U.S. patent application number 16/646094 was filed with the patent office on 2020-06-25 for fluoropolymer dispersion, method for making the fluoropolymer dispersion, catalyst ink and polymer electrolyte membrane.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Lisa P. Chen, Gregg D. Dahlke, Denis Duchesne, Steven J. Hamrock, Klaus Hintzer, Markus E. Hirschberg, Arne Thaler, Tilman C. Zipplies.
Application Number | 20200199259 16/646094 |
Document ID | / |
Family ID | 63722797 |
Filed Date | 2020-06-25 |
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United States Patent
Application |
20200199259 |
Kind Code |
A1 |
Chen; Lisa P. ; et
al. |
June 25, 2020 |
FLUOROPOLYMER DISPERSION, METHOD FOR MAKING THE FLUOROPOLYMER
DISPERSION, CATALYST INK AND POLYMER ELECTROLYTE MEMBRANE
Abstract
The fluoropolymer dispersion includes a copolymer having
divalent units represented by formula --[CF.sub.2--CF.sub.2]--,
divalent units represented by formula: [Formula should be inserted
here], and one or more divalent units independently represented by
formula: [Formula should be inserted here] dispersed in at least
one of water or organic solvent. Methods of making the
fluoropolymer dispersion and methods of using the fluoropolymer to
make a at least one of a catalyst ink or polymer electrolyte
membrane are also provided. ##STR00001##
Inventors: |
Chen; Lisa P.; (St. Paul,
MN) ; Dahlke; Gregg D.; (St. Paul, MN) ;
Duchesne; Denis; (Woodbury, MN) ; Hamrock; Steven
J.; (Stillwater, MN) ; Hintzer; Klaus; (Kastl,
DE) ; Hirschberg; Markus E.; (Muhldorf, DE) ;
Thaler; Arne; (Emmerting, DE) ; Zipplies; Tilman
C.; (Burghausen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
63722797 |
Appl. No.: |
16/646094 |
Filed: |
September 14, 2018 |
PCT Filed: |
September 14, 2018 |
PCT NO: |
PCT/US2018/051096 |
371 Date: |
March 10, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62558655 |
Sep 14, 2017 |
|
|
|
62558671 |
Sep 14, 2017 |
|
|
|
62730648 |
Sep 13, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 2810/50 20130101;
C08F 214/262 20130101; C09D 11/52 20130101; H01M 8/1023 20130101;
C08F 216/1475 20200201; C08F 2/10 20130101; H01M 8/1039 20130101;
C09D 127/18 20130101; C08F 2800/10 20130101; C08F 216/1416
20130101; C08J 5/225 20130101; C08J 3/05 20130101; C08J 2327/12
20130101; C08F 214/184 20130101; C08F 8/44 20130101; C08F 8/12
20130101; C09D 127/18 20130101; C08K 3/01 20180101; C08F 8/12
20130101; C08F 214/262 20130101; C08F 8/12 20130101; C08F 8/44
20130101; C08F 214/262 20130101 |
International
Class: |
C08F 2/10 20060101
C08F002/10; C08F 8/12 20060101 C08F008/12; C08J 5/22 20060101
C08J005/22; C08F 216/14 20060101 C08F216/14; C08F 214/26 20060101
C08F214/26; C08F 214/18 20060101 C08F214/18 |
Claims
1. A fluoropolymer dispersion comprising water and a copolymer
comprising: divalent units represented by formula
--[CF.sub.2--CF.sub.2]--; divalent units independently represented
by formula: ##STR00031## wherein a is 0 or 1, b is 2 to 8, c is 0
to 2, e is 1 to 8 with the proviso that when a and c are 0, then e
is 3 to 8, and Z is independently a hydrogen, alkyl having up to
four carbon atoms, an alkali-metal cation, or a quaternary ammonium
cation; and one or more divalent units independently represented by
formula: ##STR00032## wherein Rf is a linear or branched
perfluoroalkyl group having from 1 to 8 carbon atoms and optionally
interrupted by one or more --O-- groups, z is 0, 1, or 2, each n is
independently 1, 2, 3, or 4, and m is 0 or 1; wherein the
fluoropolymer dispersion comprises at least 10% by weight of the
copolymer, based on the total weight of the dispersion, wherein the
copolymer has an --SO.sub.3Z equivalent weight in a range from 600
to 2000, and a melt flow index of up to 80 grams per ten minutes
measured at a temperature of 265.degree. C. and at a support weight
of 5 kg using the Melt Flow Index method in the specification on a
variation of the copolymer with an --SO.sub.2F group instead of
--SO.sub.3Z.
2. The fluoropolymer dispersion of claim 1, wherein b is 2 or 3, c
is 0 or 1, and e is 4.
3. The fluoropolymer dispersion of claim 1, wherein z is 1 or 2,
C.sub.nF.sub.2n is (CF2)11, and n is 1, 2, or 3.
4. The fluoropolymer dispersion of claim 1, wherein the variation
of the copolymer in which with an --SO.sub.2F group instead of
--SO.sub.3Z has a glass transition temperature of up to 20.degree.
C. as measured by the Glass Transition Temperature method in the
specification.
5. The fluoropolymer dispersion of claim lany one of claims 1 to 1,
wherein the copolymer has an alpha transition temperature of less
than 100.degree. C. as measured by the T(.alpha.) Measurement
method in the specification.
6. The fluoropolymer dispersion of claim 1, wherein the copolymer
has an --SO.sub.3Z equivalent weight greater than 1000.
7. The fluoropolymer dispersion of claim 1, further comprising
organic solvent.
8. The fluoropolymer dispersion of claim 1, further comprising
catalyst particles.
9. A catalyst ink comprising the fluoropolymer dispersion of claim
1.
10. A method of making a fluoropolymer dispersion, the method
comprising: combining components comprising water, an organic
solvent, and at least ten percent by weight of a copolymer, based
on the total weight of the components, the copolymer comprising:
divalent units represented by formula --[CF.sub.2--CF.sub.2]--;
divalent units independently represented by formula: ##STR00033##
wherein a is 0 or 1, b is 2 to 8, c is 0 to 2, e is 1 to 8, and Z
is independently a hydrogen, alkyl having up to four carbon atoms,
an alkali-metal cation, or a quaternary ammonium cation; and one or
more divalent units independently represented by formula:
##STR00034## wherein Rf is a linear or branched perfluoroalkyl
group having from 1 to 8 carbon atoms and optionally interrupted by
one or more --O-- groups, z is 0, 1, or 2, each n is independently
1, 2, 3, or 4, and m is 0 or 1; wherein the copolymer has an
--SO.sub.3Z equivalent weight in a range from 800 to 2000, and
mixing the components at ambient pressure and a temperature less
than 100.degree. C. to make the fluoropolymer dispersion.
11. The method of claim 10, further comprising forming the
fluoropolymer dispersion into a film.
12. The method of claim 10, wherein when a and c are 0, then e is 3
to 8.
13. The method of claim 10, wherein the components further comprise
catalyst particles.
14. A polymer electrolyte membrane prepared from the fluoropolymer
dispersion of claim 1.
15. A membrane electrode assembly comprising the polymer
electrolyte membrane of claim 14.
16. The polymer electrolyte membrane of claim 14, further
comprising at least one of cerium cations, manganese cations,
ruthenium cations, or a cerium oxide.
17. The method of claim 10, wherein b is 2 or 3, c is 0 or 1, and e
is 4.
18. The method of claim 10, wherein z is 1 or 2, C.sub.nF.sub.2n is
(CF.sub.2).sub.n,and n is 1, 2, or 3.
19. The method of claim 10, wherein the copolymer has an alpha
transition temperature of less than 100.degree. C. as measured by
the T(.alpha.) Measurement method in the specification.
20. The method of claim 10, wherein the fluoropolymer dispersion
comprises at least 20% by weight of the copolymer, based on the
total weight of the dispersion.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application Nos. 62/558,671 and 62/558,655, filed Sep. 14, 2017,
and 62/730,648, filed Sep. 13, 2018, the disclosures of which are
incorporated by reference in their entirety herein.
BACKGROUND
[0002] Copolymers of tetrafluoroethylene and polyfluorovinyloxy
monomers including sulfonyl fluoride pendant groups have been made.
See, for example, U.S. Pat. No. 3,282,875 (Connolly), U.S. Pat. No.
3,718,627 (Grot), and U.S. Pat. No. 4,267,364 (Grot). Copolymers of
fluorinated olefins and polyfluoroallyloxy sulfonyl fluorides have
been made. See, for example, U.S. Pat. No. 4,273,729 (Krespan) and
U.S. Pat. No. 8,227,139 (Watakabe), and International Pat. Appl.
Pub. No. WO 00/24709 (Farnham et al.). Hydrolysis of the sulfonyl
fluoride of these copolymers to form an acid or acid salt provides
ionic copolymers, which are also called ionomers.
[0003] Certain recently disclosed ionomers are said to have high
oxygen permeability. See, for example, U.S. Pat. Appl. Pub. Nos.
2017/0183435 (Ino), 2013/0253157 (Takami), 2013/0245219 (Perry),
and 2013/0252134 (Takami), and U.S. Pat. No. 8,470,943
(Watakabe).
SUMMARY
[0004] While ionomers made from tetrafluoroethylene and
polyfluorovinyloxy or polyfluoroallyloxy sulfonyl fluorides
monomers are known, certain of these materials are highly
crystalline and difficult to disperse in common solvent (e.g.,
water and alcohol mixtures) at high solid percentages (e.g., at
least 20% solids). Achieving high percent solids may be
particularly challenging when an ionomer of high equivalent weight
is desired. A high solids percentage is useful for making thicker
membranes for membrane electrode assemblies. While for some
applications thin membranes are desirable (e.g., automotive
membranes can be about 12 micrometers thick), other applications
require thicker membranes (e.g., greater than 30 micrometers or
greater than 50 micrometers). Increasing thickness by using higher
percent solids is advantageous over a multi-pass process to build
thickness. Furthermore, increasing the solubility in common
solvents can obviate the need for using high boiling solvents such
as DMF or DMSO and allow for using lower manufacturing temperatures
during the manufacturing process of ionomer membranes. Operating at
lower coating temperature for the membrane or electrode catalyst
particle help protect the overall article of manufacture.
[0005] Easy-to-process ionomers with low hydrogen permeation for
membrane applications in fuel cells or high oxygen permeation
ionomers for electrode applications are also difficult to achieve.
Membrane electrode assemblies useful in solid polymer electrolyte
fuel cells include electrode catalyst layers including a catalyst
(e.g., platinum) and an ionomer. Since the catalysts (e.g.,
platinum) are typically expensive, decreasing the amount of
catalyst can be desirable. For an ionomer used in the electrode,
high oxygen permeability is desirable to minimize resistance. In
the ionic catalyst layer, it is desirable to have a high oxygen
permeability without lowering the ionic conductivity.
[0006] The copolymers in the fluoropolymer dispersions of the
present disclosure include vinyl ether or allyl ether monomer units
in addition to tetrafluoroethylene and sulfonyl group-containing
monomer units. Inclusion of such vinyl and allyl ethers can lead to
an improved processability profile in common solvents by improving
solubility in a dispersion. Inclusion of such monomer units can
also typically provide low hydrogen permeation for membrane
applications in fuel cells or high oxygen permeation ionomers for
electrode applications. The melt flow indexes and equivalent
weights of the copolymers typically also provide advantageous
mechanical properties and conductivity. In one aspect, the present
disclosure provides an aqueous fluoropolymer dispersion of a
copolymer including divalent units represented by formula
[CF2-CF21]--, divalent units independently represented by
formula:
##STR00002##
and one or more divalent units independently represented by
formula:
##STR00003##
In these formulas, a is 0 or 1, b is a number from 2 to 8, c is a
number from 0 to 2, e is a number from 1 to 8 with the proviso that
when a and c are 0, then e is 3 to 8, Z is independently a
hydrogen, alkyl having up to four carbon atoms, an alkali-metal
cation, or a quaternary ammonium cation, Rf is a linear or branched
perfluoroalkyl group having from 1 to 8 carbon atoms and optionally
interrupted by one or more --O-- groups, z is 0, 1, or 2, each n is
independently from 1, 2, 3, or 4, and m is 0 or 1. The
fluoropolymer dispersion comprises at least 10% by weight of the
copolymer, based on the total weight of the dispersion, and the
copolymer has an --SO.sub.3Z equivalent weight in a range from 600
to 2000. A variation of the copolymer in which --SO.sub.3Z is
replaced with --SO.sub.2F has a melt flow index of up to 80 grams
per ten minutes measured at a temperature of 265.degree. C. and at
a support weight of 5 kg. In some embodiments, the dispersion also
contains organic solvent.
[0007] In another aspect, the present disclosure provides a method
of making a fluoropolymer dispersion. The method includes combining
components including water, an organic solvent, and at least 10% by
weight of a copolymer, based on the total weight of the components,
and mixing the components at ambient temperature and pressure to
make the fluoropolymer dispersion. The copolymer includes divalent
units represented by formula --[CF.sub.2--CF.sub.2]--, divalent
units independently represented by formula:
##STR00004##
and one or more divalent units independently represented by
formula:
##STR00005##
In these formulas, a is 0 or 1, b is a number from 2 to 8, c is a
number from 0 to 2, and e is a number from 1 to 8, Z is
independently a hydrogen, alkyl having up to four carbon atoms, an
alkali-metal cation, or a quaternary ammonium cation, Rf is a
linear or branched perfluoroalkyl group having from 1 to 8 carbon
atoms and optionally interrupted by one or more --O-- groups, z is
0, 1, or 2, each n is independently from 1, 2, 3, or 4, and m is 0
or 1. The copolymer has an --SO.sub.3Z equivalent weight in a range
from 600 to 2000.
[0008] In this application:
[0009] Terms such as "a", "an" and "the" are not intended to refer
to only a singular entity but include the general class of which a
specific example may be used for illustration. The terms "a", "an",
and "the" are used interchangeably with the term "at least
one".
[0010] The phrase "comprises at least one of" followed by a list
refers to comprising any one of the items in the list and any
combination of two or more items in the list. The phrase "at least
one of" followed by a list refers to any one of the items in the
list or any combination of two or more items in the list.
[0011] "Alkyl group" and the prefix "alk-" are inclusive of both
straight chain and branched chain groups and of cyclic groups.
Unless otherwise specified, alkyl groups herein have up to 20
carbon atoms. Cyclic groups can be monocyclic or polycyclic and, in
some embodiments, have from 3 to 10 ring carbon atoms.
[0012] The terms "aryl" and "arylene" as used herein include
carbocyclic aromatic rings or ring systems, for example, having 1,
2, or 3 rings and optionally containing at least one heteroatom
(e.g., 0, S, or N) in the ring optionally substituted by up to five
substituents including one or more alkyl groups having up to 4
carbon atoms (e.g., methyl or ethyl), alkoxy having up to 4 carbon
atoms, halo (i.e., fluoro, chloro, bromo or iodo), hydroxy, or
nitro groups. Examples of aryl groups include phenyl, naphthyl,
biphenyl, fluorenyl as well as furyl, thienyl, pyridyl, quinolinyl,
isoquinolinyl, indolyl, isoindolyl, triazolyl, pyrrolyl,
tetrazolyl, imidazolyl, pyrazolyl, oxazolyl, and thiazolyl.
[0013] "Alkylene" is the multivalent (e.g., divalent or trivalent)
form of the "alkyl" groups defined above. "Arylene" is the
multivalent (e.g., divalent or trivalent) form of the "aryl" groups
defined above.
[0014] "Arylalkylene" refers to an "alkylene" moiety to which an
aryl group is attached. "Alkylarylene" refers to an "arylene"
moiety to which an alkyl group is attached.
[0015] The terms "perfluoro" and "perfluorinated" refer to groups
in which all C--H bonds are replaced by C--F bonds.
[0016] The phrase "interrupted by at least one --O-- group", for
example, with regard to a perfluoroalkyl or perfluoroalkylene group
refers to having part of the perfluoroalkyl or perfluoroalkylene on
both sides of the --O-- group. For example,
--CF.sub.2CF.sub.2--O--CF.sub.2--CF.sub.2-- is a perfluoroalkylene
group interrupted by an --O--.
[0017] All numerical ranges are inclusive of their endpoints and
nonintegral values between the endpoints unless otherwise stated
(e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).
DETAILED DESCRIPTION
[0018] The copolymer in the fluoropolymer dispersion according to
the present disclosure includes divalent units represented by
formula --[CF.sub.2--CF.sub.2]--. In some embodiments, the
copolymer comprises at least 60 mole % of divalent units
represented by formula --[CF.sub.2--CF.sub.2--], based on the total
moles of divalent units. In some embodiments, the copolymer
comprises at least 65, 70, 75, 80, or 90 mole % of divalent units
represented by formula --[CF2--CF.sub.2]--, based on the total
moles of divalent units. Divalent units represented by formula
--[CF.sub.2--CF.sub.21]-- are incorporated into the copolymer by
copolymerizing components including tetrafluoroethylene (TFE). In
some embodiments, the components to be polymerized include at least
60, 65, 70, 75, 80, or 90 mole % TFE, based on the total moles of
components to be polymerized.
[0019] The copolymer in the fluoropolymer dispersion according to
the present disclosure includes divalent units independently
represented by formula:
##STR00006##
In this formula, a is 0 or 1, b is a number from 2 to 8, c is a
number from 0 to 2, and e is a number from 1 to 8. In some
embodiments, b is a number from 2 to 6 or 2 to 4. In some
embodiments, b is 2. In some embodiments, e is a number from 1 to 6
or 2 to 4. In some embodiments, e is 2. In some embodiments, e is
4. In some embodiments, c is 0 or 1. In some embodiments, c is 0.
In some embodiments, c is 0, and e is 2 or 4. In some embodiments,
c is 0, and e is 3 to 8, 3 to 6, 3 to 4, or 4. In some embodiments,
when a and c are 0, then e is 3 to 8, 3 to 6, 3 to 4, or 4. In some
embodiments, b is 3, c is 1, and e is 2. In some embodiments, a, b,
c, and e may be selected to provide greater than 2, at least 3, or
at least 4 carbon atoms. C.sub.eF.sub.2e may be linear or branched.
In some embodiments, C.sub.eF.sub.2e can be written as
(CF.sub.2).sub.e, which refers to a linear perfluoroalkylene group.
When c is 2, the b in the two C.sub.bF.sub.2b groups may be
independently selected. However, within a C.sub.bF.sub.2b group, a
person skilled in the art would understand that b is not
independently selected. C.sub.bF.sub.2b may be linear or branched.
In some embodiments, C.sub.bF.sub.2b can be written as
(CF.sub.2).sub.b, which refers to a linear perfluoroalkylene group.
Also in this formula, each Z is independently a hydrogen, alkyl
having up to 4, 3, 2, or 1 carbon atoms, an alkali metal cation, or
a quaternary ammonium cation. The quaternary ammonium cation can be
substituted with any combination of hydrogen and alkyl groups, in
some embodiments, alkyl groups independently having from one to
four carbon atoms. In some embodiments, Z is an alkali-metal
cation. In some embodiments, Z is a sodium or lithium cation. In
some embodiments, Z is a sodium cation. Copolymers having divalent
units represented by this formula can be prepared by copolymerizing
components including at least one polyfluoroallyloxy or
polyfluorovinyloxy compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO--.sub.2X'', in which a, b, c, and e are as defined above
in any of their embodiments, and each X'' is independently --F,
--NZH, or --OZ. Suitable polyfluoroallyloxy and polyfluorovinyloxy
compounds of this formula include
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2--SO--X'',
CF.sub.2.dbd.--CFCF.sub.2--O--CF.sub.2--CF(CF.sub.3)--O--(CF.sub.2).sub.e-
--SO.sub.2X'', CF.sub.2.dbd.CF--O--CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2--SO--X'', and
CF.sub.2.dbd.CF--O--CF.sub.2--CF(CF.sub.3)--O--(CF.sub.2).sub.e--SO.sub.1-
3 2X''. In some embodiments, the compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--C.sub.eF.su-
b.2e)--SO.sub.2X'' is
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2SO.sub.2X'',
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2--SO.sub.2X''-
, or CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2SO.sub.2X''. In
some embodiments, the compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b)--O--(C.sub.eF.sub.2e)-
--SO.sub.2X'' is
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2--SO.sub.2X'',
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2--SO.sub.2X''-
, or
CF.sub.2.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2--SO.sub.2X''.
In some embodiments, the compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2X'' is
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2--SO.sub.2X'' or
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2--SO.sub.2X''-
.
[0020] Compounds represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--C.sub.eF.su-
b.2e)--SO.sub.2X'' can be made by known methods. For example acid
fluorides represented by formula FSO.sub.2(CF.sub.2).sub.e-1--C(O)F
or FSO.sub.2(CF.sub.2).sub.e--(OC.sub.bF.sub.2b).sub.c-1--C(O)F can
be reacted with perfluoroallyl chloride, perfluoroallyl bromide, or
perfluoroallyl fluorosulfate in the presence of potassium fluoride
as described in U.S. Pat. No. 4,273,729 (Krespan) to make compounds
of formula
CF.sub.2.dbd.CFCF.sub.2--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2F. Compounds of formula
CF.sub.2.dbd.CFCF.sub.2--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.sub.2e)---
SO.sub.2F can be hydrolyzed with a base (e.g., alkali metal
CF.sub.2.dbd.CFCF.sub.2--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.sub.2a)---
SO.sub.3Z.
[0021] In some embodiments of the copolymer in the fluoropolymer
dispersion according to the present disclosure, at least some of
the fluorinated divalent units are derived from at least one
short-chain SO.sub.2X''-containing vinyl ether monomer. Likewise,
short-chain SO.sub.2X''-containing vinyl ether monomers may be
useful components to be polymerized in the methods according to the
present disclosure. Short-chain SO.sub.2X''-containing vinyl ether
monomers represented by formula
CF.sub.2.dbd.--CF--O--(CF.sub.2).sub.2--SO.sub.2--X'' (e.g., those
represented by formula [CF.sub.2.dbd.CF--O--(CF.sub.2).sub.213
SO.sub.3]M, where M is an alkali metal, and
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.2--SO.sub.2NZH) can be made by
known methods. Conveniently, a compound of formula
[CF.sub.2.dbd.CF--O--(CF.sub.2).sub.2--SO.sub.3]M can be prepared
in three steps from the known compound represented by formula
FC(O)--CF(CF.sub.3)--O--(CF.sub.2).sub.2--SO.sub.2F. As reported in
Gronwald, O., et al; "Synthesis of difluoroethyl perfluorosulfonate
monomer and its application"; J. Fluorine Chem., 2008, 129,
535-540, the acid fluoride can be combined with a methanol solution
of sodium hydroxide to form the disodium salt, which can be dried
and heated in dry diglyme to effect the carboxylation.
FC(O)--CF(CF.sub.3)--O--(CF.sub.2).sub.2--SO.sub.2F can be prepared
by ring-opening and derivatization of
tetrafluoroethane-.beta.-sultone as described in U.S. Pat. No.
4,962,292 (Marraccini et al.). Compounds represented by formula
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.a--SO.sub.2X'' can also be
prepared by hydrolyzing the products from the elimination of
halogen from a compound of formula
CF.sub.2Cl--CFCl--O--(CF.sub.2).sub.2--SO.sub.2--F described in
U.S. Pat. No. 6,388,139 (Resnick) and or hydrolyzing the products
of decarboxylation of
FSO.sub.2--(CF.sub.2).sub.3-4--O--CF(CF.sub.3)--
COO.sup.-).sub.pM.sup.+P described in U.S. Pat. No. 6,624,328
(Guerra). Compounds of formula
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.2--SO.sub.2NH.sub.2 can be
prepared, for example, by reaction of a cyclic sulfone with one
equivalent of LHMDS as described by Uematsu, N., et al. "Synthesis
of novel perfluorosulfonamide monomers and their application"; J.
Fluorine Chem., 2006, 127, 1087-1095.
[0022] In some embodiments of the copolymer in the fluoropolymer
dispersion according to the present disclosure, the copolymer
includes divalent units independently represented by formula
##STR00007##
In this formula Rf is a linear or branched perfluoroalkyl group
having from 1 to 8 carbon atoms and optionally interrupted by one
or more --O-- groups, z is 0, 1 or 2, each n is independently from
1 to 4, and m is 0 or 1. In some embodiments, n is 1, 3, or 4, or
from 1 to 3, or from 2 to 3, or from 2 to 4. In some embodiments,
when z is 2, one n is 2, and the other is 1, 3, or 4. In some
embodiments, when a is 1 in any of the formulas described above,
for example, n is from 1 to 4, 1 to 3, 2 to 3, or 2 to 4. In some
embodiments, n is 1 or 3. In some embodiments, n is 1. In some
embodiments, n is not 3. When z is 2, the n in the two
C.sub.nF.sub.2a groups may be independently selected. However,
within a C.F211 group, a person skilled in the art would understand
that n is not independently selected. C.sub.nF.sub.2n may be linear
or branched. In some embodiments, C.sub.nF.sub.2n is branched, for
example, --CF.sub.2--CF(CF.sub.3)--. In some embodiments,
C.sub.nF.sub.2n can be written as (CF.sub.2).sub.n, which refers to
a linear perfluoroalkylene group. In these cases, the divalent
units of this formula are represented by formula
##STR00008##
In some embodiments, C.sub.nF.sub.2n is
--CF.sub.2--CF.sub.2--CF.sub.2--. In some embodiments,
(OC.sub.nF.sub.2n).sub.z is represented by
--O--(CF.sub.2).sub.1-4--[O(CF.sub.2).sub.1-4]-.sub.0-1. In some
embodiments, Rf is a linear or branched perfluoroalkyl group having
from 1 to 8 (or 1 to 6) carbon atoms that is optionally interrupted
by up to 4, 3, or 2 --O-- groups. In some embodiments, Rf is a
perfluoroalkyl group having from 1 to 4 carbon atoms optionally
interrupted by one --O-- group. In some embodiments, z is 0, m is
0, and Rf is a linear or branched perfluoroalkyl group having from
1 to 4 carbon atoms. In some embodiments, z is 0, m is 0, and Rf is
a branched perfluoroalkyl group having from 3 to 8 carbon
atoms.
[0023] In some embodiments, m is 1, and Rf is a branched
perfluoroalkyl group having from 3 to 8 carbon atoms or a linear
perfluoroalkyl group having 5 to 8 carbon atoms. In some
embodiments, Rf is a branched perfluoroalkyl group having from 3 to
6 or 3 to 4 carbon atoms. An example of a useful perfluoroalkyl
vinyl ether (PAVE) from which these divalent units in which m and z
are 0 are derived is perfluoroisopropyl vinyl ether
(CF.sub.2.dbd.CFOCF(CF.sub.3).sub.2), also called iso-PPVE. Other
useful PAVEs include perfluoromethyl vinyl ether, perfluoroethyl
vinyl ether, and perfluoropropyl vinyl ether.
[0024] Divalent units represented by formulas
##STR00009##
in which m is 0, typically arise from perfluoroalkoxyalkyl vinyl
ethers. Suitable perfluoroalkoxyalkyl vinyl ethers (PAOVE) include
those represented by formula
CF.sub.2.dbd.CF[O(CF.sub.2).sub.n].sub.2ORf and
CF.sub.2.dbd.CF(OC.sub.nF.sub.2n).sub.2)ORf, in which n, z, and Rf
are as defined above in any of their embodiments. Examples of
suitable perfluoroalkoxyalkyl vinyl ethers include
CF.sub.2.dbd.CFOCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub.2-
OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub-
.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2(OCF.sub.2)OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2(OCF.sub.2)OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2.dbd.CF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.3CF.sub.2.dbd.CFO-
CF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)--O--C.sub.3F.sub.7 (PVVE-2),
CF.sub.2.dbd.CF(OCF.sub.2CF(CF.sub.3)).sub.2)--O--C.sub.3F.sub.7(PPVE-3),
and
CF.sub.2.dbd.CF((OCF.sub.2CF(CF.sub.3)--O--C.sub.3F.sub.7(PPVE-4).
In some embodiments, the perfluoroalkoxyalkyl vinyl ether is
selected from CF.sub.2.dbd.CFOCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2=CFOCF.sub.2CF.sub.2CF2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2=CFOCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.-
3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2CF.sub-
.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2(OCF.sub.2).sub.3OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2(OCF.sub.2).sub.4OCF.sub.3,
CF.sub.2=CFOCF.sub.2CF.sub.2OCF.sub.2OCF.sub.2OCF.sub.3, and
combinations thereof. Many of these perfluoroalkoxyalkyl vinyl
ethers can be prepared according to the methods described in U.S.
Pat. No. 6,255,536 (Worm et al.) and U.S. Pat. No. 6,294,627 (Worm
et al.). In some embodiments, the PAOVE is
perfluoro-3-methoxy-n-propyl vinyl ether. In some embodiments, the
PAOVE is other than perfluoro-3-methoxy-n-propyl vinyl ether.
[0025] The divalent units represented by formula
##STR00010##
in which m is 1, are typically derived from at least one
perfluoroalkoxyalkyl allyl ether. Suitable perfluoroalkoxyalkyl
allyl ethers include those represented by formula
CF.sub.2.dbd.CFCF.sub.2(OC.sub.nF.sub.2n).sub.zORf, in which n, z,
and Rf are as defined above in any of their embodiments. Examples
of suitable perfluoroalkoxyalkyl allyl ethers include
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3-
, CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2-
OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub-
.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2(OCF.sub.2).sub.3OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2(OCF.sub.2).sub.4OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF2CF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.-
2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF(CF.sub.3)--O--C.sub.3F.sub.7- ,
and
CF.sub.2.dbd.CFCF.sub.2(OCF.sub.2CF(CF.sub.3)).sub.2--O--C.sub.3F.su-
b.7. In some embodiments, the perfluoroalkoxyalkyl allyl ether is
selected from CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2=CFCF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2OCF.sub.-
3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub-
.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.2CF.sub.2-
CF.sub.2OCF.sub.3,
CF.sub.2=CFCF.sub.2OCF.sub.2CF.sub.2(OCF.sub.2).sub.3OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2(OCF.sub.2).sub.4OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2OCF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2CF.sub.3,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2CF.sub.-
2CF.sub.3, and combinations thereof.
[0026] Many of these perfluoroalkoxyalkyl allyl ethers can be
prepared, for example, according to the methods described in U.S.
Pat. No. 4,349,650 (Krespan). Perfluoroalkoxyalkyl allyl ethers can
also be prepared by combining first components comprising at least
one of CF.sub.2.dbd.CF--CF.sub.2--OSO.sub.2Cl or
CF.sub.2.dbd.CF--CF.sub.2--OSO.sub.2CF.sub.3, a polyfluorinated
compound comprising at least one ketone or carboxylic acid halide
or combination thereof, and fluoride ion. Polyfluorinated compounds
comprising at least one ketone or carboxylic acid halide or
combination thereof and fluoride ions can be any of those
described, for example, in U.S. Pat. No. 4,349,650 (Krespan).
[0027] CF.sub.2.dbd.CF--CF.sub.2--OSO.sub.2Cl can convenientlhy be
prepard by reaction of boron trichloride (BCl.sub.3) and
ClSO.sub.3H to prpvode B(OSO.sub.2Cl).sub.3 and subsequently
reacting the B(OSO.sub.2Cl).sub.3 and hexafluoropropylene (HFP).
The reaction of BCl.sub.3 and CkSO.sub.3H can be carried out, for
example, by dropwise addition of neat ClSO.sub.3H to gaseous
BCl.sub.3 at below 50.degree. C. or, in the case of condensed
BC.sub.3 at sub-ambient temperature. The reaction can be carried
out at a temperature of least -20.degree. C., -10.degree. C.,
0.degree. C., 10.degree. C., or 20.degree. C. and up to 30.degree.
C., 40.degree. C., or 50.degree. C. The addition of ClSO.sub.3H to
BCl.sub.3 can be carried out at a rate, for example, to maintain
the temperature of the mixture at 10.degree. C. or below.
B(OSO.sub.2Cl).sub.3 can be isolated as a white powder after
volatile starting materials are removed under vacuum.
B(OSO.sub.2Cl).sub.3 can then be suspended or dissolved in a
solvent, and HFP can be added at below 50.degree. C., in some
embodiments, at sub-ambient temperature. For example, the reaction
can be carried out at a temperature of least -20.degree. C.,
-10.degree. C., 0.degree. C., 10.degree. C., or 20.degree. C. and
up to 30.degree. C., 40.degree. C., or 50.degree. C. Suitable
solvents include halogenated solvents (e.g., methylene chloride or
Freon-113). In some embodiments, the solvent is a non-aromatic
solvent. CF.sub.2.dbd.CF--CF.sub.2--OSO.sub.2Cl can be isolated and
optionally purified using conventional methods.
[0028] Combining components comprising M(OSO.sub.2CF.sub.3).sub.3
and hexafluoropropylene (HFP) to provide
CF.sub.2.dbd.CF--CF.sub.2--OSO.sub.2CF.sub.3, wherein M is Al or B.
Al(OSO.sub.2CF.sub.3)3 is commercially available, for example, from
chemical suppliers such as abcr GmbH (Karlsruhe, Germany) and
Sigma-Aldrich (St. Louis, Miss.). Reaction of BCl.sub.3 and
CF.sub.3SO.sub.3H can be useful to provide
B(OSO.sub.2CF.sub.3).sub.3. The reaction of BCl.sub.3 and
CF.sub.3SO.sub.3H can be carried out, for example, by dropwise
addition of neat CF.sub.3SO.sub.3H to gaseous BCl.sub.3 at below
50.degree. C. or, in the case of condensed BCl.sub.3 at sub-ambient
temperature. The reaction can be carried out at a temperature of
least -20.degree. C., -10.degree. C., 0.degree. C., 10.degree. C.,
or 20.degree. C. and up to 30.degree. C., 40.degree. C., or
50.degree. C. The addition of CF.sub.3SO.sub.3H to BCl.sub.3 can be
carried out at a rate, for example, to maintain the temperature of
the mixture at 10.degree. C. or below. B(OSO.sub.2CF.sub.3).sub.3
can be isolated as a white powder after volatile starting materials
are removed under vacuum.
[0029] B(OSO.sub.2CF.sub.3).sub.3 can combined with HFP at a
temperature above 0.degree. C. In some embodiments, the reaction
can be carried out at a temperature up to 50.degree. C., 40.degree.
C., 30.degree. C., 20.degree. C., or 10.degree. C. The reaction can
be carried out at a temperature in a range from above 0.degree. C.
to 10.degree. C., in some embodiments, in a range from 2.degree. C.
to 10.degree. C., and in some embodiments, in a range from
4.degree. C. to 8.degree. C. The reaction mixture is combined with
water at a temperature below 28.degree. C., in some embodiments, in
a range from above 25.degree. C. to 27.degree. C. The reaction
product can then be isolated and optionally purified using
conventional methods (e.g., separation of the organic fraction,
drying over a drying agent, filtering, and distilling). The product
CF.sub.2.dbd.CF--CF.sub.2OSO.sub.2CF.sub.3 can be isolated in 75%
yield, which is an improvement over the yield reported in Petrov,
V. A., J. Fluorine Chem. 1995, 73, 17-19.
[0030] The vinyl ethers and allyl ethers described above in any of
their embodiments, may be present in the components to be
polymerized in any useful amount, in some embodiments, in an amount
of up to 20, 15, 10, 7.5, or 5 mole percent, of at least 3, 4, 4.5,
5, or 7.5 mole percent, or in a range from 3 to 20, 4 to 20, 4.5 to
20, 5 to 20, 7.5 to 20, or 5 to 15 mole percent, based on the total
amount of polymerizable components. Accordingly, the copolymer in
the fluoropolymer dispersion according to the present disclosure
can include divalent units derived from these vinyl ethers and
allyl ethers in any useful amount, in some embodiments, in an
amount of up to 20, 15, 10, 7.5, or 5 mole percent, of at least 3,
4, 4.5, 5, or 7.5 mole percent, or in a range from 3 to 20, 4 to
20, 4.5 to 20, 5 to 20, 7.5 to 20, or 5 to 15 mole percent, based
on the total moles of divalent units.
[0031] In some embodiments of the copolymer in the fluoropolymer
dispersion according to the present disclosure, the copolymer
includes divalent units derived from at least one fluorinated
olefin independently represented by formula
C(R).sub.2.dbd.CF--Rf.sub.2. These fluorinated divalent units are
represented by formula --[CR.sub.2---CFRf.sub.2]-. In formulas
C(R).sub.2.dbd.CF--Rf.sub.2 and --[CR.sub.2--CFRf.sub.2]--,
Rf.sub.2 is fluorine or a perfluoroalkyl having from 1 to 8, in
some embodiments 1 to 3, carbon atoms, and each R is independently
hydrogen, fluorine, or chlorine. Some examples of fluorinated
olefins useful as components of the polymerization include,
hexafluoropropylene (HFP), trifluorochloroethylene (CTFE), and
partially fluorinated olefins (e.g., vinylidene fluoride (VDF),
tetrafluoropropylene (R1234yf), pentafluoropropylene, and
trifluoroethylene). In some embodiments, the copolymer includes at
least one of divalent units derived from chlorotrifluoroethylene or
divalent units derived from hexafluoropropylene.
[0032] Divalent units represented by formula
--[CR.sub.2--CFRf.sub.2]-- may be present in the copolymer in any
useful amount, in some embodiments, in an amount of up to 10, 7.5,
or 5 mole percent, based on the total moles of divalent units.
[0033] In some embodiments of the copolymer in the fluoropolymer
dispersion according to the present disclosure, the copolymer is
essentially free of VDF units, and the components to be
copolymerized are essentially free of VDF. For example, at a pH
higher than 8, VDF may undergo dehydrofluorination, and it may be
useful to exclude VDF from the components to be polymerized.
"Essentially free of VDF" can mean that VDF is present in the
components to be polymerized at less than 1 (in some embodiments,
less than 0.5, 0.1, 0.05, or 0.01) mole percent. "Essentially free
of VDF" includes being free of VDF. Copolymers in the fluoropolymer
dispersion of the present disclosure can comprise divalent units
independently represented by formula:
##STR00011##
wherein p is 0 or 1, q is 2 to 8, r is 0 to 2, s is 1 to 8, and Z'
is a hydrogen, an alkali-metal cation or a quaternary ammonium
cation. In some embodiments, q is a number from 2 to 6 or 2 to 4.
In some embodiments, q is 2. In some embodiments, s is a number
from 1 to 6 or 2 to 4. In some embodiments, s is 2. In some
embodiments, s is 4. In some embodiments, r is 0 or 1. In some
embodiments, r is 0. In some embodiments, r is 0, and s is 2 or 4.
In some embodiments, q is 3, r is 1, and s is 2. C.sub.sF.sub.2s
may be linear or branched. In some embodiments, C.sub.sF.sub.2s can
be written as (CF.sub.2).sub.s, which refers to a linear
perfluoroalkylene group. When r is 2, the q in the two
C.sub.qF.sub.2q groups may be independently selected. However,
within a C.sub.qF.sub.2q group, a person skilled in the art would
understand that q is not independently selected. Each Z' is
independently a hydrogen, an alkali metal cation, or a quaternary
ammonium cation. The quaternary ammonium cation can be substituted
with any combination of hydrogen and alkyl groups, in some
embodiments, alkyl groups independently having from one to four
carbon atoms. In some embodiments, Z' is an alkali-metal cation. In
some embodiments, Z' is a sodium or lithium cation. In some
embodiments, Z' is a sodium cation. Divalent units represented by
formula
##STR00012##
may be present in the copolymer in any useful amount, in some
embodiments, in an amount of up to 10, 7.5, or 5 mole percent,
based on the total moles of divalent units.
[0034] Copolymers in the fluoropolymer dispersion of the present
disclosure can also include units derived from bisolefins
represented by formula
X.sub.2C.dbd.CY--(CW.sub.2)m--(O).sub.n--R.sub.F--(O),--(CW.sub.2-
).sub.p--CY.dbd.CX.sub.2. In this formula, each of X, Y, and W is
independently fluoro, hydrogen, alkyl, alkoxy, polyoxyalkyl,
perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxyalkyl, m and p
are independently an integer from 0 to 15, and n, o are
independently 0 or 1. In some embodiments, X, Y, and W are each
independently fluoro,
[0035] CF.sub.3, C.sub.2F.sub.5, C.sub.3F.sub.7, C.sub.4F.sub.9,
hydrogen, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, C.sub.4H.sub.9.
In some embodiments, X, Y, and W are each fluoro (e.g., as in
CF.sub.2.dbd.CF--O--R.sub.F--O--CF.dbd.CF.sub.2 and
CF.sub.2.dbd.CF--CF.sub.2--O--R.sub.F--O--CF.sub.2--CF.dbd.CF.sub.2).
In some embodiments, n and o are 1, and the bisolefins are divinyl
ethers, diallyl ethers, or vinyl-allyl ethers. R.sub.F represents
linear or branched perfluoroalkylene or perfluoropolyoxyalkylene or
arylene, which may be non-fluorinated or fluorinated. In some
embodiments, RF is perfluoroalkylene having from 1 to 12, from 2 to
10, or from 3 to 8 carbon atoms. The arylene may have from 5 to 14,
5 to 12, or 6 to 10 carbon atoms and may be non-substituted or
substituted with one or more halogens other than fluoro,
perfluoroalkyl (e.g. --CF.sub.3 and --CF.sub.2CF3), perfluoroalkoxy
(e.g. --O--CF.sub.3, --OCF.sub.2CF.sub.3), perfluoropolyoxyalkyl
(e.g., --OCF.sub.2OCF.sub.3; --CF.sub.2OCF.sub.2OCF3), fluorinated,
perfluorinated, or non-fluorinated phenyl or phenoxy, which may be
substituted with one or more perfluoroalkyl, perfluoroalkoxy,
perfluoropolyoxyalkyl groups, one or more halogens other than
fluoro, or combinations thereof. In some embodiments, R.sub.F is
phenylene or mono-, di-, tri- or tetrafluoro-phenylene, with the
ether groups linked in the ortho, para or meta position. In some
embodiments, R.sub.F is CF.sub.2; (CF.sub.2).sub.q wherein q is 2,
3, 4, 5, 6, 7 or 8; CF.sub.2--O--CF.sub.2;
CF.sub.2--O--CF.sub.2--CF.sub.2; CF(CF.sub.3)CF2;
(CF.sub.2)2--O--CF(CF3)--CF.sub.2;
CF(CF.sub.3)--CF.sub.2--O--CF(CF.sub.3)CF.sub.2; or
(CF.sub.2).sub.2--O--CF(CF.sub.3)--CF2--O--CF(CF.sub.3)--CF.sub.2--O--CF(-
CF.sub.3)--CF.sub.2--O--CF.sub.2. The bisolefins can introduce long
chain branches as described in U.S. Pat. Appl. Pub. No.
2010/0311906 (LavaHee et al.). The bisolefins, described above in
any of their embodiments, may be present in the components to be
polymerized in any useful amount, in some embodiments, in an amount
of up to 2, 1, or 0.5 mole percent and in an amount of at least 0.1
mole percent, based on the total amount of polymerizable
components.
[0036] Copolymers in the fluoropolymer dispersions of the present
disclosure can also include units derived from non-fluorinated
monomers. Examples of suitable non-fluorinated monomers include
ethylene, propylene, isobutylene, ethyl vinyl ether, vinyl
benzoate, ethyl allyl ether, cyclohexyl allyl ether, norbornadiene,
crotonic acid, an alkyl crotonate, acrylic acid, an alkyl acrylate,
methacrylic acid, an alkyl methacrylate, and hydroxybutyl vinyl
ether. Any combination of these non-fluorinated monomers may be
useful. In some embodiments, the components to be polymerized
further include acrylic acid or methacrylic acid, and the copolymer
in the fluoropolymer dispersion of the present disclosure includes
units derived from acrylic acid or methacrylic acid. Typically, the
copolymer in the fluoropolymer dispersion of the present disclosure
does not include cyclic structures comprising fluorinated carbon
atoms and oxygen atoms in the main chain (that is, divalent units
comprising such cyclic structures).
[0037] In some embodiments, the copolymer in the fluoropolymer
dispersion of the present disclosure can be made from the sulfonyl
fluoride compounds, where X'' in any of the aforementioned
compounds represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2X'' is F, according to the methods described below,
for example. Hydrolysis of a copolymer having --SO.sub.2F groups
with an alkaline hydroxide (e.g. LiOH, NaOH, or KOH) solution
provides --SO.sub.3Z groups, which may be subsequently acidified to
SO.sub.3H groups. Treatment of a copolymer having --SO.sub.2F
groups with water and steam can form SO.sub.3H groups. Thus,
copolymers of the present disclosure having --SO.sub.2F groups
(that is, in which X is F) are useful intermediates for making
other copolymers of the present disclosure.
[0038] In some embodiments, the method according to the present
disclosure includes copolymerizing components including at least
one compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.3Z, in which Z, b, c, and e are as defined above in
any of their embodiments. In some embodiments, Z is an alkali-metal
cation. In some embodiments, Z is a sodium or lithium cation. In
some embodiments, Z is a sodium cation. In some embodiments, the
compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.-
sub.eF.sub.2e)--SO.sub.3Z is
CF.sub.2.dbd.CFCF.sub.2--O--CF.sub.2CF.sub.2--SO.sub.3Na.
[0039] The copolymer in the fluoropolymer dispersion according to
the present disclosure can have an --SO.sub.3Z equivalent weight of
up to 2000, 1900, 1800, or 1750. In some embodiments, the copolymer
has an --SO.sub.3Z equivalent weight of at least 600, 700, 800,
900, 950, or 1000. In some embodiments, the copolymer has an SO3Z
equivalent weight in a range from 600 to 2000, 800 to 2000, 950 to
2000, or 1000 to 2000. In general, the --SO.sub.3Z equivalent
weight of the copolymer refers to the weight of the copolymer
containing one mole of --SO3Z groups, wherein Z is as defined above
in any of its embodiments. In some embodiments, the--SO.sub.3Z
equivalent weight of the copolymer refers to the weight of the
copolymer that will neutralize one equivalent of base. In some
embodiments, the --SO.sub.3Z equivalent weight of the copolymer
refers to the weight of the copolymer containing one mole of
sulfonate groups (i.e., --SO.sub.3.sup.-). Decreasing the
--SO.sub.3Z equivalent weight of the copolymer tends to increase
proton conductivity in the copolymer but tends to decrease its
crystallinity, which may compromise the mechanical properties of
the copolymer (e.g., tensile strength). Thus, the --SO.sub.3Z
equivalent weight of the copolymer in the fluoropolymer dispersion
of the present disclosure typically and advantageously provides a
balance of the requirements for the electrical and mechanical
properties of the copolymer. Equivalent weight can be calculated
from the molar ratio of monomer units in the copolymer using, for
example, the equation shown in the Examples, below.
[0040] The copolymer in the fluoropolymer dispersion of the present
disclosure can have up to 30 mole percent of divalent units
represented by formula
##STR00013##
based on the total amount of the divalent units. In some
embodiments, the copolymer comprises up to 25 or 20 mole percent of
these divalent units, based on the total amount of these divalent
units. The components that are copolymerized in the methods
described herein can comprise up to 30 mole percent of at least one
compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2X'', in any of their embodiments described above,
based on the total amount of components. In some embodiments, the
components comprise up to 25 or 20 mole percent of a compound
represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2X'', based on the total amount of components.
[0041] The molecular weights of copolymers in fluoropolymer
dispersions according to the present disclosure can be
characterized by the melt viscosity or the melt flow index (MFI,
e.g., 265.degree. C./5 kg) of a variation of the copolymer in which
--SO.sub.3Z is replaced with --SO.sub.2F. In some embodiments, the
copolymer in the fluoropolymer dispersion of the present disclosure
has an MFI of up to 80 grams per 10 minutes, 70 grams per 10
minutes, 60 grams per 10 minutes, 50 grams per 10 minutes, 40 grams
per 10 minutes, 30 grams per 10 minutes, or 20 grams per 10
minutes. In some embodiments, the copolymer in the fluoropolymer
dispersion according to the present disclosure has an MFI of up to
15 grams per 10 minutes or up to 12 grams per 10 minutes. When the
MFI is up to 80, 70, 60, 50, 40, 30, 20, 15, or 12 grams per 10
minutes, good mechanical properties are achieved. The MFI of the
copolymer can be affected by adjusting the amount of the initiator
and/or chain-transfer agent used during polymerization, both of
which affect the molecular weight and molecular-weight distribution
of the copolymer. MFI can also be controlled by the rate of
addition of initiator to the polymerization. Variations in the
monomer composition can also affect the MFI. For the purposes of
the present disclosure, MFI is measured according to the test
method described in the Examples, below. It should be noted that an
MFI of about 20 grams per 10 minutes measured at 270.degree.
C./2.16 kg will give an MFI of 43 grams per 10 minutes measured at
265.degree. C./5 kg. In general, when an MFI is measured at
265.degree. C./5 kg, a value of more than twice than an MFI
measured at 270.degree. C./2.16 kg is obtained.
[0042] Copolymers in the fluoropolymer dispersions of the present
disclosure are generally considered ionomers. lonomers typically
exhibit a thermal transition between a state in which the ionic
clusters are closely associated and a state in which the
interactions between those clusters have been weakened. This
transition is described as an alpha transition, and the transition
temperature is T(.alpha.). lonomers with higher T(.alpha.)
typically have greater mechanical integrity at elevated
temperatures than corresponding materials with lower T(.alpha.). As
a result, to obtain high service temperatures for an ionomer, a
relatively high T(.alpha.) can be desirable for ionomers. In some
embodiments, the a-dispersion temperature T(.alpha.) of copolymers
in the fluoropolymer dispersion of the present disclosure is at
least 95.degree. C., 100.degree. C., 105.degree. C., 110.degree.
C., or 115.degree. C. However, we have found that decreasing the
T(.alpha.) can increase oxygen permeability and that selecting a
T(.alpha.) to obtain a balance of mechanical integrity and oxygen
permeability can be useful. In some embodiments, the a-dispersion
temperature [T(.alpha.)] of copolymer of the present disclosure is
up to 110.degree. C., 105.degree. C., or 100.degree. C., or less
than 100.degree. C., in some embodiments, up to 99.5.degree. C. or
99.degree. C. In some embodiments, the .alpha.-dispersion
temperature [T(.alpha.)] of copolymer of the present disclosure is
at least room temperature (e.g., 25.degree. C.), in some
embodiments, at least 60.degree. C., 65.degree. C., 70.degree. C.,
75.degree. C., 80.degree. C., 85.degree. C., 90.degree. C., or
95.degree. C. In some embodiments, the a-dispersion temperature
[T(a.alpha.] of copolymer of the present disclosure is in a range
from 60.degree. C. to 100.degree. C., 70.degree. C. to 100.degree.
C., 80.degree. C. to 100.degree. C., 90.degree. C. to 100.degree.
C., or 95.degree. C. to 100.degree. C. In some embodiments, the
a-dispersion temperature [T(.alpha.)] of copolymer of the present
disclosure is in a range from 60.degree. C. to 99.5.degree. C.,
70.degree. C. to 99.5.degree. C., 80.degree. C. to 99.5.degree. C.,
90.degree. C. to 99.5.degree. C., or 95.degree. C. to 99.5.degree.
C. In some embodiments, the a-dispersion temperature [T(.alpha.)]
of copolymer of the present disclosure is in a range from
60.degree. C. to 99.degree. C., 70.degree. C. to 99.degree. C.,
80.degree. C. to 99.degree. C., 90.degree. C. to 99.degree. C., or
95.degree. C. to 99.degree. C. In the copolymers of the present
disclosure, various factors can affect the [T(.alpha.)]. For
example, when a, b, c, and e are selected to provide greater than
2, at least 3, or at least 4 carbon atoms in the side chain of the
sulfonyl-substituted divalent units a T(.alpha.) up to 100.degree.
C. (e.g., in a range from 80.degree. C. to 100.degree. C.,
90.degree. C. to 100.degree. C., or 95.degree. C. to 100.degree.
C.) may be achieved. Also, when m, m', n, z, Rf, and Rfi are
selected to provide greater than 2, at least 3, or at least 4
carbon atoms and/or at least one or 2 oxygen atoms in the side
chain of the divalent units represented by formula
##STR00014##
a T(.alpha.) up to 100.degree. C. (e.g., in a range from 80.degree.
C. to 100.degree. C., 90.degree. C. to 100.degree. C., or
95.degree. C. to 100.degree. C.) may be achieved. Including more
than 3, 4, 4.5, 5, or 7.5 mol percent of these divalent units can
be useful for achieving a T(.alpha.) in these ranges. Also, the
cation present in the ionomer affects the T(.alpha.). Thus,
T(.alpha.) in the copolymer of the present disclosure can be
changed, for example, by ion exchange.
[0043] Dynamic mechanical analysis (DMA) is a useful tool for
measuring T(.alpha.), as polymer physical property changes
accompany this transition. The DMA sample cell may be set up in
torsion, compression, or tension. For the purposes of this
disclosure, T(.alpha.) is measured by the method described in the
Examples, below. Since the T(.alpha.) changes with different
cations, for the purposes of this disclosure, the T(.alpha.) is
understood to be the T(.alpha.) when Z is hydrogen.
[0044] The glass transition temperature (Tg) is typically defined
as the temperature at which an amorphous polymer or amorphous
region within a polymer transitions from a glassy material (below
Tg) to a rubbery one (above Tg). Gas diffusion rates are correlated
to free volume in a polymer [see, for example, Diffusion in
Polymers, Marcel Dekker (New York), 1996, edited by P. Neogi]. The
free volume increases with temperature, particularly so above the
Tg of the polymer. The molecular transport of a gas is enhanced the
more the temperature of operation exceeds the Tg of the polymer. As
a result, polymers having a relatively low Tg can be desirable for
applications in which gas diffusion is required. In some
embodiments, in the copolymers in the fluoropolymer dispersions of
the present disclosure, a, b, c, and e may be selected to provide
greater than 2, at least 3, or at least 4 carbon atoms in the side
chain of the sulfonyl-substituted divalent units to achieve a lower
Tg. In some embodiments, the variation of the copolymer in which
.alpha.SO.sub.3Z is replaced with --SO.sub.2F has a Tg less than
30.degree. C., less than room temperature, or up to 25.degree. C.,
20.degree. C., 15.degree. C., or 10.degree. C. Since multiple bulk
physical properties of the polymer are different in the glassy
state relative to the rubbery state, a variety of methods can be
used to measure the Tg. Differential scanning calorimetry (DSC) and
dilatometry detect changes in the heat capacity and thermal
expansion of the polymer in the two states, while methods such as
thermal mechanical analysis
[0045] (TMA) and dynamic mechanic analysis (DMA) detect differences
in the physical properties in the two states. For the purposes of
this disclosure, Tg is measured by the method described in the
Examples, below.
[0046] In some embodiments, the copolymer in the fluoropolymer
dispersion of the present disclosure has at least one of a relative
high T(.alpha.) (e.g., at least 100.degree. C., 105.degree. C.,
110.degree. C., 115.degree. C., 120.degree. C., or 125.degree. C.)
or a relative low Tg (e.g., up to 25.degree. C., 20.degree. C.,
15.degree. C., or 10.degree. C. as measured for a variation of the
copolymer in which --SO.sub.3Z is replaced with --SO.sub.2F). In
some embodiments, the copolymer of the present disclosure has at
least one of a relative low T(.alpha.) (e.g., up to 110.degree. C.,
105.degree. C., 100.degree. C., 99.5.degree. C., or 99.degree. C.)
or a relative low Tg (e.g., up to 25.degree. C., 20.degree. C.,
15.degree. C., or 10.degree. C.). In some embodiments, the
copolymer of the present disclosure has both a relative high
T(.alpha.) (e.g., at least 100.degree. C., 105.degree. C.,
110.degree. C., 115.degree. C., 120.degree. C., or 125.degree. C.)
and a relative low Tg (e.g., up to 25.degree. C., 20.degree. C.,
15.degree. C., or 10.degree. C. as measured for the variation of
the copolymer in which --SO.sub.3Z is replaced with --SO.sub.2F).
In some embodiments, the copolymer of the present disclosure has
both a relative low T(.alpha.) (e.g., up to 110.degree. C.,
105.degree. C., 100.degree. C., 99.5.degree. C., or 99.degree. C.)
and a relative low Tg (e.g., up to 25.degree. C., 20.degree. C.,
15.degree. C., or 10.degree. C.).
[0047] High oxygen permeability in the copolymers disclosed herein
can be useful to improve the efficiency of fuel cells, for example.
Copolymers in the fluoropolymer dispersions according to the
present disclosure typically have useful oxygen permeabilities for
fuel cell applications. Oxygen permeability can be measured by
methods known in the art including the time lag method described in
the Examples, below. As shown in comparison of Example 1 and
Comparative Example A below, the addition of the divalent unit
represented by formula
##STR00015##
can quadruple the oxygen permeability of a copolymer in comparison
to a comparable copolymer that does not include these units.
Comparable can mean similar to the copolymer of the present
disclosure in equivalent weight. When z is 1 or 2, the addition of
the divalent unit represented by formula
##STR00016##
unexpectedly can increase the oxygen permeability of a copolymer by
an order of magnitude in comparison to a comparable copolymer that
does not include these units. Thus, when z is 1 or 2, the addition
of the divalent unit represented by formula
##STR00017##
unexpectedly can increase the oxygen permeability of a copolymer to
a greater extent than when z is 0.
[0048] The methods of making the copolymer can be carried out by
free-radical polymerization. Conveniently, in some embodiments, the
methods of making the copolymer in the fluoropolymer dispersion
disclosed herein includes radical aqueous emulsion
polymerization.
[0049] In some embodiments of the method of making the copolymer, a
water-soluble initiator (e.g., potassium permanganate or a peroxy
sulfuric acid salt) can be useful to start the polymerization
process. Salts of peroxy sulfuric acid, such as ammonium persulfate
or potassium persulfate, can be applied either alone or in the
presence of a reducing agent, such as bisulfites or sulfinates
(e.g., fluorinated sulfinates disclosed in U.S. Pat. Nos. 5,285,002
and 5,378,782, both to Grootaert) or the sodium salt of hydroxy
methane sulfinic acid (sold under the trade designation "RONGALIT",
BASF Chemical Company, N.J., USA). The choice of initiator and
reducing agent, if present, will affect the end groups of the
copolymer. The concentration range for the initiators and reducing
agent can vary from 0.001% to 5% by weight based on the aqueous
polymerization medium.
[0050] In some embodiments of the method of making the copolymer,
--SO.sub.2X'' end groups are introduced in the copolymers according
to the present disclosure by generating SO.sub.3.sup.- radicals
during the polymerization process. When salts of peroxy sulfuric
acid are used in the presence of a sulfite or bisulfite salt (e.g.,
sodium sulfite or potassium sulfite), SO.sub.3.sup.- radicals are
generated during the polymerization process, resulting in
--SO.sub.3.sup.- end groups. It might be useful to add metal ions
to catalyze or accelerate the formation of --SO.sub.3.sup.-
radicals. By altering the stoichiometry of the sulfite or bisulfite
salt versus the peroxy sulfuric acid salt, one can vary the amount
of --SO.sub.2X'' end groups.
[0051] Most of the initiators described above and any emulsifiers
that may be used in the polymerization have an optimum pH-range
where they show most efficiency. Also, a pH can be selected for the
method according to the present disclosure such that the
polymerization is carried out with the salt form of the compound of
formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a.dbd.(OC.sub.bF.sub.2b).sub.c--O--(C.sub.e-
F.sub.2e)--SO.sub.3Z', wherein Z' is an alkali metal cation or an
ammonium cation, and to maintain the salt form of the copolymer.
For these reason, buffers may be useful. Buffers include phosphate,
acetate, or carbonate (e.g., (NH.sub.4).sub.2CO.sub.3 or
NaHCO.sub.3) buffers or any other acid or base, such as ammonia or
alkali-metal hydroxides. In some embodiments, the copolymerizing is
carried out at a pH of at least 8, higher than 8, at least 8.5, or
at least 9. The concentration range for the initiators and buffers
can vary from 0.01% to 5% by weight based on the aqueous
polymerization medium. In some embodiments, ammonia is added to the
reaction mixture in an amount to adjust the pH to at least 8,
higher than 8, at least 8.5, or at least 9.
[0052] Typical chain-transfer agents like H.sub.2, lower alkanes,
alcohols, ethers, esters, and CH2C12 may be useful in the
preparation of the copolymer and ionomer according to the present
disclosure. Termination primarily via chain-transfer results in a
polydispersity of about 2.5 or less. In some embodiments of the
method according to the present disclosure, the polymerization is
carried out without any chain-transfer agents. A lower
polydispersity can sometimes be achieved in the absence of
chain-transfer agents. Recombination typically leads to a
polydispersity of about 1.5 for small conversions.
[0053] Useful polymerization temperatures can range from 20.degree.
C. to 150.degree. C. Typically, polymerization is carried out in a
temperature range from 30.degree. C. to 120.degree. C., 40.degree.
C. to 100.degree. C., or 50.degree. C. to 90.degree. C. The
polymerization pressure is usually in the range of 0.4 MPa to 2.5
MPa, 0.6 to 1.8 MPa, 0.8 MPa to 1.5 MPa, and in some embodiments is
in the range from 1.0 MPa to 2.0 MPa. Fluorinated monomers such as
HFP can be precharged and fed into the reactor as described, for
example, in Modern Fluoropolymers, ed. John Scheirs, Wiley &
Sons, 1997, p. 241. Perfluoroalkoxyalkyl vinyl ethers represented
by formula CF.sub.2.dbd.CF(OC.sub.nF.sub.2n).sub.zORF and
perfluoroalkoxyalkyl allyl ethers represented by formula
CF.sub.2.dbd.CFCF.sub.2(OC.sub.nF.sub.2n).sub.2ORf, wherein n, z,
and Rf are as defined above in any of their embodiments, are
typically liquids and may be sprayed into the reactor or added
directly, vaporized, or atomized.
[0054] Conveniently, in some embodiments of the method of making
the copolymer, the polymerization process may be conducted with no
emulsifier (e.g., no fluorinated emulsifier). Surprisingly, we have
found that even with the incorporation of liquid
perfluoroalkoxyalkyl vinyl or perfluoroalkoxyalkyl allyl ethers or
bisolefins in larger amounts, no fluorinated emulsifier is needed
to ensure proper incorporation of these monomers. It can be useful
to feed the compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2n)--SO.sub.2X'' and the non-functional comonomers (e.g.,
perfluoroalkoxyalkyl vinyl or perfluoroalkoxyalkyl allyl ethers or
bisolefins) as a homogenous mixture to the polymerization. In some
embodiments, it is possible to hydrolyze some of the
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2F (e.g., up to 5 ppm) to obtain an "in
situ"-emulsifier. Advantageously, this method may be conducted in
the absence of any other fluorinated emulsifiers.
[0055] In some embodiments, however, perfluorinated or partially
fluorinated emulsifiers may be useful. Generally these fluorinated
emulsifiers are present in a range from about 0.02% to about 3% by
weight with respect to the polymer. Polymer particles produced with
a fluorinated emulsifier typically have an average diameter, as
determined by dynamic light scattering techniques, in range of
about 10 nanometers (nm) to about 500 nm, and in some embodiments
in range of about 50 nm to about 300 nm. Examples of suitable
emulsifiers include perfluorinated and partially fluorinated
emulsifier having the formula
[R.sub.f--O--L--COO.sup.-].sub.iX.sup.1+ wherein L represents a
linear partially or fully fluorinated alkylene group or an
aliphatic hydrocarbon group, Rf represents a linear partially or
fully fluorinated aliphatic group or a linear partially or fully
fluorinated aliphatic group interrupted with one or more oxygen
atoms, X.sup.i30 represents a cation having the valence i and i is
1, 2 or 3. (See, e.g., U.S. Pat. No. 7,671,112 to Hintzer et al.).
Additional examples of suitable emulsifiers also include
perfluorinated polyether emulsifiers having the formula
CF.sub.3--(OCF.sub.2).sub.x--O--CF.sub.2X', wherein x has a value
of 1 to 6 and X' represents a carboxylic acid group or salt
thereof, and the formula
CF.sub.3--O--(CF.sub.2).sub.3--(OCFCF(CF.sub.3)--CF.sub.2).sub.y--
-O--L--Y' wherein y has a value of 0, 1, 2 or 3, L represents a
divalent linking group selected from --CF(CF.sub.3)--,
--CF.sub.2--, and --CF.sub.2CF.sub.2--, and Y' represents a
carboxylic acid group or salt thereof (See, e.g., U.S. Pat. Publ.
No. 2007/0015865 to Hintzer et al.). Other suitable emulsifiers
include perfluorinated polyether emulsifiers having the formula
R.sub.f-0(CF.sub.2CF.sub.2O)CF.sub.2COOA wherein R.sub.f is
C.sub.bF(.sub.2b+.sub.i); where b is 1 to 4, A is a hydrogen atom,
an alkali metal or NH.sub.4, and x is an integer of from 1 to 3.
(See, e.g., U.S. Pat. Publ. No. 2006/0199898 to Funaki et al.).
Suitable emulsifiers also include perfluorinated emulsifiers having
the formula
[0056] F(CF.sub.2).sub.bO(CF.sub.2CF.sub.2O).sub.XCF.sub.2COOA
wherein A is a hydrogen atom, an alkali metal or NH.sub.4, b is an
integer of from 3 to 10, and x is 0 or an integer of from 1 to 3.
(See, e.g., U.S. Pat. Publ. No. 2007/0117915 to Funaki et al.).
Further suitable emulsifiers include fluorinated polyether
emulsifiers as described in U.S. Pat. No. 6,429,258 to Morgan et
al. and perfluorinated or partially fluorinated alkoxy acids and
salts thereof wherein the perfluoroalkyl component of the
perfluoroalkoxy has 4 to 12 carbon atoms, or 7 to 12 carbon atoms.
(See, e.g., U.S. Pat. No. 4,621,116 to Morgan). Suitable
emulsifiers also include partially fluorinated polyether
emulsifiers having the formula
[R.sub.f--(O).sub.i--CHF--(CF.sub.2).sub.x--COO--].sub.iX.sup.i+
wherein R.sub.f represents a partially or fully fluorinated
aliphatic group optionally interrupted with one or more oxygen
atoms, t is 0 or 1 and xis 0 or 1, X.sup.i+ represents a cation
having a valence i and i is 1, 2 or 3. (See, e.g., U.S. Pat. Publ.
No. 2007/0142541 to Hintzer et al.). Further suitable emulsifiers
include perfluorinated or partially fluorinated ether-containing
emulsifiers as described in U.S. Pat. Publ. Nos. 2006/0223924,
2007/0060699, and 2007/0142513 each to Tsuda et al. and
2006/0281946 to Morita et al. Fluoroalkyl, for example,
perfluoroalkyl carboxylic acids and salts thereof having 6-20
carbon atoms, such as ammonium perfluorooctanoate (APFO) and
ammonium perfluorononanoate (see, e.g., U.S. Pat. No. 2,559,752 to
Berry) may also be useful. Conveniently, in some embodiments, the
method of making the copolymer according to the present disclosure
may be conducted in the absence of any of these emulsifiers or any
combination thereof.
[0057] If fluorinated emulsifiers are used, the emulsifiers can be
removed or recycled from the fluoropolymer latex, if desired, as
described in U.S. Pat. No. 5,442,097 to Obermeier et al., U.S. Pat.
No. 6,613,941 to Felix et al., U.S. Pat. No. 6,794,550 to Hintzer
et al., U.S. Pat. No. 6,706,193 to Burkard et al., and U.S. Pat.
No. 7,018,541 to Hintzer et al.
[0058] In some embodiments, the obtained copolymer latices are
purified by at least one of anion- or cation-exchange processes to
remove functional comonomers, anions, and/or cations before
coagulation or spray drying (described below). As used herein, the
term "purify" refers to at least partially removing impurities,
regardless of whether the removal is complete. Anionic species that
may constitute impurities include, for example, fluoride, anionic
residues from surfactants and emulsifiers (e.g.,
perfluorooctanoate), and residual compounds represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OCF.sub.2b).sub.c--O--(C.sub.eF.sub.2e)-
--SO.sub.3Z. It should be noted, however, that it may be desirable
to not remove ionic fluoropolymer from the dispersion. Useful anion
exchange resins typically comprise a polymer (typically
crosslinked) that has a plurality of cationic groups (e.g.,
quaternary alkyl ammonium groups) paired with various anions (e.g.,
halide or hydroxide). Upon contact with the fluoropolymer
dispersion, anionic impurities in the dispersion become associated
with the anion exchange resin. After the anion exchange step, the
resultant anion-exchanged dispersion is separated from the anion
exchange resin, for example, by filtration. It was reported in U.S.
Pat. No. 7,304,101 (Hintzer et al.) that the anionic hydrolyzed
fluoropolymer does not appreciably become immobilized on the anion
exchange resin, which would lead to coagulation and/or material
loss. Anionic exchange resins are available commercially from a
variety of sources. If the anion exchange resin is not in the
hydroxide form it may be at least partially or fully converted to
the hydroxide salt form before use. This is typically done by
treating the anion exchange resin with an aqueous ammonia or sodium
hydroxide solution. Typically, better yields are obtained using
gel-type anion-exchange resins than with macroporous anion exchange
resins.
[0059] Examples of cationic impurities resulting from the
abovementioned polymerization include one or more of, alkali metal
cation(s) (e.g., Li.sup.+, Na.sup.+, K.sup.+), ammonium, quaternary
alkyl ammonium, alkaline earth cations (e.g., Mg.sup.2+,
Ca.sup.2+), manganese cations (e.g. Mn.sup.2+), and Group III metal
cations. Useful cation exchange resins include polymers (typically
cross-linked) that have a plurality of pendant anionic or acidic
groups such as, for example, polysulfonates or polysulfonic acids,
polycarboxylates or polycarboxylic acids. Examples of useful
sulfonic acid cation exchange resins include sulfonated
styrene-divinylbenzene copolymers, sulfonated crosslinked styrene
polymers, phenol-formaldehyde-sulfonic acid resins, and
benzene-formaldehyde-sulfonic acid resins. Carboxylic acid cation
exchange resin is an organic acid, cation exchange resin, such as
carboxylic acid cation exchange resin. Cation exchange resins are
available commercially from a variety of sources. Cation exchange
resins are commonly supplied commercially in either their acid or
their sodium form. If the cation exchange resin is not in the acid
form (i.e., protonated form) it may be at least partially or fully
converted to the acid form in order to avoid the generally
undesired introduction of other cations into the dispersion. This
conversion to the acid form may be accomplished by means well known
in the art, for example by treatment with any adequately strong
acid.
[0060] If purification of the fluoropolymer dispersion is carried
out using both anion and cation exchange processes, the anion
exchange resin and cation exchange resin may be used individually
or in combination as, for example, in the case of a mixed resin bed
having both anion and cation exchange resins.
[0061] To coagulate the obtained copolymer latex, any coagulant
which is commonly used for coagulation of a fluoropolymer latex may
be used, and it may, for example, be a water-soluble salt (e.g.,
calcium chloride, magnesium chloride, aluminum chloride or aluminum
nitrate), an acid (e.g., nitric acid, hydrochloric acid or sulfuric
acid), or a water-soluble organic liquid (e.g., alcohol or
acetone). The amount of the coagulant to be added may be in a range
of 0.001 to 20 parts by mass, for example, in a range of 0.01 to 10
parts by mass per 100 parts by mass of the latex. Alternatively or
additionally, the latex may be frozen for coagulation or
mechanically coagulated, for example, with a homogenizer as
described in U.S. Pat. No. 5,463,021 (Beyer et al.). Alternatively
or additionally, the latex may be coagulated by adding polycations.
It may also be useful to avoid acids and alkaline earth metal salts
as coagulants to avoid metal contaminants. To avoid coagulation
altogether and any contaminants from coagulants, spray drying the
latex after polymerization and optional ion-exchange purification
may be useful to provide solid copolymer.
[0062] A coagulated copolymer can be collected by filtration and
washed with water. The washing water may, for example, be
ion-exchanged water, pure water, or ultrapure water. The amount of
the washing water may be from 1 to 5 times by mass to the copolymer
or ionomer, whereby the amount of the emulsifier attached to the
copolymer can be sufficiently reduced by one washing.
[0063] The copolymer produced can have less than 50 ppm metal ion
content, in some embodiments, less than 25 ppm, less than 10 ppm,
less than 5 ppm, or less than 1 ppm metal ion content.
Specifically, metal ions such as alkali metals, alkaline earth
metal, heavy metals (e.g., nickel, cobalt, manganese, cadmium, and
iron) can be reduced. To achieve a metal ion content of less than
50 ppm, 25 ppm, 10 ppm. 5 ppm, or 1 ppm, polymerization can be
conducted in the absence of added metal ions. For example,
potassium persulfate, a common alternative initiator or
co-initiator with ammonium persulfate, is not used, and mechanical
and freeze coagulation described above may be used instead of
coagulation with metal salts. It is also possible to use organic
initiators as disclosed in U.S. Pat. No. 5,182,342 (Feiring et
al.). To achieve such low ion content, ion exchange can be used, as
described above, and the water for polymerization and washing may
be deionized.
[0064] The metal ion content of the copolymer can be measured by
flame atomic absorption spectrometry after combusting the copolymer
and dissolving the residue in an acidic aqueous solution.
[0065] For potassium as the analyte, the lower detection limit is
less than 1 ppm.
[0066] In some embodiments of the methods of making the copolymer,
radical polymerization also can be carried out by suspension
polymerization. Suspension polymerization will typically produce
particle sizes up to several millimeters.
[0067] A method for making the copolymer for the fluoropolymer
dispersion disclosed herein can include copolymerizing components
including SO.sub.2F-containing vinyl or allyl ethers (e.g.,
CF.sub.2.dbd.CF(CF.sub.2).sub.a--O--C.sub.bF.sub.2b).sub.c--O--(C.sub.eF.-
sub.2e)--SO.sub.2F), isolating a solid from the polymer dispersion,
hydrolyzing the polymer, optionally purifying the polymer by ion
exchange purification, and drying the resulting polymer. In some
embodiments, the method of making the copolymer includes
copolymerizing components including at least one compound
represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.3Z, optionally purifying the copolymer by
ion-exchange purification, and spray drying the resulting
dispersion. This method can conveniently eliminate the steps of
isolating solid polymer and hydrolyzing, resulting in a more
efficient and cost-effective process.
[0068] The components to be polymerized in the methods according to
the present disclosure can include more than one compound
represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.-
sub.eF.sub.2e)--SO.sub.3Z. When more than one compound represented
by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.-
sub.eF.sub.2e)--SO.sub.3Z is present, each of a, b, c, e, and Z may
be independently selected. In some of these embodiments, each Z is
independently an alkali-metal cation or a quaternary ammonium
cation.
[0069] In some cases, compounds represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b)--O--(C.sub.eF.sub.2e)-
--SO.sub.3Z are not prepared in situ from compounds represented by
formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2F. In some embodiments, the components to be
polymerized in the method disclosed herein are substantially free
of compounds represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(OC.sub.bF.-
sub.2b).sub.c--O--(C.sub.eF.sub.2e)--SO.sub.2F. In this regard,
"substantially free of compounds represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--((OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.-
sub.2e)--SO.sub.2F may mean that the components to be polymerized
in the method disclosed herein are free of compounds represented by
formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2F or that such compounds are present in an amount
of up to 5, 4, 3, 2, 1, 0.5, 0.1, 0.05, or 0.01 mole percent, based
on the total amount of components.
[0070] In other embodiments, a copolymer of the present disclosure
can be made by copolymerizing a compound represented by formula
CF.sub.2.dbd.CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b).sub.c--O--(C.sub.eF.s-
ub.2e)--SO.sub.2F and other fluorinated monomers as described above
in any of their embodiments. In these embodiments, it is possible
to hydrolyze some of the
CF.sub.2.dbd.(CF(CF.sub.2).sub.a--(OC.sub.bF.sub.2b)(.sub.c--O--(C.sub.eF-
.sub.2e)--SO.sub.2F (e.g., up to 5 ppm) to obtain an "in
situ"-emulsifier as described above.
[0071] Fluoropolymers obtained by aqueous emulsion polymerization
with inorganic initiators (e.g. persulfates, KMnO.sub.4, etc.)
typically have a high number of unstable carbon-based end groups
(e.g. more than 200 --COOM or --COF end groups per 10.sup.6 carbon
atoms, wherein M is hydrogen, a metal cation, or
[0072] NH.sub.2). For fluorinated ionomers useful, for example, in
an electrochemical cell, the effect naturally increases as
sulfonate equivalent weight decreases. These carbonyl end groups
are vulnerable to peroxide radical attacks, which reduce the
oxidative stability of the fluorinated ionomers. During operation
of a fuel cell, electrolysis cell, or other electrochemical cell,
peroxides can be formed. This degrades the fluorinated ionomers,
and correspondingly reduces the operational life of the given
electrolyte membrane.
[0073] As polymerized, the copolymer useful for the fluoropolymer
dispersion according to the present disclosure can have up to 400
--COOM and --COF end groups per 10.sup.6 carbon atoms, wherein M is
independently an alkyl group, a hydrogen atom, a metallic cation,
or a quaternary ammonium cation. Advantageously, in some
embodiments, the copolymer according to the present disclosure has
up to 200 unstable end groups per 10.sup.6 carbon atoms. The
unstable end groups are --COOM or --COF groups, wherein M is an
alkyl group, a hydrogen atom, a metallic cation, or a quaternary
ammonium cation. In some embodiments, the copolymer has up to 150,
100, 75, 50, 40, 30, 25, 20, 15, or 10 unstable end groups per
10.sup.6 carbon atoms. The number of unstable end groups can be
determined by Fourier-transform infrared spectroscopy using the
method described below. In some embodiments, the copolymer
according to the present disclosure has up to 50 (in some
embodiments, up to 40, 30, 25, 20, 15, or 10) unstable end groups
per 10.sup.6 carbon atoms, as polymerized.
[0074] Copolymers useful for fluoropolymer dispersions according to
some embodiments of the present disclosure have --SO.sub.2X'' end
groups. As described above, --SO.sub.2X'' end groups can be
introduced in the copolymers according to the present disclosure by
generating SO.sub.3.sup.- radicals during the polymerization
process. In some embodiments, reducing the number of unstable end
groups can be accomplished by carrying out the polymerization in
the methods disclosed above in the presence of a salt or
pseudohalogen as described in U.S. Pat. No. 7,214,740 (Lochhaas et
al.). Suitable salts can include a chloride anion, a bromide anion,
an iodide anion, or a cyanide anion and a sodium, potassium, or
ammonium cation. The salt used in the free-radical polymerization
may be a homogenous salt or a blend of different salts. Examples of
useful pseudohalogens are nitrile-containing compounds, which
provide nitrile end groups.
[0075] Pseudohalogen nitrile-containing compounds have one or more
nitrile groups and function in the same manner as compounds in
which the nitrile groups are replaced with a halogen. Examples of
suitable pseudohalogen nitrile-containing compounds include NC--CN,
NC--S--S--CN, NCS--CN, Cl--CN, Br--CN, I--CN, NCN.dbd.NCN, and
combinations thereof. During the free-radical polymerization, the
reactive atoms/groups of the salts or the nitrile groups of the
pseudohalogens chemically bond to at least one end of the backbone
chain of the fluoropolymer. This provides CF.sub.2Y.sup.1 end
groups instead of carbonyl end groups, wherein Y.sup.1 is chloro,
bromo, iodo, or nitrile. For example, if the free-radical
polymerization is performed in the presence of a KCl salt, at least
one of the end groups provided would be a --CF.sub.2Cl end group.
Alternatively, if the free-radical polymerization is performed in
the presence of a NC--CN pseudohalogen, at least one of the end
groups provided would be a --CF.sub.2CN end group.
[0076] Post-fluorination with fluorine gas can also be used to cope
with unstable end groups and any concomitant degradation.
Post-fluorination of the fluoropolymer can convert --COOH, amide,
hydride, --COF, --CF.sub.2Y.sup.1 and other nonperfluorinated end
groups or --CF.dbd.CF.sub.2 to --CF.sub.3 end groups. The
post-fluorination may be carried out in any convenient manner. The
post-fluorination can be conveniently C. and 250.degree. C., in
some embodiments in a range of 150.degree. C. to 250.degree. C. or
70.degree. C. to 120.degree. C., and pressures from 10 KPa to 1000
KPa. Reaction times can range from about four hours to about 16
hours. Under these conditions, most unstable carbon-based end
groups are removed, whereas --SO.sub.2X groups mostly survive and
are converted to --SO.sub.2F groups. In some embodiments,
post-fluorination is not carried out when non-fluorinated monomers
described above are used as monomers in the polymerization or when
the copolymer according to the present disclosure includes divalent
units independently represented by formula:
##STR00018##
[0077] as described above in any of their embodiments.
[0078] The groups Y.sup.1 in the end groups --CF.sub.2Y.sup.1,
described above, are reactive to fluorine gas, which reduces the
time and energy required to post-fluorinate the copolymers in these
embodiments. We have also found that the presence of alkali-metal
cations in the copolymer increases the decomposition rate of
unstable carboxylic end-groups and therefore makes a subsequent
post-fluorination step, if needed, easier, faster, and cheaper.
[0079] Some conventional fluoropolymers can be difficult to
disperse. A technique that can be useful for dispersing a
fluoropolymer in a desired medium is up-concentration of a dilute
dispersion of fluoropolymer. For example, U.S. Pat. Appl. Pub. Nos.
2017/0183435 (Ino) reports preparing a fluoropolymer electrolyte
solution by heating a solid fluoropolymer electrolyte in a solution
of 50% by weight solution of ethanol in water in an autoclave at
160.degree. C. with stirring for five hours to achieve a
fluoropolymer electrolyte solution with a solids concentration of
5% by weight. Concentration under reduced pressure provided a
fluoropolymer electrolyte solution with a solids concentration of
20% by weight.
[0080] By contrast, the method of the present disclosure allows for
direct dispersion of the copolymer disclosed herein at a
concentration of at least 10, 15, 20, or 25 percent by weight in a
solution of water and organic solvent without the need for
up-concentrating. In some embodiments, the method of the present
disclosure allows for direct dispersion of the copolymer disclosed
herein at a concentration of up to 30, 40, or 50 percent by weight
in a solution of water and organic solvent without the need for
up-concentrating. For the method of the present disclosure, it
should be understood that combining components comprising at least
ten percent by weight of the copolymer, based on the total weight
of the components, refers to the concentration of the copolymer
when the components are initially combined (e.g., when organic
solvent is first added to an aqueous dispersion of the
fluoropolymer) before any agitation of the combined components. In
some embodiments of the method of the present disclosure, Z is
hydrogen. Examples of suitable organic solvents useful for
preparing the fluoropolymer dispersions of the present disclosure
include, lower alcohols (e.g., methanol, ethanol, isopropanol,
n-propanol), polyols (e.g., ethylene glycol, propylene glycol,
glycerol), ethers (e.g., tetrahydrofuran and dioxane), diglyme,
polyglycol ethers, ether acetates, acetonitrile, acetone,
dimethylsulfoxide (DMSO), N,N dimethyacetamide (DMA), ethylene
carbonate, propylene carbonate, dimethylcarbonate,
diethylcarbonate, N,N-dimethylformamide (DMF),
N-methylpyrrolidinone (NMP), dimethylimidazolidinone,
butyrolactone, hexamethylphosphoric triamide (HMPT), isobutyl
methyl ketone, sulfolane, and combinations thereof. In some
embodiments, the copolymer, water, and organic solvent can be
heated at a pressure of up to 0.2 MPa or 0.15 MPa at a temperature
of up to 100.degree. C., 90.degree. C., 80.degree. C., 70.degree.
C., 60.degree. C., 50.degree. C., or 40.degree. C. Advantageously,
the fluoropolymer dispersion may also be made at ambient
temperature and pressure. Also advantageously, the fluoropolymer
dispersions according to the present disclosure have useful
viscosities even with a high concentration of copolymer.
[0081] The fluoropolymer dispersion of the present disclosure may
be useful, for example, in the manufacture of catalyst ink and
polymer electrolyte membranes for use in fuel cells or other
electrolytic cells. A membrane electrode assembly (MEA) is the
central element of a proton exchange membrane fuel cell, such as a
hydrogen fuel cell. Fuel cells are electrochemical cells which
produce usable electricity by the catalyzed combination of a fuel
such as hydrogen and an oxidant such as oxygen. Typical MEA's
comprise a polymer electrolyte membrane (PEM) (also known as an ion
conductive membrane (ICM)), which functions as a solid electrolyte.
One face of the PEM is in contact with an anode electrode layer and
the opposite face is in contact with a cathode electrode layer.
Each electrode layer includes electrochemical catalysts, typically
including platinum metal. Gas diffusion layers (GDL's) facilitate
gas transport to and from the anode and cathode electrode materials
and conduct electrical current. The GDL may also be called a fluid
transport layer (FTL) or a diffuser/current collector (DCC). The
anode and cathode electrode layers may be applied to GDL's in the
form of a catalyst ink, and the resulting coated GDL's sandwiched
with a PEM to form a five-layer MEA. Alternately, the anode and
cathode electrode layers may be applied to opposite sides of the
PEM in the form of a catalyst ink, and the resulting
catalyst-coated membrane (CCM) sandwiched with two GDL's to form a
five-layer MEA. Details concerning the preparation of catalyst inks
and their use in membrane assemblies can be found, for example, in
U.S. Pat. Publ. No. 2004/0107869 (Velamakanni et al.). In atypical
PEM fuel cell, protons are formed at the anode via hydrogen
oxidation and transported across the PEM to the cathode to react
with oxygen, causing electrical current to flow in an external
circuit connecting the electrodes. The PEM forms a durable,
non-porous, electrically non-conductive mechanical barrier between
the reactant gases, yet it also passes H1.sup.+ ions readily.
[0082] The fluoropolymer dispersion of the present disclosure may
be useful as and/or useful for making a catalyst ink composition.
In some embodiments, the fluoropolymer dispersion further comprises
catalyst particles (e.g., metal particles or carbon-supported metal
particles). A variety of catalysts may be useful. Typically,
carbon-supported catalyst particles are used. Typical
carbon-supported catalyst particles are 50% to 90% carbon and 10%
to 50% catalyst metal by weight, the catalyst metal typically
comprising platinum for the cathode and platinum and ruthenium in a
weight ratio of 2:1 for the anode.
[0083] However, other metals may be useful, for example, gold,
silver, palladium, iridium, rhodium, ruthenium, iron, cobalt,
nickel, chromium, tungsten, manganese, vanadium, and alloys
thereof. To make an MEA or CCM, catalyst may be applied to the PEM
by any suitable means, including both hand and machine methods,
including hand brushing, notch bar coating, fluid bearing die
coating, wire-wound rod coating, fluid bearing coating, slot-fed
knife coating, three-roll coating, or decal transfer. Coating may
be achieved in one application or in multiple applications.
Advantageously, fluoropolymer dispersions according to the present
disclosure may be useful for making a catalyst layer with one
coating application. The catalyst ink may be applied to a PEM or a
GDL directly, or the catalyst ink may be applied to a transfer
substrate, dried, and thereafter applied to the PEM or to the FTL
as a decal.
[0084] In some embodiment, the catalyst ink includes the copolymer
disclosed herein at a concentration of at least 10, 15, or 20
percent by weight and up to 30 percent by weight, based on the
total weight of the catalyst ink. In some embodiment, the catalyst
ink includes the catalyst particles in an amount of at least 10,
15, or 20 percent by weight and up to 50, 40, or 30 percent by
weight, based on the total weight of the catalyst ink. The catalyst
particles may be added to the fluoropolymer dispersion made as
described above in any of its embodiments. The resulting catalyst
ink may be mixed, for example, with heating.
[0085] The percent solid in the catalyst ink may be selected, for
example, to obtain desirable rheological properties. Examples of
suitable organic solvents useful for including in the catalyst ink
include, lower alcohols (e.g., methanol, ethanol, isopropanol,
n-propanol), polyols (e.g., ethylene glycol, propylene glycol,
glycerol), ethers (e.g., tetrahydrofuran and dioxane), diglyme,
polyglycol ethers, ether acetates, acetonitrile, acetone,
dimethylsulfoxide (DMSO), N,N dimethyacetamide (DMA), ethylene
carbonate, propylene carbonate, dimethylcarbonate,
diethylcarbonate, N,N-dimethylformamide (DMF),
N-methylpyrrolidinone (NMP), dimethylimidazolidinone,
butyrolactone, hexamethylphosphoric triamide (HMPT), isobutyl
methyl ketone, sulfolane, and combinations thereof. In some
embodiments, the catalyst ink contains 0% to 50% by weight of a
lower alcohol and 0% to 20% by weight of a polyol. In addition, the
ink may contain 0% to 2% of a suitable dispersant.
[0086] In some embodiments, the fluoropolymer dispersion may be
useful for making a polymer electrolyte membrane. The fluoropolymer
dispersion may be formed into a polymer electrolyte membrane by any
suitable method, including casting, molding, and extrusion.
Typically, the membrane is cast from the fluoropolymer dispersion
and then dried, annealed, or both. The copolymer may be cast from a
suspension. Any suitable casting method may be used, including bar
coating, spray coating, slit coating, and brush coating. After
forming, the membrane may be annealed, typically at a temperature
of 120.degree. C. or higher, more typically 130.degree. C. or
higher, most typically 150.degree. C. or higher. In some
embodiments of the method according to the present disclosure, a
polymer electrolyte membrane can be obtained by obtaining the
fluoropolymer dispersion, optionally purifying the dispersion by
ion-exchange purification, and concentrating the dispersion to make
a membrane. Typically, if the fluoropolymer dispersion is to be
used to form a membrane, the concentration of copolymer is
advantageously high (e.g., at least 20, 30, or 40 percent by
weight). Often a water-miscible organic solvent is added to
facilitate film formation. Examples of water-miscible solvents
include, lower alcohols (e.g., methanol, ethanol, isopropanol,
n-propanol), polyols (e.g., ethylene glycol, propylene glycol,
glycerol), ethers (e.g., tetrahydrofuran and dioxane), ether
acetates, acetonitrile, acetone, dimethylsulfoxide (DMSO), N,N
dimethyacetamide (DMA), ethylene carbonate, propylene carbonate,
dimethylcarbonate, diethylcarbonate, N,N-dimethylformamide (DMF),
N-methylpyrrolidinone (NMP), dimethylimidazolidinone,
butyrolactone, hexamethylphosphoric triamide (HMPT), isobutyl
methyl ketone, sulfolane, and combinations thereof.
[0087] The present disclosure provides a membrane electrode
assembly comprising at least one of a catalyst ink comprising
and/or prepared from the fluoropolymer dispersion of the present
disclosure or a polymer electrolyte membrane made from the
fluoropolymer dispersion of the present disclosure. In some
embodiments, the polymer electrolyte membrane and catalyst ink use
embodiments of the copolymer disclosed herein. The catalyst ink and
polymer electrolyte membrane may use the same or different
copolymers. In some embodiments, the catalyst ink comprises and/or
is prepared from the fluoropolymer dispersion of the present
disclosure, and the polymer electrolyte membrane includes a
conventional copolymer (e.g., one that does not include one or more
divalent units independently represented by formula:
##STR00019##
In some embodiments, the polymer electrolyte membrane is prepared
from the fluoropolymer dispersion of the present disclosure, and
the catalyst ink includes a conventional copolymer (e.g., one that
does not include one or more divalent units independently
represented by formula:
##STR00020##
[0088] In some embodiments of the fluoropolymer dispersion of the
present disclosure, a salt of at least one of cerium, manganese or
ruthenium or one or more cerium oxide or zirconium oxide compounds
is added to the acid form of the copolymer before membrane
formation. Typically the salt of cerium, manganese, or ruthenium
and/or the cerium or zirconium oxide compound is mixed well with or
dissolved within the copolymer to achieve substantially uniform
distribution.
[0089] The salt of cerium, manganese, or ruthenium may comprise any
suitable anion, including chloride, bromide, hydroxide, nitrate,
sulfonate, acetate, phosphate, and carbonate. More than one anion
may be present. Other salts may be present, including salts that
include other metal cations or ammonium cations. Once cation
exchange occurs between the transition metal salt and the acid form
of the ionomer, it may be desirable for the acid formed by
combination of the liberated proton and the original salt anion to
be removed. Thus, it may be useful to use anions that generate
volatile or soluble acids, for example chloride or nitrate.
Manganese cations may be in any suitable oxidation state, including
Mn.sup.2+, Mn.sup.3+, and Me, but are most typically Mn.sup.2+.
Ruthenium cations may be in any suitable oxidation state, including
Ru.sup.3+and Re, but are most typically Ru.sup.3+. Cerium cations
may be in any suitable oxidation state, including Ce.sup.3+ and
Ce.sup.4+. Without wishing to be bound by theory, it is believed
that the cerium, manganese, or ruthenium cations persist in the
polymer electrolyte because they are exchanged with H.sup.+ ions
from the anion groups of the polymer electrolyte and become
associated with those anion groups. Furthermore, it is believed
that polyvalent cerium, manganese, or ruthenium cations may form
crosslinks between anion groups of the polymer electrolyte, further
adding to the stability of the polymer. In some embodiments, the
salt may be present in solid form. The cations may be present in a
combination of two or more forms including solvated cation, cation
associated with bound anion groups of the polymer electrolyte
membrane, and cation bound in a salt precipitate. The amount of
salt added is typically between 0.001 and 0.5 charge equivalents
based on the molar amount of acid functional groups present in the
polymer electrolyte, more typically between 0.005 and 0.2, more
typically between 0.01 and 0.1, and more typically between 0.02 and
0.05. Further details for combining an anionic copolymer with
cerium, manganese, or ruthenium cations can be found in U.S. Pat.
Nos. 7,575,534 and 8,628,871, each to Frey et al.
[0090] The cerium oxide compound may contain cerium in the (IV)
oxidation state, the (III) oxidation state, or both and may be
crystalline or amorphous. The cerium oxide may be, for example,
CeO.sub.2 or Ce.sub.2O.sub.3. The cerium oxide may be substantially
free of metallic cerium or may contain metallic cerium. The cerium
oxide may be, for example, a thin oxidation reaction product on a
metallic cerium particle. The cerium oxide compound may or may not
contain other metal elements. Examples of mixed metal oxide
compounds comprising cerium oxide include solid solutions such as
zirconia-ceria and multicomponent oxide compounds such as barium
cerate. Without wishing to be bound by theory, it is believed that
the cerium oxide may strengthen the polymer by chelating and
forming crosslinks between bound anionic groups. The amount of
cerium oxide compound added is typically between 0.01 and 5 weight
percent based on the total weight of the copolymer, more typically
between 0.1 and 2 weight percent, and more typically between 0.2
and 0.3 weight percent. The cerium oxide compound is typically
present in an amount of less than 1% by volume relative to the
total volume of the polymer electrolyte membrane, more typically
less than 0.8% by volume, and more typically less than 0.5% by
volume. Cerium oxide may be in particles of any suitable size, in
some embodiments, between 1 nm and 5000 nm, 200 nm to 5000 nm, or
500 nm to 1000 nm. Further details regarding polymer electrolyte
membranes including cerium oxide compounds can be found in U.S.
Pat. No. 8,367,267 (Frey et al.).
[0091] The polymer electrolyte membrane, in some embodiments, may
have a thickness of up to 90 microns, up to 60 microns, or up to 30
microns. A thinner membrane may provide less resistance to the
passage of ions. In fuel cell use, this results in cooler operation
and greater output of usable energy. Thinner membranes must be made
of materials that maintain their structural integrity in use.
[0092] In some embodiments, the fluoropolymer dispersion of the
present disclosure may be imbibed into a porous supporting matrix,
typically in the form of a thin membrane having a thickness of up
to 90 microns, up to 60 microns, or up to 30 microns. Any suitable
method of imbibing the polymer into the pores of the supporting
matrix may be used, including overpressure, vacuum, wicking, and
immersion. In some embodiments, the copolymer is embedded in the
matrix upon crosslinking. Any suitable supporting matrix may be
used. Typically the supporting matrix is electrically
non-conductive. Typically, the supporting matrix is composed of a
fluoropolymer, which is more typically perfluorinated. Typical
matrices include porous polytetrafluoroethylene (PTFE), such as
biaxially stretched PTFE webs. In another embodiment fillers (e.g.
fibers) might be added to the polymer to reinforce the
membrane.
[0093] To make an MEA, GDL's may be applied to either side of a CCM
by any suitable means. Any suitable GDL may be used in the practice
of the present disclosure. Typically the GDL is comprised of sheet
material comprising carbon fibers. Typically the GDL is a carbon
fiber construction selected from woven and non-woven carbon fiber
constructions. Carbon fiber constructions which may be useful in
the practice of the present disclosure may include Toray.TM. Carbon
Paper, SpectraCarb.TM. Carbon Paper, AFN.TM. non-woven carbon
cloth, and Zoltek.TM. Carbon Cloth. The GDL may be coated or
impregnated with various materials, including carbon particle
coatings, hydrophilizing treatments, and hydrophobizing treatments
such as coating with polytetrafluoroethylene (PTFE).
[0094] In use, the MEA according to the present disclosure is
typically sandwiched between two rigid plates, known as
distribution plates, also known as bipolar plates (BPP's) or
monopolar plates. Like the GDL, the distribution plate is typically
electrically conductive. The distribution plate is typically made
of a carbon composite, metal, or plated metal material. The
distribution plate distributes reactant or product fluids to and
from the MEA electrode surfaces, typically through one or more
fluid-conducting channels engraved, milled, molded or stamped in
the surface(s) facing the MEA(s). These channels are sometimes
designated a flow field. The distribution plate may distribute
fluids to and from two consecutive MEA's in a stack, with one face
directing fuel to the anode of the first MEA while the other face
directs oxidant to the cathode of the next MEA (and removes product
water), hence the term "bipolar plate." Alternately, the
distribution plate may have channels on one side only, to
distribute fluids to or from an MEA on only that side, which may be
termed a "monopolar plate." A typical fuel cell stack comprises a
number of MEA's stacked alternately with bipolar plates.
[0095] Another type of electrochemical device is an electrolysis
cell, which uses electricity to produce chemical changes or
chemical energy. An example of an electrolysis cell is a
chlor-alkali membrane cell where aqueous sodium chloride is
electrolyzed by an electric current between an anode and a
cathode.
[0096] The electrolyte is separated into an anolyte portion and a
catholyte portion by a membrane subject to harsh conditions. In
chlor-alkali membrane cells, caustic sodium hydroxide collects in
the catholyte portion, hydrogen gas is evolved at the cathode
portion, and chlorine gas is evolved from the sodium chloride-rich
anolyte portion at the anode. The fluoropolymer dispersion of the
present disclosure may be useful, for example, in the manufacture
of catalyst ink and electrolyte membranes for use in chlor-alkali
membrane cells or other electrolytic cells.
[0097] The copolymer according to the present disclosure may also
be useful has a binder for an electrode in other electrochemical
cells (for example, lithium ion batteries). To make electrodes,
powdered active ingredients can be dispersed in a solvent with the
copolymer and coated onto a metal foil substrate, or current
collector. The resulting composite electrode contains the powdered
active ingredient in the polymer binder adhered to the metal
substrate. Useful active materials for making negative electrodes
include alloys of main group elements and conductive powders such
as graphite. Examples of useful active materials for making a
negative electrode include oxides (tin oxide), carbon compounds
(e.g., artificial graphite, natural graphite, soil black lead,
expanded graphite, and scaly graphite), silicon carbide compounds,
silicon-oxide compounds, titanium sulfides, and boron carbide
compounds. Useful active materials for making positive electrodes
include lithium compounds, such as Li.sub.4/3Ti.sub.5/3O.sub.4,
LiV.sub.3O.sub.8, LiV.sub.2O.sub.5, LiCo.sub.0.2Ni.sub.0.8O.sub.2,
LiNiO.sub.2, LiFePO.sub.4, LiMnPO.sub.4, LiCoPO.sub.4,
LiMn.sub.2O.sub.4, and LiCoO.sub.2. The electrodes can also include
electrically conductive diluents and adhesion promoters.
[0098] Electrochemical cells including the copolymer disclosed
herein as a binder can be made by placing at least one each of a
positive electrode and a negative electrode in an electrolyte.
Typically, a microporous separator can be used to prevent the
contact of the negative electrode directly with the positive
electrode. Once the electrodes are connected externally, lithiation
and delithiation can take place at the electrodes, generating a
current. A variety of electrolytes can be employed in a lithium-ion
cell. Representative electrolytes contain one or more lithium salts
and a charge-carrying medium in the form of a solid, liquid, or
gel. Examples of lithium salts include LiPF.sub.6, LiBF.sub.4,
LiClO.sub.4, lithium bis(oxalato)borate,
LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2,
LiAsF.sub.6, LiC(CF.sub.3SO.sub.2).sub.3, and combinations thereof
Examples of solid charge carrying media include polymeric media
such as polyethylene oxide, polytetrafluoroethylene, polyvinylidene
fluoride, fluorine-containing copolymers, polyacrylonitrile,
combinations thereof, and other solid media that will be familiar
to those skilled in the art. Examples of liquid charge carrying
media include ethylene carbonate, propylene carbonate, dimethyl
carbonate, diethyl carbonate, ethyl methyl carbonate, butylene
carbonate, vinylene carbonate, fluoroethylene carbonate,
fluoropropylene carbonate, gamma-butyrolactone, methyl
difluoroacetate, ethyl difluoroacetate, dimethoxyethane, diglyme
(bis(2-methoxyethyl) ether), tetrahydrofuran, dioxolane,
combinations thereof and other media that will be familiar to those
skilled in the art. Examples of charge carrying media gels include
those described in U.S. Pat. No. 6,387,570 (Nakamura et al.) and
U.S. Pat. No. 6,780,544 (Noh). The electrolyte can include other
additives (e.g., a cosolvent or a redox chemical shuttle).
[0099] The electrochemical cells can be useful as rechargeable
batteries and can be used in a variety of devices, including
portable computers, tablet displays, personal digital assistants,
mobile telephones, motorized devices (e.g., personal or household
appliances and vehicles), instruments, illumination devices (e.g.,
flashlights) and heating devices. One or more of the
electrochemical cells can be combined to provide battery pack.
Some Embodiments of the Disclosure
[0100] In a first embodiment, the present disclosure provides
fluoropolymer dispersion comprising water and a copolymer
comprising: [0101] divalent units represented by formula
--CP.sub.2--CF.sub.2--; [0102] divalent units independently
represented by formula:
##STR00021##
[0103] wherein a is 0 or 1, b is 2 to 8, c is 0 to 2, e is 1 to 8
with the proviso that when a and c are 0, then e is 3 to 8, and Z
is independently a hydrogen, alkyl having up to four carbon atoms,
an alkali-metal cation, or a quaternary ammonium cation; and
[0104] one or more divalent units independently represented by
formula:
##STR00022##
[0105] wherein Rf is a linear or branched perfluoroalkyl group
having from 1 to 8 carbon atoms and optionally interrupted by one
or more --O--groups, z is 0, 1, or 2, each n is independently 1, 2,
3, or 4, and m is 0 or 1;
[0106] wherein the fluoropolymer dispersion comprises at least 10%
by weight of the copolymer, based on the total weight of the
dispersion, wherein the copolymer has an --SO.sub.3Z equivalent
weight in a range from 600 to 2000, and wherein a variation of the
copolymer in which --SO.sub.3Z is replaced with --SO.sub.2F has a
melt flow index of up to 80 grams per ten minutes measured at a
temperature of 265.degree. C. and at a support weight of 5 kg.
[0107] In a second embodiment, the present disclosure provides the
fluoropolymer dispersion of the first embodiment, wherein b is 2 or
3, c is 0 or 1, and e is 4.
[0108] In a third embodiment, the present disclosure provides the
fluoropolymer dispersion of the first embodiment, wherein b is 2 or
3, c is 1, and e is 2 or 4.
[0109] In a fourth embodiment, the present disclosure provides the
fluoropolymer dispersion of any one of the first to third
embodiments, wherein when a is 0, then n is not 3.
[0110] In a fifth embodiment, the present disclosure provides the
fluoropolymer dispersion of any one of the first to fourth
embodiments, wherein z is 1 or 2, C.sub.nF.sub.2n is
(CF.sub.2).sub.n, and n is 1, 2, or 3.
[0111] In a sixth embodiment, the present disclosure provides the
fluoropolymer dispersion of any one of the first to fifth
embodiments, wherein at least one n is 1.
[0112] In a seventh embodiment, the present disclosure provides the
fluoropolymer dispersion of any one of the first to sixth
embodiments, wherein the copolymer further comprises at least one
of divalent units derived from chlorotrifluoroethylene or divalent
units derived from hexafluoropropylene.
[0113] In an eighth embodiment, the present disclosure provides the
fluoropolymer dispersion of any one of the first to seventh
embodiments, wherein the copolymer has an alpha transition
temperature [T(.alpha.)] of at least 100.degree. C.
[0114] In a ninth embodiment, the present disclosure provides the
fluoropolymer dispersion of any one of the first to seventh
embodiments, wherein the copolymer has a T(.alpha.) of up to
100.degree. C. or less than 100.degree. C.
[0115] In a tenth embodiment, the present disclosure provides the
fluoropolymer dispersion of any one of the first to ninth
embodiments, wherein the copolymer further comprises divalent units
independently represented by formula:
##STR00023##
[0116] wherein p is 0 or 1, q is 2 to 8, r is 0 to 2, s is 1 to 8,
and Z' is a hydrogen, an alkyl group having up to four carbon
atoms, an alkali-metal cation or a quaternary ammonium cation.
[0117] In an eleventh embodiment, the present disclosure provides
the fluoropolymer dispersion of any one of the first to tenth
embodiments, wherein the divalent units comprise at least 60 mole %
of --[CF.sub.2--CF.sub.2]--, based on the total amount of divalent
units in the copolymer.
[0118] In a twelfth embodiment, the present disclosure provides the
fluorinated dispersion of any one of the first to eleventh
embodiments, wherein the divalent units represented by formula
##STR00024##
are present at up to 20 or up to 15 mole percent, or in a range
from 3 to 20 or 4 to 15 mole percent, based on the total moles of
divalent units in the copolymer.
[0119] In a thirteenth embodiment, the present disclosure provides
the fluorinated dispersion of any one of the first to twelfth
embodiments, wherein the divalent units represented by formula
##STR00025##
are present at up to 30 or up to 25 mole percent, or in a range
from 10 to 30 or 15 to 25 mole percent, based on the total moles of
divalent units in the copolymer.
[0120] In a fourteenth embodiment, the present disclosure provides
the fluoropolymer dispersion of any one of the first to thirteenth
embodiments, wherein the copolymer further comprises divalent units
are derived from bisolefins represented by formula
X.sub.2C.dbd.CY--(CW.sub.2).sub.m--(O).sub.n--R.sub.F--(O).sub.o--(CW.sub-
.2).sub.p--CY=CX.sub.2, wherein each of X, Y, and W is
independently fluoro, hydrogen, alkyl, alkoxy, polyoxyalkyl,
perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxyalkyl, m and p
are independently an integer from 0 to 15, and n, o are
independently 0 or 1.
[0121] In a fifteenth embodiment, the present disclosure provides
the fluoropolymer dispersion of the fourteenth embodiment, wherein
X, Y, and W are each independently fluoro, CF.sub.3,
C.sub.2F.sub.5, C.sub.3F.sub.7, C.sub.4F.sub.9, hydrogen, CH.sub.3,
C.sub.2H.sub.5, C.sub.3H.sub.7, C.sub.4H.sub.9. In a sixteenth
embodiment, the present disclosure provides the fluoropolymer
dispersion of any one of the first to fifteenth embodiments,
wherein Z is an alkali metal cation.
[0122] In a seventeenth embodiment, the present disclosure provides
the fluoropolymer dispersion of the sixteenth embodiment, wherein Z
is sodium.
[0123] In an eighteenth embodiment, the present disclosure provides
the fluoropolymer dispersion of any one of the first to fifteenth
embodiments, wherein Z is hydrogen.
[0124] In a nineteenth embodiment, the present disclosure provides
the fluoropolymer dispersion of any one of the first to eighteenth
embodiments, wherein the copolymer has an --SO.sub.2X equivalent
weight greater than 1000.
[0125] In a twentieth embodiment, the present disclosure provides
the fluoropolymer dispersion of any one of the first to nineteenth
embodiments, wherein the copolymer further comprises divalent units
derived from at least one of ethylene, propylene, isobutylene,
ethyl vinyl ether, vinyl benzoate, ethyl allyl ether, cyclohexyl
allyl ether, norbornadiene, crotonic acid, an alkyl crotonate,
acrylic acid, an alkyl acrylate, methacrylic acid, an alkyl
methacrylate, or hydroxybutyl vinyl ether.
[0126] In a twenty-first embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twentieth embodiments, wherein the copolymer has up to 100 --COOM
and --COF end groups per 10.sup.6 carbon atoms, wherein M is
independently an alkyl group, a hydrogen atom, a metallic cation,
or a quaternary ammonium cation.
[0127] In a twenty-second embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twenty-first embodiments. wherein the copolymer comprises less than
25 ppm metal ions.
[0128] In a twenty-third embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twenty-second embodiments, wherein the copolymer comprises
--SO.sub.2X end groups.
[0129] In a twenty-fourth embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twenty-third embodiments, wherein the fluoropolymer dispersion
comprises at least 15% by weight of the copolymer, based on the
total weight of the dispersion.
[0130] In a twenty-fifth embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twenty-fourth embodiments, wherein the fluoropolymer dispersion
comprises at least 25% by weight of the copolymer, based on the
total weight of the dispersion.
[0131] In a twenty-sixth embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twenty-fifth embodiments, wherein the variation of the copolymer in
which --SO.sub.3Z is replaced with --SO.sub.2F has a melt flow
index of up to 40 grams per ten minutes measured at a temperature
of 265.degree. C. and at a support weight of 5 kg.
[0132] In a twenty-seventh embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twenty-sixth embodiments, wherein the variation of the copolymer in
which --SO.sub.3Z is replaced with -SO.sub.2F has a melt flow index
of up to 25 grams per ten minutes measured at a temperature of
265.degree. C. and at a support weight of 5 kg.
[0133] In a twenty-eighth embodiment, the present disclosure
provides the fluoropolymer dispersion of any one of the first to
twenty-seventh embodiments, wherein the variation of the copolymer
in which SO.sub.3Z is replaced with --SO.sub.2F has a glass
transition temperature of up to 20.degree. C. In a twenty-ninth
embodiment, the present disclosure provides the fluoropolymer
dispersion of any one of the first to twenty-eighth embodiments,
further comprising organic solvent
[0134] In a thirtieth embodiment, the present disclosure provides
the fluoropolymer dispersion of any one of the first to
twenty-ninth embodiments, further comprising catalyst
particles.
[0135] In a thirty-first embodiment, the present disclosure
provides a catalyst ink comprising the fluoropolymer dispersion of
any one of the first to thirtieth embodiments. In a thirty-second
embodiment, the present disclosure provides a polymer electrolyte
membrane prepared from the fluoropolymer dispersion of any one of
the first to twenty-ninth embodiments.
[0136] In a thirty-third embodiment, the present disclosure
provides the polymer electrolyte membrane of the twenty-fifth
embodiment, wherein the polymer electrolyte membrane further
comprises at least one of cerium cations, manganese cations,
ruthenium cations, or a cerium oxide. In a thirty-fourth
embodiment, the present disclosure provides the polymer electrolyte
membrane of the thirty-third embodiment, wherein the at least one
of cerium cations, manganese cations, or ruthenium cations are
present in a range from 0.2 to 20 percent relative to the amount of
sulfonate groups in the copolymer.
[0137] In a thirty-fifth embodiment, the present disclosure
provides a membrane electrode assembly comprising at least one of
the polymer electrolyte membrane of any one of the thirty-second to
thirty-fourth embodiments or the catalyst ink of the thirty-first
embodiment.
[0138] In a thirty-sixth embodiment, the present disclosure
provides a binder for an electrode comprising the fluoropolymer
dispersion of any one of the first to twenty-ninth embodiments.
[0139] In a thirty-seventh embodiment, the present disclosure
provides an electrochemical cell comprising the binder of the
thirty-sixth embodiment.
[0140] In a thirty-eighth embodiment, the present disclosure
provides a method of making a fluoropolymer dispersion, the method
comprising:
[0141] combining components comprising water, an organic solvent,
and at least ten percent by weight of a copolymer, based on the
total weight of the components, the copolymer comprising: [0142]
divalent units represented by formula --[CF.sub.2--CF.sub.2]--;
[0143] divalent units independently represented by formula:
[0143] ##STR00026## [0144] wherein a is 0 or 1, b is 2 to 8, c is 0
to 2, e is 1 to 8, and Z is independently a hydrogen, alkyl having
up to four carbon atoms, an alkali-metal cation, or a quaternary
ammonium cation; and [0145] one or more divalent units
independently represented by formula:
[0145] ##STR00027## [0146] wherein Rf is a linear or branched
perfluoroalkyl group having from 1 to 8 carbon atoms and optionally
interrupted by one or more --O-- groups, z is 0, 1, or 2, each n is
independently 1, 2, 3, or 4, and m is 0 or 1; [0147] wherein the
copolymer has an --SO.sub.3Z equivalent weight in a range from 600
to 2000, and mixing the components at ambient pressure and a
temperature less than 100.degree. C. to make the fluoropolymer
dispersion.
[0148] In a thirty-ninth embodiment, the present disclosure
provides the method of the thirty-eighth embodiment, further
comprising forming the fluoropolymer dispersion into a film.
[0149] In a fortieth embodiment, the present disclosure provides
the method of the thirty-eighth or thirty-ninth embodiment, wherein
when a and c are 0, then e is 3 to 8.
[0150] In a forty-first embodiment, the present disclosure provides
the method of any one of the thirty-eighth to fortieth embodiments,
wherein b is 2 or 3, c is 0 or 1, and e is 4.
[0151] In a forty-second embodiment, the present disclosure
provides the method of any one of the thirty-eighth to forty-first
embodiments, b is 2 or 3, c is 1, and e is 2 or 4.
[0152] In a forty-third embodiment, the present disclosure provides
the method of any one of the thirty-eighth to forty-second
embodiments, wherein the copolymer comprises anionic species that
are not covalently bound to the ionomer, the method further
comprising contacting the fluoropolymer dispersions with an anion
exchange resin having associated hydroxide ions, and exchanging at
least a portion of the anionic species with the hydroxide ions to
provide an anionic exchanged dispersion.
[0153] In a forty-fourth embodiment, the present disclosure
provides the method of any one of the thirty-eighth to forty-third
embodiments, wherein the copolymer comprises cationic species that
are not covalently bound to the copolymer, the method further
comprising contacting fluoropolymer dispersion with a cation
exchange resin having acidic protons, and exchanging at least a
portion of the cationic species with the protons to provide
cation-exchanged dispersion.
[0154] In a forty-fifth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to forty-fourth
embodiments, further comprising spray drying the copolymer.
[0155] In a forty-sixth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to forty-fifth
embodiments, further comprising post-fluorinating the
copolymer.
[0156] In a forty-seventh embodiment, the present disclosure
provides the method of any one of the thirty-eighth to forty-sixth
embodiments, wherein when a is 0, then n is not 3.
[0157] In a forty-eighth embodiment, the present disclosure
provides the method of any one of the thirty-eighth to
forty-seventh embodiments, wherein z is 1 or 2, C.sub.nF.sub.2n is
(CF.sub.2).sub.n, and n is 1, 2, or 3.
[0158] In a forty-ninth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to forty-eighth
embodiments, wherein at least one n is 1.
[0159] In a fiftieth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to forty-ninth
embodiments, wherein the copolymer further comprises at least one
of divalent units derived from chlorotrifluoroethylene or divalent
units derived from hexafluoropropylene.
[0160] In a fifty-first embodiment, the present disclosure provides
the method of any one of the thirty-eighth to fiftieth embodiments,
wherein the copolymer has an alpha transition temperature
[T(.alpha.)] of at least 100.degree. C.
[0161] In a fifty-second embodiment, the present disclosure
provides the method of any one of the thirty-eighth to fiftieth
embodiments, wherein the copolymer has an alpha transition
temperature [T(.alpha.)] of up to 100.degree. C. or less than
100.degree. C.
[0162] In a fifty-third embodiment, the present disclosure provides
the method of any one of the thirty-eighth to fifty-second
embodiments, wherein the copolymer further comprises divalent units
independently represented by formula:
##STR00028##
[0163] wherein p is 0 or 1, q is 2 to 8, r is 0 to 2, s is 1 to 8,
and Z' is a hydrogen, an alkyl group having up to four carbon
atoms, an alkali-metal cation or a quaternary ammonium cation.
[0164] In a fifty-fourth embodiment, the present disclosure
provides the method of any one of the thirty-eighth to fifty-third
embodiments, wherein the divalent units comprise at least 60 mole %
of --[CF.sub.2--CF.sub.2]--, based on the total amount of divalent
units in the copolymer.
[0165] In a fifty-fifth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to fifty-fourth
embodiments, wherein the divalent units represented by formula
##STR00029##
[0166] are present at up to 20 or up to 15 mole percent, or in a
range from 3 to 20 or 4 to 15 mole percent, based on the total
moles of divalent units in the copolymer.
[0167] In a fifty-sixth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to fifty-fifth
embodiments, wherein the divalent units represented by formula
##STR00030##
are present at up to 30 or up to 25 mole percent, or in a range
from 10 to 30 or 15 to 25 mole percent, based on the total moles of
divalent units in the copolymer.
[0168] In a fifty-seventh embodiment, the present disclosure
provides the method of any one of the thirty-eighth to fifty-sixth
embodiments, wherein the copolymer further comprises divalent units
that are derived from bisolefins represented by formula
X.sub.2C.dbd.CY--(CW.sub.2).sub.m--(O).sub.n--R.sub.F--(O).sub.o--(CW.sub-
.2).sub.p--CY.dbd.CX.sub.2, wherein each of X, Y, and W is
independently fluoro, hydrogen, alkyl, alkoxy, polyoxyalkyl,
perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxyalkyl, m and p
are independently an integer from 0 to 15, and n, o are
independently 0 or 1.
[0169] In a fifty-eighth embodiment, the present disclosure
provides the method of the fifty-seventh embodiment, wherein X, Y,
and W are each independently fluoro, CF.sub.3, C.sub.2F.sub.5,
C.sub.3F.sub.7, C.sub.4F.sub.9, hydrogen, CH.sub.3, C.sub.2H.sub.5,
C.sub.3H.sub.7, C.sub.4H.sub.9.
[0170] In a fifty-ninth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to fifty-eighth
embodiments, wherein Z is an alkali metal cation.
[0171] In a sixtieth embodiment, the present disclosure provides
the method of the fifty-ninth embodiment, wherein Z is sodium.
[0172] In a sixty-first embodiment, the present disclosure provides
the method of any one of the thirty-eighth to fifty-eighth
embodiments, wherein Z is hydrogen.
[0173] In a sixty-second embodiment, the present disclosure
provides the method of any one of the thirty-eighth to sixty-first
embodiments, wherein the copolymer has an --SO.sub.2X equivalent
weight greater than 1000.
[0174] In a sixty-third embodiment, the present disclosure provides
the method of any one of the thirty-eighth to sixty-second
embodiments, wherein the copolymer further comprises divalent units
derived from at least one of ethylene, propylene, isobutylene,
ethyl vinyl ether, vinyl benzoate, ethyl allyl ether, cyclohexyl
allyl ether, norbornadiene, crotonic acid, an alkyl crotonate,
acrylic acid, an alkyl acrylate, methacrylic acid, an alkyl
methacrylate, or hydroxybutyl vinyl ether.
[0175] In a sixty-fourth embodiment, the present disclosure
provides the method of any one of the thirty-eighth to sixty-third
embodiments, wherein the copolymer has up to 100 --COOM and --COF
end groups per 10.sup.6 carbon atoms, wherein M is independently an
alkyl group, a hydrogen atom, a metallic cation, or a quaternary
ammonium cation.
[0176] In a sixty-fifth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to sixty-fourth
embodiments. wherein the copolymer comprises less than 25 ppm metal
ions.
[0177] In a sixty-sixth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to sixty-fifth
embodiments, wherein the copolymer comprises --SO.sub.2X end
groups.
[0178] In a sixty-seventh embodiment, the present disclosure
provides the method of any one of the thirty-eighth to sixty-sixth
embodiments, wherein the fluoropolymer dispersion comprises at
least 20% by weight of the copolymer, based on the total weight of
the dispersion.
[0179] In a sixty-eighth embodiment, the present disclosure
provides the method of any one of the thirty-eighth to
sixty-seventh embodiments, wherein the fluoropolymer dispersion
comprises at least 25% by weight of the copolymer, based on the
total weight of the dispersion.
[0180] In a sixty-ninth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to sixty-eighth
embodiments, wherein a variation of the copolymer in which
--SO.sub.3Z is replaced with --SO.sub.2F has a melt flow index of
up to 80 grams per ten minutes measured at a temperature of
265.degree. C. and at a support weight of 5 kg.
[0181] In a seventieth embodiment, the present disclosure provides
the method of any one of the thirty-eighth to sixty-ninth
embodiments, wherein a variation of the copolymer in which
--SO.sub.3Z is replaced with --SO.sub.2F has a melt flow index of
up to 40 grams per ten minutes measured at a temperature of
265.degree. C. and at a support weight of 5 kg.
[0182] In a seventy-first embodiment, the present disclosure
provides the method of any one of the thirty-eighth to seventieth
embodiments, wherein the variation of the copolymer in which
SO.sub.3Z is replaced with --SO.sub.2F has a glass transition
temperature of up to 25.degree. C. or up to 20.degree. C.
[0183] In a seventy-second embodiment, the present disclosure
provides the method of any one of the thirty-eighth to
seventy-first embodiments, wherein the fluoropolymer dispersion
further comprises catalyst particles.
[0184] In a seventy-third embodiment, the present disclosure
provides a catalyst ink made by the method of any one of the
thirty-eighth to seventy-second embodiments.
[0185] In a seventy-fourth embodiment, the present disclosure
provides a polymer electrolyte membrane prepared from the method of
any one of the thirty-eighth to seventy-third embodiments.
[0186] In a seventy-fifth embodiment, the present disclosure
provides the polymer electrolyte membrane of the seventy-fourth
embodiment, wherein the polymer electrolyte membrane further
comprises at least one of cerium cations, manganese cations,
ruthenium cations, or a cerium oxide.
[0187] In a seventy-sixth embodiment, the present disclosure
provides the polymer electrolyte membrane of the seventy-fifth
embodiment, wherein the at least one of cerium cations, manganese
cations, or ruthenium cations are present in a range from 0.2 to 20
percent relative to the amount of sulfonate groups in the
copolymer.
[0188] In a seventy-seventh embodiment, the present disclosure
provides a membrane electrode assembly comprising at least one of
the polymer electrolyte membrane made by the method of any one of
the seventy-fourth to seventy-sixth embodiments or the catalyst ink
made by the method of the seventy-third embodiment.
[0189] In a seventy-eighth embodiment, the present disclosure
provides a binder for an electrode made by the method of any one of
the thirty-eighth to seventy-third embodiments.
[0190] In a seventy-ninth embodiment, the present disclosure
provides an electrochemical cell comprising the binder of the
seventy-eighth embodiment.
[0191] In order that this disclosure can be more fully understood,
the following examples are set forth. It should be understood that
these examples are for illustrative purposes only and are not to be
construed as limiting this disclosure in any manner.
EXAMPLES
[0192] All materials are commercially available, for example from
Sigma-Aldrich Chemical Company; Milwaukee, WI, or known to those
skilled in the art unless otherwise stated or apparent. The
following abbreviations are used in this section: L=liters,
mL=milliliters, g=grams, min=minutes, rpm=revolutions per minute,
sec=seconds, h=hours, mol =moles, mol %=mole percent, wt %=weight
percent, nm=nanometer, .mu.m=micrometer, mm=millimeter,
cm=centimeter, ppm=parts per million, NMR=nuclear magnetic
resonance, .degree. C.=degrees Celsius, kPa=kiloPascal,
mW=milliWatt, kcps=thousand counts per second.
[0193] Results were obtained using the following test methods,
unless otherwise noted.
Solid Content
[0194] Solid content was determined gravimetrically by placing
samples of the dispersions on a heated balance and recording the
mass before and after evaporation of solvent. The solid content was
the ratio of the initial mass of the sample and the mass of the
sample when the mass did not decrease further with continued
heating.
Equivalent Weight (EW)
[0195] The EW of a copolymer of TFE, a sulfonyl fluoride monomer
(M2), and a vinyl ether or allyl ether monomer (M3) can be
calculated by the formula:
EW = ( ( mol % TFE + ( molar mass M 3 / molar mass TFE ) .times.
mol % M 3 ) mol % M 2 ) .times. 100 + molar mass M 2
##EQU00001##
Copolymer Composition
[0196] .sup.19F-NMR spectra were used to determine the composition
of the purified polymers. An NMR spectrometer available under the
trade designation AVANCE II 300 from Bruker, Billerica, Mass., USA
with a 5 mm Broadband probe was used. Samples of about 13 weight
percent polymer dispersion were measured at 60.degree. C.
[0197] Determination of Carboxyl Endgroups
[0198] A Fourier transform infrared spectroscopy (FT-IR)
measurement can used to determine the number of carboxyl endgroups
per 10.sup.6 C-atoms in the copolymer. The measurement is performed
by FT-IR in a transmission technique. The measured sample has a
film thickness of 100 .mu.m. The wave numbers of the
[0199] COOH peaks of interest are 1776 cm.sup.-1 and 1807
cm.sup.-1. The wave number of the C(O)F peak is 1885 cm.sup.1.
(C(O)F will convert to a carboxyl group). To quantify the amount of
carboxyl (C(O)F) endgroups of the polymer two IR spectra are taken.
One from the carboxyl containing sample and one from a reference
sample (without carboxyl groups).
[0200] The number of endgroups per 10.sup.6 carbon atoms can be
calculated via equation 1, 2 and 3 for F.sub.1, F.sub.2 and
F.sub.3:
(peak high.times.F.sub.1)/film thickness [mm] (1)
(peak high.times.F.sub.2)/film thickness [mm] (2)
(peak high.times.F.sub.3)/film thickness [mm] (3)
with F.sub.1: calculated factor related to the reference spectrum
and .nu.=1776 cm.sup.-1 F.sub.2: calculated factor related to the
reference spectrum and .nu.=1807 cm.sup.-1 F.sub.3: calculated
factor related to the reference spectrum and .nu.=1885 cm.sup.-1
The sum of the results from the equations 1 to 3 yield the number
of carboxyl endgroups per 10.sup.6 carbon atoms.
Particle Size by Dynamic Light Scattering
[0201] The particle size determination was conducted by dynamic
light scattering according to ISO 13321 (1996). A Zeta Sizer Nano
ZS, available from Malvern Instruments Ltd, Malvern,
Worcestershire, UK, equipped with a 50 mW laser operating at 532 nm
was used for the analysis. 12 mm square glass cuvettes with round
aperture and cap (PCS 8501, available from Malvern Instruments Ltd)
were used to mount a sample volume of 1 mL. Since light scattering
of surfactants is extremely sensitive to the presence of larger
particles, e.g. dust particles, the presence of contaminants was
minimized by thoroughly cleaning the cuvettes before the
measurements. The cuvettes were washed with freshly-distilled
acetone for 8 h in a cuvette washing device. Dust discipline was
also applied to the samples by centrifuging the surfactant
solutions in a laboratory centrifuge at 14,500 G (142,196 N/kg) for
10 min prior to the measurements. The measuring device was operated
at 25.degree. C. in 173.degree. backscattering mode. Low
correlation times of 1<1.sup.-6 sec were enabled by the research
tool (the research tool is a software up-grade of the standard
instrument provided by the supplier). In order to exploit the
complete scattering ability of the sample volume, the following
settings were applied in all cases: "attenuator," 11; "measurement
position," 4.65 mm (center of the cell). Under these conditions,
the baseline scattering of pure water (reference) is around 250
kcps. Each measurement consisting of 10 sub-runs was repeated for
five times. The particle sizes are expressed as D.sub.50 value.
Melt Flow Index
[0202] The melt flow index (MFI), reported in g/10 min, was
measured with a Goettfert MPD, MI-Robo, MI4 melt indexer (Buchen,
Germany) following a similar procedure to that described in DIN EN
ISO 1133-1 at a support weight of 5.0 kg and a temperature of
265.degree. C. The MFI was obtained with a standardized extrusion
die of 2.1 mm in diameter and a length of 8.0 mm.
T(.alpha.) Measurement
[0203] A TA Instruments AR2000 EX rheometer was used to measure the
T(.alpha.) of the polymer samples. Samples were heated on a
temperature ramp from -100.degree. C. to about 125.degree. C. at
2.degree. C. per minute. Measurements were made at a frequency of
one hertz.
Glass Transition Temperature
[0204] A TA Instruments Q2000 DSC was used to measure the glass
transition temperature (Tg) of the polymer samples. Samples were
heated on a temperature ramp from -50.degree. C. to about
200.degree. C. at 10.degree. C. per minute. Transition temperatures
were analyzed on the second heats.
Oxygen Permeability
[0205] The oxygen permeability as a function of temperature for
each membrane was determined using the time lag method. The
membranes with an active area of 1 cm.sup.2 were placed in a
permeability cell. Both chambers of the cell were subsequently
evacuated for 6 hours. Time zero for the test coincided with the
pressurization of upper chamber to 760 cm Hg with the challenging
gas (oxygen). The variation of the pressure as a function of time
in the evacuated lower chamber was measured using a pressure sensor
(Baratron.RTM., MKS, Mass., USA) with a sensitivity of 10.sup.-3 cm
Hg.
[0206] The oxygen permeability P in barrer (cm.sup.3.sub.stp cm/sec
cm.sup.2 cm Hg) was calculated using the following expression:
P=[V.sub.b1/A T Rp.sub.a]dp.sub.b/dt
where V.sub.b is the volume of the lower chamber in cm.sup.3, 1 is
the membrane thickness in cm, A the exposed surface area of the
membrane in cm.sup.2, T is temperature in .degree. K, p.sub.a is
the pressure of the upper chamber in cm Hg, R is the gas constant
(6236.367 cm Hg cm.sup.3/mol .degree. K), and dp.sub.b/dt is the
rate of change of the pressure in the lower chamber as a function
of time measured in the linear part of the pressure--time curve (cm
Hg/sec).
Viscosity
[0207] The viscosities of the dispersions were measured using a TA
Instruments AR2000ex rheometer equipped with a 1.degree., 60 mm
cone fixture and a Peltier plate assembly. The measurement was done
at 20.degree. C. and a steady shear rate of 1 s.sup.-1. Data was
taken every 10 seconds over a 60 second period, and the average is
reported.
Example 1 (EX-1)
[0208] A polymer of tetrafluoroethylene (TFE),
F.sub.2C.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2SO.sub.2F
(MV4S), and CF.sub.2.dbd.CF--O--(CF.sub.2).sub.3--OCF.sub.3 (MV31)
was prepared:
[0209] MV4S was prepared according to the method described in U.S.
Pat. No. 6,624,328 (Guerra). MV31 was prepared according to the
method described in U.S. Pat. No. 6,255,536 (Worm et al.)
[0210] A 4-L polymerization kettle equipped with an impeller
agitator system was charged with ammonium oxalate monohydrate (5 g)
and oxalic acid dihydrate (1 g) in H.sub.2O (2000 g) and 40 g of a
30 wt. % aqueous solution of
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4,
prepared as described in "Preparation of Compound 11" in U.S. Pat.
No. 7,671,112. The kettle was degassed and subsequently charged
with nitrogen several times to assure that all of oxygen was
removed. Afterwards, the kettle was purged with TFE, The kettle was
then heated to 50.degree. C. and the agitation system was set to
320 rpm. A mixture of MV4S (260 g), MV31 (50 g), and 8.6 g of the
30 Wt. %
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4
solution and deionized. water (165 g) were emulsified under high
shear by an agitator available under the trade designation
"ULTRA-TURRAX T 50" from IKA Works, Wilmington, N.C., USA operated
at 24000 rpm for 2 min. The MV4S and MV31 emulsion was charged into
the reaction kettle. The kettle was further charged with TFE (127
g) to a pressure of 6 bar (600 kPa). The polymerization was
initiated by a 0.045% solution of KMnO.sub.4 (33 g) in deionized
water. As the reaction started, the reaction temperature of
50.degree. C. as well as the reaction pressure of 6 bar (600 kPa)
were maintained by feeding TFE into the gas phase. After the first
pressure drop, the continuous feeding of the MV4S and MV31 emulsion
(in total 1037 g: 557 g MV4S and 106 g MV31 and 21 g of the 30%
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4
solution in 353 deionized. water), TFE (458 g), and of a 0.045%
solution of KA/Ma.sub.lin deionized water (350 g) was continued.
The molar ratio of the continuous feed was 72 mol % TFE, 23 mol
MV4S and 5 mol % MV31. The average metering rate of the continuous
addition of the 0.045% KMnO.sub.4 solution was 92 g/h. to obtain a
polymer dispersion with a solid content of 23.2%. The
polymerization time was 228 min. The latex particle diameter was
126 nm according to dynamic light scattering.
[0211] The polymer dispersion was charged into a 100L glass vessel
equipped with a lab stirrer (PENDRAULIK). While the lab stirrer of
the glass vessel was rotated to 2500 rpm, a 65 wt-% nitric acid
(170 g) was fed continuously in the glass vessel to precipitate the
polymer. Then the mixture was rotated for 1 h under the same
stirring conditions with a final solid content of 1.4% in the
polymerization medium (water phase).
[0212] The remaining aqueous polymerization medium was removed and
the wet polymerization crumb was washed seven times with 4 L DI
water while the stirrer was rotated to 930 rpm. The pH value of the
seventh washing medium was nearly 4. The wet polymerizate was
transferred in two portions in an air circulation dryer. Each
portion was dried for 17 hours at 80.degree. C. with a final water
content of .ltoreq.0.1% determined by thermobalance.
[0213] The coagulated, washed, and dried polymer had a MFI
(265.degree. C./5 kg) of 41 g/10 min. The polymer had a composition
of 70.3 mol % TFE, 24.4 mol-% MV4S and 5.3 mol MV31 as determined
by .sup.19F-NMR. spectroscopy measurements. This corresponds to an
equivalent weight EW of 740. The glass transition temperature (Tg)
was measured using the test method described above and found to be
3.degree. C.
[0214] Hydrolysis of the polymer was done in a Parr 4554 2-Gallon
Floor Stand Reactor equipped with a Parr 4848 Reactor Controller,
2700W Heater, a Parr Magnetic Drive Mixer, and a Neslab Thermoflex
2500 chiller for cooling. The reactor was charged with 1.5 L of
deionized (DI) water, 24 g of LiOH*H.sub.2O, 14.1 g of
Li.sub.2CO.sub.3, and 141 g of the polymer. The vessel was sealed,
and the mixer was set to 300 rpm. The reactor was then heated to
255.degree. C. over a period of 111 minutes. This temperature was
held for 60 minutes. It was then cooled to 25.degree. C. over 23
minutes, and upon reaching this temperature the mixer was shut off
The dispersion was drained from the reactor into 4 L HDPE bottles
and allowed to rest overnight.
[0215] The dispersion was passed through an ion exchange bed
consisting of a Kimble Chromaflex Column with the dimensions of
38.times.500 mm filled with 300 mL of Amberlite IR-120(Plus)
Hydrogen Form Ion Exchange Resin. The resin was prepared by first
flushing the column with 3 L of DI water with the stop cock
completely open. After 900 mL of 5% HC1 solution was passed through
the column over 30 minutes followed by 600 mL of DI water over 20
minutes. Next 3 L of DI water was passed through with the stop cock
fully open. The dispersion was then ion exchanged at a rate of 1200
mL per hour. Any precipitate that formed after hydrolysis was not
fed into the ion exchange column. The resin was regenerated after
every 400 mL of dispersion using the same process outlined
above.
[0216] To dry the ionomer and prepare solvent and water based
dispersions, 20 to 25 mL of the ion exchanged dispersion was placed
into a 40-mL high density polyethylene (HDPE) bottle. The open
bottle was placed in a muffle furnace set to 70.degree. C. where it
remained for 20 to 24 hours until the moisture content dropped
below 10%, and the ionomer was a friable solid. Once the dispersion
had dried, the final moisture content was determined, and
n-propanol and DI H.sub.2O with 18.2 MOhm-cm resistivity were
added. In this example 1.96 g of ionomer was combined with 4.32 g
of n-propanol and 2.72 g of H.sub.2O to achieve a dispersion
consisting of 20% ionomer, 48% n-propanol, and 32% water. The
bottle was then placed on a roller set to 45 to 65 rpm for a period
of 24 hours. A clear dispersion was formed with no visible
undispersed material. The viscosity of the dispersion was 97 cps as
determined using the test method above.
[0217] To make a membrane, dispersion was concentrated by rotary
evaporation to near solids and then exposed to a stream of nitrogen
gas. The dried ionomer was dispersed at 28-30 wt % into a 60/40
blend of n-propanol and water at room temperature. The solution was
coated onto 2 mil (50.8 micrometer) thickness "KAPTON" polyimide
liner secured to a glass substrate. The film was dried at
120.degree. C. for 30 minutes and then transferred from the glass
substrate to an aluminum pan. Drying was continued 140.degree. C.
for 15 minutes, ramped to 160.degree. C. for 10 minutes, and then
cooled to room temperature.
[0218] The T(.alpha.) was measured according to the test method
above and determined to be 98.degree. C.
[0219] The membrane was evaluated at 30.degree. C. using the Oxygen
Permeability evaluation method described above. A value of 161
(barrer.times.10.sup.10 was measured. The oxygen permeability at
50.degree. C. and 70.degree. C. was found to be higher than the
detection limit.
Example 2 (EX-2)
[0220] A polymer of tetrafluoroethylene (TFE),
F.sub.2C.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2SO.sub.2F
(MV4S), and CF.sub.2.dbd.CF--O--(CF.sub.2).sub.3--OCF.sub.3 (MV31)
was prepared:
[0221] MV4S and MV31 were prepared as described in Example 1.
[0222] A 4-L polymerization kettle equipped with an impeller
agitator system was charged with ammonium oxalate monohydrate (5 g)
and oxalic acid dihydrate (1 g) in H.sub.2O (2000 g) and 40 g of a
30 wt. % aqueous solution of
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4. The
kettle was degassed and subsequently charged with nitrogen several
times to assure that all of oxygen was removed.
[0223] Afterwards, the kettle was purged with TEE. The kettle was
then heated to 50.degree. C. and the agitation system was set to
320 rpm. A mixture of MV4S (237 g), MV31 (78 g), and 9.6 g of the
30 wt %
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4
solution and deionized water (147 g) were emulsified under high
shear by an agitator available under the trade designation
"ULTRA-TURRAX T 50" from IKA Works, operated at 24000 rpm for 2
min. The MV4S and MV31 emulsion was charged into the reaction
kettle. The kettle was further charged with TFE (126 g) to a
pressure of 6 bar (600 kPa), The polymerization was initiated by a
0.045% solution of KMna.sub.4 (20 g) irr deionized water. As the
reaction started, the reaction temperature of 50 .sup.0C as well as
the reaction pressure of 6 bar (600 kPa) were maintained by feeding
TFE into the gas phase. After the first pressure drop, the
continuous feeding of the MV4S and MV31 emulsion (in total 1128 g:
567 g MV4S and 187 g MV31 and 23 g of the 30%
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4-solu-
tion in 351 g deionized water), TEE (351 g), and of a 0.045%
solution of KMnO.sub.4 in deionized water (120 g) was continued.
The average metering rate of the continuous addition of the 0.045%
KMnO.sub.4 solution was 37 g/h to obtain a polymer dispersion witha
solid content of 19.7%. The polymerization time was 194 min, The
latex particle diameter was 114 nm according to dynamic light
scattering.
[0224] The copolymer was coagulated, washed, and dried similarly to
Example 1. The coagulated, washed, and dried polymer had a MEI
(265.degree. C./5 kg) of 57 g/10 min. The calculated equivalent
weight EW was 742.
Example 3 (EX-3)
[0225] A polymer of tetrafluoroethylene (TFE),
F2C.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2SO.sub.2F (MV4S),
and CF.sub.2.dbd.CF--O--(CF.sub.2).sub.2--CF.sub.3 (PPVE-1) was
prepared:
[0226] A 4-L polymerization kettle with an impeller agitator system
was charged with 5 g ammonium oxalate monohydrate and 1 g oxalic
acid dihydrate in 2000 g H.sub.2O and 40 g of a 30 wt. % aqueous
solution of
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4. The
kettle was degassed and subsequently charged with nitrogen several
times to assure that all of oxygen was removed. Afterwards, the
kettle was purged with TEE. The kettle was then heated to
50.degree. C. and the agitation system was set to 320 rpm. A
mixture of 80 g MV.sub.4S, 2.7 g of a 30 wt. %
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4
solution and 51 g deionized water were emulsified under high shear
by a "ULTRA-TURRAX T 50" agitator from IKA Works operated at 24000
rpm for 2 min. The MV4S-emulsion was charged into the reaction
kettle. The kettle was further charged with 114 g
[0227] TEE and 40 g PPVE-1 to 6 bar pressure (600 kPa). The
polymerization was initiated by 16 g of a 0.09% solution of
potassium permanganate (104n04) in deionized water. As the reaction
started, the reaction temperature of 50.degree. C. as well as the
reaction pressure of 6 bar (600 kPa) was maintained by feeding TEE
and PPVE-1 into the gas phase. After the first pressure drop the
continuous feeding of 190 g of the MV4S-emulsion (114 g MV4S and 4
g of a 30 wt. %
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH-CF.sub.2--COONH.sub.4
solution in 72 deionized water). 193 g TFE, 121 g PPVE-1, and 235 g
of a 0.09% solution of KMnO.sub.4 in deionized water was continued.
The average metering rate of the continuously addition of the 0,09%
KMnO.sub.4 solution was 123 g/h to obtain a polymer dispersion with
a solid content of 14.1%. The polymerization time was 115 min and
latex particle diameter was 150 nm according to dynamic light
scattering.
[0228] The copolymer was coagulated, washed, and dried similarly to
Example 1. The coagulated, washed, and dried polymer had a MFI
(265.degree. C./5 kg) of 66 g/10 min. The polymer showed a chemical
composition of 74.2 mol-% TFE, 16.1 mol-% MV4S and 9.7 mol-% PPVE-1
as obtained by .sup.19F-NMR-spectroscopy. This corresponds to an
equivalent weight of 1000. The glass transition temperature (Tg)
was measured using the test method described above and found to be
10.degree. C.
[0229] The polymer was hydrolyzed similarly to Example 1 except
16.2 g of LiOH*H.sub.2O, 9.5 g of Li.sub.2CO.sub.3 and 129 g of the
polymer was charged into the reactor. The reactor was then heated
to 255.degree. C. over a period of 114 minutes. The dispersion was
ion exchanged, dried, and an n-propanol based dispersion was
prepared similarly to Example 1. In Example 2, 2.14 g of ionomer
was combined with 4.70 g of n-propanol and 2.96 g DI H.sub.2O. A
clear dispersion was formed with no visible undispersed material.
The viscosity of the dispersion was 41 cps as determined by the
test method above.
[0230] A membrane was made similarly to Example 1. The T(.alpha.)
was measured according to the test method above and determined to
be 93.degree. C. The membrane was evaluated at 30.degree. C. using
the Oxygen Permeability evaluation method described above. A value
of 2.6 (barrer.times.10.sup.10) was measured. The oxygen
permeability at 50.degree. C. and 70.degree. C. was found to be 5.8
and 10.1 (barrer.times.respectively.
Comparative Example A
[0231] A polymer of tetrafluoroethylene (TFE) and
F.sub.2C.dbd.CF--O--CF.sub.2CF.sub.2CF.sub.2CF.sub.2SO.sub.2F
(MV4S) was prepared:
[0232] MV4S was prepared as described above.
[0233] A 4-L polymerization kettle equipped with an impeller
agitator system was charged with ammonium oxalate monohydrate (5 g)
and oxalic acid dihydrate (1 g) in H.sub.2O (2000 g) and 40 g of a
30 wt. % aqueous solution of
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4. The
kettle was degassed and subsequently charged with nitrogen several
times to assure that all of oxygen was removed. Afterwards, the
kettle was purged with TEE. The kettle was then heated to
50.degree. C. and the agitation system was set to 320 rpm. A
mixture of MV4S (200 g), 15 g of the 30 wt. %
CF.sub.3--O--(CF.sub.2).sub.3--O--CFH---CF.sub.2--COONH.sub.4
solution and deionized water (360 g) were emulsified under high
shear by an agitator available under the trade designation
"ULTRA-TURRAX T 50" from KA Works operated at 24000 rpm for 2. nun.
The MV4S emulsion was charged into the reaction kettle. The kettle
was further charged with TFE (115 g) to a pressure of 6 bar (600
kPa). The polymerization was initiated by a 0.06% solution of
KMnO.sub.4 (13 g) in deionized water. As the reaction started, the
reaction temperature of 50.degree. C. as well as the reaction
pressure of 6 bar (600 kPa) were maintained by feeding TFE into the
gas phase. After the first pressure drop, the continuous feeding of
the MV4S emulsion (in total 1234 g: 630 g MV4S and 24 g of the 30%
CF3--O--(CF.sub.2).sub.3--O--CFH--CF.sub.2--COONH.sub.4-solution in
580 g deionized water), IFE (450 g), and of a 0.045% solution of
KMnO.sub.4 in deionized water (297 g) was continued. The average
metering rate of the continuous addition of the 0.06% KhmO.sub.4
solution was 80 g/h to obtain a polymer dispersion with a solid
content of 22%. The polymerization tune was 232 min. The latex
particle diameter was 75 nm according to dynamic light
scattering.
[0234] 4.1 kg of the polymer dispersion with a solid content of 22%
was charged into a 10-L glass vessel equipped with a lab stirrer
(PENDRAULIK). While the lab stirrer of the glass vessel was rotated
to 2500 rpm, a 65 wt-% nitric acid (170 g) was fed continuously in
the glass vessel to precipitate the polymer. Then the mixture was
rotated for 1 h under the same stirring conditions with a final
solid content of 1.4% in the polymerization medium (water phase).
The remaining aqueous polymerization medium was removed and the wet
polymerization crumb was washed seven times with 4 liter DI water
while the stirrer was rotated to 930 rpm. The pH value of the
seventh washing medium was nearly 4.
[0235] The wet polymerizate was transferred in two portions in an
air circulation dryer. Each portion was dried for 17 hours at
80.degree. C. with a final water content of .ltoreq.0.1% determined
by thermobalance. The yield of dried polymer of the was 840 g.
[0236] The copolymer was coagulated, washed, and dried similarly to
Example 1. The coagulated, washed, and dried polymer had a MFI
(265.degree. C./5 kg) of 38 g/10 min. The so-obtained polymer
showed a chemical composition of 78 mol-% TYE, 22 mol-% MV4S as
determined by .sup.19F-NMR-spectroscopy. This corresponds to an
equivalent weight of 734.
[0237] The polymer was hydrolyzed similarly to Example I except the
reactor was charged with 4 L of DI water, 200 g of LiOH*H.sub.2O,
100 g of Li.sub.2CO.sub.3, and 1000 g of the polymer. The
dispersion was ion exchanged and dried similarly to Example 1. A
dispersion was prepared similarly to Example 1. The dispersion was
clear with no visible undispersed material, however the dispersion
was very viscous. The viscosity of the dispersion was 1472 cps as
determined using the test method above.
[0238] To prepare a membrane, another dispersion consisting of 20
wt % solids dispersed in ethanol: water at a ratio 55:45 was
prepared. A clear dispersion was formed with no visible undispersed
material. The dispersion was coated similarly to Example 1 except
the film was dried at 80.degree. C. for 10 minutes and then at
200.degree. C. for 15 minutes. The T(.alpha.) was measured
according to the test method above and determined to be 104.degree.
C.
[0239] A dispersion consisting of 15 wt % ionomer, 46.75%
n-propanol, and 38.25% water was prepared similarly to Example 1. A
clear dispersion was formed with no visible undispersed material. A
membrane was made similarly to Example 1 except the film was dried
at 90.degree. C. for 10 minutes and then at 100.degree. C. for 15
minutes, and then ramped to 190.degree. C. for 12 minutes, and then
cooled to room temperature. The membrane was evaluated at
30.degree. C. using the Oxygen Permeability evaluation method
described above. A value of 0.64 (barrer.times.10.sup.10) was
measured. The oxygen permeability at 50.degree. C. and 70.degree.
C. was found to be 1.4 and 2.8 (barrer.times.10.sup.10),
respectively.
Comparative Example B
[0240] A sample of AQUIVION D72-25BS aqueous dispersion was
purchased from Sigma Aldrich. Approximately 16 mL was dried as
described in Example 1. The equivalent weight of the polymer was
reported to be 720 in the technical data sheet. The dried ionomer
was redispersed at 15 wt% solids in n-propanol:water at a weight
ratio of 60:40. The mixture formed a gel.
[0241] Various modifications and alterations of this disclosure may
be made by those skilled in the art without departing from the
scope and spirit of the disclosure, and it should be understood
that this invention is not to be unduly limited to the illustrative
embodiments set forth herein.
* * * * *