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Title

Synthesis of oligomeric poly[(1, 2‑
propanediamine)‑alt‑(oxalic acid)] and anomalous
proton conductivities of the thin films

Author(s)Nagao, Yuki; Naito, Nobuhiro; Iguchi, Fumitada;Sata, Noriko; Yugami, Hiroo

Citation

Solid State Ionics, 180(6‑8): 589‑591

Issue Date

2008‑11‑13

Type

Journal Article

Text version

publisher

URL

http://hdl.handle.net/10119/10631

RightsNOTICE: This is the author's version of a work
accepted for publication by Elsevier. Yuki Nagao,
Nobuhiro Naito, Fumitada Iguchi, Noriko Sata,
Hiroo Yugami, Solid State Ionics, 180(6‑8), 2008,
589‑591,
http://dx.doi.org/10.1016/j.ssi.2008.09.022

Description

Japan Advanced Institute of Science and Technology

1Synthesis of oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] andanomalous proton conductivities of the thin films

Yuki Nagaoa,b, Nobuhiro Naitob, Fumitada Iguchib, Noriko Satab, and Hiroo YugamibaCenter Research Strategy and Support, Tohoku University, 2-1-1 Katahira, Aoba-ku,

Sendai 980-8577, Japan and bGraduate School of Engineering, Tohoku University, 6-6-01
Aramaki Aza Aoba, Aoba-ku, Sendai 980-8579, Japanemail: y_nagao@energy.mech.tohoku.ac.jp

Abstract
New proton-conductive polyamide oligomers, oligomeric poly[(1,2-propanediamine)-alt(oxalic acid)], were synthesized to investigate the proton transport properties of bulk and thinfilms. The obtained oligomers were characterized by the X-ray diffraction, FT-IR spectra, 1H
NMR, Matrix Assisted Laser Desorption / Ionization Time of Flight (MALDI-TOF) mass
spectrum, and electrical conductivity measurements. The bulk proton conductivity is 3.0 
10-4 S cm-1 at the relative humidity (RH) of 80 %. The proton conductivity of thin film isrelatively higher than that of bulk sample. Thickness dependence of the proton conductivity
was observed in these thin films. The maximum proton conductivity of the thin film is 4.0 
10-3 S cm-1 at the relative humidity (RH) of 80 %, which is higher one order magnitude thanthat of the bulk sample. The activation energies of bulk and 200 nm thick film are 1.0 and
0.69 eV at the RH of 60 %, respectively.

Keywords: proton conduction, thin films, thickness dependence

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1. Introduction
Since Liang had reported approximately 50 times enhancement in Li+ ion conduction atroom temperature simply by dispersing ultrafine particles of inert Al2O3 in LiI [1], a large
number of two-phase composite systems have been investigated with the conductivity
enhancement of one to three orders of magnitude [2, 3]. This high ionic conductivity makesthese materials good candidates for solid-state electrolytes in the devices such as fuel cell,solid-state battery, sensor, etc. In the most cases, the second phase consists of anonconducting material such as SiO2 or Al2O3 which is nearly insoluble in the host material.
The conductivity enhancement in the 2-D system has been also reported [4-15]. These
anomalies are supposed to be attributed to interfacial effects like structural effects and/or
effects of a space charge region. The interfacial effects for the proton conduction in the 2-D
system also attract considerable attention. But the enhancement of the proton conductivity has
not been clearly reported in the thin films of the organic proton conductors. We haveinvestigated a series of the proton-conductive oligomers containing amide groups. In thispaper, we synthesized new proton-conductive polyamide oligomers, oligomeric poly[(1, 2propanediamine)-alt-(oxalic acid)], and investigated the proton transport properties of thebulk and thin films to study the enhancement of the proton conductivities.

2. Experimental
Oxalic acid dihydrate and 1, 2-propanediamine (Wako Pure Chemical Industries, Ltd.) ofreagent grade were used as received. A solution of 1, 2-propanediamine in methanol wasadded to a solution of oxalic acid dihydrate in methanol with stirring at 30 oC. The obtained

3ammonium salt was dissolved with water, and oxalic acid dihydrate was added for the
preparation of the oligomeric polyamides with the carboxyl end groups. An adhesive sample
was obtained after heating for ~6 hours.
The quality of the sample was checked by the X-ray diffraction (XRD), Fourier-transform
infrared (FT-IR) spectrum, 1H NMR, and Matrix Assisted Laser Desorption / Ionization Timeof Flight (MALDI-TOF) mass spectrum measurements. X-ray diffraction analysis was
performed with CuKα radiation using a PANalytical X’Pert PRO MPD. For the FT-IR
absorption measurement, the sample was diluted with KBr and the mixture was pressed into apellet. The FT-IR spectrum was measured with a PerkinElmer Spectrum GX in the frequency
range of 400 – 4000 cm-1. The 1H NMR spectrum in DMSO-d6, using TMS as internalreference, was obtained on a ECA-600 (JEOL) operated at 14 T. The MALDI-TOF mass
spectrum was recorded in linear mode, using a SHIMADZU AXIMA-CFR Plus mass
spectrometer, equipped with a nitrogen laser ( = 337 nm), working in a positive ion mode.
The average degree of polymerization was determined by a Kratos Analytical Ltd. Kompact
program.
The thin films were synthesized by using a Active ACT-200 Spincoater on SiO2 glass
substrates. The thickness of the thin films was determined by using a KLA-Tencor P-10
contact stylus profiler. The obtained thin films are flat, and their thicknesses are 60, 80, 200,
and 400 nm, respectively.
Impedance measurements of the bulk and thin films of oligomeric poly[(1, 2propanediamine)-alt-(oxalic acid)] were carried out in the relative humidity (RH) range of 50– 80 % at 298 K with a Solartron 1260 Impedance/Gain-Phase analyzer and a 1296 DielectricInterface system. The RH and temperature were controlled with an Espec Corp. SH-221
humidity- and temperature-controlled chamber. In the case of the impedance measurements of

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the bulk sample, the sample was processed into pellets of 2.5 mm under pressure of ~1GPaand porous gold paint (Tokuriki Chemical Research, SILBEST No. 8560) was used aselectrodes. The activation energy was studied in the temperature range of 298 -323 K. In thecase of the impedance measurements of the thin films, the electrode configuration was
selected to obtain measurements of the current flow in the plane parallel to the substratesurface. The conductivity of the SiO2 substrate is negligible because its resistance is at least
two orders of magnitude higher than that of the film over the film thickness range of 60 – 400
nm.

3. Results and Discussion
3.1 CHARACTERIZATION
Figure 1 shows the X-ray diffraction patterns of the ammonium salt (before heating) andsynthesized sample (after heating). The diffraction pattern derived from the crystal structureof the ammonium salt was disappeared after heating. The synthesized sample was found to beamorphous.
Figure 2 shows the FT-IR spectra of the ammonium salt (before heating) and synthesized
sample (after heating). The intense and broad bands at 1680 and 1525 cm-1 in the spectrum of
the synthesized sample can be assigned as the CO and NH bonds of the amide groups. The
synthesized amides was found to be polymerized by the reaction of oxalic acid and 1, 2propanediamine.
Figure 3 shows the 1H NMR spectrum of the synthesized amides in DMSO-d6. According
to the spectrum, it is suggested that the degree of polymerization is low because the width ofthe peaks is narrow. The spectrum of the oligomeric amides shows peaks at δ 2.87 – 4.03 ppm
corresponding to the methylene and methine protons (-CH2-CH-) and shows peaks at δ 1.05 –5

1.26 ppm corresponding to the methyl protons (-CH3). The peaks at δ 8.31 – 8.97 ppm are dueto the amide protons and amine protons at the end groups. Since many peaks derived from themethyl, methylene, methine, amide, or amine protons were observed, the synthesized amides
were found to be mixture of the amides with the different end groups and molecular weights.
From the MALDI-TOF mass spectrum, the peak (m / z = 391.3 (H+) and 413.3 (Na+)) due
to the low-molecular-weight amides (n = 1) with the carboxyl end groups were observed. It isalso suggested that the end groups of some amides are –NH2 and –COOH, and the average
degree of the polymerization is ~5. The peak (m / z = 151.1 (Na+) and 279.3 (Na+)) due to themacrocyclic amides (n = 1, 2) were also observed. So the synthesized amides are found to be
the mixture of the oligomers with the different end groups and low-molecular-weights
including the macrocyclic amides as shown in below.

3.2 PROTON TRANSPORT PROPERTIES OF THE BULK AND THIN FILMS
In general, the amide groups exhibit the proton exchange property because of theamide/imidic acid tautomerism. Since the obtained oligomers was found to be acidic, theoligomers could exhibit the proton transport properties. The typical complex impedance plotsof oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] at the RHs of 60 and 70 % areshown in Figure 4. A resistance is directly given by the intersection of a depressed semicircle
with the real axis. The obtained electrical conductivities at the RHs of 60 and 70 % are foundto be 1.4 × 10-6 and 5.2 × 10-5 S cm-1, respectively. The electrical conductivities of thepolyamide oligomers strongly depend on the RH. Such a large dependence of the electricalconductivity on the RH could arise from the proton conduction paths developed by the water6

uptake. The activation energy for the proton conduction of oligomeric poly[(1, 2propanediamine)-alt-(oxalic acid)] is 1.0 eV at the RH of 60 % in the temperature range of
298 – 323 K. This value is high because the oligomeric polyamides do not contain enoughwater molecules for the proton conduction at the RH of 60 %.
Figure 5 shows the RH dependence of the proton conductivity () for oligomeric poly[(1,2-propanediamine)-alt-(oxalic acid)] and their thin films. In the proton conduction of the bulk
sample, the proton conductivity increases by four orders of magnitude with increasing the RH
from 50 to 80 %. The proton conductivity of the bulk sample is 3.0  10-4 S cm-1 at the RH of
80 %. However the proton conductivity of the thin film also depends on the RH, the proton
conductivity of the thin film exhibits different value from that of the bulk sample. The proton
conductivity of the 200 nm thick film is found to be 4.0  10-3 S cm-1 at the RH of 80 %. Thisvalue is found to be one order of magnitude higher than that of the bulk sample of oligomericpoly[(1, 2-propanediamine)-alt-(oxalic acid)], however this value is one order of magnitude
lower than that of Nafion 117 membrane at the RH of 80 % [16]. The proton conductivity of
the 400 nm thick film exhibits relatively higher value than that of the bulk sample. Its
conductivity is not the same value of the 200 nm thick film at the same RH. However the
proton conductivities of the 60 and 80 nm thick films are lower than those of the 200 and 400
nm thick films, their conductivities are about three times higher than that of the bulk sample.
In many kinds of the inorganic ionic conductors, some theoretical models including the spacecharge models for understanding the enhancement phenomena of the ionic conductivities
have been discussed [3]. But the study on the proton conductivity enhancement of the organic
thin films is still unexplored. Comparing the activation energy between bulk sample and thinfilm, the activation energies of bulk and 200 nm thick film are 1.0 and 0.69 eV at the RH of
60 %, respectively. The activation energy of 200 nm thick film exhibits lower value than that7of bulk sample. These results could be originated from the structural effects like a molecularorientation by the synthesis of the thin film on the substrate rather than the interface effects
like the space charge models in this system. We have not yet estimated the quantitative
contribution of space charge region at the interface. Further investigation is required tounderstand this phenomenon.

4. Conclusions
New proton-conductive polyamide oligomers, poly[(1,2-propanediamine)-alt-(oxalicacid)], were synthesized to investigate the proton transport properties of bulk and thin films.
The proton conductivity of the bulk sample is 3.0  10-4 S cm-1 under the RH of 80 % and 298
K. The maximum proton conductivity of the thin film is 4.0  10-3 S cm-1 at the RH of 80 %,which is higher one order magnitude than that of the bulk sample. Thickness dependence ofthe proton conductivity was observed in these thin films. The activation energies of bulk and
200 nm thick film are 1.0 and 0.69 eV at the RH of 60 %, respectively. These results could beoriginated from the structural effects like a molecular orientation by the synthesis of the thinfilm on the substrate rather than the interface effects like the space charge models in thissystem. Further investigation is needed to understand this phenomenon.

Acknowledgements
The authors thank M. Sasaki for helping the synthesis of the proton-conductive oligomers,
and thank Dr. H. Maekawa and M. Ando for helping the NMR measurement, and thank A.
Haneda for the measurements of the MALDI-TOF mass spectrum. This study was supportedby Program for Improvement of Research Environment for Young Researchers from Special

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Coordination Funds for Promoting Science and Technology (SCF) commissioned by the
Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.

References[1] C.C. Liang, Journal of the Electrochemical Society 120 (1973) 1289.
[2] N.J. Dudney, Annual Review of Materials Science 19 (1989) 103.
[3] R.C. Agrawal R.K. Gupta, Journal of Materials Science 34 (1999) 1131.
[4] E. Schreck, K. Laeuger, K. Dransfeld, Zeitschrift fuer Physik B: Condensed Matter 62(1986) 331.
[5] S. Muehlherr, K. Laeuger, E. Schreck, K. Dransfeld, N. Nicoloso, Solid State Ionics
28-30 (1988) 1495.
[6] F.A. Modine, D. Lubben, J.B. Bates, Journal of Applied Physics 74 (1993) 2658.
[7] D. Lubben, F.A. Modine, Journal of Applied Physics 80 (1996) 5150.
[8] I. Kosacki, H.U. Anderson, Sensors and Actuators, B: Chemical B48 (1998) 263.
[9] N. Sata, K. Eberman, K. Eberl, J. Maier, Nature (London) 408 (2000) 946.
[10] I. Kosacki, T. Suzuki, V. Petrovsky and H.U. Anderson, Solid State Ionics 136-137(2000) 1225.
[11] X.X. Guo, J. Maier, Surface Science 549 (2004) 211.
[12] S. Azad, O.A. Marina, C.M. Wang, L. Saraf, V. Shutthanandan, D.E. McCready, A.
El-Azab, J.E. Jaffe, M.H. Engelhard, C.H.F. Peden, S. Thevuthasan, Applied Physics
Letters 86 (2005) 131906/1.
[13] I. Kosacki, C.M. Rouleau, P.F. Becher, J. Bentley, D.H. Lowndes, Solid State Ionics
176 (2005) 1319.
[14] S.-i. Furusawa, H. Tabuchi, T. Tsurui, Solid State Ionics 178 (2007) 1033.

9[15] A. Peters, C. Korte, D. Hesse, N. Zakharov, J. Janek, Solid State Ionics 178 (2007) 67.
[16] Y. Sone, P. Ekdunge, D. Simonsson, Journal of the Electrochemical Society 143(1996) 1254.

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Figure Captions
Fig. 1: X-day diffraction patterns of the ammonium salt (Before heating) and oligomericpoly[(1, 2-propanediamine)-alt-(oxalic acid)] (After heating).
Fig. 2: IR spectra of the ammonium salt and oligomeric poly[(1, 2-propanediamine)-alt(oxalic acid)].
Fig. 3: 1H NMR spectrum of oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] in
DMSO-d6.
Fig. 4: Impedance plots of oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] at theRHs of 60 and 70 %.
Fig. 5: RH dependence of the proton conductivity with bulk and thin films of oligomericpoly[(1, 2-propanediamine)-alt-(oxalic acid)].

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Fig. 1

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Fig. 2

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Fig. 3

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Fig. 4

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Fig. 5