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Title

Lyotropic ordering for high proton conductivity
in sulfonated semialiphatic polyimide thin films

Author(s)Takakura, Kensaku; Ono, Yutaro; Suetsugu, Kota;
Hara, Mitsuo; Nagano, Shusaku; Abe, Takashi;
Nagao, Yuki

Citation

Polymer Journal, 51: 31‑39

Issue Date

2018‑08‑03

Type

Journal Article

Text version

author

URL

http://hdl.handle.net/10119/16672

RightsThis is the author‑created version of Springer,
Kensaku Takakura, Yutaro Ono, Kota Suetsugu,
Mitsuo Hara, Shusaku Nagano, Takashi Abe, andYuki Nagao, Polymer Journal, 51, 2018, 31‑39. The
original publication is available atwww.springerlink.com,
https://doi.org/10.1038/s41428‑018‑0111‑1

Description

Japan Advanced Institute of Science and Technology

Lyotropic Ordering for High Proton Conductivity in
Sulfonated Semi-aliphatic Polyimide Thin Films
Kensaku Takakura,1 Yutaro Ono,1 Kota Suetsugu,2 Mitsuo Hara,2Shusaku Nagano,3 Takashi Abe,4 and Yuki Nagao1*

12School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1
Asahidai, Nomi, Ishikawa 923-1292, Japan

Department of Molecular Design & Engineering Graduate School of Engineering, Nagoya
University, Furo-cho, Chikusa, Nagoya 464-8603, Japan

3

Nagoya University Venture Business Laboratory, Nagoya University, Furo-cho, Chikusa,
Nagoya 464-8603, Japan

4

Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-no-cho,Nishi-ku, Niigata 950-2181, 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
Proton Conduction in Oriented Sulfonated Polyimide Films

1

Abstract
Influence of the semi-aliphatic backbone on the molecular ordering and proton conductivity
was investigated compared to the rigid aromatic backbone in highly proton-conductive
organized polyimide thin films. We newly synthesized two alkyl sulfonated semi-aliphatic
polyimides (ASSPIs) with different molecular weights and investigated their molecularorganized structure, proton conductivity, water uptake, and dissociation state of protons from
sulfonic acid groups in thin films by in-situ measurements for grazing incidence small-angle Xray scattering (GISAXS), quartz crystal microbalance (QCM), Fourier transform infrared (FTIR) spectra, and impedance spectra. Declining of planarity in the semi-aliphatic backbone
reduced the aggregative character and molecular ordering in the lyotropic liquid crystalline(LC) structure. However, the higher molecular weight ASSPI exhibited the oriented lamellar
structure in spite of lower planarity of the main chain. The proton conductivity of the oriented
lamellar thin film displayed a more than half order of magnitude higher value of 1.5 × 10-1 S
cm-1 than that of the non-oriented lamellar thin film (3.0 × 10-2 S cm-1) at 25°C and 95% RH.
These results indicate that, in sulfonated polyimide thin films, the lamellar orientation greatly
contributes to the high proton conductivity in the ASSPI thin films.
Keywords : Sulfonated polyimide, Thin film, Molecular orientation, Organized structure,
Proton conductivity, Lyotropic liquid crystalline property

2Introduction
Structural control of highly ion-conductive channels is a notable strategy for energy conversion
system, water treatment, and biotechnology [1-5]. Nanostructured liquid crystals that selforganize into dimensionally ordered states represents a promising approach to the developmentof structural control of ion-conductive materials [6, 7]. Thermotropic and lyotropic liquid
crystal properties can drive organized structure of various kinds. Kato et al. demonstrated
switchable ionic conductivities induced by a rectangular-hexagonal phase transition in wedgeshaped liquid-crystalline (LC) ammonium salts [8]. Several groups have also reported relations
between ionic conductivity and LC structure with thermotropic and lyotropic liquid crystal
properties [9-12].
Designing phase-separated conductive channels composed of hydrophobic backbones andhydrophilic parts is a fundamentally important strategy to create highly proton-conductive
materials [13-16]. Typical proton exchange membranes (PEMs) have sulfonic acid groups
attached to the hydrophobic polymer as a side chain [17]. State-of-the-art membranes are basedon perfluorosulfonic acid (PFSA) ionomers such as Nafion [13, 18, 19]. They exhibit highlevels of proton conductivity, water transport, and durability. Protons are transported throughwater-swollen conductive channels. Understanding the relation between the structure andproton transport property is fundamentally important, but such attempts have often been3

hampered in many highly proton-conductive polymers because less structural information canbe derived from an amorphous or amorphous-like nature.
Our recent studies have elucidated that proton conductivity enhancement originates from theimprovement of molecular ordering and main chain orientation of LC domains in alkyl
sulfonated polyimide (ASPI) thin films [20-23]. Actually, ASPI thin films with rigid backbones
exhibit lamellar organized structure by water uptake using a lyotropic LC property. However,no report describes the influence of the semi-aliphatic backbones on the organized structure andproton conductivity of alkyl-sulfonated polyimide thin films.
This study elucidated the relation between organized structure and proton conductivity byintroduction of a semi-aliphatic structure in the main chain. Lower planarity of backbones canchange the organized molecular structure and ordering in the lyotropic LC structure. For
polyimides without sulfonic acid groups, Ando et al. reported the intermolecular aggregation
structures in thin films of fully aromatic polyimides and semialiphatic polyimides by grazing
incidence X-ray scattering measurement [24]. In our work, the lyotropic LC structure andproton conductivity were assessed in two alkyl sulfonated semi-aliphatic polyimide (ASSPI)
films with different molecular weights by in-situ studies of grazing incidence small-angle Xray scattering (GISAXS), quartz crystal microbalance (QCM), Fourier transform infrared
spectra (FT-IR) and impedance analyses. From those results, we conducted systematic4

evaluations of the molecular structure, proton conductivity, water uptake, and dissociation stateof protons from sulfonic acid groups in thin films. Two ASSPI thin films exhibited different
orientation of lamellar structure and proton conductivity. On the other hand, water uptake
isotherms and the proton dissociation properties from sulfonic acid groups are almost identicalin the two thin films. Therefore, the orientation of the lyotropic lamellar structure largely
contributes to the proton conductivity enhancement. Our results indicate that not only main
chain planarity but also the increment of molecular weight affects the lyotropic LC structure
and moreover the oriented lamellar structure enhanced proton conductivity.

Materials & Methods
Materials
3,3'-Dihydroxybenzidine, 1,3-propanesultone, 9,10-dihydro-9-oxa-10-phosphaphenanthrene
10-oxide (DOPO) and 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) werepurchased from Tokyo Chemical Industry Co. Ltd., Japan and were used without further
purification. 3,3’-Bis(sulfopropoxy)-4,4’-diaminobiphenyl (3,3’-BSPA) was synthesized from
3,3’-dihydroxybendizine and 1,3-propanesultone as described in the literature [22]. Acetone
and m-cresol were purchased from Wako Pure Chemical Ind. Ltd., Japan. Triethylamine (TEA)
was used as received from Kanto Chemical Co. Inc., Japan.

5Synthesis of ASSPIThe ASSPIs of different molecular weights were synthesized using a similar polymerization
scheme. Scheme 1 represents the synthesis of the higher molecular weight (HMw) ASSPI. For
HMw ASSPI, DOPO was used as the catalyst, whereas that was not used in lower molecularweight (LMw) ASSPI case. Polymerization was conducted using 3,3’-BSPA (0.46 g), HPMDA(0.22 g), DOPO (0.86 g), m-cresol (5 ml), and TEA (0.3 ml) in a 50 mL three-necked roundbottomed flask with a mechanical stirrer under an argon atmosphere. m-Cresol was used as thesolvent. After reaction for 25 h at 180°C, the polymerized mixture was poured dropwise into
cooled acetone and was washed by centrifugation. The final product was dried under vacuum
and was subjected again to an ion-exchange process using Amberlyst. According to the previous
literature [25], molecular weight and polydispersity were examined by a gel permeation
chromatography (GPC) and results are shown in Table S1. In this scheme, we obtained the
ASSPI polymer with high molecular weight (HMw, 4.0 × 104). We also obtained the ASSPI
polymer with lower molecular weight (LMw, 2.5 × 104), which was polymerized according to
the same scheme without DOPO (Scheme S1). Obtained product was characterized 1H NMR
and FT-IR spectra (Figure S2 and S3). We selected it as comparison. (Figure S4 shows GPC
results.) The degree of sulfonation for the final product was estimated from 1H NMR data as
more than 98%. The calculated ion exchange capacity (IEC) was 2.9 meq. g-1.

6

Scheme 1. Synthesis of higher molecular weight alkyl sulfonated semi-aliphatic polyimide.

Preparation of Thin Films
ASSPI thin films onto Si, SiO2 substrates and SiO2-coated 9 MHz quartz crystals (Seiko
EG&G Co. Ltd.) were prepared from 5 wt% of ASSPI solution with a mixed solvent of MilliQ water and THF by a spincast method with a spin-coater (ACT−200D; Active Co. Ltd.).
Before film deposition, the substrates were washed by soaking in 2-propanol and plasma
treatment with a vacuum plasma system (Cute-MP; Femto Science, Korea) to improve surfacehydrophilicity. Thicknesses of the thin films were measured using a white interference
microscope (BW-S506; Nikon Corp.) and an atomic force microscope (AFM, VN-8000;
Keyence Co.).

Grazing Incidence Small-angle X-ray Scattering (GISAXS)

7

GISAXS measurements were taken with a FR-E X-ray diffractometer equipped with R-AXIS
IV two-dimensional (2D) detector (FR-E; Rigaku Corp.). Thin film samples were placed into ahumidity-controlled cell with X-ray transparent polyester film (Lumirror) windows. To control
the humidity, nitrogen carrier gas was used as received from the gas cylinder without further
dehumidification . Voltage of 45 kV, current of 45 mA, and irradiation time of 1 h were applied
to create copper Cu Kα radiation (λ = 0.1542 nm) with beam size of approximately 300 μm ×
300 μm. The camera length was 300 mm. X-ray scattering patterns were recorded on an imaging
plate (Fujifilm Corp.). The incident angle was chosen as 0.20° – 0.22°. For 1-D out-of-plane
and in-plane patterns, the integrated regions were taken, respectively, between -0.5° to +0.5° as
2 θ from the center (0°) and the width of 1° as 2θ, respectively.

Thin-Film Conductivity Measurements
For conductivity measurements of ASSPI thin films, impedance spectroscopy measurements
were taken using a two-probe method to obtain proton conductivity parallel to the film surface
with frequency response analyzer and high-frequency dielectric interface (SI1260 and SI1296;
Solartron Analytical). Gold paste was used as the thin film electrodes for the conductivity
measurements. The relative humidity (RH) and temperature were monitored by a computercontrolled environmental test chamber (SH-221; Espec Corp.). Impedance data were collected8

by application of an alternating potential of 50 mV over a frequencies ranging from 10 MHz to
1 Hz. The thin-film conductivity (σ) was calculated from the resistance value (R) obtained
directly from the impedance measurements using

σ=

d ,
Rlt

(1)

where d represents the space between the gold electrodes, t stands for the film thickness, and lexpresses the contact electrode length.

Water Uptake Measurements of Thin Films
Water uptake of ASSPI thin films was measured by an in-situ QCM system. The relative
humidity (RH) was controlled by a dry N2 gas and humidified streams using humidity controller(BEL Flow; BEL Japan Inc.). QCM substrates were connected to an oscillation circuit with a
DC power supply and frequency counter (53131A; Agilent Technologies Japan Ltd.). The
QCM substrate was placed in an in-house constructed humidity chamber with a high-resolution
RH sensor. The frequencies found before and after spin-coating of the QCM substrate wereconfirmed at the dry N2 stream for determined the mass of dry film by the Sauerbrey equation
as𝑆𝑆×�𝜌𝜌𝜌𝜌

(2)

𝛥𝛥𝑚𝑚 = 2×𝐹𝐹2 × (−𝛥𝛥𝐹𝐹),

9where S denotes the electrode surface area, ρ stands for the quartz density, µ expresses the shear
modulus of quartz, and F signifies the fundamental frequency of the QCM substrate. Water
content λ, the number of water molecules per sulfonic acid, was calculated as shown below,𝑚𝑚
𝐸𝐸𝐸𝐸− 1) ×,𝑚𝑚0
𝑀𝑀𝐻𝐻2 𝑂𝑂

(3)𝜆𝜆 = (In that equation, m represents the film mass at each RH, m0 stands for the film mass of at the
0% RH, MH2O is the molecular mass of water molecular, and EW expresses the equivalent ofeach ASSPI.

In-situ FT-IR
The dissociation state of protons from sulfonic acid groups was examined by in-situ FT-IR
measurements. ASSPI thin films on Si wafers were set in homemade cell. CaF2 windows wereused for the humidity-controlled cell. Then transmission in-situ FT-IR measurements weretaken using an FT-IR spectrometer (Nicolet 6700; Thermo Fisher Scientific Inc.) equipped with
deuterium triglycine sulfate (DTGS) detector. The relative humidity (RH) was controlled by ahumidity generator (me-40DP-2PW; Micro equipment). Thicknesses of films prepared onoxidized Si substrates used for this measurement were approximately 500 nm.

Results and discussion

10In-situ GISAXSGISAXS is powerful tool for reveal molecular packings and molecular orderings in molecularorganized thin films [26-28]. Matsui et al. showed anisotropic proton conductivity in a polymer
multilayer thin film with a well-defined lamellar structure confirmed from GISAXS
measurements [29]. Proton conductivity was enhanced by the formation of 2D hydrogenbonding networks in multilayer nanosheets [30, 31]. To investigate the influence of the semialiphatic main chain on the lyotropic organized structure, RH-dependent in-situ GISAXS
measurements were conducted in the ASSPI thin films. 2D scattering images are shown in
Figures 1 a–d and Figures 2 a–d for HMw and LMw ASSPI thin films, respectively. Series ofin-plane and out-of-plane 1D profiles for HMw and LMw thin films with various RH are depicted
in Figures 1e, f and Figures 2e, f, respectively. In the in-situ GISAXS measurements of the
HMw thin film, scattering peaks in the out-of-plane position were observed around small angle
region of 2θ = 4–5° (d = 2.1–2.7 nm) at more than 70% RH (Figures 1c and 1d). The out-ofplane peaks in the HMw thin film implied that the repeating ordered structure was formed
perpendicularly to the substrate plane in the thin film. Our earlier work demonstrated that theout-of-plane scatterings were attributed to the lamellar structure in the in-plane stacked
hydrophobic polyimide backbone with hydrophilic sulfonated side chains [21]. In a high RH
condition, this out-of-plane scattering peak was enhanced and shifted to the smaller angle region

11

(Figure 1f). At 95% RH, the out-of-plane peak reached 3° (d = 2.7 nm); it was markedly
enhanced relative to X-ray specular peak. These results reflect that the lamellar structure isconstructed by containing water through the thin film, which is incorporated selectively into
the interlamellar space. The scattering peak shift and intensity enhancement with humidity
respectively represented the lamellar expansion and ordering of the amphiphilic lamellar
structure to the out-of-plane direction. Molecular ordering is enhanced as the lamellar spacing
expands to the out-of-plane direction as humidity increases further. On the other hand, the LMw
thin film exhibited semicircle scattering at high humidity condition more than 70% RH (Figure2d-f) unlike the anisotropic scattering in the HMw thin film. In the in-plane profile, the scattering
shifted to the small angle region as humidity (Figure 2e), which indicate the formation of thesame lamellar structure as the HMw thin film. In the out-of-plane direction, however, peak shifts
were not clearly observed due to weak scattering intensity. The semicircle scattering suggests
the isotropic structure, therefore the LMw thin film formed a non-oriented lamellar structure.
Ando and co-workers have discussed details of main chain aggregations by ch-pack as anintermolecular main chain packing and π-stack as an aromatic ring stacking in both aromaticand semialiphatic polyimides with no sulfonated alkyl side chains [24]. These polyimidesconsisting of diaminocyclohexylmethane and pyromellitic dianhydride form smectic LC-likeordered structure by the main chain aggregations. Alkyl sulfonated aromatic polyimides exhibit

12

the scatterings attributed to the periodic monomer unit length and ch-pack for the polyimide
main chain in the in-plane and out-of-plane positions, respectively [20-23, 25]. The scatterings
imply the smectic LC ordering of the intermolecular aggregation in the lyotropic lamellar
structure. However, in the present both cases of ASSPI thin films, the scatterings due to themain chain aggregations were not observed. Probably, the non-planar aliphatic rings in the
ASSPI thin films inhibit the intermolecular aggregation of the main chain in the lyotropic
lamellar structure, so that the main chain smectic ordering is not formed. Thereby, ASSPI thinfilms only exhibit the scattering due to the lyotropic lamellar structure at high humidity
conditions compared to the aromatic polyimide thin films. On the other hand, the HMw thinfilm forms the oriented lamellar structure, although the LMw thin film exhibits the non-oriented
one. The reason for the structural difference might derive from the amount of shorter main
chains in ASSPI (Figure S4). Polarized optical microscope observation clearly revealed thedifference of the long range ordering and LC domain size between the HMw and LMw thickfilms (Figure S5). A birefringence textures were obviously observed in the HMw film (Figure
S5a, b), whereas LMw film only exhibited an image close to the dark field (Figure S5c, d).
These clearly indicate that the LMw film has less long range order and small domain size.
Hereinafter, we respectively designate HMw thin film as an Oriented lamellar thin film and
LMw thin film as a Non-oriented lamellar thin film.

13

Figure 1. GISAXS results for the HMw film. Panels a, b, c, and d respectively show the 2D
GISAXS patterns at 5% RH, 40% RH, 70% RH, and 95% RH. The humidity-dependent 1D
GISAXS profiles in the (e) in-plane and (f) out-of-plane directions of the Oriented lamellar thinfilm are also shown. The scattering arcs at the positions of 16 and 17 deg result from diffractionof Lumirror films used as the windows for humidity-controlled GISAXS cells.

14

Figure 2. GISAXS results for the LMw film. Panels a, b, c, and d respectively depict 2D
GISAXS patterns at 10% RH, 40% RH, 70% RH, and 95% RH. The humidity-dependent 1D
GISAXS profiles in the (e) in-plane and (f) out-of-plane directions of the Non-oriented lamellar
thin film are also shown. The scattering arcs at positions of 16 and 17 deg result from diffractionof the Lumirror film used as windows for the humidity-controlled GISAXS cell.

15

Proton Conductivity
Figure 3 depicts RH-dependent proton conductivity plots for both the Oriented lamellar andNon-oriented lamellar thin films. A linear increase in conductivity was observed by the increase
in RH, which is similar for both the Oriented lamellar and Non-oriented lamellar thin films.
However, the proton conductivity of the Oriented lamellar film displayed a more than half orderof magnitude higher value of 1.5 × 10-1 S cm-1 (at 25°C and 95% RH) than that of the Nonoriented lamellar thin film (3.0 × 10-2 S cm-1 at 25°C and 95% RH). At the high RH region, thishigher proton conductivity is probably obtained by improved molecular ordering and oriented
lamellar structure arising from increased molecular weight. Generally, the IEC value is
responsible for proton conductivity under high RH conditions [32, 33]. In present work,
however, the IEC value is fixed because of the same chemical structure of ASSPI. From thelamellar structure observed in the GISAXS measurement, the hydrophilic sulfonic acid side
chains and hydrophobic polyimide main chains are segregated to form the lamella structure
parallel to the substrate. In the high humidity condition, the hydrophilic sulfonic layers are
selectively hydrated and expanded upon the adsorption of water molecules. Such continuously
formed hydrophilic layers in the highly ordered structure promote the marked enhancement ofconductivity. To elucidate whether this increment of proton conductivity derives from structuraleffects or water uptake, in-situ QCM measurements were conducted.

16

Figure 3. RH-dependent proton conductivity plots for both the Oriented lamellar and Nonoriented lamellar thin films at 298 K.

Water Uptake
Water uptake for the proton exchange membrane affects proton conductivity because water
facilitates the transport of protons through the membrane [34]. Figure 4 shows RH-dependent
water uptake plots for both the Oriented lamellar and Non-oriented lamellar thin films. The
water uptake for both the films increased concomitantly with increasing RH, reaching a valueof λ = 16 in the Oriented lamellar thin film and λ = 14 in the Non-oriented film. Although nodifference was found in the water uptake at low humidity (30–80% RH), the Oriented lamellar
17thin film absorbs a little more water molecules than the Non-oriented film. The slightly higher
water uptake in the Oriented film results from the anisotropic expansion normal to the substrateplane at high RH condition as observed in GISAXS results.
To elucidate the relation between conductivity and water uptake, plots of conductivity vs. λwere shown in Figure 5. When the proton conductivity is compared at the same λ value, theOriented lamellar thin film showed more than a half order of magnitude higher proton
conductivity than the Non-oriented films. This fact clearly interprets that the water adsorption
is not responsibility of the enhancement of proton conductivity. Hence, we inferred that theoriented lamellar structure facilitates proton conductivity and engenders higher proton
conductivity at the high RH region.

18

Figure 4. RH-dependent water uptake plots for both the Oriented lamellar and Non-oriented
lamellar thin films.

19

Figure 5. Proton conductivity plots for both the Oriented lamellar and Non-oriented lamellar
thin films as a function of the λ value.

Dissociation State of Protons from Sulfonic Acid Groups using In-situ FT-IR.
To evaluate dissociation of proton at sulfonic acid groups in the conductivity change, in-situ
FT-IR measurements under controlled humidity were conducted. Figure 6 shows humiditydependent FT-IR spectra for the Oriented lamellar and Non-oriented lamellar thin films. The
peaks were clearly observed at the bands of 1715, 1640, 1200, and 1030 cm-1 corresponding tothe νas(C=O) symmetric stretching vibrations of imide groups, δ(H-O-H), νas(SO3-) and νs(SO3-),
respectively. With humidity increase, the absorbance of these peaks was enhanced. The amount20

of dissociated protons could be estimated by the absorbance due to the νs(SO3-) band. Figure 7
depicts the absorbance of the νs(SO3-) band at 1030 cm-1 portrayed as a function of the λ value.
The absorbance of the νs(SO3-) bands increased with the λ value and was saturated for λ > 6 inboth the Oriented lamellar and Non-oriented lamellar thin films. The saturation of the νs(SO3-)band absorbance suggests that dissociation of proton at sulfonic acid groups almost completed
in relatively low water uptake around λ = 6. However, the proton conductivity increases
considerably over λ = 6 from Figure 5. Miyatake et al. reported a similar tendency to correlate
the proton dissociation of sulfonic acid groups and proton conductivity during hydration
process in a sulfonated block poly(arylene ether sulfone ketone) membrane [33, 35]. Besides,
the both Oriented and Non-oriented films exhibited essentially the same behaviors. Therefore,
the dissociation state of proton at sulfonic acid groups is also not responsible for theenhancement of proton conductivity in the Oriented lamellar thin film.
In our earlier work, the highly proton-conductive organized structure was obtained using thelyotropic LC property derived from rigid aromatic main chains. In present work, the influenceof the semi-aliphatic structure was discussed. The molecular ordering weakens as a result of thelessened planarity of the main chain because of suppressed the (π-stack) aggregation of themain chain in the lyotropic lamellar structure. The degree of molecular ordering is found to be
improved with increasing molecular weight. An oriented lamellar organized structure is21

obtained. Although the IEC values, the water uptake and dissociation behavior of proton are
identical in both films, the Oriented lamellar film exhibits a half order of magnitude higher
proton conductivity compared to the Non-oriented film. Therefore, we inferred that the oriented
lamellar structure enhanced proton conductivity more than the non-oriented lamellar structure
did.

22

Figure 6. Humidity-dependent FT-IR spectra of (a) Oriented lamellar thin film and (b) Nonoriented lamellar thin film.

23

Figure 7. Change of the absorbance of νs(SO3-) of the ASSPI thin films observed during
hydration.

Conclusion
As described herein, the influence of the semi-aliphatic backbone for the molecular orderingand proton conductivity was discussed for the sulfonated polyimide thin films. A new alkyl
sulfonated polyimide that was less planarity for the main chain was synthesized. The lower
molecular weight of sulfonated polyimide was a non-oriented lamellar structure at 70–95% RH
condition. However, the higher molecular weight enhanced the degree of molecular orderingand gave the oriented lamellar organized structure by the lyotropic LC property. The reason forthe structural difference might derive from the amount of shorter main chains in ASSPI.
24

Moreover, proton conductivity was enhanced in the case of lamellar organized structure in thesame water amount and dissociation state of protons. We concluded that higher proton
conductivity was achieved with the oriented lamellar organized structure.

Acknowledgement
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 partially supported by Iketani Science and Technology
Foundation (ISTF), JAPAN.

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Graphical Abstract

High-molecular-weight (HMw) sulfonated polyimide thin films with the semi-aliphatic main
chain exhibited the oriented lamellar structure and high proton conductivity (1.5 × 10-1 S cm-1)
under a humidified condition. Low-molecular-weight (LMw) sulfonated polyimide thin films
with the same semi-aliphatic backbone exhibited the non-oriented lamellar structure and low
proton conductivity (3.0 × 10-2 S cm-1) under a humidified condition. Results indicate that, in
sulfonated polyimide thin films with semi-aliphatic main chain, the lamellar orientation greatly
contributes to the high proton conductivity.

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