Патент USA US2407401код для вставки
2,407,396 Patented Sept. 10, 1946 UNITED STATES PATENT; OFFICE STABILIZATION OF TETRAFLUORO ETHYLENE Merlin Martin Brubaker, Boothwyn, Pa., assignor to: ELI. du Pont deNemours &: Company, Wil.-' mington, Deli, a corporationoi Delaware No. Drawing. Application February 15, 71943, Serial‘ No. 476,027 10' Claims. (Cl. 260-6525? 1 ?uoroethylene. Under similar conditions,- un~ stabilized tetra?uoroethylene polymeri'zes completely in this length of time. comprising fluoroethylenes which‘ are stabilized against spontaneous polymerization. Example II Tetra?uoroethylene polymerizes- after standing 'I’ov a. glass tube similar to- that employed in a few days at room temperature under superat Example I‘ is added about 05 part of butyl‘-mermospheric- pressure in accordance with the teach captan and the: tube is then immersed in liquid‘ ing of U. ‘S. Patent‘ 2,230,654’. This spontaneous ethylene and‘ ?lled about half full of liquid tetra polymerization of tetra?uoroethylene is’ acutely undesirable since it necessitates costly and time 10 ?uoroethylene (about 25 parts)‘. The- tube is then placed‘ in liquid nitrogen, frozen, and sealed. consuming precautions for‘ the safe storing of After standing at room temperature'under- its own tetra?uoroethylene. Thus prior to the present vapor pressure for 625' months, there is: formed‘ invention it has been an accepted practice to store only the smallest unweighable trace of polymer. tetra?uoroethylenev at the temperature of solid carbon dioxide since only in this way could. poly 15 Under similar‘ conditions unstabilized‘ tetra?uoro ethylene polymerizes completely in about one merization be, prevented and‘ tetra?uoroethylene This invention relates to‘ new compositions of matter- and more particularly to compositions' week. stored in an appreciable quantity over a period of ~ Example I'II Example. II. is. repeated. using, ethanedithi'ol in. time. This invention has as an object the production of stabilized ?uoroethylenes which can be stored 20 place of butyl mercaptan as stabilizer. After 6.25 at normal temperature and. superatmospheric months. a very smallv amount. (considerably less pressure. for an. inde?nite. period.‘ of time without than 1% by weight of the tetra?uoroethylene). of undergoing spontaneous polymerization. Other a white greasy material is formed. objects will appear hereinafter. I have discovered that this polymerization of 25 ?uoroethylene compounds can be prevented by Example IV Example II is repeated using octyl mercaptan in place of butyl mercaptan as stabilizer. No polymerization takes place in 1.5 months under compound containing thiol sulfur and that the these conditions. stabilized product thus obtained can be stored at normal temperature and superatmospheric pres 30 ‘ Example V v incorporating therewith a small proportion of a sure for an inde?nite period of time without un dergoing polymerization. For example, tetra ?uoroethylene to which is added about 0.1% to 1% by weight of n-butyl mercaptan undergoes no spontaneous polymerization whatever on stor age under its own vapor pressure at 25° C., where as unstabilized tetra?uoroethylene undergoes ap preciable polymerization in a few days under Tetra?uoroethylene stored in the absence of its liquid phase under 200 lbs/sq. in. pressure at room temperature in a steel container under ' goes considerable spontaneous polymerization after standing for about a month. To the stor age container in which the tetra?uoroethylene is stored under the mentioned conditions is added 0.5% by weight of n-butyl mercaptan which ef such conditions. The invention is further illustrated by the 40 fectively prevents appreciable polymerization following examples: over a period of several months. Example I A thick Walled glass tube is ?lled half full of The ?uoroethylene compounds referred to herein are halogenated ethylene compounds con taining at least one ?uorine atom. Examples of liquid tetra?uoroethylene by condensation with 4.5 these compounds are vinyl fluoride, 1,1-di?uoro ethylene, l-?uoro-l-‘bromoethylene, 1-?uoro-2 the tube cooled in liquid ethylene. The free space above the liquid is then displaced with hy drogen sul?de, the tube is frozen in a bath of liquid nitrogen and then sealed. It is allowed to chloroethylene, 1,2~-difluoro-1,2-dichloroethylene, 1,1Ldi?uoro-2,2-dichloroethylene, 1,1,2-tri?uoro 2-chloroethylene, and tetra-?uoroethylene. The tions the liquid tetra?uoroethylene is under its process of this invention is particularly suitable for the stabilization of poly?uoroethylenes, i. e., own vapor pressure. those containing more than one ?uorine atom. stand at room temperature, under which condi After one week there is formed a very small quantity (less than 1% based on the tetra?uoroethylene present) of a greasy Compounds which can be employed as stabiliz ers include those having at least one thiol (—SH) material bearing little resemblance to polytetra 55 group. Examples of such compounds are hydro 2,407,396 4 3 gen sul?de, mono- and dithiols, such as ethyl As many apparently widely different embodi mercaptan, propyl mercaptan, butyl mercaptan, ethanedithiol, pentadecanethiol-8 and Z-methyl ments of this invention may be made without de parting from the spirit and scope thereof, it is to be understood that I do not limit myself to the speci?c embodiments thereof except as de?ned in pentane-2,4-dithiol. Aromatic thiols, such as thiophenol, thiocresols, and thionaphthols, can also be employed. The inventionis not limited to hydrocarbon thiols, and it is sometimes advan tageous to employ a thiol containing another functional group which may aid in the removal of the stabilizer from the ?uoroethylene when the occasion demands. Examples of such are the appended claims. I claim: . - 1. Tetra?uoroethylene stabilized with su?i cient hydrocarbon thiol to prevent polymeriza tion of the tetrafluoroethylene at 25° C. and superatmospheric pressure. 2. Tetra?uoroethylene stabilized with su?icient octyl mercaptan to prevent polymerization of the gamma-mercaptovaleric acid, delta-mercapto tetrafluoroethylene at 25° C. and superatmos valeric acid, and thiosalicylic acid. Other sub stituted thiols are operable, such as halogenated 15 pheric pressure. . 3. Tetra?uoroethylene stabilized with su?icient thiols, thiol alcohols, thiol esters, thiol amides, n-butyl mercaptan to prevent polymerization of etc. . the tetrafl'uoroethylene at 25° C. and superat The stabilizer is to be employed in amounts ranging from about 0.001% to about 5%, based'on " mospheric pressure. thiocarboxylic acids, such as thioglycolic acid, 4. A process for treating tetra?uoroethylene the monomer. In general, however, it is pre 20 which substantially reduces its tendency to spon ferred to employ the stabilizers in amounts rang taneous polymerization at normal temperature ing from about 0.01% to about 1%, based on the and superatmospheric pressure, said process com-. amount of monomer. prising mixing with the tetrafluoroethylene a Fluoroethylene compounds which are stabilized according to the method given in this invention 25 small amount of a hydrocarbon thiol. 5. The process set forth in claim 4 in which said can be stored inde?nitely without danger of poly hydrocarbon thiol is octyl mercaptan. merization. On the contrary, the unstabilized compound polymerizes on standing‘, either com '6. The process set forth'in claim 4 in which said hydrocarbon thiol is n-butyl mercaptan. pletely ?lling the container with solid polymer or 7. The process set forth in claim 4 inwhich ?lling the exit valves, so that the removal of the said hydrocarbon thiol is added in amount of remainder of the unpolymerized material is im from 0.001% to 5% by weight of the tetra?uoro possible. Since such circumstances are not only ethylene. undesirable but also dangerous, it is of great ad 8. Tetra?uoroethylene stabilized with hydro vantage to be able to store tetra?uoroethylene in de?nitely without danger of such polymerization carbon thiol in amount of from 0.001% to 5% by weight of the tetra?uoroethylene. and by means of stabilizers which are readily re 9. Tetra?uoroethylene stabilized with octyl moved from the monomer. Although it is not es mercaptan in amount of from 0.001% to 5% by sential that the stabilizers be removed before weight of the tetra?uoroethylene. catalyticvpolymerization of the ?uoroethylene, if 10. Tetra?uoroethylene stabilizedwith n-butyl desired, they can be removed, for example, by mercaptan in amount of from 0.001% to 5% by fractional distillation, by scrubbing with a lead weight of the tetra?uoroethylene. acetate solution or by passing the gas over an MERLIN MARTIN BRUBAKER. absorbent for the stabilizer.