Copolymers composed of perfluoroalkyl and ammonium-functionalized fluorenyl groups as chemically stable anion exchange membranes

Article abstract of DOI:10.1246/bcsj.20170185

We report synthesis and properties of a novel series of ammonium-functionalized perfluoroalkylene/aromatic copolymers. In particular, the effect of number and position of ammonium groups on the properties of the copolymer thin membranes was investigated. Fluorenylidene biphenylene groups were used as a scaffold for the ammonium groups. By controlling the chloromethylation reaction conditions, the ammonium groups could be introduced up to 4.0 per fluorenylidene biphenylene unit, resulting in the ion exchange capacity (IEC) of the resulting copolymers ranging from 1.0 to 1.8 meq g-1. The copolymers provided bendable and transparent membranes by solution casting. The membranes exhibited phase-separated morphology based on the hydrophilic/hydrophobic differences in the copolymer components. A copolymer membrane with IEC = 1.0 meq g-1 showed high hydroxide ion conductivity (ca. 70mScm-1) at 80°C in water and good alkaline stability in 1M KOH aq. over 1000 h at 60 °C. The membrane showed only minor degradation after the long-term alkaline stability test.

Full text of DOI:10.1246/bcsj.20170185

Advance Publication Cover Page
Copolymers Composed of Perfluoroalkyl and Ammonium-functionalized Fluorenyl
Groups as Chemically Stable Anion Exchange Membranes
Mizuki Ozawa, Taro Kimura, Ryo Akiyama, Junpei Miyake, Junji Inukai, and Kenji Miyatake*
Advance Publication on the web July 7, 2017
doi:10.1246/bcsj.20170185
© 2017 The Chemical Society of Japan

Copolymers Composed of Perfluoroalkyl and Ammonium-functionalized
Fluorenyl Groups as Chemically Stable Anion Exchange Membranes
Mizuki Ozawa,1 Taro Kimura,1 Ryo Akiyama,2 Junpei Miyake,3 Junji Inukai,3 and Kenji Miyatake*2,3
1Interdisciplinary Graduate School of Medicine, Engineering, and Agricultural Sciences, University of Yamanashi, 4 Takeda, Kofu,
Yamanashi 400-8510
2Fuel Cell Nanomaterials Center, University of Yamanashi, 6-43 Miyamae, Kofu, Yamanashi 400-0021
3Clean Energy Research Center, University of Yamanashi, 4 Takeda, Kofu, Yamanashi 400-8510
E-mail: miyatake@yamanashi.ac.jp
ion conductivity in water. Lin et al.10 also reported that
Abstract
poly(fluorene arylene ether sulfone) with pendant
imidazolium ions exhibited high hydroxide ion conductivity
(ca. 60 mS cm-1) and good chemical stability in 1 M KOH at
60 °C for 400 h. We have also developed a series of AEMs
based on fluorene-containing poly(arylene ether)s.11 The
combination of high ammonium density (each aromatic ring in
the fluorenylidene biphenylene unit was functionalized with
an ammonium group) and block copolymer structure provided
highly anion conductive AEMs. The resulting AEMs
(QPE-bl-1) exhibited high ion conductivity (144 mS cm-1 at
80 °C in water) and good fuel cell performance with no
precious metal catalysts. The maximum power density of the
fuel cell with QPE-bl-1 AEM was 297 mW cm-2 at a current
density was 826 mA cm-2.12 However, chemical stability of the
QPE-bl-1 AEMs was not sufficient and degraded in strongly
alkaline conditions.
More recently, we have developed another series of AEMs
(QPAF-1) containing perfluoroalkyl groups in the polymer
main chain.13 Because of the absence of heteroatom linkages
(e.g., ether and sulfone) in the polymer main, QPAF-1 AEMs
were much more alkaline durable and no mechanical failure
was observed during the accelerated alkaline stability test for
1000 h. The objective of the present study is to combine the
structure of QPE-bl-1 and QPAF-1 copolymers and to
evaluate the effect of the ammonium-functionalized fluorenyl
and perfluoroalkyl groups on the properties of the resulting
QPAF-2 AEMs. Synthesis, structural analyses, and properties
measurements (hydroxide ion conductivity, mechanical
strength, alkaline stability) were investigated in detail. Two
different monomers, 9,9-bis(4-chlorophenyl)fluorene (p-BCF)
and 9,9-bis(3-chlorophenyl)fluorene (m-BCF), were used in
order to evaluate the effect of the linking positions in the main
chain on the polymer properties.
We report synthesis and properties of a novel series of
ammonium-functionalized
perfluoroalkylene/aromatic
copolymers. In particular, effect of number and position of
ammonium groups on the properties of the copolymer thin
membranes was investigated. Fluorenylidene biphenylene
groups were used as a scaffold for the ammonium groups. By
controlling the chloromethylation reaction conditions, the
ammonium groups could be introduced up to 4.0 per
fluorenylidene biphenylene unit, resulting in the ion exchange
capacity (IEC) of the resulting copolymers ranging from 1.0 to
1.8 meq g-1. The copolymers provided bendable and
transparent membranes by solution casting. The membranes
exhibited phase-separated morphology based on the
hydrophilic/hydrophobic differences in the copolymer
components. The copolymer membrane with IEC = 1.0 meq
g-1 showed high hydroxide ion conductivity (ca. 70 mS cm-1)
at 80 °C in water and good alkaline stability in 1 M KOH aq.
over 1000 h at 60 °C. The membrane showed only minor
degradation after the long-term alkaline stability test.
1. Introduction
Anion exchange membranes (AEMs) have attracted much
attention for applications to energy devices such as
electrodialysis1, redox flow batteries2, electrolyzers3, and fuel
cells4. In particular, alkaline fuel cells using AEMs offer
advantages over those with proton exchange membranes;
alkaline fuel cells could use non-precious metals (Ni, Co, Fe
etc.) as electrocatalysts5. However, chemical stability and
anion conductivity of the existing AEMs do not meet the
criteria for practical use. In order to address these issues, a
wide variety of polymer structures such as poly(arylene
ether)s6 and polystyrenes7 functionalized with quaternary
ammonium groups have been studied. Ammonium-substituted
hydrophilic groups are the key components both for the
conductivity and stability of the AEMs.
Cardo structures such as phenolphthalein and fluorene
derivatives seem attractive as a scaffold for the ammonium
groups because multiple ammonium groups could be easily
substituted on them. In addition, because of their bulky
structures, a large free volume forms in the polymer
membranes serving as an ion-conducting pathway.8 For
example, Liu et al.9 reported poly(arylene ether sulfone)
containing phenolphthalein or fluorene groups with up to four
ammonium groups per cardo unit that showed high hydroxide
2. Experimental
Materials.
9,9-Bis(4-aminophenyl)fluorene (> 98%, TCI),
9,9-bis(4-amino-3-chlorophenyl)fluorene (> 97%, TCI),
hydrochloric acid (35-37%, Kanto Chemical), sodium nitrite
(> 98.5% TCI), copper(I) chloride (> 95%, Kanto Chemical),
acetic acid (> 99.7%, Kanto Chemical), phosphinic acid
(30-32%, Kanto Chemical), 2,2’-bipyridine (> 99%, TCI),
bis(1,5-cyclooctadiene)nickel(0) (Ni(cod)2) (> 95%, Kanto
Chemical), N,N-dimethylacetamide (DMAc) (> 99%, Kanto
Chemical), chloromethyl methyl ether (CMME) (> 95%, TCI),
0.5 M zinc chloride (ZnCl2) in THF solution (TCI),
1,1,2,2-tetrachloroethane (TCE) (> 98%, Kanto Chemical),

and 45 wt% trimethylamine (TMA) aqueous solution
(Aldrich) were used as received.
1.869 g, 11.9 mmol), DMAc (para : 9.6 mL, meta : 12 mL)
were charged in 100 mL three-necked flask with nitrogen inlet.
The mixture was heated at 80 °C and stirred until complete
dissolution. Then, Ni(cod)2 (para: 2.634 g, 9.57 mmol, meta :
3.291 g, 11.9 mmol) was added to the mixture, and heated at
80 °C for 3 h. After the reaction, the mixture was poured into
300 mL of methanol to precipitate a black powder. The crude
product was stirred in concentrated hydrochloric acid
overnight, washed with water and methanol several times, and
dried at 50 °C in vacuum oven overnight to obtain the product
as a white powder (PAF-2) in 85% yield.
Bis(3-chlorophenyl)perfluorohexane (PAF monomer) was
synthesized according to the literature.13
Synthesis of 9,9-Bis(4-chlorophenyl)fluorene (p-BCF).
500 mL one neck round-bottomed flask equipped with a
magnetic stirrer bar was charged with
A
9,9-bis(4-aminophenyl)fluorene (BAF: 16.5 g, 47.2 mmol)
and 6% hydrochloric acid (190 mL). To this white suspension,
sodium nitrite (7.84 g, 114 mmol) aqueous solution (25 mL)
was added. The mixture was stirred at room temperature and
the solid was gradually dissolved to afford an orange solution.
The resulting solution was added dropwise to the mixture of
copper(I) chloride (16.8 g, 170 mmol) and concentrated
hydrochloric acid (130 mL). During the addition of diazonium
salt, a yellow solid was precipitated with an evolution of gas.
After stirring overnight, the resulting solid was dissolved in
EtOAc and the layers were separated. The aqueous layer was
extracted with EtOAc. The combined organic layers were
washed with deionized water and diluted hydrochloric acid,
and concentrated under reduced pressure. The residue was
purified by silica gel column chromatography (eluent:
hexane/EtOAc = 19/1) to afford p-BCF as a white solid (10.8
Chloromethylation of PAF-2.
The chloromethyl groups
were introduced in the precursor copolymers by Friedel-Crafts
reaction. A typical procedure is as follows. A pressure proof
bottle was charged with PAF-2 (0.2 g), TCE (1.3 mL, 0.1 M
biphenylfluorene unit in PAF-2), CMME (2.3 mL, 240
equimolar to biphenylfluorene unit in PAF-2) and heated at
80 °C to dissolve the solid. Then, ZnCl2 solution (0.25 mL,
equimolar to biphenylfluorene unit in PAF-2) was added into
the mixture. After 5 days reaction, the mixture was poured
into 200 mL of methanol to precipitate a product. The crude
product was washed with water and methanol several times
and dried at 40 °C in vacuum oven overnight to obtain a pale
yellow powder (CMPAF-2).
1
g, 59% yield). H and 13C NMR spectra of the obtained solid
1
Membrane Preparation and Quaternization of CMPAF-2.
A typical procedure is as follows. CMPAF-2 (0.9 g) was
dissolved in 9.0 mL of DMAc. After filtration with a syringe
stuffed with cotton, the obtained homogeneous solution was
cast onto the flat glass plate. The solution was dried at 50 °C
overnight to obtain a transparent pale yellow membrane. The
resulting membrane was soaked in 5 wt% TMA aqueous
solution for 48 h at 40 °C, washed with 1 M HCl and water to
obtain a transparent pale brown membrane (QPAF-2).
are shown in Figure S1. H NMR (500 MHz, CDCl3):  7.12
(d, J = 8.1 Hz, 4H), 7.20 (d, J = 8.1 Hz, 4H), 7.29 (dd, J = 7.6,
7.6 Hz, 2H), 7.35 (d, J = 7.6 Hz, 2H), 7.39 (dd, J = 7.6, 7.6 Hz,
2H), 7.78 (d, J = 7.6 Hz, 2H). 13C NMR (125 MHz, CDCl3): 
64.4, 120.4, 125.8, 127.9, 128.0, 128.5, 129.4, 132.8, 140.0,
144.0, 150.3.
Synthesis of 9,9-Bis(3-chlorophenyl)fluorene (m-BCF). A
300 mL one neck round-bottomed flask equipped with a
magnetic
stirrer
bar
was
charged
with
Measurements.
1H (500 MHz), 13C (125 MHz), and 19F
9,9-bis(4-amino-3-chlorophenyl)fluorene (10.0 g, 24.0 mmol),
acetic acid (88 mL), deionized water (38 mL) and
concentrated hydrochloric acid (10 mL). To this white
suspension, sodium nitrite (3.91 g, 56.7 mmol) aqueous
solution (12.6 mL) was added. The mixture was stirred at
room temperature and the solid was gradually dissolved to
afford an orange solution. To the resulting diazonium salt
solution, phosphinic acid (32~34%, 70 mL) was added.
During the addition of phosphinic acid, an orange solid was
precipitated with an evolution of gas. After stirring for 24
hours, the resulting solid was recovered by filtration and
dissolved in EtOAc. This EtOAc solution was washed with
saturated aqueous solution of sodium hydrogen carbonate, and
concentrated under reduced pressure. The residue was purified
by silica gel column chromatography (eluent: hexane/EtOAc =
19/1) to afford m-BFC as a white solid (7.01 g, 76% yield). 1H
and 13C NMR spectra of obtained solid are shown in Figure S2.
1H NMR (500 MHz, CDCl3):  7.09 (m, 2H), 7.12 (m, 2H),
7.17 (dd, J = 7.8, 7.8 Hz, 2H), 7.20 (m, 2H), 7.29 (dd, J = 7.3,
7.3 Hz, 2H), 7.37 (d, J = 7.3 Hz, 2H), 7.39 (dd, J = 7.3, 7.3 Hz,
2H), 7.77 (d, J = 7.3 Hz, 2H). 13C NMR (125 MHz, CDCl3) 
64.9, 120.4, 126.0, 126.3, 127.1, 127.9, 128.0 (C*2), 129.6,
134.2, 140.0, 147.4, 149.6.
(471 MHz) NMR spectra were obtained on a JEOL
JNM-ECA/ECX500 using deuterated chloroform (CDCl3),
1,1,2,2-tetrachloroethane (TCE-d2), or dimethyl sulfoxide
(DMSO-d6) as a solvent and tetramethylsilane (TMS) as an
internal reference. The molecular weight was estimated by a
gel permeation chromatograph (GPC) equipped with Shodex
K-805 L columns and a Jasco 805 UV detector (270 nm) with
DMF containing 0.01 M LiBr as an eluent. The molecular
weight was calibrated with polystyrene standards. Ion
exchange capacity (IEC) was estimated by titration in a
method reported in the literature.13 Scanning transmission
electron microscopic (STEM) images were taken for
membrane samples stained with tetrachloroplatinate ions on a
Hitachi HD-2700 with an accelerating voltage of 200 kV.
Small angle X-ray scattering (SAXS) data were obtained
using
a
Nano-Viewer (Rigaku) equipped with
a
temperature/humidity controlled chamber. Cu Kα (λ = 0.154
nm) was used as an X-ray source. The scattering patterns were
collected using a Rigaku high speed 2D detector PILATUS
100K/R. The SAXS measurement was performed at 40 °C
under humidified N2 atmosphere at 30-90% RH. The AEMs in
the chloride-ion forms were placed in an SAXS cell and
equilibrated in the humidified N2 for 2 h before each
measurement. Properties of QPAF-2 membranes such as
hydroxide ion conductivity and mechanical properties were
measured according to the methods in the literature.13 The
hydroxide ion conductivities of the membranes were measured
Synthesis of Precursor Copolymers (PAF-2).
Precursor
copolymers were synthesized by Ni promoted Ullmann
coupling reaction. A typical procedure is as follows. PAF
monomer 1.879 g (3.60 mmol), p- or m-BCF 0.457 g (1.19
mmol), 2,2-bipyridine (para : 1.495 g, 9.57 mmol, meta :

in carefully degassed and deionized water (18 MΩ) to
preclude the effect of carbon dioxide from the atmosphere.
3. Results and Discussion
Synthesis of Quaternized Copolymers (QPAF-2).
QPAF-2 was synthesized as shown in Scheme1. The precursor
copolymers (PAF-2p, m) were synthesized by Ni-promoted
polycondensation reaction of PAF-monomer and p-BCF or
m-BCF. The copolymerization reaction proceeded successfully
1
as evidenced by NMR and GPC measurements. In the H
NMR spectra (Figure 1a and 2a), peaks at 7.6 and 7.7 ppm
were assigned to the aromatic protons derived from PAF
component and the other peaks were assigned to those derived
from BCF component, respectively. The copolymer
compositions were calculated from the integral ratios to be m :
n = 1.00 : 0.33 (PAF-2p) and 0.35 (PAF-2m), which were in
fair agreement with the feed comonomer ratio (m : n = 1.00 :
0.32). The molecular weights of the copolymers estimated
from the GPC analysis were Mn = 22.4 - 28.3 kDa and Mw =
100 - 125 kDa, respectively (Table 1), which were high
enough to form self-standing membranes by solution casting.
The polydispersity indices (Mw/Mn) were 4.4 - 4.7, typical for
this kind of polycondensation reaction.
The Friedel-Crafts chloromethylaion reaction of the precursor
copolymers (PAF-2p, m) was carried out with CMME using
ZnCl2 as
a
Lewis acid catalyst.14 To control the
chloromethylation reaction, effect of several parameters
including the reaction temperature and concentration of the
reactants (BCF and CMME) were carefully investigated.
Under the tested conditions, the obtained products were
soluble in many organic solvents implying no or little
cross-linking reaction. In addition, phenylene groups attached
to the perfluoroalkyl groups (derived from PAF) were intact as
Scheme 1. Synthesis of QPAF-2.
Table 1. Composition and molecular weight of PAF-2.
1
evidenced by the H NMR spectra (Figure 1b and 2b). The
degree of chloromethylation (DC) per BCF unit was estimated
from the integral ratio of the aromatic peaks (7.0-8.0 ppm) to
methylene peaks of the introduced chloromethyl groups
(4.6-5.0 ppm). The peaks at lower magnetic field (ca. 4.0-4.5
ppm) were assignable to chloromethyl groups on the main
chain and those at higher magnetic field were chloromethyl
groups on fluorenyl groups. The chloromethyl groups were
substituted on the fluorenyl groups at the early stage of the
reaction, and then on the main chain as the reaction proceeded.
Polymer (or BCF) concentration was the most crucial to
determine the DC (Table 2). The highest DC value (4.0) was
achieved under the concentrated conditions with QPAF-2p, in
which each aromatic ring of BHF unit was substituted with a
chloromethyl group. CMPAF-2s were cast from DMAc
solution to obtain thin and bendable membranes, which were
then quaternized by typical Menschutkin reaction with
trimethylamine (TMA) aqueous solution. The resulting
membranes were soluble in polar organic solvents such as
DMSO and DMAc, but not in nonpolar solvents such as
chloroform and TCE. The quaternization reaction was
confirmed by the appearance of the methyl protons (ca. 3.0
Composition (m : n)
Molecular weight
Polymer
Mn
Mw
Mw /
Mn
Feed
Obtaineda
(103) (103)
PAF-2p
PAF-2m
1.00 : 0.32
1.00 : 0.32
1.00 : 0.33
1.00 : 0.35
28.3
22.4
125
105
4.4
4.7
a Obtained by the 1H NMR spectra.
Table 2. Chloromethylation reaction conditions, DC, and IEC
of QPAF-2.
Chloromethylation
IEC (meq g-1)
conditions
Polymer
DCa
Temp. BCF
CMME
NMRb
Titrationc
(°C)
(M)
(eq./BCF)
50
80
80
80
50
80
0.01
0.01
0.05
0.1
80
240
240
240
80
1.7
2.0
3.0
4.0
1.7
2.0
1.0
1.1
1.5
2.0
1.0
1.2
1.0
1.1
1.5
1,8
1.0
1.2
QPAF-
2p
0.01
0.01
QPAF-
2m
1
ppm) in the H NMR spectra of the products (Figure 1c and
240
2c). Complete quaternization was confirmed from the integral
ratio of the aromatic peaks (7.0-8.0 ppm) to the methyl peaks
(ca. 3.0 ppm) for all samples. The IEC values obtained by
a
Degree of chloromethylation calculated from the integral
ratio of the aromatic peaks to methylene peaks in the 1H NMR
spectra. b Calculated from the 1H NMR spectra of CMPAF-2
1
titration were comparable to those estimated from the H
c
assuming complete quaternization reaction. Determined by
NMR spectra within acceptable errors (Table 2).
titration.

Methyl
H2O
Methyl
H2O
Aromatic
TCE
Aromatic
TCE
DMSO
DMSO
Methylene
g
Methylene
h
(c)
(b)
(c)
(b)
2,3
a,b,c,d,e
1,4
f
2,3
1,4
a,b,c,d,e,f
g
1,4
2,3
a,c,e
b,d
2,3
a,b,c,d,e,f,g
1,4,h
(a)
(a)
f
8.0
7.0
6.0
 ppm
5.0
(b)
4.0
3.0
8.0
(a)
7.0
6.0
5.0
4.0
(b)
3.0
 ppm
(a)
(c)
(c)
Figure 2. 1H NMR spectra of (a) PAF-2m, (b) CMPAF-2m,
and (c) QPAF-2m.
Figure 1. 1H NMR spectra of (a) PAF-2p, (b) CMPAF-2p, and
(c) QPAF-2p.
Morphology.
Morphology of QPAF-2p (IEC = 1.1, 1.0,
Then, effect of humidity on the morphology was investigated
via SAXS measurements for QPAF-2p with IEC = 1.0 meq g-1
(Figure 4). The membrane showed a clear ionomer peak at d =
8-9 nm at 30% RH, which developed more as increasing the
humidity. The periodic structure observed by SAXS patterns
could be reasonably related with the hydrophilic domains. The
domain sizes obtained by SAXS curves were similar to or
slightly larger than those in STEM images because of the
swelling with the absorbed water. Compared to our previous
AEMs (QPAF-1)13 sharing the same perfluoroalkylene
hydrophobic components but oligophenylene hydrophilic
components, the hydrophilic domains of QPAF-2 were larger
probably because of the bulky fluorenyl groups as a scaffold
for the ammonium groups.
and 1.8 meq g-1) membranes was observed by STEM (Figure
3).The membranes with IEC = 1.1 and 1.0 meq g-1 exhibited
similar phase-separated morphology with hydrophilic (dark
areas) and hydrophobic (bright areas) domains of ca. 5 to 10
nm in width. In contrast, QPAF-2p membrane with higher IEC
(1.8 meq g-1) and higher DC (= 4) contained smaller
hydrophilic and hydrophobic domains. In addition to the
larger ones (ca. 5 to 8 nm), smaller and spherical hydrophilic
domains (1 to 2 nm in diameter) were also observed within the
hydrophobic domains. It is considered that ammonium groups
on the rigid polymer main chains did not contribute much to
the development of the phase separation but caused such
unique morphology.
Figure 3. STEM dark-field images of QPAF-2p (a) DC = 2.0, IEC 1.1 meq g-1, (b) DC =1.7, IEC 1.0 meq g-1, (c) DC = 4.0, IEC
1.8 meq g-1 membranes in PtCl42- ion forms.

Hydroxide Ion Conductivity.
Hydroxide ion conductivity
Temperature(oC)
60 50 40
of the QPAF-2 membranes were measured in water at 30 °C
and plotted as a function of IEC in Figure 5. Unlike typical
AEMs that show higher ion conductivity with higher IEC, the
conductivity of QPAF-2 membranes was less dependent on
IEC and nearly constant. QPAF-2p and -2m membranes
exhibited similar conductivity and its IEC dependence. The
highest conductivity (55 mS cm-1) was obtained for QPAF-2p
with IEC = 1.5 meq g-1. The results suggest that the
ammonium groups substituted on the main chain contributed
less to the hydroxide ion conduction, than those on the
fluorenyl groups. The ammonium groups on less hindered
fluorenyl groups are more likely to participate in hydroxide
ion conduction. As discussed above in the STEM images, the
ammonium groups on the main chains (in the case of DC = 4)
contributed less to the development of the hydrophilic
domains and thus the hydroxide ion conduction. Similar
behavior was observed in our poly(arylene ether)-based AEMs
containing quaternized fluorenyl groups.15
80 70
30
10-1
QPAF-2p, IEC 1.0 meq g-1
QPAF-2m, IEC 1.0 meq g -1
10-2
2.8
2.9
3.0
3.1
3.2
3.3
1000/T (K-1)
Figure 6. Temperature dependence of the hydroxide ion
conductivity of QPAF-2 membranes in water.
Temperature dependence of the hydroxide ion conductivity of
the selected QPAF-2 membranes in water is shown in Figure 6.
The conductivity showed approximate Arrhenius type
temperature dependence. Both membranes exhibited ca. 70
mS cm-1 of hydroxide ion conductivity at 80 °C. The apparent
activation energies calculated from the slopes were Ea = 12.6
and 11.5 kJ mol-1 for QPAF-2p (IEC = 1.0 meq g-1) and -m
(IEC = 1.0 meq g-1), respectively. These values were similar to
those of our previous AEMs sharing the perfluoroalkylene
groups or quaternized fluorenyl groups,13,15 indicating that
these membranes shared similar ion conduction mechanism
109
QPAF-2p(IEC 1.0 meq g-1)
108
108
QPAF-2m(IEC 1.0 meq g-1)
involving the migration of hydrated hydroxide ions.
d (nm)
107
50
10
5
102
101
100
10-1
90% RH
70% RH
50% RH
30% RH
10-1
10-2
20
40
60
80
100
Temperature (oC)
10-1
100
Figure 7. DMA profiles of QPAF-2 (in Cl- form) membrane at
60% RH as a function of temperature.
q (nm-1)
Figure 4. Humidity dependence of SAXS patterns of
QPAF-2p (DC = 1.7, IEC 1.0 meq g-1) membrane in Cl- ion
form at 40 °C.
50
40
30
20
10
10-1
para
meta
0
500
Time (h)
1000
10-2
0.5
1.0
1.5
2.0
Ion Exchange Capacity (meq g -1)
Figure 8. Time course of the hydroxide ion conductivity of
QPAF-2m (IEC = 1.0 meq g-1) membrane in 1 M KOH
aqueous solution at 60 °C.
Figure 5. Hydroxide ion conductivity of QPAF-2 membranes
in water at 30 °C as a function of IEC.

(b)
(a)
Before
After
Before
After
2000
1500
1000
500
4000
3000
2000
1000
Wave number (cm-1)
Wave number (cm-1)
Figure 9. IR spectra of QPAF-2m (IEC = 1.0 meq g-1) membrane before and after the stability test; (a) 4000-500 cm-1 and (b)
2000-500 cm-1.
Mechanical Properties.
The mechanical properties of
chemical stability of the polymer main chain. Nevertheless,
the change in the solubility after the test might be caused by
minor chemical changes such as cross-linking via a slight
decomposition of the ammonium groups.
QPAF-2 membranes were evaluated by dynamic mechanical
analyses (DMA) at 60% RH from room temperature to 95 °C
(Figure 7). QPAF-2p membrane showed slightly higher
storage moduli than those of -2m membrane probably because
of the symmetric 1,4-phenylene main chain structure in the
hydrophilic component. Both membranes exhibited a peak at
ca. 60-70 °C in loss moduli. Compared to our previous AEMs
containing the same hydrophobic but different hydrophilic
(ammonium-substituted phenylene) groups (QPAF-1), the
peaks appeared at lower temperature for QPAF-2 membranes
than for QPAF-1 membrane (ca. 85 ºC), indicating that
quaternized fluorenyl groups were responsible for the DMA
properties.
1010
109
108
108
Alkaline Stability.
The alkaline stability of QPAF-2m
(IEC = 1.0 meq g-1 in Cl- form) membrane was examined in 1
M KOH aqueous solution at 60 °C (Figure 8). During the test,
ion exchange reaction (from Cl- to OH-) and degradation could
occur competitively with counteractive effects on the ion
conductivity. Nevertheless, the QPAF-2m membrane exhibited
high alkaline stability with no practical loss in the
conductivity after 1100 h. The conductivity after the test was
26 mS cm-1, which was comparable to or higher than that of
the initial membrane. The post-test membrane retained its
shape and flexibility. The results suggest that the QPAF-2m
membrane did not experience severe degradations under the
tested conditions.
107
10-1
Before
After
10-2
20
40
60
80
100
However, since the post-test membrane became insoluble,
FT-IR spectrum was measured (Figure 9). The peaks at
2850-3000 cm-1 assignable to aliphatic C-H stretching
vibration and at 3000-3100 cm-1 assignable to aromatic C-H
stretching vibration did not change after the stability test. In
addition, the broad and large peak at 3200-3500 cm-1
assignable to OH stretching vibration did not change after the
test. The results suggest that both polymer main chain and
ammonium groups hardly decomposed. IEC of the post-test
membrane was measured by titration. The residual IEC was
0.95 meq g-1 (95% remaining). Furthermore, the mechanical
properties were measured (Figure 10). The DMA curves
showed minor changes after the stability test. The peak
temperature in loss moduli was similar, reflecting the
Temperature (oC)
Figure 10. DMA profiles of QPAF-2m (in Cl- forms)
membrane before and after the alkaline stability test, at 60%
RH as a function of temperature.

4. Conclusion
c) A. N. Lai, L. S. Wang, C. X. Lin, Y. Z. Zhuo, Q. G.
Zhang, A. M. Zhu, and Q. L. Liu, ACS Appl. Mater.
Interfaces, 2015, 7, 8284. d) D. Guo, A. N. Lai, C. X.
Lin, Q. G. Zhang, A. M. Zhu, and Q. L. Liu, ACS Appl.
Mater. Interfaces, 2016, 8, 25279.
In order to improve the properties of anion conductive
membranes, a novel series of ammonium-functionalized
perfluoroalkylene/aromatic copolymer (QPAF-2) membranes
were designed and synthesized. Effects of the ionic density
and its position substituted on fluorenylidene biphenylene
group on the properties were studied in detail. Unlike the
conventional AEMs, high ionic density or high IEC did not
contribute to the development of the phase-separated
morphology and hydroxide ion conductivity for the QPAF-2
membranes. The results suggest that the ammonium groups on
less hindered fluorenyl groups functioned better as ion
exchange groups than those on the polymer main chains.
Accordingly, the QPAF-2 membrane with DC =2 and IEC =
1.0 meq g-1 exhibited high hydroxide ion conductivity in water.
Because of the absence of heteroatom linkages (e.g., ether,
sulfide, and sulfone) in the polymer main chains, QPAF-2
membrane was chemically stable with practical no changes in
the ion conductivity and chemical structure after 1000 h
alkaline stability test in 1.0 M KOH at 60 ºC.
10 B. Lin, L. Qiu, B. Qiu, Y. Peng, and F. Yan,
Macromolecules, 2011, 44, 9642.
11 a) M. Tanaka, M. Koike, K. Miyatake, and M.
Watanabe, Macromolecules, 2010, 43, 2657. b) M.
Tanaka, M. Koike, K. Miyatake, and M. Watanabe,
Polym. Chem., 2011, 2, 99 c) H. Ono, J. Miyake, B.
Bae, M. Watanabe, and K. Miyatake, Bull. Chem. Soc.
Jpn., 2013, 86, 663670.
12 M. Tanaka, K. Fukasawa, E. Nishino, S. Yamaguchi, K.
Yamada, H. Tanaka, B. Bae, K. Miyatake, and M.
Watanabe, J. Am. Chem. Soc., 2011, 133, 10646.
13 H. Ono, J. Miyake, S. Shimada, M. Uchidabd and K.
Miyatake, J. Mater. Chem. A, 2015, 3, 21779.
14 D. W. Seoa, M. A. Hossaina, D. H. Leea, Y. D. Lima, S.
H. Lee, H. C. Lee, T. W. Hong, W. G. Kim,
Electrochem. Acta, 2012, 86, 360.
15 M. Shimada, S. Shimada, J. Miyake, M. Uchida, K.
Miyatake, J. Polym. Sci. A: Polym. Chem., 2016, 54,
935–944
Acknowledgement
This work was partly supported by CREST (JPMJCR12C3),
Japan Science and Technology Agency (JST).
References
1
2
3
4
a) S. Singh, A. Jasti, M. Kumar and V. K. Shahi, Polym.
Chem., 2010, 1, 1302. b) T. Sata, J. Membr. Sci., 2000,
167, 1.
a) G. Hwang, H. Ohya, J. Membr. Sci., 1997, 132, 55.
b) A. Parasuramana, T. M. Lim, C. Menictasc, M.
Skyllas-Kazacosc, Electrochem. Acta, 2013, 101, 27.
a) M. Kumar, S. Singh, and V. K. Shahi, J. Phys. Chem.
B 2010, 114, 198. b) X. Wu, K. Scott, J. Power
Sources 2012, 214, 124.
a) G. Merle, M. Wessling, K. Nijmeijer, J. Membr. Sci.,
2011, 377, 1. b) J. R. Varcoe, P. Atanassov, D. R. Dekel,
A. M. Herring, M. A. Hickner, P. A. Kohl, A. R.
Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, T. Xu
and L. Zhuang, Energy Environ. Sci., 2014, 7, 3135.
a) S. Lu, J. Pan, A. Huang, L. Zhuang, and J. Lu, PNAS,
2008, 105, 20611. b) L. Lin, Q. Zhu, and A. Xu, J. Am.
Chem. Soc. 2014, 136, 11027.
a) J. Wang, Z. Zhao, F. Gong, S. Li, and S. Zhang,
Macromolecules, 2009, 42, 8711 b) J. Wang, S. Li, and
S. Zhang, Macromolecules, 2010, 43, 3890. c) M. S.
Chaa, J. Y. Leea, T. Kima, H. Y. Jeonga, H. Y. Shina, S.
G. Oh, Y. T. Hong, J. Membr. Sci., 2017, 530, 73.
a) J. R. Varcoe, R. C. T. Slade, E. L. H. Yee, S. D.
Poynton,D. J. Driscoll, and D. C. Apperley, Chem.
Mater., 2007, 19, 2686. b) Y. Luo, J. Guo, C. Wang, D.
Chu, J. Power Sources, 2010, 195, 3765. c) Q. H. Zeng,
Q. L. Liu, I. Broadwell, A. M. Zhu, Y. Xiong, X. P. Tu,
J. Membr. Sci., 2010, 349, 237.
5
6
7
8
9
K. Miyatake, B. Bae and M. Watanabe, Polym. Chem.,
2011, 2, 1919.
a) Y. Z. Zhuo,A.N Lai, Q. G. Zhang, A. M. Zhu, M.
L.Ye, Q. L. Liu, J. Membr. Sci., 2015, 491, 138, b) P. Y.
Xu, K. Zhou, G. L. Han, Q. G. Zhang, A. M. Zhu, and
Q. L. Liu, ACS Appl. Mater. Interfaces, 2014, 6, 6776.

Graphical Abstract
Copolymers Composed of Perfluoroalkyl and Ammonium-functionalized
Fluorenyl Groups as Chemically Stable Anion Exchange Membranes
Mizuki Ozawa, Taro Kimura, Ryo Akiyama, Junpei Miyake, Junji Inukai, and Kenji Miyatake
A novel series of ammonium-functionalized perfluoroalkylene/aromatic copolymers were designed and synthesized. The obtained
membrane with 1.0 meq g-1 of ion exchange capacity exhibited high hydroxide ion conductivity (ca. 70 mS cm-1) at 80 °C in water
and good alkaline stability in 1 M KOH aq. over 1000 h at 60 °C.
Temperature(oC)
80 70
60 50
40
30
10-1
QPAF-2p, IEC 1.0 meq g -1
QPAF-2m, IEC 1.0 meq g -1
10-2
2.8
2.9
3.0
3.1
3.2
3.3
1000/T (K-1
)