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Патент USA US2407401

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Patented Sept. 10, 1946
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?
?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'
stored in an appreciable quantity over a period of
Example I'II
Example. II. is. repeated. using, ethanedithi'ol in.
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
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
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
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
absorbent for the stabilizer.
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