Perfluorinated ionomer Nafion

Industrial production of perfluorinated ionomers, Nafion membranes, and all perfluorinated membranes is costly due to several factors first, the monomers used are expensive to manufacture, since the synthesis requires a large number of steps and the monomers are dangerous to handle. The precautions for safe handling are considerable and costly. Secondly, the PSEPVE monomer is not used for other applications, which limits the volume of production. The most significant cost driver is the scale of production. Today, the volume of the Nafion market for chlor-aUcali electrolysis (150,000 m year ) and fuel cells (150,000 m year ) is about 300,000 m year resulting in a production capacity of 65,000 kg year. When compared to large-scale production of polymers like Nylon (1.2 x 10 m year ), the perfluorinated ionomer membrane is a specialty polymer produced in small volumes. 

The F and NMR resonances of the perfluorinated ionomer, Nafion, are assigned to their corresponding chemical groups using 2D C- F... 

A miniature, needle-type glucose sensor based on a tri-layer membrane configuration has been prepared and evaluated both in vitro and in vivo. The perfluorinated ionomer, Nafion, was used as a protective, biocompatible, outer coating, and poly(o-phenylenediamine) as an inner coating to reduce interference by small, electroactive compounds. Glucose oxidase immobilized in a bovine serum albumin matrix was sandwiched between these coatings. Heat curing of the assembled sensor at 120 C improved the stability of the Nafion layer and extended the sensor lifetime. 

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

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 ).

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. 

Figure 3.43. Structure of Nafion-115 at ambient humidity derived from small-angle X-ray spectroscopy. The lighter areas are cluster structures in the material. (Reprinted with permission from J. Elliott, S. Hanna, A. Elliott, G. Cooley (2000). Interpretation of the small-angle X-ray scattering from swollen and oriented perfluorinated ionomer membranes, Macromolecules 33, 4161-4171. Copyright American Chemical Society.)...

Nafion, an insulator perfluorinated ionomer, has also been successfully used for preparing CNT-based electrodes [108,109]. It results in a good material for confining CNTs on an electrode substrate and also has capabilities of CNT solubilization and ion-exchange properties. 

Perfluorinated ionomers have reached a high level of industrial importance due to their outstanding performance as membranes in applications such as chior-alkali cells and fuel cells (1). The Nafion material synthesized by duPont more than twenty years ago... 

Self-diffusion coefficients of polyvalent cations in these perfluorinated ionomer membranes have not been reported. It can be inferred from the use of the sulfonate membranes as Donnan dialysis devices that transport of cations such as CuflT), Mg(II), and Al(III) under a concentration gradient is rapid. Also, column chromatographic separation of the alkaline-earth ion is readily accomplished with a powdered Nafion perfluorosulfonate polymer, which is again an indication of facile diffusion of these cations within the polymer phase. 

A good measure of past and continuing interest in ionomer membranes issued from the development of perfluorinated ionomers, the first-announced being Nafion(44). These materials are characterized by remarkable chemical resistance, thermal stability and mechanical strength, and they have a very strong acid strength, even in the carboxylic acid form. The functionalities that have been considered include carboxylate, sulfonate, and sulfonamide, the latter resulting from the reactions of amines with the sulfonyl fluoride precursor. 

Perfluorinated ionomers such as Nafion are of significant commercial importance as cation exchange membranes in brine electrolysis cells ( 1). Outstanding chemical and thermal stability make this class of polymers uniquely suited for use in such harsh oxidizing environments. The Nafion polymer consists of a perfluorinated backbone and perfluoroalkylether sidechains which are terminated with sulfonic acid and/or carboxylic acid functionality. 

In a previous paper (2), the author described a method to dissolve the sulfonyl fluoride precursor form of a perfluorinated sulfonate ionomer. Commercially available forms of Nafion are supplied as activated membranes (i.e., saponified from the precursor to the ionic form), and near-quantitative reconstitution of the precursor functionality (such as RSOjF) must first be performed using a chemical reagent such as SF. f4) before dissolution in perhalogenated solvents is possible. Besides adding to the cost of membrane manufacture, SF. is extremely toxic and corrosive and must be handled in nickel alloy pressure equipment. Therefore, a method for dissolving perfluorinated ionomers directly would be more desirable. 

T.D. Gierke, G.E. Munn and EC. Wilson, Morphology of Nafion perfluorosulfonated membrane products, as determined by wide- and small-angle X-ray studies, J. Polym. Sci., Polym. Phys. Ed., 1981, 19, 1687-1704 W.Y. Hsu and T.D. Gierke, Elastic theory for ionic clustering in perfluorinated ionomers, Macromolecules, 1982, 15, 101-105. 

FIGURE 9. Chromatographic separation of alkali metal ions using 1200 EW Nafion at 25 °C. Reprinted with permission from H. L. Yeager, in Perfluorinated Ionomer Membranes (Eds. A. Eisenberg and H. L. Yeager), Chap. 3,... 

MAJOR APPLICATIONS Nafion is the DuPont trademark for its family of perfluorinated ionomers, that is, resins and membranes. Asahi Chemical Industry Company produces Aciplex and Asahi Glass Company, Ltd., Japan, produces Flemion both are competitive products to Nafion in form and function. These perfluorinated ionomers are used in a variety of applications, the largest of which are as an ion exchange resin and in membrane separators in the commercial electrolysis of brine to produce caustic and chlorine. Nafion membranes are also being used in the development of fuel cells and as heterogeneous super acid catalysts in supported, cubed, or powdered form. 

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