1070-4272/05/7805-0794+2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 5, 2005, pp. 794 !797. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5,
2005, pp. 810!813.
Original Russian Text Copyright + 2005 by Sazanov, Novoselova, Amsharov, Ugolkov, Andreeva, Gribanov.
AND POLYMERIC MATERIALS
Prospects for Using Polyacrylonitrile for Preparing
Carbonized Polymeric Composites
Yu. N. Sazanov, A. V. Novoselova, K. Yu. Amsharov, V. L. Ugolkov,
O. A. Andreeva, and A. V. Gribanov
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, Russia
Received January 27, 2005
Abstract-The thermochemical cyclization of different polyacrylonitrile samples prepared by radical and
anionic polymerization was studied by thermal analysis, spectroscopy, and AM1 semiempirical calculations.
The possibility of using polyacrylonitrile as a cocarbonizate for preparing mixed carbon composites with
nitrogen-containing polysaccharides was examined.
Our previous studies were aimed to enhance the
heat resistance of polymers by their compounding
with polyimides . Some of the carbonized resid-
ues showed fairly high coke numbers (CNs) and ex-
hibited properties deserving a special study. Another
heat-resistant polymer is polyacrylonitrile (PAN), with
which, as with polyimides, mixed composites with en-
hanced heat resistance and strength were prepared .
In the context of development of various carbon
materials based on polymers, it is interesting to exam-
ine the effect of PAN on the thermochemical carboni-
zation of other polymers and hence on the properties
of the resulting products. From the viewpoint of the
PAN reactivity, the most promising is the step of
thermal cyclization occurring in the range 2003300oC.
Despite numerous papers concerning this process, its
mechanism is not yet elucidated unambiguously. The
scheme of formation of [ladder] polymers as infinite
chains of cyclic sequences, postulated in early studies
, was not confirmed and gave way to the concept
 according to which cyclization of PAN yields
chains with the number of cyclic sequences not ex-
ceeding 8310. Attempts to consider the mechanism of
PAN cyclization taking into account the conformation
of macromolecules [17, 18] were not properly devel-
oped, as major attention was given to solution of
materials-science and processing problems. A number
of tentative schemes reflecting attempts to take into
account the features of production of real items, main-
ly fibers, were suggested .
Our goal was to develop procedures for preparing
cocarbonizates from PAN and cellulose derivatives.
The first step was to find the most probable routes
that could ensure incorporation of the PAN structure
into other polymers by their thermochemical reaction.
To this end, we modeled cyclization of PAN in the
absence of chemical additives (catalysts, oxidants,
accelerators). Solution of this problem is complicated
by the difficulties associated with preparation of PAN
samples free of oxygen-containing functional groups
remaining in the polymer after its isolation and puri-
fication. Such polymers cannot be prepared by radical
polymerization (r-PAN). Polymerization of acryloni-
trile by the anionic mechanism under definite condi-
tions yields samples whose thermal cyclization in an
inert atmosphere [20, 21] gives products containing no
impurities and volatile low-molecular-weight cycliza-
tion products. For such samples of anionic PAN
(a-PAN), the exothermic effect appreciably shifted
toward higher temperatures. Thus, the conditions of
PAN activation can correspond to the conditions of
thermochemical reactions with other polymers. The
most suitable for this purpose are cellulose deriva-
tives; their thermal degradation occurs most actively
in the same temperature range (2003300oC) as the
cyclization of PAN [22, 23].
Returning to the modeling of suitable PAN struc-
tures, we chose samples prepared by the radical and
anionic polymerization mechanism, with different
ratio of the atactic, isotactic, and syndiotactic struc-
tures [15, 24].