JP2005075853A - Method for manufacturing fluoropolymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which can obtain a fluoropolymer having a normal bonding ratio higher than the conventional one and a reduced number of branches in the polymerization in a supercritical fluid. <P>SOLUTION: In the method for manufacturing a fluoropolymer by polymerizing a monomer in a supercritical fluid, the monomer is a radically polymerizable monomer having a fluoroolefin alone or its mixture, and the supercritical fluid comprises the above monomer and a non-ethylenic fluorocarbon having a lower critical temperature than the critical temperature of the above monomer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for producing a fluoropolymer.

Fluoropolymers exhibit excellent chemical resistance, solvent resistance, heat resistance, etc., so they are used as raw materials for sealing materials under severe conditions in a wide range of industrial fields such as the automotive industry, semiconductor industry, and chemical industry. Used in

The production of fluoropolymers has conventionally been carried out mainly by emulsion polymerization of fluoroolefins in an aqueous medium using a water-soluble initiator or suspension polymerization using an oil-soluble radical initiator. In these polymerizations, the reaction field is in an inert solvent that hardly affects the inside of the produced polymer particles or the polymerization reaction.

In the case of emulsion polymerization, the polymer chain end groups generated due to the water-soluble initiator used are ionic and thermally unstable, which causes problems such as foaming during molding. Emulsion polymerization also has a problem in that the aqueous dispersion obtained by polymerization is coagulated with a coagulant and dried to obtain a solid polymer, which is a long and complicated process and cannot be efficiently produced. When the residue of the ionic initiator is mixed into the product, there has been a problem when the molded body is used as a device part such as a semiconductor manufacturing apparatus. Furthermore, it is necessary to set the polymerization temperature high, and there is a problem that a polymer having a high normal bond ratio and a small number of branches cannot be obtained.

In the case of suspension polymerization, since the polymerization temperature can be set low, a polymer having a high normal bond ratio can be obtained. However, there is a problem in that the produced polymer is deposited on the inner wall of the reaction tank, the polymer yield is deteriorated, and the polymer production cost is increased. Moreover, in order to remove the suspension stabilizer used at the time of superposition | polymerization, there existed a problem which requires long-time washing | cleaning.

In recent years, research using a supercritical fluid centering on carbon dioxide as a reaction field has been actively conducted. A supercritical fluid has properties suitable as a reaction medium because it has good heat conduction, low viscosity, and accelerates diffusion. A supercritical fluid is a fluid in a region that exceeds both the critical temperature and the critical pressure.

As polymerization of fluoroolefin using a supercritical fluid as a reaction field, for example, radical polymerization reaction of vinylidene fluoride using supercritical carbon dioxide as a reaction field is disclosed (for example, refer to Patent Document 1 and Patent Document 2). . All of these cannot be polymerized at temperatures below the critical temperature of carbon dioxide because the supercritical fluid is limited to carbon dioxide or a mixture containing carbon dioxide. Therefore, there has been a problem that it is difficult to obtain polyvinylidene fluoride having a high normal bond ratio and a small number of branches.

As polymerization of supercritical fluoroolefin at a relatively low temperature and low pressure, a copolymerization reaction of vinylidene fluoride and hexafluoropropylene is disclosed (for example, see Patent Document 3). This document describes diluting with a non-ethylenic fluorocarbon, but there is no description of using a non-ethylenic fluorocarbon having a critical temperature lower than that of the monomer. Used. Further, there is no description about a decrease in polymerization temperature, an increase in normal bond ratio, or a decrease in the number of branches.
International Publication No. 01/34667 Pamphlet International Publication No. 01/90206 Pamphlet International Publication No. 00/47641 Pamphlet

In view of the above situation, an object of the present invention is to provide a method for obtaining a fluoropolymer having a higher normal bond ratio and a smaller number of branches than conventional ones in polymerization in a supercritical fluid.

The present invention is a fluoropolymer production method for producing a fluoropolymer by polymerizing monomers in a supercritical fluid, wherein the monomers are radically polymerizable monomers containing a fluoroolefin alone or a mixture thereof, A supercritical fluid is a method for producing a fluoropolymer, which includes the monomers and a non-ethylenic fluorocarbon whose critical temperature is lower than the critical temperature of the monomers.
The present invention is described in detail below.

The fluoropolymer production method of the present invention comprises polymerizing monomers in a supercritical fluid to produce a fluoropolymer.
In the present invention, the “supercritical fluid” is composed of multiple components including at least monomers and a non-ethylenic fluorocarbon as described later. The supercritical fluid is a fluid in a supercritical state. The supercritical state of the supercritical fluid is a state where both the critical pressure and the critical temperature inherently possessed by the multicomponent mixture constituting the supercritical fluid are exceeded.

The monomers are radically polymerizable monomers containing a fluoroolefin alone or a mixture thereof.
If the said radically polymerizable monomer contains a fluoro olefin, 1 type (s) or 2 or more types can be used. In the present specification, the “radical polymerizable monomer alone” means one kind of radical polymerizable monomer. One type of this radical polymerizable monomer is a fluoroolefin.
In the present specification, the “mixture of radical polymerizable monomers” means a mixture of two or more radical polymerizable monomers. As a mixture of the above-mentioned radical polymerizable monomers, all kinds of radical polymerizable monomers to be used may be fluoroolefin, or a mixture of fluoroolefin and a radical polymerizable monomer other than fluoroolefin. The above “radical polymerizable monomer other than fluoroolefin” is a fluorine-free ethylenic monomer having no fluorine atom in the molecule.

As the radical polymerizable monomer alone or a mixture thereof,
(I) one fluoroolefin,
(Ii) a mixture of two or more fluoroolefins;
(Iii) a mixture of one fluoroolefin and one or more fluorine-free ethylenic monomers,
(Iv) A mixture of two or more fluoroolefins and one or more fluorine-free ethylenic monomers can be employed.

Examples of the fluoroolefin include tetrafluoroethylene [TFE], hexafluoropropylene [HFP], perfluoro (alkyl vinyl ether) [PAVE],

Perfluoroethylenic monomers such as vinylidene fluoride [VdF], trifluoroethylene, vinyl fluoride, trifluoropropylene, pentafluoropropylene, tetrafluoropropylene, hexafluoroisobutene and other hydrogen-containing fluoroethylenic monomers; chlorotrifluoro Examples include chlorine-containing fluoroethylenic monomers such as ethylene [CTFE]. Examples of PAVE include perfluoro (methyl vinyl ether) [PMVE], perfluoro (ethyl vinyl ether) [PEVE], perfluoro (propyl vinyl ether) [PPVE], and the like.

The fluoroolefin is preferably composed of at least one selected from the group consisting of VdF, TFE, CTFE, and HFP.
Among the above-mentioned fluoroolefins, VdF (critical temperature [Tc] = 30.15 ° C.) is preferable because it can easily achieve a supercritical state at a relatively low temperature and low pressure, has no self-polymerization property, and is easy to handle. It is preferable to include. The fluoroolefin is preferably composed of VdF and at least one selected from TFE, HFP and CTFE from the viewpoint of improving the extrudability when the resulting fluoropolymer is formed by extrusion molding, etc. More preferably, it is CTFE (Tc = 105.85 ° C.).

As the fluoroolefin, a functional group-containing fluoroolefin can also be used. The functional group-containing fluoroolefin is not particularly limited, and for example, the following general formula

(In the formula, Y is —CH ₂ OH, —COOH, —SO ₂ F, —SO ₃ M (M is a hydrogen atom, NH ₄ or an alkali metal element), a carboxyl group forming a salt, or an alkoxycarbonyl group. Represents an epoxy group or a nitrile group, X and X ¹ are the same or different and each represents a hydrogen atom or a fluorine atom, and Rf represents a fluorine-containing alkylene group having 1 to 40 carbon atoms or an ether bond having 1 to 40 carbon atoms. Represents a fluorine-containing alkylene group to be contained.), For example,

Etc.

Examples of the fluoroolefin include perfluoro (6,6-dihydro-6-iodo-3-oxa-1-hexene) and perfluorocarbon disclosed in JP-B-5-63482 and JP-A-62-212734. It is also possible to use a fluoroolefin monomer such as fluoro (5-iodo-3-oxa-1-pentene).

The fluorine-free ethylenic monomer is not particularly limited, and examples thereof include α-olefin monomers having 2 to 10 carbon atoms such as ethylene [ET], propylene, butene and pentene; methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, cyclohexyl vinyl ether, Examples thereof include alkyl vinyl ethers having 1 to 20 carbon atoms, such as hydroxybutyl vinyl ether and butyl vinyl ether.

In polymerization in a supercritical reaction field, the following combinations of radical polymerizable monomers are preferable.
(a) one type of homopolymerization such as VdF, TFE, CTFE,
(b) copolymerization of VdF and HFP (50 to 99/1 to 50 molar ratio),
(c) copolymerization of VdF, HFP and TFE (50 to 98/1 to 40/1 to 40 molar ratio),
(d) copolymerization of HFP and ET (1-50 / 50-99 molar ratio),
(e) copolymerization of HFP, ET and TFE (1-50 / 40-98 / 1-45 molar ratio),
(f) copolymerization of PAVE and TFE (1-50 / 50-99 molar ratio),
(g) copolymerization of TFE and HFP (50 to 99/1 to 50 molar ratio),
(h) copolymerization of TFE and ET (1 to 99/1 to 99 molar ratio),
(i) copolymerization of TFE and propylene (1 to 99/1 to 99 molar ratio),
(j) copolymerization of VdF and TFE (1 to 99/1 to 99 molar ratio),
(k) copolymerization of VdF and CTFE (1 to 99/1 to 99 molar ratio),
(l) copolymerization of VdF, CTFE and TFE (50 to 98/1 to 30/1 to 30 mole ratio),
(m) Copolymerization of TFE, VdF and propylene (30 to 98/1 to 50/1 to 50 mole ratio),
(n) copolymerization of ET, HFP and VdF (10-85 / 10-45 / 1-45 molar ratio),
(o) Copolymerization of ET, HFP, VdF and TFE (10 to 85/10 to 45/1 to 45/1 to 30 mole ratio)
Of these, (a) and (k) are preferred.

In the fluoropolymer production method of the present invention, the supercritical fluid contains the monomers and a non-ethylenic fluorocarbon whose critical temperature is lower than the critical temperature of the monomers.
The critical temperature of the monomers is the critical temperature of the radical polymerizable monomer when the monomers are one kind of radical polymerizable monomer, and when the monomers are a mixture of two or more radical polymerizable monomers, The critical temperature inherent in the mixture.
In addition to the effect of lowering the critical temperature of the supercritical fluid described above, the non-ethylenic fluorocarbon acts as a diluent for the monomers in the reaction field and has the effect of helping to remove the heat of reaction. Further, the solubility of the radical polymerization initiator in the reaction field and the stability of the generated fluoropolymer particles can be improved, and the particles can be prevented from adhering to each other due to swelling. The non-ethylenic fluorocarbon is preferably inert to the polymerization reaction and free of chain transfer.

The non-ethylenic fluorocarbon is preferably a linear or cyclic saturated fluorocarbon having 1 to 5 carbon atoms, although it depends on the monomers used. Examples of such a fluorocarbon include tetrafluoroethane (critical temperature [Tc]). = 101.03 ° C.), hydrogen-containing non-ethylenic fluorocarbons such as trifluoroethane (Tc = 72.6 ° C.), trifluoromethane (Tc = 25.82 ° C.), difluoromethane (Tc = 78.4 ° C.); Perfluorocarbons such as tetrafluoromethane (CF ₄ , Tc = −45.64 ° C.), perfluoroethane (C ₂ F ₆ , Tc = 19.88 ° C.), perfluorocyclobutane (Tc = 115.22 ° C.), etc. Of these, one or a combination of two or more can be used.
As said non-ethylenic fluorocarbon, trifluoromethane or perfluorocarbons are preferable, and a C1-C2 perfluorocarbon is more preferable. The perfluorocarbon of the C 1-2, preferably CF ₄ and / or _C 2 _{F 6,} CF ₄ is more preferable.

The non-ethylenic fluorocarbon is preferably 1 to 500% by mass based on the total amount of the monomers used. If the amount is too large, the amount of non-ethylenic fluorocarbon to be recovered after the reaction increases, the amount of radical polymerization initiator dissolved in the non-ethylenic fluorocarbon increases, and the amount of fluoropolymer having a low molecular weight increases, which is not preferable. A more preferable upper limit is 300% by mass, and a still more preferable upper limit is 200% by mass.

In the fluoropolymer production method of the present invention, the radical polymerizable monomer is preferably polymerized in the presence of a radical polymerization initiator. As the radical polymerization initiator, for example, peroxides such as organic peroxides and inorganic peroxides, azo compounds, and the like can be used.
The organic peroxide is not particularly limited, and examples thereof include isobutyl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, succinic acid peroxide, and bis ( ω-hydrododecafluoroheptanoyl) peroxide and other diacyl peroxides; dinormalpropyl peroxydicarbonate, diisopropylperoxydicarbonate, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethyl Peroxydicarbonates such as peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-methoxybutyl peroxydicarbonate, diethyl peroxydicarbonate, etc. 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t-hexylperoxyneodecanoate, t-butylperoxy Neodecanoate, t-hexylperoxypivalate, t-butylperoxypivalate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 2,5-dimethyl-2, 5-bis (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, t-hexylperoxy 2-ethylhexanoate, t-butylperoxy 2 -Ethylhexanoate, t-butylperoxyisobutyrate, t-hexylperoxyisopropyl Monocarbonate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxylaurate, t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy 2-ethylhexyl monocarbonate, t-butyl Examples include peroxyesters such as peroxyacetate.

It does not specifically limit as an inorganic peroxide, For example, hydrogen peroxide, a persulfate, etc. are mentioned.
The persulfate is not particularly limited, and examples thereof include ammonium persulfate, sodium persulfate, and potassium persulfate.
Moreover, in the case of the said peroxide, it can also be used in combination with a reducing agent.

The azo compound is not particularly limited, and examples thereof include cyano-2-propylazoformamide, 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis [ N- (2-propenyl) -2-methylpropionamide], polydimethylsiloxane segment-containing macroazo compound, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'-azobis (4-methoxy) -2,4-dimethylvaleronitrile), 4,4'-azobis (4-cyanovaleric acid), dimethyl 2,2'-azobisisobutyrate, 2,2'- Zobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2,2 '-Azobis [2- (2-imidazolin-2-yl) propane], 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide} 2,2'-azobis {2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propion Amide], 2,2′-azobisisobutyramide dihydrate, 2,2′-azobis [2- (hydroxymethyl) propionitrile] and the like.
As the radical polymerization initiator, an organic peroxide is preferable because it has a low vapor pressure and does not generate unstable fluoropolymer terminals.

In the fluoropolymer production method of the present invention, since the supercritical state can be maintained at a lower temperature than the conventional supercritical state polymerization, the proper use temperature in terms of half-life can be used as a radical polymerization initiator. A low thing can be used and the fluorine-type diacyl peroxide which can make a polymer chain terminal easily a fluorine-type stable terminal can be used. Is not particularly restricted but includes fluorine-based diacyl peroxides, for example, perfluoropropionyl peroxide, formulas such as perfluoro-butyryl peroxide _{(C m F 2m + 1 COO-} ) 2 (m represents an integer of 1 to 5 .) Linear perfluorodiacyl peroxide represented by the following general formula: perfluoro (2-normalpropoxypropionyl) peroxide

And bis [2,2′-perfluoro (propoxyoxyalkylenepropynyl)] peroxide represented by the formula (n represents an integer of 0 to 2).
In the polymerization, peroxydicarbonate may be used because it is easily dissolved in a supercritical fluid.

In the fluoropolymer production method of the present invention, a chain transfer agent may be added during the polymerization in order to adjust the molecular weight of the target fluoropolymer.
Examples of the chain transfer agent include hydrocarbons, halogenated hydrocarbons, hydrocarbon alcohols, hydrocarbon esters, hydrocarbon ketones, mercaptans, and the like. It is preferable to select a chain transfer agent having excellent solubility in a supercritical fluid.

Examples of the hydrocarbons include hydrocarbons having 4 to 6 carbon atoms such as pentane, butane and hexane. Examples of halogenated hydrocarbons include tetrachloromethane, chloroform, methylene chloride, and the like. The halogenated hydrocarbons are distinguished from the above-mentioned non-ethylenic fluorocarbons having substantially no chain mobility.

Examples of hydrocarbon alcohols include methanol, ethanol, isopropanol, and the like. Examples of the hydrocarbon esters include methyl acetate, ethyl acetate, butyl acetate, ethyl propionate, ethyl acetoacetate, dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate, and diethyl carbonate.

Examples of hydrocarbon ketones include acetone, acetylacetone, cyclohexanone, and the like. Examples of mercaptans include dodecyl mercaptan. Of these, pentane, butane, isopropanol, diethyl malonate, tetrachloromethane, acetone, and dodecyl mercaptan are preferred because the molecular weight can be greatly reduced by addition of a small amount.

The blending amount of the chain transfer agent may be appropriately determined depending on the molecular weight of the target fluoropolymer, but is usually preferably 0.001 to 5% by mass with respect to the total amount of the radical polymerizable monomer. A more preferred upper limit is 2% by mass.

The fluoropolymer obtained by the fluoropolymer production method of the present invention may be a resin or an elastomer.

The fluoropolymer production method of the present invention is used in the case where polymerization is performed without using a solvent only with monomers by mixing monomers and a non-ethylenic fluorocarbon having a critical temperature lower than the critical temperature of the monomers used. A supercritical state can be realized at a lower temperature. By polymerizing at a low temperature, even when a monomer having a C—H bond is used, the branching rate is small, the number of normal bonds per 100 monomer units is large, and the fluidity and heat resistance are excellent. A fluoropolymer can be obtained.
In the present specification, the “normal bond” means that the monomer unit is represented by-(AB)-, where A is the head and B is the tail, and between adjacent monomer units in the molecular structure of the fluoropolymer is the tail. Means a bond in the order The “monomer unit” is a part of the molecular structure of the fluoropolymer and is a site derived from the monomer.
In the present specification, the “branch ratio” means the number of locations where carbon chains per 10,000 monomer units of the fluoropolymer are branched.

In the present invention, the temperature at which the polymerization is carried out is a temperature higher than the temperature at which the fluid composed of the monomers, the non-ethylenic fluorocarbon, and other solvent used as necessary becomes a supercritical state, that is, the fluid has inherently. Although it will not specifically limit if it is the temperature exceeding a critical temperature, The temperature of the critical temperature vicinity of the said fluid is preferable at points, such as energy efficiency.
For example, when VdF (critical temperature 30.15 ° C.) is used alone as a monomer, the temperature at which the polymerization is performed depends on the type and concentration of the non-ethylenic fluorocarbon and other solvent used together, but the lower limit is the above-mentioned fluid The upper limit may be a temperature lower than the critical temperature of VdF, but is preferably 25 ° C., more preferably 15 ° C. When VdF is subjected to suspension polymerization at 25 ° C. or lower, depending on other polymerization conditions, the number of normal bonds per 100 VdF monomer units in the polymer chain of polyvinylidene fluoride obtained is 92 or more, and VdF monomer. Although the number of branches per 10,000 units can be reduced to 2 or less, if the supercritical state can be realized at 25 ° C. or lower, the same number of normal bonds and branches can be obtained.

The fluoropolymer production method of the present invention can also perform polymerization without maintaining the supercritical state and liquefying the monomers even at a temperature lower than the temperature at which polymerization was conventionally performed in the supercritical state. Although the fluoropolymer produced by polymerizing the liquefied monomers tends to be unevenly distributed at the bottom of the polymerization tank, the fluoropolymer production method of the present invention performs polymerization in a supercritical fluid. It can be generated uniformly. Since the fluoropolymer can be uniformly formed, continuous polymerization in which the supply of the monomers and the discharge of the generated fluoropolymer are continuously performed is facilitated, and productivity can be improved.

The fluoropolymer obtained by the fluoropolymer production method of the present invention has a wide range of uses as a molding material used for injection molding, extrusion molding, and the like, and a powder coating material used for various linings. For example, it is suitably used as a raw material powder for an organosol paint that can form a thin film that is uniform and has no pinholes.

The fluoropolymer production method of the present invention is particularly suitable for the production of polyvinylidene fluoride [PVdF] and polychlorotrifluoroethylene [PCTFE].
PVdF obtained by the fluoropolymer production method of the present invention is, for example, lining to chemical equipment or the like by powder coating; sheet lining of SUS pickling tank or chrome plating tank by extrusion molding; corrosion-resistant lining of line pipe or the like by extrusion molding It can be used for the production of valves such as diaphragm valves by injection molding, pumps, etc., and can also be used for wire coating materials, condenser films, piezoelectric / pyroelectric films, fishing lines, and the like.
PCTFE obtained by the fluoropolymer production method of the present invention is particularly suitable for applications requiring low moisture permeability such as pharmaceutical packaging materials and electroluminescence [EL] moisture-proof films.

Since the fluoropolymer production method of the present invention has the above-described configuration, supercritical polymerization can be performed at a lower temperature than the polymerization of monomers alone, and a fluoropolymer excellent in fluidity and heat resistance can be obtained. it can.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited only to these examples.
[Calculation of the number of branches]
Dimethylformamide was used as a solvent, and a sample was prepared by maintaining the polymer concentration at 10 to 20% by mass for 10 to 15 hours at a temperature of 40 to 60 ° C.
Using this sample, it was determined from ¹³ C-NMR and ¹⁹ F-NMR.
Measuring machine: AMX500 manufactured by Bruker
Resonance frequency: 470.6MHz
Number of integrations: 20000 times For identification, the chemical shift with CCl ₃ F as a reference signal was expressed in ppm.
The number of branches per 10,000 VdF monomer units in the polymer chain of polyvinylidene fluoride was calculated by the following formula.
Number of branches per 10,000 VdF monomer units
= 10000 × [(integral value of −98.2 to −100.4 ppm) / (all integrated values)] ÷ 3
Here, the reason why it is divided by 3 is that three VdF monomer units appear to overlap the NMR peak per one branching number. All the integrated values are −65 to −130 ppm.

[Measurement and calculation of normal binding number]
Regarding the number of normal bonds of polyvinylidene fluoride, in the ¹⁹ F-NMR signal of a dimethylformamide solution of polyvinylidene fluoride, the chemical shift value using CCl ₃ F as a reference signal is -85.0 to -98.0 ppm. The signal is the absorption of the —CF ₂ — group in the head-to-tail linkage chain, and the signal at −113.0 to −120.0 ppm is of the —CF ₂ — group in the head-to-head linkage chain or the tail-to-tail linkage chain. Absorption. Therefore, the number of normal bonds per 100 VdF monomer units in the polymer chain of polyvinylidene fluoride can be calculated by the following formula.

Number of normal bonds per 100 VdF monomer units = 100 × signal intensity (−85.0 to −98.0 ppm) / [signal intensity (−85.0 to −98.0 ppm) + signal intensity (−113.0 to -120.0 ppm)]

The group in which the signal appears at −85.0 to −98.0 ppm includes, in addition to the —CF ₂ — group in the head-to-tail bond chain, a branched structure, and the vicinity of the terminal such as the initiator terminal and the continuous mobile terminal — CF ₂ -groups are mentioned, but the contribution is small compared with the total signal intensity, and can be ignored for calculating the number of normal bonds.
Example 1

A stainless steel autoclave with an internal volume of 216 ml was sufficiently purged with nitrogen, and then charged with 75 g of vinylidene fluoride (VdF, critical temperature Tc = 30.15 ° C., critical pressure Pc = 4.43 MPa) with a high-pressure plunger pump in a vacuum state. Further, 23 g of tetrafluoromethane (trade name: DF-14, critical temperature Tc = −45.64 ° C., critical pressure Pc = 3.745 MPa, manufactured by Daikin Industries, Ltd.) was charged. When the system temperature (reaction temperature) was 25 ° C., the system pressure was 5.48 MPa, and the gas-liquid interface was not observed, and a supercritical state was reached.
Next, 1.0 g of a dilute solution of bis (ω-hydrododecafluoroheptanoyl) peroxide [DHP] 8 mass% perfluorohexane as an organic peroxide radical polymerization initiator was injected into the system with nitrogen. The inside was stirred with a magnetic stirrer and allowed to react for 55 minutes.
After completion of the reaction, the residual monomer was discharged into the atmosphere, and the inside of the autoclave was confirmed. As a result, a cotton-like polymer lump that appeared to be uniformly produced inside the autoclave was produced. The polymer was dried in a vacuum at 60 ° C. for 15 hours and measured for a weight of 3.16 g. The average polymerization rate at this time was 16.0 g / (l · hour).
As a result of analyzing this polymer by size exclusion chromatography [SEC], the number average molecular weight [Mn] was 137,000 and the weight average molecular weight [Mw] was 67,000 in terms of polystyrene.
The number of normal bonds of this polymer was 92.1 per 100 VdF monomer units, and the number of branches was 0.6 per 10,000 VdF monomer units.
Comparative Example 1

A stainless steel autoclave with an internal volume of 216 ml was sufficiently purged with nitrogen, and then charged with 75 g of vinylidene fluoride (VdF, critical temperature Tc = 30.15 ° C., critical pressure Pc = 4.43 MPa) with a high-pressure plunger pump in a vacuum state. It is. When the system temperature (reaction temperature) was 25 ° C., the system pressure was 3.89 MPa, but a gas-liquid interface was observed.
Next, 0.96 g of a DHP 8 mass% perfluorohexane diluted solution as an organic peroxide radical polymerization initiator was injected into the system with nitrogen. The inside was stirred with a magnetic stirrer and allowed to react for 42 minutes.
After the completion of the reaction, the residual monomer was released into the atmosphere, and the inside of the autoclave was confirmed. As a result, a polymer that appeared to have undergone polymerization only in the vinylidene fluoride solution was attached to the bottom of the autoclave. The polymer was dried in a vacuum at 60 ° C. for 15 hours, and the mass was measured to be 2.23 g. The average polymerization rate at this time was 14.7 g / (l · hour).
As a result of analyzing this polymer by SEC, the number average molecular weight (Mn) was 132,000 and the weight average molecular weight (Mw) was 714,000 in terms of polystyrene.
The number of normal bonds of this polymer was 92.3 per 100 VdF monomer units, and the number of branches was 0.6 per 10,000 VdF monomer units.

By the fluoropolymer production method of the present invention, a polymer excellent in fluidity, heat resistance and the like can be continuously polymerized, which contributes to improvement in productivity.

Claims (6)

A fluoropolymer production method for producing a fluoropolymer by polymerizing monomers in a supercritical fluid,
The monomers are radically polymerizable monomers containing a fluoroolefin alone or a mixture thereof,
The method for producing a fluoropolymer, wherein the supercritical fluid contains the monomers and a non-ethylenic fluorocarbon whose critical temperature is lower than the critical temperature of the monomers. The method for producing a fluoropolymer according to claim 1, wherein the non-ethylenic fluorocarbon is a perfluorocarbon having 1 to 2 carbon atoms. Perfluorocarbon having 1 to 2 carbon atoms is, CF ₄ and / or C ₂ F ₆ fluoropolymer process according to claim 1 or 2, wherein. The method for producing a fluoropolymer according to claim 1, 2 or 3, wherein the fluoroolefin contains vinylidene fluoride. The method for producing a fluoropolymer according to claim 1, 2 or 3, wherein the fluoroolefin is vinylidene fluoride and / or trichlorofluoroethylene. The method for producing a fluoropolymer according to claim 1, wherein the polymerization is carried out in the presence of a fluorinated diacyl peroxide.