Production method for aqueous dispersion, production method for second fluorine-containing polymer, aqueous dispersion, and solid composition

Abstract

A production method for an aqueous dispersion according to the present invention comprises polymerizing a first monomer that includes tetrafluoroethylene in the presence of a compound represented by formula (X) and a polymerization initiator under conditions in which an aqueous medium is present but an emulsifier that includes fluorine atoms is substantially absent to produce an aqueous dispersion that includes particles of a first fluorine-containing polymer that has an average particle diameter of no more than 500 nm and does not have a melting point.　Formula (X): C(X1)(X2)=C(X3)-L-Z. 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, and Z is an anionic group or a salt of an anionic group.

Description

Method for producing aqueous dispersion, method for producing second fluorine-containing polymer, aqueous dispersion, solid composition

[0001] The present 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.

[0002] Fluorine-containing polymers are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. When producing such fluorine-containing polymers, an aqueous dispersion containing fluorine-containing polymer particles may be used. As a method for producing an aqueous dispersion, Patent Document 1 discloses a method of polymerizing a fluorine-containing monomer in the presence of a specific compound.

[0003] International Publication No. 2022 / 019241

[0004] It has been found that the method for producing an aqueous dispersion disclosed in Patent Document 1 produces a small number of fluoropolymer particles, leaving room for improvement. Furthermore, from the viewpoint of reducing the environmental burden, it is desirable to substantially not use an emulsifier having a fluorine atom. The present inventors have found that the method for producing an aqueous dispersion disclosed in Patent Document 1 does not necessarily produce a fluoropolymer with sufficient dispersibility, and have also found that there is room for improvement in the number of particles of the fluoropolymer produced. Furthermore, from the viewpoint of reducing the environmental burden, it is desirable to substantially not use an emulsifier having a fluorine atom. Another object of the present invention is to achieve a particle number of the fluoropolymer equivalent to that produced when a conventional emulsifier having a fluorine atom is used, without substantially using an emulsifier having a fluorine atom.

[0005] An object of the present invention is to provide a method for producing an aqueous dispersion, which can produce an aqueous dispersion having a large number of fluorine-containing polymer particles without substantially using an emulsifier having a fluorine atom. Another object of the present invention is to provide a method for producing a second fluorine-containing polymer, an aqueous dispersion, and a solid composition.

[0006] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by the following constitution: [1] A method for producing an aqueous dispersion, comprising polymerizing a first monomer containing tetrafluoroethylene in the presence of a compound represented by formula (X) and a polymerization initiator in the presence of an aqueous medium and substantially in the absence of an emulsifier having a fluorine atom, to produce an aqueous dispersion containing particles of a first fluorine-containing polymer having an average particle size of 500 nm or less and no melting point. C(X １ ) (X ２ ) = C(X ３ )-L-Z (X) In formula (X), １ , X ２ and X ３ 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, and Z is an anionic group or a salt of an anionic group. [2] Z is -SO ３ The method for producing an aqueous dispersion according to [1], wherein M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ and R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２may be the same or different from each other. [3] The method for producing an aqueous dispersion according to [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. [4] The method for producing an aqueous dispersion according to any one of [1] to [3], wherein the first monomer comprises a perfluoroalkyl vinyl ether. [5] A method for producing a second fluorine-containing polymer, comprising polymerizing a second monomer in the aqueous dispersion produced by the production method according to any one of [1] to [4], to produce a second fluorine-containing polymer. [6] The method for producing a second fluorine-containing polymer according to [5], wherein the content of the compound represented by formula (S1) described below is 5 ppm by mass or less relative to the total mass of the aqueous dispersion. [7] The method for producing a second fluorine-containing polymer according to [5] or [6], wherein the content of the compound represented by formula (S3) described below is 5 ppm by mass or less relative 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 comprises a perfluoroalkyl vinyl ether.

[10] A method for producing a second fluorine-containing polymer according to any one of [5] to [9], wherein the second fluorine-containing polymer has no melting point.

[11] An aqueous dispersion substantially free of a water-soluble emulsifier having fluorine atoms, and comprising fluorine-containing polymer particles and an aqueous medium, wherein the number of the particles is 0.5×10 １４an aqueous dispersion in which the concentration of the particles is 1500 ppb / mL or more, the average particle size of the particles is 500 nm or less, the fluoropolymer has units based on tetrafluoroethylene and units based on perfluoroalkyl vinyl ether, and the fluoropolymer has no melting point.

[12] The aqueous dispersion according to

[11] , wherein the 1% by mass thermal weight loss temperature of the fluoropolymer is 350°C or higher.

[13] A solid composition comprising a fluoropolymer having no melting point, wherein the fluoropolymer has units based on tetrafluoroethylene, the content of an emulsifier having a fluorine atom is 1500 ppb by mass or less relative to the total mass of the solid composition, the content of a compound represented by formula (S1) is 1500 ppb by mass or less relative to the total mass of the solid composition, and the content of a compound represented by formula (S3) is 100 ppb by mass or less relative to the total mass of the solid composition. ２ ) ｎ１ -COOM Ｓ (S1) In formula (S1), n1 is an integer of 3 to 13, and M Ｓ is a hydrogen atom, Na, K or NH ４ H-(CF ２ ) ｎ２ -SO ３ M Ｓ (S3) In formula (S3), n2 is an integer of 4 to 10, and M Ｓ is a hydrogen atom, Na, K or NH ４

[14] The solid composition according to

[13] , wherein the metal content of the solid composition is less than 5 ppm by mass, based on the total mass of the solid composition.

[0007] According to the present invention, there is provided a method for producing an aqueous dispersion which can produce an aqueous dispersion having a large number of fluoropolymer particles without substantially using an emulsifier having a fluorine atom. The present invention also provides a method for producing a second fluoropolymer, an aqueous dispersion, and a solid composition.

[0008] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer added substantially coincides with the actual content of each unit.

[0009] [Method for producing aqueous dispersion] The method for producing an aqueous dispersion of the present invention (hereinafter also referred to as "the present production method") is a method for producing an aqueous dispersion comprising polymerizing a first monomer containing tetrafluoroethylene in the presence of 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 in the substantial absence of an emulsifier having a fluorine atom, to produce an aqueous dispersion containing first fluorine-containing polymer particles having an average particle size of 500 nm or less and having no melting point (hereinafter also referred to as "first aqueous dispersion").

[0010] The reason why the number of particles of the first fluoropolymer increases according to this production method without requiring an emulsifier having fluorine atoms is presumably because the presence of compound X in the reaction system during polymerization of the first monomer improves the dispersibility of the particles of the first fluoropolymer produced in the first aqueous dispersion, thereby increasing the specific surface area of ​​the particles in the first aqueous dispersion. For example, one factor for the improvement in dispersibility is thought to be the improvement in the zeta potential of the particles of the first fluoropolymer due to compound X. It has also been found that when the second monomer is polymerized using an aqueous dispersion containing particles of the first fluoropolymer having a large particle number, the greater the number of particles of the first fluoropolymer, the faster the polymerization rate of the second monomer tends to be. Therefore, it is desirable to increase the number of particles of the first fluoropolymer. Hereinafter, the fact that the number of particles of the first fluoropolymer increases when the first fluoropolymer is produced will also be referred to as the "effect of the present invention".

[0011] <Emulsifier> The present production method is carried out under conditions in which an emulsifier having a fluorine atom is substantially absent. "Substantially absent" means that in the production of the first aqueous dispersion, the content of the emulsifier having a fluorine atom is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, relative to the total mass of the aqueous medium, and the lower limit is 0 mass ppb. The present production method is preferably carried out under conditions in which an emulsifier having a fluorine atom and an emulsifier not having a fluorine atom are substantially absent, in order to prevent a decrease in the molecular weight of the produced fluoropolymer. "Substantially absent" means that in the production of the first aqueous dispersion, the content of the emulsifier is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, relative to the total mass of the aqueous medium, and the lower limit is 0 mass ppb. 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 WO 2018 / 181904 can be used.

[0012] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom are water-soluble. A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier means an emulsifier other than the above-mentioned water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or non-ionic. Examples of the emulsifier having a fluorine atom and the emulsifier not having a fluorine atom include those not having a carbon-carbon double bond. The first fluorine-containing polymer described below and the second fluorine-containing polymer described below are both water-insoluble. Compound X described below, a polymer of compound X, the first fluorine-containing polymer described below, and the second fluorine-containing polymer described below do not all fall under the category of emulsifiers.

[0013] Examples of emulsifiers having fluorine atoms include anionic fluorine-containing emulsifiers. Examples of anionic fluorine-containing emulsifiers include emulsifiers containing fluorine atoms whose total carbon number excluding anionic groups is 20 or less, and emulsifiers containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The above-mentioned "anionic moiety" means the moiety excluding the cation of the fluorine-containing emulsifier.

[0014] The fluorine-free emulsifier does not contain fluorine atoms and has a hydrocarbon group such as an alkyl group as a hydrophobic moiety. It is also possible to substitute a hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom.

[0015] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0016] Anionic hydrocarbon emulsifiers refer to emulsifiers having a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon group, such as an alkyl group, as a hydrophobic moiety. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, and sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0017] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as the hydrophobic moiety. The hydrophilic moiety of nonionic hydrocarbon emulsifiers includes water-soluble functional groups such as polyethylene oxide chains obtained by polymerization of ethylene oxide. Examples of nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0018] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

[0052] of JP-A No. 2016-537499.

[0019] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier with silicon atom can include siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier with siloxane skeleton.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0020] The emulsifier having no fluorine atoms may be a polymer emulsifier. Examples of the polymer emulsifier include a polymer having a hydrophilic group in its side chain. Examples of such polymer emulsifiers include polymers containing units based on a compound having a site capable of polymerization reaction and a hydrophilic group. Further, examples of the polymer emulsifier include polymers obtained by subjecting a polymer containing units based on a compound having a group that can become a hydrophilic group, even if the polymer does not originally have a hydrophilic group, to post-treatment such as hydrolysis.

[0021] The emulsifier having a fluorine atom in the present invention has a molecular weight of 1,000 g / mol or less, and the emulsifier not having a fluorine atom has a molecular weight of 100,000 g / mol or less.

[0022] <Aqueous Medium> The present production method is carried out in the presence of an aqueous medium. Specific examples of the aqueous medium include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0023] Before starting polymerization of the first monomer used in polymerization of the first fluoropolymer, the content of the aqueous medium is preferably 20 to 80% by volume, more preferably 40 to 70% by volume, based on the volume of the reactor. In this specification, "before starting polymerization of the first monomer used in polymerization of the first fluoropolymer" means immediately before the start of polymerization. Here, examples of "start of polymerization" include the time when the first monomer and the polymerization initiator are brought into coexistence in the reactor after the reactor is heated to a temperature equal to or higher than the polymerization temperature, and the time when the first monomer and the polymerization initiator are brought into coexistence in the reactor after the reactor is heated to a temperature equal to or higher than the polymerization temperature.

[0024] <Compound X> In the present production method, compound X is used. Compound X can be polymerized together with a first monomer described below. Compound X is a compound represented by formula (X).

[0025] C(X １ ) (X ２ ) = C(X ３ )-L-Z (X) In formula (X), １ , X２ and X ３ 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; and Z is an anionic group or a salt of an anionic group.

[0026] In formula (X), １ , X ２ and X ３ 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 alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 carbon atom. In formula (X), X １ , X ２ and X ３ As the alkyl group, a fluorine atom or a hydrogen atom is preferred, and a hydrogen atom is preferred in terms of excellent polymerization reactivity.

[0027] In formula (X), L is a single bond or a divalent linking group. Examples of the divalent linking group include an alkylene group, a carbonyl group, an ether bond, a thioether bond, a sulfonyl group, —NH—, and —SiH ２ -, phenylene group, -CF ２ -, and groups combining two or more of these. Examples of the above groups combining two or more of these include an ester bond, a thioester bond, an amide bond, a sulfonamide bond, a combination of an alkylene group and an ether bond, a combination of an alkylene group and an ester bond, and a combination of an alkylene group and an amide bond. The alkylene group may be linear, branched, or cyclic, and is preferably linear or branched, and more preferably branched. The number of carbon atoms in the alkylene group may be, for example, 1 to 6, and preferably 1 to 4. Specific examples of L in formula (X) include a single bond, an alkylene group, an ether bond, an ester bond, * Ｃ -CO-NH-R-* Ｚ and the like, and examples thereof include a single bond, an alkylene group having 1 to 6 carbon atoms, and * Ｃ -CO-NH-R-* Ｚ is preferred, and a single bond, an alkylene group having 1 to 2 carbon atoms, and * Ｃ-CO-NH-R-* Ｚ is more preferred, and since the number of particles of the resulting fluorocopolymer increases and the content of the compound represented by (S3) in the resulting solid composition containing the fluoropolymer is reduced, Ｃ -CO-NH-R-* Ｚ is particularly preferred. Ｃ is the bonding site to the carbon atom in formula (X), and * Ｚ is a 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 branched being preferred. The alkylene group or fluoroalkylene group represented by R has 1 to 6 carbon atoms, preferably 2 to 4, and more preferably 4 carbon atoms. R is preferably a linear or branched alkylene group having 1 to 6 carbon atoms.

[0028] In formula (X), Z is an anionic group or a salt of an anionic group. Examples of the anionic group include —SO ３ H, -OSO ３ H, -P(=O)(OH) ２ , -OP(=O)(OH) ２ or -COOH. Examples of salts of anionic groups include groups in which the hydrogen ion of the above-mentioned anionic groups is replaced with a cation other than a hydrogen ion. 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 -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ From the viewpoint of productivity, Z is preferably —SO ３ M and -COOM are preferred, and -SO３ Na and —COONa are more preferred, and —SO ３ Na is more preferred. ３ When it is M, the latex tends to be more stable and the number of particles of the first fluorine-containing polymer increases.

[0029] M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ and R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent. The metal atom represented by M is preferably a metal atom of Group 1, more preferably Li, Na or K. Ｍ１ and R Ｍ２ The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and even more preferably an alkyl group or an aromatic hydrocarbon group. The substituent preferably has 1 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. The aromatic hydrocarbon group is preferably a phenyl group.

[0030] The molecular weight of compound X is, for example, 70 to 500, and from the viewpoint of dispersion stability, 70 to 450 is preferable, and 100 to 300 is more preferable. Specific examples of compound X include 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tigloylglycine, 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 metal salts thereof. Examples of the metal salts include metal salts of the metal atom represented by M.

[0031] Before the start of polymerization of the first monomer to be used in polymerization of the first fluorinated polymer, the content of compound X is preferably from 1.0 to 1000 ppm by mass, and in terms of better effects of the present invention, more preferably from 1.0 to 500 ppm by mass, still more preferably from 3.0 to 100 ppm by mass, particularly preferably from 5.0 to 30.0 ppm by mass, relative to the total mass of the aqueous medium.

[0032] <Polymerization initiator> The polymerization initiator used in the present production method is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0033] The amount of the 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 used.

[0034] <First Monomer> The first monomer used in the present production method includes tetrafluoroethylene (hereinafter also referred to as "TFE".) The first monomer may include a monomer other than TFE.

[0035] 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 %, based on the amount of the first monomer used.

[0036] The first monomer preferably contains perfluoroalkyl vinyl ether (hereinafter also referred to as "PAVE"). The PAVE is preferably a monomer represented by formula (1) from the viewpoints of excellent polymerization reactivity in producing the first fluorinated polymer and of enabling more efficient production of the second fluorinated polymer.

[0037] CF ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ is a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0038] 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"), and from the viewpoint of enabling more efficient production of the second fluorinated polymer, PMVE or PPVE is preferred, and PMVE is more preferred.

[0039] 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%, based on 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%, based on the amount of the first monomer used.

[0040] The first monomer may contain other monomers than TFE and PAVE, or may be substantially free of other monomers from the viewpoint of more efficiently producing the second fluorine-containing polymer. "Substantially free of other monomers" means that the amount of other monomers used is 0.01 mol % or less, preferably 0 mol %, based on the amount of the first monomer used.

[0041] <Steps> The polymerization method for the first fluorine-containing polymer is not particularly limited, as long as it is a method of polymerizing a first monomer containing tetrafluoroethylene using compound X and a polymerization initiator under conditions in which an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent. Examples of the method include a method in which a solution containing an aqueous medium and compound X is prepared, and the first monomer is polymerized using this solution and a polymerization initiator. More specifically, a method in which the solution and the first monomer are added to a reactor, the reactor is heated, and a polymerization initiator is added to the reactor to polymerize the first monomer is exemplified. Polymerization of the first fluorine-containing polymer results in a first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. The aqueous dispersion thus obtained, in which particles of the first fluorine-containing polymer are dispersed, may be used as the first aqueous dispersion, or another aqueous medium may be added to make the first aqueous dispersion. Alternatively, the first fluorine-containing polymer particles may be dispersed in another aqueous medium by solvent substitution, and the resulting dispersion may be used as the first aqueous dispersion.

[0042] The first monomer is charged into a reaction vessel by a conventional method. For example, the first monomer may be continuously or intermittently charged into the reactor 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 continuously or intermittently charged into the reactor. When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in portions.

[0043] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. The polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0044] (First aqueous dispersion) The first aqueous dispersion preferably does not substantially contain a water-soluble emulsifier. The water-soluble emulsifier is as described above. "Substantially does not contain a water-soluble emulsifier" means that the content of the water-soluble emulsifier is 10 mass ppm or less, more preferably 150 mass ppb or less, and even more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion. The lower limit is 0 mass ppb.

[0045] Furthermore, it is preferable that the first aqueous dispersion is substantially free of a compound represented by any of formulas (S1) to (S4). "Substantially free of a compound represented by formula (S1)" means that the content of the compound represented by formula (S1) is 10 mass ppm or less, preferably 5 mass ppm or less, more preferably 150 mass ppb or less, and even more preferably 50 mass ppb or less, relative to the total mass of the aqueous dispersion. The lower limit is 0 mass ppb. "Substantially free of a compound represented by formula (S2)" means that the content of the compound represented by formula (S2) is 10 mass ppm or less, preferably 5 mass ppm or less, more preferably 150 mass ppb or less, and even more preferably 50 mass ppb or less, relative to the total mass of the aqueous dispersion. The lower limit is 0 mass ppb. "Substantially free of compounds represented by formula (S3)" means that the content of the compounds 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, relative to the total mass of the aqueous dispersion. The lower limit is 0 ppb by mass. "Substantially free of compounds represented by formula (S4)" means that the content of the compounds represented by formula (S4) 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, relative to the total mass of the aqueous dispersion. The lower limit is 0 ppb by mass. When no emulsifier is used during the production of the first fluoropolymer contained in the first aqueous dispersion, the amount of compounds represented by any of formulas (S1) to (S4) generated 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 above-mentioned purification treatment.

[0046] H-(CF ２ ) ｎ１ -COOM Ｓ (S1) F-(CF ２ ) ｎ１ -COOM Ｓ (S2) H-(CF ２ ) ｎ２ -SO ３ M Ｓ (S3) F-(CF２ ) ｎ２ -SO ３ M Ｓ (S4) In the formulas (S1) to (S4), n1 is an integer of 3 to 13, n2 is an integer of 4 to 10, and M Ｓ is a hydrogen atom, Na, K, or NH ４ The methods for measuring each content include the methods described in the Examples.

[0047] Before the start of polymerization of the second monomer to be used in the polymerization of the second fluoropolymer, the content of the particles of the first fluoropolymer is preferably from 0.01 to 5.00 mass% relative to the total mass of the first aqueous dispersion, and from the viewpoint of enabling the second fluoropolymer to be produced more efficiently, more preferably from 0.01 to 3.0 mass%.

[0048] In this specification, "before initiating polymerization of the second monomer used in the polymerization of the second fluoropolymer" means immediately before the start of polymerization. Here, "the start of polymerization" includes the time when the second monomer and the polymerization initiator are made to coexist in the reactor after the temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the second monomer and the polymerization initiator are made to coexist in the reactor. Note that the first aqueous dispersion before the start of polymerization of the second monomer used in the polymerization of the second fluoropolymer does not contain the second monomer and the polymerization initiator used in the polymerization of the second fluoropolymer.

[0049] The first aqueous dispersion may contain components other than the various components described above. Specific examples of other components that the first aqueous dispersion may contain include a chain transfer agent, a reducing agent, and a pH adjuster. Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane. Furthermore, examples of chain transfer agents include compounds represented by formula (I) described below. 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. When 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. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0050] The solids concentration of the first aqueous dispersion is preferably 5 to 50% by mass, and more preferably 10 to 45% by mass. The solids concentration of the first aqueous dispersion can be measured, for example, by the following method. The solids 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 determining the solids concentration using the following formula: "Solids concentration (mass%) = 100 × heating residue of first aqueous dispersion (g) / mass of first aqueous dispersion (2.0 g)"

[0051] (Particles of first fluorine-containing polymer) The particles of the first fluorine-containing polymer are particles produced by the present production method. It is presumed that the particles of the first fluorine-containing polymer adsorb and incorporate the second monomer at the hydrophobic part during polymerization of the second monomer described below, thereby solubilizing the second monomer and facilitating polymerization of the second monomer even when the particles do not substantially contain an emulsifier having a fluorine atom. The first fluorine-containing polymer and the second fluorine-containing polymer described below may be the same or different from each other.

[0052] The average particle size of the particles of the first fluorine-containing polymer is 500 nm or less, and from the viewpoint of particle dispersion stability, it is preferably 300 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less. 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 particles of the first fluorine-containing polymer is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

[0053] The number of particles of the first fluorine-containing polymer is 0.5×10 １４ Preferably, the number of particles / mL or more is 1.0 x 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ More preferably, 5.0 x 10 １４ The upper limit is 2.0 × 10 １５ The particle number of the first fluoropolymer is the number of particles per mL of the first aqueous dispersion. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0054] The first fluorine-containing polymer does not have a 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, no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the category of the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0055] The 1% by mass weight loss temperature on heat of the first fluoropolymer 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% by mass weight loss temperature on heat can be measured, for example, using a thermogravimetric analyzer. Specific methods for measuring the 1% by mass weight loss temperature on heat include the measurement methods shown in the Examples section.

[0056] The first fluorine-containing polymer has units based on a first monomer. The first fluorine-containing polymer contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE units"). The content of the TFE units is preferably 5 to 80 mol%, more preferably 20 to 75 mol%, and even more preferably 50 to 75 mol%, based on all units of the first fluorine-containing polymer. Details of TFE from which the TFE units are derived are the same as those for TFE in the above-mentioned production method, and preferred embodiments are also the same.

[0057] In this specification, when 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. When 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 above also applies to other fluorine-containing polymers.

[0058] 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 content of PAVE units is preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 25 to 50 mol%, based on all units of the first fluorine-containing 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%, based on all units of the first fluorine-containing polymer. Details of PAVE from which PAVE units are derived are the same as those for PAVE in the above-mentioned production method, and preferred embodiments are also the same. When PMVE or PPVE is used as PAVE, the preferred amount used is also the same. According to this production method, even if an emulsifier is not essential, the presence of compound X in the reaction system makes it possible to obtain a first fluorine-containing polymer obtained by polymerizing a first monomer containing TFE units and PAVE units, which is particularly preferred as a polymer having a large number of particles.Furthermore, a first fluorine-containing polymer obtained by polymerizing a monomer having a TFE unit content of 5 to 80 mol % and a PAVE unit content of 20 to 95 mol % relative to the total units of the first fluorine-containing polymer is preferred because it gives a polymer having a large number of particles and no melting point.

[0059] The first fluorine-containing polymer may contain other units than TFE unit and PAVE unit, and may not substantially contain other units, from the viewpoint of more efficiently producing the second fluorine-containing polymer.The phrase "not substantially containing other units" means that the content of units based on other monomers is 0.01 mol% or less, preferably 0 mol%, based on the total units of the first fluorine-containing polymer.The details of the other monomers from which other units are derived can be exemplified by the other monomers in the second fluorine-containing polymer described below.

[0060] [Method for producing second fluoropolymer] The method for producing the second fluoropolymer is a method for producing the second fluoropolymer by polymerizing a second monomer in the first aqueous dispersion produced by the above-mentioned present production method. Preferably, the method for producing the second fluoropolymer is a method for producing the second fluoropolymer by polymerizing the second monomer using a polymerization initiator in the aqueous dispersion produced by the above-mentioned present production method.

[0061] <First aqueous dispersion> The first aqueous dispersion is an aqueous dispersion produced by the above-described production method. Preferred embodiments of the first aqueous dispersion are as described above.

[0062] It is preferable to carry out a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products from the first aqueous dispersion before using it in a method for producing a second fluorine-containing polymer, i.e., polymerization to obtain a second fluorine-containing polymer. In the purification treatment, the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion are removed, making it easy to obtain a second fluorine-containing polymer with desired physical property values. Examples of the purification method include a heat treatment and a method of removal using an ion exchange resin. As the ion exchange resin, an anion exchange resin is preferred. Purification may be carried out multiple times.

[0063] <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. 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.

[0064] The second monomer may contain a monomer other than the above-mentioned monomer. Specific examples of the other monomer include ethylene, propylene, vinyl chloride, vinylidene chloride, a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer having one or more atoms of at least one kind selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom, a monomer having a nitrile group (hereinafter also referred to as "R ＣＮ "), and a unit based on the compound (6) described below (hereinafter also referred to as a "POAVE unit").

[0065] BO is a monomer having two or more polymerizable unsaturated bonds. Specific examples of the polymerizable unsaturated bond include a carbon atom-carbon atom double bond (C═C) and a carbon atom-carbon atom triple bond (C≡C). A carbon atom-carbon atom double bond (C═C) is more preferred as the polymerizable unsaturated bond. The number of polymerizable unsaturated bonds in BO is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, in terms of superior polymerization reactivity. BO preferably further contains a fluorine atom in terms of reducing the compression set of a crosslinked rubber article at high temperatures.

[0066] BO is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２and R ２３ are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group, a1 is an integer of 2 to 6, and R ２４ is a monovalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group, ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are preferably the same. a1 is preferably 2 or 3, and more preferably 2. In terms of better polymerization reactivity of BO, R ２１ , R ２２ and R ２３ is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ and R ２３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, ２１ , R ２２ and R ２３ It is more preferable that all of R are fluorine atoms. ２４ R may be any of linear, branched, and cyclic, preferably linear or branched, and more preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ２４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and even more preferably 1 or 2. ２４ The etheric oxygen atom in R ２４ It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0067] Of the monomers represented by formula (2), specific examples of suitable monomers include the monomers represented by formula (3) and the monomers represented by formula (4).

[0068] (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 end or between the carbon-carbon bonds of the perfluorohydrocarbon group.

[0069] (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 end or between the carbon-carbon bonds of the perfluorohydrocarbon group.

[0070] Specific examples of the monomer represented by formula (3) include CF ２ = CFO (CF ２ ) ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ３ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ４ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ６ OCF = CF ２、 CF ２ = CFO (CF ２ ) ８ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ O (CF２ CF ２ O) ２ CF = CF ２ , C.F. ２ = CFO (CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , and CF ２ = CFOCF ２ CF ２ O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２ Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３ OCF = CF ２ (hereinafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter, also referred to as "C4DVE"). Specific examples of the monomer represented by formula (4) include CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２ , and C.H. ２ =CH(CF ２ ) ６ CH=CH ２ Among the monomers represented by formula (4), specific examples of more preferred monomers include CH ２ =CH(CF ２ ) ６ CH=CH２ (hereinafter also referred to as "C6DV"). Among them, C3DVE or C4DVE is preferable for BO.

[0071] Examples of the monomer having at least one atom selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom include a monomer having a bromine atom and a monomer having an iodine atom. Specific examples of the monomer having a bromine atom include CF ２ = CFOCF ２ CF ２ CF ２ OCF ２ CF ２ Br, 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. Also included are 2-bromo-perfluoroethyl perfluorovinyl ether, CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF=CFBr, ROCBr=CF ２ (wherein R is a lower alkyl group or a fluoroalkyl group), specifically, ３ OCF = CFBr and CF ３ CH ２ Specific examples of the monomer having an iodine atom include the monomer represented by the formula: CHR=CH-Z-CH ２ CHR-I (wherein R is —H or —CH ３ and Z is a linear or branched C alkyl group optionally containing one or more ether oxygen atoms.１ ~C １８ iodinated olefins of the formula I(CH) as disclosed in U.S. Pat. No. 5,717,036, which are (per)fluoroalkylene groups or (per)fluoropolyoxyalkylene groups as disclosed in U.S. Pat. No. 5,674,959. ２ CF ２ CF ２ ) ｎ OCF = CF ２ and ICH ２ CF ２ O[CF(CF ３ )CF ２ O] ｎ CF = CF ２ (wherein n = 1 to 3) and the like. Also included 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, as disclosed in U.S. Patent No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0072] R ＣＮ has a polymerizable unsaturated bond. ＣＮ From the viewpoint of polymerization reactivity, it is more preferable that the copolymer has one polymerizable unsaturated bond. Specific examples of the polymerizable unsaturated bond include a carbon-carbon double bond (C═C) and a carbon-carbon triple bond (C≡C).

[0073] R ＣＮ is preferably a monomer represented by formula (5) from the viewpoint of better mold releasability and heat resistance.

[0074] 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 R is a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group. ＣＮ From the viewpoint of excellent polymerization reactivity of R ５１ , R ５２ and R ５３ is preferably a fluorine atom or a hydrogen atom, and R ５１ , R ５２ and R ５３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, ５１ , R ５２ and R ５３ It is more preferable that all of R are fluorine atoms. ５４ R may be linear, branched or cyclic, and is preferably linear or branched. ５４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ５４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better rubber properties. ５４ The number of etheric oxygen atoms in the formula (5) is preferably 1 to 3, and more preferably 1 or 2. Specific examples of the monomer represented by the formula (5) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２ ) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２OCF (CF ３ ) CN and CF ２ = CFO (CF ２ ) ３ CN is exemplified, and 8CNVE or MV5CN is preferred in terms of better mold releasability and heat resistance.

[0075] The POAVE unit is a unit based on compound (6). 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 of 0 to 3, m is an integer of 0 to 4, and n+m is an integer of 1 to 7.

[0076] R ｆ２ In the formula (R), the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 3 or 4. When n is 1, m is preferably an integer of 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer of 1 to 3.

[0077] Specific examples of compound (6) include the following. The abbreviation for the compound is given in parentheses after the formula: 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-(OCF２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF ３

[0078] The second monomer preferably contains TFE. The second monomer preferably contains only TFE and PAVE, or contains TFE and PAVE and also contains other monomers. Examples of the other monomers include the above-mentioned monomers having one or more atoms of at least one kind selected from the group consisting of BO, chlorine atom, bromine atom, and iodine atom, and R ＣＮ It is preferable that the polymer contains at least one monomer selected from the group consisting of:

[0079] 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%, based on the total amount of all second monomers used to produce the second fluoropolymer. 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%, based on the total amount of all second monomers used to produce the second fluoropolymer. When TFE and PAVE are used as the second monomers, the suitable amounts of TFE and PAVE used are the same. The amounts of TFE and PAVE used are 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 second monomers used to produce the second fluoropolymer. The amount of the other monomer 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, relative to 100 parts by mass of the aqueous medium contained in the first aqueous dispersion.

[0080] <Polymerization initiator> In the method for producing the second fluorine-containing polymer, it is preferable to polymerize the second monomer using a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. 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"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, an organic acid, or an inorganic salt. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of a fluorine-containing polymer, a water-soluble radical initiator is more preferred, and a persulfate is even more preferred. Two or more polymerization initiators may be used in combination.

[0081] <Step> The method for producing the second fluoropolymer comprises polymerizing the second monomer in the first aqueous dispersion to produce the second fluoropolymer. Examples of the method for polymerizing the second monomer include the method for polymerizing the first monomer described above.

[0082] The polymerization of the second monomer is preferably carried out in the substantial absence of an emulsifier having a fluorine atom. The polymerization of the second monomer is more preferably carried out in the substantial absence of an emulsifier having a fluorine atom and an emulsifier not having a fluorine atom. Examples of the emulsifier include the emulsifiers mentioned above. The substantial absence of an emulsifier in the method for producing the second fluorine-containing polymer means that the content of the emulsifier is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion. The lower limit is 0 mass ppb.

[0083] In the process for producing the second fluorine-containing polymer, particles of the second fluorine-containing polymer are produced. Specifically, the process for producing the second fluorine-containing polymer produces a second aqueous dispersion in which particles of the second fluorine-containing polymer are dispersed in the aqueous medium.

[0084] (Second Fluorine-Containing Polymer) The second fluorine-containing polymer is a fluorine-containing polymer produced by the above-mentioned method for producing the second fluorine-containing polymer.

[0085] The second fluorine-containing polymer may be in the form of particles. The particles of the second fluorine-containing polymer may contain the first fluorine-containing polymer, or 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, and from the viewpoint of particle dispersion stability, more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 300 nm or less. 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 particles of the second fluorine-containing polymer can be measured in the same manner as the average particle size of the particles of the first fluorine-containing polymer.

[0086] The number of particles of the second fluorine-containing polymer is 0.5×10 １４ Preferably, the number of particles / mL or more is 1.0 x 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ More preferably, 5.0 x 10 １４ The upper limit is 10.0 × 10１５ The particle number of the second fluoropolymer is the number of particles per mL of the second aqueous dispersion. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0087] The second fluorine-containing polymer preferably does not have a melting point. "Doing not have a 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, no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the category of the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0088] The 1% by mass weight loss temperature on heat of the second fluoropolymer 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 weight loss temperature on heat can be measured, for example, using a thermogravimetric analyzer. Specific methods for measuring the 1% by mass weight loss temperature on heat include the measurement methods shown in the Examples section.

[0089] The second fluorine-containing polymer has units based on a second monomer. The second monomer is as described above, and preferred embodiments are also the same. The TFE units are preferably 5 to 80 mol%, more preferably 20 to 75 mol%, and even more preferably 50 to 75 mol%, based on all units of the second fluorine-containing polymer. The PAVE units are preferably 20 to 95 mol%, more preferably 25 to 80 mol%, and even more preferably 25 to 50 mol%, based on all units of the second fluorine-containing polymer. The TFE units and PAVE units are 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%, based on all units of the second fluorine-containing polymer. The units of other monomers are preferably 0 to 90 mol%, more preferably 0 to 80 mol%, and even more preferably 0 to 70 mol%, based on all units of the second fluorine-containing polymer.

[0090] [Second aqueous dispersion] The second aqueous dispersion is an aqueous dispersion obtained by the method for producing a second fluoropolymer. The second aqueous dispersion is preferably an aqueous dispersion containing fluoropolymer particles (hereinafter also referred to as "specific particles") and an aqueous medium. In particular, the second aqueous dispersion is an aqueous dispersion that is substantially free of a water-soluble emulsifier having fluorine atoms and contains specific particles and an aqueous medium, and the number of specific particles is 0.5 × 10 １４ The second aqueous dispersion is preferably an aqueous dispersion in which the number of specific particles is 0.5×10 or more / mL, the average particle size 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 has no melting point. １４ It is preferable that the aqueous dispersion is one in which the concentration of the specific particles is 100 / mL or more, the average particle size 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 has no melting point.

[0091] Examples of the water-soluble emulsifier having fluorine atoms include the water-soluble emulsifier having fluorine atoms in the production method described above. "Substantially free of water-soluble emulsifier having fluorine atoms" means that the content of the water-soluble emulsifier having fluorine atoms is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the second aqueous dispersion. The lower limit is 0 mass ppb. It is also preferable that the water-soluble emulsifier having no fluorine atoms is not substantially contained. Examples of the water-soluble emulsifier having no fluorine atoms include the water-soluble emulsifier having no fluorine atoms in the production method described above. "Substantially free of water-soluble emulsifier having no fluorine atoms" means that the content of the water-soluble emulsifier having no fluorine atoms is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the second aqueous dispersion. The lower limit is 0 mass ppb. It is also preferable that the second aqueous dispersion is substantially free of water-soluble emulsifiers having fluorine atoms and water-soluble emulsifiers not having fluorine atoms. Examples of water-soluble emulsifiers having fluorine atoms include the water-soluble emulsifiers having fluorine atoms used in the production method described above. Examples of water-soluble emulsifiers not having fluorine atoms include the water-soluble emulsifiers not having fluorine atoms used in the production method described above. "Substantially free of water-soluble emulsifiers having fluorine atoms and water-soluble emulsifiers not having fluorine atoms" means that the total content of water-soluble emulsifiers having fluorine atoms and water-soluble emulsifiers not having fluorine atoms is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, relative to the total mass of the second aqueous dispersion. The lower limit may be 0 mass ppb.

[0092] <Specific Particles> The specific particles are preferably particles of the second fluoropolymer described above. When the specific particles contain the second fluoropolymer, the specific particles may or may not contain the first fluoropolymer. The second aqueous dispersion may further contain particles of the first fluoropolymer in addition to the specific particles.

[0093] The number of specific particles is 0.5 x 10 １４It is preferred that the specific particle number and average particle size are the same as those of the second fluorine-containing polymer.

[0094] The fluorine-containing polymer produced in the first aqueous dispersion and the second aqueous dispersion of the present invention preferably comprises TFE units and PAVE units and has no melting point.The TFE units and PAVE units and other units contained in the fluorine-containing polymer 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 contents thereof) are the same.The meaning of "having no melting point" is as described above.

[0095] The content of the 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, from the viewpoint of dispersion stability of the specific particles.

[0096] <Aqueous Medium> Specific examples of the aqueous medium contained in the second aqueous dispersion are the same as those of the aqueous medium in the production 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, from the viewpoint of dispersion stability of the specific particles. <Solid Composition> A solid composition containing a fluorine-containing polymer having no melting point, produced in the first aqueous dispersion or the second aqueous dispersion of the present invention, wherein the solid composition has units based on TFE, the content of the emulsifier having a fluorine atom 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, and 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 of 3 to 13, and M Ｓ is a hydrogen atom, Na, K or NH ４ H-(CF ２ ) ｎ２ -SO３ M Ｓ (S3) In formula (S3), n2 is an integer of 4 to 10, and M Ｓ is a hydrogen atom, Na, K or NH ４ The methods for measuring each content include the methods described in the Examples.

[0097] The present solid composition refers to a composition having a solid content of 99% by mass or more. Here, the solid content is calculated by the following method based on the mass before and after heating. After heating 2.0 g of the solid composition at 170°C for 20 minutes, the mass of the residue is weighed and the solid content is calculated by the following formula: Solid content (mass%) = 100 x (mass of residue) / (mass of solid composition)

[0098] The present solid composition is preferably obtained by coagulating a fluoropolymer produced in the first aqueous dispersion or the second aqueous dispersion described above. Preferred embodiments of the fluoropolymer contained in the present solid composition are the same as those of the fluoropolymer contained in the first aqueous dispersion or the second aqueous dispersion described above. That is, the fluoropolymer contained in the present solid composition is preferably the first fluoropolymer or the second fluoropolymer described above. The second fluoropolymer may contain the first fluoropolymer. The present solid composition contains a first fluoropolymer or a second fluoropolymer having no melting point and containing units based on TFE. The first fluoropolymer or the second fluoropolymer having no melting point preferably contains units based on TFE and units based on PAVA. The content of the fluoropolymer 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 present solid composition.

[0099] In the present solid composition, the content of the emulsifier having a fluorine atom is 1500 mass ppb or less, preferably 1000 mass ppb or less, more preferably 900 mass ppb or less, and particularly preferably 850 mass ppb or less, relative to the total mass of the solid composition. Specific examples of emulsifiers having a fluorine atom are as described above. In the present solid composition, an emulsifier not having a fluorine atom is substantially not contained. "Substantially not containing an emulsifier not having a fluorine atom" means that the content of the emulsifier not having a fluorine atom is 10 mass ppm or less, preferably 5 mass ppm or less, more preferably 150 mass ppb or less, and even more preferably 50 mass ppb or less, relative to the total mass of the solid composition. The lower limit is 0 mass ppb. Specific examples of emulsifiers not having a fluorine atom are as described above.

[0100] The solid composition has a content of the compound represented by formula (S1) 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 has a content of the compound represented by formula (S3) of 100 ppb by mass or less, preferably 50 ppb by mass or less, more preferably 25 ppb by mass or less, still more preferably 10 ppb by mass or less, and particularly preferably 0 ppb by mass, relative to the total mass of the solid composition. When no emulsifier is used during the production of the first fluoropolymer contained in the first aqueous dispersion and the production of the second fluoropolymer contained in the second aqueous dispersion, the amounts of the compounds represented by formula (S1) and formula (S3) generated can be suppressed, making it easy to adjust the contents of these compounds in the solid composition.

[0101] The solid composition preferably has a metal content of 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 solid content of the solid composition. A metal content of less than 50 ppm by mass further improves the surface smoothness of the resulting solid composition.

[0102] <Uses> As described above, the second aqueous dispersion does not necessarily require an emulsifier such as an emulsifier having a fluorine atom, and therefore can easily be converted into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. by solvent substitution. For example, the second aqueous dispersion can be converted into a dispersion in an organic solvent by mixing the second aqueous dispersion with an organic solvent and dehydrating it by evaporation or using anhydrous sodium sulfate, etc.

[0103] The second aqueous dispersion stably disperses the fluoropolymer even without containing an emulsifier, and is therefore suitable for use in coating applications, binders, etc.

[0104] Furthermore, a solid of specific particles can be obtained by aggregating the first fluorine-containing polymer from the first aqueous dispersion or aggregating the specific particles from the second aqueous dispersion. Furthermore, the solid of specific particles obtained by aggregating can be appropriately molded by a known method. Examples of the molding method include injection molding, extrusion molding, coextrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calender molding.

[0105] Aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulant. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which a solution containing an acid is added to the second aqueous dispersion is preferred. 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. In the case of base aggregation, a method in which a solution containing a base is added to the second aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., with sodium hydroxide being preferred. The concentration of the base in the base-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 aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, a compound of the general formula M'Al(SO ４ ) ２ ・12H ２ Examples of the coagulation method include alum represented by the formula: O (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate, of which alum is preferred, and potassium alum, in which M is potassium, is more preferred. As the coagulation method, base coagulation is preferred because coagulation proceeds particularly easily.

[0106] The present invention will be described in detail below with reference to examples. Examples 1 to 5 and 7 to 11 are working examples, and Example 6 is a comparative example. However, the present invention is not limited to these examples.

[0107] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0108] <Average particle size of particles of first fluoropolymer and second fluoropolymer> 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, then purged, and returned to atmospheric pressure to obtain a measurement sample. The average particle size of the obtained measurement sample was measured using a dynamic light scattering particle size distribution measuring device (Otsuka Electronics Co., Ltd., ELSZ) with an integrated number set to 100, and was taken as the average particle size of the particles in each aqueous dispersion. Note that when the average particle size of the particles of the first fluoropolymer in raw material liquid B described below was measured in the same manner as for the first aqueous dispersion, the average particle size of the particles of the first fluoropolymer in raw material liquid B was the same as the average particle size of the particles of the first fluoropolymer in the first aqueous dispersion.

[0109] <Number of Particles of First Fluoropolymer and Second Fluoropolymer> The number of particles of the first fluoropolymer in the first aqueous dispersion and the number of particles of the second fluoropolymer in the second aqueous dispersion, Np (particles / mL), were calculated according to the following formula:

[0110] Np (pieces / mL) = [(X / 100) / (1-X / 100)] / [4 / 3×π×{(Dp / 2) ３ X: solids concentration (mass%) of the first aqueous dispersion, or solids concentration (mass%) of the second aqueous dispersion; π: circumference constant; Dp: average particle size (m) of particles of the first fluoropolymer in the first aqueous dispersion, or average particle size (m) of particles of the second fluoropolymer in the second aqueous dispersion; ρ: specific gravity of the first fluoropolymer, or specific gravity of the second fluoropolymer (ρ=2.04×10 for both). ６ (g / m ３ )

[0111] (Solid content concentration of first aqueous dispersion or second aqueous dispersion) After 2.0 g of the first aqueous dispersion or second aqueous dispersion of each example described below was heated at 170°C for 20 minutes, the mass (g) of the residue was weighed and the solid content concentration was calculated using the following formula: Solid content concentration (mass%) of first aqueous dispersion or second aqueous dispersion = 100 × (mass of residue) / (mass (2.0 g) of first aqueous dispersion or second aqueous dispersion)

[0112] <Proportion 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 is１９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0113] <Melting point> The first aqueous dispersion or second aqueous dispersion of each example described below was freeze-aggregated and then filtered to obtain a first fluorine-containing polymer or a second fluorine-containing polymer. A 5 mg sample of the obtained first fluorine-containing polymer or second fluorine-containing polymer was weighed out in an aluminum pan and heated from 20°C to 360°C at a temperature increase rate of 10°C / min in an air atmosphere using a Hitachi DSC600, and the presence or absence of a melting point peak was confirmed.

[0114] <1% mass loss temperature on heat> The first aqueous dispersion or second aqueous dispersion of each example described below was freeze-aggregated and then filtered to obtain a first fluoropolymer or a second fluoropolymer. A 10 mg sample of the obtained first fluoropolymer or second fluoropolymer was weighed out and placed in an aluminum pan, and heated from 40°C to 550°C at a heating rate of 10°C / min in an air atmosphere using a Hitachi STA200, and the 1% mass loss temperature was obtained from the resulting weight loss rate.

[0115] <Contents of Compounds Represented by Formula (S1) and Compounds Represented by Formula (S3) in Aqueous Dispersions> (Preparation of Measurement Samples) Each aqueous dispersion and each raw material liquid was freeze-aggregated at -20°C. When thawed at room temperature, polymers precipitated, which were then filtered off to recover the aqueous phase. The content of the compound represented by formula (S1) contained in the resulting aqueous phase was determined by converting each compound in formula (S1) where n1 = 3 to 13 into a perfluorocarboxylic acid having the same carbon number. Furthermore, the content of the compound represented by formula (S3) contained in the resulting aqueous phase was determined by converting each compound in formula (S3) where n2 = 4 to 10 into a perfluorosulfonic acid having the same carbon number. Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1 to 180 ng / g were first prepared, and a and a' were calculated using the following formulas (A1) and (A1') based on the respective sample concentrations and peak integrals using a first-order approximation: A=a×X (A1), where A is the peak area of ​​perfluorocarboxylic acid, and X is the concentration of perfluorocarboxylic acid (ng / g). A'=a'×X' (A1'), where A' is the peak area of ​​perfluorosulfonic acid, and X' is the concentration of perfluorosulfonic acid (ng / g).

[0116] The measuring equipment and conditions are shown in Table 1 below.

[0117]

[0118] The MRM measurement parameters are shown in Tables 2 and 3 below.

[0119]

[0120]

[0121] Specifically, first, the compound represented by formula (S1) or formula (S3) contained in the aqueous phase was measured using the liquid chromatograph mass spectrometer, and the peak areas of the compounds represented by formula (S1) and formula (S3) having each carbon number were determined using MRM.

[0122] The MRM measurement parameters are shown in Tables 4 and 5 below.

[0123]

[0124]

[0125] Next, the contents of the compound represented by formula (S1) and the compound represented by formula (S3) were calculated using the following formulas (A2) and (A2'), respectively. Note that a in formula (A2) means a calculated by the above formula (A1), and a' in formula (A2') means a' calculated by the above formula (A1'). XCm = ACm / a (A2) XCm: content (ng / g) of the compound represented by formula (S1) having carbon number (n1+1) in the aqueous phase ACm: peak area of ​​the compound represented by formula (S1) having carbon number (n1+1) in the aqueous phase X'Cm' = ACm' / a' (A2') XCm': content (ng / g) of the compound represented by formula (S3) having carbon number n in the aqueous phase ACm': peak area of ​​the compound represented by formula (S3) having carbon number n in the aqueous phase The quantitation limit in this measurement is 1 ng / g.

[0126] <Method for measuring the contents of the compound represented by formula (S1) and the compound represented by formula (S3) contained in the solid composition> (Preparation of measurement sample) The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEC Corporation) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) based on the total mass of the solid composition was added in advance to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer, and the supernatant was used as the extract. The content of the compound represented by formula (S1) contained in each extract was determined by converting each compound in formula (S1) where n1 = 3 to 13 into a perfluorocarboxylic acid with the same carbon number. The content of the compound represented by formula (S3) contained in each extract was determined by converting each compound in formula (S3) where n2 = 4 to 10 into a perfluorosulfonic acid with the same carbon number. Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1 to 180 ng / g were first prepared, and a and a' were determined using equations (A1) and (A1') by linear approximation from the respective sample concentrations and peak integrals. A = a × X (A1), where A is the peak area of ​​perfluorocarboxylic acid, X is the concentration of perfluorocarboxylic acid (ng / g), and A' = a' × X' (A1'), where A' is the peak area of ​​perfluorosulfonic acid, and X' is the concentration of perfluorosulfonic acid (ng / g).

[0127] The measuring equipment and conditions are as shown in Table 1 above.

[0128] The parameters for the MRM measurement are as shown in Table 2 above.

[0129] Specifically, first, the peak areas of the compounds represented by formula (S1) and formula (S3) contained in each of the extracts were determined using the liquid chromatograph mass spectrometer.

[0130] Next, the contents of the compound represented by formula (S1) and the compound represented by formula (S3) were calculated using formulas (A2) and (A2'), respectively. Note that a in formula (A2) means a calculated using formula (A1) above, and a' in formula (A2') means a' calculated using formula (A1') above. XCm = ACm / a (A2) XCm: content (ng / g) of the compound represented by formula (S1) with carbon number (n+1) in each extract ACm: peak area of ​​the compound represented by formula (S1) with carbon number (n+1) in each extract XCm' = ACm' / a' (A2') XCm': content (ng / g) of the compound represented by formula (S3) with carbon number n in each extract ACm': peak area of ​​the compound represented by formula (S3) with carbon number n in each extract The quantitation limit in this measurement is 1 ng / g.

[0131] The content (ZCm) of the compound represented by formula (S1) in the solid relative to the total mass of the solid was calculated using the following formula (A3): ZCm = XCm × ρ1 × La / W1 (A3) ZCm: content of the compound represented by formula (S1) with carbon number (n + 1) contained 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: mass of the sample used for extraction (2.5 g of solid in each example)

[0132] The content (ZCm') of the compound represented by formula (S3) in the solid relative to the total mass of the solid was calculated using the following formula (A4): ZCm' = XCm' × ρ1 × La / W1 (A4) ZCm': content of the compound represented by formula (S3) with carbon number n contained 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: mass of the sample used for extraction (2.5 g of solid in each example)

[0133] <Method for Quantifying Fluorine-Containing Emulsifier> The solid composition obtained in each example was freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 min, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluorine-containing polymer. The supernatant was used as the extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier in the extract was measured using a liquid chromatograph mass spectrometer. The measurement instrument configuration and LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of emulsifiers having fluorine atoms with known concentrations, methanol solutions with five or more levels of content were prepared, and LC / MS analysis of the methanol solutions with each content was performed, and the relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the emulsifiers having fluorine atoms in the extract was converted into the content of the emulsifiers having fluorine atoms.

[0134] The MRM measurement parameters are selected appropriately depending on the structure of the emulsifier containing fluorine atoms to be measured. Literature values ​​can be used for the MRM parameters, or they can be calculated using an LC-MS instrument. Specifically, when determining the MRM parameters using an LC-MS instrument, the following procedure is followed: 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, precursor adjustment, voltage optimization, and product m / z optimization. The calculated MRM measurement parameters are used.

[0135] <Quantitative Determination of Fluorine Atom-Containing Emulsifier in Solid Composition> Specifically, five levels of methanol standard solutions of fluorine atom-containing emulsifiers with known concentrations of 1 to 180 ng / g were prepared, and a'' was calculated from the sample concentration and peak integral value of each sample using a first-order approximation according to formula (A1): A'' = a'' × X (A1''), where A'' is the peak area of ​​each emulsifier, and X is the concentration (ng / g) of each emulsifier.

[0136] Next, the amount of emulsifier contained in the extract was calculated using formula (A2''). Note that a'' in formula (A2'') means a'' calculated using formula (A1'') above. XCm'' = ACm'' / a'' (A2'') XCm'': content (ng / g) of emulsifier in each extract ACm'': peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 25 ng / g.

[0137] The content of the emulsifier in the solid composition relative to the total mass of the solid composition (ZCm″) was calculated by the following formula (A3″): ZCm″=XCm″×ρ1×La / W1 (A3″) ZCm″: content of the emulsifier contained 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: mass of the sample used for extraction (2.5 g of solid composition in each example)

[0138] <Content of Metal Elements in Solid Composition> 0.5 g of the solid obtained in each example described below was collected in a blank-checked platinum crucible. The solid was heated in an ashing apparatus (Nihon Buchi, Ashing Apparatus B-440, high-temperature electric heating furnace) at 400°C for 10 minutes, then at 470°C for 20 minutes, 500°C for 15 minutes, and 550°C for 60 minutes to incinerate the solid. (1+1) sulfuric acid (Kanto Chemical, Ultrapur sulfuric acid, 1 mL) was added to the resulting ash, and the mixture was treated with white sulfuric acid fume on a hot plate. Further, (1+1) sulfuric acid (1 mL) and ultrapure water (9 mL) were added to prepare a sample solution. The metal elements in the resulting sample solution were measured using ICP-MS and quantified using the absolute calibration curve method. The metal element species 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).

[0139] Example 1 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, 7.5 mg of NaAAMPS), PMVE (105 g), and TFE (22 g) were added to a 3.2 L stainless steel pressure reactor, and the temperature was raised to 80°C while stirring at 385 rpm. The internal pressure of the reactor at 80°C was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 10 g) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the initiation 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 initiation of polymerization reached 133 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion A1. The total amount of monomers added before the initiation of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after the initiation 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 fluoropolymer A1 in the first aqueous dispersion A1 was 79.6 nm, and the number of particles of the first fluoropolymer A1 was 2.6 × 10 １４ The concentration of the first aqueous dispersion A1 was 12.4 mass%. The first aqueous dispersion A1 was freeze-aggregated and then filtered, and the obtained first fluoropolymer A1 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A1 was analyzed by NMR, and the result was that the ratio of PMVE / TFE was 33 / 67 (molar ratio). The 1 mass% thermal weight loss temperature of the first fluoropolymer A1 was 412°C. Furthermore, the first fluoropolymer A1 did not have a melting point.

[0140] Example 2 A first aqueous dispersion A2 was obtained in the same manner as in Example 1, except that the amount of the 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 fluoropolymer A2 in the first aqueous dispersion A2 was 64.3 nm, and the number of particles of the first fluoropolymer A2 was 5.0 × 10 １４ The concentration of the first aqueous dispersion A2 was 12.4% by mass. The first aqueous dispersion A2 was freeze-aggregated and then filtered, and the obtained first fluoropolymer A2 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A2 was analyzed by NMR, and the result was that the mole ratio of PMVE / TFE was 33 / 67. The 1% by mass thermal weight loss temperature of the first fluoropolymer A2 was 412°C. Furthermore, the first fluoropolymer A2 did not have a melting point.

[0141] [Example 3] Polymerization was initiated using the same procedure as in Example 1, except that the amount of 50% by mass NaAAMPS aqueous solution added was changed to 45 μL (22.5 mg of NaAAMPS). Since the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain a constant pressure. This was repeated, and when the amount of TFE added after the initiation 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 initiation of polymerization reached 325 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the reactor internal temperature was cooled to 10 ° C., the polymerization reaction was terminated, the gas remaining in the reactor was recovered, and the liquid was withdrawn to obtain a first aqueous dispersion A3. The total amount of monomers added before the initiation of polymerization was 22 g of TFE and 105 g of PMVE. The total amounts of the monomers added after the initiation of polymerization were 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 fluoropolymer A3 in the first aqueous dispersion A3 was 68.2 nm, and the number of particles of the first fluoropolymer A3 was 9.8 × 10 １４The concentration of the first aqueous dispersion A3 was 24.9% by mass. The first aqueous dispersion A3 was freeze-aggregated and then filtered, and the obtained first fluoropolymer A3 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A3 was analyzed by NMR, and the result was that the mole ratio of PMVE / TFE was 33 / 67. The 1% by mass thermal weight loss temperature of the first fluoropolymer A3 was 412°C. Furthermore, the first fluoropolymer A3 did not have a melting point.

[0142] [Example 4] Polymerization was initiated 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). Since the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the initiation 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 initiation of polymerization reached 74 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the reactor internal temperature was cooled to 10 ° C., the polymerization reaction was terminated, the gas remaining in the reactor was recovered, and the liquid was withdrawn to obtain aqueous dispersion C1. The total amount of monomers added before the initiation of polymerization was 22 g of TFE and 105 g of PMVE. The total amounts of the monomers added after the initiation of polymerization were 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 particles of the fluoropolymer C1 in the aqueous dispersion C1 was 86.9 nm, and the number of particles of the fluoropolymer C1 was 0.9 × 10 １４ The aqueous dispersion C1 had a solids concentration of 6.4% by mass. The aqueous dispersion C1 was freeze-coagulated and then filtered, and the resulting fluoropolymer C1 was washed with ultrapure water. It was then vacuum-dried at 100°C. The resulting fluoropolymer C1 was analyzed by NMR, and the ratio of PMVE / TFE was 31.8 / 68.2 (molar ratio). The 1% by mass thermal weight loss temperature of the fluoropolymer C1 was 415°C. The first fluoropolymer C1 did not have a melting point.

[0143] [Example 5] Polymerization was initiated in the same manner as in Example 1, except that the 50% by mass aqueous solution of NaAAMPS was replaced with sodium styrene vinyl sulfonate (NaSS, 7 mg). Since the pressure inside the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When the amount of TFE added after the initiation of polymerization reached 37 g, the temperature inside the reactor was cooled to 10°C to terminate the polymerization reaction, and the gas remaining in the reactor was recovered, followed by extraction of the liquid to obtain aqueous dispersion C2. The total amount of monomers added before the initiation of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after the initiation of polymerization 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 particles of the fluoropolymer C2 in the aqueous dispersion C2 was 78.1 nm, and the number of particles of the fluoropolymer C2 was 0.6 x 10 １４ The concentration of the solids in the aqueous dispersion C2 was 3.0% by mass. The aqueous dispersion C2 was freeze-aggregated and then filtered, and the resulting fluoropolymer C2 was washed with ultrapure water. It was then vacuum-dried at 100°C. The resulting fluoropolymer C2 was analyzed by NMR, and the ratio of PMVE to TFE was 31.8 / 68.2 (molar ratio). The 1% by mass thermal weight loss temperature of the fluoropolymer C2 was 363°C. The first fluoropolymer C2 did not have a melting point.

[0144] [Example 6] A 2.1 L stainless steel pressure reactor was charged with ultrapure water (1004 g), C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass aqueous solution (80.1 g) of the above, a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate, PMVE (72 g), and TFE (14 g) were added, and the temperature was raised to 80°C while stirring at 600 rpm. The internal pressure of the reactor at 80°C was 1.2 MPaG. Next, an aqueous ammonium persulfate solution (1.0% by mass, 20 g) was added to initiate polymerization. Since the pressure inside the reactor decreased with the initiation of polymerization, TFE and PMVE were further added to maintain the pressure at a constant 1.2 MPa [gauge]. When the amount of TFE added after the initiation of polymerization reached 160 g and the amount of PMVE added after the initiation of polymerization reached 133 g, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 262 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn to obtain aqueous dispersion C3. The total amounts of monomers added before the initiation of polymerization were 14 g of TFE and 72 g of PMVE. The total amounts of monomers added after the initiation of polymerization were 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 particles of the fluoropolymer C3 in the aqueous dispersion C3 was 84.2 nm, and the number of particles of the fluoropolymer C3 was 3.1 × 10 １４ The concentration of the solids in aqueous dispersion C3 was 21.1% by mass. After freeze-coagulation of aqueous dispersion C3, the aqueous dispersion C3 was filtered, and the resulting fluoropolymer C3 was washed with ultrapure water. It was then vacuum dried at 100°C. The resulting fluoropolymer C3 was analyzed by NMR, and the ratio of PMVE to TFE was 34.2 / 65.8 (molar ratio). The 1% by mass thermal weight loss temperature of the fluoropolymer C3 was 406°C. Furthermore, the first fluoropolymer C3 did not have a melting point.

[0145] [Example 7] <Production of Raw Material Solution 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 temperature was raised to 90 ° C. while stirring at 600 rpm. The internal pressure of the reactor at 90 ° C. was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 4 g) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 25 g, the addition of TFE injected after the start of polymerization was stopped, the internal temperature of the reactor was cooled to 10 ° C., the polymerization reaction was stopped, and the gas remaining in the reactor was recovered. The liquid was then extracted to obtain raw material solution A (first aqueous dispersion A4). The total amounts of monomers added before the start of polymerization were 15 g of TFE and 72 g of PMVE. The total amounts of monomers added after the start of polymerization were 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 fluoropolymer A4 in the raw material solution A was 43.5 nm, and the number of particles of the first fluoropolymer A4 was 3.9 × 10 １４ The concentration of the solids in raw material solution A was 3.3% by mass. Raw material solution A was freeze-coagulated and then filtered, and the obtained first fluoropolymer A4 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A4 was analyzed by NMR, and the result was that the mole ratio of PMVE / TFE was 33 / 67. The 1% by mass thermal weight loss temperature of first fluoropolymer A4 was 350°C. Furthermore, first fluoropolymer A4 did not have a melting point.

[0146] <Production of Raw Material Solution B> HPR4002Cl (anion exchange resin, manufactured by DuPont, 40 g) was added to raw material solution A (1000 g). 60 minutes after the start of stirring, the raw material solution A and the ion exchange resin were separated by filtration. Dowex Monosphere 650C (cation exchange resin, manufactured by DuPont, 40 g) was added to the filtered raw material solution A. 60 minutes after the start of stirring, the ion exchange resin was separated by filtration to obtain raw material solution B. The average particle size and particle number of the first fluorine-containing polymer A4 in raw material solution B were equivalent to those in raw material solution A, and the first fluorine-containing polymer A4 in raw material solution B had no melting point.

[0147] <Production of second fluorine-containing polymer> Raw material liquid B (850 g), ultrapure water (332 g), PMVE (81 g), and TFE (17 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 80 ° C. while stirring at 600 rpm. The pressure inside the reactor at 80 ° C. was 1.4 MPaG. Next, an aqueous ammonium persulfate solution (1.0 mass%, 20 g) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 25 g, 7 g of PMVE was injected. Thereafter, 7 g of PMVE was injected every time 8 g of TFE was injected. When the amount of TFE added after the initiation of polymerization reached 256 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a second aqueous dispersion B1. The total amount of monomers added before the initiation of polymerization was 17 g of TFE and 81 g of PMVE. The total amount of monomers added after the initiation 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 particles of the fluoropolymer B1 in the second aqueous dispersion B1 was 67.6 nm, and the number of particles of the fluoropolymer B1 was 3.6 × 10 １４The concentration of the second aqueous dispersion B1 was 10.5 mass%. The second aqueous dispersion B1 was freeze-aggregated and then filtered, and the resulting fluoropolymer B1 was washed with ultrapure water. It was then vacuum-dried at 100°C. The resulting fluoropolymer B1 was analyzed by NMR, and the ratio of PMVE / TFE was 33 / 67 (molar ratio). The 1 mass% thermal weight loss temperature of the fluoropolymer B1 was 411°C. Furthermore, the fluoropolymer B1 did not have a melting point.

[0148] [Example 8] Polymerization was initiated in the same manner as in Example 1, except that the amount of 50% by mass NaAAMPS aqueous solution added was changed to 45 μL (22.5 mg of NaAAMPS) and the amount of ammonium persulfate aqueous solution (2.5% by mass) added was changed to 7 g. Since the pressure inside the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the initiation of polymerization reached 37 g, octafluoro-1,4-diiodobutane (C4DI, 1.25 g) and 10 g of PMVE were injected. The rotation speed was reduced to 325 rpm, and thereafter, 10 g of PMVE was injected every time 12 g of TFE was injected. When the amount of TFE added after the initiation of polymerization reached 325 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, and the gas remaining in the reactor was recovered, and then the liquid was extracted to obtain a first aqueous dispersion A5. The total amount of monomers added before the initiation of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after the initiation 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 fluoropolymer A5 in the first aqueous dispersion A5 was 77.1 nm, and the number of particles of the first fluoropolymer A5 was 6.1 × 10 １４The concentration of the first aqueous dispersion A5 was 23.0% by mass. The first aqueous dispersion A5 was freeze-aggregated and then filtered, and the obtained first fluoropolymer A5 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A5 was analyzed by NMR, and the result was that the molar ratio of PMVE / TFE was 33 / 67. The iodine content relative to the fluoropolymer A5 was 0.1% by mass. The 1% by mass thermal weight loss temperature of the first fluoropolymer A5 was 405°C. Furthermore, the first fluoropolymer A5 did not have a melting point.

[0149] [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 temperature was raised to 80°C while stirring at 600 rpm. The internal pressure of the reactor at 80°C was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 7 g) was added to initiate polymerization. As the polymerization started, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 25 g, the rotation speed was reduced to 380 rpm, and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２2 g of CN (8CNVE) was added. Thereafter, 12 g of PMVE and 1.3 g of 8CNVE were injected every time 16 g of TFE was injected. Additional ammonium persulfate aqueous solution was appropriately injected as the polymerization progressed. When the amount of TFE added after the start of polymerization reached 185 g, the addition of TFE, PMVE, and 8CNVE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was then withdrawn. 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 was 13.7 g. The polymerization time was 400 minutes, and the amount of the added ammonium persulfate aqueous solution was 14 cc. The average particle size of the particles of the first fluoropolymer A6 in the first aqueous dispersion A6 was 76.6 nm, and the number of particles of the first fluoropolymer A6 was 5.2 × 10 １４ The concentration of the first aqueous dispersion A6 was 20.04% by mass. The first aqueous dispersion A6 was freeze-aggregated and then filtered, and the obtained first fluoropolymer A6 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A6 was analyzed by NMR, and the molar ratio was PMVE / TFE / 8CNVE = 28.05 / 71.5 / 0.45. The 1% by mass thermal weight loss temperature of the first fluoropolymer A6 was 392°C. Furthermore, the first fluoropolymer A6 did not have a melting point.

[0150] [Example 10] Before starting the polymerization, CF ２ = CFO (CF ２ ) ３ OCF = CF ２Polymerization was initiated using the same procedure as in Example 8, except that (3.69 g) of TFE was added. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the initiation of polymerization reached 37 g, octafluoro-1,4-diiodobutane (C4DI, 1.25 g) and 10 g of PMVE were injected. The rotation speed was reduced to 325 rpm, and thereafter, 10 g of PMVE was injected every time 12 g of TFE was injected. When the amount of TFE added after the initiation of polymerization reached 325 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the internal temperature of the reactor was cooled to 10 ° C., the polymerization reaction was terminated, the gas remaining in the reactor was recovered, and the liquid was withdrawn to obtain a first aqueous dispersion A5. The total amount of monomers added before the initiation of polymerization was 22 g of TFE and 105 g of PMVE. The total amounts of the monomers added after the initiation of polymerization were 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 fluoropolymer A7 in the first aqueous dispersion A7 was 94.8 nm, and the number of particles of the first fluoropolymer A7 was 4.2 × 10 １４ The concentration of the first aqueous dispersion A5 was 27.9% by mass. The first aqueous dispersion A5 was freeze-aggregated and then filtered, and the obtained first fluoropolymer A5 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A5 was analyzed by NMR, and the result was that the molar ratio of PMVE / TFE was 34 / 66. The iodine content relative to the fluoropolymer A5 was 0.1% by mass. The 1% by mass thermal weight loss temperature of the first fluoropolymer A7 was 403°C. Furthermore, the first fluoropolymer A7 did not have a melting point.

[0151] Example 11 Polymerization was initiated using the same procedure as in Example 8, except that the amount of 50% by mass aqueous solution of NaAAMPS (45 μL, 22.5 mg of NaAAMPS) added was changed to 45 μL of a 50% by mass aqueous solution of sodium 2-methacrylamido-2-methylpropanesulfonate (NaMANPS) (22.5 mg of NaMANPS). Since the pressure inside the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This process was repeated, and when the amount of TFE added after the initiation of polymerization reached 37 g, octafluoro-1,4-diiodobutane (C4DI, 1.25 g) and 10 g of PMVE were injected. The rotation speed was reduced to 325 rpm, and thereafter, 10 g of PMVE was injected every time 12 g of TFE was injected. When the amount of TFE added after the initiation of polymerization reached 325 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion A5. The total amount of monomers added before the initiation of polymerization was 22 g of TFE and 105 g of PMVE. The total amount of monomers added after the initiation 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, and the number of particles of the first fluorine-containing polymer A8 was 3.46 × 10 １４ The concentration of the first aqueous dispersion A8 was 28.8% by mass. The first aqueous dispersion A5 was freeze-aggregated and then filtered, and the obtained first fluoropolymer A5 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A5 was analyzed by NMR, and the result was that the molar ratio of PMVE / TFE was 35 / 65. The iodine content relative to the fluoropolymer A5 was 0.1% by mass. The 1% by mass thermal weight loss temperature of the first fluoropolymer A8 was 400°C. Furthermore, the first fluoropolymer A8 did not have a melting point.

[0152] In the production of Examples 1 to 5 and 7 to 11, the polymerization of the first fluorine-containing polymer was carried out under conditions in which neither an emulsifier having a fluorine atom nor an emulsifier having no fluorine atom was substantially present. Furthermore, the aqueous dispersions obtained in Examples 1 to 5 and 7 to 11 contained substantially neither an emulsifier having a fluorine atom nor an emulsifier having no fluorine atom. Furthermore, in the aqueous dispersions of Examples 1 to 5 and 7 to 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 the emulsifier. The concentration in Table 6 relative to the aqueous medium in the aqueous dispersion represents the content of Compound X.

[0153]

[0154] The table below specifically shows the contents of the compound represented by formula (S1) and the compound represented by formula (S3) in raw material solution A and raw material solution B in Example 7. The content of formula (S1) means the total 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 solution, and the content of formula (S3) means the total 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 solution.

[0155]

[0156] The following Tables 8 and 9 show the specific contents of the compound represented by (S1) and the compound represented by (S3) contained in the solid compositions of Examples 1 to 6 and 8 to 11. In the tables, N.D. indicates below the limit of quantitation in this measurement.

[0157]

[0158]

[0159] The following Table 10 shows the specific contents of the emulsifiers having fluorine atoms contained in the solid compositions of Examples 1 to 6 and 8 to 11. In the table, ND means below the limit of quantitation in this measurement.

[0160]

[0161] Table 11 below shows the specific contents (ppm) of metal elements contained in the solid compositions of Examples 1 to 3, 6, and 8 to 11.

[0162]

[0163] According to this production method, it was shown that an aqueous dispersion having a large number of fluorine-containing polymer particles can be produced without substantially using an emulsifier having fluorine atoms (Examples 1 to 5 and 7 to 11, particularly Examples 1 to 3 and 7 to 11). Moreover, Example 6 is a production method for an aqueous dispersion using an emulsifier. It was shown that the effects of the present invention are more excellent when the content of compound X is 5.0 to 30.0 ppm by mass relative to the total mass of the aqueous medium (Examples 2 and 3).

[0164] The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-205993, filed on December 6, 2023, are hereby incorporated by reference as the disclosure of the present invention.

Claims

1. A method for producing an aqueous dispersion, comprising polymerizing a first monomer containing tetrafluoroethylene in the presence of a compound represented by formula (X) and a polymerization initiator in the presence of an aqueous medium and substantially no emulsifier containing a fluorine atom to produce an aqueous dispersion containing particles of a first fluorine-containing polymer having an average particle size of 500 nm or less and no melting point. C(X １ ) (X ２ ) = C(X ３ )-L-Z (X) In formula (X), １ , X ２ and X ３ 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; and Z is an anionic group or a salt of an anionic group.

2. Z is -SO ３ The method for producing an aqueous dispersion according to claim 1, wherein M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ Or P(R Ｍ２ ) ４ And R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, R Ｍ１ Any two of R may be bonded to each other to form a ring, Ｍ１ may be the same or different, R Ｍ２ Any two of R may be bonded to each other to form a ring, Ｍ２ may be the same or different from each other.

3. The 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 based on the total mass of the aqueous medium.

4. The method for producing an aqueous dispersion according to claim 1 or 2, wherein the first monomer comprises a perfluoroalkyl vinyl ether.

5. A method for producing a second fluorine-containing polymer, comprising polymerizing a second monomer in the aqueous dispersion produced by the production method according to claim 1 or 2 to produce a second fluorine-containing polymer.

6. The process 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 based on the total mass of the aqueous dispersion. ２ ) ｎ１ -COOM Ｓ (S1) In formula (S1), n1 is an integer from 3 to 13; M Ｓ is a hydrogen atom, Na, K or NH ４ It is.

7. The process 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 based on the total mass of the aqueous dispersion. ２ ) ｎ２ -SO ３ M Ｓ (S3) In formula (S3), n2 is an integer from 4 to 10, and M Ｓ is a hydrogen atom, Na, K or NH ４ It is.

8. A process for producing a second fluorine-containing polymer according to claim 5, wherein the second monomer comprises at least one member selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene and vinylidene fluoride.

9. A process for producing a second fluorine-containing polymer according to claim 5, wherein said second monomer comprises a perfluoroalkyl vinyl ether.

10. A process for producing a second fluorine-containing polymer according to claim 5, wherein said second fluorine-containing polymer has no melting point.

11. An aqueous dispersion that is substantially free of a water-soluble emulsifier having a fluorine atom and contains fluorine-containing polymer particles and an aqueous medium, wherein the number of particles is 0.5×10 １４ particles / mL or more, an average particle size of the particles is 500 nm or less, the fluoropolymer has units based on tetrafluoroethylene and units based on perfluoroalkyl vinyl ether, and the fluoropolymer has no melting point.

12. The aqueous dispersion according to claim 11, wherein the 1% by mass weight loss temperature of the fluoropolymer is 350° C. or higher.

13. A solid composition comprising a fluorine-containing polymer having no melting point, the fluorine-containing polymer having units based on tetrafluoroethylene, the content of an emulsifier having a fluorine atom being 1500 ppb by mass or less relative to the total mass of the solid composition, the content of a compound represented by formula (S1) being 1500 ppb by mass or less relative to the total mass of the solid composition, and the content of a compound represented by formula (S3) being 100 ppb by mass or less relative to the total mass of the solid composition. ２ ) ｎ１ -COOM Ｓ (S1) In formula (S1), n1 is an integer from 3 to 13; M Ｓ is a hydrogen atom, Na, K or NH ４ H-(CF ２ ) ｎ２ -SO ３ M Ｓ (S3) In formula (S3), n2 is an integer from 4 to 10, and M Ｓ is a hydrogen atom, Na, K or NH ４ It is.

14. The solid composition according to claim 13, wherein the metal content of the solid composition is less than 5 ppm by weight, based on the total weight of the solid composition.

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