RU2454431C1 - Method of producing perfluorinated functionalised copolymer via emulsion copolymerisation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing a perfluorinated copolymer containing functional groups. The method involves emulsion copolymerisation of tetrafluoroethylene and perfluoro-2-fluorosulphonyl ethoxypropylvinyl ether using a radical initiator and a perfluorocarboxylic acid salt as an emulsion stabiliser. The method involves a step for preliminary emulsion of perfluoro-2-fluorosulphonyl ethoxypropylvinyl ether in aqueous solution of a perfluorinated surfactant, which is carried out, preferably, through ultrasonic exposure in a current of inert gas with volume ratio monomer/water phases equal to, preferably, 1:1, with subsequent transfer of the emulsion in the inert gas medium into an autoclave containing water with dissolved components of the initiator pH regulator, after which tetrafluoroethylene is fed, an anchor mixer is switched on and copolymerisation is carried out with formation of latex, which is then subjected to coagulation.

EFFECT: simple technique, constant copolymer composition, as well as formation of copolymer with optimum electrochemical and physical-mechanical properties.

6 cl, 2 tbl, 7 ex

Description

The invention relates to the production of a perfluorinated functionalized copolymer containing functional, namely sulfonyl fluoride, groups by emulsion copolymerization. Such copolymers (for example, Nafion, Flemion, Asiplex and others) are the basis for the manufacture of ion-exchange membranes for fuel cells in various electrolyzers, as well as membrane catalysts for various chemical reactions.

Membranes based on this type of copolymers are characterized by high chemical and thermal resistance, good strength and electrochemical properties.

A number of methods are known for producing copolymers of TFE (tetrafluoroethylene) and PFEPVE (perfluoro-2-fluorosulfonylethoxypropyl vinyl ether) during copolymerization in a medium of halogen-containing hydrocarbons, for example, such as trifluorochloroethane (freon 113) [US Patents 3528954, C08.09.19/06; 3642742, C08F 16/00, 02/15/1972]. These methods have disadvantages associated with the need to stop copolymerization at low conversion depths of PFEPVE (not more than 20-25%) due to a significant increase in the viscosity of the reaction mass, which complicates the mixing of the system, leads to its overheating and the possibility of local inhomogeneities in the resulting copolymer and , respectively, a change in the uniformity of the composition of the copolymer. The low yield of the copolymer complicates the technology, leads to the need for the introduction of additional stages in the technology associated with the regeneration of expensive PFEPVE and solvent, which leads to an increase in the cost of the resulting copolymer. An attempt to increase the conversion of PFEPVE above 25% makes it impossible to obtain a copolymer of constant composition and with the required equivalent mass (EM). In addition, it is known that processes in which all components are fluorine or halogen-containing are potentially hazardous, including environmentally.

More promising methods for producing perfluoropolymers with functional sulfonyl fluoride groups in an aqueous medium by the mechanism of emulsion polymerization. In processes of this type, there are no problems associated with the high viscosity of the reaction mass, since the product of emulsion copolymerization is latex, a dispersion of polymer particles in water. The absence of an organic solvent improves working conditions, reduces the environmental hazard of the process, makes the process more technological and economical in terms of reducing the cost of regeneration of products that have not reacted.

A known method for conducting emulsion copolymerization of TFE and PFEPVE [US Patent 5608022, C08F 2/16, 03/04/1997, example 15], in which ammonium perfluorocaprylate and ammonium persulfate were used as stabilizer of the emulsion and initiator, respectively, and the process was carried out at 60 ° C and TFE pressure 1.6 MPa. A distinctive feature of this method is the emulsification in water of PFEPVE in the presence of ammonium perfluorocaprylate for 30 minutes on an AVM-4 biomixer manufactured by Nippon Seiki K.K. with a stirring speed of 20,000 rpm Another distinguishing feature of the method under consideration is the use of alcohol as a chain transfer agent in the formulation. The result is a copolymer with an equivalent mass close to optimal (1025) and a melt flow rate of 1.5 g / 10 min at 270 ° C and a load of 2.16 kg, indicating the possibility of processing the copolymer into the membrane by traditional methods, for example, extrusion. The disadvantages of the method are the process at a fairly high pressure TFE and a very low conversion of PFEPVE (12%). The latter circumstance, the inventors associate with the possibility of changing the equivalent mass of the copolymer with increasing its yield.

Close in technical essence to the claimed invention is a method for the emulsion polymerization of TFE and PFEPVE described in the patent [US Patent 6602968, C08F 214/22, 08/05/2003, examples 7 and 8]. This method also uses the method of preliminary emulsification of PFEPVE in water in the presence of ammonium perfluorooctanoate using the MicroFluidizer homogenizer. Ammonium persulfate or the redox initiating system of ammonium persulfate - sodium sulfite is used as an initiator. Depending on the type of initiating system, the process is carried out either at 60 ° C or at 35 ° C. TFE pressure varies from 0.34 to 1.38 MPa.

Before copolymerization, a 4 liter reactor is subjected to special treatment with an aqueous solution of ammonium persulfate and ammonium perfluorooctanoate.

From the obtained latex, the polymer is isolated by freezing, washed repeatedly with tap and demineralized water, and then dried at 100 ° C in vacuo. The result is a copolymer with an equivalent weight of 934 and a conversion of PFEPVE of 70% upon initiation of copolymerization by a redox initiating system. If only ammonium persulfate is used as the initiator, then the equivalent mass of the copolymer is 1228, and the conversion of PFEPVE is 80%.

The disadvantages of this method are:

1. A very complex technology, requiring the use of expensive and complex equipment (MicroFluidizer, dispensers of liquid components working under pressure) and special preparation of the polymerization reactor.

2. High consumption of expensive perfluorinated surfactant (12-16% of the mass of PFEPVE loaded into the reactor).

3. The consequence of claim 2 is the large amount of water required to carry out the process and rinse the resulting copolymer. On average, 225 liters of tap water and 66 liters of demineralized water are consumed per 1 kg of the obtained copolymer, which implies significant costs for wastewater treatment.

4. The resulting copolymer has a low melt flow rate (0.214 g / 10 min at 270 ° C and a load of 1.2 kg), which may complicate its processing by extrusion.

The closest in technical essence is the method [RF Patent 2348649, C08F 2/24; C08F 2/34, 03/10/2009] the preparation of a perfluorinated copolymer containing functional groups by emulsion copolymerization of TFE and PFEPVE in the presence of a radical initiator and stabilizer of the emulsion — the perfluorocarboxylic acid salt, which includes the stage of preliminary emulsification of PFEPVE in an aqueous medium, and the emulsion copolymerization of TPVPE and TPVP and TPVE at a constant pressure of tetrafluoroethylene 0.48-0.52 MPa, stopping the process during the conversion of PFEPVE 49-77%, and at the stage of preliminary emulsification of PFEPVE in an aqueous medium as a dis ergatora type homogenizer using a rotor-stator with a rotor speed 8000-12000 rev / min, to stabilize the emulsion applying C _n F _{n + 1} COONH ₄ perfluorocarboxylic acid ammonium salt thereof, wherein: n = 7-9, and emulsification is carried out in an inert gas atmosphere . In this case, the ammonium salt of perfluorocarboxylic acid C _n F _{n + 1} COONH _{4 is} used in an amount of 2.5-3.5% by weight of PFEPVE, emulsification is carried out with a mass ratio of PFEPVE / water of 0.141-0.152.

Despite the significant advantages of this solution compared to other patent solutions, it is also not without drawbacks.

The disadvantages of this method are:

1. The lack of process performance due to the use of a low mass ratio of the phases PFEPVE / water 0.141-0.152, which allows to obtain latex with a copolymer content of not higher than 20 wt.%.

2. The complexity of using a high-speed disperser of the rotor-stator type in high-pressure reactors of 5-25 l, operating under pressure, requiring changes in the design of the reactor for incorporating the dispersant.

3. Strong foaming of the reaction mixture during the pre-emulsification stage of PFEPVE.

The invention solves the problem of improving the technology for producing the TFE-PFEPVE perfluoropolymer using the emulsion copolymerization method, in the direction of increasing the conversion of PFEPVE (up to 80% and higher), increasing the productivity of the reactor by increasing the mass ratio of PFEPVE / water in the range 0.29-0.30 ( by volume 0.16-0.17) while maintaining the optimal characteristics of the resulting copolymer (equivalent weight 825-1100, melt flow rate 3.6-100 g / 10 min) and increasing the rate of copolymerization of TFE with PFEPVE.

The process allows to reduce water consumption in the process of washing the copolymer (reducing the amount of wastewater).

The problem is solved by a method for producing a perfluorinated copolymer containing functional groups by emulsion copolymerization of tetrafluoroethylene and perfluoro-2-fluorosulfonylethoxypropyl vinyl ether using a radical initiator and a salt of perfluorocarboxylic acid as an emulsion stabilizer, including a preliminary emulsification step-emulsifier-2-fluorofluorofluorofluorofluorofluorofluoro perfluorinated surfactant solution wire preferably by ultrasonic treatment in an inert gas stream with an increased volume ratio of monomer / water phases to a certain degree of dispersion of the particles of the emulsion, followed by transfer of the emulsion in an inert gas medium to an autoclave containing water with dissolved components of the initiator and pH regulator, after which tetrafluoroethylene is fed and carry out copolymerization.

The volume ratio of the monomer / water phases is preferably 1: 1.

The water with the dissolved components of the initiator and the pH regulator is taken in an amount that makes it possible to achieve a phase ratio of perfluoro-2-fluorosulfonylethoxypropyl vinyl ether: water in the reactor, preferably up to 1: 6 by volume.

The copolymerization of tetrafluoroethylene and perfluoro-2-fluorosulfonylethoxypropyl vinyl ether is carried out at a constant pressure of tetrafluoroethylene selected in the range of 0.5-0.7 MPa for 190-280 min and a constant temperature selected in the range of 45-55 ° C.

The equivalent mass and melt flow rate of the copolymer are controlled by changing the pressure of tetrafluoroethylene and the copolymerization temperature.

The process of copolymerizing tetrafluoroethylene and perfluoro-2-fluorosulfonylethoxypropyl vinyl ether is carried out to the degree of conversion of perfluoro-2-fluorosulfonylethoxypropyl vinyl ether PFEPVE not higher than 90%, preferably 75-90%, keeping the composition of the copolymer constant, i.e. its equivalent mass (EM).

The obtained latex is coagulated by freezing, the polymer is washed from the emulsifier and unreacted PFEPVE monomer with distilled water at a temperature of 80-90 ° C until there is no perfluorinated surfactant in the washings.

The technical result is the absence of foaming of the emulsion, which ensures a constant composition of the reactants in the polymerizable system, the possibility of copolymerization at large volume ratios of the phases of PFEPVE-water of the order of 1: 6 (in the prototype 1:12), more complete use of the expensive comonomer PFEPVE - (75-90 %) with maintaining a constant composition of the resulting copolymer, regardless of the conversion of PFEPVE. In this case, the resulting copolymer has good electrochemical and physico-mechanical properties and, accordingly, the ability to process into the membrane by traditional methods.

The properties of the obtained copolymers were determined as follows.

1. The melt flow rate (MFR) was determined according to GOST 11645-73 on an IIRT-M plastometer at 270 ± 0.5 ° C, a load of 2.16 kg, a capillary diameter of 2.095 ± 0.005 mm with a sample holding time in the extrusion chamber for 5 minutes.

2. The equivalent mass of the copolymer (EM) was determined by IR Fourier spectroscopy on samples of extruded films with a thickness of 0.20 ± 0.05 mm in sulfonyl fluoride form. The integrated intensities A of the absorption bands of 2704 cm ^-1 (combined vibration frequency of the -SO ₂ F group) and 2363 cm ^-1 (overtone of vibration of the -CF ₂ group) were measured.

EM was calculated by the formula:

EM = 446 [1 + k (A ₂₃₆₃ -A ₂₇₀₄ ) / A ₂₇₀₄ ],

where: the coefficient k was determined from reference samples with a known exchange capacity determined by titration.

3. The conversion of PFEPVE was calculated based on the values of EM, the yield of the copolymer (W), the amount of PFEPVE loaded into the reaction mixture (W ₁ ), according to the formula:

Conversion of PFEPVE (%) = [446 · W · 100] / [W ₁ · EM],

where: 446 is the molecular weight of PFEPVE.

4. The membrane film material was obtained from the copolymer in sulfofluoride form by pressing and extrusion.

A portion of the copolymer for pressing (G) was calculated by the formula:

G = V · ρ · K,

where: V is the volume of the pressed film, cm ³ ,

ρ is the density of the copolymer equal to 2.1 g / cm ³

K is a correction factor of 1.1, taking into account the excess copolymer.

A portion of the copolymer in the form of a powder was poured onto a X18H10T stainless steel plate with a 100 μm thick aluminum foil gasket, the powder was leveled according to the shape limiter with dimensions 70 × 130 × 0.1 mm, and closed with an aluminum foil gasket and a massive stainless steel plate. The form with the copolymer was kept at a pressing temperature (230-250 ° С) for 15 minutes, the specific pressure was set at 20.0-23.0 MPa and the mold was kept under pressure for 5 minutes. After that, the form with the copolymer was cooled under pressure, the pressure was released, the limiter with the film was removed from the mold, cooled to room temperature. A film was obtained with a thickness of 100 μm with a smooth smooth surface without melt, inclusions, shells and other visible defects with dimensions of 70 × 130 × 0.1 mm with a thickness difference of not more than 10%.

By extrusion, the film material was obtained at a laboratory installation of Scamex (France) for processing fluoropolymers with a productivity of 0.5-5.0 kg / h. The powder of the obtained copolymer was first processed into granules at 250-270 ° C and a powder feed rate of 0.5-1.0 kg / h using a removable die on 1 strand. Two repeated granulations were performed to obtain uniform granules. Granules were obtained with dimensions: granule diameter 2 mm, granule length 2-4 mm. A film material 200 microns thick and 250-300 mm wide was obtained from the granulated copolymer F-4SF at this installation.

5. Translation of the membrane film copolymer into sulfonic acid form.

A copolymer film in sulfofluoride form, obtained by pressing or extrusion (thickness 100-200 μm), was placed in a vessel with a 15% solution of potassium hydroxide (sodium) in a mixed solvent dimethyl sulfoxide (DMSO) - distilled water (mass ratio DMSO - water = 35 : 50) and subjected to hydrolysis at 80 ° C for 5 hours. Mass ratio copolymer - alkali solution = 1:10. After hydrolysis, the alkali solution was removed, the membrane was washed with portions of deionized water (based on 100 ml of water per 1 g of copolymer) for 30 min after each washing. The process was repeated until the washings were neutral, obtaining the membrane in an alkaline form.

The completeness of the hydrolysis of the sulfonyl fluoride groups of the copolymer was checked by FTIR spectroscopy on a Bruker Tensor 27 instrument by the disappearance of the absorption band of -SO ₂ F groups in the region of 1470 cm ^-1 .

The alkali groups of the copolymer are converted into the -SO ₃ H acid form by treating the membrane with 2-3 portions of a 10-15% nitric acid solution for 2 hours at room temperature. After each acid treatment, the membrane is washed with 2-3 portions of distilled water until the washings are neutral. The result is a cation exchange membrane in -SO ₃ H form.

6. The equilibrium water content in the membrane (water absorption) was determined as follows. The membrane in the -SO ₃ H form was kept in distilled water at 25 ° C for 24 hours. The mass of the wet membrane (W ₂ ) was determined, and then it was dried in vacuum at 70 ° C to constant weight (W ₃ ). Determined the moisture content of the membrane (C _w ) by the formula:

C _w (%) = (W ₂ -W ₃ ) 100 / W ₂ .

7. Testing the mechanical properties of hydrated membranes under conditions of equilibrium swelling (holding the membrane in -SO ₃ H form in distilled water at 25 ° C for 24 hours) was carried out on a universal mechanical testing machine UTS 10 (Germany) on samples representing spatulas the dimensions of the working part are 20 × 3.5 mm with a thickness of 0.1 or 0.2 mm, with a tensile speed of the samples of 10 mm / min. The tests were carried out at a temperature of 25 ° C, measuring tensile strength (σ _p ), elastic modulus (E) and elongation at break (ε).

8. The electrical conductivity of the membranes (σ _n ) in the state of equilibrium saturation with water at 20 ° С was measured by the impendance method on an Elins impedance meter Z-3000X using a cell with stainless steel electrodes according to a four-electrode circuit in the frequency range 100-100000 Hz. The conductivity was calculated using the formula:

σ _n = L / (R _cp · h · b),

where: L is the distance between the voltage electrodes of the measuring cell, cm (L = 1.77 cm is the passport data of the measuring cell);

h is the average thickness of the membrane, cm;

b is the average width of the membrane, cm;

R _cp is the membrane resistance, Ohm.

The invention is illustrated by the following examples.

Example 1

The stage of preliminary emulsification of PFEPVE in water containing a perfluorinated surface-active substance (surfactant) is carried out in a 2 L reactor (flask) equipped with an anchor mixer. 25.7 g (2.58% by weight of PFEPVE) of ammonium perfluorononate dissolved in 558 g of water are charged to the reactor, and 558 ml (995.8 g) of PFEPVE are added. The volume ratio of PFEPVE: water is 1: 1 (the mass ratio of PFEPVE: water is 1.78: 1). The reactor is evacuated, purged with argon, and PFEPVE is dispersed at a stirring speed of 450 rpm with simultaneous ultrasonic action for 30 minutes.

Next, in a pre-treated with a 3% aqueous hydrogen peroxide solution at 90 ° C, a 5 liter stainless steel autoclave is charged with the calculated amount of the components of the initiating system and pH regulators dissolved in water. The amount of water is determined by the corresponding module of the bath (about 1: 5, 1: 6 by volume). The autoclave is purged with argon, the emulsion PFEPVE prepared by pre-emulsification is loaded into it, the reactor is purged sequentially with argon and TFE.

After loading and purging is completed, the reactor is heated to a working temperature of 50 ° C and at the same time the TFE pressure is increased to a working pressure (0.7 MPa), carrying out the process at a reactor stirrer speed of 300 rpm.

Next, the process of copolymerization of TFE with PFEPVE is carried out, maintaining a constant pressure in the reactor of 0.7 MPa. At the same time, a pressure drop is recorded in a TFE cylinder with a volume of 40 liters.

The copolymerization time was 264 minutes.

During the reaction spent 1034.4 g of TFE.

Received 5547 g of latex.

The latex polymer was frozen, the copolymer released was repeatedly washed with water at a temperature of 90 ° C until there was no perfluorinated surfactant in the wash water, which was determined spectrometrically. The water consumption for washing was 39.9 l per 1 kg of the obtained copolymer.

The mass of the dry copolymer -1838

The equivalent weight of the copolymer is 990.

Conversion by PFEPVE - 83.2%.

MFI (270 ° C, 21.2 N, 2.095 mm) - 3.6 g / 10 min.

Characteristics of a sulfonic acid-derived membrane obtained from a copolymer at 20 ° C:

- water content of 17.5%;

- specific conductivity 0.105 S / cm;

- tensile strength 17.5 MPa;

- elongation at break 75%;

- modulus of elasticity 135 MPa.

Example 2

It differs from example 1 in that the process was conducted at a constant pressure of TFE in the reactor equal to 0.5 MPa.

The copolymerization time was 253 minutes.

During the reaction, 652.6 g of TFE was consumed.

Received 5165.2 g of latex.

The water consumption for washing was 40.1 l per 1 kg of the obtained copolymer.

The dry weight of the copolymer is 1400 g.

The equivalent weight of the copolymer is 825.

Conversion by PFEPVE - 76%.

MFI (270 ° C, 21.2 N, 2.095 mm) - more than 100 g / 10 min.

Membrane characteristics at 20 ° С:

- water content of 20.5%;

- specific conductivity 0.12 S / cm;

- tensile strength 11.0 MPa;

- elongation at break of 120%;

- modulus of elasticity 95 MPa.

Example 3

It differs from example 1 in that the process was conducted at a constant TFE pressure in the reactor equal to 0.6 MPa.

The copolymerization time was 268 minutes.

During the reaction, 931.3 g of TFE was consumed.

Received 5448 g of latex.

The flushing water flow rate was 39.8 L per 1 kg of the obtained copolymer.

The mass of the dry copolymer - 1801

The equivalent weight of the copolymer is 925.

Conversion by PFEPVE - 87.3%.

MFI (270 ° C, 21.2 N, 2.095 mm) - 25.6 g / 10 min.

Membrane characteristics at 20 ° С:

- water content of 18.5%;

- specific conductivity 0.11 S / cm;

- tensile strength 14.0 MPa;

- elongation at break of 85%;

- modulus of elasticity 120 MPa.

Example 4

It differs from example 1 in that the process was conducted at a constant TFE pressure in the reactor of 0.6 MPa, and the operating temperature was 55 ° C.

The copolymerization time was 190 minutes.

During the reaction spent 1027 g of TFE.

Received 5403 g of latex.

The water consumption for washing was 38.9 l per 1 kg of the obtained copolymer.

The mass of the dry copolymer - 1798

The equivalent weight of the copolymer is 1040.

Conversion by PFEPVE - 77.4%.

MFI (270 ° C, 21.2 N, 2.095 mm) - 5.5 g / 10 min.

Membrane characteristics at 20 ° С:

- water content of 16.5%;

- specific conductivity 0.10 S / cm;

- ultimate tensile strength 16.0 MPa;

- elongation at break 83%;

- modulus of elasticity 125 MPa.

Example 5

It differs from example 4 in that the process was carried out at a working temperature in the reactor of 45 ° C.

The copolymerization time was 280 minutes.

During the reaction spent 1028 g of TFE.

Received 5378 g of latex.

The water consumption for washing was 38.5 l per 1 kg of the obtained copolymer.

The mass of the dry copolymer - 1775

The equivalent mass of the copolymer is 1060.

Conversion by PFEPVE - 75%.

MFI (270 ° C, 21.2 N, 2.095 mm) - 17 g / 10 min.

Membrane characteristics at 20 ° С:

- water content of 16.4%;

- specific conductivity 0.10 S / cm;

- tensile strength 16.1 MPa;

- elongation at break 82%;

- modulus of elasticity 126 MPa.

Example 6 (three options).

The synthesis, isolation of the copolymer from latex and the study of its properties was carried out in the same way as in Example 1, but unlike the previous examples, the process was stopped with various amounts of reacted TFE and in each case the yield of the copolymer, the conversion of PFEPVE and EM copolymer were determined. Other characteristics were measured only for the copolymer obtained at maximum TFE loading.

Recipe:

PFEPVE 995.8 g.

TFE: option 1 - 288 g, option 2 - 708 g, option 3 - 1314

The process was carried out at 50 ° C and a TFE pressure of 0.7 MPa for 60 min (option 1), 150 min (option 2), 270 min (option 3).

The copolymer yield was 487 g (option 1), 1206 g (option 2), 2210 g (option 3).

Conversion of PFEPVE 20.1% (option 1), 49.9% (option 2), 90% (option 3).

Characteristics of the copolymer:

equivalent weight: 1090 (option 1), 1080 (option 2), 1100 (option 3);

MFI: 3.5 g / 10 min (2.16 kg; 270 ° C; 2.095 mm).

Membrane characteristics at 20 ° С:

- water content of 16.5%;

- electrical conductivity of 100 S / cm;

- tensile strength 17.5 MPa;

- elongation at break 70%;

- modulus of elasticity 135 MPa.

Example 7 (prototype).

In a glass cup with a capacity of 300 cm ^3, 100 cm ^{3 of} distilled water previously purged with nitrogen was charged and 0.45 g (2.51% by weight of PFEPVE) ammonium perfluorooctanoate, 0.45 g (2.51% by weight PFEPVE) of disubstituted sodium phosphate, 0.6 g (3.35% by weight) were dissolved PFEPVE) of monosubstituted sodium phosphate and 0.15 g (0.84% by weight of PFEPVE) of potassium persulfate. Then, 17.9 g of PFEPVE was loaded into the resulting solution, a homogenizer working element was introduced, a nitrogen current was applied over the surface of the prepared mixture, and the rotation of the homogenizer rotor was turned on at a speed of 10,000 rpm. Emulsification was stopped after 15 minutes and the resulting emulsion was left under a stream of nitrogen for 30 minutes to settle the foam.

At the same time, a 200 cm ³ reactor was prepared for copolymerization. The reactor was successively evacuated and filled with TFE to a pressure of 0.05 MPa. This operation was performed three times. The resulting emulsion was loaded into the reactor and purged with nitrogen for 30 minutes. 0.045 g (0.25% by weight of PFEPVE) of sodium metabisulfite dissolved in 20 cm ^{3 of} degassed distilled water was loaded into the reactor, the reactor was closed and TFE was fed to a pressure of 0.1 MPa. Then the pressure was reduced to atmospheric and TFE was applied again to a pressure of 0.1 MPa. This operation was performed three times. After this, the reaction mass was heated to 40 ° С, the working pressure of TFE was established (0.52 MPa), and the process was conducted for 5 hours with constant feeding of TFE. Make-up was carried out with a decrease in TFE pressure of 0.02 MPa. During the reaction, 15.43 g of TFE was absorbed.

After completion of the process, the reaction mass was cooled to room temperature, TFE was blown off, the resulting latex was unloaded, coagulated by adding 50 ml of concentrated hydrochloric acid. The released copolymer was separated from the liquid phase on a Buchner funnel, washed several times with water, then placed in a glass and washed with a mixture (emulsion) of chloroform and water with vigorous stirring, after which the copolymer was separated from the liquid phase on a Buchner funnel. The described procedures were performed three times.

In total, 51 l of water per 1 kg of copolymer was used up for washing the copolymer.

The washed copolymer was dried in air at room temperature for 16 hours, and then in vacuo at 100 ° C.

The dry weight of the copolymer is 31.3 g.

The equivalent mass of the copolymer is 1010.

Conversion by PFEPVE - 77%.

MFI (270 ° C, 21.2 N, 2.095 mm) - 27 g / 10 min.

Membrane characteristics at 20 ° С:

- water content of 15.2%;

- specific conductivity 0.12 S / cm;

- tensile strength 14.1 MPa;

- elongation at break 88%;

- modulus of elasticity 130 MPa.

The main results are summarized in tables 1 and 2, and their comparison shows that the proposed technology allows to achieve a significant improvement in the main process indicators during the copolymerization of PFEPVE with TFE in the emulsion compared to the prototype.

So, for example, a higher conversion of sulfonated copolymer is achieved (examples 1, 3, 6); the reactor productivity is almost doubled due to an increase in the PFEPVE / water ratio in the emulsion polymerization system; the possibility of the normal conduct of the process of emulsion copolymerization with an increased proportion of PFEPVE in the emulsion system is doubled; it is possible to avoid foaming during pre-emulsification and copolymerization, which avoids complications during copolymerization.

It was possible to reduce the amount of wash water by ~ 15% when using new technology and another method of coagulation of latex.

Claims (6)

1. A method of producing a perfluorinated copolymer containing functional groups by emulsion copolymerization of tetrafluoroethylene and perfluoro-2-fluorosulfonylethoxypropyl vinyl ether using a radical initiator and a salt of perfluorocarbic acid as an emulsion stabilizer, comprising a pre-emulsification step, characterized in that the pre-emulsifier is 2 fluorosulfonylethoxypropyl vinyl ether in an aqueous solution of perfluorinated surfactant pr preferably, by ultrasonic treatment in an inert gas stream at a volume ratio of monomer / water phases equal to, preferably, 1: 1, followed by transfer of the emulsion in an inert gas medium into an autoclave containing water with dissolved components of the initiator and pH regulator, after which include the supply of tetrafluoroethylene, an anchor stirrer and copolymerization with the formation of latex, which is then subjected to coagulation. 2. The method according to claim 1, characterized in that the water with the dissolved components of the initiator and the pH regulator is taken in an amount that allows to achieve a phase ratio of perfluoro-2-fluorosulfonylethoxypropyl vinyl ether: water in the reactor 1: 6 by volume. 3. The method according to claim 1, characterized in that the copolymerization of tetrafluoroethylene and perfluoro-2-fluorosulfonylethoxypropyl vinyl ether is carried out at a constant pressure of tetrafluoroethylene, selected in the range of 0.5-0.7 MPa, for 190-280 minutes and a constant temperature selected in the range of 45-55 ° C. 4. The method according to claim 1, characterized in that the regulation of the equivalent mass and melt flow index of the copolymer is achieved by changing the pressure of tetrafluoroethylene and the copolymerization temperature. 5. The method according to claim 1, characterized in that the copolymerization of tetrafluoroethylene and perfluoro-2-fluorosulfonylethoxypropyl vinyl ether is carried out to a degree of conversion of perfluoro-2-fluorosulfonylethoxypropyl vinyl ether not higher than 90%, while maintaining the composition of the copolymer constant, i.e. its equivalent mass. 6. The method according to claim 1, characterized in that the obtained latex is coagulated by freezing, washing the fluorinated emulsifier and unreacted monomer is carried out using water heated to 80-90 ° C.