Perfluoro vinyl ethers

#This invention relates to a novel fluorinated copolymer useful as a starting material for production of a fluorinated cation exchange membrane or a fluorinated cation exchange resin having sulfonic acid groups and/or carboxylic acid groups and also to a process for preparing the same.

#In recent years, there has been an increasing trend for development of new chemical processes using fluorinated cation exchange membranes or resins excellent in chemical resistance and heat resistance. As a typical example of such a trend, the ion-exchange membrane process has recently attracted great attention in the chloro-alkali industry wherein caustic soda and chlorine are produced by electrolysis of sodium chloride, because it is more advantageous in various aspects such as prevention of environmental pollution and economical saving of energy than the mercury process and the diaphragm process of the prior art and also because it can produce caustic soda having substantially the same quality as that produced by the mercury process.

#The greatest factor which controls the economy of the ion-exchange membrane process is the characteristic of the cation exchange membrane employed. It is necessary for the cation exchange membrane to satisfy the requirements as set forth below. (1) To have a high current efficiency and a low electric resistance. In order to have a high current efficiency, the membrane is required to have a sufficiently high ion-exchange capacity and low water content, thus giving a high concentration of fixed ions in the membrane. On the other hand, to the effect of lower electric resistance, a higher water content is rather more advantageous. Since the water content will vary depending on the types of ion-exchange groups, the ion-exchange capacity and the concentration of external solutions, it is necessary to select the optimum combination of these factors.

#The present invention is illustrated in further detail by referring to the following Examples, by which the present invention is not limited.

#(A) In a stainless steel autoclave of 3-liter capacity, there are charged 250 g of sodium ethyl mercaptide, 530 g of dimethyl carbonate and 750 g of tetrahydrofuran, and then the reaction system is brought into a reduced pressure of 50 to 60 mm Hg. While maintaining the temperature at 15.degree. C. under vigorous agitation of the reaction system, tetrafluoroethylene is gradually blown into the system under reduced pressure. With the progress of the reaction, the rate of tetrafluoroethylene consumed is lowered until, finally at the tetrafluoroethylene pressure of 1 kg/cm.sup.2, there is no more consumption of tetrafluoroethylene. After the reaction, the reaction mixture is neutralized with 300 g of 98% sulfuric acid. The sodium sulfate formed is filtered off and the filtrate is previously evaporated by an evaporator to remove tetrahydrofuran, followed by distillation of the residue, to obtain 520 g of the fraction of distillate at 84.degree. C./30 mm Hg. Said fraction is found to have the structure of C.sub.2 H.sub.5 SCF.sub.2 CF.sub.2 COOCH.sub.3 from elemental analysis, IR and NMR spectra.

#IR characteristic absorption (liquid): 2960, 2930, 2870 cm.sup.-1 (C.sub.2 H.sub.5 --), 1780 cm.sup.-1 (--CO.sub.2 --), 1300-1100 cm.sup.-1 (--CF.sub.2 --).