MEMBRANE DE FLUOROCARBONE POLYMERE A GROUPEMENTS D'ACIDE CARBOXYLIQUE LATERAUX

FLUOROCARBON POLYMER MEMBRANE WITH PENDANT CARBOXYLIC ACID GROUPS

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A fluorocarbon polymer and a cation exchange membrane
formed of fluorocarbon polymer are characterized by the
presence in at least one surface layer of the polymer of pendant
carboxylic acid groups of the formula -- OCF2COOM --, where M
stands for hydrogen, ammonium, quaternary ammonium or a metal
atom.
- 1 -

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A cation exchange membrane comprising a
fluorocarbon polymer containing pendant carboxylic acid
groups represented by -OCF2COOM wherein M is selected from
the group consisting of hydrogen; ammonium; quaternary
ammonium; and metallic atoms.
2. A cation exchange membrane as in Claim 1,
comprising (a) a fluorocarbon polymer containing pendant
carboxylic acid groups represented by -OCF2COOM and (b) a
fluorocarbon polymer having cation exchange groups substan-
tially consisting of sulfonic acid groups represented by
-OCF2CF2SO3M, said fluorocarbon polymer (a) existing as at
least one layer in a thickness each of at least 100 .ANG. on
the surface or in an internal portion of the membrane.
3. A cation exchange membrane as in Claim 2,
wherein the fluorocarbon polymer (a) is present as surface
stratum at least about 100 .ANG. in thickness on one surface
of the membrane.
4. A cation exchange membrane as in Claim 1,
substantially consisting of the fluorocarbon polymer con-
taining pendant carboxylic acid groups represented by
-OCF2COOM.
5. A cation exchange membrane as in Claim 1,
wherein at least 20 mol percent of the ion exchange groups
contained as pendant groups of the fluorocarbon polymer are
-OCF2COOM.
6. A cation exchange membrane of Claim 1, rein-
forced with a material selected from the group consisting
of woven fabrics of inert fibres.
48

7. A cation exchange membrane of Claim 6, wherein
the inert fibres are polytetrafluoroethylene.
8. A cation exchange membrane comprising two
bonded polymer films, a first film comprising a fluorocarbon
polymer containing pendant carboxylic acid groups represented
by the formula -OCF2COOM, wherein M is selected from the
group consisting of hydrogen; ammonium; quaternary ammonium;
and metallic atoms; and a second film comprising a fluoro-
carbon polymer containing pendant sulfonic acid groups rep-
resented by the formula -OCF2CF2SO3M, wherein M is selected
from the group consisting of hydrogen; ammonium; quaternary
ammonium; and metallic atoms; the equivalent weight of the
polymer in each film being from 1000 to 2000; the equivalent
weight of the polymer in the first film being at least 150
higher than the polymer in the second film; the thickness
of the first film being up to 50% of the total thickness.
9. A cation exchange membrane as in Claim 8,
wherein the first film comprises (a) a fluorocarbon polymer
containing pendant carboxylic acid groups represented by
-OCF2COOM and (b) a fluorocarbon polymer having cation ex-
change groups substantially consisting of sulfonic acid
groups represented by -OCF2CF2SO3M, said fluorocarbon poly-
mer (a) existing as at least one layer in a thickness each
of at least 100 .ANG. on the surface or in an internal portion
of the first film.
10. A cation exchange membrane as in Claim 9,
wherein the fluorocarbon polymer (a) is present as surface
stratum at least about 100 .ANG. in thickness on one surface of
the membrane.
11. A cation exchange membrane as in Claim 8,
wherein the first film substantially consists of the
49

fluorocarbon polymer containing pendant carboxylic acid
groups represented by -OCF2COOM.
12. A cation exchange membrane as in Claim 8,
wherein at least 20 mol percent of the ion exchange groups
contained as pendant groups of the fluorocarbon polymer in
the first film are -OCF2COOM.
13. A cation exchange membrane of Claim 8, rein-
forced with a material consisting of woven fabric of inert
fibres.
14. A cation exchange membrane of Claim 13,
wherein the inert fibres are polytetrafluoroethylene.
15. A cation exchange membrane of Claim 13,
wherein the reinforcing material is embedded in the second
film.
16. A polymer having the repeating units
<IMG>
wherein
m is 0, 1 or 2,
p is 1 to 10,
q is 3 to 15,
the X's taken together are four fluorines or three fluorines
and one chlorine,

Y is F or CF3,
R1 is H, or M (?),
M is alkali metal, alkaline earth metal, ammonium or quater-
nary ammonium, and
t is the valence of M.
17. The polymer of Claim 16, wherein m is 1
18. The polymer of Claim 17, wherein the X's
taken together are four fluorines.
19. The polymer of Claim 18, wherein Y is CF3.
20. A film or membrane of a fluorinated ion
exchange polymer having the repeating units
<IMG>
wherein
m is 0, 1 or 2,
p is 1 to 10,
q is 3 to 15,
the X's taken together are four fluorines or three fluorines
and one chlorine,
Y is F or CF3,
R1 is H, or M(?),
51

M is alkali metal, alkaline earth metal, ammonium or quater-
nary ammonium, and
t is the valence of M,
said polymer having an equivalent weight no greater than
about 2000.
21. The film or membrane of Claim 20, wherein m
is 1.
22. The film or membrane of Claim 21, wherein
the X's taken together are four fluorines.
23. The film or membrane of Claim 22, wherein Y
is CF3.
24. The film or membrane of Claim 20, wherein
the equivalent weight is no greater than 1500.
25. The film or membrane of Claim 20, reinforced
with fabric.
26. A laminar structure having (a) a base layer
of a fluorinated ion exchange polymer, and having on at least
one surface thereof (b) a layer of the polymer defined in
Claim 16, the polymer of each layer having an equivalent
weight no greater than about 2000 wherein the base layer (a)
is a fluorinated ion exchange polymer which has pendant side
chains which contain -OCF2CF2SO3R2 groups wherein R2 is F, or
M(?);M is alkali metal, alkaline earth metal, ammonium or
quaternary ammonium; and t is the valence of M.
27. A laminar structure having (a) a base layer
of a fluorinated ion exchange polymer, and having on at least
one surface thereof (b) a layer of the polymer defined in Claim
19, the polymer of each layer having an equivalent weight no
greater than about 2000 wherein the base layer (a) is a
52

fluorinated ion exchange polymer which has pendant side chains
which contain -OCF2CF2SO3R2 groups wherein R2 is H, or M?; M
is alkali metal, alkaline earth metal, ammonium or
quaternary ammonium; and t is the valence of M.
28. The laminar structure of Claim 26 or 27, wherein
the layer (b) is present as surface stratum at least about
100 .ANG. in thickness on one surface thereof.
29. The laminar structure of Claim 26 or 27, wherein
the thickness of the layer (b) is up to 50% of the total
thickness.
30. A fluorocarbon polymer containing pendant
carboxylic acid groups of -OCF2COOM wherein M is selected
from the group consisting of hydrogen; ammonium; quaternary
ammonium; and metallic atoms, said polymer having the
equivalent weight not greater than about 2000.
31. A cation exchange membrane comprising a
fluorocarbon polymer according to Claim 30.
32. A cation exchange membrane as in Claim 31,
comprising (a) a fluorocarbon polymer containing pendant
carboxylic acid groups of -OCF2COOM and (b) a fluorocarbon
polymer having cation exchange groups substantially consisting
of sulfonic acid groups of -OCF2CF2SO3, said fluorocarbon
polymer (a) existing as at least one layer in a thickness of
each at least 100 .ANG. on a surface or internally of the membrane.
33. A cation exchange membrane as in Claim 32,
wherein the fluorocarbon polymer (a) is present as surface
stratum at least about 100 .ANG. in thickness of one surface of
the membrane.
34. A cation exchange membrane as in Claim 31,
53

substantially consisting of the fluorocarbon polymer con-
taining pendant carboxylic acid groups of -OCF2COOM.
35. A cation exchange membrane as in Claim 31,
wherein at least 20 mol percent of the ion exchange groups
contained as pendant groups of the fluorocarbon polymer is
-OCF2COOM.
36. A cation exchange membrane as in Claim 31,
reinforced with a woven fabric of inert fibres.
37. A cation exchange membrane as in Calim 36,
wherein the inert fibres are polytetrafluoroethylene.
38. A cation exchange membrane as in Claim 31,
comprising two bonded polymer films, a first film comprising
a fluorocarbon polymer containing pendant carboxylic acid
groups represented by the formula -OCF2COOM, wherein M is
selected from the group consisting of hydrogen; ammonium;
quaternary ammonium; and metallic atoms; and a second film
comprising a fluorocarbon polymer containing pendant sulfonic
acid groups represented by the formula -OCF2CF2SO3M, wherein
M is selected from the group consisting of hydrogen; ammonium;
quaternary ammonium; and metallic atoms; the equivalent
weight of the polymer in each film being from 1000 to 2000;
the equivalent weight of the polymer in the first film being
at least 150 higher than the polymer in the second film; the
thickness of the first film being up to 50 percent of the total
thickness.
39. A cation exchange membrane as in Claim 38,
wherein the first film comprises (a) a fluorocarbon polymer
containing pendant carboxylic acid groups of -OCF2COOM, and
(b) a fluorocarbon polymer having cation exchange groups
substantially consisting of sulfonic acid groups of
-OCF2CF2SO3M, said fluorocarbon polymer (a) existing as at
54

least one layer in a thickness of each at least 100 .ANG. on a
surface or internally of the first film.
40. A cation exchange membrane as in Claim 39,
wherein the fluorocarbon polymer (a) is present as a surface
stratum at least about 100 .ANG. in thickness on one surface of
the membrane.
41. A cation exchange membrane as in Claim 38,
wherein the first film substantially consists of the fluoro-
carbon polymer containing pendant carboxylic acid groups of
-OCF2COOM.
42. A cation exchange membrane as in Claim 38,
wherein at least 20 mol percent of the ion exchange groups
contained as pendant groups of the fluorocarbon polymer in
the first film is -OCF2COOM.
43. A cation exchange membrane of Claim 38,
reinforced with a material selected from the group consist-
ing of woven fabrics of inert fibres.
44. A cation exchange membrane of Claim 43,
wherein the inert fibres are polytetrafluoroethylene.
45. A cation exchange membrane of Claim 43,
wherein the reinforcing material is imbedded in the second
film.
46. A cation exchange membrane comprising at
least one continuous layer extending to at least one sur-
face of the membrane and formed by a fluorocarbon polymer
according to Claim 35.
47. A cation exchange membrane as claimed in
Claim 46, having only a first surface layer formed by said
polymer.

48. A cation exchange membrane according to
Claim 47, wherein the second surface layer of said membrane
is formed by a second fluorocarbon polymer containing pen-
dant sulfonic acid groups represented by -OCF2CF2SO3M, said
second polymer having an equivalent weight not greater than
about 2000.
49. An electrolytic cell comprising a housing
with separate anode and cathode compartments, separated by
a membrane according to Claim 47 or 48, wherein said first
surface layer faces the cathode compartment.
50. An electrolytic cell comprising an anode
portion and a cathode portion separated by a membrane com-
prising (a) a fluorocarbon polymer containing pendant car-
boxylic acid groups of -OCF2COOM, and (b) a fluorocarbon
polymer having cation exchange groups substantially consist-
ing of sulfonic acid groups of -OCF2CF2SO3M, said fluorocar-
bon polymer (a) existing as a surface stratum at least about
100 .ANG. in thickness on that surface of the membrane which faces
the cathode side of the cell.
51. An electrolytic cell comprising an anode
portion and a cathode portion separated by a membrane com-
prising two bonded polymer films, a first film comprising a
fluorocarbon polymer containing pendant carboxylic acid
groups represented by the formula -OCF2COOM, wherein M is
selected from the group consisting of hydrogen; ammonium;
quaternary ammonium; and metallic atoms; and a second film
comprising a fluorocarbon polymer containing pendant sulfonic
acid groups represented by the formula -OCF2CF2SO3M, wherein
M is selected from the group consisting of hydrogen; ammonium;
quaternary ammonium; and metallic atoms; the equivalent
weight of the polymer in each film being from 1000 to 2000;
the equivalent weight of the polymer in the first film being
56

at least 150 higher than the polymer in the second film;
the thickness of the first film being up to 50 percent of
the total thickness, the side of said first film facing
the cathode side of the cell.
52. A cation exchange membrane as claimed in
claim 46 or 47, wherein the layer of fluorocarbon polymer
containing pendant carboxylic acid groups is at least
about 100 .ANG. thick.
53. A cation exchange membrane of claim 46 or
47, wherein the layer of fluorocarbon polymer containing
pendant carboxylic acid groups has a thickness up to 50
percent of the total thickness.
54. A cation exchange membrane comprising at
least a layer of a fluorocarbon polymer containing pendant
carboxylic acid groups represented by -OCF2COOM wherein M
is selected from the group consisting of hydrogen, ammonium,
quaternary ammonium and metallic atoms and prepared by treat-
ing with a reducing agent a starting membrane comprising a
corresponding fluorocarbon polymer characterized by the
presence of sulfonyl groups represented by the formula:
-OCF2CF2SO2X
and/or
<IMG>
wherein X is selected from the group consisting of halogen;
hydroxyl; alkyl containing up to four carbon atoms; aryl;
and OZ wherein Z is selected from the group consisting of
metallic atoms, alkyl containing up to four carbon atoms
and aryl.
57

55. A cation exchange membrane according to
claim 54, wherein at least 20 mol percent of the functional
groups in said layer are carboxylic acid groups.
56. A cation exchange membrane according to
claim 54 or 55, wherein the thickness of said layer is at
least 100 Angstroms.
58

Description

12~9æ~9
BACKGROUND OF INVENTION
This inventlon relates to improved cation exchange
membranes and to methods for their production. The invention
is further directed to methods for the electrolysis of an
aqueous solution of an alkali metal halide by use of these
cation exchange membrane3, and to the electrolytic cells in
which the electrolysis takes place.
It has been known to the art to obtain a cation
exchange membrane of a perfluorocarbon polymer containing
pendant sulfonic acid ~roups by saponification of a membrane
prepared from a copol,yrner of tetrafluoroethylene and per-
fluoro-3,6-dioxa-4-methyl-7--octene-sulfonyl fluoride. This
known perfluorocarbon type cation exchan~e membrane contain-
ln~ only sulfonic acid ~roups, however, has the disadvantage
that the membrane~ when used in the electrolysis of an aqueous
solution of an alkali metal halide, tends to permit penetra-
tion therethrough of hydroxyl ions back mi~ratin~ from the
cathode compartment because of the high hydrophilicity of
the sulfonic acid group. As a result, the current efficiency
durin~ electrolysis is low. This is a special problem when
the electrolysis is used for the production of a~lueous sol~tion
o~ caustic soda at concentrat:lons o,~ more than 20 percent.
In this reaction, the curren~ e~icienc,~ ls so low that the
process is econornically disadvantageous compared with
electrol,vsls of aaueous solutions of sodium chloride by
conventional mercur;y process or diaphra~m process.
The disadvanta~e of such low current ef~iciency can
be alleviated b,y lowerin~ the exchange capacity o~ the sulfonic
acid group to less than 0.7 milliequivalent per gram of the
H form dr,y resin. Such lowerin~, however, results in a serious
,,~
-- 2 --
.

121939~
decrease in the electroconductivity of the membrane and a
proportional increase in the power consumption. This solution,
therefore, is not without its economic difficulties.
U. S. Patent No. 3,909,378 discloses composite
cation exchange membranes containing sulfonic acid moieties
as the ion exchange group and comprising two polymers with
different equivalent weight (EW), that is number of grams of
polymer containing one equivalent weight of ion exchange
functional group. When such membranes are utilized in the
electrolysis of aqueous solutions of sodium chloride, high
current efficiencies are obtained by effecting the electroly-
sis with the higher EW polymer side of the composite membrane
facing the cathode. For high current efficiency coupled with
low power consumption, the value of EW of the higher EW polymer
must be increased and the thickness decreased as much as
possible. It is, however, extremely difficult to produce a
composite cation exchange membrane having current efficiency
of not less than 90 percent by use of membranes containing
only sulfonic acid groups.
In U. S. Patent No. 3,784,399, Canadian Patent
Nos. 1,033,097 and 1,033,098, there are suggested cation
exchange membranes wherein the cathode sidc surface layers
of fluorcarbon cation exchan~e membranes contain sulfonamide
group, salts thereof or N-mono-substituted sulfonamide group.
These membranes, however, are deficient in electrochemical
and chemical stabilities.
An object of this invention is to provide fluoro-
carbon cation exchange membranes which, even in electrolyis

1~19~9~
for production of caustic soda at hi~h concentration, more
effectively inhibit the back migratiorl of hydroxyl ions and
enable the electrolysis to proceed constantly with higher
current efficiency than the conventional fluorocarbon cation
exchange membranes and to provide a method for the manufacture
of said membranes.
Another ob,~ect of this invention is to provide a
method for the electrolysis of the aqueous solution of an
alkali metal halide b,y use of such cation exchange membranes.
THE INVENTION
Novel cationic membranes characterized by the
presence of carboxylic acids have now been discovered. These
membranes when used in electrolysis cells, particularly when
used in such cells for the electrolysis of sodium chloride to
produce aqueous sodium hydroxide, have many advantages compared
to conventional cation exchan~e membranes. A particular
advanta~e is the durability of the membranes, it having been
found that the current efficiency of the membranes remains
stable at well above 90%, even after many months of operation.
The present invention provides a cation exchan~e
membrane comprisin~ a fluorocarbon polymer containlrl~ pend~nt
carbox~lic acld ~roups r~pre~ented b~ ~he Pormula:
-OCF2COOM
wherein M is hydro~en: ammoniùm; auaternar,v ammonium, parti-
cularly quaternar~ ammonium having a molecular weight of 500
or less; and metallic atoms, particularly alkali or alkaline
earth metals.
In its simplest form, a cation exchan~e membrane of
this invention is a film formin~ perfluorocarbon polymer.
The thickness of the film can be varied widely dependin~ on
purposes. There is no particular limit to the thiclmess, bUt
usually a thickness from 0.5 to 20 mils is suitable for many
-- 4 --

~9~99
purposes.
The preferred embodiments of membranes are
characterized by the presence of at least one surface or
internal layer at least about 100 A in thickness in which
the polymer is substituted with pendant carboxylic acid
groups represented by the fo~mula as set forth above.
The membranes of this invention can be classified
into two major groups. One is a uni-layer film wherein
equivalent weight (EW) of the cation exchange groups is
uniform throughout the membrane. The other is a two-ply film
in which a first film having higher EW value and a second
film having lower EW value are combined. In each case, the
specific fluorocarbon polymer as defined above can be present
either homogeneously throughout the film or as stratum on one
surface or in internal portion of the membrane. The membrane,
however, can sometimes have strata both on opposed surfaces
of the membrane in each of the aforesaid groups. As mentioned
above, according to preferred embodiment of the two-ply layer,
the first film having higher EW value is provided with the
specific fluorocarbon polymer, preferably as surface stratum
of at least 100 2 in thickness on the surface opposite to the
side laminated with the second film. For practical purpose,
the membrane is usually reinforced with reinforcing materials
selected from the group consisting of woven fabrics of inert
fibers and porous films of inert polymers, preferably poly-
tetrafluoroethylene fibers. When the membrane has a surfacestratum of the specific fluorocarbon polymer of the invention,
the reinforcing material is desirably embedded in the membrane
on the side opposite to the side having the surface stratum of
the specific fluorocarbon polymer of the invention. In the
two-ply layer, the reinforcing material is desirably embedded
in the second film having lower EW value.
- 5 -

~9;~9
For convenience, detailed explanation is given inthe following principally with reference to the uni-layer film
having a surface stratum of the specified carboxylic acid
groups. The structure of the first ilm in a two-ply layer
membrane with regard to functional groups is substantially the
same as the uni-layer film. 'When the membrane is used in
electrolysis, the side having the carboxylic acid group
stratum is placed in the eléctrolytic cell to face the cathode
side in order to obtain the remarkable benefits of the
invention.
The stratum may also contain sulfonic acid groups
which may be represented by the formula:
-ocF2cF2so3M
wherein M has the same meaning as abo~e.
In fact, since the cationic membranes of this
invention are derived from sulfonic acid group substituted
fluorocarbon copolymers, they may contain any predetermined
proportion of sulfonic acid groups, or derivatives thereof.
The specific fluorocarbon polymer constituting the
stratum of this invention may contain from 5 to 100 mol
percent of carboxylic acid substituents based on total
cation exchange groups. Usually, as the distance ~rom the
surface increases the relative percent of carboxylic acid
substituents decreases, and the relative percent of sulfonic
acid substituents increases. In preferred embodiments of the
invention, only one surface is predominantly carboxylic acid
substituents, and the quantity of sulfonic acid groups will
increase with distance from that surface until the opposite
surface is predominantly sulfonic acid groups. According to
one preferred embodiment, there is a cation exchange membrane
comprising (a) a fluorocarbon polymer containing pendant
carboxyli,c acid groups of -OCF2COOM and (b) a fluorocarbon
- 6 -

1~9399
polymer having cation exchan~e groups substantially consisting
of sulfonic acid groups of -OCF2CF2S03M. According to the
most preferred embodiment, the membrane consists of a film
of fluorocarbon polymer having -OCF2CF2SO3M cation exchange
groups and which is fiber reinforced on one side and has a
surface stratu~ of fluorocarbon polymer having -OCF2COOM
cation exchange groups on the other side. It is-also possible
by special procedures to prepare embodiments of this invention
in which carboxylic acid groups are uniformly distributed
thro~l ~h o~t
th~gout the membrane.
It has been observed that the presence of carboxylic
acid groups on the surface of the cation exchange membrane,
particularly on the surface facing the cathode, remarkably
impedes the back migration of hydroxyl ions from ~he cathode
compartment during the electrolysis of aqueous solutions of
alkali metal halides such as sodium chloride. These effects
are realized while operating at high current efficiencies,
normally well over 90%. Moreover, the membranes of the
invention are especially durable even in the presence of
aqueous solutions of sodium hydroxide at a concentration of
20%, or even higher, and also highly resistant to chlorine
~ '
gas generated fromZl1anode.
As indicated above, the surfAcc denHiey of cnrboxyJic
acid groups mny vary Erom 5 eo 100 mol percent~ The preferred
range is from 20 to 100 mol percent, and the best combinations
of economy and efficiency are normally realized if the density
is from 40 to 100 mol percent; all based on the total number
of all functional groups in ~he surface strata,
The depth oE the surEace strata can be ascertained
by staining techniques. For example, a section of a prepared
membrane can be immersed for several minutes in an aqueous
bm~
.~,.,,,'Z

~i93~9
solution of crystal violet cont~ining 5 to 1~ ethanol as a
solubility aid. This dye will stain only the treated
sections, and a cross section of the membrane can be
examined microscopically.
Alternatively, the thickness of the layer and the
density of the carboxylic acld groups can be ascertained by
x-ray microprobe analysis.
The membranes of this invention may take any of
several forms, as is particularly illustrated in the examples.
As mentioned above, it may be a simple unilayer film with one
or both major surfaces embodying strata with carboxylic acid
substituents. Alternatively, the membranes may be composite
membranes formed from two appropriately prepared and sub-
stituted perfluorocarbon films bonded together in each of
which the EW is from about 1000 to 2000, preferably 1000 to
1500.
If a two film membrane is employed, the first film
should have an EW which is at least 150 higher than the
second film, and its thickness should be up to one half of
the total thickness. In fact, the thin film should be as
thin as possible to minimize total electrical resistance.
Due to the difficult manufacturing techniques involved, the
thin film will generally occupy from about 10 to 45% of the
total thickness.
In other forms of the invention, the membranes may
be laminated to reinforcing materials to improve mechanical
strength. For this purpose fabrics made of polytetrafluoro-
ethylene fibers are most suitable, although other materials
which are inert to the chemical environment in which the
membranes are employed may also be used. Particularly,
-- 8

1219;~9~
polytetrafluoroethylene films may preferably be employed as
reinforcing materials. If reinforcing materials are utilized,
it is particularly advantageous to em~ed them in the polymer
membrane. This can be readily accomplished, for example, at
elevated temperature and under reduced pressure as illuestrated
in the examples.
In all of hese various constructions, the most
preferred membranes will be constructed with carboxylic groups
predominating on one surface, and sulfonic groups predominating
on the other. In composite membranes the film with the higher
EW will preferably carry the carboxyl groups.
The starting fluorocarbon polymer having the sulfonic
acid groups as the side chain thereof is produced by copolymer-
izing a fluorinated ethylene and a vinyl fluorocarbon monomer
having a sulfonyl fluoride group of the generic formula (I)
given below:
Fso2cF2cF2o(cFycF2o)ncF=cF2 (I)
(wherein, Y represents F or a fluoroalkyl group having 1 to
5 carbon atoms and n an integer having the value of 0 - 3),
if necessary, in conjunction with a monomer selected from the
class consisting of hexafluoropropylene, CF3CF=CF2 and
compounds of the generic form~la (II) ~iven below:
F(CF2)~0(CFC~20)pC~'~CF2 (II)
CF3
twherein, ~ represents an integer having the value of 1 - 3
v~r~c r~Sc 7~;
~,'i!, 25 and p an integer having the value of 0 - 2), thereby dcri-~ing
a polymer possessing a side chain of -OCF2CF2S02F shaping
the resultant polymer in the form of a membrane and thereafter
converting the side chain -OCF2CF2S02F of said polymer into
the group -OCF2CF2S03M through saponification.

~z~9;~
Typical examples of fluorinated ethylene include
vinylidene fluoride, tetrafluoroethylene and chlorotrlfluoro-
ethylene. Among them, tetrafluoroethylene is most preferred.
Typical examples of the vinyl fluorocarbon monomer
having the sul~onyl fluoride group o~ the a~orementioned
generic formula include those enumerated below:
2 2 2OCF CF2
Fso2cF2ocFcF2ocF=cF2
~F3
2CF2CF201 FCF20CFCF20CF=CF
CF3 CF~
Fso2cF2cF2cF=cF2
Fso2cF2cF2ocFcF2ocF=cF2
CF20CF3
~ f the vinyl fluorocarbon monomers having the sulfonyl
fluoride group available at all, the most desirable is per-
fluoro(3,6-dioxa-4-methyl-7-octene sulfonyl fluoride),
Fso2cF2cF2ocFcF2ocF=
CF3
A typical example of the fluorovinyl ether of the
generlc formula (II) which takes part, where necessary, in
said copolymerizat.ion is per~luoromethyl vinyl ether.
The process of the invention i~ applicable to all Or
the sulfonyl substituted polymers described in Unlted States
Patent 3,909,378.
Advanta~eously, the membrane is first formed with
the sulfonyl substituted polymer which is then converted by
reactions described more fully hereina~ter to a membrane of
the invention.
The preferred copolymer composition for starting
-- 10 --

1219;~99
materials is such that the fluorinated ethylene monomer content
is from 30 to 90 percent by wei~ht, preferably from 40 to 75
percent by weight, and the content of the perfluorovinyl
monomer possessing~ the sulfonyl fluoride group is ~rom 70 to
10 percent by weight, preferably from 50 t~ 25 percent by
weight. The materials are produced by procedures ~ell known
in the art for the homopolymerization or copolymerization of
a fluorinated ethylene.
Polymerization may be effected in either aqueous or
nonaqueous systems. Generally, the polymerization is performed
at temperatures of from 0 to 200C under pressure of from 1 to
200 kg/cm . Frequently, the polymerization in the nona~ueous
system is carried out in a fluorinated solvent. Examples of
such nona~ueous solvents include 1,1,2-trichloro-1,2,2-tri-
fluoroethane and perfluorocarbons such as perfluoromethyl-
cyclobutane, perfluorooctane and perfluorobenzene.
The aqueous system polymerization is accomplished by
brin~lng the monomers into contact with an aqueous solvent
containing a freè radical initiator and a dispersant to produce
a slurry of polymer particles, or by other well known procedures.
After the polymerization, the re~ultant ~olymer is
shaped to form a membrane usin~ any o~ a variet;y o~ well known
techni~ues.
The copolymer is desired to have an EW ln the ran~e
of from 1000 to 2000. The membrane havin~ a low EW is desirable
in the sense that; the electric resistance is proportionally
low. A membrane of a copolymer having a notably low EW is
not desirable since the mechanical strength is not sufficient.
A copolymer having a notably high EW cannot easily be shaped
in the ~orm of membrane. Thus, the most desirable ranKe o~
-- 11 --

~9~99
El~ is from 1000 to 1500.
The copolymer, after being shaped into a membrane,
a ~ ~ r;~
can be laminated with a reinforcing material such as fabric_ -
for improvement of mechanical strength. As the reinforcing
material, fabrics made of polytetra~luoroethylene fibers are
most suitable. The aforesald stratum should preferably be
allowed to be present on the surface opposite to the side
on which the reinforcing material is lined.
In case of the cation exchange membrane having two
bonded films which is the preferred embodiment of the invention
as mentioned above, two kinds of copolymers having different
EW are prepared according l;o the polymerization methods as
described above, followed by shaping, and fabricated into a
composite film. The first film is required to have an EW
f at least 150 ~rreater than the EW of the second film and
also to have a thickness of not more than one half of the
entire thickness. The thickness of the first film is
preferably as thin as possible, since electric resistance
is greatly increased as the increase in EW. Thus, the
thickness of the first film which depends on EW thereof is
required to be 50% or less o;~ th~ en~.lre thlcknes~, pre~er-
ably from ll5 t~ 10%.
It ls lmportank that the flrst film of a hig,her EW
ls present in the form of a continllou.s film formed parallel
to the surface of the membralle.
The overall thickness o~ said composite cation
exchan~e membrane, thou~h variable with the klnd of particular
ion exchange group used~ the strength required of` the copolymer
as the ion exchange membrane, the type of electrolytic cell and
the conditions of operation, generally has a lower limit of
- 12 -

~21g~99
4 mils and no upper limit. The upper limit is usua]ly fixed
in consideration of economy and other practical purposes.
Said composite membrane may be laminated with fabrics
or some other suitable reinforcing material with a view to
improvement of the mechanical strength thereof. The reinforc-
ing material is preferably embedded in the second film. As
the reinforcing material, fabrics made of polytetrafluoroethylene
filaments are most suitable.
For the preparation of the products of this invention,
10 the pendant sulfonyl groups in the form represented by the
formulas:
-OCF2CF2SO2X (A)
and/or
-OCF CF' SO ~
2 2 2 ~ O (B)
-OCF2CF2S02--
wherein X is halogen, especially fluorine or chlorine;
hydroxyl 7 alkyl containing up to four carbon atoms; aryl or
OZ where Z is a metallic atom, especially an atom of an
alkali metal, alkyl containing up to four carbon atoms or
aryl; are converted to:
-OC~2COOM
by treatment with a re~lcln~ a~r~ent.
Since the conversion to a carboxylic acid ~roup is
effected chemically, it can be controlled so as to produce
products with substant~ally any de~ree of carboxylation which
may be desired.
The starting polymers are usually formed from
sulfonyl fluoride substituted compounds which remain intact
durin~ polymerization. l'he sulfonyl fluoride groups can
directly be treated with a reducing agent to be converted to
- 13 -

1;~19;~99
t~l~e carboxylic acid groups. Alternatively, they may be fi~st
converted to any of the other derivatives of sulfonic acid
a~ defined in the above formulas (A) and (B) by known reac-
tions, followed by conversion into the carboxylic acid groups.
d~e
T 5 ~he sulfonyl chloride groups are especially preferred-~r to
higher reactivity. Therefore, it is more desirable to convert
the sulfonyl fluoride to any of the other derivatives of' sul-
fonic acid defined above in connection with the definition of
X. Such reactions can be readily carried out by procedures
well known to the art.
The formation of the carboxylic group may follo~ any
of several pathways.
It may be formed by reduction to a sulfinic acid
with a relatively weak reducing agent followed by a heat
treatment as indicated below:
-OCF2CF2S02X - red. ~ OCF2CF2S02M
~ ~ OCF2COOM.
Conversion into carboxylic acid groups can more readily be
effected when M in the above formulas is hydrogen. Alter-
natively the treatment may be stepwise in which initially asulfinic acid is produced, and this is converted to a carboxy-
lic group by the use of a str~ng reducin~ a~ent. This may
take place as indicated below:
-OCF2C~2$02X _ed. __~ 0cF2c~2so2M
- ~ OCF2COOM.
With some reducing agents, the treatment may be
directly from the sulfonlc ~roup to the carboxyl ~roup, as
indicated by,
2 2 3 ~ > OCF2Coo,~q
It is preferred that the concentration of sulfinic
acid groups in the final product be relatively low.
- ]4 -

- 1219;~99
Accordingly, it may be desirable, but not necessary, to
oxidize sulfinic acid groups to sulfonic acid groups by
the following sequence:
-CF2cF2s2M _ ~ OCF2cF2so3M
This may ~e accomplished by known procedures utilizing
aqueous mixtures of sodium hydroxide and hypochlorite.
The reducing agents which can be used in the
present invention are exemplified as shown below. Those
skilled in the art are completely familiar with these
reducing agents and many other similar reducing agents as
well as procedures by which they are employed. However,
some of the reducing agents such as hydrazine having amino
groups which are capable of forming sulfonamide groups as
disclosed in German Patent OLS No. 2,437,395 are not suitable
for the purpose of the invention, and therefore they are
excluded from the scope of the invention.
The reducing agents of the first group are metal
hydrides of the generic formula MeLH4, wherein Me represents
an alkali metal atom and L an aluminum or boron atom, or
Me'Hx, wherein Me' represents an alkali metal atom or
alkaline earth metal atom and x is an integer with a value
of 1 to 2. These include, ~or example, lithium aluminum
hydride, lithium boron hydride, potassium boron hydride,
sodium boron hydride, sodium hydride and calcium hydride.
The reducing agents of the second group are
inorganic acids possessing reducing activity such as,
for example, hydroiodic acid, hydrobromic acid, hypo-
phosphorous acid, hydrogen sulfide and arsenious acid.
The reducing agents of the third group are mixtures
- 15 -

~21~;~99
of metals and acids. Examples of these mixtures include tin~
iron, zinc and zinc amalgam and those of acids include hydro-
chloric acid, sulfuric acid and acetic acid.
The reducing a~ents o~ the fourth group are compounds
of low-valency metals. Examples of these compounds include
stannous chloride, ferrous sulfate and titanium trichloride.
They may be used in conjunction with cuch acids as hydrochloric
acid and sulfuric acid.
The reducing agents of the fifth group are organic
metal compounds. Examples of these reducing agents include
butyl lithium, Grignard reagent, triethyl aluminium and tri-
isobutyl aluminum.
The reducing agents of the sixth group are inorganic
acid salts possessing reducing activity and similar compounds.
~xamples of these reducing agents incluae potassium iodide,
sodium iodide, potassium sulfide, sodium sulfide, ammonium
sulfide, sodium sulfite, sodium d.~thionite, sodium pho~phite,
sodium arsenite, sodium poly~ulfide and phosphorl2s trisul~ide.
The reducing agents of the seventh group are mixtures
of metals with water, steam, alcohols or alkalis. Examples
of metals usable in the mixtures include sodium, llthlum,
aluminum, magneslum, zinc, iron and amal~ams thereof. Examples
of alkalls include alkal.l hydrox~des and alcoholic alkalis.
The reducln~ agents of the ei~hth groups are organic
compounds possesslng a reducing activity such as, for example,
triethanol amine and acetaldehyde.
Amon~ the groups as enumerated above, those belonging
to the second, thlrd, fourth and sixth ~roups are found to be
preferable.
The optimum conditions for treatment with a reducin~
- 16 -

lZ1~399
a~ent will be selected dependin~ on the selected reducing agent
to be used and on the kind of the substituent X in the SO2X group.
Generally, the reaction temperature is in the range of from -50C
to 250C, preferably ~rom 0C to 150C, and the reducing a~ent
is used in the form of a gas, liquid or solution. As the solvent
for the reaction, there can be used water; polar organic solvents
such as methanol, tetrahydrofuran, di~lyme, acetonitrile,
propionitrile or benzonitrile: or nonpolar organic solvents
such as n-hexane, benzene or cyclohexane or mixtures of such
solvents.
The amount of the reducin~ agent is not less than the
equivalent wei~ht of the sulfonyl group present in the surface.
Generally~ the reducing agent will be used in lar~e excess.
The pH value of the reaction system will be selected on the
basis of the particular reducin~ agent employed.
The reaction can be carried out under reduced,
normal or increased pressure. In the reaction involving the
use of a gaseous reducing a~,ent, the increased pressure can
improve the velocity of the reaction.
The reaction time generally ranges from one minute
to 100 hours.
In case of a cation exchan~e membrane rein;~orced
with a r~lnforcin~ materlal, treatment with a reduclng a~,ent
is preferably applled onto the side opposlte to the reinforced
side.
The course of the reactlon may be followed by
analysis of the infrared absorption spectrum of the membrane,
as is particularly illustrated in the examples. Key bands in
followin~ the reaction are as follows:
- 17 -

12~9;~99
sulfonyl chloride ~ 1420 cm 1
sulfinic acid salt ------------- g40 cm 1
sulfinic acid salt -------------- 1010 cm 1
carboxylic acid ~ ------------ 178Q cm 1
carboxylic acid sal~ -~--------- 1690 cm
The specific functional groups of the invention are
found to be unitary species having a neutralization point at
approximately pKa=2.5 from measurement of electric resistance
and infrared spectrum by varying pH. Said functional groups
exhibit characteristic absorptions at 1780 cm 1 (H form) and
at 1690 cm 1 ~Na form). Furthermore, when converted into
chlorides by treatment with PC15/POC13, they are found to
exhibit characteristic absorption at 1810 cm 1. From these
measurements, they are identified to be carboxylic acid groups.
By elemental analysis by combustion method, sulfur ~4m is
found to be decreased by one atom per one exchange group.
Fluorine atom is observed to be removed by two atoms per
one exchange group by alizarin-complexion method. From these
results of analysis and also from the fact that carboxylic
acids are formed by use of a reducing agent containing no
carbon atom under an atmosphere in the absence of carbon atom,
the above functional ~roups are con~lrmed to be -OCF2COOM.
This structure ls also evidenced by mca~urem~nt o~ NM~ spectrum
of C13 of the product obtained by the reactiGn~ correspondln~
to the above polymer reaction~ conducted for the monomer having
~unctional group ~ OCF2CF2S02X.
The products of the treatment with a reduclng agent
may take three typical forms. These are:
; 1) All o~ the -COOM groups required may be formed.
2) Not all -COOM groups required may be formed
- 18 -

~2~9;~99
and -SO2M groups may be present.
3) Substantially all -SO2M groups may be present.
In the first instanceg no further treatment will be
required. In the second and third case~ there are two alterna-
tives. A more powerful reducing agent may be employed, orthe -SOzM groups may be converted to carboxylic acid groups by
heat treatment, which is advantageously carried out when M is
nydrogen. The heating may take place at any selected practical
pressure at a temperature of from 60C to 400C for a period of
from 15 to 120 minutes. The preferred conditions for efficiency
and economy are atmospheric pressure, 100~C to 200C, and 30 to
60 minutes.
Any remaining sulfinic acid group may be converted
into the sulfonic acid group, if desired. This conversion o~
the sulfinic acid group to the sulfonic acid group can easily
be accomplished such as by subJecting the former group to
oxidation in an aqueous solution of 1 to 5 percent NaClO or
an aq.leous solution of 1 t;o 30 percent ~22 at 40C to 90C
for 2 to 20 hours.
The re~ucing agent to be used for the purpose of this
invention is selected, as in ordinary or~anic reactions, with
due consideration to numerous ractors such a~ the Icind Or the
substltuenl; X in the .~O2X f~rroup, the k:Lnd o~l the reducln~ ag~rent,
the kind of the solvent to be used, the temperature oi the
reaction, the concentration, the pH value~ thc reactiorl time
and the reaction pressure.
The reducin~ a~ents usable for this inv~ntion are
broadl~ divided by their reactions as follow~.
The reducing agents of the first group can be applied
to virtually all SO2X groups. Occasionally the reaction
-- 19 --

1219;~99
proceeds to an advanced extent to produce a product which
appears to be an alcohol.
The reducin~ agents of the second~ third and fourth
Kroups are particularly e~fective when applied to sulfonyl
halide groups of relatively hi~h reactivity.
The reducing agents of the fifth, sixth, seventh
and eighth groups are also effective for application to sulfonyl
halide groups, although use ol these reducing agents frequently
produces the sulfinic acid alone. Use of the -S02F group
demands specially careful selection of the reaction conditions,
for it may possibly induce hydrolysis in the presence of a
reducing a~ent from the sixth, seventh and eighth groups.
It is possible to convert the -S02Cl group directly
into the carboxylic acld group without going through the
intermediate of sulfinic acid. For example, the conversion
can be accomplished by sub~ecting the membrane of the fluoro-
carbon polymer possessin~ the -S02Cl group to elevated
temperature and/or to ultraviolet rays and/or to an organic
or inorganic pero~ide.
As a matter of course, the reaction of the present
invention can be applied to other monomers possesslng simllar
side chains. Thus, fluorocarbon monomers possesqln~, a ~ulfinlc
acid ~roup or carboxyllc aold ~Jroup can readily be syntheslzed
by sald reaction.
It will be noted that the ultimate effect of the
treatment with a reducin~ agent can be represented by the
followlng reaction:
-OCF2cI?2~o3M _ ~ -OCF2COOM .
- 20 -

~21g3g9
The membranes of this invention have many advantages,
some of which have already been mentioned above.
In the course of the electrolysis of aqueous solution
of an alkali metal halide, the portion of the fluorocarbon
polymer possessin~ the carboxylic acid group in the
cation exchange membrane is preferably on the side of the
catholyte. Even in the electrolysis performed to produce
caustic soda at a high concentration, therefore, the membrane
provides effective prevention of the back migration of hydroxyl
ions and permits the electrolysis to proceed at high current
efficiency.
Particularly when the cation exchange membrane of
two-layer construction of this invention is used as the
diaphragm in the electrolysis of aqueous solution of sodium
chloride, the prevention of the back migration of hydroxyl
ions can be obtained quite effectively and the current effi-
ciency maintained at a high level by allowing the high EW layer
resultinF~ frorn the treat~ent with the reducing a~ent to face
the cathode side of the electrolytic cell. As a consequence,
this cation exchange membrane ena~les the unit power consump~ion
to be lowered and the prime cost o~ the product proportionally
lowered an~, hence, proves ko be hi~hly ~dvanta~eous from the
commercial point oY view.
Generally, the anode compartment in the electrolysis
of aqueous solution of sodium chloride is operated in an acidic
state. In consideration of the fact that the apparent pKa
I value of the carboxylic acid is ~ the order of 2 to 3, the
presence of the thin layer of the carboxylic acîd group on the
r C C~s~ n,~
anode compartment side brings about an effect of height~ing
the potential and therefore proves disadvantageous.

~2~9;~99
Compared with the conventional membranes, the
membranes of this invention have the following advanta~es in
the process of manufacture. Manufacture of the cation exchange
rnembrane of the fluorocarbon polymer substituted with the
carboxylic acid group has heretofore proved to be extremely
difficult. This is because the properly substituted fluoro-
carbon compound monomers are extremely difficult to synthesize.
Additionally, copol~mers from such monomers with perfluorovinyl
monomers are highly susceptible to thermal decomposition and
cannot be thermally molded in the form of a membrane by conven-
tional extrusion techniques.
This invention alleviates the aforesaid difficulties
by causing the sulfonic acid group of the fluorocarbon polymer
to be converted into the carboxylic acid group.
The following examples are given by way of illustra-
tlon only, and are not to be considered limitations of this
invention, many apparent variations of whlch are possible
without department from the spirit or scope thereof.
EXAMPLE 1
Tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-
7-octene sulfonyl fluoride) were copolymerized in 1,1,2-
trichloro-1,2,2-trifluoroethane ln the pr~sence o~ per~luoro-
propionyl peroxide as tho inltla~or. The polymerlzation
temperature was held at 45C and the pressure maintalned at
5 atmospheres durin~ the copolymerization. The exchan~e
capacit,y of the resultant polymer, when measured after
saponi~ication, was 0.95 milligram equivalent/gram of dry
resin.
This copolymer was molded with heating into film
0.3 mm in thickness. It was then saponified in a rnixture of
- 22 -
,

12~939~
2.5N caustic soda/50 percent methanol at 60C for 16 hours,
converted to the H form in lN hydrochloric acid, and heated
at 120C under reflux for 20 hours in a 1:1 mixture of
phosphorus pentachloride and phosphorus oxychloride to be
converted into the sulfonyl chloride form. At the end of the
reaction, the copolymer membrane was washed with carbon tetra-
chloride and then subjec~ed to measurement of attenuated total
reflection spectrum (hereinafter referred to as A.T.R.), which
showed a strong absorption band at 1420 cm 1 characteristic of
sulfonyl chloride. In a crystal violet solution, the membrane
was not stained. Betw~en frames made of acrylic resin, two
sheets of this membrane were fastened in position by means of
packings made of polytetrafluoroethylene. The frames were
immersed in an aqueous 57 percent hydroiodic acid solution so
that one surface of each rnembrane would undergo reaction at
80C for 24 hours. The A.T.R. of the membrane was then
measured. In the spectrum, the absorption band at 1420 cm 1
characteristic of sulfonyl chloride group vanished and an
absorption band at 1780 cm 1 characterlstic of carboxylic
acld group appeared instead. In the crystal violet solution,
a layer of a thickness of about 15 microns on one surface of
the membrane was stained. The cation exchan~e ~roups ~xl8tln~
on the surrace were found to be carboxylic acld ~¢roups (100~)
by measurement o~ A . T ~ R .
3y saponifyin~ this membrane in an aqueous solution
of 2.5N caustic soda/50 percent methanol at 60C for 16 hours,
there was obtained a homogeneous and strong catlon exchange
membrane.
In an aqueous O.lN caustic soda solution, this
membrane showed a specific conductivity of 10.0 x 10 3 mho/cm.
. . .

~ig399
The specific conductivity of the membrane was
determined by initial conversion to a co~plete Na form, keeping
the membrane in a constantly renewed bath of an aqueous O.lN
caustic soda solution at about 25C for ten hours until
equilibrium and subjecting it to an alternating current of
1000 cycles while under an aqueous O.lN caustic soda solution
at 25C for measurement of the electric resistance of the
membrane.
The aforementioned Na ~orm electrolytic diaphragm
was equilibrated in an aqueous 2.5N caustic soda solution at
90C for 16 hours, incorporated in an electrolytic cell in
such way that the treated surface fell on the cathode side.
It was utilized as the membrane ih the electrolysis of sodium
chloride and its current efflciency measured. The result was
95%.
The electrolytic cell had a service area of 15 cm2
(5 cm x 3 cm) and comprised an anode compartment and a cathode
compartment separated by the cationic membrane. A metallic,
dimensionally stable DSA anode was used, and an iron plate
was used as the cathode. An aqueous 3N sodium chloride
solution at p~l 3 was circulated through the anode compartment
and an a~ueous 35 percent caustlc soda solution ~hrou~h the
cathode compartment at 90C. Under these conditlons, an
electric current was passed between the electrodes at a current
density of 50 amperes/dm2. The current efficlency was calculated
by divldlng the amount of caustic soda produced in the cathode
compartment per hour by the theoretical value calculated from
the amount of electricity passed.
COMPARISON EXAMPLE 1
The sulfonyl chloride form Or the membrane obtained
- 24 -

i2~,9;~99
in Example 1 was saponified in a mixture of 2.5N caustic
soda/50 percent methanol. The resultant sulfonic acid form
ion exchange membrane was tested for speciric conductivity and
current efficiency under the conditions as used in Example 1.
The values found were 13 0 x 10 3 mho/cm and 55% respectively
EXAMPLE 2
The polymerization of Example 1 was repeated by the
same procedure, except that the pressure was maintained at 6
atmospheres during the polymerization. The exchange capacity
of the resultant polymer was 0.79 milligram equivalent/gram
of dry resin.
The copolymer was molded with heating into a film
0.3 mm in thickness. The membrane was then converted into
the sulfonyl chloride form under the same conditions as in
Example 1. One surface of the membrane was caused to react
with an aqueous 57 percent hydroiodic acid solution at 80C
for 30 hours.
Thereafter, the treated surface of the membrane was
subJected to measurement of A.T.R. In the spectrum, the
absorption band at 1420 cm 1 characteristic of the sulfonyl
chloride group vanished and an absorptlon band at 1780 cm 1
characteristic Or carboxylic ac:Ld ~roup appeared ~nstead.
In crystal vlolet solu~,ion, a layer havlng a thlckness o~
about 15 microns on one surface of the membrane was stained.
The cation exchange ~roups on the surface were found to be
carboxylic acid groups (100%) by A.T.R.
This membrane was saponified in a solution of 2.ON
caustic soda~50 percent methanol at 60C for 40 hours and then
treated in an aqueous 2.5 percent sodium hypochlorite at 90C
for 16 hours. The resultant membrane was treated in a solution
- 25 -

~9æ~9
of 2.ON caustic soda/50 percent methanol at 90C for 16 hours.
The A.T.R. of this membrane showed the characteristic
absorption of a salt of a carboxylic acid group at 1690 cm 1
on the surface exposed to the reacticn with hydroiodic acid,
and an absorption characteristic of a salt of sulfonic acid
was observed at 1055 cm 1 on the opposite surface.
The specific conductivity of this membrane was 6.5 x
10 3 mho~cm. The current efficiency measured under the same
conditions as those of Example 1, with the surface treated
with hydroiodic acid facing the cathode compartment side, was
found to be 94%. After continuous passage of current for 1500
hours, while maintainin~ the concentration of alkali in cathode
compartment at 30%, the current efficiency was found to be as
high as 93.2%.
COMPARISON EXAMPLE 2
_ . . .
The sulfonyl chloride formof the membrane obtained
in Example 2 was saponified in a solutlon of 2.5N caustlc
sodai50 percent methanol. The resultant sulfonic acid type
ion exchange membrane was tested for specific conductivity
and current efficiency under the same conditions as in
Example 1. The values thus obtained were 7.0 x 10 3 mho/cm
and 65~ respectively.
Terpolymerization was conducted utilizin~ the mono-
mers of Example 1 plus perfluoropropyl vinyl ether following
the procedure of Example 1. When the membrane obtained was
subjected to the same procedure as tllat of Example 1, it
manifested a current efficiency as high as the membrane of
Example 1.
- 26 -
:

1~19399
EXAMPLE 4
Terpolymerization was carried out using the monomers
of Example 1 plus perfluoro-3,6-dioxa-5-methyl nonene-lg
CF3CF2CF2OCF(CF3)CF2OC~=CF2. When the membrane obtained was
subjected to the same procedure as in Example 1, there were
obtained similar results.
EXAMPLE 5
A sulfonyl fluoride form membrane having an exchange
capacity of o.65 milli~ram equivalent/gram of dry resin was
obtained by a procedure similar to that of Example 1. The
membrane was placed in a flask and t~trahydrofuran was added.
Lithium boron hydride was added in a large excess, and the
resultant reaction system heated under reflux for 50 hours.
~t the end of the react:ion, the membrane was sub~ected to
measurement of A.T.R. In the spectrum, the absorption band
at 1470 cm 1 characteristic of sulfonyl fluoride substantially
vanished and large absorption band at 16~0 cm 1 characteristic
of -COOLi small absorption bands at 940 cm 1 and 1010 cm 1
characteristic of sulfinic acid salt appeared instead. This
membrane was allowed to stand in an aqueous 0.1 percent crystal
violet solution (containinp 10 percent ethanol) ~r ~hree
minutes and, therear~er, the cro~s sec~lon o~ thc membrane was
observed under a microscope. rrhe microscopic observation
revealed a stron~ly stained layer havin~ a thickness of about
10 microns on each sur~ace of the membrane.
The carbox~lic acid group content ln the surface
layers, as determined from ~.T.R. was about 60 percent.
EXAMPLE 6
Terpolymerization was carried out using the monomers
of Example 1 plus hexafluoropropylene following the procedure
- 27 -

1219399
of Example 1. When the membrane obtained was subjected to
procedures similar to those of Example 1, similar results
were obtained.
EXAMPLE 7
The sulfonyl chloride form of the membrane obtained
in Example 1 was reduced in an aqueous 35 percent hypophosphorus
acid solution at 80C for ten hours. By A.T.R., the adsorp-
tion band at 1420 cm 1 characteristic of sulfonyl chloride
group vanished, but the absorption band at 1780 cm 1 character-
istic of carboxylic acid group was not very strong. When the
membrane was washed with water and treated in 47~ hydrobromic
acid at 80C for 20 hours, the absorption band at 1780 cm 1
characteristic of carboxylic acid group increased in intensity.
The cation exchange groups on the surface were measured by
A.T.R. to be 90%.
When the membrane was saponified in an aqueous
solution of 2.5N caustic soda/50 percent methanol and then
subjected to measurement of A.T.R. the absorption by the
carboxylic acid group at 1780 cm 1 was noted to have been
20 shifted to an absorption band at 1690 cm 1 characteristic
of carboxylic acid salt. Low intensity absorption due to
the sulfinic acid salt group appeared at 940 and 1010 cm 1,
The specific conductivity and current efficiency of the
~membrane, when measured under the conditions of Example 1,
25 were found to be 9.5 x 10 3 mho/cm and 92 percent respectively.
EXAMPLE 8
.
The sulfonyl chloride form of the membrane ~0.65
meg/g) obtained in a manner similar to Example 1 was refluxed
in an aqueous solution of tin and hydrochloric acid for
50 hours and then subjected to measurement of A.T.R.
In the spectrum, the absorption band at 1420 cm 1
~ 28 -

1219æ~9
characteristic of sulfonyl chloride group vanished and a sharp
absorption band at 1780 cm 1 characteristic of carboxylic acid
group appeared. The carboxylic acid groups were present on the
surface (100~) by measurement of A~T.R. This membrane was
saponi~ied in an aqueous solution of 2.5N caustic soda/50 percent
methanol. The specific conductivity and current efficiency of
the saponified membrane~ when measured under conditions of
Example 1 and maintainin~ the alkali concentration in cathode
compartment at 20%, were found to be 2.0 x 10 3 mho/cm and 96
percent respectively.
EXAMPLE 9
Example 8 was repeatedg except that an aqueous
solution of stannous chloride and hydrochloric acid was used
in place of the aqueous solution of tin and hydrochloric acid,
~o give a similar result.
EXAMPLE 10
The sulfonyl chloride form of the membrane obtained
in Example 1 was submerged in an aqueous 15 percent sodium
sulfide solution under a co~tinuous flow o~ nitroge~ g~s
at 60C for one hour. At the end of the reactlon, the membrane
was sub~ected to measurement of A.T.R. In the spectrum, the
absorption barld at 1420 cm 1 charac~erist1c o~ ~ul~onyl ch:loride
group completely van1~hed and sharp at)sorptlon bands ~lt 940 cm 1
and 1010 cm 1 characteristic o~ a sulrlnic acid salt appeared.
The membrane was converted into the H form by immerslon in lN
h~ydrochloric acid solution at 60C for 10 hours, and heated
under nitrogen gas at l50~C for 120 minutes. It was then
converted into the Na ~orm by lmmersicn in a 2.5N caustic
soda solution and sub,~ected to measurement of A.T~R. In the
spectrum, the absorption bands at 940 cm 1 and 1010 cm 1
- 29 -

1~19399
characteristic of the sulfinic acid salt completely disappeared
and a strong absorption band at 1690 cm 1 characteristic of
carboxylic acid salt appeared~ The cation exchange groups on
the surface were found b~ A.T.R. to be carboxylic acid groups
(100%). The membrane was immersed in an aqueous solution of
2.5N caustic soda/50 percent methanol to effect saponification
of those sulfonyl chloride groups still remairing in the
membrane interior. The specific conductivity and current
efficiency of the saponified membrane~ when measured under
the same conditions as in Example 1, were found to be 9.2 x
10 3 mho/cm and 95 percent respectively. When the current
efficiency was measured under the same conditions as those of
Example 1~ except that the alkali concentration in the cathode
compartment fixed at 40 percent, there was obtained a va]ue of
97 percent.
COMPARISON EXAMPLE 3
The sulfonyl chloride form of the membrane obtalned
in Exa~ple 1 was saponified in an aqueous solution of 2.5N
caustic soda/50 percent methanol. The current efficiency of
the saponified membrane, when measured under the same condi-
tions in Example 1, except that the alkali concentrilt;ioll in
the cathode compartment I`ixed at l~o percerlt, wal~ 52 pe~rcel1t.
EXAMPLE 11
The procedure of Example 10 was repeated, except an
aqueous 5 percent potassium iodide solution was used in place
of the aqueous 15 percent sodium sulflde solution. The results
were similar to those obtained in Example 10.
EXAMPLE 12
Two sheets of the sulfonyl chloride form of the
membrane obtained in Example 1 were incorporated in frames
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1~19~
similar to those used in Example 1. The frames were immersed
in triethanol amine so that one surface of each membrane would
undergo a reaction at 80C for 20 hours. The treated sur~aces
of each membrane were sub,lected to measurement of A.T.R. In the
spectrum, the absorption band at 1420 cm 1 characteristic of
the sulfonyl chloride group vanished and stron~ absorption
bands at 940 cm 1 and 1010 cm 1 characteristic of the sulfinic
acid salt appeared. The membrane was saponified in an aqueous
solution of 2.5N caustic soda/50 percent methanol~ then heated
in 12N hydrochloric acid at 90C for 30 hours, again converted
into the Na form by means of 2.5~ caustic soda and sub~ected
to measurement of A.T.R. A sharp absorption band character-
istic of a carboxylic acid salt appeared at 1690 cm 1. The
absorption bands at 940 cm 1 and 1010 cm 1 practically dis-
appeared. The percentage of carboxylic acid groups present
on the surface as cation exchan~e ~roups was 85~ by measurement
of A.T.R.
The specific conductivity of thiæ membrane, when
measured under the same conditions in Example 1, was found to
be 11.0 x 10 3 mho/cm. The current efficiency of the membrane,
when measured with the treated sur~ace ~aclrl~ the cathode
compartment side, was 89 percent.
~XAMPLE 13
The sulfonyl chloride form of the membrane obtairled
in Example 1 was allowed to react ln 5 percent hexane-tetra-
hydrofuran solution of butyl llthium at 60C for eight hours
and then sub~ected to measurement of A.T.R. In the spectrum,
the absorption band of the sulfonyl chloride ~roup at 1420 cm 1
dwindled by about 60 percent and absorption bands at 940 and
1010 cm 1 characteristic or' the sulfinic acid salt appeared.
- 31 -
.
, .

399
EXAMPLE_14
The sulfonyl chloride form of the membrane obtained in
Example 1 was saponified, converted into the H form with hydro-
chloric acid~ thoroughly dried~ and reacted in a tetrahydro~uran
solution of lithium aluminum hydride at 40C for 20 hours. In
A.T.R., an absorption band at 1780 cm 1 characteristic of the
carboxylic acid ~roup was slightly visible.
EXAMPLE 15
A sulfonyl fluoride form membrane 0.20 mm in thickness
was prepared by a procedure similar to th~t of Example 1. One
surface of the membrane was saponified with an aqueous solution
of 2.5N caustic soda/50 percent methanol. The membrane was
spread out with the nonsaponified surface held downwardly on
a plain-weave fabric of polytetrafluoroethylene 0.15 mm in thick-
ness with warp and filling yarns, both of 400-denier multifila-
ments, repeat each at a rate of 40 yarns per inch. The membrane
and fabric were heated to 270C with the membrane simultaneously
drawn against the fabric by means of vacuum so as to embed the
fabric in the membrane as a reinforcin~ material.
This membrane was converted to the sulfonyl chloride
form by the same method as used in ~xample 1. Wlth frames made
of acryli.c resin, two such membralle~3 wer~ held ~ast a~alnst each
other wlth the fabric-reinPorc~d surface on the inside. I'he
frames containin~ the two ad~oinin~ membranes were immersed in
an aqueous 47 percent hydrobromic acld solutlon and caused to
under~o a reaction at 80C for 20 hours. After the reaction~
the membranes were removed, saponlfied in an aqueous solution
of 2.5N caustic soda/50 percent methanol and further oxidized
ir. a solution of 2.5N caustic soda/2.5 percent sodium hypochlorite
at 90C for 16 hours. The specific conductivity and current

~Zl9~99
efficiency of the membrane, when measured under the conditions
of Example 1 with the treated surface held in the diréction
of the cathode, were found to be 5.0 x 10 3 mho/cm and 95
percent respectively.
S COMPARISON EXAMPLE 4
The reinforced membrane obtained in Example 15 was
saponified. The specific conductivity and current efficiency
of the saponified membrane, when measured under the same
conditions as in Example 1, were found to be 6.0 x 10 30 mho/cm and 58 percent respectively.
EXAMPLE 16
The treated membrane obtained in Example 1 after
oxidation (with 2.5N NaOH/2.5% NaClO) was subjected to
separate durability tests by immersion in 45% caustic soda
or in 5% sodium hypochlorite at 90C for 300 hours. There-
after, the treated surface of the membrane was subjected to
measurement of A.T.R. In the spectrum, an absorption band
at 1690 cm 1 characteristic of carboxylic acid group was
observed. When the membrane was converted into the H form
in IN hydrochloric acid, the absorption band shifted to 1780
cm 1, indicating that the membrane had undergone substantially
no change during the durability test. The specific conduc-
tivity and current efficiency of th0 membrane, when measured
after the durability test under the same condit.ions in Example
1, were found to be 9.9 x 10 3 mho/cm and 94 percent in the
case of the sample which had been subjected to the durability
test in the 45~ caustic soda and 10.2 x 10 3 mho/cm and 96
percent with the sample tested in 5% sodium hypochlorite. The
results indicate that the membrane had undergone absolutely
0 no change during the durability tests.
EXAMPLE 17
_ .
The sulfonyl chloride form of the membrane obtained
- 33 -
SP

12~9;~99
in Example 1 was saponified, then converted into the H form
with lN hydrochloric acid, thoroughly dried and treated with
phosphorus pentoxide suspended in phosphorus oxychloride at
110C ~or 24 hours. After this treatment by ~.T.R. measurement,
absorption bands at 1460 and 1470 cm 1 characteristic of sulfo-
nic anhydride were observed. The membrane was allowed to react
with lithium aluminum hydride under the same conditions as in
Example 14, whereby a similar result was obtained.
E~XAMPLE 18
The procedure of Example 2 were repeated except that
the steps of saponification and oxidation were reversed. The
results were similar to those obtained in Example 2.
EXAMP E 19
The procedure of Example 1 was repeatedg except the
reaction in the hydroiodic acid solution was carried out at
40C for four hours and, after saponification, the reaction
in hydroiodic acid solution was repeated at 80C for 25 hours.
The resultant membrane was oxidized ln an aqueous solution
of 2.5N caustic soda/2.5 percent sodium hypochlorite and then
measured for specific conductivity and current efriciency
under the same conditions as in Example 1. The vfll~eq obtained
were 11.0 x 10 mho/cm an~ per-c~nt respectlvely.
~XAMPI.~ 20
Polytetrafluoroethylene powder and ~lass fibers
were blended. The blend was compression molded under pressure
of 300 k~/cm2 to produce a polytetrafluoroethylene sheet with
a thickness of 1 millimeter. The sheet was heated in an
electric furnace at 320C for one hour to fuse the polytetra-
fluoroethylene powder, and thereafter treated with hydrofluoric
acid to dissolve the ~lass phase. Consequently, there was
- 34 -

l~9~g~
obtained a neutral membrane with a porous structure.
This neutral membrane was coated three times with
a 1~1,2-trichloro-1,2,2-trifluoroethane solution of a copolymer
of tetrafluroethylene and perfluoro~336-dioxa-4-methyl-7-
octenesulfonyl fluoride) having an exchange capacity of 1.2milligr-am equivalents/gram of dried resin, and obtained by a
po]ymerization procedure similar to that of Example 1. The
solvent was evaporated from the coated membrane. Thereafter,.
the coat was pressed on the membrane at 270C ~or 10 minutes,
to produce a laminate with a thickness of 50 ~.
Under the same conditions as those of Example 1, this
membrane was converted into the sulfonyl chloride form, and
reacted with hydrogen iodide gas at 100C for 40 hours. The
A.T.R. indicated complete disappearance of the absorption band
at 1420 cm 1 characteristic of the sulfonyl chloride group,
and showed sharp absorption at 1780 cm 1 characteristic of
carboxylic acid.
EXAMPLE 21
In 1,1,2-trichloro-1,2,2-trifluoroethane 3 tetra-
fluoroethylene and perfluoro-3,6 dioxa-4-methyl-7-octene
sulfonyl fluorlde were copolymerized in the preserce of
perfluoropropionyl peroxlde a8 the pol~ymerization inltlator,
with the polym~rlzation temperature ~lxed at 45C and the
pressure maintained at 5 Ic~/cm2G durin~ the polymerizat:Lon.
The polymer obtained is identifled as Polymer 1.
The copolymerization was repeated by the same pro-
cedure, except the pressure was maintained at 3 kg/cm2
throughout the polymerization to produce Polymer 2.
A portion of each o~ the polymers thus produced was
sub~ected to hydrolysis in a mixture of aqueous 5N caustic soda
- 35 -

12~9399
solution and methanol (volume ratio of 1:1) at 90C I'or 16 hours
to be converted into the sodium sulfonate form. The exchange
capacity of the sodium sulfonate form polymer was found to be
0.74 milliequivalent/g of dry resin in the case of Polymer 1
and 0.91 milliequivalent/g of dry resin in the case of Polymer
2.
Polymer 1 and Polymer 2 were heat molded to produce
separate membranes 2 mils and 4 mils in thickness. The two
membranes were joined face to face and molded under heating into
a composite membrane. The composite membrane was treated in the
aforementioned hydrolyzing system to be con~erted into a sodium
sulfonate form composite membrane.
The composite membrane was con~erted into the H form
by treatment in an aqueous lN hydrochloric acid solution and
subsequently converted lnto the sulfonyl chloride form by-
reactlon with a mixture of phosphorus pentachloride and phos-
phorus ox~chloride (gravimetric ratio 1:1) at 120~C for 40
hours. At the end of the reaction) the composlte membrane
was washed for four hours under reflux in carbon tetrachloride
and dried under vacuum at 40C.
The dried membrane was subjected to measurement of
A.T.R. to reveal that in both the membrane~ o~ Polymer 1 and
Polymer 2, the absorption band by sulfonyl chlorlde appeared
at 1420 cm 1 and absorption due to the sulfonic acid group
at 1060 cm 1 completely disappeared.
Two sheets of the composite membrane were held
a~ain3t each other with the Polymer 2 membrane sides facing
inwardly and, in that state, set in position in frames made
of acrylic resin and fastened up by use of packings made of
polytetrafluoroethylene. The frames were immersed in an aqueous
- 36 -

1219399
57 percent hydroiodic acid solution so that only the exposed
surfaces (Polymer 1 membrane side) l~rould undergo reaction at
80C for 30 hours. The membranes were washed with water at 60C
for 30 minutes. The infrared spectrum of each treated surface
was measured. In the spectrum, the absorption band at 1420 cm 1
characteristic of sulfonyl chloride completely vanished~ and
an absorption band at 1780 cm 1 characteristic of carboxylic
acid ~roup appeared~ In crystal violet solution, a stained
layer of a width of about 0.3 mil was observed on the Polymer 1
side of the membrane. The cation exchange groups on the surface
were found to be carboxylic acid groups (100%) by A.T.R.
The membrane was saponified in an aqueous solution
of 2.5N caustic soda/50 percent methanol at 60C for 16 hours
and then subjected to measurement of A.T.R. In the spectrum,
the absorption band of the carboxylic acid group was shifted
to 1690 cm 1 in the Polymer 1 side of the membrane. On the
Polymer 2 side of the membrane, an absorption band at 1055 cm 1
characteristic of sodlum sulfonate appeared. The membrane was
lmmersed in an aqueous 2.5 percent sodium hypochlorite solution
and oxidized at 90C for 16 hours.
The speclf~c conductivity o~ the resultant membrane,
when measured in an aqueous 0.lN cau~tlc ~30da solut:lon, was
round to be 5.2 x 10 3 ~ho/cm.
~ he speclfic conductivity of the membrane wa~
determlned after complete conversion into the Na form, keepin~
the membrane in a constantly renewed bath of an aqueous 0.lN
caustic soda solutlon at normal room temperature for ten hours
until equilibrium and subjecting it to an alternating current
of 1000 cycles whiie under an aqueous 0.lN soda solution at
25C for measurement of the electric resistance of the membrane.
- 37 -

1219;~99
The Na form cation exchange membrane was equilibrated
by immersion in an aqueous 2N caustic soda solution at 90C for
lG hours~ then incorporated in an electrolytic cell with the
reacted surface~ namely the Polymer 1 side, facing the cathode.
It was tested for current efficiency as the membrane in the
electrolysis of sodium chloride. The value thus found was 94
percent.
The service area of the e~lectrolytic cell was 15 cm2
(5 cm x 3 cm). It comprised an anode compartment and a cathode
compartment separated by the electrolytic membrane. A metallic
anode coated with a noble metal was used as the anode and an
iron plate as the cathode. An aqueous 3N sodium chloride solu-
tion at pH 3 was circulated through the anode compartment and
an aqueous 30 percent caustic soda solution was circulated
through the cathode compartment at 90C. Under these conditions,
an electric current was passed between the electrodes at a
current density of 50 amperes/dm2. The current efficiency was
calculated by dividing the amount of caustic soda produced in
the cathode compartment per hour by the theoretical value
calculated from the amount of electricity passed,
The passa~e of the electric curre~t was cont:ln~led
for 2000 hours, Thereafter, the currenk efriclency was measured
and found to be 93,8 percent.
COMPARISON EXAMPLE 5
The sulfon,vl chloride form of the composite membrane
obtalned in Rxample 21 was saponified in a solution of 2.5N
caustic soda/50 percent methanol, The specific conductivity
and current ef~icienc,v of the saponified membrane, when
measured under the conditions of Example 21, were found to be
7,5 x lC 3 mho/cm and 7~ percent.
- 38 -

1219;~9~
EXAMPLE 22
The procedure of Example 21 was repeated, except
that the s~eps of saponiri~ation and oxidation were reversed.
rrhe specific conductivity and current efficiency of the membrane
were similar to those obtained in Example 21.
EXAMPLE 23
The procedure of Example 21 was repeated, except
that the membrane was allowed to react in an aqueous 20 percent
potassium io~ide solution at 60C for 30 hours in place Or the
treatment ln hydrogen iodide. At the end of the reaction, the
treated surface was subjected to measurement of A.T.R. In the
3pectrum, absorption bands due to potassium sulfinate were
observed at 1010 cm 1 and g40 cm 1 In crystal violet solution,
a surrace layer of a thickness of 0.2 mil on the Polymer 1 side
was observed to be stained.
The membrane was saponified under the same condi~ions
a3 those of Example 21 and then allowed to react in 57 percent
h~drolodic acid at 80C for 30 hourfi. At the end of the reaction,
Ithe Polymer 1 slde Or the membrane was sub~ected to measurement
o~ A.T.R. In the spectrum~ the absorption by potassium sul~inate
completely disappeared and an absorption by carboxylic acld
appeared at 1780 cm 1 The cation exchan~.e ~roups on the surface
were found to be carboxylic acld groups (about 100%~ by A.T.R.
On the Polymer 2 side of the membrane, an absorption by sulfonic
acld appeared at 1060 cm 1. The membrane was further oxidized
under the same condltions as those of Example 21. The specific
conductiv~ty and current efflciency Or the membrane were foun~
to be 5.3 x 10 3 mho~cm a~d g4 percent respectively.
EXAMP~E 24
A copolymer (Polymer 3~ was prepared by repeating
- 3g -

~z~9~99
the procedure of Example 21, except that the pressure was
maintained at 7 kg/cm G during the polymerization.
The exchange capacity of Polymer ~ when measured
by the same procedure as that of Example 219 was found to be
0.~ milliequivalent/g of dr~ resin.
By followin~ the procedure o~ Example 21, a compo-
site membrane comprising a Polymer 2 membrane, 4 mils in
thickness, and a Polymer 3 membrane3 2 mils in thickness, was
produced.
The composite membrane was sub;ected to hydrolysis
in a mixture of an a~ueous 5N caustic soda solution and methanol
(volume ratio of 1:1) at 60C for 40 hours, converted into the
H form by treatment in an aqueous lN hydrochloric acid solution
and thereafter converted again into the ammonium sulfonate form
by treatment in an aqueous lN ammonia solution.
It was then allowed to react in a mixture o~ phos-
phorus pentachloride and phosphorus oxychloride (gravimetric
ratio 1:1) at 120C for 36 hours to be converced lnto the
sulfonyl chloride form.
The composite membrane was incorporated in a flow-
gas reaction system and so that the Polymer 3 slde of the
composite membrane was allowed to under~o a cont~ct reactlon
with 20.0 percent hydrogen iodide gas (with nitro~en as the
dilutin~ gas) at 100C for 12 hours. The treated surface of
the membrane was sub~ected to measurement of A.T.R. In the
speatrum, an absorption band due to carboxylic acid appeared
at 1780 cm 1 and the absorption band due to sulfonyl chloride
at 1420 cm disappeared. In crystal violet solution, a layer
of 0.4 mil in thickness was stained. By A.T.R. measurement,
3 about lOQ% o~ the cation exchange groups were found to be
- 40 -

~219399
carboxylic acid groups.
The composite membrane was then hydrolyzed, oxidized,
and incorporated in an electrolytic cell with the Polymer 3 side
facing the cathode compartment. In this electr~lytic system,
electrolysis of sodium chloride was carried out under the same
conditions as in Example 21, with the concentration of caustic
soda circulated to the cathode compartment fixed at 20 percent.
The current efficiency was 97 percent, and the specific conduc-
tivity was 4.3 x 10 3 mho/cm.
l'he current efficiency, when measured after 1700
hours of continued pa~sage of electric current, was 97.2
percent.
CO~PARISON EXAMPLE 6
. .
The sulfonyl chloride form of the composite membrane
obtained in Example 24 was hydrolyzed in a solution of 2.5N
caustic soda/50 percent methanol. The specific conductivity
of the resultant membrane was 5.2 x 10 3 mho/cm. The membrane
was sub~ected to electrolysis under the same conditions as
those of Example 24, with the Polymer 3 side f'acing the cathode
compartment. The current efflciency was 80.2 percent.
EXAMPLE 25
Two sheets of the sul~onyl chlorld~ form Or the
membrane obtained in ~xamF~le 24 wer-e held a~a:lnst each other
with the Polymer Z sides facin~ inwardly and~ ln that state,
set in frames of acrylic resin, immersed ln an aqueous 20
percent sodium sul~lde solutlon and allowed to react under a
continuous f`low of nltrogen gas at 70C for two hours. At
the end of the reaction, the treated surface of the membrane
was sub~ected to measurement of A.T.R. In the spectrum, the
absorption band at 1420 cm 1 characteristic of the sulfonyl

~939g
chloride group disappeared~ and absorption bands at 1010 cm 1
and 940 cm characteristic of sulfinic acid salts were observed.
The membrane was immersed in an aqueous 2.5 percent
sodium hypochlorite solution at 70C for 16 hours and was again
sub~ected to measurement of A.T.R. In the spectrumg the adsorp-
tion bands at 1010 cm 1 and 940 cm 1 vanished and an absorption
band at 1055 cm 1 characteristic of sodium sulfonate appeared.
Two sheets of the membrane treated with sodium sul~ide
as described above were washed with water and set again in the
frames so that the Polymer 3 side reacted in a solution of 47
percent hydrogen bromide at 80C for 20 hours. In A.T.R.
obtained from the membrane, a sharp absorption band due to the
carboxylic acid group appeared at 1780 cm 1
The membrane was saponified in an aqueous solution
f 2.5N caustic scda/50 percent rnethanol and sub~ected again
to measurement o:~ A.T.R. In the spectrum, the absorption band
at 1780 cm vanished, an absorption band due to sodium carboxy-
late appeared at 1690 cm 1, and mlnor absorptlon bands due to
sulfinic acid salts appeared at 940 cm 1 and 1010 cm 1. By
A.T.R. measurement, about 90% Or the cation exchange groups
on the sur~ace were found to be carboxyllc acld ~roups.
The membrane was th~n treate~ ln an aqu~ous 2.5
percent sodium h~ypochloI-lte solut:lon at 90C for 16 hours.
The specific conductivity of the treated membrane was found
to be 4.6 x 10 3 mho/cm. The current efflctency, when measured
u~der the same electrolytic conditions as those of Example 24,
was found to be 92 percent. Substantially the same current
efficiency was shown a~ter 1700 hours of continued passage of
electric current.
- 42 -

1219;~99
EXAMPLE_?6
The rnembrane treated with sodium sulfide in Example
25 was saponified in an aaueous 2.5N caustic soda/50 percent
methanol at 60C for 16 ho~rs. The membrane was then treated
in an aqueous lN hydrochloric acid solution at 60~C for 16
hours and thereafter heated in the air at 150C for one hour.
The Polymer 3 side of the membrane was subjected to measurement
of A.T.R. spectrum. In the spectrum~ an absorption band due to
the carboxylic acid group appeared at 1780 cm 1. When this
membrane was converted to the salt form, an absorption band due
to carboxylate appeared strongly at 1690 cm 1, and weak absorp-
tion bands by sulfinic acid salts appeared at 1010 cm 1 and
940 cm . The cation exchange groups on the surface were
found to be carboxylic acid groups (about 90%) by A.T.R. The
membrane was oxidized in an aqueous 2.5 percent sodium hypo-
chlorite solution at 90C for 16 hours. The specific conduc-
tivity of the oxidized membrane was found to be 4.4 x 10 3 mho/cm.
The current efficiency of the membrane, when measured under the
same conditions as those Or Example 24~ was found to be 93
percent.
EXAMPLE 27
Tetrarluoroet~yl.ene~ and perr~ oro-3,6 dioxa-ll-
methyl-7-octene sulforlyl fluorlde were emulsion polymerlzed
at 70C under 4.5 atmospheres of tetrafluoroethylene pressure,
with ammonium persulfate used as the initiator and the ammonium
salt of perfluoro-octanolc aci~ as the emulsifier.
The polymer consequently obtained was washed with
water, t~en hydroly~ed and thereafter sub~ected to measurement
of exchange capacity by a titrimetric method. The exchange
capacity was found to be 0.80 milligram equivalent/gram dry
- 43 -
~F

~19~99
resin. This polymer is identifled as Polymer 4.
By a procedure similar to that of Example 21, Polymer
2 used in Example 21 and Polymer 4 were combined to produce a
composite membrane comprising a Polymer 2 membrane which
h~d a thickness of 4 mil~, and a Polymer 4 membrane
which had a thlckness of 3 mils. ~his composite
membrane was spread out with the Polymer 2 side held downwardly
on a woven fabric of polytetrafluo~oeth,vlene about 0.15 mm in
thickness having filling yarns of 400-denier multifilaments and
warp yarns of 200-denier multifilaments x 2 repeat each at a
rate of 25 yarns per inch. The membrane and fabric were heated
to 270C with the membrane simultaneously drawn against the
membrane by means of vacuum so as to embed the fabric in the
membrane as a reinforcing material.
This membrane was converted into the sulfonyl chloride
form by the same procedure as used in Example 21. Two sheets
of the membrane were held against each other with the Polymer
2 sides (the sides having the fabric embedded) facing lnwardly
by means of frames made of acrylic resin. The Polymer 4 sides
2G of the membrane were allowed to react with hydrogen sulfide
gas introduced in a contlnuous flow at 120C for 20 hours.
The membrane was removed, ~aponirled ln an aqueous
solution of 2.5N caustlc soda/50 percent methanol and there-
after oxldized in a solution of 2,5N caustlc soda/2.5 percent
sodlum hypochlorite at 90C for 16 hour~, The specific
conductivity, when measured by the same method as used in
~xample 21, has found t,o be 3,2 x 10 3 mho~cm, The current
efficiency was 94 percent. ~ven after 1000 hours of continued
pas~age of electric current, the current. ef~iciency remained
unchanged.
- 44 -

1219;~99
COMPARISON EXAMPLE 7
The reinforced composite membrane obtained in
Example 26 was saponified. The specific conductivity and
current efficiency of the resultant membraneg when measured
under the same conditions as those of Example 219 were found
to be 3.9 x 10 3 mho/cm and 62.1 percent respectively.
EXAMPLE 28
The fluorocarbon cation exchange membrane, I'Nafion
#315," made by E. I. DuPont de ~iemours & Company was treated
by immersion in an aqueous lN hydrochloric acid solution at
60C for 16 hours and then converted into the ammonium sulfonate
form with an aqueous lN ammonia solution. The membrane was
dried under vacuum at 50C ~or 16 hours and then allowed to
.. ~7........... w;fl
react ~n a mixture of ~hosphorus pentachloride and phosphorus
oxychlorlde (gravimetrlc ratio 1:1) at 120C for 40 hours.
The surfaces, having respective equivalent weights of 1500 and
1100~ were subjected to measurement of A.T.R. In both of the
spectra, the absorption band at 1060 cm 1 characteristlc of
~.~d
sul~onic acid groupldisappeared and an absorption band at
1420 cm 1 characteristic of sulfonyl chloride was observed.
Two sheets of the membrane were held against each other with
the sides havin~ the equlvalent wel~ht 1100 ~acin~ inwardly,
inserted in frame~ m~de Or acrylic resin, lmmersed ln an
aqueous 57 percent hydrolodiC acid solution and allowed to
react at 80C for 24 hours. At the end of the reactlon, the
membrane was washed with water and the side of the membrane
having the equivalent wei~ht 1500 was subjected to measurement
of A.T.R. In the spectrum, the absorption band at 1420 cm 1
~ R
characteristic of sulfonyl chlorideldisappeared and an absorption
band at 1780 cm 1 characteristic of the carboxylic acid group
- 45 -

IZ19399
appeared. In the case of the A~T.R. obtained of the side of
the membrane having the e~uivalent weight of 110n, the absorption
at 1420 cm 1 characteristic of sulfonyl chloride remained intact.
This membrane was saponified in a solution of 2M caustic soda/50
percent methanol at 60C for 4Q hours. Then, it was oxidized
in an aqueous 2.5 percent sodium hypochlorite solution at 90C
for 16 hours. Thereafterg the membrane was placed in an
electrolytic cell with the side having the equivalent weight
1500 facing the cathode and electrolysis of sodium chloride
was carried out under the same conditions as those of Example
24. The c~lrrent efficiency was 96 percent. The specific
conductivity was 2.0 x lQ 3 mho/cm.
The current efficiency of the membrane~ when
measured after 1500 hours of continued passage of the same
5 electric current 5 was found to be essentially unchanged.
COMPARISON EXAMPLE_
The sul~onyl fluoride form membrane as prepared in
Example 1 was fastened in position between frames made of
acrylic resin. Only the one surrace was allowed to react
with a mixture of ammonia gas with air (about one vol. %)
at room temperature for 15 hours. After the reaction, the
cross section of the membrane was stained with rqethyl Red,
whereby stained layer caused by sulfonamide groups appeared
to the depth of 0.02 mm only at the reacted surface. This
membrane was subjected to saponification and equilibration
under the same conditions as in Example 1, followed by measure-
ment of specific conductivity to give the result of 9.8 x 10 3
mho/cm.
Current efficiency was measured under the same
conditions as in Example 1, with the surface having the
_ 46 -

~Z19399
sulfonamide groups facing the cathode side~ to be 87%.
Furthermore~ after continuous passage of current for 1000 hours,
the current efficiency measured was as low as 80%.
COMPARI~SON EXAMPLE 9
The sulfonyl fluoride form mem~rane as prepared in
Example 1 was treated at onl~ one surface with ethylene diamine
at room temperature for 20 hours. A~i,er the reaction, the
membrane was washed with diglymeg followed by washing with
benzene~ and finally washed with water warmed at about 40C.
When the cross section of this membrane was stained with Methyl
Red, only the treated surface was stained to the depth of 0.01 mm
to find out that N-substituted sulfonamide was formed. This
membrane was subjected to saponification and equilibration
under the same conditions as in Example 1. The specific
conductivity was measured to be 10.2 x 10 3 mho/cm.
Current efficiency was measured, with the surface
ha~-ing the N-substituted sulfonamide groups facing the cathode
side, under the same conditions as in Example 1 to be 91%.
After continuous current passage prolonged for 1000 hours, the
current efficiency was found to be lowered to 74%.
COMPARIS~N ~XAMPLE 10
The cation exchatl~e mem~rane as prep~red in Compari~on
Exanlple 9 was subLIected ko oxldatlve treatment with 2.5% aqueous
sodlum hypochlorite solution at 90C f`or 16 hours. ~ith the
surface havin~ the N-substituted sulfonamide groups f'acing
the cathode side, current ef'ficienc,y was measured under the
same condltions as in Example 1 to be 76%. Formation of
sulfonic acid groups was confirmed by measurement of A,T.R.
after the oxidative treatment.
- 47 -