Novel synthesis of electroresponsive poly(thiophenylene) through a Michael-type addition

Article abstract of DOI:10.1021/ol0068501

(equation presented) A novel poly(thiophenylene) having N,N′-diphenyl-1,4-phenylenediamine (PDA) as a redox unit was synthesized through a Michael-type addition. This polymerization proceeded at room temperature without catalysts. The polymer obtained act

Full text of DOI:10.1021/ol0068501

ORGANIC
LETTERS
2001
Vol. 3, No. 1
131-134
Novel Synthesis of Electroresponsive
Poly(thiophenylene) through a
Michael-Type Addition
Kimihisa Yamamoto,* Masayoshi Higuchi, Hirokazu Takai, and Toyohiko Nishiumi
Department of Chemistry, Faculty of Science & Technology, Keio UniVersity,
Yokohama, 223-8522 Japan
yamamoto@chem.keio.ac.jp
Received November 10, 2000
ABSTRACT
A novel poly(thiophenylene) having N,N′-diphenyl-1,4-phenylenediamine (PDA) as a redox unit was synthesized through a Michael-type addition.
This polymerization proceeded at room temperature without catalysts. The polymer obtained acted as a good electroresponsive material with
moderate thermostability.
Electroresponsive polymers have attracted the attention of
many researchers because of the wide applications in
electrical engineering. Recent interest has been stimulated
by the potential use of such polymers as electrode materials
in batteries and in capacitor, sensor, and electronic displays.
Up to now π-conjugated polymers have been developed for
this purpose due to their high electrical conductivity;1
however, they lack chemical and thermal stabilities and also
moldability. Themostable polymers with redox activity have
been strongly desired for electronic devices with good
reliability for long-term use. One approach for an alternate
material is the introduction of a redox active center onto
thermostable aromatic polymers.2 Poly(thiophenylene) (PPS)
is well-known to exhibit good thermal stability, moldability,
and chemical resistance as an excellent engineering plastic.3
Although these properties make PPS a high performance
polymer, it is difficult to synthesize under mild conditions.
Much effort has been exerted in the development of a new
synthetic method.4
Recently, polyaniline as a emeraldine base, which has a
quinoid imine oxidative state form, has been shown to react
with nucleophiles such as amines and mercaptans at room
temperature.5 This reaction is noteworthy for the arylsulfide
bond formation through the nucleophilic substitution of a
mercaptan on the imine compounds. We now report a
successful attempt to synthesize an electroresponsive PPS
containing N,N′-diphenyl-1,4-phenylenediamine (PDA) units
at room temperature. This process involves a Michael-type
(3) (a) Edmonds, J. T., Jr.; Hill, H. W., Jr. U.S. Patent 3354129, 1967;
Chem. Abstr. 1968, 68, 13598. (b) Hill, H. W., Jr. Ind. Eng. Chem., Prod.
Res. DeV. 1979, 18, 252. (c) Campbell, R. W.; Edmonds, J. T., Jr. U.S.
Patent 4038259, Chem. Abstr. 1977, 87, 854v. (d) Lenz, R. W.; Carrington,
W. K. J. Polym. Sci. 1959, 41, 333.
(4) (a) Yamamoto, K.; Shouji, E.; Nishide, H.; Tsuchida, E. J. Am. Chem.
Soc. 1993, 115, 5819. (b) Yamamoto, K.; Shouji, E.; Suzuki, F.; Kobayashi,
S.; Tsuchida, E.; J. Org. Chem. 1995, 60, 452. (c) Tsuchida, E.; Yamamoto,
K.; Miyatake, K.; Nishimura, Y. Angew. Chem., Int. Ed. Engl. 1996, 35,
2843. (d) Wang, Y.-F.; Chan, K. P.; Hay, A. S. Macromolecules 1995, 28,
6371. (e) Ding, Y.; Hay, A. S. Macromolecules 1996, 29, 6386. (f) Ding,
Y.; Hay, A. S. Macromolecules 1997, 30, 2527. (g)Wang, Z. Y.; Hay, A.
S. Tetrahedron Lett. 1990, 31, 5685.
(5) (a) Han, C.-C.; Jeng, R.-C. Chem. Commun. 1997, 553. (b) Barbero,
C.; Morales, G. M.; Grumelli, D.; Planes, G.; Salavagione, H.; Marengo,
C. R.; Miras, M. C. Synth. Met. 1999, 101, 694. (c) Mikhael, M. G.; Padias,
A. B.; Hall, Jr., H. K. J. Polym. Sci. Part A: Polym. Chem. 1997, 35, 1673.
(1) (a) Takeoka, S.; Hara, T.; Fukushima, K.; Yamamoto, K.; Tsuchida,
E. Bull. Chem. Soc. Jpn. 1998, 71, 1471. (b) Higuchi, M.; Yamamoto, K.
Org. Lett. 1999, 1, 1881. (c) Higuchi, M.; Kimoto, A.; Shiki, S.; Yamamoto,
K. J. Org. Chem. 2000, 65, 5680. (d) Wernet, W.; Wegner, G. Makromol.
Chem. 1987, 188, 1465. (e) Mu¨nstedt, H. Polymer 1988, 29, 296. (f) Lei,
J.; Martin, C. R. Chem. Mater. 1995, 7, 578.
(2) (a) Wang, P.; Martin, B. D.; Parida, S.; Rethewisch, D. G.; Dordick,
J. S. J. Am. Chem. Soc. 1995, 117, 12885. (b) Yamamoto, T.; Kimura, T.;
Shiraoshi, K. Macromolecules 1999, 32, 8886. (c) Nikles, D. E.; Chacko,
A. P.; Liang, J.; Webb, R. I. J. Polym. Sci. Part A: Polym. Chem. 1999,
37, 2339.
10.1021/ol0068501 CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/14/2000

addition on the compounds having a double bond with an
electron-attractive group.6
amount of PDI acts as an oxidant of PDA-T. As a result,
PDA as the reduced form of PDI was detected in a 17%
yield in this reaction. In other words, more than 94% of PDI
was converted in this reaction. Diphenyl disulfide as a side
product was detected only in very small amounts on the basis
of HPLC. These results suggested that the nucleophilic
addition quantitatively proceeded.
N,N′-Diphenyl-1,4-phenylenediamine (PDA) is a redox-
active unit of polyaniline and is converted to N,N′-diphenyl-
1,4-phenylenediimine (PDI) by chemical or electrochemical
oxidation as shown in Scheme 1a. A Michael-type addition
The nucleophilic reaction was demonstrated by a con-
trolled experiment using PDI. The electronic absorption
attributed to PDI at 450 nm gradually decreased with the
addition of the nucleophile during the reaction. Kinetic
analysis of its UV-vis spectra reveals that mercaptans such
as thiophenol, hexadodecyl mercaptan, and methyl mercaptan
quantitatively react with PDI. Their reactions obey pseudo-
first-order kinetics, where the rate constant for thiophenol
and dodecyl mercaptan were found to be 2.62 × 10-2 s-1
and 2.8 × 10-4 s-1, respectively. Other nucleophiles such
as sodium methoxide (5.0 × 10-3 s-1) and butylamine (2.62
× 10-2 s-1) were also confirmed to react with the imine
compounds.
Scheme 1. (a) Reversible Redox between PDA and PDI. (b)
The Michael-Type Addition Mechanism to PDI. (c) The Control
Reaction of Thiophenol with PDI
A solvent effect was observed during the nucleophilic
reaction (Figure 1). The rate constant in dichloromethane is
of nucleophiles to PDI was confirmed to proceed at room
temperature (Scheme 1b).
The control reaction of PDI with thiophenol was carried
out in dichloromethane for 2 h at room temperature (Scheme
1c). The 2-phenylthio-PDA (PDA-T) and 2,5-bis(phenylthio)-
PDA (PDA-2T) were isolated by silica gel column chroma-
tography in 71 and 6% yields, respectively.7 A Michael-type
addition of thiophenol to the quinoid ring of PDI gave PDA-
T. On the other hand, PDA-2T was formed via the addition
of thiophenol to PDI-T, which was the oxidized form of
PDA-T. Since PDA-T has lower oxidation potential (0.23
V vs SCE at pH 1.3) than that of PDA (0.28 V), some
(6) (a) Organic Reactions; Wiley: New York, 1959; Vol. 10, p 178. (b)
Dimroth, O.; Kraft, L.; Aichinger, K. Liebigs Ann. Chem. 1940, 545, 124.
(7) Synthesis of PDA-T and PDA-2T. Thiophenol (55.1 mg, 0.5 mmol)
was dissolved in dichloromethane (50 mL). In the solution, N,N′-diphenyl-
p-phenylenediimine (PDI, 129 mg, 0.5 mmol) dissolved in dichloromethane
(50 mL) was added using an additional funnel. The reaction mixture was
stirred at room temperature for 2 h. The orange color of the solution changed
to yellow. The solution was concentrated, and PDA-T (131 mg, 71%, brown
viscous liquid) and PDA-2T (11.3 mg, 6%, yellow crystal) were isolated
by silica gel column chlomatography (hexane:dichloromethane ) 3:1-1:
1). PDA-T: 1H NMR (400 MHz, DMSO-d6, TMS standard, 30 °C, ppm)
δ 8.06 (s, 1H), 7.34 (m, 5H), 7.32 (s, 1H), 7.18 (d, 1H, J ) 8.79 Hz), 7.14
(m, 4H), 6.97 (dd, 2H, J ) 2.44, 8.79 Hz), 6.90 (d, 2H, J ) 8.31 Hz), 6.86
(d, 1H, J ) 2.44 Hz), 6.81 (d, 2H, J ) 8.30 Hz), 6.74 (t, 1H, J ) 7.81 Hz),
6.70 (t, 1H, J ) 7.32 Hz); 13C NMR (100 MHz, DMSO-d6, TMS standard,
30 °C, ppm) δ 145.92, 143.47, 139.53, 134.25, 133.92, 131.26, 130.42,
129.51, 129.01, 128.89, 128.38, 124.25, 119.42, 119.27, 118.24, 117.55,
116.04, 114.98; IR (KBr) 3389 (NH), 1496 (phenyl); EI-MS 368 [M]+.
Anal. Calcd for C24H20N2S: C, 78.22; H, 5.47; N, 7.60. Found: C, 77.84;
H, 5.11; N, 7.35. PDA-2T: 1H NMR (400 MHz, DMSO-d6, TMS standard,
30 °C, ppm) δ 7.43 (s, 2H), 7.33 (m, 8H), 7.23 (m, 2H), 7.09 (t, 4H, J )
7.81 Hz), 6.98 (s, 2H), 6.77 (d, 4H, J ) 7.82 Hz), 6.72 (t, 2H, J ) 7.32
Hz); 13C NMR (100 MHz, DMSO-d6, TMS standard, 30 °C, ppm) δ 144.28,
136.91, 133.90, 130.85, 129.56, 128.87, 127.61, 127.44, 123.79, 119.32,
116.15; IR (KBr) 3366 (NH), 1507 (phenyl); EI-MS 476 [M]+. Anal. Calcd
for C30H24N2S2: C, 75.59; H, 5.08; N, 5.88. Found: C, 75.57; H, 4.71; N,
5.89.
Figure 1. Solvent effect in the reaction of PDI with thiophenol.
4 times greater than that in N-methylpyrrolidone (NMP). The
reaction rapidly proceeds in a nonpolar solvent by preventing
the stabilization of the nucleophile by solvation.
1
A combination of H-COSY and NOESY revealed that
PDA-2T was a disubstituted PDA with phenylthio groups
at the 2- and 5-positions. A nuclear Overhauser effect (NOE)
between the proton (a singlet peak at 6.98 ppm) on the central
phenyl ring and the proton (7.23 ppm) of the thiophenylene
ring at the o-position was observed. These results supported
the idea that 2,3- and 2,4-bis(phenylthio)-PDA were difficult
to form in this reaction. It is suggested that thiophenol was
preferentially substituted at the 5-position of the central
phenyl ring of PDI-T due to the steric hindrance and electron-
donating effect of the phenylthio group. This means that the
Michael-type addition should afford a linear thiophenylene
polymer in a polymerization reaction.
132
Org. Lett., Vol. 3, No. 1, 2001

As a synthetic strategy of the desired polymer, we selected
polyaddition of 4,4′-thiobisbenzenethiol (TB) to PDI-end-
capped TB (TB-2PDI) as shown in Scheme 2.
the reduction of the imine to the amine structure. The mixture
was poured into methanol to precipitate the polymer. The
PPS-PDA was isolated in a 60% yield as a white powder
and was soluble in dichloromethane, DMSO, THF, and NMP.
The molecular weight (Mw) was determined to be 5.4 × 103
on the basis of GPC (Mw/Mn ) 1.52). The temperatures for
a 10% weight loss (Td10%) and glass transition were 362 and
131 °C, respectively. The amine group (3386 cm-1) was
confirmed by the IR spectrum.
Scheme 2. Synthesis of Poly(thiophenylene) through a Michael
Addition
Polymerization via a Michael-type addition was also
1
confirmed by H NMR measurement.10 A phenylthio-PDA
unit and a bis(phenylthio)-PDA showed large differences in
the chemical shifts of peaks attributed to the amine protons.
In the spectrum of PDA-T, two peaks attributed to two amine
protons appeared at 8.06 and 7.32 ppm (Figure 2a). Similarly
TB-2PDA, which is the reduced form of TB-2PDI, was
synthesized by reaction of PDI (1.0 mmol) with TB (0.5
mmol) in dichloromethane at room temperature for 2 h.8 The
TB-2PDA was isolated by silica gel column chromatography
in a 31% yield. The obtained TB-2PDA was quantitatively
converted to the imine (TB-2PDI) by oxidation with Ca-
(OCl)2. The polymerization of TB-2PDI with TB proceeded
in dichloromethane at room temperature for 24 h to give the
corresponding polymer (PPS-PDA).9 The orange color of
the mixture disappeared during the polymerization due to
Figure 2. The 1H NMR spectra (400 MHz, DMSO-d6) of (a) PDA-
T, (b) PDA-2T, (c) TB-2PDA, and (d) PPS-PDA. The marked
peaks (*) are attributed to amine protons.
(8) Synthesis of TB-2PDA. 4,4′-Thiobisbenzenethiol (TB, 0.123 g, 0.5
mmol) was dissolved in dichloromethane (50 mL). In this solution, PDI
(0.260 g, 1.0 mmol) dissolved in dichloromethane (100 mL) was added
using an additional funnel. The reaction mixture was stirred at room
temperature for 2 h. The orange color of the solution changed to yellow.
The solution was concentrated, and TB-2PDA (112 mg, 31%, brown yellow
solid) was isolated by silica gel column chlomatography (hexane:dichlo-
romethane ) 3:1-1:1). TB-2PDA: 1H NMR (400 MHz, DMSO-d6, TMS
standard, 30 °C, ppm) δ 8.08 (s, 2H), 7.32 (s, 2H), 7.28 (d, 4H, J ) 8.31
Hz), 7.23 (d, 4H, J ) 8.31 Hz), 7.17 (d, 2H, J ) 8.30 Hz), 7.13 (t, 4H, J
) 7.32 Hz), 7.11 (t, 4H, J ) 7.32 Hz), 7.00 (dd, 2H, J ) 2.45, 8.79 Hz),
6.92 (d, 4H, J ) 7.32 Hz), 6.91 (d, 2H, J ) 2.45 Hz), 6.79 (d, 4H, J )
7.81 Hz), 6.74 (t, 2H, J ) 7.32 Hz), 6.68 (t, 2H, J ) 7.32 Hz); 13C NMR
(100 MHz, DMSO-d6, TMS standard, 30 °C, ppm) δ 145.76, 143.39, 139.53,
134.33, 134.25, 133.28, 131.54, 131.44, 129.19, 129.00, 128.84, 124.27,
119.87, 119.35, 118.27, 117.94, 116.17, 115.00; IR (KBr) 3390 (NH), 1499
(phenyl); FAB-MS 766 [M]+. Anal. Calcd for C48H38N4S3: C, 75.16; H,
4.99; N, 7.31. Found: C, 75.11; H, 4.69; N, 7.06.
(9) Synthesis of PPS-PDA. TB-2PDA (0.153 g, 0.2 mmol) was
dissolved in N-methylpyrrolidone (NMP, 4 mL). Calcium hypochlorite
(0.172 g, 1.2 mmol) was added, and the solution was stirred at room
temperature for 4 h. The orange color of the solution changed to yellow.
The reaction mixture was reprecipitated in water, and TB-2PDI (0.150 g,
98%, orange powder) was isolated by filtration. The oxidized one was
dissolved in dichloromethane (25 mL). In the solution, TB (50 mg, 0.2
mmol) dissolved in dichloromethane (25 mL) was added using an additional
funnel. The solution was stirred at room temperature for 24 h. The orange
color of the solution changed to white. The reaction mixture was
reprecipitated in methanol, and PPS-PDA (60%, yellow powder) was
isolated by filtration. PPS-PDA: 1H NMR (400 MHz, DMSO-d6, TMS
standard, 30 °C, ppm) δ 7.5-6.6 (m); IR (KBr) 3386 (NH), 1495 (phenyl).
to PDA-T, two peaks attributed to four amine protons at 8.08
and 7.32 ppm were confirmed in the spectra of TB-2PDA
(Figure 2c). On the other hand, one peak attributed to two
amine protons appeared at 7.43 ppm in the spectrum of PDA-
2T (Figure 2b). These spectra show that a peak around 8.0
ppm in a phenylthio monosubstituted PDA unit disappears
in a disubstituted one. Therefore, no peaks around 8.0 ppm
in the spectrum of PPS-PDA support conversion of the PDA
units in TB-2PDA to disubstituted ones by polymerization
on the basis of Michael-type addition (Figure 2d).
The electrochemical response of PPS-PDA was con-
firmed using the electrode modified by the polymer film (1.6
× 10-8 unit mol/cm2). The polymer shows a redox activity
in an acidic atmosphere (pH 0-4), which is similar to that
of PDI. A redox couple was observed at 0.48 V vs SCE at
pH 0.19 (Figure 3a). The redox cycle was stable for more
than 102 scans. The scanning rate in cyclic voltammetry is
(10) The PDA units of the compounds obtained are gradually oxidized
to PDI in the air with moisture, but they are stable over 6 months in a
refrigerator.
Org. Lett., Vol. 3, No. 1, 2001
133

that the electron-transfer process is associated with proton
transfer. On the basis of the Nernst plots, the slope in the
redox reaction was determined to be ca. -60 mV/pH (Figure
3b). These results indicate that the redox process involves
two electrons and two proton transfers per unit. The PPS-
PDA promotes a two-electron transfer accompanied by a two-
proton transfer and acts as a good electroresponsive material.
We developed a novel synthetic method for redox-active
poly(thiophenylene)s via a Michael-type addition. This
polymerization proceeded under mild conditions without
catalysts. The polymers obtained were good electroresponsive
materials. With this polymerization method, various redox-
active polymers are expected to be synthesized.
Acknowledgment. This work was partially supported by
Grants-in-Aid for Scientific research (Grants 11555253,
11136245, 11167273) from the Ministry of Education,
Science, Sports, and Culture, Japan, a Kanagawa Academy
of Science and Technology research Grant and the Kawakami
foundation, and a Grant-in-Aid for Unique Development for
Technology from Science and Technology agency.
Figure 3. (a) Cyclic voltammograms of PPS-PDA coated on a
glassy carbon electrode in 0.2 M Na2SO4/H2SO4 aqueous solution
(pH 0.19) and (b) the Nernst plots.
proportional to the oxidation and reduction peak potentials.
These results mean that excellent redox activity was main-
tained even in the thiophenylene polymer. The redox
potentials depend on the pH in the mixture, which means
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