Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1994-03-17
1995-03-21
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526254, C08F 432
Patent
active
053996437
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for preparing a tetrafluoroethylene/hexafluoropropylene copolymer.
RELATED ART
In the preparation of a tetrafluoroethylene/hexafluoropropylene copolymer, usually an alkali, for example, sodium bicarbonate (NaHCO.sub.3) is added to an aqueous medium before the initiation of the polymerization in order to prevent the corrosion of a polymerization reactor so that an aqueous alkaline solution is formed, and then a large amount of a diperoxide initiator is added to conduct the polymerization. The reason why the alkali is added is that an acidic material such as hydrofluoric acid is prepared by the decomposition of the monomer during the polymerization so that the acidic material may corrode the polymerization reactor.
However, since the polymerization initiator tends to be easily hydrolyzed in the aqueous alkaline solution at the beginning of the polymerization, the polymerization initiator cannot be effectively utilized.
In addition, pH of the aqueous medium varies widely so that the hydrolysis conversion is unstable. Accordingly, the initiator efficiency is not constant and a resultant copolymer has an unstable molecular weight.
SUMMARY OF THE INVENTION
An object of the present invention is to stabilize the molecular weight of the tetrafluoroethylene/hexafluoropropylene copolymer prepared by the polymerization in the aqueous medium using the di(fluoroacyl) peroxide polymerization initiator so that the utilization efficiency of the polymerization, initiator is increased.
The present invention provides a method for preparing a tetrafluoroethylene/hexafluoropropylene copolymer by polymerizing tetrafluoroethylene and hexafluoropropylene in an aqueous medium using, as a polymerization initiator, a di(fluoroacyl) peroxide of the formula: ##STR1## wherein X.sup.1 and X.sup.2 each is a hydrogen, fluorine or chlorine atom, m is an integer of 4 to 8 when X.sup.1 is the hydrogen atom, and m is an integer of 3 to 8 when X.sup.1 is the fluorine or chlorine atom, and n is an integer of 4 to 8 when X.sup.2 is the hydrogen atom, and n is an integer of 3 to 8 when X.sup.2 is the fluorine or chlorine atom, characterized in that a fluoroalkylcarboxylic acid of the formula: ##STR2## wherein Y.sup.1 is a hydrogen, fluorine or chlorine atom, and p is an integer of 4 to 8 when Y.sup.1 is the hydrogen atom, and p is an integer of 3 to 8 when Y.sup.1 is the fluorine or chlorine atom, is added to a polymerization system before the initiation of the polymerization or during the polymerization.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing a relationship between a reaction time and pH during the copolymerization of tetrafluoroethylene and hexafluoropropylene .
DETAILED DESCRIPTION OF THE INVENTION
The Y.sup.1 --C.sub.p F.sub.2p -- group in the fluoroalkylcarboxylic acid may be linear or branched. Specific examples of the fluoroalkylcarboxylic acid are .omega.-hydroperfluoroheptanoic acid, .omega.-hydroperfluorononanoic acid, .omega.-hydroperfluoroheptanoic acid, .omega.-hydroperfluoropentanoic acid, perfluoropropionic acid, perfluorobutanoic acid, perfluropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid and the like. Preferably, the amount of the used fluoroalkylcarboxylic acid is from 0.05 to 0.5 parts by weight per 100 parts by weight of water in the polymerization system.
The X.sup.1 --C.sub.m F.sub.2m -- group and the X.sup.2 --C.sub.n F.sub.2n group in the di(fluoroacyl) peroxide used as the polymerization initiator may be linear or branched and may be the same or different. Specific examples of the di(fluoroacyl)peroxide are di(.omega.-hydro-dodecafluoroheptanoyl) peroxide, di(.omega.-hydro-tetradecafluorooctanoyl) peroxide, di(.omega.-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(.omega.-chlor
REFERENCES:
patent: 4663407 (1987-05-01), Oka et al.
Honda Hiroyuki
Noda Tomohisa
Okuno Chuzo
Diakin Industries Ltd.
Sarofim N.
Schofer Joseph L.
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