AND POLYMERIC MATERIALS
Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 11, pp. 1779−1784.
Pleiades Publishing, Ltd., 2013.
Original English Text © V.V. Semenov, 2013, published in Zhurnal Prikladnoi Khimii, 2013, Vol. 86, No. 11, pp. 1831−1836.
Heat Resistant Coatings
Based on Phosphorus-Containing Organosilicon Varnish
V. V. Semenov
Razuvaev Institute of Organometallic Chemistry, Nizhni Novgorod, Russia
Received October 23, 2013
Abstract—The phosphorus-containing organosilicon varnish was synthesized by heating 3-aminopropyltriethoxysi-
lane, triphenyl phosphate, and octamethylcyclotetrasiloxane. Heat-resistant coatings formed on its basis were
investigated by thermogravimetry, electronic absorption spectroscopy, IR spectroscopy, gas chromatography–mass
spectrometry, and atomic force microscopy.
Varnish coatings based on organic oligomers and poly-
mers  in a prolonged operation at elevated temperatures
and limited access of air result in electroconductive
carbonaceous coke. With good access of air an oxidation
to volatile products occurs, whereby the product loses
its protective coating. As a result of electrical insulation
breakdown there is a conductive carbon trace. In contrast
to purely organic polymers organosilicone polymers in
heating form a crosslinked polysiloxane , which is an
excellent insulator. This explain their widespread usage
[3, 4] as insulators of copper wires subjected to high
temperatures in electric motors and generators.
Dependence of a weight loss after heating for 24 h,
which characterizes the resistance of organic and organo-
silicone polymers [1, 5] to thermal oxidative degradation,
is shown in Fig. 1. At 250°C indicators for phenol-
formaldehyde resin, nitrile rubber, and polyphenylmeth-
ylsiloxane (PPMS) are comparable and do not go beyond
10%, but the epoxy resin has lost 23% by weight, and
Increasing the temperature to 350°C transforms all the
organic polymers into thermally unstable. They lose from
68 to 94% by weight, while PPMS, only 33%. Polyalu-
mosiloxane (Al-PPMS) is of the maximum resistance.
Thermal and thermal oxidative stability of the ﬁ lms
obtained from the phenyl and phenylmethyl polysiloxanes
reaches 400°C. However, these highest possible opera-
tional parameters are implemented only after prolonged
high-temperature curing of an applied liquid layer .
Production of radio components for automatic assembly
lines requires the development of fast hardening com-
positions. Curing time of 15–17 min and temperature
150–170°C are considered as acceptable range.
The proposed coating material  does not refer to
polyorganosiloxanes but to phosphorus-containing or-
ganosilicon oligomers curable according to mechanism
of sol-gel polymerization. The mixture of oligomers was
obtained in one step from two commercial products:
3-aminopropyl triethoxysilane (APTES) and triphenyl
phosphate (TPP) (see the scheme).
The mixture is a pale yellow oily liquid, which is
cured in a thin layer spontaneously due to moisture in the
, and it forms a clear coating on a substrate surface.
Structuring time varies depending on the thickness and
temperature of from 15 minutes to 8 hours. Undiluted
oligomers mixture on a glass substrate forms a layer
thickness of 50–70 μm, which is cured at room tem-
perature for 6–8 h, at 150°C, for 15–17 min. Dilution of
oligomers with ethylcellosolve or toluene (1 : 1 to 1 : 2
by volume) allows forming a thin ﬁ lm (10–20 μm) and
shortenining the time of their structuring to 2–3 hours
at 20–25°C and 10–12 minutes at 150°C. Fast curing of
the mixture of oligomers is due to the presence in it of a
large number of amidophosphate fragments, which play