1070-4272/01/7401-0154$25.00C2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 1, 2001, pp. 154 !156. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 1,
2001, pp. 147!150.
Original Russian Text Copyright + 2001 by Grachek, Bukanova, Smolyakov, Lukashik.
AND POLYMERIC MATERIALS
Boric Acid Esters as Fungicide Additives and Heat Stabilizers
of Elastomers Based on Siloxane Rubber
V. I. Grachek, N. N. Bukanova, A. V. Smolyakov, and A. N. Lukashik
Institute of Physical Organic Chemistry, Belarussian National Academy of Sciences, Minsk, Belarus
Received August 4, 2000
Abstract-New boric acid esters with an azomethine bond were prepared. These compounds exhibit an
efficient fungicide and heat-stabilizing effect on elastomers based on SKTV-1 rubber.
Aging and stabilization of polymers is still an
urgent problem. There is a growing interest in multi-
functional stabilizers containing in the same molecule
a number of functional groups acting by different
mechanisms . It is known that organoboron com-
pounds exert a fungicide [2, 3] and heat-stabilizing
effect  on polymeric materials. With the aim to
develop promising fungicide additives and heat stabi-
lizers for siloxane rubber, we prepared new boric acid
esters containing azomethine groups, in view of the
fact that compounds containing C=N groups are effi-
cient heat-stabilizing agents for polysiloxanes .
Borates were prepared by heating of a mixture of
boric acid with pyrocatechol and hydroxy compounds
containing azomethine groups at 70380oC in benzene
with heteroazeotropic distillation of the released water.
The structure of the products was proved by IR and
H NMR spectroscopy, mass spectrometry, and ele-
The IR spectra of the compounds contain bands at
1040+ 10 and 1350+10 cm
characteristic of the
symmetrical and antisymmetrical vibrations of the
B3O group and at 1090+ 10 and 1240+10 cm
acteristic of the symmetrical and antisymmetrical vi-
brations of the C3O group. The band at 1640+5cm
is due to the CH=N vibrations, and that at 1754 cm
to the stretching vibrations of the ester carbonyl (in
III and IV).
H NMR spectra of the compounds are given
in Table 1. The proton signals of the pyrocatechol ring
are observed at 6.20+ 0.04 and 5.60+0.02 ppm. The
azomethine proton gives a signal at 8.15+ 0.03 ppm.
The chemical shifts of protons of the substituents are
also given in Table 1. In addition, the spectra of III
and IV contain signals at 1.23 and 3.58 ppm, belong-
ing to the methyl and methylene protons of the ethoxy
The mass spectra of the boric acid esters contain
molecular peaks (Table 1), but their intensity is rela-
tively low. The molecular peaks of all the compounds
have a close intensity. Apparently, the extent and
character of electron density delocalization in substit-
uents, affecting the stability of the compounds to elec-
tron impact, yield of molecular ions, and formation of
stable radicals, are similar in all the compounds.
The most characteristic and intense peaks in the
mass spectra of the borates are those at m/z 135, 108,
92, and 65. They presumably originate from the
moiety, common for all the compounds.
All the compounds contain a strong peak at m/z 65,
corresponding to the C
ion, which can form only
by rearrangement with hydrogen transfer from one
part of the molecule to another.
The physicochemical characteristics of the com-
pounds are listed in Table 2.
The synthesized esters were added to rubber stocks
based on SKTV-1 siloxane rubber. The optimal con-
tent of the additives was 1 wt part per 100 wt parts of
rubber. With larger amounts of the additives, the
physicomechanical properties of the rubbers get
worse. The rubber stocks were prepare on rollers
using standard formulations. Boric acid esters do not
exude to the surface of siloxane rubber and do not
affect the peroxide curing of rubbers.
Rubbers with triaryl borate additives were tested
for fouling with mold fungi. The fungus resistance of
rubbers (extent of fungus growth on rubber samples)
was evaluated in a six-point scale [GOST (State
Standard) 9049375]. The results are listed in Table 3.
It is seen that the borate-containing rubbers are fouled