Method for producing fluoropolymer

Abstract

The problem addressed by the present invention is to provide a method for producing a fluoropolymer by which a fluoropolymer having a small MFR can be obtained.　Provided is a method for producing a fluoropolymer that produces a fluoropolymer by polymerizing monomers including a fluoromonomer in a solvent, the production method being characterized in that the solvent includes a compound A represented by formula (A) Ra1-O-Ra2 and the total content of compound B represented by formula (B) Rb1-CF=CF-O-Rb2 and compound C represented by formula (C) Rc1-OH is 1.00 mass% or less relative to the content of compound A.

Description

Fluoropolymer manufacturing method

[0001] The present invention relates to a method for producing a fluoropolymer.

[0002] Fluoropolymers such as ethylene / tetrafluoroethylene copolymers are characterized by excellent heat resistance, weather resistance, electrical insulation, non-stickiness, water and oil repellency, etc., and also by high moldability and mechanical strength among fluororesins. Therefore, a variety of molded articles such as electrical wire coverings, tubes, sheets, films, filaments, pump casings, joints, packing, linings, and coatings are produced by melt molding methods such as extrusion molding, blow molding, injection molding, and rotational molding. In synthesizing such fluoropolymers, fluorine-containing solvents are generally used. For example, Patent Document 1 discloses a method for producing a fluorine-containing polymer using, as a polymerization medium, a hydrofluoroether having a predetermined structure in which a perfluoroalkyl group having 2 to 6 carbon atoms and an alkyl group having 1 or 2 carbon atoms are bonded via an ether bond.

[0003] Japanese Patent Application Publication No. 11-092507

[0004] The present inventors, with reference to the above-mentioned literature, have investigated a method for producing a fluoropolymer using, as a solvent, a hydrofluoroether in which partially fluorinated alkyl groups are bonded to each other via an ether bond, and have found that the MFR (Melt Flow Rate) of the obtained fluoropolymer may not satisfy the desired level.

[0005] Therefore, an object of the present invention is to provide a method for producing a fluoropolymer, which can produce a fluoropolymer having a small MFR.

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that, when a fluoropolymer is produced by polymerizing a monomer containing a fluoromonomer in a solvent, a fluoropolymer having a small MFR can be produced if the solvent contains a compound A described below and the total content of a compound B described below and a compound C described below in the solvent is 1.00 mass% or less relative to the content of compound A, and have arrived at the present invention.

[0007] That is, the inventors have found that the above problems can be solved by the following configurations. [1] A method for producing a fluoropolymer, comprising polymerizing a monomer containing a fluoromonomer in a solvent to produce a fluoropolymer, wherein the solvent contains a compound A represented by formula (A) described later, and the total content of a compound B represented by formula (B) described later and a compound C represented by formula (C) described later in the solvent is 1.00 mass% or less relative to the content of the compound A. [2] The method for producing a fluoropolymer according to [1], wherein the fluoromonomer contains at least one selected from the group consisting of tetrafluoroethylene, a compound represented by formula (1) described later, and a compound represented by formula (2) described later. [3] The method for producing a fluoropolymer according to [1] or [2], wherein the monomer further contains ethylene. [4] The method for producing a fluoropolymer according to any one of [1] to [3], wherein the content of the compound A is 50 mass% or more relative to the total mass of the solvent. [5] The method for producing a fluoropolymer, wherein the compound A is CF ３ CH ２ OCF ２ CF ２ H or CF ３ CH ２ OCH ２ CF ３ is 、 [6] The method for producing a fluoropolymer according to any one of [1] to [4]. [6] The compound B is CF ２ = CFOCH ２ CF ３ , C.F. ２ = CFOCH ２ CF ２ H, CFH=CFOCF ２ CF ２ H, or CFH=CFOCFHCF ２ [7] The method for producing a fluoropolymer according to any one of [1] to [5], wherein the compound C is CF ３ CH ２ OH, CF ２ HCF ２ OH, or CF ３[8] The method for producing a fluoropolymer according to any one of [1] to [7], wherein the total content of the compound B and the compound C in the solvent is 0.50 mass % or less relative to the content of the compound A.

[0008] According to the present invention, there can be provided a method for producing a fluoropolymer that can yield a fluoropolymer having a small MFR.

[0009] The meanings of terms used in this specification 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 stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. 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. Here, 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.

[0010] "Unit" is a general term for an atomic group derived from one molecule of the above-mentioned monomer, which is formed directly by polymerizing the monomer, and an atomic group obtained by chemically converting a part of the above-mentioned atomic group. Note that, in the following, in some cases, a unit derived from an individual monomer will be described by adding "unit" to the name of the monomer. For example, a "TFE unit" is a unit based on tetrafluoroethylene (TFE), and an "E unit" is a unit based on ethylene (E). A solvent is an inert compound that is liquid at 25°C and does not react with either the raw materials used to produce the fluoropolymer or the fluoropolymer itself.

[0011] In this specification, unless otherwise specified, the boiling point is the value at 1013 hPa.

[0012] [Method for producing fluoropolymer] The method for producing a fluoropolymer of the present invention (hereinafter also referred to as "the present production method") is a method for producing a fluoropolymer by polymerizing monomers including a fluoromonomer in a solvent, characterized in that the solvent contains compound A represented by formula (A) described later, and the total content of compound B represented by formula (B) described later and compound C represented by formula (C) described later in the solvent is 1.00 mass% or less relative to the content of compound A.

[0013] According to this production method, a fluoropolymer with a small MFR can be produced. Although the details of the reason for this are unclear, when the monomers are polymerized in the solvent, the content of compound B and compound C, which can inhibit the polymerization, is set to a predetermined value or less relative to the content of compound A, which does not inhibit the polymerization, thereby suppressing the decrease in the molecular weight of the fluoropolymer. As a result, it is presumed that a fluoropolymer with a small MFR can be obtained.

[0014] The present production method includes a step of polymerizing monomers including a fluoromonomer in a solvent (hereinafter also referred to as "step 1").

[0015] <Solvent> The solvent contains compound A. Compound A is a compound represented by formula (A). R ａ１ -O-R ａ２ (A) In formula (A), R ａ１ and R ａ２ each independently represents a partially fluorinated alkyl group having 2 carbon atoms. A partially fluorinated alkyl group having 2 carbon atoms is a group in which 1 to 4 hydrogen atoms of an alkyl group having 2 carbon atoms are substituted with fluorine atoms. Specific examples of compound A include CF ３ CH ２ OCF ２ CF ２ H and CF ３ CH ２ OCH ２ CF ３ CF ３ CH ２ OCF ２ CF ２ H (hereinafter also referred to as "HFE-347pc-f") is preferred.

[0016] The boiling point of compound A is preferably 20 to 80°C, more preferably 40 to 80°C, from the viewpoints that the polymerization proceeds smoothly and the purification treatment described below can be carried out efficiently.

[0017] The compound A may be used alone or in combination of two or more. The content of the compound A is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total mass of the solvent. The upper limit of the content of the compound A is usually 100% by mass, based on the total mass of the solvent.

[0018] The solvent may contain at least one compound selected from the group consisting of compound B and compound C. In the solvent, the total content of compound B and compound C is 1.00% by mass or less, preferably 0.50% by mass or less, and more preferably 0.10% by mass or less, relative to the content of compound A. The lower limit of the total content of compound B and compound C is 0% by mass, and is usually 0.001% by mass or more, relative to the content of compound A.

[0019] Compound B is a compound represented by formula (B). ｂ１ -CF=CF-OR ｂ２ (B) In formula (B), R ｂ１ represents a hydrogen atom or a fluorine atom, R ｂ２ represents a partially fluorinated alkyl group having two carbon atoms. Specific examples of compound B include CF ２ = CFOCH ２ CF ３ , C.F. ２ = CFOCH ２ CF ２ H, CFH=CFOCF ２ CF ２ H, and CFH=CFOCFHCF ２ H, and CF ２ = CFOCH ２ CF ３ is preferred.

[0020] The boiling point of compound B is preferably 30 to 120°C, more preferably 40 to 100°C, from the viewpoint that the purification treatment described below can be carried out efficiently.

[0021] The solvent may contain one type of compound B alone or two or more types. The content of compound B is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.08% by mass or less, based on the total mass of the solvent. The lower limit of the content of compound B is 0% by mass, and is usually 0.001% by mass or more, based on the total mass of the solvent.

[0022] Compound C is a compound represented by formula (C). ｃ１ -OH (C) In formula (C), R ｃ１ represents a partially fluorinated alkyl group having two carbon atoms. Specific examples of compound C include CF ３ CH ２ OH, CF ２ HCF ２ OH and CF ３ CFHOH is mentioned, and CF ３ CH ２ OH is preferred.

[0023] The boiling point of compound C is preferably 30 to 120°C, more preferably 40 to 100°C, from the viewpoint that the purification treatment described below can be carried out efficiently.

[0024] The solvent may contain one type of compound C alone or two or more types. The content of compound C is preferably 0.1 mass% or less, more preferably 0.05 mass% or less, and even more preferably 0.01 mass% or less, based on the total mass of the solvent. The lower limit of the content of compound C is 0 mass% based on the total mass of the solvent.

[0025] The solvent may contain a solvent different from compound A, compound B, and compound C. As the other solvent, a fluorine-containing solvent such as a perfluorocarbon, a hydrofluorocarbon, or a hydrofluoroether can be used. As the other solvent, a fluorine-free solvent such as water, an alcohol, a ketone, an ester, or a hydrocarbon can also be used.

[0026] The amount of the solvent used is preferably 2 times or more, more preferably 3 times or more, by mass ratio relative to the amount of the monomer used, and is preferably 15 times or less, more preferably 13 times or less.

[0027] The method of adding the solvent to the reaction system is not particularly limited. The solvent may be added to the reactor before the start of polymerization, or the raw materials used for polymerization, such as the polymerization initiator described below, may be dissolved in the solvent and added to the reactor as a composition. The solvent may also be added to the reaction system during the progress of polymerization. When a solvent is further added to the reaction system during the progress of polymerization, it is preferable that the total content of compound B and compound C in the solvent of the reaction system always be within a predetermined range relative to the content of compound A from the start to the end of polymerization. The composition of the solvent is preferably adjusted before addition to the reaction system. Methods for adjusting the solvent composition include a method of mixing raw materials containing compound A with other solvents, a method of removing excess components (e.g., compound B and compound C) from the raw materials, and a combination thereof. A method for removing excess components from the raw materials includes the purification treatment in step 2 described below.

[0028] <Monomer> The monomer includes a fluoromonomer.

[0029] The fluoromonomer is a monomer having a fluorine atom and a polymerizable group. However, the fluoromonomer is a compound different from the above-mentioned compounds A, B, and C. Specific examples of the fluoromonomer include fluoroolefin, fluoroalkyl vinyl ether, CF ２ =CFORf １ SO ２ Y １ (However, Rf １ is a perfluoroalkylene group having 1 to 10 carbon atoms which may contain an oxygen atom between the carbon atoms, and Y １ is a halogen atom or a hydroxyl group.), CF ２ =CFORf ２ CO ２ Y ２ (However, Rf ２ is a perfluoroalkylene group having 1 to 10 carbon atoms which may contain an oxygen atom between the carbon atoms, and Y ２ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.), CF ２ = CFO (CF ２ ) pOCF=CF ２(where p is 1 to 4), and fluorine-containing monomers having a ring structure (for example, perfluoro(2,2-dimethyl-1,3-dioxole), 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole, and perfluoro(2-methylene-4-methyl-1,3-dioxolane)), among which fluoroolefins and fluoroalkyl vinyl ethers are preferred.

[0030] Specific examples of the fluoroolefin include tetrafluoroethylene (TFE), vinyl fluoride, vinylidene fluoride, trifluoroethylene, and a compound represented by formula (1), with TFE or a compound represented by formula (1) being preferred. １ ２ =CX ２ (CF ２ ) ｍ X ３ (1) In formula (1), X １ , X ２ and X ３ each independently represents a hydrogen atom or a fluorine atom, and m represents an integer of 1 to 6. In the compound represented by formula (1), X １ and X ２ is preferably a hydrogen atom from the viewpoint of polymerizability. m is preferably an integer of 2 to 6, more preferably an integer of 2 to 4, and even more preferably 4. Examples of the compound represented by formula (1) include CF ２ =CF(CF) ２ F, CH ２ =CH(CF ２ ) ２ F, CH ２ =CH(CF ２ ) ４ F, CH ２ =CH(CF ２ ) ６ F or CH ２ =CF(CF ２ ) ４ F is preferred, CH ２ =CH(CF ２ ) ４ F (hereinafter also referred to as "PFBE") is more preferred.

[0031] An example of a fluoroalkyl vinyl ether is a compound represented by formula (2): CF ２ =CF-O-(CF ２ ) ｎ F (2) In formula (2), n represents an integer of 1 to 6.

[0032] Specific examples of the compound represented by formula (2) include CF ２ =CF-O-(CF ２ ) F, CF ２ =CF-O-(CF ２ ) ２ F, CF ２ =CF-O-(CF ２ ) ３ F (hereinafter also referred to as "PPVE"), CF ２ =CF-O-(CF ２ ) ４ F, CF ２ =CF-O-(CF ２ ) ５ F and CF ２ =CF-O-(CF ２ ) ６ F, and PPVE is preferred.

[0033] In view of the fact that the strength of the molded article produced using the fluoropolymer obtained by this production method is superior, the fluoromonomer preferably comprises at least one selected from the group consisting of TFE, the compound represented by formula (1) and the compound represented by formula (2), more preferably comprises TFE and further comprises at least one of the compound represented by formula (1) and the compound represented by formula (2), and even more preferably comprises TFE and the compound represented by formula (1).

[0034] The fluoromonomer may be used alone or in combination of two or more. The content of the fluoromonomer is preferably 30.0 to 100.0 mol%, more preferably 35.0 to 70.0 mol%, and even more preferably 40.0 to 65.0 mol%, relative to the total molar amount of the monomers. In particular, when the monomer contains ethylene, as described below, it is preferable to satisfy the above-mentioned preferred range. Furthermore, from the viewpoint of obtaining a fluoropolymer with excellent heat resistance, the content of the fluoromonomer is also preferably 90.0 to 100.0 mol%, more preferably 90.0 to 99.9 mol%, relative to the total molar amount of the monomers. In particular, from the viewpoint of obtaining a fluoropolymer with excellent melt moldability, it is also preferable to satisfy the above-mentioned preferred range. In particular, when the fluoromonomer contains a compound represented by formula (2), particularly when the fluoromonomer contains TFE and a compound represented by formula (2) and the monomer does not contain any monomer other than the fluoromonomer, it is preferable to satisfy the above-mentioned preferred range. The content of TFE is preferably 30.0 to 100.0 mol%, more preferably 35.0 to 70.0 mol%, and even more preferably 40.0 to 65.0 mol%, based on the total molar amount of monomers. In particular, when the monomer contains ethylene, as described below, it is preferable to satisfy the above-mentioned preferred range. Furthermore, the content of TFE is also preferably 90.0 to 99.9 mol%, based on the total molar amount of monomers, from the viewpoint of obtaining a fluoropolymer with excellent heat resistance, and also preferably 95.0 to 99.0 mol%, from the viewpoint of obtaining a fluoropolymer with excellent melt moldability. In particular, when the fluoromonomer contains a compound represented by formula (2), particularly when the fluoromonomer contains TFE and a compound represented by formula (2) and the monomer does not contain any monomer other than the fluoromonomer, it is preferable to satisfy the above-mentioned preferred range. The content of the compound represented by formula (1) is preferably 0.01 to 10.0 mol%, more preferably 0.10 to 5.00 mol%, and even more preferably 0.50 to 4.50 mol%, based on the total molar amount of the monomers. The content of the compound represented by formula (2) is preferably 0.10 to 5.00 mol%, more preferably 0.50 to 4.00 mol%, and even more preferably 1.00 to 3.00 mol%, based on the total molar amount of the monomers.

[0035] The monomer used in this production method may contain a fluorine atom-free monomer different from the fluoromonomer. The fluorine atom-free monomer is preferably a monomer that can be polymerized with the fluoromonomer. Specific examples of the fluorine atom-free monomer include alkenes such as ethylene, propylene, butylene, and isobutylene; alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, and cyclohexyl vinyl ether; itaconic acid, itaconic anhydride, citraconic acid, and citraconic anhydride. The monomer preferably contains a fluorine atom-free monomer, more preferably at least one selected from the group consisting of ethylene, itaconic acid, itaconic anhydride, citraconic acid, and citraconic anhydride, and even more preferably ethylene.

[0036] The fluorine atom-free monomer may be used alone or in combination of two or more. The content of the fluorine atom-free monomer is preferably 30.00 to 54.99 mol%, more preferably 35.0 to 51.9 mol%, and even more preferably 35.00 to 49.50 mol%, based on the total molar amount of the monomers. The ethylene content is preferably 30.00 to 54.99 mol%, more preferably 35.0 to 51.9 mol%, and even more preferably 35.00 to 49.50 mol%, based on the total molar amount of the monomers.

[0037] Among these, the monomer preferably contains TFE and ethylene, more preferably contains TFE and ethylene and further contains at least one of a compound represented by formula (1) and a compound represented by formula (2), and further preferably contains TFE, ethylene, and a compound represented by formula (1). The total content of TFE and ethylene is preferably 85.00 to 99.99 mol%, more preferably 90.00 to 99.90 mol%, and still more preferably 95.00 to 99.50 mol%, based on the total molar amount of the monomer.

[0038] <Polymerization Method> Polymerization methods for polymerizing monomers in a solvent include known methods such as solution polymerization, suspension polymerization, and emulsion polymerization, with solution polymerization or suspension polymerization being preferred.

[0039] In addition to the solvent and monomers described above, other components may be used during the polymerization, such as a polymerization initiator and a chain transfer agent.

[0040] In this production method, it is preferable to polymerize the monomers using a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator, with a water-soluble radical polymerization initiator being more preferable. The polymerization initiator is preferably a radical polymerization initiator having a half-life of 10 hours at a temperature of 0 to 100°C, with a temperature of 20 to 90°C being particularly preferable. Specific examples of polymerization initiators include the various polymerization initiators exemplified in International Publication No. 2013 / 015202. The polymerization initiator may be used alone or in combination of two or more. The amount of polymerization initiator used is preferably 0.01 to 0.9 parts by mass, and particularly preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of the monomer used.

[0041] In the present production method, a chain transfer agent may be used during polymerization. The chain transfer agent has a large chain transfer constant and can be added in a small amount, and is preferably an alcohol such as methanol, ethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoropropanol, 1,1,1,3,3,3-hexafluoroisopropanol, or 2,2,3,3,3-pentafluoropropanol; a hydrocarbon such as n-pentane, n-hexane, or cyclohexane; or CF ２ H ２Preferred are hydrofluorocarbons such as acetone, ketones such as acetone, mercaptans such as methyl mercaptan, esters such as methyl acetate and ethyl acetate, and ethers such as diethyl ether and methyl ethyl ether. Among these, at least one selected from the group consisting of alcohols, hydrocarbons, and hydrofluorocarbons is preferred, with alcohols being more preferred, due to their higher chain transfer constant and high stability of the end groups of the copolymer. Among alcohols, methanol or ethanol is particularly preferred. Of these, methanol is most preferred due to its reactivity and availability. Two or more chain transfer agents may be used. The amount of chain transfer agent used is preferably 0.001 times or more, more preferably 0.005 times or more, by mass, relative to the amount of monomer used. Also, the amount is preferably 5 times or less, more preferably 4 times or less.

[0042] In this production method, the monomer is introduced into a reaction system (i.e., a reactor) containing a solvent by a conventional method. For example, the monomer may be introduced into the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, a solution obtained by dissolving the monomer in a solvent may be introduced into 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., a chain transfer agent) other than those mentioned above are used, the other components may be added to the reaction system all at once or in portions.

[0043] The polymerization temperature is preferably 15 to 90°C, more preferably 20 to 80°C, and even more preferably 25 to 75°C. The polymerization pressure is preferably 0.5 to 3.0 MPa, and more preferably 0.9 to 2.5 MPa. The pressure may be a gauge pressure. The polymerization time is preferably 1 to 12 hours.

[0044] The fluoropolymer obtained in the polymerization step is recovered from the system in a conventional manner, and if necessary, subjected to treatments such as washing and drying to obtain the fluoropolymer or a solid containing the fluoropolymer.

[0045] Granulation may be performed to produce granules containing the fluoropolymer by heating the mixture containing the obtained fluoropolymer, solvent, and water while stirring. The granulation involves first preparing a mixture containing the fluoropolymer, solvent, and water. The mixture can be prepared, for example, by mixing a slurry containing the fluoropolymer and solvent with water. The mixture may be prepared by using the slurry obtained after the fluoropolymer production as is, or by concentrating the slurry, or by diluting the slurry with a dilution solvent. The dilution solvent may be the same as or different from the solvent used in the polymerization, but is preferably the same. The amount of water used in the granulation may be 20 to 500% by volume, more preferably 50 to 300% by volume, based on the total amount of the fluoropolymer and solvent.

[0046] The mixture may be prepared by adding water to a polymerization tank containing the slurry after the production of the fluoropolymer, or by transferring the slurry to a container (granulation tank) separate from the polymerization tank and mixing the slurry with water. It is preferable to transfer the slurry containing the fluoropolymer and solvent from the polymerization tank to a granulation tank that has water already added thereto and mix them. The granulation tank may be a sealable container equipped with a stirring blade for stirring the contents, a heating means for heating the container or the contents, and a discharge means for discharging the separated gas. Commonly used stirring blades such as turbine blades and anchor blades may be used as the stirring blade. Examples of heating means include a jacket, a hot water bath, an oil bath, and steam heating.

[0047] The heating temperature of the mixture during granulation is preferably in the range of 30 to 150°C, more preferably in the range of 40 to 150°C, and even more preferably in the range of 40 to 120°C. The pressure inside the vessel during granulation is preferably 0.01 to 1.0 MPa, more preferably 0.01 to 0.8 MPa, and even more preferably 0.01 to 0.7 MPa. The pressure at this time may be gauge pressure. The granulation time may be, for example, 0.5 to 24 hours, and preferably 0.5 to 12 hours.

[0048] The fluoropolymer-containing granules obtained by granulation may be collected from the container and then dried, if necessary. In the method for producing the present solid, the collected granules are preferably dried to obtain the present solid. A specific example of drying is a method in which the collected granules are transferred to a dryer and heated. By drying, substances such as water and solvent inside the granules can be further vaporized and removed.

[0049] Examples of dryers used for drying include batch rotary dryers, indirect heating dryers, vacuum dryers, and hot air dryers.

[0050] The drying temperature is preferably in the range of 60 to 250° C., more preferably in the range of 100 to 160° C. The drying time is preferably in the range of 1 to 48 hours, more preferably in the range of 1 to 24 hours.

[0051] After the fluoropolymer is recovered, the solvent remaining in the reactor may be recovered and reused. When reused, the recovered solvent may be purified by distillation, filtration, ion exchange, or the like.

[0052] <Preparation Step> The present production method preferably includes a step 2 of preparing a solvent with an adjusted composition prior to the step 1 of polymerizing a monomer in a solvent. The solvent can be produced by mixing raw materials containing a predetermined compound. In step 2, the raw materials or a mixture thereof are preferably subjected to a purification treatment in order to remove excess components and impurities from the raw materials. In particular, it is preferable to use a raw material obtained by subjecting a purification target containing compound A to a purification treatment. The purification target may be synthesized by reacting a precursor, or may be procured by purchase, etc. Methods for obtaining compound A by reacting a precursor include a method of reacting a hydrofluoroalcohol with a fluoroolefin in the presence of compound A and a catalyst. Specifically, the method described in Japanese Patent No. 4635871 can be used. In a composition containing compound A obtained by reacting a precursor, the total content of compound B and compound C is often in excess of the content of compound A. Therefore, it is preferable to perform a purification treatment to separate compound B and compound C from the obtained composition.

[0053] Distillation is preferred as the purification process. The distillation may be either atmospheric distillation or reduced pressure distillation, with atmospheric distillation being preferred. For the distillation, a distillation column having a multi-stage theoretical plate number is preferably used. The number of theoretical plates is preferably 2 or more, more preferably 5 or more. The number of theoretical plates is preferably 50 or less, more preferably 40 or less. In the distillation of a composition containing compound A obtained by reacting a precursor, the fraction includes a stage in which an initial fraction containing compounds with a boiling point lower than that of compound A is distilled, and a stage in which a high-purity main fraction containing compound A as the main component is distilled. After the distillation is stopped, a liquid containing compounds with a boiling point higher than that of compound A remains in the distillation column. Of the fractions recovered by distillation, the main fraction excluding the initial fraction is preferably used as compound A of the present invention. The distillation rate at which recovery as the main fraction begins is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, relative to the charged amount. From the viewpoint of productivity, the distillation rate at which recovery as the main fraction begins is preferably 30% by mass or less, more preferably 20% by mass or less, relative to the charged amount. By satisfying the above range, the content of compound B, which has a boiling point lower than that of compound A, in the composition containing compound A obtained as a purified product can be reduced. The distillation rate at which distillation is stopped and recovery of the main fraction is completed is preferably 95% by mass or less, more preferably 90% by mass or less, relative to the charged amount. From the viewpoint of productivity, the lower limit is preferably 70% by mass or more, more preferably 80% by mass or more, relative to the charged amount. By satisfying the above range, the content of compound C, which has a boiling point higher than that of compound A, in the composition containing compound A obtained as a purified product can be reduced. By using a raw material that has been subjected to the above purification treatment as a raw material containing compound A, the solvent composition can be appropriately adjusted, and a fluoropolymer with a small MFR can be produced.

[0054] It is also preferable to remove water from the product to be purified before the distillation. Methods for removing water include static separation, sedimentation, and the use of an adsorbent. Specific examples of adsorbents include molecular sieves.

[0055] [Fluoropolymer] This production method produces a fluoropolymer, which is a polymer of a monomer containing a fluoromonomer. The fluoropolymer contains repeating units derived from the above-mentioned fluoromonomer-containing monomer. The fluoropolymer preferably contains repeating units based on at least one compound selected from the group consisting of TFE, a compound represented by formula (1), and a compound represented by formula (2), more preferably a unit based on TFE (hereinafter also referred to as "TFE unit"). It is further preferred to contain TFE units and units based on a compound represented by formula (1), or TFE units and units based on a compound represented by formula (2), and particularly preferred to contain TFE units and units based on a compound represented by formula (1). The fluoropolymer may contain units based on a monomer not containing a fluorine atom. Examples of the monomer not containing a fluorine atom include those listed above. The unit based on a monomer not containing a fluorine atom is preferably a unit based on ethylene (hereinafter also referred to as "E unit"). Among them, fluoropolymer preferably comprises TFE unit and E unit, more preferably comprises TFE unit and E unit, and further comprises at least one of the unit that is based on the compound represented by formula (1) and the unit that is based on the compound represented by formula (2), and further preferably comprises TFE, ethylene and the unit that is based on the compound represented by formula (1).

[0056] The content of TFE units in the fluoropolymer is preferably 30.0 to 100.0 mol%, more preferably 35.0 to 70.0 mol%, and even more preferably 40.0 to 65.0 mol%, based on all units contained in the fluoropolymer. In particular, when the fluoropolymer contains E units, it is preferable that the above-mentioned preferred range is satisfied. Furthermore, the content of TFE units is preferably 90.0 to 99.9 mol%, based on all units contained in the fluoropolymer, from the viewpoint of better heat resistance, and is preferably 95.0 to 99.0 mol%, based on the viewpoint of better melt moldability. In particular, when the fluoropolymer contains units based on a compound represented by formula (2), it is preferable that the above-mentioned preferred range is satisfied. In the fluoropolymer, the content of E units is preferably 30.00 to 54.99 mol%, more preferably 35.0 to 51.9 mol%, and even more preferably 35.00 to 49.50 mol%, based on all units contained in the fluoropolymer. In the fluoropolymer, the total content of TFE units and E units is preferably 85.00 to 99.99 mol%, more preferably 90.00 to 99.90 mol%, and even more preferably 95.00 to 99.50 mol%, based on all units contained in the fluoropolymer. In the fluoropolymer, the content of units based on the compound represented by formula (1) is preferably 0.01 to 10.0 mol%, more preferably 0.10 to 5.00 mol%, and even more preferably 0.50 to 4.00 mol%, based on all units contained in the fluoropolymer. In the fluoropolymer, the content of units based on the compound represented by formula (2) is preferably 0.10 to 5.00 mol%, more preferably 0.50 to 4.00 mol%, and even more preferably 1.00 to 3.00 mol%, based on all units contained in the fluoropolymer.

[0057] The melting point of the fluoropolymer is preferably 180 to 330°C, more preferably 185 to 320°C, even more preferably 190 to 315°C, and particularly preferably 190 to 310°C. The melting point of the fluoropolymer is preferably 210 to 290°C, more preferably 215 to 280°C, and even more preferably 220 to 270°C. In particular, when the fluoropolymer contains E units, it is preferable that the above-mentioned preferred range be satisfied. Furthermore, from the viewpoint of excellent heat resistance, the melting point of the fluoropolymer is also preferably 260 to 330°C, more preferably 270 to 320°C, and even more preferably 290 to 315°C. In particular, when the fluoropolymer contains units based on the compound represented by formula (2) but does not contain E units, it is preferable that the above-mentioned preferred range be satisfied. The melting point of the fluoropolymer can be measured using a differential scanning calorimeter (DSC). Methods for adjusting the melting point of the fluoropolymer include lowering the polymerization temperature during production of the fluoropolymer and adjusting the composition of the fluoropolymer.

[0058] The MFR of the fluoropolymer is preferably 0.1 to 100 g / 10 min, more preferably 1 to 50 g / 10 min, and even more preferably 3 to 30 g / 10 min. According to the present production method, a fluoropolymer with a small MFR can be obtained.

[0059] The fluoropolymer or fluoropolymer-containing solid obtained by this production method may be melted and extruded using an extruder to form a fluoropolymer-containing solid in other forms such as pellets, granules, or threads (hereinafter simply referred to as a "solid") Furthermore, the obtained fluoropolymer, fluoropolymer-containing solid, or the above-mentioned other forms of solid may also be preferably used to produce a molded article. Specific examples of methods for forming the molded article include injection molding, extrusion molding, blow molding, press molding, rotational molding, electrostatic coating, and spray molding.

[0060] The molded article may be a coating film formed using a fluoropolymer or a solid material. Examples of a method for forming a coating film include a method in which a powder obtained by pulverizing a fluoropolymer or a solid material, or a powder containing a fluoropolymer, is used to form a coating film by rotational molding, electrostatic coating, or spray molding. The thickness of the coating film is preferably 1 μm to 10 mm, more preferably 50 μm to 5 mm, and even more preferably 100 μm to 3 mm.

[0061] Specific examples of the molded article include nuts, bolts, joints, films, bottles, gaskets, wire coatings, tubes, hoses, pipes, valves, sheets, seals, packing, tanks, rollers, containers, cocks, connectors, filter housings, filter cages, flow meters, pumps, wafer carriers, and wafer boxes.

[0062] The fluoropolymer, the solid containing the fluoropolymer, the solid material, or the above-mentioned molded article obtained by the present production method can be used for the following purposes.Fluid transfer components for food manufacturing equipment, such as food packaging films, lining materials, packings, sealing materials, and sheets for fluid transfer lines used in food manufacturing processes; chemical liquid transfer components, such as chemical stoppers, packaging films, lining materials, packings, sealing materials, and sheets for fluid transfer lines used in chemical manufacturing processes; inner lining components for chemical liquid tanks and piping in chemical plants or semiconductor factories; fuel transfer components, such as O-rings, tubes, packings, valve core materials, hoses, and sealing materials used in automobile fuel systems and peripheral devices, and hoses and sealing materials used in automobile automatic transmissions; carburetor flange gaskets, shaft seals, valve stem seals, sealing materials, and hoses used in automobile engines and peripheral devices, as well as other automobile components, such as automobile brake hoses, air conditioner hoses, radiator hoses, and wire coating materials; chemical liquid transfer components for semiconductor manufacturing equipment, such as O-rings, tubes, packings, valve core materials, hoses, sealing materials, rolls, gaskets, diaphragms, and fittings; coating and ink components such as paint rolls, hoses, tubes, and ink containers for coating equipment; food and beverage transport components such as tubes, hoses, belts, packing, and joints, such as food and beverage tubes or food and beverage hoses, food packaging materials, and glass cooking equipment; waste liquid transport components such as tubes and hoses for transporting waste liquid; high-temperature liquid transport components such as tubes and hoses for transporting high-temperature liquids; steam piping components such as tubes and hoses for steam piping; anti-corrosion tapes for piping, such as tapes wrapped around piping on ship decks, etc.; various coating materials such as electrical wire coating materials, optical fiber coating materials, and transparent surface coating materials and backing agents applied to the light-incident surface of photovoltaic elements in solar cells; sliding components such as diaphragms and various packings for diaphragm pumps; agricultural films, and weather-resistant covers for various roofing materials and side walls, etc.; interior materials used in the construction field, and glass coating materials such as non-flammable fire-resistant safety glass; lining materials such as laminated steel sheets used in home appliances, etc.; carrier films for fuel cells.

[0063] The present invention will be described in detail below with reference to examples. Examples 1 to 10 are working examples, and Examples 11 and 12 are comparative examples. However, the present invention is not limited to these examples. Various measurement methods and evaluation methods are as follows.

[0064] [Measurement] <Purity of Solvent> The purity of the solvent, the content of Compound A, and the total content of Compound B and Compound C were confirmed by gas chromatography (GC).

[0065] <Content of each unit in fluoropolymer> The content (mol %) of each unit in the fluoropolymer was calculated from the results of total fluorine measurement and melt F-NMR measurement. １ H and １３ Calculated by C-NMR measurement.

[0066] <Melting Point> The melting point (°C) of the fluoropolymer was determined from the endothermic peak observed when the fluoropolymer was heated to 300°C at a rate of 10°C / min in an air atmosphere using a differential scanning calorimeter (DSC7020 manufactured by SII Corporation).

[0067] [Evaluation Test] <MFR> Using a melt indexer (manufactured by Techno Seven Co., Ltd.), the mass (g) of the fluoropolymer flowing out of an orifice having a diameter of 2 mm and a length of 8 mm in 10 minutes was measured under conditions of a temperature of 297°C and a load of 49 N in accordance with ASTM D3159, and this was taken as the MFR (g / 10 min) of the fluoropolymer.

[0068] [Example 1] [Preparation of Solvent] 277 kg of HFE-347pc-f, 42 kg of tetraglyme (tetraethylene glycol dimethyl ether), and 32 kg of a 48% by mass aqueous solution of potassium hydroxide were charged into a reactor having an internal volume of 300 L (liters), and the temperature was then raised to 60°C. TFE was fed at 43 kg / h, CF ３ CH ２OH was continuously supplied at 41 kg / h, tetraglyme at 12 kg / h, and a 48 mass% aqueous potassium hydroxide solution at 8.4 kg / h, and the reaction was carried out while stirring so as to maintain the pressure in the reactor at 0.15 MPa and the temperature at 60° C. After 10 hours, water in the obtained crude liquid was removed by static separation. Next, the entire amount of the obtained crude liquid was poured into a bottom volume of 0.5 m ３ The mixture was charged into a distillation apparatus at 100°C, and the bottoms were heated to start distillation. When the distillate ratio from the start of distillation reached 9% by mass relative to the charged amount, recovery of the main fraction was started, and when the distillate ratio reached 84% by mass, distillation was terminated. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.5%.

[0069] [Monomer Polymerization] A 1.3 L stainless steel polymerization vessel equipped with a stirrer and a jacket was evacuated, and then 1,174 g of purified HFE-347pc-f obtained as the main fraction by the above-mentioned distillation, 8.3 g of methanol, 1.2 g of CH ２ =CH(CF ２ ) ４ 3.3 g of F(PFBE) was charged. While stirring the inside of the polymerization vessel, 144 g of TFE and 6.5 g of ethylene (E) were charged, and then warm water was flowed through the jacket to raise the temperature inside the polymerization vessel to 72°C (polymerization temperature). The pressure inside the polymerization vessel at this time was 1.5 MPaG (gauge pressure). After the temperature stabilized, 3.2 mL of a 1% by mass solution of tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") (solvent: purified HFE-347pc-f) was injected to initiate polymerization. During the polymerization, a mixed gas with a TFE / E molar ratio of 54 / 46 was added so that the internal pressure was kept constant at 1.5 MPaG. In addition, 0.4 mL of PFBE was added every time 10 g of the TFE / E mixed gas added during the polymerization was consumed. After 175 minutes from the start of the reaction, 100 g of a mixed gas with a TFE / E=54 / 46 molar ratio was added, and the polymerization vessel was cooled to terminate the polymerization. After volatilizing the solvent, the resulting polymer was dried in an oven at 150°C to obtain a fluoropolymer. The MFR, composition, and melting point of the resulting fluoropolymer are shown in Table 1.

[0070] [Example 2] Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 10% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 83% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.7%. Next, polymerization was carried out in the same manner as in Example 1, except that the purified HFE-347pc-f was used as HFE-347pc-f and the amount of methanol charged was 10.5 g. The reaction time was 173 minutes. The MFR, composition, and melting point of the resulting fluoropolymer were as shown in Table 1.

[0071] Example 3 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 12% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 80% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.8%. Next, polymerization was carried out in the same manner as in Example 1, except that the amounts charged before charging TFE and E were 1,174 g of HFE-347pc-f obtained by the above-mentioned distillation, 5.3 g of methanol, and 5.9 g of PFBE, the amount of 1% by mass solution of PBPV (solvent: HFE-347pc-f obtained by the above-mentioned distillation) injected was 6.9 mL, and the amount of PFBE added per 10 g of TFE / E mixed gas consumed during polymerization was 0.6 mL. The reaction time was 173 minutes. The MFR, composition and melting point of the resulting fluoropolymer are shown in Table 1.

[0072] Example 4 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 8% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 86% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.6%. Next, polymerization was carried out in the same manner as in Example 1, except that the amounts charged before charging TFE and E were 1,174 g of HFE-347pc-f obtained by the above-mentioned distillation, 10.9 g of methanol, and 6.2 g of PFBE, the amount of 1% by mass solution of PBPV (solvent: HFE-347pc-f obtained by the above-mentioned distillation) injected was 7.8 mL, and the amount of PFBE added per 10 g of TFE / E mixed gas consumed during polymerization was 0.7 mL. The reaction time was 165 minutes. The MFR, composition and melting point of the resulting fluoropolymer are shown in Table 1.

[0073] Example 5 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 8% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 85% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.5%. Next, polymerization was carried out in the same manner as in Example 1, except that the amounts charged before charging TFE and E were 1174 g of HFE-347pc-f obtained by the above-mentioned distillation, 7.0 g of methanol, and 8.0 g of PFBE, the amount of 1% by mass solution of PBPV (solvent: HFE-347pc-f obtained by the above-mentioned distillation) injected was 12.9 mL, and the amount of PFBE added per 10 g of TFE / E mixed gas consumed during polymerization was 0.9 mL. The reaction time was 168 minutes. The MFR, composition and melting point of the resulting fluoropolymer are shown in Table 1.

[0074] Example 6 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 7% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 94% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.2%. A 1.3 L stainless steel polymerization vessel equipped with a stirrer and a jacket was evacuated, and then 1174 g of HFE-347pc-f obtained by the above distillation, 2.5 g of methanol, and 14.4 g of PFBE were charged. While stirring the contents of the polymerization vessel, 174 g of TFE and 5.0 g of E were charged, and then warm water was flowed through the jacket to raise the temperature inside the polymerization vessel to 66°C (polymerization temperature). The pressure inside the polymerization vessel at this time was 1.5 MPaG (gauge pressure). After the temperature stabilized, 19.5 mL of a 1% by mass solution of PBPV (solvent: HFE-347pc-f obtained by the distillation described above) was injected to initiate polymerization. During polymerization, a mixed gas with a TFE / E molar ratio of 60 / 40 was added to maintain a constant internal pressure of 1.5 MPaG. In addition, 1.3 mL of PFBE was added for every 10 g of TFE / E mixed gas consumed during polymerization. 260 minutes after the start of the reaction, 100 g of a mixed gas with a TFE / E molar ratio of 60 / 40 was added, and the polymerization was terminated by cooling the polymerization vessel. After volatilizing the solvent, the resulting polymer was dried in an oven at 150 °C to obtain a fluoropolymer. The MFR, composition, and melting point of the resulting fluoropolymer were as shown in Table 1.

[0075] Example 7 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 10% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 90% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.6%. Next, polymerization was carried out in the same manner as in Example 6, except that the amounts charged before charging TFE and E were 1174 g of HFE-347pc-f obtained by the above-mentioned distillation, 7.4 g of methanol, and 6.8 g of PFBE, the amount of 1% by mass solution of PBPV (solvent: HFE-347pc-f obtained by the above-mentioned distillation) injected was 12.9 mL, and the amount of PFBE added per 10 g of TFE / E mixed gas consumed during polymerization was 0.8 mL. The reaction time was 237 minutes. The MFR, composition and melting point of the resulting fluoropolymer are shown in Table 1.

[0076] Example 8 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 11% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 82% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.7%. A 1.3 L stainless steel polymerization vessel equipped with a stirrer and a jacket was evacuated, and then 1174 g of HFE-347pc-f obtained by the above distillation, 3.9 g of methanol, and 10.9 g of PFBE were charged. While stirring the contents of the polymerization vessel, 150 g of TFE and 12 g of E were charged, and then warm water was flowed through the jacket to raise the temperature inside the polymerization vessel to 66°C (polymerization temperature). The pressure inside the polymerization vessel at this time was 1.5 MPaG (gauge pressure). After the temperature stabilized, 14.2 mL of a 1% by mass solution of PBPV (solvent: HFE-347pc-f obtained by the distillation described above) was injected to initiate polymerization. During polymerization, a mixed gas with a TFE / E molar ratio of 51 / 49 was added to maintain a constant internal pressure of 1.5 MPaG. In addition, 1.3 mL of PFBE was added for every 10 g of TFE / E mixed gas consumed during polymerization. 237 minutes after the start of the reaction, 100 g of the mixed gas with a TFE / E molar ratio of 51 / 49 was added, and the polymerization was terminated by cooling the polymerization vessel. After volatilizing the solvent, the resulting polymer was dried in an oven at 150°C to obtain a fluoropolymer. The MFR, composition, and melting point of the resulting fluoropolymer were as shown in Table 1.

[0077] Example 9 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 8% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 88% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.5%. A 1.3 L polymerization vessel equipped with a stirrer was degassed, and 899 g of HFE-347pc-f obtained by the above distillation, 271 g of water, CF ２ = CFO (CF ２ ) ３82.3 g of F(PPVE) and 21.2 g of methanol were charged into the polymerization vessel. Next, the temperature inside the polymerization vessel was raised to 50 ° C (polymerization temperature), 181 g of TFE was further charged, and the pressure inside the polymerization vessel was increased to 1.28 MPa (gauge pressure). 2 mL of a 0.06 mass% solution of heptafluorobutyroyl peroxide (solvent: HFE-347pc-f obtained by the above-mentioned distillation) was charged as a polymerization initiator solution, polymerization was initiated, and the above polymerization initiator solution was then continuously added. Furthermore, TFE was continuously charged so that the pressure during polymerization was maintained equal to the pressure at the start of polymerization. 300 minutes after the start of polymerization, 49 mL of the polymerization initiator solution was added, and at the point when 160 g of TFE was charged, the polymerization vessel was cooled and the polymerization was terminated. After volatilizing the solvent, the obtained polymer was dried in an oven at 150 ° C to obtain a fluoropolymer. The MFR, composition and melting point of the resulting fluoropolymer are shown in Table 1.

[0078] Example 10 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that collection of the main fraction was started when the distillate ratio from the start of distillation reached 11% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 82% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.7%. Copolymer 10 was obtained in the same manner as in Example 9, except that the amount of PPVE and the amount of methanol initially charged to the polymerization vessel were changed to 113.0 g and 22.7 g, respectively, and the amount of polymerization initiator solution (the solvent for the polymerization initiator solution was HFE-347pc-f obtained by the distillation described above) continuously charged was changed to 47 mL. The polymerization time was 475 minutes. After volatilization of the solvent, the resulting polymer was dried in an oven at 150°C to obtain a fluoropolymer. The MFR, composition, and melting point of the resulting fluoropolymer were as shown in Table 1.

[0079] Example 11 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 2% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 99% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 97.5%. It was confirmed by GC that the total amount of Compound B and Compound C in the obtained main fraction exceeded 1.00% by mass relative to the content of HFE-347pc-f. Next, polymerization was carried out in the same manner as in Example 5, except that HFE-347pc-f obtained by the above-mentioned distillation was used as HFE-347pc-f. The reaction time was 545 minutes. The MFR, composition, and melting point of the obtained fluoropolymer were as shown in Table 1.

[0080] Example 12 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 1% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 98% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 96.8%. It was confirmed by GC that the total amount of Compound B and Compound C in the obtained main fraction exceeded 1.00% by mass relative to the content of HFE-347pc-f. Next, polymerization was carried out in the same manner as in Example 6, except that HFE-347pc-f obtained by the above-mentioned distillation was used as HFE-347pc-f. The reaction time was 545 minutes. The MFR, composition, and melting point of the obtained fluoropolymer were as shown in Table 1.

[0081] Example 13 Synthesis and purification of HFE-347pc-f were carried out in accordance with Example 1, except that collection of the main fraction was started when the distillate ratio from the start of distillation reached 10% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 83% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.7%. Next, polymerization was carried out in the same manner as in Example 1, except that 1173 g of the purified HFE-347pc-f was used as HFE-347pc-f, the charged amounts of methanol were 11.3 g, the charged amounts of PPVE were 16.6 g, 1.0 mL of a 1% by mass solution of PBPV (solvent: purified HFE-347pc-f) was injected, and 0.81 g of PPVE was added for every 10 g of the mixed gas consumed. The reaction time was 146 minutes. The MFR, composition and melting point of the resulting fluoropolymer are shown in Table 1.

[0082] Example 14 Synthesis and purification of HFE-347pc-f were carried out in the same manner as in Example 1, except that recovery of the main fraction was started when the distillate ratio from the start of distillation reached 8% by mass relative to the charged amount, and distillation was terminated when the distillate ratio reached 86% by mass. The purity of the purified HFE-347pc-f obtained as the main fraction was 99.6%. Next, polymerization was carried out in the same manner as in Example 1, except that the charged amounts before charging TFE and E were 1171 g of HFE-347pc-f obtained by the above distillation, 13.2 g of methanol, and 44.1 g of PPVE, the injected amount of 1% by mass solution of PBPV (solvent: purified HFE-347pc-f) was 2.0 mL, and 2.15 g of PPVE was added for every 10 g of mixed gas consumed. The reaction time was 106 minutes. The MFR, composition and melting point of the resulting fluoropolymer are shown in Table 1.

[0083] Table 1 shows the composition, MFR, melting point and solvent composition of the fluoropolymer in each example.In the table, (B+C) / A column shows the total content (unit: mass%) of compound B and compound C relative to the content of compound A in the solvent.In the table, "TFE unit" column, "E unit" column, "PFBE unit" and "PPVE unit" column show the content (unit: mol%) of each unit relative to the total unit contained in the obtained fluoropolymer.

[0084]

[0085] As shown in the table, it was confirmed that the fluoropolymer obtained by polymerizing a monomer containing a fluoromonomer in a solvent in which the total content of compound B represented by formula (B) and compound C represented by formula (C) is 1.0 mass% or less relative to the content of compound A represented by formula (A) has a small MFR.

[0086] The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2024-021264, filed on February 15, 2024, are incorporated herein by reference as the disclosure of the present invention.

Claims

1. A method for producing a fluoropolymer by polymerizing a monomer including a fluoromonomer in a solvent, wherein the solvent contains a compound A represented by formula (A), and the total content of the compound B represented by formula (B) and the compound C represented by formula (C) in the solvent is 1.00 mass% or less relative to the content of the compound A. R ａ１ -O-R ａ２ (A) R ｂ１ -CF=CF-OR ｂ２ (B) R ｃ１ -OH (C) In formula (A), R ａ１ and R ａ２ each independently represents a partially fluorinated alkyl group having 2 carbon atoms. ｂ１ represents a hydrogen atom or a fluorine atom, R ｂ２ represents a partially fluorinated alkyl group having 2 carbon atoms. ｃ１ represents a partially fluorinated alkyl group having two carbon atoms.

2. The method for producing a fluoropolymer according to claim 1, wherein the fluoromonomer comprises at least one selected from the group consisting of tetrafluoroethylene, a compound represented by formula (1), and a compound represented by formula (2). １ ２ =CX ２ (CF ２ ) ｍ X ３ (1) CF ２ =CF-O-(CF ２ ) ｎ F (2) In formula (1), X １ , X ２ and X ３ each independently represents a hydrogen atom or a fluorine atom, and m represents an integer of 1 to 6. In formula (2), n represents an integer of 1 to 6.

3. The method for producing a fluoropolymer according to claim 1 or 2, wherein the monomer further comprises ethylene.

4. The method for producing a fluoropolymer according to claim 1 or 2, wherein the content of compound A is 50% by mass or more based on the total mass of the solvent.

5. The compound A is CF ３ CH ２ OCF ２ CF ２ H or CF ３ CH ２ OCH ２ CF ３ is 、 A method for producing the fluoropolymer according to claim 1 or 2.

6. The compound B is CF ２ = CFOCH ２ CF ３ , C.F. ２ = CFOCH ２ CF ２ H, CFH=CFOCF ２ CF ２ H, or CFH=CFOCFHCF ２ 3. The method for producing a fluoropolymer according to claim 1 or 2, wherein the fluoropolymer is H.

7. The compound C is CF ３ CH ２ OH, CF ２ HCF ２ OH, or CF ３ The method for producing the fluoropolymer according to claim 1 or 2, wherein the fluoropolymer is CFHOH.

8. A method for producing a fluoropolymer according to claim 1 or 2, wherein the total content of compound B and compound C in the solvent is 0.50 mass% or less relative to the content of compound A.

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