Poly(phthalazinone ether ketone) ionomers synthesized via N-C coupling reaction for fuel cell applications

Article abstract of DOI:10.1021/ma050902q

Sulfonated poly(phthalazinone ether ketone)s with different sulfonation degrees were directly polymerized via N-C coupling reaction. The resulting polymers with inherent viscosity ranging from 0.97 to 1.29 dL/g were characterized by ¹H NMR and elemental analysis. Membranes were obtained by casting 5% solution in DMAc (N,N′-dimethylacetamide) of the polymers at 60°C. Because of their specially designed structure, the membranes of the polymer have excellent thermal and oxidative stability. TGA curves showed that the loss of sulfonic groups occurred at around 300°C. The membranes demonstrated excellent acidic stability; their forms could be maintained for at least 47 h when subjected to Fenton's reagent (30 ppm FeSO₄ in 30% H₂O₂) at 25°C. For the polymer with a sulfonation degree of 2, the highest water uptake of 46% at 80°C and the best proton conductivity of 1.77 × 10^-2 S/cm at 95°C 100% relative humidity were obtained, and a low E_a of 5.6 kJ/mol was calculated.

Full text of DOI:10.1021/ma050902q

Macromolecules 2005, 38, 10007-10013
10007
Poly(phthalazinone ether ketone) Ionomers Synthesized via N-C
Coupling Reaction for Fuel Cell Applications
Yu-lin Chen,† Yue-zhong Meng,*,† Xiu-hua Li,† and Allan S. Hay‡
State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University,
Guangzhou 510275, P. R. China, and Department of Chemistry, McGill University,
801 Sherbrooke West, Montreal, Quebec H3A 2K6, Canada
Received April 28, 2005; Revised Manuscript Received September 21, 2005
ABSTRACT: Sulfonated poly(phthalazinone ether ketone)s with different sulfonation degrees were directly
polymerized via N-C coupling reaction. The resulting polymers with inherent viscosity ranging from
1
0.97 to 1.29 dL/g were characterized by H NMR and elemental analysis. Membranes were obtained by
casting 5% solution in DMAc (N,N′-dimethylacetamide) of the polymers at 60 °C. Because of their specially
designed structure, the membranes of the polymer have excellent thermal and oxidative stability. TGA
curves showed that the loss of sulfonic groups occurred at around 300 °C. The membranes demonstrated
excellent acidic stability; their forms could be maintained for at least 47 h when subjected to Fenton’s
reagent (30 ppm FeSO4 in 30% H2O2) at 25 °C. For the polymer with a sulfonation degree of 2, the highest
water uptake of 46% at 80 °C and the best proton conductivity of 1.77 × 10-2 S/cm at 95 °C 100% relative
humidity were obtained, and a low Ea of 5.6 kJ/mol was calculated.
Introduction
biphenylene moieties23 and tetraphenylphenylene, per-
fluorobiphenylene, and tetrakis(sulfophenyl)phenylene.24
In previous work, we reported the synthesis of poly-
(arylene ether sulfone)s with pendant phosphorous acid
groups meta to the ether group25 and the synthesis of
poly(arylene ether)s from masked bisphenol whose ortho
positions to the ether bond were occupied by methyl
groups, in which the sulfonation can only take place at
the para positions on the pendant phenyl rings.26,27
It is of great interest to develop sulfnonated polymers
by direct polymerization, of which the sulfonic acid
groups are attached to the deactivated aromatic rings.
It is expected that such sulfonic acid groups might
enhance stability and higher acidity of the resulting
polymer and thus make the transportation of protons
more easily.28-34 In the present investigation, we em-
ployed bisphthalazinone, dihalide, and sulfonated di-
halide monomers to directly polymerize to give high-
molecular-weight sulfonated polymers via N-C coupling
reaction. Since it is the heterocyclic N-C bond ortho to
the sulfonic acid group but not to the aromatic ether
bond, such sulfonated polymers showed excellent ther-
mal, chemical stability, and resistance to oxidation.
Moreover, the membranes of the polymers had reason-
able water affinity and good proton conductivity.
Along with the progress of proton exchange mem-
branes (PEMs), a number of approaches have been
introduced to prepare novel nonfluorosulfonic polymers
including polyketones,1-4 polyimides,5-11 poly(phenylene
sulfide),12 and polysulfones13-16 as promising alternative
materials to replace perfluorosulfonic copolymers. Du-
Pont’s Nafion, for exemple, possesses good mechanical
strength, chemical stability, and high conductivity, but
it has some drawbacks such as high cost, low conductiv-
ity at elevated temperature, and high methanol cross-
over.
There are two strategies to prepare sulfonated iono-
mers. The first one is postsulfonation of prepared
polymers by different sulfonation agents such as con-
centrated sulfuric acid,2-4,17-19 fuming sulfuric acid,1,20
chlorosulfonic acid,13,15,19,21 trimethylsilyl chlorosul-
fonate,16 and sulfur trioxide-triethyl phosphate com-
plex.22 The other method is direct polymerization of
modified sulfonated monomers.
In the postsulfonation reactions, the sulfonic acid
groups are usually restricted to the activated position
ortho to the aromatic ether bond, which might deterio-
rate the chemical stability of the polymer because of the
cleavage of ether bond. In addition, the sulfonic acid
groups are relatively easy to hydrolyze. Moreover, the
degree of sullfonation is difficult to control, and too high
sulfonation degree often results in solubility of func-
tionalized polymers in water. Finally, postsulfonation
might suffer from the partial degradation and cross-
linking of polymers especially when strong sulfonation
agents such as chlorosulfonic acid are employed.
However, the aforementioned shortcomings can be
avoided and the stability of polymer can be enhanced
through molecular design. More recently, Miyatake et
al. have designed and reported the aromatic copolymers
containing sulfonated tetraphenylphenylene, hexa-
phenylbiphenylene, fluorinated alkane, and perfluoro-
Experimental Section
Materials. 2-(4-Chlorophenyl)benzoic acid was prepared
from phthalic anhydride and chlorobenzene via a Friedel-
Crafts reaction. 4,4′-Dihydrodiphenyl, 4,4′-difluorobenzophe-
none, and dimethyl sulfoxide (DMSO) were purchased from
Aldrich Chemical Co. and used as received. Sulfonated 4,4′-
difluorobenzophenone (SDFBP), 5, was obtained by the sul-
fonation of 4,4′-difluorobenzophenone as described in the
literature.35 Reagent-grade N,N′-dimethylacetamide (DMAc),
toluene, methanol, and anhydrous potassium carbonate were
obtained from commercial sources and used without further
purification.
1
Instrumentation. The H NMR spectra were recorded on
a Bruker NMR instrument (model DRX 400 MHz) using
dimethyl-d6 sulfoxide (DMSO-d6) as a solvent; chemical shifts
are given in ppm against tetramethylsilane as an internal
standard. Elemental analyses were performed on a Varios EL
elemental analyzer for C, H, N, and S determination. Melting
† Sun Yat-Sen University.
‡ McGill University.
* Corresponding author: Tel & Fax +8620-84114113; e-mail
stdpmeng@zsu.edu.cn.
10.1021/ma050902q CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/04/2005

10008 Chen et al.
Macromolecules, Vol. 38, No. 24, 2005
points were measured on a melting point testing apparatus.
The thermal stability of the polymers from 70 to 600 °C was
determined with a Seiko SSC-5200 thermogravimetric ana-
lyzer [thermogravimetric analysis (TGA)/differential thermal
analysis] under a nitrogen atmosphere (200 mL/min). The
heating rate was 20 °C/min. The glass-transition temperatures
(Tg’s) were determined on a Seiko 220 DSC instrument at a
heating rate of 20 °C/min under nitrogen protection. The
second scan was immediately initiated after the sample was
cooled to room temperature. Inherent viscosity was determined
for a solution of 0.5 g/dL in DMAc at 30 °C with a calibrated
Ubbelohde viscometer. The water uptake of the membrane was
evaluated by measuring the weight change between dried and
humidified forms at 80 °C. The ion exchange capacity (IEC)
has been determined by titration. Proton conductivity mea-
surement was performed on hydrated film samples by a
Solartron 1255B frequency response analyzer functioning with
an oscillating voltage of 10 mV using two probes with the
frequency between 1 MHz and 5 kHz. The proton conductivity
of the membrane was measured at temperatures ranging from
20 to 95 °C and at 100% relative humidity. The cell assembly
was similar to that used in the literature.23
Proton-form polymer was obtained by precipitating the 5%
solution of sodium-form polymer in DMAc out of 100 mL of
10% hydrogen chloride aqueous solution followed by keeping
at 60 °C for 6 h. The precipitate polymer was dialyzed to
remove inorganic salts. The treated polymer was filtered and
washed with water for three times and then dried at 110 °C
1
for 24 h. H NMR (400 MHz, DMSO-d6) δ: 7.20 (d, 8H), 7.66
(d, 2H), 7.71 (d, 4H), 7.80 (m, 4H), 7.86-7.98 (m, 8H), 8.38
(m, 4H). (C53H32N4O11S2‚6H2O)n (1073.08)n: Calcd C, 59.32; H,
4.28; N, 5.22; S, 5.98. Found C, 59.25; H, 5.15; N, 6.84; S, 6.07.
Preparation of Sulfonated Poly(phthalazinone ether
ketone) 7b. The polymerization was carried out with the same
procedure used for the synthesis of polymer 7a. The mixture
of 0.3378 g (0.8 mmol) of sulfonated difluoride ketone 5 and
0.0436 g (0.2 mmol) of 4,4′-difluorobenzophenone 6 was used
as an activated dihalide instead of sulfonated difluoride ketone
5. After workup, 0.9453 g of polymer 7b was obtained (in yield
of 98%). 1H NMR (400 MHz, DMSO-d6) δ: 7.19 (m, 8H), 7.65-
7.72 (m, 6.4H), 7.79-7.81 (m, 3.6H), 7.86-7.96 (m, 8.8H), 8.38
(m, 3.6H). (C53H32N4O9.8S1.6‚6H2O)n (1041.02)n: Calcd C, 61.15;
H, 4.26; N, 5.44; S, 4.93. Found C, 60.66; H, 4.50; N, 5.23; S,
5.17.
Preparation of Dicarboxylic Acid 3 Containing Bi-
phenyl Moiety.36 A 100 mL three-necked round-bottom flask
equipped with a Dean-stark trap, a condenser, nitrogen inlet/
outlet, and magnetic stirrer was charged with 2-(4-chloro-
phenyl)benzoic acid, 1 (10.4268 g 40 mmol), 4,4′-dihydrodi-
phenyl, 2 (3.7242 g 20 mmol), anhydrous K2CO3 (6.0812 g 44
mmol), DMAc (30 mL), and toluene (30 mL). Nitrogen was
purged through the reaction mixture with stirring for 10 min,
and then the mixture was kept at 150 °C for 3 h. After the
produced water was azeotroped off with toluene, the mixture
was heated to 170 °C and kept at this temperature for another
20 h. After cooling, the resulting mixture was diluted with
water (200 mL), and then concentrated HCl was added
dropwise to the stirred mixture to precipitate the product.
After filtration, the residue was washed with water for three
times. After dried, the desired product (12.00 g, 95%) was
collected and directly used to prepare bisphthalazinone. Some
pure compound was separated by crystallizing the crude
product from water/methanol for characterization; mp 282-
283 °C. 1H NMR (400 MHz, DMSO-d6) δ: ) 7.09 (d, 4H), 7.20
(d, 4H), 7.40 (d, 2H), 7.62-7.75 (m, 12H), 7.98 (d, 2H).
Preparation of Bisphthalazinone 4 Containing Bi-
phenyl Moiety.36 To a 500 mL round-bottom flask equipped
with a condenser containing 11.77 g of bicarboxylic acid 3 and
250 mL of methanol was slowly introduced 2 g (40 mmol) of
hydrazine monohydrate. The clear solution was heated to
reflux. The product precipitated out of the solution as the
reaction proceeded. After 24 h, the mixture was allowed to cool
to room temperature. The precipitates were collected by
filtration. The crude product was recrystallized from DMAc
to yield 4 as a white powder (11.03 g, 95%); mp 358-360 °C.
1H NMR (400 MHz, DMSO-d6) δ: 7.20-7.23 (m, 8H), 7.63 (d,
4H), 7.73-7.75 (m, 6H), 7.88-7.92 (m, 4H), 8.33 (m, 2H), 12.85
(s, 2H). C40H26N4O4 (626.67): Calcd C, 76.66; H, 4.18; N, 8.94.
Found C, 75.86; H, 4.68; N, 8.37.
Preparation of Sulfonated Poly(phthalazinone ether
ketone) 7c. The polymerization was carried out with the same
procedure used for the synthesis of polymer 7a. The mixture
of 0.2534 g (0.6 mmol) of sulfonated difluoride ketone 5 and
0.0873 g (0.4 mmol) of 4,4′-difluorobenzophenone 6 was used
as an activated dihalide instead of sulfonated difluoride ketone
5. After workup, 0.9046 g of polymer 7c was obtained (in yield
of 98%). 1H NMR (400 MHz, DMSO-d6) δ: 7.18 (m, 8H), 7.65-
7.72 (m, 6.8H), 7.79-7.80 (m, 3.2H), 7.86-7.95 (m, 9.6H), 8.38
(m, 3.2H). (C53H32N4O8.6S1.2‚5H2O)n (991.00)n: Calcd C, 64.24;
H, 4.27; N, 5.65; S, 3.88. Found C, 64.23; H, 4.62; N, 5.30; S,
4.04.
Preparation of Sulfonated Poly(phthalazinone ether
ketone) 7d. The polymerization was carried out with the same
procedure used for the synthesis of polymer 7a. The mixture
of 0.2111 g (0.5 mmol) of sulfonated difluoride ketone 5 and
0.1091 g (0.5 mmol) of 4,4′-difluorobenzophenone 6 was used
as an activated dihalide instead of sulfonated difluoride ketone
5. After workup, 0.8841 g of polymer 7d was obtained (in yield
of 97%). 1H NMR (400 MHz, DMSO-d6) δ: 7.18 (m, 8H), 7.65-
7.70 (m, 7H), 7.78-7.80 (m, 3H), 7.86-7.95 (m, 10H), 8.38 (m,
3H). (C53H32N4O8S‚5H2O)n (974.99)n: Calcd C, 65.29; H, 4.34;
N, 5.75; S, 3.28. Found C, 65.90; H, 4.62; N, 5.39; S, 3.38.
Preparation of Sulfonated Poly(phthalazinone ether
ketone) 7e. The polymerization was carried out with the same
procedure used for the synthesis of polymer 7a. The mixture
of 0.1689 g (0.4 mmol) of sulfonated difluoride ketone 5 and
0.1309 g (0.6 mmol) of 4,4′-difluorobenzophenone 6 was used
as an activated dihalide instead of sulfonated difluoride ketone
5. After workup, 0.8537 g of polymer 7e was obtained (in yield
of 96%). 1H NMR (400 MHz, DMSO-d6) δ: 7.18 (m, 8H), 7.65-
7.70 (m, 7.2H), 7.78-7.80 (m, 2.8H), 7.86-7.95 (m, 10.4H), 8.38
(m, 3H). (C53H32N4O7.4S0.8‚4H2O)n (940.96)n: Calcd C, 66.24;
H, 4.20; N, 5.83; S, 2.67. Found C, 67.93; H, 4.37; N, 5.75; S,
2.98.
Preparation of Sulfonated Poly(phthalazinone ether
ether ketone) 7a. To a 25 mL three-necked round-bottomed
flask fitted with a Dean-stark trap, a condenser, a nitrogen
inlet/outlet, and magnetic stirrer was added bisphthalazinone
monomer 4 (0.6267 g, 1 mmol), sulfonated difluoride ketone 5
(0.4223 g, 1 mmol), anhydrous potassium carbonate (0.1935
g, 1.4 mmol), 5 mL of DMSO, and 6 mL of toluene. Nitrogen
was purged through the reaction mixture with stirring for 10
min, and then the mixture was slowly heated to 140 °C and
kept stirring for 2 h. After water generated was azoetroped
off with toluene. The temperature was slowly increased to 175
°C. The temperature was maintained for 20 h, and the viscous
solution was cooled to 100 °C followed by diluting with 2 mL
of DMSO and, thereafter, precipitated into 100 mL of 1: 1 (v/
v) methanol/water. The precipitates were filtered and washed
with water for three times. The fibrous residues were collected
and dried at 110 °C under vacuum for 24 h. A total of 0.9423
g of polymer 7a was obtained in high yield of 93%.
Preparation of Sulfonated Poly(phthalazinone ether
ketone) 7f. The polymerization was carried out with the same
procedure used for the synthesis of polymer 7a. The mixture
of 0.0845 g (0.2 mmol) of sulfonated difluoride ketone 5 and
0.1746 g (0.8 mmol) of 4,4′-difluorobenzophenone 6 was used
as activated dihalides instead of sulfonated difluoride ketone
5. After workup, 0.7863 g of polymer 7f was obtained (in yield
of 93%). 1H NMR (400 MHz, DMSO-d6) δ: 7.18 (m, 8H), 7.65-
7.70 (m, 7.6H), 7.78-7.80 (m, 2.4H), 7.86-7.95 (m, 11.2H), 8.38
(m, 2.4H). (C53H32N4O6.2S0.4‚2H2O)n (874.91)n: Calcd C, 72.76;
H, 4.15; N, 6.40; S, 1.47. Found C, 73.03; H, 4.26; N, 5.91; S,
1.62.
Preparation of Membranes. Membrane of the proton-
form polymer was prepared by casting a 5% solution in DMAc
on a glass plate in a dust-free environment. Membrane was
dried at 60 °C for 12 h and then at 110 °C under vacuum for
48 h.

Macromolecules, Vol. 38, No. 24, 2005
Poly(phthalazinone ether ketone) Ionomers 10009
Table 1. Polymerization Results and Analytical Data of
Scheme 1. Synthesis of Bisphalazinone Monomer 4
Polymers 7a-f
SDb
a
yield
(%)
ηinh
measd by
element analysis
m/n
(dL/g)
calcd
7a
7b
7c
7d
7e
7f
10/0
8/2
6/4
5/5
4/6
2/8
93
98
98
97
96
93
1.02
1.22
1.16
0.97
1.29
1.03
2.00
1.60
1.20
1.00
0.80
0.40
2.03
1.67
1.24
1.02
0.87
0.44
a Tested in 0.5 g/dL solution in DMAc at 30 °C. b Degree of
sulfonation, number of sulfonic acid groups per repeating unit.
was heated to 175 °C for 20 h to afford sulfonated
polymer 7. The polymerization results and the charac-
terization data of 7a-f are displayed in Table 1. Figure
1, 2, and 3 showed the 1H NMR spectra of polymers 7a,
7b, and 7c, respectively. Although the systems were
complicated because of the overlap of chemical shifts of
aryl hydrogen, assignment was made possible by com-
parison with the data of the monomer and the corre-
sponding polymers. It can be seen from the figures that
because of the strong electron-withdrawing effect of the
phthalazinone, the signals of hydrogen on the former
dihalide aryl ring moved downfield dramatically.
Properties of Sulfonated Poly(phthalazinone
ether ketone) 7. The thermal stability of the polymer
was investigated using TGA and DSC. A two-step
degradation profile observed for the polymers is shown
in Figure 4. The first weight loss at about 300 °C was
attributed to the elimination of sulfonic acid group,
whereas the second weight loss peak at about 500 °C
was due to main-chain degradation. It also can be seen
from Figure 4 that the beginning and the end of the first
weight loss were quite similar, but the curves were
steeper with the increase of sulfonation degree. To
minimize the effects of the absorbed water, the samples
were heated to 200 °C to get rid of any water in nitrogen
flow followed by cooling to 70 °C, and the trace from 70
to 600 °C was recorded. The second weight losses had
the same pattern as the first one, which implied that
Results and Discussion
Synthesis of Sulfonated Poly(phthalazinone
ether ketone) 7. Bisphthalazinone monomer 4 was
synthesized in a two-step sequence as shown in Scheme
1. The nucleophilic substitution reaction of 1 with 2 gave
dicarboxylic acid, which was converted to bisphthal-
azinone 4 by refluxed with hydrazine monohydrate in
methanol via the ring-closure reaction. The desired
bisphthalazinone 4 was confirmed by elemental analysis
1
and the H NMR spectrum.
As depicted in Scheme 2, sulfonated poly(phthalazi-
none ether ketone) 7 was successfully synthesized via
novel N-C coupling reaction. Polycondensation of the
bisphthalazinone 4 with stoichiometric amounts of
activated dihalides (5 and 6) was carried out in the
presence of excess potassium carbonate as base in
DMSO in a manner analogous to the conventional
polyether synthesis. The degree of sulfonation was
controlled by changing the ratios of monomers 5 and 6,
and the amounts of 5 and 6 were equal to that of 4. The
reaction was first held at 140 °C for 2 h under nitrogen
to azeotropically remove water with toluene and then
Figure 1. 1H NMR spectrum of sulfonated poly(phthalazinone ether ether ketone) 7a.

10010 Chen et al.
Macromolecules, Vol. 38, No. 24, 2005
Figure 2. 1H NMR spectrum of sulfonated poly(phthalazinone ether ether ketone) 7b.
Figure 3. 1H NMR spectrum of sulfonated poly(phthalazinone ether ether ketone) 7c.
the degradation of the backbones were quite similar.
DSC measurement of the polymer within a temperature
from 30 to 300 °C did not reveal glass transition
temperatures below thermal decomposition.
The solubility of the polymers and the properties of
their membrane are shown in Table 2. All the polymers
were soluble in common aprotic solvents, such as
DMSO, DMAc, dimethylformamide (DMF), and N-
methylpyrroridone (NMP). Tough and smooth film was
obtained by evaporating the solvent of the 5% solution
in DMAc at 60 °C in a dust-free environment.
The water uptakes of the membranes were evaluated
by measuring the weight change between dried and
humidified forms at 80 °C. The membrane samples were
immerged in the deionized water at 80 °C for 24 h and
wiped with a filter paper and immediately weighed.
Then the membranes were dried at 110 °C for 24 h, and
the weight of sample which was free of water was
obtained. The water uptakes of membranes were re-
ported in weight percentage of water (g) per dry
membrane (g).
The ion exchange capacity (IEC) of the membrane was
determined by titration. The membranes were first
immerged in 2 M NaCl solution for 24 h to exchange
the sodium ions for protons. The resulting solution was
then titrated with 0.1 M NaOH using phenolphthalein
as an indicator.
As shown in Table 2, the water uptake was dropped
with the decrease of IEC which was proportional to
sulfonation degree. When the sulfonation degree was
2, the highest water uptake was obtained. It dropped
gradually from 46% to 13% as the sulfonation degree
decreased.
Membrane stability to oxidation was investigated by
soaking the film in Fenton’s reagent (30 ppm FeSO4 in
30% H2O2) at 25 °C. The results were reported by the

Macromolecules, Vol. 38, No. 24, 2005
Poly(phthalazinone ether ketone) Ionomers 10011
Figure 4. TGA curves of sulfonated poly(phthalazinone ether ether ketone)s 7a-f.
Table 2. Solubility of Polymers 7a-f and Properties of Their Membranes
resistance to oxidation,a h
IEC, meq/g
by titration
solubility
t1
t2
water uptake,b %
calcd
Ea, kJ/mol
7a
7b
7c
7d
7e
7f
47
49
51
51
54
51
63
46
38
33
28
21
13
2.04
1.55
1.31
1.10
0.89
0.45
2.07
1.71
1.33
1.13
0.92
0.48
5.6
13
DMF
DMAc
DMSO
NMP
250
250
250
15
19
22
d
d
-
-
26
a t1 and t2 refer to the expended time that the membrane began to rupture and disappeared in the solution. b Measured at 80 °C.
c Calculated from the slope of the Arrhenius plot, Nafion 117 was 11 kJ/mol. d Undegradable.
Figure 5. Temperature dependence of the proton conductivity for polymers 7a-f with different sulfonation degrees and Nafion
117 (denoted as Nf) at 100% RH.

10012 Chen et al.
Macromolecules, Vol. 38, No. 24, 2005
Scheme 2. Synthesis of Sulfonated Poly(phthalazinone ether ether ketone) 7a-f
Scheme 3. Synthesis of Sulfonated Poly(phthalazinone ether ether ketone) 9a-f
time that the membrane took to become brittle and
at 100% relative humidity. Prior to the measurements,
the membrane was allowed to equilibrate with the
saturated water vapor at a specific temperature, and
the data were collected after the proton conductivity had
reached a constant value. (It usually took 2-3 h.) The
experimental results are summarized in Figure 5. The
proton conductivity of these membranes increased with
increasing temperature with the exception of polymer
7f which began to slightly decrease at 95 °C. Polymer
7a with a sulfonation degree of 2 showed the highest
conductivity of 1.77 × 10-2 S/cm at 95 °C. It was
noteworthy that all values for polymer 7a were higher
than 10-2 S/cm in the test temperature range, and other
copolymers 7b-e can also surmount the value of 10-2
S/cm at elevated temperatures.
disappear in the solution. The results listed in Table 2
indicated that the membranes were more resistant to
oxidation than other sulfonated polymers.6-7,23 The
antioxidation properties of the synthesized polymers
validate our assumption that the sulfonic groups on the
polymers adjacent to the N-C heterocyclic bond and
placed in the deactivated aromatic rings have better
resistance to oxidation. Moreover, the N-C bonds
exhibited much stable oxidation property due to that
nitrogen atom locates on an aromatic ring, which
stabilized the N-C bonds.
Proton Conductivity of Sulfonated Poly(phthal-
azinone ether ketone) 7. The influence of temperature
on the proton conductivity of the membranes was
assessed in the temperature range from 20 to 95 °C and

Macromolecules, Vol. 38, No. 24, 2005
Poly(phthalazinone ether ketone) Ionomers 10013
Table 3. Physical Properties of Polymers 9a-f
015007), Canton Province Sci & Tech Bureau (Key
Strategic Project Grant A1100402), and Guangzhou Sci
& Tech Bureau for financial support of this work.
resistance to
oxidation,c h
water
conductivity,e
S/cm
p/q ηinh SDb
t1
t2
uptake,d %
a
References and Notes
9a 10/0 1.22 2.0
46
60
69
86
130
f
52
132
153
240
300
f
36
22
19
16
14
9
4.32 × 10-3
1.81 × 10-3
1.07 × 10-3
7.46 × 10-4
1.08 × 10-4
2.88 × 10-5
9b 8/2
9c 6/4
9d 5/5
9e 4/6
9f 8/2
0.93 1.6
0.87 1.2
1.02 1.0
0.95 0.8
0.91 0.4
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a Tested in 0.5 g/dL solution in DMAc at 25 °C. b Degree of
sulfonation, number of sulfonic acid groups per repeating unit.c t1
and t2 refer to the expended time that the membrane began to
rupture and disappeared in the solution. d Measured at 80 °C.
e Measured at 20 °C 100% relative humidity for hydrate membrane
samples, Nafion 117 was 2.03 × 10-2 S/cm under the same
conditions. f Undegradable.
The apparent activation energies (Ea) for the conduc-
tion processes derived from the Arrhenius relation are
listed in Table 2. It can be seen that the Ea values
increase with the decrease in the sulfonation degree.
Polymer 7a was characterized by its low Ea value of 5.6
kJ/mol, which is presumably attributed to its regular
sulfonation structure and higher sulfonation degree
compared with other copolymers 7b-f, leading to
transport proton easily. The low activation energy also
resulted from the low EW value for the synthesized
membrane when compared with Nafion. The ionic
polymers were susceptibly separated into two phases,
i.e., hydrophilic ionic domain and hydrophobic polymeric
matrix. The fully hydrated membrane then provides the
ionic pathway for proton transportation.
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Comparison of Sulfonated Poly(phthalazinone
ether ketone)s 7 and 9. Bisphthalazinone 8 containing
hexafluoroisopylidene diphenyl moiety could also react
with activated dihalides (5 and 6) to offer high-molec-
ular-weight sulfonated poly(phthalazinone ether ketone)
9 (Scheme 3). Table 3 displayed the physical properties
of polymers 9a-f. Polymers 9a-f showed improved
property of resistance to oxidation compared to polymers
8a-f for they had higher EW (equivalent weight)
values. But when the hydrophobic hexafluoroisopylidene
group was introduced to the polymer, the water uptakes
of their membranes decreased, which led to the decrease
of proton conductivity. Furthermore, the decrease in
absorbed water made the membranes become a little
brittle. The results indicated that polymer 8 has an
advantage over polymer 9.
Conclusions
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Sulfonated poly(phthalazinone ether ether ketone)s
with different sulfonation degrees were synthesized via
N-C coupling reactions using bisphthalazinone mono-
mer, difluoride, and sulfonated difluoride. This is the
first report that such strategy was employed to prepare
sulfonated polymer. Because of the sulfonic groups
adjacent to the N-C heterocyclic bond, the polymers
were found to have better thermal and oxidative stabil-
ity. The membranes of the polymers showed reasonable
water affinity and good proton conductivity, which may
find wide applications as proton exchange membranes
for fuel cells.
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Acknowledgment. The authors thank the China
High-Tech Development 863 Program (Grant
2003AA302410), Natural Science Foundation of
Guangdong Province (Excellent Team Project, Grant
MA050902Q