JP7848945B2 - Method for producing an aqueous dispersion, method for producing a second fluorine-containing polymer, aqueous dispersion, solid composition - Google Patents

Description

This invention relates to a method for producing an aqueous dispersion, a method for producing a second fluorine-containing polymer, an aqueous dispersion, and a solid composition.

Fluorine-containing polymers are used in various industrial fields because of their excellent heat resistance, chemical resistance, flame retardancy, and weather resistance. In the production of such fluorine-containing polymers, aqueous dispersions containing fluorine-containing polymer particles are sometimes used.
As a method for producing an aqueous dispersion, Patent Document 1 discloses a method for polymerizing a fluorine-containing monomer in the presence of a specific compound.

International Publication No. 2022/019241

We found that the method for producing an aqueous dispersion described in Patent Document 1 results in a small number of fluorine-containing polymer particles, indicating room for improvement.
Furthermore, in terms of reducing environmental impact, it is desirable to substantially avoid using emulsifiers containing fluorine atoms.
The present inventors have found that the method for producing an aqueous dispersion described in Patent Document 1 does not necessarily result in sufficient dispersibility of the fluorine-containing polymer produced, and have further found that there is room to improve the particle count of the fluorine-containing polymer produced.
Furthermore, from the viewpoint of reducing environmental impact, it is desirable to substantially avoid using emulsifiers containing fluorine atoms. This invention also aims to achieve the same number of fluorine-containing polymer particles as when conventional emulsifiers containing fluorine atoms are used, without substantially using emulsifiers containing fluorine atoms.

The present invention aims to provide a method for producing an aqueous dispersion that allows for the production of an aqueous dispersion with a large number of fluorine-containing polymer particles without substantially using an emulsifier containing fluorine atoms.
Furthermore, the present invention also aims to provide a method for producing a second fluorine-containing polymer, an aqueous dispersion, and a solid composition.

As a result of diligent research, the inventors have found that the above problem can be solved by the following configuration.
[1]
Under conditions where an aqueous medium is present and an emulsifier containing a fluorine atom is substantially absent, a first monomer containing tetrafluoroethylene is polymerized in the presence of a compound represented by formula (X) and a polymerization initiator.
A method for producing an aqueous dispersion, comprising producing an aqueous dispersion containing particles of a first fluorine-containing polymer having an average particle diameter of 500 nm or less and having no melting point.
C(X ¹ )(X ² )=C(X ³ )−L−Z (X)
In formula (X),
^X1 , ^X2 , and ^X3 are each independently a hydrogen atom, a fluorine atom, a perfluoromethyl group, or an alkyl group.
L is a single bond or a divalent linking group.
Z is an anionic group or a salt of an anionic group.
[2]
A method for producing the aqueous dispersion described in [1], wherein Z is _-SO3M .
M is a hydrogen atom, a metal atom, N( ^RM1 ) ₄ , or P( ^RM2 ) ₄ .
^RM1 and ^RM2 are each independently hydrogen atoms or substituents, any two of ^RM1 may be bonded to each other to form a ring, and multiple ^RM1 may be the same or different from each other, any two of ^RM2 may be bonded to each other to form a ring, and multiple ^RM2 may be the same or different from each other.
[3]
A method for producing an aqueous dispersion according to [1] or [2], wherein the content of the compound represented by the above formula (X) is 1.0 to 1000 ppm by mass with respect to the total mass of the aqueous medium.
[4]
A method for producing an aqueous dispersion according to any one of [1] to [3], wherein the first monomer contains a perfluoroalkyl vinyl ether.
[5]
In an aqueous dispersion produced by any one of the manufacturing methods described in [1] to [4],
A method for producing a second fluorine-containing polymer, comprising polymerizing a second monomer to produce a second fluorine-containing polymer.
[6]
The method for producing the second fluorine-containing polymer according to [5], wherein the content of the compound represented by formula (S1) described later is 5 ppm by mass or less with respect to the total mass of the aqueous dispersion.
[7]
A method for producing the second fluorine-containing polymer according to [5] or [6], wherein the content of the compound represented by formula (S3) described later is 5 ppm by mass or less with respect to the total mass of the aqueous dispersion.
[8]
A method for producing a second fluorine-containing polymer according to any one of [5] to [7], wherein the second monomer comprises at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride.
[9]
A method for producing a second fluorine-containing polymer according to any one of [5] to [8], wherein the second monomer contains a perfluoroalkyl vinyl ether.
[10]
A method for producing the second fluorine-containing polymer according to any one of [5] to [9], wherein the second fluorine-containing polymer does not have a melting point.
[11]
An aqueous dispersion that is substantially free of water-soluble emulsifiers containing fluorine atoms, and contains particles of a fluorine-containing polymer and an aqueous medium,
The above particle count is 0.5 × ^10¹⁴ particles/mL or more.
The average particle diameter of the above particles is 500 nm or less.
The above fluorine-containing polymer has units based on tetrafluoroethylene and units based on perfluoroalkyl vinyl ether,
An aqueous dispersion in which the above-mentioned fluorine-containing polymer does not have a melting point.
[12]
The aqueous dispersion according to [11], wherein the 1% by mass thermoweight loss temperature of the fluorine-containing polymer is 350°C or higher.
[13]
A solid composition containing a fluorine-containing polymer that does not have a melting point,
The fluorine-containing polymer has units based on tetrafluoroethylene,
The content of the emulsifier having fluorine atoms is 1500 ppb by mass or less relative to the total mass of the solid composition.
The content of the compound represented by formula (S1) is 1500 ppb by mass or less relative to the total mass of the solid composition.
A solid composition in which the content of the compound represented by formula (S3) is 100 ppb by mass or less relative to the total mass of the solid composition.
H-(CF ₂ ) _n1 -COOM ^S (S1)
In formula (S1),
n1 is an integer between 3 and 13.
M ^S is a hydrogen atom, Na, K, or _NH4 .
H-(CF ₂ ) _n2 -SO ₃ M ^S (S3)
In formula (S3),
n² is an integer between 4 and 10.
M ^S is a hydrogen atom, Na, K, or _NH4 .
[14]
The solid composition according to [13], wherein the metal content of the solid composition is less than 5 ppm by mass with respect to the total mass of the solid composition.

According to the present invention, it is possible to provide a method for producing an aqueous dispersion that has a large number of fluorine-containing polymer particles without substantially using an emulsifier containing fluorine atoms.
Furthermore, the present invention can provide a method for producing a second fluorine-containing polymer, an aqueous dispersion, and a solid composition.

The meanings of the terms used in this invention are as follows:
Numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Also, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values shown in the examples.
In this specification, each component may be represented by a single substance or by a combination of two or more substances. When two or more substances are used in combination for each component, the content of that component refers to the total content of the combined substances unless otherwise specified.
In this specification, a combination of two or more preferred embodiments is a more preferred embodiment.
A "unit" is a general term for an atomic group derived from one monomer molecule, which is directly formed by the polymerization of monomers, and an atomic group obtained by chemically transforming a part of the above atomic group. A "unit based on monomers" will also be simply referred to as a "unit" below.
The content (mass %) of each unit relative to the total number of units contained in a polymer is determined by analyzing the polymer using solid-state nuclear magnetic resonance spectroscopy (NMR). However, the content of each unit calculated from the amount of each monomer added usually closely matches the actual content of each unit.

[Method for producing aqueous dispersion]
The present invention provides a method for producing an aqueous dispersion (hereinafter also referred to as "this production method"), which involves polymerizing a compound represented by formula (X) (hereinafter also referred to as "compound X") and a polymerization initiator in the presence of an aqueous medium and a substantially absent emulsifier containing fluorine atoms, to produce an aqueous dispersion (hereinafter also referred to as "first aqueous dispersion") containing particles of a first fluorine-containing polymer having an average particle size of 500 nm or less and no melting point.

The reason why this manufacturing method does not require an emulsifier containing fluorine atoms and results in a large number of particles of the first fluorine-containing polymer is presumed to be that the presence of compound X in the reaction system during polymerization of the first monomer improves the dispersibility of the particles of the first fluorine-containing polymer produced in the first aqueous dispersion, thereby increasing the specific surface area of the particles in the first aqueous dispersion. For example, one possible factor contributing to the improved dispersibility is the improvement in the zeta potential of the particles of the first fluorine-containing polymer due to compound X.
Furthermore, it was found that when polymerizing the second monomer using an aqueous dispersion containing a large number of particles of the first fluorine-containing polymer, the polymerization rate of the second monomer tends to increase as the number of particles of the first fluorine-containing polymer increases. Therefore, it is desirable to increase the number of particles of the first fluorine-containing polymer.
Hereinafter, the fact that the number of particles in the first fluorine-containing polymer increases when the first fluorine-containing polymer is manufactured will also be referred to as "the effect of the present invention."

<Emulsifier>
This manufacturing method is carried out under conditions where emulsifiers containing fluorine atoms are substantially absent.
The statement that the emulsifier containing fluorine atoms is substantially absent means that, in the production of the first aqueous dispersion, the content of the emulsifier containing fluorine atoms is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total mass of the aqueous medium. The lower limit is 0 ppb by mass.
This manufacturing method is preferably carried out under conditions where emulsifiers containing fluorine atoms and emulsifiers without fluorine atoms are substantially absent, in order to prevent a decrease in the molecular weight of the fluorine-containing polymer produced.
The term "substantially absent" means that, in the production of the first aqueous dispersion, the emulsifier content is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total mass of the aqueous medium. The lower limit is 0 ppb by mass.
The content of various emulsifiers can be measured using a liquid chromatograph-mass spectrometer. Specifically, the measurement method described in paragraphs [0721] to [0732] of International Publication No. 2018/181904 is an example.

Emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms are characterized by being water-soluble. A water-soluble emulsifier means an emulsifier whose solubility in 1000 g of water at 25°C is 100 mg or more, and a non-water-soluble emulsifier means an emulsifier other than the water-soluble emulsifier described above. Water-soluble emulsifiers may be either ionic or nonionic.
Emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms include those that do not have a carbon-carbon double bond.
The first fluorine-containing polymer and the second fluorine-containing polymer, described later, are both water-insoluble.
Compound X, the polymer of Compound X, the first fluorine-containing polymer, and the second fluorine-containing polymer, described later, are not emulsifiers.

Examples of emulsifiers containing fluorine atoms include anionic fluorine-containing emulsifiers.
Examples of anionic fluorine-containing emulsifiers include emulsifiers containing fluorine atoms with a total carbon number of 20 or less in the portion excluding the anionic group, and emulsifiers containing fluorine atoms with a molecular weight of 800 or less in the anionic portion. The above-mentioned "anionic portion" refers to the portion of the fluorine-containing emulsifier excluding the cation.

A fluorine-free emulsifier is one that does not contain fluorine atoms and has hydrocarbon groups such as alkyl groups as its hydrophobic portion. It is also possible to substitute the hydrogen atoms of the hydrocarbon groups in a fluorine-free emulsifier with halogen atoms other than fluorine atoms.

Examples of emulsifiers that do not contain fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

Anionic hydrocarbon emulsifiers refer to emulsifiers having a negatively charged hydrophilic portion such as a carboxylic acid group, sulfonic acid group, sulfate group, phosphonic acid group, and phosphate group, and a hydrophobic portion such as an alkyl group or other hydrocarbon group.
Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, a highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, sodium linear alkyl polyethersulfonate supplied by BASF as the Avanel® S series, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity without dissociating into ions in water and have hydrocarbon groups such as alkyl groups as their hydrophobic portion.
Examples of hydrophilic portions of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Examples of nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

Furthermore, other nonionic hydrocarbon emulsifiers include those described in paragraphs [0043] to [0052] of Japanese Patent Publication No. 2016-537499.

Emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms may also contain silicon atoms. Examples of emulsifiers containing silicon atoms include siloxane emulsifiers. Siloxane emulsifiers are hydrocarbon-containing emulsifiers having a siloxane skeleton.
Examples of siloxane emulsifiers include those described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

Emulsifiers that do not contain fluorine atoms may also be polymer emulsifiers. Examples of polymer emulsifiers include polymers having hydrophilic groups in their side chains. Such polymer emulsifiers include polymers that contain units based on compounds having both a site that can react in polymerization and a hydrophilic group. Also included are polymers that have undergone post-treatment such as hydrolysis, and which contain units based on compounds that have a group that can become a hydrophilic group, even if they do not initially have a hydrophilic group.

In this invention, the emulsifier containing fluorine atoms has a molecular weight of 1,000 g/mol or less, and the emulsifier without fluorine atoms has a molecular weight of 100,000 g/mol or less.

<Aqueous medium>
This manufacturing method is carried out under conditions where an aqueous medium is present.
Specific examples of aqueous media include water and mixed solvents of water and water-soluble organic solvents. Specific examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

Before initiating the polymerization of the first monomer used in the polymerization of the first fluorine-containing polymer, the content of the aqueous medium is preferably 20 to 80% by volume, and more preferably 40 to 70% by volume, relative to the volume of the reactor.
In this specification, "before the polymerization of the first monomer used in the polymerization of the first fluorine-containing polymer is started" means immediately before the start of polymerization. Here, "the start of polymerization" refers to the time when the reactor is heated to a temperature above the polymerization temperature and the first monomer and polymerization initiator are brought into the reactor together, and the time when the reactor is heated to a temperature above the polymerization temperature after the first monomer and polymerization initiator are brought into the reactor together.

<Compound X>
In this manufacturing method, compound X is used. Compound X can be polymerized together with the first monomer described later.
Compound X is a compound represented by formula (X).

C(X ¹ )(X ² )=C(X ³ )−L−Z (X)
In formula (X),
^X1 , ^X2 , and ^X3 are each independently a hydrogen atom, a fluorine atom, a perfluoromethyl group, or an alkyl group.
L is a single bond or a divalent linking group.
Z is an anionic group or a salt of an anionic group.

In formula (X), ^X1 , ^X2 , and ^X3 are each independently a fluorine atom, a perfluoromethyl group, a hydrogen atom, or an alkyl group.
The alkyl group may be linear, branched, or cyclic.
The number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 3, and even more preferably 1.
In formula (X), ^X1 , ^X2 , and ^X3 are preferably fluorine atoms or hydrogen atoms, and hydrogen atoms are preferred in all cases from the viewpoint of excellent polymerization reactivity.

In formula (X), L is a single bond or a divalent linking group.
Examples of the above-mentioned divalent linking groups include alkylene groups, carbonyl groups, ether bonds, thioether bonds, sulfonyl groups, -NH-, _-SiH2- , phenylene groups, _-CF2- , and groups formed by combining two or more of these. Examples of groups formed by combining two or more of these include ester bonds, thioester bonds, amide bonds, sulfonamide bonds, combinations of alkylene groups and ether bonds, combinations of alkylene groups and ester bonds, and combinations of alkylene groups and amide bonds.
The alkylene group may be linear, branched, or cyclic, with linear or branched being preferred, and branched being more preferred. The number of carbon atoms in the alkylene group can be, for example, 1 to 6, with 1 to 4 being preferred.
In formula (X), specific examples of L include a single bond, an alkylene group, an ether bond, an ester bond, and * ^C -CO-NH-R-* ^Z. A single bond, an alkylene group having 1 to 6 carbon atoms, and * ^C -CO-NH-R-* ^Z are preferred, and a single bond, an alkylene group having 1 to 2 carbon atoms, and * ^C -CO-NH-R-* ^Z are more preferred. * ^C -CO-NH-R-* ^Z is particularly preferred because it increases the number of particles in the resulting fluorine-containing copolymer and reduces the content of the compound represented by (S3) in the solid composition containing the resulting fluorine-containing polymer. Here, * ^C is the bonding site with a carbon atom in formula (X), * ^Z is the bonding site with Z in formula (X), and R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms.
The alkylene group or fluoroalkylene group may be linear, branched, or cyclic, with a branched configuration being preferred.
The alkylene group or fluoroalkylene group of R has 1 to 6 carbon atoms, preferably 2 to 4, and more preferably 4.
R is preferably a linear or branched alkylene group having 1 to 6 carbon atoms.

In formula (X), Z is an anionic group or a salt of an anionic group.
Examples of anionic groups include _-SO₃H , _-OSO₃H , -P(=O)(OH) _₂ , -OP(=O)(OH) _₂ , or -COOH.
Examples of salts of anionic groups include groups in which the hydrogen ions of the above-mentioned anionic group are replaced with cations other than hydrogen ions.
Examples of cations include metal ions, ammonium ions, imidazolium cations, pyrrolidinium cations, pyridinium cations, piperidinium cations, and phosphonium cations.
Examples of metal ions include alkali metal ions such as sodium ions, potassium ions, and lithium ions; and alkaline earth metal ions such as calcium ions and magnesium ions.
In formula (X), Z is preferably _-SO3M , _-OSO3M , -P(=O)(OM) ₂ , -OP(=O)(OM) ₂ , or -COOM.
From the viewpoint of productivity, _-SO3M and -COOM are preferred for Z, _-SO3Na and -COONa are more preferred, and _-SO3Na is even more preferred.
When Z is _-SO₃M , the latex becomes more stable, and the number of particles of the primary fluorine-containing polymer increases.

M is a hydrogen atom, a metal atom, N( ^RM1 ) ₄ , or P( ^RM2 ) ₄ , where ^RM1 and ^RM2 are independently a hydrogen atom or a substituent.
The metal atom represented by M is preferably a metal atom from Group 1, and more preferably Li, Na, or K.
The substituents represented by ^RM1 and ^RM2 are preferably monovalent organic groups, more preferably monovalent hydrocarbon groups, and even more preferably alkyl or aromatic hydrocarbon groups.
The number of carbon atoms in the substituent is preferably 1 to 10.
The alkyl group may be linear, branched, or cyclic.
The above aromatic hydrocarbon group may be monocyclic or polycyclic. A phenyl group is preferred as the above aromatic hydrocarbon group.

Examples of the molecular weight of compound X include 70 to 500, and from the viewpoint of dispersion stability, 70 to 450 is preferred, and 100 to 300 is more preferred.
Specific examples of compound X include 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tigroylglycine, 6-acrylamidohexanoic acid, 1,1-difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, 3-methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and their metal salts.
Examples of the above-mentioned metal salts include metal salts of metal atoms represented by M.

Before initiating the polymerization of the first monomer used in the polymerization of the first fluorine-containing polymer, the content of compound X is preferably 1.0 to 1000 ppm by mass relative to the total mass of the aqueous medium, more preferably 1.0 to 500 ppm by mass, even more preferably 3.0 to 100 ppm by mass, and particularly preferably 5.0 to 30.0 ppm by mass, in terms of achieving superior effects of the present invention.

<Polymerization Initiator>
The polymerization initiator used in this manufacturing method is preferably a water-soluble polymerization initiator, more preferably persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, more preferably organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride, even more preferably persulfates, and particularly preferably ammonium persulfate.

The amount of polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the first monomer.

<First Monomer>
The first monomer used in this manufacturing method contains tetrafluoroethylene (hereinafter also referred to as "TFE").
The first monomer may contain monomers other than TFE.

The amount of TFE used is preferably 5 to 80 mol%, more preferably 20 to 75 mol%, and even more preferably 50 to 75 mol%, relative to the amount of the first monomer used.

The first monomer preferably contains a perfluoroalkyl vinyl ether (hereinafter also referred to as "PAVE").
PAVE is preferred as a monomer represented by formula (1) because it exhibits excellent polymerization reactivity when producing the first fluorine-containing polymer and allows for more efficient production of the second fluorine-containing polymer.

CF ₂ =CF-O-R ^f1 (1)
In formula (1),
R ^f1 is a perfluoroalkyl group having 1 to 10 carbon atoms.
The number of carbon atoms in R ^f1 is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and particularly preferably 1 to 3, from the viewpoint of superior polymerization reactivity.
Perfluoroalkyl groups may be linear or branched.

Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"). PMVE or PPVE is preferred, and PMVE is more preferred, as they allow for more efficient production of the second fluorine-containing polymer.

The amount of PAVE used is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 25 to 50 mol%, relative to the amount of the first monomer used.
The amount of TFE units and PAVE units used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, relative to the amount of the first monomer used.

The first monomer may contain monomers other than TFE and PAVE, and may substantially omit other monomers in order to produce the second fluorine-containing polymer more efficiently.
"Substantially free of other monomers" means that the amount of other monomers used is 0.01 mol% or less relative to the amount of the first monomer used, and 0 mol% is preferred.

<Process>
The polymerization method for the first fluorine-containing polymer is not particularly limited, as long as it involves polymerizing the first monomer containing tetrafluoroethylene using compound X and a polymerization initiator under conditions where an aqueous medium is present and an emulsifier containing fluorine atoms is substantially absent.
One example of the above method is to prepare an aqueous medium and a solution containing compound X, and then use this solution and a polymerization initiator to polymerize the first monomer. More specifically, one method is to add the above solution and the first monomer to a reactor, heat the reactor, and then add a polymerization initiator to the reactor to polymerize the first monomer.
Polymerization of the first fluorine-containing polymer yields the first fluorine-containing polymer dispersed in particulate matter in an aqueous medium. The aqueous dispersion containing the particles of the first fluorine-containing polymer obtained in this way may be used as the first aqueous dispersion as is, or another aqueous medium may be added to it to obtain the first aqueous dispersion. Alternatively, the particles of the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution to obtain the first aqueous dispersion.

The first monomer is introduced into the reaction vessel by a conventional method. For example, the first monomer may be introduced into the reactor continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the first monomer may be dissolved in an aqueous medium, and the resulting solution may be introduced into the reactor continuously or intermittently.
When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in separate portions.

The polymerization temperature is preferably 10 to 95°C, and more preferably 15 to 90°C.
The polymerization pressure is preferably 0.5 to 4.0 MPaG, and more preferably 0.6 to 3.5 MPaG.
The polymerization time is preferably 90 to 1000 minutes, and more preferably 90 to 700 minutes.

(First aqueous dispersion)
The first aqueous dispersion preferably contains substantially no water-soluble emulsifiers. Water-soluble emulsifiers are as described above.
"Substantially free of water-soluble emulsifiers" means that the content of water-soluble emulsifiers is 10 ppm by mass or less, relative to the total mass of the first aqueous dispersion, more preferably 150 ppb by mass or less, and even more preferably 50 ppb by mass or less. The lower limit is 0 ppb by mass.

Furthermore, it is preferable that the first aqueous dispersion substantially does not contain any compound represented by any of formulas (S1) to (S4).
"Substantially free of the compound represented by formula (S1)" means that the content of the compound represented by formula (S1) is 10 ppm by mass or less, preferably 5 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppb by mass or less, with a lower limit of 0 ppb by mass.
"Substantially free of the compound represented by formula (S2)" means that the content of the compound represented by formula (S2) is 10 ppm by mass or less, preferably 5 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppb by mass or less, with a lower limit of 0 ppb by mass.
"Substantially free of the compound represented by formula (S3)" means that the content of the compound represented by formula (S3) is 10 ppm by mass or less, preferably 5 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppb by mass or less, with a lower limit of 0 ppb by mass.
"Substantially free of the compound represented by formula (S4)" means that the content of the compound represented by formula (S4) is 10 ppm by mass or less relative to the total mass of the aqueous dispersion, preferably 5 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppb by mass or less. The lower limit is 0 ppb by mass.
If an emulsifier is not used during the production of the first fluorine-containing polymer contained in the first aqueous dispersion, the amount of compounds represented by any of formulas (S1) to (S4) can be suppressed, making it easier to adjust the content of these compounds. Furthermore, the content of these compounds can also be reduced by the purification process described above.

H-(CF ₂ ) _n1 -COOM ^S (S1)
F-(CF ₂ ) _n1 -COOM ^S (S2)
H-(CF ₂ ) _n2 -SO ₃ M ^S (S3)
F-(CF ₂ ) _n2 -SO ₃ M ^S (S4)
In formulas (S1) to (S4),
n1 is an integer between 3 and 13.
n² is an integer between 4 and 10.
M ^S is a hydrogen atom, Na, K, or _NH4 .
The measurement methods described in the examples are examples of methods for measuring each content.

Before initiating the polymerization of the second monomer used in the polymerization of the second fluorine-containing polymer, the content of particles of the first fluorine-containing polymer is preferably 0.01 to 5.00% by mass relative to the total mass of the first aqueous dispersion, and more preferably 0.01 to 3.0% by mass, from the viewpoint of being able to produce the second fluorine-containing polymer more efficiently.

In this specification, "before the polymerization of the second monomer used in the polymerization of the second fluorine-containing polymer is started" means immediately before the start of polymerization. Here, "the start of polymerization" refers to the time when the reactor is heated to above the polymerization temperature and the second monomer and polymerization initiator are brought into the reactor together, and the time when the reactor is heated to above the polymerization temperature after the second monomer and polymerization initiator are brought into the reactor together.
Furthermore, the first aqueous dispersion, used before initiating the polymerization of the second monomer used in the polymerization of the second fluorine-containing polymer, does not contain the second monomer used in the polymerization of the second fluorine-containing polymer or the polymerization initiator.

The first aqueous dispersion may contain other components besides those described above.
Specific examples of other components that the first aqueous dispersion may contain include chain transfer agents, reducing agents, and pH adjusters.
Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane. Compounds represented by formula (I), described later, can also be used as chain transfer agents.
Specific examples of pH adjusters include inorganic salts and ammonia. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.
If the first aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass per 100 parts by mass of the aqueous medium.
If the first aqueous dispersion contains a pH adjusting agent, the content of the pH adjusting agent is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

The solid content concentration of the first aqueous dispersion is preferably 5 to 50% by mass, and more preferably 10 to 45% by mass.
The solid content concentration of the first aqueous dispersion can be measured, for example, by the following method.
The solid content concentration of the first aqueous dispersion is calculated by heating 2.0 g of the first aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and then determining the solid content concentration using the following formula.
"Solid content concentration (mass%) = 100 × heating residue of the first aqueous dispersion (g) / mass of the first aqueous dispersion (2.0g)"

(Particles of the first fluorine-containing polymer)
The particles of the first fluorine-containing polymer are the particles produced by this manufacturing method.
It is presumed that the particles of the first fluorine-containing polymer, during the polymerization of the second monomer described later, adsorb and incorporate the second monomer at their hydrophobic regions, thereby solubilizing the second monomer even if they substantially do not contain an emulsifier containing fluorine atoms, and thus facilitating the polymerization of the second monomer.
The first fluorine-containing polymer may be the same as or different from the second fluorine-containing polymer described later.

The average particle size of the particles of the first fluorine-containing polymer is 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less, from the viewpoint of particle dispersion stability. The lower limit is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more.
The average particle size of the first fluorine-containing polymer is the particle size calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

The number of particles of the first fluorine-containing polymer is preferably 0.5 × ^10¹⁴ particles/mL or more, preferably 1.0 × ^10¹⁴ particles/mL or more, more preferably 2.0 × ^10¹⁴ particles/mL or more, even more preferably 3.0 × ^10¹⁴ particles/mL or more, and particularly preferably 5.0 × ^10¹⁴ particles/mL or more. The upper limit is preferably 2.0 × ^10¹⁵ particles/mL or less.
The number of particles of the first fluorine-containing polymer is the number of particles per 1 mL of the first aqueous dispersion. An example of a method for measuring the number of particles is the method shown in the Examples section.

The first fluorine-containing polymer has no melting point.
"Having no melting point" means that when the melting point of the first fluorine-containing polymer is measured using a differential scanning calorimeter, no melting peak is observed. Specifically, this means that no melting peak is observed in the temperature range of 150°C or higher (preferably in the temperature range of 150°C to 330°C). Note that the glass transition peak does not fall under the category of a melting peak.
Specific methods for measuring the melting point include those shown in the Examples section.

The 1% by mass thermoweight loss temperature of the first fluorine-containing polymer is preferably 350°C or higher, more preferably 375°C or higher, and even more preferably 400°C or higher. The upper limit is preferably 600°C or lower.
The 1% mass thermogravimetric temperature can be measured, for example, using a thermogravimetric analyzer. Specific methods for measuring the 1% mass thermogravimetric temperature are shown in the Examples section.

The first fluorine-containing polymer has units based on the first monomer.
The first fluorine-containing polymer contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE units").
The TFE unit content is preferably 5 to 80 mol%, more preferably 20 to 75 mol%, and even more preferably 50 to 75 mol%, relative to the total units of the first fluorine-containing polymer.
The details of the TFE from which the TFE units are derived are the same as those of the TFE in the manufacturing method described above, and the preferred embodiment is also the same.

In this specification, if there is only one type of first fluorine-containing polymer, "all units of the first fluorine-containing polymer" means all units contained in that one type of first fluorine-containing polymer. If there are two or more types of first fluorine-containing polymers, "all units of the first fluorine-containing polymer" means all units contained in the two or more types of first fluorine-containing polymers. The same applies to other fluorine-containing polymers.

Furthermore, it is preferable that the first fluorine-containing polymer further contains units based on perfluoroalkyl vinyl ether (hereinafter also referred to as "PAVE units").
The PAVE unit content is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 25 to 50 mol%, relative to the total units of the first fluorine polymer.
The total content of TFE units and PAVE units is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, relative to the total units of the first fluorine-containing polymer.
The details of PAVE, from which the PAVE unit is derived, are the same as those of PAVE in the manufacturing method described above, and the preferred embodiment is also the same. The preferred amount to use is also the same when PMVE or PPVE is used as PAVE.
With this manufacturing method, even without the necessity of an emulsifier, the presence of compound X in the reaction system results in a first fluorine-containing polymer obtained by polymerizing a first monomer containing TFE units and PAVE units, which is preferable because it results in a polymer with a large number of particles. Furthermore, a first fluorine-containing polymer obtained by polymerizing monomers in which the TFE unit content is 5 to 80 mol% and the PAVE unit content is 20 to 95 mol% relative to the total units of the first fluorine-containing polymer is preferable because it yields a polymer with a large number of particles and no melting point.

The first fluorine-containing polymer may contain units other than TFE units and PAVE units, and may substantially omit other units in order to produce the second fluorine-containing polymer more efficiently.
"Substantially free of other units" means that the content of units based on other monomers is 0.01 mol% or less relative to the total units of the first fluorine-containing polymer, and 0 mol% is preferred.
Details of other monomers from which other units are derived include other monomers in the second fluorine-containing polymer described later.

[Method for producing the second fluorine-containing polymer]
The method for producing the second fluorine-containing polymer involves polymerizing the second monomer in the first aqueous dispersion produced by the above-described production method to produce the second fluorine-containing polymer.
Furthermore, the preferred method for producing the second fluorine-containing polymer is one in which the second monomer is polymerized using a polymerization initiator in the aqueous dispersion produced by the above-described production method to produce the second fluorine-containing polymer.

<First aqueous dispersion>
The first aqueous dispersion is an aqueous dispersion produced by the manufacturing method described above.
The preferred embodiment of the first aqueous dispersion is as described above.

It is preferable to perform a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products from the first aqueous dispersion, and then use it in the method for producing the second fluorine-containing polymer, i.e., in polymerization to obtain the second fluorine-containing polymer.
In the purification process, the polymerization initiator and its decomposition products that may be present in the first aqueous dispersion are removed, making it easier to obtain a second fluorine-containing polymer with the desired physical properties.
Purification methods include heat treatment and removal using an ion exchange resin. Anion exchange resin is preferred as the ion exchange resin. Purification may be performed multiple times.

<Second Monomer>
The second monomer preferably contains at least one selected from the group consisting of TFE, chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), vinylidene fluoride (hereinafter also referred to as "VdF"), PAVE, and hexafluoropropylene, and more preferably contains at least one selected from the group consisting of TFE, CTFE, and VdF. Furthermore, the second monomer also preferably contains at least one selected from the group consisting of TFE and PAVE, and more preferably contains both TFE and PAVE.

The second monomer may contain other monomers besides the monomers described above.
Other specific examples of monomers include ethylene, propylene, vinyl chloride, vinylidene chloride, monomers having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), monomers having at least one atom selected from the group consisting of chlorine, bromine, and iodine atoms, monomers having a nitrile group (hereinafter also referred to as " _RCN "), and units based on compounds (6) described later (hereinafter also referred to as "POAVE units").

BO is a monomer having two or more polymerizable unsaturated bonds.
Specific examples of polymerizable unsaturated bonds include carbon-carbon double bonds (C=C) and carbon-carbon triple bonds (C≡C). A carbon-carbon double bond (C=C) is more preferred as a polymerizable unsaturated bond.
In BO, the number of polymerizable unsaturated bonds is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, from the viewpoint of superior polymerization reactivity.
BO is preferably further enriched with fluorine atoms, as this reduces the compression set of the crosslinked rubber article at high temperatures.

BO is preferably a monomer represented by formula (2) because it provides superior release properties for cross-linked rubber articles.
(CR ²¹ R ²² =CR ²³ -) _a1 R ²⁴ (2)
In formula (2),
^R21 , ^R22 , and ^R23 are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group.
a1 is an integer between 2 and 6.
R ²⁴ is a 1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the perfluorohydrocarbon group.
The multiple ^R21 , multiple ^R22 , and multiple ^R23 may be the same as or different from each other, but it is preferable that they be the same as each other.
a1 is preferably 2 or 3, and more preferably 2.
From the viewpoint of superior polymerization reactivity of BO, it is preferable that ^R21 , ^R22 , and ^R23 are fluorine atoms or hydrogen atoms, more preferably that all of ^R21 , ^R22 , and ^R23 are fluorine atoms or all of them are hydrogen atoms, and even more preferably that all of ^R21 , ^R22 , and ^R23 are fluorine atoms from the viewpoint of superior release properties of the crosslinked rubber article.
^R24 may be linear, branched, or cyclic, with linear or branched being preferred, and linear being more preferred. The number of carbon atoms in ^R24 is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and particularly preferably 3 to 5.
^R24 may or may not have etheric oxygen atoms, but it is preferable that it has etheric oxygen atoms because it exhibits superior crosslinking reactivity and rubber properties.
The number of etheric oxygen atoms in R ²⁴ is preferably 1 to 6, more preferably 1 to 3, and even more preferably 1 or 2. The etheric oxygen atoms in R ²⁴ are preferably located at the terminal ends of R ²⁴ .

Among the monomers represented by formula (2), suitable specific examples include the monomer represented by formula (3) and the monomer represented by formula (4).

(CF ₂ =CF-) ₂ R ³¹ (3)
In formula (3), R ³¹ is a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the perfluorohydrocarbon group.

(CH ₂ =CH-) ₂ R ⁴¹ (4)
In formula (4), R ⁴¹ is a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the perfluorohydrocarbon group.

Specific examples of monomers represented by equation (3) include: _CF₂ = CFO( _CF₂ ) _₂ OCF = _CF₂ , _CF₂ = CFO( _CF₂ ) _₃ OCF = _CF₂ , _CF₂ = CFO( _CF₂ ) _₄ OCF = _CF₂ , _CF₂ = CFO( _CF₂ ) _₆ OCF = _{CF₂, CF₂ =} CFO( _CF₂ ) _₆ OCF(CF₃) _CF₂ OCF = _CF₂ , _CF₂ = CFO( _CF₂ ) _₆ O(CF _{( CF₃ ) CF₂O} ) _₆ CF _{= CF₂ 2} , _CF2 = _CFOCF2O ( _CF2CF2O ) _2CF = _CF2 , _CF2 =CFO( _CF2O ) _3O (CF( _CF3 ) _CF2O ) _2CF = _{CF2 , CF2} = _CFOCF2CF ( _CF3 )O( _CF2 ) _2OCF ( _CF3 ) _CF2OCF = _CF2 , and _CF2 = _{CFOCF2CF2O ( CF2O ) 2CF2CF2OCF} = _{CF2 .}
Among the monomers represented by formula (3), more suitable specific examples of monomers include _CF₂ = CFO( _CF₂ ) _₃OCF = _CF₂ (hereinafter also referred to as "C3DVE") and _CF₂ = CFO( _CF₂ ) _₄OCF = _CF₂ (hereinafter also referred to as "C4DVE").
Specific examples of monomers represented by equation (4) include _CH₂ =CH( _CF₂ ) _₂CH = _CH₂ , _CH₂ =CH( _CF₂ ) _₄CH = _CH₂ , and _CH₂ =CH( _CF₂ ) _₆CH = _CH₂ .
Among the monomers represented by formula (4), a more suitable specific example of a monomer is _CH₂ =CH( _CF₂ ) _₆CH = _CH₂ (hereinafter also referred to as "C6DV").
In particular, BO is preferably C3DVE or C4DVE.

Monomers having at least one atom selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms include monomers having bromine atoms and monomers having iodine atoms.
Specific examples of monomers containing a bromine atom include _CF₂ = _{CFOCF₂CF₂CF₂OCF₂CF₂Br} , _{bromotrifluoroethylene} , 4-bromo-3,3,4,4 _- tetrafluorobutene- _{1 (} BTFB), vinyl bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide, 4-bromo-1,1,2-trifluorobutene-1, 4-bromo-1,1,3,3,4,4-hexafluorobutene, 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Furthermore, fluorinated compounds such as 2-bromo-perfluoroethyl perfluorovinyl ether and _CF₂Br - _Rf -O-CF= _CF₂ (where _Rf is a perfluoroalkylene group), and fluorovinyl ethers such as _{CF₂BrCF₂O} -CF= _CF₂ , ROCF=CFBr, and ROCBr= _CF₂ (where R is a lower alkyl group or fluoroalkyl group), specifically _CH₃OCF =CFBr _{and CF₃CH₂OCF} =CFBr _, are also mentioned.
Specific examples of monomers containing an iodine atom include iodized olefins of the formula: CHR=CH-Z- _CH2CHR -I (wherein R is -H or _-CH3 ; Z is a linear or branched _C1 - _C18 (per)fluoroalkylene group, or a (per)fluoropolyoxyalkylene group disclosed in U.S. Patent No. 5,674,959, which may contain one or more ether oxygen atoms). Also included are unsaturated ethers of the formulas: _I ( _CH2CF2CF2 ) _nOCF = _{CF2 and ICH2CF2O} [CF( _CF3 ) _{CF2O ]nCF = CF2} (wherein n=1 to 3), disclosed in U.S. Patent No. 5,717,036. Also, as disclosed in U.S. Patent 4,694,045, are iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene. Additionally, allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether are also mentioned.

_RCN has a polymerizable unsaturated bond. From the viewpoint of polymerization reactivity, it is more preferable for _RCN to have one polymerizable unsaturated bond. Specific examples of polymerizable unsaturated bonds include carbon-carbon double bonds (C=C) and carbon-carbon triple bonds (C≡C).

_RCN is preferably a monomer represented by formula (5) because it has superior release properties and heat resistance.

CR ⁵¹ R ⁵² =CR ⁵³ -R ⁵⁴ -CN (5)
In formula (5), R ⁵¹ , R ⁵² , and R ⁵³ are each independently a hydrogen atom, a fluorine atom, or a methyl group.
R ⁵⁴ is a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the perfluorohydrocarbon group.
From the viewpoint of excellent polymerization reactivity of _RCN , it is preferable that ^R51 , ^R52 , and ^R53 are fluorine atoms or hydrogen atoms, more preferably that all of ^R51 , ^R52 , and ^R53 are fluorine atoms or all of them are hydrogen atoms, and even more preferably that all of ^R51 , ^R52 , and ^R53 are fluorine atoms from the viewpoint of superior mold release properties and heat resistance of the crosslinked rubber article.
R ⁵⁴ may be linear, branched, or cyclic, with linear or branched being preferred. The number of carbon atoms in ^{R 54} is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and particularly preferably 3 to 5.
R ⁵⁴ may or may not have etheric oxygen atoms, but it is preferable that it has etheric oxygen atoms because it provides superior rubber properties.
The number of etheric oxygen atoms in R ⁵⁴ is preferably 1 to 3, and more preferably 1 or 2.
Specific examples of monomers represented by formula (5) include _CF₂ = _CFOCF₂CF ( _CF₃ ) _{OCF₂CF₂CN} (hereinafter also referred to as " _8CNVE "), CF₂ = CFO(CF₂) _₅CN (hereinafter also referred to as "MV5CN"), _CF₂ = _{CFOCF₂CF₂CF₂OCF} ( _{CF₃ )} CN, _{and CF₂} = CFO( _CF₂ ) _₃CN . 8CNVE or _MV5CN are preferred because _they offer superior release properties and heat resistance.

The POAVE unit is a unit based on compound (6).
CF ₂ = CF (OCF ₂ CF ₂ ) _n - (OCF ₂ ) _m -OR ^f2 (6)
However, R ^f2 is a perfluoroalkyl group having 1 to 4 carbon atoms, n is an integer from 0 to 3, m is an integer from 0 to 4, and n+m is an integer from 1 to 7.

In R ^f2 , the perfluoroalkyl group may be linear or branched. The number of carbon atoms in ^{R f2} is preferably 1 to 3.
When n is 0, m is preferably 3 or 4. When n is 1, m is preferably an integer from 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer from 1 to 3.

Specific examples of compound (6) are listed below. The abbreviations in parentheses after each formula indicate the compound.
CF ₂ =CF-OCF ₂ CF ₂ -(OCF ₂ ) ₄ -OCF ₃ (C9PEVE),
CF ₂ =CF-OCF ₂ CF ₂ -(OCF ₂ ) ₂ -OCF ₃ (C7PEVE),
CF ₂ =CF-(OCF ₂ CF ₂ ) ₂ -OCF ₂ CF ₃ (EEAVE),
CF ₂ =CF-(OCF ₂ CF ₂ ) ₃ -OCF ₂ CF ₃ (EEEAVE),
CF ₂ =CF-OCF ₂ -OCF ₃ , CF ₂ =CF-OCF ₂ -OCF ₂ -OCF ₃

The second monomer preferably contains TFE. Furthermore, the second monomer preferably consists only of TFE and PAVE, or contains TFE and PAVE, and also contains other monomers. The other monomers preferably include a monomer having at least one atom selected from the group consisting of BO, chlorine, bromine, and iodine, and at least one monomer selected from the group consisting of _RCN .

The amount of TFE used is preferably 5 to 80 mol%, more preferably 20 to 75 mol%, and even more preferably 50 to 75 mol%, relative to the total amount of all secondary monomers used to produce the secondary fluorine polymer.
The amount of PAVE used is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 25 to 50 mol%, relative to the total amount of all secondary monomers used to produce the secondary fluorine polymer.
When TFE and PAVE are used as the second monomer, the preferred amounts of TFE and PAVE used are the same.
The amount of TFE and PAVE used is preferably 95.0 to 100.0 mol%, more preferably 97.0 to 100.0 mol%, and even more preferably 99.0 to 100.0 mol%, based on the total amount of all secondary monomers used to produce the secondary fluorine polymer.
The amount of other monomers used is preferably 0 to 5.0 mol%, more preferably 0 to 3 mol%, and even more preferably 0 to 1 mol%, relative to the amount of the second monomer used.
The amount of the second monomer used is preferably 1 to 80 parts by mass, more preferably 1 to 70 parts by mass, and even more preferably 1 to 65 parts by mass, based on 100 parts by mass of the aqueous medium used in the first aqueous dispersion.

<Polymerization Initiator>
In the method for producing the second fluorine-containing polymer, it is preferable to polymerize the second monomer using a polymerization initiator.
Preferred polymerization initiators are oil-soluble radical initiators, water-soluble radical initiators, or water-soluble redox catalysts.
Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP").
Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, disuccinic acid peroxide, bisglutaric acid peroxide, and water-soluble organic peroxides such as tert-butyl hydroperoxide (hereinafter also referred to as "TBHP").
As a water-soluble redox catalyst, a combination of an oxidizing agent such as bromate or its salt, chloric acid or its salt, persulfate or its salt, permanganate or its salt, or hydrogen peroxide, and a reducing agent such as sulfurous acid or its salt, bisulfite or its salt, thiosulfate or its salt, organic acid, or inorganic salt is preferred. As persulfates, potassium persulfate or ammonium persulfate is preferred. As sulfites, sodium sulfite is preferred. As inorganic salts, combinations of sulfate anions, sulfite anions or chloride anions, and metal ions are examples. As metal ions, transition metals are preferred, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. As inorganic salts, iron(II) sulfate is preferred.
The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator, with water-soluble radical initiators being more preferred and persulfates being even more preferred, as they allow for more efficient production of fluorine-containing polymers.
Two or more polymerization initiators may be used in combination.

<Process>
The method for producing the second fluorine-containing polymer involves polymerizing the second monomer in the first aqueous dispersion to produce the second fluorine-containing polymer.
One method for polymerizing the second monomer is the method of polymerizing the first monomer as described above.

Polymerization of the second monomer is preferably carried out in the absence of substantially any emulsifier containing fluorine atoms.
Polymerization of the second monomer is more preferably carried out in the absence of substantially both fluorine-containing and fluorine-free emulsifiers.
Examples of emulsifiers include those mentioned above.
The term "substantially absent emulsifier" means that, in the method for producing the second fluorine-containing polymer, the emulsifier content is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total mass of the first aqueous dispersion. The lower limit is 0 ppb by mass.

In the method for producing the second fluorine-containing polymer, particles of the second fluorine-containing polymer are generated. Specifically, the method for producing the second fluorine-containing polymer yields a second aqueous dispersion in which particles of the second fluorine-containing polymer are dispersed in the aqueous medium.

(Second fluoropolymer)
The second fluorine-containing polymer is a fluorine-containing polymer produced by the method for producing the second fluorine-containing polymer described above.

The second fluorine-containing polymer may also be in the form of particles.
The particles of the second fluorine-containing polymer may contain the first fluorine-containing polymer, or they may not contain the first fluorine-containing polymer.
The average particle size of the particles of the second fluorine-containing polymer is preferably 500 nm or less, more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 300 nm or less, from the viewpoint of particle dispersion stability. The lower limit is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more.
The average particle size of the second fluorine-containing polymer can be measured using the same method as the average particle size of the first fluorine-containing polymer.

The number of particles of the second fluorine-containing polymer is preferably 0.5 × ^10¹⁴ particles/mL or more, preferably 1.0 × ^10¹⁴ particles/mL or more, more preferably 2.0 × ^10¹⁴ particles/mL or more, even more preferably 3.0 × ^10¹⁴ particles/mL or more, and particularly preferably 5.0 × ^10¹⁴ particles/mL or more. The upper limit is preferably 10.0 × ^10¹⁵ particles/mL or less.
The number of particles of the second fluorine-containing polymer is the number of particles per 1 mL of the second aqueous dispersion. An example of a method for measuring the above particle count is the method shown in the Examples section.

The second fluorine-containing polymer preferably has no melting point.
"Having no melting point" means that when the melting point of the second fluorine-containing polymer is measured using a differential scanning calorimeter, no melting peak is observed. Specifically, this means that no melting peak is observed in the temperature range of 150°C or higher (preferably in the temperature range of 150°C to 330°C). Note that the glass transition peak does not fall under the category of a melting peak.
Specific methods for measuring the melting point include those shown in the Examples section.

The 1% by mass thermogravimetric temperature of the second fluorine-containing polymer is preferably 350°C or higher, more preferably 375°C or higher, and even more preferably 380°C or higher. The upper limit is preferably 600°C or lower. The 1% by mass thermogravimetric temperature can be measured, for example, using a thermogravimetric analyzer. Specific methods for measuring the 1% by mass thermogravimetric temperature are shown in the Examples section.

The second fluorine-containing polymer has units based on the second monomer.
The second monomer is as described above, and the preferred embodiment is the same.
The amount of TFE units is preferably 5 to 80 mol%, more preferably 20 to 75 mol%, and even more preferably 50 to 75 mol%, relative to the total units of the second fluorine-containing polymer.
The amount of PAVE units is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 25 to 50 mol%, relative to the total units of the second fluorine-containing polymer.
The TFE units and PAVE units are preferably in an amount of 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, relative to the total units of the second fluorine-containing polymer.
The other monomer units are preferably in an amount of 0 to 90 mol%, more preferably 0 to 80 mol%, and even more preferably 0 to 70 mol%, relative to the total units of the second fluorine-containing polymer.

[Second aqueous dispersion]
The second aqueous dispersion is an aqueous dispersion obtained by the method for producing the second fluorine-containing polymer.
The second aqueous dispersion is preferably an aqueous dispersion containing particles of a fluorine-containing polymer (hereinafter also referred to as "specific particles") and an aqueous medium.
In particular, the second aqueous dispersion is preferably an aqueous dispersion that substantially does not contain a water-soluble emulsifier having fluorine atoms, and contains specific particles and an aqueous medium, wherein the number of specific particles is 0.5 × ^10¹⁴ particles/mL or more, the average particle diameter of the specific particles is 500 nm or less, the fluorine-containing polymer has units based on tetrafluoroethylene and units based on perfluoroalkyl vinyl ether, and the fluorine-containing polymer does not have a melting point.
Furthermore, the second aqueous dispersion is preferably an aqueous dispersion that substantially does not contain water-soluble emulsifiers having fluorine atoms or water-soluble emulsifiers not having fluorine atoms, and contains specific particles and an aqueous medium, wherein the number of specific particles is 0.5 × ^10¹⁴ particles/mL or more, the average particle diameter of the specific particles is 500 nm or less, the fluorine-containing polymer has units based on tetrafluoroethylene and units based on perfluoroalkyl vinyl ether, and the fluorine-containing polymer does not have a melting point.

Examples of water-soluble emulsifiers containing fluorine atoms include the water-soluble emulsifiers containing fluorine atoms described in the above-mentioned manufacturing method.
"Substantially free of water-soluble emulsifiers containing fluorine atoms" means that the content of water-soluble emulsifiers containing fluorine atoms is 10 ppm by mass or less, relative to the total mass of the second aqueous dispersion, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less. The lower limit is 0 ppb by mass.
Furthermore, it is preferable that the product substantially does not contain water-soluble emulsifiers that do not contain fluorine atoms. Examples of water-soluble emulsifiers that do not contain fluorine atoms include the water-soluble emulsifiers that do not contain fluorine atoms in the above-described manufacturing method.
"Substantially free of water-soluble emulsifiers that do not contain fluorine atoms" means that the content of water-soluble emulsifiers that do not contain fluorine atoms is 10 ppm by mass or less, relative to the total mass of the second aqueous dispersion, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less. The lower limit is 0 ppb by mass.
Furthermore, it is preferable that the product substantially does not contain water-soluble emulsifiers containing fluorine atoms or water-soluble emulsifiers that do not contain fluorine atoms. Examples of water-soluble emulsifiers containing fluorine atoms include the water-soluble emulsifiers containing fluorine atoms in the above-described manufacturing method. Examples of water-soluble emulsifiers that do not contain fluorine atoms include the water-soluble emulsifiers that do not contain fluorine atoms in the above-described manufacturing method.
"Substantially free of water-soluble emulsifiers containing fluorine atoms and water-soluble emulsifiers not containing fluorine atoms" means that the total content of water-soluble emulsifiers containing fluorine atoms and water-soluble emulsifiers not containing fluorine atoms is 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total mass of the second aqueous dispersion. The lower limit is 0 ppb by mass.

<Specific particles>
The specific particles are preferably particles of the second fluorine-containing polymer described above.
If the specific particles contain a second fluorine-containing polymer, the specific particles may also contain a first fluorine-containing polymer, or they may not contain a first fluorine-containing polymer.
The second aqueous dispersion may further contain particles of the first fluorine-containing polymer in addition to the specific particles.

It is preferable that the specific particle count is 0.5 × ^10¹⁴ particles/mL or more, and the average particle diameter is 500 nm or less.
The preferred configurations for the specific number of particles and average particle diameter are the same as the preferred configurations for the number of particles and average particle diameter of the second fluorine-containing polymer.

The fluorine-containing polymer produced in the first aqueous dispersion and the second aqueous dispersion of the present invention preferably contains TFE units and PAVE units and has no melting point.
The TFE units and PAVE units contained in the fluorine-containing polymer, as well as other units, include the units that can be contained in the first fluorine-containing polymer and the second fluorine-containing polymer, and the preferred embodiments (types and their content) are the same.
The meaning of "having no melting point" is as described above.

The content of specific particles is preferably 1 to 50% by mass, more preferably 1 to 45% by mass, and even more preferably 1 to 40% by mass, relative to the total mass of the second aqueous dispersion, in terms of the dispersion stability of the specific particles.

<Aqueous medium>
Specific examples of the aqueous medium contained in the second aqueous dispersion are the same as the specific examples of the aqueous medium in the present manufacturing method described above.
The content of the aqueous medium is preferably 50 to 99% by mass, more preferably 50 to 90% by mass, and even more preferably 50 to 80% by mass, relative to the total mass of the second aqueous dispersion, in terms of the dispersion stability of specific particles.
<Solid composition>
A solid composition comprising a fluorine-containing polymer having no melting point, which is produced in the first aqueous dispersion or the second aqueous dispersion of the present invention,
The solid composition has units based on TFE,
The content of the emulsifier having fluorine atoms is 1500 ppb by mass or less relative to the total mass of the solid composition.
The content of the compound represented by formula (S1) is 1500 ppb by mass or less relative to the total mass of the solid composition.
The content of the compound represented by formula (S3) is 100 ppb by mass or less relative to the total mass of the solid composition.
H-(CF ₂ ) _n1 -COOM ^S (S1)
In formula (S1),
n1 is an integer between 3 and 13.
M ^S is a hydrogen atom, Na, K, or _NH4 .
H-(CF ₂ ) _n2 -SO ₃ M ^S (S3)
In formula (S3),
n² is an integer between 4 and 10.
M ^S is a hydrogen atom, Na, K, or _NH4 .
The measurement methods described in the examples are examples of methods for measuring each content.

This solid composition refers to a composition in which the solid content mass is 99% by mass or more.
Here, the solid content mass is calculated based on the mass before and after heating using the following method.
After heating 2.0 g of the solid composition at 170°C for 20 minutes, the mass of the residue is weighed, and the mass of solids is calculated using the following formula.
Solid content mass (mass%) = 100 × (mass of residue) / (mass of solid composition)

The solid composition is preferably obtained by agglomerating a fluorine-containing polymer produced in the first aqueous dispersion or the second aqueous dispersion described above.
The preferred embodiment of the fluorine-containing polymer contained in this solid composition is the same as the preferred embodiment of the fluorine-containing polymer contained in the first aqueous dispersion or the second aqueous dispersion described above.
In other words, the fluorine-containing polymer contained in this solid composition is preferably the first fluorine-containing polymer or the second fluorine-containing polymer described above. The second fluorine-containing polymer may contain the first fluorine-containing polymer.
This solid composition contains a first fluorine-containing polymer or a second fluorine-containing polymer that has no melting point and has units based on TFE. Preferably, the first fluorine-containing polymer or the second fluorine-containing polymer that has no melting point contains units based on TFE and units based on PAVA.
The content of the fluorine-containing polymer is preferably 99.0 to 100% by mass, more preferably 99.5 to 100% by mass, and even more preferably 99.8 to 100% by mass, based on the total mass of the solid composition.

In this solid composition, the content of the emulsifier having fluorine atoms is 1500 ppb by mass or less, preferably 1000 ppb by mass or less, more preferably 900 ppb by mass or less, and particularly preferably 850 ppb by mass or less, based on the total mass of the solid composition.
Specific examples of emulsifiers containing fluorine atoms are as described above.
This solid composition is substantially free of emulsifiers that do not contain fluorine atoms. "Substantially free of emulsifiers that do not contain fluorine atoms" means that the content of emulsifiers that do not contain fluorine atoms is 10 ppm by mass or less, preferably 5 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppb by mass or less, with a lower limit of 0 ppb by mass.
Specific examples of emulsifiers that do not contain fluorine atoms are as described above.

The solid composition contains a compound represented by formula (S1) at a concentration of 1500 ppb by mass or less, preferably 1000 ppb by mass or less, more preferably 900 ppb by mass or less, and particularly preferably 850 ppb by mass or less, relative to the total mass of the solid composition.
The solid composition contains a compound represented by formula (S3) in an amount of 100 ppb by mass or less, preferably 50 ppb by mass or less, more preferably 25 ppb by mass or less, even more preferably 10 ppb by mass or less, and particularly preferably 0 ppb by mass.
When emulsifiers are not used during the production of the first fluorine-containing polymer contained in the first aqueous dispersion and the second fluorine-containing polymer contained in the second aqueous dispersion, the amount of compounds represented by formulas (S1) and (S3) can be suppressed, making it easier to adjust the content of these compounds in the solid composition.

The metal content of this solid composition is preferably less than 50 ppm by mass, more preferably 10 ppm by mass or less, and particularly preferably 5 ppm by mass or less, based on the total amount of solids in the solid composition.
By having a metal content of less than 50 ppm by mass, the surface smoothness of the resulting solid composition is further improved.

<Application>
As mentioned above, the second aqueous dispersion does not require emulsifiers such as emulsifiers containing fluorine atoms, and therefore can be easily converted into a dispersion of organic solvents such as N-methylpyrrolidone or acetone by solvent substitution.
For example, the second aqueous dispersion can be mixed with an organic solvent and dehydrated by evaporation or using anhydrous sodium sulfate or the like to obtain a dispersion of the organic solvent.

The second aqueous dispersion allows for stable dispersion of fluorine-containing polymers even without the presence of emulsifiers. Therefore, it is suitable for use in coating applications, binders, and the like.

Furthermore, a solid of specific particles can be obtained by agglomerating a first fluorine-containing polymer from a first aqueous dispersion, or by agglomerating specific particles from a second aqueous dispersion. The solid of specific particles obtained by agglomeration can then be appropriately molded by known methods. Examples of molding methods include injection molding, extrusion molding, co-extrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calendering.

Methods of coagulation include, but are not limited to, freeze coagulation, acid coagulation, base coagulation, mechanical coagulation, and coagulation using coagulants.
In the case of freeze-coagulation, the coagulation temperature is preferably -20 to 0°C. The coagulation time is preferably 1 hour or more, and more preferably 2 hours or more.
In the case of acid agglutination, it is preferable to add an acid-containing solution to a second aqueous dispersion. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, with nitric acid being preferred. The concentration of the acid in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass.
For base aggregation, a method of adding a solution containing a base to a second aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with sodium hydroxide being preferred. The concentration of the base in the solution containing the base is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass.
For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specifically, these include aluminum sulfate, alum represented by the general formula M'Al( _SO₄ ) _₂ · _12H₂O [wherein M' is a monovalent cation other than lithium], calcium nitrate, and magnesium sulfate. Alum is preferred, and potassium alum, where M is potassium, is more preferred.
As for the aggregation method, base aggregation is preferred because it is particularly easy to achieve.

The present invention will be described in detail below with reference to examples. Examples 1 to 5 and Examples 7 to 11 are embodiments, and Example 6 is a comparative example. However, the present invention is not limited to these examples.

[Measurement and evaluation methods]
The various measurement and evaluation methods are as follows.

<Average particle size of particles of the first and second fluorine-containing polymers>
The first aqueous dispersion of each example described below was degassed at 25°C for 5 minutes, pressurized with nitrogen gas to 0.2 MPaG, purged, and returned to atmospheric pressure to obtain the measurement sample. The average particle size of the obtained measurement sample was measured using a dynamic light scattering particle size distribution analyzer (Otsuka Electronics Co., Ltd., ELSZ) with the number of integration cycles set to 100, and this was taken as the average particle size of the particles in each aqueous dispersion.
Furthermore, when the average particle size of the particles of the first fluorine-containing polymer in the raw material liquid B described later was measured using the same method as for the first aqueous dispersion, the average particle size of the particles of the first fluorine-containing polymer in the raw material liquid B was found to be the same as the average particle size of the particles of the first fluorine-containing polymer in the first aqueous dispersion.

<Number of particles in the first and second fluorine-containing polymers>
The number of particles of the first fluorine-containing polymer in the first aqueous dispersion, or the number of particles Np (particles/mL) of the second fluorine-containing polymer in the second aqueous dispersion, were calculated using the following formula.

Np (pieces/mL) = [(X/100)/(1-X/100)]/[4/3×π×{(Dp/2) ³ }×ρ]
X: Solid content concentration (mass%) of the first aqueous dispersion, or solid content concentration (mass%) of the second aqueous dispersion.
π: Pi (the ratio of a circle's circumference to its diameter) Dp: Average particle diameter (m) of the particles of the first fluorine-containing polymer in the first aqueous dispersion, or the average particle diameter (m) of the particles of the second fluorine-containing polymer in the second aqueous dispersion.
ρ: Specific gravity of the first fluorine-containing polymer, or the specific gravity of the second fluorine-containing polymer (in both cases, ρ = 2.04 × ^10⁶ was used) (g/ ^m³ )

(Solid content concentration of the first aqueous dispersion or the second aqueous dispersion)
After heating 2.0 g of either the first or second aqueous dispersion from each of the examples described below at 170°C for 20 minutes, the mass (g) of the residue is weighed, and the solid content concentration is calculated using the following formula.
Solid content concentration (mass%) of the first aqueous dispersion or the second aqueous dispersion = 100 × (mass of residue) / (mass of the first aqueous dispersion or the second aqueous dispersion (2.0 g))

<Percentage of each unit in the first fluorine-containing polymer and the second fluorine-containing polymer>
The proportion of each unit in the fluorine-containing polymer was determined by ^19F -NMR analysis and infrared absorption spectroscopy.

<Melting point>
The first or second aqueous dispersion of each example described below was freeze-coagulated and then filtered to obtain the first or second fluorine-containing polymer. A 5 mg sample of the obtained first or second fluorine-containing polymer was weighed into an aluminum pan and heated from 20°C to 360°C in an air atmosphere at a heating rate of 10°C/min using a Hitachi DSC600 to check for the presence or absence of a melting point peak.

<1 mass% thermogravimetric reduction temperature>
The first or second aqueous dispersion of each example described below was freeze-coagulated and then filtered to obtain the first or second fluorine-containing polymer. A 10 mg sample of the obtained first or second fluorine-containing polymer was weighed into an aluminum pan and heated from 40°C to 550°C in an air atmosphere at a heating rate of 10°C/min using a Hitachi STA200. The 1% thermal weight loss temperature was obtained from the resulting weight loss rate.

<Content of the compound represented by formula (S1) and the compound represented by formula (S3) in the aqueous dispersion>
(Preparation of measurement sample)
Each aqueous dispersion and each raw material solution was frozen and condensed at -20°C. Upon thawing at room temperature, polymers precipitated, so the aqueous phase was filtered off and recovered. The content of the compound represented by formula (S1) in the obtained aqueous phase was determined by converting each compound with n1 = 3 to 13 in formula (S1) to a perfluorocarboxylic acid with the same number of carbon atoms. Similarly, the content of the compound represented by formula (S3) in the obtained aqueous phase was determined by converting each compound with n2 = 4 to 10 in formula (S3) to a perfluorosulfonic acid with the same number of carbon atoms.
Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1 to 180 ng/g were prepared. Using a first-order approximation based on the sample concentration and the integral value of the peak, a and a' were determined using the following equations (A1) and (A1').
A = a × X (A1)
A: Peak area of perfluorocarboxylic acid, X: Concentration of perfluorocarboxylic acid (ng/g)
A'=a'×X'(A1')
A': Peak area of perfluorosulfonic acid, X': Concentration of perfluorosulfonic acid (ng/g)

The measuring equipment and conditions are shown in Table 1 below.

The MRM measurement parameters are shown in Tables 2 and 3 below.

Specifically, first, the compounds represented by either formula (S1) or formula (S3) contained in the aqueous phase were measured using the liquid chromatograph-mass spectrometer described above. The peak areas of the compounds represented by formulas (S1) and (S3) for each number of carbon atoms were determined using the MRM method.

The MRM measurement parameters are shown in Tables 4 and 5 below.

Next, the content of the compound represented by formula (S1) and the compound represented by formula (S3) was calculated using the following formulas (A2) and (A2'). Note that in formula (A2), a represents the a obtained by formula (A1) above, and in formula (A2'), a' represents the a' obtained by formula (A1') above. XCm = ACm/a (A2)
XCm: Content (ng/g) of the compound represented by formula (S1) for the number of carbon atoms (n1+1) in the aqueous phase.
ACm: Peak area of the compound represented by equation (S1) for the number of carbon atoms (n1+1) in the aqueous phase. X'Cm' = ACm'/a'(A2')
XCm': Content (ng/g) of the compound represented by formula (S3) for the number of carbon atoms n in the aqueous phase.
ACm': Peak area of the compound represented by formula (S3) for the number of carbon atoms n in the aqueous phase. Note that the limit of quantification in this measurement is 1 ng/g.

<Method for measuring the content of compounds represented by formula (S1) and formula (S3) in a solid composition>
(Preparation of measurement sample)
The solid compositions obtained in each of the examples described below were freeze-milled using a freeze mill 6775 (manufactured by SPEC) under the following conditions. Before freeze-milling, 10% by mass of dibutylhydroxytoluene (BHT) was added to the total mass of the solid composition to obtain a pulverized powder. The freeze-milling conditions were: solid composition: 3 g, BHT: 0.3 g, Run time: 5 min, Rate: 15 cps, Cycle: 3.
0.25 g of the obtained pulverized powder was mixed with 5 mL of methanol and subjected to sonication at 50°C for 2 hours. Centrifugation (5000 rpm, 5 minutes) was then performed to settle each fluorine-containing polymer, and the supernatant was used as the extract.
The content of the compound represented by formula (S1) in each extract was determined by converting each compound with n1 = 3 to 13 in formula (S1) to a perfluorocarboxylic acid with the same number of carbon atoms. Similarly, the content of the compound represented by formula (S3) in each extract was determined by converting each compound with n2 = 4 to 10 in formula (S3) to a perfluorosulfonic acid with the same number of carbon atoms.
Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations ranging from 1 to 180 ng/g were prepared. Using a first-order approximation based on the sample concentration and the integral value of the peak, a and a' were determined using equations (A1) and (A1').
A = a × X (A1)
A: Peak area of perfluorocarboxylic acid, X: Concentration of perfluorocarboxylic acid (ng/g)
A' = a' × X'(A1')
A': Peak area of perfluorosulfonic acid, X': Concentration of perfluorosulfonic acid (ng/g)

The measuring equipment and measurement conditions are as described in Table 1 above.

The parameters for MRM measurement are as shown in Table 2 above.

Specifically, first, the peak areas of the compounds represented by formulas (S1) and (S3) contained in each of the extracts were determined using the liquid chromatograph-mass spectrometer described above.

Next, the content of the compound represented by formula (S1) and the compound represented by formula (S3) was calculated using formulas (A2) and (A2'), respectively. In formula (A2), a means the a obtained by formula (A1) above, and a' means the a' obtained by formula (A1') above.
XCm=ACm/a (A2)
XCm: Content (ng/g) of the compound represented by formula (S1) for each extract with (n+1) carbon atoms.
ACm: Peak area of the compound represented by formula (S1) for each extract with (n+1) carbon atoms. XCm' = ACm' / a'(A2')
XCm': Content (ng/g) of the compound represented by formula (S3) with n carbon atoms in each extract.
ACm': Peak area of the compound represented by formula (S3) for n carbon atoms in each extract. Note that the limit of quantification in this measurement is 1 ng/g.

The content (ZCm) of formula (S1) relative to the total mass of the solid was determined by the following formula (A3).
ZCm=XCm×ρ1×La/W1 (A3)
ZCm: Content of the compound represented by formula (S1) with (n+1) carbon atoms in the solid. ρ1: Density of the extraction solvent (methanol in each example). La: Volume of the extraction solvent (5 mL in each example).
W1: Sample mass used for extraction (2.5 g of solids in each example)

The content (ZCm') of formula (S3) relative to the total mass of the solid was determined by the following formula (A4).
ZCm'=XCm'×ρ1×La/W1 (A4)
ZCm': Content of the compound represented by formula (S3) with n carbon atoms in the solid. ρ1: Density of the extraction solvent (methanol in each example). La: Volume of the extraction solvent (5 mL in each example).
W1: Sample mass used for extraction (2.5 g of solids in each example)

<Method for quantifying fluorine-containing emulsifiers>
The solid compositions obtained in each example were freeze-milled using a freeze mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-milling, 10% by mass of dibutylhydroxytoluene (BHT) was added to the total mass of the solid composition to obtain a pulverized powder. The freeze-milling conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 mins, rate: 15 cps, cycle: 3.
0.25 g of the obtained pulverized powder was mixed with 5 mL of methanol and subjected to sonication at 50°C for 2 hours. Centrifugation (5000 rpm, 5 min) was performed to settle each fluorine-containing polymer, and the supernatant was used as the extract. The obtained extract was subjected to LC/MS/MS analysis. The emulsifiers containing fluorine atoms in the extract were measured using a liquid chromatograph-mass spectrometer. The configuration of the measuring instruments and LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of emulsifiers containing fluorine atoms of known concentration, methanol solutions with five or more levels of content were prepared, and LC/MS analysis was performed on the methanol solutions with each content. The relationship between the content and the area area corresponding to that content was plotted, and a calibration curve was drawn. Using the above calibration curve, the area area of the LC/MS chromatogram of the emulsifiers containing fluorine atoms in the extract was converted to the content of the emulsifiers containing fluorine atoms.

The MRM measurement parameters should be appropriately selected according to the structure of the emulsifier containing fluorine atoms to be measured. MRM parameters can be obtained using literature values or calculated using an LC-MS instrument. When determining MRM parameters using an LC-MS instrument, the specific procedure is as follows: Using an LC/MS instrument (Shimadzu Corporation, LCMS-8060NX), select product ion search, input the molecular weight of the emulsifier containing fluorine atoms to be measured, and perform precursor ion selection, precursor adjustment, voltage optimization, and product m/z optimization. The calculated MRM measurement parameters are then used.

<Quantitative determination of emulsifiers containing fluorine atoms in solid compositions>
Specifically, first, methanol standard solutions of emulsifiers containing fluorine atoms of known concentration ranging from 1 to 180 ng/g were prepared at five different levels. Then, using a first-order approximation based on the sample concentration and the integral value of the peak, a'' was determined using equation (A1).
A''=a''×X (A1'')
A'': Peak area of each emulsifier, X: Concentration of each emulsifier (ng/g)

Next, the amount of emulsifier contained in the extract was calculated using formula (A2''). Note that a'' in formula (A2'') refers to the a'' obtained using formula (A1'') above.
XCm''=ACm''/a''(A2'')
XCm'': Emulsifier content in each extract (ng/g)
ACm'': Peak area of the emulsifier in each extract. The limit of quantification in this measurement is 25 ng/g.

The amount of emulsifier (ZCm'') relative to the total mass of the solid composition was determined by the following formula (A3'').
ZCm''=XCm''×ρ1×La/W1 (A3'')
ZCm'': Content of emulsifier in the solid composition ρ1: Density of the extraction solvent (methanol in each example) La: Volume of the extraction solvent (5 mL in each example)
W1: Sample mass used for extraction (2.5 g of solid composition in each example)

<Content of metal elements in the solid composition>
0.5 g of the solid obtained in each of the examples described below was taken into a platinum crucible that had been blank-checked. The solid was then incinerated in an ashing device (B-440, manufactured by Nippon Buch, high-temperature electric heating furnace) by heating at 400°C for 10 minutes, then at 470°C for 20 minutes, at 500°C for 15 minutes, and finally at 550°C for 60 minutes.
To the obtained ash, (1+1) sulfuric acid (Kanto Chemical Co., Ltd., Sulfuric Acid Ultrapur, 1 mL) was added and treated with sulfuric acid fumes on a hot plate. Furthermore, (1+1) sulfuric acid (1 mL) and ultrapure water (9 mL) were added to prepare the sample solution. The metal elements of the obtained sample solution were measured by ICP-MS and quantified using the absolute calibration curve method.
The metal elements to be measured are 29 types of metal elements (Li, Be, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi).

[Example 1]
In a 3.2 L stainless steel pressure reactor, ultrapure water (1774 g), a 50% by mass aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to compound X) (15 μL, containing 7.5 mg of NaAAMPS), PMVE (105 g), and TFE (22 g) were added, and the mixture was heated to 80°C while stirring at 385 rpm. The reactor pressure at 80°C was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 10 g) was added to start polymerization. As polymerization began, the pressure in the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added since the start of polymerization reached 37 g, 10 g of PMVE was injected. Thereafter, 10 g of PMVE was injected each time 12 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 133 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was withdrawn to obtain the first aqueous dispersion A1. The total amount of monomers added before the start of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after the start of polymerization was 133 g of TFE and 80 g of PMVE. The total amount of TFE added was 155 g, and the total amount of PMVE added was 185 g.
The average particle size of the particles of the first fluorine-containing polymer A1 in the first aqueous dispersion A1 was 79.6 nm, the number of particles of the first fluorine-containing polymer A1 was 2.6 × ^10¹⁴ particles/mL, and the solid content concentration of the first aqueous dispersion A1 was 12.4% by mass.
The first aqueous dispersion A1 was freeze-coagulated and then filtered to obtain the first fluorine-containing polymer A1, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A1 revealed a PMVE/TFE ratio of 33/67 (molar ratio). The 1% mass thermoweight loss temperature of the first fluorine-containing polymer A1 was 412°C.
Furthermore, the first fluorine-containing polymer A1 did not have a melting point.

[Example 2]
First aqueous dispersion A2 was obtained using the same procedure as in Example 1, except that the amount of 50% by mass aqueous solution of NaAAMPS added was changed to 30 μL (15 mg of NaAAMPS).
The average particle size of the particles of the first fluorine-containing polymer A2 in the first aqueous dispersion A2 was 64.3 nm, the number of particles of the first fluorine-containing polymer A2 was 5.0 × ^10¹⁴ particles/mL, and the solid content concentration of the first aqueous dispersion A2 was 12.4% by mass.
The first aqueous dispersion A2 was freeze-coagulated and then filtered to obtain the first fluorine-containing polymer A2, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A2 revealed a PMVE/TFE ratio of 33/67 (molar ratio). The 1% mass thermoweight loss temperature of the first fluorine-containing polymer A2 was 412°C.
Furthermore, the first fluorine-containing polymer A2 did not have a melting point.

[Example 3]
Polymerization was started using the same procedure as in Example 1, except that the amount of 50% by mass aqueous solution of NaAAMPS added was changed to 45 μL (22.5 mg of NaAAMPS). As polymerization began, the pressure in the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added after polymerization started reached 37 g, 10 g of PMVE was injected. Thereafter, 10 g of PMVE was injected every time 12 g of TFE was injected. When the amount of TFE added after polymerization started reached 325 g, the addition of TFE and PMVE injected after polymerization started was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was drained to obtain the first aqueous dispersion A3. The total amount of monomers added before polymerization started was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after polymerization began was 325 g of TFE and 240 g of PMVE. The total amount of TFE added was 347 g, and the total amount of PMVE added was 345 g.
The average particle size of the particles of the first fluorine-containing polymer A3 in the first aqueous dispersion A3 was 68.2 nm, the number of particles of the first fluorine-containing polymer A3 was 9.8 × ^10¹⁴ particles/mL, and the solid content concentration of the first aqueous dispersion A3 was 24.9% by mass.
The first aqueous dispersion A3 was freeze-coagulated and then filtered to obtain the first fluorine-containing polymer A3, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A3 revealed a PMVE/TFE ratio of 33/67 (molar ratio). The 1% mass thermoweight loss temperature of the first fluorine-containing polymer A3 was 412°C.
Furthermore, the first fluorine-containing polymer A3 did not have a melting point.

[Example 4]
Polymerization was started using the same procedure as in Example 1, except that the 50% by mass aqueous solution of NaAAMPS was replaced with a 25% by mass aqueous solution of sodium vinyl sulfonate (VSA) (17 μL). As polymerization began, the pressure in the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added after the start of polymerization reached 37 g, 10 g of PMVE was injected. Thereafter, 10 g of PMVE was injected every time 12 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 74 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was drained to obtain aqueous dispersion C1. The total amount of monomers added before the start of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after polymerization began was 74 g of TFE and 40 g of PMVE. The total amount of TFE added was 96 g, and the total amount of PMVE added was 145 g.
The average particle size of the fluorine-containing polymer C1 particles in the aqueous dispersion C1 was 86.9 nm, the number of fluorine-containing polymer C1 particles was 0.9 × ^10¹⁴ particles/mL, and the solid content concentration of the aqueous dispersion C1 was 6.4% by mass.
After freezing and condensing the aqueous dispersion C1, it was filtered off, and the resulting fluorine-containing polymer C1 was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained fluorine-containing polymer C1 revealed a PMVE/TFE ratio of 31.8/68.2 (molar ratio). The 1% mass thermoweight loss temperature of fluorine-containing polymer C1 was 415°C.
Furthermore, the first fluorine-containing polymer C1 did not have a melting point.

[Example 5]
Polymerization was started using the same procedure as in Example 1, except that the 50% by mass aqueous solution of NaAAMPS was replaced with sodium styrene vinyl sulfonate (NaSS, 7 mg). As polymerization began, the pressure in the reactor decreased, so TFE was added to maintain a constant pressure. When the amount of TFE added after polymerization started reached 37 g, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was drained to obtain aqueous dispersion C2. The total amount of monomers added before polymerization started was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after polymerization started was 37 g of TFE and 0 g of PMVE. The total amount of TFE added was 59 g, and the total amount of PMVE added was 105 g.
The average particle size of the fluorine-containing polymer C2 particles in the aqueous dispersion C2 was 78.1 nm, the number of fluorine-containing polymer C2 particles was 0.6 × ^10¹⁴ particles/mL, and the solid content concentration of the aqueous dispersion C2 was 3.0% by mass.
After freezing and condensing the aqueous dispersion C2, it was filtered off, and the resulting fluorine-containing polymer C2 was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained fluorine-containing polymer C2 revealed a PMVE/TFE ratio of 31.8/68.2 (molar ratio). The 1% mass thermoweight loss temperature of the fluorine-containing polymer C2 was 363°C.
Furthermore, the first fluorine-containing polymer C2 did not have a melting point.

[Example 6]
In _{a 2.1 L stainless steel pressure reactor, ultrapure water (1004 g), a 30% by mass aqueous solution of C₂F₅OCF₂CF₂OCF₂COONH₄ ( 80.1 g ) as} a water-soluble emulsifier containing fluorine atoms, a 5% by mass aqueous solution of disodium hydrogen phosphate dodecahydrate (10.49 g), PMVE (72 g), and TFE (14 g) were added, and the mixture was heated to 80°C while stirring at 600 rpm. The internal pressure of the reactor at 80°C was 1.2 MPaG. Next, an aqueous solution of ammonium persulfate (1.0% by mass, 20 g) was added, and polymerization was started. As polymerization began, the pressure inside the reactor decreased, so TFE and PMVE were further added to maintain a constant pressure of 1.2 MPa [gauge]. The reactor was cooled and the polymerization reaction was terminated when the amount of TFE added after the start of polymerization reached 160 g and the amount of PMVE added after the start of polymerization reached 133 g. The polymerization time was 262 minutes. After recovering the gas remaining in the reactor, the liquid was drained to obtain aqueous dispersion C3. The total amount of monomers added before the start of polymerization was 14 g of TFE and 72 g of PMVE. The total amount of monomers added after the start of polymerization was 160 g of TFE and 133 g of PMVE. The total amount of TFE added was 174 g and the total amount of PMVE added was 205 g.
The average particle size of the fluorine-containing polymer C3 particles in the aqueous dispersion C3 was 84.2 nm, the number of fluorine-containing polymer C3 particles was 3.1 × ^10¹⁴ particles/mL, and the solid content concentration of the aqueous dispersion C3 was 21.1% by mass.
After freezing and condensing the aqueous dispersion C3, it was filtered off, and the resulting fluorine-containing polymer C3 was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained fluorine-containing polymer C3 revealed a PMVE/TFE ratio of 34.2/65.8 (molar ratio). The 1% mass thermoweight loss temperature of the fluorine-containing polymer C3 was 406°C.
Furthermore, the first fluorine-containing polymer C3 did not have a melting point.

[Example 7]
<Manufacturing of raw material liquid A>
Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (20 μL, 10 mg of NaAAMPS), PMVE (72 g), and TFE (15 g) were added to a 2.2 L stainless steel pressure reactor, and the mixture was heated to 90°C while stirring at 600 rpm. The reactor pressure at 90°C was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 4 g) was added, and polymerization was started. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added after polymerization had started reached 25 g, the addition of TFE injected after polymerization had started was stopped, the reactor temperature was cooled to 10°C, the polymerization reaction was stopped, the remaining gas in the reactor was recovered, and the liquid was drained to obtain raw material solution A (first aqueous dispersion A4). The total amount of monomers added before polymerization began was 15 g of TFE and 72 g of PMVE. The total amount of monomers added after polymerization began was 25 g of TFE and 0 g of PMVE. The total amount of TFE added was 40 g, and the total amount of PMVE added was 72 g.
The average particle size of the particles of the first fluorine-containing polymer A4 in raw material liquid A was 43.5 nm, the number of particles of the first fluorine-containing polymer A4 was 3.9 × ^10¹⁴ particles/mL, and the solid content concentration of raw material liquid A was 3.3% by mass.
After freezing and condensing the raw material liquid A, it was filtered, and the obtained first fluorine-containing polymer A4 was washed with ultrapure water. Then, it was vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A4 showed a PMVE/TFE ratio of 33/67 (molar ratio). The 1% mass thermal weight loss temperature of the first fluorine-containing polymer A4 was 350°C.
Furthermore, the first fluorine-containing polymer A4 did not have a melting point.

<Manufacturing of raw material liquid B>
40 g of HPR4002Cl (DuPont, anion exchange resin) was added to 1000 g of raw material solution A. After 60 minutes of stirring, raw material solution A and the ion exchange resin were filtered off. 40 g of Dowex Monosphere 650C (DuPont, cation exchange resin) was added to the filtered raw material solution A. After 60 minutes of stirring, the ion exchange resin was filtered off to obtain raw material solution B.
Furthermore, the average particle size and number of particles of the first fluorine-containing polymer A4 in raw material liquid B were equivalent to those in raw material liquid A, and the first fluorine-containing polymer A4 in raw material liquid B did not have a melting point.

<Production of the second fluorine-containing polymer>
In a 2.2 L stainless steel pressure reactor, 850 g of raw material solution B, 332 g of ultrapure water, 81 g of PMVE, and 17 g of TFE were added, and the mixture was heated to 80°C while stirring at 600 rpm. The reactor pressure at 80°C was 1.4 MPaG. Next, 20 g of ammonium persulfate aqueous solution (1.0 mass%) was added, and polymerization was started. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added since the start of polymerization reached 25 g, 7 g of PMVE was injected. Thereafter, 7 g of PMVE was injected each time 8 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 256 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was withdrawn to obtain the second aqueous dispersion B1. The total amount of monomers added before the start of polymerization was 17 g of TFE and 81 g of PMVE. The total amount of monomers added after the start of polymerization was 256 g of TFE and 203 g of PMVE. The total amount of TFE added was 273 g, and the total amount of PMVE added was 284 g.
The average particle size of the fluorine-containing polymer B1 particles in the second aqueous dispersion B1 was 67.6 nm, the number of fluorine-containing polymer B1 particles was 3.6 × ^10¹⁴ particles/mL, and the solid content concentration of the second aqueous dispersion B1 was 10.5% by mass.
The second aqueous dispersion B1 was freeze-coagulated and then filtered to obtain the fluorine-containing polymer B1, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained fluorine-containing polymer B1 revealed a PMVE/TFE ratio of 33/67 (molar ratio). The 1% mass thermoweight loss temperature of fluorine-containing polymer B1 was 411°C.
Furthermore, the fluorine-containing polymer B1 did not have a melting point.

[Example 8]
Polymerization was started using the same procedure as in Example 1, except that the amount of 50% by mass aqueous solution of NaAAMPS added was changed to 45 μL (22.5 mg of NaAAMPS), and the amount of 2.5% by mass aqueous solution of ammonium persulfate added was changed to 7 g. As polymerization began, the pressure in the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added since the start of polymerization reached 37 g, octafluoro-1,4-diiodobutane (C4DI, 1.25 g) and 10 g of PMVE were injected by injection. The rotation speed was reduced to 325 rpm, and thereafter, 10 g of PMVE was injected by injection every time 12 g of TFE was injected by injection. When the amount of TFE added after the start of polymerization reached 325 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was withdrawn to obtain the first aqueous dispersion A5. The total amount of monomers added before the start of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after the start of polymerization was 325 g of TFE and 240 g of PMVE. The total amount of TFE added was 347 g, and the total amount of PMVE added was 345 g.
The average particle size of the particles of the first fluorine-containing polymer A5 in the first aqueous dispersion A5 was 77.1 nm, the number of particles of the first fluorine-containing polymer A5 was 6.1 × ^10¹⁴ particles/mL, and the solid content concentration of the first aqueous dispersion A5 was 23.0% by mass.
The first aqueous dispersion A5 was freeze-coagulated and then filtered to obtain the first fluorine-containing polymer A5, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A5 revealed a PMVE/TFE ratio of 33/67 (molar ratio). The iodine content relative to fluorine polymer A5 was 0.1% by mass. The 1% by mass thermoweight loss temperature of the first fluorine-containing polymer A5 was 405°C.
Furthermore, the first fluorine-containing polymer A5 did not have a melting point.

[Example 9]
Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (30 μL, 15 mg of NaAAMPS), PMVE (81 g), and TFE (17 g) were added to a 2.2 L stainless steel pressure reactor, and the mixture was heated to 80°C while stirring at 600 rpm. The reactor pressure at 80°C was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 7 g) was added to start polymerization. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added since the start of polymerization reached 25 g, the rotation speed was reduced to 380 rpm, and ₂ g of _CF₂ = CFOCF₂ CF( _CF₃ ) _{OCF₂ CF₂CN} (8CNVE) was added. Subsequently, 12 g of PMVE and 1.3 g of 8CNVE were added each time 16 g of TFE was injected. Ammonium persulfate aqueous solution was added as needed in accordance with the progress of polymerization. When the amount of TFE added after the start of polymerization reached 185 g, the addition of TFE, PMVE, and 8CNVE added after the start of polymerization was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was drained. The total amount of monomers added before the start of polymerization was 17 g of TFE, 81 g of PMVE, and 0 g of 8CNVE. The total amount of monomers added after the start of polymerization was 185 g of TFE, 108 g of PMVE, and 13.7 g of 8CNVE. The total amount of TFE added was 202 g, the total amount of PMVE added was 189 g, and the amount of 8CNVE added was 13.7 g. The polymerization time was 400 minutes, and 14 cc of ammonium persulfate aqueous solution was added.
The average particle size of the particles of the first fluorine-containing polymer A6 in the first aqueous dispersion A6 was 76.6 nm, the number of particles of the first fluorine-containing polymer A6 was 5.2 × ^10¹⁴ particles/mL, and the solid content concentration of the first aqueous dispersion A6 was 20.04% by mass.
The first aqueous dispersion A6 was freeze-coagulated and then filtered to obtain the first fluorine-containing polymer A6, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A6 revealed a PMVE/TFE/8CNVE ratio of 28.05/71.5/0.45 (molar ratio). The 1% mass thermoweight loss temperature of the first fluorine-containing polymer A6 was 392°C.
Furthermore, the first fluorine-containing polymer A6 did not have a melting point.

[Example 10]
Polymerization was started using the same procedure as in Example 8, except that _CF₂ = CFO( _CF₂ ) _₃OCF = _CF₂ (3.69 g) was added before starting polymerization. As polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added after the start of polymerization reached 37 g, octafluoro-1,4-diiodobutane (C4DI, 1.25 g) and 10 g of PMVE were injected by injection. The rotation speed was reduced to 325 rpm, and thereafter, 10 g of PMVE was injected by injection every time 12 g of TFE was injected by injection. When the amount of TFE added after the start of polymerization reached 325 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was withdrawn to obtain the first aqueous dispersion A5. The total amount of monomers added before polymerization began was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after polymerization began was 325 g of TFE and 240 g of PMVE. The total amount of TFE added was 347 g, and the total amount of PMVE added was 345 g.
The average particle size of the particles of the first fluorine-containing polymer A7 in the first aqueous dispersion A7 was 94.8 nm, the number of particles of the first fluorine-containing polymer A7 was 4.2 × ^10¹⁴ particles/mL, and the solid content concentration of the first aqueous dispersion A5 was 27.9% by mass.
The first aqueous dispersion A5 was freeze-coagulated and then filtered to obtain the first fluorine-containing polymer A5, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A5 revealed a PMVE/TFE ratio of 34/66 (molar ratio). The iodine content relative to fluorine polymer A5 was 0.1% by mass. The 1% by mass thermogravimetric loss temperature of the first fluorine-containing polymer A7 was 403°C.
Furthermore, the first fluorine-containing polymer A7 did not have a melting point.

[Example 11]
Polymerization was started using the same procedure as in Example 8, except that the amount of 50% by mass aqueous solution of NaAAMPS added was changed from 45 μL (22.5 mg of NaAAMPS) to 45 μL (22.5 mg of NaMAMPS) of 50% by mass aqueous solution of sodium 2-methacrylamide-2-methylpropanesulfonate (NaMAMPS). As polymerization began, the pressure in the reactor decreased, so TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added since the start of polymerization reached 37 g, octafluoro-1,4-diiodobutane (C4DI, 1.25 g) and 10 g of PMVE were injected by injection. The rotation speed was reduced to 325 rpm, and thereafter, 10 g of PMVE was injected by injection each time 12 g of TFE was injected by injection. When the amount of TFE added after the start of polymerization reached 325 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the reactor temperature was cooled to 10°C to stop the polymerization reaction, the remaining gas in the reactor was recovered, and the liquid was withdrawn to obtain the first aqueous dispersion A5. The total amount of monomers added before the start of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after the start of polymerization was 325 g of TFE and 240 g of PMVE. The total amount of TFE added was 347 g, and the total amount of PMVE added was 345 g.
The average particle size of the particles of the first fluorine-containing polymer A8 in the first aqueous dispersion A8 was 103.1 nm, the number of particles of the first fluorine-containing polymer A8 was 3.46 × ^10¹⁴ particles/mL, and the solid content concentration of the first aqueous dispersion A8 was 28.8% by mass.
The first aqueous dispersion A5 was freeze-coagulated and then filtered to obtain the first fluorine-containing polymer A5, which was washed with ultrapure water. It was then vacuum-dried at 100°C. NMR analysis of the obtained first fluorine-containing polymer A5 revealed a PMVE/TFE ratio of 35/65 (molar ratio). The iodine content relative to fluorine polymer A5 was 0.1% by mass. The 1% by mass thermoweight loss temperature of the first fluorine-containing polymer A8 was 400°C.
Furthermore, the first fluorine-containing polymer A8 did not have a melting point.

In the production of Examples 1-5 and 7-11, the polymerization of the first fluorine-containing polymer was carried out under conditions where emulsifiers containing fluorine atoms and emulsifiers without fluorine atoms were substantially absent. Furthermore, the aqueous dispersions obtained in Examples 1-5 and 7-11 substantially contained neither emulsifiers containing fluorine atoms nor emulsifiers without fluorine atoms. In addition, in the aqueous dispersions of Examples 1-5 and 7-11, the content of the compound represented by formula (S1) relative to the total mass of the aqueous dispersion, and the content of the compound represented by formula (S3) relative to the total mass of the aqueous dispersion, were both 5 ppm by mass or less (50 ppb by mass or less). On the other hand, since an emulsifier was used in the production of Example 6, the aqueous dispersion of Example 6 contained an emulsifier.
The concentrations of compound X in the aqueous dispersions in Table 6 represent the content of compound X in the aqueous medium.

The table below specifically shows the content of the compound represented by formula (S1) and the compound represented by formula (S3) in raw material liquid A and raw material liquid B in Example 7. The content of formula (S1) refers to the sum of the content of each compound in formula (S1) where n1 is an integer from 3 to 13, relative to the total mass of each raw material liquid, and the content of formula (S3) refers to the sum of the content of each compound in formula (S3) where n2 is an integer from 4 to 10, relative to the total mass of each raw material liquid.

Tables 8 and 9 below specifically show the content of the compound represented by (S1) and the compound represented by (S3) in the solid compositions of Examples 1-6 and 8-11. In the tables, N.D. indicates that the content is below the limit of quantification in this measurement.

Table 10 below specifically shows the content of emulsifiers containing fluorine atoms in the solid compositions of Examples 1-6 and 8-11. In the table, N.D. indicates that the amount is less than the limit of quantification in this measurement.

Table 11 below specifically shows the content (ppm) of metal elements contained in the solid compositions in Examples 1-3, 6, and 8-11.

This manufacturing method demonstrates that an aqueous dispersion with a large number of fluorine-containing polymer particles can be produced without substantially using an emulsifier containing fluorine atoms (Examples 1 to 5 and 7 to 11, particularly Examples 1 to 3 and 7 to 11). Example 6 is a method for producing an aqueous dispersion using an emulsifier.
The effects of the present invention were shown to be superior when the content of compound X was 5.0 to 30.0 ppm by mass relative to the total mass of the aqueous medium (Examples 2 and 3).

Furthermore, the entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-205993, filed on December 6, 2023, are incorporated herein by reference as disclosure of the present invention.

Claims (10)

Under conditions where an aqueous medium is present and an emulsifier containing a fluorine atom is substantially absent, a first monomer containing tetrafluoroethylene is polymerized in the presence of a compound represented by formula (X) and a polymerization initiator.
A method for producing an aqueous dispersion, comprising producing an aqueous dispersion containing particles of a first fluorine-containing polymer having an average particle diameter of 500 nm or less and having no melting point.
C(X ¹ )(X ² )=C(X ³ )−L−Z (X)
In formula (X),
^X1 , ^X2 , and ^X3 are each independently a hydrogen atom or an alkyl group.
L is a single bond or a divalent linking group.
The divalent linking group is selected from an alkylene group, a carbonyl group, an ether bond, a thioether bond, a sulfonyl group, -NH-, _-SiH2- , a combination of an alkylene group and an ester bond, a combination of an alkylene group and an amide bond, and * ^C -CO-NH-R-* ^Z (where * ^C is the bonding site with a carbon atom in formula (X), * ^Z is the bonding site with Z in formula (X), and R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms) .
Z is an anionic group or a salt of an anionic group. A method for producing an aqueous dispersion according to claim 1, wherein Z is _-SO3M .
M is a hydrogen atom, a metal atom, N( ^RM1 ) ₄ , or P( ^RM2 ) ₄ .
^RM1 and ^RM2 are each independently hydrogen atoms or substituents, any two of ^RM1 may be bonded to each other to form a ring, and multiple ^RM1 may be the same or different from each other, any two of ^RM2 may be bonded to each other to form a ring, and multiple ^RM2 may be the same or different from each other. A method for producing an aqueous dispersion according to claim 1 or 2, wherein the content of the compound represented by formula (X) is 1.0 to 1000 ppm by mass relative to the total mass of the aqueous medium. A method for producing an aqueous dispersion according to claim 1 or 2, wherein the first monomer contains a perfluoroalkyl vinyl ether. In an aqueous dispersion produced by the manufacturing method described in claim 1 or 2,
A method for producing a second fluorine-containing polymer, comprising polymerizing a second monomer to produce a second fluorine-containing polymer. The method for producing the second fluorine-containing polymer according to claim 5, wherein the content of the compound represented by formula (S1) is 5 ppm by mass or less with respect to the total mass of the aqueous dispersion.
H-(CF ₂ ) _n1 -COOM ^S (S1)
In formula (S1),
n1 is an integer between 3 and 13.
M ^S is a hydrogen atom, Na, K, or _NH4 . The method for producing the second fluorine-containing polymer according to claim 5, wherein the content of the compound represented by formula (S3) is 5 ppm by mass or less with respect to the total mass of the aqueous dispersion.
H-(CF ₂ ) _n2 -SO ₃ M ^S (S3)
In formula (S3),
n² is an integer between 4 and 10.
M ^S is a hydrogen atom, Na, K, or _NH4 . The method for producing a second fluorine-containing polymer according to claim 5, wherein the second monomer comprises at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, and vinylidene fluoride. The method for producing the second fluorine-containing polymer according to claim 5, wherein the second monomer comprises a perfluoroalkyl vinyl ether. The method for producing the second fluorine-containing polymer according to claim 5, wherein the second fluorine-containing polymer does not have a melting point.