Article
Chem. Mater., Vol. 22, No. 3, 2010 1023
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are of great interest to be used as the matrix of PEM. PBI-
based proton exchange membranes have been intensively
intermolecular interaction like polybenzothiazoles,
and thus sPBT could not form homogeneous membrane
by extrusion or by blow molding. Accordingly, the sPBT
membranes for PEM applications might be prepared only
by casting polymer solution. This demands that sulfo-
nated polybenzothiazoles exhibit good solubility as well
as high molecular weight in order to obtain good proces-
sability and mechanical properties. As a result, it is
significant to synthesize such sulfonated polybenzothia-
zoles and to evaluate whether they could be employed as
PEM materials or not.
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5,28-36
developed.
have also been investigated for PEM applications.
Polybenzoxazole based membranes
7-39
3
However, few polybenzothiazoles have been studied
as proton exchange membrane materials because of their
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poor processability.
Great attempts have been put
forth to enhance their solubility by incorporating
the bulky pendant groups or flexible linkage into the
resulting polybenzothiazoles, but the result was not
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satisfactory.
On the other hand, though polybenzothiazoles have
high tensile strength, tensile modulus, and thermal stabi-
lity, they showed poor compressive properties in addition
In this article, sulfonated polybenzothiazoles were prepared
by polycondensation of 2,5-diamino-1,4-benzenedithiol
dihydrochloride and bis(3-sulfonate-4-carboxyphenyl)
sulfone with bis(4-carboxyphenyl) sulfone or diphenyl
sulphone-2,5-dicarboxylic acid or 2,2-bis(4-carboxyphe-
nyl)hexafluoropropane. The effects of the structural moi-
eties such as diphenyl sulfone, hexafluoroisopropylidene,
and phenylsulfonyl pendant groups on the properties of
the resulting polymers were investigated. The incorpora-
tion of the phenylsulfonyl pendant groups or the flexible
hexafluoroisopropylidene moieties to the resulting sulfo-
nated polybenzothiazoles was expected to enhance the
solubility and to achieve high molecular weight products.
In this case, such sulfonated polybenzothiazoles could be
cast into homogeneous membranes and could be further
investigated as PEM. Their structure and properties
as PEM, especially their solubility, swelling, hydrolytic
stability, oxidative stability, and proton conductivity,
were studied in detail so as to evaluate whether they are
a promising PEM material or not.
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to poor processability.
These disadvantages heavily
limited their applications. To overcome these drawbacks,
polybenzothiazoles with sulfonic acid groups were pre-
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pared by direct polycondensation.
sized polymers were used as structural materials and were
The as-synthe-
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not evaluated as proton exchange membranes.
Furthermore, few studies relevant to sulfonated polyben-
zothiazoles were reported. It could also be found that the
characterization of their structure and properties is very
limited and that sPBT with high molecular weight as well
as good solubility have not been reported until now. In
addition, sulfonated polybenzothiazoles exhibit no soft-
ening behavior and glass transition prior to thermal
degradation because of their rigid structure and strong
(
(
(
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Synthesis of Diphenyl Sulfone-2,5-dicarboxylic Acid. 2,5-Di-
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