Process for producing fluoropolymer

Details Process for producing fluoropolymer Process for producing fluoropolymer

1999-03-23

2001-07-10

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S242000, C526S252000, C526S253000

Reexamination Certificate

active

06258907

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method for producing a fluorine-containing polymer. More particularly, it relates to a method for efficiently producing a fluorine-containing polymer having excellent heat resistance, solvent resistance or chemical resistance, by using a polymerization medium which is less likely to bring about environmental destruction.
BACKGROUND ART
In recent years, fluorine-containing polymers are used for various applications, utilizing their characteristics as high polymer materials excellent in heat resistance, solvent resistance, chemical resistance, etc.
As a method of producing a fluorine-containing polymer, a solution polymerization method, a suspension polymerization method or an emulsion polymerization method has been known. As a polymerization medium of the solution polymerization method or the suspension polymerization method, an inert solvent such as a chlorofluorocarbon (CFC) has been commonly used, since a copolymer having a high molecular weight can be obtained or the speed of polymerization is high. As a specific example of CFC, trichlorofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane or dichlorotetrafluoroethane may be mentioned. Among these, trichlorotrifluoroethane has been mainly used in view of handling.
However, destruction of the ozone layer has been internationally taken up as an environmental problem of global scale, and use of certain CFCs which are considered to be causal substances has been prohibited Therefore, there is substantial demand for developing a substitute for CFC to be used for producing a fluorine-containing polymer.
As a substitute for CFC, a hydrofluorocarbon (HFC) having hydrogen atoms has been proposed, as it has a small ozone destruction coefficient. However, it is known that a substance having C—bonds shows a chain transfer property to a fluoroolefin. Accordingly, it may sometimes be difficult to use it as a polymerization medium for producing a fluoroolefin polymer having a high molecular weight. As another substitute for a polymerization medium, e.g. t-butanol has been known (JPB-52-24073). However, it is necessary to carry out polymerization under high pressure, in order to obtain a copolymer having an adequately high molecular weight.
DISCLOSURE OF THE INVENTION
The present invention provides a method for efficiently producing a fluorine-containing polymer having an excellent heat resistance, solvent resistance or chemical resistance, wherein the speed of polymerization is high, the molecular weight of the fluorine-containing polymer can be made high enough and CFC having a high ozone destruction coefficient is not used.
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have conducted extensive studies to solve the above problems and as a result, have found that a (perfluoroalkyl)alkyl ether of the formula 1 (hereinafter referred to as PFAE) has a small chain transfer property, and by using it as a polymerization medium, the object of the present invention can be achieved:
R—O—R′  Formula 1
wherein R is a C
2-6
perfluoroalkyl group and R′ is a C
1-2
alkyl group.
Namely, the present invention provides a method for producing a fluorine-containing polymer by polymerization in a polymerization medium, wherein PFAE represented by the formula 1 is used as the polymerization medium.
The fluorine-containing polymer of the present invention is a polymer having polymer units based on a fluorine-containing monomer having a polymerizable double bond group. The preferred polymer may, for example, be a polymer having polymer units based on a fluoroolefin as the main constituting units, a polymer having polymer units based on a fluorine-containing monomer having at least two polymerizable double bond groups as the main constituting units, or a polymer having polymer units based on a fluorine-containing monomer having an alicyclic structure as the main constituting units.
Further, the fluorine-containing polymer may be a copolymer of the fluorine-containing monomer having at least two polymerizable double bond groups and the fluorine-containing monomer having an alicyclic structure as mentioned above.
The fluorine-containing polymer having polymer units based on a fluoroolefin as the main constituting units is produced by polymerizing a fluoroolefin monomer alone or at least two types thereof, or copolymerizing a fluoroolefin monomer with the following monomer copolymerizable with the fluoroolefin monomer.
The fluoroolefin monomer to be used in the present invention is an olefin having at least one fluorine atom in the molecule, preferably a fluoroolefin monomer having a carbon number of 2 or 3, in view of polymerizability and characteristics of the polymer obtained.
Specific examples of such a fluoroolefin monomer include a fluoroethylene such as CF
2
═CF
2
, CF
2
═CFCl and CF
2
═CH
2
, and a fluoropropylene such as CF
2
═CFCF
3
and CF
2
═CHCF
3
. Such fluoroolefin monomers may be used alone or in combination as a mixture of two or more of them.
The monomer copolymerizable with such a fluoroolefin monomer may, for example, a (perfluoroalkyl) ethylene having a C
4-12
perfluoroalkyl group such as F(CF
2
)
4
CH═CH
2
or F(CF
2
)
4
CF═CH
2
, a perfluorovinylether such as R
f
(OCFXCF
2
)
m
OCF═CF
2
, wherein R
f
is a C
1-6
perfluoroalkyl group, X is a fluorine atom or a trifluoromethyl group, and m is an integer of from 1 to 6, a vinyl ether having a group which is easily converted to a carboxylic acid group or a sulfunic acid group, such as CH
3
OCOCF
2
CF
2
CF
2
OCF═CF
2
or FSO
2
CF
2
CF
2
OCF(CF
3
)CF
2
OCF═CF
2
, or an olefin monomer such as ethylene, propylene or isobutylene. They may be used alone or in combination as a mixture of two or more of them.
As the fluorine-containing polymer having polymer units based on a fluoroolefin as the main constituting units, a tetrafluoroethylene/ethylene copolymer, a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer, a tetrafluoroethylene/hexafluoropropylene copolymer or a tetrafluoroethylene/hexafluoropropylene/perfluoro(alkyl vinyl ether) copolymer may, for example, be mentioned.
The fluorine-containing polymer having polymer units based on a fluorine-containing monomer having at least two polymerizable double bond groups as the main constituting units, is produced by polymerizing the fluorine-containing monomer alone or copolymerizing it with a fluoroolefin monomer in PFAE.
Specific examples of the fluorine-containing monomer having at least two polymerizable double bond groups include perfluoro(butenyl vinyl ether), perfluoro(allyl vinyl ether) and perfluoro(bisvinyloxymethane). As the fluoroolefin monomer copolymerizable with such a fluorine-containing monomer, CF
2
═CF
2
or CF
2
═CFCF
3
is preferred.
The fluorine-containing polymer having polymer units based on a fluorine-containing monomer having an alicyclic structure as the main constituting units, is produced by polymerizing the fluorine-containing monomer alone or copolymerizing it with a fluoroolefin monomer in PFAE.
Specific examples of the fluorine-containing monomer having an alicyclic structure include perfluoro(2,2-dimethyl-1,3-dioxole), 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole and perfluoro(2-methylene-4-methyl-1,3-dioxolan). As the fluoroolefin monomer copolymerizable with such a fluorine-containing monomer, CF
2
═CF
2
or CF
2
═CFCF
3
is preferred.
In the present invention, it is necessary to use PFAE as a polymerization medium. If the carbon number of PFAE is too small, the boiling point is too low, and PFAE is in a form of gas at normal temperature, thereby it is inconvenient to handle it when removing the polymerization medium, and if the carbon number is too high, the boiling point is too high, whereby it becomes difficult to separate the polymer and the solvent. Further, as it is necessary to suppress the chain transfer property, it is preferred that PFAE has a small hydrogen content.
Accordingly, R in PFAE is a C
2-6
perfluoroalkyl group, part

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