Perfluoroelastomer and crosslinked rubber article

Abstract

The present invention addresses the problem of providing a perfluoroelastomer having an excellent roll winding property. The present invention also addresses the problem of providing a crosslinked rubber article obtained by crosslinking the perfluoroelastomer.　Provided is a perfluoroelastomer in which a molecular weight distribution curve is obtained from a calibration curve of polymethyl methacrylate as a standard substance and a value measured by gel permeation chromatography, such curve showing a first peak indicating a first peak top in a region of a molecular weight from 1,000 to 100,000, and a second peak indicating a second peak top in a region of a molecular weight of more than 100,000.

Description

Perfluoroelastomers, cross-linked rubber products

[0001] The present invention relates to perfluoroelastomers and crosslinked rubber articles.

[0002] Crosslinked rubber articles obtained by crosslinking perfluoroelastomers are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Patent Document 1 describes a fluorine-containing elastic copolymer (perfluoroelastomer) having units based on tetrafluoroethylene and units based on perfluoro(methyl vinyl ether) and having a metal content within a specified range (see Example 5).

[0003] Patent No. 7140118

[0004] Further performance improvements for perfluoroelastomers are required. From the viewpoint of production efficiency when producing crosslinked rubber articles and the like using perfluoroelastomers, perfluoroelastomers that are excellent in processability, particularly in wrapability around rolls (hereinafter also referred to as "roll wrapability") when kneading perfluoroelastomers or raw materials containing perfluoroelastomers using a roll kneader, are required. In response to such requirements, the present inventors evaluated the perfluoroelastomers described in Patent Document 1 and found that there is room for further improvement in wrapability around rolls.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a perfluoroelastomer having excellent roll-wrapping properties. Another object of the present invention is to provide a crosslinked rubber article obtained by crosslinking the perfluoroelastomer.

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that roll winding properties can be improved by using a perfluoroelastomer in which, in a molecular weight distribution curve of the perfluoroelastomer obtained from values ​​measured by gel permeation chromatography and a calibration curve using polymethyl methacrylate as a standard substance, a first peak having a first peak top in the molecular weight region of 1,000 to 100,000 and a second peak having a second peak top in the molecular weight region of more than 100,000, are observed, and have arrived at the present invention.

[0007] That is, the present inventors have found that the above-mentioned problems can be solved by the following configuration. [1] A perfluoroelastomer satisfying the following requirement 1. Requirement 1: In a molecular weight distribution curve of the perfluoroelastomer obtained from values ​​measured by gel permeation chromatography and a calibration curve using polymethyl methacrylate as the standard substance, a first peak having a first peak top in the molecular weight region of 1,000 to 100,000 and a second peak having a second peak top in the molecular weight region of more than 100,000 are observed. [2] The perfluoroelastomer according to [1], which further satisfies the following requirement 2. Requirement 2: In a molecular weight distribution curve of the perfluoroelastomer obtained from values ​​measured by gel permeation chromatography and a calibration curve using polymethyl methacrylate as the standard substance, Mw / Mn, the ratio of weight average molecular weight Mw to number average molecular weight Mn, is 1.40 or more. [3] The perfluoroelastomer according to [1] or [2], which has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [4] The perfluoroelastomer according to [3], wherein the content of units based on tetrafluoroethylene is 20 to 80 mol % relative to the total content of all units of the perfluoroelastomer, and the content of units based on perfluoro(alkyl vinyl ether) is 20 to 80 mol % relative to the total content of all units of the perfluoroelastomer. [5] A crosslinked rubber article obtained by crosslinking the perfluoroelastomer according to any one of [1] to [4].

[0008] According to the present invention, a perfluoroelastomer having excellent roll-wrapping properties can be provided, and a crosslinked rubber article obtained by crosslinking the perfluoroelastomer can be provided.

[0009] FIG. 1 is a diagram showing an example of a molecular weight distribution curve of the present elastomer obtained from values ​​measured by gel permeation chromatography (hereinafter also referred to as "GPC") and a calibration curve using polymethyl methacrylate as a standard substance.

[0010] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer charged substantially coincides with the actual content of each unit.

[0011] [Perfluoroelastomer] The perfluoroelastomer of the present invention (hereinafter also referred to as "the present elastomer") satisfies the following Requirement 1. Requirement 1: In a molecular weight distribution curve of the perfluoroelastomer obtained from values ​​measured by GPC and a calibration curve using polymethyl methacrylate as a standard substance, a first peak having a first peak top in the molecular weight region of 1,000 to 100,000 and a second peak having a second peak top in the molecular weight region of more than 100,000 are observed. The top of the first peak indicates that the perfluoroelastomer contains a low-molecular-weight component, and it is believed that the low-molecular-weight component functions as a plasticizing component. The top of the second peak indicates that the perfluoroelastomer contains a high-molecular-weight component, and it is believed that the high-molecular-weight component functions as a component that imparts rigidity. It is presumed that the roll winding property of the perfluoroelastomer is improved by the favorable expression of the functions of the low-molecular-weight component and the high-molecular-weight component.

[0012] Figure 1 shows an example of the molecular weight distribution curve (differential molecular weight distribution curve) of the present elastomer obtained from values ​​measured by GPC and a calibration curve using polymethyl methacrylate as a standard substance. In Figure 1, the horizontal axis represents the logarithm of molecular weight (log(M)), and the vertical axis represents dw / dlog(M), which is the derivative of the concentration fraction w by the logarithm of molecular weight log(M). In Figure 1, P1 represents the top of the first peak present in the molecular weight region of 1,000 to 100,000, and P2 represents the top of the second peak present in the molecular weight region exceeding 100,000.

[0013] In the molecular weight distribution curve of the present elastomer, there may be one peak or two or more peaks in the region of molecular weights from 1,000 to 100,000. In the molecular weight distribution curve of the present elastomer, there may be one peak or two or more peaks in the region of molecular weights above 100,000.

[0014] The peak top molecular weight of the first peak is 1,000 to 100,000, and is preferably 2,000 or more, more preferably 10,000 or more, and more preferably 50,000 or more from the viewpoint of excellent heat resistance, and is preferably 90,000 or less, more preferably 80,000 or less from the viewpoint of excellent effects of the present invention. The peak top molecular weight of the second peak is more than 100,000, and is preferably 130,000 or more, more preferably 200,000 or more from the viewpoint of excellent rigidity, and is preferably 500,000 or less, more preferably 400,000 or less from the viewpoint of excellent moldability.

[0015] In order to achieve better effects of the present invention, it is preferable that the present elastomer further satisfy Requirement 2. Requirement 2: In a molecular weight distribution curve of the present elastomer obtained from values ​​measured by GPC and a calibration curve using polymethyl methacrylate as a standard substance, Mw / Mn (molecular weight distribution), which is the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn), is 1.40 or more.

[0016] The Mw / Mn ratio of the present elastomer is preferably 1.40 or more, and from the viewpoint of superior effects of the present invention, it is more preferably 1.45 or more, and even more preferably 1.80 or more. From the viewpoint of moldability, it is preferably 400 or less, more preferably 300 or less, even more preferably 100 or less, and most preferably 10 or less. The Mw of the present elastomer is preferably 100,000 to 1,000,000, more preferably 100,000 to 800,000, and even more preferably 150,000 to 500,000, from the viewpoint of superior heat resistance. The Mn of the present elastomer is preferably 50,000 to 600,000, more preferably 80,000 to 500,000, and even more preferably 100,000 to 400,000.

[0017] The peak top molecular weight of the first peak, the peak top molecular weight of the second peak, the number average molecular weight (Mn), and the weight average molecular weight (Mw) can be obtained by measuring with GPC. Specifically, a molecular weight distribution curve of the present elastomer is obtained by a calibration curve method using polymethyl methacrylate as a standard substance, and the peak top molecular weight of the first peak, the peak top molecular weight of the second peak, the number average molecular weight (Mn), and the weight average molecular weight (Mw) can be obtained from the obtained molecular weight distribution curve. The apparatus used for GPC and more detailed measurement conditions for preparing the molecular weight distribution curve are as described in the Examples section below.

[0018] The upper limit of the intensity ratio of the peak intensity of the first peak top to the peak intensity of the second peak top (first peak intensity / second peak intensity×100(%)) is preferably 90% or less, more preferably 80% or less from the viewpoint of excellent rigidity, even more preferably 75% or less, and even more preferably 70% or less. The lower limit of the intensity ratio is preferably 5% or more, more preferably 10% or more from the viewpoint of excellent moldability.

[0019] [Composition] In the present invention, the term "perfluoroelastomer" refers to a perfluoropolymer having a glass transition temperature of 20°C or less and a melting peak (ΔH) of 4.5 J / g or less, and further, a polymer in which the proportion of fluorine atoms contained in the perfluoropolymer is 65% by mass or more. Here, "perfluoropolymer" refers to a polymer that does not substantially contain hydrogen atoms bonded to carbon atoms, has fluorine atoms instead of those hydrogen atoms, and has a main chain consisting of a chain of carbon atoms. The content of hydrogen atoms contained in the perfluoropolymer is determined by analysis using solid-state nuclear magnetic resonance spectroscopy (NMR). The side chain of the perfluoropolymer may have a polyvalent atom other than carbon atoms, and oxygen atoms are preferred as the polyvalent atom. Here, "substantially does not contain hydrogen atoms" means that the content of hydrogen atoms in the perfluoropolymer is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and even more preferably 0.05% by mass or less. The lower limit is 0% by mass. When the content of hydrogen atoms is within the above range, good heat resistance or chemical resistance is likely to be obtained. The composition of the present elastomer will be explained below.

[0020] The present elastomer preferably has units based on tetrafluoroethylene (hereinafter also referred to as "TFE") and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"). Hereinafter, the units based on TFE will also be referred to as "TFE units," and the units based on PAVE will also be referred to as "PAVE units."

[0021] The PAVE from which the PAVE unit is derived is preferably a monomer represented by formula (1) from the viewpoints of excellent polymerization reactivity in producing the specific polymer described below and of enabling the present elastomer to be produced more efficiently. ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0022] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and PMVE or PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the present elastomer.

[0023] The content of TFE units in the present elastomer is preferably 5 to 90 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 80 mol%, and particularly preferably 40 to 75 mol%, based on the total content of TFE units and PAVE units. The content of PAVE units in the present elastomer is preferably 10 to 95 mol%, more preferably 20 to 80 mol%, even more preferably 20 to 70 mol%, and particularly preferably 25 to 60 mol%, based on the total content of TFE units and PAVE units. The preferred amount of PAVE units used is also the same when PMVE units or PPVE units are used as PAVE units. The total content of TFE units and PAVE units in the present elastomer is preferably 70 to 100 mol%, more preferably 80 to 100 mol%, still more preferably 90 to 100 mol%, and particularly preferably 95 to 100 mol%, based on the total content of all units in the present elastomer.

[0024] The content of TFE units in the present elastomer is preferably 5 to 90 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 80 mol%, and particularly preferably 40 to 75 mol%, based on the total content of all units in the present elastomer. The content of PAVE units in the present elastomer is preferably 10 to 95 mol%, more preferably 20 to 80 mol%, even more preferably 20 to 70 mol%, and particularly preferably 25 to 60 mol%, based on the total content of all units in the present elastomer. Furthermore, the preferred amount of PAVE units used is the same when PMVE units or PPVE units are used as PAVE units.

[0025] The present elastomer may contain units based on monomers other than TFE units and PAVE units (hereinafter also referred to as "other monomers"), and preferably contains units based on other monomers. Specific examples of other monomers include a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer having one or more atoms of at least one kind selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom (hereinafter also referred to as "R Ｈａｌ "), a monomer having a nitrile group (hereinafter referred to as "R ＣＮ"), and a compound represented by formula (6) described below (hereinafter also referred to as "POAVE").

[0026] BO is a monomer having two or more polymerizable unsaturated bonds. Examples of the polymerizable unsaturated bond include a carbon atom-carbon atom double bond (C=C) and a carbon atom-carbon atom triple bond (C≡C). The number of polymerizable unsaturated bonds that BO has is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, from the viewpoint of more excellent polymerization reactivity. BO preferably contains a fluorine atom, from the viewpoint of further reducing the compression set of the crosslinked rubber article at high temperatures.

[0027] BO is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２ , and R ２３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a1 represents an integer of 2 to 6; R ２４ represents an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms. ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are particularly preferably the same. a1 is preferably 2 or 3, and particularly preferably 2. In view of better polymerization reactivity of BO, R ２１ , R ２２ , and R ２３ is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ , and R ２３ are more preferably all fluorine atoms or all hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, R ２１ , R２２ , and R ２３ It is particularly preferred that all of R are fluorine atoms. ２４ R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ２４ Although R may or may not have an etheric oxygen atom, it is preferable that R has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and even more preferably 1 or 2. ２４ The etheric oxygen atom in R ２４ It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0028] Of the monomers represented by formula (2), specific examples of suitable monomers include the monomers represented by formula (3) and the monomers represented by formula (4).

[0029] (CF ２ =CF-) ２ R ３１ (3) In formula (3), R ３１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0030] (CH ２ =CH-) ２ R ４１ (4) In formula (4), R ４１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0031] Specific examples of the monomer represented by formula (3) include CF ２ = CFO (CF ２ ) ２ OCF = CF ２ , C.F. ２=CFO(CF ２ ) ３ OCF = CF ２ , CF ２ =CFO(CF ２ ) ４ OCF = CF ２ , CF ２ =CFO(CF ２ ) ６ OCF = CF ２、 CF ２ =CFO(CF ２ ) ８ OCF = CF ２ , CF ２ =CFO(CF ２ ) ２ OCF(CF ３ )CF ２ OCF = CF ２ , CF ２ =CFO(CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , CF ２ =CFOCF ２ O(CF ２ CF ２ O) ２ CF = CF ２ , CF ２ =CFO(CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , CF ２ =CFOCF ２ CF(CF ３ )O(CF ２ ) ２ OCF(CF ３ )CF ２ OCF = CF ２ , and, CF ２ =CFOCF ２ CF ２ O(CF ２ O) ２ CF ２ CF ２ OCF = CF ２Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３ OCF = CF ２ (hereinafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter also referred to as "C4DVE").

[0032] Specific examples of the monomer represented by formula (4) include CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２ , and C.H. ２ =CH(CF ２ ) ６ CH=CH ２ Among the monomers represented by formula (4), specific examples of more preferred monomers include CH ２ =CH(CF ２ ) ６ CH=CH ２ (hereinafter also referred to as "C6DV"). Among them, C3DVE or C4DVE is preferable for BO.

[0033] R Ｈａｌ Examples of the monomer having a bromine atom include a monomer having a bromine atom and a monomer having an iodine atom. Specific examples of the monomer having a bromine atom include CF ２ = CFOCF ２ CF ２ CF ２ OCF ２ CF ２Br, bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB), vinyl bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide, 4-bromo-1,1,2-trifluorobutene-1, 4-bromo-1,1,3,3,4,4-hexafluorobutene, 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Also included are 2-bromo-perfluoroethyl perfluorovinyl ether and CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF = CFBr, and ROCBr = CF ２ (wherein R is a lower alkyl group or a fluoroalkyl group), more specifically fluorovinyl ethers such as CH ３ OCF = CFBr and CF ３ CH ２ Specific examples of the monomer having an iodine atom include the monomer represented by the formula: CHR=CH-Z-CH ２ CHR-I (wherein R is —H or —CH ３ and Z is a linear or branched C alkyl group optionally containing one or more ethereal oxygen atoms. １ ~C １８ iodinated olefins of the formula I(CH) as disclosed in U.S. Pat. No. 5,717,036, which are (per)fluoroalkylene groups or (per)fluoropolyoxyalkylene groups as disclosed in U.S. Pat. No. 5,674,959. ２ CF ２ CF ２ ) ｎ OCF = CF ２ and ICH ２ CF ２ O[CF(CF ３ )CF２ O] ｎ CF = CF ２ (wherein n = 1 to 3) and the like. Also included are iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene, as disclosed in U.S. Pat. No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0034] R ＣＮ From the viewpoint of polymerization reactivity, it is preferable that the copolymer has a polymerizable unsaturated bond, and more preferably has one polymerizable unsaturated bond. Specific examples of the polymerizable unsaturated bond include a carbon-carbon double bond (C═C) and a carbon-carbon triple bond (C≡C).

[0035] R ＣＮ is preferably a monomer represented by the following formula (5) in view of better mold releasability and heat resistance of the crosslinked rubber article: ５１ R ５２ =CR ５３ -R ５４ -CN (5) In formula (5), R ５１ , R ５２ , and R ５３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R ５４ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. ＣＮ From the viewpoint of excellent polymerization reactivity of R ５１ , R ５２ , and R ５３is preferably a fluorine atom or a hydrogen atom, and R ５１ , R ５２ , and R ５３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, ５１ , R ５２ , and R ５３ It is particularly preferred that all of R are fluorine atoms. ５４ R may be linear, branched, or cyclic, and is preferably linear or branched. ５４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ５４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in order to obtain better rubber properties. ５４ The number of etheric oxygen atoms in the formula (5) is preferably 1 to 3, and particularly preferably 1 or 2. Specific examples of the monomer represented by formula (5) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２ ) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN and CF ２ = CFO (CF ２ ) ３ CN is exemplified, and 8CNVE or MV5CN is preferred in that the crosslinked rubber article has better mold releasability and heat resistance.

[0036] POAVE is a compound represented by formula (6): CF ２ =CF(OCF ２ CF ２ ) ｎ -(OCF ２ ) ｍ -ORｆ２ (6) In formula (6), R ｆ２ represents a perfluoroalkyl group having 1 to 4 carbon atoms, n represents an integer of 0 to 3, m represents an integer of 0 to 4, and n+m represents an integer of 1 to 7.

[0037] R ｆ２ In the formula, the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 1 or 2. When n is 1, m is preferably an integer of 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer of 1 to 3. R ｆ２ When the number of carbon atoms, n, and m are within the above ranges, the low-temperature properties of the crosslinked rubber article are excellent, and the productivity of the crosslinked rubber article is improved.

[0038] Specific examples of POAVE include the following. The abbreviation for the compound is given in parentheses after the formula. CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ４ -OCF ３ (C9PEVE), CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ２ -OCF ３ (C7PEVE), CF ２ =CF-(OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE), CF ２ =CF-(OCF ２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF ３As the POAVE, C9PEVE, C7PEVE, EEAVE, or EEEAVE is preferred in terms of superior low-temperature properties and productivity of crosslinked rubber articles. These compounds can be produced from the corresponding alcohols by the method described in WO 00 / 056694.

[0039] The content of other units in the present elastomer is preferably 0.01 to 30 mol %, more preferably 0.01 to 20 mol %, still more preferably 0.01 to 10 mol %, and most preferably 0.01 to 5 mol %, based on the total content of all units in the present elastomer.

[0040] In order to achieve superior crosslinkability, the present elastomer preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group, and more preferably contains at least one selected from the group consisting of a chlorine atom, a bromine atom, an iodine atom, and a nitrile group. It is particularly preferable that the present elastomer has such an atom or group at at least one of its terminals and side chains. When producing the present elastomer, by using the above-mentioned other monomers in addition to TFE and PAVE, it is possible to introduce a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, or a nitrile group into the side chain or terminal of the present elastomer. Furthermore, by polymerizing a monomer using a chain transfer agent having an iodine atom, it is possible to introduce an iodine atom into the terminal of the present elastomer. When the present elastomer contains iodine atoms, the content of iodine atoms is preferably 0.01 to 5.00 mass%, more preferably 0.01 to 2.00 mass%, and even more preferably 0.01 to 1.00 mass%, relative to the total mass of the present elastomer.

[0041] [Method for producing perfluoroelastomer] The method for producing the present elastomer can be, for example, copolymerizing monomers such as TFE and PAVE and other monomers that are optionally used in the presence of a polymerization initiator.The polymerization method can be, for example, emulsion polymerization, solution polymerization, suspension polymerization, and emulsion polymerization is preferred from the viewpoint of excellent productivity and the ability to adjust molecular weight and copolymerization composition.When producing the present elastomer by emulsion polymerization, for example, it can be carried out by heating the above-mentioned monomers in the presence of an aqueous medium, a polymerization initiator, and an optionally used emulsifier.

[0042] A preferred embodiment of the method for producing the present elastomer is a method for producing a perfluoroelastomer, which comprises polymerizing a monomer composition containing TFE and PAVE (hereinafter also referred to as the "specific monomer composition") in an aqueous dispersion (hereinafter also referred to as the "first aqueous dispersion") containing a specific polymer, which is a fluorine-containing polymer substantially free of water-soluble emulsifiers and contains TFE units and PAVE units, and an aqueous medium, and then stirring the resulting aqueous dispersion containing the perfluoroelastomer (hereinafter also referred to as the "second aqueous dispersion") to coagulate the perfluoroelastomer and recover the coagulated perfluoroelastomer. In the production method, the step of polymerizing the specific monomer composition in the first aqueous dispersion to obtain a second aqueous dispersion containing the perfluoroelastomer is also referred to as "step 1," and the step of stirring the second aqueous dispersion to coagulate the perfluoroelastomer and recovering the coagulated perfluoroelastomer (the present elastomer) is also referred to as "step 2." According to the above-mentioned production method, a perfluoroelastomer satisfying the above-mentioned requirements 1 and 2 can be easily obtained. More specifically, a perfluoroelastomer satisfying the above-mentioned requirement 1 can be easily obtained by appropriately adjusting the ratio of the units constituting the specific monomer described below, by appropriately adjusting the content of the specific monomer used in the first aqueous dispersion, and by appropriately adjusting the ratio of each monomer used in the specific monomer composition. Furthermore, a perfluoroelastomer satisfying the above-mentioned requirement 2 can be easily obtained by appropriately adjusting the amount of initiator used in the production of the first aqueous dispersion, by appropriately adjusting the composition of the specific monomer used in the first aqueous dispersion, and by appropriately adjusting the ratio of each monomer used in the specific monomer composition. Furthermore, a perfluoroelastomer satisfying the above-mentioned intensity ratio between the peak intensity of the first peak top and the peak intensity of the second peak top can be easily obtained by appropriately adjusting the ratio of the specific polymer. Each step will be described below.

[0043] <Step 1> In step 1, a specific monomer composition is polymerized in a first aqueous dispersion that is substantially free of a water-soluble emulsifier and that contains a specific polymer and an aqueous medium.

[0044] (First aqueous dispersion) - Emulsifier - The first aqueous dispersion does not use a water-soluble emulsifier and is substantially free of a water-soluble emulsifier. "Substantially free of a water-soluble emulsifier" means that the content of the water-soluble emulsifier in the first aqueous dispersion is 10 ppm by mass or less, preferably 100 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total mass of the first aqueous dispersion. It is also preferable that the content is below the quantitation limit of the measurement method in the examples. An example of a lower limit is 1 ppb by mass. The content of the water-soluble emulsifier can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement methods described in paragraphs 0721 to 0732 of WO 2018 / 181904 can be mentioned, and the measurement method shown in the examples is preferred.

[0045] A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1,000 g of water at 25°C. Examples of water-soluble emulsifiers include water-soluble emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms. Note that the specific polymers and perfluoroelastomers described below do not fall under the category of emulsifiers. The water-soluble emulsifier may be either ionic or nonionic.

[0046] Examples of the emulsifier having fluorine atoms include anionic fluorine-containing emulsifiers, such as emulsifiers containing fluorine atoms whose total carbon number excluding the anionic group is 20 or less, and fluorine-containing emulsifiers whose anionic moiety has a molecular weight of 800 or less.

[0047] The fluorine-free emulsifier does not have a fluorine atom but has a hydrocarbon group such as an alkyl group. The hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier may be substituted with a halogen atom other than a fluorine atom. Examples of the fluorine-free emulsifier include ionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0048] Ionic hydrocarbon emulsifiers include anionic hydrocarbon emulsifiers, which have a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon moiety, such as an alkyl group, as a hydrophobic moiety. Examples of anionic hydrocarbon emulsifiers include the highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, sodium dodecyl sulfate, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0049] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have a hydrocarbon group such as an alkyl group as the hydrophobic moiety. Examples of the hydrophilic moiety of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained by polymerization of ethylene oxide. Examples of nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, for example, block copolymers having polyethylene oxide and polypropylene oxide. Examples of nonionic hydrocarbon emulsifiers include the emulsifiers described in paragraphs

[0043] to

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

[0050] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier containing silicon atom can include siloxane emulsifier.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0051] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of the polymer emulsifier include a water-soluble polymer having a hydrophilic group in a side chain. Examples of such a polymer emulsifier include a polymer containing a unit based on a compound having a site capable of reacting by polymerization and a hydrophilic group. Further examples include polymers obtained by subjecting a polymer based on a compound having a group that can become a hydrophilic group, even if it does not have hydrophilicity during polymerization, to post-treatment such as hydrolysis.

[0052] It is preferable that the first aqueous dispersion is substantially free of an emulsifier represented by any one of formulas (S1) to (S4). When no emulsifier is used during the production of the specific polymer contained in the first aqueous dispersion, the amount of the compound represented by any one of formulas (S1) to (S4) generated can be suppressed, making it easier to adjust the content of these compounds.

[0053] H-(CF ２ ) ｎ１ -COOM (S1) F-(CF ２ ) ｎ１ -COOM (S2) H-(CF ２ ) ｎ２ -SO ３ M (S3) F-(CF ２ ) ｎ２ -SO ３ M (S4) In formulas (S1) to (S4), n1 is an integer of 3 to 19, n2 is an integer of 4 to 20, and each M is independently a hydrogen atom, Na, K, or NH ４ is.

[0054] -Specific Polymer- The specific polymer is a fluorine-containing polymer containing TFE units and PAVE units. It is believed that the specific polymer adsorbs and incorporates the specific monomer composition at its hydrophobic portion during polymerization of the specific monomer composition described below, solubilizing the specific monomer composition even when the first aqueous dispersion does not contain an emulsifier, facilitating the polymerization of the specific monomer composition. It is also believed that the specific polymer contributes to stabilizing the dispersion of the perfluoroelastomer in the first aqueous dispersion. When an emulsifier is used, polymerization proceeds uniformly within each particle, producing a polymer with a monomodal molecular weight distribution. However, polymerization without an emulsifier in the presence of the specific polymer produces a polymer with a bimodal molecular weight distribution, with a first peak having a first peak top in the molecular weight range of 1,000 to 100,000 and a second peak having a second peak top in the molecular weight range above 100,000.

[0055] The details of PAVE are the same as those of the PAVE from which the PAVE units in the present elastomer are derived, and the preferred embodiments are also the same.

[0056] The content of TFE units relative to the total content of TFE units and PAVE units in the specific polymer is preferably 20 to 95 mol%, more preferably 40 to 85 mol%, and from the viewpoint of more efficient production of the present elastomer, even more preferably 50 to 75 mol%, and particularly preferably 60 to 70 mol%. The content of PAVE units relative to the total content of TFE units and PAVE units in the specific polymer is preferably 5 to 80 mol%, more preferably 15 to 60 mol%, and from the viewpoint of more efficient production of the present elastomer, even more preferably 25 to 55 mol%, and even more preferably 30 to 40 mol%. The total content of TFE units and PAVE units in the specific polymer is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, relative to all units of the specific polymer.

[0057] The specific polymer may contain units based on monomers other than TFE and PAVE, and from the viewpoint of more efficient production of the present elastomer, it is also preferable that the specific polymer is substantially free of units based on other monomers. "Substantially free of units based on other monomers" means that the content of units based on other monomers is 0.01 mol% or less, and preferably 0 mol%, relative to the total content of all units in the specific polymer.

[0058] The content of the specific polymer before the initiation of polymerization of the specific monomer composition is preferably 0.01 to 4.0 mass%, more preferably 0.01 to 0.6 mass%, and even more preferably 0.01 to 0.5 mass%, relative to the total mass of the first aqueous dispersion, in order to produce the present elastomer more efficiently. In this specification, "before the initiation of polymerization of the specific monomer composition" refers to the time immediately before the initiation of polymerization. Examples of the "initiation of polymerization" include the time when the reactor is heated to a temperature equal to or higher than the polymerization temperature and then the monomers (or, if a polymerization initiator is used, the polymerization initiator and the monomers) are introduced into the reactor, or the time when the reactor is heated to a temperature equal to or higher than the polymerization temperature and then the monomers (or, if a polymerization initiator is used, the polymerization initiator and the monomers) are introduced into the reactor. The first aqueous dispersion before the initiation of polymerization of the specific monomer composition does not contain the specific monomer composition or the polymerization initiator.

[0059] The content (solid content concentration) of the specific polymer in the first aqueous dispersion can be measured, for example, by the following method. 2.0 g of the first aqueous dispersion is heated at 170° C. for 20 minutes, and then the mass of the residue is weighed and the solid content concentration is calculated by the following formula: "Solid content concentration (mass %) = 100 × mass (g) of heated residue of first aqueous dispersion / mass (2.0 g) of first aqueous dispersion"

[0060] A preferred embodiment of Step 1 is an embodiment in which the content of PAVE units in the specific polymer relative to the total content of TFE units and PAVE units is 20 to 95 mol %, and the content of the specific polymer is 0.01 to 4.0 mass % relative to the total mass of the first aqueous dispersion before starting polymerization of the specific monomer composition.

[0061] As a method for producing the specific polymer, a method of polymerizing a monomer containing TFE and PAVE in an aqueous medium in the presence of a polymerization initiator is preferred.Thereby, a specific polymer dispersed in particulate form in an aqueous medium can be obtained.The aqueous medium thus obtained in which the specific polymer particles are dispersed can be used as the first aqueous dispersion as is.Alternatively, the solvent can be replaced, and the specific polymer can be dispersed in another aqueous medium, which can be used as the first aqueous dispersion.

[0062] The polymerization initiator used for polymerizing the specific polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0063] Examples of the aqueous medium used in producing the specific polymer include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0064] In producing the specific polymer, the aqueous medium containing the monomer preferably does not substantially contain an emulsifier. The emulsifier (type of emulsifier, definition of "substantially free") is as described above.

[0065] The first aqueous dispersion containing the specific polymer is preferably subjected to a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products before being used for polymerization of the specific monomer composition. By removing the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion containing the specific polymer through the purification treatment, the present elastomer having the desired physical properties is easily obtained. Examples of purification treatment methods include heating treatment and passing the dispersion through an ion exchange resin (preferably an anion exchange resin). The purification treatment may be performed multiple times.

[0066] Specific examples of the aqueous medium contained in the first aqueous dispersion include the aqueous medium used in the production of the specific polymer described above. As described above, the aqueous medium used as the polymerization solvent in the production of the specific polymer may be used. Before the start of polymerization of the specific monomer composition, the content of the aqueous medium is preferably 60 to 99.9 mass%, more preferably 96 to 99.9 mass%, and even more preferably 98 to 99.9 mass%, relative to the total mass of the first aqueous dispersion.

[0067] The first aqueous dispersion may contain components other than the specific polymer and the aqueous medium. Specific examples of such other components include a reducing agent, a pH adjuster, and a chain transfer agent, which will be described later. Specific examples of pH adjusters include inorganic salts and ammonia. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0068] (Specific Monomer Composition) The specific monomer composition is a monomer composition containing TFE and PAVE. A preferred embodiment of PAVE as the specific monomer composition is the same as the preferred embodiment of PAVE in the specific polymer described above. The total amount of TFE and PAVE used is preferably 50 to 100 mol%, more preferably 53 to 100 mol%, and even more preferably 60 to 100 mol%, based on the amount of the specific monomer composition used.

[0069] The specific monomer composition may contain a monomer other than TFE and PAVE (hereinafter also referred to as "other monomer"). Specific examples of the other monomer include BO, R Ｈａｌ , R ＣＮ and POAVE. Preferred embodiments of these other monomers are the same as preferred embodiments of other monomers in the description of units based on other monomers that may be contained in the present elastomer.

[0070] The amount of the other monomer used is preferably 0 to 50 mol %, more preferably 0 to 47 mol %, and even more preferably 0 to 40 mol %, based on the amount of the specific monomer composition used.

[0071] The specific monomer composition consists of only TFE and PAVE, or contains TFE and PAVE and BO, R Ｈａｌ and R ＣＮ It is preferable that the polymer contains at least one monomer selected from the group consisting of:

[0072] In step 1, the specific monomer composition is preferably polymerized in the first aqueous dispersion in the presence of a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, disuccinic acid peroxide, bisglutaric acid peroxide, and water-soluble organic peroxides such as tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, organic acid, or inorganic salt. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of a fluorine-containing polymer, a water-soluble radical initiator is more preferred, and a water-soluble organic peroxide is even more preferred. Two or more polymerization initiators may be used in combination.

[0073] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the specific monomer composition used.

[0074] (Chain Transfer Agent) In step 1, it is also preferable that the specific monomer composition is polymerized in the first aqueous dispersion in the presence of a chain transfer agent. Specific examples of chain transfer agents include chain transfer agents having iodine atoms, ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane, with chain transfer agents having iodine atoms being preferred. By polymerizing the specific monomer composition using a chain transfer agent having iodine atoms, the present elastomer having iodine atoms at its terminals can be produced.

[0075] The chain transfer agent having an iodine atom is preferably a compound represented by formula (I): (R ｆ ) - (X) ２ (I) In formula (I), R ｆ is a fluoroalkylene group having 1 to 16 carbon atoms or an aromatic ring group, and X is an iodine atom or a bromine atom, and at least one of X is an iodine atom. ｆ The fluoroalkylene group of R may be linear or branched. ｆ Preferably, X is a perfluoroalkylene group. Preferably, all of X are iodine atoms.

[0076] Specific examples of the compound represented by formula (I) include 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,3-diiodoper ...4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodoperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,12-diiodoperfluorododecane, 1,16 Examples of the compound represented by formula (I) include iodoethane, 1,3-diiodo-n-propane, (2-iodoethyl)-substituted benzene, 1-iodo-4-bromoperfluorobutane, 1-iodo-6-bromoperfluorohexane, 1-iodo-8-bromoperfluoroctane, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, and diiodomonobromo-substituted benzene. C4DI is preferred as the compound represented by formula (I).

[0077] The amount of the chain transfer agent used is preferably 0 to 10 parts by mass, more preferably 0 to 5 parts by mass, and even more preferably 0 to 3 parts by mass, per 100 parts by mass of the specific monomer composition used.

[0078] In order to obtain a more excellent crosslinkability of the produced elastomer, the method for producing a perfluoroelastomer according to the present invention is characterized in that the specific monomer composition is a copolymer of the above-mentioned BO, R Ｈａｌ and R ＣＮ or the first aqueous dispersion preferably contains a chain transfer agent containing an iodine atom.

[0079] Step 1 is a step of polymerizing the specific monomer composition described above in the first aqueous dispersion described above to obtain a second aqueous dispersion containing a perfluoroelastomer (the present elastomer). The specific monomer composition is added to the reaction system (i.e., a polymerization reaction vessel) by a conventional method. For example, the specific monomer composition may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer composition may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions. When other components (e.g., chain transfer agents) other than those described above are used, the other components may be added to the reaction system all at once or in portions.

[0080] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0081] The polymerization of the specific monomer composition is preferably carried out in a reaction system substantially free of emulsifiers, without using an emulsifier. Examples of emulsifiers include the above-mentioned emulsifiers. The absence of an emulsifier means an environment in which the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the first aqueous dispersion.

[0082] In step 1, the present elastomer is produced, and a second aqueous dispersion in which particles containing the present elastomer are dispersed in an aqueous medium is obtained.

[0083] (Second aqueous dispersion) The second aqueous dispersion is an aqueous dispersion containing the present elastomer obtained in step 1. In other words, the second aqueous dispersion is an aqueous dispersion in which particles containing the present elastomer (hereinafter also referred to as "specific particles") are dispersed in an aqueous medium. The specific particles may or may not contain a specific polymer. The second aqueous dispersion may contain the specific polymer dispersed in particulate form.

[0084] The preferred embodiment of the present elastomer contained in the second aqueous dispersion is as described above. From the viewpoint of dispersion stability of the specific particles, the content of the specific particles containing the present elastomer is preferably 1 to 50 mass %, more preferably 1 to 40 mass %, and even more preferably 1 to 30 mass %, relative to the total mass of the second aqueous dispersion.

[0085] The average particle size of the specific particles is preferably 1 μm or less, and from the viewpoint of dispersion stability of the specific particles, it is more preferably 500 nm or less, and even more preferably 400 nm or less. From the viewpoint of recovery efficiency in step 2 described below, the average particle size of the specific particles is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 100 nm or more. The average particle size of the specific particles is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using a monodisperse cumulant method.

[0086] Specific examples and preferred embodiments of the aqueous medium contained in the second aqueous dispersion are the same as those of the aqueous medium contained in the first aqueous dispersion. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, based on the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0087] The content of the emulsifier in the second aqueous dispersion is preferably 100 mass ppm or less, more preferably 75 mass ppm or less, even more preferably 50 mass ppm or less, even more preferably 1 mass ppm or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the second aqueous dispersion. It is also preferable that the content is below the quantitation limit of the above-mentioned method for measuring the content of the emulsifier. An example of a lower limit is 1 mass ppb. It is preferable that no emulsifier is used in the second aqueous dispersion. The content of the emulsifier can be measured by the same method as that for the first aqueous dispersion. Specific examples of the emulsifier are as described above. The emulsifier in the second aqueous dispersion may or may not be water-soluble.

[0088] <Step 2> Step 2 is a step of subjecting the second aqueous dispersion obtained in Step 1 to a stirring treatment to aggregate the present elastomer and obtain the aggregated present elastomer.

[0089] (Stirring Treatment) As the stirring treatment, known stirring treatments that impart shear force to the second aqueous dispersion can be applied, and among these, stirring treatments using a stirring device that rotates a stirring shaft equipped with stirring blades are preferred. Specific examples of the shape of the stirring blades include paddle blades, inclined paddle blades, propeller blades, disk blades, three-bladed swept blades, anchor blades, turbine blades, and disk turbine blades, with paddle blades or disk turbine blades being preferred in terms of excellent stirring efficiency. The number of the stirring blades is preferably 1 to 10, more preferably 2 to 4. Specific examples of the shape of the tank used in the stirring treatment include cylindrical, conical, elliptical, rectangular, and pyramidal shapes, with cylindrical being preferred in terms of mixability and fluidity. The stirring device may be provided with a baffle.

[0090] The stirring time is preferably 0.1 to 24 hours, more preferably 0.1 to 12 hours, and even more preferably 0.1 to 6 hours. The peripheral speed of stirring is preferably 2 to 50 m / s, more preferably 3 to 30 m / s, and even more preferably 5 to 30 m / s. The peripheral speed may be constant during stirring or may change during stirring. It is also preferable that the peripheral speed is faster than the peripheral speed in step 1. The peripheral speed of stirring represents the speed of the blade at the tip of the stirring blade. The temperature of the aqueous dispersion during stirring treatment is preferably 10 to 90°C, more preferably 10 to 80°C, and even more preferably 15 to 70°C.

[0091] The stirring treatment results in a solid material containing the aggregated present elastomer. In this specification, the term "solid material" refers to a solid material that is not stably dispersed in an aqueous medium. A dispersoid stably dispersed in an aqueous medium is considered not to be a solid material, even if it is insoluble in the aqueous medium. For example, among the insoluble components (e.g., specific particles) contained in the second aqueous dispersion after stirring, dispersoids stably dispersed in the aqueous medium are not included in the solid material, while sediments and floating matter that are not stably dispersed in the aqueous medium are included in the solid material. Examples of the solid material include aggregates of the present elastomer. Examples of the stably dispersed dispersoid include dispersoids that pass through Type 5A filter paper as specified in JIS P 3801 [Filter Paper (for Chemical Analysis)].

[0092] The present elastomer containing TFE units and PAVE units can be obtained by recovering the agglomerates of the present elastomer separated by the stirring treatment. Specific examples of the method for recovering the agglomerates of the present elastomer include filtration and centrifugation, with filtration being preferred.

[0093] <Washing Step> The method for producing the present elastomer preferably further includes a step of washing the recovered present elastomer (hereinafter also referred to as "Step 3"). Step 3 allows other components (e.g., emulsifiers, monomers, polymerization initiators, and their reaction products) adhering to the present elastomer to be removed, making it easier to obtain a crosslinked rubber article with desired physical properties. The washing liquid used in the washing step may be the aqueous medium described above, with water being preferred and ultrapure water being more preferred. Specific examples of washing methods include immersing the recovered present elastomer in a washing liquid and stirring it, and showering the recovered present elastomer with a washing liquid. Washing and dehydration of the present elastomer may be repeated multiple times. Specific examples of dehydration methods include crushing and centrifugation. The amount of washing liquid used in the washing step is preferably 1 to 50 times, more preferably 2 to 30 times, and even more preferably 2 to 15 times the total mass of the present elastomer. The temperature of the washing liquid in the washing step is preferably 5 to 100°C, more preferably 10 to 80°C, and even more preferably 20 to 70°C.

[0094] (Perfluoroelastomer) The present elastomer can be obtained by the above production method. In particular, it is preferable to produce the present elastomer by the above production method, in which the content of PAVE units relative to the total content of TFE units and PAVE units in the present elastomer is 20 to 95 mol %.

[0095] [Solid Composition] The present elastomer obtained by the above production method may be in the form of a solid composition. In this specification, a solid composition means a composition having a solid content of 99% by mass or more. The solid content is calculated using the following method based on the mass before and after heating. 2.0 g of the solid composition is heated at 170°C for 20 minutes, and the mass of the residue is weighed, and the solid content is calculated using the following formula: Solid content (mass %) = 100 × (mass of residue) / (mass of solid composition). The content of the present elastomer in the solid composition is preferably 99.0 to 100% by mass, more preferably 99.5 to 100% by mass, and even more preferably 99.8 to 100% by mass, based on the total mass of the solid composition.

[0096] Preferably, the solid composition containing the present elastomer is substantially free of an emulsifier. "The solid composition is substantially free of an emulsifier" means that no emulsifier is used in the production process of the solid composition containing the present elastomer, and the solid composition contains an emulsifier in an amount of 10 ppm by mass or less, preferably 150 ppb by mass or less, and more preferably 50 ppb by mass or less, based on the total mass of the solid composition. The lower limit of the emulsifier content is 0 ppb by mass. The method for measuring the emulsifier content and the emulsifier that may be contained in the solid composition are as described above.

[0097] The present elastomer and the present solid composition preferably do not substantially contain a compound (emulsifier) ​​represented by any one of formulas (S1) to (S4). If no emulsifier is used during the production of the specific polymer contained in the first aqueous dispersion, the amount of a compound represented by any one of formulas (S1) to (S4) generated can be suppressed, making it easier to adjust the content of these compounds. The definition of "substantially free" is the same as the definition for the case where an emulsifier is not substantially contained, as described above.

[0098] H-(CF ２ ) ｎ１ -COOM (S1) F-(CF ２ ) ｎ１ -COOM (S2) H-(CF ２ ) ｎ２ -SO ３ M (S3) F-(CF ２ )ｎ２ -SO ３ M (S4) In formulas (S1) to (S4), n1 is an integer of 3 to 19, n2 is an integer of 4 to 20, and each M is independently a hydrogen atom, Na, K, or NH ４ is.

[0099] The metal content of the solid composition is preferably 50 ppm by mass or less, more preferably 20 ppm by mass or less, and even more preferably 10 ppm by mass or less, relative to the total mass of the solid composition. It is also preferably below the measurement limit of the following measurement method. The lower limit can be 1 ppb by mass. The metal content is the total content of 29 metal elements (Fe, Na, K, Li, Be, Mg, Al, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi) measured by the absolute calibration curve method using an inductively coupled plasma mass spectrometer. The metal content of the solid composition can be measured by ashing the solid composition, dissolving the resulting ash in acid, and measuring the resulting solution using an inductively coupled plasma mass spectrometer. In the method for producing the present elastomer, by using a stirring device equipped with the above-mentioned stirring blades, it is not necessary to use a metal-containing flocculant when recovering the present elastomer, and therefore the metal content of the solid composition can be easily adjusted to within the above-mentioned range.

[0100] <Shape> The solid composition containing the present elastomer can be transformed into an appropriate shape depending on the manufacturing method and application of the crosslinked rubber article. The solid composition may be, for example, a sheet, granules, a tube, or a fiber, or may be in an irregular shape.

[0101] Uses The elastomers are preferably used in the manufacture of crosslinked rubber articles.

[0102] Crosslinked rubber articles can be produced by crosslinking the present elastomer or the solid composition, for example, by adding a crosslinking agent to the present elastomer or the solid composition and kneading or molding the mixture.

[0103] Specific examples of crosslinking agents include organic peroxides, polyols, amines, and triazines, with organic peroxides being preferred because they provide excellent productivity, heat resistance, and chemical resistance to crosslinked rubber articles. Specific examples of organic peroxides include dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene, benzoyl peroxide, tert-butylperoxybenzene, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane. Specific examples of dialkyl peroxides include 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, tert-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, tert-butylperoxymaleic acid, and tert-butylperoxyisopropyl carbonate.

[0104] In producing crosslinked rubber articles, components other than the crosslinking agent may be used. Examples of other components include catalysts, crosslinking aids, acid acceptors, fillers and reinforcing materials, scorch retarders, crown ethers, and mold release agents. Examples of molding methods include injection molding, extrusion molding, coextrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calender molding.

[0105] The crosslinked rubber article is suitably used as a material for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. Furthermore, the crosslinked rubber articles can be used for heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, wire coating materials, sealing materials for semiconductor devices, sealing materials for liquid crystal display panel manufacturing equipment, sealing materials for light-emitting diode manufacturing equipment, corrosion-resistant rubber coating materials, sealing materials for urea-resistant grease, etc., rubber coating materials, adhesive rubbers, hoses, tubes, calendered sheets (rolls), sponges, rubber rolls, oil drilling components, heat-dissipating sheets, solution-crosslinked products, rubber sponges, bearing seals (urea-resistant grease, etc.), linings (chemical-resistant), insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands for watches, endoscope packings (amine-resistant), bellows hoses (processed from calendered sheets), water heater packings / valves, fenders (marine civil engineering, ships), fibers / nonwoven fabrics (protective clothing, etc.), board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration isolators, vibration-damping agents, sealants, additives for other materials, and toys.

[0106] The present invention will be described in detail below with reference to examples. Examples 1 and 2 are working examples, and Example 3 is a comparative example. However, the present invention is not limited to these examples.

[0107] <Production of Raw Material Liquid A> Ultrapure water (1,130 g), 30 mass% aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g) were charged into a 2.2 L stainless steel pressure reactor equipped with an anchor impeller, and the temperature was raised to 90°C while stirring at 600 rpm. Next, an aqueous ammonium persulfate solution (5.0 mass%, 30 cc) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. When 4 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction, yielding a fluoropolymer 1A. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated raw material liquid A. Raw material liquid A was freeze-aggregated and then filtered. The resulting fluoropolymer 1A was analyzed by NMR, revealing that the ratio of PMVE units to TFE units was 30 / 70 (molar ratio).

[0108] <Production of Raw Material Solution B> To the raw material solution A, HPR4002Cl (anion exchange resin, manufactured by DuPont, 200 g) was added. 150 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. Next, AmberLite (registered trademark) HPR650H (cation exchange resin, manufactured by DuPont, 50 g) was added to the filtrate. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution B. In raw material solution B, particles of fluoropolymer 1A (specific polymer) were dispersed in an aqueous medium, and the content of fluoropolymer 1A was 0.6 mass% relative to the total mass of raw material solution B.

[0109] [Example 1] A stainless steel pressure reactor having an internal volume of 2.2 L and equipped with an anchor impeller was charged with raw material liquid B (1,000 g) and ultrapure water (175 g) to obtain aqueous dispersion B (first aqueous dispersion). The content of fluoropolymer 1A was 0.4 mass% relative to the total mass of aqueous dispersion B.

[0110] Perfluoro-1,4-diiodobutane (2.0 g), PMVE (72 g), and TFE (14 g) were charged to aqueous dispersion B, and the temperature was raised to 80 ° C. while stirring at 600 rpm. TFE and PMVE were injected into the reactor until the pressure reached 1.2 MPa [gauge], and an aqueous ammonium persulfate solution (APS aqueous solution, 1.0 mass%, 20 mL) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 160 g of TFE and 133 g of PMVE had been injected, the reactor was cooled, and the polymerization reaction was terminated, yielding perfluoroelastomer 1. The polymerization time was 300 minutes.

[0111] After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and the liquid was then extracted from the reactor. This liquid was designated as aqueous dispersion 1 (second aqueous dispersion). Aqueous dispersion 1 was a dispersion in which particles containing perfluoroelastomer 1 (average particle diameter 92.7 nm) were dispersed in an aqueous medium, and had a solids concentration of 20.5% by mass. The aqueous dispersion 1 was stirred with a disc turbine blade for 150 minutes at 1,000 rpm, and the aggregates were then collected by filtration. The collected aggregates were washed with 2,000 g of ultrapure water at 30 ° C. and dried to obtain perfluoroelastomer 1.

[0112] The obtained perfluoroelastomer 1 was analyzed by NMR, and as a result, the content of TFE units was 66 mol% relative to the total content of all units in perfluoroelastomer 1, and the content of PAVE units (PMVE units) was 34 mol% relative to the total content of all units in perfluoroelastomer 1. In addition, as a result of the NMR analysis, the content of iodine atoms in perfluoroelastomer 1 was 0.05 mass% relative to the total mass of perfluoroelastomer 1.

[0113] The obtained perfluoroelastomer 1 had a glass transition temperature (Tg) of -3°C, a melting peak (ΔH) of 0.0 J / g or less, and a fluorine atom ratio of 70% by mass. Tg was measured using a NEXTA DSC600 manufactured by Hitachi High-Tech Corporation. Specifically, 5 mg of a sample for measurement was weighed into an aluminum sample pan, and the sample was cooled to -40°C at a cooling rate of 10°C / min under a nitrogen atmosphere and held at that temperature for 10 minutes. The temperature was then increased to 40°C at 10°C / min. After reaching the predetermined temperature, the sample was cooled to -40°C at 10°C / min, held at that temperature for 10 minutes, and then heated again to 40°C at 10°C / min. Tg was estimated from the inflection point observed in this second heating operation. The melting peak (ΔH) was calculated from the area of ​​the melting peak that appeared in the melting curve obtained by the above-mentioned operation. The proportion of fluorine atoms in the perfluoroelastomer was calculated by the fundamental parameter method after the sheet composition obtained by hot pressing the perfluoroelastomer into a 3,100 μm sheet was subjected to fluorescent X-ray analysis using a ZSX Primus II (manufactured by RIGAKU).

[0114] <Production of Raw Material Liquid C> A fluoropolymer 1C was polymerized in the same procedure as in the production of raw material liquid A, except that the amounts of each component were appropriately changed, and this liquid was used as raw material liquid C. Raw material liquid C was freeze-coagulated and then filtered, and the resulting fluoropolymer 1C (specific polymer) was analyzed by NMR, and as a result, it was found that the ratio of PMVE units to TFE units was 32 / 68 (molar ratio).

[0115] <Production of Raw Material Liquid D> Raw material liquid D was produced in the same procedure as for raw material liquid B, except that raw material liquid C was used instead of raw material liquid A. Raw material liquid D contained particles of fluoropolymer 1C dispersed in an aqueous medium, and the content of fluoropolymer 1C was 0.6% by mass relative to the total mass of raw material liquid D.

[0116] [Example 2] A stainless steel pressure reactor having an internal volume of 2.2 L and equipped with an anchor impeller was charged with raw material liquid D (1,000 g) and ultrapure water (175 g), to obtain aqueous dispersion D (first aqueous dispersion). The content of fluoropolymer 1C was 0.4 mass% relative to the total mass of aqueous dispersion D.

[0117] PMVE (72 g), perfluoro-1,4-diiodobutane (2.0 g), and TFE (14 g) were charged to aqueous dispersion D, and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected into the reactor until the pressure reached 1.5 MPa [gauge], and an aqueous APS solution (0.5% by mass, 16 ml) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 256 g of TFE and 217 g of PMVE had been added, the reactor was cooled, and the polymerization reaction was terminated, yielding perfluoroelastomer 2. The polymerization time was 290 minutes.

[0118] After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and the liquid was then extracted from the reactor. This liquid was designated as aqueous dispersion 2 (second aqueous dispersion). Aqueous dispersion 2 was a dispersion in which particles containing perfluoroelastomer 2 (average particle diameter 140.3 nm) were dispersed in an aqueous medium, and had a solids concentration of 28.6% by mass. The aqueous dispersion 2 was stirred with a paddle impeller for 150 minutes at 1,000 rpm, and the aggregates were then collected by filtration. The collected aggregates were washed with 2,000 g of ultrapure water at 60 ° C. and dried to obtain perfluoroelastomer 2.

[0119] The obtained perfluoroelastomer 2 was analyzed by NMR, and as a result, the content of TFE units was 66 mol% relative to the total content of all units in perfluoroelastomer 2, and the content of PAVE units (PMVE units) was 34 mol% relative to the total content of all units in perfluoroelastomer 2. In addition, as a result of the NMR analysis, the content of iodine atoms in perfluoroelastomer 2 was 0.05 mass% relative to the total mass of perfluoroelastomer 2.

[0120] The obtained perfluoroelastomer 2 had a glass transition temperature (Tg) of -5°C, a melting peak (ΔH) of 0.0 J / g or less, and a fluorine atom ratio of 69 mass%. The measurement methods were the same as in Example 1.

[0121] [Example 3] A stainless steel pressure reactor with an internal volume of 2.1 L and equipped with an anchor blade was degassed, and then ultrapure water (1,004 g), an emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass solution (80.1 g) of (emulsifier A) and a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (72 g) and TFE (14 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous solution of APS (1.0% by mass, 20 ml) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE and PMVE were added to maintain a constant pressure of 1.2 MPa [gauge]. When 160 g of TFE and 133 g of PMVE were injected, the reactor was cooled, and the polymerization reaction was terminated to obtain perfluoroelastomer 3. The polymerization time was 262 minutes. After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and the liquid was extracted from the reactor. This liquid was designated as aqueous dispersion 3. Aqueous Dispersion 3 was a dispersion in which particles containing Perfluoroelastomer 3 (average particle diameter 84 nm) were dispersed in an aqueous medium, and had a solids concentration of 21.1% by mass. An aqueous aluminum sulfate solution was added to the dispersion to effect coagulation. Perfluoroelastomer 3 was obtained by drying.

[0122] The obtained perfluoroelastomer 3 was analyzed by NMR, and as a result, the content of TFE units was 66 mol % relative to the total content of all units in perfluoroelastomer 3, and the content of PAVE units (PMVE units) was 34 mol % relative to the total content of all units in perfluoroelastomer 3. The content of iodine atoms in perfluoroelastomer 3 was 0.03 mass % relative to the total mass of perfluoroelastomer 3.

[0123] The obtained perfluoroelastomer 3 had a glass transition temperature (Tg) of −3° C., a melting peak (ΔH) of 0.0 J / g, and a fluorine atom ratio of 70 mass %. The measurement methods were the same as in Example 1.

[0124] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0125] <Average Particle Diameter> The average particle diameter of particles in the aqueous dispersion was measured using the aqueous dispersion of each example as a sample with a dynamic light scattering particle diameter measuring device (ELSZ, manufactured by Otsuka Electronics Co., Ltd.).

[0126] [Method for measuring iodine content] The perfluoroelastomer was hot-pressed to form a 300 μm sheet. The obtained sheet composition was subjected to fluorescent X-ray analysis using a ZSX Primus II (manufactured by RIGAKU), and the iodine content in the perfluoroelastomer was calculated by the fundamental parameter method.

[0127] <Molecular Weight> Using the apparatus and measurement conditions shown in Table 1, the molecular weight distribution curve of the perfluoroelastomer in each example was determined by the calibration curve method using polymethyl methacrylate as the standard substance. From the obtained molecular weight distribution curve, the peak-top molecular weight of the first peak, the peak-top molecular weight of the second peak, and the molecular weight distribution (Mw / Mn) of the perfluoroelastomer in each example were determined. The results are shown in Table 2. The peak observed in the molecular weight range of 1,000 to 100,000 was defined as the first peak, and the peak observed in the molecular weight range exceeding 100,000 was defined as the second peak. Here, in the molecular weight distribution curves of the perfluoroelastomers in Examples 1 and 2, only one first peak and one second peak were observed. On the other hand, in the molecular weight distribution curve of the perfluoroelastomer in Example 3, no first peak was observed, and only one second peak was observed.

[0128]

[0129] <Method for Quantifying Emulsifiers in Solid Compositions> (Preparation of Measurement Samples) The solid compositions obtained in each of the examples described below were freeze-pulverized using a freeze-pulverizer, Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 min, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5,000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as the extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier and hydrocarbon emulsifier in the extract were measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations, aqueous solutions with five or more levels of content were prepared, and LC / MS analysis was performed on the aqueous solutions with each content. The relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon emulsifier in the extract was converted into the content of the fluorine-containing emulsifier and hydrocarbon emulsifier.

[0130]

[0131] The MRM measurement parameters are selected appropriately depending on the structures of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured. Literature values ​​can be used for the MRM parameters, or they can be calculated using an LC-MS instrument. The specific procedure for determining MRM parameters using an LC-MS instrument is as follows: Using an LC / MS instrument (Shimadzu Corporation, LCMS-8060NX), select product ion search, input the molecular weights of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured, and then perform precursor ion, precursor adjustment, voltage optimization, and product m / z optimization. The calculated MRM measurement parameters are used. As an example, the MRM measurement parameters for compounds (S2) and (S4), which are fluorine-containing emulsifiers, are shown in the table below. In formulas (S2) and (S4), MS represents a hydrogen atom, a metal atom, NR4 (wherein R may be the same or different and represents a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. F-(CF2)n1-COOMS (S2) F-(CF2)n2-SO3MS (S4) where n1 is an integer from 3 to 17 and n2 is an integer from 4 to 12.

[0132]

[0133]

[0134] (Quantitative Analysis of Fluorine-Containing Emulsifier and Hydrocarbon Emulsifier Contained in Solid Composition) Specifically, five levels of methanol standard solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations of 1 to 180 ng / g were prepared, and a was calculated from the sample concentration and peak integral value of each emulsifier using a first-order approximation according to formula (A1-1): A = a × X (A1-1), where A is the peak area of ​​each emulsifier and X is the concentration (ng / g) of each emulsifier.

[0135] Next, the amount of emulsifier contained in the extract was calculated using formula (A1-2). Note that a in formula (A1-2) means a obtained by the above formula (A1-1). XCm = ACm / a (A1-2) XCm: content (ng / g) of emulsifier in each extract ACm: peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 1 ng / g.

[0136] The content of the emulsifier in the solid composition relative to the total mass of the solid composition (ZCm) was calculated using the following formula (A1-3): ZCm = XCm × ρ1 × La / W1 (A1-3) ZCm: content of the emulsifier contained in the solid composition ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid composition in each example)

[0137] <Method for Quantifying Formula (S1) and Formula (S3) Contained in Solid Composition> The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.5 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5,000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as the extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier in the extract was measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions were as described above. Using aqueous solutions of emulsifiers containing fluorine atoms with known concentrations, methanol solutions with five or more different concentrations were prepared. LC / MS analysis of the methanol solutions with each concentration was performed, and the relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the emulsifier containing fluorine atoms in the extract was converted to the content of the emulsifier containing fluorine atoms. The content of the compound represented by formula (S1) contained in each extract was determined by converting each compound in formula (S1) where n1 = 3 to 13 into a perfluorocarboxylic acid (formula (S2)) with the same carbon number. Furthermore, the content of the compound represented by formula (S3) contained in each extract was determined by converting each compound in formula (S3) where n2 = 4 to 10 into a perfluorosulfonic acid (formula (S4)) with the same carbon number. The MRM parameters for formulas (S1) and (S3) are shown in Tables 5 and 6. Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1 to 180 ng / g were first prepared, and a and a' were calculated from the respective sample concentrations and peak integral values ​​using linear approximation according to formulas (A2-1) and (A2-1').A = a × X (A2-1) A: peak area of ​​perfluorocarboxylic acid, X: concentration of perfluorocarboxylic acid (ng / g) A' = a' × X' (A2-1') A': peak area of ​​perfluorosulfonic acid, X': concentration of perfluorosulfonic acid (ng / g).

[0138]

[0139] Specifically, first, the peak areas of the compounds represented by formula (S1) and formula (S3) contained in each of the extracts were determined using the liquid chromatograph mass spectrometer.

[0140] Next, the contents of the compound represented by formula (S1) and the compound represented by formula (S3) were calculated using formulas (A2-2) and (A2-2'), respectively. Note that a in formula (A2-2) means a calculated using formula (A2-1) above, and a' in formula (A2-2') means a' calculated using formula (A2-1') above. XCm ​​= ACm / a (A2-2) XCm: content (ng / g) of the compound represented by formula (S1) and having carbon number (n+1) in each extract ACm: peak area of ​​the compound represented by formula (S1) and having carbon number (n+1) in each extract XCm' = ACm' / a' (A2-2') XCm': content (ng / g) of the compound represented by formula (S3) and having carbon number n in each extract ACm': peak area of ​​the compound represented by formula (S3) and having carbon number n in each extract The quantitation limit in this measurement is 1 ng / g.

[0141] The content (ZCm) of the compound represented by formula (S1) in the solid relative to the total mass of the solid was calculated using the following formula (A2-3): ZCm = XCm × ρ1 × La / W1 (A2-3) ZCm: content of the compound represented by formula (S1) with carbon number (n+1) contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0142] The content (ZCm') of the compound represented by formula (S3) in the solid relative to the total mass of the solid was calculated using the following formula (A2-4): ZCm' = XCm' × ρ1 × La / W1 (A2-4) ZCm': content of the compound represented by formula (S3) with carbon number n contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0143] <Roll Wrapping Property> The perfluoroelastomer obtained in each example was kneaded using a roll mixer (Yamatetsu Corporation test roll machine) to produce a sheet, and the roll wrapping property was confirmed. The roll mixer was equipped with two rolls (roll diameter 8 inches, roll length 18 inches) and two guide members arranged in the gap between the rolls and near both ends of the rolls. The guide members maintain the width of the workpiece, which spreads in the axial direction of the rolls after passing through the rolls, at a predetermined width. 200 g of perfluoroelastomer was weighed out and placed in a dryer to heat to 50°C, and then the fluoropolymer was introduced between the guide members of the roll mixer set under the following conditions. The time (also referred to as the "winding time") from the introduction of the perfluoroelastomer until the perfluoroelastomer (bank) accumulated in the roll gap between the guide members was gone and all of the perfluoroelastomer was wrapped around the roll was measured. Roll temperature: 40° C. Roll gap: 4.2 mm Front roll rotation speed: 22 rpm Rear roll rotation speed: 20 rpm Width between guide members: 150 mm The roll temperature was adjusted using a water heater (WTC40, manufactured by Nakamura Scientific Industrial Co., Ltd.).

[0144] The roll wrapping property of the perfluoroelastomer was evaluated based on the measurement time according to the following evaluation criteria: (Evaluation criteria for roll wrapping property) ⊚ (Excellent): The wrapping time was within 3 minutes. ◯ (Good): The wrapping time was more than 3 minutes but not more than 5 minutes. Δ (Unacceptable): None of the perfluoroelastomer was wrapped around the roll, or the wrapping time was more than 5 minutes.

[0145]

[0146] As shown in Table 7, in the molecular weight distribution curve of the perfluoroelastomer obtained from the values ​​measured by GPC and the calibration curve using polymethyl methacrylate as the standard, a first peak having a first peak top in the molecular weight region of 1,000 to 100,000 and a second peak having a second peak top in the molecular weight region of more than 100,000 (Requirement 1) were observed, and it was confirmed that the perfluoroelastomer had excellent roll-winding properties (Examples 1 and 2). In contrast, it was confirmed that the perfluoroelastomer of Example 3, which did not satisfy Requirement 1, had insufficient roll-winding properties.

[0147] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-222224, filed on December 28, 2023, are hereby incorporated by reference as the disclosure of the specification of the present invention.

[0148] P1 Top of the first peak P2 Top of the second peak

Claims

1. A perfluoroelastomer that satisfies the following requirement 1. Requirement 1: In the molecular weight distribution curve of the perfluoroelastomer obtained from the calibration curve using polymethyl methacrylate as a standard substance and the value measured by gel permeation chromatography, a first peak showing a first peak top in the region of molecular weight 1,000 to 100,000 and a second peak showing a second peak top in the region of molecular weight over 100,000 are observed.

2. The perfluoroelastomer according to claim 1, further satisfying the following requirement 2. Requirement 2: In the molecular weight distribution curve of the perfluoroelastomer obtained from the calibration curve using polymethyl methacrylate as a standard substance and the value measured by gel permeation chromatography, Mw / Mn, which is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn, is 1.40 or more.

3. The perfluoroelastomer according to claim 1, having a unit based on tetrafluoroethylene and a unit based on perfluoro(alkyl vinyl ether).

4. The perfluoroelastomer according to claim 3, wherein the content of the unit based on tetrafluoroethylene is 20 to 80 mol% with respect to the total content of all units of the perfluoroelastomer, and the content of the unit based on perfluoro(alkyl vinyl ether) is 20 to 80 mol% with respect to the total content of all units of the perfluoroelastomer.

5. A crosslinked rubber article obtained by crosslinking the perfluoroelastomer according to any one of claims 1 to 4.

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