JAIST Repository
https://dspace.jaist.ac.jp/Title

Effect of Molecular Orientation to Proton
Conductivity in Sulfonated Polyimides with bent
backbones

Author(s)Nagao, Yuki; Ohno, Kazuki; Tsuyuki, Shinya;
Suetsugu, Kota; Hara, Mitsuo; Nagano, Shusaku

Citation

Molecular Crystals and Liquid Crystals, 686(1):84‑91Issue Date

2019‑10‑10

Type

Journal Article

Text version

author

URL

http://hdl.handle.net/10119/16897

RightsThis is an Author's Accepted Manuscript of anarticle published in Molecular Crystals andLiquid Crystals, 686(1), 2019, pp.84‑91.
Copyright (C) 2019 Taylor & Francis, available
online at:https://doi.org/10.1080/15421406.2019.1648041

Description

Japan Advanced Institute of Science and Technology

Effect of Molecular Orientation to Proton Conductivity in SulfonatedPolyimides with bent backbones
Yuki Nagaoa,*, Kazuki Ohnoa, Shinya Tsuyukia, Kota Suetsugub, Mitsuo Harab, Shusaku
Naganoca

School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai,Nomi, Ishikawa 923-1292, Japanb

Department of Molecular Design & Engineering Graduate School of Engineering, Nagoya

University, Furo-cho, Chikusa, Nagoya 464-8603, Japanc

Nagoya University Venture Business Laboratory, Nagoya University, Furo-cho, Chikusa,

Nagoya 464-8603, Japan
Corresponding Author*(Y.N.) E-mail: ynagao@jaist.ac.jp. Telephone: +81(Japan)-761-51-1541. Fax: +81(Japan)761-51-1149

Running Head :Effect of Molecular Orientation to Proton Conductivity in Sulfonated Polyimides

1

ABSTRACTTwo organized sulfonated polyimides (ASPIs) with bent polymer backbones were synthesized tostudy a relation between structure and proton conductivity. Proton conductivity exhibited
different values between the thin film and bulk pelletized forms. Results from small-angle X-ray
scattering (SAXS) and attenuated total reflection measurements suggest that the orientation ofbackbones is different between the thin film and bulk forms. SAXS results suggest excess
amount of water uptake in the bulk samples compared to the thin film form. These structure andwater uptake property could contribute the difference of the proton conductivity between the thinfilm and bulk pelletized forms.

Keywords : Sulfonated polyimide, Molecular orientation, In-plane orientation, Organizedstructure, Proton conductivity, Lyotropic liquid crystalline property

2Introduction
Research on constructing ion conducting channels based on a hierarchical structure byorganizing molecules and polymers has been attracting attention. A Nafion membrane,[1-2]which is well known as a high proton conductive polymer, has a phase segregated structure byhydrophilic side chain and hydrophobic backbone. Because of the less molecular ordering natureof Nafion, controlling the polymer structure is not easy work to enhance the property and reduce
the production cost. From this background, an organized structure, which enables X-ray
scattering techniques for discussing the structure, has attracted attention for the development of
the highly proton-conductive polymers.[3]From the viewpoint of structural control, functional design based on liquid crystalline (LC)property that spontaneously forms periodic molecular aggregates could give high protontransport property through a formation of self-assembled transport channels because ofintermolecular interaction such as hydrophilic and hydrophobic interactions. Kato and coworkers demonstrated ion-transport pathways by the LC property. [4-6] In recent years, studies
on the organized structure and ionic conductivity in various LC phases have been reported bythermotropic and lyotropic LC property. [7-10] Matsui and co-workers demonstrated a 2D highproton conduction in multi-lamellar organized structure by a Langmuir–Blodgett technique. [1113]。
The first highly proton-conductive thin films with the organized structure have been reported
by Nagao and coworkers in 2014.[14] The thin film of the alkyl sulfonated polyimide (ASPI)
exhibits an organized lamellar structure by water uptake. The polymer backbone oriented parallelto the substrate surface (in-plane orientation). The lamellar distance can reversibly vary by the3amount of water uptake. The degree of the molecular ordering was also improved by wateruptake. This reversible structural change occurs by the lyotropic LC property. The formed waternano-channel in the lamellar organized structure contributes to high proton conductivity of 10-1 S
cm-1. Some ASPI thin films have been synthesized and investigated for the relation between theorganized structure and proton conductivity.[14-19] Compared to the planar and bent polymer
backbones in ASPI thin films, ASPI-1 and ASPI-2 thin films with a planar backbone exhibit thehigher proton conductivity.[18] And proton conductivity of the thin film was higher than that of
the bulk pelletized sample because of the difference of the degree of in-plane orientation of thepolymer backbone.[14] However, there is no discussion for the relation between the polymer
orientation and proton conductivity in the bulk pelletized samples with bent backbone structure.
In this study, two ASPI-3 and ASPI-4 with bent backbones as shown in Scheme 1 weresynthesized and studied on the proton conductivity and polymer structure by impedance
spectroscopy, small-angle X-ray scattering (SAXS), and attenuated total reflection (ATR)
measurements.

Experimental
4,4'-oxydiphthalic dianhydride (ODPA), and 4,4'-biphthalic dianhydride (BPDA) were used asreceived from TCI, Japan. For the monomer of the proton source, 3,3'-Bis(sulfopropoxy)benzidine (BSPB) was synthesized according to previous reports.[14] The synthesis of thepolymers, BSPB-ODPA (ASPI-3) and BSPB-BPDA (ASPI-4), were carried out according to theprevious reports.[18] The obtained samples were checked by 1H nuclear magnetic resonance(NMR), Fourier-transform infrared (FT-IR), and GPC measurements. No amic acid in the4

polymer backbone was observed from 1H NMR spectra. The weight average molecular weightand polydispersity of ASPI-3 and ASPI-4 were 4.4 × 105, 3.7 and 9.6 × 105, 3.8, respectively.
Proton conductivity was examined through impedance spectroscopy in the frequency range of
1 Hz and 10 MHz with an applied alternating potential of 50 mV using a Solartron 1260
frequency response analyzer equipped with a high-frequency Solartron 1296 dielectric interface.
The relative humidity (RH) and temperature were established using a computer-controlledenvironmental test chamber (SH-221; Espec Corp). The conductivity measurements wereperformed at 298 K and various RH values. The pelletized samples were prepared as bulk
samples. Porous gold electrodes were used for the both sizes of the pelletized surfaces. The
conductivity (σ) of the bulk sample was estimated by the following relation,𝑑𝑑

𝜎𝜎 = 𝑅𝑅𝑅𝑅(1)

where d is the distance between the gold electrodes, R is the resistance value obtained directlyfrom the impedance measurement, and S is the area of electrode.
SAXS measurements in the bulk sample were performed on a Rigaku FR-E X-ray
diffractometer with an R-AXIS IV two-dimensional (2D) detector and Cu Kα radiation (λ =1.542 Å). A dry sample was placed in a capillary tube and was irradiated with the X-ray beam
without further adjustments. For the measurements under the high-humidified condition, weplaced both a portion of dry sample and a water droplet in the same capillary tube and thensealed it. After 7 days, we used the sealed capillary sample as the humidified bulk sample for
SAXS measurements.

5Grazing Incidence Small-angle X-ray Scattering (GISAXS) measurements were taken with thesame machine of SAXS measurements. Thin film samples were prepared by spin coat and placed
into a humidity-controlled cell with X-ray transparent polyester film (Lumirror) windows.
Nitrogen carrier gas was used as received from the gas cylinder without further dehumidification
to control the humidity. Voltage of 45 kV, current of 45 mA, and irradiation time of 1 h wereapplied with beam size of approximately 300 μm × 300 μm and camera length of 300 mm. X-ray
scattering patterns were recorded on an imaging plate (Fujifilm Corp.). The incident angle waschosen as 0.20° – 0.22°. For 1D out-of-plane and in-plane profiles, the integrated regions weretaken between -0.5° to +0.5° as 2 θ from the center (0°) and the width of 1° as 2θ, respectively.
FT-IR spectroscopy using an ATR method was carried out using an FT-IR spectrometer(Nicolet 6700; Thermo Fisher Scientific Inc.) equipped with deuterium triglycine sulfate (DTGS)
detector to both square-shape samples of ASPI-3 and ASPI-4. The square-shape samples wereprepared from the pelletized sample and cut it as a cubic-shape.

Results and discussion
Figure 1a shows RH dependence of proton conductivity for the thin film and bulk sample ofASPI-3. The proton conductivity between the thin film and bulk sample exhibited similar value
in the low RH, however, the conductivity of the thin film was found to be much higher value
than that of the bulk sample. The conductivity of thin film and bulk sample showed 6.1 × 10-2 Scm-1[18] and 1.3 × 10-2 S cm-1 at RH = 95% and 298K, respectively. Figure 1b demonstrates theRH dependence of proton conductivity for the thin film and bulk sample of ASPI-4. The
conductivity of the thin film was also higher than that of the bulk sample. The conductivity of6thin film and bulk sample showed 8.0 × 10-2 S cm-1[18] and 1.6 × 10-2 S cm-1 at RH = 95% and298K, respectively. To discuss the difference of the proton conductivity between thin films andbulk samples, SAXS measurements were carried out.
Figure 2 shows SAXS profiles of the bulk ASPI-3(a) and ASPI-4(b) under both dry andhumidified conditions. In the dry condition, a weak scattering appeared at 4.6° (1.9 nm) and 5.3°
(1.7 nm) for ASPI-3(a) and ASPI-4(b), respectively. After the humidified condition, bothscatterings were enhanced and shifted to the smaller angle to 2.3°(3.9 nm) and 2.5° (3.6 nm) forASPI-3(a) and ASPI-4(b), respectively. These trends for the peak shift and enhancement can beobserved in another ASPI.[14] In the previous report, the ASPIs exhibits a lamellar structure
parallel to the substrate surface in thin films and a non-oriented lamellar structure in bulk. The
obtained peaks in bulk samples can be attributed as a non-oriented lamellar structure. Figure 3
shows GISAXS profiles for ASPI-3(a) and ASPI-4(b) thin films. The lamellar scatterings in bothfilms were observed in the out-of-plane direction. The maximum lamellar distances are 3.08 and2.94 nm, respectively. The observed lamellar distance of bulk ASPI-3 and ASPI-4 samples arelarger than those of the thin films. Results suggest that the excess water was introduced to eachbulk sample in the high RH region.
To check whether each bulk pelletized sample has a specific orientation or not, ATR spectra
were carried out using square-shape samples. Figure 4a shows a schematic view of incident
angles with X-, Y-, and Z-direction to samples. All spectra in each sample were found to beidentical as shown in Figure 4b and 4c. The observed vibrational modes at 1380 cm–1 and 1500
cm–1 can be assigned to the C–N bonds of the main chain and to the phenyl C–C bonds,respectively. Adjacent vibrational modes at 1710 cm–1 and 1780 cm–1 correspond to the C=O

7

asymmetric and symmetric stretching vibrations of imide groups. Therefore both bulk ASPI-3
and ASPI-4 samples exhibit non-oriented lamellar structure.
In the dry state, proton conductivity did not exhibit an apparent difference between the thinfilms and bulk samples in both bulk ASPI-3 and ASPI-4 samples. The scattering intensity forboth thin film and bulk sample with bent polymer backbone was found to be very weak in thedry state. The results suggests that the thin films and bulk in the dry state exhibit less molecularordered structure and low proton conductivity. This suggestion is consistent with the previous
report that the amorphous region contributes to the proton conduction in the dry state.[17] In thehigh RH region, the in-plane orientation of the polymer backbone along the substrate surface in
the ASPI thin films can enhance the proton conductivity.[14-16] The molecular lamellar ordering
was improved by water uptake in both thin films and bulk. On the other hand, the degree of
backbone orientation in bulk samples should be less than that in thin films because of a lack ofsubstrate. Moreover, the excess water uptake occurs in the bulk samples from the SAXS results.
These two differences between thin films and bulk samples could affect the difference of theproton conductivity in the high RH region.

SummaryThis work demonstrates that less orientation of the polymer backbone and excess water could
decrease the proton conductivity. Results can extend the polymer design using the organizedstructure for the development of the highly proton-conductive polymers.

8Acknowledgments
This work was supported in part by the Nanotechnology Platform Program (Molecule andMaterial Synthesis) of the Ministry of Education, Culture, Sports, Science and Technology(MEXT), Japan. This work was supported by JSPS KAKENHI Grant Number JP18K05257.

References[1]T. D. Gierke, G. E. Munn, and F. C. Wilson. J. Polym. Sci. Pol. Phys., 19, 1687 (1981).

[2]

W. Y. Hsu and T. D. Gierke. J. Membr. Sci., 13, 307 (1983).

[3]

Y. Nagao. Langmuir, 33, 12547 (2017).

[4]

T. Kato, N. Mizoshita, and K. Kishimoto. Angew. Chem. Int. Ed., 45, 38 (2006).

[5]

T. Kato, M. Yoshio, T. Ichikawa, B. Soberats, H. Ohno, and M. Funahashi. Nat. Rev.
Mater., 2, 17001 (2017).

[6]

T. Kato, J. Uchida, T. Ichikawa, and T. Sakamoto. Angew. Chem. Int. Ed., 57, 4355
(2018).

[7]

Y. Chen, M. D. Lingwood, M. Goswami, B. E. Kidd, J. J. Hernandez, M. Rosenthal, D. A.
Ivanov, J. Perlich, H. Zhang, X. Zhu, M. Möller, and L. A. Madsen. J. Phys. Chem. B,118, 3207 (2014).

[8]

J. J. Hernandez, H. Zhang, Y. Chen, M. Rosenthal, M. D. Lingwood, M. Goswami, X.
Zhu, M. Moeller, L. A. Madsen, and D. A. Ivanov. Macromolecules, 50, 5392 (2017).

[9]

I. Tonozuka, M. Yoshida, K. Kaneko, Y. Takeoka, and M. Rikukawa. Polymer, 52, 6020
(2011).

[10]

J. H. Lee, K. S. Han, J. S. Lee, A. S. Lee, S. K. Park, S. Y. Hong, J.-C. Lee, K. T.
Mueller, S. M. Hong, and C. M. Koo. Adv. Mater., 28, 9301 (2016).

[11]

J. Matsui, H. Miyata, Y. Hanaoka, and T. Miyashita. ACS Appl. Mater. Inter., 3, 1394
(2011).

[12]

T. Sato, Y. Hayasaka, M. Mitsuishi, T. Miyashita, S. Nagano, and J. Matsui. Langmuir,31, 5174 (2015).

9

[13]

T. Sato, M. Tsukamoto, S. Yamamoto, M. Mitsuishi, T. Miyashita, S. Nagano, and J.
Matsui. Langmuir, 33, 12897 (2017).

[14]

K. Krishnan, H. Iwatsuki, M. Hara, S. Nagano, and Y. Nagao. J. Mater. Chem. A, 2, 6895
(2014).

[15]

K. Krishnan, T. Yamada, H. Iwatsuki, M. Hara, S. Nagano, K. Otsubo, O. Sakata, A.
Fujiwara, H. Kitagawa, and Y. Nagao. Electrochemistry, 82, 865 (2014).

[16]

K. Krishnan, H. Iwatsuki, M. Hara, S. Nagano, and Y. Nagao. J. Phys. Chem. C, 119,21767 (2015).

[17]

Y. Nagao, K. Krishnan, R. Goto, M. Hara, and S. Nagano. Anal. Sci., 33, 35 (2017).

[18]

Y. Ono, R. Goto, M. Hara, S. Nagano, T. Abe, and Y. Nagao. Macromolecules, 51, 3351
(2018).

[19]

K. Takakura, Y. Ono, K. Suetsugu, M. Hara, S. Nagano, T. Abe, and Y. Nagao. Polymer
Journal, (2018).

10

Scheme caption and Scheme
Scheme 1. Chemical structure of sulfonated polyimides. (a) ASPI-3 (b) ASPI-4.

(a)

O
NO

HO3S

O

O

SO3H

O(b)

O
NOO

O

N

NnO

HO3SOOOn

SO3H

Scheme 1. (Y. Nagao et al.)11

Figure captions
Figure 1. RH dependence of proton conductivity at 298 K. (a) Proton conductivity of thinfilm[18] and bulk in ASPI-3. (b) Proton conductivity of thin film[18] and bulk in ASPI-4.

Figure 2. SAXS profiles under dry and humidified condition in glass capillary. (a) bulk ASPI-3(b) bulk ASPI-4.

Figure 3. GISAXS 2D profiles at RH = 95%. (a) ASPI-3 thin film (b) ASPI-4 thin film.

Figure 4. ATR spectra. (a) Schematic view of incident angles with X-, Y-, and Z-direction forATR measurements to the square-shape samples. (b) bulk ASPI-3 (c) bulk ASPI-4.

12

Figures

Figure 1. (Y. Nagao et al.)13Figure 2. (Y. Nagao et al.)14

Figure 3. (Y. Nagao et al.)15Figure 4. (Y. Nagao et al.)16