Method for producing fluorine-containing elastomer and fluorine-containing elastomer

Abstract

Provided is a method for producing a fluorine-containing elastomer by polymerizing a fluoromonomer and a polyfunctional fluorine-free monomer in the presence of a diiodo compound.

Description

Method for producing fluorine-containing elastomer and fluorine-containing elastomer

[0001] The present disclosure relates to a method for producing a fluorine-containing elastomer, a fluorine-containing elastomer, a crosslinkable composition, and a molded article.

[0002] Patent Document 1 describes a copolymer that does not contain bromine and / or iodine, which is obtained by copolymerizing a specific type of fluorine-containing vinyl compound with a specific type of alkenyl isocyanurate and / or alkenyl cyanurate, and which has reactive double bonds in the side chains and can be crosslinked by free radicals under mild conditions. The copolymer is essentially non-crosslinked.

[0003] Patent Document 2 describes a method for producing a liquid fluororubber that can be pumped at least at slightly elevated temperatures (60-120°C) and processed in a conventional thermoplastic processing machine, in which a) vinylidene fluoride and optionally further fluorine-containing monomers and / or fluorine-free monomers are polymerized by a free radical mechanism in the presence of b) at least one compound selected from the group consisting of diiodomethane, 1,2-diiodo-1,1-difluoroethane, 1-iodo-2-bromo-1,1-difluoroethane, 1-bromo-2-iodo-1,1-difluoroethane, and 1,2-dibromo-1,1-difluoroethane, or a mixture thereof, and in the presence of an initiator or a further auxiliary, or both, at a temperature of 0°C to 70°C.

[0004] Patent Document 3 describes a compound of the formula: XCH ２ CF ２ CF ２ (OCH ２ CF ２ CF ２ ) ｍ -(OCFYCF ２ ) ｎ OCF = CF ２ The present invention discloses a copolymer comprising a repeating unit derived from a fluorovinyl ether represented by the formula: [wherein X represents hydrogen or a halogen, Y represents fluorine or a trifluoromethyl group, m represents an integer of 0 to 5, and n represents an integer of 0 to 2.]

[0005] JP 05-086135, JP 10-067821, JP 62-012734

[0006] An object of the present disclosure is to provide a novel method for producing a fluorine-containing elastomer and a novel fluorine-containing elastomer.

[0007] According to the present disclosure, there is provided a method for producing a fluorine-containing elastomer, which comprises polymerizing a fluoromonomer and a polyfunctional fluorine-free monomer in the presence of a diiodo compound to obtain a fluorine-containing elastomer.

[0008] According to the present disclosure, a novel method for producing a fluorine-containing elastomer and a novel fluorine-containing elastomer can be provided.

[0009] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0010] (First Production Method) In the first production method of the present disclosure, a fluoromonomer and a polyfunctional fluorine-free monomer are polymerized in the presence of a diiodo compound to obtain a fluorine-containing elastomer.

[0011] The first production method of the present disclosure has such a configuration, and therefore can produce a fluorine-containing elastomer that is crosslinkable by peroxide crosslinking and that can be easily removed from a mold when a molded article is produced using the mold.

[0012] Conventionally, as a method for producing a fluorine-containing elastomer, the production methods described in Patent Documents 1 to 3 have been known.

[0013] However, as described in Patent Document 1, when a fluorine-containing elastomer is produced using a specific type of fluorine-containing vinyl compound and a specific type of alkenyl isocyanurate and / or alkenyl cyanurate, there is a problem that it is difficult to produce a fluorine-containing elastomer that has sufficient crosslinkability and gives a molded article excellent in compression set resistance.

[0014] Furthermore, as described in Patent Document 2, when a fluorine-containing elastomer is produced using diiodomethane, there is a problem that it is difficult to produce a fluorine-containing elastomer that gives a molded article excellent in mold releasability and compression set resistance.

[0015] Furthermore, as described in Patent Document 3, when a fluoroelastomer is produced using a fluorovinyl ether containing a halogen atom, a fluoroelastomer having excellent properties can be produced. However, the fluorovinyl ether described in Patent Document 3 has the problem that its production is time-consuming and expensive.

[0016] It has been found that the problems of the prior art can be successfully solved by polymerizing a fluoromonomer and a polyfunctional fluorine-free monomer in the presence of a diiodo compound in a method for producing a fluorine-containing elastomer. The fluorine-containing elastomer obtained by the first production method of the present disclosure can be crosslinked by peroxide crosslinking. Furthermore, molded articles obtained by crosslinking the fluorine-containing elastomer obtained by the first production method of the present disclosure have excellent mold releasability, so can be produced with high productivity, and are also excellent in heat resistance and compression set resistance.

[0017] (Diiodo Compound) The diiodo compound used in the first production method may be a fluorine-containing diiodo compound (11) or a fluorine-free diiodo compound (12). By using a diiodo compound, iodine atoms can be introduced into the polymer terminals of a fluorine-containing elastomer. By introducing crosslinkable iodine atoms into the polymer terminals, a fluorine-containing elastomer that can be efficiently crosslinked by peroxide crosslinking can be produced.

[0018] The fluorine-containing diiodo compound (11) is a compound having a fluorine atom and two iodine atoms. Examples of the fluorine-containing diiodo compound (11) include 1,3-diiodoperfluoropropane, 1,4-diiodoperfluoro-n-butane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoro-n-pentane, 1,7-diiodoperfluoro-n-octane, 1,2-di(iododifluoromethyl)perfluorocyclobutane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, and 1,16-diiodoperfluorohexadecane.

[0019] As the fluorine-containing diiodo compound (11), a fluorine-containing diiodo compound having two or more carbon atoms is preferred, and 1,4-diiodoperfluoro-n-butane is more preferred.

[0020] The fluorine-free diiodo compound (12) is a compound that contains no fluorine atoms but two iodine atoms. Examples of the fluorine-free diiodo compound (12) include diiodomethane, 1,2-diiodoethane, 1,3-diiodo-n-propane, and 1,2-diiodo-1,1-difluoroethane.

[0021] As the fluorine-containing diiodo compound (12), a fluorine-containing diiodo compound having one carbon atom is preferable, and diiodomethane is more preferable. By using a fluorine-containing diiodo compound having a small number of carbon atoms as the fluorine-containing diiodo compound (12), the production cost of the fluorine-containing elastomer can be reduced.

[0022] In one embodiment of the first production method, both the fluorine-containing diiodo compound (11) and the fluorine-free diiodo compound (12) are used, which allows the fluorine-containing elastomer to be produced more cheaply than in a production method using only a fluorine-containing diiodo compound as a chain transfer agent.

[0023] In one embodiment of the first production method, a fluoromonomer is polymerized in the presence of a diiodo compound (1), and then the fluoromonomer is polymerized in the presence of a fluorine-free diiodo compound (12). This allows the production of a fluorine-containing elastomer more cheaply than in a production method using only a fluorine-containing diiodo compound as a chain transfer agent.

[0024] The diiodo compound (1) may be added all at once or continuously. The timing of adding the diiodo compound (1) is not particularly limited, but it is preferable to add at least a part of the diiodo compound (1) until a fluorine-containing elastomer having a mass corresponding to 10% by mass of the finally obtained fluorine-containing elastomer is produced.

[0025] The fluorine-free diiodo compound (12) may be added all at once or continuously. The timing of adding the fluorine-free diiodo compound (12) is not particularly limited, but it is preferable to add at least a part of the fluorine-free diiodo compound (12) after the production of a fluorine-containing elastomer in an amount corresponding to 30 to 90% by mass of the final fluorine-containing elastomer.

[0026] In one embodiment of the first production method, a fluoromonomer is polymerized in the presence of the diiodo compound (1) until a fluoroelastomer is produced in an amount corresponding to 30 to 90% by mass of the mass of the finally obtained fluoroelastomer, and then the fluoromonomer is polymerized in the presence of the fluorine-free diiodo compound (12). This allows the fluoroelastomer to be produced more cheaply than in a production method using only a fluorine-containing diiodo compound as a chain transfer agent.

[0027] The polymerization of the fluoromonomer in the presence of the diiodo compound (1) is carried out until a fluoroelastomer is produced in an amount corresponding to preferably 30 to 90% by mass, more preferably 40% by mass or more, more preferably 80% by mass or less, based on the mass of the finally obtained fluoroelastomer.

[0028] In one embodiment of the first production method, a fluoromonomer is polymerized in the presence of a fluorine-containing diiodo compound (11), and then polymerized in the presence of a fluorine-free diiodo compound (12). Conventionally, diiodomethane is known as a chain transfer agent used in production methods for fluoroelastomers, as described in Patent Document 2. However, when a fluoroelastomer is produced using diiodomethane, the reaction rate is low, particularly in the early stages of the polymerization reaction, making it difficult to produce the fluoroelastomer with high productivity. On the other hand, if the amount of initiator is significantly increased to increase productivity, the iodine groups at the polymer terminals are replaced with initiator terminals, resulting in a decrease in compression set resistance. By polymerizing a fluoromonomer in the presence of a fluorine-containing diiodo compound (11), and then polymerizing the fluoromonomer in the presence of a fluorine-free diiodo compound (12), a fluoroelastomer that can be crosslinked by peroxide crosslinking can be produced with high productivity, and the fluoroelastomer can be produced more cheaply than a production method that uses only a fluorine-containing diiodo compound as a chain transfer agent.

[0029] In one embodiment of the first production method, a fluoromonomer is polymerized in the presence of a fluorine-containing diiodo compound (11) until a fluoroelastomer is produced in an amount corresponding to 30 to 90% by mass of the mass of the finally obtained fluoroelastomer, and then the fluoromonomer is polymerized in the presence of a fluorine-free diiodo compound (12). This makes it possible to produce a fluoroelastomer crosslinkable by peroxide crosslinking with higher productivity, and also to produce a fluoroelastomer more cheaply than in a production method using only a fluorine-containing diiodo compound as a chain transfer agent.

[0030] The polymerization of the fluoromonomer in the presence of the fluorine-containing diiodo compound (11) is carried out until a fluoroelastomer is produced in an amount corresponding to preferably 30 to 90% by mass, more preferably 40% by mass or more, more preferably 80% by mass or less, based on the mass of the finally obtained fluoroelastomer.

[0031] The amount of the diiodo compound (when both a fluorine-containing diiodo compound and a fluorine-free diiodo compound are used, the total amount of these) is preferably 0.2 × 10 based on the total amount of monomers used in the polymerization. －３ up to 2 mol%, more preferably 1.0 × 10 －３ % or more, and more preferably 1 mol % or less.

[0032] The amount of the fluorine-containing diiodo compound (11) is preferably 0.2×10 based on the total amount of monomers used in the polymerization. －３ up to 2 mol%, more preferably 1.0 × 10 －３ % or more, and more preferably 1 mol % or less.

[0033] The amount of the fluorine-free diiodo compound (12) is preferably 0.2×10 based on the total amount of monomers used in the polymerization. －３ up to 2 mol%, more preferably 1.0 × 10 －３ % or more, and more preferably 1 mol % or less.

[0034] (Polyfunctional Fluorine-Free Monomer) The polyfunctional fluorine-free monomer used in the first production method is a monomer having two or more functional groups and not containing a fluorine atom. By using a polyfunctional fluorine-free monomer, a polyfunctional fluorine-free monomer unit can be introduced into the fluorine-containing elastomer. The polyfunctional fluorine-free monomer unit in the fluorine-containing elastomer imparts a branched structure to the fluorine-containing elastomer or functions as a site crosslinkable by peroxide crosslinking. Therefore, by crosslinking the fluorine-containing elastomer obtained by the first production method of the present disclosure, a molded article having heat resistance and compression set resistance can be obtained. Furthermore, it has now been found that the introduction of iodine atoms and a polyfunctional fluorine-free monomer unit into the fluorine-containing elastomer improves the mold releasability of the fluorine-containing elastomer.

[0035] The polyfunctional non-fluorine-containing monomer has two or more functional groups. The number of functional groups of the polyfunctional non-fluorine-containing monomer is preferably 2 to 6, more preferably 3 or more, more preferably 5 or less, and even more preferably 4 or less. The number of functional groups of the polyfunctional non-fluorine-containing monomer is particularly preferably 3.

[0036] The polyfunctional non-fluorine-containing monomer preferably has an unsaturated functional group. The unsaturated functional group is a functional group having an unsaturated bond such as a carbon-carbon double bond. The unsaturated functional group is preferably at least one selected from the group consisting of a vinyl group, an isopropenyl group, an allyl group, and a methallyl group, and more preferably at least one selected from the group consisting of an allyl group and a methallyl group.

[0037] The polyfunctional fluorine-free monomer preferably has a nitrogen-containing heterocycle. The number of members of the nitrogen-containing heterocycle is preferably 4 to 10, and more preferably 6. The number of nitrogen atoms forming the nitrogen-containing heterocycle is preferably 1 to 5, and more preferably 3. The nitrogen-containing heterocycle is preferably a 6-membered ring formed by three carbon atoms and three nitrogen atoms, and more preferably a 1,3,5-triazine ring.

[0038] Examples of polyfunctional fluorine-free monomers include triallyl cyanurate, triallyl isocyanurate (TAIC), trimethallyl isocyanurate, tris(diallylamine-s-triazine), triallyl phosphite, N,N-diallyl acrylamide, hexaallyl phosphoramide, N,N,N',N'-tetraallyl tetraphthalamide, N,N,N',N'-tetraallyl malonamide, trivinyl isocyanurate, 2,4,6-trivinylmethyltrisiloxane, and tri(5-norbornene-2-methylene) cyanurate.

[0039] Of these, the polyfunctional fluorine-free monomer is preferably at least one selected from the group consisting of triallyl isocyanurate and trimethallyl isocyanurate.

[0040] The polyfunctional fluorine-free monomer may be added all at once or continuously. The timing of adding the polyfunctional fluorine-free monomer is not particularly limited. When a fluoromonomer is polymerized in the presence of a diiodo compound (1) and then polymerized in the presence of a fluorine-free diiodo compound (12), it is preferable to add at least a part of the polyfunctional fluorine-free monomer when polymerizing the fluoromonomer in the presence of the diiodo compound (1), and it is more preferable to add the polyfunctional fluorine-free monomer after adding the diiodo compound (1) to the polymerization system. This makes it easy to produce a fluorine-containing elastomer with excellent mold releasability and excellent moldability.

[0041] The amount of the polyfunctional non-fluorine-containing monomer is preferably 0.005 to 0.2 mol %, more preferably 0.01 mol % or more, and more preferably 0.1 mol % or less, based on the total amount of monomers used in the polymerization.

[0042] The molar ratio of the amount of the polyfunctional fluorine-free monomer to the amount of the diiodo compound (polyfunctional fluorine-free monomer / diiodo compound) is preferably 0.01 to 1.0, more preferably 0.05 or more, and more preferably 0.5 or less. If the amount of the polyfunctional fluorine-free monomer used is too large relative to the amount of the diiodo compound used, the resulting fluorine-containing elastomer tends to gel. Furthermore, when the resulting fluorine-containing elastomer is crosslinked to produce a crosslinked sheet, the crosslinked sheet tends to warp, making it difficult to produce a molded article having a desired shape.

[0043] (Fluoromonomer) The fluoromonomer used in the first production method is a monomer containing a fluorine atom.

[0044] Fluoromonomers include vinylidene fluoride (VdF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE), chlorotrifluoroethylene (CTFE), trifluoroethylene, trifluoropropylene, tetrafluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, vinyl fluoride, iodine-containing fluorinated vinyl ethers, and compounds represented by the general formula (2): CHX ３１ =CX ３２ Rf ３１ (2) (wherein, X ３１ and X ３２ is H on one side and F on the other side, and Rf ３１ and fluorine-containing monomers such as fluoromonomer (2) represented by (wherein R is a linear or branched fluoroalkyl group having 1 to 12 carbon atoms).

[0045] As the PAVE, perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(propyl vinyl ether) (PPVE) are more preferred, and PMVE is particularly preferred.

[0046] PAVE is also represented by the formula: CF ２ = CFOCF ２ ORf ｃ (In the formula, Rf ｃ is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms, a cyclic perfluoroalkyl group having 5 to 6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms), and perfluorovinyl ethers such as CF ２ = CFOCF ２ OCF ３ , C.F. ２ = CFOCF ２ OCF ２ CF ３ or CF ２ = CFOCF ２ OCF ２ CF ２ OCF３ is preferred.

[0047] The fluoromonomer (2) may be Rf ３１ is a linear fluoroalkyl group, and Rf ３１ More preferred is a monomer in which Rf is a linear perfluoroalkyl group. ３１ The number of carbon atoms is preferably 1 to 6.

[0048] The fluoromonomer (2) is CH ２ =CFCF ３ , C.H. ２ =CFCF ２ CF ３ , C.H. ２ =CFCF ２ CF ２ CF ３ , C.H. ２ =CFCF ２ CF ２ CF ２ CF ３ , CHF=CHCF ３ (1,3,3,3-tetrafluoropropene), CHF=CHCF ３ (E form), CHF=CHCF ３ (Z-isomer), among which CH ２ =CFCF ３ Preferred is 2,3,3,3-tetrafluoropropylene represented by the following formula:

[0049] The fluoromonomer used in the first production method preferably contains at least one selected from the group consisting of vinylidene fluoride and tetrafluoroethylene, and more preferably contains vinylidene fluoride.

[0050] (Other Materials) The polymerization in the first production method can be carried out, for example, by charging a surfactant and an aqueous medium into a pressure-resistant polymerization vessel equipped with a stirrer, deoxidizing, then charging the monomer, bringing the temperature to a predetermined value, adding a polymerization initiator to start the reaction, and charging the diiodo compound during the polymerization reaction. Since the pressure decreases as the reaction progresses, additional monomer is continuously or intermittently supplied to maintain the initial pressure. Once a predetermined amount of monomer has been supplied, the supply is stopped, the monomer in the reaction vessel is purged, and the temperature is returned to room temperature to terminate the reaction.

[0051] The polymerization in the first production method can be carried out in the presence of a polymerization initiator. Examples of the polymerization initiator include a radical polymerization initiator. The polymerization initiator is not particularly limited as long as it can generate radicals at the polymerization temperature, and oil-soluble polymerization initiators, water-soluble polymerization initiators, etc. can be used, but water-soluble polymerization initiators are preferred. The polymerization initiator may also be used as a redox initiator in combination with a reducing agent, etc.

[0052] The amount of the polymerization initiator is appropriately determined depending on the type of monomer, the molecular weight of the target fluoroelastomer, and the reaction rate, and is preferably 0.00001 to 10% by mass, more preferably 0.0001 to 1% by mass, based on 100% by mass of the total amount of monomers.

[0053] As the polymerization initiator, an oil-soluble radical polymerization initiator, a water-soluble radical polymerization initiator, or an azo compound can be used.

[0054] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and the like. Also usable are di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluorooctanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples include di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexafluorobutyryl)peroxide, di(ω-chlorodecafluorohexanoyl)peroxide, di(ω-chlorotetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundecafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undecachlorodotriacontafluorodocosanoyl)peroxide.

[0055] Examples of the azo compound include azodicarboxylate, azodicarboxyldiamide, 2,2'-azobisisobutyronitrile, 2,2'-azobis2,4-dimethylvaleronitrile, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 4,4'-azobis(4-cyanovaleric acid).

[0056] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perborate, perchloric acid, perphosphoric acid, or percarbonate; organic peroxides such as disuccinic acid peroxide or diglutaric acid peroxide; t-butyl permaleate; t-butyl hydroperoxide; etc. A reducing agent such as a sulfite may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0057] As the water-soluble peroxide, a salt of persulfate is preferred because it is easy to adjust the amount of radicals generated. ２ S ２ O ８ ), ammonium persulfate ((NH ４ ) ２ S ２ O ８ ), sodium persulfate (Na ２ S ２ O ８ ) is preferred, with ammonium persulfate being most preferred.

[0058] When polymerization is carried out using a water-soluble peroxide at a polymerization temperature of 45° C. or higher, it is preferable to carry out the polymerization without using a reducing agent.

[0059] For example, when polymerization is carried out at a low temperature of 60° C. or less, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent as the polymerization initiator. That is, it is preferable to carry out polymerization in the presence of the redox initiator.

[0060] Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and bromates. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, oxalic acid, and metal sulfinates. Examples of persulfates include ammonium persulfate, potassium persulfate, and sodium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. To increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate. When using copper salts or iron salts, it is particularly preferable to add a chelating agent. A preferred chelating agent is ethylenediaminetetraacetic acid disodium salt dihydrate.

[0061] Examples of the redox initiator include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / iron(II) sulfate, ammonium persulfate / sulfite / iron(II) sulfate, ammonium persulfate / sulfite, ammonium persulfate / iron(II) sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, bromate / sulfite, bromate / bisulfite, ammonium persulfate / sodium hydroxymethanesulfinate dihydrate, and hydrogen peroxide / ascorbic acid (described in JP-A-55-102615), with ammonium persulfate / sodium hydroxymethanesulfinate dihydrate being preferred.

[0062] When a redox initiator is used, either the oxidizing agent or the reducing agent may be charged into a polymerization vessel in advance, and then the other may be added continuously or intermittently to initiate polymerization. For example, when ammonium persulfate / sodium hydroxymethanesulfinate dihydrate is used, it is preferred to charge ammonium persulfate into a polymerization vessel and then continuously add sodium hydroxymethanesulfinate dihydrate thereto.

[0063] The amount of persulfate used in the redox initiator is preferably 0.001 to 2.0% by mass, more preferably 0.01 to 1.5% by mass, and particularly preferably 0.05 to 1.0% by mass, based on the aqueous medium used in the polymerization.

[0064] The amount of the reducing agent used is preferably from 0.01 to 30% by mass, more preferably from 0.05 to 10% by mass, and particularly preferably from 0.1 to 5% by mass, based on the amount of the aqueous medium used in the polymerization.

[0065] The amount of the third component (such as the copper salt or iron salt) used is preferably 0.001 to 0.5% by mass, more preferably 0.005 to 0.4% by mass, and particularly preferably 0.01 to 0.3% by mass, based on the aqueous medium used in the polymerization.

[0066] The polymerization in the first production method can be carried out in the presence of a surfactant. The surfactant may be either a reactive surfactant or a non-reactive surfactant. The surfactant may also be either a fluorine-containing surfactant or a non-fluorine-containing surfactant. The surfactant may also be any of an anionic surfactant, a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant. The polymerization in the first production method can also be carried out in the absence of a surfactant, as described in WO 2007 / 129735.

[0067] The polymerization in the first production method can be carried out in an aqueous medium. The aqueous medium refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an alcohol, an ether, or a ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or lower.

[0068] The polymerization temperature in the first production method is preferably 10 to 120° C. The polymerization pressure in the first production method is preferably 0.5 to 10 MPaG.

[0069] According to the first production method, a fluorine-containing elastomer can be obtained. In one embodiment, the fluorine-containing elastomer obtained by the first production method has a multimodal molecular weight distribution. In another embodiment, the fluorine-containing elastomer obtained by the first production method has a bimodal molecular weight distribution. The fluorine-containing elastomer preferably has a bimodal molecular weight distribution such that the ratio ((A) / (B)) of the area of ​​the peak on the high molecular weight side (A) to the area of ​​the peak on the low molecular weight side (B) appearing in a GPC curve is 90 / 10 to 30 / 70. When the fluorine-containing elastomer has such a molecular weight distribution, a molded article having excellent mold releasability, heat resistance, and compression set resistance can be obtained, and the moldability of the fluorine-containing elastomer is improved.

[0070] The ratio ((A) / (B)) of the fluorine-containing elastomer obtained by the first production method is preferably 90 / 10 to 30 / 70, more preferably 80 / 20 or less, and more preferably 40 / 60 or more.

[0071] By the polymerization, an aqueous dispersion containing a fluorine-containing elastomer is usually obtained. The aqueous dispersion of the fluorine-containing elastomer may be subjected to treatment such as coagulation or heating.

[0072] The coagulation can be carried out by adding alkaline earth and earth metal salts to the aqueous dispersion, such as sulfates, nitrates, hydrochlorides, and acetates of calcium, magnesium, aluminum, and the like.

[0073] The coagulated fluoroelastomer may be washed with water to remove small amounts of impurities such as buffer solutions and salts present in the fluoroelastomer, and then the washed fluoroelastomer may be dried at a drying temperature of preferably 40 to 200°C, more preferably 60 to 180°C, and even more preferably 80 to 150°C.

[0074] The form of the fluorine-containing elastomer obtained after coagulation is not particularly limited, and may be gum, crumb, powder, pellets, etc., with gum or crumb being preferred. Gum is small granular masses of fluorine-containing elastomer, and crumb is an amorphous mass formed when the fluorine-containing elastomer cannot maintain its granular form as a gum at room temperature and instead fuses with other fluorine-containing elastomers. Gum or crumb is preferably obtained by coagulating, drying, etc., the aqueous dispersion obtained by the production method of the present disclosure using a conventionally known method.

[0075] (Fluorine-containing elastomer) According to the first production method, a fluorine-containing elastomer can be obtained. In one embodiment, the fluorine-containing elastomer has an iodine content of 0.1 to 1.0 mass % and contains a fluoromonomer unit and a polyfunctional non-fluorine-containing monomer unit.

[0076] Since the fluorine-containing elastomer according to one embodiment of the present disclosure has such a constitution, it can be crosslinked by peroxide crosslinking to obtain a molded article, and further, when a molded article is produced using a mold, it can be easily removed from the mold. Therefore, by using the fluorine-containing elastomer according to the present disclosure, beautiful molded articles can be produced with high productivity. Furthermore, molded articles obtained from the fluorine-containing elastomer according to the present disclosure also have excellent heat resistance and compression set resistance.

[0077] The iodine content in the fluorine-containing elastomer is 0.05 to 2.0% by mass, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and preferably 1.5% by mass or less, more preferably 1.0% by mass or less.

[0078] The iodine content in the fluorine-containing elastomer can be measured by elemental analysis.

[0079] The polyfunctional fluorine-free monomer unit in the fluorine-containing elastomer is a repeating unit based on a polyfunctional fluorine-free monomer. Examples of the polyfunctional fluorine-free monomer include the polyfunctional fluorine-free monomer used in the first production method, and the same is preferably used.

[0080] The content of the polyfunctional non-fluorine-containing monomer units is preferably 0.005 to 0.2 mol %, more preferably 0.01 mol % or more, and more preferably 0.1 mol % or less, based on the total monomer units.

[0081] The fluorine-containing elastomer may be one obtained by polymerizing a polyfunctional fluorine-free monomer in an amount corresponding to preferably 0.005 to 0.2 mol %, more preferably 0.01 mol % or more, more preferably 0.1 mol % or less, based on the total monomer units of the fluorine-containing elastomer.

[0082] The content of polyfunctional fluorine-free monomer units in the fluorine-containing elastomer can be calculated by appropriately combining NMR, FT-IR, elemental analysis and X-ray fluorescence analysis depending on the type of monomer.

[0083] The fluoromonomer units in the fluorine-containing elastomer are repeating units based on a fluoromonomer. Examples of the fluoromonomer include the fluoromonomers used in the first production method, and the same are preferred.

[0084] In one embodiment, the fluorine-containing elastomer has a multimodal molecular weight distribution. In another embodiment, the fluorine-containing elastomer has a bimodal molecular weight distribution. The fluorine-containing elastomer preferably has a bimodal molecular weight distribution such that the ratio ((A) / (B)) of the area (A) of the peak on the high molecular weight side appearing in a GPC curve to the area (B) of the peak on the low molecular weight side is 90 / 10 to 30 / 70. When the fluorine-containing elastomer has such a molecular weight distribution, it is possible to obtain a molded article having excellent mold releasability, heat resistance, and compression set resistance, and the moldability of the fluorine-containing elastomer is improved.

[0085] The ratio of the fluorine-containing elastomers ((A) / (B)) is preferably 90 / 10 to 30 / 70, more preferably 80 / 20 or less, and more preferably 40 / 60 or more.

[0086] The fluorine-containing elastomer may be a fully fluorinated elastomer or a partially fluorinated elastomer. In one embodiment, the fluorine-containing elastomer is a partially fluorinated elastomer. The partially fluorinated elastomer is a fluoropolymer that contains fluoromonomer units, has a perfluoromonomer unit content of less than 90 mol% relative to all monomer units, has a glass transition temperature of 20°C or less, and has a melting peak (ΔH) magnitude of 4.5 J / g or less.

[0087] In the present disclosure, a perfluoromonomer is a monomer that does not contain a carbon atom-hydrogen atom bond in the molecule. In addition to carbon atoms and fluorine atoms, perfluoromonomers may be monomers in which some of the fluorine atoms bonded to carbon atoms have been substituted with chlorine atoms, or may be monomers that contain nitrogen atoms, oxygen atoms, sulfur atoms, phosphorus atoms, boron atoms, or silicon atoms in addition to carbon atoms. A perfluoromonomer is preferably a monomer in which all hydrogen atoms have been substituted with fluorine atoms. Perfluoromonomers do not include monomers that provide crosslinkable groups.

[0088] Examples of fluorine-containing elastomers include tetrafluoroethylene (TFE), vinylidene fluoride (VdF), and fluororesin having the general formula: CF ２ =CF-Rf ａ (In the formula, Rf ａ Ha-CF ３ or -ORf ｂ (Rf ｂIt is preferable that the fluorine-containing elastomer contains a monomer unit based on at least one monomer selected from the group consisting of perfluoroethylenically unsaturated compounds represented by the formula (I) (where I is a perfluoroalkyl group having 1 to 5 carbon atoms) (for example, hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE) etc.). Among these, the fluorine-containing elastomer preferably contains a VdF unit or a TFE unit, and more preferably contains a VDF unit.

[0089] More specific examples of the fluorine-containing elastomer include VdF-based fluorine-containing elastomers, TFE / propylene (Pr)-based fluorine-containing elastomers, TFE / Pr / VdF-based fluorine-containing elastomers, ethylene (Et) / HFP-based fluorine-containing elastomers, Et / HFP / VdF-based fluorine-containing elastomers, Et / HFP / TFE-based fluorine-containing elastomers, Et / TFE / PAVE-based fluorine-containing elastomers, etc. Among these, VdF-based fluorine-containing elastomers, TFE / Pr-based fluorine-containing elastomers, TFE / Pr / VdF-based fluorine-containing elastomers and Et / TFE / PAVE-based fluorine-containing elastomers are more preferred in terms of good heat aging resistance and oil resistance.

[0090] The VdF-based fluorine-containing elastomer is a fluorine-containing elastomer having VdF units. The content of VdF units in the fluorine-containing elastomer is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and particularly preferably 60 mol% or more, based on the total number of moles of VdF units and monomer units based on other monomers. In the VdF-based fluorine-containing elastomer, the VdF units preferably account for 20 mol% or more and 90 mol% or less, more preferably 40 mol% or more and 85 mol% or less, still more preferably 45 mol% or more and 80 mol% or less, and particularly preferably 50 mol% or more and 80 mol% or less, of the total number of moles of VdF units and monomer units based on other monomers.

[0091] The other monomer in the VdF-based fluorine-containing elastomer is not particularly limited as long as it is a monomer copolymerizable with VdF, and for example, the above-mentioned fluoromonomers can be used.

[0092] The VdF-based fluorine-containing elastomer is preferably at least one copolymer selected from the group consisting of VdF / HFP copolymer, VdF / TFE / HFP copolymer, VdF / CTFE copolymer, VdF / CTFE / TFE copolymer, VdF / PAVE copolymer, VdF / TFE / PAVE copolymer, VdF / HFP / PAVE copolymer, VdF / HFP / TFE / PAVE copolymer, VdF / TFE / Pr copolymer, VdF / Et / HFP copolymer, and VdF / fluoromonomer (2) copolymer. Furthermore, it is more preferable that the fluoromonomer other than VdF is at least one fluoromonomer selected from the group consisting of TFE, HFP, and PAVE.

[0093] Of these, the VdF-based fluorine-containing elastomer is preferably at least one copolymer selected from the group consisting of VdF / HFP copolymer, VdF / TFE / HFP copolymer, VdF / fluoromonomer (2) copolymer, VdF / PAVE copolymer, VdF / TFE / PAVE copolymer, VdF / HFP / PAVE copolymer and VdF / HFP / TFE / PAVE copolymer, and more preferably at least one copolymer selected from the group consisting of VdF / HFP copolymer, VdF / HFP / TFE copolymer, VdF / fluoromonomer (2) copolymer and VdF / PAVE copolymer.

[0094] The VdF / PAVE copolymer preferably has a VdF / PAVE composition of (65 to 90) / (35 to 10) (mol %). Another preferred embodiment has a VdF / PAVE composition of (50 to 78) / (50 to 22) (mol %).

[0095] The VdF / TFE / PAVE copolymer preferably has a VdF / TFE / PAVE composition of (40-80) / (3-40) / (15-35) (mol %).

[0096] The VdF / HFP / PAVE copolymer preferably has a VdF / HFP / PAVE composition of (65 to 90) / (3 to 25) / (3 to 25) (mol %).

[0097] The VdF / HFP / TFE / PAVE copolymer preferably has a VdF / HFP / TFE / PAVE composition of (40 to 90) / (0 to 25) / (0 to 40) / (3 to 35) (mol %), and more preferably has a VdF / HFP / TFE / PAVE composition of (40 to 80) / (3 to 25) / (3 to 40) / (3 to 25) (mol %).

[0098] The VdF / fluoromonomer (2) copolymer preferably has a VdF / fluoromonomer (2) unit ratio of (85-20) / (15-80) (mol %), and monomer units other than VdF and fluoromonomer (2) account for 0-50 mol % of all monomer units, and more preferably has a VdF / fluoromonomer (2) unit molar ratio of (80-20) / (20-80). Another preferred embodiment has a VdF / fluoromonomer (2) unit composition of (78-50) / (22-50) (mol %).

[0099] Also preferred is a copolymer of VdF / fluoromonomer (2) in which the VdF / fluoromonomer (2) units are (85 to 50) / (15 to 50) (mol %) and the other monomer units than VdF and fluoromonomer (2) account for 1 to 50 mol % of all monomer units. Preferred other monomers than VdF and fluoromonomer (2) are TFE, HFP, PMVE, perfluoroethyl vinyl ether (PEVE), PPVE, CTFE, trifluoroethylene, hexafluoroisobutene, vinyl fluoride, Et, Pr, alkyl vinyl ethers, and monomers that provide crosslinkable groups, which are exemplified as other monomers in VdF-based fluorine-containing elastomers, and among these, PMVE, CTFE, HFP, and TFE are more preferred.

[0100] The TFE / Pr-based fluorine-containing elastomer refers to a fluorine-containing copolymer consisting of 45 to 70 mol % of TFE and 55 to 30 mol % of Pr. In addition to these two components, a specific third component may be contained.

[0101] The specific third component may include, for example, fluoromonomers such as fluorine-containing olefins other than TFE (e.g., VdF, HFP, CTFE, perfluoro(butyl ethylene), etc.), fluorine-containing vinyl ethers (perfluoro(propyl vinyl ether), perfluoro(methyl vinyl ether), etc.); hydrocarbon monomers such as α-olefins (ethylene, 1-butene, etc.), vinyl ethers (ethyl vinyl ether, butyl vinyl ether, hydroxybutyl vinyl ether, etc.), and vinyl esters (vinyl acetate, vinyl benzoate, vinyl crotonate, vinyl methacrylate, etc.). The specific third component may be used alone or in combination of two or more.

[0102] The TFE / Pr-based fluorine-containing elastomer preferably contains VdF, and among TFE / Pr-based fluorine-containing elastomers, an elastomer consisting of TFE, Pr and VdF is called a TFE / Pr / VdF-based fluorine-containing elastomer.

[0103] The TFE / Pr / VdF-based fluorine-containing elastomer may further contain the specific third component other than VdF. The specific third component may be one type or a combination of two or more types. The total content of the third components in the TFE / Pr-based fluorine-containing elastomer is preferably 35 mol% or less, more preferably 33 mol% or less, and even more preferably 31 mol% or less.

[0104] The Et / HFP copolymer preferably has an Et / HFP composition of (35 to 80) / (65 to 20) (mol %), more preferably (40 to 75) / (60 to 25) (mol %).

[0105] The Et / HFP / TFE copolymer preferably has an Et / HFP / TFE composition of (35 to 75) / (25 to 50) / (0 to 15) (mol %), more preferably (45 to 75) / (25 to 45) / (0 to 10) (mol %).

[0106] The Et / TFE / PAVE copolymer preferably has an Et / TFE / PAVE composition of (10-40) / (32-60) / (20-40) (mol %), more preferably (20-40) / (40-50) / (20-30) (mol %). PMVE is preferred as the PAVE.

[0107] The fluorine-containing elastomer is preferably a fluorine-containing elastomer containing a VdF unit, more preferably a VdF / HFP copolymer or a VdF / HFP / TFE copolymer, and particularly preferably one having a VdF / HFP / TFE composition of (32-85) / (10-34) / (0-40) (mol%), more preferably (32-85) / (15-34) / (0-34) (mol%), and even more preferably (47-81) / (17-32) / (0-28) (mol%).

[0108] For example, in the above VdF / HFP copolymer, the VdF / HFP composition is preferably (45 to 85) / (15 to 55) (mol%), more preferably (50 to 83) / (17 to 50) (mol%), still more preferably (55 to 81) / (19 to 45) (mol%), and particularly preferably (60 to 80) / (20 to 40) (mol%).

[0109] The above-mentioned structure is the structure of the main monomer of the fluorine-containing elastomer, and does not include the content of polyfunctional fluorine-free monomer units. Furthermore, in addition to the main monomer, a monomer that provides a crosslinkable group (excluding polyfunctional fluorine-free monomers) may be copolymerized. The monomer that provides a crosslinkable group may be any monomer that can introduce an appropriate crosslinkable group into the fluorine-containing elastomer depending on the production method and crosslinking system, and examples thereof include known polymerizable compounds containing a crosslinkable group such as an iodine atom, a bromine atom, a carbon-carbon double bond, a cyano group, a carboxyl group, a hydroxyl group, an amino group, or an ester group.

[0110] Preferred examples of the monomer that provides a crosslinkable group include those represented by the general formula (3): CY １ ２ =CY ２ R ｆ ２ X １(3) (wherein, Y １ , Y ２ is a fluorine atom, a hydrogen atom, or —CH ３ ;R ｆ ２ represents a linear or branched fluorine-containing alkylene group in which some or all of the hydrogen atoms have been substituted with fluorine atoms, which may have one or more ether-bonded oxygen atoms and which may have an aromatic ring; X １ is an iodine atom or a bromine atom).

[0111] Specific examples of the monomer that provides a crosslinkable group include those represented by the general formula (4): CY １ ２ =CY ２ R ｆ ３ CHR １ -X １ (4) (wherein, Y １ , Y ２ , X １ is the same as above, and R ｆ ３ is a linear or branched fluorine-containing alkylene group which may have one or more ether-bonded oxygen atoms and in which some or all of the hydrogen atoms have been substituted with fluorine atoms, i.e., a linear or branched fluorine-containing alkylene group in which some or all of the hydrogen atoms have been substituted with fluorine atoms, a linear or branched fluorine-containing oxyalkylene group in which some or all of the hydrogen atoms have been substituted with fluorine atoms, or a linear or branched fluorine-containing polyoxyalkylene group in which some or all of the hydrogen atoms have been substituted with fluorine atoms; R １ is a hydrogen atom or a methyl group), iodine- or bromine-containing monomers represented by the general formulas (5) to (22): CY ４ ２ =CY ４ (CF ２ ) ｎ -X １ (5) (wherein, Y ４ are the same or different and are a hydrogen atom or a fluorine atom, and n is an integer of 1 to 8) CF ２ =CFCF ２ R ｆ ４ -X １(6) (wherein, R ４ is -(OCF ２ ) ｎ - or - (OCF (CF ３ )) ｎ -, and n is an integer from 0 to 5) CF ２ =CFCF ２ (OCF (CF ３ )CF ２ ) ｍ (OCH ２ CF ２ CF ２ ) ｎ OCH ２ CF ２ -X １ (7) (wherein m is an integer of 0 to 5, and n is an integer of 0 to 5) CF ２ =CFCF ２ (OCH ２ CF ２ CF ２ ) ｍ (OCF (CF ３ )CF ２ ) ｎ OCF (CF ３ )-X １ (8) (wherein m is an integer of 0 to 5, and n is an integer of 0 to 5) CF ２ =CF(OCF ２ CF (CF ３ )) ｍ O (CF ２ ) ｎ -X １ (9) (wherein m is an integer of 0 to 5, and n is an integer of 1 to 8) CF ２ =CF(OCF ２ CF (CF ３ )) ｍ -X １ (10) CF (wherein m is an integer of 1 to 5) ２ = CFOCF ２ (CF (CF ３ ) OCF ２ ) ｎ CF(-X １ )CF ３ (11) CF (wherein n is an integer from 1 to 4) ２ = CFO (CF ２ ) ｎ OCF (CF ３)-X １ (12) CF (wherein n is an integer of 2 to 5) ２ = CFO (CF ２ ) ｎ -(C ６ H ４ )-X １ (13) CF (wherein n is an integer from 1 to 6) ２ =CF(OCF ２ CF (CF ３ )) ｎ OCF ２ CF (CF ３ )-X １ (14) (wherein n is an integer of 1 to 2) CH ２ =CFCF ２ O(CF(CF ３ )CF ２ O) ｎ CF (CF ３ )-X １ (15) (wherein n is an integer of 0 to 5), CF ２ = CFO (CF ２ CF (CF ３ ) O) ｍ (CF ２ ) ｎ -X １ (16) (wherein m is an integer of 0 to 5, and n is an integer of 1 to 3) CH ２ =CFCF ２ OCF (CF ３ ) OCF (CF ３ )-X １ (17) CH ２ =CFCF ２ OCH ２ CF ２ -X １ (18) CF ２ = CFO (CF ２ CF (CF ３ ) O) ｍ CF ２ CF (CF ３ )-X １ (19) (wherein m is an integer of 0 or more) CF ２ = CFOCF(CF ３ )CF ２ O (CF ２ ) ｎ -X １(20) (wherein n is an integer of 1 or more) CF ２ = CFOCF ２ OCF ２ CF (CF ３ ) OCF ２ -X １ (21) CH ２ =CH-(CF ２ ) ｎ X １ (22) (wherein n is an integer of 2 to 8) (in the general formulas (5) to (22), X １ are the same as above), and the like, which can be used alone or in any combination.

[0112] The iodine- or bromine-containing monomer represented by the general formula (4) includes a monomer represented by the general formula (23): (wherein m is an integer of 1 to 5, and n is an integer of 0 to 3), and more specifically, Among these, ICH ２ CF ２ CF ２ OCF = CF ２ is preferred.

[0113] More specifically, the iodine- or bromine-containing monomer represented by the general formula (5) is ICF ２ CF ２ CF=CH ２ , I(CF ２ CF ２ ) ２ CF=CH ２ are preferred.

[0114] More specifically, the iodine- or bromine-containing monomer represented by the general formula (9) is I(CF ２ CF ２ ) ２ OCF = CF ２ are preferred.

[0115] More specifically, the iodine- or bromine-containing monomer represented by the general formula (22) is CH ２ = CHCF ２ CF ２I, I (CF ２ CF ２ ) ２ CH=CH ２ are preferred.

[0116] Also, the formula: R ２ R ３ C=CR ４ -Z-CR ５ =CR ６ R ７ (In the formula, R ２ , R ３ , R ４ , R ５ , R ６ and R ７ are the same or different and are both H or an alkyl group having 1 to 5 carbon atoms; Z is a linear or branched alkylene or cycloalkylene group having 1 to 18 carbon atoms, which may contain an oxygen atom and is preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene group). Bisolefin compounds represented by these are also preferred as monomers that provide crosslinkable groups. In the present disclosure, the term "(per)fluoropolyoxyalkylene group" means a "fluoropolyoxyalkylene group or a perfluoropolyoxyalkylene group."

[0117] Z is preferably a (per)fluoroalkylene group having 4 to 12 carbon atoms, and R ２ , R ３ , R ４ , R ５ , R ６ and R ７ is preferably a hydrogen atom.

[0118] When Z is a (per)fluoropolyoxyalkylene group, the formula: -(Q) ｐ -CF ２ O-(CF ２ CF ２ O) ｍ -(CF ２ O) ｎ -CF ２ -(Q) ｐ- (wherein Q is an alkylene group having 1 to 10 carbon atoms or an oxyalkylene group having 2 to 10 carbon atoms, p is 0 or 1, and m and n are integers such that the m / n ratio is 0.2 to 5 and the molecular weight of the (per)fluoropolyoxyalkylene group is in the range of 500 to 10,000, preferably 1,000 to 4,000). In this formula, Q is preferably -CH ２ OCH ２ - and -CH ２ O (CH ２ CH ２ O) ｓ CH ２ -(s=1 to 3).

[0119] Preferred bisolefins are CH ２ =CH-(CF ２ ) ２ -CH=CH ２ , C.H. ２ =CH-(CF ２ ) ４ -CH=CH ２ , C.H. ２ =CH-(CF ２ ) ６ -CH=CH ２ , Formula: CH ２ = CH-Z １ -CH=CH ２ (In the formula, Z １ Ha-CH ２ OCH ２ -CF ２ O-(CF ２ CF ２ O) ｍ -(CF ２ O) ｎ -CF ２ -CH ２ OCH ２ - (m / n is 0.5, and the molecular weight is preferably 2000).

[0120] Among them, CH ２ =CH-(CF ２ ) ６ -CH=CH ２Preferred is 3,3,4,4,5,5,6,6,7,7,8,8-dodecafluoro-1,9-decadiene represented by the following formula:

[0121] The number average molecular weight Mn of the fluorine-containing elastomer is preferably from 1,000 to 1,000,000, more preferably from 10,000 to 500,000, and particularly preferably from 20,000 to 300,000.

[0122] The fluorine content of the fluorine-containing elastomer is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more. The upper limit of the fluorine content is preferably 75% by mass or less, and more preferably 73% by mass or less. １９ F-NMR and １ It is calculated based on measurements such as H-NMR and elemental analysis.

[0123] The Mooney viscosity at 121°C of the fluorine-containing elastomer (ML1+10(121°C)) is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, and particularly preferably 10 or more. It is also preferably 200 or less, more preferably 170 or less, even more preferably 150 or less, even more preferably 130 or less, and particularly preferably 100 or less. The Mooney viscosity is measured in accordance with ASTM D1646 and JIS K6300-1.

[0124] The number average molecular weight of the fluorine-containing elastomer is preferably from 1,000 to 300,000, and more preferably from 10,000 to 200,000. The number average molecular weight is measured by gel permeation chromatography (GPC).

[0125] The weight average molecular weight of the fluorine-containing elastomer is preferably from 1,500 to 450,000, and more preferably from 15,000 to 300,000. The weight average molecular weight is measured by gel permeation chromatography (GPC).

[0126] The glass transition temperature of the fluorine-containing elastomer is preferably −50 to 0° C. The glass transition temperature is more preferably −2° C. or lower, and even more preferably −3° C. or lower. The glass transition temperature is more preferably −45° C. or higher, and even more preferably −40° C. or higher. The glass transition temperature may be −10° C. or higher, or may be −9° C. or higher. Here, the glass transition temperature can be determined from the DSC differential curve in accordance with JIS K6240:2011, using a differential scanning calorimeter (for example, X-DSC7000 manufactured by Hitachi High-Tech Science Corporation) by heating 10 mg of a sample at a rate of 20° C. / min to obtain a DSC curve.

[0127] (Second Production Method) In the second production method of the present disclosure, a fluoromonomer is polymerized in the presence of a fluorine-containing diiodo compound (11), and then the fluoromonomer is polymerized in the presence of a fluorine-free diiodo compound (12), thereby obtaining a fluorine-containing elastomer.

[0128] As described in Patent Document 2, diiodomethane has been known as a chain transfer agent used in the production of fluorine-containing elastomers. However, when a fluorine-containing elastomer is produced using diiodomethane, the reaction rate is low, particularly in the early stage of the polymerization reaction, making it difficult to produce the fluorine-containing elastomer with high productivity. Furthermore, there is also the problem that it is difficult to produce a fluorine-containing elastomer that can give a molded article having excellent compression set resistance.

[0129] The second production method of the present disclosure, having the above-mentioned configuration, can produce a fluorine-containing elastomer crosslinkable by peroxide crosslinking with high productivity, and can produce the fluorine-containing elastomer more cheaply than a production method using only a fluorine-containing diiodo compound as a chain transfer agent. Furthermore, the molded article obtained by crosslinking the fluorine-containing elastomer obtained by the first production method of the present disclosure is excellent in heat resistance and compression set resistance.

[0130] The fluorine-containing diiodo compound (11) used in the second production method is a compound having a fluorine atom and two iodine atoms. Examples of the fluorine-containing diiodo compound (11) include the fluorine-containing diiodo compound (11) used in the first production method, and the same is preferable.

[0131] The fluorine-containing diiodo compound (11) may be added all at once or continuously. The timing of adding the fluorine-containing diiodo compound (11) is not particularly limited, but it is preferable to add at least a part of the fluorine-containing diiodo compound (11) until a fluorine-containing elastomer having a mass corresponding to 10 mass % of the mass of the finally obtained fluorine-containing elastomer is produced.

[0132] The fluorine-free diiodo compound (12) used in the second production method is a compound containing no fluorine atoms and two iodine atoms. Examples of the fluorine-free diiodo compound (12) include the fluorine-free diiodo compound (12) used in the first production method, and the same is preferably used.

[0133] The fluorine-free diiodo compound (12) may be added all at once or continuously. The timing of adding the fluorine-free diiodo compound (12) is not particularly limited, but it is preferable to add at least a part of the fluorine-free diiodo compound (12) after the production of a fluorine-containing elastomer in an amount corresponding to 30 to 90% by mass of the final fluorine-containing elastomer.

[0134] In one embodiment of the second production method, a fluoromonomer is polymerized in the presence of a fluorine-containing diiodo compound (11) until a fluoroelastomer is produced in an amount corresponding to 30 to 90% by mass of the mass of the finally obtained fluoroelastomer, and then the fluoromonomer is polymerized in the presence of a fluorine-free diiodo compound (12). This makes it possible to produce a fluoroelastomer crosslinkable by peroxide crosslinking with higher productivity, and also to produce a fluoroelastomer more cheaply than in a production method using only a fluorine-containing diiodo compound as a chain transfer agent.

[0135] The polymerization of the fluoromonomer in the presence of the fluorine-containing diiodo compound (11) is carried out until a fluoroelastomer is produced in an amount corresponding to preferably 30 to 90% by mass, more preferably 40% by mass or more, more preferably 80% by mass or less, based on the mass of the finally obtained fluoroelastomer.

[0136] The amount of the fluorine-containing diiodo compound (11) is preferably 0.2×10 based on the total amount of monomers used in the polymerization. －３ up to 2 mol%, more preferably 1.0 × 10 －３ % or more, and more preferably 1 mol % or less.

[0137] The amount of the fluorine-free diiodo compound (12) is preferably 0.2×10 based on the total amount of monomers used in the polymerization. －３ up to 2 mol%, more preferably 1.0 × 10 －３ % or more, and more preferably 1 mol % or less.

[0138] In the second production method, a polyfunctional fluorine-free monomer may be further polymerized in addition to the fluoromonomer. By using a polyfunctional fluorine-free monomer, a polyfunctional fluorine-free monomer unit can be introduced into the fluoroelastomer. The polyfunctional fluorine-free monomer unit in the fluoroelastomer imparts a branched structure to the fluoroelastomer or functions as a site crosslinkable by peroxide crosslinking. Therefore, by crosslinking the fluoroelastomer obtained by further polymerizing a polyfunctional fluorine-free monomer in addition to the fluoromonomer, a molded article having even better heat resistance and compression set resistance can be obtained. Furthermore, by introducing iodine atoms and a polyfunctional fluorine-free monomer unit into the fluoroelastomer, the mold releasability of the fluoroelastomer is improved.

[0139] The polyfunctional fluorine-free monomer used in the second production method is a monomer having two or more functional groups and not containing a fluorine atom. Examples of the polyfunctional fluorine-free monomer include the polyfunctional fluorine-free monomer used in the first production method, and the same monomers are preferably used and can be used in the same amounts.

[0140] The fluoromonomer used in the second production method is a monomer containing a fluorine atom. Examples of the fluoromonomer include the fluoromonomer used in the first production method, and the same fluoromonomers are preferred and can be used in the same amounts.

[0141] The polymerization in the second production method can be carried out, for example, by charging a surfactant and an aqueous medium into a pressure-resistant polymerization vessel equipped with a stirrer, deoxidizing, then charging the monomer, adjusting the temperature to a predetermined level, adding a polymerization initiator to start the reaction, and charging the diiodo compound during the polymerization reaction. Since the pressure decreases as the reaction proceeds, additional monomer is continuously or intermittently supplied to maintain the initial pressure. Once a predetermined amount of monomer has been supplied, the supply is stopped, the monomer in the reaction vessel is purged, and the temperature is returned to room temperature to terminate the reaction.

[0142] The polymerization in the second production method can be carried out in the presence of a polymerization initiator. Examples of the polymerization initiator include the polymerization initiators used in the first production method, and the same initiators can be used preferably in the same amounts.

[0143] The polymerization in the second production method can be carried out in the presence of a surfactant. Examples of the surfactant include those used in the first production method, and the same surfactants are preferred.

[0144] The polymerization in the second production method can be carried out in an aqueous medium. Examples of the aqueous medium include the aqueous medium used in the first production method, and the same is preferable.

[0145] The polymerization temperature in the second production method is preferably 10 to 120° C. The polymerization pressure in the first production method is preferably 0.5 to 10 MPaG.

[0146] According to the second production method, a fluorine-containing elastomer can be obtained. In one embodiment, the fluorine-containing elastomer obtained by the second production method has a multimodal molecular weight distribution. In another embodiment, the fluorine-containing elastomer obtained by the second production method has a bimodal molecular weight distribution. The fluorine-containing elastomer preferably has a bimodal molecular weight distribution such that the ratio ((A) / (B)) of the area of ​​the peak on the high molecular weight side (A) to the area of ​​the peak on the low molecular weight side (B) appearing in a GPC curve is 90 / 10 to 30 / 70. When the fluorine-containing elastomer has such a molecular weight distribution, a molded article having excellent heat resistance and compression set resistance can be obtained, and the moldability of the fluorine-containing elastomer is improved.

[0147] The ratio ((A) / (B)) of the fluorine-containing elastomer obtained by the second production method is preferably 90 / 10 to 30 / 70, more preferably 80 / 20 or less, and more preferably 40 / 60 or more.

[0148] The fluorine-containing elastomer obtained by the second production method may have the same structure as the fluorine-containing elastomer obtained by the first production method, except that the inclusion of a polyfunctional fluorine-free monomer unit is optional.

[0149] (Crosslinkable composition) A crosslinkable composition can be produced by adding a crosslinking agent, etc. to the fluorine-containing elastomer obtained by the first production method, the fluorine-containing elastomer according to one embodiment of the present disclosure, or the fluorine-containing elastomer obtained by the second production method. A molded article can be obtained by crosslinking the crosslinkable composition containing the fluorine-containing elastomer and the peroxide crosslinking agent.

[0150] The type and amount of the crosslinking agent are not particularly limited and may be within known ranges. As the crosslinking agent, a peroxide crosslinking agent is preferred, and an organic peroxide is more preferred.

[0151] The organic peroxide may be any organic peroxide that can easily generate peroxy radicals in the presence of heat or a redox system, and examples thereof include 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α,α-bis(t-butylperoxy)-p-diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3, benzoyl peroxide, t-butylperoxybenzene, t-butylperoxymaleic acid, t-butylperoxyisopropyl carbonate, and t-butylperoxybenzoate. Among these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3 are preferred.

[0152] The amount of the organic peroxide to be blended is preferably 0.1 to 15 parts by mass, more preferably 0.3 to 5 parts by mass, per 100 parts by mass of the fluorine-containing elastomer.

[0153] The crosslinkable composition preferably further contains a crosslinking aid. Examples of the crosslinking aid include triallyl cyanurate, triallyl isocyanurate (TAIC), triacryl formal, triallyl trimellitate, N,N'-m-phenylene bismaleimide, dipropargyl terephthalate, diallyl phthalate, tetraallyl terephthalate amide, triallyl phosphate, bismaleimide, fluorinated triallyl isocyanurate (1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine-2,4,6-trimethylsilyl)propan-2-one, and the like. Examples of suitable terpolymers include methyltrimethylsiloxane, ...

[0154] The amount of cross-linking aid blended is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 7.0 parts by mass, and even more preferably 0.1 to 5.0 parts by mass, per 100 parts by mass of the fluorine-containing elastomer. If the amount of cross-linking aid is less than 0.01 part by mass, the mechanical properties and flexibility tend to deteriorate. If the amount exceeds 10 parts by mass, the heat resistance tends to deteriorate and the durability of the molded product also tends to deteriorate.

[0155] The crosslinkable composition may be blended with various additives that are commonly blended into elastomers, such as fillers (carbon black, barium sulfate, etc.), processing aids (wax, etc.), plasticizers, colorants, stabilizers, tackifiers (coumarone resins, coumarone-indene resins, etc.), release agents, electrical conductivity imparting agents, thermal conductivity imparting agents, surface non-tackifying agents, flexibility imparting agents, heat resistance improving agents, and flame retardants, as well as one or more commonly used crosslinking agents and crosslinking accelerators different from the above-mentioned ones.

[0156] The content of the filler such as carbon black is not particularly limited, but is preferably from 0 to 300 parts by mass, more preferably from 1 to 150 parts by mass, still more preferably from 2 to 100 parts by mass, and particularly preferably from 2 to 75 parts by mass, per 100 parts by mass of the fluorine-containing elastomer.

[0157] The content of the processing aid such as wax is preferably 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, per 100 parts by mass of the fluorine-containing elastomer. When a processing aid, plasticizer or release agent is used, the mechanical properties and sealing properties of the resulting molded article tend to deteriorate, so it is necessary to adjust the content of these agents within a range that allows the desired properties of the resulting molded article.

[0158] The method for preparing the crosslinkable composition is not particularly limited as long as it can uniformly mix the fluorine-containing elastomer and the crosslinking agent. For example, there is a method in which powder obtained by coagulating the fluorine-containing elastomer alone is kneaded with other additives and compounding ingredients, if necessary, in a kneader such as an open roll.

[0159] (Molded Article) A molded article can be obtained by crosslinking the crosslinkable composition. Alternatively, a molded article can be obtained by molding and crosslinking the composition. The composition can be molded by a conventionally known method. The molding and crosslinking methods and conditions may be within the range of known methods and conditions for the molding and crosslinking employed. The order of molding and crosslinking is not limited, and molding may be followed by crosslinking, crosslinking may be followed by molding, or molding and crosslinking may be performed simultaneously.

[0160] Examples of molding methods include, but are not limited to, compression molding, casting, injection molding, extrusion molding, and rotocure molding. Examples of crosslinking methods that can be used include steam crosslinking, heat crosslinking, and radiation crosslinking, with steam crosslinking and heat crosslinking being preferred. Specific crosslinking conditions, which are not limited to, are typically a temperature range of 140 to 250°C, a crosslinking time of 1 minute to 24 hours, and can be determined appropriately depending on the types of crosslinking accelerator, crosslinking agent, acid acceptor, etc.

[0161] Furthermore, by heating the obtained molded article in an oven or the like, it is possible to improve the mechanical properties and the compression set characteristics at high temperatures, etc. Specific crosslinking conditions, which are not limited to any particular conditions, are usually in the temperature range of 140 to 300°C and the time range of 30 minutes to 72 hours, and may be appropriately determined depending on the type of crosslinking agent, etc.

[0162] The obtained molded articles can be used as various parts in various fields such as the automotive industry, the aircraft industry, the semiconductor industry, etc. The molded articles can be used for applications similar to the crosslinked rubber molded articles described in JP-A-2013-216915 and the fluororubber molded articles described in JP-A-2019-94430, such as sealing materials, sliding members, and non-adhesive members.

[0163] Examples of uses of the molded articles include various sealing materials and packings such as rings, packings, gaskets, diaphragms, oil seals, and bearing seals. As sealing materials, they can be used in applications requiring excellent non-stick properties and low friction. In particular, they can be suitably used as various sealing materials in the automotive industry, etc.

[0164] It can also be used as a tube, hose, roll, various rubber rolls, flexible joint, rubber plate, coating, belt, damper, valve, valve seat, valve body, chemical-resistant coating material, laminating material, lining material, etc.

[0165] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0166] <1> According to a first aspect of the present disclosure, there is provided a method for producing a fluorine-containing elastomer, comprising polymerizing a fluoromonomer and a polyfunctional fluorine-free monomer in the presence of a diiodo compound to obtain a fluorine-containing elastomer. <2> According to a second aspect of the present disclosure, there is provided a production method according to the first aspect, in which the fluoromonomer contains at least one selected from the group consisting of vinylidene fluoride and tetrafluoroethylene. <3> According to a third aspect of the present disclosure, there is provided a production method according to the first or second aspect, in which the polyfunctional fluorine-free monomer has 2 to 6 functional groups. <4> According to a fourth aspect of the present disclosure, there is provided a production method according to any of the first to third aspects, in which the polyfunctional fluorine-free monomer has an unsaturated functional group. <5> According to a fifth aspect of the present disclosure, there is provided a production method according to any of the first to fourth aspects, in which the polyfunctional fluorine-free monomer has at least one unsaturated functional group selected from the group consisting of a vinyl group, an isopropenyl group, an allyl group, and a methallyl group. <6> According to a sixth aspect of the present disclosure, there is provided a production method according to any one of the first to fifth aspects, in which the polyfunctional fluorine-free monomer has a nitrogen-containing heterocycle. <7> According to a seventh aspect of the present disclosure, there is provided a production method according to any one of the first to sixth aspects, in which the polyfunctional fluorine-free monomer is at least one selected from the group consisting of triallyl isocyanurate and trimethallyl isocyanurate. <8> According to an eighth aspect of the present disclosure, there is provided a production method according to any one of the first to seventh aspects, in which the diiodo compound is both a fluorine-containing diiodo compound and a fluorine-free diiodo compound. <9> According to a ninth aspect of the present disclosure, there is provided a production method according to any one of the first to eighth aspects, in which the diiodo compound is both a fluorine-containing diiodo compound having two or more carbon atoms and a fluorine-free diiodo compound having one carbon atom. <10> A tenth aspect of the present disclosure provides the production method according to any one of the first to ninth aspects, wherein the diiodo compound is both 1,4-diiodoperfluoro-n-butane and diiodomethane.<11> According to an eleventh aspect of the present disclosure, there is provided a production method according to any of the first to tenth aspects, which comprises polymerizing a fluoromonomer in the presence of a diiodo compound (1), and then polymerizing the fluoromonomer in the presence of a fluorine-free diiodo compound (12) to obtain a fluorine-containing elastomer. <12> According to a twelfth aspect of the present disclosure, there is provided a production method according to any of the first to eleventh aspects, which comprises polymerizing a fluoromonomer in the presence of a diiodo compound (1) until a fluoroelastomer is produced in an amount corresponding to 30 to 90 mass% of the mass of the finally obtained fluorine-containing elastomer, and then polymerizing the fluoromonomer in the presence of a fluorine-free diiodo compound (12) to obtain a fluorine-containing elastomer. <13> According to a thirteenth aspect of the present disclosure, there is provided a production method according to any of the first to twelfth aspects, in which the molar ratio of the amount of the polyfunctional fluorine-free monomer to the amount of the diiodo compound (polyfunctional fluorine-free monomer / diiodo compound) is 0.05 to 0.5. <14> According to a fourteenth aspect of the present disclosure, there is provided a fluorine-containing elastomer having an iodine content of 0.1 to 1.0 mass %, which contains a fluoromonomer unit and a polyfunctional non-fluorine-containing monomer unit. <15> According to a fifteenth aspect of the present disclosure, there is provided a fluorine-containing elastomer according to the fourteenth aspect, in which the content of the polyfunctional non-fluorine-containing monomer unit is 0.01 to 0.2 mol % based on the total monomer units. <16> According to a sixteenth aspect of the present disclosure, there is provided a fluorine-containing elastomer according to the fourteenth or fifteenth aspect, in which the fluoromonomer contains at least one selected from the group consisting of vinylidene fluoride and tetrafluoroethylene. <17> According to a seventeenth aspect of the present disclosure, there is provided a fluorine-containing elastomer according to any one of the fourteenth to sixteenth aspects, in which the polyfunctional non-fluorine-containing monomer has 2 to 6 functional groups. <18> According to an eighteenth aspect of the present disclosure, there is provided a fluorine-containing elastomer according to any one of the fourteenth to seventeenth aspects, in which the polyfunctional non-fluorine-containing monomer has an unsaturated functional group.<19> According to a nineteenth aspect of the present disclosure, there is provided a fluorine-containing elastomer according to any one of the fourteenth to eighteenth aspects, wherein the polyfunctional non-fluorine-containing monomer has at least one unsaturated functional group selected from the group consisting of a vinyl group, an isopropenyl group, an allyl group, and a methallyl group. <20> According to a twentieth aspect of the present disclosure, there is provided a fluorine-containing elastomer according to any one of the fourteenth to nineteenth aspects, wherein the polyfunctional non-fluorine-containing monomer has a nitrogen-containing heterocycle. <21> According to a twenty-first aspect of the present disclosure, there is provided a fluorine-containing elastomer according to any one of the fourteenth to twentieth aspects, wherein the polyfunctional non-fluorine-containing monomer is at least one selected from the group consisting of triallyl isocyanurate and trimethallyl isocyanurate. <22> According to a twenty-second aspect of the present disclosure, there is provided a fluorine-containing elastomer according to any one of the fourteenth to twenty-first aspects, wherein the polyfunctional non-fluorine-containing monomer is at least one selected from the group consisting of triallyl isocyanurate and trimethallyl isocyanurate. <23> According to a twenty-third aspect of the present disclosure, there is provided a fluorine-containing elastomer according to any one of the fourteenth to twenty-second aspects, which has a bimodal molecular weight distribution, and in which the ratio ((A) / (B)) of the area of ​​the peak on the high molecular weight side (A) to the area of ​​the peak on the low molecular weight side (B) appearing in a GPC curve is 90 / 10 to 30 / 70. <24> According to a twenty-fourth aspect of the present disclosure, there is provided a crosslinkable composition containing the fluorine-containing elastomer according to any one of the fourteenth to twenty-third aspects and a peroxide crosslinking agent. <25> According to a twenty-fifth aspect of the present disclosure, there is provided a molded article obtained by crosslinking the crosslinkable composition according to the twenty-fourth aspect. <25> According to a twenty-sixth aspect of the present disclosure, there is provided a method for producing a fluorine-containing elastomer, which comprises polymerizing a fluoromonomer in the presence of a fluorine-containing diiodo compound (11), and then polymerizing the fluoromonomer in the presence of a fluorine-free diiodo compound (12), thereby obtaining the fluorine-containing elastomer. <27> According to a twenty-seventh aspect of the present disclosure, there is provided the production method according to the twenty-sixth aspect, wherein the fluorine-containing diiodo compound (11) has a carbon number of 2 or more. <28> According to a twenty-eighth aspect of the present disclosure, there is provided the production method according to the twenty-sixth or twenty-seventh aspect, wherein the fluorine-containing diiodo compound (11) is 1,4-diiodoperfluoro-n-butane.<29> According to a 29th aspect of the present disclosure, there is provided the production method according to any of the 26th to 28th aspects, wherein the number of carbon atoms in the fluorine-free diiodo compound (12) is 1. <30> According to a 30th aspect of the present disclosure, there is provided the production method according to any of the 26th to 29th aspects, wherein the fluorine-free diiodo compound (12) is diiodomethane. <31> According to a 31st aspect of the present disclosure, there is provided the production method according to any of the 26th to 30th aspects, wherein a fluoromonomer is polymerized in the presence of a fluorine-containing diiodo compound (11) until a fluoroelastomer is produced in an amount corresponding to 30 to 90 mass% of the mass of the finally obtained fluoroelastomer, and then the fluoromonomer is polymerized in the presence of a fluorine-free diiodo compound (12), thereby obtaining a fluoroelastomer. <32> According to a thirty-second aspect of the present disclosure, there is provided the production method according to any one of the twenty-sixth to thirty-first aspects, wherein the finally obtained fluorine-containing elastomer has a bimodal molecular weight distribution, and the ratio ((A) / (B)) of the area of ​​the peak on the high molecular weight side (A) to the area of ​​the peak on the low molecular weight side (B) appearing in a GPC curve is 90 / 10 to 30 / 70. <33> According to a thirty-third aspect of the present disclosure, there is provided the production method according to any one of the twenty-sixth to thirty-second aspects, wherein a polyfunctional non-fluorine-containing monomer is further polymerized in addition to the fluoromonomer.

[0167] Next, an embodiment of the present disclosure will be described using experimental examples, but the present disclosure is not limited to such experimental examples.

[0168] The values ​​in the experimental examples were measured by the following methods.

[0169] <Composition analysis> １９ Measurement was performed using F-NMR (Bruker AC300P model), with the TAIC unit being measured by the method described below.

[0170] <Iodine Content> Iodine content is measured using a Yokogawa Hewlett-Packard G2350A.

[0171] <Content of TAIC units> The TAIC used in copolymerization was uniformly dissolved in acetone to give concentrations of 0.02 mol%, 0.04 mol%, and 0.06 mol% for Polymer A obtained in Comparative Experimental Example 1, in which TAIC was not copolymerized. This solution was applied to an aluminum cup, and the acetone was dried in an electric furnace at 90°C until a constant weight was reached. Each of the obtained samples was measured in the ATR mode of an infrared spectrophotometer. －１ The height of the peak due to the carbonyl group (-C=O) of TAIC and the main peak at 1180 cm －１ A calibration curve was prepared based on the ratio of the height of the peak derived from the C—F group of the fluororubber. The amount of TAIC copolymerization of the test sample was calculated using this calibration curve. Measurements were performed at three locations for each sample, and the average value was used as the amount of copolymerization. The height of the peak derived from the carbonyl group (—C═O) of TAIC was calculated as 1700 to 1715 cm －１ The average value of the height of the IR spectrum appearing within the range of

[0172] <Weight-average molecular weight (Mw) and number-average molecular weight (Mn)> Apparatus: HLC-8320 (manufactured by Tosoh Corporation) Columns: GPC KF-806M (2 columns), GPC KF-801 (1 column), GPC KF-802 (1 column) Detector: differential refractometer Developing solvent: tetrahydrofuran Temperature: 40°C Sample concentration: 0.2 wt% Standard sample: various monodisperse polystyrenes ((Mw / Mn) = 1.14 (Max)), TSK standard POLYSTYRENE (manufactured by Tosoh Corporation)

[0173] <Mooney Viscosity> Measured in accordance with ASTM-D1646 and JIS K6300-1. Measuring instrument: Automatic Mooney Viscometer manufactured by Ueshima Seisakusho Co., Ltd. Rotor rotation speed: 2 rpm Measurement temperature: 121°C

[0174] Experimental Example 1 2200 ml of pure water and C as an emulsifier were placed in a 3.0 L stainless steel reaction vessel. ５ F １１ CHOONH ４4.456 g, 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(1,1,2-trifluoroallyloxy)propoxy]propionic acid ammonium salt 0.224 g was added, and the internal space was thoroughly substituted with nitrogen gas, and then a mixed gas A having a molar ratio of VdF / TFE / HFP of 19 / 11 / 70 was charged, and the reaction vessel temperature was raised to 80 ° C. with stirring, and then the pressure was adjusted to 2.0 MPa. Thereafter, 10 g of a 0.45% aqueous solution of ammonium persulfate (hereinafter abbreviated as APS) was injected to initiate polymerization. Thereafter, the pressure dropped to 1.9 MPa, and the pressure was repeatedly increased to 2.0 MPa with a mixed gas B of TFE / VDF / HFP = 27 / 49 / 24. When the amount of mixed gas B charged reached 16 g, 5.544 g of 1,4-diiodoperfluoro-n-butane (hereinafter abbreviated as DI) was injected, and polymerization was continued. Every 3 hours from the start of polymerization, 10 g of an aqueous APS solution of the same concentration as above was continuously added until the polymerization was complete. When the amount of mixed gas B charged reached 166 g, 0.447 g of TAIC was injected. Thereafter, when the amount of mixed gas B charged reached 828 g, the polymerization was terminated by blowing and cooling the monomers in the polymerization vessel, and 2,987 g of an emulsion was obtained. The solids content of this emulsion was 27.0%. The time required for polymerization was 9 hours and 28 minutes. A portion of the emulsion was taken, and a 5% aqueous aluminum sulfate solution was added to coagulate the polymer. The polymer was then washed and dried. The composition of the resulting polymer was determined by F-NMR to be VDF / TFE / HFP = 50.5 / 27.8 / 21.7. The iodine content measured by the combustion ion method was 0.37% by weight, and the copolymerization amount of TAIC measured by IR was 0.022 mol%. The number average molecular weight Mn measured by GPC was 65,600, Mw was 128,700, and the Mooney viscosity ML measured at 121°C was １２１℃ was 23.0.

[0175] Experimental Example 2 Polymerization was carried out in the same manner as in Experimental Example 1, except that the amount of TAIC added was changed to 0.067 g. The obtained emulsion weighed 3,012 g, and the solids content of this emulsion was 26.8%. The time required for polymerization was 10 hours and 41 minutes. The composition of Polymer 2 obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=51.0 / 27.9 / 21.1 as determined by F-NMR. The iodine content was 0.54 wt% by combustion ion spectroscopy, and the amount of copolymerization of TAIC measured by IR was 0.036 mol%. GPC could not be measured because the polymer was insoluble in the solvent, but the Mooney viscosity (ML) measured at 121°C was １２１℃ was 12.7.

[0176] Experimental Example 3 Polymerization was carried out in the same manner as in Experimental Example 1, except that the amount of TAIC added was changed to 1.005 g. The obtained emulsion weighed 3,039 g, and the solids content of this emulsion was 27.1%. The time required for polymerization was 13 hours and 40 minutes. The composition of Polymer 3 obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=50.1 / 27.5 / 22.4 as determined by F-NMR. The iodine content was 0.53 wt % by combustion ion spectroscopy, and the amount of copolymerization of TAIC measured by IR was 0.057 mol %. GPC could not be measured because the polymer was insoluble in the solvent, but the Mooney viscosity (ML) measured at 121°C was １２１℃ was 22.8.

[0177] Experimental Example 4 Polymerization was carried out in the same manner as in Experimental Example 1, except that the amount of TAIC added was changed to 1.340 g. The obtained emulsion weighed 3,076 g, and the solids content of this emulsion was 26.8%. The time required for polymerization was 10 hours and 41 minutes. The composition of Polymer 4 obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=50.7 / 27.4 / 22.0 as determined by F-NMR. The iodine content was 0.49 wt% by combustion ion spectroscopy, and the copolymerization amount of TAIC measured by IR was 0.060 mol%. GPC could not be measured because the polymer was insoluble in the solvent, but the Mooney viscosity (ML) measured at 121°C was １２１℃ was 23.4.

[0178] Experimental Example 5 7.392 g of DI was added to CH ２ I２ Change to 3.490 g, and CH ２ I ２ Polymerization was carried out in the same manner as in Experimental Example 1, except that the method of charging the initiator APS after charging was changed as follows. When the amount of charged mixed gas B reached 16 g, CH ２ I ２ When 3.490 g of the initiator was added, the polymerization temporarily stopped, and 10 g of a 0.45% aqueous solution of the initiator APS was added. The same amount of 0.45% aqueous solution of the initiator APS was then added every hour until the polymerization rate recovered. In this polymerization, the polymerization rate recovered after 12 additions, so the APS addition method described in Experimental Example 1 was used again. The resulting emulsion weighed 2984 g, and the solids content of this emulsion was 27.0%. The polymerization time was 9 hours and 28 minutes. The composition of Polymer 5, obtained in the same manner as in Experimental Example 1, was determined by F-NMR to be VDF / TFE / HFP = 50.6 / 26.9 / 22.5. The iodine content was 0.39 wt % by combustion ionization spectroscopy, and the copolymerization amount of TAIC measured by IR was 0.025 mol %. The number average molecular weight Mn measured by GPC was 60,500, the weight average molecular weight Mw was 156,600, and the Mooney viscosity ML measured at 121°C １２１℃ was 26.0.

[0179] Experimental Example 6 2200 ml of pure water and C as an emulsifier were placed in a 3.0 L stainless steel reaction vessel. ５ F １１ CHOONH ４4.457 g of the above and 0.224 g of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(1,1,2-trifluoroallyloxy)propoxy]propionic acid ammonium salt were added, and the internal space was thoroughly purged with nitrogen gas. Then, a mixed gas A having a molar ratio of VdF / TFE / HFP of 19 / 11 / 70 was charged, and the reaction vessel temperature was raised to 80°C with stirring. The pressure was then adjusted to 2.0 MPa, and 10 g of a 0.45% aqueous solution of APS was injected to initiate polymerization. Thereafter, the pressure dropped to 1.9 MPa, and the pressure was repeatedly increased to 2.0 MPa with a mixed gas B of TFE / VDF / HFP = 27 / 49 / 24. When the amount of mixed gas B charged reached 16 g, 2.867 g of 1,4-diiodoperfluoro-n-butane (hereinafter abbreviated as DI) was injected, and polymerization was continued. Every 3 hours after the start of polymerization, 10 g of an aqueous solution of APS having the same concentration as above was added to CH ２ I ２ When the amount of mixed gas B reached 166 g, 0.392 g of TAIC was added, and when the amount reached 497 g, 0.392 g of CH ２ I ２3.241 g was added, but as in Experimental Example 5, the polymerization temporarily stopped, and the initiator APS charging method described in Experimental Example 5 was repeated until the polymerization rate recovered. In this polymerization, the polymerization rate recovered after eight chargings, and the APS charging method described in Experimental Example 1 was resumed thereafter. Thereafter, when the charged amount of mixed gas B reached 553 g, 0.789 g of TAIC was added, and when the charged amount of mixed gas B reached 828 g, the monomer in the polymerization vessel was blown out and cooled to terminate the polymerization, yielding 3,103 g of an emulsion. The solids content of this emulsion was 27.3%. The time required for polymerization was 11 hours and 58 minutes. A portion of the emulsion was taken, a 5% aqueous aluminum sulfate solution was added, and the polymer was coagulated. The polymer was then washed and dried, and the composition of the resulting polymer 6 was determined by F-NMR to be VDF / TFE / HFP=51.0 / 27.4 / 21.6. The iodine content measured by the combustion ion method was 0.57% by weight, and the amount of copolymerization of TAIC measured by IR was 0.041 mol%. The number average molecular weight Mn measured by GPC was 53,700, the weight average molecular weight Mw was 177,800, and the Mooney viscosity ML measured at 121°C was １２１℃ was 28.4.

[0180] Experimental Example 7 Polymerization was carried out in the same manner as in Experimental Example 6, except that TAIC was not added when the amount of mixed gas B charged reached 553 g. The resulting emulsion weighed 3,072 g, and the solids content of this emulsion was 27.2%. The time required for polymerization was 11 hours and 58 minutes. The composition of Polymer 7 obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=51.0 / 27.4 / 21.6 as determined by F-NMR. The iodine content measured by combustion ion spectroscopy was 0.52 wt %, and the amount of TAIC copolymerized measured by IR was 0.021 mol %. The number average molecular weight Mn measured by GPC was 47,300, the weight average molecular weight Mw was 161,100, and the Mooney viscosity ML measured at 121°C was 0.021 mol %. １２１℃ was 22.0.

[0181] Experimental Example 8 When the amount of mixed gas B charged reached 16 g, 2.867 g of DI was added to CH ２ I ２ Polymerization was carried out in the same manner as in Experimental Example 6, except that the amount of CH２ I ２ is charged twice, and each time the CH ２ I ２ The initiator APS was charged in the same manner as in Example 1. Five charges of the initiator were made after the first charge, and four charges of the initiator were made after the second charge. The resulting emulsion weighed 3,152 g, and the solids content of this emulsion was 26.6%. The time required for polymerization was 14 hours and 6 minutes. The composition of Polymer 8 obtained in the same manner as in Example 1 was VDF / TFE / HFP=51.3 / 25.9 / 22.8 as determined by F-NMR. The iodine content measured by combustion ion spectroscopy was 0.52 wt %, and the amount of copolymerization of TAIC measured by IR was 0.030 mol %. The number average molecular weight Mn measured by GPC was 54,900, the weight average molecular weight Mw was 184,700, and the Mooney viscosity ML measured at 121°C was 0. １２１℃ was 33.8.

[0182] Comparative Experiment 1: In a 3.0 L stainless steel reactor, 2012 ml of pure water and C as an emulsifier were placed. ５ F １１ CHOONH ４4.457 g of 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(1,1,2-trifluoroallyloxy)propoxy]propionic acid ammonium salt was added, and the internal space was thoroughly substituted with nitrogen gas. Then, a mixed gas A having a molar ratio of VdF / TFE / HFP of 19 / 11 / 70 was charged, and the reactor temperature was raised to 80 ° C. with stirring, and the pressure was adjusted to 2.0 MPa. Thereafter, 10 g of a 0.45% aqueous solution of ammonium persulfate (hereinafter abbreviated as APS) was injected to initiate polymerization. Thereafter, the pressure dropped to 1.9 MPa, and the pressure was repeatedly increased to 2.0 MPa with a mixed gas B of TFE / VDF / HFP = 27 / 49 / 24. When the amount of mixed gas B charged reached 16 g, 7.392 g of DI was injected, and the polymerization was continued. Every 3 hours from the start of the polymerization, 10 g of the same aqueous APS solution as above was continuously added until the polymerization was completed. When the amount of mixed gas B charged reached 828 g, the polymerization was terminated by blowing out and cooling the monomers in the polymerization tank, and 2,947 g of an emulsion was obtained. The solids content of this emulsion was 27.0%. The time required for the polymerization was 7 hours and 48 minutes. A portion of the emulsion was taken, and a 5% aqueous aluminum sulfate solution was added to coagulate the polymer. The polymer was washed and dried. The composition of the obtained polymer A was determined by F-NMR to be VDF / TFE / HFP=50.6 / 27.9 / 21.5. The iodine content was 0.52 wt% by combustion ion spectrometry. The number average molecular weight Mn was 41,300, the weight average molecular weight Mw was 59,900, and the Mooney viscosity ML measured at 121°C was １２１℃ was 3.6.

[0183] Comparative Experimental Example 2 Polymerization was carried out in the same manner as in Comparative Experimental Example 1, except that the amount of DI charged was changed to 4.332 g. The obtained emulsion weighed 3,079 g, and the solids content of this emulsion was 26.7%. The time required for polymerization was 7 hours and 24 minutes. The composition of Polymer B obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=51.2 / 26.0 / 22.8 as determined by F-NMR. The iodine content was 0.25 wt% as determined by the combustion ion method. The number average molecular weight Mn measured by GPC was 62,700, the weight average molecular weight Mw was 102,200, and the Mooney viscosity ML measured at 121°C was 0.25 wt%.１２１℃ was 22.0.

[0184] Comparative Experiment 3 7.392 g of DI was injected into CH ２ I ２ Change to 3.514 g, and CH ２ I ２ Polymerization was carried out in the same manner as in Comparative Experimental Example 1, except that the APS charging method described in Experimental Example 5 was adopted after charging of APS. In this polymerization, APS was charged 10 times until the polymerization rate recovered. The obtained emulsion weighed 3,217 g, and the solids content of this emulsion was 25.9%. The time required for polymerization was 16 hours and 52 minutes. The composition of Polymer C obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=50.5 / 27.3 / 22.3 as determined by F-NMR. The iodine content was 0.37 wt% as determined by the combustion ionization method. The number average molecular weight Mn measured by GPC was 49,800, the weight average molecular weight Mw was 95,100, and the Mooney viscosity ML measured at 121°C was 0.37 wt%. １２１℃ was 13.0.

[0185] Comparative Experimental Example 4 Polymerization was carried out in the same manner as in Experimental Example 6, except that TAIC was not added twice during the polymerization. ２ I ２ After the charging, APS was charged four times. The obtained emulsion weighed 3,037 g, and the solid content of this emulsion was 27.1%. The time required for polymerization was 8 hours and 59 minutes. The composition of Polymer D obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=51.4 / 27.4 / 21.2 by F-NMR. The iodine content measured by the combustion ion method was 0.55 wt%. The number average molecular weight Mn measured by GPC was 42,100, the weight average molecular weight Mw was 83,300, and the Mooney viscosity ML measured at 121°C was 0.55 wt%. １２１℃ was 11.6.

[0186] Comparative Experimental Example 5 Polymerization was carried out in the same manner as in Experimental Example 8, except that TAIC was not added during the polymerization. ２ I ２The number of times APS was charged after the first charge was 9 times, and after the second charge it was 3 times. The obtained emulsion weighed 3,142 g, and the solids content of this emulsion was 26.0%. The time required for polymerization was 14 hours and 22 minutes. The composition of Polymer E obtained in the same manner as in Experimental Example 1 was VDF / TFE / HFP=50.9 / 27.4 / 21.6 by F-NMR. The iodine content was 0.55 wt% by combustion ion method. The number average molecular weight Mn measured by GPC was 35,043, the weight average molecular weight Mw was 66,900, and the Mooney viscosity ML measured at 121°C was 0.55 wt%. １２１℃ was 9.3.

[0187] Experimental Examples 9 to 16, Comparative Experimental Examples 6 to 10 In these Experimental Examples, crosslinkable compositions were prepared by the following method using the polymers (fluorine-containing elastomers) obtained in the above Experimental Examples and Comparative Experimental Examples. Various physical properties were measured using the obtained crosslinkable compositions. The results are shown in Tables 1 and 2.

[0188] (Breakdown of crosslinkable composition) Fluorine-containing elastomer 100 parts by mass Carbon black MT-C 20 parts by mass Triallyl isocyanurate (TAIC) 4 parts by mass Perhexa 25B (trade name, manufactured by NOF Corporation) (PO) 1.5 parts by mass

[0189] (Crosslinking conditions) Kneading method: Roll kneading Press crosslinking: 10 minutes at 160°C Oven crosslinking: 4 hours at 180°C

[0190] <Crosslinking characteristics> A crosslinking curve of the crosslinkable composition at 170°C was obtained using a rheometer (Premier MDR, manufactured by Alpha Technology Co., Ltd.), and the minimum viscosity minimum torque (ML), maximum degree of vulcanization torque (MH), induction time (T10) and optimum crosslinking time (T90) were determined.

[0191] <100% Modulus (M100)> The crosslinkable composition was subjected to primary press crosslinking and secondary oven crosslinking under the above-mentioned crosslinking conditions to prepare a sheet having a thickness of 2 mm, and the 100% modulus at 23°C of the obtained sheet was measured in accordance with JIS-K6251.

[0192] <Tensile Breaking Strength (Tb) and Tensile Breaking Elongation (Eb)> The crosslinkable composition was subjected to primary press crosslinking and secondary oven crosslinking under the above-described crosslinking conditions to prepare a sheet having a thickness of 2 mm, and the tensile breaking strength (Tb) and tensile breaking elongation (Eb) of the obtained sheet at 23°C were measured in accordance with JIS-K6251.

[0193] <Hardness (Hs)> The crosslinkable composition was subjected to primary press crosslinking and secondary oven crosslinking under the above-mentioned crosslinking conditions to prepare a sheet having a thickness of 2 mm, and the hardness (Hs: type A durometer, peak value) of the obtained sheet at 23°C was measured in accordance with JIS-K6253.

[0194] <Heat Resistance> A 2 mm thick sheet was prepared by subjecting the crosslinkable composition to primary press crosslinking and secondary oven crosslinking under the above-mentioned crosslinking conditions, and the obtained sheet was heat treated at 250°C for 72 hours. Thereafter, the 100% modulus (M100), tensile strength at break (Tb), tensile elongation at break (Eb) and hardness (Hs) after heat treatment were measured by the above-mentioned methods. Then, the rate of change in the measured values ​​of these physical properties before and after heat treatment was calculated according to the following formula: ΔX=(X−X ０ ) / X ０ ×100 ΔX: Rate of change (%) X ０ : Measured value before heat treatment X: Measured value after heat treatment

[0195] <Compression Set (CS)> A JIS block was prepared by subjecting the crosslinkable composition to primary press crosslinking and secondary oven crosslinking under the above-mentioned crosslinking conditions, and the compression set (CS) was measured in accordance with JIS-K6301 (the JIS block was held at 200°C for 72 hours under 25% compression and then left in a thermostatic chamber at 25°C for 30 minutes).

[0196] <Warping of Sheet> A 2 mm thick sheet was prepared by subjecting the crosslinkable composition to primary press crosslinking and secondary oven crosslinking under the above-described crosslinking conditions, and the obtained sheet was left in a thermostatic chamber at 25°C for 30 minutes. After leaving the sheet, the four corners of the sheet were visually observed and evaluated according to the following criteria: Yes: Warping was observed at the four corners of the sheet No: No warping was observed at the four corners of the sheet

[0197] <Mold Releasability> Using a mold capable of molding 20 O-rings, primary press crosslinking was carried out at 170°C for 5 minutes without applying a mold release agent, and the obtained O-rings were manually removed from the mold. The number of O-rings that were significantly adhered to the mold and difficult to release after this operation, or O-rings that had cracks or dents, was recorded as the number of mold release defects. This operation was repeated five times, and the average number of O-rings that were defective in mold release per operation was calculated and evaluated according to the following evaluation criteria. Excellent: 3 or less Good: 4 to 7 Fair: 8 to 11 Poor: 12 to 15 Very Poor: 16 or more

[0198]

[0199]

Claims

1. A method for producing a fluorine-containing elastomer, comprising polymerizing a fluoromonomer and a polyfunctional non-fluorine-containing monomer in the presence of a diiodo compound to obtain a fluorine-containing elastomer.

2. 2. The process according to claim 1, wherein the fluoromonomer comprises at least one member selected from the group consisting of vinylidene fluoride and tetrafluoroethylene.

3. The method according to claim 1 or 2, wherein the polyfunctional non-fluorine-containing monomer has 2 to 6 functional groups.

4. The method according to claim 1 or 2, wherein the polyfunctional non-fluorine-containing monomer has an unsaturated functional group.

5. 3. The process according to claim 1, wherein the polyfunctional fluorine-free monomer has at least one unsaturated functional group selected from the group consisting of a vinyl group, an isopropenyl group, an allyl group and a methallyl group.

6. The method according to claim 1 or 2, wherein the polyfunctional fluorine-free monomer has a nitrogen-containing heterocycle.

7. 3. The method according to claim 1, wherein the polyfunctional fluorine-free monomer is at least one selected from the group consisting of triallyl isocyanurate and trimethallyl isocyanurate.

8. 3. The method according to claim 1 or 2, wherein the diiodo compound is both a fluorine-containing diiodo compound and a fluorine-free diiodo compound.

9. 3. The method according to claim 1 or 2, wherein the diiodo compound is both a fluorine-containing diiodo compound having two or more carbon atoms and a fluorine-free diiodo compound having one carbon atom.

10. 3. The method according to claim 1, wherein the diiodo compound is both 1,4-diiodoperfluoro-n-butane and diiodomethane.

11. 3. The process according to claim 1 or 2, wherein a fluoromonomer is polymerized in the presence of the diiodo compound (1), and then the fluoromonomer is polymerized in the presence of the fluorine-free diiodo compound (12), thereby obtaining a fluorine-containing elastomer.

12. The process according to claim 1 or 2, wherein a fluoromonomer is polymerized in the presence of a diiodo compound (1) until a fluoroelastomer having a mass corresponding to 30 to 90 mass% of the mass of the finally obtained fluoroelastomer is produced, and then the fluoromonomer is polymerized in the presence of a fluorine-free diiodo compound (12) to obtain a fluoroelastomer.

13. 3. The method according to claim 1, wherein the molar ratio of the amount of the polyfunctional non-fluorine-containing monomer to the amount of the diiodo compound (polyfunctional non-fluorine-containing monomer / diiodo compound) is 0.05 to 0.

5.

14. The iodine content is 0.1 to 1.0% by mass, Contains fluoromonomer units and polyfunctional non-fluorine-containing monomer units Fluorine-containing elastomer.

15. The fluorine-containing elastomer according to claim 14, wherein the content of the polyfunctional non-fluorine-containing monomer unit is 0.01 to 0.2 mol % based on the total monomer units.

16. 16. The fluorine-containing elastomer according to claim 14 or 15, wherein the fluoromonomer comprises at least one member selected from the group consisting of vinylidene fluoride and tetrafluoroethylene.

17. 16. The fluorine-containing elastomer according to claim 14, wherein the polyfunctional non-fluorine-containing monomer has 2 to 6 functional groups.

18. 16. The fluorine-containing elastomer according to claim 14 or 15, wherein the polyfunctional non-fluorine-containing monomer has an unsaturated functional group.

19. 16. The fluorine-containing elastomer according to claim 14 or 15, wherein the polyfunctional fluorine-free monomer has at least one unsaturated functional group selected from the group consisting of a vinyl group, an isopropenyl group, an allyl group and a methallyl group.

20. The fluorine-containing elastomer according to claim 14 or 15, wherein the polyfunctional fluorine-free monomer has a nitrogen-containing heterocycle.

21. 16. The fluorine-containing elastomer according to claim 14 or 15, wherein the polyfunctional fluorine-free monomer is at least one member selected from the group consisting of triallyl isocyanurate and trimethallyl isocyanurate.

22. 16. The fluorine-containing elastomer according to claim 14 or 15, which has a multimodal molecular weight distribution.

23. The fluorine-containing elastomer according to claim 14 or 15, which has a bimodal molecular weight distribution, and the ratio ((A) / (B)) of the area of ​​a peak on the high molecular weight side appearing in a GPC curve to the area (B) of a peak on the low molecular weight side is 90 / 10 to 30 / 70.

24. A crosslinkable composition comprising the fluorine-containing elastomer according to claim 14 or 15 and a peroxide crosslinking agent.

25. A molded article obtained by crosslinking the crosslinkable composition according to claim 24.

26. A method for producing a fluorine-containing elastomer, comprising polymerizing a fluoromonomer in the presence of a fluorine-containing diiodo compound (11), and then polymerizing the fluoromonomer in the presence of a fluorine-free diiodo compound (12), to obtain a fluorine-containing elastomer.

27. The method according to claim 26, wherein the fluorine-containing diiodo compound (11) has 2 or more carbon atoms.

28. The method according to claim 26 or 27, wherein the fluorine-containing diiodo compound (11) is 1,4-diiodoperfluoro-n-butane.

29. The method according to claim 26 or 27, wherein the non-fluorine-containing diiodo compound (12) has one carbon atom.

30. The method according to claim 26 or 27, wherein the fluorine-free diiodo compound (12) is diiodomethane.

31. The process according to claim 26 or 27, wherein a fluoromonomer is polymerized in the presence of a fluorine-containing diiodo compound (11) until a fluoroelastomer having a mass corresponding to 30 to 90 mass% of the mass of the finally obtained fluoroelastomer is produced, and then the fluoromonomer is polymerized in the presence of a fluorine-free diiodo compound (12), thereby obtaining a fluoroelastomer.

32. The process according to claim 26 or 27, wherein the finally obtained fluorine-containing elastomer has a bimodal molecular weight distribution, and the ratio ((A) / (B)) of the area of ​​a peak on the high molecular weight side appearing in a GPC curve to the area (B) of a peak on the low molecular weight side is 90 / 10 to 30 / 70.

33. The method according to claim 26 or 27, further comprising polymerizing a polyfunctional non-fluorine-containing monomer in addition to the fluoromonomer.