Method for producing fluorine-containing polymer

Abstract

Provided is a method for producing a fluorine-containing polymer capable of producing a fluorine-containing polymer having excellent melt elongation and having low ion exchange capacity when converted into acid form.　This method for producing a fluorine-containing polymer produces a fluorine-containing polymer by copolymerizing TFE with a monomer m1 represented by the formula CF2=CF-O-Rf1-A (Rf1 is a perfluoroalkylene group that may contain an oxygen atom between carbon atoms, and A is a group that can be converted into a sulfonic acid-type functional group) in the presence of an organic solvent in a reaction vessel. The ratio M1, which is the molar ratio of the content of the monomer m1 to the content of TFE in the reaction vessel during copolymerization, is maintained so as to be 0.45 to 3.0, and the composition change rate is -20 to 20%.

Description

Method for producing fluorine-containing polymer

[0001] The present invention relates to a method for producing a fluorine-containing polymer.

[0002] The ion exchange membrane (electrolyte membrane) of a polymer electrolyte fuel cell or a water electrolysis device is obtained by forming a fluoropolymer having an ion exchange group such as a sulfonic acid group into a membrane. As a method for producing such a fluoropolymer having an ion exchange group, Example 1 of Patent Document 1 describes a method for producing a fluoropolymer containing tetrafluoroethylene and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ A monomer represented by F is copolymerized in the presence of a radical polymerization initiator at a temperature of 100 to 200°C, and then -SO ２ A method is disclosed in which the F group is hydrolyzed to convert it into an acid form and into a sulfonic acid group.

[0003] International Publication No. 2016 / 104379

[0004] The sulfonic acid group-containing fluoropolymer obtained by the method described in Example 1 of Patent Document 1 has a high ion exchange capacity, but in recent years, depending on the application, there has been a demand for a fluoropolymer having a low ion exchange capacity when converted to an acid form. The present inventors produced a fluoropolymer that has a low ion exchange capacity when converted to an acid form by referring to the method described in Example 1 of Patent Document 1, and found that there is room for improvement in the melt elongation of the obtained fluoropolymer.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a fluoropolymer which can produce a fluoropolymer which has a low ion exchange capacity when converted to an acid form and is excellent in melt elongation.

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that, when tetrafluoroethylene and a monomer represented by formula (m1) described below are copolymerized in the presence of an organic solvent, the desired effects can be obtained if the molar ratio of the content of the monomer represented by formula (m1) to the content of tetrafluoroethylene in a reactor is maintained within a specific range and the rate of change in composition calculated by formula (C1) described below is within a specific range, thereby completing the present invention.

[0007] That is, the inventors have found that the above-mentioned problems can be solved by the following constitution: [1] A method for producing a fluoropolymer by copolymerizing tetrafluoroethylene with a monomer m1 represented by the following formula (m1) in the presence of an organic solvent in a reactor, characterized in that during the copolymerization, a ratio M1, which is the molar ratio of the content of the monomer m1 to the content of the tetrafluoroethylene in the reactor, is maintained at 0.45 to 3.0, and the rate of composition change calculated by the following formula (C1) is -20 to 20%. ２ =CF-O-R ｆ１ -A In formula (m1), R ｆ１is a perfluoroalkylene group which may contain an oxygen atom between the carbon atoms, and A is a group which can be converted to a sulfonic acid type functional group. Formula (C1) Composition change rate (%) = 100 × {(ratio M1 at the time of terminating copolymerization) - (ratio M1 at the time of starting copolymerization)} / (ratio M1 at the time of starting copolymerization) [2] The method for producing a fluoropolymer according to [1], wherein the copolymerization is carried out in the presence of a radical polymerization initiator, and a ratio R1 of the total amount of the radical polymerization initiator charged into the reactor to the sum of the total amount of the organic solvent and the total amount of the monomer m1 charged into the reactor is 1 to 1,000 ppm by mass. [3] The method for producing a fluoropolymer according to [1] or [2], wherein the temperature during the copolymerization is 100°C or lower. [4] The method for producing a fluoropolymer according to any of [1] to [3], wherein the tetrafluoroethylene and the monomer m1 are added into the reactor continuously or sequentially. [5] The method for producing a fluoropolymer according to any one of [1] to [4], wherein the fluoropolymer is used for producing an ion exchange membrane of an electrolytic hydrogenation apparatus used in the electrolytic hydrogenation of an aromatic compound. [6] The method for producing a fluoropolymer according to any one of [2] to [5], wherein the ratio R1 is 100 ppm by mass or more and 800 ppm by mass or less. [7] The method for producing a fluoropolymer according to any one of [2] to [5], wherein the monomer m1 is CF ２ =CF-O-(CF ２ ) ｗ -SO ２ F, CF ２ =CF-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ F or CF ２ =CF-[O-CF ２ CF (CF ３ )] ｖ -SO ２ The method for producing a fluoropolymer according to any one of [1] to [6], wherein w is an integer of 1 to 8, and v is an integer of 1 to 5.

[0008] According to the present invention, there can be provided a method for producing a fluoropolymer which can produce a fluoropolymer which has a low ion exchange capacity when converted to an acid form and is excellent in melt elongation.

[0009] The following definitions of terms apply throughout the present specification and claims unless otherwise specified. A "sulfonic acid functional group" refers to a sulfonic acid group (-SO ３ Here, the form of the sulfonate group is, for example, (—SO ３ － ) Ma ＋ , (-SO ３ － ) ２ Mb ２＋ , and (-SO ３ － ) ３ Mc ３＋ (However, Ma ＋ is an alkali metal ion or a quaternary ammonium cation, and Mb ２＋ is a divalent metal ion, Mc ３＋ is a trivalent metal ion.) When there are two ligands, the number of ion exchange groups is counted as two, and when there are three ligands, the number of ion exchange groups is counted as three. The term "group that can be converted into a sulfonic acid functional group" refers to a group that can be converted into a sulfonic acid functional group by known treatments such as hydrolysis treatment and acidification treatment.

[0010] A "unit" in a polymer refers to an atomic group derived from one molecule of a monomer formed by polymerization of the monomer. The unit may be an atomic group formed directly by the polymerization reaction, or may be an atomic group in which part of the atomic group is converted into a different structure by treating the polymer obtained by the polymerization reaction. In the following, units derived from individual monomers may be referred to by the name of the monomer followed by "unit" in some cases.

[0011] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0012] "Total amount of A added" refers to the total amount of A added to the reactor for use in polymerizing the polymer. For example, when A is added to the reactor before and during polymerization, it refers to the sum of the amount of A added to the reactor before polymerization and the amount of A added to the reactor during polymerization. "A" refers to a component used in polymerization, such as TFE, monomer m1, or a radical polymerization initiator, as described below. "During copolymerization" refers to the period from the start of copolymerization to the end of copolymerization. Examples of the "time at which copolymerization is started" include the time when the monomer and the radical polymerization initiator are allowed to coexist in the reactor under a predetermined pressure after the reactor is heated to a predetermined temperature or higher, and the time when the reactor is heated to a predetermined temperature or higher after the monomer and the radical polymerization initiator are allowed to coexist in the reactor. A specific example of the predetermined temperature is 75°C. A specific example of the predetermined pressure is a pressure at which the partial pressure of the monomer tetrafluoroethylene is 0.1 MPa or higher. Examples of the "time point at which copolymerization is terminated" include the time point at which the temperature inside the reactor is lowered below a predetermined temperature, the time point at which the monomer tetrafluoroethylene is purged (released), the time point at which a polymerization inhibitor is added to the reactor, etc. Purging tetrafluoroethylene means that the partial pressure of tetrafluoroethylene is reduced to 0.01 MPa or less.

[0013] [Method for producing a fluoropolymer] The method for producing a fluoropolymer of the present invention is a method for producing a fluoropolymer by copolymerizing tetrafluoroethylene (hereinafter also referred to as "TFE") and a monomer represented by formula (m1) described below (hereinafter also referred to as "monomer m1") in the presence of an organic solvent in a reactor. During the copolymerization, the ratio M1, which is the molar ratio of the content of monomer m1 to the content of TFE in the reactor, is maintained at 0.45 to 3.0, and the composition change rate calculated by formula (C1) described below is -20 to 20%. The fluoropolymer obtained by this production method is also referred to as "polymer F" in this specification. A polymer obtained by converting groups of polymer F that can be converted into sulfonic acid functional groups into sulfonic acid functional groups by known treatments such as hydrolysis treatment and acidification treatment is also referred to as "polymer H".

[0014] According to this production method, obtain a fluoropolymer that has low ion exchange capacity and excellent melt elongation when converted to acid form.The details of the reason for this have not yet been clarified, but it is presumed to be due to the following reasons.When the structure of continuous TFE units increases in the fluoropolymer, crystallization occurs in the fluoropolymer, causing the decrease in melt elongation.When attempting to form a membrane using such a fluoropolymer with low melt elongation, there are problems such as difficulty in thinning.In response to this problem, it is considered that by maintaining the above-mentioned ratio M1 to be above the lower limit value and by making the above-mentioned composition change rate within the above range, the generation of crystallization caused by the continuous structure of TFE units in the obtained fluoropolymer is suppressed, and as a result, a fluoropolymer that has excellent melt elongation is obtained.In addition, it is considered that by maintaining the above-mentioned ratio M1 to be below the upper limit value, the ratio of TFE unit and m1 unit is adjusted, and a fluoropolymer that has low ion exchange capacity when converted to acid form is obtained.

[0015] <Monomer m1> Monomer m1 is a monomer represented by the following formula m1: Formula (m1): CF ２ =CF-O-R ｆ１ -A In formula (m1), R ｆ１is a perfluoroalkylene group which may contain an oxygen atom between the carbon atoms. The number of carbon atoms in the perfluoroalkylene group is preferably 1 or more, more preferably 2 or more, and is preferably 20 or less, more preferably 10 or less. In formula (m1), A is a group which can be converted into a sulfonic acid type functional group. The group which can be converted into a sulfonic acid type functional group is preferably a functional group which can be converted into a sulfonic acid type functional group by hydrolysis. Specific examples of groups which can be converted into a sulfonic acid type functional group include -SO ２ F, -SO ２ Cl, —SO ２ Br is an example.

[0016] The monomer m1 is preferably a compound represented by formula (m1-1): Formula (m1-1) CF ２ =CF-(OCF ２ CFY) ｘ -O-(CF ２ ) ｙ -SO ３ In formula (m1-1), x is an integer of 0 to 2, y is an integer of 1 to 4, and Y is F or CF ３ is.

[0017] Specific examples of the compound represented by formula (m1) include the following compounds: In the formula, w is an integer of 1 to 8, and v is an integer of 1 to 5. CF ２ =CF-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ FCF ２ =CF-[O-CF ２ CF (CF ３ )] ｖ -SO ２ F

[0018] <Organic Solvent> The organic solvent is a polymerization solvent used in the copolymerization in the present production method. Specific examples of the organic solvent include chlorofluorocarbons, hydrochlorofluorocarbons (e.g., 1-chloro-2,3,3-trifluoro-1-propene (HCFO-1233yd)), hydrofluorocarbons, and hydrofluoroethers, of which hydrofluorocarbons and hydrofluoroethers are preferred. The organic solvents may be used alone or in combination of two or more.

[0019] The number of carbon atoms in the hydrofluorocarbon is preferably 4 to 10, more preferably 4 to 8. The ratio of the number of hydrogen atoms to the number of fluorine atoms on a molar basis in the hydrofluorocarbon (hereinafter referred to as H / F) is preferably 0.05 to 20, more preferably 0.06 to 1. When the H / F ratio is 0.05 or more, the solubility of the radical polymerization initiator is good. When the H / F ratio is 20 or less, the chain transfer constant of the polymerization reaction becomes appropriate, making it easy to obtain a fluoropolymer with a desired molecular weight.

[0020] The molecular structure of the hydrofluorocarbon may be linear or branched. Specific examples of hydrofluorocarbons include the following compounds: CF ３ CF ２ CH ２ CH ３ CF ３ CH ２ CF ２ CH ３ CHF ２ CF ２ CF ２ CHF ２ CH ３ CF ２ CHFCF ３ CF ３ CF ２ CHFCF ３ CF ３ CF ２ CF ２ CF ２ H (CF ３ ) ２ CFCH ２ CH ３ CH ３ CHFCF２ CF ２ CH ２ CH ３ CH ３ CF ２ CF ２ CF ２ CHF ２ CF ３ CHFCHFCF ２ CF ３ CF ３ CF ２ CF ２ CF ２ CH ２ CH ３ CF ３ CF ２ CH ２ CH ２ CF ２ CF ３ CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ H (CF ３ ) ２ CFCHFCHFCF ３ CH ３ CF ２ CF ２ CF ２ CF ２ CF ２ CF ２ H CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ CF ２ H CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ CH ２ CH ３ CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ CF ２ CHF ２

[0021] Hydrofluorocarbons are preferred because they have an appropriate boiling point and can produce high molecular weight fluorine-containing polymers. ｎ＋ｍ F ２ｎ＋１ H ２ｍ＋１ (where n is an integer of 2 to 8, and m is an integer of 0 to 3), and CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ H (1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, H / F ratio = 0.077), CF ３ CF ２ CF ２ CF ２ CH ２ CH ３ (1,1,1,2,2,3,3,4,4-nonafluorohexane, H / F ratio = 0.56), CF ３ CF ２ CF ２ CF ２ CF ２ CF ２ CH ２ CH ３ (1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane, H / F ratio=0.38) is more preferred.

[0022] The hydrofluoroether is preferably a compound represented by formula (X) (hydrofluoroalkyl ether, hereinafter referred to as HFE). ｘ１ -O-R ｘ２ (X)

[0023] R ｘ１ and R ｘ２ is a polyfluoroalkyl group, and R ｘ１ and R ｘ２ At least one of R ｘ１ and R ｘ２ The total number of carbon atoms in R is 3 to 8. The polyfluoroalkyl group is preferably a linear or branched hydrofluoroalkyl group or a perfluoroalkyl group. ｘ１ and R ｘ２When one of R is a perfluoroalkyl group, the other is a hydrofluoroalkyl group. ｘ１ and R ｘ２ may be the same or different polyfluoroalkyl groups. ｘ１ and R ｘ２ The total number of fluorine atoms contained in R is preferably greater than the total number of hydrogen atoms. ｘ１ and R ｘ２ The total number of fluorine atoms contained in R is preferably 60% or more, more preferably 65% ​​or more, based on the total number of hydrogen atoms and fluorine atoms. ｘ１ and R ｘ２ The total number of carbon atoms is preferably 3 to 8, and more preferably 4 to 6.

[0024] As HFE, CF ３ CH ２ OCF ２ CF ２ H, CHF ２ CF ２ CH ２ OCF ２ CF ２ H, and CF ３ CF ２ CH ２ OCF ２ CF ２ At least one selected from the group consisting of H is preferred, and CF ３ CH ２ OCF ２ CF ２ H is more preferred.

[0025] <Radical Polymerization Initiator> The copolymerization in the present production method is preferably carried out in the presence of a radical polymerization initiator. Specific examples of the radical polymerization initiator include diacyl peroxides (e.g., disuccinic acid peroxide, benzoyl peroxide, perfluorobenzoyl peroxide, lauroyl peroxide, bis(pentafluoropropionyl)peroxide), azo compounds (e.g., 2,2'-azobis(2-amidinopropane) hydrochlorides, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(dimethyl isobutyrate), azobisisobutyronitrile), and peroxyesters. (for example, t-butyl peroxyisobutyrate, t-butyl peroxypivalate), peroxydicarbonates (for example, diisopropyl peroxydicarbonate, bis(2-ethylhexyl)peroxydicarbonate), hydroperoxides (for example, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide), dialkyl peroxides (for example, di-t-butyl peroxide, perfluoro-di-t-butyl peroxide). The radical polymerization initiator may be used alone or in combination of two or more.

[0026] <Other Components> In the present production method, components such as a polymerization inhibitor and a chain transfer agent (e.g., methanol, chloroform, cyclohexane, n-pentane, n-hexane) may be used. Use of a chain transfer agent can further improve the melt elongation of Polymer F. This is presumably because the chain transfer reaction can suppress the generation of crystals due to the continuous structure of TFE units.

[0027] <Copolymerization> The copolymerization in the present production method is carried out by a solution polymerization method using the above organic solvent.

[0028] The copolymerization temperature of monomer m1 and TFE is preferably 100°C or less, more preferably 95°C or less, even more preferably 90°C or less, particularly preferably 80°C or less, from the viewpoint of being able to control side reactions; and from the viewpoint of further improving the reaction rate of the monomer, it is preferably 20°C or more, more preferably 40°C or more, even more preferably 60°C or more.

[0029] In this production method, it is preferable to charge monomer m1 into the reactor in advance and then initiate copolymerization. TFE may be added to the reactor together with monomer m1 before the start of copolymerization, or it may be added to the reactor already charged with monomer m1. When a radical polymerization initiator is used, the radical polymerization initiator may be added to the reactor together with monomer m1 before the start of copolymerization, or it may be added to the reactor already charged with monomer m1. TFE, monomer m1, and the initiator may each be added continuously, sequentially, or all at once to the reactor. Of these, continuous or sequential addition of TFE and monomer m1 is preferred. Furthermore, it is preferable to add the initiator all at once. Here, in the present invention, "sequential addition" refers to a method in which the additive to be used in polymerization (e.g., monomer, radical polymerization initiator) is added intermittently in portions, in which a period in which the additive to be added and a period in which the additive to be added are not added are alternately repeated, with the period in which the additive to be added occurring twice or more times. In the present invention, "continuous addition" refers to a method of adding a substance to be added (e.g., a monomer, a radical polymerization initiator) to be used in polymerization without interruption within a predetermined period, and does not add the substance outside the predetermined period. In the present invention, "lump addition" refers to a method of adding the entire amount of a substance to be added (e.g., a monomer, a radical polymerization initiator) to be used in polymerization at once.

[0030] During copolymerization in this production method, the ratio M1 (monomer m1 content / TFE content), which is the molar ratio of the content of monomer m1 to the content of TFE in the reactor, is maintained at 0.45 to 3.0. In this specification, "the molar ratio of the content of monomer m1 to the content of TFE in the reactor during copolymerization" is also referred to as "ratio M1." From the viewpoint of further improving the melt elongation of polymer F, the ratio M1 is preferably maintained at 0.50 or more during copolymerization, more preferably at 0.65 or more, and even more preferably at 0.80 or more. From the viewpoint of reducing the ion exchange capacity of polymer H, the ratio M1 is preferably maintained at 2.75 or less during copolymerization, more preferably at 2.50 or less, and even more preferably at 2.20 or less. As a method for adjusting the ratio M1 so that it can maintain the above value during copolymerization, a method can be mentioned in which the amount of at least one of TFE and monomer m1 added during copolymerization is adjusted by sequential addition or continuous addition.Here, the judgment of whether the ratio M1 can maintain the above value is carried out by measuring the ratio M1 every 10 minutes from the time when copolymerization is started.If all the measured ratios M1 satisfy the above value, it is judged that the ratio M1 can maintain the above value.However, if the copolymerization time is less than 10 minutes, the ratio M1 at the time when copolymerization is stopped is measured, and it is judged whether this value satisfies the above value.

[0031] In this production method, the composition change rate calculated by the following formula (C1) is -20 to 20%. Formula (C1) Composition change rate (%) = 100 × {(ratio M1 at time of terminating copolymerization) - (ratio M1 at time of starting copolymerization)} / (ratio M1 at time of starting copolymerization) The composition change rate is preferably -10% or more, more preferably -3% or more, and is preferably 10% or less, more preferably 3% or less, from the viewpoint of being able to suppress the generation of crystals due to a structure of continuous TFE units or further improving the melt elongation of polymer F. Examples of a method for adjusting the composition change rate so that it satisfies the above range include a method in which the amount of at least one of TFE and monomer m1 added during copolymerization is adjusted by sequential or continuous addition.

[0032] When copolymerization is carried out in the presence of a radical polymerization initiator, the ratio of the total amount of radical polymerization initiator added to the reactor to the sum of the total amount of organic solvent added and the total amount of monomer m1 added to the reactor (total amount of radical polymerization initiator added / (total amount of organic solvent added+total amount of monomer m1 added); hereinafter also referred to as "ratio R1") is preferably 1 ppm by mass or more, and from the viewpoint of being able to suppress a decrease in molding processability due to high molecular weight, it is more preferably 50 ppm by mass or more, even more preferably 100 ppm by mass or more, and particularly preferably 200 ppm by mass or more. From the viewpoint of being able to further suppress thermal degradation of the polymer due to the introduction of terminal groups of the radical polymerization initiator, ratio R1 is preferably 1000 ppm by mass or less, more preferably 800 ppm by mass or less, even more preferably 700 ppm by mass or less, and particularly preferably 600 ppm by mass or less.

[0033] The melt elongation of polymer F2 is preferably 5 m / min or more, more preferably 15 m / min or more, and even more preferably 25 m / min or more, from the viewpoint of being able to form a thin film, and is preferably 300 m / min or less, more preferably 250 m / min or less, and even more preferably 200 m / min or less, from the viewpoint of preventing the polymer from being stretched by its own weight and becoming oriented. The melt elongation of polymer F2 is determined by the method described in the Examples section below.

[0034] <Physical Properties> The TQ value of Polymer F is preferably 180° C. or higher, more preferably 190° C. or higher, and even more preferably 200° C. or higher, and is preferably 300° C. or lower, more preferably 280° C. or lower, and even more preferably 260° C. or lower. The TQ value is a value related to the molecular weight of the polymer, and ３ The TQ value of Polymer F is determined by the method described in the Examples section below.

[0035] As described above, polymer H is obtained by converting the groups of polymer F that can be converted to sulfonic acid functional groups into sulfonic acid functional groups by known treatments such as hydrolysis and acidification. The ion exchange capacity of polymer H is preferably 1.0 meq / g dry resin or less, more preferably 0.9 meq / g dry resin or less, and even more preferably 0.8 meq / g dry resin or less, from the viewpoint of suitability for the production of ion exchange membranes in the electrolytic hydrogenation apparatus described below. The ion exchange capacity of polymer H is preferably 0.4 meq / g dry resin or more, more preferably 0.5 meq / g dry resin or more, and even more preferably 0.6 meq / g dry resin or more, from the viewpoint of better performance of the electrolytic hydrogenation apparatus described below. The ion exchange capacity of polymer H is determined by the method described in the Examples section below.

[0036] <Applications> The application of polymer F obtained by this production method is not particularly limited, but it is preferably used for the production of ion exchange membranes of electrolytic hydrogenation apparatuses used for the electrolytic hydrogenation of aromatic compounds (e.g., benzene, toluene, naphthalene). Details of the electrolytic hydrogenation apparatus used for the electrolytic hydrogenation of aromatic compounds are as described in WO 2021 / 157639.

[0037] The present invention will be described in detail below with reference to examples. Examples 1 to 8 are working examples, and Examples 9 and 10 are comparative examples. The fluoropolymer having fluorosulfonyl groups according to the examples is referred to as "polymer F", and the fluoropolymer having fluorosulfonyl groups according to the comparative examples is referred to as "polymer F'". Furthermore, the polymer obtained by converting the fluorosulfonyl groups of polymer F to sulfonic acid groups is referred to as "polymer H", and the polymer obtained by converting the fluorosulfonyl groups of polymer F' to sulfonic acid groups is referred to as "polymer H'". It should be noted that the present invention is not limited to these examples. Furthermore, the amount of each component in the tables described below is based on mass unless otherwise specified.

[0038] [Ion Exchange Capacity] Polymer F or polymer F' obtained in each example was subjected to press molding at a temperature 10°C higher than the TQ value or 260°C, whichever was lower, and at 4 MPa (gauge pressure) to obtain a membrane of polymer F or polymer F'. The membrane of polymer F or polymer F' was immersed in an alkaline aqueous solution (aqueous solution A: potassium hydroxide / water = 20 / 80 (mass ratio)) at 80°C for 16 hours to remove -SO of polymer F or polymer F'. ２ F is hydrolyzed to form -SO ３ The polymer film was then immersed in a 3 mol / L aqueous hydrochloric acid solution at 50°C for 30 minutes, and then in ultrapure water at 80°C for 30 minutes. The cycle of immersion in an aqueous hydrochloric acid solution and immersion in ultrapure water was repeated five times in total, and the -SO ３ K to -SO ３ The polymer membrane was converted to H. Washing with ultrapure water was repeated until the pH of the water in which it was immersed reached 7. The polymer membrane was sandwiched between filter paper and air-dried to obtain a membrane of polymer H and polymer H' in each example. The membranes of polymer H and polymer H' were dried in vacuo at 120°C for 12 hours and then immersed in a 0.85 mol / g sodium hydroxide solution (solvent: water / methanol = 10 / 90 (mass ratio)) to neutralize the ion exchange groups. The sodium hydroxide solution after neutralizing the ion exchange groups was back-titrated with 0.1 mol / L hydrochloric acid to determine the ion exchange capacities of polymer H and polymer H'.

[0039] [TQ value] A flow tester (Shimadzu Corporation, Capillary Tube Rheometer Flow Tester, CFT-500D) equipped with a nozzle having an inner diameter of 1 mm and a length of 1 mm was used to measure the TQ value. ２ Polymer F or Polymer F' filled in a cylinder of 100 mm diameter was extruded from a nozzle at 260°C under a load of 30 kg and a pressure of 2.94 MPa. When the extrusion rate of the polymer stabilized, the volume flow rate (mm ３ / sec) was taken as the Q value at 260°C. Next, the volumetric flow rate Q value measured at different temperatures was ３ The temperature at which the temperature reached 1 / second was taken as the TQ value.

[0040] [Melt elongation] Using a capillary rheometer (Capillograph (registered trademark) Model F-1, manufactured by Toyo Seiki Seisakusho) equipped with a capillary having a diameter of 1 mm and a length of 10 mm, the fluoropolymer having fluorosulfonyl groups obtained in each example and filled into a cylinder having a diameter of 9.55 mm was extruded from a nozzle at 270°C under a load of 25 kN. The extruded fluoropolymer (in the form of a strand) was extruded using a pulley at an acceleration of 5 m / s ２ The speed (m / min) at which the fluoropolymer strand broke was measured, and this speed was taken as the melt elongation. ◎: 25 m / min or more ◯: 15 m / min or more but less than 25 m / min △: 5 m / min or more but less than 15 m / min ×: less than 5 m / min

[0041] Example 1 A 2.7 L stainless steel reactor (autoclave) equipped with a stirrer was degassed under vacuum and then charged with CF as the polymerization solvent. ３ CF ２ CF ２ CF ２ CF ２ CF ２ 1,652 g of 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane (hereinafter also referred to as "CH"), CF ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ２ SO ２ 163 g of PSVE (hereinafter also referred to as "PSVE") was charged, and the internal temperature of the reactor was raised to 75°C.

[0042] Next, 73 g of tetrafluoroethylene (hereinafter also referred to as "TFE") and 4 g of a solution prepared by dissolving 2,2'-azobis(dimethyl isobutyrate) (hereinafter also referred to as "V-601") as an initiator in a polymerization solvent at a concentration of 10% by mass were charged, and polymerization was initiated. The ratio M1 at the time of starting copolymerization, calculated from the charged amounts, was 2.00. During the polymerization reaction, TFE was continuously added so as to maintain the same pressure as at the time of starting copolymerization, and PSVE was also continuously added so as to maintain the ratio M1 in the range of 0.45 to 3.0 depending on the mass of TFE added. Furthermore, to confirm whether the ratio M1 was being maintained at the above value during copolymerization, sampling was performed every 10 minutes from the time of starting copolymerization, and the amount of unreacted TFE and the amount of unreacted PSVE in the reactor were confirmed. When the amount of TFE introduced from the start of the reaction (excluding the amount charged at the time of starting copolymerization; in Table 1 below, this is referred to as "post-addition amount of TFE") reached 134 g, the reactor was cooled to 10°C, and unreacted TFE was discharged outside the system to terminate the polymerization. The amount of PSVE introduced from the start of the reaction (excluding the amount charged at the time of starting copolymerization; in Table 1 below, this is referred to as "post-addition amount of PSVE") was 55 g. The definition of ratio M1 is as described above.

[0043] The entire slurry content in the reactor was taken out and its mass was measured, and the mass of unreacted TFE at the time of terminating the copolymerization was calculated from the difference with the total charged amount. Subsequently, methanol was added to the slurry content and stirred, and the polymer was coagulated and precipitated. The polymer was recovered from the coagulated crude liquid by suction filtration and dried at 80 ° C for 10 hours, obtaining 180 g of fluoropolymer F1, which is a TFE / PSVE copolymer, as a white powder. Furthermore, when the coagulated crude liquid was quantitatively analyzed by gas chromatography (GC), it was found that it contained 8.1 mass % of PSVE, so the mass of unreacted PSVE at the time of terminating the copolymerization was calculated. Similarly, in order to calculate the ratio M1 in the reaction environment every 10 minutes from the time of starting copolymerization, GC of the liquid sampled every 10 minutes was measured, and the masses of unreacted TFE and unreacted PSVE in the liquid phase were calculated. The masses of unreacted TFE and unreacted PSVE present in the gas phase were calculated from the gas state equation taking into account the vapor pressure of PSVE, the space volume and temperature of the reactor, and the pressure, and the ratio M1 was calculated from the sum of the masses of the liquid phase and the gas phase. As a result, it was confirmed that the ratios M1 measured every 10 minutes were all within the range of 2.00 to 2.01, so in the production method of Example 1, it can be said that the ratio M1 can be maintained in the range of 0.45 to 3.0 during copolymerization. Furthermore, since the ratio M1 at the time of stopping copolymerization was 2.01, the composition change rate calculated by the following formula (C1) was 0.5%. Composition change rate (%)=100×{(ratio M1 at the time when copolymerization is stopped)−(ratio M1 at the time when copolymerization is started)} / (ratio M1 at the time when copolymerization is started)

[0044] The TQ value of fluoropolymer F1 was 247°C, and the ion exchange capacity (hereinafter also referred to as "IEC") of fluoropolymer H1 corresponding to fluoropolymer F1 was 0.64 milliequivalents / g dry resin. In Table 1, "meq / g" means "milliequivalents / g dry resin", which is a unit of ion exchange capacity. The evaluation results of the melt elongation of fluoropolymer F1 are also shown in Table 1.

[0045] [Examples 2 to 3] Polymerization solvent CH was replaced with CF ３ CH ２ OCF ２ CF２ Fluoropolymers F2 to F3 in Examples 2 to 3 were obtained in the same manner as in Example 1, except that the melt elongation and melt viscosity of the fluoropolymers F2 to F3 were changed to Asahiklin AE-3000 (manufactured by AGC Inc., hereinafter referred to as "AE3000") and the conditions in Example 1 were changed as shown in Table 1. Table 1 shows the TQ value and melt elongation of the fluoropolymers F2 to F3, and the IEC of the fluoropolymers H2 to H3 corresponding to the fluoropolymers F2 to F3.

[0046] Example 4 Fluoropolymer F4 in Example 4 was obtained in the same manner as in Example 1, except that the conditions in Example 1 were changed as shown in Table 1. Table 1 shows the TQ value and melt elongation of fluoropolymer F4, and the IEC of fluoropolymer H4 corresponding to fluoropolymer F4.

[0047] [Examples 5 to 7] Polymerization solvent CH was replaced with CF ３ CH ２ OCF ２ CF ２ Fluoropolymers F5 to F7 in Examples 5 to 7 were obtained in the same manner as in Example 1, except that the melt elongation and melt viscosity of the fluoropolymers F5 to F7 were changed to Asahiklin AE-3000 (manufactured by AGC Inc., hereinafter referred to as "AE3000") and the conditions in Example 1 were changed as shown in Table 1. Table 1 shows the TQ value and melt elongation of the fluoropolymers F5 to F7, and the IEC of the fluoropolymers H5 to H7 corresponding to the fluoropolymers F5 to F7.

[0048] [Example 8] Fluoropolymer F8 in Example 8 was obtained in the same manner as in Example 1, except that the conditions in Example 1 were changed as shown in Table 1. Table 1 shows the TQ value and melt elongation of fluoropolymer F8, and the IEC of fluoropolymer H8 corresponding to fluoropolymer F8.

[0049] [Example 9] A 2.7 L stainless steel reactor (autoclave) equipped with a stirrer was degassed under vacuum, and then 1636 g of CH and 184 g of PSVE were charged as the polymerization solvent, and the internal temperature of the reactor was raised to 75 ° C. Next, 74 g of TFE and 17 g of a solution prepared by dissolving V-601 as an initiator in the polymerization solvent at a concentration of 10% by mass were charged, and polymerization was initiated. The ratio M1 at the time of starting copolymerization, calculated from the charged amounts, was 1.78. During the polymerization reaction, TFE was continuously added so as to maintain the same pressure as at the time of starting copolymerization. When the amount of TFE introduced from the start of the reaction (i.e., the amount of TFE added later) reached 134 g, the reactor was cooled to 10 ° C., and then the unreacted TFE was released from the system to terminate the polymerization.

[0050] The entire slurry content in the reactor was removed, its mass was measured, and the weight of unreacted TFE released outside the system at the time of terminating the copolymerization was calculated from the difference from the total charged amount. Subsequently, methanol was added to the slurry content and stirred to flocculate and precipitate the polymer. The polymer was recovered from the flocculated crude liquid by suction filtration and dried at 80°C for 10 hours to obtain 177 g of fluoropolymer F'1, a TFE / PSVE copolymer, as a white powder. Furthermore, when the flocculated filtrate was quantitatively analyzed by gas chromatography (GC), it was found to contain 6.7% by mass of PSVE, and therefore the weight of unreacted PSVE at the time of terminating the copolymerization was calculated. Furthermore, the ratio M1 in the reaction environment was measured every 10 minutes from the start of copolymerization using the same method as in Example 1, and it was confirmed that all ratios M1 were within the range of 1.78 to 2.49. Furthermore, since the ratio M1 at the time when copolymerization was terminated was 2.49, it was confirmed that the above-mentioned composition change rate did not satisfy the range of -20 to 20%.

[0051] The TQ value of fluoropolymer F'1 was 232° C., and the IEC of fluoropolymer H'1 corresponding to fluoropolymer F'1 was 0.63 meq / g dry resin. The evaluation results of melt elongation of fluoropolymer F'1 are shown in Table 1.

[0052] Example 10 Fluoropolymer F'2 in Example 10 was obtained in the same manner as in Example 9, except that the conditions in Example 9 were changed as shown in Table 1. Table 1 shows the TQ value and melt elongation of fluoropolymer F'2, and the IEC of fluoropolymer H'2 corresponding to fluoropolymer F'2.

[0053]

[0054] As shown in Table 1, it was confirmed that, so long as the value of the ratio M1 in the reactor is maintained at 0.45 to 3.0 during copolymerization and the rate of composition change is within the range of -20 to 20%, a fluoropolymer which has a low ion exchange capacity when converted to an acid form and is excellent in melt elongation can be produced (Examples 1 to 8).

[0055] The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-147444, filed on September 12, 2023, are incorporated herein by reference as part of the disclosure of the present invention.

Claims

1. A method for producing a fluoropolymer by copolymerizing tetrafluoroethylene with a monomer m1 represented by the following formula (m1) in the presence of an organic solvent in a reactor, characterized in that during the copolymerization, a ratio M1, which is a molar ratio of the content of said monomer m1 to the content of said tetrafluoroethylene in the reactor, is maintained at 0.45 to 3.0, and the rate of composition change calculated by the following formula (C1) is -20 to 20%. ２ =CF-O-R ｆ１ -A In formula (m1), R ｆ１ is a perfluoroalkylene group which may contain an oxygen atom between the carbon atoms, and A is a group which can be converted into a sulfonic acid functional group. Formula (C1) Composition change rate (%)=100×{(ratio M1 at the time when copolymerization is terminated)−(ratio M1 at the time when copolymerization is started)} / (ratio M1 at the time when copolymerization is started) 2. The method for producing a fluoropolymer according to claim 1, wherein the copolymerization is carried out in the presence of a radical polymerization initiator, and a ratio R1 of a total amount of the radical polymerization initiator charged in the reactor to a sum of a total amount of the organic solvent and a total amount of the monomer m1 charged in the reactor is 1 to 1000 ppm by mass.

3. The method for producing a fluoropolymer according to claim 1 or 2, wherein the temperature in the copolymerization is 100° C. or lower.

4. The process for producing a fluoropolymer according to claim 1 or 2, wherein said tetrafluoroethylene and said monomer m1 are added to said reactor continuously or stepwise.

5. The method for producing a fluoropolymer according to claim 1 or 2, wherein the fluoropolymer is used for producing an ion exchange membrane of an electrolytic hydrogenation apparatus used for the electrolytic hydrogenation of aromatic compounds.

6. The method for producing a fluoropolymer according to claim 2, wherein the ratio R1 is 100 ppm by mass or more and 800 ppm by mass or less.

7. The monomer m1 is CF ２ =CF-O-(CF ２ ) ｗ -SO ２ F, C.F. ２ =CF-O-CF ２ CF (CF ３ )-O-(CF ２ ) ｗ -SO ２ F or CF ２ =CF-[O-CF ２ CF (CF ３ ) ] ｖ -SO ２ The process for producing a fluorine-containing polymer according to claim 1 or 2, wherein (In the formula, w is an integer from 1 to 8, and v is an integer from 1 to 5.)