Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-09-26
2003-12-09
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S089000, C526S229000, C526S250000, C526S942000
Reexamination Certificate
active
06660818
ABSTRACT:
The present invention relates to a method for producing a fluoropolymer in the presence of fluoroform and water.
Heterogeneous polymerization employing supercritical carbon dioxide has been proposed. Carbon dioxide is inexpensive and safe and presents little influence over the environment, and it is thus preferred as a solvent for polymerization. U.S. Pat. No. 5,312,882 to DeSimone et al discloses a heterogeneous polymerization method for synthesizing a water-insoluble polymer in carbon dioxide. This heterogeneous reaction mixture contains carbon dioxide, a monomer and a surfactant, but does not contain water or a water-rich phase.
Further, carbon dioxide is used as a polymerization medium for polymerization of a hydrocarbon type monomer and a fluoromonomer. For example, U.S. Pat. No. 3,522,228 to Fukui et al discloses a method for polymerizing a vinyl monomer employing a hydrocarbon type polymerization initiator in carbon dioxide. U.S. Pat. No. 4,861,845 to Slocum et al discloses a method for gas phase polymerization of tetrafluoroethylene and another fluoromonomer diluted with gaseous carbon dioxide. WO93/20116 by DeSimone of North Carolina University, discloses a method for producing a fluoropolymer, wherein a fluoromonomer is solubilized and polymerized in a solvent containing carbon dioxide. In this example, a fluoromonomer selected from the group consisting of a fluoroacrylate, a fluoroolefin, a fluorostyrene, a fluorovinyl ether and a fluoroalkylene oxide, is used.
In the foregoing examples, in each case, carbon dioxide in a supercritical state is employed, but there is no case where fluoroform in a supercritical state is used.
WO00/47641 discloses a polymerization method for a fluoropolymer in a supercritical state of a fluorocarbon. However, there is no disclosure or indication about a medium wherein a fluorocarbon in a supercritical state and water are coexistent.
It is an object of the present invention to provide a method for producing a fluoropolymer, wherein an inexpensive and environmentally preferred medium is used, and a formed polymer can be separated from the medium relatively easily. Namely, the object of the present invention is to provide a method for producing a fluoropolymer, which comprises polymerizing a monomer containing a fluoromonomer having a polymerizable double bond in a medium containing fluoroform and water, under a condition such that fluoroform is in a supercritical state.
That is, the present invention provides a method for producing a fluoropolymer, which comprises polymerizing a monomer containing a fluoromonomer having a polymerizable double bond, using an initiator, in a medium containing fluoroform and water, under a condition such that fluoroform is in a supercritical state.
Now, the present invention will be described in detail with reference to the preferred embodiments.
The method for producing a fluoropolymer of the present invention is carried out in a medium containing fluoroform and water under a condition such that fluoroform is in a supercritical state. By letting fluoroform be in a supercritical state, the dispersion state of the resulting fluoropolymer will be good.
Usually, gas becomes liquid upon application of pressure, but at a temperature higher than the critical temperature specific to the gas, it will not be liquefied even if pressure is applied and will be in a supercritical state having a nature intermediate between liquid and gas. In a supercritical state, it is capable of dissolving many substances like a liquid and exhibits high flowability like a gas. As conditions to bring fluoroform in a supercritical state, the critical temperature is about 26° C., and the pressure is at least about 48.5 MPa.
In the present invention, the degree of polymerization of the fluoropolymer to be produced, can be controlled by changing the mixing ratio of fluoroform and water as the medium. The mixing ratio of fluoroform/water in the medium is preferably from 1/99 to 99/1 by mass ratio. It is more preferably from 10/90 to 90/10, most preferably from 30/70 to 70/30.
The fluoromonomer in the present invention is a fluoromonomer having a polymerizable double bond. As such a fluoromonomer, a monomer having at least one fluorine atom, perfluoroalkyl group or perfluoroalkoxy group, which is bonded directly to the polymerizable double bond, is preferred.
Specific examples include a fluoroolefin such as tetrafluoroethylene, hexafluoropropylene, vinyl fluoride, vinylidene fluoride or chlorotrifluoroethylene, a perfluoro(alkyl vinyl ether) such as perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether) or perfluoro(propyl vinyl ether), a perfluoro(alkyl vinyl ether) having a functional group, such as CF
2
=CFOCF
2
CF(CF
3
)OCF
2
CF
2
SO
2
F or CF
2
=CFOCF
2
CF(CF
3
)OCF
2
CF
2
CO
2
CH
3
, a fluoromonomer having an alicyclic structure, such as perfluoro(2,2-dimethyldioxazole), a fluoromonomer having a curable site, such as bromotrifluoroethylene, and a (perfluoroalkyl)ethylene having a perfluoroalkyl group having from 1 to 6 carbon atoms. These monomers may be used alone or in combination as a mixture of two or more of them. The fluoromonomer may be gaseous or liquid.
The fluoromonomer is preferably at least one member selected from the group consisting of tetrafluoroethylene, hexafluoropropylene and a perfluoro(alkyl vinyl ether), more preferably tetrafluoroethylene. Tetrafluoroethylene has good polymerizability, and the resulting polymer has a wide range of industrial applications.
It is also preferred that the monomer in the present invention contains a monomer other than the fluoromonomer. As the monomer other than the fluoromonomer, a monomer copolymerizable with the fluoromonomer, is preferred, and a hydrocarbon type monomer having a polymerizable double bond, is more preferred.
Specific examples for the monomer other than the fluoromonomer include an olefinic monomer such as ethylene, propylene, isoprene, chloroprene, butadiene or vinyl chloride, a vinyl carboxylate monomer such as vinyl acetate, a (meth)acrylate monomer such as an alkyl methacrylate, methacrylic acid, an alkyl acrylate, acrylic acid or acrylamide, a styrene monomer such as styrene or tert-butylstyrene, a vinyl ether monomer such as ethyl vinyl ether, n-butyl vinyl ether, hydroxybutyl vinyl ether or cyclohexyl vinyl ether, acrylonitrile, and maleic anhydride.
The content of the monomer is preferably from 1 to 100 parts by mass, more preferably from 5 to 50 parts by mass, per 100 parts by mass of the total of water and fluoroform as the medium.
In the method for producing a fluoropolymer of the present invention, an initiator is used. Preferably, a water-soluble initiator is used. When a water-soluble initiator is used, the residue of the initiator dissolves in the water phase after polymerization and scarcely remains as an impurity in the resulting polymer.
The water-soluble initiator may, for example, be an inorganic peroxide such as hydrogen peroxide, persulfate ions, potassium permanganate or disuccinic acid peroxide, an alkali metal persulfate or bisulfate, ammonium persulfate, ferrous sulfate, silver nitrate, copper sulfate, or a redox initiator made of a combination thereof.
The initiator is used preferably in an amount of from 0.00001 to 3.0 parts by mass, more preferably from 0.0001 to 1.0 part by mass, per 100 parts by mass of the monomer.
To the medium in the present invention, a water-soluble additive may be incorporated. Such a water-soluble additive may, for example, be a surfactant, a stabilizer, an acid, a base, a salt, a pH buffering agent or an alcohol.
The surfactant may, for example, be an anionic surfactant, a cationic surfactant, a non-ionic surfactant, an amphoteric surfactant or a polymer surfactant.
The anionic surfactant may, for example, be perfluorooctanoic acid and its salts (inclusive of sodium and ammonium salts).
The cationic surfactant is preferably e.g. a stearyltrimethylammonium halide or a laurylstearyltrimethylammonium halide (inclusive of chloride and bromide).
The nonionic surfactant is preferably e.g. polyethyl
Mori Toshiaki
Okahata Yoshio
Tsuchiya Yuri
Asahi Glass Company Limited
Zitomer Fred
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