4.2. The membranes on the basis of perfluoralkansulfoacids.

Since 1960 the research regarding synthesis of fluorine containing ion-exchange membranes was started for the purpose of creating of diaphragms for fuel elements (electricity generation by interaction of hydrogen and oxygen on catalysts, applied on electrodes), used according to airspace programme. In 1972 "Du Pont" company created such corrosion and acid resistant membrane on the basis of perfluoralkanesulfo-acid under the trade mark Nafion. The structure of Nafion is the following:

The last mentioned one allowed to increase operating temperature of the element and its capacity [191]. Later this acid had found an application in Olah works  as solid strong acid in organic synthesis [192].

The synthesis of such membranes consists of several stages. In the beginning perfluorovinyl monomer with sulfofluoride group is obtained, which later is used for turning into ionogenic group. After that co-polymerization of this monomer with tetrafluorethylene is carried out. [193].

The using of sultones allowed authors of the work [194] to develop the new creating methodology of polymer electrolytes, which are successfully used for production of lithium batteries. The obtaining scheme of such materials is the following:

The electroconductivity of lithium salt of poly(2-oxo-diflluoroethylenesulfonyl)imide  (LiPI) is high (6*10^-3 S*cm^-1) and this salt  is a high dissocated poly-anion.  This polymer is compatible with matrix made of polyesters.

The intermediate sulfofluoride is used for obtaining of different monomers, containing sulfo-groups, for example, SO₂F, SO₃H, which are used for obtaining of copolymers with such monomers as ethylene oxide and its derivatives. [195].

Such polymers are applied as solid electrolytes (electroconductivity is about 10^-5-10^-6 S * cm^-1. That makes them interesting materials, which properties are similar to Nafion-H.

The heating of tetrafluoroethane disulfofluoride with liquid ammonia in presence of sodium methylate give the salt H(Na)NSO₂CF₂CF₂SO₂N(Na)H, this salt together with HN(SiMe₃)₂ produces Me₃Si(Na)SO₂CF₂CF₂SO₂N(Na)SiMe₃. This compound polymerizes accompanied trimethylfluorosilane elimination with FSO₂CF₂CF₂SO₂F, producing new ionic polymer -[CF₂CF₂SO₂N(Na)SO₂]-n. The membranes on the basis of such polymers appeared to be rather effective.

The creation of such membranes allowed to proceed from mercury method of sodium chloride electrolysis to non-mercury one at obtaining of caustic alkali. Electrochemical and mechanic properties of membranes have a decisive influence on economy of the electrolysis process using ion-exchange membranes. From this point of view the membranes on the basis of sulfoacids have a number of drawbacks, which decrease, if you use membranes, which along with sulfogroups have carboxyl groups. High density of these groups usually exists on applied membranes, because the higher is the volume capacity, the easier is the transferring process of gegenions (sodium ions) and the higher is the electroconductivity of membranes. The fields of appliction of such membranes are described in [4].

Conclusion

The author of this review had paid attention to relatively new class of organic compounds - the compounds, containing perfluoralkylsulfonyl group, as long as along with theoretical questions, connected with reveal of fluorine atoms influence on organic molecule properties and their use as model objects for solving the fundamental questions of organic reactions theory, many of materials on the basis of this class compounds have found a wide application.

The author thinks, that the new information gathering together, reveal of problems, facing fluor-organic compounds chemistry and reveal of primary tasks, which can recall chemists attention to this interesting and fast developing field of chemistry and also help specialists, working in the field of synthesis of new materials for technical purposes.

At the same time the author didn’t plan to give full and detailed review of perfluorinated sulphur-containing compounds chemistry, but made an attempt to analyze of main tendencies in development of synthesis methods of such compounds with the purpose of reveal of new approaches for their obtaining, showing the opportunity of using of perfluorolefines and …. As synthons for obtaining of this class compounds and prognosis of most new and advantageous ways of synthesis taking into account specific properties of fluorine-containing semi products.