Fluororesin and method for producing fluororesin

Abstract

The purpose of the present disclosure is to provide a fluororesin from which it is possible to obtain a melt-molded body having excellent transparency and a high dioxole content proportion. A fluororesin according to one mode of the present disclosure includes a residue unit A represented by formula (1) and a residue unit B represented by formula (2). With respect to the total amount of all residue units, the contained amount of the residue unit A is 30-70 mol% and the contained amount of the residue unit B is 30-70 mol%. The haze value of a 100 µm-thick melt-molded body of the fluororesin is 4% or less. (In the formulae, R1 represents a hydrogen atom or a fluorine atom. Rf1-Rf4 each independently represent a fluorine atom or a perfluoroalkyl group. The perfluoroalkyl group optionally has an ether bond. Rf1 and Rf2, and Rf3 and Rf4 are optionally bonded to each other to form rings.)

Description

Fluororesin and method for producing fluororesin

[0001] The present invention relates to fluororesins and methods for producing fluororesins, and more particularly to fluororesins containing dioxolane and methods for producing said fluororesins.

[0002] Fluororesins are used in various components such as protective films for electronic components including semiconductors, water-repellent films for inkjet printer heads, waterproof and oil-repellent coatings for filters, and optical components, due to their excellent heat resistance, electrical properties, chemical resistance, water resistance, liquid and oil repellency, and optical properties. Among these, fluororesins containing dioxolane have a bulky ring structure, resulting in an amorphous state with high transparency and high heat resistance.

[0003] For example, Patent Document 1 discloses a fluororesin having dioxolane and dioxol, which have bulky ring structures.

[0004] Non-patent document 1 discloses a method for producing perfluoro-2-methylene-4-methyl-1,3-dioxolane, which is a type of fluororesin containing dioxolane.

[0005] Japanese Special Publication No. 9-512854

[0006] Macromolecules 2005, 38, 4237-4245

[0007] As a result of our investigations, we have found that in fluororesins that are copolymers of dioxolane and dioxol, as described in Patent Document 1, the transparency of the molten molded article obtained using the fluororesin is impaired when the dioxol content is increased. On the other hand, there is a need to develop fluororesins with a high dioxol content that maintain transparency in the molten molded article while imparting further physical properties different from those of dioxolane alone.

[0008] The present invention has been made in view of the above-mentioned problems, and its objective is to provide a fluororesin that can produce a melt-molded article with excellent transparency even when it has a higher dioxol content.

[0009] In order to solve the above problems, the fluororesin according to the present invention is a fluororesin containing a residue unit A represented by the following general formula (1) and a residue unit B represented by the following general formula (2), wherein the content of the residue unit A is 30 mol% or more and 70 mol% or less, and the content of the residue unit B is 30 mol% or more and 70 mol% or less with respect to the total amount of all residue units, and the haze value of a melt-molded body having a thickness of 100 μm of the fluororesin is 4% or less.

[0010] (In the formula, Rf １ and Rf ２ each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have an ether bond between any carbon-carbon bond. Further, Rf １ and Rf ２ may combine with each other to form a ring.)

[0011] (In the formula, R １ represents a hydrogen atom or a fluorine atom. Rf ３ and Rf ４ each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have an ether bond between any carbon-carbon bond. Further, Rf ３ and Rf ４ may combine with each other to form a ring.)

[0012] According to the present invention, it is possible to provide a fluororesin capable of obtaining a melt-molded body having a high content ratio of dioxol and excellent transparency.

[0013] Hereinafter, an embodiment of the fluororesin according to the present invention will be described.

[0014] In the present invention, the "residue unit" represents a repeating unit or a constituent unit in the resin.

[0015] When a numerical range is described with "~", the numerical range includes its upper limit value and lower limit value.

[0016] [1. Fluororesin] (Fluororesin) The fluororesin in this embodiment is a fluororesin containing a fluororesin that includes a residue unit A represented by general formula (1) and a residue unit B represented by general formula (2).

[0017] Residue unit A is a residue unit represented by the following general formula (1).

[0018] In formula (1), Rf １ and Rf ２ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf １ and Rf ２ These may be joined together to form a ring.

[0019] Rf １ and Rf ２ The C1-C6 perfluoroalkyl group in this combination may be a linear perfluoroalkyl group having C1-C6, a branched perfluoroalkyl group having C3-C6, or a cyclic perfluoroalkyl group having C3-C6.

[0020] In this specification, the phrase "having an ether bond between any carbon-carbon bonds" of a perfluoroalkyl group includes not only cases where an ether bond is present between any carbon-carbon bonds within the perfluoroalkyl group, but also cases where an ether bond is present between the carbon atom to which the perfluoroalkyl group is bonded and the carbon-carbon bond between the perfluoroalkyl group and the perfluoroalkyl group.

[0021] Examples of linear perfluoroalkyl groups having 1 to 6 carbon atoms include trifluoromethyl, pentafluoroethyl, heptafluoro-n-propyl, nonafluoro-n-butyl, undecafluoro-n-pentyl, and tridecafluoro-n-hexyl groups.

[0022] Examples of branched perfluoroalkyl groups having 3 to 6 carbon atoms include heptafluoroisopropyl group, nonafluoroisobutyl group, nonafluoro-sec-butyl group, and nonafluoro-tert-butyl group.

[0023] Examples of cyclic perfluoroalkyl groups having 3 to 6 carbon atoms include pentafluorocyclopropyl, heptafluorocyclobutyl, and undecafluorocyclohexyl groups.

[0024] Examples of linear perfluoroalkyl groups having an ether bond between any carbon-carbon bonds include perfluoro(methoxymethyl) group, perfluoro(ethoxymethyl) group, perfluoro(methoxyethyl) group, and perfluoro(ethoxyethyl) group.

[0025] Examples of cyclic perfluoroalkyl groups having an ether bond between any carbon-carbon bonds include the 2-(2,3,3,4,4,5,5,6,6-decafluorotetrahydro)-pyranyl group, the 4-(2,3,3,4,4,5,5,6,6-decafluorotetohydro)-pyranyl group, and the 2-(2,3,3,4,4,5,5-heptafluorotetrahydro)-furanyl group.

[0026] Rf １ and Rf ２ As an example of a case where they are connected to each other to form a ring, specifically, Rf １ The carbon atoms to which it is bonded and Rf ２ Examples include hexafluoropropylene groups and octafluorobutylene groups, which are formed including carbon atoms to which the group is bonded.

[0027] Among these, from the viewpoint of ease of monomer production, trifluoromethyl, pentafluoroethyl, and perfluoro(methoxymethyl) groups are preferred as perfluoroalkyl groups, with trifluoromethyl being more preferred.

[0028] Rf in equation (1) １ and Rf ２In particular, each of these is independently a fluorine atom or a trifluoromethyl group. In one embodiment, Rf １ and Rf ２ It is especially preferable that all of them are fluorine atoms. In another embodiment, Rf １ fluorine atom and Rf ２ It is especially preferable that the group is a trifluoromethyl group.

[0029] The following are some specific examples of residue units that can be considered as residue unit A, but they are not limited to these.

[0030] The residue unit A contained in the fluororesin may be of only one type, or it may be of two or more types. If there are two or more types of residue unit A contained in the fluororesin, they may be composed in any ratio and any combination.

[0031] Residue unit B is a residue unit represented by the following general formula (2).

[0032] In formula (2), R １ Rf represents a hydrogen atom or a fluorine atom. ３ and Rf ４ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf ３ and Rf ４ These may be joined together to form a ring.

[0033] R １ represents a hydrogen atom or a fluorine atom, with a fluorine atom being preferred.

[0034] Rf ３ and Rf ４ The C1-C6 perfluoroalkyl group in this combination may be a linear perfluoroalkyl group having C1-C6, a branched perfluoroalkyl group having C3-C6, or a cyclic perfluoroalkyl group having C3-C6.

[0035] Examples of linear perfluoroalkyl groups having 1 to 6 carbon atoms include trifluoromethyl, pentafluoroethyl, heptafluoro-n-propyl, nonafluoro-n-butyl, undecafluoro-n-pentyl, and tridecafluoro-n-hexyl groups.

[0036] Examples of branched perfluoroalkyl groups having 3 to 6 carbon atoms include heptafluoroisopropyl group, nonafluoroisobutyl group, nonafluoro-sec-butyl group, and nonafluoro-tert-butyl group.

[0037] Examples of cyclic perfluoroalkyl groups having 3 to 6 carbon atoms include pentafluorocyclopropyl, nonafluorocyclobutyl, and tridecafluorocyclohexyl groups.

[0038] Examples of linear perfluoroalkyl groups having an ether bond between any carbon-carbon bonds include perfluoro(methoxymethyl) group, perfluoro(ethoxymethyl) group, perfluoro(methoxyethyl) group, and perfluoro(ethoxyethyl) group.

[0039] Examples of cyclic perfluoroalkyl groups having an ether bond between any carbon-carbon bonds include the 2-(2,3,3,4,4,5,5,6,6-decafluoro)pyrinyl group, the 4-(2,3,3,4,4,5,5,6,6-decafluoro)pyrinyl group, and the 2-(2,3,3,4,4,5,5-heptafluoro)furanyl group.

[0040] Rf ３ and Rf ４ As an example of a case where they are connected to each other to form a ring, specifically, Rf ３ and Rf ４ Examples include hexafluoropropylene groups and octafluorobutylene groups, which are formed including carbon atoms to which the group is bonded.

[0041] Among these, from the viewpoint of ease of monomer production, trifluoromethyl, pentafluoroethyl, and perfluoro(methoxymethyl) groups are preferred as perfluoroalkyl groups, with trifluoromethyl and pentafluoroethyl groups being more preferred.

[0042] Rf in equation (2) ３ and Rf ４ Preferably, each of these is independently a fluorine atom or a perfluoroalkyl group having 1 to 2 carbon atoms. In one embodiment, Rf ３ and Rf ４ It is especially preferable that all of them are trifluoromethyl groups. In another form, Rf ３ fluorine atom and Rf ４ It is especially preferable that it is a pentafluoroethyl group.

[0043] In equation (2), in one form, R １ is a fluorine atom, Rf ３ and Rf ４ It is especially preferable that all of them are trifluoromethyl groups. In another embodiment, R １ is a fluorine atom, Rf ３ fluorine atom and Rf ４ It is especially preferable that it is a pentafluoroethyl group.

[0044] The residue unit B contained in the fluororesin may be of only one type, or it may be of two or more types. If there are two or more types of residue unit B contained in the fluororesin, they may be composed of any ratio and any combination.

[0045] The content of residue unit A in the fluororesin is 30 mol% or more of the total amount of all residue units. This results in a fluororesin with excellent transparency. The content of residue unit A can be 32 mol% or more, 35 mol% or more, and even 36 mol% or more.

[0046] The content of residue unit B in the fluororesin is 30 mol% or more of the total amount of all residue units. The higher the content of residue unit B, the more the heat resistance of the fluororesin tends to improve. Therefore, by keeping the content of residue unit B within the above range, a fluororesin with excellent heat resistance is obtained. The content of residue unit B can be 32 mol% or more, and furthermore, it can be 35 mol% or more.

[0047] Regarding the upper limit of the content of residue unit A, the content of residue unit A in fluororesins is 70 mol% or less of the total amount of all residue units. This allows for a higher proportion of residue unit B in the fluororesin, resulting in a fluororesin with excellent heat resistance. The content of residue unit A can be 68 mol% or less, and furthermore, 66 mol% or less.

[0048] Regarding the upper limit of the content of residue unit B, the content of residue unit B in fluororesin is 70 mol% or less of the total amount of all residue units. This results in a fluororesin that has excellent transparency. Furthermore, the haze value of the molten molded article of the fluororesin can be reduced. The content of residue unit B can be 68 mol% or less, 65 mol% or less, and even 64 mol% or less.

[0049] The content of each residue unit in the fluororesin is: １９ This can be determined by performing F-NMR measurements and calculating the ratio of the integrated values ​​of the detected peaks. １９ F-NMR measurement can be performed, for example, by dissolving the fluororesin in hexafluorobenzene and using an NMR analyzer (JNM-ECZS400) manufactured by JEOL Ltd. For example, if the fluororesin consists of residue unit A and residue unit B, it can be calculated by the ratio of the integral value of the peak attributed to residue unit A to the integral value of the peak attributed to residue unit B. Structural units that were not detected or were below the detection limit are calculated as 0 mol%. In detail, the content of each residue unit can be calculated by the ratio of the integral value of the peak in the range of -88 ppm to -72 ppm (corresponding to 5F of residue unit A and 6F of residue unit B) to the integral value of the peak in the range of -135 ppm to -100 ppm (corresponding to 3F of residue unit A and 2F of residue unit B).

[0050] In this embodiment, the fluororesin may contain other residue units as long as the content of residue unit A and residue unit B is within the above range. If other residue units are included, only one type may be included, or two or more types may be included.Other residue units include structures in which the following double bonds are cleaved to form repeating units: halogenated olefins such as tetrafluoroethylene, hexafluoropropylene, octafluoroisobutylene, chlorotrifluoroethylene, 1,1-dichloro-2,2-difluoroethylene, 1,2-dichloro-1,2-difluoroethylene, trichlorofluoroethylene, tetrachloroethylene, 1,1-dichlorohexafluoro-1-butene, 2,3-dichlorohexafluoro-2-butene, 4-chloroheptafluoro-1-butene, 6-chloroperfluoro-1-butene and 8-chloroperfluoro-1-butene; perfluorovinyl ethers such as perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), perfluoro(n-propyl vinyl ether), perfluoro(isopropyl vinyl ether), perfluoro(3-methoxypropyl vinyl ether) and 2-(heptafluoropropoxy)hexafluoropropyltrifluorovinyl ether; styrene, phenyl Styrene compounds such as fluorostyrene, 2-fluorostyrene, 2-trifluoromethylstyrene, 3-trifluoromethylstyrene, and 4-trifluoromethylstyrene; acrylic acid compounds such as acrylic acid, methyl acrylate, methacrylic acid, and methyl methacrylate; vinyl compounds such as ethylene, propylene, 1-butene, isobutene, vinyl chloride, vinyl acetate, maleic anhydride, maleic acid, fumaric acid, maleimide, N-methylmaleimide, and N-phenylmaleimide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexyl vinyl ether, ethylene glycol vinyl ether, diethylene glycol divinyl ether, 1,4-butanediol vinyl ether, 1,4-butanediol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, and 2-chloroethyl vinyl ether.

[0051] If the fluororesin in this embodiment contains other residue units, the content of the other residue units is not particularly limited, but may be, for example, 20 mol% or less, 10 mol% or less, or 5 mol% or less relative to the total amount of all residue units. Alternatively, the fluororesin in this embodiment may contain only residue unit A and residue unit B.

[0052] The weight-average molecular weight of the fluororesin is preferably 1,000 to 1,000,000, more preferably 10,000 to 500,000, even more preferably 30,000 to 300,000, and particularly preferably 80,000 to 160,000, based on standard polymethyl methacrylate. Having the weight-average molecular weight of the fluororesin within the above range allows for a balance between the heat resistance and moldability of the resin.

[0053] In this embodiment, the molecular weight distribution Mw / Mn, expressed as the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of the fluororesin, is not particularly limited and may be, for example, in the range of 1.0 to 8.0, 1.0 to 5.0, or even 1.0 to 4.5. The lower limit of the molecular weight distribution Mw / Mn may be 1.1 or higher or 1.2 or higher in each of the above ranges. By having the molecular weight distribution Mw / Mn within the above ranges, a balance can be achieved between the heat resistance and moldability of the resin.

[0054] The weight-average molecular weight and number-average molecular weight of fluororesins can be measured by gel permission chromatography (GPC). In this method, a solvent in which the fluororesin is soluble can be used as the eluent. For example, an eluent can be Asahi Clean AK-225 (manufactured by AGC Inc.) to which 10 wt% of 1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) has been added relative to AK-225. The measurement temperature can be 40°C.

[0055] The form of the fluororesin in this embodiment is not limited, but it is preferably in the form of particles due to its excellent fluidity and moldability. There are no particular limitations on the particle size of the fluororesin, but it is preferably 1 to 10,000 μm, more preferably 1 to 2,000 μm, even more preferably 1 to 1,000 μm, and particularly preferably 10 to 1,000 μm, as this provides excellent handling during molding. The volume-average particle size of the fluororesin can be evaluated by particle size distribution measurement (volume distribution) using laser diffraction scattering. The particle size distribution using laser diffraction scattering can be measured by dispersing the resin particles in water or an organic solvent such as methanol.

[0056] The glass transition temperature (Tg), an indicator of the heat resistance of fluororesins, can be measured by determining the intermediate glass transition temperature using a differential scanning calorimeter (DSC). For example, the measurement conditions involve placing the sample in an aluminum sample pan and heating it under a nitrogen atmosphere: 1st time: -50°C → 180°C → -50°C (heating rate: 10°C / min), 2nd time: -50°C → 180°C (heating rate: 10°C / min). The glass transition temperature can be calculated by determining the intermediate glass transition temperature from the chart obtained during the second heating step, according to the description in JIS-K7121. In this case, a DSC calibrated with standard materials such as indium or tin can be used.

[0057] (Haze value of fluororesin molten article) The fluororesin according to this embodiment is a fluororesin in which, when a molten article with a thickness of 100 μm is obtained by molten molding using the fluororesin, the haze value of the molten article is 4% or less.

[0058] A 100 μm thick molten body for measuring haze values ​​is obtained as follows: First, 100 μm thick polyimide films, cut to 50 mm x 10 mm, are placed on both ends of a quartz plate (50 mm square, 2 mm thick) (the polyimide films act as spacers). Fluororesin is placed on top of this quartz plate, and another quartz plate (50 mm square, 2 mm thick) is placed on top of it, sandwiching the fluororesin between the quartz plates. This is then placed in a press machine and heated at 230°C for 10 minutes without pressure, and then heated and pressed in the press machine at a pressure of 10 MPa and 230°C for 30 minutes. After that, the pressure is released and it is cooled to obtain a 100 μm thick molten body sandwiched between quartz substrates.

[0059] The haze value of the obtained heated press-molded product can be determined by measuring it in accordance with JIS K7136 using a commercially available haze meter (for example, the SH7000 spectroscopic haze meter manufactured by Nippon Denshoku Industries Co., Ltd.). The haze value of the molten molded body may be measured after removing the molten molded body from the quartz substrate, or while the molten molded body is sandwiched between the quartz substrates.

[0060] The fluororesin according to this embodiment is a fluororesin in which the haze value of a 100 μm thick molten molded article obtained by melt-molding the fluororesin is 4% or less. Preferably, it is a fluororesin in which the haze value of the molten molded article is 2% or less, and more preferably, it is a fluororesin in which the haze value of the molten molded article is 1% or less. There is no lower limit to the haze value, and the lower the haze value of the resulting molten molded article, the better. For example, the haze value of the resulting molten molded article can be 0.01% or more.

[0061] A fluororesin having the above-described residue-unit composition, wherein a molten molded article of the fluororesin with a thickness of 100 μm has a haze value of 4% or less, can be produced by precipitation polymerization as described below. Therefore, the fluororesin according to this embodiment may be a precipitate polymer.

[0062] [2. Method for producing fluororesin] One aspect of the method for producing fluororesin according to the present invention will be described.

[0063] The method for producing fluororesin according to this embodiment includes polymerizing a mixture containing monomer A represented by general formula (3) and monomer B represented by general formula (4) in an organic solvent by precipitation polymerization.

[0064] Monomer A is a monomer represented by the following general formula (3).

[0065] In formula (3), Rf ５ and Rf ６ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf ５ and Rf ６ These may be joined together to form a ring.

[0066] Rf ５ and Rf ６ These are, respectively, Rf in residue unit A. １ and Rf ２ This corresponds to Rf. ５ and Rf ６ For a detailed explanation and examples, see the above Rf １ and Rf ２ This is the same as the explanation and examples provided in [the relevant section].

[0067] Monomer B is a monomer represented by the following general formula (4).

[0068] In formula (4), R ２ Rf represents a hydrogen atom or a fluorine atom. ７ and Rf ８ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf ７ and Rf ８ These may be joined together to form a ring.

[0069] R ２ , Rf ７ and Rf ８ These are, respectively, R in the insurance unit B. １ , Rf３ and Rf ４ This corresponds to R. ２ , Rf ７ and Rf ８ For a detailed explanation and examples, see the above R １ , Rf ３ and Rf ４ This is the same as the explanation and examples provided in [the relevant section].

[0070] The content of monomer A and monomer B in the monomer mixture is sufficient to achieve the content of residue units A and residue units B in the fluororesin described above. For example, the content of monomer A in the mixture can be 10 mol% to 90 mol%, more preferably 20 mol% to 80 mol%, and more preferably 40 mol% to 70 mol%, based on the total amount of monomers. Similarly, the content of monomer B in the mixture can be 10 mol% to 90 mol%, more preferably 20 mol% to 80 mol%, and more preferably 30 mol% to 60 mol%, based on the total amount of monomers.

[0071] The organic solvent used in the manufacturing method according to this embodiment is a solvent in which at least monomer A and monomer B dissolve, and at least a portion of the resin containing residue units A and B produced by polymerization does not dissolve, resulting in the formation of a resin precipitate. The resin produced by polymerization precipitates in the organic solvent as particles. The organic solvent used in the fluororesin manufacturing method of this embodiment may be described as a "precipitating polymerization solvent." Unlike emulsion polymerization, precipitation polymerization, and dispersion polymerization, the manufacturing method using a precipitating polymerization solvent does not require additives such as emulsifiers, suspending agents, and dispersants. These additives can remain inside the resin particles, becoming foreign matter, and may also cause discoloration when the resin is heated, potentially impairing transparency and heat resistance. Therefore, it is preferable not to add such additives in the manufacturing method according to this embodiment.

[0072] In the manufacturing method of this embodiment, by producing a fluororesin by a polymerization reaction using a precipitation polymerization solvent, it is possible to obtain a fluororesin that has excellent transparency even when the content of residue unit B in the resin is 30 mol% or more.

[0073] Examples of precipitation polymerization solvents include non-halogenated organic solvents such as acetone, methyl ethyl ketone, hexane, and butyl acetate, as well as chlorinated organic solvents such as dichloromethane and chloroform, and organic solvents containing fluorine atoms in their molecules.

[0074] Furthermore, as a precipitation polymerization solvent, organic solvents containing fluorine and hydrogen atoms in their molecules are preferred because they are less prone to chain transfer reactions in radical polymerization, offer excellent polymerization yield, and facilitate the acquisition of high molecular weight products. Specific precipitation polymerization solvents containing fluorine and hydrogen atoms in their molecules include: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, 1,2,2,3,3,4,4-heptafluorocyclopentane, 1,1,1,4,4,4-hexafluoro-2-butene, 1H,1H-pentafluoropropanol, 1H,1H-heptafluorobutanol, 2-perfluorobutylethanol, 4,4,4-trifluorobutanol, 1H,1H,3H-tetrafluoropropanol, 1H,1H,5H-octafluoropropanol, 1H,1H,7H-dodecafluoroheptanol, 1H,1H,3H-he Examples include xafluorobutanol, 2,2,3,3,3-pentafluoropropyldifluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, and 2,2,3,4,4,4-hexafluorobutyldifluoromethyl ether.

[0075] Among these, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, 1,2,2,3,3,4,4-heptafluorocyclopentane, and 1,1,1,4,4,4-hexafluoro-2-butene are preferred because they exhibit excellent polymerization yield and make it easy to obtain high molecular weight products. Therefore, 1,2,2,3,3,4,4-heptafluorocyclopentane and 1,1,1,4,4,4-hexafluoro-2-butene are preferred. As for the ratio of fluorine atoms to hydrogen atoms in the molecule of the precipitate polymerization solvent, a ratio of fluorine atoms to hydrogen atoms of 1:9 to 9:1 is preferred in terms of the number of atoms, more preferably 1:9 to 7:3, and even more preferably 4:6 to 7:3, because it exhibits excellent polymerization yield.

[0076] As a precipitation polymerization solvent, it is preferable that the solvent contains both fluorine and hydrogen atoms in its molecule, as this results in excellent polymerization yield, and that the hydrogen atom content in the solvent is preferably 1% by weight or more, and more preferably 1.5% by weight or more, relative to the weight of the solvent molecule. Furthermore, as this results in excellent polymerization yield and facilitates the acquisition of high molecular weight products, it is preferable that the solvent contains 1% to 5% by weight, and more preferably 1.5% to 4% by weight. Additionally, as a precipitation polymerization solvent, it is preferable that the solvent does not contain chlorine atoms in its molecule, as this results in excellent polymerization yield and facilitates the acquisition of high molecular weight products.

[0077] The ratio of the total amount of monomer to the precipitation polymerization solvent is preferably 1:99 to 50:50 by weight, more preferably 5:95 to 40:60, and even more preferably 5:95 to 30:70, in order to obtain a resin with excellent productivity and flow properties.

[0078] In the manufacturing method according to this embodiment, polymerization can be carried out using a radical polymerization initiator. Examples of the radical polymerization initiator include organic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide, tert-butyl peroxyacetate, perfluoro(di-tert-butyl peroxide), bis(perfluorobenzoyl) peroxide, tert-butyl peroxybenzoate, tert-butyl perpivalate, diisopropyl peroxydicarbonate; perfluoro organic peroxides such as bis(perfluorobenzoyl) peroxide, (CF ３ COO) ２ ,(CF ３ CF ２ COO) ２ ,(C ３ F ７ COO) ２ ,(C ４ F ９ COO) ２ ,(C ５ F １１ COO) ２ ,(C ６ F １３ COO) ２ ,(C ７ F １５ COO) ２ ,(C ８ F １７ COO) ２ ; and azo initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 1,1'-azobis(cyclohexane-1-carbonitrile), etc.

[0079] (Summary) As can be understood from the above description, the present invention encompasses the following embodiments. Embodiment 1: A fluororesin comprising residue unit A represented by the following general formula (1) and residue unit B represented by the following general formula (2), wherein the content of residue unit A is 30 mol% or more and 70 mol% or less with respect to the total amount of all residue units, and the content of residue unit B is 30 mol% or more and 70 mol% or less, and the haze value of a 100 μm thick mol-molded article of the fluororesin is 4% or less. (wherein, Rf １ and Rf ２ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, and the perfluoroalkyl group may have an ether bond between any carbon-carbon bonds, and Rf １ and Rf ２ They may join together to form a ring. (In the formula, R １ Rf represents a hydrogen atom or a fluorine atom. ３ and Rf ４ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, and the perfluoroalkyl group may have an ether bond between any carbon-carbon bonds, and Rf ３ and Rf ４ They may bond to each other to form a ring. ) Embodiment 2: The fluororesin of Embodiment 1, wherein the haze value of a 100 μm thick molten molded article of the fluororesin is 2% or less. Embodiment 3: The fluororesin of Embodiment 1 or 2, wherein the content of residue unit A is 35 mol% or more and 70 mol% or less, and the content of residue unit B is 30 mol% or more and 65 mol% or less, relative to the total amount of all residue units. Embodiment 4: Rf in formula (2) ３ and Rf ４A fluororesin according to any one of embodiments 1 to 3, wherein each is independently a fluorine atom or a perfluoroalkyl group having 1 to 2 carbon atoms. Embodiment 5: A fluororesin according to any one of embodiments 1 to 4, wherein the weight-average molecular weight is 30,000 to 300,000 in terms of standard polymethyl methacrylate. Embodiment 6: A method for producing a fluororesin according to any one of embodiments 1 to 5, comprising polymerizing a mixture containing monomer A represented by the following formula (3) and monomer B represented by the following formula (4) in an organic solvent by precipitation polymerization. (wherein, Rf ５ and Rf ６ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf ５ and Rf ６ They may join together to form a ring. (In the formula, R ２ Rf represents a hydrogen atom or a fluorine atom. ７ and Rf ８ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf ７ and Rf ８ They may join together to form a ring.

[0080] The embodiments of the present invention will be further described in detail below, with reference to the following examples. Of course, the present invention is not limited to the following examples, and it goes without saying that various embodiments are possible in terms of details. Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims, and embodiments obtained by appropriately combining the disclosed technical means are also included in the technical scope of the present invention. In addition, all references cited herein are incorporated by reference.

[0081] (Method for measuring haze value) A 100 μm thick polyimide film, cut to 50 mm x 10 mm, was placed on both ends of a quartz plate (50 mm square, 2 mm thick) (the polyimide film acted as a spacer). 1 g of fluororesin was placed on top of this quartz plate, and another quartz plate (50 mm square, 2 mm thick) was placed on top of it, sandwiching the fluororesin between the quartz plates. This was placed in a press machine and heated at 230°C for 10 minutes without pressure, then heated and pressed in the press machine at a pressure of 10 MPa and 230°C for 30 minutes. After that, the pressure was released and it was cooled to obtain a 100 μm thick molten molded body sandwiched between quartz substrates. The haze value (%) of the obtained 100 μm thick molten molded body was determined by measuring it according to JIS K7136 using a spectroscopic haze meter "SH7000" (light source: white LED) manufactured by Nippon Denshoku Industries, Ltd. The haze value was measured with the molten body sandwiched between quartz substrates.

[0082] (NMR measurement) Using an NMR analyzer (JNM-ECZS400) manufactured by JEOL Ltd, １９ F-NMR measurements were performed, and the content of each residue unit, determined by the ratio of the integrated values ​​of the detected peaks, is indicated. １９ In F-NMR, hexafluorobenzene is used as the solvent, and CFCl ３ The peak was defined as 0 ppm.

[0083] (Measurement method for weight-average molecular weight Mw and molecular weight distribution Mw / Mn) Measurements were performed using gel permission chromatography equipped with a TSKgel SuperHZM-M column and an RI detector manufactured by Tosoh Corporation. Asahi Clean AK-225 (manufactured by AGC Inc.) was used as the eluent, to which 10 wt% of 1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added relative to AK-225. Standard polymethyl methacrylate manufactured by Agilent was used as the standard sample, and the weight-average molecular weight Mw and molecular weight distribution Mw / Mn in terms of polymethyl methacrylate were calculated from the elution times of the sample and the standard sample.

[0084] (Measurement of Glass Transition Temperature) A sample was prepared by weighing approximately 10 mg of the sample into an aluminum sample pan (Hitachi High-Tech Science Co., Ltd. 52-023P), covering it with an aluminum lid (Hitachi High-Tech Science Co., Ltd. 52-023C), and sealing the sample using an electric sample sealer (die) (Hitachi High-Tech Science Co., Ltd.). The sample was heated using a DSC instrument (Hitachi High-Tech Science Co., Ltd. DSC6220) under a nitrogen flow (500 mL / min) with the following programs: 1st time: -50°C → 180°C → -50°C (heating rate: 10°C / min), 2nd time: -50°C → 180°C (heating rate: 10°C / min). At this time, the glass transition temperature was calculated by determining the intermediate glass transition temperature from the chart obtained during the second heating, according to the description in JIS-K7121. The DSC instrument used was temperature calibrated with indium and tin as standard materials.

[0085] [Example 1] In a 100 mL stainless steel autoclave, 5.9 g (24.0 mmol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer A, 3.9 g (16.0 mmol) of perfluoro(2,2-dimethyl-1,3-dioxol) (indicated as PDD in Table 1) as monomer B, 0.04 g (0.09 mmol) of bis(perfluorobenzoyl) peroxide as a radical polymerization initiator, and 40.2 g of Zeolora H (manufactured by Nippon Zeon, 1,2,2,3,3,4,4-heptafluorocyclopentane) as a polymerization solvent were added to obtain a polymerization preparation solution. After degassing this polymerization preparation solution under reduced pressure, a radical polymerization reaction was carried out by stirring at 55°C for 24 hours. After cooling to room temperature, a suspension was obtained in which the resin precipitated as a solid. This suspension was filtered, the filtered resin was washed, and then dried under reduced pressure to obtain solid fluororesin 1 (yield 82%).

[0086] Table 1 summarizes the analysis results of the content of each residue unit, weight-average molecular weight, molecular weight distribution, and glass transition temperature of the obtained fluororesin 1, as well as the haze value of a 100 μm thick molten molded body obtained by melt molding fluororesin 1. １９F-NMR; δ -76.7 ppm (residue unit A, 2F), -79.8 ppm (residue unit A, 3F), -81.6 ppm (residue unit B, 6F), -107.4 ppm (residue unit A, 2F), -116.1 ppm (residue unit B, 2F), -121.3 ppm (residue unit A, 1F).

[0087] [Example 2] The same experiment as in Example 1 was carried out, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 6.8 g (28.0 mmol), perfluoro(2,2-dimethyl-1,3-dioxol) to 2.9 g (12.0 mmol), bis(perfluorobenzoyl) peroxide to 0.08 g (0.19 mmol), and zeolora H to 45.9 g, and a solid fluororesin 2 was obtained (yield 78%).

[0088] Table 1 summarizes the analysis results of the content of each residue unit of the obtained fluororesin 2, weight-average molecular weight, molecular weight distribution, and glass transition temperature, as well as the haze value of the 100 μm thick molten molded body obtained by melt molding the fluororesin 2. １９ F-NMR; δ -76.5 ppm (residue unit A, 2F), -79.9 ppm (residue unit A, 3F), -81.3 ppm (residue unit B, 6F), -107.1 ppm (residue unit A, 2F), -116.4 ppm (residue unit B, 2F), -121.1 ppm (residue unit A, 1F).

[0089] [Example 3] The same experiment as in Example 1 was carried out, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 3.9 g (16.1 mmol), perfluoro(2,2-dimethyl-1,3-dioxol) to 5.9 g (24.1 mmol), bis(perfluorobenzoyl) peroxide to 0.01 g (0.02 mmol), and zeolora H to 63.3 g, and a solid fluororesin 3 was obtained (yield 76%).

[0090] Table 1 summarizes the analysis results of the content of each residue unit of the obtained fluororesin 3, weight-average molecular weight, molecular weight distribution, and glass transition temperature, as well as the haze value of a 100 μm thick molten molded body obtained by melt molding the fluororesin 3. １９F-NMR; δ -76.4 ppm (residue unit A, 2F), -80.1 ppm (residue unit A, 3F), -81.4 ppm (residue unit B, 6F), -107.3 ppm (residue unit A, 2F), -115.9 ppm (residue unit B, 2F), -120.9 ppm (residue unit A, 1F).

[0091] [Example 4] The same experiment as in Example 1 was carried out, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 5.8 g (23.9 mmol), bis(perfluorobenzoyl)peroxide to 0.05 g (0.12 mmol), and zeolora H to 81.6 g, and 3.9 g (16.1 mmol) of perfluoro(2-ethyl-1,3-dioxol) (indicated as PED in Table 1) was used as monomer B instead of perfluoro(2,2-dimethyl-1,3-dioxol), and a solid fluororesin 4 was obtained (yield 84%).

[0092] Table 1 summarizes the analysis results of the content of each residue unit of the obtained fluororesin 4, weight-average molecular weight, molecular weight distribution, and glass transition temperature, as well as the haze value of the 100 μm thick molten molded body obtained by melt molding the fluororesin 4. １９ F-NMR; δ -75.3 ppm (residue unit B, 1F), -76.4 ppm (residue unit A, 2F), -81.4 ppm (residue unit B, 3F), -107.8 ppm (residue unit A, 2F), -116.1 ppm (residue unit B, 2F), -121.2 ppm (residue unit A, 1F), -128.9 ppm (residue unit B, 2F).

[0093] [Example 5] The same experiment as in Example 1 was carried out, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 3.9 g (16.1 mmol), bis(perfluorobenzoyl)peroxide to 0.10 g (0.24 mmol), and zeolora H to 74.7 g, and perfluoro(2-ethyl-1,3-dioxol) was used as monomer B instead of perfluoro(2,2-dimethyl-1,3-dioxol) to obtain solid fluororesin 5 (yield 78%).

[0094] Table 1 summarizes the analysis results of the content of each residue unit of the obtained fluororesin 5, weight-average molecular weight, molecular weight distribution, and glass transition temperature, as well as the haze value of the 100 μm thick molten molded body obtained by melt molding the fluororesin 5. １９ F-NMR; δ -75.7 ppm (residue unit B, 1F), -76.6 ppm (residue unit A, 2F), -81.2 ppm (residue unit B, 3F), -108.0 ppm (residue unit A, 2F), -116.3 ppm (residue unit B, 2F), -121.0 ppm (residue unit A, 1F), -129.1 ppm (residue unit B, 2F).

[0095] [Example 6] The same experiment as in Example 1 was carried out, except that the amount of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added was changed to 5.9 g (24.0 mmol), perfluoro(2,2-dimethyl-1,3-dioxol) added to 3.9 g (16.0 mmol), and bis(perfluorobenzoyl)peroxide added to 0.26 g (0.40 mmol), and the amount of Opteon SF33 (manufactured by Mitsui Chemours, 1,1,1,4,4,4-hexafluoro-2-butene) added was changed to 63.8 g instead of Zeolora H, and a solid fluororesin 6 was obtained (yield 69%).

[0096] Table 1 summarizes the analysis results of the content of each residue unit of the obtained fluororesin 6, weight-average molecular weight, molecular weight distribution, and glass transition temperature, as well as the haze value of the 100 μm thick molten molded body obtained by melt molding the fluororesin 6. １９ F-NMR; δ -76.1 ppm (residue unit A, 2F), -80.3 ppm (residue unit A, 3F), -81.1 ppm (residue unit B, 6F), -107.3 ppm (residue unit A, 2F), -115.9 ppm (residue unit B, 2F), -120.9 ppm (residue unit A, 1F).

[0097] [Example 7] The same experiment as in Example 1 was carried out, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 5.9 g (24.0 mmol), perfluoro(2,2-dimethyl-1,3-dioxol) to 3.9 g (16.0 mmol), and zeolora H to 76.2 g, and 0.03 g (0.04 mmol) of perloyl IPP (manufactured by NOF Corporation, diisopropyl peroxydicarbonate) was used instead of bis(perfluorobenzoyl)peroxide, to obtain solid fluororesin 7 (yield 62%).

[0098] Table 1 summarizes the analysis results of the content of each residue unit of the obtained fluororesin 7, weight-average molecular weight, molecular weight distribution, and glass transition temperature, as well as the haze value of a 100 μm thick molten molded body obtained by melt molding the fluororesin 7. １９ F-NMR; δ -76.4 ppm (residue unit A, 2F), -80.1 ppm (residue unit A, 3F), -81.4 ppm (residue unit B, 6F), -107.3 ppm (residue unit A, 2F), -115.7 ppm (residue unit B, 2F), -120.9 ppm (residue unit A, 1F).

[0099] [Example 8] The same experiment as in Example 1 was carried out, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 3.9 g (16.1 mmol), perfluoro(2,2-dimethyl-1,3-dioxol) to 5.9 g (24.1 mmol), bis(perfluorobenzoyl)peroxide to 0.03 g (0.07 mmol), and zeolora H to 63.4 g, and a solid fluororesin 8 was obtained (yield 75%).

[0100] Table 1 summarizes the analysis results of the content of each residue unit of the obtained fluororesin 8, weight-average molecular weight, molecular weight distribution, and glass transition temperature, as well as the haze value of the 100 μm thick molten molded body obtained by melt molding the fluororesin 8. １９ F-NMR; δ -76.4 ppm (residue unit B, 2F), -80.2 ppm (residue unit A, 3F), -81.2 ppm (residue unit B, 6F), -107.0 ppm (residue unit A, 2F), -115.9 ppm (residue unit B, 2F), -120.8 ppm (residue unit A, 1F).

[0101] [Comparative Example 1] In a 100 mL stainless steel autoclave, 5.9 g (24.0 mmol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as monomer A, 3.9 g (16.0 mmol) of perfluoro(2,2-dimethyl-1,3-dioxol) as monomer B, 0.02 g (0.06 mmol) of bis(perfluorobenzoyl) peroxide as a radical polymerization initiator, and 40.8 g of FC-72 as a polymerization solvent were added to obtain a polymerization preparation solution. After degassing this polymerization preparation solution under reduced pressure, a radical polymerization reaction was carried out by stirring at 55°C for 24 hours. After cooling to room temperature, a viscous liquid in which the resin was dissolved as a liquid was obtained. 92 g of FC-72 was added to this viscous liquid to obtain a resin dilution solution. Separately, in a beaker equipped with a stirring bar, 400 g of hexane was stirred, and the obtained resin dilution solution was added dropwise to solidify the resin. The solidified resin was filtered, washed, and then dried under reduced pressure to obtain a solid comparative fluororesin 1 (yield 72%).

[0102] Table 1 summarizes the analysis results of the content of each residue unit, weight-average molecular weight, molecular weight distribution, and glass transition temperature of the obtained comparative fluororesin 1, as well as the haze value of a 100 μm thick molten molded body obtained by melt molding comparative fluororesin 1. １９ F-NMR; δ -76.7 ppm (residue unit A, 2F), -79.6 ppm (residue unit A, 3F), -81.6 ppm (residue unit B, 6F), -107.5 ppm (residue unit A, 2F), -116.4 ppm (residue unit B, 2F), -121.2 ppm (residue unit A, 1F).

[0103] [Comparative Example 2] The same experiment as in Comparative Example 1 was conducted, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 3.9 g (16.0 mmol), perfluoro(2,2-dimethyl-1,3-dioxol) to 5.9 g (24.0 mmol), bis(perfluorobenzoyl)peroxide to 0.03 g (0.07 mmol), and FC-72 to 41.0 g, to obtain a comparative solid fluororesin 2 (yield 70%).

[0104] Table 1 summarizes the analysis results of the content of each residue unit, weight-average molecular weight, molecular weight distribution, and glass transition temperature of the obtained comparative fluororesin 2, as well as the haze value of a 100 μm thick molten molded body obtained by melt molding comparative fluororesin 2. １９ F-NMR; δ -76.9 ppm (residue unit A, 2F), -79.7 ppm (residue unit A, 3F), -81.1 ppm (residue unit B, 6F), -107.3 ppm (residue unit A, 2F), -116.1 ppm (residue unit B, 2F), -121.1 ppm (residue unit A, 1F).

[0105] [Reference Example] The same experiment as in Comparative Example 1 was conducted, except that the amounts of perfluoro(4-methyl-2-methylene-1,3-dioxolane) added were changed to 7.8 g (32.1 mmol), perfluoro(2,2-dimethyl-1,3-dioxol) to 2.0 g (8.0 mmol), bis(perfluorobenzoyl)peroxide to 0.02 g (0.06 mmol), and FC-72 to 38.0 g, and a reference solid fluororesin was obtained (yield 77%).

[0106] Table 1 summarizes the analysis results of the content of each residue unit, weight-average molecular weight, molecular weight distribution, and glass transition temperature of the obtained reference fluororesin, as well as the haze value of a 100 μm thick molten body obtained by melt molding the reference fluororesin. １９ F-NMR; δ -76.6 ppm (residue unit A, 2F), -79.9 ppm (residue unit A, 3F), -81.2 ppm (residue unit B, 6F), -107.2 ppm (residue unit A, 2F), -116.0 ppm (residue unit B, 2F), -121.0 ppm (residue unit A, 1F).

[0107]

[0108] This invention can be used in fields that utilize fluororesins.

Claims

1. A fluororesin comprising a residue unit A represented by the following general formula (1) and a residue unit B represented by the following general formula (2), wherein the content of the residue unit A is 30 mol% or more and 70 mol% or less, and the content of the residue unit B is 30 mol% or more and 70 mol% or less, based on the total amount of all residue units, and the haze value of a melt-molded body having a thickness of 100 μm of the fluororesin is 4% or less. (In the formula, Rf １ and Rf ２ each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, and the perfluoroalkyl group may have an ether bond between any carbon-carbon bond, and Rf １ and Rf ２ may be bonded to each other to form a ring.) (In the formula, R １ represents a hydrogen atom or a fluorine atom. Rf ３ and Rf ４ each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, and the perfluoroalkyl group may have an ether bond between any carbon-carbon bond, and Rf ３ and Rf ４ may be bonded to each other to form a ring.) 2. The fluororesin according to claim 1, wherein the haze value of a 100 μm thick molten molded article of the fluororesin is 2% or less.

3. The fluororesin according to claim 1, wherein the content of residue unit A is 35 mol% or more and 70 mol% or less with respect to the total amount of all residue units, and the content of residue unit B is 30 mol% or more and 65 mol% or less.

4. Rf in formula (2) ３ and Rf ４ The fluororesin according to claim 1, wherein each of them is independently a fluorine atom or a perfluoroalkyl group having 1 to 2 carbon atoms.

5. The fluororesin according to claim 1, wherein the weight-average molecular weight is 30,000 to 300,000 in terms of standard polymethyl methacrylate.

6. A method for producing a fluororesin according to any one of claims 1 to 5, comprising polymerizing a mixture containing monomer A represented by the following formula (3) and monomer B represented by the following formula (4) in an organic solvent by precipitation polymerization. (wherein, Rf ５ and Rf ６ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf ５ and Rf ６ They may join together to form a ring. (In the formula, R ２ Rf represents a hydrogen atom or a fluorine atom. ７ and Rf ８ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Also, Rf ７ and Rf ８ They may join together to form a ring.

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