Synthesis of N-phosphonoethylated cardo poly(benzimidazole) and testing of proton-conducting membranes made of it

Full text of DOI:10.1134/S0012500810060042

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 432, Part 2, pp. 168–174. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © Iv.I. Ponomarev, I.I. Ponomarev, P.V. Petrovskii, Yu.A. Volkova, D.Yu. Razorenov, I.B. Goryunova, Z.A. Starikova, A.I. Fomenkov, A.R. Khokhlov, 2010,
published in Doklady Akademii Nauk, 2010, Vol. 432, No. 5, pp. 632–638.
CHEMISTRY
Synthesis of NꢀPhosphonoethylated Cardo Poly(benzimidazole)
and Testing of ProtonꢀConducting Membranes Made of It
Iv. I. Ponomarev, I. I. Ponomarev, P. V. Petrovskii, Yu. A. Volkova, D. Yu. Razorenov,
I. B. Goryunova, Z. A. Starikova, A. I. Fomenkov, and Academician A. R. Khokhlov
Received January 19, 2010
DOI: 10.1134/S0012500810060042
Poly(benzimidazoles) (PBIs) are one of the most
promising and wellꢀstudied classes of polymers utiꢀ
A polymer based on 3,3',4,4'ꢀtetraaminodiphenyl
oxide and 3,3ꢀbis( ꢀcarboxyphenyl)phthalide (PBIꢀ
OꢀPH) was prepared for the first time at the Nesmeyꢀ
p
lized as membranes in hydrogenꢀbased highꢀtemperaꢀ anov Institute of Organoelement Compounds, Rusꢀ
sian Academy of Sciences, and was successfully used
in the design of membrane–electrode assembly
ture fuel cells (HTFC) as polymer–electrolyte comꢀ
plexes with orthophosphoric acid [1, 2].
(MEA) of hydrogenꢀbased HTFC [3, 4].
O
O
HO
OH
O
N
N
O
O
N
N
H
+
H
O
H2N
H2N
NH2
NH2
O
O
n
PBIꢀОꢀPH
Scheme 1.
The current–voltage characteristics of MEA with for making MEA. Therefore, we used an approach of
PBIꢀOꢀPH membrane are on a level with the best
world’s samples, however, require further elaboration [4].
Previously [5], we prepared PBIs with rather high
molecular weights from monomers containing five
P–OH groups per repeating unit of the polymer.
However, the films made of these PBIs proved to have
insufficient strength properties and could not be used
polymerꢀanalogous transformation of highꢀmolecuꢀ
larꢀweight filmꢀforming PBIꢀOꢀPH into its phosphoꢀ
rylated analogue. For this purpose, in this work we
have studied previously unknown reaction of 2ꢀarylꢀ
substituted benzimidazoles with O,Oꢀdiethyl
vinylphosphonate (DEVP) using 2ꢀphenylbenzimidaꢀ
zole (2ꢀPhBI) as an example and have carried out
polymerꢀanalogous transformation of PBIꢀOꢀPH into
phosphonoethylated polymer (PEPBIꢀOꢀPH) used
for the preparation of protonꢀconducting membranes
successfully tested in a model of HTFC MEA.
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28, Moscow,
119991 Russia
168

SYNTHESIS OF NꢀPHOSPHONOETHYLATED CARDO POLY(BENZIMIDAZOLE)
169
EXPERIMENTAL
white crystalline precipitate was separated by filtraꢀ
tion, washed with water, and dried in a vacuum at
100 (Scheme 3) to give 1.50 g (99%) of compound II
Tm 265 (DSC).
The methods for studying individual compounds
and polymers have been described in detail in our
recent works [3–5].
°
C
.
=
°
C
Polybenzimidazole PBIꢀOꢀPH was obtained by
our procedures [3]. Phosphonoethylation reaction was
For C15H15N2O3P anal. calcd. (%): C, 59.60;
H, 5.00; N, 9.27; P, 10.25. = 302.27. Found (%):
C, 59.59; H, 5.27; N, 9.14; P, 10.18.
M
carried out with a polymer sample having ηr
2.1 dL/g (0.5% solution in NꢀMP at 25 ), which
Mn = 155000/64400 = 2.4 accordꢀ
=
°
С
corresponds to Mw
/
1H NMR (DMSOꢀd6
, ppm): 2.14–2.40 (m, 2H,
,
δ
ing to GPC [3].
СН2Р), 4.49–4.74 (m, 2H, NСН2), 7.60–8.10 (m,
9H, arom.).
Synthesis and Xꢀray diffraction study of O,Oꢀdiethyl
2ꢀ(2ꢀphenylꢀ1 ꢀbenzimidazolꢀ1ꢀyl)ethylphosphonate (I).
H
A mixture of 1.94 g (0.01 mol) of 2ꢀphenylbenzimidaꢀ
zole, 10 mL of NꢀMP, and 1 mL of a solution of 0.02 g
(0.5 mmol) of NaOH and 0.028 g (0.5 mmol) of KOH
31Р{1H} NMR (DMSOꢀd6
,
δ
, ppm): 19.57 s.
Phosphonoethylation of PBIꢀOꢀPH with
O,Oꢀdiethyl
in MeOH was stirred at 60 С in a dry argon flow for
°
vinylphosphonate. PBIꢀOꢀPH (0.532 g, 1 mmol) was
dissolved in 10 mL of NꢀMP, and 1 mL of a catalyst
solution (10 mol % as calculated for reacting groups)
in methanol (for example, a mixture of NaOH (4 mg,
0.1 mmol) and KOH (5.6 mg, 0.1 mmol)) was added.
5 h; then, 3.28 g (0.02 mol) of DEVP was added and
the mixture was stirred for another 10 h (Scheme 2).
The reaction course was monitored by TLC (toluene–
ethanol, 5 : 1 (v/v) as eluent) and 31Р{1H} NMR specꢀ
troscopy. The reaction mixture was evaporated in a
The solution was stirred at 60 С for 8 h in a dry argon
°
vacuum at 90–100 С (0.133 Pa), and the oily matter
°
was flooded with 10 mL of water and allowed to stand
for 72 h in a refrigerator. The resultant colorless crysꢀ
tals were separated by filtration and dried in a vacuum
flow, and then DEVP (0.656 g, 4 mmol, a twofold
molar excess) was added (Scheme 4). The reaction of
DEVP addition was studied at 20–90 С. The reaction
°
at 60
mixture of two kinds of crystals with Tm = 67 and
82.8 (DSC).
For C19H23N2O3P anal. calcd. (%): C, 63.68;
H, 6.47; N, 7.82; P, 8.64. = 358.38. Found (%):
C, 63.59; H, 6.57; N, 7.79; P, 8.68.
°
C to give 3.47 g (97%) of the product that was a
course was monitored by 31Р{1H} NMR spectroscopy
by sampling the reaction solution. The sample was
diluted with DMSOꢀd6, the extent of phosphonoethyꢀ
lation was calculated from the ratio of the integrated
°
C
M
intensities of the 31P NMR signals at
DEVP and = 26.50 ppm for PEPBIꢀOꢀPH, taking
into account the partial polymerization of DEVP (31P
NMR signal at
= 28.56 ppm) and alkylation (31P
NMR signal at = 14.15 ppm).
δ
= 16.95 ppm for
δ
1H NMR (DMSOꢀd6
, ppm,
СН3
3JHH = 7.0), 2.27 (dt, 2H, СН2Р
2JHР = 18.5), 4.47 (dt, 2H, NСН2 3JHH = 9.4, 3JHР
6.7), 3.88 (dq, 4H, ОСН2
3JHH 3JHР = 7.2), 7.23–
7.39 (m, 2H, СHꢀ5, 6), 7.55–7.65 (m, 3H, m,pꢀ
,
δ
J
, Hz): 1.11 (t, 6H,
,
,
3JHH = 7.7,
δ
,
=
δ
,
≈
The samples were simultaneously analyzed by
GPC.
3
C6H5), 7.65 (d, 1H, СНꢀ4, JHH = 7.7), 7.71 (d, 1H,
СНꢀ7, 3JHH = 7.6), 7.75–7.85 (d, 2H,
ꢀC6H5).
31Р{1H} NMR (DMSOꢀd6
, ppm): 26.63 s.
Colorless platelet crystals of compound
obtained from water as monohydrate, С19H23N2О3P ·
H2O ( = 376.38)
o
To obtain PEPBIꢀOꢀPH membranes, the reaction
solution was poured onto a glass support and the solꢀ
,
δ
vent was evaporated at 60–80
the films were removed from the glass and heated for
30 min up to 350 in air to form spatially crosslinked
°С on a hot bench. Then,
I
were
M
.
°
С
structure of the polymer. The doping of the memꢀ
branes for MEA and the study of discharge characterꢀ
istics were carried out similarly to the works [4, 5].
Atomic coordinates and thermal parameters, bond
lengths, and bond angles are deposited with the Camꢀ
bridge Crystallographic Data Center (CCDC
no. 747698) and available free of charge at
http://www.ccdc.cam.uk/conts/retrieving.html (or
from CCDC, 12 Union Road, Cambridge CB2 1EZ;
fax: +44 1223 335 033; or deposit@ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
In this work, we have studied in detail for the first
time the model reaction of 2ꢀPhBI with DEVP. The
processes that occur in NꢀMP (or DMSO) in the presꢀ
Synthesis of 2ꢀ(2ꢀphenylꢀ1
yl)ethylphosphonic acid (II). A suspension of 1.79 g
(5 mmol) of compound in 20 mL of 18% HCl was
Hꢀbenzimidazolꢀ1ꢀ
I
heated under reflux for 2 h and cooled; the resultant ence of basic catalysts is shown in Scheme 2.
DOKLADY CHEMISTRY Vol. 432
Part 2
2010

170
PONOMAREV et al.
N
31P, δ 16.95 ppm
N
CH2 CH3
N
N
31P, δ 26.63 ppm
(DEVP)
CH2 CH P(O)(OEt)2
NꢀМP (DMSО), Cat.
20–100°C
(Cat. = NaOH, KOH, NaOH + KOH, ТEBAH)
N
H
N
I
CH2 CH2 P(O)(OEt)2
2ꢀPhBI
Hydrolysis of
polyDEVP
CH2 CH
EtO P O
OEt
CH2 CH
EtO P O
OH
n
n
31P, δ 28.56 ppm
)ОН
CH2 CH P(O)(OEt)(OH)
Dealkylation
Hydrolysis of
DEVP
Scheme 2.
Depending on reaction temperature and the nature analysis of its monohydrate (Fig. 1). The molecule
of the solvent and catalyst used, the formation of
desired addition product was found to be accompaꢀ
of compound
ters. The phenyl substituent is tilted toward the benꢀ
zimidazole plane by 41.5 . The molecules are
hydrogen bonded in crystal via N(2)⋅ ⋅ ⋅H(O
(N⋅ ⋅ ⋅H 2.11 ) and O(1)⋅ ⋅ ⋅H(O ) (О⋅ ⋅ ⋅Н 2.07
I has standard geometrical parameꢀ
I
nied by the side reactions of polymerization and
dealkylation (hydrolysis) of DEVP and ethylation of
2ꢀPhBI to give 1ꢀethylꢀ2ꢀphenylbenzimidazole that
proceed intensely above 80
tions (60 , NꢀMP, 10 mol % of a mixture of NaOH +
°
w)
Å
w
Å
)
°
С. Under optimal condiꢀ
interactions to form layers parallel to the diagonal
plane of the ab cell.
°С
KOH (1 : 1)), the reaction affords compound
tually quantitative yield.
I in virꢀ
When crystals of
for 2 h, a complete hydrolysis takes place to form
1H and 31Р{1Н} NMR spectral data and by the Xꢀray phosphonic acid II (Scheme 3).
I are heated at reflux in 18% HCl
The structure of this compound was confirmed by
N
N
N
N
CH2 CH2 P(O)(OEt)2
CH2 CH2 P(O)(OH)2
I
II
Scheme 3.
and a band at 2300–3100 cm–1 typical for the vibraꢀ
The IR spectrum of Nꢀphosphonoethylated 2ꢀ
PhBI ( ) shows the lack of a wide band of stretching
I
tions of P–O–H and + –H groups.
N
vibrations of NH group of benzimidazole in the region
3450 cm–1 and the presence of a strong band of P=O
stretching vibrations at 1272 cm–1. The spectrum of
acid II shows a wide absorption band in the region
936–1150 cm–1 that includes a series of vibrational
bands of phosphonic groups partially dissociated due
The data obtained in the study of model reacꢀ
tions were further used for the examination of polyꢀ
merꢀanalogous transformation of PBIꢀOꢀPH. The
general scheme for the synthesis of PEPBIꢀOꢀPH
(Scheme 4) and its repeating unit irregularity [6] are
to protonation of nitrogen atoms of benzimidazole shown below.
DOKLADY CHEMISTRY Vol. 432
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2010

SYNTHESIS OF NꢀPHOSPHONOETHYLATED CARDO POLY(BENZIMIDAZOLE)
171
N
N
O
N
H
N
H
O
O
n
PBIꢀОꢀPH
N
N
N
N
N
CH2=CH–P(O)(OEt)2 (DEVP)
O
NꢀМP, NaOH + KOH
N
10 mol %, 60–90°C
H
m
Et
l
k
O
(EtO)2P(O)
n
O
k, l = 0 – 2
(k + l = 2)
PEPBIꢀOꢀPH
Scheme 4.
The optimization of the process of modification of given in the table. This table shows that the use of
PBIꢀOꢀPH was carried out taking into account data potassium tertꢀbutoxide as a catalyst of PBIꢀOꢀPH
obtained previously in the work [7]. Some results are phosphonoethylation at 20–45°С leads to the lack of
С(12)
N(2)
С(6)
С(11)
С(13)
С(7)
С(5)
С(4)
С(8)
С(10)
С(1)
N(1)
С(9)
С(2)
С(14)
С(3)
С(15)
P(1)
O(2)
С(17)
С(16)
O(3)
O(1)
C(18)
C(19)
Fig. 1. Crystal structure of
O,Oꢀdiethyl 2ꢀ(2ꢀphenylꢀ1Hꢀbenzimidazolꢀ1ꢀyl)ethylphosphonate (I).
DOKLADY CHEMISTRY Vol. 432
Part 2 2010

172
PONOMAREV et al.
Study of the reaction of phosphonoethylation of PBIꢀOꢀPH
Content of phosphoꢀ Content of
noethylation product* poly(DEVP)*
Polymer
1
T
,
°
C
Reaction time, h
P/PE** (%)
DMF, ꢀBuOK
t
40
60
60
4.5
10
0
0
36
48
–
–
8
24
11.5
0.96/13.4
2
20
40
45
56
96
<1
0
0
0
–
–
–
~3.5
12
144
DMF, TEBAH
<1
<1
3
4
45
80
4
–
–
–
42
100
DMF, TEBAH (in 4 portions)
50
80
80
80
80
80
80
80
8
10
52
56
64
72
80
88
0
2
0
0
–
–
25
42
53
60
63
63
0
–
5
–
12
14
14
14
–
–
–
4.81/67
NꢀMP, NaOH + KOH
5
55
70
80
85
90
24
6
24
48
76
84
0
0
0
0
1
–
32
48
56
80
–
–
–
4.52/63
6***
80
80
80
80
18
96
13
55
76
80
0
0
1
–
–
192
216
–
~1.5
5.83/81
31
1
* According to P{ H} NMR data.
** The ratio of phosphorus content to the content of diethoxyphosphoryl groups in PEPBIꢀOꢀPH according to elemental analysis data (the
calculated content of P is 7.2/100) for the polymer precipitated with alcohol.
*** According to elemental analysis data for the polymer precipitated with water.
the target addition product (the yield is not higher
than 12–13%). At 60 , the polymerization of DEVP
(Scheme 2) proceeds much faster than its addition to
the benzimidazole ring. Triethylbenzylammonium
hydroxide (TEBAH) is also a good catalyst for DEVP
The best results were obtained when the reaction
was carried out in an NꢀMP medium at 70–90 in
the presence of an equimolar mixture of NaOH and
KOH as a catalyst. Under these conditions, virtually
no polymerization of DEVP is observed (1.5%), while
the conversion of PBIꢀOꢀPH reaches 80–81%.
Figure 2 shows kinetic curves for the phosphonoetꢀ
hylation of PBIꢀOꢀPH and the side reactions of polyꢀ
merization of DEVP and its dealkylation resulting in
the ethylation of PBIꢀOꢀPH according to Scheme 4.
The process of the polymerꢀanalogous transformaꢀ
tion of PBIꢀOꢀPH was also monitored by GPC. Figꢀ
°
С
°
С
polymerization: the yield of the polymer at 80
tually 100% over 42 h. However, if the catalyst is added
in four portions within 50–80 , PEPBIꢀOꢀPH conꢀ
°
С is virꢀ
°
С
taining up to 63–67% of diethoxyphosphoryl groups
can be obtained within 88 h. The content of polymerꢀ
ized DEVP in this case is not higher than 14%.
DOKLADY CHEMISTRY Vol. 432
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SYNTHESIS OF NꢀPHOSPHONOETHYLATED CARDO POLY(BENZIMIDAZOLE)
173
of the polymer in NꢀMP and, after thermal treatment
at 160 , had good mechanical properties (tensile
strength was 120–140 MPa, ultimate elongation was
12–18%, and Young’s modulus was 2500–3000 MPa).
According to the data of dynamic TGA in air, the
obtained polymers show high thermal stability compaꢀ
rable to that of the known polymers of the PBI family
[1–3]. The temperatures of their fast degradation are
β
, с, %
°
С
1
80
60
40
20
0
higher than 580
ture is 360 for the diethoxyphosphoryl derivative of
PEPBIꢀOꢀPH and ~400 for its Р(О)(ОН)2 derivaꢀ
tive.
°
С, while degradation onset temperaꢀ
°
С
°
С
2
3
With the aim to transform the diethoxyphosphoryl
groups of the polymers into acid ones, the films were
refluxed for 5 h in 18% HCl, which resulted in phosꢀ
0
50
100
150
200
250
, h
31
phonic acids with the P NMR chemical shift
δ
~
τ
19.5 ppm (HCOOD).
Fig. 2. Kinetics of phosphonoethylation of PBIꢀOꢀPH
80 , NꢀMP, 10 mol % of NaOH + KOH (1 : 1, mol)):
, extent of phosphonoethylation ( ); , content of
dealkylated DEVP (content of Nꢀethyl groups in PEPBIꢀ
OꢀPH); , content of poly(DEVP) in reaction solution.
Measurements of the proton conductivity of the
film samples of PEPBIꢀOꢀPH showed that its value is
within 10–3–10–4 S/cm, whereas the conductivity of
known PBIs doped with orthophosphoric acid (PA)
reaches 0.15 S/cm [8–10]. Such a large difference in
proton conductivity seems to result from the fact that
the doped systems involve up to 5–6 Н3РО4 molecules
per polymer repeating unit, which is equivalent to 15–
18 P–OH groups, whereas the obtained PEPBIs conꢀ
tain only 3–3.5 P–OH groups per unit. For the pracꢀ
tical application of membranes in HTFC, the required
(
1
°С
β
2
3
ure 3 shows the chromatograms of the initial polymer
and its phosphonoethylation product (yield 80–81%)
obtained for their solutions in DMF with LiCl addiꢀ
tives (the table, polymer 6) [3]. It follows from the figꢀ
ure that the content in PEPBIꢀOꢀPH of the microgel
that is present in the initial PBIꢀOꢀPH considerably
decreases (from 33% to 8%) [3], and the molecular
weight distribution of the main fraction becomes
proton conductivity values are
≥
5 mS/cm at 150–
200 , better 50 mS/cm; therefore, the application
°
С
≥
of the films of undoped PEPBIꢀOꢀPH appear to be
inappropriate. However, the preparation of complexes
much wider (Mw/Mn increases from 1.7 to 9.90).
Strong and elastic films based on PEPBIꢀOꢀPH of this polymer with PA may decrease the total amount
were cast onto glass supports from reaction solutions of free PA necessary to maintain the optimal perforꢀ
U, mV
log
M
500
400
300
200
100
0
7
6
5
4
1
2
3
3
0
5
10
Time, min
15
20
Fig. 3. Chromatograms of initial PBIꢀOꢀPH (1), its phosphonoethylation product (2), and calibration curve (3) relative to polyꢀ
styrene.
DOKLADY CHEMISTRY Vol. 432
Part 2
2010

174
PONOMAREV et al.
The MEA designed in this paper has worked in a
galvanostatic mode (current density
= 0.4 A/cm2) for
100 h at 160 and 300 h at 180 , showing a stable
= 0.595 and 0.615 V, respecꢀ
Δ
U, mV
j
950
850
750
650
550
450
°
С
°
С
potential difference
Δ
U
tively.
ACKNOWLEDGMENTS
We are grateful to Z.S. Klemenkova for recording
IR spectra and E.I. Goryunov for discussion of the
results.
This work was supported in part by the Russian
Academy of Sciences (Complex Program no. 7 of the
Division of Chemistry and Materials Science “Develꢀ
opment of Scientific Principles of Novel Chemical
Technologies and Preparation of Experimental
Batches of Compounds and Materials”).
3
2
1
4
0
0.2
0.4
0.6
0.8
, A/cm2
i
Fig. 4. Temperature dependences of discharge characterisꢀ
tics of sevenꢀlayer hydrogen–air MEA with membranes on
REFERENCES
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1
–
3
), PBIꢀOꢀPH (
4
), and
= 0.4 A/cm , star), PEMEAS Pꢀ1000
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180 ( ), 200 ( ); for PBIꢀOꢀPH: 160.
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®
[4], with the use of BASF Celtec P1000 commercial
electrodes (Germany). Figure 4 shows the discharge
characteristics of this MEA at 160, 180, and 200°С.
It is obvious that the MEA on the basis of PEPBIꢀ
OꢀPH has higher currentꢀvoltage characteristics than
an analog assembled with the use of nonꢀphosphoryꢀ
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Unit Polymers), Moscow: Nauka, 1977.
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®
above 0.2 A/cm2 is on a level of BASF Celtec P comꢀ
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mercial reference sample.
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We explain the slightly lowered values of open cirꢀ
cuit voltage (OCV) of the tested MEA (0.760 V) by the
features of the chemical structure of PEPBIꢀOꢀPH;
the polymer seems to have enhanced gas permeability
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DOKLADY CHEMISTRY Vol. 432
Part 2
2010