Fluorinated compounds, fluorinated copolymers, and compositions of fluorinated copolymers

Abstract

This invention provides a fluorinated compound suitable for obtaining rubber with excellent short-term and long-term heat resistance, a fluorinated copolymer using the same, and a fluorinated copolymer composition. A fluorinated compound represented by the following formula (1), a fluorinated copolymer using the same, and a fluorinated copolymer composition. In equation (1), R 1~R 3. Each can be independently a hydrogen atom or a fluorine atom; R 4 represents a hydrogen atom, a fluorine atom, or a monovalent organic group consisting of 1 to 8 carbon atoms without a carbonyl group; Z represents an oxygen atom, a sulfur atom, or -N(R) 5)-, R 5 represents a hydrogen atom or a monovalent organic group consisting of 1 to 4 carbon atoms. X represents a single bond or a difluoromethylene group; Y represents... 1~Y 4 are each independently a fluorine atom or a trifluoromethyl group; Q is a perfluoroalkyl group with 1 to 8 carbon atoms that may contain an ether-containing oxygen atom.

Description

Fluorinated compounds, fluorinated copolymers, and compositions of fluorinated copolymers The present invention relates to a fluorinated compound that can be effectively used as a monomer constituting a fluorinated copolymer, a fluorinated copolymer using the same, and a composition comprising the fluorinated copolymer. FFKM is a fluorinated copolymer containing perfluoroalkyl vinyl ethers such as tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE) as monomer structural units, also known as a perfluoroelastomer. Due to its excellent heat resistance and chemical resistance, FFKM crosslinked rubber is widely used in semiconductor manufacturing, vehicles, aircraft, general machinery, construction, chemical plants, and other applications as a sealing material or cushioning material, such as O-rings, gaskets, oil seals, and pads. Regarding the crosslinking process, for example, the following method is known: using a peroxide such as 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane as a crosslinking agent to crosslink the monomer at the terminal iodine atom site. Furthermore, some literature proposes using bismaleimide compounds as crosslinking aids from the viewpoint of increasing the rate of the crosslinking reaction (see Patent Document 1). Furthermore, it is also known to introduce a fluorinated compound having a nitrile group as a monomeric structural unit into FFKM and use tetraphenyltin as a catalyst to form a cross-linked structure comprising a tri-ring formed by trimerization of the nitrile group (see, for example, Patent Document 2). Furthermore, some literature proposes a method based on the viewpoint of reducing the compressive permanent strain of crosslinked materials at high temperatures around 300°C: introducing a fluorinated compound with a nitrile group as a monomeric structural unit into FFKM, and using a diaminophenol compound such as 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane as a crosslinking agent to form a crosslinked structure containing an oxazolium ring (see Patent Documents 3 and 4). Previous Art Documents Patent Documents Patent Document 1: International Publication No. 2021 / 166664; Patent Document 2: Japanese Patent Publication No. 63-5409; Patent Document 3: Japanese Patent Publication No. 2-59177; Patent Document 4: International Publication No. 2021 / 210503 The problem this invention aims to solve is that as the applications of rubber expand in various industries, there is a growing demand for rubbers that can maintain excellent properties at higher temperatures. Furthermore, it is desirable to further improve the heat resistance of rubbers obtained through FFKM crosslinking. However, even with the rubber described in Patent Documents 1 to 4, it is still difficult to say that it can simultaneously and fully satisfy both short-term and long-term heat resistance. The present invention was made in view of the above-mentioned situation, and aims to provide a fluorinated compound suitable for obtaining rubber with excellent short-term and long-term heat resistance, a fluorinated copolymer using the same, and a fluorinated copolymer composition. The present invention is based on the following insight: by introducing a predetermined fluorinated compound into the monomer structural unit of FFKM, the crosslinked product obtained from the fluorinated copolymer using the fluorinated compound exhibits excellent short-term and long-term heat resistance. The present invention provides the following means. [1] A fluorine-containing compound, represented by the following formula (1): [Chemical Formula 1] In equation (1), R 1 ~R 3 Each can be independently a hydrogen atom or a fluorine atom; R 4 Z is a hydrogen atom, a fluorine atom, or a monovalent organic group consisting of 1 to 8 carbon atoms without a carbonyl group; Z is an oxygen atom, a sulfur atom, or -N(R) 5 )-, R 5 X is a monovalent organic group consisting of 1 to 4 carbon atoms; X is a single bond or a difluoromethylene group; Y 1 ~Y 4 Each is independently a fluorine atom or a trifluoromethyl group; Q is a perfluoroalkyl group with 1 to 8 carbon atoms that may contain an ether-containing oxygen atom. [2] As in [1], a fluorinated compound in which Z is an oxygen atom. [3] As in [1] or [2], a fluorinated compound in which R is an oxygen atom. 1 ~R 3 R is a fluorine atom. 4 It is a hydrogen atom. [4] A fluorinated copolymer comprising: a structural unit (A) derived from tetrafluoroethylene; a structural unit (B) derived from a perfluoroalkyl vinyl ether; and a structural unit (C) derived from a fluorinated compound of any one of [1] to [3]. [5] In the fluorinated copolymer of [4], of the total 100% by mass of the aforementioned structural units (A) to (C), structural unit (A) is 29.9 to 80% by mass, structural unit (B) is 19.9 to 70% by mass, and structural unit (C) is 0.1 to 20% by mass. [6] A fluorinated copolymer composition comprising: a fluorinated copolymer as described in [4] or [5]; and a compound (D) having two or more structures (d) as shown in formula (2) below; [Formula 2] In equation (2), -a 1 -b indicates a single bond, bonded to a hydrogen atom, a methyl group, or an aromatic ring that may have substituents; 1 ~-b 5 Each represents a single key, and -b 1 and -b 5 At least one of them is bonded to a hydrogen atom; furthermore, the benzene ring in formula (2) is referred to as benzene ring A. [7] A fluorinated copolymer composition as in [6], wherein the aforementioned compound (D) has one or more of the following structures: a structure in which the benzene ring A of one of the aforementioned structures (d) is linked to the benzene ring A of another of the aforementioned structures (d) by a single bond. [8] A fluorinated copolymer composition as in [6] or [7], wherein the content of the aforementioned compound (D) is 0.1 to 10 parts by mass relative to 100 parts by mass of the aforementioned fluorinated copolymer. [9] A crosslinked fluorinated copolymer obtained from a fluorinated copolymer composition as in any one of [6] to [8]. Effects of the Invention According to the present invention, a fluorinated rubber compound suitable for obtaining excellent short-term and long-term heat resistance, a fluorinated copolymer using the same, and a fluorinated copolymer composition thereof are provided, wherein the aforementioned fluorinated compound is provided. The definitions and meanings of the terms and symbols used in this specification are shown below. "Room temperature" means 20~25°C. "Short-term heat resistance" means that, in a test according to the "tensile vibration-non-resonance method" specified in JIS K 7244-4:1999, the mechanical properties, especially the storage modulus of elasticity, hardly change when heated from room temperature to approximately 300°C. Specifically, it is evaluated using the thermomechanical analysis method described in the examples. "Long-term heat resistance" means that the mechanical properties are maintained at a high temperature of approximately 300°C for more than 72 hours. Specifically, it is evaluated using the suspension method described in the examples. The content of monomer structural units in the fluorinated copolymer is obtained from a nuclear magnetic resonance (NMR) measuring device. 1 H-NMR and 19 The value is calculated from the F-NMR measurement results. Specifically, it is obtained by the method described in the examples. [Fluorine-containing compounds] The fluorine-containing compound of the present invention (hereinafter also referred to as "fluorine-containing compound of the present invention") is represented by the following formula (1). This compound is a novel fluorine-containing compound having a vinyl or fluorovinyl group in the main chain and a carbonyl group as a polymerizable unsaturated bond. The fluorine-containing compound having the above structure can be introduced into FFKM as a monomeric structural unit to form a crosslinked fluorine-containing copolymer with a crosslinked structure containing an indole ring. The crosslinked product has excellent short-term and long-term heat resistance. By using the fluorine-containing compound of the present invention, a fluorine-containing copolymer suitable for obtaining the crosslinked product can be formed. [Chemical Formula 3] In formula (1), R 1 ~R 3 are each independently a hydrogen atom or a fluorine atom; from the viewpoint of polymerization reactivity, it is preferable that all are hydrogen atoms or all are fluorine atoms; from the viewpoint of heat resistance, it is more preferable that all are fluorine atoms. R 4 is a hydrogen atom, a fluorine atom, or a monovalent organic group having 1 to 8 carbon atoms without a carbonyl group. From the viewpoint of the ease of synthesis of the fluorine-containing compound of this embodiment, the number of carbon atoms of the organic group is preferably 1 to 7, more preferably 1 to 6, and even more preferably 1 to 5. The organic group can be any of linear, branched, or cyclic, and is preferably linear or branched. The organic group may also contain heteroatoms such as nitrogen atoms, oxygen atoms, or sulfur atoms. R 4 also varies depending on the crosslinking agent used, but in view of becoming the crosslinking site of the fluorine-containing copolymer, it is a hydrogen atom, that is, the fluorine-containing compound preferably has an acetyl group containing R 4 at the molecular end. Z is an oxygen atom, a sulfur atom, or -N(R 5 ), and R 5 is a hydrogen atom or a monovalent organic group having 1 to 4 carbon atoms. From the viewpoint of the ease of synthesis of the fluorine-containing compound of this embodiment, the number of carbon atoms of the organic group is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1. The organic group can be any of linear, branched, or cyclic, and is preferably linear or branched. The organic group may also contain heteroatoms such as nitrogen atoms, oxygen atoms, or sulfur atoms. From the viewpoint of the good rubber properties of the crosslinked product of the fluorine-containing copolymer having the fluorine-containing compound of this embodiment as a monomer structural unit, Z is preferably an oxygen atom or a sulfur atom, and more preferably an oxygen atom. X is a single bond or a difluoromethylene group, and from the viewpoint of the ease of synthesis of the fluorine-containing compound of this embodiment, it is preferably a single bond. Y 1 ~Y 4 are each independently a fluorine atom or a trifluoromethyl group; from the viewpoints of polymerization reactivity and heat resistance, Y 1 and Y 3 are preferably fluorine atoms; from the viewpoint of the ease of synthesis of the fluorine-containing compound of this embodiment, it is more preferably Y 1 [[ID=4成]]~Y 4 It consists entirely of fluorine atoms. Q is a perfluoroalkyl group with 1 to 8 carbon atoms, which can contain ether-containing oxygen atoms. From the viewpoint of ease of synthesis of fluorinated compounds, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 7, more preferably 1 to 6. When containing ether-containing oxygen atoms, the number of oxygen atoms is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1. Q can be linear or branched, but linear is preferred. From the viewpoint of ease of synthesis of fluorinated compounds, Q is preferably a perfluoroalkyl group, especially preferably with 1 carbon atom, i.e., a difluoromethylene group. Specific examples of the compounds shown in formula (1) can be listed: CF 2 = CFO(CF) 2) 2(C=O)CH 3. CF 2 = CFO(CF) 2) 3(C=O)CH 3 (hereinafter also referred to as CSM-1), CF 2 = CFO(CF) 2) 4(C=O)CH 3. CF 2 = CFO(CF) 2) 3O(CF 2) 2(C=O)CH 3. CF 2=CFOCF 2C(CF 3)FO(CF 2) 2(C=O)CH 3. CF 2=CFOCF 2C(CF 3)FO(CF 2) 3(C=O)CH 3. From the perspective of ease of synthesis, etc., CSM-1 is the most suitable among these. [Method for Manufacturing Fluorine-Containing Compounds] The fluorine-containing compounds of this embodiment can be obtained, for example, by reacting a perfluorovinyloxy polyether carboxylic acid or a derivative thereof with a Grignard reagent or an organolithium reagent to generate a ketone. Examples of carboxylic acid derivatives include esters and carboxylic acid halides. For example, when using a Grignard reagent (organomagnesium halide: general formula RMgX), the following synthetic method can be applied: replacing the substituent (terminal group) of the perfluorovinyloxy polyether carboxylic acid or a derivative thereof bonded to the carbonyl group with the organic group R of the Grignard reagent. Specifically, the method described in the examples can be used for synthesis, and commercially available products are also available. [Fluoropolymers] The fluoropolymers of this embodiment (hereinafter also referred to as "fluoropolymers of this embodiment") comprise: structural units (A) derived from tetrafluoroethylene (TFE); structural units (B) derived from perfluoroalkyl vinyl ethers (PAVE); and structural units (C) derived from the aforementioned fluorine-containing compounds. By introducing the structural units (C) derived from the aforementioned fluorine-containing compounds into FFKM, a crosslinked product with excellent short-term and long-term heat resistance can be obtained from the fluoropolymers of this embodiment. The unit of structural unit (A) is TFE. The monomer serving as structural unit (B) is PAVE. From the viewpoint of good polymerization reactivity or rubber properties, the number of carbon atoms in the perfluoroalkyl group of PAVE is preferably 1 to 10, more preferably 1 to 8, even more preferably 1 to 6, and still more preferably 1 to 5, and especially preferably 1 to 3. The perfluoroalkyl group can be linear or branched. Specific examples of PAVE include perfluoromethyl vinyl ether (PMVE), perfluoroethyl vinyl ether (PEVE), and perfluoropropyl vinyl ether (PPVE). PAVE can be used alone or in combination with two or more types. From the perspective of polymerization reactivity, PMVE and PEVE are preferred, with PMVE being the most suitable. The monomer serving as structural unit (C) is a fluorinated compound of this embodiment. The fluorinated compound of this embodiment may be a single compound or two or more compounds may be used together. From the viewpoint of polymerization reactivity, CSM-1 is preferred among them. From the viewpoint of the good heat resistance and rubber properties of the crosslinked product, the fluorinated copolymer of this embodiment is preferably composed of the following: of the total 100% by mass of structural units (A) to (C), structural unit (A) preferably comprises 29.9 to 80% by mass, structural unit (B) preferably comprises 19.9 to 70% by mass, and structural unit (C) preferably comprises 0.1 to 20% by mass. The content of structural unit (A) in the total 100% by mass of structural units (A) to (C) is preferably 29.9 to 80% by mass, more preferably 38.8 to 75% by mass, and even more preferably 45.5 to 70% by mass. The content of structural unit (B) in the total 100% by mass of structural units (A) to (C) is preferably 19.9 to 70% by mass, more preferably 24.8 to 60% by mass, and even more preferably 29.5 to 50% by mass. The content of structural unit (C) in the total 100% mass of structural units (A) to (C) is preferably 0.1 to 20% by mass, more preferably 0.2 to 15% by mass, and even more preferably 0.5 to 10% by mass. In addition to structural units (A) to (C), the fluorinated copolymer of this embodiment may also have structural units mainly composed of other monomers. From the viewpoint of the heat resistance of the crosslinked product of the fluorinated copolymer of this embodiment, relative to the total mass of 100% of the total monomer structural units of the fluorinated copolymer of this embodiment, the total mass of other monomer structural units should preferably be 0-20% by mass, more preferably 0-15% by mass, and even more preferably 0-10% by mass. It is best if it does not contain other monomers. Other monomers that serve as structural units other than structural units (A) to (C) include, for example, difluoroethylene, trifluorochloroethylene, hexafluoropropylene, fluorinated monomers with two polymerizable unsaturated groups (hereinafter referred to as "DVM"), 2,3,3,3-tetrafluoro-1-propene, hydrocarbon monomers, etc. Other monomers may be a single type or two or more types may be used together. From the viewpoint of the heat resistance of the crosslinked fluorinated copolymer of this embodiment, DVM is preferably a compound as shown in formula (3) below. By using DVM, which has two polymerizable unsaturated groups as monomers, a branched fluorinated copolymer can be obtained. (CR) 21 R 22 =CR 23 ) 2R 24 (3) In equation (3), R 21 R 22 and R 23Each can be independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. Multiple Rs 21 R 22 and R 23 They can be the same or different; they should ideally be the same. From the perspective of polymerization reactivity, R 21 R 22 and R 23 It is preferable to have hydrogen atoms or fluorine atoms, with all hydrogen atoms or all fluorine atoms being more suitable; from the perspective of heat resistance, it is even more preferable to have all fluorine atoms. R 24 It is a perfluoroalkyl group with 1 to 10 carbon atoms, which may contain ether-like oxygen atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, and even more preferably 1 to 4. When containing ether-like oxygen atoms, the number of oxygen atoms is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1. R 24 It can be any of the following: linear, branched, or cyclic. It is preferable to be linear or branched, with linear being more suitable. Specific examples of DVM can be listed: CF 2 = CFO(CF) 2) 2OCF=CF 2. CF 2 = CFO(CF) 2) 3OCF=CF 2. CF 2 = CFO(CF) 2) 4OCF=CF 2. CF 2 = CFO(CF) 2) 6OCF=CF 2. CF 2 = CFO(CF) 2) 8OCF=CF 2. CF 2 = CFO(CF) 2) 2OCF(CF 3) CF 2OCF=CF 2、CF 2=CFO(CF 2) 2O(CF(CF 3)CF 2O) 2CF=CF 2、CF 2=CFOCF 2O(CF 2CF 2O) 2CF=CF 2、CF 2=CFO(CF 2O) 3(CF(CF 3)CF 2O) 2CF=CF 2、CF 2=CFOCF 2CF(CF 3)O(CF 2) 2OCF(CF 3)CF 2OCF=CF 2、CF 2=CFOCF 2CF 2O(CF 2O) 2CF 2CF 2OCF=CF 2、CF 2=CFO(CF 2) 2CF=CF 2、CH 2=CH(CF 2) 2CH=CH 2、CH 2=CH(CF 2) 4CH=CH 2、CH 2=CH(CF 2) 6CH=CH Class 2. Among these, CF is particularly suitable. 2 = CFO(CF) 2) 3OCF=CF 2. CF 2 = CFO(CF) 2) 4OCF=CF 2 or CH 2=CH(CF 2) 6CH=CH 2. Examples of hydrocarbon monomers include olefins such as ethylene, propylene, isobutylene, and 1-butene. [Manufacturing Method of Fluorinated Copolymers] The fluorinated copolymers of this embodiment can be obtained, for example, by copolymerizing monomers as structural units using emulsion polymerization, solution polymerization, suspension polymerization, etc., in the presence of a free radical polymerization initiator, but the manufacturing method is not particularly limited. Free radical polymerization initiators can be those known in the manufacture of fluorinated copolymers, selected appropriately depending on the polymerization method. For emulsion polymerization in an aqueous medium such as water, water-soluble free radical polymerization initiators are preferable, such as: persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate; disuccinate peroxide; azobisisobutylamidine dihydrochloride; tributyl hydroperoxide; peroxydicarbonates, etc., among which persulfates are preferable, with ammonium persulfate being more suitable. Alternatively, a redox polymerization initiator can be formed by combining persulfate or hydrogen peroxide with reducing agents such as sodium bisulfite or sodium thiosulfate, or further combined with a small amount of metals or metal compounds such as iron, ferrous salts, or silver sulfate. As a free radical polymerization initiator in solution polymerization using solvents such as 1H-perfluorohexane, organic peroxides such as bis(pentafluoropropionic acid peroxide), trimethylacetyl tributyl peroxide, and diisopropyl peroxide dicarbonate can be used. The free radical polymerization initiator can be added in batches or sequentially. The amount of free radical polymerization initiator used relative to 100 parts by mass of the total monomers supplied for the polymerization reaction should preferably be 0.0001 to 3 parts by mass, more preferably 0.001 to 2 parts by mass, and even more preferably 0.01 to 1 part by mass. In the reaction system, chain transfer agents can be added to adjust the moldability or mechanical properties of the fluoropolymer. Examples of chain transfer agents include: saturated hydrocarbon compounds such as hexane and cyclohexane; alkyl aromatic compounds such as xylene and ethylbenzene; aliphatic alcohols such as methanol and isopropanol; carbonyl compounds such as acetic acid, methyl acetate, acetone, dimethyl carbonate, dimethylacetamide, N-methylsuccinimide, and tetramethylurea; and nitrile compounds such as acetonitrile. From the viewpoint of chain transfer performance and the heat resistance of the molded product, ketones are particularly suitable among these. A pH buffer may also be added to the reaction system. Examples of pH buffers include disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, sodium carbonate, and their hydrates. Examples of emulsifiers used in emulsion polymerization include: hydrocarbon-based emulsifiers such as sodium lauryl sulfate and sodium dodecylbenzenesulfonate; and ammonium perfluorooctanoate, sodium perfluorooctanoate, ammonium perfluorohexanoate, and CF32O4 emulsifiers. 3(CF 2) 2O(CF(CF 3) CF 2O) 2CF(CF 3) COONH 4. CF 3(CF 2) 2OCF(CF 3) CF 2OCF(CF 3) COONH 4. CF 3(CF 2) 2OCF 2CF 2OCF 2COONH 4. CF 3(CF 2) 2O(CF 2CF 2O) 2CF 2COONH 4. CF 3(CF 2) 3OCF 2CF 2OCF 2COONH 4. CF 3(CF 2) 3O(CF 2CF 20) 2CF 2COONH 4. CF 3(CF 2) 2OCF 2CF 2OCF 2COONa、CF 3(CF 2) 2O(CF 2CF 20) 2CF 2COONa、CF 3(CF 2) 3OCF 2CF 2OCF 2COONa、CF 3(CF 2) 3O(CF 2CF 20) 2CF 2COONa、CF 3CF 2OCF 2CF 2OCF 2COONH 4. CF 3CF 2O(CF 2CF 20) 2CF 2COONH 4. CF 3CF 2OCF 2CF 2OCF 2COONa、CF 3CF 2O(CF 2CF 20) 2CF 2COONa、CF 3OCF 2CF 2CF 2OCF 2COONH 4. CF 3OCF 2CF 2CF 2OCF(CF 3) COONH 4. CF 3OCF 2CF 2CF 2OCF 2COONa、CF 3OCF 2CF 2CF 2OCF(CF 3) COONa, CF 3O(CF 20) 3CF 2COONH 4. CF 3O(CF 20) 3CF 2COONa、CF 3OCF(CF 3)CF 2OCF(CF 3) COONH 4. CF 3OCF(CF 3)CF 2OCF(CF 3) COONa, CF 3O(CF 2CF 2O) 2CF 2COONH 4. CF 3O(CF 2CF 2O) 2CF Fluorinated emulsifiers such as 2COONa. Emulsifiers can be a single type or a combination of two or more. Among these, ammonium perfluorooctanoate (PFOA) and CF2 are particularly suitable. 3(CF 2) 3OCF 2CF 2OCF 2COONH 4. CF 3(CF 2) 2OCF 2CF 2OCF 2COONH 4. CF 3CF 2OCF 2CF 2OCF 2COONH 4. CF 3OCF 2CF 2CF 2OCF 2COONH 4. Emulsifiers can be added in batches or gradually. The amount of emulsifier used relative to 100 parts by weight of the aqueous medium should preferably be 0.01 to 20 parts by weight, more preferably 0.05 to 15 parts by weight, and even more preferably 0.1 to 10 parts by weight. The pressure and temperature conditions of the polymerization reaction can be appropriately set according to the monomer composition or the decomposition temperature of the free radical polymerization initiator. Generally, the pressure should be 0.1~20 MPaG, preferably 0.3~10 MPaG, and even more preferably 0.3~5 MPaG. The temperature should be 0~100℃, preferably 10~90℃, and even more preferably 20~85℃. In emulsion polymerization, fluorinated copolymers can be obtained in latex form and purified by agglomeration using known methods such as adding metal salts, inorganic acids like hydrochloric acid or sulfuric acid, mechanical shearing, or freeze-thaw cycles. In solution polymerization, purification can be achieved by washing with an aqueous medium such as methanol. [Fluoropolymer Composition] The fluoropolymer composition of this embodiment (hereinafter also referred to as "the composition of this embodiment") comprises: the fluoropolymer of this embodiment described above; and a compound (D) having two or more structures (d) as shown in formula (2) below. The compound (D) acts as a crosslinking agent for the fluoropolymer of this embodiment, and the composition of this embodiment reacts to obtain a crosslinked fluoropolymer. By using compound (D) as a crosslinking agent, the fluoropolymer of this embodiment can form a crosslinked structure containing an indole ring. [Chemical Formula 4] In equation (2), -a 1 This indicates a single bond, bonded to a hydrogen atom, a methyl group, or an aromatic ring that may have substituents. From the viewpoint of the heat resistance of the crosslinked compound, the aromatic ring should contain a benzene ring or a naphthalene ring, preferably a monocyclic or condensed ring with 6 to 12 carbon atoms that may contain heteroatoms. The substituents on the aromatic ring should preferably be alkyl groups with 1 to 6 carbon atoms, more preferably 1 to 5, and even more preferably 1 to 4. The alkyl group can be straight-chain or branched. -b 1 ~-b 5 Each represents a single key, and -b 1 and -b 5 At least one of them is bonded to a hydrogen atom in order to form an indole ring during the crosslinking reaction. -b 1 or -b 5 It can also be bound to -a 1 The aryl group bonds together to form a nitrogen-containing condensation ring. From the viewpoint of ease of synthesis and heat resistance of the fluorinated copolymer crosslinked product of this embodiment, compound (D) preferably has one or more of the following structures: a structure in which the benzene ring A of one structure (d) is linked to the benzene ring A of another structure (d) by a single bond. Furthermore, from the perspective of cross-linking reactivity, structure (d) possesses -a 1 The hydrazine skeleton is bonded to a hydrogen atom, and compound (D) should preferably consist of two structures (d) with this hydrazine skeleton and -b 1 ~-b 5The compound (D) is preferably a compound in which two hydrazinobenzene rings A are bonded to each other by single bonds. The bond positions of the single bonds connecting the two benzene rings A can be -b. 1 ~-b 5 Any one of the following. If it is the structure described above, the resulting cross-linked structure has high thermal stability, and a cross-linked product with better heat resistance can be obtained. From the viewpoint of the thermal stability of the resulting cross-linked structure and the availability of raw materials, it is preferable that the hydrazine group is located at the para (p-) position relative to the single bond connecting the benzene rings A to each other in the compound, such as the compounds shown in the following formulas (CLA-1 to CLA-3), especially CLA-1. [Chemical Formula 5] CLA-1 can be obtained, for example, from 4,4'-diiodobiphenyl by substituting the iodine atom with a hydrazine group using a known method, in the form of a hydrochloride salt. CLA-1 can also be obtained commercially available. Furthermore, CLA-2 can be synthesized, for example, by the method described in the examples, and CLA-3 can also be synthesized by the same method. Compound (D) is also preferably composed of two structures (d) separated by one or more bonds selected from the group consisting of oxygen atoms, sulfur atoms, sulfonyl groups, perfluoroalkyl groups, perfluoropolyether groups, and divalent aromatic rings that may have substituents. Other specific examples of compound (D) are shown below. [Chemical Formula 6] [Chemical Formula 7] In the composition of this embodiment, from the viewpoint of sufficient heat resistance and rubber properties of the crosslinked fluorinated copolymer, the content of compound (D) is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 8 parts by mass, and even more preferably 0.3 to 5 parts by mass, relative to 100 parts by mass of the fluorinated copolymer of this embodiment. Compound (D) can be used alone or in combination with two or more compounds. Without impairing the effects of the invention, the composition of this embodiment may include other additives besides the fluorinated copolymer and compound (D) of this embodiment. Other additives may include, for example, crosslinking aids, fillers, reinforcing materials, scorch inhibitors, release agents, acid scavengers, crown ethers, and pigments. Each additive may be used individually or in combination of two or more of these additives. From the perspective of utilizing compound (D) to promote the crosslinking reaction of fluorinated copolymers, the crosslinking aid should preferably be an acid catalyst. We believe that if the composition of this embodiment contains an acid catalyst, it can promote the interisomerization of aryl hydrazones generated within the system to alkylenehydrazines, and also accelerate the formation of indole rings. Examples of acid catalysts include protic acids and Lewis acids, specifically: aliphatic carboxylic acids such as acetic acid, trifluoroacetic acid, lauric acid, and stearic acid (including fluorinated fatty acids), aromatic carboxylic acids such as benzoic acid, sulfuric acid, zinc chloride, boron trifluoride diethyl ether complexes, polyphosphates, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. From the perspective of crosslinking reactivity, aliphatic carboxylic acids, aromatic carboxylic acids, polyphosphates, and p-toluenesulfonic acid are particularly suitable among these. Crosslinking aids can be used as additives to the composition, or they can be pre-quaternary ammonium salts of compound (D) using known methods. Examples of relative anions of quaternary ammonium cations include carboxylic acid anions and sulfonic acid anions. From the perspective of crosslinking reactivity, it is advisable to use the conjugate anion of acids in water with a dissociation constant of 4 or less. Examples of fillers and reinforcing materials include: carbon materials such as carbon black, fullerene, carbon nanotubes, fluorinated graphite, and fluorinated carbon; fluoropolymers such as polytetrafluoroethylene, tetrafluoroethylene-fluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and ethylene-tetrafluoroethylene copolymer; barium sulfate; calcium metasilicate; metal oxides such as silicon dioxide, titanium dioxide, yttrium oxide, and aluminum oxide; metal carbides such as silicon carbide and aluminum carbide; metal nitrides such as silicon nitride and aluminum nitride; amide fillers such as polyamide, polyamide-amide, and polyether-amide; polyaryl ether ketones such as polyetheretherketone (PEEK), polyetherketone (PEK), and polyetherketoneketone (PEKK); polyesters; polyether sulfide; polyphenylene sulfide; clay; and talc. Examples of anti-scorching agents include phenolic hydroxyl compounds such as bisphenol A, hydroquinone derivatives such as hydroquinone, and α-methylstyrene dimers such as 2,4-diphenyl-4-methyl-1-pentene. Examples of mold release agents include sodium stearate. Examples of acid absorbers include aliphatic polyesters; aliphatic metal salts; and oxides of divalent metals such as calcium oxide, zinc oxide, and lead oxide. Examples of crown ethers include 18-crown-6. Examples of pigments include inorganic pigments such as zinc oxide, titanium dioxide, and carbon black; and organic pigments with pyrrolopyrrole dione, isoindolineone, quinacrine, anthraquinone, polyaryl, and amide skeletons. From the perspective of improving the heat resistance and plasma resistance of quenching energy against free radicals or redox reactive species, organic pigments are more suitable among these. When the composition of this embodiment contains other additives, the total content of other additives should be greater than 0 parts by mass and less than 30 parts by mass relative to 100 parts by mass of the fluorinated copolymer of this embodiment, more preferably less than 25 parts by mass, and even more preferably less than 20 parts by mass. [Crosslinked Composites] In crosslinking using heat, for example, fluorinated copolymers can be crosslinked by heating at 80-300°C for 0.1-24 hours. The temperature can also be changed to further heat the already heated fluorinated copolymer. That is, secondary crosslinking can also be performed after primary crosslinking. From the viewpoint of ensuring adequate crosslinking reaction, it is preferable, for example, to perform primary crosslinking at 80-200°C for 0.1-6 hours, followed by secondary crosslinking at 200-300°C for 1-24 hours. During primary crosslinking, the mixture can also be appropriately shaped. Shaping methods include, for example, compression molding, injection molding, extrusion molding, calendering, and impregnation or coating onto a substrate after dissolving in a solvent. As described above, the crosslinked product obtained by reacting the components of this embodiment has a crosslinked structure containing an indole ring. Compared to crosslinked products without a ring structure, crosslinked products with a ring structure exhibit superior heat resistance. Furthermore, when the ring structure contained in the crosslinked structure is an indole ring, superior heat resistance can be obtained compared to cases where the ring structure is a benzene ring, acetazole ring, or trifurcation ring. In particular, both short-term and long-term heat resistance are excellent. The crosslinked fluorinated copolymer of this embodiment is suitable as a sealing or cushioning material for O-rings, V-rings, gaskets, oil seals, pads, partitions, sheets, etc. Furthermore, it is also suitable for various applications including: heat-resistant and chemical-resistant sealants, heat-resistant and oil-resistant sealants, wire sheathing materials, sealants for semiconductor devices, corrosion-resistant rubber coatings, sealants for urea-based greases, rubber coatings, adhesive rubber, hoses, fittings, calendered sheets (rolls), sponges, rubber rolls, components for oil excavation, heat sinks, solution crosslinkers, rubber sponges, bearing seals, linings, automotive insulating sheets, electronic machinery insulating sheets, watch rubber strips, endoscope gaskets, telescopic hoses, water heater gaskets / valve, fender materials, fibers, non-woven fabrics (protective clothing, etc.), base plate sealants, rubber gloves, stators of single-shaft eccentric screw pumps, parts for urea SCR (selective catalytic reduction) systems, vibration dampers, shock absorbers, sealants, additives for other materials, and toy applications. The present invention will be specifically described below with reference to the embodiments. However, the present invention is not limited to the following embodiments and various modifications can be made without departing from the spirit of the present invention. [Compounds Used] The following is a description of the abbreviations of the various compounds used. • PX1: A TFE / PMVE copolymer with iodine atoms at the ends; derived from the structural units of TFE and PMVE, with a molar ratio of 66 / 34 and an iodine atom content of 0.15% by mass (manufacturing method refers to Example 1 of International Publication No. 2018 / 225586). • PX2: A TFE / PMVE / CF copolymer with iodine atoms at the ends. 2 = CFO(CF) 2) 3OCF=CF 2. Copolymers; derived from TFE, PMVE and CF 2 = CFO(CF) 2) 3OCF=CF The molar ratio of the structural unit 2 is 65.9 / 34.0 / 0.1, and the iodine atom content is 0.20% by mass (the manufacturing method refers to copolymer 4 of the embodiment in International Publication No. 2020 / 184427 (except that the aggregation in potassium aluminum sulfate is changed to aggregation in nitric acid)). • PX3: TFE / PMVE / CF with iodine atoms at the ends. 2 = CFO(CF) 2) 3OCF=CF 2. Copolymers; derived from TFE, PMVE and CF 2 = CFO(CF) 2) 3OCF=CF The molar ratio of the structural unit 2 is 71.40 / 28.43 / 0.17, and the iodine atom content is 0.10% by mass (the manufacturing method refers to copolymer 1 of Example in International Publication No. 2020 / 184427). • P25B: 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; "PERHEXA (registered trademark) 25B", manufactured by Nippon Oil Company Limited. • BOAP: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, manufactured by Tokyo Chemical Industry Co., Ltd. • TAIC (registered trademark): triallyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd. • C6-DV: 1,6-divinylperfluorohexane, manufactured by Tosoh Finechem Corporation. • FB-BMI: bismaleimine compound as shown in the following formula (refer to Patent Document 1) [Chemical Formula 8] • 2E4MZ: 2-Ethyl-4-methylimidazole, manufactured by Tokyo Chemical Industry Co., Ltd. [Analytical Methods] <Nuclear Magnetic Resonance (NMR) Measurement> The synthesized compounds were measured using a nuclear magnetic resonance apparatus ("JNM-AL300", manufactured by Nippon Electron Ltd.; hereinafter the same). 1 H-NMR and 19 Structural analysis was performed using F-NMR. <Mass Analysis (MS)> Furthermore, the molecular weight was determined using a gas chromatography mass analyzer ("GCMS-QP2010 Ultra", manufactured by Shimadzu Corporation; chemical ionization method (CI)). <Content of monomer structural units in fluorinated copolymers> obtained from NMR measurements. 1 H-NMR and 19 The content (mass ratio and molar ratio) of monomer structural units in fluorinated copolymers was calculated from the F-NMR results. A 1H-perfluorohexane solution of the fluorinated copolymer and 1,4-bis(trifluoromethyl)benzene (standard) was used as the test sample. The content of PMVE structural units in the fluorinated copolymer was calculated by converting the integral ratio of the peak of the trifluoromethyl fluorine atom belonging to PMVE to the peak of the trifluoromethyl fluorine atom belonging to 1,4-bis(trifluoromethyl)benzene. The content of CSM-1 structural units in the fluorinated copolymer was calculated by converting the integral ratio of the peak of the methyl hydrogen atom belonging to the CSM-1 unit to the peak of the aromatic ring hydrogen atom belonging to 1,4-bis(trifluoromethyl)benzene. The content of 8CNVE structural units in fluorinated copolymers is calculated by converting the peak of the fluorine atom belonging to the difluoromethylene group adjacent to the nitrile group in 8CNVE with the peak of the fluorine atom belonging to the trifluoromethyl group in 1,4-bis(trifluoromethyl)benzene. The content of TFE in fluorinated copolymers is calculated by taking the remaining portion of the content of PMVE structural units and CSM-1 structural units. [Synthesis of Monomers] (Synthesis Example 1) Synthesis of CSM-1 [Chemical Formula 9] 107 g (350 mmol) of the starting compound (1) and 750 mL of diethyl ether were fed into a 2 L four-necked flask, and the reaction solution was cooled to below -65 °C using a dry ice / acetone bath. The reaction solution was kept below -60 °C, and 436 mL (approximately 3 mol / L) of a 35% magnesium methyl bromide diethyl ether solution was added dropwise over 2 hours, allowing the reaction to proceed for 4 hours. The reaction solution was kept below -38 °C, and a mixture of 150 mL of 36% hydrochloric acid and 150 mL of tetrahydrofuran, cooled to 5 °C, was added dropwise over 2.5 hours. After the product was brought to room temperature, 170 mL of deionized water was added for separation, and the organic phase was recovered. 170 mL of diethyl ether was added to the aqueous phase for extraction, and the extract was combined with the previous organic phase. The resulting organic phase was washed with 170 mL of a 5% sodium bicarbonate aqueous solution, followed by washing with 170 mL of saturated brine, and then dried with anhydrous sodium sulfate. After removing the residue by vacuum filtration, the product was concentrated under reduced pressure (27 kPa) at 35°C using a distiller. The concentrate was transferred to a 200 mL flask, fitted with a Vigerreux column, and purified by vacuum distillation to obtain 68 g of CSM-1 (68% yield). The data for CSM-1 identification are as follows. Furthermore, the symbol added to the fluorine atom (F) corresponds to the symbol in formula (I) above. 1 H-NMR (CDCl) 3): δ [ppm] 2.46 (s, 3H) 19 F-NMR (CDCl) 3): δ[ppm]-85.3(m, 2F, F-3),-113.6(dd, 1F, J=65.6, 82.4Hz, F-1b),-121.4(t, 2F, J=9.16Hz, F-5),-121.8(ddt, 1F, J=6.10, 83.9, 112.9, F-1a),-126.5(s, 2F, F-4),-135.4(ddt, 1F, J=6.10, 65.6, 112.9, F-2) MS(CI) m / z: 291(M+H + ) [Synthesis of Crosslinking Agents] (Synthesis Example 2-1) Synthesis of CLA-1 [Chemical Formula 10] Under nitrogen atmosphere, 25.0 g (1.6 mmol) of 4,4'-diiodobiphenyl, 170 mL of dimethyl sulfoxide (DMSO), and tributyl hydrazide (BocNHNH) were fed into a 1 L four-necked flask. 2) 19.5 g (148 mmol), copper iodide (I) 1.17 g (6.14 mmol), and cesium carbonate 60.2 g (185 mmol) were reacted in an oil bath at a liquid temperature of 54 °C for 21 hours. The reaction solution was then brought to room temperature, 600 mL of deionized water was added, and the mixture was stirred for 30 minutes. The precipitated solid was recovered by vacuum filtration and dried under reduced pressure to obtain a crude solid. The crude solid and the filtrate were purified by heating under reflux and drying under reduced pressure to obtain 12.4 g (yield 49%) of compound (2) as a pale yellow solid. The data for the identification of compound (2) are as follows. 1 H-NMR (DMSO-d) 6): δ[ppm] 7.58(d, 4H, J=8.54Hz, Ar-H), 7.54(d, 4H, J=8.54Hz, Ar-H), 5.09(s, 4H, NH 2), 1.47(s, 18H, N-Boc) [Chemical Formula 11] Next, under nitrogen atmosphere, 8.87 g (21.4 mmol) of compound (11) and 107 mL of dichloromethane were fed into a 500 mL four-necked flask. The mixture was cooled in a dry ice bath, and under this condition, 93 mL of 1,4-dimethylhydrochloride solution (approximately 4 mol / L) was added dropwise. After returning to room temperature, the mixture was allowed to react for 14 hours. The precipitated solid was recovered by vacuum filtration, washed with diethyl ether, and dried under reduced pressure to obtain 5.76 g of CLA-1 hydrochloride (94% yield). Under nitrogen atmosphere, 5.00 g (17.35 mmol) of CLA-1 hydrochloride, 30 mL of dichloromethane, and 20 mL of 10% sodium hydroxide aqueous solution were fed into a 100 mL four-necked flask. The mixture was stirred at room temperature for 1 hour. The precipitated solid was recovered by vacuum filtration, washed with deion-exchanged water, and dried under reduced pressure to obtain 3.36 g of CLA-1 (90% yield). The data for the identification of CLA-1 hydrochloride and CLA-1 are as follows. Furthermore, the symbol added to the hydrogen atom (H) corresponds to the symbol in formula (II-1) above. <CLA-1 hydrochloride> 1 H-NMR (DMSO-d) 6): δ[ppm] 10.3 (s, 6H, -NH) 3Cl), 8.35(s, 2H, -NH-), 7.57(d, 4H, J=8.54Hz, H-1), 7.05(d, 4H, J=8.54Hz, H-2) <CLA-1> 1 H-NMR (DMSO-d) 6): δ[ppm] 7.31(d, 4H, J=8.54Hz, Ar-H), 6.79(d, 4H, J=8.54Hz, Ar-H), 6.64(s, 2H), 3.93(s, 4H) (Synthetic Example 2-2) Synthesis of CLA-2 (hydrochloride) [Chemical Formula 12] 14.1 mL of 20% hydrochloric acid was added to a 100 mL four-necked flask and cooled in a dry ice bath. While stirring, 2.00 g (6.25 mmol) of compound (12) (manufactured by Tokyo Chemical Industry Co., Ltd.) was added. While maintaining the reaction solution below 2.5 °C, an aqueous solution containing 0.89 g (12.9 mmol) of sodium nitrite dissolved in 20 mL of deionized water was added dropwise over 2 hours, with further stirring for 30 minutes. Next, a mixture of 6.85 g (30.4 mmol) of stannous(II) dihydrate and 8.7 mL of 36% hydrochloric acid was added dropwise over 2 hours, with further stirring for 45 minutes. The precipitated solid was recovered by vacuum filtration and dried under reduced pressure at 35 °C to obtain 0.485 g of crude product. 20 mL of chloroform and 11 mL of 0.5 mol / L sodium hydroxide aqueous solution were added to the crude product, and the organic phase was fractionally distilled off. The aqueous phase was re-extracted by adding 20 mL of chloroform and combined with the previous organic phase. Anhydrous sodium sulfate was added to the resulting organic phase and the mixture was dried. After removing the residue by vacuum filtration, the mixture was concentrated under reduced pressure at 30°C using a distiller. The final concentration was achieved using a silicone column chromatography system ("Silicone 60 (spherical) NH..."). 2” (Prepared by Kanto Chemical Co., Ltd., 16g; mobile phase: chloroform; hereinafter the same) The concentrate was separated and purified to obtain CLA-2 97.6mg. CLA-2 97.6mg, diethyl ether 4mL and about 1mol / L diethyl ether hydrogen chloride solution 1mL were added to a 50mL round-bottom flask and stirred. The precipitated solid was recovered by vacuum filtration and dried under reduced pressure to obtain CLA-2 hydrochloride 74.7mg (yield 3%). The data for the identification of CLA-2 and CLA-2 hydrochloride are as follows. Furthermore, the symbol added to the hydrogen atom (H) corresponds to the symbol in formula (II-2) above. <CLA-2> 1 H-NMR (CDCl) 3): δ[ppm] 7.18(d, 2H, J=2.56Hz, H-3), 7.12(d, 2H, J=7.68Hz, H-1), 6.94(dd, 2H, J=2.56, 8.54Hz, H-2), 5.40(brs, 2H, -NHNH 2), 3.66(brs, 4H, -NHNH 2) 19 F-NMR (CDCl) 3): δ[ppm]-59.0(s, 6F, -CF) 3) <CLA-2 hydrochloride> 1 H-NMR (DMSO-d) 6): δ[ppm] 10.39(brs, 6H,-NHNH 3Cl), 8.81(brs, 2H, -NHNH 3Cl), 7.39(d, 2H, J=2.56Hz, H-3), 7.3~7.2(m, 4H, H-1 and H-2) 19 F-NMR (DMSO-d) 6): δ[ppm]-56.7(s, 6F,-CF) 3) (Synthetic Example 2-3) Synthesis of CLA-3 (hydrochloride) [Chemical Formula 13] 6.8 mL of 20% hydrochloric acid was added to a 100 mL four-necked flask and cooled in a dry ice bath. While stirring, 1.00 g (2.99 mmol) of compound (13) (manufactured by Tokyo Chemical Industry Co., Ltd.) was added. While maintaining the reaction solution below 2.0 °C, an aqueous solution containing 0.43 g (6.16 mmol) of sodium nitrite dissolved in 9.5 mL of deionized water was added dropwise over 2 hours, with further stirring for 1 hour. Next, a mixture of 3.28 g (14.5 mmol) of stannous(II) dihydrate and 4.2 mL of 36% hydrochloric acid was added dropwise over 2 hours, with further stirring for 30 minutes. The precipitated solid was recovered by vacuum filtration and dried under reduced pressure at 35 °C to obtain 0.269 g of crude product. 10 mL of chloroform and 6 mL of 0.5 mol / L sodium hydroxide aqueous solution were added to the crude product, and the organic phase was fractionally distilled off. The aqueous phase was re-extracted with 15 mL of chloroform and combined with the previous organic phase. Anhydrous sodium sulfate was added to the resulting organic phase and the mixture was dried. After removing the residue by vacuum filtration, the mixture was concentrated under reduced pressure at 30 °C using a distiller's apparatus. The concentrate was purified by silica gel column chromatography to obtain 22.8 mg of CLA-3. 22.8 mg of CLA-3, 1 mL of diethyl ether, and 0.25 mL of approximately 1 mol / L diethyl ether hydrogen chloride solution were added to a 10 mL round-bottom flask and stirred. The precipitated solid was recovered by vacuum filtration and dried under reduced pressure to obtain 14.9 mg of CLA-3 hydrochloride as a pale yellow solid (yield 1%). <CLA-3> 1 H-NMR (CDCl) 3): δ[ppm] 7.2~7.3(m, 4H, H-1), 6.78(d, 4H, J=9.39Hz, H-2), 5.31(brs, 2H,-NHNH 2), 3.60(brs, 4H,-NHNH 2) 19 F-NMR (CDCl) 3): δ[ppm]-64.8(s, 6F,-CF) 3) <CLA-3 hydrochloride> 1 H-NMR (DMSO-d) 6): δ[ppm] 10.34(brs, 6H,-NHNH 3Cl), 8.65(brs, 2H, -NHNH 3Cl), 7.23(d, 4H, J=8.54Hz, H-1), 7.03(d, 4H, J=8.54Hz, H-2) 19 F-NMR (DMSO-d) 6): δ[ppm]-62.9(s, 6F,-CF) 3) [Preparation of Fluorinated Copolymers] (Synthesis Example 3-1) Emulsion Polymerization (1) After degassing a 200 mL stainless steel autoclave equipped with a stirrer, feed in 82 g of pre-degassed de-pressurized ion-exchange water, 0.023 g (0.065 mmol) of disodium hydrogen phosphate dodecahydrate, and 30% CF32-F4 ... 3CF 2OCF 2CF 2OCF 2COONH 10.2 g (8.3 mmol) of aqueous solution, 0.062 g (0.27 mmol) of ammonium persulfate, and 0.082 g (0.27 mmol) of CSM-1 were prepared, and the gas phase was nitrogen-purged. While stirring the reaction mixture at 300 rpm, 1.4 g (14 mmol) of TFE and 6.5 g (39 mmol) of PMVE were added to an autoclave, and the temperature was raised to 80°C. The internal pressure of the autoclave was 0.8 MPaG. After stirring at 300 rpm for 4 hours while maintaining the liquid temperature, the internal pressure decreased to 0.6 MPaG. After releasing the residual gas in the gas phase, the autoclave was released to obtain a latex containing a fluorinated copolymer. The latex was frozen and then thawed to allow the fluorinated copolymer to aggregate. The fluorinated copolymer was filtered, washed with deionized water, then washed with methanol, and dried under vacuum at 50°C to obtain 1.9 g of a white fluorinated copolymer (P1). The obtained fluorinated copolymer (P1) contains structural units derived from TFE, PMVE and CSM-1 in the following proportions (mass ratio): 56.7 / 42.3 / 1.0 (molar ratio: 69.0 / 30.6 / 0.4). (Synthesis Example 3-2) Emulsion Polymerization (2) In Synthesis Example 3-1, the amount of ammonium persulfate was set to 0.030 g (0.13 mmol), and the liquid temperature after TFE and PMVE were pressed into the autoclave was maintained at 65°C. Otherwise, polymerization was carried out in the same manner as in Synthesis Example 3-1 to obtain a latex containing a fluorinated copolymer, resulting in 0.68 g of a white fluorinated copolymer (P2). In addition, during the polymerization reaction, the internal pressure of the autoclave was reduced from 0.7 MPaG to 0.6 MPaG. The content (mass ratio) of the structural units derived from TFE, PMVE, and CSM-1 in the obtained fluorinated copolymer (P2) was 52.8 / 40.8 / 6.4 (molar ratio: 68.2 / 29.1 / 2.7). (Synthesis Example 3-3) Solution Polymerization (1) 1.2 g (3.8 mmol) of CSM-1, 0.5 g (1.5 mmol) of bis(pentafluoropropionic acid) peroxide, and 57 g of 1H-perfluorohexane were fed into a 200 mL stainless steel autoclave equipped with a stirrer, followed by two freeze-degassing cycles. While stirring the reaction mixture at 300 rpm, 15 g (0.15 mol) of TFE and 103 g (0.62 mol) of PMVE were added to the autoclave, maintaining the liquid temperature at 28 °C. The internal pressure of the autoclave was 0.7 MPaG. After stirring at 300 rpm for 24 hours while maintaining the liquid temperature, the internal pressure decreased to 0.5 MPaG. After releasing the residual gas in the gas phase, the autoclave was released to obtain a solution containing the fluorinated copolymer. The obtained solution containing the fluorinated copolymer was vacuum dried to obtain a viscous liquid. The liquid was dissolved in 200 mL of 1H-perfluorohexane, and the solution was added to 1 L of methanol and stirred for 30 minutes to form a white solid. The solid and supernatant were separated using a centrifuge. The obtained solid was dried under vacuum at 50 °C to obtain 37.1 g of a white fluorinated copolymer (P3). The content (mass ratio) of the structural units derived from TFE, PMVE, and CSM-1 in the obtained fluorinated copolymer (P3) was 56.1 / 42.8 / 1.1 (molar ratio: 68.5 / 30.5 / 1.0). (Synthesis Examples 3-4) Solution Polymerization (2) In Synthesis Example 3-3, the amount of CSM-1 was set to 12 g (38 mmol), and polymerization was carried out in the same manner as in Synthesis Example 3-3 to obtain a solution containing the fluorinated copolymer, resulting in 3.2 g of a white fluorinated copolymer (P4). Furthermore, during the polymerization reaction, the internal pressure of the autoclave was reduced from 0.7 MPaG to 0.5 MPaG. The content (mass ratio) of the structural units derived from TFE, PMVE, and CSM-1 in the obtained fluorinated copolymer (P4) was 52.3 / 38.5 / 9.2 (molar ratio: 69.3 / 21.7 / 9.0). (Synthetic Examples 3-5) Modification of FFKM using CSM-1 (1) 34 g of PX1, 32 g (0.11 mol) of CSM-1, 0.88 g (2.2 mmol) of lauryl peroxide, and 135 g of 1H-perfluorohexane were fed into a 200 mL stainless steel autoclave equipped with a stirrer, and the mixture was subjected to two freeze-drying processes. The reaction mixture was stirred at 300 rpm while the temperature was raised to 90 °C and stirred at 300 rpm for 4 hours while maintaining the temperature. The autoclave was cooled to room temperature and then released to obtain a solution containing the fluorinated copolymer. The obtained solution containing the fluorinated copolymer was vacuum dried to obtain a white solid. The solid was dissolved in 1 L of 1H-perfluorohexane, and the solution was added to 5 L of methanol and stirred for 5 minutes to produce a white solid. The solid was filtered, washed with methanol, and then dried under vacuum at 50°C to obtain 29g of white fluorinated copolymer (P5) (containing 0.4% CSM-1 by mass). (Synthesis Example 3-6) FFKM Modification using CSM-1 (2) In Synthesis Example 3-5, PX2 was used to replace PX1. Otherwise, a solution containing the fluorinated copolymer was obtained in the same manner as in Synthesis Example 3-5, and 24g of white fluorinated copolymer (P6) (CSM-1 content 0.4% by mass) was obtained. (Synthetic Examples 3-7) Fluorinated copolymers with nitrile groups were degassed in a 2L stainless steel autoclave equipped with a stirrer, and then fed with 30% C by mass. 2F 5O(CF 2) 2OCF 2COONH 4. Aqueous solution 880g, CF 2=CFOCF 2CF(CF 3) OCF 2CF 7.3 g (18.8 mmol) of 2CN (hereinafter referred to as 8CNVE) and 15.9 g of a 5% (w / w) aqueous solution of disodium hydrogen phosphate dodecahydrate were added, and the gas phase was nitrogen-purged. While stirring the reaction mixture at 375 rpm, 137 g (1.37 mol) of TFE and 635 g (3.82 mol) of PMVE were added into an autoclave, and the liquid temperature was raised to 80°C. The internal pressure of the autoclave was 0.90 MPaG. While maintaining the liquid temperature, 28 mL of a 3% (w / w) ammonium persulfate aqueous solution was added to initiate polymerization. At the point where the internal pressure decreased to 0.89 MPaG, 119.3 g of TFE, 3.7 g of 8CNVE, 74 g of PMVE, and 3.7 g of 8CNVE were added sequentially. This operation was repeated for 9 cycles. After this, 119.3 g of TFE was added, and the reaction was allowed to proceed for 375 minutes. At the point where the polymerization rate gradually decreased, a 3% (w / w) ammonium persulfate aqueous solution was added as needed. The total amount of 3% (w / w) ammonium persulfate aqueous solution added after polymerization initiation was 35 mL. The autoclave was cooled to 10°C to obtain a latex containing the fluorinated copolymer. The latex was added to a 5% (w / w) potassium aluminum sulfate aqueous solution to cause the fluorinated copolymer to aggregate. The fluorinated copolymer was filtered, washed with deionized water, and vacuum dried at 50°C to obtain a white fluorinated copolymer (P7). The content (mass ratio) of structural units derived from TFE, PMVE, and 8CNVE in the obtained fluorinated copolymer (P7) was 56.8 / 41.3 / 1.9 (molar ratio: 69.1 / 30.3 / 0.6). [Preparation of Crosslinked Composites] (Example 1) 100 parts by weight of a fluorinated copolymer (P1), 2.5 parts by weight of CLA-1, and 2.5 parts by weight of acetic acid were kneaded using a biaxial kneader ("HAAKE MiniLab3", manufactured by Thermo Fisher Scientific Inc.). Using a mold measuring 100 mm long, 60 mm wide, and 1 mm thick, the kneaded components were subjected to a first crosslinking process using a thermocompression press ("SA-401", manufactured by TESTER SANGYO CO., LTD.) at atmospheric pressure of 1 MPa and 90°C for 3 hours. A second crosslinking process was then performed using an oven ("KDF-75", manufactured by Yamato Scientific Co., Ltd.) at 240°C for 3 hours, resulting in a crosslinked composite containing an indole ring structure. (Examples 2-10) Each crosslinked product was manufactured in the same manner as in Example 1, using the blending composition, primary crosslinking, and secondary crosslinking conditions shown in Table 1 below. In addition, in Example 10, the secondary crosslinking was carried out by heating at 90°C for 2 hours, then raising the temperature to 200°C for 2 hours, heating at 200°C for 4 hours, then raising the temperature to 305°C for another 2 hours, and heating at 305°C for 12 hours. [Evaluation of the heat resistance of the crosslinked products] The heat resistance of test pieces (20 mm long, 4 mm wide, and 1 mm thick) cut from the crosslinked products of the fluorinated copolymers obtained in each example was evaluated using the following two methods. The evaluation results are shown in Table 1. Examples 1-6 are exemplary cases, and Examples 7-10 are comparative examples. <Thermomechanical Analysis (TMA)> Following JIS K 7244-4:1999, a thermomechanical analysis apparatus ("TA7000", manufactured by Hitachi High-Tech Science Co.) was used. The test piece was heated from the initial test temperature of -40°C to 330°C at a rate of 5°C / min, and then held at 330°C for 30 minutes. The presence of fracture was observed, and the storage modulus of elasticity was measured. The test results were evaluated according to the following criteria: (Evaluation Criteria) A: The test piece did not fracture, and no change in the storage modulus of elasticity was observed. No decrease. B: The test piece did not fracture, but the storage modulus of elasticity decreased. C: The test piece fractured. The heat resistance assessment using TMA is considered an indicator of short-term heat resistance. Evaluation A is rated as good, evaluation B as slightly better, and evaluation C as poor. <Suspension Method> A portion of the test piece, measuring 3 mm from one longitudinal end, is suspended through a stainless steel wire (1 mm in diameter) and placed in an oven (KDF-75, manufactured by Yamato Scientific Co., Ltd.). After heating under nitrogen atmosphere according to the conditions shown in Table 1, the test piece is removed and observed for deformation. The test results are evaluated according to the following criteria: (Evaluation Criteria) A: Test piece not deformed. C: Test piece deformed. The heat resistance evaluation using the suspension method is an indicator of long-term heat resistance. Evaluation A is considered good, and evaluation C is considered poor. [Table 1] As shown in Table 1, the evaluation results confirm that the crosslinked products of fluorinated copolymers (Examples 1-6) obtained using the fluorinated compounds of the present invention have excellent short-term and long-term heat resistance. (none)

Claims

1. A fluorine-containing compound represented by the following formula (1): [Chemical Formula 1] In formula (1), R1 to R3 are each independently a hydrogen atom or a fluorine atom; R4 is a hydrogen atom, a fluorine atom or a monovalent organic group with 1 to 8 carbon atoms without a carbonyl group; Z is an oxygen atom, a sulfur atom or -N(R5)-, and R5 is a hydrogen atom or a monovalent organic group with 1 to 4 carbon atoms; X is a single bond or a difluoromethylene group; Y1 to Y4 are each independently a fluorine atom or a trifluoromethyl group; Q is a perfluoroalkyl group with 1 to 8 carbon atoms that may contain an ether-containing oxygen atom.

2. The fluorine-containing compound as claimed in item 1, wherein Z is an oxygen atom.

3. The fluorine-containing compound as claimed in claim 1 or 2, wherein R1 to R3 are fluorine atoms and R4 is a hydrogen atom.

4. A fluorinated copolymer comprising: a structural unit (A) derived from tetrafluoroethylene; a structural unit (B) derived from a perfluoroalkyl vinyl ether; and a structural unit (C) derived from a fluorinated compound as claimed in claim 1.

5. The fluorinated copolymer of claim 4, wherein of the total 100% by mass of the aforementioned structural units (A) to (C), structural unit (A) is 29.9 to 80% by mass, structural unit (B) is 19.9 to 70% by mass, and structural unit (C) is 0.1 to 20% by mass.

6. A fluorinated copolymer composition comprising: a fluorinated copolymer as claimed in claim 4 or 5; and a compound (D) having two or more structures (d) as shown in formula (2) below; [Formula 2] In formula (2), -a 1 represents a single bond and is bonded to a hydrogen atom, a methyl group or an aromatic ring that may have substituents; -b 1 to -b 5 each represent a single bond, and at least one of -b 1 and -b 5 is bonded to a hydrogen atom; Furthermore, the benzene ring in formula (2) is designated as benzene ring A.

7. The fluorinated copolymer composition of claim 6, wherein the aforementioned compound (D) has one or more of the following structures: a structure in which a benzene ring A of one of the aforementioned structures (d) is linked to a benzene ring A of another of the aforementioned structures (d) by a single bond.

8. The fluorinated copolymer composition of claim 6, wherein the content of the aforementioned compound (D) is 0.1 to 10 parts by mass relative to 100 parts by mass of the aforementioned fluorinated copolymer.

9. A crosslinked fluorinated copolymer obtained from the fluorinated copolymer composition of claim 6.