1070-4272/02/7506-0980 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 6, 2002, pp. 980!984. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 6, 2002,
Original Russian Text Copyright + 2002 by Salimgareeva, Sannikova, Kolesov, Leplyanin.
AND POLYMERIC MATERIALS
Influence of Dibenzyl-o-carborane on Radiation Aging
of Polymethyl Methacrylate
V. N. Salimgareeva, N. S. Sannikova, S. V. Kolesov, and G. V. Leplyanin
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences, Ufa, Bashkortostan, Russia
Received December 10, 2001; in final form, January 2002
Abstract-Radiation aging of polymethyl methacrylate produced in the presence of dibenzyl-o-carborane
was studied. The influence of dibenzyl-o-carborane addition on the thermomechanical properties of the result-
ing polymer was analyzed.
High-energy radiation significantly affects the phys-
icochemical characteristics of polymer materials. The
composition, structure, electrical conductivity, creep
rate, and tensile strength of a polymer are changed,
which results in deterioration of its performance. To
decrease or prevent these consequences, stabilizing
additives incorporated into the polymer chain or pres-
ent as mechanical impurities are added. Various clas-
ses of organic compounds show protective properties.
For example, polymethyl methacrylate (PMMA) is
stabilized with compounds containing bivalent sulfur
 and aromatic hydrocarbons . Owing to a va-
cant d orbital of sulfur and the p-electron system of
the benzene ring, aromatic and organosulfur com-
pounds act as [energy sponges] absorbing and dis-
sipating in the form of heat or fluorenscence the en-
ergy absorbed by the polymer. Aromatic compounds
effect intermolecular energy transfer without any sig-
nificant variations. Sulfur-containing compounds un-
dergo cleavage across the S3S (or C3S) bond to form
the corresponding stable thiyl radicals which deacti-
vate active polymer radicals initiating degradation
(or cross-linking) of macromolecules.
Organosulfur and aromatic compounds also exert
inhibiting effect on thermal degradation of irradiated
polymer, initiated by [defects] arising in the macro-
melecule (tertiary carbon atoms and unsaturation)
under the action of high-energy radiation [3, 4].
Radiation-induced chemical processes in polymers
are also affected by boron-containing compounds,
among which carboranes are of particular interest.
Carboranes are boron compounds with cage structure
necessarily incorporating one or more carbon atoms.
Owing to delocalization of valent electrons, boranes
exhibit properties typical of aromatic systems, such
as high thermal stability and low reactivity toward var-
ious agents . Their ability to absorb energy is used
in synthesis of radiation-resistant polymers to raise the
strength of adjacent bonds in the macrochain [5, 6].
For example, addition of carboranes to polyethylene
as a comonomer in copolymer of ethylene and isoprop-
ylene carborane supresses cross-linkings of macro-
molecules under the action of gamma radiation .
It was of interest to examine the influence of car-
boranes on the radiation resistance of polymethyl
methacrylate for the example of dibenzyl-o-carborane
was synthesized by the procedure described in ;
mp 1513152oC; compound with limited solubility in
methyl methacrylate (MMA) and polymethyl meth-
acrylate (PMMA); the solubility of DBOC in MMA is
approximately 15%, and the compatibility of DBOC
with PMMA is preserved at concentrations not ex-
ceeding 10 wt %.
The characteristics of PMMA were studied on
block samples produced by polymerization of MMA
in the bulk at 40oC until complete conversion of
the monomer in the presence of 0.05 wt % initiating
agent (dicyclohexyl peroxydicarbonate, CPC) and up
to 10 wt % DBOC.
The polymerization kinetics was studied by dila-
tometry at 40 + 0.2oC. To remove the stabilizing