Refining method for fluorine resins, production method for refined fluorine resin, fluorine resin, optical material, electronic material, and plastic optical fiber

Abstract

One aspect of the present invention is a refining method for fluorine resins that involves refining a fluorine resin that includes a first fluorine-containing aliphatic ring structure in the molecular chain thereof by bringing the fluorine resin into contact with a fluorinating agent at a temperature of at least (Tg1-35)°C, where Tg1 is the glass transition temperature of the fluorine resin. The present invention makes it possible to produce a fluorine resin that is suitable for use in plastic optical fibers. The first fluorine-containing aliphatic ring structure may have a dioxolane skeleton.

Description

Method for refining fluororesin, method for producing refined fluororesin, fluororesin, optical material, electronic material, and plastic optical fiber

[0001] The present invention relates to a method for purifying a fluororesin, a method for producing the purified fluororesin, and a fluororesin. The present invention also relates to an optical material, an electronic material, and a plastic optical fiber containing the fluororesin.

[0002] Fluorine resins containing a fluorinated alicyclic structure in the molecular chain are generally amorphous and have excellent transparency, as well as various excellent properties such as liquid repellency, durability, and electrical properties, and are therefore used in a variety of applications including optical and electronic applications. One example of an optical application is plastic optical fiber. Non-Patent Document 1 discloses poly(perfluoro-2-methylene-4-methyl-1,3-dioxolane) as a fluororesin containing a fluorinated alicyclic structure in the molecular chain.

[0003] Macromolecules,2005,38,4237-4245

[0004] According to the investigations of the present inventors, when a fluororesin containing a fluorinated alicyclic structure in its molecular chain is used in a plastic optical fiber, the optical transmission loss may be greater than expected from the chemical structure of the fluororesin.

[0005] An object of the present invention is to provide a technique for producing a fluororesin suitable for use in a plastic optical fiber.

[0006] The present invention provides a method for purifying a fluororesin, comprising purifying a fluororesin having a first fluorinated alicyclic structure in its molecular chain by contacting the fluororesin with a fluorinating agent at a temperature of (Tg1 - 35)°C or higher, where Tg1 is the glass transition temperature of the fluororesin.

[0007] From another aspect, the present invention provides a method for producing a purified fluororesin, wherein the fluororesin contains a first fluorinated alicyclic structure in a molecular chain, the method comprising purifying the fluororesin by the above-mentioned method for purifying a fluororesin of the present invention.

[0008] From another aspect, the present invention provides a polymerizable composition comprising a polymer having a structural unit including a first fluorinated alicyclic structure having a dioxolane skeleton, and a chemical structure including a second fluorinated alicyclic structure having a dioxolane skeleton at an end of a molecular chain, wherein, in a mass spectrum evaluated by gas chromatography mass spectrometry (GC-MS), the area I of a peak derived from a terminal group containing a hydrogen atom among terminal groups bonded to a carbon atom at the second position of the dioxolane skeleton in the chemical structure is 1 / 2. H The area I of the peak derived from the terminal group containing a fluorine atom relative to F Ratio I F / I H The present invention provides a fluororesin having a γ-value of 7 or more.

[0009] From another aspect, the present invention provides an optical material comprising the fluororesin of the present invention.

[0010] From another aspect, the present invention provides an electronic material comprising the fluororesin of the present invention.

[0011] From another aspect, the present invention provides a plastic optical fiber comprising a layer containing the fluororesin of the present invention.

[0012] According to the present invention, a technique can be provided that can produce a fluororesin suitable for use in a plastic optical fiber.

[0013] FIG. 1 is a cross-sectional view schematically showing an example of a plastic optical fiber containing a fluororesin obtained through the fluororesin purification method of the present invention. FIG. 2A shows a GC-MS mass spectrum of the fluororesin before purification in Example 1. FIG. 2B shows a GC-MS mass spectrum of the fluororesin after purification in Example 1. FIG. 3A shows an extracted ion chromatogram in selected ion mode (SIM) of the fluororesin after purification in Example 1. FIG. 3B shows an extracted ion chromatogram in SIM of the fluororesin after purification in Example 1. FIG. 3C shows an extracted ion chromatogram in SIM of the fluororesin after purification in Example 1.

[0014] A method for purifying a fluororesin according to a first aspect of the present invention includes purifying a fluororesin containing a first fluorinated alicyclic structure in its molecular chain by contacting the fluororesin with a fluorinating agent at a temperature of (Tg1 - 35)°C or higher, where Tg1 is the glass transition temperature of the fluororesin.

[0015] In a second aspect of the present invention, for example, in the purification method according to the first aspect, the fluororesin is purified by contacting the fluororesin in a powder state with the fluorinating agent.

[0016] In a third aspect of the present invention, for example, in the refining method according to the second aspect, the powder has a median diameter (d50) of 5 to 100 μm.

[0017] In a fourth aspect of the present invention, for example, in the purification method according to any one of the first to third aspects, the fluorinating agent is fluorine gas.

[0018] In a fifth aspect of the present invention, for example, in the purification method according to any one of the first to fourth aspects, the fluororesin is purified by contacting it with the fluorinating agent at a temperature of (Tg1-20)°C or higher.

[0019] In a sixth aspect of the present invention, for example, in the purification method according to any one of the first to fifth aspects, the first fluorinated alicyclic structure has a dioxolane skeleton.

[0020] In a seventh aspect of the present invention, for example, in the purification method according to any one of the first to sixth aspects, the fluororesin has a structural unit (A) represented by the following formula (1): In formula (1), R ff 1 ~R ff 4 R each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. ff 1 and R ff 2 may be linked to form a ring.

[0021] In an eighth aspect of the present invention, for example, in the purification method according to the seventh aspect, the structural unit (A) is a unit derived from perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0022] In a ninth aspect of the present invention, for example, in the purification method according to any one of the first to eighth aspects, the fluororesin has a chemical structure containing a second fluorinated alicyclic structure having a dioxolane skeleton at an end of a molecular chain, and in a mass spectrum of the fluororesin evaluated by gas chromatography mass spectrometry (GC-MS), the area I of a peak derived from the end group containing a hydrogen atom among end groups bonded to the carbon atom at the second position of the dioxolane skeleton in the chemical structure is H The area I of the peak derived from the terminal group containing a fluorine atom relative to F Ratio I F / I H The fluororesin is purified so that the fluorine content is 7 or more.

[0023] In a tenth aspect of the present invention, for example, in the purification method according to the ninth aspect, the chemical structure located at the end of the molecular chain is a structure represented by the following formula (α), and in the mass spectrum, among the terminal groups R bonded to the carbon atom at the second position of the dioxolane skeleton in the structure of formula (α), the area I of the peak derived from the terminal group R which is a hydrogen atom is H1 The area I of the peak derived from the terminal group R which is a fluorine atom, relative to F1 and the area I of the peak due to the terminal group R, which is a CF group. F2 The ratio of the sum of (I F1 +I F2 ) / I H1 The fluororesin is purified so that the fluorine content is 7 or more. In formula (α), * indicates the bonding atom to the molecular chain.

[0024] A production method according to an eleventh aspect of the present invention is a method for producing a purified fluororesin, wherein the fluororesin contains a first fluorinated alicyclic structure in a molecular chain, and the production method includes purifying the fluororesin by the method for purifying a fluororesin according to any one of the first to tenth aspects.

[0025] A fluororesin according to a twelfth aspect of the present invention has a structural unit containing a first fluorinated alicyclic structure having a dioxolane skeleton, and has a chemical structure containing a second fluorinated alicyclic structure having a dioxolane skeleton at an end of a molecular chain, and in a mass spectrum evaluated by gas chromatography mass spectrometry (GC-MS), the area I of a peak derived from an end group containing a hydrogen atom among end groups bonded to the carbon atom at the second position of the dioxolane skeleton in the chemical structure is H The area I of the peak derived from the terminal group containing a fluorine atom relative to F Ratio I F / I H is 7 or more.

[0026] In a thirteenth aspect of the present invention, for example, in the fluororesin according to the twelfth aspect, the chemical structure located at the end of the molecular chain is a structure represented by the following formula (α), and in the mass spectrum, among the terminal groups R bonded to the carbon atom at the second position of the dioxolane skeleton in the structure of formula (α), the area I of the peak derived from the terminal group R which is a hydrogen atom is H1 The area I of the peak derived from the terminal group R which is a fluorine atom, relative to F1 and the area I of the peak due to the terminal group R, which is a CF group. F2 The ratio of the sum of (I F1 +I F2 ) / I H1 is 7 or more. In formula (α), * indicates the bonding atom to the molecular chain.

[0027] In a fourteenth aspect of the present invention, for example, in the fluororesin according to the twelfth or thirteenth aspect, the structural unit is a structural unit (A) represented by the following formula (1): In formula (1), R ff1 ~R ff 4 R each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. ff 1 and R ff 2 may be linked to form a ring.

[0028] An optical material according to a fifteenth aspect of the present invention includes the fluororesin according to any one of the twelfth to fourteenth aspects.

[0029] An electronic material according to a sixteenth aspect of the present invention includes the fluororesin according to any one of the twelfth to fourteenth aspects.

[0030] A plastic optical fiber according to a seventeenth aspect of the present invention comprises a layer containing a fluororesin according to any one of the twelfth to fourteenth aspects.

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description of the preferred embodiments of the present invention is not intended to limit the present invention to the specific embodiments.

[0032] [Fluororesin Purification Method] The purification method of this embodiment involves purifying a fluororesin containing a fluorinated alicyclic structure (first fluorinated alicyclic structure) in its molecular chain by contacting it with a fluorinating agent at a temperature of (Tg1-35)°C or higher. Tg1 is the glass transition temperature of the fluororesin to be purified. According to the inventors' studies, the increase in optical transmission loss that can occur when the above fluororesin is used in a plastic optical fiber is presumably due to the presence of a C-H bond in the fluorinated alicyclic structure (second fluorinated alicyclic structure) located at the end of the molecular chain (note that, according to the inventors' studies, this C-H bond can also be present when a perfluoromonomer is homopolymerized). Aliphatic C-H bonds typically exhibit absorption at wavelengths that overlap the wavelength range of the light source used in optical fiber communications. According to the purification method of this embodiment, it is possible to fluorinate the C-H bond, for example, to convert it to a C-F bond or a C-CF3 bond. Fluorinated bonds usually do not exhibit absorption at wavelengths overlapping with the above wavelength range. The fluorination of the C—H bonds can be confirmed by, for example, GC-MS.

[0033] The contact with the fluorinating agent may be carried out at (Tg1 - 30)°C or higher, (Tg1 - 25)°C or higher, (Tg1 - 20)°C or higher, (Tg1 - 15)°C or higher, or even (Tg1 - 10)°C or higher. The contact with the fluorinating agent may also be carried out at (Tg1 + 40)°C or lower, (Tg1 + 35)°C or lower, (Tg1 + 30)°C or lower, (Tg1 + 25)°C or lower, (Tg1 + 20)°C or lower, (Tg1 + 15)°C or lower, or even (Tg1 + 10)°C or lower, or may be carried out within a temperature range of (Tg1 ± 30)°C, a temperature range of (Tg1 ± 25)°C, or even a temperature range of (Tg1 ± 20)°C. The contact at each of the above temperatures (purification temperatures) can contribute to the diffusion of the fluorinating agent into the interior of the fluororesin, more specifically, into each molecular chain of the fluororesin. Furthermore, contact at the above temperatures (refining temperatures) is particularly suitable for preventing adhesion of powder particles when the fluororesin is in powder form. The Tg of the fluororesin is the midpoint glass transition temperature (T mg )

[0034] The Tg1 of the fluororesin is, for example, 80°C to 140°C, and may be 100°C or higher, 105°C or higher, 110°C or higher, 115°C or higher, or even 120°C or higher.

[0035] The fluororesin may be contacted with the fluorinating agent in a powder state. Contact in a powder state can contribute to the diffusion of the fluorinating agent into each molecular chain of the fluororesin. The size of the powder, expressed in terms of median diameter (d50), may be, for example, 1 mm or less, 800 μm or less, 500 μm or less, 300 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, or even 40 μm or less. The lower limit of the powder size, expressed in terms of d50, may be, for example, 1 μm or more, 5 μm or more, 10 μm or more, or even 15 μm or more. The d50 of the powder may be 5 to 100 μm. The d50 of the powder can be evaluated, for example, by laser diffraction particle size distribution measurement. However, the shape of the fluororesin is not limited to a powder and may be, for example, a pellet.

[0036] The fluorinating agent is typically a gas. Contact with the gaseous fluorinating agent can contribute to the diffusion of the fluorinating agent into each molecular chain of the fluororesin. Furthermore, contact with the gaseous fluorinating agent is also suitable for purifying fluororesins that are difficult to dissolve in a solvent. An example of a gaseous fluorinating agent is fluorine gas (F2). The gaseous fluorinating agent may be contacted with the fluororesin alone or as a mixed gas with another gas. Examples of other gases include inert gases such as nitrogen and argon. The proportion of fluorine gas contained in the mixed gas is, for example, 5 to 95% by volume, 10 to 90% by volume, 15 to 85% by volume, or even 20 to 80% by volume. The proportion may be 70% by volume or less, 60% by volume or less, 50% by volume or less, 40% by volume or less, or even 30% by volume or less.

[0037] The time for contacting the fluororesin with the fluorinating agent (purification time) is, for example, 5 hours or more, and may be 10 hours or more, 20 hours or more, 30 hours or more, 40 hours or more, 50 hours or more, or even 60 hours or more. The upper limit of the purification time is, for example, 120 hours or less.

[0038] When the fluorinating agent is gaseous, the pressure of the atmosphere in which the fluororesin and the fluorinating agent are brought into contact (purification pressure) is expressed as absolute pressure (the same applies hereinafter to pressure) and is, for example, 10 kPa to 3 MPa. The upper limit of the purification pressure may be 1 MPa or less, 500 kPa or less, 200 kPa or less, or even 100 kPa or less (atmospheric pressure or less). The purification pressure may be the pressure of the mixed gas.

[0039] The contact between the fluororesin and the fluorinating agent can be carried out, for example, by introducing the fluorinating agent into a chamber containing the fluororesin, although the method and mode of contact are not limited to the above example.

[0040] (Fluororesin) The fluororesin contains a first fluorinated alicyclic structure. The first fluorinated alicyclic structure may be contained in the main chain or a side chain of the fluororesin. The fluororesin may have a structural unit containing the first fluorinated alicyclic structure.

[0041] An example of the first fluorine-containing alicyclic structure has a dioxolane skeleton, but the first fluorine-containing alicyclic structure is not limited to the above example.

[0042] An example of a fluororesin containing a first fluorinated alicyclic structure having a dioxolane skeleton (polymer (P)) will be described below, although the fluororesin is not limited to the example shown below.

[0043] The polymer (P) has, for example, a structural unit (A) represented by the following formula (1). In formula (1), R ff 1 ~R ff 4 R each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. ff 1 and R ff 2 may be linked to form a ring. "Perfluoro" means that all hydrogen atoms bonded to a carbon atom are replaced with fluorine atoms.

[0044] In formula (1), the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1. The perfluoroalkyl group may be linear or branched. Examples of the perfluoroalkyl group include a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group.

[0045] In formula (1), the number of carbon atoms in the perfluoroalkyl ether group is preferably 1 to 5, and more preferably 1 to 3. The perfluoroalkyl ether group may be linear or branched. Examples of the perfluoroalkyl ether group include a perfluoromethoxymethyl group.

[0046] R ff 1 and R ff 2When they are linked to form a ring, the ring may be a 5-membered ring or a 6-membered ring. Examples of the ring are a perfluorotetrahydrofuran ring, a perfluorocyclopentane ring, and a perfluorocyclohexane ring.

[0047] Specific examples of the structural unit (A) are represented by the following formulas (A1) to (A8).

[0048] Of the structural units represented by formulas (A1) to (A8) above, the structural unit (A2) may be a structural unit represented by the following formula (2): The structural unit of formula (2) is a unit derived from perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0049] The polymer (P) may have one or more types of structural unit (A). The content of the structural unit (A) in the polymer (P) is preferably 20 mol% or more, more preferably 40 mol% or more, relative to the total of all structural units. When the structural unit (A) is contained in 20 mol% or more, the polymer (P) tends to have higher heat resistance. When the structural unit (A) is contained in 40 mol% or more, the polymer (P) tends to have higher transparency and high mechanical strength in addition to high heat resistance. In the polymer (P), the content of the structural unit (A) is preferably 95 mol% or less, more preferably 70 mol% or less, relative to the total of all structural units.

[0050] The structural unit (A) is derived from, for example, a compound represented by the following formula (3): ff 1 ~R ff 4 is the same as formula (1). The compound represented by formula (3) can be obtained by known production methods, such as the production method disclosed in JP-A-2007-504125.

[0051] Specific examples of the compound represented by the above formula (3) are compounds represented by the following formulas (M1) to (M8).

[0052] The polymer (P) may further include a structural unit other than the structural unit (A). Examples of the other structural units are the following structural units (B) to (D).

[0053] The structural unit (B) is represented by the following formula (4).

[0054] In formula (4), R 1 ~R 3 R each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. 4 represents a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms.

[0055] The polymer (P) may have one or more types of structural unit (B). The content of the structural unit (B) in the polymer (P) is preferably 5 to 10 mol % relative to the total of all structural units. The content of the structural unit (B) may be 9 mol % or less, or may be 8 mol % or less.

[0056] The structural unit (B) is derived from, for example, a compound represented by the following formula (5): 1 ~R 4 is the same as formula (4). The compound represented by formula (5) is a fluorine-containing vinyl ether such as perfluorovinyl ether.

[0057] The structural unit (C) is represented by the following formula (6).

[0058] In formula (6), R 5 ~R 8 each independently represents a fluorine atom or a perfluoroalkyl group having 1 to 7 carbon atoms. The perfluoroalkyl group may have a ring structure. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms.

[0059] The polymer (P) may have one or more types of structural unit (C). The content of the structural unit (C) in the polymer (P) is preferably 5 to 10 mol % relative to the total of all structural units. The content of the structural unit (C) may be 9 mol % or less, or may be 8 mol % or less.

[0060] The structural unit (C) is derived from, for example, a compound represented by the following formula (7): 5 ~R 8 is the same as formula (6). The compound represented by formula (7) is a fluorine-containing olefin such as tetrafluoroethylene or chlorotrifluoroethylene.

[0061] The structural unit (D) is represented by the following formula (8).

[0062] In formula (8), Z is an oxygen atom, a single bond, or —OC(R 19 R 20 ) O—, R 9 ~R 20 each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkoxy group may be substituted with halogen atoms other than fluorine atoms. s and t each independently represent an integer of 0 to 5, and s+t is an integer of 1 to 6 (provided that Z is -OC(R 19 R 20 ) In the case of O-, s+t may be 0.

[0063] The structural unit (D) is preferably represented by the following formula (9): The structural unit represented by formula (9) is the structural unit represented by formula (8) above, where Z is an oxygen atom, s is 0, and t is 2.

[0064] In formula (9), R 141 , R 142 , R 151 , and R 152each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 5 carbon atoms, or a perfluoroalkoxy group having 1 to 5 carbon atoms. Some of the fluorine atoms may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkyl group may be substituted with halogen atoms other than fluorine atoms. Some of the fluorine atoms in the perfluoroalkoxy group may be substituted with halogen atoms other than fluorine atoms.

[0065] The polymer (P) may contain one or more types of structural unit (D). In the polymer (P), the content of the structural unit (D) is preferably 30 to 67 mol% relative to the total of all structural units. The content of the structural unit (D) is, for example, 35 mol% or more, and may be 60 mol% or less, or may be 55 mol% or less.

[0066] The structural unit (D) is derived from, for example, a compound represented by the following formula (10): 9 ~R 18 , s and t are the same as in formula (8). The compound represented by formula (10) is a fluorine-containing compound which has two or more polymerizable double bonds and is capable of cyclopolymerization.

[0067] The structural unit (D) is preferably derived from a compound represented by the following formula (11): 141 , R 142 , R 151 , and R 152 is the same as equation (9).

[0068] Specific examples of the compound represented by formula (10) or formula (11) include the following compounds. CF2=CFOCF2CF=CF2 CF2=CFOCF(CF3)CF=CF2 CF2=CFOCF2CF2CF=CF2 CF2=CFOCF2CF(CF3)CF=CF2 CF2=CFOCF(CF3)CF2CF=CF2 CF2=CFOCFClCF2CF=CF2 CF2=CFOCCl2CF2CF=CF2 CF2=CFOCF2OCF=CF2 CF2=CFOC(CF3)2OCF=CF2 CF2=CFOCF2CF(OCF3)CF=CF2 CF2=CFCF2CF=CF2 CF2=CFCF2CF2CF=CF2 CF2=CFCF2OCF2CF=CF2 CF2=CFOCF2CFClCF=CF2 CF2=CFOCF2CF2CCl=CF2 CF2=CFOCF2CF2CF=CFCl CF2=CFOCF2CF(CF3)CCl=CF2 CF2=CFOCF2OCF=CF2 CF2=CFOCCl2OCF=CF2 CF2=CClOCF2OCCl=CF2

[0069] The polymer (P) may further contain other structural units besides the structural units (A) to (D), but preferably does not substantially contain other structural units besides the structural units (A) to (D). Here, "the polymer (P) does not substantially contain other structural units besides the structural units (A) to (D)" means that the total of the structural units (A) to (D) relative to the total of all structural units in the polymer (P) is 95 mol % or more, and preferably 98 mol % or more.

[0070] It is preferable that the fluororesin is substantially free of hydrogen atoms. In this specification, "the fluororesin is substantially free of hydrogen atoms" means that the content of hydrogen atoms in the fluororesin is 1 mol % or less.

[0071] The fluororesin may have a chemical structure containing a second fluorinated alicyclic structure having a dioxolane skeleton at an end of the molecular chain. The second fluorinated alicyclic structure may be the same as or different from the first fluorinated alicyclic structure having a dioxolane skeleton. When the fluororesin is a homopolymer, the second fluorinated alicyclic structure is usually the same as the first fluorinated alicyclic structure. The chemical structure may be a structure derived from a compound represented by formula (3), a structure derived from a compound represented by formulas (M1) to (M8), or a structure derived from perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0072] However, the above chemical structure that the fluororesin may have at the end of the molecular chain may have a C-H bond in the second fluorine-containing alicyclic structure. The degree of C-H bond can be evaluated, for example, by the mass spectrum of the fluororesin evaluated by GC-MS. More specifically, by focusing on the peak of the terminal group bonded to the carbon atom at the second position of the dioxolane skeleton in the mass spectrum, the area I of the peak derived from the terminal group containing a hydrogen atom can be calculated. H and the area I of the peak derived from the terminal group containing a fluorine atom. F Ratio I F / I H It can be evaluated by the ratio I F / I H From this viewpoint, in the purification method of the present embodiment, the area I of the peak derived from the terminal group containing a hydrogen atom among the terminal groups bonded to the carbon atom at the second position of the dioxolane skeleton in the above chemical structure that the fluororesin may have at the end of the molecular chain is determined. H The area of ​​the peak derived from the terminal group containing a fluorine atom relative to F Ratio I F / I H The fluororesin may be purified so that the ratio I is 7 or more. F / I HThe reaction may be carried out so that the value of the peak area is 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more. When a plurality of peaks originating from terminal groups containing hydrogen atoms (or fluorine atoms) are present, the sum of the areas of the respective peaks is calculated as I H (or I F ) Ratio I F / I H varies depending on, for example, the median diameter of the fluororesin, the type and concentration of the fluorinating agent, and the purification conditions (temperature, pressure, time, etc.).

[0073] When the chemical structure that can be present at the end of the molecular chain is a structure represented by the following formula (α), in the mass spectrum of the fluororesin, among the terminal groups R bonded to the carbon atom at the second position of the dioxolane skeleton in the structure of formula (α), the area I of the peak derived from the terminal group R which is a hydrogen atom is H1 The area I of the peak derived from the terminal group R, which is a fluorine atom, relative to F1 and the area I of the peak due to the terminal group R, which is a CF group F2 The ratio of the sum of (I F1 +I F2 ) / I H1 The fluororesin may be purified so that the ratio (I F1 +I F2 ) / I H1 may be 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more.

[0074] In formula (α), * indicates the bonding atom to the molecular chain, which is the carbon atom at the 2-position of the dioxolane skeleton.

[0075] Ratio I F / I HTaking note of the fact that the larger the value, the lower the degree of C—H bond, the present invention, from another aspect different from the above, comprises purifying a fluororesin containing a first fluorinated alicyclic structure in its molecular chain by contacting it with a fluorinating agent, wherein the fluororesin has a chemical structure containing a second fluorinated alicyclic structure having a dioxolane skeleton at an end of its molecular chain, and in a mass spectrum of the fluororesin evaluated by GC-MS, the area I of the peak derived from the end group containing a hydrogen atom among end groups bonded to the carbon atom at position 2 of the dioxolane skeleton in the chemical structure is H The area I of the peak derived from the terminal group containing a fluorine atom relative to F Ratio I F / I H The fluororesin is purified so that the ratio I is 7 or more. F / I H The ratio I may be 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more. F / I H varies depending on, for example, the median diameter of the fluororesin, the type and concentration of the fluorinating agent, and the purification conditions (temperature, pressure, time, etc.). Examples of these values, types, conditions, etc. are as described above. When the chemical structure that can be present at the end of the molecular chain is the structure represented by the above formula (α), in the mass spectrum of the fluororesin, the area I of the peak derived from the terminal group R, which is a hydrogen atom, among the terminal groups R bonded to the carbon atom at the second position of the dioxolane skeleton in the structure of formula (α) is H1 The area I of the peak derived from the terminal group R, which is a fluorine atom, relative to F1 and the area I of the peak due to the terminal group R, which is a CF group F2 The ratio of the sum of (I F1 +I F2 ) / I H1 The fluororesin may be purified so that the ratio (I F1 +I F2 ) / I H1 may be 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more.

[0076] The fluororesin can typically be formed by radical polymerization, and known polymerization methods such as solution polymerization, bulk polymerization, and precipitation polymerization can be used for the polymerization of the fluororesin.

[0077] Additives such as polymerization initiators and chain transfer agents may be used in the polymerization of fluororesin. The additives may be perfluorinated compounds. However, since perfluorinated compounds tend to have poor stability during polymerization, the use of compounds containing hydrogen atoms may be appropriate, particularly in industrial fluororesin production. However, compounds containing hydrogen atoms are likely to have double bonds or carboxyl groups due to the elimination of hydrogen atoms caused by heat during molding of the fluororesin, which in turn can easily cause discoloration, foaming, cracks, etc. in the resulting resin molded product. While it is possible to remove such compounds by reprecipitation of the fluororesin before molding, compounds chemically bonded to the molecular chain of the fluororesin, such as chain transfer agents, are difficult to remove. Given that chain transfer agents are usually bonded to the ends of the molecular chain, it is possible to sever the bonds by heating, but according to the inventors' studies, sufficient removal remains difficult. Furthermore, fluororesins containing a first fluorinated alicyclic structure having a dioxolane skeleton may be difficult to dissolve in a solvent once thermally melted. However, sufficient removal becomes even more difficult when the heating temperature is reduced to avoid thermal melting. On the other hand, the purification method of the present embodiment can also contribute to the removal of compounds containing hydrogen atoms. In other words, the purification method of the present embodiment is also suitable for obtaining a fluororesin that is suppressed from generating discoloration, foaming, cracks, and the like during molding.

[0078] Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide, tert-butyl peroxyacetate, perfluoro(di-tert-butyl peroxide), bis(2,3,4,5,6-pentafluorobenzoyl) peroxide, tert-butyl peroxybenzoate, and tert-butyl perpivalate; and azo polymerization 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-carbonitrile).

[0079] Examples of perfluorinated polymerization initiators include bis(perfluorobenzoyl) peroxide (PFBPO), (CF3COO)2, (CF3CF2COO)2, (C3F7COO)2, (C4F9COO)2, (C5F 11 COO)2, (C6F 13 COO)2, (C7F 15 COO)2, and (CF 17 and perfluoroorganic peroxides such as methyl methyl ether (Methyl methyl ether), ...

[0080] Examples of chain transfer agents are organic compounds containing hydrogen atoms and / or chlorine atoms and having 1 to 20 carbon atoms. Specific examples of chain transfer agents include organic compounds containing hydrogen atoms and having 1 to 20 carbon atoms, such as toluene, acetone, ethyl acetate, tetrahydrofuran, methyl ethyl ketone, methanol, ethanol, and isopropanol; and organic compounds containing hydrogen atoms and / or chlorine atoms and having 1 to 20 carbon atoms, such as chloroform, dichloromethane, tetrachloromethane, chloromethane, dichloroethane, trichloroethane, tetrachloroethane, pentachloroethane, hexachloroethane, benzyl chloride, pentafluorobenzyl chloride, and pentafluorobenzoyl chloride.

[0081] The weight average molecular weight (Mw) of the fluororesin is, for example, 10,000 to 1,000,000. Mw can be evaluated by gel permeation chromatography (GPC).

[0082] The purification method of this embodiment may include additional steps. An example of such additional step is a drying step in which the fluororesin (e.g., powder or pellets) is dried before purification. The fluororesin can be dried, for example, by vacuum drying, reduced-pressure drying, atmospheric pressure drying, blowing air drying, shaking drying, hot air drying, or heat drying. Another example of such additional step is a step in which the purified fluororesin is vacuum devolatilized and / or heated to remove the remaining fluorinating agent. In one example of a step of heating the purified fluororesin (annealing step), the fluororesin that has been contacted with the fluorinating agent is maintained at a predetermined temperature in an atmosphere of an inert gas such as nitrogen. The annealing step is also suitable for reducing the amount of fluorine-based gas (e.g., F gas, HF gas) contained in the fluororesin. The temperature in the annealing step may be selected from the range exemplified above for the temperature at which the fluororesin is contacted with the fluorinating agent. The duration of the annealing step is, for example, 1 to 20 hours. The annealing step can be performed, for example, by discharging the fluorinating agent from a chamber containing the fluororesin and then introducing an inert gas into the chamber. The method and mode of the annealing step are not limited to the above examples.

[0083] [Method for producing fluororesin] The purification method provided by the present invention can produce, for example, a purified fluororesin containing a first fluorinated alicyclic structure in its molecular chain. From this aspect, the method for producing a fluororesin of the present embodiment is a method for producing a purified fluororesin, in which the fluororesin contains the first fluorinated alicyclic structure in its molecular chain, and the production method includes purifying the fluororesin by the purification method provided by the present invention.

[0084] For the fluororesin having a chemical structure containing a second fluorine-containing alicyclic structure having a dioxolane skeleton at the end of the molecular chain, for example, the ratio I of the peak areas in the above mass spectrum F / I H The purified fluororesin can be confirmed by the F / I His, for example, 7 or more, and may be 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more.

[0085] Furthermore, when the chemical structure that the fluororesin may have at the end of the molecular chain is the structure represented by the formula (α), the fluororesin is purified, for example, when, in the mass spectrum, the area I of the peak derived from the terminal group R that is a hydrogen atom, among the terminal groups R bonded to the carbon atom at the second position of the dioxolane skeleton in the structure of formula (α), is 0.05 or more. H1 The area I of the peak derived from the terminal group R, which is a fluorine atom, relative to F1 and the area I of the peak due to the terminal group R, which is a CF group F2 The ratio of the sum of (I F1 +I F2 ) / I H1 The ratio of the purified fluororesin (I F1 +I F2 ) / I H1 is, for example, 7 or more, and may be 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more.

[0086] [Fluororesin] The fluororesin of this embodiment has a structural unit containing a first fluorinated alicyclic structure having a dioxolane skeleton, and a chemical structure containing a second fluorinated alicyclic structure having a dioxolane skeleton at the end of the molecular chain. In addition, in a mass spectrum evaluated by GC-MS, the area I of the peak derived from the end group containing a hydrogen atom among the end groups bonded to the carbon atom at the second position of the dioxolane skeleton in the chemical structure is H The area of ​​the peak derived from the terminal group containing a fluorine atom relative to F Ratio I F / I H is 7 or more. F / I H may be 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more. Examples of the first fluorinated alicyclic structure, the second fluorinated alicyclic structure and the fluororesin are as described above in the description of the purification method of this embodiment.

[0087] In the fluororesin of this embodiment, the chemical structure located at the end of the molecular chain may be a structure represented by the following formula (α). In this case, in the mass spectrum, among the terminal groups R bonded to the carbon atom at the second position of the dioxolane skeleton in the structure of formula (α), the area I of the peak derived from the terminal group R which is a hydrogen atom is H1 The area I of the peak derived from the terminal group R, which is a fluorine atom, relative to F1 and the area I of the peak due to the terminal group R, which is a CF group F2 The ratio of the sum of (I F1 +I F2 ) / I H1 The ratio (I F1 +I F2 ) / I H1 may be 7.5 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, or even 13 or more.

[0088] In formula (α), * indicates the bonding atom to the molecular chain, which is the carbon atom at the 2-position of the dioxolane skeleton.

[0089] In the fluororesin of this embodiment, the structural unit containing the first fluorinated alicyclic structure may be a structural unit (A) represented by the following formula (1).

[0090] In formula (1), R ff 1 ~R ff 4 R each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. ff 1 and R ff 2 may be linked to form a ring.

[0091] The structural unit (A) may be a unit derived from perfluoro(2-methylene-4-methyl-1,3-dioxolane).

[0092] The fluororesin of this embodiment may have the same structure as the purified fluororesin described above in the description of the purification method of this embodiment.

[0093] The fluororesin of this embodiment can be produced, for example, through the purification method provided by the present invention or by the production method provided by the present invention, although the production method of the fluororesin of this embodiment is not limited to the above examples.

[0094] The fluororesin of this embodiment can be used, for example, as an optical material or an electronic material. An example of an optical component is a plastic optical fiber (POF). The POF can include a layer containing the fluororesin of this embodiment. However, the uses of the fluororesin of this embodiment are not limited to the above examples.

[0095] [POF] An example of a POF containing a fluororesin according to this embodiment is shown in Fig. 1. The POF 1 in Fig. 1 is composed of multiple layers including a core 2 and a clad 3. The core 2 is a layer located at the center of the POF 1 and transmits light. The clad 3 is a layer located outward of the core 2 with respect to the central axis of the POF 1 and covers the core 2. The core 2 has a relatively high refractive index, and the clad 3 has a relatively low refractive index. The POF 1 in Fig. 1 further includes a coating layer (overclad) 4 that covers the outer periphery of the clad 3. The POF 1 may be a graded index (GI) type.

[0096] The fluororesin of this embodiment may be contained in at least one layer constituting the POF 1. The fluororesin of this embodiment may be contained preferably in the core 2 and the clad 3, more preferably in the core 2. The core 2, the clad 3, and the coating layer 4 may contain a resin that may be contained in the corresponding layer of a known POF. Examples of resins that may be contained in the core 2 and the clad 3 include fluorine-containing resins, acrylic resins such as methyl methacrylate, styrene-based resins, and carbonate-based resins. Examples of resins that may be contained in the coating layer 4 include polycarbonate, various engineering plastics, cycloolefin polymers, polytetrafluoroethylene (PTFE), modified PTFE, and perfluoroalkoxyalkane (PFA). Each layer may contain an additive such as a refractive index adjuster.

[0097] The POF 1 can be manufactured by, for example, a melt spinning method, in which raw resin is melt-extruded to form the layers that make up the optical fiber.

[0098] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0099] [Glass transition temperature Tg1] The Tg1 of the fluororesin was measured by the above-mentioned method under the following conditions: Measurement device: Q-2000 manufactured by TA Instruments Temperature program: temperature increase from 30°C to 200°C (temperature increase rate 10°C / min) Atmospheric gas: nitrogen (flow rate 50 mL / min) Measurement rate: 10°C / min Sample amount: 5 mg

[0100] [Terminal Fluorination Ratio] The terminal fluorination ratio of a fluororesin is determined by the peak area ratio (I F1 +I F2 ) / I H1 It was calculated as follows. H1 is the area of ​​the peak (ion mass m / z=195) derived from the hydrogen atom bonded to the carbon atom at the 2-position of the dioxolane skeleton in the second fluorine-containing alicyclic structure located at the end of the molecular chain. F1 is the area of ​​the peak (ion mass m / z = 213) derived from the fluorine atom bonded to the carbon atom at the 2nd position. F2 is the area of ​​the peak (ion mass m / z = 263) derived from the CF3 group bonded to the carbon atom at position 2.

[0101] [GC-MS] GC-MS for the fluororesin was performed under the following conditions. Thermal desorption apparatus: TDS / CIS manufactured by Gerstel GC / MS apparatus: 6980plus / 5973N manufactured by Agilent Technologies GC column: HP-5ms UI, 30 m x 0.25 mm, id x 0.25 μm manufactured by Agilent Technologies Sample amount: 10 mg (contained in a glass tube) Sample heating conditions: Heat from 20°C to 270°C (rate 60°C / min) and hold for 30 minutes Other: Gas generated by heating the sample was cold trapped and all components were analyzed. Measurements were performed in scan mode and selected ion detection mode (SIM).

[0102] [Heating Test] A heating test of a fluororesin simulating molding was carried out as follows. 10 g of the fluororesin to be evaluated was placed in a PFA tube with an inner diameter of 10 mm, one end of which was sealed with a PTFE stopper. The fluororesin in the tube was then heated to 270°C for 20 hours to melt, and then allowed to cool to room temperature to form a rod. After cooling, the removed rod was observed under an optical microscope (magnification 10 to 20 times) to confirm the presence of cracks and bubbles in the field of view of the microscope. Observation was carried out at 10 random locations.

[0103] Example 1 One kilogram of poly(perfluoro(2-methylene-4-methyl-1,3-dioxolane); (PFMMD) powder was spread evenly across a PFA tray (internal dimensions: length 287 mm, width 382 mm, depth 48 mm) and placed in a chamber. The median diameter (d50) of the powder evaluated by laser diffraction particle size distribution measurement was 30 μm. The Tg of PFMMD was 131° C. Next, the atmosphere in the chamber was replaced with nitrogen gas several times to maintain a nitrogen gas atmosphere. After that, the temperature was raised to 130°C. When the temperature reached 130°C, a mixed gas of fluorine gas / nitrogen gas (volume ratio 20:80) was introduced into the chamber as a fluorinating agent (flow rate 10.50 L / min) while the pressure inside the chamber was set to 90 kPa. After maintaining the treatment conditions of 130°C and 90 kPa for approximately 65 hours, the atmosphere inside the chamber was replaced with nitrogen to stop exposure of the PFMMD to the fluorinating agent, and the chamber was cooled to room temperature, completing the purification of the PFMMD.

[0104] The mass spectra of PFMMD before and after purification are shown in Figures 2A and 2B, respectively. As shown in Figures 2A and 2B, the peak area I H1 The extracted ion chromatograms of the purified PFMMD in the selected ion detection mode (SIM) are shown in Figures 3A, 3B, and 3C. The spectral peaks in Figures 3A, 3B, and 3C were integrated to determine the area of ​​the region corresponding to the fragment ion of each terminal group R. H1 , I F1 and I F2 are 44494, 302242 and 250940, respectively, and the ratio (IF1 +I F2 ) / I H1 The viscosity was 12.4. No cracks or bubbles were observed in the formed rod.

[0105] (Example 2) Purification of PFMMD was completed in the same manner as in Example 1, except that the fluorinating agent was changed to a single gas of fluorine gas. F1 +I F2 ) / I H1 The viscosity was 13.4. No cracks or bubbles were observed in the formed rod.

[0106] (Example 3) Purification of PFMMD was completed in the same manner as in Example 1, except that the exposure time of PFMMD to the fluorinating agent was changed to 30 hours. F1 +I F2 ) / I H1 The viscosity was 13.1. No cracks or bubbles were observed in the formed rod.

[0107] (Example 4) Purification of PFMMD was completed in the same manner as in Example 1, except that the exposure time of PFMMD to the fluorinating agent was changed to 90 hours. F1 +I F2 ) / I H1 The viscosity was 13.1. No cracks or bubbles were observed in the formed rod.

[0108] (Example 5) Purification of PFMMD was completed in the same manner as in Example 1, except that the exposure time of PFMMD to the fluorinating agent was changed to 5 hours. F1 +I F2 ) / I H1 The viscosity was 7.2. Slight cracks and bubbles were observed in the formed rod.

[0109] (Example 6) Purification of PFMMD was completed in the same manner as in Example 1, except that the temperature at which PFMMD was exposed to the fluorinating agent was changed to 100°C. The ratio of PFMMD after purification (I F1 +I F2 ) / I H1The viscosity was 7.0. Slight cracks and bubbles were observed in the formed rod.

[0110] (Example 7) Purification of PFMMD was completed in the same manner as in Example 1, except that the temperature at which PFMMD was exposed to the fluorinating agent was changed to 100°C and pellet-shaped PFMMMD having a thickness of 2 mm and a shape of 1 cm square was used instead of powder. The ratio of PFMMD after purification (I F1 +I F2 ) / I H1 The viscosity was 8.0. Slight cracks and bubbles were observed in the formed rod.

[0111] (Example 8) Purification of PFMMD was completed in the same manner as in Example 1, except that pellet-shaped PFMMMD having a thickness of 2 mm and a shape of 1 cm square was used instead of powder. The ratio of PFMMD after purification (I F1 +I F2 ) / I H1 The viscosity was 13.0. No cracks or bubbles were observed in the formed rod.

[0112] (Example 9) Purification of PFMMD was completed in the same manner as in Example 1, except that the temperature at which PFMMD was exposed to the fluorinating agent was changed to 160°C. The ratio of PFMMD after purification (I F1 +I F2 ) / I H1 The viscosity was 14.0. No cracks or bubbles were observed in the formed rod.

[0113] (Example 10) Purification of PFMMD was completed in the same manner as in Example 1, except that the temperature at which PFMMD was exposed to the fluorinating agent was changed to 160°C and pellet-shaped PFMMMD having a thickness of 2 mm and a shape of 1 cm square was used instead of powder. The ratio of PFMMD after purification (I F1 +I F2 ) / I H1 The viscosity was 12.0. No cracks or bubbles were observed in the formed rod.

[0114] (Comparative Example 1) Unpurified PFMMD F1 +I F2 ) / I H1When unpurified PFMMD was used to form a rod by the above method, many cracks and bubbles were observed in the formed rod.

[0115] The purification conditions and evaluation results are summarized in Table 1 below.

[0116]

[0117] The fluororesin obtained through the purification method of the present invention can be used, for example, as an optical material or an electronic material. One example of an optical material is POF.

Claims

1. A fluororesin containing a first fluorinated alicyclic structure in its molecular chain is prepared in a powder state, and the glass transition temperature of the fluororesin is set to Tg 1 as (Tg 1 purifying the fluorinated product by contacting the fluorinated product with a fluorinating agent at a temperature of (Tg 1 + 30)°C or higher and (Tg 1 + 35)°C or lower; A method for purifying fluororesin.

2. 2. The method for purifying a fluororesin according to claim 1, wherein the fluororesin is purified by contacting the fluororesin with the fluorinating agent in a gaseous state under a gaseous atmosphere.

3. 2. The method for purifying a fluororesin according to claim 1, wherein the powder has a median diameter (d50) of 5 to 100 μm.

4. 2. The method for purifying a fluororesin according to claim 1, wherein the fluorinating agent is fluorine gas.

5. The fluororesin is 1 2. The method for purifying a fluororesin according to claim 1, wherein the fluororesin is purified by contacting the fluororesin with the fluorinating agent at a temperature of -20°C or higher.

6. The method for purifying a fluororesin according to claim 1, wherein the fluororesin is purified by contacting it with the fluorinating agent at a temperature of (Tg 1 + 20)°C or lower.

7. The method for purifying a fluororesin according to claim 1, wherein the fluororesin is purified by contacting it with the fluorinating agent at a temperature of (Tg 1 + 10)°C or lower.

8. A method for purifying a fluororesin according to claim 1, wherein the fluororesin is purified by contacting the fluororesin with the fluorinating agent for 30 hours or more and 120 hours or less.

9. 2. The method for purifying a fluororesin according to claim 1, wherein the first fluorinated alicyclic structure has a dioxolane skeleton.

10. 2. The method for purifying a fluororesin according to claim 1, wherein the fluororesin has a structural unit (A) represented by the following formula (1): 【Chemical 1】 In formula (1), R ff 1 ~R ff 4 R each independently represents a fluorine atom, a perfluoroalkyl group having 1 to 7 carbon atoms, or a perfluoroalkyl ether group having 1 to 7 carbon atoms. ff 1 and R ff 2 may be linked to form a ring.

11. The method for purifying a fluororesin according to claim 10, wherein the structural unit (A) is a unit derived from perfluoro(2-methylene-4-methyl-1,3-dioxolane).

12. the fluororesin has a chemical structure including a second fluorinated alicyclic structure having a dioxolane skeleton at an end of a molecular chain, In the mass spectrum of the fluororesin evaluated by gas chromatography mass spectrometry (GC-MS), The area I of the peak derived from the terminal group containing a hydrogen atom among the terminal groups bonded to the carbon atom at the 2nd position of the dioxolane skeleton in the chemical structure is H The area I of the peak derived from the terminal group containing a fluorine atom relative to F Ratio I F / I H The method for purifying a fluororesin according to claim 1, wherein the fluororesin is purified so that the fluororesin has a molecular weight of 7 or more.

13. The chemical structure located at the end of the molecular chain is a structure represented by the following formula (α): In the mass spectrum, The area I of the peak derived from the terminal group R which is a hydrogen atom among the terminal groups R bonded to the carbon atom at the 2-position of the dioxolane skeleton in the structure of the formula (α) is H1 The area I of the peak derived from the terminal group R which is a fluorine atom, relative to F1 and CF 3 The area I of the peak derived from the terminal group R is F2 The ratio of the sum of (I F1 +I F2 ) / I H1 The method for purifying a fluororesin according to claim 12, wherein the fluororesin is purified so that the fluororesin has a molecular weight of 7 or more. 【Chemistry 2】 In formula (α), * indicates the bonding atom to the molecular chain.

14. A method for producing a purified fluororesin, comprising: the fluororesin contains a first fluorinated alicyclic structure in a molecular chain, The production method includes purifying the fluororesin by the method for purifying a fluororesin according to any one of claims 1 to 13. Manufacturing method.

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