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Title

Alkaline stability of ether bond free fluorene-based
anion exchange polymer containing cycloaliphatic
quaternary ammonium groups

Author(s)Salma, Umme; Nagao, Yuki

Citation

Polymer Degradation and Stability, 179: 109299

Issue Date

2020-07-12

Type

Journal Article

Text version

author

URL

http://hdl.handle.net/10119/18024

RightsCopyright (C)2020, Elsevier. Licensed under theCreative Commons Attribution-NonCommercialNoDerivatives 4.0 International license (CC BY-NCND 4.0). [http://creativecommons.org/licenses/bync-nd/4.0/] NOTICE: This is the author's version ofa work accepted for publication by Elsevier. Umme
Salma, Yuki Nagao, Polymer Degradation andStability, 179, 2020, 109299,
http://dx.doi.org/10.1016/j.polymdegradstab.2020.
109299Description

Japan Advanced Institute of Science and Technology

Alkaline stability of ether bond free fluorene-based anion
exchange polymer containing cycloaliphatic quaternaryammonium groups
Umme Salmaa, b, Yuki Nagaoa, *aSchool of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi,

Ishikawa 923-1292, Japanb

Department of Chemistry, Mawlana Bhashani Science and Technology University, Santosh,

Tangail 1902, Bangladesh

ABSTRACTQuaternary piperidinium cation was incorporated into aryl-ether-bond-free fluorenebased polymer by flexible alkyl side chains to synthesize a highly conductive andchemically stable anion exchange membrane (AEM). The membrane of the OH- formshows good solubility in dimethyl sulfoxide and methanol but not soluble in water. In afully hydrated state, the OH- conductivity reached 58 mS cm-1 at 80 °C. The results of 1H
NMR spectra revealed that the alkyl-substituted N-methylpiperidinium cationic group
was excellent alkaline stable as only 13% cationic group was degraded after 168 h storage
in 1 M NaOH solution at 80 °C.

Keywords: Anion exchange membrane, alkaline stability, polyfluorene, quaternaryammonium, degradation
11. Introduction
Due to our modern lifestyle, the demand for energy is increasing day by day. In recent
years, worldwide attention is growing on the conversion and storage of electricity fromrenewable energy to protect the environment and depletion of fossil fuel [1]. Alkaline
anion exchange membrane fuel cells (AEMFCs) generate electricity directly from thestored energy in fuels, for example, MeOH, H2. AEMFCs do not rely on the platinum
catalyst, and the kinetics of oxygen reduction reaction is faster in comparison to the othersorts of fuel cells [2]. So researchers are extensively motivated to develop catalystmaterials and membranes for AEMFCs [3-9]. In the AEMFCs, a molecular design is oneof the main challenges to synthesize the new AEM with high durability, high ionic
conductivity, and longtime alkaline stability at 80 oC [10].
In AEMFCs, the attack of nucleophilic OH- degrades the cationic groups and thepolymer backbones of AEMs. For example, if polymer backbones contain electronwithdrawing sulfone and/or ketone groups, these groups stimulate the nucleophilic attack
by OH- groups and resulting in chain scission of backbones [11, 12]. On the other hand,
AEMs without electron-withdrawing sulfone and/or ketone groups, for example,
polyphenylene oxide (PPO), are practically stable in the alkaline environment [13].
Polymers without aryl ether links, for instance, polyarylene alkylenes [12, 14-16] and2polyphenylenes [17] are potentially even more stable. Lee et al. and Hibbs et al. [14, 1821] synthesized some AEMs without any aryl-ether-bond in the main chain and observedmuch improved alkaline stability.
Aromatic backbones containing fluorenyl groups have attracted much attention due tothe possibility of diverse chemical modifications. Before the polymerization reaction,
alkyl or dialkyl groups are introduced to the C-9 position of the fluorene to increase thesolubility of the polymer. The water uptake (WU) plays an important role in ionic
conductivity. Adequate amounts of WU are necessary for the formation of a hydrated
ionic domain and faster ionic migration through the membrane. Bulky fluorene groups
could force each polymer chain apart and enhance free volumes or interchain separations
in which water molecules might be confined [22, 23]. AEMs containing fluorenyl groups
not only exhibited high thermal and alkaline stability but also have high ionic conductivity[24, 25]. Bae et al. reported that aryl-ether-bond free polyfluorene AEMs were stable for
30 days in 1 M NaOH solution at 80 oC [19]. In this study we have chosen a similar typeof aryl-ether-bond free polyfluorene backbone as in alkaline conditions it can provide
high alkaline stability. And can reduce excessive swelling and water uptake of the AEMs
due to higher chain rigidity of polyfluorene backbone. There are some reports of theliterature containing fluorenyl group as one of the monomers as shown in Scheme 1A3

[26-29] but polyfluorene based literature is rare which contains fluorene as both monomer
and comonomer (Scheme 1B).

Scheme 1. Different design strategies of polyfluorene AEMs.
For the design of side chains and cations, long alkyl tethered cationic groups show
more thermal stability than benzyl tethered cationic groups under alkaline conditions [30].
So, in our research we have chosen one monomer containing two bromohexyl chains
which act as a scaffold for the cationic group as shown in Scheme 1C. A co-monomer
containing two octyl chains has been employed as the IEC can be controlled, the solubility4

of the polymer can be increased and the flexibility of the membrane can be enhanced.
For the selection of cations as our AEM, often the serious problem is the degradationof quaternary ammonium (QA) cations by several different pathways, such as different
rearrangement reactions, Hofmann (β) elimination, and nucleophilic substitution [8]. The
degradation pathway is dominated by the cationic structure, and how the cationic groupis incorporated into the polymer backbone. Therefore, numerous cationic groups
including modified tetraalkylammonium, imidazolium, benzimidazolium, guanidinium,
and pyridinium have been extensively studied [8, 30-36]. Some heterocycloaliphatic QA
cationic groups have been reported as predominantly long-lived in alkaline conditions. Ina systematic study, Marino and Kreuer found a longer half-life time of piperidinium andpyrrolidinium than the benchmark tetramethylammonium (TMA) in 6 M NaOH solution
at 160 °C [37]. Cyclic QAs were identified as particularly more alkaline stable becauseof the rotationally restricted anti-periplanar β-protons in the ring. The combination of lowring strain and conformational restrictions of the ring increases the transition state energy
for both Hofmann β-elimination and ring-opening substitution reactions [37]. Larger ring
sizes such as azepanium (7-membered ring) and additional heteroatoms e.g.,morpholinium destabilize the ring structures and have considerably lower chemical
stability than the N,N-dimethylpiperidinium cation [38]. N-spirocyclic QA like 6-azonia5

spiro[5.5]undecane (ASU) cation is even more stable. However, the attachment process
of QAs with N-spirocyclic structures into the polymer backbone is rather complicated; asa result, a few reports are available [39-45]. In contrast, the incorporation of aliphatic
monocyclic QA cations is relatively straightforward and less expensive. The ether-free
AEM with alkyl N-methylpiperidinium groups were synthesized by Ren and co-workers
and they observed no measurable degradation of the AEM in 1 M NaOH solution at 80 °C
for 1200 h [46]. Jannach et al. also reported alkali stable PPO based alkyl Nmethylpiperidinium functionalized AEMs [10, 47].
To combine high alkaline stability and high ionic conductivity in this study, we haveincorporated N-methylpiperidinium (Pip) cations to the polyfluorene backbone via alkyl
side chains and evaluated the properties of ion exchange capacity (IEC), hydroxide
conductivity, thermal and chemical stability, and WU. The synthesized solventprocessable membrane exhibited adequate hydroxide conductivity, well-controlled IEC,
and good thermal and alkaline stability. The major advantage of this study is the facile
synthetic strategy that avoids any complicated modifications.

62. Experimental
2.1. Materials
1,6-Dibromohexane,
tetrabutylammonium

2,7-dibromofluorene,
bromide(TBAB),

bis(pinacolato)diboron,

2,7-dibromo-9,9-dioctyl

fluorene,tetrakis(triphenylphosphine)palladium(0) denoted as Pd(PPh3)4 were purchased from
Tokyo Chemical Industry Co. Ltd., Japan. [1,1-Bis(diphenylphosphino)ferrocene]
dichloropalladium(II)methylpiperidine,(PdCl2)(dppf)

dioxane,(Sigma-Aldrichdichloromethane,

Corp.)

chloroform,

wastoluene,

used.

N-

ethanol,tetrahydrofuran (THF), diethyl ether, N,N-dimethylformamide (DMF), potassium
carbonate, hexane, acetonitrile, ethyl acetate, methanol, ethanol, sodium chloride, sodiumhydroxide, potassium hydroxide, anhydrous magnesium sulfate, potassium acetate, andhydrochloric acid were obtained from Fujifilm Wako Pure Chemical Corp., Japan. For all
experimental work, deionized (DI) water was used.
2.2. Synthesis of Monomers and Polymers
In this study, we have presented a facile synthetic procedure for the synthesis ofpiperidinium functionalized fluorene based AEM. The synthetic strategy for monomers
and polyfluorenes (PF) is shown in Scheme 2.

7

Br

Br + BrBr

TBAB, NaOH (50 wt%)
60 °C, 8 h

R

R
Br

Br

Compound A
R = C6H12Br
Bis(pinacolato)diboron
KOAc
85 °C, 24 h
DioxanePdCl2(dppf)

R''

R''

+

Br

Br

R R

O

B
O

R'' = C8H17

B

OO

Compound B
R = C6H12Br

Pd(PPh3)42M K2CO3 100 °C, 36 h
Toluene
R

R
R''

R''

n

PFBr
R = C6H12Br, R'' = C8H17
THF
60 °C
7 days
R'

N

Pip

R'

n
R''

R''

PF-PipBr
R' = C6H12Pip, R'' = C8H17

Scheme 2. Synthesis route of piperidinium functionalized polyfluorenes. Red means alkyl
side chains containing bromine atom and the blue stands for piperidinium functionalizedalkyl side chains.

82.2.1. Synthesis of 2,7-dibromo-9,9-bis(6ʹ-bromohexyl)fluorene (Compound A), 2,7bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-(6ʹ-dibromohexyl)fluorene(Compound B), poly[(9,9-bis(6ʹ-bromohexyl)fluorene)-co-(9,9-bis(6ʹ-octyl)fluorene)](PFBr)
2,7-Dibromo-9,9-bis(6ʹ-bromohexyl)fluorene (Compound A) was synthesized by thereaction between 2,7-dibromofluorene and 1,6-dibromohexane [48]. 2,7-bis(4,4,5,5tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-(6ʹ-dibromohexyl)fluorene (Compound B) was
prepared from compound A and bis(pinacolato)diboron [49]. And by using Pd-catalyzed
Suzuki cross-coupling reaction the polymer poly[(9,9-bis(6ʹ-bromohexyl)fluorene)-co(9,9-bis(6ʹ-octyl)fluorene)] (PFBr) was synthesized from compound B and 2,7-dibromo9,9-dioctyl fluorene [19]. The detail synthetic procedures are provided in Supporting
Information.
2.2.2. Synthesis of poly[(9,9-bis(6ʹ-(N-methylpiperidinium)hexyl)fluorene)-co-(9,9-bis(6ʹ-octyl)fluorene)]bromide (PF-PipBr)
A solution was prepared by dissolving brominated polymer PFBr (200 mg, 0.2 mmol)
in 5 mL THF. To this, 8 mL N-methylpiperidine was added and the solution was heatedat 60 °C for 7 days with the continuous stirring condition under argon. The solvents were
evaporated in a vacuum evaporator. The concentrate was dissolved in 2 mL of MeOH,
9

precipitated in THF. The desired PF-PipBr polymer (217 mg, 88%) was dried at 60 °C
under vacuum condition. The polymer was characterized by 1H NMR spectrum in
CH3OH-d4.
2.3. Membrane Casting
The PF-PipBr membrane was fabricated by a 4 wt% solution of the polymer in DMF.
The solution was poured on a clean PTFE sheet. Then slowly dried for 48 h at 60 ºC to
avoid the air bubbles and finally dried the membrane under vacuum for 48 h at 60 ºC. The
membrane thickness was 70-80 μm.
2.4. Ion Exchange of Polymers in Hydroxide Ion form
To obtain the OH- ion form membranes we have immersed the PF-PipBr membranes
in argon saturated 1 M NaOH aq. solution at room temperature for 48 h. Within this time,
we have exchanged three times the NaOH solution with fresh solution. Then themembranes were soaked in argon saturated DI water and finally, the OH- ion form AEMs
(PF-Pip) were washed by degassed DI water until the pH becomes neutral.
2.5. Characterization and Measurements
The experimental details of each measurement including

1

H and

13

C NMR

spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, mass spectrometry, gelpermeation chromatography (GPC), energy dispersive X-ray spectroscopy (EDX),
10

scanning electron microscopy (SEM), ion sputter equipment, transmission electron
microscopy (TEM), small-angle X-ray scattering (SAXS), thermogravimetric analyzer(TGA), mechanical properties, WU, SR, IEC, hydroxide ion conductivity, and alkaline
stability are included in Supporting Information.
3. Results and Discussions
3.1. Synthesis and Characterization of Monomers and Polymers
The chemical structure of the compound A and B was confirmed by 1H and 13C NMR,
and mass spectra (shown in Supporting Information). The PFBr polymer wascharacterized by 1H NMR spectrum as shown in Fig. 1A. The signals for the aromatic
protons (Ar-H) of fluorene units were observed at 7.30 - 7.80 ppm. The signal appeared
at 3.20 - 3.25 ppm due to the protons of methylene bromide (-CH2Br), the chemical shifts
found between 0.75 - 2.06 ppm for the additional methylene (-CH2-) protons. The integral
ratio and peak position confirmed that the polymerization reaction was successful. The
PFBr polymer was soluble in THF and chloroform but insoluble in water. The molecularweight (Mw) of PFBr was 2.2 x 104 g mol-1 in Table S1. Fig. 1B shows the 1H NMR
spectrum of the PF-PipBr polymer. The new signals appeared at 2.90 ppm and 3.20 ppm
due to the protons of -N+CH3 and -N+CH2 of the cyclopiperidinium group. The ratio of
the peak area between protons of -N+CH3 at 2.90 ppm and the aromatic protons from 7.30
11

to 7.80 ppm determined the full substitution of N-methylpiperidine in PFBr polymer. The
Br- form polymer, PF-PipBr, was soluble in organic solvents, for example, DMF, CH3OH,
and DMSO at room temperature but was not soluble in H2O.

Fig. 1. 1H NMR spectra of PFBr and PF-PipBr.
The EDX spectra before and after ion exchange of Br- form to OH- form as shownin Fig. 2A and 2B confirmed that Br- ions almost disappeared or declined after thealkalization. More than 92% of Br- ions have been exchanged by OH- ions. The remaining
bromine elements in Fig 2B may come from the end group of the polymer.

12Fig. 2. EDX spectra for (A) PF-PipBr and (B) PF-Pip
3.2. Membrane Morphology
The PF-PipBr membrane was fabricated from 4 wt% solutions in DMF and was cast
on a flat PTFE sheet. The resultant membrane becomes transparent as shown in Fig. 3A
after evaporation of the solvent. The SEM images of Fig. 3B and 3C showed that themembrane surface and cross-section were homogeneous, tight and dense, and no poresand crack were visible at this scale.

Fig. 3 (A) Photograph, SEM images of (B) membrane surface and (C) cross section of13

the PF-PipBr polymer.
TEM was also used to investigate the morphology of the PF-Pip membrane. The crosssectional TEM image of the membrane was observed after stained withtetrachloroplatinate ion. The bright regions represent the hydrophobic domains and dark
regions correspond to the hydrophilic domains. The domain size of the hydrophilic group
was observed as 1 to 2 nm as shown in Fig. 4. This morphology is similar to themembranes of literature [50, 51] containing fluorenyl group. The hydrophilic andhydrophobic domains were homogeneously distributed throughout the sight. This
microphase-separated morphology would have a great influence on the hydroxide ion
conduction through the PF-Pip membrane.

Fig. 4. Cross sectional TEM image of the PF-Pip membrane.
14We have tried SAXS measurements to clarify the surface morphology of the membranein both dry and submerged condition. A weak scattering peak was observed for PF-PipBr
AEM in both samples at q = 0.21 Å-1 which corresponds to d = 3 nm as shown in Fig. 5.
A small broad band between 0.25 – 1.25 Å-1 appeared in humidified and water conditions.
This could be attributed as the size of ionic domains. No significant profile changes wereobserved in humidified and submerged conditions.

Fig. 5. The SAXS profile of PF-PipBr AEM, measured under dry and submerged
conditions.
3.3. Thermal Stability
The thermal stability is always a concern for the AEMs. Aromatic polymers are thepreferred candidates for application in high temperature AEMFCs because of outstanding
thermal stability. Fig. 6 shows the results of the thermogravimatric analysis. The firstweight loss below 150 °C; this weight loss possibly originates from the evaporation of15

adsorbed water in the membrane. In the second step, 5% weight loss occurred between
150 ºC to 190 ºC due to the degradation of the methyl group of piperidinium cations of
the polymer. The third degradation at temperatures above 390 °C might be due to thedecomposition of the polyfluorene backbones. The overall result of thermal analysis
implies that the resultant polymer maintains high thermal stability up to 150 oC, which ishigher than benzyl quaternary ammonium cationic groups [52]. The thermal stability isclearly well above the desired temperature range for fuel cell applications.

Fig. 6. TGA graph of PF-Pip under N2 flow. Heating rate: 10 ºC min-1.
3.4. Mechanical Properties
The tensile strength of PF-PipBr polymer was observed as 10.5 MPa with anelongation at break of 2.5% in water (Table S2). The Young’s modulus was found to be
354 MPa.

16

3.5. Water Uptake (WU), Ion Exchange Capacity (IEC), and Swelling Ratio (SR)For AEMs, sufficient amounts of WU are essential for the formation of hydrated
ionic domain phase and faster migration of ions through the membrane [3, 5, 7, 10].
However, the balanced WU is important since excessive WU may influence undesirable
membrane swelling and mechanical properties. Furthermore, the charge carriers e.g.,anions are diluted due to high water contents, and conductivity decreases [10, 53]. As
anticipated, the WU of AEM increases with increasing temperature [47]. The WU of thesynthesized PF-Pip membrane is shown in Fig. 7 as a function of temperature from 20 to
80 °C after soaked in water. We found 35 wt% WU at 20 °C and 81 wt% at 80 °C. The
WU of the synthesized PF-Pip membrane is comparable with the reported literature [16,38]. The IEC of the membranes represents the number of exchangeable ions. The backtitration technique was used to determine the IEC of the synthesized membrane (seeSupporting Information). It was found to be 1.82 mmol/g. The obtained IEC shows good
agreement with the value of 1.89 mmol/g obtained from the 1H NMR result. The SR
increased with increasing temperature. The SR of the PF-Pip membrane was 11% at 20 °C
and 20% at 80 °C as shown in Fig. 7.

17

Fig. 7. The WU and SR of the PF-Pip membrane.
3.6. Hydroxide Ion Conductivity and Activation Energy
Hydroxide conductivity is one of the vital performances of AEMs. The hydroxide
conductivity of the resultant PF-Pip membrane at different temperatures is shown in Fig.
8A. The PF-Pip membrane exhibited hydroxide conductivity of 9 mS cm-1 at 20 oC andincreased to 58 mS cm-1 at 80 oC. The hydroxide conductivity of the AEMs increases withincreasing temperature. Higher temperature can cause faster water diffusivity and ionicmigrations. The AEMs containing piperidinium cationic groups, have high WU [54] andtherefore facilitate the ionic migration through the water clusters. The hydroxide
conductivity of the PF-Pip membrane follows the Arrhenius behavior from 20 to 80 oC as
shown in Fig. 8B. The activation energy of polymer PF-Pip was 27 kJ mol-1, which wascomparable with some reported AEMs [55-57].

18

Fig. 8. (A) Hydroxide conductivity and (B) Arrhenius plots of the hydroxide conductivity
for the PF-Pip membrane.
3.7. Alkaline Stability
The thermochemical stability of AEMs is the most important challenge for practicalapplication, particularly in the high-pH medium of AEMFCs. Fig. 9 shows the 1H NMR
spectra of PF-Pip before and after the alkaline test. After 96 h and 168 h storage in 1 M
NaOH aq. solution the peak intensity of the methyl protons (-N+CH3) at 2.9 ppm andmethylene protons linked to N atom at 3.2 ppm, was slightly reduced. The reduction ofpeak intensity at 2.9 ppm indicated the substitution of the methyl group and at 3.2 ppm
corresponded to the Hofmann β hydrogen elimination reaction of the Nmethylpiperidinium cationic group. According to the literature, the degradation
mechanisms of the N-methylpiperidinium group can be suggested as Scheme 3 [16, 37].
Bae et al. reported that the degradation of the N-methylpiperidinium cation was caused19

by nucleophilic substitution of methyl groups and degradation by ring opening reaction
was not observed [36]. Marino and Kreuer [37] confirmed from the results of 1H NMR
spectroscopy that the extreme degradation of N,N-methylpiperidinium group was takenby the substitution at the methyl groups in 6 M NaOH solution at 160 °C. In addition, aslight decay comes from the slower ring opening elimination processes. Jannasch et al.
observed new peaks in the region from 5 to 6.5 ppm for vinylic protons due to thedegradation of quaternary piperidinium groups by Hofmann β elimination [16, 38].
However, we did not observe these peaks for the vinylic protons. According to theliterature [36, 37] we concluded that the major degradation of N-methylpiperidinium was
the methyl substitution by the attack of OH- ion. The 1H NMR spectra of the PF-Pip
membrane revealed that only 13% of the initial cationic group was lost after 96 h ofstorage in 1 M NaOH solution by following the degradation mechanism of Path A in
Scheme 3. Further, no loss of cationic group was observed after stored for 168 h.

20

Fig. 9. 1H NMR spectra of PF-Pip (OH- form) membrane after soaking in 1 M NaOH
solution for 80 °C for 96 h and 168 h.
N

+

CH3OH

+

H2O

A
N

1M NaOH

B

N

o

80 C

C
N

OH

Scheme 3. Reported degradation pathways of N-methylpiperidinium cationic group (A)nucleophilic substitution of the methyl group, (B) Hofmann β elimination, and (C)substitution (ring opening) [37].
To complement the NMR results, we also measured the OH- conductivity of the PF21

Pip membrane after storage for 168 h in 1 M NaOH solution at 80 °C. The results revealed
that only 15% of the initial conductivity was lost in water at 80 °C. Some other literature
also observed a slight decline of conductivity [10, 47] after storage in alkaline conditions.
The above results on fluorene-based membrane containing alkyl-substituted Nmethylpiperidinium cationic groups indicate that this cationic group is relatively alkaline
stable at 80 ºC.
4. Conclusions
In summary, we have synthesized ether-bond-free polyfluorene AEM by using Pd
catalyzed Suzuki cross-coupling reaction with piperidinium cations at the alkyl side
chains. The properties of AEM were investigated including OH- conductivity, WU andswelling behavior, IEC, thermal and chemical stability. The AEM in OH- form exhibited
good thermal stability. The hydroxide conductivity reached 58 mS cm-1 at 80 °C. The
piperidinium cationic group of 13% was degraded after 168 h storage in 1 M NaOH
solution at 80 °C. This study suggests that the alkyl substituted N-methylpiperidinium
cationic group is relatively stable in alkaline conditions at 80 ºC. It should be noted that
the N-methylpiperidinium cation group decomposes slightly under alkaline conditions
depending on the structure. The simple synthetic procedure presented is the majoradvantage in this study for synthesizing solvent-processable fluorene based AEM that22

avoids any complicated modifications.
Acknowledgments
We are grateful to Prof. Noriyoshi Matsumi at Japan Advanced Institute of Science andTechnology (JAIST) for supporting glovebox. We also gratefully thank Assoc. prof.
Shusaku Nagano at Nagoya University for SAXS and GPC measurement. We like tothank Hayato Watanabe at Nagoya University for his cordial assistance during SAXS
measurement. We are also grateful to Prof. Kazuaki Matsumura and Zhao Yibo at JAIST
for supporting mechanical strength measurement. We thankfully appreciate the kind
support of Dr. Akio Miyazato (technical staff of mass spectrometry, JAIST) for mass
spectra measurements. We thankfully acknowledge the kind cooperation of Koichi
Higashimine (senior technical specialist, center for nanomaterials and technology, JAIST)
and Shoko Kobayashi (technical staff, center for nanomaterials and technology, JAIST)
for transmission electron microscope (TEM) image measurements. We also gratefully
acknowledge cordial support of Assoc. Prof. Guangtong Wang (Harbin Institute ofTechnology, China) during the synthesis of the polymer. This work was partially
supported by JSPS KAKENHI Grant Number JP18K05257.

23

Declaration of competing interest
Declarations of interest: none
Research data for this article
Data not available/Data will be available on request.
Supporting Information
Supporting information contains synthesis procedures for Compound A, Compound B,PFBr polymer. Details of characterizations and measurements including 1H and 13C NMR
spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, mass spectrometry, gelpermeation chromatography (GPC), scanning electron microscopy (SEM), energy
dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), smallangle X-ray scattering (SAXS), thermogravimetric analyzer (TGA), mechanicalproperties, water uptake (WU), swelling ratio (SR), ion exchange capacity (IEC),
hydroxide ion conductivity, alkaline stability of the membrane. GPC results of precursor
PFBr polymer.
Author information
Corresponding author*ynagao@jaist.ac.jp Phone: +81(Japan)-761-51-1541, Fax: +81(Japan)-761-51-1149,
Address: 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
24

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34

Graphical Abstract

Alkaline stability of ether bond free fluorene-based anion exchange
polymer containing cycloaliphatic quaternary ammonium groups
Umme Salma and Yuki Nagao

35