JPH06211933A - Production of fluoropolymer - Google Patents

Abstract

PURPOSE:To avoid the inclusion of chlorine and safely obtain a fluoropolymer of high degree of polymerization prevented from causing environmental disruption, by polymerizing a fluoroolefin monomer in the presence of perfluorocyclobutane. CONSTITUTION:At least one monomer selected from fluoroolefins represented by the formulas CF2=CF2, CH2=CF2, CF2=CF-CF3, CF2=CFCl and CF2= CFORf is polymerized in the presence of perfluorocyclobutane to give an objective fluoropolymer. In the formulas, Rf is a 1-9C fluoroalkyl group or a fluoropolyether group. The incorporation of perfluorocyclobutane beforehand into a fluoroolefin or its mixture with ethylene serving as the raw material can prevent explosion not only during the storage and transfer of the monomer but also during the polymerization thereof. The amount of the perfluorocyclobutane used for this purpose is preferably 1-20mol% of the monomer from the viewpoint of service conditions.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a fluoropolymer. More specifically, it relates to a method for producing a fluoropolymer by polymerizing or copolymerizing a fluoroolefin or a fluoroolefin with ethylene.

[0002]

2. Description of the Related Art Conventionally, bulk, solution suspension, emulsion polymerization and the like have been known as a method for producing a fluorine-containing polymer, and in particular, a solution polymerization method or a suspension polymerization method is generally well adopted. In these solution polymerization and suspension polymerization, an inert solvent such as chlorofluorocarbon is usually used as a polymerization solvent, and a polymerization reaction is carried out using a radical initiator. Examples of the chlorofluorocarbon include trichlorotrifluoroethane (hereinafter abbreviated as R-113) and dichlorotetrafluoroethane (hereinafter R-114).
Abbreviated) and the like. However, these R-1
13 and R-114 have recently been considered to cause destruction of the ozone layer due to their stability, their use is restricted, and they will be totally abolished in the near future. Therefore, these R-113, R-1
It is necessary to consider the use of a solvent instead of regulated CFCs such as 14. In recent years, as a part of the study of alternatives to regulated CFCs, studies have been conducted on compounds that do not contain a large number of chlorine atoms in the molecule so as not to destroy the ozone layer. Examples of this type of CFC substitute include R-134a which is a kind of hydrofluorocarbon.
_{(CH 3 CHF 2) R-} 142b which is one type of hydrochlorofluorocarbons _{(CH 3 CClF 2), R} -141b
(CH ₃ CCl ₂ F) and the like. However, it has been clarified that hydrogen present in the molecule of such a CFC alternative is not necessarily suitable as a solvent for polymerizing a fluorinated olefin because it exhibits chain transfer activity for the polymerization of a fluorinated olefin. Further, a general-purpose organic solvent also exhibits chain transfer activity and is not suitable as a solvent for polymerizing a fluorinated olefin. On the other hand, in recent years, highly purified fluoropolymers have been required in the fields of semiconductor and pharmaceutical industry. One of the methods for high purification is to reduce the amount of chlorine contained in the polymer. This is particularly effective in suppressing coloring and deterioration due to chlorine corrosion of the metal due to contact of the polymer with the metal. In that sense, the use of R-113 and R-114 as the polymerization solvent is not preferable because the chlorine that has undergone chain transfer is contained in the polymer, although the amount is very small. Moreover, there is a natural demand that the polymer production should be carried out safely. This means that self-explosion often occurs in a high-pressure compressed gas of unsaturated hydrocarbons, fluorocarbons alone or in a mixture, and this must be suppressed as much as possible.

[0003]

DISCLOSURE OF THE INVENTION The present invention relates to R-113 and R-1 as a solvent used for producing a fluoropolymer.
14 to provide a substance to be a substitute, contribute to the prevention of environmental damage, and reduce the content of chlorine, which is an impure bound substance of a fluoropolymer produced using these fluorocarbon substances, and It is intended to provide a method for safely carrying out polymerization.

[0004]

Means for Solving the Problems The present inventors have made various studies in order to solve such problems. As a result, in the production of a fluoropolymer mainly containing a fluorinated olefin, it was found that the above problems can be solved by carrying out the polymerization in the presence of perfluorocyclobutane, and the present invention was completed based on such findings. It was That is, the present invention is
_{Formula: CF 2 = CF 2, CH} 2 = CF 2, CF 2 = CF-C
F ₃ , CF ₂ = CFCl and CF ₂ = CFORf (wherein
Rf represents a fluoroalkyl group having 1 to 9 carbon atoms or a fluoropolyether group) and at least one monomer selected from the group consisting of fluorine-containing olefins is polymerized in the presence of perfluorocyclobutane. The gist is a method for producing a coalescence. Further, the gist of the present invention is to copolymerize ethylene with at least one monomer selected from the group consisting of the fluorinated olefins represented by the above formula in the presence of perfluorocyclobutane. The present invention also has as its gist a method for preventing the explosion of the monomer, which comprises adding perfluorocyclobutane to the above-mentioned fluorine-containing olefin or a mixture thereof with ethylene. The present invention will be described in detail below.

The fluorine-containing olefin used in the present invention is represented by the above formula, and has the general formula CF ₂ ═C.
Examples of the fluorine-containing olefin represented by FORf include

[Chemical 1] Etc. The present invention is applicable not only to the case of polymerizing these fluorinated olefins alone, but also to the case of copolymerizing two or more kinds of the fluorinated olefins. During the copolymerization, a preferable combination of fluorine-containing olefins is tetrafluoroethylene / vinylidene fluoride,
Examples thereof include tetrafluoroethylene / perfluoroalkyl vinyl ether. In the case of copolymerization, the molar ratio of the fluorine-containing monomer used is not limited. In terms of the physical properties of the polymer to be obtained, a particularly preferable range is shown. In the tetrafluoroethylene / vinylidene fluoride copolymer, the molar ratio is 5:95 to 95: 5, and more preferably 18:82 to 22:78. In the tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, the content of the perfluoroalkyl vinyl ether is 1.0 to 50.0% by weight.

The present invention can also be applied to the case of copolymerization of the above-mentioned fluorine-containing olefin and ethylene. In this case, two or more fluorine-containing olefins may be used. Preferred combinations of monomers include tetrafluoroethylene / ethylene and chlorotrifluoroethylene / ethylene. The molar ratio of ethylene to fluorine-containing olefin in the copolymerization is generally 70:30 to 30: 7.
The range is 0. In terms of physical properties of the resulting polymer, a particularly preferable composition is shown as an example. In the above ethylene / tetrafluoroethylene copolymer and ethylene / chlorotrifluoroethylene copolymer, the molar ratio is 30:70 to 70: 3.
It is 0.

In the production of the fluoropolymer of the present invention, various monomers as a modifier can be added and copolymerized in order to improve physical properties such as high temperature mechanical properties.
Examples of such a modifier include the formula: CH ₂ = CFR'f (wherein
R'f represents a fluoroalkyl group having 1 to 10 carbon atoms),
_{CH 2 = C (CF 3)} 2, CH 2 = CFOCH 2 (CF 2) nX
(In the formula, X is hydrogen, fluorine or chlorine, and n is 1 to 10
Represents an integer of). These monomers are used in the range of 0.5 to 20% by weight, preferably 1.0 to 10.0% by weight based on the total amount of the monomers used.

Further, in the production of the copolymer of the present invention,
For controlling the molecular weight, ordinary chain transfer agents such as cyclohexane, n-pentane, n-hexane, isopentane, methanol and ethanol can be used, and carbon tetrachloride, chloroform, methylene chloride and methyl chloride can be used if necessary. Etc. can also be used.

The present invention is characterized in that the polymerization of the above-mentioned fluorine-containing olefin or the copolymerization of ethylene with the above-mentioned fluorine-containing olefin is carried out in the presence of perfluorocyclobutane (hereinafter sometimes abbreviated as C-318). Is. Since C-318 is abundantly produced as a by-product in the tetrafluoroethylene production process or the hexafluoropropylene production process, a C-318 pure product can be obtained from the process and used in the present invention. In addition to C-318, perfluoro-1-butene, perfluoro-2-butene and the like are by-produced during the hexafluoropropylene production process. However, they are difficult to separate by rectification. Therefore, as a separation method, perfluoro-1-butene or perfluoro-2-butene having a double bond is added with hydrogen, chlorine, bromine, fluorine, hydrogen fluoride, methanol or the like to obtain a saturated compound, It can be separated from C-318 by rectification.

As the polymerization method, known methods such as solution polymerization, suspension polymerization and emulsion polymerization can be adopted. That is, in solution polymerization, perfluorocyclobutane is used as a solvent, and a system in which a monomer comprising a fluorinated olefin or an ethylene / fluorine-containing mixture is dissolved is polymerized. In suspension polymerization or emulsion polymerization, a system in which a solution in which a monomer is dissolved in perfluorocyclobutane is dispersed or emulsified in water is polymerized. In some cases, perfluorocyclobutane is added to the monomer to carry out the polymerization in the gas phase. Suspension polymerization in an aqueous medium is industrially preferable. C
The amount of -318 used is preferably 10 to 100% by weight with respect to water, from the viewpoints of suspending and dispersing properties and economical efficiency. In the method of the present invention, it is possible to add all the monomers used in the polymerization vessel containing the medium at one time, but to charge only a part of the monomers to be used for the polymerization, and to carry out the polymerization to obtain a monomer commensurate with the consumed monomer. It is preferable to carry out the polymerization while replenishing. Specifically, a method of supplying a monomer to the polymerization system so as to maintain a constant pressure can be adopted.

An organic peroxide is used as a polymerization initiator. Preferred organic peroxides have the general formula:

[Chemical 2] (In the formula, Y represents hydrogen, fluorine or chlorine, and m is 2 to
And a di (?-Hydroperfluorohexanoyl) peroxide, a di (?-Chloroperfluoropropionyl) peroxide. Examples thereof include oxide. Also the formula:

[Chemical 3] (In the formula, n is an integer of 1 to 10) peroxides such as di (trichloroperfluorohexanoyl)
Peroxide and the like are also preferable. Further, hydrocarbon-based organic peroxides such as diisobutyl peroxide, diisopropyl peroxydicarbonate, dinormal propyl peroxydicarbonate and isobutyryl peroxide are also suitable. The polymerization initiator is generally used in an amount of 0.01 to 1% by weight based on all monomers.

The polymerization temperature is not particularly limited, but is generally 0 to 100 ° C. In the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, when the polymerization temperature becomes high, the β-
Dissociation easily occurs and unstable ends are easily generated.

[Chemical 4] (In the formula, Rf represents a fluoroalkyl group.) In such a case, a relatively low temperature, for example, about 0 to 25 ° C. is preferable in consideration of the decomposability of the initiator and the terminal stability. In the ethylene-tetrafluoroethylene copolymer, a low temperature is generally preferable in order to avoid a decrease in heat resistance due to the formation of ethylene-ethylene chains.

[0013] The polymerization pressure is usually well polymerization operation on a 0~50kg / cm ² G is desirably relatively low pressure 1~20kg / cm ² G. However, the polymerization pressure is appropriately determined according to the amount of the solvent to be used and other polymerization conditions such as vapor pressure and polymerization temperature.

In the polymerization of the fluorinated olefin of the present invention or the copolymerization of ethylene and the fluorinated olefin, self-decomposition and explosion may occur. The perfluorocyclobutane of the present invention has an effect of preventing such an explosion. . For example, when the composition of ethylene-tetrafluoroethylene is in the range of 50:50 to 40:60 mol%, it is about 8
Polymerization pressure is 8 kg / cm ² because it belongs to the explosion range at kg / cm ² G
Above G, safe operation cannot be guaranteed. By adding 5 mol% of perfluorocyclobutane to all the monomers, the explosion limit increased to 18 kg / cm ² G or more. Further, it was clarified that the addition of 10 mol% of C-318 to such a mixed gas does not enter the explosion range even at 20 kg / cm ² G. From these facts, it becomes possible to safely carry out the polymerization reaction even at a polymerization pressure of 10 to 50 kg / cm ² G by adding 1 to 20 mol% of C-318 to the additional monomer mixed gas with respect to the total amount. It was

Explosions can occur during storage and transfer of monomers, but the perfluorocyclobutanes of the present invention can prevent such explosions. Therefore, the raw material fluorinated olefin (including a mixture) or ethylene and fluorinated olefin (including a mixture)
If perfluorocyclobutane is mixed in advance with, not only explosion during storage and transfer of the monomer can be prevented but also explosion during polymerization can be prevented. The perfluorocyclobutane used for this purpose is particularly preferably 1 to 20 mol% based on the conditions of use.

[0016]

EXAMPLES Next, the present invention will be described concretely by showing Examples. The physical properties of the copolymer were measured as follows. Melting point: 1 using Perkin-Elmer type II DSC apparatus
The melting peak when the temperature is raised at a rate of 0 ° C./min is recorded, and the temperature corresponding to the maximum value is taken as the melting point. Melt flow rate (MFR value): Using a Koka type flow tester, under a load of 5 kg, inner diameter 2 mm and length 8 mm
Through a nozzle of 300 ° C for ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-
The tetrafluoroethylene copolymer was extruded at 230 ° C., and the extrusion amount per unit time was measured. Melt viscosity: Using a Koka type flow tester, under a load of 7 kg, pass a nozzle with an inner diameter of 2 mm and a length of 8 mm to 380
It was measured by extrusion at 0 ° C. Chlorine analysis: Measured by activation analysis.

Example 1 1040 g of deoxygenated water was placed in a glass-lined autoclave having an internal volume of 4 l, and the autoclave was evacuated to obtain a solvent C-318 8.
The temperature in the tank was kept at 15 ° C. by adding 00 g. 40 g of perfluoro (propyl vinyl ether) was charged, and tetrafluoroethylene was injected under pressure to 3.6 kg / cm ² G with stirring.
Then, 3.2 g of di (ω-hydroperfluorohexanoyl) peroxide was charged to initiate polymerization. Since the pressure lowered with the progress of polymerization, when it dropped 0.5 kg / cm ² G, i.e. tetrafluoroethylene to 3.6 kg / cm ² G where intracisternal pressure became 3.1 kg / cm ² G Press fit.
This operation was repeated 40 times to complete the polymerization. Polymerization time is 2.
It was one hour. After the completion of the polymerization, the content was recovered to obtain 270 g of a tetrafluoroethylene-perfluoro (propyl vinyl ether) copolymer powder. The perfluoro (propyl vinyl ether) content in the copolymer was 3.2% by weight. Melting point 309.4 ° C., melt viscosity 4.09 × 10 ⁶ poise (380 ° C.), chlorine content 0 ppm.

Comparative Examples 1 to 6 Fluorine-containing polymers were produced in the same manner as in Example 1 except that the solvents shown in Table 1 were used. The results are shown in Table 1.

[0019]

[Table 1]

As is clear from this table, any fluorine-containing solvent having hydrogen in the molecule lowers the molecular weight of the tetrafluoroethylene-perfluoropropyl vinyl ether copolymer. C as the method polymerization solvent of the present invention
It can be understood that the essential advantage of using -318 is that a polymer having a high molecular weight can be obtained, if necessary, with a yield and a melt viscosity comparable to those of R-114. Next, for the production of tetrafluoroethylene-ethylene copolymer and vinylidene fluoride-tetrafluoroethylene copolymer, C
Examples of a method characterized by using -318 as a polymerization solvent and comparative examples will be described.

Example 2 200 L of deoxygenated water was placed in a glass-lined autoclave having an internal volume of 500 L to make a vacuum, and C-318 20
0 kg was charged and the temperature of the bath was kept at 35 ° C. CH ₂
= 830 g of CF (CF ₂ ) ₃ H and 400 g of cyclohexane
Was charged and stirred with tetrafluoroethylene / ethylene /
C-318 mixed gas (molar ratio 73.8: 16.2: 10) was injected under pressure up to 8.5 kg / cm ² G. Then, 400 g of diisopropyl peroxydicarbonate was charged to initiate polymerization. Since the pressure decreases as the polymerization progresses, tetrafluoroethylene / ethylene / CH ₂ ═CF (CF ₂ ) ₃ H /
C-318 (molar ratio 47.9: 41.6: 1.5: 9.0) was additionally injected to maintain the polymerization pressure at 8.5 kg / cm ² G. Polymerization was carried out for 81 hours. After the completion of the polymerization, the content was recovered to obtain 143.9 kg of polymer powder. The composition of the obtained copolymer is tetrafluoroethylene: ethylene: CH ₂ : CF (CF ₂ ) ₃ H
= 54.1: 44.5: 1.4 (molar ratio). Melting point 2
65.0 ° C., MFR (300 ° C.) = 22.3 g / 10
Min, chlorine content 0ppm.

Example 3 1 liter of deoxygenated water was put into a glass-lined autoclave having an internal volume of 4 liters, a vacuum was put therein, and 0.84 kg of C-318 was placed therein, and the temperature inside the vessel was kept at 35 ° C. CH ₂ = CF
6.1 g of (CF ₂ ) ₃ H and 2.8 g of cyclohexane were charged, and tetrafluoroethylene / ethylene / C-3 was added with stirring.
12 kg of 18 mixed gas (molar ratio 73.5: 16.5: 10)
Pressed up to / cm ² G. Then, 4 g of diisopropyl peroxydicarbonate was charged to initiate polymerization. Since the pressure decreases as the polymerization progresses, tetrafluoroethylene / ethylene / CH ₂ ═CF (CF ₂ ) ₃ H / C-318
(Molar ratio 47.1: 40.2: 3.5: 9.3) was additionally injected to keep the polymerization pressure at 12 kg / cm ² G. The polymerization was carried out for 7 hours. After the polymerization was completed, the content was recovered and polymer powder 246g
Got Copolymer composition of tetrafluoroethylene: _{ethylene: CH 2 = CF (CF 2} ) 3 H = 52.0: 44.4: 3.
It was 6 (molar ratio). Melting point 268.5 ° C, MFR
(300 ° C.) = 12.4 g / 10 minutes, chlorine content 0 ppm.

Comparative Example 7 200 l of deoxygenated water was placed in a glass-lined autoclave having an inner volume of 500 l to make a vacuum, 200 kg of R-114 (dichlorotetrafluoroethane) was placed therein, and the temperature inside the tank was kept at 35 ° C. CH ₂ = CF (CF ₂ ) ₃ H
Charge 930 g and cyclohexane 1300 g, and stir with stirring tetrafluoroethylene / ethylene mixed gas (molar ratio 81.
7: 18.3) was press-fitted to 7.5 kg / cm ² G. Then, 400 g of diisopropyl peroxydicarbonate was charged to initiate polymerization. Since the pressure decreases as the polymerization proceeds, tetrafluoroethylene / ethylene / CH ₂ ═C
The polymerization pressure was maintained at 7.5 kg / cm ² G by additionally pressurizing F (CF ₂ ) ₃ H (molar ratio 51.5: 46.3: 2.2). Polymerization 3
It went for 8 hours. After the completion of the polymerization, the content was recovered to obtain 140 kg of polymer powder. Copolymerization composition tetrafluoroethylene: _{ethylene: CH 2 = CF (CF 2} ) 3 H = 51.5: 46.
It was 3: 2.2 (molar ratio). Melting point 268.4 ° C, M.
FR (300 ° C) = 4.3g / 10 minutes, chlorine content 3.2
ppm.

Comparative Example 8 1 l of deoxygenated water was placed in a glass-lined autoclave having an internal volume of 4 l, a vacuum was applied, and 1 kg of R-114 was placed therein to keep the temperature inside the bath at 35 ° C. CH ₂ = CF (CF
₂ ) ₃ H (5.5 g) and cyclohexane (4.0 g) were charged, and tetrafluoroethylene / ethylene mixed gas (molar ratio 8
2:18) was press-fitted to 7.5 kg / cm ² G. Then, 4 g of diisopropyl peroxydicarbonate was charged to initiate polymerization. Since the pressure decreases as the polymerization progresses, tetrafluoroethylene / ethylene / CH ₂ ═CF (CF ₂ )
₃ H (molar ratio 50.4: 46.6: 3.0) was additionally injected to keep the polymerization pressure at 7.5 kg / cm ² G. Polymerization was carried out for 3.5 hours. After the polymerization was completed, the contents were recovered and polymer powder 100g
Got The copolymerization composition of tetrafluoroethylene: _{ethylene: CH 2 = CF (CF 2} ) 3 H = 50.4: 46.6: 3.0
(Molar ratio). Melting point 268.4 ° C, MFR (3
(00 ° C.) = 9.28 g / 10 minutes, chlorine content 3.8 ppm.

Example 4 250 L of deoxygenated water was put into a glass-lined autoclave having an internal volume of 500 L to make a vacuum, and C-318 25
0 kg was added and the temperature inside the tank was maintained at 37 ° C. Tetrafluoroethylene-vinylidene fluoride / C-318 with stirring
Mixed gas (molar ratio 18:72:10) with 12.0 kg / cm ² G
Pressed up. Then isobutyryl peroxide 32
The polymerization was started by charging 0 g. Since the pressure decreases as the polymerization progresses, tetrafluoroethylene / vinylidene fluoride / C-318 (molar ratio 18.2: 72.7: 9.
1) Add the mixed gas additionally and set the polymerization pressure to 12.0 kg / cm ^2.
I kept it at G. Isobutyryl peroxide 1 every 5 hours
50 g was additionally pressed. The polymerization was carried out for 24 hours. 140 kg of polymer powder was obtained. The composition of the copolymer was tetrafluoroethylene: vinylidene fluoride = 20: 80 (molar ratio). Melting point 130 ° C, MFR (230 ° C) =
20g / 10 minutes, chlorine content 0ppm.

Comparative Example 9 250 L of deoxygenated water was placed in a glass-lined autoclave having an internal volume of 500 L and a vacuum was applied to R-11425.
0 kg was added and the temperature inside the tank was maintained at 37 ° C. With stirring, a tetrafluoroethylene-vinylidene fluoride mixed gas (molar ratio 20:80) was injected up to 8.5 kg / cm ² G. Then, 320 g of isobutyryl peroxide was charged to initiate polymerization. Since the pressure decreases as the polymerization progresses, tetrafluoroethylene / vinylidene fluoride (molar ratio 2
0:80) The mixed gas is additionally injected, and the polymerization pressure is 8.5 kg /
It was kept at cm ² G. 150 g of isobutyryl peroxide was additionally pressed in every 5 hours. The polymerization was carried out for 25 hours.
After the completion of the polymer, the content was recovered to obtain 140 kg of polymer powder. The composition of the copolymer was tetrafluoroethylene: vinylidene fluoride = 20: 80 (molar ratio). Melting point 130 ° C., MFR (230 ° C.) = 19.8 g / 10 minutes,
Chlorine content 4.2ppm.

[0027]

As described above, when the perfluorocyclobutane of the present invention is used, a high degree of polymerization is obtained when a fluoropolymer is produced by polymerizing a fluorinated olefin or by copolymerizing ethylene and a fluorinated olefin. Degree of polymer can be obtained. Therefore, it can be used as a substitute for the conventionally used R-113 or R-114.
Further, it is possible to avoid mixing chlorine into the polymer, which is recognized in R-113 and the like. Furthermore, the method of the present invention increases the safety of polymerization.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08F 2/18 MBF 7442-4J 2/22 MBM 7442-4J ZAB 7442-4J (72) Inventor Sogabe Toshio Nishiichitsuya 1-1, Settsu-shi, Osaka Daikin Industries, Ltd. Yodogawa Works (72) Inventor Yoshikazu Nakano Nishiichitsuya 1-1, Settsu-shi, Osaka Daikin Industries Ltd. Yodogawa Works

Claims (5)

[Claims] 1. The formula: CF ₂ ═CF ₂ , CH ₂ ═CF ₂ , CF.
_{2 = CF-CF 3, CF} 2 = CFCl and CF ₂ = CFO
At least one monomer selected from the group consisting of fluorine-containing olefins represented by Rf (wherein Rf represents a fluoroalkyl group or a fluoropolyether group having 1 to 9 carbon atoms) in the presence of perfluorocyclobutane. A method for producing a fluoropolymer, which comprises polymerizing. 2. A method for producing a fluoropolymer, which comprises copolymerizing the monomer according to claim 1 and ethylene in the presence of perfluorocyclobutane. 3. Further, CH ₂ ═CFR′f (wherein R′f represents a fluoroalkyl group having 2 to 10 carbon atoms), CH ₂
═C (CF ₃ ) ₂ or CH ₂ ═CFOCH ₂ (CF ₂ ) nX
(In the formula, X represents hydrogen, fluorine or chlorine, and n is 1
The method according to claim 1 or 2, wherein the copolymerization is carried out by adding an integer of 10 to 10). 4. The method according to claim 1, wherein the polymerization or copolymerization is suspension polymerization or emulsion polymerization using water as a medium. 5. A method for preventing self-explosion of a monomer, which comprises adding perfluorocyclobutane to a monomer containing a fluorinated olefin or a mixture of a fluorinated olefin and ethylene.