Perfluorinated Nafion

Kyu, T. and Yang, J. C. 1990. Miscibility studies of perfluorinated Nafion iono-mer and PVDF blends. Macromolecules 23 176-182. 

Perfluorinated Nafion ionomer/ PVDF blends Dimethylformamide, dimethylacetamide, l-Methyl-2-pyrrolidinone The spherulitic crystalline moiphology of PVDF showed strong dependence on the casting temperature and compositions. Mixed a- and y-forai crystals were obtained. DSC, SAXS, microscope, dielectric thermal analyzer (Kyu and Yang 1990)... 

The upper part of Fig. 2 shows the molecular structure of the perfluorinated Nafion cation exchange membranes with sulfonic acid as well as with carboxylic acid groups as fixed ions. These are covalently bonded at the end of side chains of the PTFE (polytetrafiuoroethylene) polymer backbone. The polymer has excellent chemical and thermal stability, similar to PTFE [9]. 

Baiagern et al. [8] assigned hydrolyzed poly(TEE-co-PSEPVE) chemical shifts through characterization of the prepolymer, the sulfonyl fluoride form of Nafion perfluoropolymer membrane (12). It was assumed that the chemical shifts of the prepolymer would closely match those of the final polymer since the structures are nearly identical. The perfluorinated Nafion prepolymer was characterized with i F-i F selective COSY and gradient crisis -HSQC (gc2HSQC). 

Among the various types of fuel cells listed in the preceding, the PEMFC, which uses a sheet of polymer membrane as the solid electrolyte, is the subject of this book. The solid polymer electrolyte membrane is the most important constituent of these fuel cells that allows protons, but not electrons, to pass through. These fuel cells currently use perfluorinated Nafion membranes (Du Pont), which exhibit a number of shortcomings to optimum efficiency. Also, the polymer membranes represent approximately 30% of the material cost of the fuel cell. The membrane in... 

T. Kyu arid J.-CK Yang, Miidbllity studies of perfluorinated nafion ionomers and poly (vinylidene fluoride) blends, Macromoleailes 23 176 (1990). 

To solve some of the environmental problems of mixed-acid nitration, we were able to replaee sulfuric acid with solid superacid catalysts. This allowed us to develop a novel, clean, azeotropic nitration of aromatics with nitric acid over solid perfluorinated sulfonic acid catalysts (Nafion-H). The water formed is continuously azeotroped off by an excess of aromatics, thus preventing dilution of acid. Because the disposal of spent acids of nitration represents a serious environmental problem, the use of solid aeid eatalysts is a significant improvement. 

Whereas superaeid (HF/BF3, HF/SbF, HF/TaF FS03FI/SbF3, etc.)-eatalyzed hydroearbon transformations were first explored in the liquid phase, subsequently, solid aeid eatalyst systems, sueh as those based on Nafion-H, longer-chain perfluorinated alkanesulfonic acids, fluorinated graphite intercalates, etc. were also developed and utilized for heterogeneous reactions. The strong acidic nature of zeolite catalysts was also successfully explored in cases such as FI-ZSM-5 at high temperatures. 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Nafion-H (144), a perfluorinated resin-sulfonic acid, is an efficient Bronsted-acid catalyst which has two advantages it requires only catalytic amounts since it forms reversible complexes, and it avoids the destruction and separation of the catalyst upon completion of the reaction [94], Thus in the presence of Nafion-H, 1,4-benzoquinone and isoprene give the Diels-Alder adduct in 80% yield at 25 °C, and 1,3-cyclohexadiene reacts with acrolein at 25 °C affording 88 % of cycloadduct after 40 h, while the uncatalyzed reactions give very low yields after boiling for 1 h or at 100 °C for 3.5 h respectively [95], Other examples are given in Table 4.24. In the acid-catalyzed reactions that use highly reactive dienes such as isoprene and 2,3-dimethylbutadiene, polymerization of alkenes usually occurs with Nafion-H, no polymerization was observed. 

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts. Mercuric oxide in the presence of an acid is also a common reagent. Since the addition follows Markovnikov s rule, only acetylene gives an aldehyde. All other triple-bond compounds give ketones (for a method of reversing the orientation for terminal alkynes, see 15-16). With allqmes of the form RC=CH methyl ketones are formed almost exclusively, but with RC=CR both possible products are usually obtained. The reaction can be conveniently carried out with a catalyst prepared by impregnating mercuric oxide onto Nafion-H (a superacidic perfluorinated resinsulfonic acid). ... 

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... 

Furthermore, the same sol-gel matrices have been used in a system where acid and base catalysis occur in the same pot without quenching either catalyst [29]. In this case, the acids were either entrapped Nafion (perfluorinated resin sulfonic super acid, a3) or entrapped molybdic acid (M03-Si02, a2), while the bases were two ORMOSILs (organically modified silica sol-gel materials), one with H2N (CH2)2NH(CH2)3 groups (bi) and the other guanidine base residues (b2) (Scheme 5.12). 

Nafion, a perfluorinated sulfonated polymer, is a typical example of an ion-exchangeable resin with high promise as a catalyst support. Its properties are significantly different from those of common polymers (stability towards strong bases, and strong oxidizing and reducing acids and thermal stability up to at least 120 °C if the counter ion is a proton, and up to 200-235 °C if it is a... 

Nafion-H, a perfluorinated sulfonic acid resin, is another strongly acidic solid that has been explored as alkylation catalyst. Rprvik et al. (204) examined unsupported Nafion-H with a nominal surface area of 0.2 m2/g (surface area of a swellable polymer is difficult to define) in isobutane/2-butene alkylation at 353 K and compared it with a CeY zeolite. The zeolite gave a better alkylate and higher conversion than Nafion-H, which produced significant amounts of octenes and heavy-end products. The low surface area of the resin and questions about the accessibility of the sulfonic acid groups probably make the comparison inadequate. 

The membrane, made from a perfluorinated polymer bearing sul-phonic acid groups, is known in the trade as Nafion . 

Their availability has greatly expanded the potential for electrolytic processes in synthesis and fuel cells as well as in environmental control. Perfluorinated cation exchange membranes such as Nafion outlast the material that preceeded them by up to four and a half years [48], Unfortunately very little has been published on their behaviour outside their use in chlor-alkali electrolysis. 

The reason for Nafion LB-film fabrication was the wish to obtain the highly ordered systems from perfluorinated ion exchange polymer with multilayered structure, where the ionic layers (conductors) would alternate with fluorocarbon polymer layers (insulators), and to investigate the properties of such films.74 This polymer contains a hydrophobic fluorocarbon polymeric chain and hydrophilic ionic groups, so it is sufficiently amphiphilic it has a comblike structure that makes it a suitable polymer for LB-film deposition. 

Peet, D.L. Austin, J.H. (1986) Nafion perfluorinated membranes operation in chlor-alkali plants. 

In Nafion, the hydrophobic perfluorinated segments of the polymer are incompatible with the hydrophilic sulfonic acid groups and thus phase separation occurs. When exposed to water, the hydrophilic domains swell to provide channels for proton transport, whereas the hydrophobic domains provide mechanical integrity and, at least in the case of lower lEC samples. 

Perfluorinated PEMs with sulfonic acid (la = Nafion, Flemion lb = Aciplex 2a = DOW, Hyflon-ion 2b = 3M, 2c = Asahi Kasei 3 = Asahi Glass) and b)s[(perfluoroalkyl sulfonyl] (4) groups for proton conduction. 

An alternative approach to the use of partially fluorinated systems to reduce the cost of fluorinated PEMs has been developed by DeSimone et al. a perfluo-rinated vinyl ether is copolymerized with a hydrocarbon monomer (styrene), sulfonated, and then subsequently fluorinated to replace existing C-H bonds with C-E bonds (Eigure 3.18). Thus yields the perfluorinated, cross-linked sul-fonyl fluoride membrane that can then be hydrolyzed to give the PEM (7). Because the membranes are cross-linked, considerably higher acid contents (up to 1.82 meq/g) are possible for these materials in comparison to Nafion, leading also to higher proton conductivity values. 

Gierke, T. D., Munn, G. E. and Wilson, F. C. 1981. The morphology in Nafion perfluorinated membrane products, as determined by wide-angle and small-angle x-ray studies. Journal of Polymer Science Polymer Physics 19 1687-1704. 

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