WO2025057732A1 - Method for producing fluorine-containing polymer - Google Patents

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-R^f1-A (R^f1 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 fluoropolymer

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

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

International Publication No. 2016/104379

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

The present invention was made in consideration of the above problems, and aims to provide a method for producing a fluoropolymer that has a low ion exchange capacity when converted to an acid form and excellent melt elongation.

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

That is, the inventors discovered that the above problems can be solved by the following configuration.
[1]
A method for producing a fluoropolymer by copolymerizing tetrafluoroethylene and a monomer m1 represented by the following formula (m1) in the presence of an organic solvent in a reactor, comprising the steps of:
A method for producing a fluoropolymer, characterized in that during the copolymerization, a ratio M1, which is a 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 a composition change rate calculated by the following formula (C1) is −20 to 20%.
Formula (m1) CF 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 type functional group.
Formula (C1) 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)
[2]
The copolymerization is carried out in the presence of a radical polymerization initiator,
The method for producing a fluoropolymer according to [1], wherein 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 [1] or [2], wherein the temperature in the copolymerization is 100° C. or lower.
[4]
The process for producing a fluoropolymer according to any one of [1] to [3], wherein the tetrafluoroethylene and the monomer m1 are added continuously or successively to the reactor.
[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 monomer m1 is
CF ₂ =CF-O-(CF ₂ ) _w -SO ₂ F,
The method for producing a fluorine- _containing polymer according to any _one of [1] to [6], wherein 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 F.
(In the formula, w is an integer from 1 to 8, and v is an integer from 1 to 5.)

The present invention provides a method for producing a fluoropolymer that has a low ion exchange capacity when converted to an acid form and has excellent melt elongation.

The following definitions of terms apply throughout the specification and claims, unless otherwise stated.
The term "sulfonic acid functional group" refers to a sulfonic acid group (-SO ₃ H) or a sulfonate group. Examples of the form of the sulfonate group include (-SO ₃ ^- )Ma ⁺ , (-SO ₃ ^- ) _2Mb ²⁺ , and (-SO ₃ ^- ) _3Mc ³⁺ (where Ma ⁺ is an alkali metal ion or a quaternary ammonium cation, Mb ²⁺ is a divalent metal ion, and 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 a known treatment such as hydrolysis treatment or acidification treatment.

The term "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 processing the polymer obtained by the polymerization reaction. In the following, units derived from individual monomers will sometimes be referred to by the name of the monomer with "unit" added.

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

"Total amount of A added" means the total amount of A added into the reactor for use in polymerizing the polymer, and for example, when A is added into the reactor before and during polymerization, it means the total amount of A added into the reactor before polymerization and A added into the reactor during polymerization. Note that "A" is a component used in polymerization, and examples thereof include TFE, monomer m1, or a radical polymerization initiator, which will be described later.
The term "during copolymerization" refers to the period from the start of copolymerization to the end of copolymerization.
Examples of the "time to start copolymerization" include the time when the monomer and the radical polymerization initiator are made 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 made 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 to terminate the copolymerization" include the time when the temperature inside the reactor is lowered below a predetermined temperature, the time when the monomer tetrafluoroethylene is purged (released), the time when 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.

[Method of producing fluoropolymer]
The process for producing a fluoropolymer of the present invention is a process 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 the monomer m1 to the content of the TFE in the reactor, is maintained at 0.45 to 3.0, and the composition change rate calculated by the formula (C1) described below is −20 to 20%.
The fluoropolymer obtained by this production method is also referred to in this specification as "Polymer F." Moreover, a polymer obtained by converting a group capable of being converted into a sulfonic acid type functional group of Polymer F into a sulfonic acid type functional group by a known treatment such as hydrolysis treatment or acidification treatment is also referred to as "Polymer H."

According to the present production method, a fluoropolymer having a low ion exchange capacity and excellent melt elongation when converted to an acid form can be obtained. Although the details of the reason for this are not yet clear, it is presumed to be due to the following reasons.
When the number of structures in which TFE units are continuous increases in the fluoropolymer, crystals are generated in the fluoropolymer, which causes the melt elongation to decrease.When attempting to form a membrane using such a fluoropolymer with low melt elongation, there are problems such as difficulty in making it thin.
It is believed that, in response to this problem, by maintaining the above ratio M1 at or above the lower limit and by setting the above composition change rate within the above range, the generation of crystals due to the continuous structure of TFE units in the obtained fluoropolymer is suppressed, and as a result, a fluoropolymer excellent in melt elongation is obtained.
Moreover, it is considered that by maintaining the above ratio M1 at not more than the upper limit, the ratio of TFE units to m1 units is adjusted to obtain a fluoropolymer having a low ion exchange capacity when converted to an acid form.

<Monomer m1>
The monomer m1 is a monomer represented by the following formula m1.
Formula (m1) CF ₂ =CF-O-R ^f1 -A
In formula (m1), R ^f1 is a perfluoroalkylene group which may contain an oxygen atom between 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 that can be converted into a sulfonic acid functional group. The group that can be converted into a sulfonic acid functional group is preferably a functional group that can be converted into a sulfonic acid functional group by hydrolysis. Specific examples of the group that can be converted into a sulfonic acid functional group include _-SO2F , _-SO2Cl , and _-SO2Br .

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 F
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 _CF3 .

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 F
CF ₂ =CF-O-CF ₂ CF(CF ₃ )-O-(CF ₂ ) _w -SO ₂ F
CF ₂ =CF-[O-CF ₂ CF(CF ₃ )] _v -SO ₂ F

<Organic Solvent>
The organic solvent is a polymerization solvent used in the copolymerization in this 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.

The hydrofluorocarbon preferably has 4 to 10 carbon atoms, and more preferably has 4 to 8 carbon atoms.
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, and a fluoropolymer having a desired molecular weight is easily obtained.

The molecular structure of the hydrofluorocarbon may be linear or branched.
Specific examples of hydrofluorocarbons include the following compounds:
_{CF3CF2CH2CH3 ​ ​ ​
CF3CH2CF2CH3 ​ ​ ​
CHF2CF2CF2CHF2 ​ ​ ​
CH3CF2CHFCF3 ​ ​}
CF ₃ CF ₂ CHFCF _{3
CF3CF2CF2CF2H ​ ​ ​
( CF3 ) 2CFCH2CH3
CH3CHFCF2CF2CH2CH3 ​ ​ ​ ​
CH3CF2CF2CF2CHF2 ​ ​ ​ ​}
CF ₃ CHFCHFCF ₂ CF _{3
CF3CF2CF2CF2CH2CH3 ​ ​ ​ ​ ​
CF3CF2CH2CH2CF2CF3 ​ ​ ​ ​ ​
CF3CF2CF2CF2CF2CF2H ​ ​ ​ ​ ​}
(CF ₃ ) ₂ CFCHFCHFCF ₃
CH ₃ CF ₂ CF ₂ CF ₂ CF ₂ CF ₂ CF ₂ H
_{CF3CF2CF2CF2CF2CF2CF2H ​ ​ ​ ​ ​ ​
CF3CF2CF2CF2CF2CF2CH2CH3 ​ ​ ​ ​ ​ ​ ​}
CF ₃ CF ₂ CF ₂ CF ₂ CF ₂ CF ₂ CF ₂ CHF ₂

The hydrofluorocarbon is preferably a hydrofluorocarbon represented by C _n+m F _2n+1 H _2m+1 (wherein n is an integer of 2 to 8, and m is an integer of 0 to 3) because it has an appropriate boiling point and because a high molecular weight fluorine-containing polymer can be obtained, and examples of the hydrofluorocarbon include 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 CH 2} More preferred is CH ₃ (1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane, H/F ratio=0.38).

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

R ^x1 and R ^x2 are polyfluoroalkyl groups, at least one of R ^x1 and R ^x2 has a hydrogen atom, and the total number of carbon atoms of R ^x1 and R ^x2 is 3 to 8.
The polyfluoroalkyl group is preferably a linear or branched hydrofluoroalkyl group or a perfluoroalkyl group. When one of ^{R x1} and R ^x2 is a perfluoroalkyl group, the other is a hydrofluoroalkyl group. R ^x1 and R ^x2 may be the same or different polyfluoroalkyl groups.
The total number of fluorine atoms possessed by R ^x1 and R ^x2 is preferably greater than the total number of hydrogen atoms. The total number of fluorine atoms possessed by R ^x1 and R ^x2 is preferably 60% or more, more preferably 65% or more, of the total number of hydrogen atoms and fluorine atoms.
The total number of carbon atoms in R ^x1 and R ^x2 is preferably 3 to 8, and more preferably 4 to 6.

As _the HFE, at _{least one} selected _{from the group} consisting _{of CF3CH2OCF2CF2H} , _{CHF2CF2CH2OCF2CF2H and CF3CF2CH2OCF2CF2H is} preferred _{, with CF3CH2OCF2CF2H being} more _{preferred .}

<Radical Polymerization Initiator>
The copolymerization in this 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, perfluoro-benzoyl 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(dimethylisobutyrate), azobisisobutyronitrile), and peroxyesters. (e.g., t-butyl peroxyisobutyrate, t-butyl peroxypivalate), peroxydicarbonates (e.g., diisopropyl peroxydicarbonate, bis(2-ethylhexyl)peroxydicarbonate), hydroperoxides (e.g., diisopropylbenzene hydroperoxide, t-butyl hydroperoxide), dialkyl peroxides (e.g., di-t-butyl peroxide, perfluoro-di-t-butyl peroxide).
The radical polymerization initiator may be used alone or in combination of two or more kinds.

<Other Ingredients>
In the present production method, components such as a polymerization inhibitor and a chain transfer agent (for example, 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.

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

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, and particularly preferably 80°C or less, from the viewpoint of controlling side reactions, and is preferably 20°C or more, more preferably 40°C or more, and even more preferably 60°C or more, from the viewpoint of further improving the reaction rate of the monomers.

In this production method, it is preferable to charge the monomer m1 in advance into the reactor and then start the copolymerization.
TFE may be added to the reactor together with monomer m1 before the start of copolymerization, or may be added to the reactor in which monomer m1 has been charged.
When a radical polymerization initiator is used, the radical polymerization initiator may be added to the reactor together with the monomer m1 before the start of copolymerization, or may be added to the reactor in which the monomer m1 has been charged.
TFE, monomer m1 and initiator may be added continuously, successively or all at once into the reactor. Among them, TFE and monomer m1 are preferably added continuously or successively. In addition, initiator is preferably added all at once.
Here, in the present invention, the term "sequential addition" refers to a method of adding an additive (e.g., a monomer, a radical polymerization initiator) to be used in polymerization in portions and intermittently, in which a period in which the additive is added and a period in which the additive is not added are alternately repeated, and the period in which the additive is added is two or more times.
In the present invention, the term "continuous addition" refers to a method in which an additive to be used in polymerization (e.g., a monomer, a radical polymerization initiator) is added continuously within a predetermined period, and the additive is not added outside the predetermined period.
In the present invention, the term "addition all at once" refers to a method in which the entire amount of the substances to be added (for example, monomers, radical polymerization initiator) used in the polymerization is added at once.

During the copolymerization in this production method, the ratio M1 (content of monomer m1/content of TFE), 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 maintained at 0.65 or more, and even more preferably maintained at 0.80 or more.
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, in order to reduce the ion exchange capacity of polymer H.
As a method for adjusting the ratio M1 so as to maintain the above value during copolymerization, there can be mentioned a method in which the amount of at least one of TFE and monomer m1 added during copolymerization is adjusted by successive 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 start of copolymerization. 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 is measured at the time of stopping the copolymerization, and it is judged whether this value satisfies the above value.

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 the time when copolymerization is stopped)−(ratio M1 at the time when copolymerization is started)}/(ratio M1 at the time when copolymerization is started)
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 in which TFE units are continuous, or of further improving the melt elongation of polymer F.
As a method for adjusting the composition change rate so as to satisfy the above range, there can be mentioned a method in which the amount of at least one of TFE and monomer m1 added during copolymerization is adjusted by gradual or continuous addition.

When the copolymerization is carried out in the presence of a radical polymerization initiator, the ratio of the total amount of radical polymerization initiator added charged into the reactor to the sum of the total amount of organic solvent added and the total amount of monomer m1 added charged into 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 moldability due to high molecular weight, is more preferably 50 ppm by mass or more, further preferably 100 ppm by mass or more, and particularly preferably 200 ppm by mass or more.
The ratio R1 is preferably 1000 ppm by mass or less, more preferably 800 ppm by mass or less, still more preferably 700 ppm by mass or less, and particularly preferably 600 ppm by mass or less, from the viewpoint of further suppressing thermal deterioration of the polymer due to the introduction of a radical polymerization initiator terminal group.

The melt elongation of polymer F 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 under its own weight and becoming oriented.
The melt elongation of polymer F2 is determined by the method described in the Examples section below.

<Physical Properties>
The TQ value of Polymer F is preferably 180° C. or more, more preferably 190° C. or more, and even more preferably 200° C. or more, and is preferably 300° C. or less, more preferably 280° C. or less, and even more preferably 260° C. or less.
The TQ value is related to the molecular weight of the polymer and is indicated at the temperature exhibiting a volumetric flow rate of 100 mm ³ /sec.
The TQ value of Polymer F is determined by the method described in the Examples section below.

As described above, polymer H can be obtained by converting the 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.
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, because this is suitable for producing an ion exchange membrane 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 can be determined by the method described in the Examples section below.

<Applications>
The use of Polymer F obtained by this production method is not particularly limited, but it is preferably used for producing an ion exchange membrane for an electrolytic hydrogenation apparatus used in 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.

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 fluorosulfonyl group-containing fluoropolymer of the examples is referred to as "Polymer F", and the fluorosulfonyl group-containing fluoropolymer of 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'".
However, the present invention is not limited to these examples. Furthermore, the blending amount of each component in the tables described below is based on mass unless otherwise specified.

[Ion exchange capacity]
Using the polymer F or polymer F' obtained in each example, press molding was performed 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 film of polymer F or polymer F'. The film 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, and -SO ₂ F of polymer F or polymer F' was hydrolyzed and converted to -SO ₃ K. Furthermore, the polymer film was immersed in a 3 mol/L aqueous hydrochloric acid solution at 50°C for 30 minutes, and then immersed in ultrapure water at 80°C for 30 minutes. A cycle of immersion in an aqueous hydrochloric acid solution and immersion in ultrapure water was performed a total of 5 times, and -SO ₃ K of the polymer was converted to -SO ₃ H. Washing with ultrapure water was repeated until the pH of the water in which the polymer film was immersed became 7. The polymer films were sandwiched between filter papers and air-dried to obtain films of Polymer H and Polymer H' in each example.
The membranes of Polymer H and Polymer H' were vacuum-dried 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'.

[TQ value]
Using a flow tester (Shimadzu Corporation, Capillary Rheometer Flow Tester, CFT-500D) equipped with a nozzle with an inner diameter of 1 mm and a length of 1 mm, polymer F or polymer F' filled in a cylinder with a cross-sectional area of 1 ^cm2 was extruded from the nozzle at 260°C under a load of 30 kg and a pressure of 2.94 MPa. At that time, the volume flow rate ( ^mm3 /sec) of the extruded polymer when the extrusion rate of the polymer stabilized was taken as the Q value at 260°C. Next, the temperature was changed, and the temperature at which the volume flow rate Q value reached 100 ^mm3 /sec was taken as the TQ value.

[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 packed in 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 taken up using a pulley at an acceleration rate of 5 m/ ^s2 , and the speed (m/min) at which the strand of fluoropolymer broke was measured, and this speed was regarded as the melt elongation.
◎: 25 m/min or more 〇: 15 m/min or more, less than 25 m/min △: 5 m/min or more, less than 15 m/min ×: Less than 5 m/min

[Example 1]
A 2.7 L stainless steel reactor (autoclave) equipped with a stirrer was degassed under vacuum, and then 1652 g _of CF ₃ CF ₂ CF ₂ CF ₂ CF ₂ H (1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane (hereinafter also referred to as "C6H") and 163 g of CF ₂ ═CFOCF ₂ CF(CF ₃ )O(CF ₂ ) ₂ SO ₂ F (hereinafter also referred to as "PSVE") were charged as a polymerization solvent, and the internal temperature of the reactor was raised to 75° C.

Next, 73 g of tetrafluoroethylene (hereinafter also referred to as "TFE") and 4 g of a solution of 2,2'-azobis(dimethylisobutyrate) (hereinafter also referred to as "V-601") as an initiator dissolved in a polymerization solvent at a concentration of 10% by mass were charged, and polymerization was started. The ratio M1 at the time of starting copolymerization converted from the charged amount 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 that the ratio M1 could be maintained in the range of 0.45 to 3.0 depending on the mass of TFE added. Furthermore, in order to confirm whether the ratio M1 can be 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 described later, this is referred to as "amount of TFE added later") reached 134 g, the reactor was cooled to 10° C., and then 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 start of copolymerization; in Table 1 below, this is referred to as "PSVE post-addition amount") was 55 g.
The ratio M1 is defined as above.

The slurry contents in the reactor are all taken out, and their mass is measured, and the mass of unreacted TFE at the time of stopping copolymerization that is discharged outside the system is calculated from the difference with the total amount charged.Subsequently, methanol is put into the slurry contents, and stirred, so that polymer is flocculated and precipitated.By suction filtration, polymer is recovered from the flocculated crude liquid, and dried at 80°C for 10 hours, and 180g of fluoropolymer F1, which is white powder, is obtained as TFE/PSVE copolymer.
Furthermore, the coagulated crude liquid was quantitatively analyzed by gas chromatography (GC), and it was found that PSVE was contained in an amount of 8.1% by mass, so that the mass of unreacted PSVE at the time of stopping the copolymerization was calculated. Similarly, in order to calculate the ratio M1 in the reaction environment every 10 minutes after the start of copolymerization, the 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. In addition, the masses of unreacted TFE and unreacted PSVE present in the gas phase were calculated from the gas state equation considering 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 that 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.
In addition, since the ratio M1 at the time when the copolymerization was terminated 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)

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

[Examples 2 to 3]
The polymerization solvent C6H was changed to CF ₃ CH ₂ OCF ₂ CF ₂ H (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. Except for this, fluoropolymers F2 to F3 in Examples 2 to 3 were obtained in the same manner as in Example 1.
Table 1 shows the TQ value and melt elongation of fluoropolymers F2 to F3, and the IEC of fluoropolymers H2 to H3 corresponding to fluoropolymers F2 to F3.

[Example 4]
A 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.

[Examples 5 to 7]
Fluorine-containing polymers F5 to F7 in Examples 5 to 7 were obtained in the same manner as in Example 1, except that the polymerization solvent C6H was changed to CF ₃ CH ₂ OCF ₂ CF ₂ H (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 values and melt elongations of the fluoropolymers F5 to F7, and the IEC values of the fluoropolymers H5 to H7 corresponding to the fluoropolymers F5 to F7.

[Example 8]
A 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.

[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 a 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 in which V-601 was dissolved in a polymerization solvent at a concentration of 10% by mass as an initiator were charged, and polymerization was initiated. The ratio M1 at the time of starting copolymerization, calculated from the charged amount, 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 unreacted TFE was discharged outside the system to terminate the polymerization.

The slurry content in the reactor is taken out and its mass is measured, and the weight of unreacted TFE discharged outside the system at the time of stopping copolymerization is calculated from the difference with the total amount charged.Subsequently, methanol is put into the slurry content and stirred, and polymer is flocculated and precipitated.The polymer is recovered from the flocculated crude liquid by suction filtration, and dried at 80°C for 10 hours, and 177g of fluoropolymer F'1, which is a white powder TFE/PSVE copolymer, is obtained.
Furthermore, the coagulated filtrate was quantitatively analyzed by gas chromatography (GC) and found to contain 6.7% by mass of PSVE, from which the weight of unreacted PSVE at the time of terminating the copolymerization was calculated. In addition, the ratio M1 in the reaction environment was measured every 10 minutes from the start of the copolymerization in the same manner as in Example 1, and it was confirmed that all ratios M1 were within the range of 1.78 to 2.49.
Moreover, since the ratio M1 at the time when the 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%.

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.
Moreover, the evaluation results of the melt elongation of the fluoropolymer F′1 are shown in Table 1.

[Example 10]
A 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.

As shown in Table 1, if the ratio M1 in the reactor is maintained between 0.45 and 3.0 during copolymerization and the composition change rate is within the range of -20% to 20%, it has been confirmed that a fluoropolymer with low ion exchange capacity and excellent melt elongation when converted to an acid form can be produced (Examples 1 to 8).

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

Claims (7)

A method for producing a fluoropolymer by copolymerizing tetrafluoroethylene and a monomer m1 represented by the following formula (m1) in the presence of an organic solvent in a reactor, comprising the steps of:
A method for producing a fluoropolymer, 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 a composition change rate calculated by the following formula (C1) is −20 to 20%.
Formula (m1) CF 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 type functional group.
Formula (C1) 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) The copolymerization is carried out in the presence of a radical polymerization initiator,
The method for producing a fluoropolymer according to claim 1, wherein a ratio R1 of a total amount of the radical polymerization initiator charged into the reactor to a sum of a total amount of the organic solvent and a total amount of the monomer m1 charged into the reactor is 1 to 1000 ppm by mass. The method for producing a fluoropolymer according to claim 1 or 2, wherein the copolymerization temperature is 100°C or less. The method for producing a fluoropolymer according to claim 1 or 2, wherein the tetrafluoroethylene and the monomer m1 are added continuously or sequentially to the reactor. The method for producing a fluoropolymer according to claim 1 or 2, wherein the fluoropolymer is used to produce an ion exchange membrane of an electrolytic hydrogenation apparatus used in the electrolytic hydrogenation of aromatic compounds. 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. The monomer m1 is
CF ₂ =CF-O-(CF ₂ ) _w -SO ₂ F,
3. The process for producing a fluorine-containing polymer according to claim 1 or 2, wherein 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 F.
(In the formula, w is an integer from 1 to 8, and v is an integer from 1 to 5.)