New poly(1,2,3-triazolesulfonic acids) for proton exchange membranes of fuel cell

Full text of DOI:10.1134/S0012500809120027

ISSN 0012ꢀ5008, Doklady Chemistry, 2009, Vol. 429, Part 2, pp. 305–310. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © I.I. Ponomarev, M.Yu. Zharinova, P.V. Petrovskii, Z.S. Klemenkova, 2009, published in Doklady Akademii Nauk, 2009, Vol. 429, No. 4, pp. 490–495.
CHEMISTRY
New Poly(1,2,3ꢀtriazolesulfonic acids)
for Proton Exchange Membranes of Fuel Cell
I. I. Ponomarev, M. Yu. Zharinova, P. V. Petrovskii, and Z. S. Klemenkova
Presented by Academician A.R. Khokhlov May 29, 2009
Received June 3, 2009
DOI: 10.1134/S0012500809120027
Fuel cells (FCs) based on proton exchange memꢀ disulfonic acid, hydroquinone, 4,4'ꢀisopropylideneꢀ
branes are promising as electric power sources. They diphenol, cyanuric chloride, metanilic acid, sodium
provide a possibility to receive energy from hydrogen, hydroxide from Acrus were used without additional
synthetic or biosynthetic fuel and can operate with purification.
higher efficiency as compared with heat engines [1, 2].
1,3,5ꢀTriethinylbenzene (6) from Alfa Aesar and
Hydrated sulfonicꢀacid polymerꢀelectrolyte proꢀ
ton exchange membrane (PEM) in an FC provides a
transfer of protons resulting from electrochemical oxiꢀ
dation of fuel on anode to cathode and separates
anode and cathode space.
2,2'ꢀbenzidinedisulfonic acid from Kodak were also
used without additional purification.
1H NMR spectra of studied compounds were
recorded on a Bruker AvanceTM 400 spectrometer
operating at 400.13 MHz in DMSOꢀd6 solution.
Polymer films used as PEMs in FCs, in particular,
Chemical shifts were determined using residual proꢀ
δ
in lowꢀtemperature fuel cells operating at 60–90 C,
°
ton signals of the deuterated solvent as an internal refꢀ
erence.
should meet a number of stringent and conflicting
requirements, which are not always fulfilled. Thus, the
Thermogravimetric (TGA) studies of polymers
were carried out on an MOM Qꢀ1000 derivatograph
(Hungary) in air at a heating rate of 5 K/min with a
sample weight of ~20 mg.
most widespread perfluorinated PEM Nafion ,
®
which shows excellent mechanical properties and proꢀ
ton conduction in a hydrated state, readily loses water
above 60
°
C and can provide fuel cell performance only
under conditions of forced humidification (
humidity), which decreases the total efficiency of cell
and makes its design more complicated [1–4].
≥
80%
Thermomechanical (TMA) studies were perꢀ
formed in air at a heating rate of 2.5 K/min, load of
100 g, rod diameter of 4 mm,
σ
= 0.08 MPa.
Films alternative to Nafion , soꢀcalled hydrocarꢀ
®
The IR absorption spectra of samples were
recorded as thin films or as KBr pellets on a Nicolet
MagnaꢀIR 750 FTIR spectrophotometer in the range
4000–400 cm–1.
bon membranes based on sulfonated aromatic heteroꢀ
chain polymers and a number of polyheteroarylenes,
which show comparable performance characteristics
and rather low cost, have much lower durability than
Reaction course and purity of isolated products
were monitored by TLC on Silufol UVꢀ254 plates.
Visualization under UV light.
Nafion [2–4]. Therefore, the search for methods for
®
the synthesis of new types of proton exchange filmꢀ
forming polymers is an important task of polymer
chemistry.
Reduced viscosity was measured with a capillary
Ubbelohde viscometer at a polymer concentration of
0.5 g/dL in
N
ꢀmethylpyrrolidone at 25 C.
°
EXPERIMENTAL
Dimethyl sulfoxide (DMSO), sodium nitrite,
sodium azide, potassium carbonate, propargyl broꢀ
mide, propargyl alcohol, 4,4'ꢀdiaminostilbeneꢀ2,2'ꢀ
Synthesis of Monomers and Sodium
3ꢀAzidobenzenesulfonate
Aromatic diazides
1 and 2 with sulfonic groups
(Scheme 1) are not described in the literature but
readily obtained from corresponding diamines by
standard procedures: diamines were first subjected to
diazotization according to [6], then the resultant diaꢀ
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28,
Moscow, 119991 Russia
305

306
PONOMAREV et al.
Monomer structure
⎝
⎜
⎜
⎜
⎛
ꢀ
ꢀꢀ
R =
ꢀꢀ
NaO3S
R
⎜
(for 1)
⎜
ꢀ ꢀ
ꢀ ꢀ
ꢀ
1, 2
N3
N3
⎜
⎜
⎜
⎝
⎜
⎜
⎛
Ordinary bond (for 2)
SO3Na
O
O
O
O
3
4
⎝
⎜
⎜
⎜
⎜
⎛
⎜
⎜
ꢀ
ꢀꢀ
O
⎜ꢀꢀ
5, 6
ꢀ ꢀ
⎜
R1
⎜
ꢀ ꢀ ⎜
⎜
ꢀꢀ
R1
=
N
N
;
⎜
⎜
⎜
⎜
⎝
ꢀ ꢀ
ꢀ
O
N
(for 5)
O
⎜
⎛
(for 6)
Scheme 1.
zonium salts were reacted on cooling with a 10%
molar excess of a 20% aqueous sodium azide solution.
The azides were isolated after partial removal of water
on a rotary evaporator and then were recrystallized
from water or ethanol. The yield of the products after
recrystallization was 70–75%.
Dipropargylic ethers of 4,4'ꢀisopropylidenedipheꢀ
nol ( ) and hydroquinone ( ) (Scheme 1) were
obtained by reacting the initial diphenols with proparꢀ
gyl bromide in the presence of K2CO3 according to the
known procedures [8].
3
4
Compound 3: mp. 77–79
°
C (lit. 74–76
°
C), yield
85%.
Compound 1. 1H NMR (
, ppm): 7.14 (dd, 2H,
δ
Compound 4: mp. 41–43
75%.
°
C (lit. 49–51
°
C), yield
HCꢀ5,5', 4JHH = 3.2 Hz, 3JHH = 11.1 Hz), 7.52 (d, 2H,
4
HCꢀ3,3', JHH = 3.2 Hz), 7.65 (d, 2H, HCꢀ6,6',
2,4,6ꢀTris(2ꢀpropynyloxy)ꢀ1,3,5ꢀtriazine
(5)
3JHH = 11.1 Hz), 8.05 (s, 2H, HCvinyl). IR (
ν
, cm–1):
(Scheme 1) was obtained from cyanuric chloride and
propargyl alcohol in the presence of sodium hydroxide
2117 (N3), 1189, 1080, 1023 (
S
O–3 ).
by the known procedure [9]. Mp 73–75
78 C), yield 79%.
°
C (lit. 77–
Compound 2. 1H NMR (
2H, HCꢀ5,5'), 7.31–7.38 (m, 2H, HCꢀ6,6'), 7.65 (s,
2H, HCꢀ3,3'). IR (
, cm–1): 2116 (N3), 1233, 1205,
1043, 1032 (
O–3 ).
δ, ppm): 6.93–7.00 (m,
°
ν
Synthesis of model compounds
The reactions of compounds
3
ꢀ
7
,
5
ꢀ
7
, and
6ꢀ7
S
3,
5
, and
6
with comꢀ
pound
100 C and total concentration of initial compounds of
0.5 g/mL during 6 h, CuI was used as a catalyst in
amount of 10 mol %. The yield of products
and after purification was at least 85%; the comꢀ
7 (Scheme 2) were carried out in DMSO at 70–
Sodium 3ꢀazidobenzenesulfonate (
7) was obtained
°
similarly to compound
2
as described in [7]. 1H NMR
( , ppm): 7.04–7.09 (m, 1H, HCꢀ4), 7.27–7.31 (m,
δ
3ꢀ7, 5ꢀ7,
1H, HCꢀ2), 7.38 (t, 1H, HCꢀ5, 3JHH = 7.6 Hz), 7.42
6ꢀ7
1
pounds were characterized by H NMR and FTIR
spectroscopy. IR spectra show the lack of absorption at
2100–2120 cm–1 typical for azide group, as well as at
3
(d, 1H, HCꢀ6, JHH = 7.6 Hz). IR (
ν
, cm–1): 2107
(N3), 1213, 1175, 1047 (S
O–3 ).
DOKLADY CHEMISTRY Vol. 429
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NEW POLY(1,2,3ꢀTRIAZOLESULFONIC ACIDS)
307
Synthesis of model compounds
SO3Na
+
N3
O
O
7
3
O
O
N
N
N
N
SO3Na
N
N
SO3Na
3ꢀ7
SO3Na
N N
N
+
R1
N3
R1
N
N
N
SO3Na
N
SO3Na
N
N
5, 6
7
NaO3S
5ꢀ7, 6ꢀ7
⎝
⎜
⎜
⎜
⎜
⎛
⎜
⎜
ꢀ
ꢀꢀ
O
N
⎜ꢀꢀ
ꢀ ꢀ
⎜
⎜
ꢀ ꢀ ⎜
⎜
ꢀꢀ
R1 =
N
N
;
⎜
⎜
⎜
⎜
⎝
ꢀ ꢀ
ꢀ
O
O
⎜
⎛
(for 5)
(for 6)
Scheme 2.
3260–3290 and 2110–2140 cm–1 inherent in terminal
acetylene group.
Compound 5ꢀ7. 1H NMR (
HCtriazole), 8.13 (s, HCarom.), 7.87 (d, 3H, HCarom.
3JHH = 7.8 Hz), 7.72 (d, 3H, HCarom. 3JHH = 7.6 Hz),
3JHH = 7.8 Hz), 5.64 (s, 6H,
δ
, ppm): 9.04 (s, 3H,
,
,
Compound 3ꢀ7. 1H NMR (
HCtriazole), 8.12 (s, 2H, HCarom.), 7.87 (d, 2H,
HCarom.
3JHH = 7.1 Hz), 7.72 (d, 2H, HCarom.
3JHH = 7.1 Hz), 7.58 (t, 2H, HCarom. 3JHH
7.4 Hz), 7.15 (d, 4H, HCarom.
3JHH = 8.1 Hz), 6.99
(d, 4H, HCarom.
3JHH = 8.1 Hz), 5.19 (s, 4H, CH2),
δ
, ppm): 9.00 (s, 2H,
7.58 (t, 3H, HCarom.
,
CH2).
,
,
Compound 6ꢀ7. 1H NMR (
HCtriazole), 8.66 (s, 3H, HCarom.), 8.27 (s, 3H, HCarom.),
8.04 (d, 3H, HCarom.
3JHH = 7.6 Hz), 7.77 (d, 3H,
HCarom.
3JHH = 7.5 Hz), 7.65 (t, 3H, HCarom. 3JHH
7.8 Hz).
δ, ppm): 9.61 (s, 3H,
,
=
,
,
,
,
,
=
1.61 (s, 6H, CH3).
DOKLADY CHEMISTRY Vol. 429
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308
PONOMAREV et al.
Synthesis of linear polymers
NaO3S
+
N3
R
N3
O
O
SO3Na
3
1, 2
O
O
N
NaO3S
N
N
N
N
R
N
n
SO3Na
3ꢀ1, 3ꢀ2
NaO3S
+
O
O
N3
R
N3
SO3Na
4
1, 2
O
O
N
NaO3S
R
N
N
N
N
N
SO3Na
n
4ꢀ1, 4ꢀ2
Synthesis of polymer networks
N
N
N
N
SO3Na
SO3Na
NaO3S
R
+
N3
N3
R1
R
N
N
N
R
R1
N
SO3Na
N
NaO3S
n
5, 6
1
5ꢀ1, 5ꢀ2, 6ꢀ1, 6ꢀ2
Scheme 3.
Synthesis of Linear Polymers
Synthesis of polymers 3ꢀ1, 3ꢀ2, 4ꢀ1, 4ꢀ2 (Scheme 3)
was carried out in DMSO under conditions similar to
the model reactions. Polymerization of equimolar
smoothly at concentrations of 0.4–0.5 g/mL at 60–
100 C during 10–12 h in the presence of 5–10 mol %
of CuI. The polymers were precipitated with isoproꢀ
panol or films were obtained immediately by pouring
reaction mixture on a glass followed by evaporation of
°
amounts of diazides and dipropargyl ethers proceeds the solvent. The polymers were characterized by visꢀ
DOKLADY CHEMISTRY Vol. 429
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NEW POLY(1,2,3ꢀTRIAZOLESULFONIC ACIDS)
309
1
Table 1. Physicochemical characteristics of linear PTA
cometry, H NMR and IR spectroscopy, TGA, and
TMA data (Table 1). The 1H NMR spectrum of polyꢀ
IC,
mol
Polymer
(in Na form) dL/g
ηred,
mer
3ꢀ
2
with ηred = 0.6 dL/g is exemplified below.
Compound 3ꢀ2. 1H NMR (
Td
,
°
C
T5%
,
°
C
equiv/g
*
δ
, ppm): 9.00 (s, 2H,
HCtriazole), 8.40 (s, 2H, HCarom.), 7.78 (m, 2H,
HCarom.), 7.58 (m, 2H, HCarom.), 7.17 (m, 4H,
HCarom.), 7.00 (m, 4H, HCarom.), 5.22 (s, 4H, CH2),
1.61 (m, 6H, CH3).
3ꢀ1
3ꢀ2
4ꢀ1
4ꢀ2
0.8
0.6
0.6
0.4
330
260
220
290
160
160
160
160
2.76
2.86
3.33
3.43
A film obtained from polymer
terized by strength test (Table 2).
4ꢀ1 was also characꢀ
* Calculated ionꢀexchange capacity.
Synthesis of Polymer Networks
Polytriazole networks 5ꢀ1, 5ꢀ2, 6ꢀ1, and 6ꢀ2
Table 2. Physicomechanical characteristics of selected
PTAs
(Scheme 3) were obtained by pouring a preliminary filꢀ
tered 3–4% solution of monomers and CuI (5–10 mol %
of the sum of moles of the monomers) in DMSO on a
glass support (Petri dish) followed by evaporation of
Polymer
(in Na form)
E ,
10–3
MPa
×
σ
,
MPa
ε, %
5ꢀ1
6ꢀ1
70.1
5.1
5.5
7.8
2.3
3.7
3.4
the solvent on heating to 40 C for 10–20 h. The degree
°
127.0
121.8
of reaction was determined from the decrease in the
intensity of the absorption band of azide group at
2100–2120 cm–1 in the IR spectra of resultant films.
6ꢀ1
(
H form)
4ꢀ1
56
4.5
1.8
The films prepared from polytriazoles 5ꢀ1 and 6ꢀ1
(Table 2) were characterized by strength tests.
and polymers and evident availability of starting mateꢀ
rials for their synthesis.
RESULTS AND DISCUSSION
To prove the possibility of polymer synthesis, we
first studied in detail the features of the Huisgen reacꢀ
tion with azides containing sulfonic groups using
model compounds (Scheme 2). We prepared a series of
triazoles modeling the monomer unit of linear or polyꢀ
triazole networks.
One of the possible ways to solve the aboveꢀnoted
problems is the transfer from traditional reactions to
organic reactions unconventional for polymer chemꢀ
istry, in particular, to click reactions, among which the
Huisgen reaction, a 1,3ꢀdipolar azide cycloaddition to
terminal acetylenes in the presence of monovalent
copper salts to form 1,2,3ꢀtriazoles in high yields, is an
important one. Poly(1,2,3ꢀtriazoles) (PTAs) can be
more stable toward oxidation and hydrolysis than hetꢀ
erochain polymers because it was reported in the literꢀ
ature that the triazole ring shows high stability toward
attacks of oxidizing agents and water and elevated
temperature [5].
The synthesis of linear polymers was carried out
using the equimolar ratio of diazide and diacetylene in
DMSO medium at 60–100 C in the presence of 5–
°
10 mol % of CuI and total monomer concentration of
40–50%. During polymerization, the equimolar
amount (with respect to Cu(I)) of sodium ascorbate
was added at intervals to recover monovalent copper.
After completion of the reaction, viscous solution of
polymer was diluted with DMSO to 5% and either
precipitated with isopropanol or filtered and poured
on a warmed glass support to prepare films.
Until now, the Huisgen reaction has been little used
for the synthesis of linear polymers because authors
failed to prepare highꢀmolecularꢀweight products
suitable for manufacturing strong films and fibers [10,
11], while there was no attempt to obtain proton
exchange polytriazoles.
The obtained polymers after precipitation as powꢀ
ders are soluble in aprotic dipolar solvents (DMF,
DMSO, and NMP) and water on heating both as
sodium salt and in free acid form.
In the context of work on the design of new polyꢀ
meric materials for proton exchange membranes
(PEM) of lowꢀtemperature fuel cells, we prepared for
At relatively low values of reduced viscosity (0.4–
the first time highꢀmolecularꢀweight filmꢀforming 0.8 dL/g), all the polymers form films removable from
polytriazoles 3ꢀ1 3ꢀ2 4ꢀ1 4ꢀ2 5ꢀ1 5ꢀ2 6ꢀ1, and 6ꢀ2 support, which can be transformed into acid form
containing sulfonic groups on the basis of sulfonated upon keeping in a MeOH–HCl mixture (10 : 1, v/v).
aromatic diazides and as well as twoꢀ and threeꢀ The linear dimensions of hydrated films of the polyꢀ
functional terminal alkynes (Scheme 3). It should mers vary considerably upon keeping in water (by
be noted that the main driving force of this study is the 20 40% depending on temperature and time). This
obvious simplicity of preparation of the monomers fact can sharply limit the possibility of practical appliꢀ
,
,
,
,
,
,
1
2
3–6
⎯
DOKLADY CHEMISTRY Vol. 429
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310
PONOMAREV et al.
cation of PEM in fuel cells. Moreover, films prepared membrane–electrode assemblies of lowꢀtemperature
from the linear polytriazoles are insufficiently strong hydrogen and methanol fuel cells.
to make membrane–electrode assembly (MEA) that
can operate for a long time. Therefore we prepared
polytriazole networks based on diꢀ and trifunctional
ACKNOWLEDGMENTS
monomers that will show limited swelling in water and
may be stronger due to crosslinked structure.
We are grateful to V.V. Kazantseva for conducting
strength tests of PTA film samples.
First, we carried out test gelation reactions of difꢀ
ferent monomers to obtain polytriazole networks in
DMSO solution. We noted that solid transparent gel
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°
C when diazide 1
5
6
2
2
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DOKLADY CHEMISTRY Vol. 429
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2009