Manufacturing method of fluororesin

Abstract

The present invention provides a method for producing fluororesins with low melt viscosity. [Solution] A method for producing a fluororesin containing residue units represented by general formula (1), comprising polymerizing monomers in an organic solvent in the presence of a polymerization initiator and a chain transfer agent to obtain a fluororesin, wherein the organic solvent is an organic solvent containing hydrogen atoms, fluorine atoms and oxygen atoms in its molecule, and the weight of oxygen atoms is 15 wt% or more, and the molecular weight distribution Mw / Mn of the fluororesin is 3.5 or more. [Formula 1] JPEG2026073750000011.jpg33139 (In formula (1), Rf1 to Rf4 each independently represent a fluorine atom, etc.)

Description

Technical Field

[0001] The present invention relates to a method for producing a fluororesin, and more particularly to a method for producing a fluororesin containing a dioxolane ring.

Background Art

[0002] Fluororesins are excellent in heat resistance, electrical properties, chemical resistance, waterproofness, oil repellency, and optical properties, and are therefore used in protective films for electronic components such as semiconductors, water-repellent films for inkjet printer heads, waterproof and oil-repellent coatings for filters, and optical members.

[0003] Among them, fluororesins containing a dioxolane ring have a bulky ring structure, and thus are amorphous and have high transparency and high heat resistance. In addition, since the fluororesin is composed only of carbon, fluorine, and oxygen, it has high electrical properties, chemical resistance, waterproofness, and oil repellency. Furthermore, since the resin is amorphous, it can be melt-molded. Patent Documents 1 and 2 describe production examples of fluororesins containing a dioxolane ring.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, fluororesins containing dioxolane rings can be melt-molded, but to improve their processability, a low melt viscosity when heated and melted is required. As a result of the inventors' investigations, the resins obtained by the methods described in the examples of Patent Document 1 and Patent Document 2 are not necessarily sufficient, and further improvement in melt viscosity is required. Patent Document 2 describes that the problem of high melt viscosity when heated and melted, resulting in poor moldability in melt molding such as melt extrusion molding, can be solved by fluororesins having a specific molecular weight distribution. However, Patent Document 2 does not describe a method for obtaining fluororesins with molecular weight distributions other than those shown in its examples, and therefore, the development of a method for obtaining fluororesins with low melt viscosity is still needed.

[0006] Therefore, the present invention has been made in view of the above-mentioned problems, and its purpose is to provide a method for producing a fluororesin with low melt viscosity. [Means for solving the problem]

[0007] The present invention provides a method for producing a fluororesin that includes a residue unit represented by the following general formula (1), in order to solve the above problems, and comprises polymerizing a monomer represented by the following general formula (2) in an organic solvent in the presence of a polymerization initiator and a chain transfer agent to obtain the fluororesin, wherein the organic solvent is an organic solvent that contains a hydrogen atom, a fluorine atom, and an oxygen atom in its molecule, and the weight of the oxygen atom is 15 wt% or more, and the molecular weight distribution Mw / Mn of the fluororesin is 3.5 or more. [ka] (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms, and the perfluoroalkyl group may have ether bonds between any carbon-carbon bonds, and two or more groups of Rf1, Rf2, Rf3, and Rf4 may be linked to each other to form a ring having 4 to 8 carbon atoms.) [ka] (In formula (2), Rf5, Rf6, Rf7, and Rf8 each independently represent a fluorine atom and a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have ether bonds between any carbon-carbon bonds, and two or more groups of Rf5, Rf6, Rf7, and Rf8 may be linked to each other to form a ring having 4 to 8 carbon atoms.) [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a resin that is excellent in molding processes such as melt extrusion molding. [Modes for carrying out the invention]

[0009] The following describes one embodiment of the method for producing fluororesin according to the present invention.

[0010] In this invention, "residue unit" refers to a repeating unit in a resin or a constituent unit in a resin.

[0011] Furthermore, when a numerical range is indicated using "~", that range shall include both its upper and lower limits.

[0012] The method for producing fluororesin in this embodiment is a method for producing fluororesin that includes a residue unit represented by the following general formula (1) (hereinafter referred to as "residue unit A"). [ka]

[0013] In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms, and the perfluoroalkyl group may have ether bonds between any carbon-carbon bonds. Two or more groups of Rf1, Rf2, Rf3, and Rf4 may be linked to each other to form a ring having 4 to 8 carbon atoms.

[0014] The perfluoroalkyl group having 1 to 7 carbon atoms may be a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms.

[0015] In this specification, that the perfluoroalkyl group "has an ether bond between any carbon-carbon bonds" is not limited to the case where there is an ether bond between any carbon-carbon bonds in the perfluoroalkyl group, and also includes the case where there is an ether bond between the carbon-carbon bond between the carbon atom to which the perfluoroalkyl group is bonded and the perfluoroalkyl group.

[0016] Examples of the linear perfluoroalkyl group having 1 to 7 carbon atoms include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoro-n-propyl group, a nonafluoro-n-butyl group, an undecafluoro-n-pentyl group, a tridecafluoro-n-hexyl group, and a pentadecafluoro-n-heptyl group.

[0017] Examples of the branched perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluoroisopropyl group, a nonafluoroisobutyl group, a nonafluoro-sec-butyl group, and a nonafluoro-tert-butyl group.

[0018] Examples of the cyclic perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluorocyclopropyl group, a nonafluorocyclobutyl group, and a tridecafluorocyclohexyl group.

[0019] Examples of the linear perfluoroalkyl group having an ether bond between any carbon-carbon bonds include a perfluoro(methoxymethyl) group, a perfluoro(ethoxymethyl) group, a perfluoro(methoxyethyl) group, and a perfluoro(ethoxyethyl) group.

[0020] 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.

[0021] Examples of cases where two or more Rf1, Rf2, Rf3, and Rf4 groups are linked to each other to form a ring include, specifically, hexafluoropropylene groups and octafluorobutylene groups, which are formed including the carbon atom to which Rf1 is bonded and the carbon atom to which Rf3 is bonded.

[0022] In residue unit A, it is preferable that at least one of Rf1, Rf2, Rf3, and Rf4 is a linear perfluoroalkyl group having 1 to 7 carbon atoms or a branched or cyclic perfluoroalkyl group having 3 to 7 carbon atoms. This allows the resulting fluororesin to exhibit excellent heat resistance. Furthermore, a fluororesin in which one of Rf1, Rf2, Rf3, and Rf4 is a perfluoroalkyl group and the rest are fluorine atoms is even more preferable.

[0023] Specific examples of residue unit A include the following residue units. [ka]

[0024] The fluororesin in this embodiment may contain other monomeric residue units. Examples of other monomeric residue units include residue units derived from monomers such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluoroalkylethylene, fluorovinyl ether, vinyl fluoride (VF), vinylidene fluoride (VDF), perfluoro-2,2-dimethyl-1,3-dioxole (PDD), perfluoro(allyl vinyl ether), and perfluoro(butenyl vinyl ether). If other monomeric residue units are included, only one type may be included, or two or more types may be included.

[0025] If the fluororesin in this embodiment contains other monomer residue units, the content of the other monomer residue units is not particularly limited, but may be, for example, less than 50% by weight, 40% by weight or less, 30% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, 5% by weight or less, 3% by weight or less, or 1% by weight or less, relative to the total amount of residue units. Alternatively, the fluororesin in this embodiment may contain only residue unit A.

[0026] In this embodiment, the molecular weight distribution Mw / Mn of the fluororesin, expressed as the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn, is 3.5 or higher, preferably 3.6 or higher, and more preferably 3.7 or higher. A molecular weight distribution Mw / Mn of 3.5 or higher in the resulting fluororesin results in a lower melt viscosity compared to conventional resins, making it a resin excellent for molding processes such as melt extrusion molding. There is no particular upper limit to the molecular weight distribution Mw / Mn, but Mw / Mn may be, for example, 20 or less, 15 or less, or 10 or less.

[0027] The weight-average molecular weight of the fluororesin is preferably 50,000 to 400,000, more preferably 50,000 to 300,000, and even more preferably 50,000 to 200,000, based on standard polymethyl methacrylate. Having the weight-average molecular weight of the fluororesin within this range allows for a balance between the heat resistance and moldability of the resin.

[0028] 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 Wako Pure Chemical Industries, Ltd.) has been added. The measurement temperature can be 40°C.

[0029] In the method for producing fluororesin according to this embodiment, the monomer represented by the following general formula (2) is polymerized in an organic solvent in the presence of a polymerization initiator and a chain transfer agent to obtain the fluororesin. [ka]

[0030] In formula (2), Rf5, Rf6, Rf7, and Rf8 each independently represent a fluorine atom and a perfluoroalkyl group having 1 to 7 carbon atoms, and the perfluoroalkyl group may have ether bonds between any carbon-carbon bonds, and two or more groups of Rf5, Rf6, Rf7, and Rf8 may be linked to each other to form a ring having 4 to 8 carbon atoms.

[0031] Rf5, Rf6, Rf7, and Rf8 are groups corresponding to Rf1, Rf2, Rf3, and Rf4 in residue unit A, respectively. Therefore, examples and preferred groups of Rf5, Rf6, Rf7, and Rf8 are the same as those described above for Rf1, Rf2, Rf3, and Rf4.

[0032] The organic solvent used in this embodiment is an organic solvent containing a hydrogen atom, a fluorine atom, and an oxygen atom in its molecule, wherein the weight of the oxygen atom in the molecule is 15 wt% or more. The weight of the oxygen atom in the molecule only needs to be 15 wt% or more; for example, it may be 16 wt% or more. An example of such an organic solvent is 2,2,2-trifluoroethanol.

[0033] The ratio of monomer to organic solvent represented by formula (2) 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.

[0034] In this embodiment, the polymerization reaction is carried out in the presence of a chain transfer agent. By using a chain transfer agent, the molecular weight can be adjusted. Examples of chain transfer agents include organic compounds having 1 to 20 carbon atoms that contain at least one atom selected from the group consisting of hydrogen atoms and chlorine atoms. Specifically, examples of chain transfer agents include organic compounds having 1 to 20 carbon atoms that contain hydrogen atoms, such as toluene, acetone, ethyl acetate, tetrahydrofuran, methyl ethyl ketone, methanol, ethanol, and isopropanol; and organic compounds having 1 to 20 carbon atoms that contain chlorine atoms, such as chloroform, dichloromethane, tetrachloromethane, chloromethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, hexachloroethane, benzyl chloride, pentafluorobenzyl chloride, and pentafluorobenzoyl chloride.

[0035] In particular, from the viewpoint of polymerization control, the chain transfer agent is preferably an organic compound having 1 to 20 carbon atoms that contains a chlorine atom, and more preferably an organic compound having 1 to 20 carbon atoms that contains a hydrogen atom and a chlorine atom.

[0036] From the viewpoint of molecular weight control, the amount of the chain transfer agent is preferably 0.01 to 50% by weight, more preferably 0.01 to 40% by weight, and even more preferably 0.01 to 30% by weight, relative to the total amount of the monomer represented by formula (2) and the chain transfer agent.

[0037] In the method for producing fluororesin according to this embodiment, polymerization is carried out in the presence of a polymerization initiator. Examples of polymerization initiators include radical polymerization initiators, such as organic peroxides including benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tetr-butyl peroxide, tetr-butylcumyl peroxide, dicumyl peroxide, tetr-butyl peroxyacetate, perfluoro(di-tetr-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl) peroxide, tetr-butyl peroxybenzoate, and tetr-butyl perpivalate; as well as azo-based initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and 1,1'-azobis(cyclohexane-1-carbonitride).

[0038] Alternatively, a radical polymerization initiator represented by the following formula (3) can be used. [ka]

[0039] In equation (3), j is an integer between 3 and 20. Preferably, j is an integer between 3 and 15, and more preferably, j is an integer between 3 and 10.

[0040] From the viewpoint of suppressing yellowing during heat melt molding of fluororesin molded products, especially thick molded products, the radical polymerization initiator is preferably a radical polymerization initiator represented by the above formula (3).

[0041] From the viewpoint of molecular weight control, the amount of radical polymerization initiator is preferably 0.05 to 3% by weight, more preferably 0.07 to 3% by weight, and even more preferably 0.09 to 3% by weight, based on 100% by weight of monomer.

[0042] From the viewpoint of suppressing yellowing of molded products, the radical polymerization initiator represented by formula (3) above is preferred as the polymerization initiator to be used. However, in the fluororesin obtained by polymerizing the monomer represented by general formula (2) above in the organic solvent in the above embodiment using this polymerization initiator, it has been confirmed that if a chain transfer agent is not added to the polymerization reaction, the resin becomes multimodal with multiple peaks in the molecular weight distribution (GPC chart), or even if there is only one peak, it becomes a broad peak with tails on both the low molecular weight side and the high molecular weight side (hereinafter, these states will be collectively referred to as "multimodal"). Resins with a multimodal molecular weight distribution have a large amount of high molecular weight components, which leads to the problem of poor molding process when heated and melted. Surprisingly, by adding a chain transfer agent to the polymerization reaction, it is possible to obtain a unimodal fluororesin with only a single peak in the molecular weight distribution, rather than a multimodal resin, while achieving a molecular weight distribution Mw / Mn of 3.5 or higher Mw / Mn.

[0043] In the method for producing fluororesin according to this embodiment, the polymerization method can be solution polymerization or precipitation polymerization. Among these, precipitation polymerization is preferred because the resulting resin powder has high fluidity, allows for continuous supply to molding machines and the like, suppresses solvent residue in the fluororesin, has high bulk density and increased packing capacity, and provides a powder that is easy to handle during molding. Fluororesin can be produced by precipitation polymerization by using an organic solvent in which at least the monomer represented by formula (2) dissolves, and at least a portion of the fluororesin produced by polymerization does not dissolve, resulting in a precipitate of fluororesin. Examples of such organic solvents include 2,2,2-trifluoroethanol.

[0044] In a manufacturing method according to one embodiment of the present invention, a monomer represented by general formula (2) can be polymerized in a specific organic solvent in the presence of a polymerization initiator and a chain transfer agent to produce a fluororesin containing residue unit A, in which the molecular weight distribution Mw / Mn is 3.5 or higher. Because the molecular weight distribution is broader compared to conventional resins, the melt viscosity of the fluororesin is lower compared to conventional resins, resulting in a resin that is excellent for molding processes such as melt extrusion molding. In other words, according to a manufacturing method according to one aspect of the present invention, a fluororesin with low melt viscosity and excellent molding processes such as melt extrusion molding can be produced.

[0045] In this specification, "low melt viscosity" and "lower melt viscosity compared to conventional materials" may vary depending on the composition of the resin, but in one embodiment, at 260°C and a frequency of 10°C, the following conditions apply: -2 (rad·s -1 The complex viscosity is measured in ), and when the obtained complex viscosity value is taken as the melt viscosity, the melt viscosity is 400 Pa·s or less. For example, a resin of a homopolymer of perfluoro(4-methyl-2-methylene-1,3-dioxolane) with a weight-average molecular weight of 8.2 × 10 4 In the case of such resins, the intention is for the melt viscosity to be less than 400 Pa·s. However, there is no lower limit to the melt viscosity; for example, it could be 100 Pa·s or higher.

[0046] For example, a method for measuring melt viscosity can be exemplified by measurement using a commercially available rotary rheometer, and the method described in JIS K7244-10 can be cited as an example.

[0047] (summary) As can be understood from the above description, the present invention encompasses the following aspects.

[0048] Embodiment 1: A method for producing a fluororesin containing residue units represented by the above-described general formula (1), comprising polymerizing monomers represented by the above-described general formula (2) in an organic solvent in the presence of a polymerization initiator and a chain transfer agent to obtain the fluororesin, wherein the organic solvent is an organic solvent containing hydrogen atoms, fluorine atoms and oxygen atoms in its molecule, and the weight of oxygen atoms is 15 wt% or more, and the molecular weight distribution Mw / Mn of the fluororesin is 3.5 or more. Embodiment 2: A method for producing the fluororesin according to Embodiment 1, wherein the weight-average molecular weight Mw of the fluororesin is 50,000 to 300,000. Appearance 3: 260℃, frequency 10 -2 (rad·s -1 A method for producing a fluororesin according to embodiment 1 or 2, wherein the melt viscosity of the fluororesin in the ) is 400 Pa·s or less. Embodiment 4: A method for producing a fluororesin according to any one of Embodiments 1 to 3, wherein the polymerization initiator is a radical polymerization initiator represented by the general formula (3) described above. [Examples]

[0049] The embodiments of the present invention will be further described in detail below with reference to some examples. Of course, the present invention is not limited to the following embodiments, and it goes without saying that various forms 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.

[0050] (Measurement of 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 manufactured by Tosoh Corporation and an RI detector. Asahi Clean AK-225 (manufactured by Asahi Glass Co., Ltd.) was used as the eluent, with 10 wt% of 1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Wako Pure Chemical Industries, Ltd.) added to AK-225. Standard polymethyl methacrylate from Agilent was used as the standard sample, and the weight-average molecular weight Mw and number-average molecular weight Mn (in terms of polymethyl methacrylate) were calculated from the elution times of the sample and the standard sample. Furthermore, the molecular weight distribution Mw / Mn, which is the ratio of weight-average molecular weight Mw to number-average molecular weight Mn, was calculated from the obtained weight-average molecular weight Mw and number-average molecular weight Mn.

[0051] (Measurement of melt viscosity) Using an Anton-Paar MCR-300 rotary rheometer, at 260°C, frequency 10 -2 (rad·s -1 The complex viscosity was measured in ) and the value of the complex viscosity was expressed as the melt viscosity.

[0052] [Example 1] The inside of a 3L SUS316 autoclave, equipped with paddle-type agitators, a nitrogen inlet tube, and a thermometer, was purged with nitrogen. A solution was prepared by dissolving 0.621 g (0.000954 mol) of bis(perfluorocyclohexylcarbonyl) peroxide, an initiator, in a mixed solution of 5.46 g (3M) and 46.3 g (AGC) of bis(perfluorocyclohexylcarbonyl) peroxide. This solution was then mixed with 234 g (0.955 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 724 g of 2,2,2-trifluoroethanol (Tosoh Finechem) as a polymerization solvent, and 51.4 g (0.431 mol, 18% by weight relative to the total amount of monomer and chain transfer agent) of chloroform (Fujifilm Wako Pure Chemical Industries) as a chain transfer agent. The mixture was then placed in an autoclave after removing dissolved oxygen and kept at 40°C for 24 hours under stirring to carry out precipitation polymerization. As a result, a cloudy slurry was obtained in which the resin precipitated in the polymerization solvent. The slurry was cooled to room temperature, the resulting resin particles were recovered by filtration, washed with acetone, and vacuum-dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 86%). Table 1 shows the results of measurements of the weight-average molecular weight Mw, molecular weight distribution Mw / Mn, and melt viscosity of the obtained resin. When no chain transfer agent is added, the molecular weight distribution of the obtained resin shows a multimodal pattern (Comparative Example 4 described later), but when a chain transfer agent is added, the resin obtained in this example shows a unimodal pattern.

[0053] [Comparative Example 1] A 3L SUS316 autoclave equipped with a paddle-type stirring blade, nitrogen inlet tube, and thermometer was purged with nitrogen. A solution of 3.04 g (0.000478 mol) of bis(perfluorocyclohexylcarbonyl) peroxide, an initiator, dissolved in 28.0 g of FC-72 (manufactured by 3M), 117 g (0.478 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, 424 g of Zeolora H as a polymerization solvent, and 13 g (0.109 mol, 10 wt% of the total amount of monomer and chain transfer agent) of chloroform (manufactured by Fujifilm Wako Pure Chemical Industries) as a chain transfer agent were added to the autoclave after removing dissolved oxygen, and precipitate polymerization was carried out by holding the mixture at 40°C for 24 hours under stirring. As a result, a cloudy slurry was obtained in which the resin precipitated in the polymerization solvent. The slurry was cooled to room temperature, the resulting resin particles were recovered by filtration, washed with acetone, and vacuum-dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 85%). The weight-average molecular weight Mw, molecular weight distribution Mw / Mn, and melt viscosity of the obtained resin are shown in Table 1.

[0054] [Comparative Example 2] A 30mm diameter glass ampoule equipped with a magnetic stirrer contained a solution of 0.255g (0.0000408 mol) of bis(perfluorocyclohexylcarbonyl) peroxide, the initiator, dissolved in 2.63g of FC-72 (3M), 10.0g (0.408 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as the monomer, 37.2g of hexafluoro-2-propanol (Fujifilm Wako Pure Chemical Industries) as the polymerization solvent, and 1.1g (0.00931 mol, 10% by weight of the total monomer and chain transfer agent) of chloroform (Fujifilm Wako Pure Chemical Industries) as a chain transfer agent. The ampoule was subjected to repeated nitrogen purging and depressurization by freeze-degassing, and then sealed under reduced pressure. Precipitation polymerization was carried out by holding the ampoule upright at 40°C for 24 hours while stirring with a magnetic stirrer. As a result, a cloudy slurry was obtained in which the resin precipitated in the polymerization solvent. After cooling the slurry to room temperature, the ampoule was opened, the liquid containing the generated resin particles was filtered off, washed with acetone, and vacuum dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 87%). The weight-average molecular weight Mw, molecular weight distribution Mw / Mn, and melt viscosity of the obtained resin are shown in Table 1.

[0055] [Comparative Example 3] A 30mm diameter glass ampoule equipped with a magnetic stirrer contained a mixed solution of 0.464g of FC-72 (manufactured by 3M) and 2.137g of AE-3000 (manufactured by AGC), in which 0.052g (0.0000800 mol) of bis(perfluorocyclohexylcarbonyl) peroxide, an initiator, was dissolved. 10.0g (0.0410 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) was added as the monomer, 36.2g of AE-3000 (manufactured by AGC) as the polymerization solvent, and 0.4167g (0.00349 mol, 4 wt%) of chloroform (manufactured by Fujifilm Wako Pure Chemical Industries) was added as a chain transfer agent. After repeated freezing, degassing, nitrogen purging, and pressure reduction, the ampoule was sealed under reduced pressure. Precipitative polymerization was carried out by holding the ampoule upright at 40°C for 24 hours while stirring with a magnetic stirrer. As a result, a cloudy slurry was obtained in which the resin precipitated in the polymerization solvent. After cooling the slurry to room temperature, the ampoule was opened, the liquid containing the generated resin particles was filtered off, washed with acetone, and vacuum dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 91%). The weight-average molecular weight Mw, molecular weight distribution Mw / Mn, and melt viscosity of the obtained resin are shown in Table 1.

[0056] [Comparative Example 4] A 30mm diameter glass ampoule equipped with a magnetic stirrer contained a solution of 0.255g (0.0000408 mol) of bis(perfluorocyclohexylcarbonyl) peroxide, an initiator, dissolved in 2.63g of FC-72 (manufactured by 3M), 10.0g (0.408 mol) of perfluoro(4-methyl-2-methylene-1,3-dioxolane) as a monomer, and 31.9g of 2,2,2-trifluoroethanol (manufactured by Tosoh Finechem Co., Ltd.) as a polymerization solvent. The ampoule was subjected to repeated nitrogen purging and pressure reduction by freeze-degassing, and then sealed under reduced pressure. Precipitation polymerization was carried out by holding the ampoule upright at 40°C for 24 hours while stirring with a magnetic stirrer. As a result, a cloudy slurry was obtained in which the resin precipitated in the polymerization solvent. After the slurry was cooled to room temperature, the ampoule was opened, the liquid containing the generated resin particles was filtered off, washed with acetone, and vacuum-dried to obtain powdered perfluoro(4-methyl-2-methylene-1,3-dioxolane) resin (yield: 84%). The weight-average molecular weight Mw, molecular weight distribution Mw / Mn, and melt viscosity of the obtained resin are shown in Table 1. [Table 1] [Industrial applicability]

[0057] This invention can be used in fields where fluororesins are melt-molded.

Claims

1. A method for producing a fluororesin containing a residue unit represented by the following general formula (1), The process includes polymerizing a monomer represented by the following general formula (2) in an organic solvent in the presence of a polymerization initiator and a chain transfer agent to obtain the fluororesin, The organic solvent is an organic solvent that contains a hydrogen atom, a fluorine atom, and an oxygen atom in its molecule, and the weight of the oxygen atom is 15 wt% or more. A method for producing a fluororesin, characterized in that the molecular weight distribution Mw / Mn of the fluororesin is 3.5 or more. 【Chemistry 1】 (In formula (1), Rf １ , Rf ２ , Rf ３ and Rf ４ Each of these independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms, and the perfluoroalkyl group may have an ether bond between any carbon-carbon bonds, Rf １ , Rf ２ , Rf ３ and Rf ４ Two or more of these groups may be linked together to form a ring with 4 to 8 carbon atoms. 【Chemistry 2】 (In formula (2), Rf ５ , Rf ６ , Rf ７ and Rf ８ each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms, and the perfluoroalkyl group may have an ether bond between any carbon-carbon bond, Rf ５ , Rf ６ , Rf ７ and Rf ８ two or more groups of may be linked to each other to form a ring having 4 to 8 carbon atoms.)

2. The method for producing a fluororesin according to claim 1, wherein the weight-average molecular weight Mw of the fluororesin is 50,000 to 300,000.

3. 260°C, frequency 10 －２ (rad.s －１ A method for producing a fluororesin according to claim 1, wherein the melt viscosity of the fluororesin in the ) is 400 Pa·s or less.

4. The method for producing a fluororesin according to claim 1, wherein the polymerization initiator is a radical polymerization initiator represented by the following general formula (3). 【Transformation 3】 (In equation (3), j is an integer between 3 and 20.)

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