Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 2, pp. 162−166.
Pleiades Publishing, Ltd., 2013.
Original Russian Text © V.F. Burdukovskii, B.Ch. Kholkhoev, D.M. Mognonov, 2013, published in Zhurnal Prikladnoi Khimii, 2013, Vol. 86, No. 2, pp. 178−182.
AND INDUSTRIAL INORGANIC CHEMISTRY
Preparation of Polybenzimidazoles by Oxidative
Dehydrocyclization of Polyamidines
V. F. Burdukovskii, B. Ch. Kholkhoev, and D. M. Mognonov
Baikal Institute of Nature Management, Siberian Branch, Russian Academy of Sciences, Ulan-Ude, Buryatia, Russia
Received August 29, 2012
Abstract—Dehydrocyclization of polyamidines into polybenzimidazoles under the action of various oxidants was
studied. The strength and proton conductivity of membranes based on a blend of the polybenzimidazole obtained
with poly(amino imide) resin were determined.
Polybenzimidazoles (PBIs) attract growing attention
among diverse heat-resistant polyheteroarylenes, because
PBI-based membranes combine the capability to preserve
mechanical strength at high operation temperatures with
proton conductivity, which allows their use in fuel cells
Traditional methods for preparing aromatic PBIs
are based on reactions of aromatic tetraamines with
dicarboxylic acids or their derivatives. The synthesis is
performed under severe conditions: prolonged heating
at high temperature in an inert atmosphere and then in a
vacuum . The use of tetraamines involves problems
with selective polyacylation of amino groups, which
can lead to branching and cross-linking. It should also
be taken into account that tetraamines are expensive,
difﬁ cultly available, unstable to oxidation, and toxic.
Therefore, search for an alternative method for preparing
PBIs from stable and available monomers under milder
conditions is a topical problem.
As one of such methods, Brand et al.  outlined
interesting possibility of preparing PBIs by oxidative
dehydrocyclization of polyamidines (PADs) synthesized
by migration copolymerization of dinitriles with diamines.
However, the polymers formed had low molecular weight
and were incapable of forming ﬁ lms and press materials.
Previously , using ionic liquids based on 1,3-dialkyl-
substituted imidazolium, we prepared film-forming
PADs of higher molecular weight. Therefore, it seemed
appropriate to study in detail oxidative dehydrocyclization
of these PADs and to analyze the operation characteristics
of PBI membranes prepared by this procedure:
The idea of preparing PBI from PAD hydrochloride
I consisted in generation from the azomethine bond in
PAD of an uncharged electron-deﬁ cient species, nitrene
II, which, being extremely reactive, undergoes addition
at the o-position of the benzene ring, thus closing the
benzimidazole heteroring III. The assumed mechanism of
cyclization of PAD into PBI is shown below (see scheme).
The transformation was performed in solution using