Preparation of acid-functionalized poly(phenylene oxide)s and poly(phenylene sulfone) and their proton conductivity

Article abstract of DOI:10.1246/bcsj.80.1429

A series of highly acid-functionalized poly(phenylene oxide)s and poly(phenylene sulfone) were prepared and proton conductivity in their membranes is discussed. Phosphorylated poly(phenylene oxide)s were prepared via the oxidative polymerization of phosph

Full text of DOI:10.1246/bcsj.80.1429

Ó 2007 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 80, No. 7, 1429–1434 (2007) 1429
Preparation of Acid-Functionalized Poly(phenylene oxide)s and
Poly(phenylene sulfone) and Their Proton Conductivity
ꢀ
Takahiro Tago, Norikazu Kuwashiro, and Hiroyuki Nishide
Department of Applied Chemistry, Waseda University, Tokyo 169-8555
Received January 9, 2007; E-mail: nishide@waseda.jp
A series of highly acid-functionalized poly(phenylene oxide)s and poly(phenylene sulfone) were prepared and pro-
ton conductivity in their membranes is discussed. Phosphorylated poly(phenylene oxide)s were prepared via the oxida-
tive polymerization of phosphonoxyphenols in alkaline water, along with a facile monomer preparation. A poly(phenyl-
ene oxide) bearing a sulfamide acid group was prepared by reacting amidosulfate with the corresponding carboxylated
poly(phenylene oxide). A sulfonated poly(phenylene sulfone) was prepared by hydrogen peroxide oxidation of the sul-
fonated poly(phenylene sulfide). All these acid-functionalized polymers showed appropriate thermal stability based on
the aromatic backbone. The polymers had a high ion-exchange capacity, were water-soluble, but gave transparent and
flexible membranes after compositing with the poly(ethylene oxide). Some of the membranes displayed a high proton
conductivity of 10ꢁ4 S cmꢁ1 at 120 ꢂC under dry conditions.
Acid-functionalized polymers have recently become inter-
esting because of their potential usefulness as proton-conduct-
ing polymer electrolyte membranes (PEMs) for fuel cells.1–4
Besides the proton conductivity, thermostability is also crucial
for PEMs, and one of the approaches to provide thermostable
PEMs is the functionalization of acid groups onto aromatic
polymers which have a thermal degradation temperature >250
ꢂC; examples of the backbone aromatic polymers include
a polyimide,5,6 poly(etheretherketone),7 polysulfone,8 poly-
(phenylene),9 poly(phenylene sulfide),10 and poly(phenylene
oxide).11
Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), which has a
compact repeating unit structure of a rigid aromatic ring and
flexible ether linkage, is widely used as a high-performance
engineering plastic because it has a high glass-transition tem-
perature (Tg ¼ 205{210 ꢂC), good mechanical property, and
high hydrolytic and oxidative stabilities.12 PPO is prepared
both industrially and on a laboratory scale by the oxidative
polymerization of 2,6-dimethylphenol with a copper–amine
catalyst.13,14 The polymerization proceeds at room tempera-
ture, and it is an ideal atom economical reaction that does
not require any leaving groups for producing the polymer.12–16
It has been reported that the sulfonation and phosphonation of
PPO produced acid-functionalized PPOs.17–20 However, the
ion-exchange capacity (IEC) of the obtained acid-functional-
ized PPOs remained up to 1.8 meq gꢁ1 based on previous re-
ports. On the other hand, oxidative polymerization of the
acid-functionalized phenols has been examined; however, it
has been impeded by both their high oxidation potential and
also by the formation of a chelate complex with a copper–
amine catalyst.14 From the aspect of a green chemical process,
we have developed the oxidative polymerization of 2,6-
dimethylphenol to form PPO using alkaline water as the reac-
tion solvent.15,16 It has been concluded that the reaction in
alkaline water reduces the oxidation potential of the acid-
functionalized phenols and facilitates the polymerization.
The formation of a chelate complex with the catalyst or cata-
lyst inactivation can also be prevented by using a metal oxide,
such as a silver oxide, as the oxidizing agent to yield the PPO.
We have succeeded in the oxidative polymerization of sulfo-
natopropoxyphenols in alkaline water using silver oxide to
prepare the sulfoalkoxy-pendant PPOs.21
Phosphoric acid is known to show a high acid dissociation
degree of 13% in the bulk and to display a high proton conduc-
tivity of almost 10ꢁ1 S cmꢁ1 at its melting point (42 ꢂC) in a
water-free state.22 Proton-conducting polymers bearing the
phosphoric acid group have been studied in hopes of not only
a higher proton conductivity in a low humidified and a dry
state, but also higher thermal and chemical stabilities than
those of the sulfonated polymers.23–25 In this paper, we first re-
port the preparation of phosphorylated PPOs (1 and 2) via the
oxidative polymerization of the corresponding phosphonoxy-
phenols (OPP and MPP) in alkaline water using silver oxide,
as well as a facile preparation of the monomer (Schemes 1
and 2).
Recently, we have reported that sulfamide acid (sulf-
amidocarbonyl: –CONHSO3H) is a novel proton source for
PEMs.26,27 The sulfamide acid has both an electron-withdraw-
ing carbonyl group and a conjugated structure possibly afford-
ing a very high proton-dissociation ability in a water-free state
upon PEM application in addition to good hydrolytic and
thermal stabilities. We have also reported the preparation of a
carboxylated PPO via oxidative polymerization and its high
thermal stability.11 We now describe in this paper the prepara-
tion of PPO bearing a sulfamide acid group (4) and its proton
conductivity (Scheme 3).
Poly(1,4-phenylene sulfone) (PPSU) is one of the high-
performance engineering plastics with good thermal, chemical,
and mechanical stabilities.28 PPSU has also been prepared
from poly(phenylene sulfide) by oxidation using hydrogen per-
oxide.29 On the other hand, Miyatake et al. have successfully
reported a very high proton conductivity of 10ꢁ3 S cmꢁ1 for
Published on the web July 11, 2007; doi:10.1246/bcsj.80.1429

1430 Bull. Chem. Soc. Jpn. Vol. 80, No. 7 (2007)
Acid-Functionalized Poly(phenylene oxide)s
OH
OPO3H2
OPO3H2
OH
P2O5
Ag2O
HCl
n
n
O
OH
n
NaOH, H2O
OPP
1
Scheme 1.
CH3
OPO3H2
OH
CH3
OPO3H2
OPO3H2
OH
OPO3H2
P2O5
Ag2O
NaOH, H2O
HCl
n
OH
CH3
l
m
+
OH
CH3
O
O
m
l
CH3
2
MPP
Scheme 2.
COOH
CONHSO3H
(a)
10 µA
O
O
n
n
CH3
CH3
3
4
(b)
(c)
Scheme 3.
O
S
O
H2O2
HCl
S
n
n
CF3COOH
SO3H
SO3H
m
m
0
0.2
0.4
0.6
5
6
Potential / V vs. Ag/AgCl
Scheme 4.
Fig. 1. Cyclic voltammograms of the 10 mM (a) 2,6-di-
methylphenol, (b) OPP, and (c) MPP in a 50 mM aqueous
sodium hydroxide solution at a scan rate of 25 mV sꢁ1
the highly sulfonated poly(1,4-phenylene sulfide) (PPS) (5)
composite membrane with poly(ethylene oxide).30 In this
paper, we also describe the preparation of the sulfonated PPSU
(6) by the simple hydrogen peroxide oxidation of the sulfo-
nated PPS (Scheme 4): We expect for the sulfonated PPSU an
enhanced proton conductivity due to the electron-withdrawing
sulfone group. The thermal stability of these acid-functional-
ized polymers is also described in this paper.
.
Table 1. Oxidative Polymerizations of OPP and MPPaÞ
bÞ
Temp Time Yield Mw
/ꢂC /day
Entry Monomer
Mw=Mn
/% (ꢃ105)
cÞ
1
2
3
4
5
6
OPP
MPP
MPP
MPP
MPP
MPP
r.t.
r.t.
r.t.
50
1
1
8
1
1
1
26
21
14
22
34
87
—
—
1.5
1.9
1.6
2.0
1.9
1.0
0.8
1.0
1.5
1.0
Results and Discussion
80
100
Phosphonoxyphenols, o-phosphonoxyphenol (OPP), and
methylphosphonoxyphenols (MPP), which are the monomers
used to produce the phosphorylated PPO polymers, were pre-
pared in high yields by simply mixing the corresponding cate-
chols with diphosphorus pentaoxide at a temperature slightly
higher than their melting points.31 MPP was obtained as 2-
methyl-6-phosphonoxyphenol and its structural isomer, 3-
methyl-2-phosphonoxyphenol, in a 5/3 molar ratio estimated
a) The polymerization of the phenol (3 mmol) was carried
out in water (30 mL) with sodium hydroxide (15 mmol) and
silver oxide (15 mmol) in air. b) The molecular weight was
measured using gel permeation chromatography with poly(4-
styrenesulfonic acid) standards and a water eluent. c) Poly-
(phosphonoxyphenylene oxide) was insoluble in water.
1
from the H NMR spectra of the reaction product. Irreversible
oxidation currents of OPP and MPP in the alkaline water were
observed in the cyclic voltammograms with their peak poten-
tial at 0.49 and 0.45 V (vs. Ag/AgCl), respectively (Fig. 1).
The electron-donating methyl group of MPP is considered to
reduce the oxidation potential of phenol when compared to
that of OPP. The current value at the oxidation peak potential
of OPP was lower than those of 2,6-dimethylphenol and MPP,
probably due to the low solubility of OPP in the alkaline water.
Anyway, the oxidation potentials of OPP and MPP were
not very high and comparable to that (0.33 V) of 2,6-dimethyl-
phenol, which suggests the oxidative polymerizability of OPP
and MPP in the alkaline water solvent.
The oxidative polymerizations of OPP and MPP were exam-
ined in the alkaline water using silver oxide as an oxidizing
agent (Table 1). As the polymerization proceeded, a silver
mirror formed on the flask glass. Poly(phosphonoxyphenylene
oxide) (1) was obtained as a solvent-insoluble polymer during
the polymerization at room temperature (Table 1, Entry 1).
The poor solvent-solubility of OPP in a sodium hydroxide
aqueous solution and the cross-linking of the phenylene oxide

T. Tago et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 7 (2007) 1431
at the o-position of OPP were considered to produce the
solvent-insoluble polymer 1. Poly(methylphosphonoxyphenyl-
ene oxide) (2) with a high molecular weight of 105 was ob-
tained from the polymerization of MPP at room temperature
for 1 day (Table 1, Entry 2). The polymerization yield increas-
ed with an increase in reaction temperature, but the molecular
weight of the polymer 2 remained at almost 105 (Table 1,
Entries 3–6). Polymers 1 and 2 were obtained as a light-brown
7.0
9.0
8.0
δ / ppm
1
powder and characterized by IR, H, and 31P NMR spectros-
copies. The solid-state 31P NMR spectrum of the polymer 1
showed a peak at 2.5 ppm ascribed to the phosphoric acid
group. IR spectrum of the polymer 2 had broad absorption
bands at 1233 (ꢀP=O of –PO3H2), 1196 (ꢀP=O of –HPO3ꢁ), and
Fig. 2. 1H NMR spectrum of the polymer 6.
1219 cmꢁ1) by the phenylene oxide remained. After drying
in vacuo at 100 ꢂC for 3 days, the polymer 4 with IEC = 3.6
meq gꢁ1 was partially soluble in water, methanol, DMF, and
dimethyl sulfoxide, while 3 and 4 with IEC = 0.41 meq gꢁ1
was soluble in the same organic solvents, but insoluble in
water. The poor solvent solubility of 4 after heating suggested
intra- and/or inter-polymer hydrogen-bond formation through
the sulfamide acid groups in the solid-state polymer.
The sulfonated poly(1,4-phenylene sulfone) (PPSU) 6 was
prepared by the following hydrogen peroxide oxidation
(Scheme 4) of the sulfonated poly(1,4-phenylene sulfide) 5
with IEC = 4.4 meq gꢁ1, which was prepared according to a
previous report:10,30 The backbone sulfide of the polymer 5
was oxidized to the sulfone with an excess of a hydrogen
peroxide aqueous solution and trifluoromethanesulfonic acid,
based on a previous paper for the oxidation of poly(phenylene
sulfide).29 The polymer 6 was obtained as an off-white powder
1077 cmꢁ1 (ꢀP=O of –PO3 ) ascribed to the phosphoric acid
2ꢁ
group. The peak at 1474 cmꢁ1 (ꢁP{O{C) and the shoulder at
1271 cmꢁ1 (ꢀP{O{C) supported the phosphonoxy structure. The
peak at 1201 cmꢁ1 (ꢀC{O{C) attributed to the aromatic ether
bond, which overlapped with the broad P=O band, supported
the formation of the phenylene oxide polymer. Polymer 2
was insoluble in organic solvents, suggesting a slightly branch-
ing and/or cross-linking of the phenylene oxide at the o-
position of the phenol. Multiplet peaks in the solution 1H NMR
spectrum of 2 indicated a o- and p-substituted branched or
cross-linked structure of the phenylene oxide. However, 2
was soluble in water, an aqueous hydrochloric acid solution,
and an aqueous sodium hydroxide solution. The o-methyl
group of MPP is presumed to suppress the cross-linking
at the o-position in order to maintain the solubility of the
formed polymer. The IEC value of the polymer 2 was deter-
mined by acid–base titration to be 4.7 meq gꢁ1 and almost
agreed with the calculated IEC based on the chemical structure
of 2 (4.9 meq gꢁ1).
1
and characterized by H NMR and IR spectroscopies. In the
1H NMR spectrum of 6, peaks at 6.70–7.25 ppm ascribed to
the phenylene protons between the sulfide groups completely
disappeared, while new peaks at 8.35–8.64 ppm ascribed to
the phenylene protons between the sulfone and sulfonic acid
groups clearly appeared (Fig. 2). This supported the almost
quantitative conversion of the sulfide backbone to the sulfone
one. The IR spectrum of 6 also supported both the introduction
of the sulfone and the structure of the sulfonic acid group. The
characteristic S=O absorptions at 1334 and 1168 cmꢁ1 and
1218 and 1114 cmꢁ1 were ascribed to the sulfone and the
sulfonic acid, respectively. The polymer 6 was soluble in
water, DMF, and dimethyl sulfoxide, but insoluble in meth-
anol, ethanol, acetonitrile, and chloroform. The IEC of the
polymer 6 was determined by acid–base titration to be 3.7
meq gꢁ1 (the calculated IEC based on the chemical structure
of 6 = 6.7 meq gꢁ1).
Poly(2-methyl-6-sulfamidocarbonyl-1,4-phenylene oxide) (4)
was prepared by the following polymer reaction (Scheme 3) of
poly(2-carboxy-6-methyl-1,4-phenylene oxide) (3), which was
prepared according to a previous paper.11 The carboxylic acid
group of the polymer 3 was converted to the corresponding
acid chloride, which was reacted with an excess of triethyl-
ammonium amidosulfate, then treated with a cation-exchange
resin to yield the polymer 4 with the conversion to the sulf-
amide acid group of 76 and 9% for the water-soluble and
insoluble part of 4, respectively. The IEC values of the water-
soluble and -insoluble 4 estimated from sulfur elemental
analysis were 3.6 and 0.41 meq gꢁ1, respectively, and almost
1
consistent with the IEC value determined from the H NMR
spectra (the calculated IEC based on the chemical structure
of 4 = 4.4 meq gꢁ1). The polymer 4 with IEC = 3.6 meq gꢁ1
was obtained as a light-brown powder and characterized
by 1H NMR and IR spectroscopy. In the 1H NMR spectrum
of 4, the phenylene proton peaks at 7.11 and 6.94 ppm ascribed
to those of 3 significantly decreased, and new phenylene
proton peaks at 7.85 and 7.45 ppm clearly appeared, which
supported the high conversion (determined by the elemental
analysis) from the carboxylic acid derivative to the sulfamide
acid one. From the IR spectrum of 4 the introduction of the
sulfamide acid group and the structure of the phenylene oxide
backbone were evident: The new absorptions (ꢀC=O ¼ 1644
cmꢁ1 and ꢀS=O ¼ 1171, 1037 cmꢁ1) for the sulfamide acid
The thermal property of the obtained acid-functionalized
polymers 2–6 was measured by thermogravimetry (TG) and
differential scanning calorimetry (DSC). TG curves for the
polymers 2–6 are shown in Fig. 3, and the 10%-degradation
temperatures (Td10%) are listed in Table 2. The Tg of the poly-
mers was estimated by DSC and given also in Table 2.
Because of their hygroscopicity, the polymers were dried
in vacuo at 100 ꢂC for 3 days before the measurement. The
Td10% and Tg of the phosphorylated PPO 2 were more than
70 ꢂC higher than those of the sulfoalkoxy-pendant PPO
(Td10% ¼ 288 and Tg ¼ 115 ꢂC21). The thermal stability of 2
was as high as those of the previously reported poly(arylene
ether)s bearing the phosphoric acid group and probably
group clearly appeared and the strong absorption (ꢀC{O{C
¼

1432 Bull. Chem. Soc. Jpn. Vol. 80, No. 7 (2007)
Acid-Functionalized Poly(phenylene oxide)s
derived from the intra- and/or inter-polymer hydrogen-
bonding or cross-linking through the phosphoric acids, as
has been described for the previous phosphoric acid-bearing
poly(arylene ether)s.23 The Td10% of a PPO bearing the sulf-
amide acid group 4 with IEC = 3.6 meq gꢁ1 was ca. 40 ꢂC
higher than that of the starting carboxylated PPO 3, but the
Tg of the polymer 4 was ca. 40 ꢂC lower than that of 3. It
was considered that the higher Td10% of 4 was derived from
the stability of the sulfamide acid group conjugated with the
backbone, and the lower Tg of 4 was from the relatively weak
interaction between the phenylene oxide backbone with the
large sulfamide acid group. The Td10% of the sulfonated PPSU
6 was 130 ꢂC lower than that of the sulfonated PPS 5, but the
Tg of the polymer 6 was 50 ꢂC higher than that of the polymer
5, which could be due to the strong electron-withdrawing sul-
fone group on the backbone. All these obtained acid-function-
alized polymers showed a sufficient Tg and Td10% of more than
160 and 350 ꢂC, respectively, based on the aromatic backbone.
Membranes of the acid-functionalized polymers 2 and 4–6
were prepared by casting from their aqueous solutions, and
that of 3 was from the methanol solution. All of the homo-
polymer membranes were transparent, but not self-independent
enough for the proton conductivity measurement. Compositing
of the polymers 2–6 with poly(ethylene oxide) of Mw ¼ 600 in
a 1/1 weight ratio produced transparent and flexible mem-
branes (The composite membrane for the carboxylated PPO
3 with poly(ethylene oxide) in a 1/1 weight ratio was too
flexible to measure the conductivity, therefore, the membrane
was prepared in a 2/1 weight ratio). The membranes were
dried in vacuo at 100 ꢂC for 3 days before the conductivity
measurement.
The proton conductivity of the dry membranes using the
acid-functionalized polymers 2–6 composited with poly(ethyl-
ene oxide) was plotted as a function of the temperature from
30 to 170 ꢂC along with the control data of the NafionÒ117
(Fig. 4). The proton conductivity of the composite membrane
of the phosphorylated PPO 2 was on the order of 10ꢁ4
–
10ꢁ6 S cmꢁ1 which was higher than that of the NafionÒ117
membrane (10ꢁ5–10ꢁ8 S cmꢁ1) with IEC = 0.9 meq gꢁ1 under
the same measurement conditions. The proton conductivity of
the composite membranes of the PPO bearing the sulfamide
acid group 4 with IEC = 3.6 meq gꢁ1 and sulfonated PPSU
6 was on the order of 10ꢁ5–10ꢁ6 and 10ꢁ4–10ꢁ7 S cmꢁ1, re-
spectively, which was remarkably higher than those (10ꢁ7
–
10ꢁ12 and 10ꢁ5–10ꢁ9 S cmꢁ1) for the pre-polymer 3 and 5, re-
spectively. The highest conductivity reached 10ꢁ4 S cmꢁ1 at
>120 ꢂC for the composite membrane composed of polymers
2 and 6 among all the obtained polymers. The conductivity in-
crease with temperature from 30 to 170ꢂC obeyed an Arrhenius
type plot to give the activation energies of 29, 18, and
Temperature / °C
180150 120 90
60
30
–3
–5
100
–7
–9
σ
5
90
4
80
2
–11
3
2.2
2.6
3.0
3.4
70
1000 × T–1 / K–1
6
Fig. 4. Proton conductivity of the dry membranes compos-
ited with poly(ethylene oxide) for 2 ( ), 3 ( ), 4 with
IEC = 3.6 meq gꢁ1 ( ), 4 with IEC = 0.41 meq gꢁ1 ( ),
5 ( ), and 6 ( ), and a control of dry NafionÒ117
membrane ( ).
60
0
100 200 300 400 500
Temperature / °C
Fig. 3. TG curves of the polymers 2–6.
Table 2. Properties of Acid-Functinalized Polymers 2–6
bÞ
IECaÞ
/meq gꢁ1
Mw
Mw=Mn
Tg
/ꢂC
Td10%
/ꢂC
SolubilitycÞ
CH3OH
Polymer
(ꢃ104)
10
2.0
N. A.
1.3
1.5
CHCl3
DMF
H2O
2
3
4
5
6
4.7
6.7
3.6
4.4
3.7
1.9
1.7
N. A.
2.3
2.3
180
193
154
202
255
383
350
390
486
360
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
+
ꢄ
ꢁ
ꢁ
ꢁ
+
ꢄ
+
+
+
ꢁ
ꢄ
+
+
a) IEC (ion-exchange capacity) for the most acidic proton. b) The molecular weight was measured using gel permea-
tion chromatography with poly(4-styrenesulfonic acid) standards and a water eluent for 2, and with polystyrene
standards and a DMF eluent for 3–6. c) + = Soluble, ꢄ = partially soluble, ꢁ = insoluble.

T. Tago et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 7 (2007) 1433
119.9, 119.3, 117.0, 16.6, 16.1; 31P NMR (202 MHz, D2O,
H3PO4) ꢁ ꢁ2:17, ꢁ3:19; IR (KBr, cmꢁ1) 1477 (ꢁP{O{C), 1276
(ꢀP{O{C), 1209 (ꢀP=O of –PO3H2), 1182 (ꢀP=O of –HPO3ꢁ), 1083
(ꢀP=O of –PO32ꢁ), 1031 (ꢀP=O of –HPO3ꢁ), 977 (ꢀP{O{H); ESI-
MS (m=z) 203.5 (Mꢁ), 203.0 (calcd); Anal. Calcd for C7H9O5P:
C, 41.1; H, 4.4%. Found: C, 39.7; H, 4.6%.
49 kJ molꢁ1 for the composite membrane of polymers 2, 4, and
6, respectively. These activation energies for the proton con-
ductivity of the composite membranes were significantly lower
than those (69, 86, and 121 kJ molꢁ1) of the NafionÒ117
membrane and the composite membrane of polymers 3 and
4 with IEC = 0.41 meq gꢁ1. A high conductivity and low acti-
vation energy for the composite membranes of the polymers 2,
4, and 6 could be considered to be caused by the high proton
concentration in the membrane which was derived from the
high IEC and the high proton-dissociation ability of the phos-
phoric acid group, the sulfamide acid group, and the sulfonic
acid group conjugated with the electron-withdrawing sulfone
group for 2, 4, and 6, respectively.
In conclusion, the poly(phenylene oxide)s bearing a phos-
phoric acid group and a sulfamide acid group and sulfonated
poly(phenylene sulfone) with high IEC were prepared as ther-
mostable proton-conducting PEMs. These highly acid-func-
tionalized polymers gave transparent and flexible membranes
after compositing with poly(ethylene oxide). The composite
membranes for the phosphorylated poly(phenylene oxide)
and the sulfonated poly(phenylene sulfone) displayed the high
proton conductivity of 10ꢁ4 S cmꢁ1 at >120 ꢂC under dry
conditions.
Oxidative Polymerization of Phosphonoxyphenols. A typi-
cal procedure is described as follows. Methylphosphonoxyphenol
(0.61 g, 3 mmol) was dissolved in water (30 mL) containing so-
dium hydroxide (0.60 g, 15 mmol). Silver oxide (3.48 g, 15 mmol)
was added to the solution, and the mixture was stirred at room
temperature for 24 h. After centrifugation, the residue solution
was stirred in 10% aqueous hydrochloric acid (20 mL) for 6 h
and dialyzed (Mw cut off = 1000) in water for 2 days. After
evaporation and drying in vacuo at 100 ꢂC for 3 days, poly(meth-
ylphosphonoxyphenylene oxide) (2) was obtained as a light-
brown powder (0.13 g, yield 21%). 1H NMR (500 MHz, D2O) ꢁ
7.35–6.00 (m, aromatic C–H), 2.27–1.58 (m, CH3); 31P NMR
(202 MHz, D2O, H3PO4) ꢁ ꢁ4:74; IR (KBr, cmꢁ1) 1474
(ꢁP{O{C), 1271 (ꢀP{O{C), 1233 (ꢀP=O of –PO3H2), 1201 (ꢀC{O{C),
1196 (ꢀP=O of –HPO3ꢁ), 1077 (ꢀP=O of –PO32ꢁ), 985 (ꢀP{O{H);.
GPC (poly(4-styrenesulfonic acid) standards and water eluent)
Mw ¼ 1:0 ꢃ 105.
Preparation of Poly(2-methyl-6-sulfamidocarbonyl-1,4-phen-
ylene oxide) (4). Poly(2-carboxy-6-methyl-1,4-phenylene oxide)
(3) was prepared according to the previous paper.11 The polymer
3 (0.15 g, 1 unit mmol) was dissolved in anhydrous DMF (20 mL).
Thionyl chloride (0.30 g, 2.5 mmol) was added to the solution,
and the mixture was stirred under nitrogen at room temperature
for 6 h. Amidosulfuric acid (0.49 g, 5 mmol) and triethylamine
(0.51 g, 5 mmol) were mixed in dichloromethane (5 mL) to form
a clear solution of triethylammonium amidosulfate. The triethyl-
ammonium amidosulfate solution was added to the polymer solu-
tion, and the mixture was stirred under nitrogen at room tempera-
ture for 16 h. The reaction mixture was concentrated, dialyzed
(Mw cut off = 1000) in water for 2 days, and evaporated. Water-
soluble and -insoluble parts were separated by filtration. The resi-
due was dissolved in methanol (400 mL), stirred with a cation-
exchange resin, AmberlystÒ 15JWET (Organo Co.), at room
temperature for 12 h, and the solvent was evaporated. After
drying in vacuo at 100 ꢂC for 3 days, poly(2-methyl-6-sulfamido-
carbonyl-1,4-phenylene oxide) (4) with IEC = 3.6 and 0.41 meq
gꢁ1 for water-soluble and -insoluble parts, respectively, was
Experimental
Preparation of o-Phosphonoxyphenol (OPP).
Catechol
(4.95 g, 45 mmol) was warmed at a temperature slightly higher
than its melting point (110 ꢂC), and diphosphorus pentaoxide
(4.26 g, 30 mmol) was slowly added with vigorous stirring for
2 h. As the reaction proceeded, the mixture became a brownish
viscous liquid. After cooling to room temperature, the mixture
was dissolved in water (50 mL) and extracted with diethyl ether.
The extract was dried over anhydrous sodium sulfate and evapo-
rated. The residue was dissolved in dichloromethane (300 mL)
containing a few drop of methanol, and the solution was concen-
trated. After cooling to room temperature, the precipitate was col-
lected by filtration and dried in vacuo to give OPP as a white pow-
1
der (5.57 g, yield 65%). H NMR (500 MHz, acetone-d6, TMS) ꢁ
7.19 (1H, d, aromatic C–H), 7.03 (1H, t, aromatic C–H), 6.93 (1H,
d, aromatic C–H), 6.80 (1H, t, aromatic C–H); 13C NMR (125
MHz, acetone-d6, TMS) ꢁ 148.7, 140.0, 127.4, 122.3, 121.1,
118.2; 31P NMR (202 MHz, D2O, H3PO4): ꢁ ꢁ1:87; IR (KBr,
cmꢁ1) 1461 (ꢁP{O{C), 1264 (ꢀP{O{C), 1241 (ꢀP=O of –PO3H2),
1182 (ꢀP=O of –HPO3ꢁ), 1102 (ꢀP=O of –PO32ꢁ), 1035 (ꢀP=O of
–HPO3ꢁ), 976 (ꢀP{O{H);. ESI-MS (m=z) 189.1 (Mꢁ), 189.0
(calcd); Anal. Calcd for C6H7O5P: C, 37.9; H, 3.7%. Found: C,
37.9; H, 3.7%.
Preparation of Methylphosphonoxyphenol (MPP). 3-Meth-
ylcatechol (5.59 g, 45 mmol) was warmed at 100 ꢂC or a temper-
ature slightly higher than its melting point (95 ꢂC). Diphosphorus
pentaoxide (4.26 g, 30 mmol) was slowly added with vigorous stir-
ring for 2 h. The reaction mixture was dissolved in water (50 mL)
and extracted with diethyl ether. The extract was dried over anhy-
drous sodium sulfate, and the solvent was evaporated. Recrystal-
lization from dichloromethane gave MPP as white plate crystals
(6.80 g, yield 74%). mp 92 ꢂC. 1H NMR (500 MHz, acetone-d6,
TMS) ꢁ 7.06 (1H, d, aromatic C–H), 6.92 (1H, d, aromatic C–H),
6.91 (1H, t, aromatic C–H), 6.76 (1H, d, aromatic C–H), 6.71 (1H,
d, aromatic C–H), 6.70 (1H, t, aromatic C–H), 2.27 (3H, s, CH3),
2.20 (3H, s, CH3); 13C NMR (125 MHz, acetone-d6, TMS) ꢁ
149.5, 147.1, 139.6, 138.7, 132.2, 127.9, 127.8, 126.2, 122.7,
obtained as a light-brown powder (4 with IEC = 3.6 meq gꢁ1
0.028 g, yield 13%; 4 with IEC = 0.41 meq gꢁ1: 0.13 g, yield
85%). 4 with IEC = 3.6 meq gꢁ1 1H NMR (500 MHz, CD3OD,
:
:
TMS) ꢁ 7.85 (1H, m, aromatic C–H), 7.45 (1H, m, aromatic C–H),
1.98 (3H, m, CH3); IR (KBr, cmꢁ1) 1714, 1644 (ꢀC=O), 1219
(ꢀC{O{C), 1171, 1037 (ꢀS=O); Anal. Calcd for C8H7NO5S: C, 41.9;
H, 3.1; N, 6.1; S, 13.9%. Found: C, 42.2; H, 5.6; N, 3.2; S, 10.7%.
Preparation of Sulfonated Poly(1,4-phenylene sulfone) 6.
Sulfonated poly(1,4-phenylene sulfide) 5 was prepared according
to the previous paper.10,30 The polymer 5 with IEC = 4.4 meq gꢁ1
(0.42 g, 2.5 unit mmol) was dissolved in 30% hydrogen peroxide
solution (12 mL) and trifluoromethanesulfonic acid (60 mL). The
mixture was stirred at 70 ꢂC for 10 h and dialyzed (Mw cut
off = 1000) in water for 2 days. 10% Aqueous hydrochloric acid
(20 mL) was added to the polymer solution. The mixture was
stirred at room temperature for 6 h, dialyzed (Mw cut off = 1000)
in water for 2 days, and the solvent was evaporated. After drying
in vacuo at 100 ꢂC for 3 days, the sulfonated poly(1,4-phenylene
sulfone) 6 with IEC = 3.7 meq gꢁ1 was obtained as a off-white

1434 Bull. Chem. Soc. Jpn. Vol. 80, No. 7 (2007)
Acid-Functionalized Poly(phenylene oxide)s
powder (0.48 g, yield 97%). 1H NMR (500 MHz, D2O) ꢁ 8.64–
8.35 (br, aromatic C–H), 8.32–8.00 (br, aromatic C–H); IR
(KBr, cmꢁ1) 1334, 1168 (ꢀSO2), 1218, 1114 (ꢀSO3H).
Membrane Preparation. A typical procedure is as follows.
The polymer (30 mg) and poly(ethylene oxide) (30 mg) with
Mw ¼ 600 were dissolved in water (0.3 mL), mixed, and cast onto
a gold plate (ꢂ ¼ 1:5 cm), followed by drying at 70 ꢂC for 2 h and
in vacuo at 100 ꢂC for 3 days.
Materials. Catechol and 3-methylcatechol were purchased
from the Kanto Chemical Co. and purified by recrystallization
from chloroform and hexane, respectively. The NafionÒ117 mem-
brane was purchased from the Aldrich Chemical Co. All other
reagents and solvents were purchased from the Kanto Chemical
Co. and used without further purification.
Rev. 2004, 104, 4637.
N. Asano, M. Aoki, S. Suzuki, K. Miyatake, H. Uchida, M.
Watanabe, J. Am. Chem. Soc. 2006, 128, 1762.
C. Genies, R. Mercier, B. Sillion, N. Cornet, G. Gebel, M.
Pineri, Polymer 2001, 42, 359.
K. Miyatake, H. Zhou, H. Uchida, M. Watanabe, Chem.
Commun. 2003, 368.
4
5
6
7
8
D. J. Jones, J. Roziere, J. Membr. Sci. 2001, 185, 41.
F. Wang, M. Hickner, Q. Ji, W. Harrison, J. Mecham, T. A.
Zavodzinski, J. E. McGrath, Macromol. Symp. 2001, 175, 387.
T. Kobayashi, M. Rikukawa, K. Sanui, N. Ogata, Solid
State Ionics 1998, 106, 219.
9
10 K. Miyatake, E. Shouji, K. Yamamoto, E. Tsuchida,
Macromolecules 1997, 30, 2941.
Proton Conductivity Measurement. The membrane pressed
between a pair of gold plate electrodes was mounted in the two-
probe cell. The cell was placed in the temperature-controlled
chamber. The proton conductivity was measured using an Autolab
PGSTAT30 AC impedance spectrometer over the frequency range
from 1 Hz to 1 MHz and the temperature range from 170 to 30 ꢂC
at intervals of 20 ꢂC after keeping the cell in the chamber at
170 ꢂC for 3 h.
Thermal Analysis. The thermal analyses were performed via
TG/DTA-MS using a Rigaku TG8120 equipped with a Shimadzu
GC-17A gas chromatograph mass spectrometer over the tempera-
ture range from 60 to 500 ꢂC at a heating rate of 10 ꢂC minꢁ1 after
keeping it at 150 ꢂC for 1 h and cooling to 60 ꢂC at a cooling rate
of 5 ꢂC minꢁ1 under helium and via DSC by a Rigaku DSC8230
over the temperature range from 30 to 300 ꢂC at a heating rate
of 5 ꢂC minꢁ1 under nitrogen.
11 K. Saito, T. Tazaki, R. Matsubara, H. Nishide, Ind. Eng.
Chem. Res. 2005, 44, 8626.
12 D. Aycock, V. Abolins, D. M. White, Encyclopedia of
Polymer Science and Engineering, 2nd ed., John Wiley & Sons,
New York, 1986, Vol. 13, p. 1.
13 A. S. Hay, J. Polym. Sci., Part A: Polym. Chem. 1998, 36,
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14 E. Tsuchida, H. Nishide, Makromol. Chem. 1975, 176,
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15 K. Saito, T. Masuyama, H. Nishide, Green Chem. 2003, 5,
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16 K. Saito, T. Tago, T. Masuyama, H. Nishide, Angew.
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17 B. Kruczek, T. Matsuura, J. Membr. Sci. 1998, 146, 263.
18 K. Ramya, K. S. Dhathatheryan, J. Appl. Polym. Sci. 2003,
88, 307.
Other Measurements. 1H, 13C, and 31P NMR, mass, and
infrared spectra were recorded on JEOL Lambda 500, Thermo
Quest Finnigan LCQ DECA, and JASCO FT/IR-410 spectrome-
ters, respectively. The cyclic voltammetry was carried out for
the 10 mM phenol in a 50 mM sodium hydroxide solution using
19 K. Miyatake, H. Zhou, M. Watanabe, J. Polym. Sci., Part
A: Polym. Chem. 2005, 43, 1741.
20 K. Chander, R. C. Anand, I. K. Varma, J. Macromol. Sci.,
Chem. 1983, 20, 697.
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a BAS 100B electrochemical analyzer at a scan rate of 25 mV sꢁ1
.
Platinum working and Ag/AgCl reference electrodes were used.
The formal potential of the ferrocyane/ferricyane couple in water
was 0.39 V versus this reference electrode. The molecular weights
were determined by gel permeation chromatography (GPC) at 40
ꢂC using a Tosoh TSK GEL ꢃ-4000 ꢃ 2, ꢃ-3000 ꢃ 1, and ꢃ-
2500 ꢃ 1 with a water eluent, and a Tosoh TSK GELꢃ-3000 ꢃ 1
and ꢃ-2500 ꢃ 1 with a DMF eluent. The elemental analysis was
performed on a Perkin-Elmer PE-2400. The IEC was measured
by acid–base titration. The membranes were soaked in a saturated
aqueous sodium chloride solution. The released proton was titrat-
ed using a 1 mM aqueous sodium hydroxide solution.
22 T. Dippel, K. D. Kreuer, J. C. Lassegues, D. Rodriguez,
Solid State Ionics 1993, 61, 41.
23 K. Miyatake, A. S. Hay, J. Polym. Sci., Part A: Polym.
Chem. 2001, 39, 3770.
24 Y. Z. Meng, S. C. Tjong, A. S. Hay, S. J. Wang, Eur.
Polym. J. 2003, 39, 627.
25 M. Rikukawa, D. Inagaki, K. Kaneko, Y. Takeoka, I. Ito,
Y. Kanzaki, K. Sanui, J. Mol. Struct. 2005, 739, 153.
26 T. Tago, N. Morishita, H. Nishide, Proc. Int. Congr.
Membr. Membr. Processes 2005, 105.
27 A. Sonai, T. Tago, H. Nishide, Jpn. Kokai Tokkyo Koho JP
2005251523, 2005.
28 R. N. Johnson, A. G. Farnham, R. A. Clendinning, W. F.
Hale, C. N. Merriam, J. Polym. Sci., Part A: Polym. Chem.
1967, 5, 2375.
This work was partially supported by a Grants-in-Aid for
Scientific Research and the 21COE Program ‘‘Practical
Nano-Chemistry’’ from MEXT, Japan.
29 H. M. Colquhoun, P. L. Aldred, F. H. Kohnke, P. L.
Herbertson, I. Baxter, D. J. Williams, Macromolecules 2002, 35,
1685.
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