Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1997-02-21
1998-10-20
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526208, 526216, 526254, C08F 200
Patent
active
058247556
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention pertains to a novel process for the production of a fluoroelastomer.
In particular, it pertains to a process for the production of a fluoroelastomer in which the vulcanized product has excellent heat resistance, oil resistance, and chemical resistance and wherein the Mooney viscosity at the same molecular weight is lower than that of a fluoroelastomer prepared by the emulsion polymerization method of the prior art, the permanent compression set is low, the mold-releasing properties are excellent, and mold contamination is insignificant. The fluoroelastomer is produced by carrying out suspension polymerization in an aqueous medium. It is a safe and efficient process because no ozone layer-depleting chlorofluorocarbon solvents are used and recovery of monomers and solvents is simple.
Fluoroelastomers having excellent heat resistance, oil resistance, and chemical resistance have been used widely for containers, sealing materials, and hoses which are used under severe conditions in the industry. Industrially useful fluoroelastomers include fluoroelastomer dipolymers comprising vinylidene fluoride (VF.sub.2) and hexafluoropropylene (HFP) units and fluoroelastomer terpolymers comprising VF.sub.2, HFP, and tetrafluoroethylene (TFE) units.
Production of such fluoroelastomers by emulsion polymerization, suspension polymerization, and solution polymerization methods is known in the art. In the suspension polymerization method, polymerization is carried out by dispersing a monomer, or organic solvent with a monomer dissolved therein, in water and using an oil soluble organic peroxide. This method is preferable on an industrial scale because the post treatment is simple, and the fluoroelastomer prepared has excellent thermal stability, workability, and mechanical properties as disclosed in U.S. Pat. Nos. 3,801,552 and 4,985,520.
In the case of suspension polymerization, halogenated hydrocarbons such as, for example, trichlorotrifluoroethane, are used as solvent media. Such halogenated hydrocarbons improve affinity between fluoroelastomer product and monomer, and permit the monomer to be dissolved in the polymer particles. However, after polymerization, it is difficult to recover the solvent, e.g. trichlorotrifluoroethane, and monomer. In addition, halogenated hydrocarbons such as chlorofluorocarbons are alleged to be ozone layer depleting compounds and their use is gradually being curtailed internationally.
In order to prepare a high molecular weight fluoroelastomer, the use of halogenated hydrocarbons having low chain transfer reactivity in the polymerization reaction, such as CFC-113 (CCl.sub.2 FCClF.sub.2) and HC-141b (CH.sub.3 CFCl.sub.2), is optimal. Because the chain transfer reactivity of hydrocarbon solvents is generally high, preparation of high molecular weight fluoroelastomers in the latter solvents has not been utilized.
There is a method for carrying out suspension polymerization in the absence of halogenated hydrocarbon by simply adding an oil soluble organic (1991) and 3-247,608 (1993)!. In this method, the oil soluble organic peroxide is not diluted. Consequently, the safety at the time of handling, for example in transportation, is a problem, and this method is not practical.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide a safe and efficient process for the production of a fluoroelastomer which uses no ozone layer depleting chlorofluorocarbon type solvent by carrying out suspension polymerization in an aqueous medium. It is a further objective of the invention to provide a process which produces fluoroelastomer product which, when vulcanized, has excellent heat resistance, oil resistance, and chemical resistance, low compression set, excellent mold-releasing properties, and exhibits insignificant mold fouling. Further, in the product so produced the Mooney viscosity at the same molecular weight is lower than that of a fluoroelastomer prepared by the emulsion polymerization method of the prior art.
In particular, the present
REFERENCES:
patent: 3553185 (1971-01-01), Amagi et al.
Hashimura Kenzo
Hayashi Ken-ichi
Ikeda Yukihiro
Kasahara Michio
Bromels Marilyn H.
E. I. Du Pont de Nemours and Company
Sarafin N.
Schofer Joseph L.
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