POLYSILOXANE STRUCTURES CROSS-LINKED WITH HYDROQUINONE AND PHLOROGLUCINOL
1411
Table 1. Gelation rate in the Si(OEt)4–H2O–EtOH–HCl
system at various amounts of HCl solution
All the above parameters were determined for
samples that did not crack in the course of drying and
measurements. The gel point was characterized by the
time after which the system lost mobility.
Amount SiO2 content of
of 0.01 N liquid oligomer,
State
of solidified
gel
*
t1
*
t2
Oli-
gomer
HCl, g
%
h
Thermal analysis was performed with a Q-1500D
derivatograph (Hungary). The samples were heated to
1000°C at a rate of 20 deg min–1.
1.1
59.13
98 106 Monolithic
V
1.2
57.90
44 48
IV
″
Electron-microscopic examination of xerogels was
performed with an EM-125 device at an accelerating
voltage of 75 kV.
*
(t1) Time of formation of the liquid oligomer with the maximum
attained SiO2 content at which the mixture remained mobile;
(t2) gelation time.
To prepare hybrid coatings by the sol–gel proce-
dure, to tetraethoxysilane hydrolyzate we added or-
ganic components: hydroquinone I (Vekton) or phloro-
glucinol II (Merck). We also used 1,4-bis(triethoxy-
silyloxy)benzene III and 1,3,5-tris(triethoxysilyloxy)ben-
zene IV prepared by the reactions of Si(OEt)4 with
hydroquinone and phloroglucinol in 2:1 and 3:1 molar
ratios, respectively, in the presence of CF3COOH as
catalyst, according to the general equation
Table 2. Physicochemical properties of polymer film samples
VII–XI*
Phenol
content,
g
Com-
posite
t,**
h
MH,
ρ,
W, %
Oligomer
kg mm–2
g cm–3
0.03
18
18
18
21
23
1.45
1.46
1.44
1.48
1.53
37
35
37
35
32
90
90
VII
VIII
IX
V
V
0.045
0.045
0.03
88
VI
VI
VI
96
X
0.03
101
XI
* Films prepared with (VII–IX) hydroquinone and (X, XI)
phloroglucinol.
1,4-Bis(triethoxysilyloxy)benzene III. A mixture
of 10.0 g (0.048 mol) of tetraethoxysilane (TEOS),
1.32 g (0.012 mol) of hydroquinone, and 0.2 g of
CF3COOH was refluxed for 4 h, after which the
released ethanol was distilled off. The residue was
distilled in a vacuum to obtain 2.5 g (yield 48%) of III,
bp 180–190°C (0.01 mm Hg). H NMR spectrum
(CDCl3): 6.88 s (4H, Har), 3.89 q (12H, –Si–O–CH2–),
1.23 t (18H, CH3).
**
(t) Time of film drying at 80°C.
in polypropylene jars with screwed caps (three samples
for each system) and kept for 2–4 days in a thermostat
at 90°C to obtain a xerogel (Table 1).
1
The formation of polymeric composites based on
products of the condensation of a mixture of oligo-
ethoxysiloxanols V and VI with hydroquinone and
phloroglucinol involves the following main reactions
(with hydroquinone as example):
1,3,5-Tris(triethoxysilyloxy)benzene IV was
prepared similarly from 10.0 g (0.048 mol) of TEOS,
1.0 g (0.008 mol) of phloroglucinol, and 0.2 ml of
CF3COOH. Yield 1.2 g (25%), bp 210–220°C (0.01
mm Hg). 1H NMR spectrum (CDCl3): 6.64 s (3H, Har),
3.85 q (18H, –Si–O–CH2–), 1.24 t (27H, CH3).
Compounds III and IV are readily hydrolyzable color-
less liquids with a weak odor.
To perform these reactions, to 0.5 g of a mixture
of polyethoxysiloxanols V or VI in dimethylacetamide
(DMAA) heated to 70–80°C we added a solution of hy-
droquinone I or phloroglucinol II in DMAA and 0.2 ml
of CF3COOH. The amount of hydroquinone was var-
ied from 0.015 to 0.075, and that of phloroglucinol,
from 0.01 to 0.04 g. The hot mixture was cast onto a
glass plate and dried at 80°C in a DMAA vapor for 1–
2 days. In the process, polymer films formed on the
glass surface. The physicochemical parameters of
some film samples are listed in Table 2.
To prepare a polysiloxane matrix, we used a
mixture of polyethoxysiloxanes V and VI prepared by
controllable hydrolytic polycondensation of tetraeth-
oxysilane under the conditions of acid catalysis.
To prepare oligomers V and VI, we took 9.8 g
(0.044 mol) of TEOS, 4.8 g (0.104 mol) of ethanol,
and 1.1 and 1.2 g of 0.01 N HCl, respectively. The com-
ponents were mixed in the following order: ethanol,
HCl solution, TEOS. The resulting mixture was placed
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 8 2008