1070-4272/01/7407-1169$25.00C2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 7, 2001, pp. 1169!1172. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 7,
2001, pp. 1137!1141.
Original Russian Text Copyright + 2001 by Sviderskii, Voronkov, S. Klimenko, V. Klimenko.
AND INDUSTRIAL ORGANIC CHEMISTRY
Thermal Transformations of Polymetallosiloxanes Prepared
by the Sol!Gel Procedure
V. A. Sviderskii, M. G. Voronkov, S. V. Klimenko, and V. S. Klimenko
Kiev Polytechnic Institute, National Technical University of Ukraine, Kiev, Ukraine
Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences, Irkutsk, Russia
Received October 30, 2000; in final form, April 2001
Abstract-Thermal stability and crystal structure transformations of polyalkoxymetallosiloxanes (metallo-
silicas) prepared by the sol3gel procedure involving hydrolytic polycondensation of tetraethoxysilane with
salts and oxides of Group I, II, and IV metals (Cu, Zn, Hg, Sn, and Pb) were studied.
Incorporation of metal atoms (M) into polysiloxane
structure to form Si3O3M3O3Si groups strongly
affects thermal and hydrolytic stability, adhesion, and
cohesion of the initial silicon polymers and imparts to
them biological activity and some other important
properties . This is due to changes in the steric
and stereoelectronic structure of their crystal lattice
and changes in the nature of the intramolecular inter-
actions. The strength of the Si3O3M fragments ap-
preciably depends on the nature of the heteroatom M
and its ability to form M 4 O coordination bonds .
Although the structure and properties of hetero-
siloxanes are extensively studied, precise prediction of
their thermal and chemical transformations is difficult
and requires special investigation. This is, in particu-
lar, due to the fact that the structure and properties of
polymetallosiloxanes depend on the preparation proce-
dure and can strongly differ even at almost identical
composition [1, 4].
Taking into account theoretical and practical im-
portance of this problem, we studied thermal trans-
formations of polymetallosiloxanes prepared previous-
ly by the sol3gel procedure .
Heterosiloxanes (polyalkoxymetallosiloxanes or
metallosilicas) were prepared by hydrolytic polycon-
densation of partially hydrolyzed tetraethoxysilane
(Etilsilikat-40) with Group I, II, and IV metal com-
pounds in the presence of NH
OH as a catalyst. The
products were dried at 120+0.5oC to the xerogel state.
The initial metal compounds were CuO, CuSO
O, and finely dispersed zinc powder.
We studied thermal transformations of the metallo-
siloxanes during programmed heating in air with a
10 deg min
rate (MOM derivatograph, Hungary).
The structural transformations were studied by powder
X-ray diffraction (DRON-3 diffractometer).
Incorporation of metal atoms into the siloxane
lattice appreciably enhances the thermal stability of
silica xerogels. The DTA curves of ethoxylated xero-
gel contain a weak exothermic peak at 265oC, whereas
several exothermic effects are observed at higher tem-
peratures in the DTA curves of the tested metallo-
siloxanes (Table 1). This is likely due to shielding of
the residual ethoxy groups by the Si3O3M3O3Si frag-
ments and indicates higher thermooxidative stability
of the heterosiloxanes.
The exothermic peaks in the DTA curves of the
metallosilica xerogels containing copper, zinc, and
mercury(II) heteroatoms are usually broad (diffuse)
with the main maxima at 700oC. These peaks are
probably due to several parallel and consecutive
(1) Thermal degradation of residual ethoxy groups
shielded by the Si3O3Si and Si3O3M bonds. This is
confirmed by the weight loss at 2003600oC (Table 2).
(2) Formation of additional Si3O3M3O3Si groups
in this temperature range by the following condensa-
=SiOEt + XM36=Si3O3M + EtX,
=SiOH + XM36=Si3O3M + HX,