Kawai H., Small-angle x-ray scattering study of perfluorinated ionomer membranes. 2. Models for ionic scattering maximum. Macromolecules, 15, 136, 1982. 

Du Font s Nafion membranes have been the first truly successful membranes in these applications. They are made of a perfluorinated and sulfonated polyal-kylene ionomer (-CFj- or >CF- throughout). Such a composition leads to... 

Ionomer membranes are used in fuel cells in order to separate the anode and cathode compartment and to allow the transport of protons from the anode to the cathode. The typical membrane is Nation , which consists of a perfluorinated backbone and side chains terminated by sulfonic groups. In the oxidizing environment of fuel cells, Nation , as well as other membranes, is attacked by reactive oxygen radicals, which reduce the membrane stability. Direct ESR was used recently in our laboratory to detect and identify oxygen radicals as well as radical intermediates formed in perfluorinated membranes upon exposure to oxygen radicals [73,74]. The three methods used to produce oxygen radicals in the laboratory and the corresponding main reactions are shown below. 

M. Seko, S. Ogawa, and K. Kimoto, in Perfluorinated Ionomer Membranes, ACS Symposium Series 180, American Chemical Society., Washington, D.C. (1982), pp. 365 110. 

Gebel, G. and Lambard, J. 1997. Small-angle scattering study of water-swollen perfluorinated ionomer membranes. Macromolecules 30 7914—7920. 

Xie, T., Hayden, C., Olson, K. and Healy, J. 2005. Chemical degradation mechanism of perfluorinated sulfonic acid ionomer. In Advances in materials for proton exchange membrane fuel cell systems, Pacific Grove, CA, Feb. 20-23, abstract 24. 

Atkins, J. R., Sides, C. R., Greager, S. E., Harris, J. L., Pennington, W. T., Thomas, B. H. and DesMarteau, D. D. 2003. Effect of equivalent weight on water sorption, PTFE-like crystallinity, and ionic conductivity in bis[(perfluoroalkyl) sulfonyl] imide perfluorinated ionomers. Journal of New Materials for Electrochemical Systems 6 9-15. 

Yang, J. C. and Kyu, T. 1990. Kinetics of phase separation of Nafion perfluorinated ionomer and poly(vinylidene fluoride) blends. Macromolecules 23 182-186. 

For instance, the Dow experimental membrane and the recently introduced Hyflon Ion E83 membrane by Solvay-Solexis are "short side chain" (SSC) fluoropolymers, which exhibit increased water uptake, significantly enhanced proton conductivity, and better stability at T > 100°C due to higher glass transition temperatures in comparison to Nafion. The membrane morphology and the basic mechanisms of proton transport are, however, similar for all PFSA ionomers mentioned. The base polymer of Nation, depicted schematically in Figure 6.3, consists of a copolymer of tetrafluoro-ethylene, forming the backbone, and randomly attached pendant side chains of perfluorinated vinyl ethers, terminated by sulfonic acid head groups. °... 

Nafion ionomers were developed and are produced by the E. I. DuPont Company. These materials are generated by copolymerization of a perfluorinated vinyl ether comonomer with tetrafluoroethylene (TEE), resulting in the chemical structure given below. 

A lesser number of papers have appeared regarding the carboxylate version of Nafion, and the works of Yeager et al., - Seko et al., and Perusich et al. ° are of special note. Nafion-like carboxylate materials have also been reported." These similar materials will not be discussed here, as the exclusive emphasis is on the stronger-acid sulfonated versions because this critical review is within a collection of articles in which perfluorinated ionomers are considered within the context of fuel cells. 

The DuPont Nafion materials, both sulfonate and carboxylate varieties, are not entirely unique, as similar perfluorinated ionomers have been developed by others such as the Asahi Chemical Company (commercial name Aciplex) and the Asahi Glass Company (commercial name Flemion). The comonomer chemical structures of and further information on these materials are given in the recent review article by Doyle and Rajendvan. Now commercially unavailable, but once considered a viable alternative, the Dow Chemical Company developed a somewhat similar perfluorinated ionomer that resembled the sulfonate form of Nafion except that the side chain of the former is shorter and contains one ether oxygen, rather than two ether oxygens, that is, —O—... 

Other reviews of the literature on Nafion and similar perfluorinated ionomers have appeared over the years. The early book (1982) by Eisenberg and... 

Scheme 1. Structure of the perfluorinated ionomer membrane (Nafion ).

Ionomers - pONOMERS] (Vol 14) - [OLEFIN POLYMERS - POLYETHYLENE - LOW DENSITY POLYETHYLENE] (Vol 17) -in food packaging FOOD PACKAGING] (Vol 11) -perfluorinated FUEL CELLS] (Vol 11)... 

Other perfluorinated ionomer membranes, chemically very similar to Nafion, are also available commercially. Aciplex, manufactured by the Asahi Chemical Company, is very similar to Nafion, except that it has perfluoropropanesulfonic acid side chains. Flemion (Asahi Glass Company), in contrast, possesses perfluorobutanoic acid functions. 

Fig. 2 Different orange-red luminescent layers for O2 sensing, a Indicator layer containing the tris(4,7-diphenyl-l,10-phenanthroline)ruthenium(II) dye adsorbed on CPG particles embedded in a poly(dimethylsiloxane) film [8]. b Perfluorinated (Nation) ionomer membrane doped with the same cationic dye. Although the former appears as a homogeneous material, even under the optical microscope, the luminescent indicator is actually sitting down in various domains as evidenced by its emission kinetics profile [9]...

A. Eisenberg, and H. L. Yeager (eds.), Perfluorinated Ionomer Membranes, The American Chemical Society, Washington, DC, 1982. 

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