Fluorine-containing polymer production method, solid, and crosslinked product

Abstract

This fluorine-containing polymer production method is for producing a fluorine-containing polymer not having a melting point, by polymerizing, in the presence of a polymerization initiator and a compound represented by formula (X), a monomer 1 that has a fluorine atom, and a monomer 2 that belongs to a type different from that of the monomer 1 and that has a hydrogen atom bound to a carbon atom, under a condition in which an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent.　(X): C(X1)(X2)=C(X3)CONH-R-Z

Description

Method for producing fluorine-containing polymer, solid product, crosslinked product

[0001] The present disclosure relates to a method for producing a fluorine-containing polymer, a solid product, and a crosslinked product thereof.

[0002] Fluorine-containing polymers are used in various industrial fields because of their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. When producing such fluorine-containing polymers, a method of polymerizing a monomer in the presence of an aqueous medium is known. As a method for producing a fluorine-containing polymer, Patent Document 1 discloses a method of emulsion polymerization of a monomer having a fluorine atom in the presence of an aqueous medium.

[0003] Japanese Patent Application Laid-Open No. 2007-211233

[0004] In the method for producing a fluorine-containing polymer disclosed in Patent Document 1, the obtained fluorine-containing polymer may be contaminated with impurities other than the fluorine-containing polymer, and there is room for improvement. Specifically, metal elements and fluorine-containing by-products may be contaminated, and there is a need to reduce these.

[0005] An object of the present disclosure is to provide a method for producing a fluorinated polymer that can suppress the inclusion of metal elements and fluorine-containing by-products. Another object of the present disclosure is to provide a solid product and a crosslinked product.

[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 a fluorine-containing polymer, comprising polymerizing a fluorine-containing monomer 1 and a fluorine-containing monomer 2, which is a monomer different from the monomer 1 and has a hydrogen atom bonded to a carbon atom, in the presence of an aqueous medium and substantially no fluorine-containing emulsifier, in the presence of a compound represented by formula (X) described below and a polymerization initiator, to produce a fluorine-containing polymer having no melting point. [2] A method for producing a fluorine-containing polymer, wherein Z is -SO ３[3] The method for producing a fluoropolymer according to [1], wherein the content of the compound represented by formula (X) is 1.0 to 1000.0 ppm by mass relative to the total mass of the aqueous medium. [4] The method for producing a fluoropolymer according to any one of [1] to [3], wherein the monomer 1 is at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and chlorotrifluoroethylene. [5] The method for producing a fluoropolymer according to any one of [1] to [4], wherein the monomer 2 is propylene or vinylidene fluoride. [6] A solid material containing a fluorine-containing polymer which uses units based on a monomer 1 having a fluorine atom and units based on a monomer 2 which is a different type of monomer from the monomer 1 and has a hydrogen atom bonded to a carbon atom, and which has no melting point, wherein the content of metal elements in the solid material is 1000.0 ppm by mass or less relative to the total mass of the solid material. [7] The solid material according to [6], wherein the fluorine-containing polymer has an iodine atom or a bromine atom. [8] A crosslinked material obtained by crosslinking the solid material according to [6] or [7].

[0007] According to the present disclosure, it is possible to provide a method for producing a fluorinated polymer that can suppress the inclusion of metal elements and fluorine-containing by-products. Furthermore, the present disclosure can provide a solid product and a crosslinked product.

[0008] The meanings of terms used in this disclosure 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 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 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 monomer that is formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the 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 a fluoropolymer] The method for producing a fluoropolymer of the present disclosure (hereinafter also referred to as "the method for producing") is a method for producing a fluoropolymer having no melting point by polymerizing a fluorine atom-containing monomer 1 and a monomer 2, which is a different type of monomer from monomer 1 and has a hydrogen atom bonded to a carbon atom, 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 substantially no emulsifier having a fluorine atom. Hereinafter, a monomer containing monomer 1 and monomer 2 will be referred to as a "specific monomer".

[0010] One of the features of the present production method is the use of compound X. By using compound X, the desired fluorine-containing polymer can be obtained efficiently without requiring an emulsifier having a fluorine atom, and the production of fluorine-containing by-products can be suppressed. Furthermore, the use of compound X can reduce the use of raw materials containing metal atoms, and it is presumed that the incorporation of metal elements can also be suppressed. In particular, when the fluorine-containing polymer is in the form of particles, it is presumed that compound X contributes to the stability of the particles. Hereinafter, the ability to suppress the incorporation of metal elements and fluorine-containing by-products into the obtained fluorine-containing polymer is also referred to as the "effect of the present disclosure."

[0011] <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.

[0012] Before starting polymerization of the specific monomer used in the polymerization of the 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 specific monomer used in the polymerization of the fluoropolymer" means immediately before the start of polymerization. Here, "the start of polymerization" includes the time when the specific 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 specific monomer and the polymerization initiator are made to coexist in the reactor.

[0013] <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 present production method, the content of an emulsifier having a fluorine atom is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, relative to the total mass of the aqueous medium. A concentration below the limit of quantitation of the measurement method using a liquid chromatograph mass spectrometer described below is also preferred. Examples of the lower limit include 0 ppb by mass or 1 ppb by mass. 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 (hereinafter collectively referred to as "emulsifier") are substantially absent, in order to prevent a decrease in the molecular weight of the fluoropolymer produced. "Substantially absent" means that, in the present production method, the content of an emulsifier is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, relative to the total mass of the aqueous medium. The lower limit is 0 ppb by mass. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement method described in paragraphs

[0721] to

[0732] of WO 2018 / 181904 can be mentioned. If the content is below the quantitation limit in the measurement using the liquid chromatograph mass spectrometer, it can be determined to be 0 ppb by mass.

[0014] The emulsifier may be either a water-soluble emulsifier or a water-insoluble emulsifier. Note that neither Compound X described later nor the fluorine-containing polymer described later falls under the category of emulsifier. Furthermore, the fluorine-containing polymer described later is water-insoluble. A water-soluble emulsifier refers to an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier refers to an emulsifier other than the above-mentioned water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or nonionic. Examples of the emulsifier include emulsifiers that do not have a carbon-carbon double bond.

[0015] 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.

[0016] The fluorine-free emulsifier is an emulsifier that 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.

[0017] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0018] 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.

[0019] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as their hydrophobic moieties. The hydrophilic moieties of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers (e.g., block copolymers having polyethylene oxide and polypropylene oxide).

[0020] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0021] The emulsifier may contain silicon atom.The emulsifier having silicon atom includes siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier having siloxane skeleton.The siloxane emulsifier includes 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.).

[0022] The emulsifier may be a polymer emulsifier. Examples of the polymer emulsifier include polymers having a hydrophilic group in a side chain, specifically polymers containing units based on a compound having a site capable of polymerization reaction and a hydrophilic group. In addition, examples of the polymer emulsifier include polymers that do not originally have a hydrophilic group but are subjected to post-treatment such as hydrolysis of a polymer containing units based on a compound having a group that can become a hydrophilic group.

[0023] When the specific monomer is polymerized in the presence of an emulsifier having no fluorine atoms, the amount of the emulsifier having no fluorine atoms used is preferably 0.1 to 15 parts by mass per 100 parts by mass of the aqueous medium.

[0024] <Compound X> The present production method uses compound X. Compound X can be polymerized together with a specific monomer described below. Use of a compound having —CONH— such as compound X is preferable in that, as described above, a desired fluorine-containing polymer can be efficiently obtained without requiring an emulsifier having a fluorine atom, the production of fluorine-containing by-products can be suppressed, and the use of raw materials containing metal atoms can be reduced, thereby suppressing the incorporation of metal elements. Compound X is a compound represented by formula (X):

[0025] C(X １ ) (X ２ ) = C(X ３ ) CONH-R-Z (X)

[0026] 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, R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms, Z is —SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM, where M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from each other, 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 Ｍ２ may be the same or different from each other.

[0027] X １ , X ２ and X ３are 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. 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.

[0028] 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 the fluoroalkylene group may be linear, branched, or cyclic, and is preferably branched. The alkylene group or the fluoroalkylene group has 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms, and more preferably 4 carbon atoms. R is preferably an alkylene group having 1 to 6 carbon atoms.

[0029] Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM. Z is -SO ３ M is preferred, and —SO ３ Na is more preferred. ３ When it is M, the latex tends to be more stable and the number of fluorine-containing polymer particles increases.

[0030] 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 Ｍ２The 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.

[0031] Specific examples of compound X include 2-acrylamido-2-methyl-1-propanesulfonic acid (2-methacrylamido-2-methylpropylsulfonic 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. As the compound X, (meth)acrylamides having a sulfonic acid group and metal salts thereof are preferred, and 2-acrylamido-2-methyl-1-propanesulfonic acid or sodium 2-acrylamido-2-methyl-1-propanesulfonate (hereinafter also referred to as NaAAMPS) is preferred. Examples of the metal salt include metal salts of the metal atom represented by M.

[0032] Before the start of polymerization of the specific monomer to be used in polymerization of the fluoropolymer, the content of compound X is preferably from 1.0 to 1000.0 ppm by mass, more preferably from 1.0 to 500.0 ppm by mass, still more preferably from 3.0 to 100.0 ppm by mass, and particularly preferably from 5.0 to 30.0 ppm by mass, relative to the total mass of the aqueous medium.

[0033] <Polymerization initiator> The present production method uses a polymerization initiator. The polymerization initiator 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.

[0034] 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 specific monomer used.

[0035] <Specific Monomer> In the present production method, a specific monomer is polymerized. The specific monomer is a monomer containing a monomer 1 having a fluorine atom and a monomer 2 having a hydrogen atom bonded to a carbon atom. Note that the monomer 2 is a different type of monomer from the monomer 1. In other words, the specific monomer used in the polymerization of the fluorine-containing polymer contains at least two types of monomers, the monomer 1 and the monomer 2.

[0036] (Monomer 1) Monomer 1 is a monomer having a fluorine atom. However, monomer 1 does not have a hydrogen atom bonded to a carbon atom. Specific examples of monomer 1 include at least one selected from the group consisting of tetrafluoroethylene (hereinafter also referred to as "TFE"), hexafluoropropylene (hereinafter also referred to as "HFP"), chlorotrifluoroethylene, perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), and perfluoroallyl vinyl ether. TFE, HFP, or chlorotrifluoroethylene is preferred, and TFE or HFP is more preferred. The amount of monomer 1 used is preferably 5 to 90% by mass, more preferably 10 to 85% by mass, and even more preferably 15 to 80% by mass, relative to the amount of the specific monomer used.

[0037] (Monomer 2) Monomer 2 is a monomer of a different type from the above-mentioned Monomer 1, and is a monomer having a hydrogen atom bonded to a carbon atom. Specific examples of Monomer 2 include ethylene (hereinafter also referred to as "EL"), propylene (hereinafter also referred to as "PL"), vinylidene fluoride (hereinafter also referred to as "VdF"), fluoroalkyl ethylene, vinyl chloride, and vinylidene chloride, with PL or VdF being preferred. The amount of Monomer 2 used is preferably 10 to 95% by mass, more preferably 15 to 90% by mass, and even more preferably 20 to 85% by mass, based on the amount of the specific monomer used. The amount of Monomer 2 used is preferably 10 to 95% by mass, more preferably 15 to 90% by mass, and even more preferably 20 to 85% by mass, based on the total amount of Monomer 1 and Monomer 2 used.

[0038] As a combination of monomer 1 and monomer 2, a combination of TFE (40 to 70 mol%) and PL (30 to 60 mol%), a combination of HFP (10 to 50 mol%) and VdF (50 to 90 mol%), a combination of TFE and VdF, or a combination of TFE (10 to 30 mol%), HFP (15 to 40 mol%) and VdF (75 to 30 mol%) is preferred, a combination of TFE and PL, or a combination of HFP and VdF is more preferred, and a combination of TFE (40 to 70 mol%) and PL (30 to 60 mol%) is even more preferred. Note that the mol% shown in the parentheses indicates the content of each specific monomer relative to the total amount.

[0039] (Other Monomers) The specific monomer may contain other monomers in addition to the monomers exemplified as Monomer 1 and Monomer 2. Examples of other monomers include a monomer having an iodine atom or a bromine atom, a monomer having two or more polymerizable unsaturated bonds, and a monomer having a nitrile group.

[0040] The monomer having an iodine atom or a bromine atom includes a monomer having an iodine atom and a monomer having a bromine atom. Specific examples of the monomer having an iodine atom include a monomer having a formula: CHR=CH-Z-CH ２ CHR-I (wherein R is —H or —CH ３Z is a linear or branched C 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) unsaturated ethers are also included. 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. Pat. No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether. Specific examples of monomers having a bromine atom include CF ２ = CFOCF ２ CF ２ CF ２ OCF ２ CF ２Br, 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 OCF=CFBr is an example.

[0041] When a monomer having a bromine atom or an iodine atom is used, the amount of the monomer having a bromine atom or an iodine atom used is preferably 0.1 to 10 mass %, more preferably 0.3 to 7 mass %, and even more preferably 0.5 to 5 mass %, based on the amount of the specific monomer used.

[0042] The total amount of Monomer 1 and Monomer 2 used is preferably 80 to 100% by mass, more preferably 85 to 99.7% by mass, and even more preferably 90 to 99.5% by mass, based on the amount of the specific monomer used. Furthermore, the total amount of Monomer 1 and Monomer 2 used is also preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass, based on the amount of the specific monomer used. When the specific monomer contains other monomers, the amount of the other monomers used is preferably 0.001 to 5% by mass, more preferably 0.005 to 4% by mass, and even more preferably 0.01 to 3% by mass, based on the amount of the specific monomer used.

[0043] The amount of the specific 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, per 100 parts by mass of the aqueous medium.

[0044] <Chain Transfer Agent> In the present production method, the polymerization of the monomers may be carried out in the presence of a chain transfer agent. Examples of the chain transfer agent include chain transfer agents having an iodine atom or a bromine atom and chain transfer agents having no iodine atom or a bromine atom.

[0045] The chain transfer agent having an iodine atom or a bromine atom is preferably a compound represented by formula (1): Rf-(X) ２ (1) In formula (1), Rf represents a fluoroalkylene group or an aromatic ring group, and X represents an iodine atom or a bromine atom. The fluoroalkylene group represented by Rf preferably has 1 to 16 carbon atoms. The fluoroalkylene group may be either linear or branched. Rf is preferably a perfluoroalkylene group. X is preferably an iodine atom.

[0046] Specific examples of chain transfer agents having an iodine atom or a bromine atom include 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, Examples of iodoethane include 1,3-diiodo-n-propane, 2-iodoethyl-substituted benzene, 1-iodo-4-bromoperfluorobutane, 1-iodo-6-bromoperfluorohexane, 1-iodo-8-bromoperfluorooctane, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, and diiodomonobromo-substituted benzene, and C4DI is preferred.

[0047] When polymerization is carried out in the presence of a chain transfer agent having an iodine atom or a bromine atom, the content of the chain transfer agent having an iodine atom or a bromine atom is preferably 0.1 to 5 parts by mass relative to 100 parts by mass of the aqueous medium. When polymerization is carried out in the presence of a chain transfer agent having an iodine atom or a bromine atom, the amount of the chain transfer agent having an iodine atom or a bromine atom used is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the total amount of the specific monomers used.

[0048] Specific examples of chain transfer agents that do not contain iodine or bromine atoms include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0049] <Step> In the present production method, a specific monomer is polymerized in the presence of 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. The polymerization is preferably carried out in the substantial absence of the emulsifier.

[0050] Examples of the above method include a method in which a solution containing an aqueous medium and compound X is prepared, and the specific monomer is polymerized using this solution and a polymerization initiator. More specifically, the method includes a method in which the solution and the specific monomer are added to a reactor, the reactor is heated, and a polymerization initiator is added to the reactor to polymerize the specific monomer.

[0051] The specific monomer is charged into a reaction vessel by a conventional method. For example, the specific monomer may be charged into the reactor continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be charged into the reactor continuously or intermittently. The polymerization initiator may be added to the reactor all at once or in portions.

[0052] 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.

[0053] (Fluorine-Containing Polymer) A fluorine-containing polymer is obtained by this production method. The fluorine-containing polymer is preferably a fluorine-containing polymer using units based on a specific monomer, and more preferably has units based on a specific monomer. The specific monomer is as described above, and preferred embodiments are also the same. The content of units based on monomer 1 is preferably 5 to 98% by mass, more preferably 10 to 95% by mass, and even more preferably 15 to 90% by mass, based on all units constituting the fluorine-containing polymer. The content of units based on monomer 2 is preferably 1 to 85% by mass, more preferably 5 to 80% by mass, and even more preferably 10 to 75% by mass, based on all units constituting the fluorine-containing polymer. Furthermore, the total content of units based on monomer 1 and units based on monomer 2 is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass, based on all units constituting the fluorine-containing polymer. The content of units based on the specific monomer is preferably from 90 to 100% by mass, more preferably from 95 to 100% by mass, and even more preferably from 99 to 100% by mass, based on all units constituting the fluorine-containing polymer.

[0054] The fluorine-containing polymer may be a fluorine-containing polymer using units other than units based on the specific monomer, and preferably has other units. Examples of other units include units based on the above-mentioned other monomers and units based on compound X. In other words, the fluorine-containing polymer may be a fluorine-containing polymer using units based on the specific monomer and other units (preferably units based on compound X).

[0055] The fluorine-containing polymer preferably contains iodine atoms or bromine atoms. The source of iodine atoms or bromine atoms is not particularly limited, but is preferably a component containing iodine atoms or bromine atoms in the present production method, more preferably a monomer containing iodine atoms or bromine atoms, or a chain transfer agent containing iodine atoms or bromine atoms. The content of iodine atoms or bromine atoms (preferably the total content of iodine atoms and bromine atoms) is preferably 3000 ppm by mass or less, more preferably 2000 ppm by mass or less, and even more preferably 1000 ppm by mass or less, relative to the total mass of the fluorine-containing polymer. The lower limit is 0 ppm by mass. The content of iodine atoms or bromine atoms can be measured, for example, using an X-ray fluorescence analyzer.

[0056] The fluoropolymer does not have a melting point. "Having no melting point" means that when the melting point of the fluoropolymer 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.

[0057] The fluorine-containing polymer may be in the form of particles. The average primary particle size of the fluorine-containing polymer particles is preferably 500 nm or less, and from the viewpoint of particle dispersion stability, is 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 primary particle size of the particles is the average primary particle size calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method, and detailed measurement conditions are as described in the Examples section.

[0058] A first preferred embodiment of the present production method includes a method (hereinafter also referred to as "production method A") in which a first monomer A containing the above-mentioned monomer 1 and the above-mentioned monomer 2 is polymerized in the presence of the above-mentioned compound 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 first fluorine-containing polymer particles having an average primary particle size of 500 nm or less (hereinafter also referred to as "first aqueous dispersion A"), and the above-mentioned fluorine-containing polymer is recovered from the first aqueous dispersion A. Hereinafter, in production method A, the step of producing first aqueous dispersion A will also be referred to as "step A1", and the step of recovering the above-mentioned fluorine-containing polymer from first aqueous dispersion A will also be referred to as "step A2".

[0059]

[0023] A second preferred embodiment of this production method includes a method (hereinafter also referred to as "production method B") in which a first monomer B containing the above-mentioned monomer 1 is polymerized in the presence of the above-mentioned compound X and a polymerization initiator in the presence of an aqueous medium and substantially no emulsifier having a fluorine atom to produce an aqueous dispersion containing particles of a first fluorine-containing polymer B having an average primary particle size of 500 nm or less (hereinafter also referred to as "first aqueous dispersion B"); a second monomer B containing the above-mentioned monomer 2 is polymerized in the first aqueous dispersion B to produce a second aqueous dispersion B containing a second fluorine-containing polymer B; and the above-mentioned fluorine-containing polymer is recovered from the second aqueous dispersion B. Hereinafter, in production method B, the step of producing the first aqueous dispersion B will be referred to as "step B1," the step of producing the second aqueous dispersion B will be referred to as "step B2," and the step of recovering the above-mentioned fluorine-containing polymer from the second aqueous dispersion B will be referred to as "step B3." Each step will be described in detail below.

[0060] <Production method A> (Step A1) In step A1, a first monomer A containing the above-mentioned monomer 1 and the above-mentioned monomer 2 is polymerized in the presence of 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 (preferably in the substantial absence of an emulsifier) ​​to synthesize a first fluorine-containing polymer A and obtain a first aqueous dispersion A. This suppresses a decrease in the molecular weight of the polymer produced, making it easier to obtain the above-mentioned fluorine-containing polymer.

[0061] The aqueous medium, emulsifier, compound X, polymerization initiator, monomer 1 and monomer 2 in production method A have the same definitions as those in the above-mentioned production method for a fluorine-containing polymer, except as defined below, and preferred embodiments are also the same.

[0062] -First Monomer A- The first monomer A includes the above-mentioned monomer 1 and monomer 2. There are no particular limitations on the first monomer A, as long as it includes the above-mentioned monomer 1 and monomer 2. For example, the first monomer A may include the above-mentioned other monomers. As combinations of monomer 1 and monomer 2, a combination of TFE (40 to 70 mol%) and PL (30 to 60 mol%), a combination of HFP (10 to 50 mol%) and VdF (50 to 90 mol%), a combination of TFE and VdF, or a combination of TFE (10 to 30 mol%), HFP (15 to 40 mol%) and VdF (75 to 30 mol%) is preferred, a combination of TFE and PL or a combination of HFP and VdF is more preferred, and a combination of TFE (40 to 70 mol%) and PL (30 to 60 mol%) is even more preferred. The mole percentages in parentheses indicate the content of each specific monomer relative to the total amount of the specific monomer. The total amount of Monomer 1 and Monomer 2 used is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass, relative to the amount of First Monomer A used.

[0063] -Method- The method of step A1 is not particularly limited as long as it is a method of polymerizing a first monomer A in the presence of a 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 a compound X is prepared, and the first monomer A is polymerized using this solution and a polymerization initiator. More specifically, a method in which the solution and the first monomer A are added to a reactor, the reactor is heated, and a polymerization initiator is added to the reactor to polymerize the first monomer A is exemplified. It is preferable that step A1 does not include a step of terminating the polymerization midway and deactivating or purifying the polymerization initiator. It is also preferable that step A1 is performed in the same reactor.

[0064] Polymerization of the first monomer A gives a first fluorine-containing polymer A (corresponding to the above-mentioned fluorine-containing polymer) dispersed in the form of particles in an aqueous medium. The aqueous dispersion thus obtained in which particles of the first fluorine-containing polymer A are dispersed may be used as the first aqueous dispersion A as is, or another aqueous medium may be added to give the first aqueous dispersion A. Alternatively, the first aqueous dispersion A may be obtained by dispersing particles of the first fluorine-containing polymer A in another aqueous medium by solvent substitution.

[0065] The first monomer A is added to the reactor by a conventional method. For example, the first monomer A may be added to the reactor continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the first monomer A may be dissolved in an aqueous medium, and the resulting solution may be added to the reactor continuously or intermittently. Different monomers of the first monomer A may be added to the reactor at the same time, or may be added at different times. For example, the first monomer may be added to the reactor in advance, and the second monomer may be added after the polymerization has started. When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in portions, and is preferably added intermittently.

[0066] -First aqueous dispersion A- Step A1 provides a first aqueous dispersion A, which is an aqueous dispersion containing particles of a first fluoropolymer A having an average primary particle size of 500 nm or less. Preferably, the first aqueous dispersion A is substantially free of a water-soluble emulsifier. "The first aqueous dispersion A is substantially free of a water-soluble emulsifier" means that the content of the water-soluble emulsifier is 10 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 first aqueous dispersion A. It is also preferably below the quantitation limit of the measurement method using the liquid chromatograph mass spectrometer described above (the measurement method described in WO 2018 / 181904). Examples of the lower limit include 0 ppb by mass or 1 ppb by mass.

[0067] Furthermore, it is preferable that the first aqueous dispersion A is substantially free of a compound represented by any one of formulas (S1) to (S4). "Substantially free of a compound represented by any one of formulas (S1) to (S4)" means that the content of the compound represented by any one of formulas (S1) to (S4) 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 first aqueous dispersion A. The lower limit is 0 mass ppb. H-(CF ２ ) ｎ１ -COOM Ｓ (S1) F-(CF ２ ) ｎ１ -COOM Ｓ (S2) H-(CF ２ ) ｎ２ -SO ３ M Ｓ (S3) F-(CF ２ ) ｎ２ -SO ３ M Ｓ (S4) In the formulas (S1) to (S4), n1 is an integer of 3 to 13, 15, or 17, n2 is an integer of 4 to 10, or 12, and M Ｓ is a hydrogen atom, Na, K, or NH ４ is.

[0068] The content of the particles of the first fluorine-containing polymer A is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass, relative to the total mass of the first aqueous dispersion A. The solid content concentration of the first aqueous dispersion A is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass. The solid content concentration of the first aqueous dispersion A can be measured, for example, by the following method. The solid content concentration of the first aqueous dispersion A 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 calculating the solid content concentration using the following formula: "Solid content concentration (mass%) = 100 × heating residue of first aqueous dispersion A (g) / mass of first aqueous dispersion A (2.0 g)"

[0069] -First fluoropolymer A- Particles of the first fluoropolymer A are particles produced in step A1. The first fluoropolymer A corresponds to the fluoropolymer produced by the above-mentioned method for producing a fluoropolymer, and preferred embodiments are the same as those of the first fluoropolymer A.

[0070] (Step A2) Step A2 is a step of recovering the above-mentioned fluoropolymer from the first aqueous dispersion A obtained in step A1. By agglomerating the particles of the first fluoropolymer A from the first aqueous dispersion A, a solid fluoropolymer can be obtained.

[0071] Examples of aggregation methods include freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulation agent. 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 an acid-containing solution is added to an 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 acid concentration 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 base-containing solution is added to an aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, and ammonium carbonate, with ammonium carbonate being preferred. The base concentration 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. In the case of aggregation using a coagulation agent, known coagulation agents can be used. The coagulant may include aluminum salts, calcium salts, and magnesium salts, specifically aluminum sulfate, salts of the general formula M'Al(SO ４ ) ２ ・12H ２ Examples of the coagulation method include alum represented by the formula: [wherein M' is a monovalent cation other than lithium], calcium nitrate, and magnesium sulfate. 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.

[0072] <Production Method B> (Step B1) The specific method and preferred embodiments of Step B1 are the same as those of Step A1 described above, except that the first monomer A is the first monomer B and the resulting aqueous dispersion is the first aqueous dispersion B containing the first fluoropolymer B.

[0073] -First Monomer B- The first monomer B includes the above-mentioned monomer 1. The first monomer B may include a monomer other than the above-mentioned monomer 1. The amount of the monomer 1 used is preferably 20.0 to 100.0 mol %, more preferably 25.0 to 100.0 mol %, and still more preferably 50.0 to 100.0 mol %, relative to the amount of the first monomer B used.

[0074] The first monomer B may contain other monomers other than the monomer 1, and preferably does not substantially contain other monomers. "Substantially does not contain other monomers" means that the amount of other monomers used is 0.01 mol % or less, and preferably 0 mol %, relative to the amount of the first monomer B used.

[0075] -First aqueous dispersion B- Step B1 provides a first aqueous dispersion B, which is an aqueous dispersion containing particles of a first fluoropolymer B having an average primary particle size of 500 nm or less. The first aqueous dispersion B preferably contains substantially no water-soluble emulsifier. The first aqueous dispersion B preferably contains substantially no compound represented by any of formulas (S1) to (S4). The definitions and preferred embodiments of the first aqueous dispersion B containing substantially no water-soluble emulsifier and substantially no compound represented by any of formulas (S1) to (S4) are the same as those for the first aqueous dispersion A described above.

[0076] The solids concentration of the first aqueous dispersion B obtained in step B1 is preferably 1 to 50% by mass, and more preferably 5 to 45% by mass. The solids concentration of the first aqueous dispersion B can be measured, for example, by the following method. The solids concentration of the first aqueous dispersion B is calculated by heating 2.0 g of the first aqueous dispersion B 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 B (g) / mass of first aqueous dispersion B (2.0 g)"

[0077] The aqueous dispersion in which particles of the first fluoropolymer B obtained by polymerization of the first monomer B are dispersed may be used as the first aqueous dispersion B as it is, or another aqueous medium may be added to form the first aqueous dispersion B. Alternatively, the first aqueous dispersion B may be formed by dispersing particles of the first fluoropolymer B in another aqueous medium by solvent substitution.

[0078] -First Fluorine-Containing Polymer B- Particles of the first fluorine-containing polymer B are particles produced in step B1. The first fluorine-containing polymer B may be the same as or different from the second fluorine-containing polymer B described below. The average primary particle size of the particles of the first fluorine-containing polymer B 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, even more preferably 150 nm or less, and particularly preferably 100 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 primary particle size of the particles of the first fluorine-containing polymer B can be calculated in the same manner as for the particles of the first fluorine-containing polymer A described above.

[0079] The number of particles of the first fluorinated polymer B is 1.0 × 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ The upper limit is 2.0 × 10 １５ The particle number of the first fluoropolymer B is the number of particles per mL of the first aqueous dispersion B. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0080] The first fluorine-containing polymer B preferably does not have a melting point.

[0081] The 1% by mass weight loss temperature on heat of the first fluoropolymer B is preferably 150° C. or higher, more preferably 200° C. or higher, and even more preferably 250° C. or higher. The upper limit is preferably 600° C. The 1% by mass weight loss temperature on heat can be measured, for example, using a thermogravimetric analyzer.

[0082] The first fluorine-containing polymer B is preferably a fluorine-containing polymer using units based on monomer 1, and more preferably contains units based on monomer 1. The content of units based on monomer 1 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 B. The first fluorine-containing polymer B may contain units other than the first monomer B, or may be substantially free of other units. "Substantially free of other units" means that the content of other monomers is 0.01 mol% or less, preferably 0 mol%, based on all units of the first fluorine-containing polymer B.

[0083] (Step B2) Step B2 is a step of polymerizing a second monomer B containing a monomer 2 in the first aqueous dispersion B obtained in step B1 to obtain a second aqueous dispersion B containing a second fluorine-containing polymer B.

[0084] Suitable embodiments of the first aqueous dispersion B are as described above. It is preferable to use the first aqueous dispersion B for polymerization of the second monomer B after carrying out a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products from the first aqueous dispersion B. In the purification treatment, the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion B are removed, making it easy to obtain a second fluorine-containing polymer B having 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.

[0085] The first aqueous dispersion B may contain components other than the aqueous medium and the first fluoropolymer B. Specific examples of other components that the first aqueous dispersion B 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 the above formula (1). 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 B 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 B 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.

[0086] In step B2, the content of the particles of the first fluoropolymer B before the start of polymerization of the second monomer B is preferably from 0.01 to 5 mass%, more preferably from 0.1 to 3 mass%, relative to the total mass of the first aqueous dispersion B. Note that the first aqueous dispersion B before the start of polymerization of the second monomer B does not contain the second monomer B or the polymerization initiator.

[0087] - Second Monomer B - The second monomer B contains monomer 2. Monomer 2 has the same meaning as monomer 2 in the above-mentioned method for producing a fluorinated polymer, and preferred embodiments are also the same. The amount of monomer 2 used is preferably 20.0 to 100.0 mol %, more preferably 25.0 to 100.0 mol %, and still more preferably 50.0 to 100.0 mol %, based on the amount of second monomer B used. The second monomer B may contain a monomer other than monomer 2. Examples of the other monomer include the other monomers mentioned above.

[0088] In step B2, it is preferable to polymerize the second monomer B 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.

[0089] 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, relative to 100 parts by mass of the second monomer B used.

[0090] -Method- In step B2, a second fluorine-containing polymer B (corresponding to the above-mentioned fluorine-containing polymer) is produced by polymerizing the second monomer B in the above-mentioned first aqueous dispersion B. Examples of the method for polymerizing the second monomer B include the above-mentioned method for polymerizing the first monomer B.

[0091] The polymerization of the second monomer B is preferably carried out under conditions in which an emulsifier having a fluorine atom is substantially absent, and more preferably under conditions in which an emulsifier is substantially absent. "Substantially absent" means that, in the method for producing the second fluorine-containing polymer B, 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 B. It is also preferable that the content is below the quantitation limit of the measurement method using the liquid chromatograph mass spectrometer described above (the measurement method described in WO 2018 / 181904). The lower limit can be 0 mass ppb or 1 mass ppb.

[0092] - Second Fluorine-Containing Polymer B - In step B2, the second fluorine-containing polymer B is produced, and a second aqueous dispersion in which particles of the second fluorine-containing polymer B are dispersed in an aqueous medium is obtained.

[0093] The second fluorine-containing polymer B may be in the form of particles. The particles of the second fluorine-containing polymer B may contain the first fluorine-containing polymer B, or may not contain the first fluorine-containing polymer B. The average primary particle size of the particles of the second fluorine-containing polymer B 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 primary particle size of the particles of the second fluorine-containing polymer B can be measured in the same manner as the average primary particle size of the particles of the first fluorine-containing polymer B.

[0094] The number of particles of the second fluorine-containing polymer B is 1.0 × 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 １４The upper limit is 10.0 × 10 １５ The number of particles of the second fluoropolymer B is the number of particles per mL of the second aqueous dispersion B. Examples of a method for measuring the number of particles include the measurement methods shown in the Examples section.

[0095] The second fluorine-containing polymer B preferably does not have a melting point.

[0096] The second fluorine-containing polymer B is preferably a fluorine-containing polymer using units based on the second monomer B, and more preferably a fluorine-containing polymer containing units based on the second monomer B.

[0097] - Second aqueous dispersion B - Step B2 provides a second aqueous dispersion B, which is an aqueous dispersion containing particles of the second fluoropolymer B. The second aqueous dispersion B is preferably an aqueous dispersion containing the above-mentioned fluoropolymer particles (hereinafter also referred to as "specific particles") and an aqueous medium.

[0098] The second aqueous dispersion B preferably does not substantially contain an emulsifier having a fluorine atom, and more preferably does not substantially contain an emulsifier. The second aqueous dispersion B substantially does not contain an emulsifier 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 second aqueous dispersion B. It is also preferable that the content is below the quantitation limit of the measurement method using the above-mentioned liquid chromatograph mass spectrometer (the measurement method described in WO 2018 / 181904). Examples of the lower limit include 0 mass ppb or 1 mass ppb.

[0099] The specific particles are preferably particles of the above-mentioned second fluoropolymer B. When the specific particles contain the second fluoropolymer B, the specific particles may or may not contain the first fluoropolymer B. The second aqueous dispersion B may further contain particles of the first fluoropolymer B in addition to the specific particles.

[0100] The preferred embodiments of the specific particle number and average primary particle diameter are the same as the preferred embodiments of the particle number and average primary particle diameter of the second fluorine-containing polymer B. The specific particle number is 1×10１４ It is preferable that the concentration of the particles is 500 nm or less and the average primary particle size of the particles is 500 nm or less.

[0101] The content of the specific particles is preferably 1 to 50 mass %, more preferably 1 to 45 mass %, and even more preferably 1 to 40 mass %, relative to the total mass of the second aqueous dispersion B, from the viewpoint of dispersion stability of the specific particles.

[0102] Specific examples and preferred embodiments of the aqueous medium contained in the second aqueous dispersion B are the same as the specific examples and preferred embodiments of the aqueous medium contained in the first aqueous dispersion B. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, relative to the total mass of the second aqueous dispersion B, from the viewpoint of dispersion stability of the specific particles.

[0103] <Step B3> Step B3 is a step of recovering the above-mentioned fluoropolymer (e.g., elastomer) from the second aqueous dispersion B obtained in step B2. A solid fluoropolymer (e.g., elastomer) can be obtained by aggregating particles of the second fluoropolymer B from the second aqueous dispersion B. As the aggregating method, the methods listed in step A2 above can be used.

[0104] [Another embodiment of the method for producing a fluorine-containing polymer] Another embodiment of the method for producing a fluorine-containing polymer includes a method for producing a fluorine-containing polymer, which comprises polymerizing a fluorine-containing monomer 1 and a monomer 2, which is a different type of monomer from the monomer 1 and has a hydrogen atom bonded to a carbon atom, in the presence of a polymerization initiator in the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom, to produce a fluorine-containing polymer having no melting point, excluding the combination in which the monomer 1 contains TFE and the monomer 2 contains PL. The above embodiment is the same as the above-mentioned present production method, except that compound X is not used, and preferred embodiments are also the same.

[0105] In another embodiment of the method for producing a fluorine-containing polymer, the combination of monomer 1 and monomer 2 is preferably a combination of HFP (10 to 50 mol%) and VdF (50 to 90 mol%), or a combination of TFE (10 to 30 mol%), HFP (15 to 40 mol%) and VdF (75 to 30 mol%). The mol% shown in the parentheses above indicates the content of each specific monomer relative to the total amount of the specific monomer. The specific monomer, which is a monomer containing monomer 1 and monomer 2, may contain other monomers in addition to the monomers exemplified as monomer 1 and monomer 2.

[0106] Specifically, a preferred aspect of the above embodiment includes a method of polymerizing a first monomer A containing the above-mentioned monomer 1 and the above-mentioned monomer 2 in the presence of 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 primary particle size of 500 nm or less, and recovering the above-mentioned fluorine-containing polymer from the first aqueous dispersion.

[0107] A preferred mode of the above embodiment includes a method in which a first monomer B containing the above-mentioned monomer 1 is polymerized in the presence of 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 particles of a first fluorine-containing polymer B having an average primary particle size of 500 nm or less, a second monomer B containing the above-mentioned monomer 2 is polymerized in the first aqueous dispersion to produce a second aqueous dispersion containing a second fluorine-containing polymer B, and the above-mentioned fluorine-containing polymer is recovered from the second aqueous dispersion.

[0108] [Solid] The solid may be a solid containing the above-mentioned fluorine-containing polymer produced by the present production method. Alternatively, the solid may contain a fluorine-containing polymer that uses units based on monomer 1 having a fluorine atom and units based on monomer 2, which is a monomer different from monomer 1 and has a hydrogen atom bonded to a carbon atom, and that has no melting point, and the content of metal elements in the solid may be 1000.0 ppm by mass or less relative to the total mass of the solid. A solid means that the solid is in a solid form (solid) at a temperature of 25°C.

[0109] The fluorine-containing polymer is as described above. The fluorine-containing polymer preferably has an iodine atom or a bromine atom. The content of the fluorine-containing polymer is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on the total mass of the solid material. The upper limit is less than 100% by mass.

[0110] The solid may contain a metal element. The content of the metal element in the solid is preferably 1000.0 ppm by mass or less, more preferably 100.0 ppm by mass or less, and even more preferably 50.0 ppm by mass or less, relative to the total mass of the solid. The content of the metal element can be measured, for example, by ICP-MS as described below. When measuring the 29 types of metal elements, the content of the metal elements in the solid is a total value obtained by adding up the contents of the 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) measured by an absolute calibration curve method using an inductively coupled plasma mass spectrometer (ICP-MS 7500cs (product name), manufactured by Agilent Technologies, Inc.) after the solid is placed in a platinum crucible and incinerated in a high-temperature electric heating furnace, followed by treatment with white sulfuric acid and dissolving the solid in dilute nitric acid.

[0111] Preferably, the solid material is substantially free of the above-mentioned emulsifier. Substantially free of emulsifier means that the content of the 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 solid material. It is also preferable that the content is below the quantitation limit of the measurement method using the above-mentioned liquid chromatograph mass spectrometer (the measurement method described in WO 2018 / 181904). Examples of the lower limit include 0 mass ppb or 1 mass ppb.

[0112] Preferably, the solid material is substantially free of any of the compounds represented by formulas (S1) to (S4), and more preferably substantially free of all of the compounds represented by formulas (S1) to (S4). "Substantially free of the compound represented by formula (S1)" means that the content of the compound represented by formula (S1) is 10 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 material. It is also preferably below the quantitation limit of the measurement method using a liquid chromatograph mass spectrometer in the examples. Examples of lower limits include 0 mass ppb or 1 mass ppb. "Substantially free of the 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 solid material. It is also preferable that the content be below the limit of quantitation in the measurement method using a liquid chromatograph mass spectrometer in the examples. Examples of the lower limit include 0 mass ppb or 1 mass ppb. "Substantially free of the compound represented by formula (S3)" means that the content of the compound represented by formula (S3) 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 material. It is also preferable that the content be below the limit of quantitation in the measurement method using a liquid chromatograph mass spectrometer in the examples. Examples of the lower limit include 0 mass ppb or 1 mass ppb. "Substantially free of the compound represented by formula (S4)" means that the content of the compound represented by formula (S4) 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 material. It is also preferable that the content be below the limit of quantitation in the measurement method using a liquid chromatograph mass spectrometer in the examples. The lower limit may be 0 ppb by mass or 1 ppb by mass."Substantially free of all compounds represented by any one of formulas (S1) to (S4)" means that the total content of compounds represented by any one of formulas (S1) to (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, based on the total mass of the solid matter. A content below the quantitation limit of the measurement method using a liquid chromatograph mass spectrometer in the examples is also preferred. Examples of lower limits include 0 ppb by mass or 1 ppb by mass. When compound X is used without using an emulsifier during the production of the fluoropolymer, the amount of compound represented by any one of formulas (S1) to (S4) generated can be suppressed, making it easy to adjust the content of these compounds. Furthermore, the content of these compounds can also be reduced by the above-mentioned purification treatment.

[0113] In addition to the various components in the solid material described above, the solid material may contain the various components used in the present production method described above and the various components that may be contained in the aqueous dispersion described below.

[0114] The solid material is preferably obtained by agglomerating fluoropolymer particles from an aqueous dispersion containing the fluoropolymer particles obtained by the present production method. The aqueous dispersion will be described later.

[0115] The aggregation method may be the aggregation method described above in step A2.

[0116] (Aqueous Dispersion) The aqueous dispersion is preferably an aqueous dispersion in which particles containing a fluoropolymer are produced in an aqueous medium by polymerization of a specific monomer in the production method of the present invention, and the particles containing the fluoropolymer are dispersed in the aqueous medium.

[0117] The various components and steps in this production method are as described above. The number of particles of the fluoropolymer is 1.0 × 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ The upper limit is 10.0 × 10 １５The number of particles of the fluoropolymer is the number of particles per mL of the aqueous dispersion. Examples of a method for measuring the number of particles include the measurement methods shown in the Examples section.

[0118] The aqueous dispersion preferably does not substantially contain the above-mentioned emulsifier. "Substantially does not contain an emulsifier" means that the content of the 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 aqueous dispersion. The lower limit is 0 mass ppb.

[0119] The aqueous dispersion preferably does not substantially contain any of the compounds represented by formulas (S1) to (S4), and more preferably does not substantially contain any of the compounds represented by formulas (S1) to (S4). Formulas (S1) to (S4) are as described above. Substantially not containing the 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. It is also preferable that the content is below the quantitation limit of the measurement method using the liquid chromatograph mass spectrometer described above (the measurement method described in WO 2018 / 181904). Examples of the lower limit include 0 mass ppb or 1 mass ppb. "Substantially free of the 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 quantitation limit of the measurement method using the liquid chromatograph mass spectrometer described above (the measurement method described in WO 2018 / 181904) is also preferred. Examples of the lower limit include 0 mass ppb or 1 mass ppb. "Substantially free of the compound represented by formula (S3)" means that the content of the compound represented by formula (S3) 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 quantitation limit of the measurement method using the liquid chromatograph mass spectrometer described above (the measurement method described in WO 2018 / 181904) is also preferred. The lower limit includes 0 mass ppb or 1 mass ppb. "Substantially free of the compound represented by formula (S4)" means that the content of the compound represented by formula (S4) 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. It is also preferable that the content is below the quantitation limit of the measurement method using the above-mentioned liquid chromatograph mass spectrometer (the measurement method described in WO 2018 / 181904).Examples of the lower limit include 0 ppb by mass or 1 ppb by mass. "Substantially free of all compounds represented by any of formulas (S1) to (S4)" mean that the total content of compounds represented by any of formulas (S1) to (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 solid matter. A concentration below the quantitation limit of the measurement method using a liquid chromatograph mass spectrometer (the measurement method described in WO 2018 / 181904) is also preferred. Examples of the lower limit include 0 ppb by mass or 1 ppb by mass. When compound X is used without using an emulsifier during the production of the fluoropolymer contained in the aqueous dispersion, the amount of compound 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.

[0120] The aqueous dispersion may contain components other than the various components of the aqueous dispersion described above. Specific examples of other components that the aqueous dispersion may contain include a chain transfer agent, a reducing agent, and a pH adjuster. Specific examples of chain transfer agents include the chain transfer agent used in the production method described above. 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. Preferred phosphates are disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the 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 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.

[0121] The solids concentration of the aqueous dispersion is preferably 5 to 50% by mass, and more preferably 10 to 45% by mass. The solids concentration of the aqueous dispersion can be measured, for example, by the following method. The solids concentration of the aqueous dispersion is calculated by heating 2.0 g of the aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and calculating the solids concentration using the following formula: "Solids concentration (mass%) = 100 × heating residue of aqueous dispersion (g) / mass of aqueous dispersion (2.0 g)"

[0122] [Another embodiment of the solid] In addition, another embodiment of the solid may be a solid containing the above-mentioned fluorine-containing polymer produced by another embodiment of the above-mentioned method for producing a fluorine-containing polymer.The preferred mode of the other embodiment of the above-mentioned solid is the same as the above-mentioned [solid], except that compound X is not used and the combination of monomer 1 containing TFE and monomer 2 containing PL is excluded.Specifically, as a preferred mode of the above-mentioned embodiment, the fluorine-containing polymer preferably has an iodine atom or a bromine atom.

[0123] [Uses] The solid material and another embodiment of the solid material can be appropriately molded by known methods. Examples of molding methods include injection molding, extrusion molding, coextrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calendar molding. In addition, the solid material and another embodiment of the solid material are used, for example, as packing and sealing materials in semiconductor manufacturing equipment and various plants such as petrochemical plants.

[0124] The crosslinked product is obtained by crosslinking the solid material or another embodiment of the solid material. The use of the crosslinked product obtained by crosslinking the solid material or another embodiment of the solid material can suppress the inclusion of by-products, and therefore the crosslinked product can be used particularly for coating applications and binder applications.

[0125] Since the aqueous dispersion does not necessarily require an emulsifier such as an emulsifier having a fluorine atom, it can easily be converted into a dispersion in an organic solvent such as N-methylpyrrolidone or acetone by solvent substitution. Specifically, the aqueous dispersion can be converted into a dispersion in an organic solvent by mixing the aqueous dispersion with an organic solvent and dehydrating the mixture by evaporation or anhydrous sodium sulfate.

[0126] The aqueous dispersion stably disperses the fluoropolymer even without containing an emulsifier, and is therefore suitable for use in coating applications, binders, etc.

[0127] The present disclosure will be described in detail below with reference to examples. Examples 1 to 5 are working examples, and Example 6 is a comparative example. However, the present disclosure is not limited to these examples.

[0128] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0129] <Average primary particle diameter of fluoropolymer particles> The aqueous dispersion of each example described below was degassed at 25°C for 5 minutes, pressurized with nitrogen gas to 0.2 MPaG, purged, and returned to atmospheric pressure to obtain a measurement sample. The average primary particle diameter of the obtained measurement sample was measured using a dynamic light scattering particle size distribution measurement device (Otsuka Electronics Co., Ltd., ELSZ) with an accumulation number set to 100, and this was taken as the average primary particle diameter of the particles in each aqueous dispersion.

[0130] <Number of Fluoropolymer Particles> The number of fluoropolymer particles Np (particles / mL) in the aqueous dispersion was calculated by the following formula.

[0131] Np (pieces / mL) = [(X / 100) / (1-X / 100)] / [4 / 3×π×{(Dp / 2) ３}×ρ] X: solids concentration (% by mass) of the aqueous dispersion π: circular constant Dp: average primary particle size of the fluoropolymer particles in the aqueous dispersion ρ: specific gravity of the fluoropolymer Note that ρ in Examples 1 and 2 and 5 was set to 1.55, and ρ in Examples 3 and 4 and Reference Example 1 was set to 1.82.

[0132] <Solid content concentration of aqueous dispersion> 2.0 g of the aqueous dispersion of each example described below was heated at 170°C for 20 minutes, and then the mass (g) of the residue was weighed and the solid content concentration was calculated using the following formula: Solid content concentration of aqueous dispersion (mass%) = 100 × (mass of residue) / (mass of aqueous dispersion (2.0 g))

[0133] <Proportion of each unit in the fluorine-containing polymer> The proportion of each unit in the fluorine-containing polymer is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0134] <Method for measuring the content of iodine atoms> The solid product obtained in each of the examples described below was hot-pressed at 100° C. to produce a film having a thickness of 200 μm. The obtained film was subjected to elemental analysis using an X-ray fluorescence analyzer (Vanta (registered trademark) handheld X-ray fluorescence analyzer, manufactured by EVIDENT) to measure the content of iodine atoms relative to the content of fluorine-containing polymer in the solid product.

[0135] <Melting Point> A 5 ​​mg sample of the solid material obtained in each example described below was weighed out and placed 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.

[0136] <Metal Element Content> 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).

[0137] <Compounds Represented by Formula (S1) and Compounds Represented by Formula (S3)> (Preparation of Measurement Samples) The solids obtained in each of the examples described below were 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) based on the total mass of the solids was added in advance to obtain a pulverized powder. The freeze-pulverization conditions were: solid: 3 g, BHT: 0.3 g, run time: 5 min, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.5 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 n = 3 to 13, 15, and 17 into a perfluorocarboxylic acid having the same number of carbon atoms. 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 n = 4 to 10 and 12 into a perfluorosulfonic acid having the same number of carbon atoms. Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1 to 180 ng / g were first prepared, and a and a' were determined from the respective sample concentrations and peak integrals using first-order approximations using formulas (A1) and (A1'). 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).

[0138] The measuring equipment and conditions are shown in Table 1 below.

[0139]

[0140] The MRM measurement parameters are shown in Tables 2 and 3.

[0141]

[0142]

[0143] Specifically, first, the compound represented by formula (S1) or formula (S3) contained in each of the extracts 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 the MRM method.

[0144] Next, the contents of the compound represented by formula (S1) and the compound represented by formula (S3) were calculated using formula (A2) and formula (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) having carbon number (n+1) in each extract ACm: peak area of ​​the compound represented by formula (S1) having carbon number (n+1) in each extract XCm' = ACm' / a' (A2') XCm': content (ng / g) of the compound represented by formula (S3) having carbon number n in each extract ACm': peak area of ​​the compound represented by formula (S3) having carbon number n in each extract The quantitation limit in this measurement is 1 ng / g.

[0145] 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)

[0146] 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)

[0147] Example 1 Ultrapure water (1874 g) and a 50% by weight aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to Compound X) (360 μL, 180 mg of NaAAMPS) were placed in a 3.2 L stainless steel pressure reactor, and the temperature was raised to 75°C while stirring at 300 rpm. A mixed gas (TFE / PL = 88 / 12 (molar ratio)) was injected into the reactor until the pressure inside the reactor reached 2.6 MPaG. Next, an aqueous ammonium persulfate solution (14% by weight, 3 mL) was added to initiate polymerization. As the pressure inside the reactor decreased with the initiation of polymerization, the mixed gas (TFE / PL = 88 / 12 (molar ratio)) was added to maintain the pressure constant. After the addition of the initiator, an aqueous ammonium persulfate solution (14% by weight, 3 mL) was added every 15 minutes, and the addition was terminated when the total amount added reached 6 mL. When 50 g of the mixed gas (TFE / PL=88 / 12 (molar ratio)) had been added, C4DI (1 mL) was injected. When the amount of the mixed gas added reached 550 g, the addition of the mixed gas to be injected after polymerization was stopped, the temperature inside the reactor was cooled to 15° C. to terminate the polymerization reaction, the gas remaining in the reactor was recovered, and the liquid was then withdrawn to obtain an aqueous dispersion A. The average primary particle diameter of the particles of the fluoropolymer A in the aqueous dispersion A was 111 nm, and the number of particles of the fluoropolymer A was 2.5×10 １４ The concentration of iodine atoms in the aqueous dispersion A was 1888 ppm by mass. The aqueous dispersion A had a solid content of 21.4% by mass. Ammonium carbonate was added to the aqueous dispersion A to cause coagulation, followed by filtration. The resulting solid containing fluoropolymer A was washed with ultrapure water. It was then vacuum dried at 100°C. The resulting fluoropolymer A was analyzed by NMR, and the molar ratio was TFE / PL=56 / 44. The content of iodine atoms in the solid relative to the content of fluoropolymer A was 1888 ppm by mass. The fluoropolymer A did not have a melting point.

[0148] [Example 2] Ultrapure water (1874 g) and a 50% by weight aqueous solution of NaAAMPS (360 μL, 180 mg of NaAAMPS) were added to a 3.2 L stainless steel pressure reactor, and the temperature was raised to 75°C while stirring at 300 rpm. A mixed gas (TFE / PL = 88 / 12 (molar ratio)) was injected until the pressure inside the reactor reached 2.6 MPaG. Next, an aqueous solution of ammonium persulfate (14% by weight, 3 mL) was added to initiate polymerization. As the pressure inside the reactor decreased with the start of polymerization, the mixed gas (TFE / PL = 88 / 12 (molar ratio)) was added to maintain the pressure constant. After the addition of the initiator, an aqueous solution of ammonium persulfate (14% by weight, 3 mL) was added every 15 minutes, and the addition was terminated when the total amount added reached 6 mL. When 10 g of the mixed gas (TFE / PL=88 / 12 (molar ratio)) had been added, C4DI (1.3 g) was injected. When the amount of the mixed gas added reached 650 g, the addition of the mixed gas to be injected after polymerization was stopped, the temperature inside the reactor was cooled to 15° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was then withdrawn to obtain an aqueous dispersion B. The average primary particle diameter of the particles of the fluoropolymer B in the aqueous dispersion B was 122 nm, and the number of particles of the fluoropolymer B was 2.2×10 １４ The concentration of iodine atoms in the aqueous dispersion B was 24.9%. Ammonium carbonate was added to aqueous dispersion B to cause coagulation, followed by filtration. The resulting solid containing fluoropolymer B was washed with ultrapure water. It was then vacuum dried at 100°C. The resulting fluoropolymer B was analyzed by NMR, and the molar ratio was TFE / PL=56 / 44. The content of iodine atoms in the solid relative to the content of fluoropolymer B was 700 ppm. Fluoropolymer B did not have a melting point.

[0149] [Example 3] Ultrapure water (1874 g) and a 50% by weight aqueous solution of NaAAMPS (360 μL, 180 mg of NaAAMPS) were added to a 3.2 L stainless steel pressure reactor. After degassing under reduced pressure, a mixed gas (VdF / HFP = 65 / 35 (molar ratio)) was injected under reduced pressure and the pressure was increased to 1.5 MPaG at 75 °C. Next, an aqueous ammonium persulfate solution (14% by weight, 3 mL) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, a mixed gas (VdF / HFP = 78 / 22 (molar ratio)) was added to maintain a constant pressure. After the addition of the initiator, an aqueous ammonium persulfate solution (14% by weight, 3 mL) was added every 15 minutes, and the addition was terminated when the total amount added reached 6 mL. When 25 g of the mixed gas (VdF / HFP = 78 / 22 (molar ratio)) had been added, C4DI (0.5 mL) was injected. When the amount of the mixed gas (VdF / HFP=78 / 22 (molar ratio)) added reached 650 g, the addition of the mixed gas to be injected after polymerization was stopped, the temperature inside the reactor was cooled to 15° C. to terminate the polymerization reaction, and the gas remaining in the reactor was recovered, followed by drawing out the liquid to obtain an aqueous dispersion C. The average primary particle diameter of the particles of the fluoropolymer C in the aqueous dispersion C was 112 nm, and the number of particles of the fluoropolymer C was 2.5×10 １４ The concentration of iodine atoms in the solid was 950 ppm relative to the content of fluoropolymer C. The fluoropolymer C had no melting point.

[0150] [Example 4] Ultrapure water (1874 g) and a 50% by weight aqueous solution of NaAAMPS (360 μL, 180 mg of NaAAMPS) were added to a 3.2 L stainless steel pressure reactor, and the reactor was degassed under reduced pressure. A mixed gas (VdF / TFE / HFP = 19 / 11 / 70 (molar ratio)) was then injected under reduced pressure, and the pressure was increased to 2.0 MPaG at 75 °C. Next, an aqueous solution of ammonium persulfate (14% by weight, 3 mL) was added to initiate polymerization. Since the pressure inside the reactor decreased with the initiation of polymerization, a mixed gas (VdF / TFE / HFP = 50 / 20 / 30 (molar ratio)) was added to maintain a constant pressure. After the addition of the initiator, an aqueous solution of ammonium persulfate (14% by weight, 3 mL) was added every 15 minutes, and the addition was terminated when the total amount added reached 6 mL. When 25 g of the mixed gas ((VdF / TFE / HFP=50 / 20 / 30 (molar ratio)) had been added, C4DI (0.5 mL) was injected. When the amount of the mixed gas ((VdF / TFE / HFP=50 / 20 / 30 (molar ratio)) added reached 650 g, the addition of the mixed gas to be injected after polymerization was stopped, the temperature inside the reactor was cooled to 15° C. to terminate the polymerization reaction, the gas remaining in the reactor was recovered, and the liquid was withdrawn to obtain an aqueous dispersion D. The average primary particle diameter of the particles of the fluoropolymer D in the aqueous dispersion D was 114 nm, and the number of particles of the fluoropolymer D was 2.4×10 １４ The concentration of iodine in the solid was 940 ppm relative to the content of fluoropolymer D. Fluoropolymer D had no melting point.

[0151] [Example 5] Ultrapure water (1,874 g) and 2-Methacrylamido-2-methylpropylsulfonic acid (180 mg) were added to a 3.2 L stainless steel pressure reactor and degassed under reduced pressure. A mixed gas (VdF / TFE / HFP = 19 / 11 / 70 (molar ratio)) was then injected under reduced pressure and the pressure was increased to 2.0 MPaG at 75°C. Next, an aqueous ammonium persulfate solution (14% by mass, 3 mL) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so the mixed gas (VdF / TFE / HFP = 50 / 20 / 30 (molar ratio)) was added to maintain a constant pressure. After the initiator was added, an aqueous ammonium persulfate solution (14% by mass, 3 mL) was added every 15 minutes, and the addition was terminated when the total amount added reached 6 mL. When 25 g of the mixed gas ((VdF / TFE / HFP=50 / 20 / 30 (molar ratio)) had been added, C4DI (0.5 mL) was injected. When the amount of the mixed gas ((VdF / TFE / HFP=50 / 20 / 30 (molar ratio)) added reached 650 g, the addition of the mixed gas to be injected after polymerization was stopped, the temperature inside the reactor was cooled to 15° C. to terminate the polymerization reaction, the gas remaining in the reactor was recovered, and the liquid was withdrawn to obtain an aqueous dispersion X. The average primary particle diameter of the particles of fluoropolymer X in aqueous dispersion X was 111 nm, and the number of particles of fluoropolymer X was 2.4×10 １４ The concentration of iodine in the solid was 920 ppm relative to the content of fluoropolymer X in the solid. The fluoropolymer X had no melting point.

[0152] [Example 6] Ultrapure water (1674 g), 20% by mass aqueous sodium hydroxide solution (4.85 g), disodium hydrogen phosphate dodecahydrate (59.6 g), sodium lauryl sulfate (9.6 g), t-butanol (136.4 g), ammonium persulfate (5.64 g), and C4DI (10.7 g) were charged into a 3.2 L stainless steel pressure reactor, and the temperature was raised to 25 ° C. while stirring at 215 rpm. A mixed gas (TFE / PL = 88 / 12 (molar ratio)) was injected until the pressure in the reactor reached 2.5 MPaG, and a reducing agent (Rongalite, 2.3% by mass, 7 mL) was added to initiate polymerization. A reducing agent (Rongalite, 2.4% by mass, 2 mL) was added every 10 minutes from the start of polymerization. As the polymerization started, the pressure inside the reactor decreased, so a mixed gas (TFE / PL=56 / 44 (molar ratio)) was added to keep the pressure constant. When 1,000 g of the mixed gas (TFE / PL=56 / 44 (molar ratio)) had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 340 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn to obtain an aqueous dispersion E. The average primary particle diameter of the particles of the fluoropolymer E in the aqueous dispersion E was 110 nm, and the number of particles of the fluoropolymer E was 4.7 × 10 １４ The concentration of iodine atoms in the solid was 600 ppm relative to the content of fluoropolymer E. The fluoropolymer E had no melting point.

[0153] In the production of Examples 1 to 5, polymerization of fluorine-containing polymers was carried out under conditions in which neither an emulsifier having a fluorine atom nor an emulsifier having a fluorine atom was substantially present. Moreover, the aqueous dispersions obtained in Examples 1 to 5 did not substantially contain any emulsifier having a fluorine atom nor any emulsifier having a fluorine atom.

[0154] In the following table, "S1 + S3" indicates the total content (ppm by mass) of the compound represented by formula (S1) and the compound represented by formula (S3) in the solid material of each example relative to the total mass of the solid material. The abbreviations for Monomer 1 and Monomer 2 are as described above.

[0155]

[0156] The table below specifically shows the content of the compound represented by formula (S1) and the content of the compound represented by formula (S3) in the solid of each example. The content of formula (S1) means the total content of each compound in formula (S1) where n is 3 to 13, 15, and 17 relative to the total mass of the solid of each example, and the content of formula (S3) means the total content of each compound in formula (S3) where n is 4 to 10, and 12 relative to the total mass of the solid of each example.

[0157]

[0158]

[0159] It was confirmed that this production method can suppress the inclusion of metal elements and fluorine-containing by-products (comparison of Examples 1 to 6). Furthermore, the use of a crosslinked product (e.g., crosslinked rubber) obtained by crosslinking the solid material obtained by this production method can suppress the inclusion of by-products, and therefore the crosslinked product can be used particularly for coating applications and binder applications.

[0160] Reference Example 1, which corresponds to the above-mentioned "Another embodiment of the method for producing a fluoropolymer", will be shown below.

[0161] Reference Example 1 (Production of Raw Material Liquid A) Distilled water (717 g), HFP (42 g), and VdF (4.5 g) were charged into a 1.0 L stainless steel pressure reactor, and the temperature was raised to 90°C while stirring at 500 rpm. The pressure inside the reactor when it reached 90°C was 1.98 MPaG. Next, an aqueous ammonium persulfate solution (3.6 mass%, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, and when the pressure reached 1.81 MPaG, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 96 minutes. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated raw material liquid A.

[0162] (Production of Raw Material Liquid B) To the above raw material liquid A (712 g) was added a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g). 60 minutes after the start of stirring, the raw material liquid and the cation exchange resin were separated by filtration. To a part (690 g) of the filtered raw material liquid, an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g) was added. 60 minutes after the start of stirring, the raw material liquid and the anion exchange resin were separated by filtration to obtain raw material liquid B. Raw material liquid B is a dispersion of particles of a first fluoropolymer in an aqueous medium. The particles of the first fluoropolymer in raw material liquid B had an average primary particle diameter of 114 nm. The content of the first fluoropolymer was 1.0 mass% relative to the total mass of raw material liquid B.

[0163] (Production of second fluorine-containing polymer) A 3.2 L stainless steel pressure reactor was charged with raw material liquid B (1714 g), ultrapure water (160 g), and C4DI (1.0 g). After degassing under reduced pressure, a mixed gas (VdF / HFP = 65 / 35 (molar ratio)) was injected under reduced pressure, and the pressure was increased to 1.5 MPaG at 75 ° C. Next, an aqueous ammonium persulfate solution (14 mass%, 3 mL) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, a mixed gas (VdF / HFP = 78 / 22 (molar ratio)) was added to maintain the pressure constant. When the amount of mixed gas (VdF / HFP = 78 / 22 (molar ratio)) added reached 320 g, the addition of the mixed gas to be injected after polymerization was stopped, the temperature inside the reactor was cooled to 15 ° C., the polymerization reaction was stopped, and the gas remaining in the reactor was recovered. The liquid was then extracted to obtain an aqueous dispersion Z. The average primary particle diameter of the particles of fluoropolymer Z in aqueous dispersion Z was 270 nm, and the number of particles of fluoropolymer Z was 0.073 × 10 １４The concentration of iodine atoms in the solid was 12.0%. The aqueous dispersion Z was freeze-aggregated and then filtered, and the resulting solid containing the fluoropolymer Z was washed with ultrapure water. It was then vacuum-dried at 100°C. The resulting fluoropolymer Z was analyzed by NMR, and the molar ratio of VdF / HFP was 78 / 22. The content of iodine atoms in the solid relative to the content of the fluoropolymer Z was 1230 ppm. The fluoropolymer Z did not have a melting point.

[0164] The disclosure of Japanese Patent Application No. 2024-098618, filed on June 19, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

In the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom, a compound represented by formula (X) and a polymerization initiator are reacted to form a polymerizable emulsion. A method for producing a fluorine-containing polymer, comprising polymerizing a monomer 1 having a fluorine atom with a monomer 2 which is a different type of monomer from the monomer 1 and has a hydrogen atom bonded to a carbon atom, to produce a fluorine-containing polymer having no melting point. C(X １ )(X ２ )=C(X ３ )CONH-R-Z (X) In formula (X), X １ , X ２ and X ３ each independently represents a hydrogen atom, a fluorine atom, a perfluoromethyl group, or an alkyl group, R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms, Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM, M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from one another; 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 Ｍ２ may be the same or different from each other. Z is -SO ３ The process for producing a fluorine-containing polymer according to claim 1, wherein M is M. 　 The method for producing a fluoropolymer according to claim 1 or 2, wherein the content of the compound represented by formula (X) is 1.0 to 1000.0 ppm by mass relative to the total mass of the aqueous medium.

3. The process for producing a fluorine-containing polymer according to claim 1 or 2, wherein said monomer 1 is at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and chlorotrifluoroethylene.

3. The process for producing a fluorine-containing polymer according to claim 1 or 2, wherein said monomer 2 is propylene or vinylidene fluoride. A solid material comprising a fluorine-containing polymer which uses units based on a monomer 1 having a fluorine atom and units based on a monomer 2 which is a monomer different from the monomer 1 and has a hydrogen atom bonded to a carbon atom, and which has no melting point, A solid material, wherein the content of metal elements in the solid material is 1000.0 ppm by mass or less, relative to the total mass of the solid material. 　 The solid material according to claim 6 , wherein the fluorine-containing polymer has an iodine atom or a bromine atom. 　 A crosslinked product obtained by crosslinking the solid material according to claim 6 or 7.

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