Received: September 3, 2015 | Accepted: September 18, 2015 | Web Released: December 5, 2015
CL-150837
P O MsOH-mediated Facile Synthesis of Semi-aromatic Polyketones
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5
Bearing 1,4-Cyclohexanediyl Units
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1
2
2
Katsuya Maeyama,* Ayumu Katada, Nanako Mizuguchi, and Hiroshi Matsutani
Department of Polymer Science and Engineering, Graduate School of Science and Engineering, Yamagata University,
-3-16 Jonan, Yonezawa, Yamagata 992-8510
Polymer Technology Group, Tsukuba Research Laboratory, Hitachi Chemical Co., Ltd., 48 Wadai, Tsukuba, Ibaraki 300-4247
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4
2
(
E-mail: maeyama@yz.yamagata-u.ac.jp)
Direct polycondensation of trans-1,4-cyclohexanedicarbox-
ylic acid with several electron-rich arenes in a P O CH SO H
P2O5-MsOH
0 oC, 24 h
O
C
O
C
H-Ar-H
a-e
+
HO2C
CO2H
Ar
2
5
3
3
6
n
(MsOH) mixture gave semi-aromatic polyketones bearing
1
2
3a-e
OMe
1,4-cyclohexanediyl units in the main chains. The resulting
OR
polyketones have sufficiently high thermal stability and
excellent transparency.
O
O
-Ar-
:
RO
MeO
1
1
a/3a(R = Me)
b/3b(R = Pr)
1d/3d
1e/3e
Aromatic polyketones have received much attention from
the viewpoint of their excellent chemical and physical stability,
high mechanical strength, and biocompatibility.1 In general,
almost all aromatic polyketones, including poly(ether ether
ketone) (PEEK), have pale yellow or brown color. If colorless
and transparent aromatic polyketones had been developed, they
would have been applied in high-performance optical materials
such as transparent films and camera lenses. One of the effective
approaches is the replacement of part of the aromatic units with
alicyclic ones, and various semi-aromatic polymers have been
1c/3c(R = Hex)
,2
Scheme 1. P O MsOH-mediated direct polycondensation of
electron-rich arenes 1a1e with trans-1,4-cyclohexanedicarbox-
ylic acid (2).
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affording the corresponding aromatic polyketones 3d and 3e. IR
measurements of polyketones 3a3e disclosed a peak at 1671
1672 cm , which is assignable to the ketonic C=O stretching
vibration. Structural identification, that is regioselectivity, was
¹
1
3
developed thusly. Turner et al. reported aromatic poly(ether
1
sulfone)s and poly(ether ether ketone)s bearing 1,4-cyclohex-
anediyl units using 1,4-cyclohexanedicarboxylic acid as the
confirmed by H NMR spectral measurements of the model
compounds of monomers 1a, 1d, and 1e with cyclohexanecar-
boxylic acid (See Supporting Information, 5a, 5d, and 5e). As
for 1a, the reaction proceeded at the 5,5¤-positions regioselec-
tively, due to the strong electron-donating effect of methoxy
groups. As for 1d, the reaction proceeded regioselectively at the
p-positions, due to the electron-donating effect of the ether unit.
No reaction at the o-positions relative to the ether unit
proceeded. As for 1e, the reaction proceeded at the 5,5¤-
positions, i.e., the p-positions relative to the methoxy groups
because methoxy groups are more electron-donating than
aryloxy ones. On the other hand, 1,4-dimethoxybenzene or
1,3-dimethoxybenzene, which is activated by two methoxy
groups, was inapplicable to these polymerizations. In fact, 1,3-
dimethoxybenzene reacted with 2 equimolar amounts of cyclo-
hexanecarboxylic acid in P O MsOH to form only a mono-
4
a
starting material. We also reported the synthesis of aromatic
poly(ether ketone)s bearing alicyclic units in the main chains
through nucleophilic aromatic substitution polymerization be-
4
b
tween bisphenols and bis(fluorobenzoyl)cycloalkanes. The
resulting polyketones have relative transparency against typical
aromatic polyketones.1 There is, however, ample room for
further improvement of transparency. This motivated us to
synthesize highly transparent semi-aromatic polyketones through
another polymerization method, i.e., electrophilic aromatic
substitution polymerization.
,2
In this letter, we report the facile synthesis of transparent
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semi-aromatic polyketones through P2O5MsOH -mediated di-
rect polycondensation between electron-rich arenes 1a1e and
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trans-1,4-cyclohexanedicarboxylic acid (2), which is one of the
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simple and commercially available alicyclic dicarboxylic acids
acylated product (See Supporting Information, 6f). After the
first acylation of 1,3-dimethoxybenzene proceeded, the electron
density of the monoacylated arene decreased, which would
prevent further acylation of the monoacylated product. In
contrast, 2,2¤-dimethoxybiphenyl (1a) reacted with 2 equimolar
amounts of cyclohexanecarboxylic acid in P2O5MsOH to
form the diacylated product along with trace amounts of the
monoacylated product. Although the electron density of the
directly acylated benzene ring of the monoacylated arene
decreases, the electron density of the other benzene ring does
not decrease so much due to the twisting structure between two
benzene rings, i.e., less overlapping between two benzene rings,
which maintains both the reactivity and regioselectivity at the
(
Scheme 1).
2
,2¤-Dimethoxybiphenyl (1a)2a was allowed to react with
trans-1,4-cyclohexanedicarboxylic acid (2) in a P2O5MsOH
mixture as a mediator and a solvent at 60 °C for 24 h. As the
reaction proceeded, the reaction mixture turned highly viscous.
The viscous reaction mixture was poured into methanol for work
up. The resulting polymer 3a was clearly a white powder, but
was insoluble in CHCl3. To improve the solubility of the
polyketone, 2,2¤-alkoxybiphenyls with long alkyl chains 1b and
1c were employed. The resulting polyketones 3b and 3c were
white powders that dissolved completely in CHCl3. As other
2
a
electron-rich acyl-acceptant monomers, diphenyl ether (1d)
and 2,2¤-dimethoxydiphenyl ether (1e)2a were also employed,
5¤-position of the other benzene ring. As for 1d and 1e, the
2a
© 2015 The Chemical Society of Japan | 1783
Maeyama, Katsuya
