Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1996-03-22
1998-08-04
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526255, C08F 200
Patent
active
057895040
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for preparing low molecular weight polytetrafluoroethylene (hereinafter referred to as "low molecular weight PTFE").
DESCRIPTION OF THE CONVENTIONAL ART
Low molecular weight PTFE is not used in the form of a molded article, since it is PTFE having a molecular weight of several thousand to several hundred thousand (60.times.10.sup.4 or less) so that its mechanical strength is very low. But, fundamentally, it maintains the functions of PTFE such as lubricating properties, water repellency, and so on, and is added to other plastics, rubbers, paints, greases, etc. to impart the lubricating properties, water repellency, and so on to surface properties of such materials. In such case, the low molecular weight PTFE is used in a form of fine powder having a particle size of several micrometers to several ten micrometers, or a dispersion in various solvents.
Hitherto, as a preparation process of the low molecular weight PTFE, conventional polymerization methods, pyrolysis of high molecular weight PTFE, decomposition by irradiation, and the like are known. As the polymerization method, there are known a method comprising telomerization of tetrafluoroethylene in a solvent, and an emulsion polymerization method.
As a prior art relating to the telomerization of tetrafluoroethylene in the solvent, only U.S. Pat. No. 3,067,262 is known. Basically, this method comprises polymerizing tetrafluoroethylene in the presence of an active telogen and a free radical generator dissolved in trichlorotrifluoroethane, that is, tetrafluoroethylene is polymerized in the presence of 1.7 to 15 moles of trichlorotrifluoroethane, 0.01 to 0.6 mole of the active telogen, both per one mole of tetrafluoroethylene, and 0.05 to 3 wt. % of the free radical generator based on the weight of tetrafluoroethylene. A reaction temperature is in the range between 75.degree. C. and 200.degree. C., and pressure is from 200 to 600 psig.
The production of the polymerization solvent trichlorotrifluoroethane known from the above prior art is banned by the end of 1995 because of the destruction of the ozone layer, and the selection of a substitute solvent therefor is necessary.
When the polymerization is performed under the above conditions, a temperature control in a batchwise reaction is very difficult in an initial stage of the polymerization in which a tetrafluoroethylene concentration is highest, because of the vary rapid polymerization. In particular, the polymerization is very difficult at a relatively low polymerization temperature of 100.degree. C. or lower in which the temperature can be controlled by warm water which is preferred from the economical view point.
It is described to maintain a constant pressure by supplementing necessary components including tetrafluoroethylene at the same time as the continuous removal of a reaction product from a reaction system. But, since the polymerization pressure is very high, for example, 400 to 600 psig, it is dangerous for operation.
SUMMARY OF THE INVENTION
The present invention solves the above problems of the conventional art, and provides a process for preparing low molecular weight PTFE by polymerizing tetrafluoroethylene in a solvent which is a substitute for trichlorotrifluoroethane and which has a low ozone destruction factor or does not destroy the ozone, under economically advantageous low pressure which can be controlled safely.
According to an aspect of the present invention, there is provided a process for preparing low molecular weight polytetrafluoroethylene having a melting point of 250.degree. C. to 325.degree. C. comprising polymerizing tetrafluoroethylene in at least one polymerization solvent selected from the group consisting of hydrochlorofluorocarbons, hydrofluorocarbons and perfluorocarbons which have boiling points in the range between -10.degree. C. and 70.degree. C. under constant pressure by the supplement of tetrafluoroethylene.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, at least one pol
REFERENCES:
patent: 3067262 (1962-12-01), Brady
patent: 5182342 (1993-01-01), Feiring et al.
patent: 5281680 (1994-01-01), Grot
patent: 5310870 (1994-05-01), Peavy
Cheimcal Abstracts 121:231656, Jul. 5, 1994.
Chemical Abstracts 71:22454, Mar. 31, 1969.
"The CFC-Ozone Issue: Progress on the Development of Alternatives to CFCs" by L.E. Manzer, Science 249, pp. 31-35 (1990).
Ihara Kiyohiko
Maruya Yoshiki
Nakai Kazuhiro
Daikin Industries Ltd.
Sarofim N.
Schofer Joseph L.
LandOfFree
Process for preparing low molecular weight polytetrafluoroethyle does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for preparing low molecular weight polytetrafluoroethyle, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing low molecular weight polytetrafluoroethyle will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1178121