Chemical modification of cardo poly(benzimidazole) using "click" reaction for membranes of high-temperature hydrogen fuel cells

Full text of DOI:10.1134/S0012500812110018

ISSN 0012ꢀ5008, Doklady Chemistry, 2012, Vol. 447, Part 1, pp. 227–232. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © Iv.I. Ponomarev, I.I. Ponomarev, E.I. Goryunov, Yu.A. Volkova, D.Yu. Razorenov, Z.A. Starikova, I.V. Blagodatskikh, M.I. Buzin, A.R. Khokhlov, 2012,
published in Doklady Akademii Nauk, 2012, Vol. 447, No. 1, pp. 38–43.
CHEMISTRY
Chemical Modification of Cardo Poly(benzimidazole)
Using “Click” Reaction for Membranes of HighꢀTemperature
Hydrogen Fuel Cells
Iv. I. Ponomarev, I. I. Ponomarev, E. I. Goryunov, Yu. A. Volkova, D. Yu. Razorenov,
Z. A. Starikova, I. V. Blagodatskikh, M. I. Buzin, and Academician A. R. Khokhlov
Received July 20, 2012
DOI: 10.1134/S0012500812110018
Poly(benzimidazole)s (PBIs) are one of the most anov Institute of Organoelement Compounds, Rusꢀ
promising and studied classes of polymers used as sian Academy of Sciences, by the polymer analogous
membranes in highꢀtemperature hydrogen fuel cells
HTFC) as polymer–electrolyte complexes with
orthophosphoric acid [1, 2].
reaction of highꢀmolecularꢀweight PBI–O–PT polyꢀ
mer [3] via the reaction with O,Oꢀdiethyl vinylphosꢀ
phonate [4] (Scheme 1) and successfully studied in the
(
Phosphonethylated poly(benzimidazole)s (PEPꢀ construction of the membraneꢀelectrode block
BIs) were obtained for the first time in the Nesmeyꢀ (MEB) of the hydrogen HTFC.
N
N
O
N
H
N
H
O
PBI–O–PT
O
n
N
N
N
N
O
O
||
N
N
H C=CH–P(OEt)
2
2
k
l
Et
NꢀMP, KOH/NaOH
0 mol %, 60–90°C
H
m
O
O
1
O
P (OEt)2
n
m
,
k
+
,
l
k
= 0–2
= 2)
PEPBI–O–PT
(m
+ l
Scheme 1.
The current–voltage characteristics of the MEB based groups per repeat unit of the polymer. However, films
on PEPBI–O–PT membrane are comparable with the prepared from these PBIs were found to have insuffiꢀ
®
best commercial products of BASF, Celtec ꢀP1000, and ciently high strength and could not be used for assemꢀ
®
bling MEBs [5].
Celtec ꢀV [4–7]; however, such MEBs need further
improvement.
Earlier [5], we also obtained rather highꢀmolecuꢀ
larꢀweight Nꢀarylꢀsubstituted PBIs with five –P–OH
In this work, we have studied an approach that conꢀ
sists in a twoꢀstep polymer analogous reaction of filmꢀ
forming highꢀmolecularꢀweight PBI–O–PT with
propargyl bromide followed by transformation into a
phosphorylated analogue by 1,3ꢀdipolar addition of
diethyl (4ꢀazidobenzyl)phosphonate (Scheme 2,
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28,
Moscow, 119991 Russia
compound
3). For this purpose, we also studied in this
227

228
PONOMAREV et al.
work for the first time such reactions by using model 2ꢀ
phenylbenzimidazole (2ꢀPBI, ) as an example. We also
EXPERIMENTAL
1
Dimethyl sulfoxide,
Nꢀmethylpyrrolidone (NꢀMP),
carried out the polymer analogous transformations of
highꢀmolecularꢀweight PBI–O–PT into phosphoryꢀ
lated triazolopolybenzimidazole (PTPBI) (Scheme 3),
which was used to prepare protonꢀconducting memꢀ
branes tested in a model of MEB of HTFC.
2
ꢀphenylbenzimidazole (2ꢀPBI), diethyl (4ꢀaminoꢀ
benzyl)phosphonate, propargyl bromide (PB), sodium
hydroxide, potassium carbonate, triethylamine, copꢀ
per(I) iodide, sodium azide, and 85% phosphoric acid
were purchased from Sigma–Aldrich and used as
received.
O
N
N
BrH C–≡ (PB)
2
+
(EtO)2P
2
NꢀMP, K CO ,
2
3
N3
N
H
20–30°C
N1
1
2
3
2'
2
ꢀPBI
1'
N 2''
N1''
EtOH, CuI, NEt3
CH2
4'
4
N1'
3' N
4
N
O
2
'
1
P(OEt)2
Scheme 2.
Methods of Study of Individual Compounds
and Polymers
Molecularꢀweight characteristics were analyzed by
GPC on an Agilent 1100 chromatograph equipped
with a diode array detector and column with hydroxyꢀ
containing methyl acrylate sorbent by procedure [3]
using a solution of LiCl in DMF (50 mmol/L) as an
eluent. The calibration curve was plotted with the use
of polystyrene standards.
1
31
The H and P NMR spectra of obtained comꢀ
pounds were recorded on a Bruker Avanceꢀ400 specꢀ
trometer (operating at 400.13 and 161.98 MHz,
respectively) in a DMSOꢀd6 or HCOOD solution.
Chemical shifts (δ) were calculated using residual proton
signals of a deuterated solvent as an internal reference
1
31
Synthesis of Individual Compounds
(
H) and 85% Н PО as an external reference ( P).
3 4
Poly(benzimidazole) PBIꢀOꢀPT was obtained by
The IR absorption spectra were recorded on a procedures developed by us [3]. Polymer with
η
red
=
Nicolet MagmaꢀIR 750 IR Fourierꢀtransform specꢀ
2
.1 dL/g (0.5% solution in NꢀMP at 25°C) was used in
–1
trophotometer in the range of 4000–400 cm as thin the reaction with propargyl bromide.
films or KBr pellets. Thermogravimetric studies
Synthesis of 2ꢀphenylꢀ1ꢀpropꢀ2'ꢀynylꢀ1Hꢀbenzimiꢀ
(
TGA) were performed on a MOM DerivatographꢀC
dazole (2) and its Xꢀray diffraction study. A mixture of
.94 g (0.01 mol) of 2ꢀPBI ( ), 1.40 g (0.011 mol) of
instrument (Hungary) in air at a heating rate of
1
1
5
K/min using ~15 mg samples.
potassium carbonate, and 1.30 g (0.011 mol) of PB was
stirred in 10 mL of NꢀMP at 50°C in a dry argon flow
for 10 h with intermittent sonication. The reaction was
monitored by TLC using toluene as an eluent. The
reaction solution was poured into water, neutralized
The reaction course and the purity of the initial
reagents and isolated products were monitored by
TLC on Silufol UVꢀ254 plates with visualization
under UV light or in iodine vapors.
with acetic acid to pH 6, and
30 mL). The extract was dried with
capillary Ubbelohde viscometer at 25°C at the conꢀ calcium chloride, filtered, and concentrated to 20 mL.
centration of polymer solutions of 0.5 g/dL.
The filtrate was placed in a refrigerator, the precipiꢀ
1 was extracted with
The reduced viscosity of PBI was measured in a diethyl ether (3
×
DOKLADY CHEMISTRY Vol. 447
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2012

CHEMICAL MODIFICATION OF CARDO POLY(BENZIMIDAZOLE)
229
C11
C12
C10
C13
C9
C8
O1S
O2S
C1
N1 C14
N2
C7
C15 C16
O2S
C2
C6
C3
C5
C4
Fig. 1. Crystal structure of 2ꢀphenylꢀ1ꢀpropꢀ2'ꢀynylꢀ1Hꢀbenzimidazole acetate (2).
tated colorless crystals were filtered off and dried in a
The structure contains molecules of
2
and acetic
vacuum at 60°C to give 2.1 g (90%) of crystalline comꢀ acid (Fig. 1) bound by the strong hydrogen bond
pound
2
, mp 71–73
°
C
(lit.: 72°C).
N2⋅⋅⋅H–O1S (distances N2–O1S are 2.699(2) Å
N2⋅⋅⋅H 1.81(2) , H–O1S 0.90(2) Å, H–O1S 0.90(2) Å,
angle N2⋅⋅⋅H–O1S 172(1)°) and the weak hydrogen
,
Å
1
H NMR (DMSOꢀd6,
δ, ppm, J, Hz): 3.52 (t, 1H,
С, 4JHH 2.5), 5.16 (d, 2H, СН2, 4JHH 2.5), 7.28– bond С16–Н16⋅⋅⋅O2S (distances С16⋅⋅⋅O2S 3.212(2),
H16⋅⋅⋅O2S 2.44(2) , and C16–H16 0.95(2) Å, angle
С16–H16⋅⋅⋅O2S 138(1)°).
НС≡
.38 (m, 2H, Н5,6), 7.57–7.66 (m, 3H,
.68–7.75 (m, 2H, Н4,7), 7.84–7.90 (m, 2H,
Å
7
7
m
ꢀ + pꢀС Н5),
6
оꢀС Н5).
6
Synthesis of ꢀdiethyl (4ꢀazidobenzyl)phosphoꢀ
O,O
Pale yellow needleꢀlike crystals of acetate of comꢀ
pound were obtained from diethyl ether, С H N
СH СОOН (FW = 293.3), monoclinic, at 100 K
nate (3). Diazonium diethyl (4ꢀaminobenzyl)phosꢀ
phonate was obtained by a standard procedure. Then,
the equivalent amount of 30% aqueous solution of
sodium azide was added to an aqueous solution of the
diazonium salt cooled to 0°С in such a manner that
temperature did not rise above 5°С. The supernatant
above the precipitated oil was decanted, and the oil
was washed twice with water. The oil was dried in a
2
·
2
=
=
1
6
12
a
3
1
1
0.9958(8)
01.944(1)°,
= 4, dcalcd = 1.295 g/cm . The experimental set of
8 887 reflections was obtained on a Bruker APEX II
CCD area detector diffractometer at 100 K ( Мо
radiation, = 60.0°) from a single crystal of 0.35
.20 0.16 mm in size. All calculations were perꢀ
formed with the SHELXTL PLUS 5 software package. 1.17 (t, 6H, СН , 3JН–Н 7.1), 3.23 (d, 2H, СН Р,
Å
,
V
b
= 7.6562(5)
Å
,
c
= 18.2065(13),
β
3
= 1499.6(2) Å , space group
P2 /n,
1
3
Z
1
λ
К
α
vacuum over Р2О5. The yield of azide
3
is quantitative.
2θ
×
max
1H NMR (400 MHz, DMSOꢀd
,
6
δ
, ppm, , Hz):
J
0
×
3
2
2JН–Р 21.5), 3.95 (dq, 4H, СН СН , 3JН–Н ~ 3JН–Р
3
2
Atomic coordinates, bond lengths, bond angles, and
thermal parameters are deposited with the Cambridge
Crystallographic Data Center (CCDC no. 770666)
7
.3), 7.04–7.12 (m, 2H, С Н ), 7.28–7.36 (m, 2H).
6 4
Synthesis of
O
,
O
ꢀdiethyl 4ꢀ{4'ꢀ[(2''ꢀphenylꢀ1''
ꢀ1',2',3'ꢀtriazolꢀ1'ꢀ
http://www.ccdc.cam.uk/conts/retrieving.html (or yl}benzylphosphonate (4). Compound
(2.32 g,
from CCDC, 12 Union Road, Cambridge CB2 1EZ; 0.01 mol) and 2.69 g (0.01 mol) of azide
was heated
fax: +44 1223 335 033; or deposit@ccdc.cam.ac.uk).
at reflux in 20 mL of ethanol for 2 h in the presence of
Hꢀ
and are available free upon request through benzimidazolꢀ1''ꢀyl)methyl]ꢀ1'
H
2
3
DOKLADY CHEMISTRY Vol. 447
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2012

230
PONOMAREV et al.
0
.2 g (0.001 mol) of CuI and 0.5 mL of triethylamine. over methylhydroquinone) in 5 mL was added dropꢀ
The reaction course was monitored by TLC using tolꢀ wise, and stirring was continued (24, 48, 72, and 96 h)
uene–methanol as an eluent. After reactants and with intermittent sonication for 20–30 min at 40–
2
3
1
disappeared, the reaction solution was filtered through 50°C and sampling for H NMR analysis of the substiꢀ
a thin layer of silica gel, concentrated to 5–6 mL, and tution extent. The polymer was precipitated with
allowed to crystallize in a refrigerator to give pale yelꢀ water, acidified with acetic acid to pH 5, filtered, and
low crystals, mp 114–116°C.
the polymer powder was refluxed twice in distilled
water for 1–2 h each to remove the solvent. The powꢀ
der was dried at 100°C in a vacuum. Depending on conꢀ
ditions and reactant ratio, the alkylation degree may be
For C H N O P anal. calcd. (%): C, 64.66; H,
.63; N, 13.96; P, 6.18, FW = 501.52.
27
28
5
3
5
Found (%): C, 64.51; H, 5.68; N, 13.76; P, 6.13.
25–100%. Propargylꢀcontaining PBI–O–PT–Pg is
1
H NMR (DMSOꢀd + CF COOD, δ, ppm, J, Hz):
6
3
readily soluble in amide solvents and DMSO.
1
2
.15 (t, 6H, СН3, 3JHH 6.8), 3.30 (d, 2H, СН Р, 2JHР
2
1.6), 3.95 (dq, 4H, СН О, 3J
3J
1,3ꢀDipolar addition of 4ꢀazidobenzylphosphonate (3)
to PBI–O–PT–Pg to form PTPBI. PBI–O–PT–Pg
~
7.1), 5.84
HP
2
HH
2
4
(
s, 2H, CH N), 7.46 (d, 2H, C H ,6, 3JHH 7.7), 7.58–
2
6
(
0.608 g, 1 mmol) was dissolved in 6 mL of DMSO, a
7
.67 (m, 2H, Н5'',6''), 7.71–7.84 (m, 5H,
mꢀ + pꢀС Н +
6 5
solution of 0.55 g (~2.2 mmol of azide in 5 mL of
3
C H ), 7.85–7.93 (m, 1H, Н4''), 8.05–8.16 (m, 3H, DMSO and a solution of 0.04 g of CuI, 0.5 mL of Et N
3
,5
6
4
3
in 3 mL of DMSO were added. The reaction mixture
was stirred for 8 h at 60–80°C, filtered through a fritꢀ
ted glass filter, and precipitated with 1% aqueous
ammonia solution. The precipitate was separated by
filtration, dried at 100°C in a vacuum, and studied by
NMR and IR spectroscopy and by elemental analysis.
In all cases, irrespective of the alkylation extent of
PBI–O–PT, the polymer analogous “click” reaction
о
ꢀС Н + Н7''), 8.94 (s, 1H, H5').
6 5
3
1
1
P{ H} NMR (DMSOꢀd ,
δ
, ppm): 26.00 s.
Alkylation of PBI–O–PT with propargyl bromide.
Alkylation (Scheme 3) was carried out using the samꢀ
ples of PBI–O–PT with = 1.4–3.0 dL/g (0.5%
solution in NꢀMP at 25
according to GPC data to Mw = 60000–90000 [3].
6
η
red
°
C), which corresponds
The polymer (0.532 g, 1 mmol) was dissolved in 6 mL proceeded quantitatively. Completely alkylated PBI–
of NꢀMP, 0.3 g (~2.2 mmol) of K CO was added, and O–PT undergoes 100% addition of azide to give
2
3
the mixture was stirred for 30 min on a water ultraꢀ PTPBI containing 5.2% of phosphorus at a calculated
sound bath at 40–50°C. Then, a solution of 0.5 g value of 5.18%. The polymer is soluble in amide solꢀ
(
~4.4 mmol) of propargyl bromide (freshly distilled vents, DMSO, and HCOOH.
1
5
10
Rh, nm
0
.010
.008
0
1
2
3
0.006
0.004
0.002
0
0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
log
M
Fig. 2. Molecular weight distribution function relative to PS (lower axis) and hydrodynamic radius distribution (upper axis) for
) PBI–O–PT, ( ) PBI–O–PT–Pg (modification extent of 80%), and ( ) the corresponding PTPBI–O–PT. is the weight
fraction of polymer.
(1
2
3
W
DOKLADY CHEMISTRY Vol. 447
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CHEMICAL MODIFICATION OF CARDO POLY(BENZIMIDAZOLE)
231
RESULTS AND DISCUSSION
stretching vibrations of phosphonate P=O group at
–1
1
272 cm .
In this work, we have studied in detail the model
reactions of 2ꢀPBI (
lowed by the reaction of intermediate alkyne
phosphorylated azide to give (Scheme 2).
The chemical structure of products and
confirmed by the data of H and P NMR, Fourierꢀ
transform IR spectroscopy, and Xꢀray crystallography.
1) with propargyl bromide folꢀ
According to Xꢀray diffraction data (Fig. 1), moleꢀ
cule 2 is nonplanar, the phenyl ring is turned by 45.8°
relative to benzimidazole plane, and the propynyl subꢀ
stituent is disposed orthogonally (dihedral angle is
2
with
3
4
2
4
was
1
31
8
4.9
values. Molecules in crystal form chains extended
along the axis.
°). The bond lengths and angles have common
The IR spectrum of compound
2 lacks a broad
a
band of stretching vibrations of benzimidazole NH
group at 3200–3400 cm–1 and shows a new band of
The data obtained in the study of model reactions
stretching vibrations of the
≡
CH terminal acetylene were further used to examine polymer analogous reacꢀ
fragment at 3290 cm . The IR spectrum of the prodꢀ tions of PBI–O–PT. The general scheme of PTPBI–
uct of the “click” reaction ( ) displays a strong band of O–PT synthesis (Scheme 3) is shown above.
–1
4
N
N
O
N
H
N
H
O
O
n
PBI–O–PT
N
N
N
O
N
3
n
BrH C–ϵ
n K CO ,
(
PB
)
2
NꢀMP, 2.2
ultrasound, 20–50°C, 72 h
2
3
O
O
n
PBI–O–PT–Pg
N
N
N
O
O
N
DMSO, CuI, NEt3
0–80°C
+
3n
N3
6
P(OEt)2
O
3
N
N
N n
N
O
N
N
O
P(OEt)2
О
P(OEt)2
PTPBI–O–PT
Scheme 3.
K = 4.07 × a =
10–4 dL g,
The alkylation of PBI–O–PT with propargyl broꢀ constants for PS in eluent:
mide was monitored by NMR and IR spectroscopy 0.53). GPC data indicate an increase in the hydrodyꢀ
and GPC. Figure 2 shows the molecularꢀweight distriꢀ namic size of chains caused by the first stage of modiꢀ
bution curves for initial PBI, its propargylꢀcontaining fication and the extension of size distribution. This
products, and final PTPBI–O–PT, as well as the calꢀ fact can be explained by both the increase in chain
culated hydrodynamic radius distribution (using the rigidity on account of hindered rotation around virtual
Stokes equation and the determined MarkꢀHouwink bonds and the improvement of thermodynamic qualꢀ
DOKLADY CHEMISTRY Vol. 447
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232
PONOMAREV et al.
ity of the solvent. As a result, the apparent values of Mw
relative to PS) alter from 60000 to 166 000 and 184000,
while Mw Mn ratio is changed from 2.05 to 5.3 and 5.9,
respectively.
U
= 0.580 and 0.602 V, respectively, at a constant
openꢀcircuit voltage of ~0.94 V.
(
/
ACKNOWLEDGMENTS
We are grateful to Z.S. Klemenkova for recording
IR spectra and P.V. Petrovskii for recording NMR
spectra and their discussion.
The obtained polymers, according to the data of
TGA in air, have a high thermal stability comparable
with that of the known polymers of the PBI family [1–6].
Their intense decomposition temperatures are above
This work was supported by the Russian Academy
of Sciences (Complex Program no. 7 of the Division of
Chemistry and Materials Science) and the Russian
Foundation for Basic Research (project no. 11–03–
5
~
80
350
and ~400
°
C, the onset of oxidative destruction occurs at
C for diethoxyphosphoryl form of PTPBI–O–PT
C for PBI–O–PT–Pg. To transform the
°
°
1
2115ꢀofiꢀmꢀ2011).
diethoxyphosphoryl groups of the polymers into acidic
groups, PTPBI films were refluxed for 5 h in 18%
hydrochloric acid to give phosphonic acids as probed
REFERENCES
31
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capable of forming protonꢀconducting membranes
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. www.fuelꢀcell.basf.com/ca/internet/Fuel_Cell/en_GB/
content/
®
electrodes Celtec Pꢀ1000 [7] in galvanostatic mode
2
(
3
current density of 0.4 A/cm ) for 200 h at 160°C and
50 h at 180°C showing a stable potential difference
DOKLADY CHEMISTRY Vol. 447
Part 1
2012