Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-08-10
2004-04-06
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S255000
Reexamination Certificate
active
06716942
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for preparing a fluoropolymer by polymerizing in a supercritical state.
BACKGROUND ART
Fluoropolymers have excellent chemical resistance, solvent resistance and heat resistance and therefore are used widely in an industrial field such as automobile industry, semi-conductor industry and chemical industry as a starting material for a sealing member to be used under critical conditions.
Hitherto preparation of fluoropolymers has been carried out by emulsion polymerization or suspension polymerization of a fluoroolefin in an aqueous medium by using a water soluble radical initiator or an oil soluble radical initiator. A polymerization reaction field thereof was substantially in produced polymer particles or in an inactive solvent which hardly affect the polymerization reaction.
In a conventional emulsion polymerization method which is carried out by employing an aqueous medium, generally a water soluble initiator is used, and therefore an end group of a produced polymer is ionic. When the polymer is used as a rubber, an end group thereof reduces a vulcanization reaction rate at vulcanizing and compression set of a final vulcanized article increases. Also when the polymer is used for other applications, the end group has an adverse effect on a molded article, i.e. causing a foaming of the molded article. A solid polymer is prepared by agglomerating an aqueous dispersion obtained after the polymerization reaction by using a proper coagulant and then dehydrating and drying, which, however, requires long and :complicated steps and cannot be said to be an effective preparation process. Further if a residue of the ionic initiator is mixed to the product, there is a problem when an obtained molded article is used as parts for semi-conductor production apparatuses.
In case of the suspension polymerization, there arises a problem with an adherence of a produced polymer on walls of a reactor due to precipitation thereof, which causes a decrease in yield of polymer and an increase in polymer production cost.
In recent years researches have been made actively with respect to use of a supercritical fluid, mainly carbon dioxide, as a reaction field. The supercritical fluid is a fluid having temperature and pressure range higher than the both of critical temperature and critical pressure, and generally the range not so exceeding critical points greatly tends to be used positively from economical point of view.
The supercritical fluid has properties suitable as a reaction medium because of a good thermal conductivity, a rapid diffusion and a small viscosity.
With respect to polymerization of a fluoroolefin which is carried out by employing a supercritical fluid, for example, Japanese Patent Publication No. 505429/1995 discloses a radical polymerization reaction of fluoroacrylate by using supercritical carbon dioxide as a reaction field. Also U.S. Pat. No. 5,312,882 discloses polymerization by using supercritical carbon dioxide as a continuous phase and a monomer as a dispersion phase in the presence of a surfactant which has a moiety having affinity for carbon dioxide. U.S. Pat. No. 5,527,865 discloses a radical polymerization of tetrafluoroethylene in two separate phases in the presence of a fluorine-containing anionic surfactant by using supercritical carbon dioxide and water simultaneously. Further U.S. Pat. No. 5,618,894 describes that polymerization of tetrafluoroethylene, copolymerization of tetrafluoroethylene and perfluoro(propyl vinyl ether) and copolymerization of vinylidene fluoride and hexafluoropropylene are carried out under non-aqueous condition in supercritical carbon dioxide by using a radical polymerization initiator being capable of generating stable polymer end groups. In all of those polymerization reactions, the supercritical fluid is limited to carbon dioxide or a mixture containing carbon dioxide. Japanese Patent Publication No.502691/1998 discloses a reaction by using a liquid being maintained at a pressure higher than atmospheric pressure, supercritical fluid such as carbon dioxide, hydrofluorocarbon, perfluorocarbon, or a mixture thereof. However a dispersion aid is required as an essential component in the reaction field, which is not preferable from the viewpoint of an increase in a purity of an obtained polymer, and a monomer which is a reactive substance is not used as a supercritical fluid.
Examples of polymerization reaction of fluoroolefin in a supercritical fluid by using the monomer itself as the supercritical fluid are tetrafluoroethylene/hexafluoropropylene copolymerization described in U.S. Pat. No. 3,062,793, tetrafluoroethylene/hexafluoropropylene copolymerization and vinylidene fluoride/hexafluoropropylene copolymerization described in WO96/24624, and the like. However in the former publication, there is no description as to vinylidene fluoride, and the reaction is carried out under the condition of about 200 MPa or more. In the latter publication, the reaction is carried out under critical conditions of very high temperature and pressure of from 41 to 690 MPa and from 200° to 400° C., respectively. Therefore there is a disadvantage that installation cost in commercial scale becomes high.
As a result of intensive study to solve the problems such as generation of unstable polymer end groups, lowering of a purity and complicated post-treatment, the inventors of the present invention could solve the above-mentioned problems by forming a supercritical state in the presence of minimum components for polymerization reaction and have completed a process for preparing a fluoropolymer which can reduce an installation cost in commercial scale.
DISCLOSURE OF INVENTION
Namely the present invention relates to the process for preparing a fluoropolymer by polymerizing one or more radically polymerizable monomers comprising at least one fluoroolefin monomer in the presence of a radical polymerization initiator in a reaction field where at least one of the monomers is in a supercritical state.
Also the present invention relates to the process for preparing a fluoropolymer by polymerizing one or more radically polymerizable monomers comprising at least one fluoroolefin monomer substantially in the absence of water in the presence of a radical polymerization initiator in a reaction field where the whole pressure in the polymerization system is 40 MPa or less in an absolute pressure and at least one of the monomers is in a supercritical state.
Also the present invention relates to the process for preparing a fluoropolymer by polymerizing one or more radically polymerizable monomers comprising at least one fluoroolefin monomer in the presence of a radical polymerization initiator and an inactive fluorocarbon in a reaction field where at least one selected from the group consisting of the monomers and fluorocarbon is in a supercritical state.
Also the present invention relates to the process for preparing a fluoropolymer by polymerizing one or more radically polymerizable monomers comprising at least one fluoroolefin monomer substantially in the absence of water in the presence of a radical polymerization initiator and an inactive fluorocarbon in a reaction field where the whole pressure in the polymerization system is 40 MPa or less in an absolute pressure and at least one selected from the group consisting of the monomers and fluorocarbon is in a supercritical state.
Further in those polymerization processes, the polymerization may be carried out in a reaction field where a chain transfer agent is present.
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, “a reaction field where at least one of the monomers is in a supercritical state” and “a reaction field where at least one selected from the group consisting of the monomers and fluorocarbon is in a supercritical state” mean the following reaction fields.
{circle around (1)} In case of using no fluorocarbon and using one monomer, a reaction field in a state exceeding both of critical pressure and critical temperature of the monomer.
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Higuchi Tetsuya
Komatsu Satoshi
Koyama Satoshi
Saito Hideya
Daikin Industries Ltd.
Lipman Bernard
Sughrue & Mion, PLLC
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