U.S. patent application number 12/377263 was filed with the patent office on 2010-08-05 for polymer electrolyte material, polymer electrolyte molded product using the polymer electrolyte material, and method for manufacturing the polymer electrolye molded product, membrane electrode composite, and solid polymer fuel cell.
This patent application is currently assigned to TORAY INDUSTRIES, INC.. Invention is credited to Daisuke Izuhara, Yuriko Okada.
Application Number | 20100196782 12/377263 |
Document ID | / |
Family ID | 39033016 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100196782 |
Kind Code |
A1 |
Izuhara; Daisuke ; et
al. |
August 5, 2010 |
POLYMER ELECTROLYTE MATERIAL, POLYMER ELECTROLYTE MOLDED PRODUCT
USING THE POLYMER ELECTROLYTE MATERIAL, AND METHOD FOR
MANUFACTURING THE POLYMER ELECTROLYE MOLDED PRODUCT, MEMBRANE
ELECTRODE COMPOSITE, AND SOLID POLYMER FUEL CELL
Abstract
It is an object of the present invention to provide a polymer
electrolyte material which has excellent proton conductivity even
under the conditions of a low humidity or a low temperature and is
excellent in mechanical strength and fuel barrier properties, and
which moreover can achieve high output, high energy density and
long-term durability in forming a polymer electrolyte fuel cell
therefrom, and a polymer electrolyte form article using the same
and a method for producing the same, a membrane electrode assembly
and a polymer electrolyte fuel cell, each using the same. The
present invention employs the following means. Namely, the polymer
electrolyte material of the present invention is a polymer
electrolyte material including a constituent unit (A1) containing
an ionic group and a constituent unit (A2) substantially not
containing an ionic group, wherein a phase separation structure is
observed by a transmission electron microscope and a
crystallization heat measured by differential scanning calorimetry
is 0.1 J/g or more, or a phase separation structure is observed by
a transmission electron microscope and the degree of crystallinity
measured by wide angle X-ray diffraction is 0.5% or more. Also, the
polymer electrolyte form article, the membrane electrode assembly
and the polymer electrolyte fuel cell of the present invention are
characterized by being composed of such polymer electrolyte
materials.
Inventors: |
Izuhara; Daisuke; (Tokyo,
JP) ; Okada; Yuriko; (Tokyo, JP) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
TORAY INDUSTRIES, INC.
Tokyo
JP
|
Family ID: |
39033016 |
Appl. No.: |
12/377263 |
Filed: |
August 8, 2007 |
PCT Filed: |
August 8, 2007 |
PCT NO: |
PCT/JP2007/065490 |
371 Date: |
February 11, 2009 |
Current U.S.
Class: |
429/483 ;
429/304; 429/479 |
Current CPC
Class: |
H01M 2300/0082 20130101;
C08J 5/2256 20130101; Y02P 70/50 20151101; C08J 2371/10 20130101;
C08L 2205/05 20130101; H01B 1/122 20130101; Y02P 20/582 20151101;
H01M 8/1025 20130101; Y02E 60/50 20130101; C08J 5/2262 20130101;
C08G 65/4012 20130101; C08G 65/4056 20130101; C08J 2371/12
20130101; H01M 2008/1095 20130101; C08J 2387/00 20130101; H01M
8/1072 20130101; H01M 8/1067 20130101 |
Class at
Publication: |
429/483 ;
429/304; 429/479 |
International
Class: |
H01M 8/10 20060101
H01M008/10; H01M 6/18 20060101 H01M006/18 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 2006 |
JP |
2006-219539 |
Claims
1. A polymer electrolyte material including a constituent unit (A1)
containing an ionic group and a constituent unit (A2) substantially
not containing an ionic group, wherein a phase separation structure
is observed by a transmission electron microscope and a
crystallization heat measured by differential scanning calorimetry
is 0.1 J/g or more, or a phase separation structure is observed by
a transmission electron microscope and the degree of crystallinity
measured by wide angle X-ray diffraction is 0.5% or more.
2. The polymer electrolyte material according to claim 1, wherein
the polymer electrolyte material is an ionic group-containing block
copolymer composed of a block (B1) containing an ionic group and a
block (B2) substantially not containing an ionic group and a ratio
W1/W2 of a molar amount W1 of B1 to a molar amount W2 of B2 is 0.2
or more and 5 or less.
3. The polymer electrolyte material according to claim 1, wherein
the ionic group-containing copolymer is an aromatic
polyetherketone-type polymer.
4. The polymer electrolyte material according to claim 2, wherein
the block (B2) substantially not containing an ionic group
comprises a constituent unit represented by the following general
formula (Q1): ##STR00026## Z.sup.1 and Z.sup.2 in the general
formula (Q1) represent a divalent organic group containing an
aromatic ring and each of Z.sup.1 and Z.sup.2 may represent two or
more kinds of groups but does not substantially contain an ionic
group; and a and b each independently represents a positive
integer.
5. The polymer electrolyte material according to claim 4, wherein
the Z.sup.1 in said general formula (Q1) is a phenylene group and
the Z.sup.2 in said general formula (Q1) is at least one selected
from the following general formulas (X-1), (X-2), (X-4) and (X-5):
##STR00027## the groups represented by the general formula (X-1),
(X-2), (X-4) or (X-5) may be optionally substituted with a group
other than the ionic group.
6. The polymer electrolyte material according to claim 4, wherein
the Z.sup.1 and the Z.sup.2 in the general formula (Q1) are a
phenylene group.
7. The polymer electrolyte material according to claim 1, wherein
said ionic group is a sulfonic acid group.
8. The polymer electrolyte material according to claim 1, wherein
the density of the sulfonic acid group of the block (B1) containing
an ionic group is 1.7 to 5.0 mmol/g and the density of the sulfonic
acid group of the block (B2) substantially not containing an ionic
group is 0 to 0.5 mmol/g.
9. The polymer electrolyte material according to claim 1, wherein
the block (B1) containing an ionic group comprises constituent
units represented by the following general formulas (P1) and (P2):
##STR00028## in the general formulas (P1) and (P2), A represents a
divalent organic group containing an aromatic ring and M.sup.1 and
M.sup.2 represent hydrogen, a metal cation, or an ammonium cation;
and A may represent two or more kinds of groups.
10. The polymer electrolyte material according to claim 9, wherein
said A is: at least one kind of constituent unit selected from the
following general formulas (X-1) to (X-7): ##STR00029## the groups
represented by the general formulas (X-1) to (X-7) may be
optionally substituted.
11. A method for producing a polymer electrolyte form article
composed of an ionic group-containing block copolymer, having a
block (B1) containing an ionic group and a block (B2) substantially
not containing an ionic group, in which a ratio W1/W2 of weight W1
of the B1 to weight W2 of the B2 is 0.2 or more and 5 or less,
wherein a polymer electrolyte material formed by introducing
protective groups into at least the block (B2) substantially not
containing an ionic group is formed and then at least a portion of
the protective groups contained in the form article is
deprotected.
12. A polymer electrolyte form article, which is composed of the
polymer electrolyte material according to claim 1.
13. A membrane electrode assembly, which is composed of the polymer
electrolyte material according to claim 1.
14. A polymer electrolyte fuel cell, which is composed of the
polymer electrolyte material according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a highly practical polymer
electrolyte material which has excellent proton conductivity even
under the conditions of a low humidity or a low temperature and can
achieve excellent mechanical strength, fuel barrier properties and
long-term durability, as well as a polymer electrolyte form
article, a membrane electrode assembly and a polymer electrolyte
fuel cell, each using the same.
BACKGROUND ART
[0002] A fuel cell is a kind of electric power supply capable of
generating electric energy by electrochemically oxidizing a fuel
such as hydrogen or methanol, and an intense interest has been
shown towards the fuel cell, as a clean energy supply source,
recently. Particularly, it is expected that a polymer electrolyte
fuel cell is widely used as a distributed power generation facility
of comparatively small scale, and a power generator of mobile
bodies such as automobile and marine vessel, because of such high
standard operation temperature as about 100.degree. C. and high
energy density. Also, an intense interest has been shown towards
the polymer electrolyte fuel cell as a power supply of portable
mobile equipment and a portable device, and it is expected to
install the polymer electrolyte fuel cell in a cellular phone and a
personal computer in place of a secondary cell such as
nickel-hydrogen cell or lithium ion cell.
[0003] In the polymer electrolyte fuel cell, an intense interest
has been shown towards a direct methanol type fuel cell in which
methanol is directly supplied as a fuel (hereinafter, referred to
as DMFC), in addition to a conventional polymer electrolyte fuel
cell (hereinafter, referred to as PEFC) using a hydrogen as a fuel.
DMFC has such an advantage that the fuel is liquid and no reformer
is used and, therefore, energy density is high and an operating
time per one fueled of the portable device is very long.
[0004] In the fuel cell, anode and cathode in which the reaction
capable of generating electricity occurs, and a polymer electrolyte
membrane using as a proton conductor between the anode and the
cathode constitute a membrane electrode assembly (hereinafter
abbreviated to MEA) and a cell comprising separators and MEA
interposed between the separators is formed as a unit. The polymer
electrolyte membrane is mainly composed of the polymer electrolyte
material. The polymer electrolyte material is also used for a
binder of an electrocatalyst layer or the like.
[0005] As required properties of the polymer electrolyte membrane,
high proton conductivity is exemplified, first. Also, since the
polymer electrolyte membrane functions as a barrier which prevents
a direct reaction between a fuel and oxygen, low fuel permeability
is required. Particularly, in a polymer electrolyte membrane for
DMFC in which an organic solvent such as methanol is used as the
fuel, methanol permeation is referred to as methanol crossover
(hereinafter sometimes abbreviated to MCO) and causes a problem
such as decrease in cell output and energy efficiency. As other
required properties, resistance to solvents is also an important
property as long-term durability against a high concentration fuel
in DMFC in which the high concentration fuel such as methanol is
used. Other required properties include chemical stability for
enduring a strong oxidizing atmosphere during operation of a fuel
cell, and mechanical strength and physical durability for enduring
thinning and cycling of swelling and drying.
[0006] As the material of the polymer electrolyte membrane,
NAFION.RTM. (manufactured by DuPont Co.) as a perfluorosulfonic
acid-type polymer has widely been used. NAFION.RTM. is very
expensive because it is prepared through multi-step synthesis, and
also has a problem that fuel crossover is large because of its
cluster structure. Also, there were problems that mechanical
strength and physical durability of the membrane formed by swelling
and drying are lost because of poor resistance to hot water and
poor resistance to hot methanol, and that it cannot be used at high
temperature because of low softening point, and a problem such as
waste disposal after use and a problem that it is difficult to
recycle the material.
[0007] Furthermore, there was a problem that since proton
conductivity depends on a water content of the membrane, it is
necessary to maintain a high humidity condition to exert high power
generation performance as a fuel cell and a load of a humidifier is
increased. Also, below freezing point, there was also a problem
that proton conductivity is largely reduced because water in a
conducting membrane concerning conductivity is frozen and therefore
power generation becomes impossible.
[0008] To solve these problems, some studies on a polymer
electrolyte material containing a hydrocarbon-type polymer of a
nonperfluoro-type polymer as a base have been made. As a polymer
structure, particularly intensive study on an aromatic polyether
ketone and an aromatic polyethersulfone has been made in view of
heat resistance and chemical stability.
[0009] For example, there have been proposed a sulfonated compound
of a poorly-soluble aromatic polyetherether ketone (examples
thereof include such as VICTREX.RTM. PEEK.RTM., manufactured by
VICTREX Co.) which is an aromatic polyetherketone (see, for
example, non-patent document 1), polysulfone in a narrow sense as
an aromatic polyethersulfone (hereinafter sometimes abbreviated to
PSF) (examples thereof include UDEL P-1700, manufactured by BP
Amoco Polymers, Inc.), a sulfonated compound of polyethersulfone
(hereinafter sometimes abbreviated to PES) (examples thereof
include Sumikaexcel.degree. PES, manufactured by Sumitomo Chemical
Co., Ltd.) in a narrow sense (see, for example, non-patent document
2) and the like, but there were a problem that if a content of the
ionic group is increased in order to enhance the proton
conductivity, a prepared membrane swells and therefore fuel
crossover such as methanol or the like is large, and a problem that
since the polymer electrolyte material is low in a cohesive force
of a polymer chain, stability of a polymer higher-order structure
is insufficient and mechanical strength and physical durability of
a prepared membrane are insufficient.
[0010] Also, in the sulfonated compound (for example, non-patent
documents 1 and 2) of an aromatic polyetherketone (hereinafter
sometimes abbreviated to PES) (examples thereof include VICTREX
PEEK-HT, manufactured by VICTREX Co.), there was a problem that
because its crystallinity is high, a polymer having the composition
of low density of a sulfonic acid group becomes insoluble in a
solvent, resulting in poor processability because of a remained
crystal moiety. To the contrary, when the density of the sulfonic
acid group is increased so as to enhance processability, the
polymer is not crystalline and drastically swells in water and,
therefore, the membrane thus formed not only shows large fuel
crossover but also is insufficient in mechanical strength and
physical durability.
[0011] Furthermore, there have been proposed an aromatic
polyethersulfone block copolymer (for example, patent document 3)
and an aromatic polyetherketone block copolymer (for example,
non-patent document 3 and patent document 4). However, also in
these copolymers, there was a problem that polymers are brittle and
low in structural stability since these polymers use an amorphous
polymer such as a PES-type polymer or a PEK-type polymer having a
bulky side chain as a base structure because of solubility
constraint and membranes prepared are inferior in dimensional
stability, mechanical strength and physical durability.
[0012] As described above, the polymer electrolyte material
according to prior art is insufficient as a measures for improving
economic efficiency, processability, proton conductivity under the
conditions of a low humidity or a low temperature, fuel crossover,
mechanical strength and therefore long-term durability, and there
has never been obtained an industrially useful polymer electrolyte
material for a fuel cell.
Non-Patent Document 1: "Polymer", 1987, vol. 28, 1009
Non-Patent Document 2: Journal of Membrane Science, 83 (1993)
211-220
Non-Patent Document 3: "Polymer", 2006, vol. 47, 4132
Patent Document 1: Japanese Unexamined Patent Publication (Kokai)
No. 6-93114
Patent Document 2: Published Japanese Translation No. 2004-528683
of the PCT Application
Patent Document 3: Japanese Unexamined Patent Publication (Kokai)
No. 2003-31232
Patent Document 4: Published Japanese Translation No. 2006-512428
of the PCT Application
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0013] In view of the above state of the art, it is an object of
the present invention to provide a polymer electrolyte material
which has excellent proton conductivity even under the conditions
of a low humidity or a low temperature and is excellent in
mechanical strength and fuel barrier properties, and which moreover
can achieve high output, high energy density and long-term
durability in forming a polymer electrolyte fuel cell therefrom,
and a polymer electrolyte form article using the same and a method
for producing the same, a membrane electrode assembly and a polymer
electrolyte fuel cell, each using the same.
Means for Solving the Problems
[0014] The present invention employs the following means so as to
solve such problems. Namely, the polymer electrolyte material of
the present invention is a polymer electrolyte material including a
constituent unit (A1) containing an ionic group and a constituent
unit (A2) substantially not containing an ionic group, wherein a
phase separation structure is observed by a transmission electron
microscope and a crystallization heat measured by differential
scanning calorimetry is 0.1 J/g or more, or a phase separation
structure is observed by a transmission electron microscope and the
degree of crystallinity measured by wide angle X-ray diffraction is
0.5% or more. Also, the polymer electrolyte form article, the
membrane electrode assembly and the polymer electrolyte fuel cell
of the present invention are characterized by being composed of
such polymer electrolyte materials.
EFFECTS OF THE INVENTION
[0015] According to the present invention, it is possible to
provide a polymer electrolyte material which has excellent proton
conductivity even under the conditions of a low humidity or a low
temperature and is excellent in mechanical strength and fuel
barrier properties, and which moreover can achieve high output,
high energy density and long-term durability in forming a polymer
electrolyte fuel cell therefrom, and a polymer electrolyte form
article using the same and a method for producing the same, a
membrane electrode assembly and a polymer electrolyte fuel cell,
each using the same.
BEST MODE FOR CARRYING OUT THE INVENTION
[0016] Hereinafter, the present invention will be described in
detail.
[0017] The present invention has intensively studied on the above
problem, namely, a polymer electrolyte material which has excellent
proton conductivity even under the conditions of a low humidity or
a low temperature and is excellent in mechanical strength,
resistance to solvents and fuel barrier properties, and which
moreover can achieve high output, high energy density and long-term
durability in forming a polymer electrolyte fuel cell therefrom,
and found that proton conductivity performance of the polymer
electrolyte material is largely influenced by a phase separation
structure of the polymer electrolyte material, namely, an
aggregation state of a constituent unit (A1) containing an ionic
group and a constituent unit (A2) substantially not containing an
ionic group and a configuration of the aggregation, and that
performance of fuel barrier properties, mechanical strength and
long-term durability of the polymer electrolyte material are
largely influenced by the stabilization of a polymer higher-order
structure, namely, crystallinity or a crystalline state and an
amorphous state of a polymer.
[0018] Namely, it was found that when the polymer electrolyte
material is a polymer electrolyte material including the
constituent unit (A1) containing an ionic group and the constituent
unit (A2) substantially not containing an ionic group, wherein a
phase separation structure is observed by a transmission electron
microscope and a crystallization heat measured by differential
scanning calorimetry is 0.1 J/g or more, or a phase separation
structure is observed by a transmission electron microscope and the
degree of crystallinity measured by wide angle X-ray diffraction is
0.5% or more, the polymer electrolyte material not only has
excellent proton conductivity and fuel barrier properties, but also
can achieve resistance to solvents, high strength, high toughness
and a long-term durability through stabilization of a polymer
higher-order structure, and can solve these problems at once.
[0019] In the polymer electrolyte material of the present
invention, it is necessary that a phase separation structure is
observed by a transmission electron microscope. The polymer
electrolyte material is characterized by having excellent proton
conductivity even under the conditions of a low humidity or a low
temperature by controlling the phase separation structure of the
polymer electrolyte material, namely, an aggregation state of the
constituent unit (A1) containing an ionic group and the constituent
unit (A2) substantially not containing an ionic group and a
configuration of the aggregation. The phase separation structure
can be analyzed visually or with such as a scanning electron
microscope (SEM), a transmission electron microscope (TEM) and an
atomic force microscope (AFM), but in the present invention, the
presence or absence of the phase separation structure is determined
by a transmission electron microscope (TEM).
[0020] Particularly, in the present invention, in order to clearly
identify the aggregation state of the constituent unit (A1)
containing an ionic group and the constituent unit (A2)
substantially not containing an ionic group, the polymer
electrolyte material is observed by TEM after an ionic group of the
polymer electrolyte material is ion-exchanged with cesium by
immersing the polymer electrolyte material in a 10 wt % ethanol
solution of cesium acetate.
[0021] In the present invention, "A phase separation structure is
observed" is defined as a state in which a phase separation
structure is observed when TEM observations is carried out at
50000-fold magnification and an average interlaminar distance or an
average distance between particles measured by image processing is
8 nm or more. An upper limit of the average interlaminar distance
or the average distance between particles is not particularly
limited, but 5000 nm or less is a practical value in view of a
balance between the distance and mechanical properties.
Particularly, the average interlaminar distance or the average
distance between particles is more preferably 10 nm or more and
2000 nm or less, and most preferably 15 nm or more and 200 nm or
less. When the phase separation structure is not observed by a
transmission electron microscope or the average interlaminar
distance or the average distance between particles is less than 8
nm, it is not preferable since the continuity of an ionic channel
may be deficient and ionic conductivity may be low. Further, when
the average interlaminar distance is more than 5000 nm, it is not
preferable since mechanical strength or dimensional stability may
become poor.
[0022] Further, the phase separation structure more preferably has
anisotropy in which a direction of a membrane thickness is longer
than a direction of a membrane surface from the viewpoint of ionic
conductivity. The anisotropy is preferably two times or more and
more preferably three times or more. Further, from the viewpoint of
constructing a proton conductive path, the phase separation
structure furthermore preferably has a bicontinuous structure in
which a constituent component containing an ionic group continues
in a direction of a membrane thickness.
[0023] Observations of the phase separation structure of such
polymer electrolyte materials by TEM is carried out by a method
described in Examples.
[0024] Since the polymer electrolyte material of the present
invention is characterized by having crystallization capacity while
having the phase separation structure, it is necessary that
crystallinity is identified by differential scanning calorimetry
(DSC) or wide angle X-ray diffraction. Namely, one aspect of the
polymer electrolyte material of the present invention is a polymer
electrolyte material in which a crystallization heat measured by
differential scanning calorimetry is 0.1 J/g or more (hereinafter,
may be referred to as an aspect A), and the other aspect is a
polymer electrolyte material in which the degree of crystallinity
measured by wide angle X-ray diffraction is 0.5% or more
(hereinafter, may be referred to as an aspect B). In the present
invention, both of the aspect A and the aspect B are preferable
aspects, but particularly, the aspect A is more preferable from the
viewpoint of high toughness and durability.
[0025] In the present invention, "a polymer has crystallinity"
means that the polymer can be crystallized on heating temperature,
has a crystallization capacity, or has already been crystallized.
Also, the amorphous polymer means a polymer which is not a
crystalline polymer, in which crystallization does not
substantially proceed. Accordingly, even a crystalline polymer can
be in an amorphous state as a polymer state when crystallization
does not adequately proceed.
[0026] First, the aspect A of the polymer electrolyte material of
the present invention will be described. In the aspect A of the
polymer electrolyte material of the present invention, it is
necessary that the crystallization heat AH per unit weight (g) of a
dried polymer as measured by differential scanning calorimetry
(DSC) is 0.1 J/g or more. As the differential scanning calorimetry
(DSC), temperature modulation DSC can be more preferably used in
point of measuring accuracy. Particularly, it is more preferable
from the viewpoint of mechanical strength, long-term durability,
resistance to hot methanol and fuel barrier properties that
.DELTA.H is 2 J/g or more. Particularly, .DELTA.H is more
preferably 5 J/g or more, still more preferably 10 J/g or more, and
most preferably 15 J/g or more. The upper limit of .DELTA.H is not
specifically limited, but is practically 500 J/g or less.
[0027] Here, a method for measuring crystallinity by differential
scanning calorimetry (DSC) will be described. Since a chemical
structure and a higher order structure (crystal and amorphous
state) of the polymer varies as a result of crystallization,
melting and thermal decomposition of the polymer, the crystallinity
of the polymer electrolyte material of the present invention is
evaluated type on whether a crystallization temperature is
recognized in a first heating in the differential scanning
calorimetry or not and an area of the crystallization peak in heat
flow-temperature chart of DSC. That is, in the aspect A of the
polymer electrolyte material of the present invention, it is
necessary that a crystallization temperature is recognized in the
first heating and AH is 0.1 J/g or more in the differential
scanning calorimetry.
[0028] In case the polymer is thermally decomposed, after
preliminarily confirming a thermal decomposition temperature of the
polymer by thermogravimetry/differential thermal (TG-DTA), the
presence or absence of a crystallization temperature is confirmed
during heating the temperature which is the thermal decomposition
temperature or lower. In case a crystallization temperature is
recognized at the temperature which is the thermal decomposition
temperature or higher, there is a possibility that the chemical
structure of the polymer varies, and therefore it cannot be decided
that the polymer had crystallization capacity.
[0029] The polymer electrolyte material, in which a crystallization
temperature is recognized in the first heating in the differential
scanning calorimetry, means that it has crystallization capacity.
In a polymer electrolyte material composed of an amorphous polymer,
the crystallization temperature is not recognized in the
differential scanning calorimetry. As the polymer electrolyte
material of the present invention, the aspect A having an amorphous
moiety, in which crystallization proceeds through heating, is a
preferable example. There may be cases where by leaving the
amorphous moiety in which crystallization proceeds through heating,
the polymer electrolyte material not only has excellent proton
conductivity and fuel barrier properties, but also can achieve
extremely excellent resistance to solvents, mechanical strength and
physical durability.
[0030] Confirmation of the presence or absence of crystallization
temperature and measurement of crystallization heat of such an
ionic group-containing block copolymer by temperature modulation
DSC is performed by a method described in Examples. A thermal
decomposition temperature is preferably confirmed separately by
thermogravimetry/differential thermal or the like.
[0031] The crystallization temperature is recognized in an
irreversible process and is recognized at a temperature of a glass
transition temperature or higher and a melting temperature or lower
as a temperature. Crystallization heat can be calculated from the
area of the crystallization peak in heatflow-temperature chart of
DSC. In case of a polymer electrolyte material having a sulfonic
acid group, the crystallization temperature is close to a thermal
decomposition temperature or a melting temperature and the high
temperature of the crystallization temperature may be influenced by
decomposition or melting. Therefore, in the present invention, the
value, which is obtained by doubling heat from the low temperature
to a peak top, is defined as crystallization heat.
[0032] Next, the aspect B of the polymer electrolyte material of
the present invention will be described. In the aspect B of the
polymer electrolyte material of the present invention, it is
necessary that the degree of crystallinity measured by wide angle
X-ray diffraction is 0.5% or more. A degree of crystallinity of the
polymer electrolyte material of the present invention can be
evaluated by the crystallinity measured by wide angle X-ray
diffraction, and particularly, from the viewpoint of dimensional
stability, mechanical strength and long-term durability, the degree
of crystallinity is more preferably 3% or more, and furthermore
preferably 5% or more. The upper limit of the degree of
crystallinity, is not particularly limited, but is practically 50%
or less. When the degree of crystallinity is less than 0.5% and the
crystallization heat measured by DSC is less than 0.1 J/g, it is
not preferred because a polymer is amorphous, dimensional stability
may be insufficient because of unstable structure and long-term
durability may be insufficient because of insufficient
toughness.
[0033] The case where the crystallization temperature is not
recognized in the first heating in the differential scanning
calorimetry can be separated specifically into the case where the
polymer is amorphous without having crystallinity and the case
where the polymer has already been crystallized. The polymer
electrolyte material already crystallized becomes the aspect B of
the polymer electrolyte material of the present invention and
exhibits the degree of crystallinity, measured by wide angle X-ray
diffraction, of 0.5% or more. However, in a polymer electrolyte
material composed of an amorphous polymer, it is impossible to
attain sufficient dimensional stability, mechanical strength,
physical durability, fuel barrier properties and resistance to
solvents because its structure is unstable, and it is impossible to
achieve a high energy capacity or long-term durability in using the
polymer electrolyte material in the fuel cell.
[0034] The measurement of the degree of crystallinity by wide angle
X-ray diffraction of such polymer electrolyte materials is
performed by a method described in Examples.
[0035] Preferable examples of the polymer electrolyte material of
the present invention, whose phase separation structure is observed
by TEM, include such as a block copolymer composed of a block (B1)
containing an ionic group and a block (B2) substantially not
containing an ionic group, a polymer alloy or a polymer mixture
composed of a polymer containing an ionic group and a polymer
substantially not containing an ionic group, and a polymer
containing an ionic group in either a main chain or a side chain,
but the polymer electrolyte material can be used without being
limited to these.
[0036] Among these polymers, a block copolymer composed of a block
(B1) containing an ionic group and a block (B2) substantially not
containing an ionic group is more preferable as the polymer
electrolyte material of the present invention, and a ratio W1/W2 of
a molar amount W1 of the B1 to a molar amount W2 of the B2 is more
preferably 0.2 or more and 5 or less from the viewpoint of a
balance between proton conductivity and mechanical properties or
durability, furthermore preferably 0.25 or more and 4 or less, and
most preferably 0.33 or more and 3 or less. When the ratio W1/W2 is
less than 0.2 or more than 5, it is not preferable because an
effect as a block copolymer becomes insufficient and the block
copolymer become deficient in proton conductivity, dimensional
stability or mechanical properties.
[0037] In addition, in the present invention, it is stated that the
block (B2) does not substantially contain an ionic group, but the
block (B2) may contain a small amount of ionic groups within a
range which does not affect adversely an effect of the present
invention, particularly crystallinity.
[0038] In the present invention, the block copolymer refers to a
block copolymer composed of two or more kinds of blocks. Also, the
block in the present invention is a partial structure of the block
copolymer, and comprises one kind of a repeating unit or a
combination of a plurality kinds of repeating units, and refers to
those having a formula weight of 2000 or more. Furthermore, the
domain means a cluster made of aggregation of similar blocks in one
or a plurality of polymer chains.
[0039] Examples of the ionic group-containing block copolymer to be
used for the present invention include such as a block copolymer
formed by reacting an ionic group-containing monomer and a monomer
not containing an ionic group separately to form an ionic
group-containing block and/or a block not containing an ionic group
and then reacting these blocks, a block copolymer formed by
reacting an ionic group-containing monomer and a polymer not
containing an ionic group, a block copolymer formed by reacting a
monomer not containing an ionic group and an ionic group-containing
polymer, and furthermore a block copolymer formed by forming a
block taking advantage of the difference in reactivity between
monomers. Further, it is also possible that after obtaining a block
copolymer having different reactivities, an ionic group is
selectively introduced into only a highly reactive site.
[0040] When two or more kinds of block chains which are immiscible
with one another, namely, a block copolymer, in which a block (B1)
containing an ionic group and a block (B2) substantially not
containing an ionic group form one polymer chain linked by a
covalent bond, is employed, it is possible to control an
arrangement of chemically different components on a nanoscale to a
microscale. In the block copolymer, by short-range interaction
generated from the incompatibility between chemically different
blocks, the copolymer is phase separated into regions (nanometer
scaled (nano order) structure) comprising each block chain but each
microdomain is arranged keeping a specific order by virtue of
long-range interaction generated from a covalent bond between block
chains. A structure created by aggregation of microdomains
comprising each block chain is referred to as a microphase
separation structure.
[0041] A channel structure formed in a membrane by an ionically
conductive component is thought to be extremely important for ionic
conduction. From the view that ions are transferred through a
channel, a spatial arrangement of an ionic conduction site in the
membrane becomes important. It is one of the objects of the present
invention to attain a polymer electrolyte membrane exhibiting
excellent ionic conductivity by controlling the spatial arrangement
of an ionic conduction site in the membrane.
[0042] By adjusting a block length, a packing property, polarity,
rigidity and hydrophilicity/hydrophobicity of the ionic
group-containing block copolymer used for the present invention, it
is possible to control the processability of the polymer
electrolyte material and the polymer electrolyte form article
composed thereof, a size of the domain,
crystallinity/noncrystallinity and fuel crossover, durability,
resistance to solvents and mechanical characteristics.
[0043] However, when conventional aromatic polyethersulfone block
copolymer or aromatic polyetherketone block copolymer is used as a
polymer electrolyte material, there were a problem that if a
content of the ionic group of the block copolymer is increased in
order to enhance the proton conductivity under the conditions of a
low humidity or a low temperature, a membrane swells significantly
because of the aggregation of ionic groups and therefore fuel
crossover such as methanol or the like is large, and problem that
since the polymer electrolyte material is low in a cohesive force
of polymer chains, stability of a polymer higher-order structure is
insufficient and dimensional stability of a membrane, mechanical
strength and physical durability are insufficient.
[0044] Further, the ionic group-containing block copolymer, in
which similar blocks aggregate to form a domain, could not be used
as a polymer electrolyte material because processability becomes
poor if a crystalline block exists.
[0045] On the other hand, the polymer electrolyte material of the
present invention could control noncrystallinity/crystallinity
through introduction of a protective group/deprotection, enhance
the stability of a higher-order structure of the polymer
electrolyte material through a pseudo-crosslinking effect by
imparting crystallinity to the ionic group-containing block
copolymer to be used, and achieve excellent dimensional stability,
fuel barrier properties, mechanical strength and physical
durability while having excellent proton conductivity under the
conditions of a low humidity or a low temperature. That is, the
domain formed by aggregation of the block (B1) containing an ionic
group plays a role of enhancing proton conductivity and the domain
formed by aggregation of the block (B2) substantially not
containing an ionic group plays a role of enhancing performance of
dimensional stability, fuel barrier properties, mechanical strength
and long-term durability by a pseudo-crosslinking effect by
crystal. That is, the present invention forms a phase separation
structure by blocking the sites having different functions of ionic
conductivity and crystallinity. The ionically-conductive block
exhibits excellent proton conductivity by constructing an
ionically-conductive path, and the crystalline block forms a
crystal structure which is more robust than a random copolymer, and
by this functional separation, the present invention achieves
compatibility between a power generating property and
durability.
[0046] Next, the ionic group-containing block copolymer used in the
polymer electrolyte material of the present invention will be
described specifically. The ionic group-containing block copolymer
used for the present invention is more preferably a
hydrocarbon-type polymer from the viewpoint of crystallinity and
mechanical strength. An ionic group-containing hydrocarbon-type
polymer referred to in the present invention means a polymer having
an ionic group other than a perfluoro-type polymer.
[0047] As used herein, a perfluoro-type polymer refers to a polymer
in which most of or all of hydrogen of alkyl groups and/or alkylene
groups in the polymer are substituted with a fluorine. In the
present specification, a polymer, in which 85% or more of hydrogen
of alkyl groups and/or alkylene groups are substituted with a
fluorine, is defined as a perfluoro-type polymer.
[0048] Typical examples of a perfluoro-type polymer having an ionic
group of the present invention include commercialized products such
as NAFION.RTM. manufactured by DuPont Co., Flemion.RTM.
manufactured by Asahi Glass Co., Ltd. and Aciplex.RTM. manufactured
by Asahikasei Corporation. Structures of these perfluoro-type
polymers having such an ionic group can be represented by the
following formula (N1):
##STR00001##
[0049] In the formula (N1), n1 and n2 each independently represents
a natural number; and k1 and k2 each independently represents an
integer of 0 to 5.
[0050] In these perfluoro-type polymers having an ionic group,
since a hydrophobic moiety and a hydrophilic moiety in the polymer
form a define phase structure, a channel of water referred to as a
cluster is formed in the polymer in a state of containing water. In
this channel of water, fuel such as methanol readily moves, and
therefore, it cannot be expected to reduce fuel crossover. Further,
crystallinity is not recognized because of a bulky side chain and
therefore it is not preferable.
[0051] The ionic group-containing block copolymer to be used for
the present invention is more preferably a polymer having an
aromatic ring in a main chain among hydrocarbon-type polymers from
the viewpoint of mechanical strength, physical durability and
chemical stability. That is, a polymer having an aromatic ring in a
main chain, which has an ionic group, is more preferable. A
structure of the main chain is not particularly limited as long as
it has an aromatic ring in a main chain, and for example, those
having sufficient mechanical strength and physical durability,
which are used as an engineering plastic, are preferable.
[0052] Specific examples of the polymer having an aromatic ring in
a main chain to be used for an ionic group-containing block
copolymer include polymers containing at least one of constituent
components such as polysulfone, polyethersulfone, polyphenylene
oxide, polyarylene ether-type polymer, polyphenylene sulfide,
polyphenylene sulfide sulfone, polyparaphenylene, polyarylene-type
polymer, polyaryleneketone, polyether ketone, polyarylene
phosphinoxide, polyether phosphinoxide, polybenzoxazole,
polybenzthiazole, polybenzimidazole, polyamide, polyimide,
polyetherimide and polyimidesulfone.
[0053] As used herein, polysulfone, polyethersulfone and polyether
ketone are generic names of polymers having a sulfone bond, an
ether bond and a ketone bond in the molecular chain and include,
for example, polyether ketoneketone, polyetherether ketone,
polyetherether ketoneketone, polyether ketone ether ketoneketone,
and polyether ketone sulfone, but it is not intended to limit a
specific polymer structure.
[0054] Among the above polymers having an aromatic ring in a main
chain, polymers such as polysulfone, polyethersulfone,
polyphenylene oxide, polyarylene ether-type polymer, polyphenylene
sulfide, polyphenylene sulfide sulfone, polyarylene ketone,
polyether ketone, polyarylene phosphinoxide, and polyether
phosphinoxide are preferable in view of mechanical strength,
physical durability, processability and resistance to
hydrolysis.
[0055] Specific examples thereof include polymers containing an
aromatic ring in a main chain, which have a repeating unit
represented by the following general formula (T1):
##STR00002##
[0056] Wherein Z.sup.1 and Z.sup.2 represent an organic group
containing an aromatic ring and each of Z.sup.1 and Z.sup.2 may
represent two or more kinds of groups, and at least a portion of at
least one kind of Z.sup.1 and Z.sup.2 has an ionic group; Y.sup.1
represents an electron-withdrawing group; Y.sup.2 represents oxygen
or sulfur; and a and b each independently represents 0 or a
positive integer, provided that a and b does not simultaneously
represent 0.
[0057] Among the polymer comprising a repeating unit represented by
the general formula (T1), which has an aromatic ring in a main
chain, a polymer comprising repeating units represented by the
general formulas (T1-1) to (T1-6) is more preferable in view of
resistance to hydrolysis, mechanical strength, physical durability
and production cost. Among the polymers comprising these repeating
units, in view of mechanical strength, physical durability and
production cost, an aromatic polyether-type polymer in which
Y.sup.2 is 0 is more preferable, and a polymer comprising a
repeating unit represented by the general formula (T1-3), namely,
an aromatic polyether ketone-type polymer, in which Y.sup.1 is a
--CO-- group and Y.sup.2 is O, is most preferable.
##STR00003##
[0058] Wherein Z.sup.1 and Z.sup.2 represent an organic group
containing an aromatic ring and each of Z.sup.1 and Z.sup.2 may
represent two or more kinds of groups, and at least a portion of at
least one kind of Z.sup.1 and Z.sup.2 has an ionic group; and a and
b each independently represents 0 or a positive integer, provided
that a and b does not simultaneously represent 0.
[0059] An organic group as Z.sup.1 and Z.sup.2 is preferably a
phenylene group, a naphthylene group, or a biphenylene group. These
groups include a group containing an ionic group. Further, these
groups may be substituted with a group other than the ionic group,
but nonsubstituted groups are more preferable in point of imparting
crystallinity. Z.sup.1 and Z.sup.2 are furthermore preferably a
phenylene group and a phenylene group having an ionic group, and
most preferably a p-phenylene group and a p-phenylene group having
an ionic group.
[0060] Preferable examples of the organic group represented by
R.sup.p in the general formula (T1-4) are a methyl group, an ethyl
group, a propyl group, an isopropyl group, a cyclopentyl group, a
cyclohexyl group, a norbornyl group, a vinyl group, an allyl group,
a benzyl group, a phenyl group, a naphthyl group, and a
phenylphenyl group. In view of industrial availability, R.sup.p is
most preferably a phenyl group.
[0061] In the present invention, the aromatic polyether type
polymer refers to a polymer which includes ether bonds as a form to
bond, with aromatic ring units to one another in a polymer mainly
composed of aromatic rings. The examples of chemical bonding such
as a direct bond, ketone, sulfone, sulfide, various alkylenes,
imide, amide, ester and urethane, which are commonly used for
forming an aromatic polymer, may exist in addition to the ether
bond. It is preferred that one or more ether bonds exist per
repeating unit of a principal constituent component. The aromatic
ring may include, in addition to the hydrocarbon-type aromatic
ring, a hetero ring. Also, an aliphatic unit may partially
constitute the polymer, along with the aromatic ring unit. The
aromatic unit may have optional substituents, for example, a
hydrocarbon-type group such as alkyl group, a halogen group, a
nitro group, a cyano group, an amino group, a halogenated alkyl
group, a carboxyl group, a phosphonic acid group, and a hydroxyl
group.
[0062] As used herein, the aromatic polyether ketone-type polymer
is a generic name of a polymer having at least an ether group and a
ketone group in the molecular chain and includes such as polyether
ketone, polyether ketoneketone, polyetherether ketone,
polyetherether ketoneketone, polyether ketone ether ketoneketone,
polyether ketone sulfone, polyether ketone phosphine oxide, and
polyether ketone nitrile, and is not limited to a specific polymer
structure. The aromatic polyether ketone-type polymer containing
phosphine oxide or nitrile in large quantity may have insufficient
solubility in a solvent in the ionic group-containing polymer
having a protective group, and the aromatic polyether ketone-type
polymer containing sulfone in large quantity may have insufficient
crystallinity, resistance to solvents such as resistance to hot
methanol and resistance to hot water.
[0063] Next, preferable examples of the block (B2) substantially
not containing the ionic group to be used in the polymer
electrolyte material of the present invention will be exemplified
specifically.
[0064] In the block (B2) to be used in the polymer electrolyte
material of the present invention, an aromatic polyether ketone
(PEK)-type polymer, namely, a polymer, which comprises a
constituent unit represented by the following general formula (Q1)
and does not substantially contain the ionic group, is particularly
preferable in that it exhibits crystallinity because of its good
packing and very strong intermolecular cohesive force, and has a
property of being insoluble in a common solvent:
##STR00004##
[0065] Z.sup.1 and Z.sup.2 in the general formula (Q1) represent a
divalent organic group containing an aromatic ring and each of
Z.sup.1 and Z.sup.2 may represent two or more kinds of groups but
does not contain an ionic group; and a and b each independently
represents a positive integer.
[0066] In the block (B2) to be used in the polymer electrolyte
material of the present invention, a small amount of ionic group
may be contained within a range which does not affect adversely an
effect of the present invention, particularly crystallinity.
[0067] An organic group as Z.sup.1 and Z.sup.2 in the general
formula (Q1) is more preferably a phenylene group for Z1 and at
least one selected from the following general formulas (X-1),
(X-2), (X-4) and (X-5) for Z2. Also, these groups may be
substituted with a group other than the ionic group, but
nonsubstituted groups are more preferable in point of imparting
crystallinity. Z.sup.1 and Z.sup.2 are more preferably a phenylene
group, and most preferably a p-phenylene group.
##STR00005##
[0068] the groups represented by the general formula (X-1), (X-2),
(X-4) or (X-5) may be optionally substituted with a group other
than the ionic group.
[0069] Preferable specific examples of the constituent unit
represented by the above general formula (Q1) include such as
constituent units represented by the following general formulas
(Q2) to (Q7), but it is not limited to these constituent units, and
it can be appropriately selected in consideration of crystallinity
or mechanical strength. Particularly, the constituent unit
represented by the above general formula (Q1) is more preferably a
constituent unit represented by the following general formulas
(Q2), (Q3), (Q6) and (Q7), and most preferably the following
general formulas (Q2) and (Q7) in point of crystallinity and
production cost:
##STR00006##
[0070] the general formulas (Q2) to (Q7) are all shown in the form
of a bond at a para-position, but they may include the form of a
bond at another position such as an ortho-position or a
meta-position as long as they have crystallinity. However, the
para-position is more preferable from the viewpoint of
crystallinity.
[0071] Next, preferable examples of the block (B1) containing the
ionic group to be used in the polymer electrolyte material of the
present invention will be exemplified specifically. In the polymer
electrolyte material of the present invention, the block (B1) has
the ionic group to form a domain, and whereby, a polymer
electrolyte material or a polymer electrolyte membrane can exhibit
high proton conductivity in wide use conditions.
[0072] The ionic group to be used in the polymer electrolyte
material of the present invention is preferably an atomic group
having negative charge and a group having a proton exchange
capability. As the functional group, a sulfonic acid group, a
sulfoneimide group, a sulfuric acid group, phosphonic acid group, a
phosphoric acid group, and a carboxylic acid group are preferably
used. As used herein, the sulfonic acid group means a group
represented by the following general formula (f1), the sulfoneimide
group means a group represented by the following general formula
(f2) [in the general formula, R means an atomic group], the
sulfuric acid group represents a group represented by the following
general formula (f3), the phosphonic acid group means a group
represented by the following general formula (f4), the phosphoric
acid group means a group represented by the following general
formula (f5) or (f6), and the carboxylic, acid group means a group
represented by the following general formula (f7).
##STR00007##
[0073] Such an ionic group includes the case where the functional
groups (f1) to (f7) are in the form of a salt. Examples of the
cation, which forms the salt, include any metal cation, and
NR.sub.4.sup.+ (R is an any organic group). In case of a metal
cation, its valence is not specifically limited and any metal
cation can be used. Preferable specific examples of the metal ion
include ions of Li, Na, K, Rh, Mg, Ca, Sr, Ti, Al, Fe, Pt, Ru, Ir,
and Pd. Particularly, as the ionic group-containing block copolymer
to be used for the present invention, Na, K, and Li, which are
inexpensive and are easily capable of proton substitution, are
preferably used.
[0074] Two or more kinds of these ionic groups can be contained in
the polymer electrolyte material, and there may be cases where a
combination of these ionic groups is more preferable. This
combination is appropriately determined depending on a structure of
a polymer. Among these ionic groups, it is more preferable to have
at least a sulfonic acid group, a sulfoneimide group, and a
sulfuric acid group in view of high proton conductivity, and it is
most preferable to have at least a sulfonic acid group in view of
resistance to hydrolysis.
[0075] When the polymer electrolyte material of the present
invention has a sulfonic acid group, in view of proton conductivity
and fuel barrier properties, the density of the sulfonic acid group
thereof is preferably from 0.1 to 5.0 mmol/g, more preferably from
0.3 to 3 mmol/g, and most preferably from 0.5 to 2.5 mmol/g.
By setting the density of the sulfonic acid group at 0.1 mmol/g or
more, conductivity, namely, output performance can be maintained,
and by setting the density of the sulfonic acid group at 5 mmol/g
or less, sufficient fuel barrier properties, wet mechanical
strength and long-term durability can be obtained in case of using
as an electrolyte membrane for a fuel cell.
[0076] Particularly, from the viewpoint of balance between proton
conductivity and mechanical strength or long-term durability, more
preferably, the density of the sulfonic acid group of the block
(B1) containing an ionic group is 1.7 to 5.0 mmol/g and the density
of the sulfonic acid group of the block (B2) substantially not
containing an ionic group is 0 to 0.5 mmol/g. From the viewpoint of
balance between proton conductivity and mechanical strength or
long-term durability, the density of the sulfonic acid group of the
block (B1) containing an ionic group is furthermore preferably 3.0
to 4.5 mmol/g, and most preferably 3.5 to 4.0 mmol/g. From the
viewpoint of balance between proton conductivity and mechanical
strength or long-term durability, the density of the sulfonic acid
group of the block (B2) substantially not containing an ionic group
is furthermore preferably 0 to 0.2 mmol/g, and most preferably 0
mmol/g.
[0077] When the density of the sulfonic acid group of the block
(B1) containing an ionic group is less than 1.7 mmol/g or more than
5.0 mmol/g, it is not preferable because conductivity may be
insufficient, or mechanical strength or dimensional stability may
be deficient. Further, when the density of the sulfonic acid group
of the block (B2) substantially not containing an ionic group is
more than 0.5 mmol/g, it is not preferable because a phase
separation structure becomes imprecise and conductivity may be
deficient.
[0078] As used herein, the density of the sulfonic acid group is
the number of mols of sulfonic acid groups introduced per unit
dried weight of the polymer electrolyte material or the polymer
electrolyte membrane, and as the value of the density increases, a
degree of sulfonation increases. The density of the sulfonic acid
group can be measured by elemental analysis or acid-base titration.
Among these methods, it is preferable that the density is
calculated from a S/C ratio using an elemental analysis method
because of ease of the measurement. However, when the polymer
electrolyte membrane contains a sulfur other than the sulfonic acid
group, it is also possible to determine the ion-exchange capacity
by a acid-base titration method. The polymer electrolyte material
and the polymer electrolyte membrane of the present invention, as
described later, include an aspect as a complex comprising an ionic
group-containing block copolymer used for the present invention and
other components, and in this case, the density of the sulfonic
acid group is determined based on the total amount of the
complex.
[0079] The procedure of the acid-base titration is carried out as
follows. The measurement is carried out three or more times and the
obtained values are averaged.
(1) A sample is ground by a mill and screened through a net sieve
#50 and the particles passed through the net sieve is used as a
measuring sample. (2) A sample tube (with a cap) is weighed by
precision balance. (3) About 0.1 g of the sample obtained in (1) is
put in the sample tube and vacuum-dried at 40.degree. C. for 16
hours. (4) The sample tube containing the sample was weighed to
determine a dry weight of the sample. (5) Sodium chloride is
dissolved in an aqueous 30 wt % methanol solution to prepare a
saturated saline. (6) 25 mL of the saturated saline obtained in (5)
is added to the sample, followed by ion exchange while stirring for
24 hours. (7) Hydrochloric acid produced is titrated using an
aqueous 0.02 mol/L sodium hydrate solution. As an indicator, two
drops of a commercially available phenolphthalein solution for
titration (0.1% by volume) are added and it is judged as the end
point when the solution shows a reddish purple color. (8) The
density of the sulfonic acid group is determined by the following
equation.
Density of sulfonic acid group (mmol/g)=[Concentration (mmol/ml) of
aqueous sodium hydroxide solution.times.amount (ml) added
dropwise]/Dry weight (g) of sample
[0080] Examples of a method for introducing the ionic group in
order to obtain these ionic group-containing block copolymers to be
used for the present invention include a method of using a monomer
having an ionic group to polymerize it, and a method of introducing
an ionic group by a polymer reaction.
[0081] In the method of using a monomer having an ionic group to
polymerize it, a monomer having an ionic group in a repeating unit
may be used. Such a method is described in, for example, Journal of
Membrane Science, 197, 2002, p. 231-242. This method can be easily
applied to industries and very preferable since the density of the
sulfonic acid group of a polymer can be easily controlled.
[0082] A example of the method of introducing an ionic group by a
polymer reaction is described as follows. Introduction of a
phosphonic acid group into an aromatic polymer can be performed by
a method described in, for example, Polymer Preprints, Japan, 51,
2002, p. 750. Introduction of a phosphoric group into an aromatic
polymer can be performed, for example, by phosphate esterifying an
aromatic polymer having a hydroxyl group. Introduction of a
carboxylic acid group into an aromatic polymer can be performed,
for example, by oxidizing an aromatic polymer having an alkyl group
or a hydroxyalkyl group. Introduction of a sulfate group into an
aromatic polymer can be performed, for example, by sulfate
esterifying an aromatic polymer having a hydroxyl group. As a
method of sulfonating an aromatic polymer, namely, a method of
introducing a sulfonic acid group, methods described in, for
example, Japanese Unexamined Patent Publication (Kokai) No.
2-16126, and Japanese Unexamined Patent Publication (Kokai) No.
2-208322 are publicly known.
[0083] Specifically, the aromatic polymer can be sulfonated, for
example, by reacting the aromatic polymer with a sulfonating agent
like chlorosulfonic acid in a solvent such as chloroform, or by
reacting the aromatic polymer in concentrated sulfuric acid or
fuming sulfuric acid. The sulfonating agent is not particularly
limited as long as it is an agent to sulfonate the aromatic
polymer, and sulfur trioxide or the like can also be used in
addition to the above sulfonating agent. When the aromatic polymer
is sulfonated by this method, a degree of sulfonation can be easily
controlled by an amount of the sulfonating agent to be used, a
reaction temperature and a reaction time. Introduction of a
sulfonimide group into the aromatic polymer can be performed, for
example, by a method of reacting a sulfonic acid group with a
sulfonamide group.
[0084] Next, a main chain structure of the block (B1) containing an
ionic group to be used in the polymer electrolyte material of the
present invention will be described specifically.
[0085] First, the method for synthesizing an aromatic polyether
type polymer to be used for the present invention is not
specifically limited as long as it is a method capable of
substantially increasing a molecular weight. For example, the
polymer can be synthesized by the aromatic nucleophilic
substitution reaction of an aromatic active dihalide compound and a
diphenolic compound, or the aromatic nucleophilic substitution
reaction of a halogenated aromatic phenol compound. The aromatic
active dihalide compound is not specifically limited as long as the
molecular weight can be increased by the aromatic nucleophilic
substitution reaction with the diphenolic compound.
[0086] It is preferred to use a monomer of a compound obtained by
introducing an ionic group into an aromatic active dihalide
compound as an aromatic active dihalide compound to be used for the
block (B1) containing an ionic group from the viewpoint that the
amount of the ionic group can be accurately controlled. Specific
examples of the monomer having a sulfonic acid group as the ionic
group include, but are not limited to,
3,3'-disulfonate-4,4'-dichlorodiphenylsulfone,
3,3'-disulfonate-4,4'-difluorodiphenylsulfone,
3,3'-disulfonate-4,4'-dichlorodiphenylketone,
3,3'-disulfonate-4,4'-difluorodiphenylketone,
3,3'-disulfonate-4,4'-dichlorodiphenylphenylphosphine oxide, and
3,3'-disulfonate-4,4'-difluorodiphenylphenylphosphine oxide.
[0087] From the viewpoint of proton conductivity and resistance to
hydrolysis, as the ionic group, a sulfonic acid group is most
preferable, but the monomer having an ionic group used for the
present invention may have another ionic group. Among these
monomers, 3,3'-disulfonate-4,4'-dichlorodiphenylketone and
3,3'-disulfonate-4,4'-difluorodiphenylketone are more preferable in
view of resistance to hot methanol and inhibitory effect of fuel
crossover, and 3,3'-disulfonate-4,4'-difluorodiphenylketone is most
preferably in view of polymerization activity.
[0088] A polymer electrolyte material synthesized by use of
3,3'-disulfonate-4,4'-dichlorodiphenylketone and
3,3'-disulfonate-4,4'-difluorodiphenylketone as a monomer having an
ionic group further contains a constituent unit represented by the
following general formula (p1) and is preferably employed. This
aromatic polyether-type polymer is more preferably used because it
becomes a component which is more excellent in resistance to hot
methanol than a sulfonic acid group in addition to a characteristic
of high crystallinity of a ketone group, and becomes a component
useful for a material excellent in dimensional stability,
mechanical strength and physical durability at elevated temperature
in methanol water used as a fuel. In case of the polymerization, a
sulfonic acid group is preferably combined with a monovalent cation
species to form a salt. Examples of the monovalent cation species
include sodium, potassium or other metal species, and various
amines cation species, and it is not limited to these. These
aromatic active dihalide compounds can be used alone or in
combination.
##STR00008##
[0089] In the general formula (p1), M.sup.1 and M.sup.2 represent
hydrogen, a metal cation, or an ammonium cation, and a1 and a2
represent an integer of 1 to 4; and the constituent unit
represented by the general formula (p1) may be optionally
substituted.
[0090] Further, with respect to the aromatic active dihalide
compound, it is also possible to control the density of an ionic
group by copolymerizing a compound having an ionic group with a
compound not having an ionic group. However, it is more preferable
for the block (B1) having an ionic group of the present invention
that an aromatic active dihalide compound not having an ionic group
is not copolymerized from the viewpoint of securing continuity of a
proton conduction path.
[0091] Preferred specific examples of the aromatic active dihalide
compound not having an ionic group include
4,4'-dichlorodiphenylsulfone, 4,4'-difluorodiphenylsulfone,
4,4'-dichlorodiphenylketone, 4,4'-difluorodiphenylketone,
4,4'-dichlorodiphenylphenylphosphine oxide,
4,4'-difluorodiphenylphenylphosphine oxide,
2,6-dichlorobenzonitrile, and 2,6-difluorobenzonitrile. Among these
dihalide compounds, 4,4'-dichlorodiphenylketone and
4,4'-difluorodiphenylketone are more preferable from the viewpoint
of imparting crystallinity, mechanical strength and physical
durability, resistance to hot methanol and inhibitory effect of
fuel crossover, and 4,4'-difluorodiphenylketone are most preferable
from the viewpoint of a polymerization activity. These aromatic
active dihalide compounds can be used alone or in combination.
[0092] A polymer electrolyte material synthesized by use of
4,4'-dichlorodiphenylketone and 4,4'-difluorodiphenylketone as an
aromatic active dihalide compound further contains a constituent
unit represented by the following general formula (p2) and is
preferably employed. This constituent unit is preferably used
because it becomes a component to impart an intermolecular cohesive
force and crystallinity, and becomes a component useful for a
material excellent in dimensional stability, mechanical strength
and physical durability at elevated temperature in methanol water
used as a fuel and becomes a component useful for a material
excellent in mechanical strength and durability in a polymer
electrolyte fuel cell using hydrogen as a fuel.
##STR00009##
[0093] the constituent unit represented by the general formula (p2)
may be optionally substituted, but does not contain the ionic
group.
[0094] Examples of the halogenated aromatic phenol compound is not
also particularly limited, and include
4-hydroxy-4'-chlorobenzophenone, 4-hydroxy-4'-fluorobenzophenone,
4-hydroxy-4'-chlorodiphenylsulfone,
4-hydroxy-4'-fluorodiphenylsulfone,
4-(4'-hydroxybiphenyl)(4-chlorophenyl)sulfone,
4-(4'-hydroxybiphenyl) (4-fluorophenyl)sulfone,
4-(4'-hydroxybiphenyl) (4-chlorophenyl) ketone, and
4-(4'-hydroxybiphenyl)(4-fluorophenyl)ketone. These halogenated
aromatic phenol compounds can be used alone or in combination. In
the reaction of an activated dihalogenated aromatic compound and an
aromatic dihydroxy compound, an aromatic polyether-type compound
may be synthesized by reacting together with a halogenated aromatic
phenol compound.
[0095] Examples of the block (B1) containing an ionic group to be
used for the present invention is particularly preferably an
aromatic polyetherketone-type copolymer comprising constituent
units represented by the following general formulas (P1) and (P2)
containing constituent units represented by the above general
formulas (p1) and (p2):
##STR00010##
[0096] In the general formulas (P1) and (P2), A represents a
divalent organic group containing an aromatic ring and M.sup.1 and
M.sup.2 represent hydrogen, a metal cation, or an ammonium cation;
and "A" in formula P2 may represent two or more kinds of
groups.
[0097] By changing the composition ratio of constituent units
represented by the general formulas (P1) and (P2), it is possible
to control the density of a sulfonic acid group, but an amount of
P1 to be introduced based on a total molar amount of P1 and P2 is
preferably 50 mol % or more, more preferably 75 mol % or more, and
most preferably 90 mol % or more. When the amount of P1 to be
introduced is less than 50 mol %, construction of a proton
conduction path becomes inadequate and it is not preferable.
[0098] Herein, as the divalent organic group A containing an
aromatic ring in the general formulas (P1) and (P2), various
diphenolic compounds, which can be used for polymerization of an
aromatic polyether-type polymer by the aromatic nucleophilic
substitution reaction, can be employed, and it is not particularly
limited. It is also possible to use a compound obtained by
introducing a sulfonic acid group into these aromatic dihydroxy
compounds as a monomer.
[0099] Preferable specific examples of the divalent organic group A
containing an aromatic ring include groups represented by the
following general formulas (X-1) to (X-29):
##STR00011##
[0100] Wherein the group represented by the formulas (X-1) to (X-7)
may be optionally substituted.
##STR00012## ##STR00013##
[0101] Wherein n and m represent an integer of 1 or more, and Rp
represents an optional organic group.
##STR00014## ##STR00015##
[0102] These may have a substituent and an ionic group. A divalent
organic group A having an aromatic ring in the side chain is also
preferable example. These can be used in combination, if
necessary.
[0103] Among these groups, from the viewpoint of crystallinity,
dimensional stability and mechanical strength, groups represented
by the general formulas (X-1) to (X-7) are more preferable, groups
represented by the general formulas (X-1) to (X-5) are furthermore
preferable, and a group represented by the general formula (X-2) or
(X-3) is most preferable.
[0104] The polymer electrolyte material of the present invention is
suitably used for the polymer electrolyte form article. In the
present invention, the polymer electrolyte form article means a
form article containing the polymer electrolyte material of the
present invention.
[0105] The polymer electrolyte form article in the present
invention can take various forms such as membrane (including film
and film-shaped article), plate-like, fiber-like, hollow
fiber-like, particle-like, bulk-like, microporous-like, coatings,
foams and the like according to the purposes. It can be adapted to
wide use because it can improve design flexibility of a polymer and
various characteristics such as mechanical properties and
resistance to a solvent. Particularly, the polymer electrolyte form
article is preferable in a membrane form.
[0106] When the polymer electrolyte material of the present
invention is used as fuel cell, the material is preferably used for
the polymer electrolyte membrane and the electrocatalyst layer.
Particularly, the material is preferably used for the polymer
electrolyte membrane. The reason for this is that in case of using
the material as fuel cell, the material is usually used as the
polymer electrolyte membrane or a binder of the electrocatalyst
layer in a membrane state.
[0107] The polymer electrolyte membrane of the present invention
can be applied to various purposes. For example, the polymer
electrolyte membrane can be applied to medical purposes such as
extracorporeal circulation column and artificial skin, purposes for
filtration, purposes for ion exchange resin such as
chlorine-tolerant reverse osmosis membrane, purposes for various
structural materials, electrochemical purposes, humidifying
membranes, antifogging membranes, antistatic membranes, membranes
for solar cell, and gas barrier materials. Moreover, the polymer
electrolyte membrane is suited for artificial muscle and actuator
materials. Among these purposes, the polymer electrolyte material
or the polymer electrolyte form article can be more preferably used
for various electrochemical purposes. The electrochemical purposes
include, for example, a fuel cell, a redox flow cell, a water
electrolysis apparatus, and a chloroalkali electrolysis apparatus.
Among these purposes, a fuel cell is most preferable.
[0108] Next, a production method for obtaining the polymer
electrolyte form article of the present invention is described as
follows.
[0109] Conventional ionic group-containing block copolymers were
all amorphous polymers because they have a bulky ionic group such
as a sulfonic acid group and due to the synthetic constraint that
solubility in a solvent is required in polymerization or in forming
a membrane. Since these amorphous ionic group-containing block
copolymer is low in a cohesive force of a polymer chain, they are
deficient in toughness or stability of a polymer higher-order
structure and could not achieve sufficient mechanical strength and
physical durability when being formed into the form of membrane.
Further, since a thermal decomposition temperature of the ionic
group is lower than a melting point, melt processing is difficult
and solution casting method is usually employed, and therefore an
uniform and tough membrane could not be obtained in a polymer
containing a crystal insoluble in a solvent.
[0110] The polymer electrolyte form article of the present
invention is a polymer electrolyte material composed of an ionic
group-containing block copolymer having a block (B1) containing an
ionic group and a block (B2) substantially not containing an ionic
group, in which a ratio W1/W2 of weight W1 of the B1 to weight W2
of the B2 is 0.2 or more and 5 or less, and it is obtained by
forming a polymer electrolyte material in which protecting groups
are introduced into at least a block (B2), and then deprotecting at
least a portion of the protective groups contained in the form
article.
[0111] When the block (B2) substantially not containing an ionic
group is crystalline, since processability tends to become poor due
to crystallization of a polymer by domain formation compare with
the case where a random copolymer is used, it is preferred to
improve the processability by introducing protective groups into at
least the block (B2). Also with respect to the block (B1)
containing an ionic group, it is preferred to introduce protective
groups when the processability becomes poor.
[0112] Specific examples of the protective group to be used for the
present invention include a protective group used commonly in
organic synthesis, and the protective group is a substituent
temporarily introduced on the assumption that it is removed in the
following stages, which protects a functional group having high
reactivity and makes the functional group inert for a subsequent
reaction, and can deprotect the functional group after the reaction
to return to an original functional group. That is, the protective
group is a group paired with a functional group to be protected,
and examples thereof include the case where a t-butyl group is used
as a protective group of a hydroxyl group, but the case where a
t-butyl group is introduced into an alkylene chain is not referred
to as a protective group. The reaction for introducing a protective
group is referred to as a protection (reaction), while the reaction
for removing a protective group is referred to as a deprotection
(reaction).
[0113] Such a protection reaction is described in detail, for
example, in Theodora W. Greene, "Protective Groups in Organic
Synthesis", U.S.A., John Wiley & Sons, Inc, 1981, and the
protection reaction can be preferably used. The protective group
can be appropriately selected taking account of reactivity and
yield of the protection reaction and deprotection reaction,
stability of protective group-containing state, and production
cost. The stage, at which the protective group is introduced in the
polymerization reaction, may be a monomer, an oligomer or a
polymer, and can be appropriately selected.
[0114] Specific examples of the protection reaction include a
method for protecting/deprotecting a ketone group with a ketal
group, and a method for protecting/deprotecting a ketone group with
a heteroatom analog of a ketone group, for example, thioketal.
These methods are described in Chapter 4 of aforementioned
"Protective Groups in Organic Synthesis". Examples thereof further
include a method for protection/deprotection between sulfonic acid
and a soluble ester derivative, and a protection method of
introducing a t-butyl group into an aromatic ring and a
deprotection method through de-t-butylation with an acid. However,
the protection/deprotection is not limited to these, and any
protection/deprotection can be preferably used as long as a group
is a protective group. In view of improving solubility of the
polymer in a common solvent, it is preferred to use, as the
protective group, an aliphatic group having large steric hindrance,
particularly an aliphatic group containing a cyclic moiety.
[0115] The position of the functional group, at which the
protective group is introduced, is preferably a main chain of the
polymer. In the polymer electrolyte material of the present
invention, since the protective group is introduced into a polymer
having good packing for the purpose of improving processability,
sometimes an adequate effect of the present invention cannot be
achieved even though the protective groups are introduced into the
side chain of the polymer. As used herein, the functional group,
which is present in the main chain of the polymer, is defined as a
functional group in which a polymer chain is cleaved when the
functional group is eliminated. For example, this means that if a
ketone group of aromatic polyetherketone is eliminated, benzene
rings are isolated from one another.
[0116] More preferable protection reaction are a method for
protecting/deprotecting a ketone group with a ketal group, and a
method for protecting/deprotecting a ketone group with a heteroatom
analog of a ketone group, for example, thioketal in view of
reactivity and stability. In the polymer electrolyte material and
the polymer electrolyte membrane the present invention, a
constituent unit containing a protective group is more preferably a
constituent unit containing at least one selected from the
following general formulas (P3) and (P4).
##STR00016##
[0117] In the formulas (P3) and (P4), Ar.sub.1 to Ar.sub.4
represent an optional divalent arylene group, R.sub.1 and R.sub.2
represent a least one group selected from H and an alkyl group,
R.sub.3 represents an optional alkylene group, E represents O or S,
and each group may represent two or more kinds of groups; and
groups represented by the formulas (P3) and (P4) may be optionally
substituted.
[0118] Particularly, E is O in the above general formulas (P3) and
(P4) in view of smell, reactivity and stability of a compound, that
is, a method for protecting/deprotecting a ketone group with a
ketal group is most preferable.
[0119] R.sub.1 and R.sub.2 in the general formula (P3) are more
preferably an alkyl group in view of stability, furthermore
preferably an alkyl group having 1 to 6 carbon atoms, and most
preferably an alkyl group having 1 to 3 carbon atoms. Further,
R.sub.3 in the general formula (P4) is more preferably an alkylene
group having 1 to 7 carbon atoms in view of stability, and most
preferably an alkylene group having 1 to 4 carbon atoms. Specific
examples of R.sub.3 include, but are not limited to,
--CH.sub.2CH.sub.2--, --CH(CH.sub.3) CH.sub.2--, --CH(CH.sub.3)
CH(CH.sub.3)--, --C(CH.sub.3).sub.2CH.sub.2--,
--C(CH.sub.3).sub.2CH(CH.sub.3)--,
--C(CH.sub.3)O(CH.sub.3).sub.2--, --CH.sub.2CH.sub.2CH.sub.2--, and
--CH.sub.2C(CH.sub.3).sub.2CH.sub.2--.
[0120] The constituent unit having at least the general formula
(P4) of the above constituent unit having the general formula (P3)
or (P4) is preferably used from the viewpoint of stability such as
resistance to hydrolysis. Furthermore, R.sub.3 in the general
formula (P4) is preferably an alkylene group having 1 to 7 carbon
atoms, that is, a group represented by C.sub.n1H.sub.2n1 (n1 is an
integer of 1 to 7), and most preferably at least one selected from
--CH.sub.2CH.sub.2--, --CH(CH.sub.3)CH.sub.2--, or
--CH.sub.2CH.sub.2CH.sub.2-- in view of stability and ease of
synthesis.
[0121] An organic group as Ar.sub.1 to Ar.sub.4 in the general
formulas (P3) and (P4) is preferably a phenylene group, a
naphthylene group, or a biphenyl group. These organic groups may be
optionally substituted. As the aromatic polyether-type polymer of
the present invention, in view of solubility and ease of
availability, both Ar.sub.3 and Ar.sub.4 in the above general
formula (24) are more preferably a phenylene group, and both
Ar.sub.3 and Ar.sub.4 are most preferably a p-phenylene group,
[0122] In the present invention, the method of protecting a ketone
group with ketal includes a method of reacting a precursor compound
having a ketone group with a monofunctional and/or difunctional
alcohol in the presence of an acid catalyst. For example, it can be
produced by reacting 4,4'-dihydroxybenzophenone which is a ketone
precursor with monofunctional and/or difunctional alcohol in the
presence of an acid catalyst such as hydrogen bromide in a solvent
such as aliphatic or aromatic hydrocarbons. The alcohol is
aliphatic alcohol having 1 to 20 carbon atoms. An improved method
for producing a ketal monomer to be used for the present invention
comprises reacting 4,4'-dihydroxybenzophenone which is a ketone
precursor with difunctional alcohol in the presence of alkyl ortho
ester and a solid catalyst.
[0123] In the present invention, a method in which at least a part
of a ketone group protected with ketal is deprotected to form a
ketone group is not particularly limited. The above deprotection
reaction can be performed in the presence of water and acid under a
nonuniform or uniform condition, but a method, in which an acid
treatment is performed after forming a membrane, is more preferable
from the viewpoint of mechanical strength, physical durability and
resistance to solvents. Specifically, the formed membrane can be
deprotected by immersing it in a hydrochloric acid aqueous solution
or a sulfuric acid aqueous solution, and a concentration of acid or
a temperature of the aqueous solution can be appropriately
selected.
[0124] A weight ratio of the required acid aqueous solution to the
polymer is preferably 1 to 100 times, but a larger amount of water
can also be used. An acid catalyst is preferably used in a
concentration of 0.1 to 50% by weight of water being present.
Examples of preferable acid catalyst include a strong mineral acid
such as hydrochloric acid, nitric acid, fluorosulfonic acid, or
sulfuric acid, and a strong organic acid such as p-toluenesulfonic
acid or trifluoromethanesulfonic acid. According to the membrane
thickness of a polymer, the acid catalyst, an amount of excess
water and a reaction pressure can be appropriately selected.
[0125] In case of a membrane having a thickness of 50 .mu.m, it is
possible to deprotect almost all of protective groups by immersing
the membrane in an aqueous 6N hydrochloric acid solution and
heating at 95.degree. C. for 1 to 48 hours. It is also possible to
deprotect almost all of protective groups by immersing the membrane
in an aqueous 1N hydrochloric acid solution at 25.degree. C. for 24
hours. However, the conditions of deprotection are not limited to
these conditions and it is possible to deprotect with an acidic gas
or an organic acid, or a heat treatment.
[0126] Also when the aromatic polyether-type polymer includes a
bond form such as a direct bond other than an ether bond, a
position of the protective group introduced is more preferably a
portion of the aromatic ether-type polymer from the viewpoint of
improving processability.
[0127] Specifically, the aromatic polyether-type polymer comprising
constituent unit represented by the general formula (P3) or (P4)
can be synthesized by using, as a diphenolic compound, a compound
represented by the following general formulas (P3-1) and (P4-1),
followed by the aromatic nucleophilic substitution reaction of the
compound with an aromatic active dihalide compound. The constituent
units represented by the general formulas (P3) and (P4) may be
derived from either the diphenolic compound or the aromatic active
dihalide compound, but are more preferably derived from the
diphenolic compound taking account of reactivity of the
monomer.
##STR00017##
[0128] In the general formulas (P3-1) and (P4-1), Ar.sub.1 to
Ar.sub.4 represent an optional divalent arylene group, R.sub.1 and
R.sub.2 represent at least one kind of a group selected from H and
an alkyl group, R.sub.3 represents an optional alkylene group, and
E represents O or S; and the groups represented by the general
formulas (P3-1) and (P4-1) may be optionally substituted.
[0129] Specific examples of particularly preferable diphenolic
compound to be used for the present invention include compounds
represented by the following general formulas (r1) to (r10), and
derivatives derived from these diphenolic compounds.
##STR00018## ##STR00019##
[0130] Among these diphenolic compounds, compounds represented by
the general formulas (r4) to (r10) are more preferable in view of
stability, more preferably compounds represented by the general
formulas (r4), (r5) and (r9), and most preferably a compound
represented by the general formula (r4).
[0131] In the polymer electrolyte membrane of the present
invention, the proton conductivity per unit area and per unit
thickness is preferably 10 mS/cm or more, more preferably 20 mS/cm
or more, and still more preferably 50 mS/cm or more. A sample of a
membrane was immersed in pure water at 25.degree. C. for 24 and
taken out in an atmosphere at 25.degree. C. and a relative humidity
of 50 to 80%, and then proton conductivity was measured as quick as
possible using a potentiostatic AC impedance method.
[0132] When proton conductivity per unit area and per unit
thickness is 10 mS/cm or more, sufficient proton conductivity,
namely, sufficient cell power can be obtained when the membrane is
used as a polymer electrolyte membrane for fuel cell. The higher
proton conductivity, the better. However, when proton conductivity
is too high, the membrane having high proton conductivity is likely
to be dissolved or collapsed by the fuel such as methanol water and
also fuel crossover may increase. Therefore, actual upper limit is
5,000 mS/cm.
[0133] In the polymer electrolyte membrane of the present
invention, methanol crossover per unit area and per unit thickness
with respect to an aqueous 1 mol % methanol solution under the
condition of 20.degree. C. is 100 nmol/min/cm or less. Methanol
crossover is more preferably 50 nmol/min/cm or less, and still more
preferably 10 nm/min/cm or less. The reason is as follows. That is,
in the fuel using the membrane of the polymer electrolyte material,
it is desired that fuel crossover is small so as to maintain high
concentration of the fuel in view of obtaining high power and high
energy capacity in the region of high concentration of the fuel. On
the other hand, In view of ensuring proton conductivity, fuel
crossover is more preferably 0.01 nmol/min/cm or more.
[0134] The proton conductivity per unit area, measured under the
above conditions, is preferably 3 S/cm.sup.2 or more, more
preferably 5 S/cm.sup.2 or more, and furthermore preferably 7
S/cm.sup.2 or more. By adjusting proton conductivity per unit area
to 0.3 S/cm.sup.2 or more, a high-power fuel cell can be obtained.
On the other hand, since the membrane having high proton
conductivity is likely to be dissolved or collapsed by the fuel
such as methanol water and its fuel crossover tends to increase.
Therefore, actual upper limit of the proton conductivity is 500
S/cm.sup.2.
[0135] In the polymer electrolyte membrane of the present
invention, methanol crossover per unit area with respect to an
aqueous 1 mol % methanol solution under the condition of 20.degree.
C. is preferably 5 .mu.mol/min/cm.sup.2 or less. The reason is as
follows. That is, in the fuel using the membrane of the polymer
electrolyte material, it is desired the fuel crossover is small so
as to maintain high concentration of the fuel in view of obtaining
high power and high energy capacity in the region of high
concentration of the fuel. From such a view point, it is more
preferable that the methanol crossover is 2 .mu.mol/min/cm.sup.2 or
less, and most preferable 1 .mu.mol/min/cm.sup.2 or less. From the
view point of ensuring the proton conductivity, 0.01
.mu.mol/min/cm.sup.2 or more is preferable.
[0136] The polymer electrolyte material of the present invention,
in case of using it in DMFC, preferably achieves low methanol
crossover and high proton conductivity as described above at the
same time. The reason for this is that to achieve one of low
methanol crossover and high proton conductivity is easy even in the
prior art, but compatibility between high power and high energy
capacity becomes possible by achieving both low methanol crossover
and high proton conductivity.
[0137] In the polymer electrolyte material and the polymer
electrolyte membrane of the present invention, in view of fuel
barrier properties and an increase of energy capacity using a high
concentration fuel, it is more preferable that the polymer
electrolyte material is excellent in resistance to solvents, that
is, weight loss of the polymer electrolyte material after immersing
in N-methyl pyrrolidone at 100.degree. C. for 2 hours is 70% by
weight or less. As the liquid fuel, alcohols such as methanol are
often used. In the present invention, resistance to solvents is
evaluated using N-methylpyrrolidone having excellent solubility
regardless of the kind of the polymer. Weight loss is more
preferably 50% by weight or less, and most preferably 30% by weight
or less. Weight loss of more than 70% by weight is not preferred
because mechanical strength and physical durability are
insufficient because of insufficient fuel barrier properties and
insufficient crystallinity. In case of using for DMFC in which an
aqueous high-temperature and high-concentration methanol solution
is used as the fuel, the membrane solves or swells drastically.
Moreover, it becomes difficult to directly apply a catalyst paste
on the polymer electrolyte membrane to produce a membrane electrode
assembly, and thus not only production cost increases but also
interface resistance with the catalyst layer increases and
sufficient power generation characteristics may not be
obtained.
[0138] In the present invention, to be excellent in resistance to
hot water and resistance to hot methanol means that changes in
dimensions (swelling) in hot water and hot methanol, respectively,
are small. When this dimensional change is large, it is not
preferable because the membrane breaks or the membrane is peeled
off from an electrocatalyst layer due to swelling to cause an
increase in resistivity during using as a polymer electrolyte
membrane. Further, when it is inferior in resistance to hot water
and resistance to hot methanol, it is not preferable because in
case of using a high concentration fuel such as a high
concentration methanol aqueous solution, the polymer electrolyte
membrane or a binder of a catalyst layer is dissolved in the fuel.
These characteristics of resistance to hot water and resistance to
hot methanol are both important characteristics required to an
electrolyte polymer used in a polymer electrolyte fuel cell.
[0139] In the polymerization by the aromatic nucleophilic
substitution reaction, which is carried out in order to obtain an
aromatic polyether-type polymer to be used in the present
invention, a polymer can be obtained by reacting a mixture of the
above monomers in the presence of a basic compound. The
polymerization can be carried out at a temperature within a range
from 0 to 350.degree. C., but the temperature is preferably 50 to
250.degree. C. When the temperature is lower than 0.degree. C., the
reaction may not tend to proceed adequately, and when the
temperature is higher than 350.degree. C., decomposition of the
polymer may tend to be initiated. The reaction can be carried out
in the absence of a solvent, but is preferably carried out in a
solvent. Examples of usable solvent include aprotic polar solvents
such as N,N-dimethylacetamide, N,N-dimethylformamide,
N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane,
1,3-dimethyl-2-imidazolidinone, and hexamethylphosphonetriamide,
but the usable solvent is not limited to these solvent and may be
any solvent which can be used as a stable solvent in the aromatic
nucleophilic substitution reaction. These organic solvents can be
used alone or in combination.
[0140] Examples of the basic compound include sodium hydroxide,
potassium hydroxide, sodium carbonate, potassium carbonate, sodium
hydrogen carbonate, and potassium hydrogen carbonate, but the basic
compound can be used without being limited to these compounds as
long as it can convert aromatic diols into an active phenoxide
structure.
[0141] In the aromatic nucleophilic substitution reaction, water is
sometimes produced as by-product. In this case, water can also be
removed out of the system in the form of an azeotrope by making
toluene or the like coexist irrespective of a polymerization
catalyst in the reaction system. As the method of removing water
out of the system, an absorbent such as molecular sieve can be
used.
[0142] An azeotropic agent used for removing reaction water or
water introduced during the reaction is generally any inert
compound which does not substantially interfere with
polymerization, is azeotropically distilled with water and boiled
at a temperature of about 25 to about 250.degree. C. Common
azeotropic agent is such as benzene, toluene, xylene,
chlorobenzene, methylene chloride, dichlorobenzene, and
trichlorobenzene. Naturally, it is useful to select such azeotropic
agent that its boiling point is lower than that of a dipolar
solvent used. Generally, the azeotropic agent is used, but it is
not always necessary when a high reaction temperature, for example,
a temperature of 200.degree. C. or higher, is employed,
particularly when an inert gas is continuously flowed over a
reaction mixture. Generally, the reaction is desirably performed in
a state of oxygen-free in an inert atmosphere.
[0143] When the aromatic nucleophilic substitution reaction is
carried out in a solvent, the monomer is preferably charged so as
to adjust the concentration of the resulting polymer within a range
from 5 to 50% by weight. When the concentration is less than 5% by
weight, the polymerization degree may hardly increase. On the other
hand, when the concentration is more than 50% by weight, viscosity
of the reaction system increases and it may become difficult to
subject the reaction product to a post-treatment.
[0144] After the completion of the polymerization reaction, the
reaction solution is vaporized to remove the solvent and the
residual substance is optionally washed to obtain a desired
polymer. Also, the reaction solution is poured into a solvent
having low solubility with a polymer and high solubility with an
inorganic salt produced as by-product, thereby to remove the
inorganic salt and to precipitate a polymer as a solid, and the
precipitate is collected by filtration to obtain a polymer. The
recovered polymer is optionally washed with water, an alcohol or
other solvents, and then dried. When a desired molecular weight is
obtained, a halide end group or a phenoxide end group can be
optionally reacted by introducing a phenoxide or a halide end group
sealing agent to produce a stable end group.
[0145] A molecular weight of the ionic group-containing polymer of
the present invention thus obtained is 1000 to 5000000, and
preferably 10000 to 500000 in terms of a polystyrene equivalent
weight average molecular weight. When the molecular weight is less
than 1000, cracks may be produced in the formed membrane and either
of mechanical strength, physical durability and resistance to
solvents may be insufficient. On the other hand, when the molecular
weight is more than 500000, there are problems that solubility
becomes inadequate, viscosity of a solution is high and
processability becomes poor.
[0146] In addition, a chemical structure of the polymer electrolyte
material of the present invention can be identified by S=0
absorption at 1,030 to 1,045 cm.sup.-1 and 1,160 to 1,190
cm.sup.-1, C--O--C absorption at 1,130 to 1,250 cm.sup.-1 and
C.dbd.O absorption at 1,640 to 1,660 cm.sup.-1 through infrared
absorption spectrum, and the composition ratio thereof can be
determined by acid-base titration or elemental analysis of sulfonic
acid groups. Also, the structure can be confirmed by a peak of an
aromatic proton at 6.8 to 8.0 ppm through a nuclear magnetic
resonance spectrum (.sup.1H-NMR). Also, the position and
arrangement of a sulfonic acid group can be confirmed through
solution .sup.13C-NMR and solid-state .sup.13C-NMR.
[0147] Next, a specific method of the ionic group-containing block
copolymer comprising a block (B1) containing an ionic group and a
block (B2) substantially not containing an ionic group is
exemplified. However, the present invention is not limited
these.
[0148] Examples of the ionic group-containing block copolymer to be
used for the present invention include a block copolymer formed by
reacting an ionic group-containing monomer and a monomer not
containing an ionic group separately to form an ionic
group-containing block represented by the following formula (H3-2),
and/or a block not containing an ionic group represented by the
following formula (H3-1), and then random copolymerizing these
blocks. Further, examples of the ionic group-containing block
copolymer include a block copolymer formed by reacting an ionic
group-containing monomer and a polymer not containing an ionic
group represented by the following formula (H3-1), a block
copolymer formed by reacting a monomer not containing an ionic
group and an ionic group-containing polymer represented by the
following formula (H3-2), and a block copolymer by spontaneously
forming a block from only a monomer taking advantage of the
difference in reactivity between monomers. Furthermore, it is also
possible that after obtaining a block copolymer having aromatic
rings with different reactivities of a sulfonation reaction,
namely, with different electron densities, an ionic group is
selectively introduced into only a highly reactive site.
[0149] However, in the above method of forming an ionic
group-containing block represented by the following formula (H3-2),
and/or a block not containing an ionic group represented by the
following formula (H3-1), and then random copolymerizing these
blocks, control of a block length was difficult since the
reactivity of the ionic group-containing block is significantly
different from that of the block not containing an ionic group
because of steric hindrance.
[0150] Accordingly, in the present invention, a method of forming
an ionic group-containing block represented by the following
formula (H3-4), and/or a block not containing an ionic group
represented by the following formula (H3-3), and then
cross-copolymerizing these blocks can be more preferably used.
According to the above description, it becomes possible to
synthesize a block copolymer having a required block length.
[0151] Here, in the following formulas (H3-3) and (H3-4), an ionic
group-containing block of F terminal and a block not containing an
ionic group of OK terminal are shown, but these may be
reversed.
##STR00020##
[0152] In the above formulas (H3-1) to (H3-4), a halogen atom is
represented by E, and an alkaline metal is represented by Na and K,
but they are not limited to these and others can be used. The above
formulas are inserted for the purpose of helping the understanding
of readers, and do not always express precisely a chemical
structure, exact composition, arrangement, a position of a sulfonic
acid, quantity and a molecular weight of polymerizing components,
of a polymer, and the present invention is not limited to these
chemical structural formulas.
[0153] Furthermore, in the aforementioned formulas (H3-1) to
(H3-4), a ketal group is introduced into any block as a protective
group. However, in the present invention, the protective group may
be introduced into a component having high crystallinity and low
solubility and the aforementioned formulas (H3-2) and (H3-4) do not
necessarily require the protective group, and it is preferable that
there is no the protective group from the viewpoint of durability
and dimensional stability.
[0154] Further, with respect to a block shown in the formula
(H3-3), an oligomer with a controlled molecular weight can be
synthesized by reacting a bisphenol component and an aromatic
dihalide component in proportions of N.sub.3:(N.sub.3+1). The same
holds true with regard to the formula (H3-4).
[0155] The method of forming the polymer electrolyte material of
the present invention into a polymer electrolyte membrane is not
particularly limited, and a method of forming a membrane from a
solution state or a method of forming a membrane from a molten
state can be used in a stage of having a protective group such as
ketal.
[0156] In the former, for example, the polymer electrolyte material
is dissolved in a solvent such as N-methyl-2-pyrrolidone and the
solution is applied and spread over a glass plate, and then the
solvent is removed to form a membrane.
[0157] As the solvent be used to form a membrane, any can be used
as long as a polymer electrolyte material can be dissolved in it
and it can be removed, and an aprotic polar solvent such as
N,N-dimethylacetamide, N,N-dimethylformamide,
N-methyl-2-pyrrolidone, dimethyl sulfoxide, sulfolane,
1,3-dimethyl-2-imidazolidinone, and hexamethylphosphonetriamide; an
ester-type solvent such as .gamma.-butyrolactone or butyl acetate;
a carbonate-type solvent such as ethylene carbonate or propylene
carbonate; an alkylene glycol monoalkyl ether such as ethylene
glycol monomethyl ether, ethylene glycol monoethyl ether, propylene
glycol monomethyl ether, and propylene glycol monoethyl ether; an
alcohol-type solvent such as isopropanol; water and a mixture
thereof are preferably used, and an aprotic polar solvent is
preferable because of its high solubility.
[0158] Further, in the present invention, when the block copolymer
is used, selection of the solvent is important for a phase
separation structure, and a method of mixing an aprotic polar
solvent and a less polar solvent to use is preferable.
[0159] It is preferred to subject a polymer solution prepared so as
to have a required solid content to filtration under pressured or
not to remove impurities (or unknown substances) contained in the
polymer electrolyte solution, in order to obtain a tough membrane.
A filter medium used herein is not specifically limited and is
preferably a glass filter or a metal filter. A minimum pore size of
the filter, through which the polymer solution passes in the
filtration, is preferably 1 .mu.m or less. If the polymer is not
subjected to filtration, it is not preferable since it allows
impurities matters to mix in to cause break of a membrane or
deterioration of durability.
[0160] Then, in the resulting polymer electrolyte membrane, it is
preferred to heat treatment at least a part of the ionic group in a
state of metal salt. If the polymer electrolyte material to be used
is a polymer which is polymerized in a state of metal salt in
polymerization, it is preferably formed into a membrane and heat
treated as it is. Metals in metal salts may be those capable of
forming salts with sulfonic acid, but it is preferably Li, Na, K,
Rb, Cs, Mg, Ca, Sr, Ba, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, and
W, and among these metals, Li, Na, K, Ca, Sr, and Ba are more
preferable, and Li, Na, K are furthermore preferable.
[0161] The temperature of the heat treatment is preferably from 150
to 550.degree. C., more preferably from 160 to 400.degree. C., and
particularly preferably from 180 to 350.degree. C. The time for
heat treatment is preferably from 10 seconds to 12 hours, more
preferably from 30 seconds to 6 hours, and particularly preferably
from one minute to one hour. When the temperature of the heat
treatment is too low, an effect of inhibiting fuel crossover,
elastic modulus and strength at break are insufficient. On the
other hand, when the temperature of the heat treatment is too high,
a membrane material tends to deteriorate. When a time of a heat
treatment is less than 10 seconds, an effect of heat treatment is
deficient. On the other hand, when the time of a heat treatment is
more than 12 hours, a membrane material tends to deteriorate. The
polymer electrolyte membrane obtained by the heat treatment is
capable of proton substitution by immersing it in an acid aqueous
solution as required. Forming by this method enables the polymer
electrolyte membrane of the present invention it to achieve proton
conductivity and fuel barrier properties simultaneously in a good
balance.
[0162] As a method for converting the polymer electrolyte material
used in the present invention to a membrane, there is a method in
which a membrane composed of the polymer electrolyte material is
prepared by the above technique, and then at least a part of a
ketone group protected with ketal is deprotected to form a ketone
group. In accordance with this method, it becomes possible to form
a membrane from a solution of a block copolymer with low solubility
comprising a block not containing an ionic group, and it becomes
possible to achieve proton conductivity and fuel barrier properties
simultaneously, and excellent resistance to solvents, mechanical
strength and physical durability.
[0163] In the polymer electrolyte membrane of the present
invention, the polymer structure can be furthermore optionally
crosslinked by means such as irradiation. By crosslinking such
polymer electrolyte membrane, it is possible to expect an effect of
further inhibiting fuel crossover and swelling due to fuel, and
mechanical strength may be improved and the electrolyte membrane
may become better. Irradiation includes, for example, irradiation
with electron beam and irradiation with .gamma.-ray.
[0164] With respect to a membrane thickness of the polymer
electrolyte membrane of the present invention, a membrane having a
thickness of 1 to 2,000 .mu.m is preferably used. For the purpose
of obtaining the mechanical strength and the physical durability of
a membrane enduring practical use, the thickness is more preferably
more than 1 .mu.m, and for the purpose of decreasing membrane
resistance, namely, improving of power generation performance, the
thickness is preferably less than 2000 .mu.m. The thickness is more
preferably from 3 to 500 .mu.m, and particularly preferably from 5
to 250 .mu.m. The thickness can be controlled by the concentration
of the solution or the thickness of the coat on a substrate.
[0165] Moreover, additives used in a conventional polymer compound,
for example, crystallization nucleating agents, plasticizers,
stabilizers, antioxidants and releasants can be added to the
polymer electrolyte membrane as long as the object of the present
invention is not adversely affected.
[0166] Further, as long as various properties described above are
not adversely affected, the polymer electrolyte membrane obtained
according to the present invention can contain various polymers,
elastomers, fillers, fine particles and various additives for the
purpose of improving mechanical strength, thermal stability and
processability. Moreover, the membrane may be reinforced with a
fine porous membrane, a nonwoven fabric or a mesh.
[0167] Further, a membrane electrode assembly obtained according to
the present invention means a membrane electrode assembly
containing the polymer electrolyte membrane of the present
invention or the polymer electrolyte material of the present
invention in a polymer electrolyte membrane or in a catalyst layer.
The membrane electrode assemblies are parts in which the polymer
electrolyte membrane and an electrode are assembled.
[0168] The method for assembling a polymer electrolyte membrane
with an electrode when the polymer electrode membrane is used for
fuel cell is not specifically limited, and well-known methods (for
example, chemical plating method described in Electrochemistry,
1985, 53, p. 269, and thermal press-bonding method by a gas
diffusion electrode, described in Electrochemical Science and
Technology, edited by J. Electrochem. Soc., 1988, 135, 9, p. 2209)
are applicable thereto.
[0169] In case of assembling using a hot press, the temperature and
the pressure are appropriately selected according to the thickness
of the electrolyte membrane, the moisture content, the catalyst
layer or the electrode substrate. Moreover, in the present
invention, assembling can be carried out by press even if the
electrolyte membrane is dried or the membrane is water-absorbed.
Specific examples of the press method includes roll press in which
the pressure and the clearance are defined, and flat plate press in
which the pressure is defined, and the press is preferably carried
out at a temperature within a range of 0 to 250.degree. C. from the
viewpoint of industrial productivity and inhibition of thermal
decomposition of the polymer electrolyte material having an ionic
group. It is preferable that the pressure is as low as possible
from the viewpoint of protection of the polymer electrolyte
membrane and the electrode, and in the case of the flat plate
press, the pressure is preferably 10 MPa or less, and it is one of
preferable choices from the viewpoint of prevention of
short-circuit of anode and cathode to laminate an electrode and a
polymer electrolyte membrane to manufacture a fuel cell without
assembling by a hot press process. In case of this method, when
power generation is repeated as the fuel cell, deterioration of the
polymer electrolyte membrane, which is considered to be caused by
the short-circuited portion, may be inhibited and durability as a
fuel cell is improved.
[0170] The fuel of the fuel cell using the membrane electrode
assembly of the present invention includes oxygen, hydrogen, an
organic compound having 1 to 6 carbon atoms such as methane,
ethane, propane, butane, methanol, isopropyl alcohol, acetone,
glycerin, ethylene glycol, formic acid, acetic acid, dimethyl
ether, hydroquinone, or cyclohexane, and a mixture of water of the
compound, and these fuels may be used alone or in combination.
Particularly, from the viewpoint of power generation efficiency and
the system simplification of the entire cell, hydrogen and a fuel
containing an organic compound having 1 to 6 carbon atoms are
preferably used, and in view of power generation efficiency,
hydrogen and an aqueous methanol solution are particularly
preferably used. In case of using an aqueous methanol solution, the
concentration of methanol is appropriately selected according to
the system of the fuel cell to be used. However, the concentration
is preferably as high as possible from the viewpoint of long-term
operation. For example, in the active-type fuel cell having
auxiliary machines such as a system of supplying a medium required
for power generation to the membrane electrode assembly, for
example, a liquid supply pump and a blower fan, a cooling fan, a
fuel diluting system and a product recovery system, it is
preferable that the fuel having the methanol concentration of 30 to
100% or more is injected from a fuel tank or a fuel cassette,
diluted to about 0.5 to 20% and then supplied to the membrane
electrode assembly. A fuel having a methanol concentration of 10 to
100% is preferable for a passive-type fuel cell having no auxiliary
machine.
[0171] Furthermore, applications of a polymer electrolyte fuel cell
using the polymer electrolyte membrane of the present invention,
but not particularly limited, are preferably electric power supply
for mobile objects. Particularly, it is preferably used as electric
power supply for portable devices such as cellular phone, personal
computer, PDA, television set, radio, music player, game machine,
headset and DVD player, various robots such as industrial humanoid
robot and animal type robot, household appliances such as cordless
cleaners, toys, and mobile bodies, for example, vehicles such as
electric bicycle, motorcycle, automobile, bus and trucks, marine
vessels and railroads; substitutions of conventional primary and
secondary cells, such as stationary type power generator; or hybrid
power sources in which this polymer electrolyte fuel cell is used
in combination with conventional primary and secondary cells.
EXAMPLES
[0172] The present invention will now be described by way of
examples, but the present invention is not limited to the following
examples. Measuring conditions of the respective physical
properties are as follows. Further, chemical structural formulas
are inserted in the present Examples, but these chemical structural
formulas are inserted for the purpose of helping the understanding
of readers, and do not always express precisely a chemical
structure, exact composition, arrangement, a position of a sulfonic
acid and a molecular weight of polymerizing components of a
polymer, and the present invention is not limited to these chemical
structural formulas.
(1) Density of Sulfonic Acid Group
[0173] A sample of a membrane as a specimen was immersed in pure
water at 25.degree. C. for 24 hours and, after vacuum drying at
40.degree. C. for 24 hours, elemental analysis was carried out.
Analysis of carbon, hydrogen and nitrogen was carried out by a full
automatic elemental analysis apparatus varioEL, analysis of sulfur
was carried out by flask combustion method and titration with
barium acetate, and analysis of fluorine was carried out by flask
combustion and ion chromatogram methods. Density (mmol/g) of
sulfonic acid group per unit gram was calculated from a composition
ratio of a polymer.
(2) Proton. Conductivity
[0174] After a sample of a membrane was immersed in pure water at
25.degree. C. for 24 hours, it was held in a thermo-hygrostat of
80.degree. C. and a relative humidity of 95% for 30 minutes, and
then proton conductivity was measured by a potentiostatic AC
impedance method.
[0175] As a measuring apparatus, an electrochemical measuring
system manufactured by Solartron (Solartron 1287 Electrochemical
Interface and Solartron 1255B Frequency Response Analyzer) was
used, and a potentiostatic impedance was measured by a two-terminal
method to determine proton conductivity. An AC amplitude was set at
50 mV. As a sample, a membrane of 10 mm in width and 50 mm in
length was used. A measuring jig was made of a phenolic resin and a
measuring section was opened. Platinum plates (two plates of 100
.mu.m in thickness) were used as an electrode. The electrodes were
located at a distance of 15 mm on topside and reverse side of a
sample membrane so as to be parallel to each other and orthogonal
to a longitudinal direction of the sample membrane.
(3) Number Average Molecular Weight, Weight Average Molecular
Weight
[0176] A number average molecular weight and a weight average
molecular weight of a polymer were measured by GPC. Using
HLC-8022GPC manufactured by TOSOH Corporation as an integrated-type
apparatus of an ultraviolet detector and a differential
refractometer and two TSK gel SuperHM-H (inner diameter: 6.0 mm,
length: 15 cm) manufactured by TOSOH Corporation as a GPC column, a
polystyrene equivalent number average molecular weight and weight
average molecular weight were measured at a sample concentration of
0.1% by weight, a flow rate of 0.2 mL/min, and a temperature of
40.degree. C., using a N-methyl-2-pyrrolidone solvent (a
N-methyl-2-pyrrolidone solvent containing 10 mmol/L of lithium
bromide).
(4) Membrane Thickness
[0177] Using Model ID-C112 manufactured by Mitutoyo Corporation set
to Granite Comparator Stand BSG-20 manufactured by Mitutoyo
Corporation.
(5) Measurement of Crystallization Calorie by Differential Scanning
Calorimetry (DSC)
[0178] A polymer electrolyte material (3.5 to 4.5 mg) as a specimen
was preliminarily dried at a temperature at which sulfonic acid
group is not decomposed (for example, 40 to 100.degree. C.) to
remove moisture, and then the weight is measured. In this case,
since there is a possibility that a chemical structure and a
conformational structure of the polymer vary, the temperature
should not raised to the temperature higher than the
crystallization temperature or thermal decomposition temperature.
After measuring the weight, the polymer electrolyte material was
subjected to temperature modulation differential scanning
calorimetry in a first temperature rising stage under the following
conditions.
[0179] DSC apparatus: DSC Q100 manufactured by TA Instruments
Co.
[0180] Measuring temperature range: 25.degree. C. to thermal
decomposition temperature (for example, 310.degree. C.)
[0181] Temperature raising rate: 5.degree. C./rain
[0182] Amplitude: .+-.0.796.degree. C.
[0183] Amount of sample: about 4 mg
[0184] Sample pan: crimp pan made of aluminum
[0185] Measuring atmosphere: nitrogen, 50 ml/min
[0186] Preliminary drying: vacuum drying at 60.degree. C. for one
hour
[0187] A value obtained by duplicating heat from the low
temperature side to a peak top was calculated as a crystallization
heat. Since the specimen contained moisture, the moisture content
was calculated from detected evaporation heat of moisture and then
the weight of the polymer electrolyte material was corrected.
Enthalpy (or Heat) of evaporation of water is 2277 J/g.
Weight (g) of moisture in sample=Enthalpy of evaporation (J/g) of
moisture of sample.times.amount (g) of sample/2277 (J/g)
Enthalpy of crystallization Correction Value (J/g)=Enthalpy of
crystallization (J/g).times.Amount (g) of Sample/(Amount of Sample
Weight (g) of Moisture in Sample)
(6) Measurement of the Degree of Crystallinity by Wide Angle X-Ray
Diffraction (XRD)
[0188] A polymer electrolyte material as a specimen was set to a
diffractometer and X-ray diffraction was carried out under the
following conditions.
[0189] X-ray diffractometer: RINT2500V manufactured by Rigaku
Corporation
[0190] X-ray: Cu-K.alpha.
[0191] X-ray output: 50 kV-300 mA
[0192] Optical system: concentration optical system
[0193] Scan speed: 2.theta.=2.degree./min
[0194] Scan method: 2.theta.-.theta.
[0195] Scan range: 2.theta.=5 to 60.degree.
[0196] Slit: divergence slit-1/2.degree., light receiving slit-0.15
mm, scattering slit-1/2.degree.
[0197] The degree of crystallinity was determined as follows: That
is, each component was separated by profile fitting and a
diffraction angle and an integrated intensity of each component
were determined, and then the degree of crystallinity was
calculated from a calculation equation of the general formula (S2)
using an integrated intensity of the resulting crystalline peak and
amorphous halo.
The degree of crystallinity (%)=(Sum of integrated intensity of
entire crystalline peak)/(Sum of integrated intensity of entire
crystalline peak and amorphous halo).times.100 (S2)
(7) Visual Identification of Presence or Absence of Phase
Separation Structure
[0198] A sample of a membrane was immersed in pure water at
25.degree. C. for 24 and taken out in an atmosphere at 25.degree.
C. and a relative humidity of 50 to 80%, and the presence or
absence of a phase separation structure was visually
identified.
(8) Observation of Phase Separation Structure by Transmission
Electron Microscope (TEM)
[0199] A sample of a membrane was Cut into a piece of 5 mm.times.15
mm, and this sample piece was immersed in a 10 wt % solution of
cesium acetate (solvent: ethanol) as a dyeing agent and was allowed
to stand at 25.degree. C. for 24 hours. The sample subjected a
dyeing treatment was taken out and cut into a piece of 1 mm.times.5
mm, and the piece was embedded in a visible light curable resin and
irradiated for 30 seconds with visible light to be fixed.
[0200] A sample was sliced off at room temperature using a
ultramicrotome, and the resulting section was recovered on a Cu
grid and subjected to TEM observation. TEM observation was carried
out at an accelerate voltage of 100 kV and microphotographs were
taken at 5000-fold, 20000-fold and 50000-fold magnifications. As
measuring apparatus, Ultramicrotome ULTRACUT UCT (manufactured by
Leica Microsystems AG) and TEM H-7650 (manufactured by Hitachi,
Ltd.) were used.
[0201] Further, with respect to image processing, processing of
shading correction, density conversion, and spatial filter was
performed on TEM original images in an automatic mode using LUZEX
AP manufactured by NIRECO Corporation. Furthermore, processed
images were expressed in 256 tones of from black to white in an
automatic mode of this apparatus. In the case where tones of 0 to
128 was defined as black color and tones of 129 to 256 was defined
as white color, measurement was performed with parameters of a
circle equivalent diameter, a distance between particles, a maximum
length, a width of each layer and an interlayer distance to
determine an average interlaminar distance and an average distance
between particles.
(9) Measuring Method of Purity
[0202] Quantitative analysis was carried out in the following
conditions with a gas chromatography (GC).
Column: DB-5 (manufactured by J&W) L=30 m .phi.=0.53 mm D=1.50
.mu.m Carrier: helium (line speed-35.0 cm/sec) Analyzing condition
INJ. temp. 300.degree. C. Detct. temp. 320.degree. C.
Oven 50.degree. C. for 1 min
Rate 10.degree. C./min
Final 300.degree. C. for 15 min
[0203] SP ratio 50:1
(10) Resistance to Hot Water and Resistance to Hot Methanol
[0204] Resistance to hot water and resistance to hot methanol of an
electrolyte membrane were evaluated by measuring a dimensional
change ratio in an aqueous 30 wt % methanol solution at 60.degree.
C. The electrolyte membrane was cut into strips having a length of
about 5 cm and a length of about 1 cm and, after immersing in water
at 25.degree. C. for 24 hours, the length (L1) of each strip was
measured by a caliper. The electrolyte membrane was immersed in an
aqueous 30 wt % methanol solution at 60.degree. C. for 12 hours and
the length (L2) was measured again by a caliper, and then the
dimensional change was visually observed.
Synthesis Example 1
Synthesis of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane represented by
the following general formula (G1)
##STR00021##
[0206] Into a 500 ml flask equipped with a stirrer, a thermometer
and a distillate tube, 49.5 g of 4,4'-dihydroxybenzophenone, 134 g
of ethylene glycol, 96.9 g of trimethyl orthoformate and 0.50 g of
p-toluenesulfonic acid monohydrate were charged to be dissolved.
Thereafter, the resulting solution was kept at a temperature of 78
to 82.degree. C. and stirred for 2 hours. Furthermore, an internal
temperature was gradually raised to 120.degree. C. and heating was
continued until distillation of methyl formate, methanol and
trimethyl orthoformate completely ceases. This reaction solution
was cooled to room temperature and then diluted with ethyl acetate,
and an organic layer was washed with 100 ml of a 5% aqueous
solution of potassium carbonate and separated, and a solvent was
distilled off. To a residue, 80 ml of dichloromethane was added to
precipitate a crystal and the resulting mixture was filtered and
dried to obtain 52.0 g of 2,2-bis(4-hydroxyphenyl)-1,3-dioxolane.
This crystal was analyzed by gas chromatography to yield 99.8% of
2,2-bis(4-hydroxyphenyl)-1,3-dioxolane and 0.2% of
4,4'-dihydroxybenzophenone.
Synthesis Example 2
Synthesis of Disodium 3,3'-disulfonate-4,4'-difluorobenzophenone
represented by the following general formula (G2)
##STR00022##
[0208] 109.1 g of 4,4'-difluorobenophenone (Aldrich reagent) was
reacted at 100.degree. C. for 10 hours in 150 ml of a fuming
sulfuric acid (50% SO.sub.3) (manufactured by Wako Pure Chemical
Industries, Ltd.). Thereafter, the reactant was charged into a
large amount of water little by little, and the resulting mixture
was neutralized with NaOH, and to this, 200 g of common salt was
added to precipitate a synthetic product. The resulting precipitate
was filtered and then recrystallized from an aqueous ethanol
solution to obtain disodium
3,3'-disulfonate-4,4'-difluorobenzophenone represented by the above
general formula (G2). Purity was 99.3%. The structure was confirmed
by .sup.1H-NMR. Impurities were quantitatively analyzed by
capillary electrophoresis (organic matter) and ion chromatography
(inorganic matter).
Example 1
Polymerization of Prepolymer a1 Represented by the Following
General Formula (G3)
##STR00023##
[0210] Into a 500 mL three-necked flask equipped with a stirrer, a
nitrogen introducing tube and a Dean-Stark trap, 13.82 g (Aldrich
reagent, 100 mmol) of potassium carbonate, 20.66 g (80 mmol) of
K-DHBP obtained in the above Synthesis Example 1, and 17.46 g
(Aldrich reagent, 80 mmol) of 4,4'-difluorobenzophenone were
charged, and after the atmosphere in the flask was replaced by
nitrogen, the resulting mixture was dehydrated at 180.degree. C. in
90 mL of N-methyl pyrrolidone (NMP) and 45 mL of toluene, and the
dehydrated content was heated to remove toluene and polymerization
was carried out at 230.degree. C. for 1 hour. The reaction solution
was purified by reprecipitating with a large amount of water to
obtain a prepolymer a1 represented by the general formula (G3). The
prepolymer a1 had a weight average molecular weight of 50,000.
(Polymerization of Block Copolymer B1)
[0211] Into a 500 mL three-necked flask equipped with a stirrer, a
nitrogen introducing tube and a Dean-Stark trap, 6.91 g (Aldrich
reagent, 50 mmol) of potassium carbonate, 8.73 g (20 mmol) of the
prepolymer a1, 10.33 g (40 mmol) of K-DHBP obtained in the above
Synthesis Example 1, 3.49 g (Aldrich reagent, 16 mmol) of
4,4'-difluorobenzophenone, and 10.13 g (24 mmol) of disodium
3,3'-disulfonate-4,4'-difluorobenzophenone obtained in the above
Synthesis Example 2 were charged, and after the atmosphere in the
flask was replaced by nitrogen, the resulting mixture was
dehydrated at 180.degree. C. in 120 mL of N-methylpyrrolidone (NMP)
and 45 mL of toluene, and the dehydrated content was heated to
remove toluene and polymerization was carried out at 230.degree. C.
for 10 hours. The reaction solution was purified by reprecipitating
with a large amount of water to obtain a block polymer b1. The
block polymer b1 had a weight average molecular weight of
250,000.
[0212] The block polymer b1 is composed of a block (B2) of the
prepolymer a1 in which the above general formula (G3) is a
repeating unit and a block (B1) of a repeating unit which is
composed of the above general formula (G1), benzophenone, and
disulfonate in proportions of 10:4:6. A ratio W1/W2 of the block
polymer b1 was 40 mmol/20 mmol, namely, 2.
[0213] A 25 wt % N-methylpyrrolidone (NMP) solution, in which the
resulting block polymer b1 was dissolved, was pressure-filtered
using a glass fiber filter and then applied and spread over a glass
substrate. After drying at 100.degree. C. for 4 hours and heating
to 300.degree. C. over 30 minutes under nitrogen, a heat treatment
was carried out at 300.degree. C. for 10 minutes to obtain a
polyketal ketone membrane (membrane thickness 30 .mu.m). The
solubility of a polymer was extremely good. The resulting membrane
was immersed in 6N hydrochloric acid at 95.degree. C. for 24 hours,
subjected to proton substitution and deprotection reaction, and
then sufficiently washed by immersing in a large excess amount of
pure water for 24 hours to obtain polymer electrolyte membrane. The
density of a sulfonic acid group was 1.7 mmol/g.
[0214] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage) and a crystallization heat was 28.0 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the polymer electrolyte
membrane was an extremely tough electrolyte membrane and formed a
phase separation structure because it appeared to become opaque.
Its proton conductivity was 110 mS/cm. Further, even when the
membrane was immersed in hot water or hot methanol, the membrane
was neither dissolved nor collapsed and the rate L2/L1 of
dimensional change was as small as 10%, and therefore the membrane
was extremely excellent in resistance to hot water and resistance
to hot methanol.
[0215] Moreover, a phase separation structure in which an average
interlaminar distance was 200 nm could be identified by TEM
observations. With respect to a sea component, the component in a
membrane thickness direction is four times larger than that of a
membrane surface direction and anisotropy was recognized.
Example 2
Polymerization of Prepolymer a2 Represented by the Above General
Formula (G3)
[0216] In the same manner as in Example 1, except that a
polymerization time was changed from 1 hour to 1.5 hours, a
prepolymer a2 was obtained by polymerization. The prepolymer a2 had
a weight average molecular weight of 60,000.
(Polymerization of Block Copolymer B2)
[0217] In the same manner as in Example 1, except for charging
17.46 g (40 mmol) of the prepolymer a2 in place of the prepolymer
a1, a polyketal ketone polymer and a polymer electrolyte membrane
were prepared. The polyketal ketone polymer had a weight average
molecular weight of 280,000. The solubility of the polymer was
extremely good. A ratio W1/W2 of the block polymer b2 was 1. The
density of a sulfonic acid group of the resulting membrane was 1.4
mmol/g.
[0218] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage) and a crystallization heat was 33.2 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the polymer electrolyte
membrane was an extremely tough electrolyte membrane and formed a
phase separation structure because it appeared to become opaque.
Its proton conductivity was 72 mS/cm. Even when the membrane was
immersed in hot water or hot methanol, the membrane was neither
dissolved nor collapsed and the rate L2/L1 of dimensional change
was as small as 7%, and therefore the membrane was extremely
excellent in resistance to hot water and resistance to hot
methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 400 nm could be identified by TEM
observations.
Example 3
[0219] The polymer electrolyte membrane obtained in Example 2 was
heated to 270.degree. C. in DSC and quenched and a sample of the
polymer electrolyte membrane was taken out. In addition,
270.degree. C. is a temperature at which crystallization proceeds
but thermal decomposition does not occur. This sample exhibited a
crystallization heat of 0 when DSC was measured again. On the other
hand, in wide angle X-ray diffraction (XRD), the degree of
crystallinity of 14% was observed. Also, by TEM observations, a
phase separation structure in which an average interlaminar
distance is 40 nm can be identified.
Example 4
Polymerization of Prepolymer a4 Represented by the Above General
Formula (G3)
[0220] In the same manner as in Example 1, except that a
polymerization time was changed from 1 hour to 0.5 hour, a
prepolymer a4 was obtained by polymerization. The prepolymer a4 had
a weight average molecular weight of 30,000.
(Polymerization of Block Copolymer B4)
[0221] In the same manner as in Example 1, except for charging
17.46 g (40 mmol) of the prepolymer a4 in place of the prepolymer
a1, 3.46 g (25 mmol) of potassium carbonate in place of 6.91 g
(Aldrich reagent, 50 mmol) of that, 5.17 g (20 mmol) of K-DHBP
obtained in the above Synthesis Example 1, 1.75 g (Aldrich reagent,
8 mmol) of 4,4'-difluorobenzophenone, and 5.06 g (12 mmol) of
disodium 3,3'-disulfonate-4,4'-difluorobenzophenone obtained in the
above Synthesis Example 2, a polyketal ketone polymer and a polymer
electrolyte membrane were prepared. The polyketal ketone polymer
had a weight average molecular weight of 320,000. The solubility of
the polymer was extremely good. A ratio W1/W2 of the block polymer
b4 was 0.5. The density of a sulfonic acid group of the resulting
membrane was 1.0 mmol/g.
[0222] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage) and a crystallization heat was 35.2 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the polymer electrolyte
membrane was an extremely tough electrolyte membrane and formed a
phase separation structure because it appeared to become opaque.
Its proton conductivity was 41 mS/cm. Even when the membrane was
immersed in hot water or hot methanol, the membrane was neither
dissolved nor collapsed and the rate L2/L1 of dimensional change
was as small as 2%, and therefore the membrane was extremely
excellent in resistance to hot water and resistance to hot
methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 120 nm could be identified by TEM
observations.
Example 5
Polymerization of Prepolymer a54 Represented by the Above General
Formula (G3)
[0223] In the same manner as in Example 1, except that a
polymerization time was changed from 1 hour to 1 hour and 10
minutes, a prepolymer a5 was obtained by polymerization. The
prepolymer a5 had a weight average molecular weight of 40,000.
(Polymerization of Block Copolymer B5)
[0224] In the same manner as in Example 1, except for charging 4.36
g (10 mmol) of the prepolymer a5 in place of the prepolymer a1,
4.36 g (20 mmol) of 4,4'-difluorobenzophenone in place of 3.49 g
(Aldrich reagent, 16 mmol) of that, and 8.45 g (20 mmol) of
disodium 3,3'-disulfonate-4,4'-difluorobenzophenone obtained in the
above Synthesis Example 2 in place of 10.13 g (24 mmol) of that, a
polyketal ketone polymer and a polymer electrolyte membrane were
prepared. The resulting polyketal ketone polymer had a weight
average molecular weight of 210,000. The solubility of the polymer
was extremely good. A ratio W1/W2 of the block polymer b5 was 4.
The density of a sulfonic acid group of the resulting membrane was
1.7 mmol/g.
[0225] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage) and a crystallization heat was 27.5 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the polymer electrolyte
membrane was an extremely tough electrolyte membrane and formed a
phase separation structure because it appeared to become opaque.
Its proton conductivity was 114 mS/cm. Even when the membrane was
immersed in hot water or hot methanol, the membrane was neither
dissolved nor collapsed and the rate L2/L1 of dimensional change
was as small as 9%, and therefore the membrane was extremely
excellent in resistance to hot water and resistance to hot
methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 140 nm could be identified by TEM
observations.
Comparative Example 1
[0226] A commercially available NAFION.RTM. 111 membrane
(manufactured by DuPont Co.) was used to evaluate various
properties. NAFION.RTM. 111 membrane was immersed in a 5% hydrogen
peroxide water at 100.degree. C. for 30 minutes, immersed in 5%
dilute sulfuric acid at 100.degree. C. for 30 minutes and then
adequately washed with deionized water at 100.degree. C. In the
resulting polymer electrolyte membrane, a crystallization
temperature was not recognized in DSC (first heating stage). Also,
as a result of wide angle X-ray diffraction, no crystalline peak
was recognized: Since the polymer electrolyte membrane was visually
transparent, a phase separation structure was not formed. Its
proton conductivity was 80 mS/cm. Further, when the membrane was
immersed in hot water or hot methanol, it swelled intensely and
became difficult to handle, and therefore it sometimes broke in
picking up. The rate L2/L1 of dimensional change was as large as
26%, and therefore the membrane was inferior in resistance to hot
water and resistance to hot methanol. Moreover, a phase separation
structure (cluster structure) in which an average interlaminar
distance was 6 nm could be identified by TEM observations.
Comparative Example 2
Polymerization of Prepolymer c1 Represented by the Following
General Formula (G4)
##STR00024##
[0228] Into a 500 mL three-necked flask equipped with a stirrer, a
nitrogen introducing tube and a Dean-Stark trap, 13.82 g (Aldrich
reagent, 100 mmol) of potassium carbonate, 21.47 g (80 mmol) of
1,1-bis(4-hydroxyphenyl)cyclohexane, and 17.46 g (Aldrich reagent,
80 mmol) of 4,4'-difluorobenzophenone were put, and after the
atmosphere in the flask was replaced by nitrogen, the resulting
mixture was dehydrated at 180.degree. C. in 90 mL of
N-methylpyrrolidone (NMP) and 45 mL of toluene, and the dehydrated
content was heated to remove toluene and polymerization was carried
out at 230.degree. C. for 1 hour. The reaction solution was
purified by reprecipitating with a large amount of water to obtain
a prepolymer c1 represented by the general formula (G4). The
prepolymer c1 had a weight average molecular weight of 50,000.
(Polymerization of Block Copolymer d1)
[0229] Into a 500 mL three-necked flask equipped with a stirrer, a
nitrogen introducing tube and a Dean-Stark trap, 6.91 g (Aldrich
reagent, 50 mmol) of potassium carbonate, 8.94 g (20 mmol) of the
prepolymer c1, 10.73 g (40 mmol) of
1,1-bis(4-hydroxyphenyl)cyclohexane, 2.18 g (Aldrich reagent, 10
mmol) of 4,4'-difluorobenzophenone, and 12.67 g (30 mmol) of
disodium 3,3'-disulfonate-4,4'-difluorobenzophenone obtained in the
above Synthesis Example 2 were charged, and after the atmosphere in
the flask was replaced by nitrogen, the resulting mixture was
dehydrated at 180.degree. C. in 120 mL of N-methylpyrrolidone (NMP)
and 45 mL of toluene, and the dehydrated content was heated to
remove toluene and polymerization was carried out at 230.degree. C.
for 10 hours. The reaction solution was purified by reprecipitating
with a large amount of water to obtain a block polymer d1. The
block polymer d1 had a weight average molecular weight of 250,000.
A ratio W1/W2 of the block polymer d1 was 2.
[0230] A 25 wt % N-methylpyrrolidone (NMP) solution, in which the
resulting block polymer d1 was dissolved, was pressure-filtered
using a glass fiber filter and then applied and spread over a glass
substrate. After drying at 100.degree. C. for 4 hours and heating
to 300.degree. C. over 30 minutes under nitrogen, a heat treatment
was carried out at 300.degree. C. for 10 minutes to obtain a
membrane (membrane thickness 30 .mu.m). The solubility of a polymer
was extremely good. The membrane was immersed in a large excess
amount of pure water for 24 hours and then sufficiently washed to
obtain a polymer electrolyte membrane. The density of a sulfonic
acid group of the resulting membrane was 1.9 mmol/g.
[0231] In the resulting polymer electrolyte membrane, a
crystallization temperature was not recognized in DSC (first
heating stage). Also, a crystalline peak was not recognized in wide
angle X-ray diffraction (the degree of crystallinity 0%) Since the
resulting polymer electrolyte membrane had only such low strength
that the membrane is broken when picked up with tweezers and formed
a phase separation structure because it appeared to become opaque.
Its proton conductivity was 118 mS/cm. Further, when the membrane
was immersed in hot water or hot methanol, it swelled intensely and
the rate L2/L1 of dimensional change was 56%, and therefore the
membrane was inferior in resistance to hot water and resistance to
hot methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 200 nm could be identified by TEM
observations.
Comparative Example 3
[0232] In the same manner as in Example 1, except that the charge
amount of 20.66 g (80 mmol) of K-DHBP obtained in the above
Synthesis Example 1 was changed, to 17.1 g (80 mmol) of DHBP, a
polyetherketone polymer was obtained by polymerization. From the
initial stage of the polymerization, a polymer was precipitated and
the polymerization was hardly carried out. Since the polymer was
insoluble in a solvent, polymerization of a block polymer was
difficult.
Comparative Example 4
[0233] Into a 500 mL three-necked flask equipped with a stirrer, a
nitrogen introducing tube and a Dean-Stark trap, 13.82 g (Aldrich
reagent, 100 mmol) of potassium carbonate, 20.66 g (80 mmol) of
K-DHBP obtained in the above Synthesis Example 1, 12.2 g (Aldrich
reagent, 56 mmol) of 4,4'-difluorobenzophenone, and 10.1 g (24
mmol) of disodium 3,3'-disulfonate-4,4'-difluorobenzophenone
obtained in the above Synthesis Example 2 were charged, and after
the atmosphere in the flask was replaced by nitrogen, the resulting
mixture was dehydrated at 180.degree. C. in 100 mL of
N-methylpyrrolidone (NMP) and 50 mL of toluene, and the dehydrated
content was heated to remove toluene and polymerization was carried
out at 230.degree. C. for 6 hours. The reaction solution was
purified by reprecipitating with a large amount of water to obtain
a polyketal ketone random copolymer. The polyketal ketone random
copolymer had a weight average molecular weight of 250,000.
[0234] Next, a polymer electrolyte membrane was prepared by the
method described in Example 1. A ratio W1/W2 of the membrane
becomes 1/0. The density of a sulfonic acid group of the resulting
membrane was 0.9 mmol/g. Since the resulting membrane was
transparent, a phase separation structure was not recognized
visually. The membrane was excellent in dimensional stability, but
it was inferior in proton conductivity to Example 1. Moreover, by
TEM observations, a pattern in which an average distance between
particles was 6 nm could be identified, but a phase separation
structure having an interlaminar distance of 10 nm or more, shown
in the definition of the present invention, could not
identified.
Comparative Example 6
Polymerization of Prepolymer a6 Represented by the Following
General Formula (G5)
##STR00025##
[0236] Into a 500 mL three-necked flask equipped with a stirrer, a
nitrogen introducing tube and a Dean-Stark trap, 13.82 g (Aldrich
reagent, 100 mmol) of potassium carbonate, 20.66 g (80 mmol) of
K-DHBP obtained in the above Synthesis Example 1, and 19.2 g
(Aldrich reagent, 88 mmol) of 4,4'-difluorobenzophenone were
charged, and after the atmosphere in the flask was replaced by
nitrogen, the resulting mixture was dehydrated at 180.degree. C. in
90 mL of N-methyl pyrrolidone (NMP) and 45 mL of toluene, and the
dehydrated content was heated to remove toluene and polymerization
was carried out at 210.degree. C. for 1 hours. The reaction
solution was purified by reprecipitating with a large amount of
water and a prepolymer a6 represented by the general formula (G5)
was obtained by washing the precipitate with hot methanol. An
average of N3 is 10 and the prepolymer a6 had a number average
molecular weight of 5,000.
(Polymerization of Block Copolymer b6)
[0237] Into a 500 mL three-necked flask equipped with a stirrer, a
nitrogen introducing tube and a Dean-Stark trap, 8.29 g (Aldrich
reagent, 60 mmol) of potassium carbonate, 11.36 g (44 mmol) of
K-DHBP obtained in the above Synthesis Example 1, and 16.89 g (40
mmol) of disodium 3,3'-disulfonate-4,4'-difluorobenzophenone
obtained in the above Synthesis Example 2 were charged, and after
the atmosphere in the flask was replaced by nitrogen, the resulting
mixture was dehydrated at 180.degree. C. in 90 mL of N-methyl
pyrrolidone (NMP) and 45 mL of toluene, and the dehydrated content
was heated to remove toluene and polymerization was carried out at
210.degree. C. for 1 hour to obtain a prepolymer. The resulting
prepolymer had a number average molecular weight of 7,000.
[0238] Next, 17.46 g (40 mmol) of prepolymer a6 and 20 mL of
toluene were added, and the resulting mixture was dehydrated at
180.degree. C. again, and the dehydrated content was heated to
remove toluene and polymerization was carried out at 230.degree. C.
for 8 hours to obtain a block polymer b6. The resulting block
polymer b6 had a weight average molecular weight of 235,000.
[0239] The block polymer b6 is composed of a block (B2) of the
prepolymer a1 in which the above general formula (G5) is a
repeating unit and a block (B1) of a repeating unit which is
composed of the above general formula (G1) and
disulfonate-benzophenone in proportions of 1:1. A ratio W1/W2 of
the block polymer b6 is 20 mmol/20 mmol, namely, 1.
[0240] A 25 wt % N-methylpyrrolidone (NMP) solution, in which the
resulting block polymer b6 was dissolved, was pressure-filtered
using a glass fiber filter and then applied and spread over a glass
substrate. After drying at 100.degree. C. for 4 hours and heating
to 300.degree. C. over 30 minutes under nitrogen, a heat treatment
was carried out at 300.degree. C. for 10 minutes to obtain a
polyketal ketone membrane (membrane thickness 30 .mu.m). The
solubility of a polymer was extremely good. The membrane was
immersed in 6N hydrochloric acid at 95.degree. C. for 24 hours,
subjected to proton substitution and deprotection reaction, and
then was immersed in a large excess amount of pure water for 24
hours and then sufficiently washed to obtain a polymer electrolyte
membrane. The density of a sulfonic acid group of the resulting
membrane was 2.1 mmol/g.
[0241] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage), and a crystallization heat was 26.8 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the polymer electrolyte
membrane was an extremely tough electrolyte membrane and formed a
phase separation structure because it appeared to become opaque.
Its proton conductivity was 120 mS/cm. Even when the membrane was
immersed in hot water or hot methanol, the membrane was neither
dissolved nor collapsed and the rate L2/L1 of dimensional change
was as small as 11%, and therefore the membrane was extremely
excellent in resistance to hot water and resistance to hot
methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 18 nm could be identified by TEM
observations.
Comparative Example 7
Polymerization of Prepolymer a7 Represented by the Above General
Formula (G5)
[0242] In the same manner as in Example 6, except that the charge
amount of 4,4'-difluorobenzophenone was changed to 18.33 g (Aldrich
reagent, 84 mmol), a prepolymer a7 represented by the general
formula (G5) was obtained. An average of N3 is 20 and the resulting
prepolymer a7 had a number average molecular weight of 10,000.
(Polymerization of Block Copolymer b7)
[0243] In the same manner as in Example 6, except that the charge
amount of 11.36 g (44 mmol) of K-DHBP obtained in the above
Synthesis Example 1 was changed to 10.85 g (42 mmol), a prepolymer
was obtained. The resulting prepolymer had a number average
molecular weight of 14,000.
[0244] Next, 17.46 g (40 mmol) of prepolymer a6 and 20 mL of
toluene were added, and the resulting mixture was dehydrated at
180.degree. C. again, and the dehydrated content was heated to
remove toluene and polymerization was carried out at 230.degree. C.
for 8 hours to obtain a block polymer b7. The block polymer b7 had
a weight average molecular weight of 255,000. A ratio W1/W2 of the
block polymer b7 was 20 mmol/20 mmol, namely, 1.
[0245] A polymer electrolyte membrane was prepared by the method
described in Example 6 to obtain a polyketal ketone membrane
(membrane thickness 30 .mu.m). The solubility of the polymer was
extremely good. The density of a sulfonic acid group of the
resulting membrane was 2.1 mmol/g.
[0246] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage), and a crystallization heat was 34.1 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the polymer electrolyte
membrane was an extremely tough electrolyte membrane and formed a
phase separation structure because it appeared to become opaque.
Its proton conductivity was 131 mS/cm. Even when the membrane was
immersed in hot water or hot methanol, the membrane was neither
dissolved nor collapsed and the rate L2/L1 of dimensional change
was as small as 13%, and therefore the membrane was extremely
excellent in resistance to hot water and resistance to hot
methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 40 nm could be identified by TEM
observations.
Comparative Example 8
Polymerization of Prepolymer a8 Represented by the Above General
Formula (G5)
[0247] In the same manner as in Example 6, except that the charge
amount of 4,4'-difluorobenzophenone was changed to 17.89 g (Aldrich
reagent, 82 mmol), a prepolymer a8 represented by the general
formula (G5) was obtained. An average of N3 is 40 and the
prepolymer a7 had a number average molecular weight of 20,000.
(Polymerization of Block Copolymer b8)
[0248] In the same manner as in Example 6, except that 7.63 g of
4,4'-biphenol (manufactured by TOKYO CHEMICAL INDUSTRY Co., Ltd.,
41 mmol) was used in place of 11.36 g (44 mmol) of K-DHBP obtained
in the above Synthesis Example 1, a prepolymer was obtained. The
prepolymer had a number average molecular weight of 29,000.
[0249] Next, 17.46 g (40 mmol) of prepolymer a8 and 20 mL of
toluene were added, and the resulting mixture was dehydrated at
180.degree. C. again, and the dehydrated content was heated to
remove toluene and polymerization was carried out at 230.degree. C.
for 8 hours to obtain a block polymer b8. The block polymer b8 had
a weight average molecular weight of 245,000. A ratio W1/W2 of the
block polymer b8 was 20 mmol/20 mmol, namely, 1.
[0250] A polymer electrolyte membrane was prepared by the method
described in Example 6 to obtain a polyketal ketone membrane
(membrane thickness 30 .mu.m). The solubility of the polymer was
extremely good. The density of a sulfonic acid group of the
resulting membrane was 2.1 mmol/g.
[0251] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage), and a crystallization heat was 22.4 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the polymer electrolyte
membrane was an extremely tough electrolyte membrane and formed a
phase separation structure because it appeared to become opaque.
Its proton conductivity was 144 mS/cm. Even when the membrane was
immersed in hot water or hot methanol, the membrane was neither
dissolved nor collapsed and the rate L2/L1 of dimensional change
was as small as 14%, and therefore the membrane was extremely
excellent in resistance to hot water and resistance to hot
methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 110 nm could be identified by TEM
observations.
Comparative Example 9
Polymerization of Prepolymer a9 Represented by the Above General
Formula (G5)
[0252] In the same manner as in Example 6, except that the charge
amount of 4,4'-difluorobenzophenone was changed to 20.95 g (Aldrich
reagent, 96 mmol), a prepolymer a9 represented by the general
formula (G5) was obtained. An average of N3 is 5 and the resulting
prepolymer a9 had a number average molecular weight of 3,000.
(Polymerization of Block Copolymer b9)
[0253] In the same manner as in Example 6, except that 8.94 g of
4,4'-biphenol (manufactured by TOKYO CHEMICAL INDUSTRY Co., Ltd.,
48 mmol) was used in place of 11.36 g (44 mmol) of K-DHBP obtained
in the above Synthesis Example 1, a prepolymer was obtained. The
resulting prepolymer had a number average molecular weight of
4,000.
[0254] Next, 17.46 g (40 mmol) of prepolymer a8 and 20 mL of
toluene were added, and the resulting mixture was dehydrated at
180.degree. C. again, and the dehydrated content was heated to
remove toluene and polymerization was carried out at 230.degree. C.
for 8 hours to obtain a block polymer b9. The block polymer b9 had
a weight average molecular weight of 271,000. A ratio W1/W2 of the
block polymer b9 was 20 mmol/20 mmol, namely, 1.
[0255] A polymer electrolyte membrane was prepared by the method
described in Example 6 to obtain a polyketal ketone membrane
(membrane thickness 30 .mu.m). The solubility of the polymer was
extremely good. The density of a sulfonic acid group of the
resulting membrane was 2.1 mmol/g.
[0256] In the resulting polymer electrolyte membrane, a
crystallization temperature was recognized in DSC (the first
heating stage), and a crystallization heat was 20.1 J/g. Also, a
crystalline peak was not recognized in wide angle X-ray diffraction
(the degree of crystallinity 0%). Since the resulting polymer
electrolyte membrane was an extremely tough electrolyte membrane
and formed a phase separation structure because it appeared to
become opaque. Its proton conductivity was 121 mS/cm. Even when the
membrane was immersed in hot water or hot methanol, the membrane
was neither dissolved nor collapsed and the rate L2/L1 of
dimensional change was as small as 10%, and therefore the membrane
was extremely excellent in resistance to hot water and resistance
to hot methanol. Moreover, a phase separation structure in which an
average interlaminar distance was 10 nm could be identified by TEM
observations.
Comparative Example 10
[0257] A membrane was evaluated as a reverse osmosis membrane. In
this example, a salt removal rate was determined by measuring a
salt concentration of a supplied solution and a salt concentration
of a permeated solution and substituting the resulting measurements
into the following equation:
Salt removal rate (%)={1-(salt concentration of permeated
solution)/(salt concentration of supplied solution)}.times.100.
[0258] Further, water permeability was expressed by a water
quantity (m.sup.3/m.sup.2d) passed through a membrane per unit time
(day) and unit area (m.sup.2)
[0259] A cloth-reinforced polysulfone support membrane
(ultrafiltration membrane) which is used as a microporous support
membrane was produced by the following technique. That is, a wet
nonwoven fabric with a size of 30 cm long and 20 wide, which
comprises mixed fiber of polyester fiber of 0.5 dtex in finess of
single yarns and polyester fiber of 1.5 dtex in finess of single
yarns and has permeability of 0.7 cm.sup.3/cm.sup.2sec and an
average pore size of 7 .mu.m or less, was fixed onto a glass plate,
and a dimethylformamide (DMF) solution (2.5 poise: 20.degree. C.)
having 15% by weight of polysulfone was casted thereon in such a
way that an overall thickness is 200 .mu.m, and the resulting glass
plate was immediately immersed in water to prepare a microporous
support membrane of polysulfone.
[0260] Next, a 25% by weight n-methylpyrrolidone (NMP) solution of
the block polymer b6 obtained in Example 6 was applied onto the
obtained microporous support membrane of polysulfone to form a
functional layer having a thickness of 1 .mu.m.
[0261] A complex semipermeable membrane thus obtained was subjected
to a reverse osmosis test under the conditions of 0.5 MPa and
25.degree. C. using a 0.2% by weight sodium chloride aqueous
solution adjusted to a pH 6.5 as a raw water. Consequently, the
water permeability was 0.60 m.sup.3/m.sup.2d and sodium chloride
removal rate was 97.0%, and this membrane exhibited a function as a
reverse osmosis membrane.
INDUSTRIAL APPLICABILITY
[0262] The polymer electrolyte material and the polymer electrolyte
membrane of the present invention can be applied for various
electrochemical apparatus, for example, fuel cell, water
electrolysis apparatus and chloroalkali electrolysis apparatus, and
are preferably for a fuel cell, particularly preferably for fuel
cell, using an aqueous hydrogen or methanol solution as a fuel.
[0263] The application of the polymer electrolyte fuel cell of the
present invention is not particularly limited, and is preferably
used as power supply sources for portable devices such as cellular
phone, personal computer, PDA, video cameras, and digital cameras;
household appliances such as cordless cleaners; toys; mobile
objects, for example, vehicles such as electric bicycle,
motorcycle, automobile, bus, and trucks, marine vessels, and
railroads; substitutions of conventional primary and secondary
cells, such as stationary type power generator; and combinations of
these fuel cells with a hybrid power supply.
* * * * *