RU2412948C1 - Method of producing perfluorinated copolymer with sulfo-groups - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of producing perfluorinated polymers with sulfo-groups and is used in production of proton conducting ion-exchange membranes. The method involves copolymerisation of tetrafluoroethylene with perfluoro(3,6-dioxa-4-methyl-7-octene)sulfonylfluoride in the medium of an organic solvent - perfluoromethyl diethylamine at temperature 50°C and pressure 2.5-5 atm. The initiator used is bis(perfluorocyclohexanoyl)peroxide.

EFFECT: invention solves the problem of increasing molecular weight of a copolymer of tetrafluoroethylene with perfluoro(3,6-dioxa-4-methyl-7-octene)-sulfonyl fluoride and replacing the ozone-depleting solvent with an environmentally safe solvent.

2 dwg, 1 tbl, 13 ex

Description

The invention relates to the chemistry of polymers, in particular to methods for producing perfluorinated polymers with sulfo groups.

Perfluorinated copolymers with sulfo groups are used for the production of proton-conducting ion-exchange membranes [B.C. Bagotsky et al. Electrochemistry, 2003, Volume 39, No. 9, pp. 1027-1045].

Perfluorinated polymers with sulfo groups are obtained predominantly by copolymerization of tetrafluoroethylene (TFE) and perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride (FS-141):

In Russia, this copolymer is known as ftoroplast F-4SF. After the film is obtained from P-4SF by extrusion, the sulfonyl fluoride groups of the polymer are hydrolyzed to sulfonic acid groups.

Upon receipt of the TFE copolymer with FS-141, copolymerization methods are mainly used in an organic solvent (solution polymerization) or in an aqueous medium (emulsion polymerization) [Kirsch et al. Uspekhi Khimii, Nauka 1990, vol. 59, issue 6 , p. 970-994].

The copolymerization in an aqueous medium is accompanied by the formation of large volumes of wastewater, which are difficult to dispose of. Moreover, the partial hydrolysis of sulfonyl fluoride groups taking place complicates the extrusion processing of the polymer.

More attractive, from a technological point of view, is the method of polymerization in solution.

The present invention relates to copolymerization in an organic solvent.

The known method [US patent 3282875, cl. C07C 309/82, op. 11/01/1966] obtaining the F-4SF copolymer by solution polymerization in perfluoro (dimethylcyclobutane) medium, however this solvent is expensive and difficult to access, since it is not produced in our country.

Describes a method of obtaining [US patent 3528954, CL. C08F 214/26, 09/15/1970] of the indicated copolymer in the medium of 1,2,2-trifluoro-1,1,2-trichloroethane (freon 113) by copolymerization of TFE with the sulfonomer FS-141 according to the radical mechanism, carried out at a temperature of 40-50 ° C. Perfluorodiacyl peroxide, preferably bis-perfluoropropionyl peroxide, is used as the polymerization initiator. The pressure in the reactor is kept constant up to 20 atm due to the feeding of TFE during the polymerization process.

The disadvantage of this method is that freon 113 is used as a solvent, which is an ozone-depleting compound, the production of which is prohibited by the Montreal Protocol, and the copolymer is obtained as low molecular weight due to the breakdown of growing chains due to the detachment of chlorine atoms from solvent molecules.

A method has been developed, the use of which allows to increase the molecular weight of the F-4SF copolymer [Application No. 2009162836 (037362), IPC: C08F 02/04, 02/06, priority from 07/13/2009]. This is achieved by polymerization in a medium of 1,2-dichlorohexafluorocyclobutane (freon RC-316).

The challenge facing the authors of the present invention is to expand the range of available available solvents used to carry out the described copolymerization and obtain a copolymer with a high molecular weight.

The essence of the invention lies in the fact that the copolymerization of TFE with perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride (FS-141) using bis (perfluorocyclohexanoyl) peroxide as an initiator is carried out at a temperature of 50 ° C and pressure 2.5-5.5 atm in the environment of a perfluorinated solvent - perfluoromethyldiethylamine (MD-46). This solvent in available quantities is available in our country (according to TU 602-2-794-84).

The polymerization is carried out in a jacketed reactor (200 ml stainless steel autoclave) equipped with a frame stirrer. TFE is fed into the reactor through an adsorber filled with activated carbon to purify the triethylamine inhibitor. The solvent MD-46, FS-141 and DAPC are loaded into the reactor. Then the reactor is sealed, with slow stirring, cooled to 5 °, vacuum and load TFE up to 1 ATM. After that, the reactor is heated to operating temperature and TFE is supplied until the working pressure is reached, which is maintained by periodic supply of TFE to the reactor. These parameters are maintained during the polymerization, mixing at a speed of 300 rpm. After polymerization is complete, the reactor is cooled to room temperature. Unreacted TFE is blown off, the unreacted FS 141 monomer is washed with chloroform, and then the polymer is filtered off and dried under vacuum at 60 ° C to constant weight.

The equivalent mass of the copolymer (EM) is determined by IR spectroscopy. Equivalent mass is the molecular weight of the copolymer per 1 sulfo group, which is a characteristic of the composition of the copolymer.

The melt flow rate (MFR) of the copolymer is determined on an IIRT-2 device with a die diameter of 2.095 mm, a load of 2.16 kg at a temperature of 270 ° C. MFI is a characteristic of the molecular weight of the polymer: the lower the MFI, the higher the molecular weight.

The following are examples of the solution copolymerization of tetrafluoroethylene with perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride according to the developed method.

Example 1

A 200 ml stainless steel reactor with a frame stirrer and a jacket is charged with: 67 ml of perfluoromethyldiethylamine solvent, 30 ml (53 g) of perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride and 0.1 g of bis ( perfluorocyclohexanoyl) peroxide. The reactor is sealed, with slow stirring, cooled to 5 ° C, vacuum and fed through an adsorber tetrafluoroethylene up to 1 ATM. Then the reactor is heated to 50 ° C, tetrafluoroethylene is fed into the reactor to a pressure of 4.5 atm, and the pressure in the reactor is kept constant within 5 atm by feeding tetrafluoroethylene. For 4 hours of the method, 16 g of tetrafluoroethylene are fed into the reactor. Then the reactor is cooled to ambient temperature (about 18-20 ° C), unreacted tetrafluoroethylene is blown off. The polymer is washed with chloroform to wash unreacted perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride, filtered and dried under vacuum at 60 ° C to constant weight. The resulting polymer 32 g has an equivalent weight of 890 (determined by IR spectroscopy). The melt flow rate (determined on the device ИИРТ-2) of the obtained polymer (MFI) is 11 g / 10 min at 270 ° C.

The installation for copolymerization in examples 2-13 is similar to example 1. The conditions for their implementation are presented in the Table.

The polymerization in examples 2-13 was carried out using the same amounts of the following substances: solvent 67 g, monomer FS-141 53 g, polymerization initiator bis (perfluorocyclohexanoyl) peroxide 0.1 g.

Examples 1-6 were carried out using perfluoromethyldiethylamine and with a bis (perfluorocyclohexanoyl) peroxide initiator, examples 4-7 are comparative, using 1,2,2-trifluoro-1,1,2-trichloroethane and the same initiator, examples 8-13 carried out with 1,2-dichlorohexafluorocyclobutane and bis (perfluorocyclohexanoyl) peroxide.

The results of the experiments show that:

1. The equivalent weight of the copolymer obtained using the new perfluoromethyldtethylamine solvent is lower than in 1,2-dichlorohexafluorocyclobutane medium under the same polymerization conditions (Figure 1). This is due to the higher solubility of tetrafluoroethylene in 1,2-dichlorohexafluorocyclobutane compared to perfluoromethyldiethylamine. With increasing pressure, this difference is leveled.

2. Samples of the F-4SF copolymer obtained in perfluoromethyldiethylamine medium have a lower melt flow rate (hence, higher molecular weight) than samples with the same equivalent mass, that is, the same composition, but obtained in a 1.2- dichlorohexafluorocyclobutane (Figure 2).

Thus, carrying out the method under the developed conditions, namely using perfluoromethyldiethylamine as a solvent in the indicated temperature and pressure parameters, using bis (perfluorocyclohexanoyl) peroxide initiator allows to obtain a polymer with a significantly higher molecular weight, especially for samples with a low equivalent weight . In addition, this method provides the replacement of an ozone-depleting solvent with an environmentally friendly one.

Claims (1)

A method of producing a perfluorinated copolymer with sulfo groups by copolymerization of tetrafluoroethylene with perfluoro (3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride using bis (perfluorocyclohexanoyl) peroxide as an initiator in an organic solvent medium, characterized in that the copolymerization is carried out at a temperature of 50 ° C and a pressure of 2.5-5 atmospheres in a solvent medium - perfluoromethyldiethylamine.

Images