Efficient thermal conversion of poly(pyridinediylbutadiynylene)s to nitrogen-containing microporous carbon

Article abstract of DOI:10.1246/cl.2006.844

Poly(pyridinediylbutadiynylene)s, a conjugated polymer alternatively consisted of the pyridine and butadiyne units, were synthesized by oxidative polycondensation of diethynylpyridine with the Hay catalyst. They converted to microporous carbons in high yi

Full text of DOI:10.1246/cl.2006.844

8
44
Chemistry Letters Vol.35, No.8 (2006)
Efficient Thermal Conversion of Poly(pyridinediylbutadiynylene)s
to Nitrogen-containing Microporous Carbon
ꢀ
Masashi Kijima, Takayuki Oda, Takahisa Yamazaki, Yasunori Tazaki, and Junji Nakamura
Institute of Materials Science, Graduate School of Pure and Applied Science, University of Tsukuba,
1-1-1 Tennodai, Tsukuba 305-8573
(Received May 1, 2006; CL-060523; E-mail: kijima@ims.tsukuba.ac.jp)
Poly(pyridinediylbutadiynylene)s, a conjugated polymer
1
00
(a)
alternatively consisted of the pyridine and butadiyne units, were
synthesized by oxidative polycondensation of diethynylpyridine
with the Hay catalyst. They converted to microporous carbons in
high yields with a high efficiency of fixation of nitrogen by heat-
9
8
0
0
ꢁ
ing up from room temperature to 900 C under flowing of argon.
(
b)
Incorporation of electron-donating nitrogen into porous car-
bons has attracted attention to change the physical and chemical
1
properties of carbon materials especially on the surface. One
possible application would be the electrode of electric double-
2
layer capacitors (EDLC). The achievement need of the elec-
2
00
400
T / °C
600
800
trode made from the nitrogen-enriched carbon is basically hav-
ing a large surface area with low resistivity. However, the reac-
tivity of nitrogen-containing pre-carbon materials makes diffi-
cult to prepare porous carbons in high yield with high content
of nitrogen by the usual carbonization and activation methods.
We have recently reported that the pyrolytic carbonization of
conjugated polymers having carbon–carbon triple bonds such
as poly(phenylenebutadiynylene)s under an argon flow could
Figure 1. TG/DTA curves of P25PyB (—), P26PyB (- - - -),
P35PyB (–ꢂ–), and PmPB (ꢂ ꢂ ꢂ ꢂ ꢂ ꢂ).
5
respectively.
The results of thermogravimetric and differential thermal
analysis (TG/DTA) for PPyBs were compared with that of poly-
(m-phenylenebutadiynylene) PmPB. In all cases, the carboniza-
3
afford microporous carbons in high yields above 80%. It is
ꢁ
tion yields at 900 C were about 85%. In the DTA curves
ꢁ
thought that if the phenylene portion of the polymer is sub-
stituted by a thermal-stable N-containing aromatic portion, this
pyrolytic method would be simple, efficient and alternative
to the ingenious methods reported so far for preparation of
the nitrogen-enriched porous carbons. Thus, in this paper,
we attempted to synthesize poly(pyridinediylbutadiynylene)s
(
Figure 1b), PPyBs showed an exothermic peak around 200 C
accompanying no mass loss, which suggested that the cross-link-
ing reaction occurred at the butadiyne portion during the exo-
3
thermal process as well as PmPB. In the case of PmPB, most
ꢁ
of mass loss in the range from 500 to 700 C was due to dehydro-
genation from the phenylene portion, while the TG curves of
PPyBs (Figure 1a) suggested that nitrogen-containing fragments
would continuously eliminate in the temperature region above
(
acterized the carbonized products.
PPyBs) and investigated their carbonization behavior, and char-
According to the reaction course shown in Scheme 1, the
monomer, diethynylpyridine, was synthesized by Sonogashira
coupling of 2,5-, 2,6-, or 3,5-dibromopyridine with trimethyl-
silylacetylene, and the successive elimination of trimethyl-
ꢁ
3
00 C in addition to the dehydrogenation process.
The polymer in a form of pellet (ꢀ ¼ 13 mm) was carbon-
ized in a quartz tube by heating up from room temperature to
ꢁ ꢁ
4
300 C at a rate of 0.5 C/min and successively from 300 to
ꢁ ꢁ
00 C at a rate of 10 C/min under flowing argon in a furnace.
silyl by the alkaline treatment. The monomer underwent oxida-
tive polycondensation in tetrahydrofuran under O2 in the pres-
ence of Hay catalyst, giving P25PyB, P26PyB, and P35PyB,
9
After carbonization, the sample was allowed to cool to room
temperature and stored in a desiccator. The carbonization results
and some analytical data of the carbonized samples are summa-
rized in Table 1.
H
SiMe3
Pd cat
Br
Br
Me3Si
H
SiMe3
N
N
The carbonization yields of the disk-pellet samples of
PPyBs are comparable to the TG results. The contraction of vol-
ume was about 30%. The bulk density of the carbonized pellet
THF
K2CO3
H
3
CH Cl , MeOH
was about 1.2 g/cm . The electrical conductivity was about
5 S/cm. The N2 adsorption isotherm shown in Figure 2 is of
Type I, suggesting the microporous nature of carbon. The spe-
2
2
N
O , Cu cat.
2
cific surface area (SBET) of the carbonized PPyBs was in the
range of 300–400 m /g. The N elimination during the carboniza-
tion affected increasing meso- and macroporosities of the carbon
THF
n
2
N
PPyBs
Scheme 1. Synthesis of PPyBs with 2,5-, 2,6-, and 3,5-linkage.
(Vmicro=Vtotal) compared to PmPB. The subtracting pore effect
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.8 (2006)
Table 1. Carbonization results of PPyBs
845
402.6 eV. These peaks suggest the presence of N-bonding states
of pyridine (398.5), pyridone (2-hydroxypyridine) (400.5), and
oxidized nitrogen (402.9) rather than the usually considered qua-
d
Yielda
SBETb
Vmicroc
EA /%
Vmicro/
Vtotal
Polymer
Dfixe
2
ꢃ1
3
ꢃ1
/%
/m g
/cm g
C
N
1
ternary N (401.2). In the C1s region, three peaks at 284.5, 285.2,
P25PyB
P26PyB
P35PyB
PmPB
a
81
85
85
94
306
305
416
471
0.12
0.12
0.18
0.20
0.46 73.97 6.25 0.59
0.48 84.93 6.26 0.57
0.62 88.51 5.05 0.46
and 287.7 eV fall in a region of graphite, carbons with N, and
carbons with O, respectively. These results suggest that the sur-
face of the carbonized PPyBs is easily oxidized and sufficiently
polar to adsorb moisture, which is appropriate to the observation
of abundance of O (21 mass %) by XPS. The EDLC capacitance
of the disk pellet of the carbonized P35PyB measured by a
constant current method (0.02 A/g) using a three-electrode cell
0.71 94.37
—
—
ꢁ
b
Carbonization yield at 900 C. Surface area was estimated by
c
Brunauer–Emmett–Teller method. Micropore volume was estimat-
d
ed by ꢁs method. Elemental analysis data (wt %) of the carbonized
polymers. Degree of N-fixation at 900 C defined as the N content
e
ꢁ
3
was quite high (452 F/g) in 1 mol/dm H2SO4, which might
(wt %) ratio of the carbonized PPyB to the untreated PPyB.
be affected by abundance of the pyridine-like carbons on the
surface.
2
1
00
00
0
This work was partially supported by the Grant-in-Aid
for the Scientific Research (C) from the Japan Society for the
Promotion of Science (No. 15550170), Ogasawara foundation,
and Promotion of Creative Interdisciplinary Materials Science
for Novel Functions by The 21st Century COE program. We
thank to the Research Facility Center for Science and Technol-
ogy, Chemical Analysis Division, University of Tsukuba, for
TG/DTA, N2 adsorption, NMR spectroscopic, and elemental
analysis data.
References and Notes
J. Lahaye, G. Nans e´ , A. Bagreev, V. Strelko, Carbon 1999,
7, 585; C.-M. Yang, K. Kaneko, Carbon 2001, 39, 1075;
0
0.2
0.4
0.6
P/P0
0.8
1
1
3
Figure 2. N2 adsorption–desorption isotherm of the carbonized
ꢁ
E. Raymundo-Pi n˜ ero, D. Cazorla-amor o´ s, A. Linares-Solano,
J. Find, U. Wild, R. Schl o¨ gl, Carbon 2002, 40, 597; W. J.
Gammon, O. Kraft, A. C. Reilly, B. C. Holloway, Carbon
P35PyB at ꢃ196 C.
6
analysis of the ꢁs plots of the carbonized PPyBs gave results of
a surface area larger than SBET and an average pore width in the
range of 0.71–0.77 nm.
From elemental analysis, the carbonized PPyBs retain about
mass % of N with a high efficiency of N-fixation (Dfix). How-
ever, the total mass % of C, H, and N was always below 95% in
all cases, which suggested that considerable amount of O is pres-
ent on the surface. The results of X-ray photoelectron spectros-
copy (XPS) for the carbonized P35PyB in the region of O1s, N1s,
and C1s are shown in Figure 3. The peak value of main Gaussian
component of O1s (532.5 eV) falls in a range between phenolic
compounds. The fitting of the peaks in the region of N1s shows
three contributions at binding energies of 398.1, 400.5, and
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´
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General procedure of polymerization: To the catalyst solution
prepared by mixing CuCl (2 mmol) and N,N,N ,N -tetra-
methylethylenediamine (2 mmol) in THF (50 mL) for 15
min with bubbling of O2 was added corresponding diethynyl-
pyridine (8 mmol) in THF (35 mL), which was further stirred
for 48 h at room temperature under O2. After evaporation of
the solvent, the insoluble precipitated product was washed
with stirring in MeOH (300 mL) containing concd HCl
(
a)
(b)
(c)
O1s
N1s
C1s
0
0
B
B
B
A
C
A
A
C
(
3 mL). The product collected by filtration was sequentially
C
washed with 7.5% aq NH3, H2O, MeOH, and acetone. A pow-
dery brown polymer was obtained over 85% yield after drying
under vacuum in each case.
5
35
530
405
400
395
290
285
Binding Energy /eV
Figure 3. XPS spectra of the carbonized P35PyB and the fitting
results with Gaussian.
6
K. Kaneko, C. Ishii, H. Kanoh, Y. Hanzawa, N. Setoyama, T.
Suzuki, Adv. Colloid Interface Sci. 1998, 76–77, 295.
Published on the web (Advance View) June 27, 2006; doi:10.1246/cl.2006.844