JP2021155735A - Fluororesin and method for producing the same - Google Patents

Abstract

To provide a fluororesin having an oxolane ring, which is suppressed in yellowing after heating and melting and which is reduced in coloring especially in molding of a thick wall product.SOLUTION: Provided is a fluororesin which contains a residue unit represented by the following formula (1) and a terminal group formed of a specific perfluorinated C4-21 alicyclic hydrocarbon. (In formula (1), Rf1, Rf2, Rf3, and Rf4 each independently represent one selected from the group consisting of a fluorine atom, C1-7 linear perfluoroalkyl groups, C3-7 branched perfluoroalkyl groups, or C3-7 cyclic perfluoroalkyl groups. The perfluoroalkyl group may have an ethereal oxygen. Further, Rf1, Rf2, Rf3, and Rf4 may be linked to each other to form a C4-8 ring and the ring may be one containing an ethereal oxygen.)SELECTED DRAWING: None

Description

The present invention relates to a fluororesin and a method for producing the same.

Fluororesin is excellent in heat resistance, electrical characteristics, chemical resistance, waterproofness, liquid-repellent oil-repellent property, and optical characteristics, so it is a protective film for electronic parts such as semiconductors, a water-repellent film for inkjet printer heads, and waterproof protection for filters. It is used for oil coating, optical members, etc.

Among them, the fluororesin containing an oxorane ring is amorphous and has high transparency and high heat resistance because it has a bulky ring structure. In addition, it has high electrical properties, chemical resistance, waterproofness, and liquid-repellent oil-repellent properties because it is composed only of carbon, fluorine, and oxygen. Furthermore, since it is amorphous, it can be melt-molded.

Non-Patent Document 1 describes perfluoro-2-methylene-4-methyl-1,3-dioxolan (PFMMD), which is a kind of fluororesin containing an oxolan ring, and perfluorobenzoyl peroxide as a radical polymerization initiator. There is a description about the synthesis and properties of the polymer (poly PFMMD) obtained by polymerization using. Poly PFMMD has excellent heat resistance. According to the study by the present inventors, the poly PFMMD described in Non-Patent Document 1 has a remarkable yellowing after heat melt molding, and a particularly thick molded product has a remarkable yellowing. Therefore, there is an urgent need for a technique capable of exhibiting high transparency with less coloring even in a thick molded product of poly PFMMD.

As a method for reducing coloration of a fluororesin during heating, a method for obtaining a fluororesin having an aliphatic perfluoroalkyl group terminal by using an aliphatic total fluorine initiator is known. For example, Non-Patent Document 2 reports an example in which perfluoro (butenyl vinyl ether) is cyclized by bulk polymerization using _{(CF 3} CF ₂ CF ₂ COO) _2. However, according to the studies by the present inventors, it cannot be said that the yellowing of the poly PFMMD after heat melt molding is sufficiently reduced even if the technique described in Non-Patent Document 2 is used for the synthesis of the poly PFMMD. Met. In addition, the yield was extremely poor, the productivity was inferior, and the molecular weight distribution Mw / Mn was large.

Macromolecules 2005, 38, 4237-4245 Journal of the Japanese Society of Chemistry 2001, No. 12, 659-668

The present invention has been made for the purpose of solving a problem in a fluororesin containing an oxolane ring. Specifically, it is an object of the present invention to provide a fluororesin containing an oxorane ring in which yellowing after heating and melting is suppressed, particularly in which coloring is reduced even in molding of a thick-walled product, and a method for producing the same.

As a result of diligent studies, the present inventors have found that a fluororesin containing an oxolane ring having a terminal group having a specific structure can solve the above-mentioned problems, and have completed the present invention.

That is, the present invention is a fluororesin containing a residue unit represented by the following formula (1) and a terminal group represented by the following formula (2).

(In the formula (1), Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ are independently branched with a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, and 3 to 7 carbon atoms. It represents one of a group consisting of a perfluoroalkyl group having a shape or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ may be linked to each other to form a ring having 4 or more and 8 or less carbon atoms, and the ring may be a ring containing an etheric oxygen atom.)

(In equation (2), i is an integer of 3 to 20)

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a fluororesin containing an oxolane ring in which yellowing is suppressed during melt molding of a thick molded product, and a method for producing the same.

The fluororesin, which is one aspect of the present invention, will be described in detail below.

The fluororesin of the present invention contains a residue unit represented by the following formula (1) and a terminal group represented by the following formula (2).

(In the formula (1), Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ are independently fluorine atoms, linear perfluoroalkyl groups having 1 to 7 carbon atoms, and branched carbon atoms having 3 to 7 carbon atoms. It represents one of a group consisting of a perfluoroalkyl group or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an ethereal oxygen atom, and Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ may be linked to each other to form a ring having 4 or more and 8 or less carbon atoms, and the ring may be a ring containing an etheric oxygen atom.)

(In equation (2), i is an integer of 3 to 20)
Since the fluororesin of the present invention has a bulky ring structure contained in the specific formula (1), it is amorphous and has high transparency and high heat resistance. In addition, it has high electrical properties, chemical resistance, waterproofness, and liquid-repellent oil-repellent properties because it is composed only of carbon atoms, fluorine atoms, and oxygen atoms.

In the formula (1), Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ are independently branched with a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, and 3 to 7 carbon atoms. It represents one of a group consisting of a perfluoroalkyl group having a shape or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms. The perfluoroalkyl group may have an ethereal oxygen atom. Further, Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ may be linked to each other to form a ring having 4 or more and 8 or less carbon atoms, and the ring may be a ring containing an etheric oxygen atom.

Examples of the linear perfluoroalkyl group having 1 to 7 carbon atoms include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, a nonafluorobutyl group, an undecafluoropentyl group, and a tridecafluorohexyl group. Examples thereof include a pentadecafluoroheptyl group.

Examples of the branched perfluoroalkyl group having 3 to 7 carbon atoms include a heptafluoroisopropyl group, a nonafluoroisobutyl group, a nonafluorosec-butyl group, and a nonafluorotert-butyl group.

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

The etheric oxygen atom which may have a linear perfluoro alkyl group having 1 to 7 carbon atoms, _e.g., -CF 2 OCF _{3 group, - (CF 2) 2 OCF} 3 group, - (CF ₂ ) ₂ OCF ₂ CF ₃ units and the like.

Examples of the cyclic perfluoroalkyl group which may have an ethereal oxygen atom having 3 to 7 carbon atoms include 2- (2,3,3,4,4,5,5,6,6-decafluoro). ) -Pyrynyl group, 4- (2,3,3,4,5,5,6,6-decafluoro) -Pyrynyl group, 2- (2,3,3,4,5,5- Heptafluoro) -furanyl group and the like can be mentioned.

At _{least one of Rf 1} , Rf ₂ , Rf ₃ , and Rf ₄ is a linear perfluoroalkyl group having 1 to 7 carbon atoms, a branched perfluoroalkyl group having 3 to 7 carbon atoms, or a carbon number of carbon atoms. It is preferably a fluororesin which is one of a group consisting of 3 to 7 cyclic perfluoroalkyl groups. As a result, the fluororesin of the present invention exhibits more excellent heat resistance.

Specific examples of the residue unit represented by the formula (1) include the residue unit represented by the following formula (3).

Among these, a fluororesin containing a residue unit represented by the following formula (4) is preferable because of its excellent heat resistance and molding processability, and perfluoro (4-methyl-2-methylene-1,3-dioxolane). Fluororesin containing a residue unit is more preferable.

The fluororesin of the present invention contains a terminal group represented by the following formula (2). As a result, yellowing during melt molding of a thick molded product is suppressed.

Here, the "terminal group" means a group existing at the terminal portion of the main chain of the polymer.

The terminal group represented by the formula (2) preferably has a structure represented by the following formula (5).

It can be confirmed, for example, by the following method that the fluororesin of the present invention contains a terminal group unit represented by the formula (5).

That is, ^{when it is confirmed in the solid 19} F-NMR spectrum analysis of the fluororesin that the peaks showing the maximum are shown in the ranges of -140 ppm or more and 142 ppm or less and -143 ppm or more and 145 ppm or less, the fluororesin of the present invention is used. It can be determined that it has a terminal group represented by the formula (5). -140ppm above 142ppm or less, and a peak indicating the maximum in each 145ppm following range of -143ppm the 3-position of formula (5), 4, -CF ₂ 5-position - is assigned to group.

For the solid ¹⁹ F-NMR measurement of ^{the fluororesin, a general 19} F-NMR measuring device may be used. For example, using VNMRS-400 manufactured by Varian, using a magnetic field strength of 376.18 MHz (19F) and using a 1.6 mm FASTMAS probe, a pulse width of 1.3 μs, a spectrum width of 250 kHz (664.6 ppm), and a spectrum by the han-echo method. Center: -120 ppm, waiting time: 10 seconds, MAS rotation speed: 39 kHz, integration number 2048 times, solid ¹⁹ F-NMR measurement is performed using about 10 mg of fluororesin based on PTFE (-122.0 ppm). The method can be exemplified.

^{In the solid 19} F-NMR spectrum analysis of the fluororesin of the present invention, the integrated value of the area of the terminal peak (6F) due to the terminal group showing the maximum in the range of -140 ppm or more and 142 ppm or less and -143 ppm or more and 145 ppm or less is , The integrated value of the area of the main chain peak (5F) showing the maximum at the position of −81 ppm is preferably 0.001 to 10 in total, more preferably 0.01 to 5, and 0. It is more preferably .05-5. As a result, yellowing of the fluororesin is further suppressed. Here, the main chain peak (5F) showing the maximum at the position of −81 ppm is assigned to the _{−CF 2} O − group and the − CF _{3 group.}

The fact that the fluororesin of the present invention contains a residue unit represented by the formula (2) or the formula (5) can also be confirmed by ^{, for example, measuring the oligomer of the fluororesin by solid 13 C-NMR.} For example, in the manufacturing process, an oligomer or the like dissolved in a solvent such as Zeolola H is isolated, and the obtained oligomer is subjected to solid ¹³ C-NMR measurement. At this time, if a peak showing a maximum in the range of 90 to 92 ppm derived from the F atom at the 1-position of the perfluorocycloalkyl group directly bonded to the residue unit represented by the formula (1) is observed, fluorine It can be confirmed that the resin contains a terminal group represented by the formula (2) or the formula (5).

It is preferable that the terminal group represented by the formula (2) or the formula (5) is directly bonded to the residue unit represented by the general formula (1) without interposing other functional groups. Further, it is preferable that the fluororesin of the present invention does not contain a carbonyl group.

Fluororesin of the present invention preferably has a weight average molecular weight Mw is in the range of ^{5 × 10 4 ~3 × 10 5} . When the weight average molecular weight Mw is in this range, the melt molding processability and the defoaming property at the time of melting are excellent. Further, when the weight average molecular weight Mw is in this range, cracks are less likely to occur during heating and cooling. Fluororesin of the present invention is excellent in melt-moldability, it is preferable from the viewpoint of excellent defoaming during melting, more preferably in the range of weight average molecular weight Mw of ^{5 × 10 4 ~2 × 10 5} .

The weight average molecular weight Mw of the fluororesin of the present invention can dissolve, for example, standard polymethyl methacrylate having a known molecular weight as a standard sample and both the standard sample and the fluororesin as an eluent using gel permission chromatography (GPC). It can be calculated from the elution time of the sample and the standard sample and the molecular weight of the standard sample using a solvent. As the solution, asahiclean AK-225 (manufactured by Asahi Glass Co., Ltd.) and 10 wt% of 1,1,1,3,3,3-hexafluoro-2-propanol (Wako Pure Chemical Industries, Ltd.) with respect to AK-225. An industrial product) is added.

The molecular weight distribution Mw / Mn, which is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn of the fluororesin of the present invention, is not particularly limited, but yellowing after heating and melting is suppressed, excellent melt molding processability, and melting. The molecular weight distribution Mw / Mn is preferably 1.2 to 8, and more preferably 1.2 to 5, from the viewpoint of excellent defoaming property at the time and less crack generation during heating and cooling. , 1.5 to 3, more preferably 2.0 to 3. The number average molecular weight Mn can be measured by the same method as the above-mentioned method for measuring the weight average molecular weight Mw, and the molecular weight distribution Mw / Mn can be calculated by dividing the weight average molecular weight Mw by the number average molecular weight Mn.

The fluororesin of the present invention has a yellowness (YI) of 10 measured in the diameter direction of a thick melt-molded product (a columnar molded body having a diameter of 10 mm and a height of about 17 mm, which is molded by heating and melting at 280 ° C. for 24 hours in a test tube). It is preferably less than or equal to, more preferably 4 or less, still more preferably 3 or less. According to the present inventors, when melt molding of a thick molded product is performed in a closed state, yellowing of the fluororesin after heat melt molding becomes remarkable as compared with heating in an open environment. As a method for evaluating the yellowness and coloring of a melt-molded product of a thick molded product, for example, it is obtained by melting and molding 3 g of the fluororesin of the present invention by heating it at 280 ° C. for 24 hours in a test tube having an outer diameter of 13 mm. A method of evaluating the yellowness (YI) of a cylindrical body (diameter 10 mm × height about 17 mm) measured in the radial direction can be mentioned. Here, the radial direction is the vertical direction when the test tube is laid down sideways on a desk or the like. With the obtained resin molded product in the test tube, the test tube is laid on its side on white paper, a digital photograph is taken from above, and the obtained image is used as a software to determine the yellowness of the molded product. The RGB value is read, and the read RGB value is calculated by the following formula X = 0.4124R + 0.3576G + 0.1805B.
Y = 0.2126R + 0.7152G + 0.0722B
Z = 0.0193R + 0.1192G + 0.9505B
The tristimulus values X, Y, and Z of the XYZ color system are obtained from X, Y, and Z, and the yellowness (YI) at the C light source (auxiliary illuminant C) is calculated according to the method of JIS K7373. be able to.

The fluororesin of the present invention preferably has a yellowness (YI) of 1 or less in a flaky melt-molded product (thickness of 3 mm, molded by heating and melting at 280 ° C. for 24 hours in a petri dish). Examples of the molding method and the evaluation method include the methods described in Examples.

The fluororesin of the present invention may contain other monomer residue units, and examples of the other monomer residue units include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and chlorotri. Fluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutylene, perfluoroalkylethylene, fluorovinyl ether, vinyl fluoride (VF), vinylidene fluoride (VDF), perfluoro-2,2-dimethyl-1,3-dioxol (PDD), perfluoro (allyl vinyl ether), perfluoro (butenyl vinyl ether) and the like.

The particle size of the fluororesin of the present invention is not particularly limited, but the fluidity of the resin powder is high, continuous supply to a molding machine or the like is possible, residual solvent can be suppressed in the resin, and the bulk density is large. The volume average particle size is preferably 1 to 1000 μm, preferably 1 to 500 μm, and even more preferably 1 to 300 μm, because the filling property is increased and the handleability during molding is excellent. ..

The volume average particle size of the fluororesin of the present invention can be evaluated by measuring the particle size distribution (volume distribution) by the laser diffraction / scattering method. The particle size distribution by the laser diffraction / scattering method can be measured by dispersing the resin particles in water or an organic solvent such as methanol. As a laser scatterometer, a microtrack manufactured by Microtrack Bell Co., Ltd. can be exemplified.

The volume average particle size is also called a Mean Volume Diameter, which is an average particle size expressed on a volume basis. The particle size distribution is divided for each particle size channel, and the representative particle size value of each particle size channel is d, each. It is represented by Σ (vd) / Σ (v), where v is the volume-based percentage for each particle size channel.

The fluororesin of the present invention is preferably in the form of powder and has a volume average particle size of 1 to 1000 μm.

The method for producing a fluororesin, which is one aspect of the present invention, will be described in detail below.

The fluororesin of the present invention can be produced by polymerizing a mixture containing a radical polymerization initiator represented by the following formula (6) and a monomer represented by the following formula (7).

(In equation (6), j is an integer of 3 to 20)

(In the formula (7), Rf ₅ , Rf ₆ , Rf ₇ , and Rf ₈ are independently fluorine atoms, linear perfluoroalkyl groups having 1 to 7 carbon atoms, and branched forms having 3 to 7 carbon atoms, respectively. The perfluoroalkyl group is one of a group consisting of a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf ₅ , Rf ₆ , Rf ₇ , and Rf ₈ may be linked to each other to form a ring having 4 or more and 8 or less carbon atoms, and the ring may be a ring containing an etheric oxygen atom.)
Rf ₅ , Rf ₆ , Rf ₇ , and Rf ₈ in the formula (7) are synonymous with _{Rf 1} , Rf ₂ , Rf ₃ , and Rf ₄ in the formula (1), respectively.

In the method for producing a fluororesin of the present invention, a radical polymerization initiator represented by the formula (6) is used to obtain a fluororesin in which yellowing is suppressed during melt molding of a thick molded product. be able to. Further, a fluororesin having a narrow molecular weight distribution Mw / Mn can be obtained. By narrowing the molecular weight distribution Mw / Mn, the heat melt moldability is improved. Further, the fluororesin can be obtained with excellent yield and productivity. Further, by using the radical polymerization initiator represented by the formula (6), the radical polymerization initiator is decarbonated and then added to the polymer, so that the obtained polymer contains almost no carbonyl group. The structure in which the terminal group represented by (2) is directly added to the polymer is advantageous in obtaining a fluororesin in which yellowing is suppressed during melt molding of a thick molded product.

In the method for producing a fluororesin of the present invention, it is more preferable to use a radical polymerization initiator represented by the following formula (8). By using the radical polymerization initiator represented by the following formula (8), it is possible to obtain a fluororesin in which yellowing during melt molding of a thick molded product is further suppressed. Further, a fluororesin having a narrow molecular weight distribution Mw / Mn can be obtained. By narrowing the molecular weight distribution Mw / Mn, the heat melt moldability is improved. Further, the fluororesin can be obtained with excellent yield and productivity. In the present specification, the radical polymerization initiator represented by the following formula (8) may be referred to as bis (perfluorocyclohexylcarbonyl) peroxide.

Bis (perfluorocyclohexylcarbonyl) peroxide is available from JP-A-11-49749 and J. Am. App. Polym. It can be obtained by the method described in Sci, 1999, 72, 1101-1108. At that time, as the solvent, perfluorohexane (FC-72, manufactured by 3M Japan Ltd.) or the like can be used instead of AK-225. The bis (perfluorocyclohexylcarbonyl) peroxide of the present invention may be synthesized by a method other than the methods described in the above-mentioned documents. For example, Chem. Rev, 1996, 96, 1779-1808 describes a method for synthesizing fluorinated peroxide. In addition to a method for reacting acid fluoride with hydrogen peroxide, a method for reacting acid chloride with hydrogen peroxide, acid anhydrous. Examples thereof include a method of reacting an object with hydrogen peroxide. At that time, the reaction proceeds due to the presence of a base such as sodium hydroxide in the system.

In the method for producing a fluororesin of the present invention, a chain transfer agent may be used for the purpose of adjusting the molecular weight. Examples of the chain transfer agent include organic compounds having 1 to 20 carbon atoms containing at least one atom selected from the group consisting of hydrogen atoms and chlorine atoms. Specific examples of the chain transfer agent include organic compounds having 1 to 20 carbon atoms containing hydrogen atoms such as toluene, acetone, ethyl acetate, tetrahydrofuran, methyl ethyl ketone, methanol, ethanol and isopropanol; chloroform, dichloromethane, tetrachloromethane and chloro. Examples thereof include organic compounds having 1 to 20 carbon atoms containing chlorine atoms such as methane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, hexachloroethane, benzyl chloride, pentafluorobenzyl chloride, and pentafluorobenzoyl chloride. Among them, an organic compound having 1 to 20 carbon atoms containing a chlorine atom is preferable from the viewpoint of suppressing yellowing after heating and melting, and an organic compound having 1 to 20 carbon atoms containing a hydrogen atom and a chlorine atom is preferable. More preferred. The amount of the chain transfer agent is, for example, 0.01 to 50% by weight based on the total amount of the monomer and the chain transfer agent.

In the method for producing a resin of the present invention, the polymerization method is not limited, and examples thereof include methods such as solution polymerization, precipitation polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization.

In the production method of the present invention, it is preferable to further mix an organic solvent with the mixture in the step of polymerizing.

In the method for producing a resin of the present invention, the fluidity of the resin powder is high, continuous supply to a molding machine or the like is possible, residual solvent can be suppressed in the resin, bulk density is large, and filling property is increased. Since a powder having excellent handleability during molding can be obtained, at least the monomer represented by the formula (7) is dissolved as an organic solvent, and at least a part of the resin produced by the polymerization is not dissolved. It is an organic solvent that causes precipitation of the resin, and it is preferable to use an organic solvent that precipitates in the organic solvent as particles of the resin produced by the polymerization. In the method for producing a resin of the present invention, the organic solvent may be referred to as a "precipitation polymerization solvent". By using the precipitation polymerization solvent, the resin produced by the polymerization reaction can be precipitated as particles having a specific volume average particle size, and as a result, resin particles having excellent moldability and filling property can be produced. .. Further, since a polymerization aid such as an emulsifier and a dispersant is not used, resin particles that do not contain an emulsifier and a dispersant that cause a decrease in transparency and heat resistance can be produced.

Here, the precipitation polymerization solvent means a solvent in which the resin particles remaining after the resin particles containing the residue unit represented by the formula (1) are immersed in the organic solvent for a long time. Specifically, a resin particle having a weight average molecular weight Mw of 5 × 10 ⁴ to 70 × 10 ⁴ including a residue unit represented by 1 is 10 times as much (w / w) as that of the resin particle. When the resin particles can be visually confirmed in the organic solvent after being immersed in the organic solvent at 50 ° C. for 5 hours or more, the organic solvent can be regarded as the precipitation polymerization solvent A. The precipitation polymerization solvent A is 50. The resin is preferably an organic solvent in which the solution is cooled to 25 ° C. after being immersed at ° C. for 5 hours or more, the resin sample remaining in a solid state is recovered, and the weight loss rate of the resin sample is less than 20% by weight. The weight loss rate of the sample is more preferably less than 12% by weight, still more preferably less than 10% by weight.

The rate of decrease in resin weight can be measured by the following method. After filtering the above cooled solution with a filter, the solid on the filter is rinsed with the solvent, washed with acetone a plurality of times, and then dried to collect the resin sample on the filter. The weight of the recovered resin is measured, and the value obtained by subtracting the weight of the recovered resin from the amount of resin immersed in the organic solvent is divided by the amount of resin immersed in the organic solvent. do.

Examples of the precipitation polymerization solvent include non-halogen organic solvents such as acetone, methyl ethyl ketone, hexane and butyl acetate, chlorine organic solvents such as dichloromethane and chloroform, and organic solvents containing a fluorine atom in the molecule.

Further, as the precipitation polymerization solvent, an organic solvent containing a fluorine atom and a hydrogen atom in the molecule is preferable because a chain transfer reaction is unlikely to occur in radical polymerization, the polymerization yield is excellent, and a high molecular weight compound can be easily obtained. Specific examples of the precipitation polymerization solvent containing a fluorine atom and a hydrogen atom in the molecule include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 2,2,2-tri. Fluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, 1,2,2,3,3,4,4-heptafluorocyclopentane, 1H, 1H-pentafluoropropanol, 1H, 1H- Heptafluorobutanol, 2-perfluorobutylethanol, 4,4,4-trifluorobutanol, 1H, 1H, 3H-tetrafluoropropanol, 1H, 1H, 5H-octafluoropropanol, 1H, 1H, 7H-dodecafluorohepta Nord, 1H, 1H, 3H-hexafluorobutanol, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2 -Tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropylmethyl ether , 1,1,3,3,3-pentafluoro-2-trifluoromethylpropylmethyl ether, 1,1,2,3,3,3-hexafluoropropylmethyl ether, 1,1,2,3,3 , 3-Hexafluoropropyl ethyl ether, 2,2,3,4,5,4-hexafluorobutyldifluoromethyl ether and the like.

Among them, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoro Isopropanol and 1,2,2,3,3,4,4-heptafluorocyclopentane are preferable, and since the polymerization yield is excellent and a high molecular weight substance can be easily obtained, 1,2,2,3,3,4. 4-Heptafluorocyclopentane is preferred. The ratio of fluorine atoms to hydrogen atoms in the molecule of the precipitation polymerization solvent is preferably fluorine atoms: hydrogen atoms = 1: 9 to 9: 1 in terms of the number of atoms, because the polymerization yield is excellent. It is more preferably 9 to 7: 3, and even more preferably 4: 6 to 7: 3. The precipitation polymerization solvent preferably contains a fluorine atom and a hydrogen atom in the molecule because of its excellent polymerization yield, and the content of the hydrogen atom in the solvent is preferably 1% by weight or more based on the weight of the solvent molecule. 5% by weight or more is more preferable. Further, since the polymerization yield is excellent and a high molecular weight substance can be easily obtained, 1% by weight or more and 5% by weight or less is preferable, and 1.5% by weight or more and 4% by weight or less is preferable. Further, as the precipitation polymerization solvent, a solvent containing no chlorine atom in the molecule is preferable because the polymerization yield is excellent and a high molecular weight compound can be easily obtained.

As the ratio of the monomer represented by the formula (7) to the precipitation polymerization solvent, particles having excellent productivity and excellent flow characteristics can be obtained. Therefore, in terms of weight ratio, monomer: precipitation polymerization solvent = 1: 99. It is preferably ~ 50:50, more preferably 5:95 to 40:60, and even more preferably 5:95 to 30:70.

In the production method of the present invention, the monomer represented by the formula (7) is perfluoro (4-methyl-2-methylene-1,3-dioxolane) represented by the following formula (9), and the formula ( It is preferable that the residue unit represented by 1) is a perfluoro (4-methyl-2-methylene-1,3-dioxolane) residue unit represented by the formula (4).

By producing by the method of the present invention, it is possible to obtain a fluororesin in which yellowing is suppressed during melt molding of a thick molded product. Further, it is possible to obtain a fluororesin having a narrow molecular weight distribution Mw / Mn while exhibiting the above characteristics. Further, the fluororesin can be obtained with excellent yield and productivity while exhibiting the above characteristics.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Measurement of weight average molecular weight Mw and molecular weight distribution Mw / Mn]
Measurements were performed using a column TSKgel SuperHZM-M manufactured by Tosoh Corporation and gel permission chromatography equipped with an RI detector. As an eluent, Asahiclean AK-225 (manufactured by Asahi Glass Co., Ltd.) and 1,1,1,3,3,3-hexafluoro-2-propanol (manufactured by Wako Pure Chemical Industries, Ltd.) in an amount of 10 wt% based on AK-225. Was used. Using standard polymethyl methacrylate manufactured by Agilent as a standard sample, the weight average molecular weight Mw and the molecular weight distribution Mw / Mn in terms of polymethyl methacrylate were calculated from the elution times of the sample and the standard sample.

[ ^{Measurement of solid 19} F-NMR]
Varian VNMRS-400, magnetic field strength 376.18 MHz (19F), 1.6 mm FASTMAS probe, hann-echo method, pulse width 1.3 μs, spectrum width 250 kHz (664.6 ppm), spectral center: ^{Solid 19} F-NMR measurement was carried out using about 10 mg of fluororesin based on PTFE (-122.0 ppm) at −120 ppm, waiting time: 10 seconds, MAS rotation speed: 39 kHz, and integration number of 2048 times.

[ ^{Measurement of solid 13} C-NMR]
Varian VNMRS-400 with magnetic field strength of 100.55 MHz (13C), 4.0 mm MAS probe, CP / MAS method, spectral width 30.5 kz, spectral center: 77.5 ppm, waiting time: 3 seconds. , MAS rotation speed: 10 kHz, integration number 4096 times, solid ¹³ C-NMR measurement was carried out using about 50 mg of fluororesin based on TMS (0 ppm).

[Measurement of yellowness (YI) of thick melt molded product (φ10 mm × H17 mm, in vitro 280 ° C. 24 h)]
Put 3.0 g of fluororesin in a glass test tube (made by Nichiden Rika Glass, ST-13M) with an outer diameter of φ13 mm and a total length of 100 mm, and cover the mouth of the test tube with aluminum foil and an aluminum cap (Maruem, M-1). A columnar resin molded product was obtained in the test tube by standing it on a test tube rack, placing it in an oven, heating it at 280 ° C. for 24 hours, and then allowing it to cool (diameter: 10 mm, height: about 17 mm). With the obtained resin molded product in the test tube, place the test tube sideways on white paper and take a digital photograph from above under a white fluorescent lamp using the PowerShotSX620HS (manufactured by Canon Inc.). , The RGB value of the molded product was read from the obtained image using Paint (image processing software manufactured by Microsoft Corporation). The read RGB value is calculated by the following formula X = 0.4124R + 0.3576G + 0.1805B
Y = 0.2126R + 0.7152G + 0.0722B
Z = 0.0193R + 0.1192G + 0.9505B
The tristimulus values X, Y, and Z of the XYZ color system were obtained from the above. From X, Y, Z, the yellowness (YI) of the C light source (auxiliary illuminant C) was calculated according to the method of JIS K7373, and the yellowness (φ10 mm × H17 mm, in vitro 280 ° C. 24 h) of the thick melt molded product (φ10 mm × H17 mm, in vitro 280 ° C. 24 h) was calculated. YI) was asked.

[Yellowness (YI) of flaky melt molded product (3 mm thick, 280 ° C. 24 h in petri dish)]
Weigh 2.0 g of fluororesin into a petri dish with an inner diameter of 26.4 mm (only the receiver of the flat petri dish lid and receiver set made by Flat Co., Ltd., the glass thickness at the bottom of the receiver is 1 mm), and inert oven (Yamato Scientific Co., Ltd.) The product was placed in a DN411I), allowed to stand at room temperature for 30 minutes under an air stream (20 L / min), heated to 280 ° C. over 30 minutes, and then heated at 280 ° C. for 24 hours. After that, while maintaining the air flow (20 L / min), keep the oven door closed, turn off the power of the inert oven, allow it to cool for 12 hours, and then take out the sample to make it 3 mm thick on the petri dish. A fluororesin heat-melt molded product having a diameter of 26.4 mm was obtained. At this time, as the air, air compressed by a compressor was passed through a dehumidifier (dew point temperature −20 ° C. or lower). The obtained fluororesin heat-melt molded product was measured for each petri dish using a spectrophotometer (U-4100 manufactured by Hitachi High-Tech Science Co., Ltd.) at wavelengths of 200 nm to 1500 nm at 1 nm intervals. Data at 5 nm intervals at wavelengths of 380 nm to 780 nm were extracted from the measured transmittance data, and the tristimulus values X, Y, and Z of the XYZ color system were calculated according to the method of JIS Z8701. Further, according to the method of JIS K7373, the yellowness (YI) of the C light source (auxiliary illuminant C) was calculated, and the yellowness (YI) of the fluororesin heat-melt molded product including the petri dish was obtained. By measuring the yellowness (YI) of the petri dish (receiver only) and subtracting the yellowness (YI) of the petri dish (receiver only) from the yellowness (YI) of the fluororesin molded product including the petri dish, the thickness is increased. The yellowness (YI) of a 3 mm fluororesin heat-melt molded product was determined. The yellowness (YI) of the petri dish alone (receiver only) was 0.21.

[Measurement of volume average particle size]
The volume average particle size (unit: μm) was measured using Microtrac MT3000 manufactured by Microtrac Bell Co., Ltd. and metall as a dispersion medium.

[Example 1]
The inside of a 3 L SUS316 autoclave equipped with a paddle-type stirring blade, a nitrogen introduction tube and a thermometer was replaced with nitrogen. A solution of 2.33 g (0.0036 mol) of bis (perfluorocyclohexylcarbonyl) peroxide as an initiator dissolved in FC-72 (perfluorohexane manufactured by 3M Japan): 230 g, perfluoro as a monomer. (4-Methyl-2-methylene-1,3-dioxolane): 175 g (0.72 mol), FC-72: 470 g as a polymerization solvent was placed in an autoclave after removing dissolved oxygen, and 24 at 55 ° C. under stirring. Solution polymerization was carried out by holding for a long time to obtain a viscous liquid in which the resin was dissolved. After cooling to room temperature, the ampoule was opened, and the resin solution obtained for viscosity adjustment was added to FC-72: 875 g and diluted to prepare a resin diluted solution. In a plastic cup equipped with a stirring blade, Zeolara H (manufactured by Zeon Corporation, 1,2,2,3,3,4,4-heptafluorocyclopentane, content of hydrogen atom in solvent molecule: 1.55 weight) %, Fluorine atom in solvent molecule: Hydrogen atom = 7: 3 (number ratio)) 5250 g was added, and the resin was precipitated by adding the above resin diluted solution to a plastic cup under stirring. The precipitated resin was recovered by filtration, washed with acetone twice, and vacuum dried to obtain a powdered perfluoro (4-methyl-2-methylene-1,3-dioxolane) resin (yield). Rate: 93%).

The weight average molecular weight of the obtained fluororesin 9.5 × 10 ^4, a molecular weight distribution Mw / Mn was 3.74. Table 1 shows the evaluation results of the fluororesin.

^{As a result of solid 19} F-NMR measurement on the obtained fluororesin, peaks derived from the terminal perfluorocyclohexyl group were confirmed at -140.7 ppm and -143.9 ppm. The integral value of the peak (6F) derived from the terminal group was 1.46 in total, while the integral value of the main chain peak (5F) of -81.3 ppm was 500.

Further, the filtrate obtained by precipitating the resin with Zeolola H during the above operation was dried to dryness, and the solid was washed with acetone and vacuum dried to obtain an oligomer.

^{As a result of solid 13} C-NMR measurement of the obtained oligomer, a peak derived from the F atom at the 1-position of the perfluorocyclohexyl group directly bonded to the end of the polymer was confirmed at 91 ppm. On the other hand, no peak was observed in the carbonyl group region at 130 to 150 ppm.

[Example 2]
The inside of a 3 L SUS316 autoclave equipped with a paddle-type stirring blade, a nitrogen introduction tube and a thermometer was replaced with nitrogen.

A solution prepared by dissolving 0.80 g (0.0012 mol) of bis (perfluorocyclohexylcarbonyl) peroxide as an initiator in FC-72: 80 g, and perfluoro (4-methyl-2-methylene-1, 4-methyl-2-methylene-1, as a monomer. 3-Dioxolan): 300 g (1.23 mol), Zeolola-H: 1120 g as a polymerization solvent, chloroform as a chain transfer agent (manufactured by Wako Pure Chemical Industries, Ltd.): 33.33 g (0.279 mol, amount of chain transfer agent: simple (10% by weight based on the total of the monomer and the chain transfer agent) is placed in an autoclave after removing the dissolved oxygen, and the mixture is held at 40 ° C. for 24 hours under stirring to carry out precipitation polymerization. A slurry precipitated in the above was obtained. The slurry is cooled to room temperature, the produced resin particles are collected by filtration, washed with acetone, and vacuum dried to obtain a powdered perfluoro (4-methyl-2-methylene-1,3-dioxolane) resin. Obtained (yield: 90%).

The weight average molecular weight of the obtained fluororesin was 8.8 × 10 ⁴ , and the molecular weight distribution Mw / Mn was 2.48. Further, the volume average particle size of the obtained fluororesin was 26 μm, which was excellent in the fluidity of the powder, and was more excellent in the fluidity of the powder than in Example 1.

[Example 3]
^{As a result of solid 19} F-NMR measurement of the fluororesin obtained in Example 2, peaks derived from the terminal perfluorocyclohexyl group were confirmed at -140.2 ppm and -144.4 ppm. The integral value of the peak (6F) derived from the terminal group was 0.23 in total, while the integral value of the main chain peak (5F) of -81.3 ppm was 500.

[Comparative Example 1]
Bis (2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator in a glass ampoule having a capacity of 75 mL: 0.173 g (0.000410 mol), perfluoro (4-methyl-2) as a monomer -Methylene-1,3-dioxolane): 10.0 g (0.0410 mol) and FC-72: 40.0 g as a polymerization solvent were added, and after repeating nitrogen substitution and depressurization by freeze degassing, the mixture was melted under reduced pressure. Sealed (monomer / solvent = 20/80 (wt / wt)). This ampoule was placed in a constant temperature bath at 55 ° C. and held for 24 hours to carry out radical solution polymerization to obtain a viscous liquid in which the resin was dissolved. After cooling to room temperature, the ampoule was opened, and the obtained resin solution was added to FC-72: 50 g for viscosity adjustment and diluted to prepare a resin diluted solution. Zeolola H: 240 g was placed in a beaker equipped with a stirrer, and the resin was precipitated by adding the above resin dilution solution to the beaker under stirring. The precipitated resin was recovered by filtration, washed with acetone twice, and dried in vacuum to obtain a massive perfluoro (4-methyl-2-methylene-1,3-dioxolane) resin (yield). 94%).

The weight average molecular weight of the obtained fluororesin 21 × 10 ^4, molecular weight distribution Mw / Mn was 2.8. Further, the obtained fluororesin was in the form of a lump and was inferior in the fluidity of the powder. Table 1 shows the evaluation results of the fluororesin.

When the solid ¹⁹ F-NMR measurement of the fluororesin was carried out, peaks showing maximums were not detected at -140 to 142 ppm and -143 to 145 ppm. The filtrate obtained by precipitating the resin on Zeolola H was dried by the above operation, the solid was washed with acetone, vacuum dried, and the obtained oligomer was ^{measured by solid 13} C-NMR. As a result, a peak was confirmed in the region of 80 to 100 ppm. Was not done. In addition, carbonyl group peaks were detected at 139 ppm and 143 ppm.

[Comparative Example 2]
A glass amplifier with a diameter of 30 mm equipped with a magnetic stirrer, bis (2,3,4,5,6-pentafluorobenzoyl) peroxide as an initiator: 0.0865 g (0.000205 mol), perfluoro as a monomer (4-Methyl-2-methylene-1,3-dioxolane): 10.0 g (0.0205 mol), Zeolola-H (manufactured by Nippon Zeon, 1, 2, 2, 3, 3, 4, 4) as a polymerization solvent -Heptafluorocyclopentane): 40.0 g, chloroform (manufactured by Wako Pure Chemical Industries, Ltd.): 1.111 g (0.00931 mol) as a chain transfer agent, and after repeating nitrogen substitution and depressurization by freeze degassing, the pressure is reduced. (Amount of chain transfer agent: 10% by weight based on the total of monomer and chain transfer agent). Precipitation polymerization was carried out by holding the magnetic stirrer at 55 ° C. for 24 hours while stirring the magnetic stirrer in an upright state, and a slurry was obtained in which the resin became cloudy and the resin was precipitated in the polymerization solvent. After cooling to room temperature, the ampoule is opened, the liquid containing the produced resin particles is filtered off, washed with acetone, and vacuum dried to form particulate perfluoro (4-methyl-2-methylene-1,3-dioxolane). ) Resin was obtained (yield: 82%).

The weight average molecular weight of the obtained fluororesin 9.6 × 10 ^4, a molecular weight distribution Mw / Mn was 2.6.

[Comparative Example 3]
_{A solution obtained by diluting (CF 3} CF ₂ CF ₂ COO) ₂ : 0.52 g (0.0012 mol) with FC-72: 52 g as an initiator in a glass ampoule having a capacity of 75 mL, and perfluoro (4-methyl) as a monomer. -2-Methylene-1,3-dioxolane): 30.0 g (0.12 mol) was added, and after repeating nitrogen substitution and depressurization by freeze degassing, the mixture was sealed under reduced pressure. Radical polymerization was carried out by holding this ampoule at 25 ° C. for 24 hours. The ampoule is opened, the contents are placed in a beaker containing 600 g of hexane under stirring, the solid is collected by filtration, washed twice with acetone, and vacuum dried to obtain a massive perfluoro (4-methyl-2). -Methylene-1,3-dioxolane) resin was obtained (yield 18%). Table 1 shows the evaluation results of the fluororesin. The weight average molecular weight of the obtained fluororesin 86 × 10 ^4, a molecular weight distribution Mw / Mn was 26.2. The yield was very low and the molecular weight distribution was very large.

[Comparative Example 4]
Perfluoro (4-methyl-2-methylene-1,3-dioxolane): 4.8 g (0.020 mol) as a monomer in a glass tube for polymerization equipped with a stirrer, and dichloropentafluoropropane (AGC) as a solvent. company Ltd., AK-225): 3mL, ammonium perfluorooctanoate as an _{emulsifier: 0.21g, Na 2 HPO 4 ·} 7H 2 O as a pH adjusting agent: 0.24 g, as an initiator _{(NH 4) 2 S} 2 O _8: 0.15 g, and distilled water was degassed with _{N 2} as a solvent was charged with 50 mL. After the headspace present above the solution was purged with N _2, it was N ₂ slight pressure state. Next, the contents of this tube were heated at 75 ° C. for 5 hours while stirring with a stir bar. The resulting reaction mixture was treated with aqueous HCl (6.3M): 80 mL to precipitate the polymer. The polymer was washed 3 times with 200 mL of distilled water and then 3 times with 200 mL of acetone. Next, this polymer was placed in a vacuum oven and dried under vacuum (150 mmHg) at 150 ° C. for 24 hours to obtain a white powdery polymer (yield: 3%). The above-mentioned operation from polymerization to drying was separately performed twice more, and the obtained polymers were mixed to obtain a polymer for evaluation. The evaluation results of the obtained polymer are shown in Table 2. The weight average molecular weight of the obtained fluororesin was 34 × 10 ⁴ , and the molecular weight distribution Mw / Mn was 25. The yield was very low and the molecular weight distribution was very large. When the solid ¹⁹ F-NMR measurement of the fluororesin was carried out, peaks showing maximums were not detected at -140 to 142 ppm and -143 to 145 ppm.

[Comparative Example 5]
Perfluoro (4-methyl-2-methylene-1,3-dioxolane): 10.0 g (0.041 mol) as a monomer, AK-225: 35 g as a solvent, and 4 as an initiator in a glass ampoule having a capacity of 75 mL. , 4-Bis (t-butylcyclohexyl) peroxydicarbonate (manufactured by NOF, perloyl TCP): 0.02 g was charged. After repeating nitrogen replacement and depressurization by freezing and degassing, the mixture was sealed under reduced pressure. The ampoule was heated in a constant temperature shaker at 60 ° C. for 3 hours under shaking. The polymer taken out from this ampoule was dried under vacuum (150 mmHg) at 100 ° C. for 24 hours to obtain a polymer (yield: 76%). The above-mentioned operation from polymerization to drying was separately performed twice more, and the obtained polymers were mixed to obtain a polymer for evaluation. The evaluation results of the obtained polymer are shown in Table 2. The weight average molecular weight of the obtained fluororesin 12 × 10 ^4, a molecular weight distribution Mw / Mn was 1.8. When the solid ¹⁹ F-NMR measurement of the fluororesin was carried out, peaks showing maximums were not detected at -140 to 142 ppm and -143 to 145 ppm.

[Comparative Example 6]
^{When the solid 19} F-NMR measurement of the fluororesin obtained in Comparative Example 2 was carried out, peaks showing maximums were not detected at −140 to 142 ppm and 143 to 145 ppm.

[Comparative Example 7]
^{When the solid 19} F-NMR measurement of the fluororesin obtained in Comparative Example 3 was carried out, peaks showing maximums were not detected at −140 to 142 ppm and 143 to 145 ppm.

[Reference example 1]
The resin particles obtained in Example 2 were immersed in 10 times the amount of various solvents at 50 ° C. for 5 hours, and it was visually observed whether the resin particles remained.

-The organic solvents in which the residual resin particles were confirmed with the naked eye are as follows:
1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoroisopropanol, 1 , 2,2,3,3,4,5-heptafluorocyclopentane, chloroform.

Then, the mixture was cooled to 25 ° C., filtered through a filter, rinsed with the solvent to remove the resin particles, washed twice with 10 times the amount of acetone, vacuum dried, and recovered from the dry weight. The recovery rate was 90% or more in each case. Further, when the filtrate obtained above was distilled off and the solid content in the filtrate was determined, the solid content in the filtrate was less than 10% with respect to the resin particles used. From the above results, it was confirmed that the weight reduction rate of the resin weight was less than 10% by weight.

As shown in Examples 1 and 2, the fluororesin of the present invention has a smaller yellowness and a thicker molding of a thick melt molded product (φ10 mm × H17 mm, in a test tube at 280 ° C. 24 h) as compared with Comparative Examples 1 to 2. Yellowing is suppressed even in the body.

The method for producing a fluororesin of the present invention has a higher yield than the method of Comparative Example 3, and as shown in Examples 1 and 2, the fluororesin can be produced in a yield of 80% or more. Depending on the yield, the fluororesin can be produced in a yield of 85% or more, further 90% or more.

The fluororesin obtained by the method for producing a fluororesin of the present invention has improved yellowness of a product heated at 280 ° C. for 24 hours in a test tube, has a narrower molecular weight distribution than the method of Comparative Example 3, and has a molecular weight distribution of Mw / Mn. Fluororesin of 5 or less, 4 or less depending on the conditions, and further 3 or less can be produced.

The fluororesin of the present invention is useful in the field related to the fluororesin.

Claims (7)

A fluororesin containing a residue unit represented by the following formula (1) and a terminal group represented by the following formula (2).

(In the formula (1), Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ are independently branched with a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, and 3 to 7 carbon atoms. It represents one of a group consisting of a perfluoroalkyl group having a shape or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an etheric oxygen atom, and Rf ₁ , Rf ₂ , Rf ₃ , and Rf ₄ may be linked to each other to form a ring having 4 or more and 8 or less carbon atoms, and the ring may be a ring containing an etheric oxygen atom.)

(In equation (2), i is an integer of 3 to 20) The fluororesin according to claim 1, wherein the terminal group represented by the formula (2) has a structure represented by the following formula (3).

The fluororesin according to claim 1 or 2, which shows a peak showing a maximum in the range of −140 ppm or more and 142 ppm or less and 143 or more and 145 ppm or less in the solid ^{19 F-NMR spectrum analysis.} The fluororesin according to any one of claims 1 to 3, wherein the fluororesin is in the form of powder and has a volume average particle diameter of 1 to 1000 μm. The fluororesin according to any one of claims 1 to 4, which comprises a step of polymerizing a mixture containing a radical polymerization initiator represented by the following formula (4) and a monomer represented by the following formula (5). Manufacturing method.

(In equation (4), j is an integer of 3 to 20)

(In the formula (5), Rf ₅ , Rf ₆ , Rf ₇ , and Rf ₈ are independently a fluorine atom, a linear perfluoroalkyl group having 1 to 7 carbon atoms, and a branched form having 3 to 7 carbon atoms. It represents one of a group consisting of a perfluoroalkyl group or a cyclic perfluoroalkyl group having 3 to 7 carbon atoms, and the perfluoroalkyl group may have an ethereal oxygen atom, and Rf ₅ , Rf ₆ , Rf ₇ , and Rf ₈ may be linked to each other to form a ring having 4 or more and 8 or less carbon atoms, and the ring may be a ring containing an etheric oxygen atom.) The method for producing a fluororesin according to claim 5, wherein the radical polymerization initiator represented by the formula (4) is a radical polymerization initiator represented by the following formula (6).

In the step of polymerization, an organic solvent is further mixed with the mixture, and the mixture is further mixed.
The organic solvent is a solvent in which at least the monomer is dissolved and at least a part of the resin produced by the polymerization is not dissolved to cause precipitation of the resin, and the resin produced by the polymerization is contained in the organic solvent as particles. The method for producing a fluororesin according to claim 5 or 6, which precipitates in.