Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This inven-tion concerns improvements in and
relating to fluorinated ion exchange polymers, and particu-
larly to such polymers used in the form of films and membranes
used in chloralkali electrolysis cells.
Fluorinated ion exchange membranes are known in
the art. The fluorinated ion exchange polymer in such membranes
can be derived from a fluorinated precursor polymer which
contains pendant side chains in sulfonyl fluoride form. The
sulfonyl fluoride functional groups have been converted to
ionic form in various ways, for example, to sulfonate salts
by hydrolysis with an alkaline materi`al, to the sulfonic acid
by acdification of the salts, and to -the sulfonamide by
treatment with ammonia. Examples of such teachings in the art
can be found in U.S. 3,282,875, U.S. 3,784,399 and
U.S. 3,849,243.
Although such polymers and membranes have many
desirable properties which make them attractive for use in
the harsh chemical environment of a chloralkali cell, such as
good long-term chemical stability, their current efficiencies
are not as high as is desired, especially when the caustic
is produced at high concentration. As transport of hydroxyl
ion in a chloralkali cell from the catholyte through the
membrane to the anolyte increases, current efficiency drops.
Larger amounts of oxygen impurity in the chlorine are
thereby produced, and there is a greater buildup of chlorate
and hypochlorite contaminants in the brine, which contami-
nants must be removed and discarded to maintain acceptable
cell operation. Current efficiencies of at least 90% are
highly desirable.
- 2
~%~49L3
Accordingly, there is a need for polymers and
membranes which will permit cell operation at high current
efficiencies, and especially for those which will permit
operation at high efficiencles over long periods of time.
Additiona].ly, it was desired to find a method for modifying
the known polymers and membranes which have pendant side
chains in sulfonyl fluoride form in such a way to obtain
polymers and membranes which will have the high current
efficiencies desired.
SUMMARY OF THE INVENTION
It has now been found that fluorinated ion
exchange polymers and membranes which contain pendant side
chains in ionic carboxylic form and pendant side chains in
ionic sulfonyl form have high current efficiencies.
According to the present invention, there is pro-
~` vided a process which comprises contacting a first fluorinated
polymer which contains pendant side chains containing
-CF-CF2-SO2-~1\groups, wherein Rf is F, Cl or a Cl to C10
Rf ~n/
perfluoroalkyl radical, M is H, an alkali metal, an alkaline
earth metal, ammonium, substituted ammonium including qua-
ternary ammonium, or hydrazinium including substituted
hydrazinium, and n is the valence of M, with an oxidizing
agent, and separating therefrom a second fluorinated poly-
mer which contains pendant side chains containing
-CF-COO-~\groups.
Rf ~nJ
There is also provided according to the present
invention a fluorinated polymer which contains pendant side
chains containing -CF-CF2-SO2-~
Rf n
~1
49~3
groups, wherein Rf is F, Cl or a Cl to Cl0 perfluoroalkyl
radical, M is H, an alkali metal or an alkaline earth metal,
ammonium, substituted ammonium including quaternary
ammonium, or hydrazinium including substituted hydrazinium,
and n is the valence of M. More specifically, the polymer
which contains pendant side chains which contain sulfinic
yroups is
lo ~ CP2 t ~ t
CF2 C,F2
m CF-Z
CF-Rf CF-Rf
CF2 CF2
S2M P S2
wherein
m is O, 1 or 2,
p is l to 10,
q is 3 to 15,
s is O, 1 or 2,
t is O to 10,
the X's taken together are four fluorines or three
fluorines and one chlorine,
Y is F or CF3,
Z is F or CF3,
Rf is F, Cl or a Cl to Cl0 perfluoroalkyl radical,
R is F, Cl or OM~
M is H, alkali metal, alkaline earth metal, ammonium,
substituted ammonium including quaternary ammonium,
hydrazinium including substituted hydrazinium, and
n is the valence of M. When reduction of sulfonic
to sulfinic groups is essentially complete, t in this
polymer will be O. More often, both p and t wlll be at
least 1.
There is also provided a fluorinated polymer which
contains pendant side chains, about 10 to about 95% of
which side chains contain -0-C~F - COO-~l)groups and about 5 to
: Rf n
about 90% of which side chains contain -C,F-CF2-SO3-M(l)
groups, wherein Rf is F, Cl or a Cl to C10 perfluoroalkyl
radical, M is H, an alkall metal, an alkaline earth metal,
ammonium, substituted ammonium including quaternary
ammonium, or hydrazinium including substituted hydrazinium,
and n is the valence of M.
More specifically, such a polymer has the
repeating units
~ ~ j 2 ~ _ C~ - CF2- -
20. ~ m Y CF - z
~COO(l) ~ ¦ S3(1
whereln
m is O, 1 or 2,
p is 1 to 10,
q is 3 to 15,
--5--
~s
~;~./l
~2~43
r ls 1 to 10,
s is o, 1, 2, or 3,
the X's taken together are four fluorines or three
fluorines and one chlorine,
Y is F or CF3
Z is F or CF3
Rf is F, Cl or a Cl to C10 perfluoroalkyl radical,
M is H, alkali metal, alkaline earth metal, ammonium,
substituted ammonium includlng quaternary ammonium,
hydrazinium including substituted hydrazinium, and
n is the valence of M.
With reference to part of the definition of M,
"ammonium, substituted ammonium including quaternary
ammonium, or hydrazinium including substituted hydrazinium"
includes groups defined more specifically as
R5
R4- N - R6, wherein
R7
R4 is H, lower alkyl such as Cl to C6, or NH2; and R5, R6
and R7 are each independently H or lower alkyl such as C
to C6, with the understanding that any two of R4, R5, R6
and R7 may join to form a hetero ring, such as a piperidine or
morpholine ring.
Further within the purview of the present invention is
the process for converting chemical compounds containing a
-CF-CF2-SO2-~1)group to chemical compounds containing a
-CF-COO-M(l) group, wherein Rf, M and n are as
R~ n
~, "~;, .
~z~
defined above, by reaction with an oxidizing agent. There
is also provided according to the invention certain novel
chemical compounds made with this process, including novel
vinyl monomers which contain carboxylic functional groups
and which are useful in making the above polymers; also,
films and membranes of the polymers; and laminar structures
containing the polymers. ~ ;
There is further provided according to the inven- ~
tion a process for making a fluorinated polymer which has :
10 pendant side chains which contain -OCF-COF groups by contac- ~:
Rf
ting a fluorinated polymer which has pendant side chains
which contain -OCFCF2SO3H groups or salts thereof with
Rf
mixture of fluorine and oxygen. Hydrolysis o the polymer
thus obtained produces a fluorinated ion exchange polymer
which contains -OCF-COOH groups or salts thereof, or both
f
-OCF-COOH and -OCF-CF2SO3H groups or salts thereof.
Rf Rf
The ion exchange membranes of the present inven-
tion which contain both ionizable carboxylic and ionizable
sulfonyl groups as active ion exchange sites are highly ~-~
desirable in comparison with prior art ion exchange mem-
branes for several distinct reasons. Most importantly,
outstandsng efficiencies in a chlor-alkali cell have been
obtained in comparison with membranes which contain only
sulfonic acid ion exchange groups obtained by hydrolysis of
pendant sulfonyl groups. For example, treatment of a mem-
brane having pendant sulfonyl groups to modify a surface
layer to incorporate carboxylic groups according to the
present invention results in a dramatic increase in current
-- 7 --
efficiency in a chlor-alkali cell. This improvement is
considered to be of predominant importance in commercial
applicability in reducing the cost of producing a unit of
chlorine and caustic. Illustratively, in a chlor-alkali
plant producing, Eor example, 1000 tons per day of chlorine,
the direct savings in electrical power for only a 1~ increase
in efficiency are very significant.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A need has developed in the chlor-alkali industry
10 for improved ion exchange materials which can be used to replace
existing cell compartment separators which have been used
for decades without substantial improvement in design.
For use in the environment of a chlor-alkali
cell, the membrane must be fabricated from a material which
is capable of withstanding exposure to a hostile environ-
ment, such as chlorine and solutions which are highly
alkaline. Generally, hydrocarbon ion exchange membranes
are totally unsatisfactory for this kind of use because
such membranes cannot withstand this environment.
For commercial use in the chlor-alkali industry,
a film must go beyond the ability to be operable for pro-
longed time periods in the production of chlorine and
caustic. A most important criterion is the current effi~
ciency for conversion of brine in the electrolytic cell to
the desired products. Improvement in current efficiency can
translate into pronounced savings in the cost of production
of each unit of chlorine and caustic. Additionally, from
a commercial standpoint the cost of production of each unit
of products will be determinative of the commercial suit-
30 ability of an ion exchange membrane.
43
The ion exchange polymers of the present inven-
tion possess pendan-t side chains which contain carboxylic
groups and pendant side chains which contain sulfonyl groups
attached to carbon atoms having at least one fluorine atom
connected thereto. The ion exchange polymers of the inven-
tion can be made from polymers which contain pendant side
chains containing -CF-CF2-SO2-~) groups wherein Rf is F,
Rf n
Cl or a Cl to C10 perfluoroalkyl raidcal, M is as defined
above, and n is the valence of M, by subjecting them to an
oxidation. A variety of oxidizing agents are found effec-
tive for oxidizing pendant side chains containing
-CF-CF2SO2-~groups to side chains containing -CF-COO-~
Rf n Rf
groups.
Among suitable oxidizing agents are oxygen!
chromic acid, permanganate salts, vanadate salts in acid
solution, nitrous acid, and hypochlorite salts, The term
"oxygen" is intended to encompass mixtures of gases which
contain oxygen, such as air. The preferred oxidizing agents
are oxygen, chromic acid, permanganate salts and vanadate
salts because they are more effective.
Oxygen can be used to oxidize the pendant ~roups
defined above when M is H, that is, when the functional
group is the free sulfinic acid. ~ith this oxidizing agent,
it is preferred to carry out the oxidation in the presence
of a metal catalyst. It is also preferred to employ an
elevated temperature. At or near room temperature without
a catalyst, although oxygen has littie or no observable
effect even over a period of a few days, significant con-
version to carboxyl groups is observed after three to four
_g _
weeks. At higher temperatures the oxidation is faster;for example, at 50-60~C., without a catalyst, there is a
significant amount of oxidation to carboxyl groups by air
after only a few days. When oxygen is the oxidant, the
polymer, film or membrane to be so treated can simply be
exposed to the gas, or it can be contacted with oxygen in
a liquid medium such as water. The use of a catalyst is
preferred as it speeds the reaction. Metals which can
exist in more than one valence state can be used as catalyst.
10 (For present purposes, zero is not counted as a valence
state.) For example, salts of iron, vanadium, uranium,
cobalt, nickel, copper and manganese have been found effec-
tive.
Other effective oxidizing agents for the pendant
groups, when the functional group is either in the free
sulfinic acid form or in the form of an alkali metal or
alkaline earth metal salt thereof, include permanganate in
either acidic or basic media, chromic acid, vanadate salts
in acidic media, nitrous acid, and hypochlorite salts in
20 basic medi~. It should be understood that the polymer can
be in either free acid form, or salt thereof, when intro-
duced to such oxidizing agents, and that the acid or salt
forms may interconvert depending on the pH of the oxidizing
medium used. The oxidations are ordinarily carried out at
- temperatures above room temperature. These oxidations
can be carried out in media such as water, or in the
presence of inorganic or organic acids such as sulfuric
acid, hydrochloric acid, acetic acid, etc.
It has also been observed that pendant -CF-CF2-~O
Rf
--10--
'~'15~
groups can be converted to -CF-COO~ groups by placing them
Rf
in b~iling water or a boiling organic or inorganic acid
such as formic acid for a period of at least several hours.
It is believed that air oxidation may be occurring under
such conditions. Some oxidizing agents, such as hydrogen
peroxide and nitric acid are ineffective for present purposes.
It is a simple matter to distinguish oxidizing agents effec-
tive for present purposes ~rom those that are ineffective,
merely by determining the presence or absence of character-
istic absorption bands in the infrared spectrum of the
product corresponding to carboxylic acid groups at about
1785 cm-l or to salts thereof at about 1680 cm-l.
It has also been found that a fluorinated compound
contain~ng a -CF-CF2-SO2-M~)group, wherein Rf, M and n are
Rf
as defined above can be oxidized to a -CF-COO-MQ group
Rf
using oxidizing agents and reaction conditions as described
above. The process is generally applicable for compounds
V-CF-CF2-SO2 ~), where V is a straight-chain or branched C
to C20 perhalogenated radical, optionally containing one or
more ether linkages, and the halogen atoms are fluorine
and/or chlorine. To cite but a few examples, V can be
x 2x~1, where x is 1 to 20;
CF2Cl-CFCl-CyF2y~, where y is 1 to 18;
and CF2Cl-CFClO~CF2-CF-0~z, where z is 1 to 3,
Rf
and Rf is as defined above.
-11-
~?r~ ~ ~
~z~
The resulting carboxylic compounds are in some cases known
compounds useful, for example, for conversion to vinyl
esters from which polymers can be made and fabricated into
films, etc. The sulfinic acid having a terminal CF2Cl-CFCl-
group can be derived, for example, starting from a known
sulfonyl compound which has a terminal vinyl group, by first
adding chlorine to saturate the terminal vinyl group, then
reducing the sulEonyl to the sulfinic group with bisulfite
or a hydrazine. The intermediate sulfinic acid compound is
then oxidized to the carboxylic compound which still has
the terminal CF2Cl-CFCL- group, and this in turn can then
be dechlorinated, as with zinc, to make an olefinic car-
boxylic acid which is useful for making polymers and copoly-
mers. The polymers and copolymers can be used, for example,
in making films and in ion exchange applications.
The ion exchange polymers of the present invention
possess pendant side chains which contain carboxylic groups
attached to carbon atoms having at least one fluorine atom
connected thereto, and pendant side chains which contain
sulfonyl groups attached to carbon atoms having at least
one fluorine atom connected thereto, as set forth above.
The ion exchange polymers of the present invention
which possess pendant side chains which contain carboxylic
groups and pendant side chains which contain sulfonyl groups
possess general utility as ion exchange resins. When used
in a film or membrane to separate the anod~ and cathode
compartments of an electrolysis cell, such as a chloralkali
cell, the polymer should have a total ion exchange capac-
ity of 0.5 to 1.6 meq/g (milliequivalents/gram~, preferably
from 0.8 to 1.2 meq/g. Below an ion exchange capacity of
-12-
.
L3
0.5 meq/g, the electrical resistivity becomes too high,
and above 1.6 meq/g the mechanical properties are poor
because of excessive swelling of the polymer. The values
of p, q and r in the above Eormulas of the copolymer should
be adjusted or chosen such that the polymer has an equiva-
lent weight no greater than about 2000, preferably no
greater than about 1500, for use as an ion exchange barrier
in an electrolytic cell. The equivalent weight above
which the resistance of a film or membrane becomes too high
for practical use in an electrolytic cell varies somewhat
with the thickness of the film or membrane. For thinner
films and membranes, equivalent weights up to about 2000
can be tolerated. For most purposes, however, and for
films of ordinary thickness, a value no greater than about
1500 is preferred.
The polymers which contain pendant side chains
containing -CF CF2-SO2-~groups, wherein Rf, M and n are
Rf n
as defined hereinabove, are in turn made from known percur-
sor fluorinated polymers which contain pendant side chains
containing -CF-CF2-SO2A groups wherein Rf is as defined
Rf
above, and A is F or Cl, preferably F. Ordinarily, the
functional group in the side chains of the precursor poly-
mer will be present in terminal -O-CF-CF2SO2A groups. When
Rf
this is the case, the intermediate polymer will contain
-O-~F-CF2SO2- ~ (sulfinic) groups, and the polymers prepared
Rf
therefrom will contain both -O-CF-COORl and -O-CF-CF2SO2R
Rf Rf
~z64q~3
groups. The precursor fluorinated polymers employed can
be of the type disclosed in U.S.P~ 3,282,875, U.S.P.3,560,568
and U.S.P. 3,718,627. More specifically, the precursor
polymers can be prepared from monomers which are fluorinated
or Eluorine substituted vinyl compounds. The precursor
polymers are made from at least two monomers, with at least
one of the monomers coming from each of the two groups
described below.
The first group is fluorinated vinyl compounds
lQ such as vinyl fluoride, he~afluoropropylene, vinylidene
fluoride, trifluoroethylene, chlorotrifluoroethylene,
; perfluoro ~alkyl vinyl ether), tetrafluoroethylene and mix-
tures thereof. In the case of copolymers which will be used
in electolysis of brine, the precursor vinyl monomer desir-
ably will not contain hydrogen.
The second group is the sulfonyl-containing
monomers containing the precursor group -CF-CF2-SO2A,
Rf
wherein Rf and A are as defined above. Additional examples
can be represented by the general formula CF2=CF-Tk-CF2SO2F
wherein T is a bifunctional perfluorinated radical com-
prising 1 to 8 carbon atoms, and k is 0 or 1. The particu-
lar chemical content or structure of the radical T is not
critical, but it must have a fluorine atom attached to the
carbon atom to which the -CF2SO2F group is attached. Other
atoms connected to this carbon can include fluorine, chlorine,
or hydrogen although generally hydrogen will be excluded in
use of the copolymer for ion exchange in a chlor-alkali cell.
The T radical of the formula above can be either branched
or unbranched, i.e., straight-chain, and can have one or
-14-
4;3
more ether linkages. It is preferred that vinyl radical in
this group of sulfonyl fluoride containing comonomers be
joined to the T group through an ether lin~age, i.e., that
the comonomer be of the formula CF2=CF O-T-CF2-SO2F.
Illustrative of such sulEonyl fluoride containing comonomers
are CF2=CFOCF2CF2SO2F,
CF2=CFOCE'2CIFOCF2CF2S02F,
CF3
CF2=CFOCF21FOC~2lFOcF2cF2sO
3 C 3
CF2=CFCF2CF2SO2F, and
CF2=cFocF2fFocF~2cF2so2F
l F2
I
CF3
The most preferred sulfonyl fluoride containing comonomer
is perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride),
CF2=CFOCF2fFOCF2CF2S02F.
CF3
The sulfonyl-containing monomers are disclosed in such
references as U.S.P. 3,282,875, U.S.P. 3,041,317, U.S.P.
3,718,627 and U.S.P. 3,560,568~
The preferred copolymers utilized as the precursor
are perfluorocarbon although others can be utilized as long
as the T group has a fluorine atom attached to the carbon
-15-
~2~ 3
atom which is attached to the -CF2SO2F group. The most
preferred copolymer is a copolymer of tetrafluoroethylene
and perfluoro(3,6-dioxa-4-methyl-7~octenesulfonyl fluoride)
which comprises 20 to 65 percent, preferably, 25 to 50
percent by weight of the latter.
The precursor copolymer used in the present invention
is prepared by general polymerization techniques developed for
homo- and copolymerizations of fluorinated ethylenes, partic-
ularly those employed for tetrafluoroethylene which are
described in the literature. Nonaqueous techniques for
preparin~ the copolymers of the present invention include
that of U.S.P. 3,041,317, that ;~s, by the polymerization of
a mixture of the major monomer therein, such as tetrafluoro-
ethylene, and a fluorinated ethylene containing a sulfonyl
fluoride group in the presence of a free radical initiator,
preferably a perfluorocarbon peroxide or azo compound, at a
temperature in the range 0-200 Q~C and at pressures in the
range 1-200, or more atmospheres. The nonaqueous polymeriza-
tion may, if desired, be carried out in the presence of a
fluorinated solvent. Suitable fluorinated solvents are
inert, liquld, perflourinated hydrocarbons, such as per-
fluoromethylecyclohexane, perfluorodimethylcyclobutane,
perfluorooctane, perfluorobenzene and the like, and inert,
liquId chlorofluorocarbons such as 1,1,2-trichloro-
1,2,2,--trifluoroethane, and the like.
Aqueous techn~ques for preparing the copolymer of
this invention include contacting t~e monomers ~ith an
aqueous medium conta~ning a free~radical initiator to obtain
a slurry of polymer particles ~n non-water-wet or granular
- 16 -
~ ~ ....
43
form, as disclosed in U.S. Patent 2,393,967, or contacting
the monomers with an aqueous medium containing both a free-
radical initiator and a telogenically inactive dispersing
agent, to obtain an aqueous colloidal dispersion of polymer
particles, and coagulating the dispersion, as disclosed, for
example, in U.S.P. 2,559,752 and U.S.P. 2,593,583.
The novel intermediate polymers which contain
pendant side chains containing -CF-CF2-SO2-~1)groups are
Rf n
10 made from the known precursor fluorinated polymers which
contain pendant side chains containing -CF-CF2 SO2X groups
Rf ~R8
by reduction with a compound having the formula H2NN\ g
wherein R is H or Cl to C8 alkyl radical, and R9 is H or a
Cl to C8 alkyl radical, preferably H. The pre~erred reducing
agent is hydrazine in view of its ready availability.
Another effective compound is methylhydrazine. Accordingly,
the preferred reducing agents are those which have the
formula H2NNHR .
A variety of reaction conditions can be used for
the reduction. For example hydrazine has been found effec-
tive when used anhydrous, as the known hydrazine hydrate,
as a 50~ by weight solution in water, or in solution in
other solvents such as dimethylsulfoxide. The reduction
with a hydrazine can advantageously be carried out in the
presence of an acid acceptor. The acid acceptor can be a
tertiary amine such N-methylmorpholine, N,N,N , N1-tetra~
methylethylenediamine, pyridine or triethylamine, or a metal
hydroxide such as KOH or NaOHO Use of a hydroxide or
tertiary amine is preferred because the sulfinic acid
~ C;. ~f~
/ ~
product and by-product hydrogen fluoride can form salts
with the hydrazine reagent, and the hydroxide or tertiary
amine forms a salt with the sulfinic acid and frees the
hydrazine to be available for reducing other sulfonyl
halide groups.
Reduction with a hydrazine is ordinarily done at
temperatures from about room temperature to ahout 40C.,
although higher temperatures can also be used. The reaction
rate increases as the amount of water in the reaction
medium is decreased. Also the reaction rate increases in
dimethylsulfoxide as a medium, and in the presence of a
hydroxide or tertiary amine.
The sulfinic groups in the reduced polymer will
be in the form of sulfinic acid groups, or an alkali metal
or alkaline earth metal salt thereof. Similarly, any sulf-
onyl halide groups that have been hydrolyzed will be in the
form of sulfonic acid groups, or an alkali or alkaline earth
metal salt thereof. In both cases, the form will depend on
the nature of the last medium with which the polymer was
treated, and will ordinarily be the salt of the strongest
base in medium (or the last medium) to which it is (or was)
exposed. Interconversion between acid and salt forms can
be accomplished by treatment with solutions of acids or
bases, as desired. Treatment times must, of course, be
increased as the thickness of the layer to be treated is
increased. Following reduction by a hydrazine, it is best
to wash the pol~mer to free it of excess hydrazine before
proceeding to the oxidation step. At the same time, an
acid or alkaline wash can be carried out, if desired, to
put the polymer in free acid or salt form if a specific
- 18 -
"~
~L3
form is desired for the particular oxidizing agent to be
used.
Although the precursor fluorinated polymer can
be in the form of powder or granules when subjected to the
reduction and oxidation reactions described hereinabove,
more often it will be in the Eorm of a film or ~embrane
when subjected to these reactions.
The polymers of the invention which posses pen-
dant side chains which contain carboxylic groups and pendant
10 side chains which contain sulfonyl groups can also be made
by copolymerizing a mixture of the appropriate monomers.
The carboxyl-containing monomer is one or more compounds
from a third group represented by the formula
CF2=CF~CF2CFtmCF COOR
~ Rf
wherein
Rf is F, Cl, or a Cl to C10 perfluoroalkyl radical,
Rl is lower alkyl or ~
M is H, alkali metal, alkaline earth metal, ammonium
or quaternary ammonium,
n is the valence of M,
Y is F or CF3, and
m is 0, 1 or 2.
The most preferred monomers are those wherein R is lower
alkyl, generally C1 to C5, or M where M is Hr because of
ease of polymerization. Those monomers wherein m is 1 are
also preferred because their preparation and isolation in
good yield is more easily accomplished than when n is 0 or
2.
-- 19 --
'~
The novel compounds
CF2=CFOCF2CFOCF2COOCH3
CF3
and the corresponding Eree carboxylic acid are especially
useful monomers.
Monomers of this third group can be pre~ared,
for example, from compounds havin~ the fo~mula
CF2=CF~OCF2C,F~OC,FCF2SO2
10 wherein Rf, m and Y are as defined ab~ve, by (1) saturating
the terminal vinyl group with chlorine to ~rotect it in
subsequent steps by converting it to a CF2Cl-CFCl- ~roup;
(2) oxidation with nitrogen dioxide to convert the
-OCFCF2SO2F group to an -OCFCOF group; (3~ esteriflcation
Rf Rf
with an alcohol such as methanol to form an -OCFCQQCX3
Rf
group; and (4) dechlorination with zInc dust to re~enerate
the terminal CF2=CF- group. It is also possible to re~lace
steps (2) and (3) of this sequence by the steps (a) reduc-
tion of the -OCFCF2SO2F group to a sulfinic acid
R~
-OCFCF2SO2H or alkali metal or alkaline earth metal salt
Rf
thereof by treatment with a sulfite salt or hydxazine, (b)
oxidation of the sulfinic acid or salt thereof with oxygen
or chromic acid, whereby -OCFCOOH groups or metal salts
thereof are formed as is more fully described hereinab~ve,
and (c) esterification to -OCFCOOCH3 by known methods.
Rf
The carboxyl-containing monomer of the third
group is copolymerized with fluorinated vinyl compounds
`- 20 -
,~ .
9L3
from each of the first and second groups of comonomers
defined hereinabove, and under non-aqueous polymerization
techniques also defined hereinabove.
Yet another method for preparing copolymers of
the invention which possess pendant side chains which
contain carboxylic groups and pendant side chains which
contain sulfonyl groups is by treating a fluorinated
polymer which has pendant side chains which contain
-CFCF2SO2R groups wherein R is ~1 ' M is H or alkali
f
metal or alkaline earth metal, and n is the valence of M,
with a mixture of fluorine and oxygen, whereby
-CFCOF groups are formed. The -CFCOF groups can then be
Rf Rf
hydrolized to ion exhcnage groups - CFCOORl wherein R is
Rf
. Hydrolysis of -CF-COF groups to -CF-COOH groups
n Rf Rf
occurs so readily that the product isolated from the
fluorine/oxygen reaction will ordinarily be at least
20 partially hydrolyzed to the free carboxylic acid.
Conversion of -CFCF2SO2R groups to -CFCOF and -CFCOOR
R~ Rf Rf
groups can vary from low percentages such as 10% to per-
centages of more than 50%, at least in regard to the
surface layer of the article so treated, depending on the
amount o~ treating reagents used, duration of treatment, etc.
In this method, the molar ratio of fluorine to oxygen
can vary widely, e.g., from 1:5 to 1:1000, preferably 1:50
to 1:200. Diluent gases such as nitrogen, helium or argon
can be used. Total gas pressure in the system can also
30 vary widely e.g., from 0.1 to 1000 atomospheres. Ordinarily
- 21
~"
the pressure will be about 75 atmospheres. Temperatures from
-100C. to 250C. can be used, from 20 t 70C. Treatment can
conveniently be carried out in a corrosion resistant metal
pressure vessel.
A sPecific example oE the tyPe of polymer which can
be treated with a fluorine/oxygen mixture is one having the
repeating units
q ~ r
CF - Z
~s
~ CF - Rf
C,F2
SO 2R2
r+p
wherein Rf, p, q, r, s, X, and Z are as defined hereinabove,
and R2 is O~where M and n are as defined hereinabove.
Following treatment with fluorine/oxygen and hydrolysis, the
resulting ion exchange polymer will have r of the sulfonyl
containing groups remaining, and p of them converted to
-OCF2COF and/or -OCF2COOH groups. It should be understood
that while treatment with a mixture of fluorine and oxygen
will effectively destroy and remove all of the sulfonate
groups on at least the surface of the initial polymer, not
all of the pendant side chains from which the sulfonate groups
are removed will be converted to pendant side chains which
contain carboxylic groups; it is believed that some are con-
verted to pendant side chains which terminate in a -CF3 group.
It should be further understood, however, that by proper choice
of the initial polymer,copolymer of the invention containing both
-22-
~2~ 3
carboxylic and sulfonyl groups meeting the composition defined
hereinabove can be prepared.
The initial polymer which contains r+p sulfonyl-con-
taining side chains is in turn made by copolymerizing fluorinated
vinyl monomers of the first and second groups of monomers
described above. Such fluoroinated polymers are described in
U.S.P. 3,282,875, U.S.P. 3,560,568 and U.S.P. 3,718,627.
Although the sulfonyl-containing fluorinated
polymer to be treated with a mixture of fluorine and
oxygen can be in the form of powder or granules when sub-
jected to such treatment, more often it will be in the
form of a film or membrane when it is so treated.
A convenient method for controlling the extent
of the reaction brought about by treatment with fluorine
and oxygen is to begin with a film or membrane of a polymer
which has pendant side chains which contain -O-CFCF2SO2F
groups, and to bring about a partial hydrolysis to
-O-CFCF2SO3H (or metal salts thereof) such that the film
Rf
or membrane is hydrolyzed on either one or both surfaces
thereof to a controlled depth. Upon subsequent treatment
with a mixture of fluorine and oxygen, the layer in sulfony~
fluoride form remains unaffected, and the layer in sulfonic
acid form reacts such that -O-CFCOF groups are produced as
Rf
described above. Upon subjecting the film or membrane to
a full hydrolytic treatment, the interior layer will have
only -O-CFCF2SO3H groups (or salts thereof), and the surface
Rf
23 -
~æ~
layer or layers will have both -O-CFCOOH and -O-CFCF2SO3H
Rf Rf
groups (or salts thereof).
The polymers of the present lnvention can be in
the form of Eilms and membranes.
When the polymers of the invention are in the form
of a film, desirable thicknesses of the order of 0.002 to
.02 inch are ordinarily used. Excessive film thicknesses
will aid in obtaining higher strength, but with the result-
ing deficiency of increased electrical resistance.
The term "membrane" refers to non-porous struc-
tures for separating compartments of an electrolysis cell
and which may have layers of different materials, formed,
for example, by surface modification of films or by lamina-
tion, and to structures having as one layer a support, such
as a fabric imbedded therein.
It is possible according to the present invention
to make films and membranes wherein the pendant side chains
are essentially wholly (i.e., 90% or more) or wholly
(i.e., up to about 996) in the carboxylic form throughout
the structure, and also wherein the pendant side chains
throughout the structure are in carboxylic and sulfonyl form,
for example 10 t0 90% of each. Control in this respect is
exercised during the reduction of the precursor polymer
which contains sulfonyl halide groups to the intermediate
polymer which contains sulfinic groups, by using or not
using competing reactions which produce different products.
For example, when 100% hydrazine is used as the reagent in
the reduction reaction, conversion to sulfinic functional
group, and eventually to carboxylic functional group can be
- 24 -
~",
quite high, of the order of 90-95~, and it is believed that
in the ultimate surface layers conversion to sulfinic or
carboxyl groups can be as high as 98 or 99%. Use of a
combination oE hydrazine and a hydroxide in a solvent like
water or dimethylsulfoxide will result in reduction of
some groups to sulfinic form and hydrolysis of others to
sulfonic acid salt form; because the sulfonic salt form is
not affected during the oxidation step, the ultimate result
is a combination of carboxylic and sulfonyl groups in rela-
tive amount which varies with the relative amounts of hydra-
zine, water a~d hydroxide used. Control of the relative
amounts of carboxylic and sulfonyl functional groups can
also be exercized to some extent during the oxidation
step. Some oxidizing agents such as chromic and vanadate
salts will produce relatively larger amounts of carboxylic
and small amounts of the original sulfonic groups, while
other oxidizing agents such as hypochlorite will produce
relatively smaller amounts of carboxylic and larger amounts
of the original sulfonic groups~
In similar fashion, it is possible to make pro-
ducts where various other functional groups are present in
pendant side chains, in combination with carboxylic groups
in other pendant side chains. For example, the precursor
polymer which contains sulfonyl halide groups can be treated
with hydrazine in combination with ammonia or a primary
amine, whereby not only will some sulfonyl groups be reduced
to sulfinic form, but others will be converted to sulfonamide
or N-substituted sulfonamide groups. The technique whereby
groups of the precursor polymer can be converted to the
form -(SO2NH)mQ, wherein Q is H, NH4, cation of an alkali
- 25 -
~' .
~12G~3
metal and/or cation of an alkaline earth metal and m is the
valence of Q, are set forth in U.S.P. 3,784,399. Preferred
definitions of Q include NH4 and/or cation of an alkali
metal particularly sodium or potassium. The technique
whereby sulfonyl groups of the precursor polymer can be
converted ko N-monosubstituted sulfonamide groups and salts
thereof are as set forth in U.S. Patent 4,085,071, which
issued 1978 April 18.
So that the final film or membrane will have as
low an electrical resistivity as possible, it is desirable
; that essentially all of the sulfonyl halide groups in the
precursor polymer be converted to ac-tive cation exchange
groups, i.e. to either carboxylic or sulfonyl groups of a
type which will ionize or form metal salts. In this respect,
it is highly undesirable that a film or membrane to be
used for ion exchange purposes in an electroly-tic cell to
have a neutral layer, or that a film or membrane to be used
in a chloralkali cell have either a neutral layer or an anion
exchange layer. The film and membrane of the present inven-
tion do not have neutral or anion exchange layers. In this
context, fiber or fabric reinforcing is not considered as a
neutral layer, inasmuch as such reinforcing has openings, i.e.,
its effective area is not coextensive with the area of the
film or membrane.
In the case of films and membranes to be used as
separators in a chloralkali cell, polymers which contain 40-
95% pendant side chains containing carboxylic groups and
5-60% pendant side chains containing sulfonyl groups provide
excellent current efficiency. An equally important criterion
in a chlor-alkali cell, however, is the amount of power
- 26 -
required for each unit of chlorlne and caustic. It is
considered that the polymers of the type disclosed herein
permit a proper combination of operatlng conditions to
realize an excellent and unexpected reduction in power.
Since the power requirement (which may be expressed in
watt-hours) is a function of both cell voltage and current
efficiency, low cell voltages are desirable and necessary.
However, a polymer without a high current efficiency cannot
operate effectively from a commercial standpoint even with
extremely low cell voltages. Additionally, a polymer with
an inherent high current efficiency allows a proper combina-
tion of parameters as in fabrication into the film and/or
operation of the electrolytic cell to realize the potential
theoretical reduction in power. Il]ustratively, the poly-
mer can be fabricated at a lower equivalent weight which
may result in some loss of current efficiency which is more
than compensated by a reduction in voltage. Polymers of the
present invention which have 50-95% pendant side chains
containing carboxylic groups and 5-50% pendant side chains
` 20 containing sulfonyl groups have low power consumption.
It is also possible according to the present
invention to make films and membranes which are structured
to have one surface wherein the polymer has pendant side
chains which are in carboxylic form, and pendant side chains
which are in sulfonyl form, and the other surface wherein
-the pendant side chains of the polymer are wholly in the
sulfonyl form. It is further possible to make films and
membranes structured to have both surfaces wherein the
polymer has pendant side chains in carboxylic form and
pendant side chains in sulfonyl form, and an interior layer
- 27 -
L3
wherein the pendant side chains of the polymer are wholly
in the sulfonyl ~rm.
When only one surface of the precursor structure
is modified to contain carboxylic groups, the depth of the
modiEied layer will normally be from 0.01% to 80% of the
thickness. When both surfaces are modified, the depth of
each modified layer will be less than half the thickness
of the structure, and will normally be from 0.01 to 40%
of the thickness. The thickness of a layer modified to
contain carboxylic groups will ordinarily be at least 200
angstroms in thickness. A convenient way to treat only
one surface of a film or membrane is to fabricate a bag-
like configuration which is sealed shut, and to treat only
the outside or inside of the bag. When only one surface is
modified to contain carboxylic groups, that surface can
face either the anode or cathode in an electrolysis cell,
and in the case of a chloralkali cell it will ordinarily
face the cathode.
Under most circumstances, layered structures will
be such that the layer of carboxylic polymer will be about
1/4 to 5 mils thick, the base layer of sulfonyl polymer will
be about 1 to 15 mils thick, and the total thickness of
the structure will be about 2 to 20 mils thick. The indica-
ted thicknesses are effective film thicknesses, i.e.,
thicknesses which exclude reinforcing fibers and other
members which do not contain ion exchange groups.
Polymers according to the present invention which
contain both carboxylic and sulfonyl groups have utility to
function for ion exchange. Accordingly, general utility
of the polymer for ion exchange is directly contemplated.
- 28 -
~2G,9~3
Illustratively, permeation selection of cations is directly
encompassed. One method of determination of cation exchange
properties is a measurement of permselectivity with separa-
tion of the same cations in solutions but at different
concentrations. This involves cation transport, and a
permselectivity measurement of no voltage would indicate
the polymer does not function for ion exchange.
The polymers which contain sulfinic groups are
useful as intermediates to polymers, films and membranes
which contain carboxylic groups.
A specific use for the polymers of the present
invention which contain both carboxylic and sulfonyl groups
is in a chloralkali cell, such as disclosed in German
patent application 2,251,660, published April 26, 1973, and
Netherlands patent application 72.17598, published June
29, 1973. In a similar fashion as these teachings, a
conventional chloralkali cell is employed with the critical
; distinction of the type of polymeric film used to separate
the anode and cathode portions of the cell. While the
description of said German and Dutch publications is
directed to use in a chloralkali cell, it is within the
scope of the present disclosure to produce alkali or
alkaline earth metal hydroxides and halogen such as
chlorine from a solution of the alkali or alkali earth
metal salt. While efficiencies in current and power
consumption differ, the operating conditions of the cell
are similar to those disclosed for sodium chloride.
An outstanding advantage has been found in terms
of current efficiency in a chlor-alkali cell with the
fluorinated polymers of the type disclosed herein with
~ - 29 -
9L3
pendant groups which contain carboxylic groups and pendant
groups which contain sulfonyl groups.
To further illustrate the innovative aspects of
the present invention, the following examples are provided.
Example ]
A 4-mil film of a copolymer of tetrafluoroethy-
lene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl
fluoride) having an equivalent weight of 1100 was immersed
for 16 hours at room temperature in 85% hydrazine hydrate,
1~ washed with water and immersed for 30 minutes at room
temperature in a 5% solution of potassium hydroxide. The
film was washed with water and immersed at room tempera-
ture in a mixture of 25 ml formic acid and 5 ml 37%
- hydrocloric acid in an atmosphere of oxygen. Increasing
conversion to the carboxylic acid form was observed by
IR analysis after 5 and 60 hours at room temperature and
after an additional 2 hours at 70-80C. in this medlum.
The degree of conversion to the carboxylic acid
form was further increased by heating the film (after a
water wash) for 2 hours at 50C in a mixture of 75% acetic
acid, 3% concentrated sulfuric acid, 2% chromium trioxide
and 20% water. The film was washed with water, and con-
ditioned for cell testing by heating for 2 hours to 70QC
in a 10% solution of sodium hydroxide. Aqueous sodium
chloride was electrolyzed at a current density of 2.0 asi
(aimps/in ) to give 35% NaOH at a current efficiency of 91
at a cell voltage of 4.9 volts.
Example 2
A 4-mil film of a copolymer of tetrafluoroethy-
lene and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl
- 30 -
~'
fluoride) having an equivalent weight of 1100 was immersed
for 48 hours at room temperature in 85Yo hydrazine hydrate.
IR analysis at this point indicates essentially complete
conversion to the sulfinic salt form through the entire
thickness of the film. The film was then heated for 20
minutes to 90C in a solution of potassium hydroxide (13%)
in aqueous dimethyl sulfoxide (30%), rinsed with water and
immersed for 20 minutes at room temperature in a mixture
of 20 ml aqueous hydrochloric acid and 100 ml glacial
acetic acid. The film was again rinsed with water and then
heated for 16 hours to 130C. in an atmosphere of oxygen.
IR analysis at this point indicated the formation of
-CF2CO2H functional groups, the presence of -CF2SO3H groups,
and the complete absence of -SO~F of the starting material
as well as -SO2R groups of the sulfinate intermediate.
The film was conditioned for cell testing by
heating for 2 hours in a 10% solution of sodium hydroxide.
Aqueous sodium chloride was electrolyzed at a current
density of 2.0 asi to give 32% NaOH at a current efficiency
of 91% at a cell voltage of 4.7 volts.
Example 3
A 4-mil film of a copolymer of tetrafluoroethylene
and perfluoro(3,6-diox~4i~ethyl-7-octenesulfonyl fluoride)
having an equivalent weight of 1100 was immersed for 20
hours at room temperature in a mixture of 300 ml dimethyl-
sulfoxide, 100 ml N-methylmorpholine and 80 ml 85% hydrazine
hydrate. The film was then washed with dilute potassium
hydroxide solution and water and immersed for 10 minutes at
room temperature in a mixture of 200 ml acetic acid, 10 ml.
concentrated sulfuric acid, 2 gm ammonium vanadate, 1 gm
~ - 31 -
64~3
vanadyl sulfate and 300 ml water. After that the iilm
was washed with water and exposed to air at room tempera-
ture for 6 days.
The film was then converted to the potassium
salt form by heating for 30 minutes to 90C in a solution
containing 13% potassium hydroxide and 30% dimethylsulfoxide
and washing with water.
Analysis by X-ray fluorescence at this point
showed a potassium content of 0.965 gram atoms per kg and
0.075 gm atoms of sulfur per kg. This indicates a content
of 0.89 meq/gm of carboxylate groups and 0.075 meq/gm of
sulfonate groups.
Aqueous sodium chloride was electrolyzed at a
current density of 2.0 asi in a cell with this film as the
membrane to produce 35% NaOH as a current efficiency of
92% at a cell voltage of 4.9 volts.
Example 4
A 4-mil film of a copolymer of tetrafluoroethylene
and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride)
20 having an equivalent weight of 1100 was immersed for 30
hours at room temperature in 85% hydrazine hydrate (54%
hydrazine on an anhydrous basis~. The film was then washed
with water and a dilute solution of potassium hydroxide.
Infrared analysis indicated that this treatment caused
substantially complete reduction of sulfonyl groups to
sulfinic groups through the entire thickness of the film.
The film was then heated for 17 hours to 70C.
in a solution containing 5% chromium trioxide and 50%
acetic acid in water, rinsed with water, and conditioned
30 for cell testing by heating for 2 hours to 70C in a 10%
- 32 -
~æ~3
solution of sodium hydroxide. Aqueous sodium chloride was
electrolyzed at a current density of 2.0 asi to produce 33%
sodium hydroxide at a current efficiency of 90~ and a cell
voltage of 4.1 volts.
~xam~l~e 5
A 7-mil film of a copolymer of tetrafluoroethylene
and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride)
having an equivalent weight of 1100 was placed as a liner
in a dish and anhydrous hydrazine (95%) was poured into the
liner so as to contact only the upper surface of the film.
After 2 minutes at room temperature, the hydrazine was
removed and the film was washed with water.
The film was then immersed in 50 ml glacial
acetic acid, and 25 ml of a 20% solution of sodium nitrite
was added in portions during a period of 1 hour. The film
was again washed with water. Staining of a cross-section
with Sevron~Brilliant Red 4G indicated a depth of reaction
of 0.5 mils.
The unreacted SO2F groups were hydrolyzed by
heating for 30 minutes to 90C. in a solution of potassium
hydroxide (13%) in a~ueous dimethylsulfoxide (30%). The
film was installed in a chloralkali cell with the
hydrazine treated and oxidized side toward the catholyte.
Aqueous sodium chloride was electrolyzed at a current
density of 2.0 asi to give 25% NaOH at a current efficiency
of 81% at a cell voltage of 4.3 volts.
Example 6
A 4-mil film of a copolymer of tetrafluoroethylene
and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride)
30 having an equivalent weight of 1100 was immersed for 16
- 33 -
,~,
~ ~Z64~;~
hours at room temperature in 85% hydrazine hydrate. The
film was rinsed with water, then with a hot 2% solution of
sodium hydroxide, and again with water. The film was
then heated for 1 hour to S0-60C in a solution of 1~
potassium bisulfate in 80% acetic acid (balance water),
wiped off and exposed to room temperature air for 3 days.
The oxidation was completed by 2 hours immersion in a solu-
tion of 2% CrO3 and 3% H2SO4 in 75% acetic acid (balance
water) at 50C.
The film was washed with water, then heated to
70C. for 1 hour in a 10% solution of NaOH, and evaluated
in a chloralkali cell. Aqueous sodium chloride was elec-
trolyzed at a current density of 2.0 asi (2.0 amps/in2)
to give 30~ sodium hydroxide at a current efficiency of 91%
at a cell voltage of 4.5 volts. After 130 days of opera-
tion sodium hydroxide was being produced at a concentration
of about 32.5~ at a current efficiency of 89% and a cell
voltage of 4.3 volts.
Example 7
A 7-mil film of a copolymer of tetrafluoroethylene
and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride)
having an equivalent weight of 1100, having a T-24 "Teflon"
fabric imbedded therein, and having one surface layer of about 1
mil depth which had been hydrolyzed to the corresponding potassium
salt of the sulfonic acid, was exposed on the sulfonyl fluoride
side to a solution of 18 ml hydrazine hydrate and 45 ml N-methyl-
morpholine in 35 ml dimethylsulfoxide for 15 minutes at room
temperature. me sheet was washed with water, dilute potassium
hydroxidR and again with water. Cutting the sheet through its
thickness and staining with Sevron~Brilliant Red 4G at this point
- 34 -
',if
,.,J~,
indicated that reaction wIth hy~razine had occurred to a depth pf 0.6 mils.
The sample was then washed with 5% sulfuric acid
and exposed to air for 2Q hours at room temperature~
followed by chromic aci~d oxidati~on li~]ce that described i~
Example 6, The she.et was evaluated in a chloralkali cell
at a current density of 2.0 asi~, and sodium hydroxide was
p~oduced at a concentration of 37% at a current efficiency
of 88% a~d a cell voltage o~ 4,6 volts a$ter 20 days of
operati~o~,
Example 8
A 7-mil film of a copolymer of tetrafluoroethylene
and perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride)
having an equivalent weight of 1100 was folded and sealed
to a bag, except for a small opening to permit the intro-
duction of reagents. A mixture of 250 ml dimethylsulfoxide,
100 ml N~methylmorpholine and 90 ml hydrazine hydrate was
poured into the bag and permitted to react for 7 minutes at
room temperature. The bag was then emptied, rinsed with
water and exposed for 1 hour on the inside with a solution
containing 10% KOH and 10% dimethylsulfoxide, rinsed again
with water, and then with dilute acetic acid. The bag was
then opened, the film was cut through its thickness, and
staining with Sevron~Brilliant Red 4G indicated a depth of
reaction of 0.6 mils. The film was then treated for 30
minutes with a solution of 5 gm VOSO4, 5 gm NH4VO3 and 5 ml
concentrated H2SO4 in 3 liters of water, washed with water
and hung up for drying.
After 3 days of air exposure at room temperature,
the film was treated for 1 hour with a solution containing
' '~'"f'
~,,,. .~
~26~3
5% acetic acid, 2% K2SO4 and 2% KHSO4 in water.
The film was then washed with water and vacuum
laminated to a T-25 Teflon~ fabric, followed by total
hydrolysis for 20 minutes in a solution of KOH in aqueous
dimethylsulfoxide.
The resulting membrane was evaluated in a chlor-
alkali cell with the hydrazine treated and oxidized surface
facing the catholyte. Sodium hydroxide was produced at a
concentration of 31% by weight at a current efficiency of
87% and a cell voltage of 5.8 volts at a current density
of 2 asi.
Example 9 Preparation of CF2-CFOCF2CF(CF3)OCF2COOOEI3,
Methyl perfluoro-4-methyl-3,6-dioxa-7-octenoate
A 2-liter 3-necked flask was fitted with a stir-
rer, gas inlet tube and dry ice cooled condenser. ~he
apparatus was blanketed with nitrogen, 3276Ol g of per-
fluoro[2-(2-fluorosulfonylethoxy)-propyl vinyl ether] added
and chlorine bubbled into the flask while irradiating with
a sunlamp until no more chlorine was absorbed. Distillation
yielded 2533.8 g (66.7%) of perfluoro[2-(2-fluorosulfonyl-
ethoxy)-propyl-1,2-dichloroethyl ether], bp 165C.
To a quartz tube (l-inch outside diameter and 1
foot long) heated to 550C. were added nitrogen dioxide at
a rate of approximately 0.2 g/min and 37.6 g perfluoro [2-
(2-fluorosulfonylethoxy)-propyl-1,2-dichloroethyl ether] at
a rate of 0.33 ml/min. The product was trapped in a dry
ice cooled trap, allowed to come to room temperature, treated
with 20 ml methanol, and washed with 250 ml water to give
19.3 g of product. The combined distillation of a number
- 36 -
,,~
of similar runs yielded methyl perfluoro-7,8-dichloro-4-
methyl-3,6-dioxaoctanoate, bp 167C., whose structure was
conflrmed by infrared and NMR spectroscopy.
~ mixture of 10 g crude methyl perfluoro-7,8-
dichloro-4-methyl-3,6-dioxaoctanoate, 5 g zinc dust, 50 ml
anhydrous diethylene glycol dimethyl ether and 0.1 g iodine
was heated 140C. and then distilled. The distillate was
washed with water and the product chromatographed to yield
appreciable amounts of CF2=CFOCF2CF(CF3)OCF2COOCH3.
The structure of the final product was proven by IR spec-
troscopy and by conversion with bromine to
CF2BrCFsrOCF2CF(CF3)OCF2COOCH. The structure of the vinyl
ether was further confirmed by its boiling point, 75C. at
50 mm of Hg, and its NMR spectrum.
Example 10
A piece of 7-mil film of a copolymer of tetra-
fluoroethylene and perfluoro(3,6-dioxa-4-methyl-7-octenesul-
fonyl fluoride) having an equivalent weight of 1200, and
containing one surface layer of approximately l-mil depth
which had been converted to the corresponding sodium salt
of the sulfonic acid, was heated with 15 psi (absolute) of
25% fluorine in nitrogen and 400 psi (absolute) of compressed
air at 50C. for 2 hours. The excess gases were removed~
air added, and the film removed. The infrared spectrum of
the whole film thickness showed the presence of sulfonyl
fluoride groups and absorption at 5.6 microns due to
carboxylic acid. The infrared spectrum of the starting
film was almost identlcal, but lacked the 5.6 micron
absorption.
- 37 -
,f
~L~;Z64~3
.~
A piece of 7~mil film of a copolymer of tetra-
fluoroethylene and perfluorot3,6-dioxa-4-methyl-7-octenesul-
fonyl fluoride) having an e~uivalent weight of 1100, and
containing one surface layer of approximately 1 mil depth
which had been converted to the corresponding sodium salt
of the sulfonic acid, was heated with 15 psi (gauge) of
25% fluorine in nitrogen and 1000 psi (gauge) of oxygen at
30C. for 4 hours. The film was removed and treated at
90C. with a mixture of dimethylsulfoxide, water and
potassium hydroxide for 1 hour. After washing, the film
was mounted in a chloralkali cell, and aqueous sodium
chloride electrolyzed at a current density of 2.0 asi to
give 33.0-38.6% NaOH at current efficiencies of 75.8-
81.7% at a cell voltage of 3.9-4.2 volts.
Example 12
Conversion of CclF2cclF2ocF2cF(cF3)ocF2cF2so2F to
CClF2CClFOCF2CF(CF3)0CF2COOCH3
A mixture of 150 ml water, 50 ml 1,2-dimethoxy-
ethane, 76 g sodium sulfite and 103.4 g
CClF2CClFOCF2CF(CF3)OCF2CF2SO2F was heated in a nitrogen
atmosphere for 16 hours at 85-87C. The mixture was cooled
to 50C., 600 ml of isopropanol added, heated to 70C. and
filtered. The solids were washed twice with hot
isopropanol, and all the filtrates were combined and
evaporated to dryness.
The resulting solid was dissolved in 600 ml
water, and the solution was cooled and acidified with 50
ml concentrated sulfuric acid while keeping the temperature
- 38 -
7,
~:~2~
below 10C. Two grams of ferrous ammonium sulfate was
added and air was bubbled through the solution at room
temperature for 48 hours. The reaction mixture which
contained two liquid layers and a solid was extracted
three times with ether, and the ether extracts were com-
bined and distilled to give 53.8g of a colorless liquid,
b.p. 92-110C at 11 mm Hg.
The 53.8g of liquid was added to 70 ml anhydrous
methanol and 1 ml concentration sulfuric acid and refluxed
for 22 hours; the mixture was added to 300 ml water, and a
lower layer separated. The lower layer was ~ashed with
water and dried with calcium chloride to give 35.6g (40.2%
yield based on starting CClF2CClFOCF2CF(CF3)OCF2CF2SO2F)
of CClF2CClFOCF2CF(CF3)OCF2COOCH3 whose infrared spectrum
and gas chromatographic retention time were identical to
authentic material.
Although the invention has been described by way
of specific embodiments, it is not intended to be limited
thereto. As will be apparent to those skilled in the art,
numerous embodiments can be made without departing from
the spirit of the invention or the scope of the following
claimsO
- 39 -
. ~ ,~ ,.
