Synthesis and properties of sulfonated poly(phenylene sulfone)s without ether linkage by Diels-Alder reaction for PEMFC application

Article abstract of DOI:10.1016/j.electacta.2013.11.190

A new sulfonated poly(phenylene sulfone) polymer (SPPS) was synthesized by Diels-Alder polymerization from 1,4-bis(2,4,5-triphenylcyclopentadienone)benzene (BTPCPB) and 4,4′-diethynylphenylsulfone, and followed by sulfonation reaction with chlorosulfuric

Full text of DOI:10.1016/j.electacta.2013.11.190

Electrochimica Acta 119 (2014) 16–23
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Synthesis and properties of sulfonated poly(phenylene sulfone)s
without ether linkage by Diels–Alder reaction for PEMFC application
Youngdon Lima,1, Hyunchul Leea,1, Soonho Leea, Hohyoun Janga, Md. Awlad Hossaina,
Younggil Choa, Taeho Kimb, Youngtaik Hongb, Whangi Kima,∗
a Department of Applied Chemistry, Konkuk University, Chungju, 380-701, Korea
b Energy Material Research Center, Korea Research Institute of Chemical Technology, Daejeon, 305-600, Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 March 2013
Received in revised form 15 October 2013
Accepted 29 November 2013
Available online 16 December 2013
A new sulfonated poly(phenylene sulfone) polymer (SPPS) was synthesized by Diels-Alder polymeriza-
tion from 1,4-bis(2,4,5-triphenylcyclopentadienone)benzene (BTPCPB) and 4,4ꢀ-diethynylphenylsulfone,
and followed by sulfonation reaction with chlorosulfuric acid. A series of sulfonated poly(phenylene
sulfone)s (SPPS) with different degrees of sulfonation was prepared in a controllable manner with
chlorosulfuric acid. These polymers showed good solubility in aprotic polar solvents, dimethyl acetamide
(DMAC) and dimethyl sulfoxide (DMSO). Three different polymer membranes were studied by 1H NMR
spectroscopy, and thermogravimetric analysis (TGA). The ion exchange capacity (IEC) and proton con-
ductivity of SPPS were evaluated according to the degrees of sulfonation. The water uptake (WU) of the
synthesized SPPS membranes ranged from 38%∼75%, compared with 32% for Nafion 211® at 80 ◦C. The
SPPS membranes exhibited proton conductivities (at 80 ◦C under 90% RH) of 110.2 mS/cm compared with
102.7 mS/cm for Nafion 211®. Power density was performed by single cell and showed similar to Nafion
value.
Keywords:
Poly(phenylene sulfone)
Proton exchange membrane
Fuel cell
PEMFC
Diels-Alder reaction
© 2013 Elsevier Ltd. All rights reserved.
1. Introduction
based PEM materials has good thermal stability, and closely to the
Nafion’s performance [19–21]. But the chemical stability is unap-
Proton exchange membrane fuel cell (PEMFC) technology has
the capability to be renewable energy source of an impend-
ing hydrogen economy owing to its high efficiency, high energy
density, quiet operation, and environmental friendliness.[1] Most
current PEM is based on perfluorosulfonic acid polymer mem-
branes, represented by Dupont’s Nafion. Nafion exhibits generally
good chemical stability and proton conductivity at high relative
humidity (RH) and low temperature [2,3]. However, they suf-
fer from such disadvantages as limited operation temperature
(0∼80 ◦C), high cost, and high fuel permeability. This has stimulated
the development of research focused on non-fluorinated polymeric
proton-conducting materials with low cost and high performance
[4–8]. To overcome the drawbacks, a certain number of polymer
families, such as polyphosphazenes [9,10], polybenzimidazole [11],
poly(ether sulfone)s, and poly(ether ketone)s [12–18], were used to
prepare membranes for fuel cell applications. These polymers have
received much attention because of their high thermal, oxidative,
and chemical stability in fuel cell environments. Most hydrocarbon
proachable to Nafion, because of their structure with acid functional
groups attached on main chain, and ether linkage possibly attacked
by nucleophiles [11,22].
The sulfonated poly(phenylene) polyelectrolytes were synthe-
sized from 1,4-bis(2,4,5-triphenylcyclopentadienone)benzene and
1,4-diethynylbenzene by Diels-Alder polymerization [23,24]. The
resultant polymers are consisted of carbon-carbon bonded struc-
ture which is tough rigid-rod material with high chemical stability,
and the backbone stiffness does not negatively affect membrane
properties. However this rigid-rod polymer membrane has sol-
ubility problem because of the unique structural nature even
though polymer membrane could be cast solution into robust
and creaseable films. And also this wholly aromatic structure has
difficult to control the degree of sulfonation and everywhere as sul-
fonation occurs. Therefore, our research group has focused on this
problem, get around to making hydrocarbon PEM material have
modified with sulfone linkage which is most stable chemical struc-
ture and where is no sulfonation reaction.
This research is an attempt to synthesize poly(phenylene sul-
fone) without ether and with sulfone groups by Diels-Alder
reaction. The sulfonation reaction was selectively taken on pendant
hexa-phenyl groups of side chain. The proposed polymer mem-
branes, in which sulfonic acid groups attached on side phenyl rings
∗
Corresponding author. Tel.: +82 43 840 3579.
E-mail address: wgkim@kku.ac.kr (W. Kim).
These authors contributed equally to this work.
1
0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.electacta.2013.11.190

Y. Lim et al. / Electrochimica Acta 119 (2014) 16–23
17
and without ether linkage structure, were promising units to good
2.5. Preparation of bis(p-acetylphenyl)sulfide
chemically stability and proton conductivity. The polymer mem-
branes are easily sobluble in aprotic organic solvents. Polymer
membranes were studied by 1H-NMR spectroscopy, thermo gravi-
metric analysis (TGA), water uptake, ion exchange capacity (IEC),
Fenton test, proton conductivity, and cell performance.
To a flask, phenyl sulfide (25 g, 0.13 mol) and acetyl chloride
(31.58 g, 0.40 mol) dissolved in 250 mL of carbon disulfide at 0 ◦C.
And aluminum chloride (62. 64 g, 0.47 mol) was added slowly to
this solution at 0 ◦C. After addition, temperature was increase to
room temperature and stirred for 8 h. The reaction was quenched
by poured to 500 mL of crushed ice, the organic layer was extracted
with chloroform, and the combined organic layers were washed
with a saturated brine solution and dried over anhydrous mag-
nesium sulfate, and evaporated solvent. The product was purified
by a simple recrystallization from a mixture of MC and n-hexane.
Filtered product was dried in vacuum at 60 ◦C for 24 h (yield = 94%).
2. Experimental
2.1. Materials
1,4-Diiodobenzene, phenylacetylene, bis(triphenylphosphine)
palladium dichloride, copper iodide, ortho-periodic acid, 1,3-
diphenylacetone, acetylchloride, aluminum chloride, m-chlor-
operbenzoic acid, triethylamine, phenyl sulfide, glacial acetic acid,
chlorosulfuric acid, m-chloroperoxybenzoic acid (mCPBA), sodium
hydroxide, pottassiumhydroxidewerefromSigma-AldrichandTCI,
and used as received. Other commercially available solvents–1,4-
dioxane, carbon disulfide, tetrahydrofuran (THF), dichloromethane
(MC), ethyl ether, diphenyl ether, ethyl acetate, n-hexane, chlo-
roform, ethanol, acetone, methanol, water–were used without
further purification.
2.6. Preparation of
3,3ꢀ-(thiodi-4,1ꢀ-phenylene)-bis[3-chloro-2-propenal]
To a flask, phosphorus oxytrichloride (91.2 g, 0.59 mol) dissolved
in 230 mL of DMF at 0 ◦C for 10 min, and added slowly a solution of
bis(p-acetylphenyl)sulfide (40.0 g, 0.15 mol) in 200 mL of DMF. The
reaction was quenched by poured to excess amount of aqueous
sodium acetate solution after 2 h. The organic layer was extracted
with MC, and the combined organic layers were washed with 5 wt%
of aqueous sodium bicarbonate solution and dried over anhydrous
magnesium sulfate, and evaporated solvent. The product was puri-
fied by a simple recrystallization from a mixture of MC and ethyl
ether. The filtered product was dried in vacuum at 60 ◦C for 24 h
(yield = 45%).
2.2. Synthesis of 1,4ꢀ-Bis(2-phenylethynyl)benzene
Under an N2 atmosphere, a three-necked flask equipped with a
magnetic stirrer was charged with 1,4-diiodobenzene (10 g,
0.03 mol), phenyl acetylene (0.08 mol, 8.10 g), bis(triphenylphos-
phine)palladium dichloride (1.066 g, 1.52 mmol), and copper iodide
(0.576 g, 3.04 mmol) were mixed together with in THF (40 mL) at
room temperature. And 80 mL of triethylamine was added drop-
wise to this solution. After dropping, reaction mixture stirred for
20 h at room temperature. Over the reaction was checked by TLC,
the mixture was pour to 200 mL of MC and stirring for 20 min. The
organic layer was washed with water (100 mL× 3) and dried over
anhydrous magnesium sulfate and evaporated to afford the prod-
uct. The crude product was purified by a simple recrystallization
from a mixture of MC and methanol. The product was filtered and
dried under vacuum at 60 ◦C for 24 h (yield = 75%).
2.7. Preparation of bis(4-ethynylphenyl)sulfide
To a flask, sodium hydroxide (10 g, 0.25 mol) dissolved in
80 mL of water at 80 ◦C. A solution of 3,3ꢀ-(thiodi-4,1ꢀ-phenylene)-
bis[3-chloro-2-propenal] (8 g, 0.02 mol) in 100 mL 1,4ꢀ-dioxane was
added dropwise to this solution, and stirred at 80 ◦C for 2 h. Reac-
tion mixture was poured to 500 mL of water. The organic layer was
extracted with ethyl ether, and the combined organic layers were
washed with a saturated brine solution and dried over anhydrous
magnesium sulfate, and evaporated solvent to afford the viscous
red oil. After simple distillation, giving the crystalline solid with
yielded 37%.
2.3. Synthesis of p-di(phenylglyoxalyl)benzene
2.8. Preparation of bis(4-ethynylphenyl)sulfone (BEPS)
To a flask, 1,4ꢀ-bis(2phenylethynyl)benzene (3.5 g, 0.025 mol)
and ortho-periodic acid (5.7 g, 0.025 mol) were dissolved in 188 mL
of glacial acetic acid. This mixture was stirred at 55 ◦C for 20 h. After
reaction, the mixture was poured to mixture of water/chloroform
(200 mL/100 mL). The organic layer was washed with 5 wt% aque-
ous sodium bicarbonate solution (100 mL) and water (100 mL × 2).
And this organic layer was separated and dried over anhydrous
magnesium sulfate, and evaporated to afford the yellow crystalline
solid with yielded 70%.
To a flask, mCPBA (22.1 g, 0.13 mol) was added to a solution of
bis(4-ethynylphenyl) sulfide (6.0 g, 0.03 mol) in 300 mL of MC and
the mixture was stirred overnight. Reaction mixture was poured to
200 mL of water. The organic layer was extracted with MC, and the
combined organic layers were washed with a saturated brine solu-
tion and dried over anhydrous magnesium sulfate, and the product
was isolated following silica gel chromatography by elution with
MC (yield = 80%).
2.4. Preparation of
2.9. Preparation of poly(phenylene sulfone) by Diels- Alder
reaction (PPS)
1,4ꢀ-bis(2,4,5-triphenylcyclopentadienone)benzene (BTPCPB)
To a flask, p-di(phenylglyoxalyl)benzene (10 g, 0.03 mol) and
1,3ꢀ-diphenylacetone was dissolved in 100 mL of ethanol with
10 mL of toluene. And solution of potassium hydroxide (2.1 g,
0.04 mol) in 10 mL of methanol was added dropwise to this solution
at room temperature. After dropping, the mixture was refluxed for
1 h at 130 ◦C. The resulting mixture was cooling to 0 ◦C and crystal-
ized itself. The solid collected by filtration and washed with cold
ethanol. Filtered product was dried in vacuum at 60 ◦C for 24 h
(yield = 80%).
BTPCPB (5.00 g, 7.24 mmol), BEPS (1.93 g, 7.24 mmol), and
diphenyl ether (50 mL) were added, and heating under nitrogen at
180 ◦C for 24 h. Subsequently, additional BEPS (0.02 g, 0.08 mmol)
was added to the viscous slurry for reaction of remaining unre-
acted materials and higher molecular weight. The mixture was
stirred for an additional 12 h at 180 ◦C. The reaction flask was cooled
to room temperature. The polymer was precipitated into 200 mL
of acetone. The resultant white solid was washed with acetone
and dried in a vacuum oven at 80 ◦C for 24 h. The weight average

18
Y. Lim et al. / Electrochimica Acta 119 (2014) 16–23
molecular weight (Mw) and number average molecular weight (Mn)
are 853,300 and 38,200 respectively, and polydispersity is 2.32.
Perkin-Elmer TGA-7 analyzer. The molecular weight of polymers
was determined relative to polystyrene standards by gel perme-
ation chromatography (GPC) in DMSO as the eluent on a Perkin
Elmer series 200 high pressure-liquid chromatographer and a RI
detector.
2.10. Sulfonation of PPS (SPPS)
In a typical sulfonation, PPS (2.3 g) was added to a flask under
nitrogen and dissolved in 25 mL of MC. The solution was cooled to
0 ◦C, and chlorosulfonic acid (1.16 g, 9.96 mmol) diluted in 5.8 mL
of MC was added dropwise for 30 min. after dropping, stirred for
3 h at this temperature. This amount of chlorosulfonic acid gave a
4:1 ratio of acid to polymer repeat unit. Other ratios of sulfonating
agent to polymer repeat unit were prepared to attain polymers with
various ion exchange capacities (SPPS 1: 0.69 g, 5.92 mmol and SPPS
2: 0.92 g, 7.89 mmol of chlorosulfuric acid). After reaction, this mix-
ture poured to hot water. Filtered polymer was thoroughly washed
with water and dried under vacuum at 80 ◦C for 24 h.
The membranes were vacuum-dried at 100 ◦C for 24 h, weighed
and immersed in deionized water at 30 ◦C and 80 ◦C for 24 h. The
wet membranes were wiped to dry and quickly weighed again.
The water uptakes of membranes are reported in weight per-
cent as follows: water uptake = {(Wwet–Wdry)/Wdry} × 100%, where
Wwet and Wdry are the weights of the wet and dry membranes,
respectively. Dimensional change was investigated by immers-
ing the membrane into water at room temperature for 24 h, the
changes in thickness and length were calculated from the equa-
tion, ꢁt = {(t-ts)/ts} × 100%, ꢁl = {(l-ls)/ls} × 100%, where ts and ls
are the thickness and diameter of the dried membrane, respec-
tively; t and l refer to the similar parameters of the membrane
immersed in water for 24 h. The titration method was used to deter-
mine the IEC of the membranes. The membranes in the acid form
(H+) were converted to the sodium salt form by immersing the
membranes in a 1.0 M NaCl solution for 24 h to exchange the H+
ions with Na+ ions. Then, the exchanged H+ ions within the solu-
tions were titrated with a 0.02 N NaOH solution. The theoretical IEC
calculated from sulfonated degree was obtained from the formula:
IEC (meq./g) = Ionic mmol concentration/Mass of dry membrane at
25 ◦C. Proton conductivity through plane direction of membranes
were determined using Scribner membrane test system (MTS-740)
with a Newtons 4th Ltd (N4L) impedance analysis interface (PSM
1735) at 40-80 ◦C under 80% humidity, and at 80 ◦C under 30-90%
humidity. EIS was conducted at the open circuit condition by apply-
ing a small alternating voltage (10 mV) and varying the frequency
of the alternating voltage from 1 to 1 × 105 Hz.
2.11. Accelerated Chemical Membrane Degradation
Membrane degradation was studied by immersion in Fenton
reagent (4 ppm Fe2+, 3% H2O2) at 75 ◦C. Samples were SPPSs mem-
branes, generally linear sulfonated poly(ether sulfone)s (S-PES 40),
and Nafion 211®. The initial sample weight was measured and the
samples were put in to the solution of iron (II) sulfate heptahy-
drate in MilliQ water (45 mL) and heat to 75 ◦C, and 5 mL of 30%
H2O2 added to this solution. The membrane samples were taken
out regularly during the experiment for weighing. Washing the
sample in distilled water quenched the degradation reaction and
the exposed membranes were dried before the final weight was
determined [25–27].
2.12. Membrane Preparation and Characterization
Membrane electrode assemblies (MEAs) with an active area of
9 cm2 were prepared using a decal method based on a catalyst
coated membrane (CCM). A 20 wt% wet-proofed Toray carbon paper
(TGPH-060, Toray Inc.) of 190 ␮m in thickness was employed as a
gas diffusion layer (GDL) for the anode and cathode sides. Carbon-
supported Pt (Hispec 13100, Johnson Matthey Inc.) was used as
catalyst for both anode and cathode. The loading of the catalyst
layer in this work was 0.2 mg Pt/cm2 for the anode and cathode.
Membranes (25 ␮m) were prepared by the dissolution of the
polymer in DMSO to afford 20 wt% transparent solutions and
casting of the solutions at elevating temperatures of 60, 80, 100,
and 120 ◦C. The polymer structure was confirmed by 1H NMR
spectra were recorded on a Bruker DRX (400 MHz) spectrometer
using DMSO-d6 as solvent and tetramethylsilane (TMS) as internal
standard and thermo gravimetric analysis (TGA) were performed
Pd[PPh3]Cl2
/ CuI
I
I
TEA / THF
O
O
O
O
H5IO6
Acetic acid
O
1,3-diphenylacetone
KOH / MeOH / EtOH / Toluene
O
BTPCPB
O
O
Cl
Cl
Acetyl chloride
POCl3
DMF
/ CS2
AlCl3
S
CHO
CHO
S
S
NaOH / H2O
1,4-dioxane
m-CPBA
DCM
S
S
O
O
BEPS
Scheme 1. Preparation of BTPCPB and BEPS.

Y. Lim et al. / Electrochimica Acta 119 (2014) 16–23
19
O
O
S
O
O
Diels-Alder
O
S
O
n
PPS
sulfonation
chlorosulfuric acid
(SO3H)x/6
(SO3H)x/6
(SO3H)x/6
O
S
O
Fig. 1. 1H NMR spectra of BTPCPB and BEPS.
n
(SO3H)x/6
(SO3H)x/6
substituted with strong electron-withdrawing groups such as car-
bonyl and sulfone are deactivated toward electrophilic sulfonation.
[8,34,35]. And also, sulfonation is generally occurring to the para
positions of the pendant phenyl rings rather than ortho posi-
tion because of the conjugated planar, rigid-rod backbone, and
steric hindrance [23]. Therefore, the sulfonic acid groups can be
introduced solely on the pendant phenyls in the main chain The
sulfonation reactions were controlled by different mole concen-
tration of chmorosulfuric acid to prepare different IEC values of
membranes. The procedure shows in Scheme 2. The chemical struc-
tures of the BTPCPB and BEPS were confirmed by 1H NMR. In Fig. 1
(BTPCPB), inside phenylene proton peaks (Ha) appeared at 6.68-
6.97 ppm, and the other protons peaks (Hb) on pendant phenyl ring
appeared at little down field at 7.00-7.32 ppm because of electron
withdrawing effect of cyclophetadienone. In Fig. 1 (BEPS), Ha peaks
of sulfone’s ortho position appeared at 7.86-7.97 ppm, and Hb peaks
of sulfone’s meta position appeared at 7.62-7.71 ppm. And Hc peaks
of terminal alkyne group’s protons appeared at 3.31 ppm. In Fig. 2
(PPS), Ha peaks of centered phenyl ring’s protons on multiphenyl
unit appeared at 6.17-6.30 ppm, and Hb peaks of sulfone’s ortho
position appeared far down field at 7.65 ppm. The other phenyl
ring’s protons (Hc) appeared at 6.53-7.54 ppm. In Fig. 2 (SPPS),
Ha peaks of centered phenylene ring’s protons on multiphenyl
unit appeared broad shape at 6.05-6.40 ppm, and Hb peaks of sul-
fone’s ortho position appeared at 7.52-7.73 ppm without change,
which means no sulfonation reaction on diphenylsulfone unit. Hc
peaks of the other pendant phenyl ring’s protons appeared at
6.54-7.50 ppm. The sulfonation reaction was selectively occurred
pendant six phenyl groups on side chain. The integration ratios of
proton peaks were confirmed molar ratios of each component of
copolymer.
(SO3H)x/6
SPPS
Scheme 2. Preparation of SPPS.
Then, the catalyst layer was transferred on the membrane at 130
◦C and 10 MPa for 5 min by decal method to form the CCM. The GDL
was placed on the anode and cathode side of the CCM to form the
MEAs [28]. Cell performance was performed by PEMFC test station
(CNL Energy Co.). The tensile stress-strain properties of the mem-
branes were tested using a Com-Ten Industries 95 T series load
frame equipped with a 200 lbf load cell and computerized data
acquisition software. Samples of 9 mm width were deformed at a
crosshead speed of 5 mm/min with gauge length of 30 mm [23].
3. Results and Discussion
3.1. Preparation of monomer and polymers
Synthesis of BTPCPB and BEPS were carried out as the follow-
ing procedure. BTPCPB monomer was synthesized by Sonogashira
coupling reaction, oxidation and potassium hydroxide catalyzed
condensation reaction [23,29–31]. BESP monomer was subse-
quently synthesized by Friedel-Craft acylation, bis-chloroaldehyde
formation by reacted with POCl3, alkynation with NaOH, and oxi-
dation with mCPBA [32,33]. The procedure shows in Scheme 1.
The PPS polymer was successfully synthesized via a Diels-Alder
reaction. A series of SPPS were synthesized by post-sulfonation
with different ratio of chlosulfuric acid. The repeat unit of PPS
has six pendent phenyl groups which are possible to occur sul-
fonation reaction. (Scheme 2) It is well-known that benzene rings

20
Y. Lim et al. / Electrochimica Acta 119 (2014) 16–23
Fig. 2. 1H NMR spectra of PPS and SPPS.
3.2. Properties of SPPSs
acid groups. As the sulfonation level increased, SPPS 1, 2, and 3
lost 12.25, 14.70, and 17.72 wt% which are close to the theoreti-
cal value 11.23, 15.47, and 19.61 wt% respectively. The SPPSs were
found to be soluble in aprotic polar solvents like, DMSO, DMAc and
NMP, etc., and were casted in DMSO solution to form light yel-
low transparent films. The molecular weight of the polymers was
determined by gel permeation chromatography (GPC). The weight
average molecular weights (Mw) and polydispersities (Mw/Mn) of
the synthesized polymers are ranged from 85,300 to 87,900 and
2.2–2.3 (Table 1). As shown in Fig. 4, the IECs of SPPS 1, 2, and
3 were 1.49, 1.81 and 2.34 meq./g, whereas the IEC of the Nafion
211® was 0.91 meq./g, respectively. By increasing the percentage
of sulfonic acid group, there was an increase in the IEC of SPPSs
membranes. Fig. 4 shows the water uptake of SPPSs membranes
Thermooxidative stabilities of PPS and SPPSs were studied by
thermo gravimetric analysis (TGA) with results shown in Fig. 3.
PPS polymer showed excellent thermooxidative stability with a
5% weight loss occurring at 550 ◦C. Thermal gravimetric analysis
of SPPSs in the acid form tends to three stage-weight loss pat-
tern. The initial weight loss of SPPSs was appeared 0.5-1.5 wt% at
280 ◦C by water and solvent even though the polymer was well
dried at 100 ◦C for 24hr. The second weight loss of SPPS was around
280–450 ◦C which is assigned to the decomposition of sulfonic
acid groups. The second weight loss over 500 ◦C was attributed
to degradation of the polymer main chain. These results suggest
the first weight loss in SPPs is analyzed to the loss of sulfonic
Table 1
Properties of membranes.
polymer
SPPS 1
SPPS 2
SPPS 3
Nafion 211
Titrated IEC a/b (meq./g)
Water uptake at 30 ◦C (%)
Water uptake at 80 ◦C (%)
ꢀt (%)
1.49/1.13
26.43
38.29
17.21
15.28
66.4
37,200/86,000
(2.31)
1197/319
15/8
1.81/1.51
46.11
50.19
20.42
19.83
90.1
38,500/87,900
(2.28)
1208/308
14/8
2.34/1.88
68.94
74.52
27.71
26.83
110.2
39,100/87,200
(2.23)
1209/304
14/9
0.91/0.90
-
32.13
14.10
13.84
102.7
-
ꢀl (%)
Proton Conductivityc (mS/cm)
Molecular weight Mn/Mw (polydipersity)
Young’s modulusd (MPa)
Elongation to breake (%)
208/56
177/170
IECa measured before Fenton Test, IECb measured after 9 hour in Fenton test. c Proton conductivity at 80 ◦C under 90%RH. d,e dry/wet conditions.

Y. Lim et al. / Electrochimica Acta 119 (2014) 16–23
21
Fig. 3. TGA curves of SPPSs.
Fig. 5. Proton conductivity of membranes at 80 ◦C under different RH.
as a function of the sulfonation level at 80 ◦C. The water uptake of
SPPS 1, 2, and 3 membranes are 38.29, 50.19 and 74.52% compared
with 32.13% of Nafion 211® at 80 ◦C. The SPPSs membranes show
relatively lower water uptake than the sulfonated poly(phenylene)
membranes [23]. Cornelius’s membranes have randomly sufonated
on polymer backbone, but these SPPS membranes are selectively
sufonated on pendant six phenyl rings. These behaviors would
affect hydrophobic and hydrophilic morphology in terms of dif-
ferent chemical structure. The WU significantly depends on the
IEC, therefore, the number of sorbed water molecules per sulfonic
acid group (l) was used to evaluate the relationship between the
polymer structure and WU. ␭ can be calculated from the equation
␭=(10 × WU)/(IEC × 18). ␭ in water for SPPS are in the range of 14-
18. The dimensional changes of SPPSs membranes were evaluated
through-plane (ꢀt) and in-plane (ꢀl) of membrane by comparing
their hydrated state with dry state. The results of SPPS 1, 2, and 3
membranes ꢀt values are 17.21, 20.42, and 27.71%, and ꢀl values
are 15.28, 19.83, and 26.83% each (Table 1). The small change of
through-plane with high proton conductivity is desirable behavior
for maintaining dimensional stability during operation of PEMFC
stack. Proton conductivities of the series of SPPSs were measured
as a function of the mole fraction of sulfuric acid groups. The pro-
ton conductivities of SPPSs membranes were measured at 40-80 ◦C
under 80% RH (Fig. 5), and at 80 ◦C in the range of 30-90% RH (Fig. 6).
The results were estimated from AC impedance spectroscopy data
and the results at different conditions were presented in Fig. 5 and
6, in comparison with Nafion 211®. The proton conductivities of the
resulting of SPPSs membranes were in the range of 66.4 to 110.2
mS/cm compared with 102.7mS/cm of Nafion 211® at 80 ◦C with
90% humidity. At 80 ◦C and under conditions of varied humidity,
the proton conductivity of SPPSs membranes showed increasing as
humidity increases. The conductivities of all the samples increased
in the range of evaluated temperatures, and the membrane with
higher IEC value had higher proton conductivity. The proton con-
ductivity of membrane SPPS 3 was higher than Nafion 211® at 80 ◦C
under 80∼90% RH. Ex situ hydrogen peroxide tests were carried
out for all membranes, SPPSs, Nafion 211®, and SPES 40 (SPES 40:
sulfonated linear poly(ether sulfone) containing 40 mol% of 4,4-
biphenol) at the same temperature. The tests were evaluated in hot
Fenton reagent for 9 hrs as an accelerated chemical degradation test
of membranes. Weight loss of the membranes after the testing are
presented as the remaining mass of membranes a function of time,
and shown in Fig. 7. These curves showed that SPPSs membranes
were less degradated and remained around 88 wt% than SPES 40
which is almost degradated. IEC values of SPPS membranes before
and after tests were listed in Table 1. This result suggested that
all carbon-carbon bonded hydrocarbon membranes are a candi-
date of alternative material to Nafion because they are quite stable
under severe chemi-oxidative condition. Fig. 8, displays a compari-
son of measured polarization and power density curves for SPPS
1, 2, 3 and Nafion 211® under fully humidified inlet condition
Fig. 4. IEC and water uptake of membranes.
Fig. 6. Proton conductivity of membranes at different temperature under 80% RH.

22
Y. Lim et al. / Electrochimica Acta 119 (2014) 16–23
was synthesized by Diels-Alder reaction, and followed post-
sulfonation with different amount of chlorosulfuric acid. When
compared with Nafion® 211 membrane, the SPPSs showed com-
parable IECs from 1.49 to 2.34 meq./g, water uptake from 38.29 to
74.52%, proton conductivity from 66.4 to 110.2 mS/cm, maximum
power density from 0.41 to 0.67 W/cm2, and high thermal stability,
respectively. The proton conductivity of SPPS 3 was higher than
Nafion 211® at 80 ◦C under 80-90%RH. These membranes shows
high water uptakes, that because of high IEC and large size of free
volume possibly to take water molecules. But these membranes
show very good stability in ex situ degradation test. This result from
the structure of polymer has no ether linkage possibly attacked by
nucleophiles. These results showed that the morphology of poly-
mer matrix greatly affected the performance and stability.
Acknowledgement
“This work was supported by the National Research Foundation
of Korea Grant funded by the Korean Government (MEST)” (NRF-
2009-C1AAA001-0093168). and This Research has been performed
as a cooperation project of KRICT OWN Project (KOREA RESEARCH
INSTITUTE of CHEMICAL TECHNOLOGY).
Fig. 7. Accelerated chemical membrane degradation test in 4 ppm Fe2+ Fenton
reagent.
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