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Preparation and properties of polyhedral oligomeric silsesquioxaneЦpolysiloxane copolymers.

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Full Paper
Received: 9 June 2009
Revised: 11 September 2009
Accepted: 11 September 2009
Published online in Wiley Interscience: 21 October 2009
(www.interscience.com) DOI 10.1002/aoc.1562
Preparation and properties of polyhedral
oligomeric silsesquioxane–polysiloxane
copolymers
Takahiro Gunjia∗ , Takahiro Shiodaa , Koji Tsuchihiraa , Hiroyasu Sekia ,
Takashi Kajiwaraa and Yoshimoto Abea,b
All siloxane-type siloxane–polyhedral oligomeric silsesquioxane [(HSiO3/2 )8 , T8 H ] copolymers were synthesized by the
dehydrogenative condensation of T8 H with diphenylsilanediol, tetraphenyldisiloxane-1,3-diol or silanol-terminated polydimethylsiloxanes in the presence of diethylhydroxylamine followed by trimethylsilylation. Coating films were prepared by
spin-coating of the coating solutions prepared from the dehydrogenative condensation products. The hardness of the coating
films was evaluated by a pencil hardness test and was found to increase up to 6H with increases in the curing temperature. Silica
gels were prepared by concentrating the coating solution following by pyrolysis. These silica gels showed a specific surface
area 449 m2 /g at 650 ◦ C corresponding to the formation of a silica network in response to combustion of the phenyl groups.
c 2009 John Wiley & Sons, Ltd.
Copyright Keywords: polyhedral oligomeric silsesquioxane; diphenylsilanediol; diethylhydroxylamine; dehydrogenative condensation; silica gel
Introduction
Appl. Organometal. Chem. 2010, 24, 545–550
∗
Correspondence to: Takahiro Gunji, Tokyo University of Science, Department
of Pure and Applied Chemistry, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
E-mail: gunji@rs.noda.tus.ac.jp
a Department of Pure and Applied Chemistry, Faculty of Science and Technology,
Tokyo University of Science, Tokyo, Japan
b Department of Food Science, Faculty of Health and Nutrition, Tokyo Seiei
College, Tokyo, Japan
c 2009 John Wiley & Sons, Ltd.
Copyright 545
Polyhedral oligomeric silsesquioxanes (POSS) consist of the
structure unit (RSiO3/2 )8 and have attracted considerable attention
from the perspective of synthesis and applications due to their
nano-sized three-dimensional structure consisting of a silica
backbone, an angstrom-sized cavity, high thermal stability and,
for R H, a reactive hydrosilyl group.[1 – 13] These features make
POSS molecules potential candidates for providing functional
nano-building blocks.
To date, many ocatasilsesquioxane derivatives have been
synthesized[13] and they may be classified into three groups:
(a) alkyl- and aryl-substituted cubes; (b) carbo-functional cubes;
and (c) sila-functional cubes. A large numbers of cubes belong
to groups (a) and (b). In group (a), the cubes are prepared
by the hydrolysis of trichloro- or trialkoxysilanes. The POSS
derivatives in group (b) are synthesized by the hydrosilylation of
the corresponding carbo-functional olefines with POSS prepared
by the hydrolysis of trichlorosilane.[14] Group (c) includes cubes
with sila-functional groups such as chloro and methoxy groups
together with hydrido and tetraalkylammonium oxy groups. For
example, (MeOSiO3/2 )8 is synthesized by the reaction of methyl
formate with (ClSiO3/2 )8 ,[15] which is derived by chlorination of
POSS.
These reactions were applied to the preparation of POSS-based
polymers. The hydrosilylation of octahydridooctasilsesquioxane,
T8 H , with the corresponding olefins is the simplest and the most
widely used technique to produce organic–inorganic hybrids.
Such organic–inorganic hybrids are also prepared by the reaction
of carbo-functional groups on silicon atoms, for example the
polymerization of methacryloyloxy groups for the compound
octakis(methacryloyloxypropyl)octasilsesquioxane. On the other
hand, the preparation of siloxane-based hybrids has been
insufficiently investigated due to the difficulty in synthesizing
sila-functionalized POSS derivatives through conventional means:
mesoporous silica materials were prepared by the hydrolytic
polycondensation of {[(EtO)3−n Men SiO]SiO3/2 }8 in the presence
of polymer surfactants.[16] Films with heat-resistivity and easily
modulate films with high heat resistance were prepared by
the reaction of (PhSiO3/2 )8 [(HO)PhSiO]2 with chloro-terminated
polydimethylsiloxane.[17]
We have reported the synthesis of octaalkoxylated T8 H
derivatives by the reaction of T8 H with alcohols in the presence of
diethylhydroxylamine.[18] In this reaction, alkoxy groups replaced
hydrido group in T8 H with the evolution of hydrogen gas. This
reaction suggested that T8 H -based hybrid materials could be
prepared by the reaction of T8 H with silanols. Since these hybrids
are composed of only a siloxane framework, we can expect them
to have high heat-resistivity.
Therefore, we report herein the synthesis and characterization
of T8 H –siloxane hybrid materials based on the reaction of T8 H
with silanols in the presence of diethylhydroxylamine according
to Scheme 1. More specifically, the syntheses of diphenylsilanediol (DPS)–T8 H copolymer (1), tetraphenyldisiloxane-1,3-diol
(TPDD)–T8 H copolymer (2), silanol-terminated polydimethylsiloxane (STPDMS) (MW 550)–T8 H copolymer (3), STPDMS (MW
1100)–T8 H copolymer (4) and STPDMS (MW 4200)–T8 H copolymer
T. Gunji et al.
(5), and the properties of siloxane coating films and silica gels, are
presented.
Experimental
Synthesis of 4
Reagents and Substrate
T8 H , (HSiO3/2 )8 , was synthesized by a previously described
method.[14] Other chemicals were of reagent grade or higher
and purified according to standard protocols.
Synthesis of 1
Into a 100 ml two-necked flask fitted with a reflux condenser,
T8 H 0.25 g (0.59 mmol), THF 50 ml and DPS 0.25g (1.18 mmol)
or 0.51 g (2.36 mmol) were charged. Diethylhydroxylamine 8 µl
(80 µmol) was added to this mixture and stirred for 2 h at room
temperature under a nitrogen atmosphere. Chlorotrimethylsilane
0.78 g (0.59 mmol) was then added and stirred for 0.5 h.
Triethylamine 0.88 g (0.59 mmol) was added to the mixture and
subjected to reflux for 0.5 h. Triethylamine–hydrogen chloride salt
was separated by filtration. The filtrate was concentrated under
reduced pressure and then poured into methanol with vigorous
stirring. After filtration, the residue was dried under reduced
pressure to give a white powder.
Spectral data of 1: 29 Si NMR (CDCl3 , ppm) δ 12 (Me3 SiO), −45
(Ph2 SiO2 ), −83 (HSiO3 ), and −109 (SiO4 ). IR (CCl4 , cm−1 ) 2294
(νSi−H ), 1100 (νSi−O−Si ).
Synthesis of 2
Into a 100 ml two-necked flask fitted with a reflux condenser,
T8 H 0.25 g (0.59 mmol), THF 50 ml and TPDD 0.49g (1.18 mmol)
or 0.97 g (2.36 mmol) were charged. Diethylhydroxylamine 8 µl
(80 µmol) was added to this mixture and stirred for 2 h at room
temperature under a nitrogen atmosphere. Chlorotrimethylsilane
0.78 g (0.59 mmol) was then added and stirred for 0.5 h.
Triethylamine 0.88 g (0.59 mmol) was added to the mixture and
subjected to reflux for 0.5 h. Triethylamine–hydrogen chloride salt
was separated by filtration. The filtrate was concentrated under
reduced pressure and then poured into methanol with vigorous
stirring. After filtration, the residue was dried under reduced
pressure to give a white powder.
Spectral data of 2: 29 Si NMR (CDCl3 , ppm) δ 12 (Me3 SiO), −45
(Ph2 SiO2 ), −83 (HSiO3 ) and −109 (SiO4 ). IR (CCl4 , cm−1 ) 2294
(νSi−H ), 1100 (νSi−O−Si ).
Synthesis of 3
546
Into a 100 ml two-necked flask fitted with a reflux condenser,
T8 H 0.2 g (0.47 mmol), THF 40 ml and STPDMS (MW 550) 0.52 g
(9.45 mmol) were charged. Diethylhydroxylamine 4 µl (40 µmol)
was added to this mixture and subjected to reflux for 1 h under a
nitrogen atmosphere. Chlorotrimethylsilane 0.61 g (5.6 mmol) was
then added and subjected to reflux for 1 h. Triethylamine 0.57 g
(5.6 mmol) was added to the mixture and subjected to reflux for
1 h.
The solution was concentrated to 5 ml under reduced pressure,
and triethylamine–hydrogen chloride salt was then separated by
filtration. The filtrate was poured into methanol with vigorous
stirring and then filtered. The residue was dried under reduced
pressure to give a white powder.
www.interscience.wiley.com/journal/aoc
Spectral data of 3: 29 Si NMR (CDCl3 , ppm) δ 13 (Me3 SiO), −22
(Me2 SiO2 ), −83 (HSiO3 ), and −109 (SiO4 ). IR (CCl4 , cm−1 ) 2276
(νSi−H ), 1100 (νSi−O−Si ).
Into a 100 ml two-necked flask fitted with a reflux condenser,
T8 H 0.2 g (0.47 mmol), THF 40 ml and STPDMS (MW 1100) 1.03 g
(9.45 mmol) were charged. Diethylhydroxylamine 4 µl (40 µmol)
was added to this mixture and subjected to reflux for 1 h under
a nitrogen atmosphere. Chlorotrimethylsilane 0.61 g (5.6 mmol)
was then added and subjected to reflux for 1 h. Triethylamine
0.57 g (5.6 mmol) was added to the mixture and subjected to
reflux for 1 h. The solution was concentrated to 5 ml under
reduced pressure and then diethyl ether 20 ml was added.
Triethylamine–hydrogen chloride salt was separated by filtration.
The filtrate was concentrated under reduced pressure to give a
colorless highly viscous liquid.
Spectral data of 4: 29 Si NMR (CDCl3 , ppm) δ 13 (Me3 SiO), −22
(Me2 SiO2 ), −83 (HSiO3 ), and −109 (SiO4 ). IR (CCl4 , cm−1 ) 2276
(νSi−H ), 1100 (νSi−O−Si ).
Synthesis of 5
Into a 100 ml two-necked flask fitted with a reflux condenser,
T8 H 0.2 g (0.47 mmol), THF 40 ml and STPDMS (MW 4200) 3.95 g
(9.45 mmol) were charged. Diethylhydroxylamine 4 µl (40 µmol)
was added to this mixture and subjected to reflux for 1 h under
a nitrogen atmosphere. Chlorotrimethylsilane 0.61 g (5.6 mmol)
was then added and subjected to reflux for 1 h. Triethylamine
0.57 g (5.6 mmol) was added to the mixture and subjected to
reflux for 1 h. The solution was concentrated to 5 ml under
reduced pressure and then diethyl ether 20 ml was added.
Triethylamine–hydrogen chloride salt was separated by filtration.
The filtrate was concentrated under reduced pressure to give a
colorless highly viscous liquid.
Spectral data of 5: 29 Si NMR (CDCl3 , ppm) δ 13 (Me3 SiO), −22
(Me2 SiO2 ), −83 (HSiO3 ), and −109 (SiO4 ). IR (CCl4 , cm−1 ) 2276
(νSi−H ), 1100 (νSi−O−Si ).
Preparation of Coating Films and Silica Gels
Into a 100 ml two-necked flask fitted with a reflux condenser,
T8 H 0.25 g (0.59 mmol), THF 50 ml and DPS 0.25 g (1.18 mmol)
or TPDD 0.49 g (1.18 mmol) were charged. Diethylhydroxylamine
8 µl (80 µmol) was added to this mixture and stirred for 2 h at
room temperature under a nitrogen atmosphere. The coating
solution was obtained by concentrating the reaction mixture to
10 wt%.
The coating film was prepared by spin-coating of the coating
solution on a silicon wafer (2000 rpm for 30 s) using a spincoating machine (Kyowariken K-359 S-1) followed by heating
in an electrical furnace at 100–700 ◦ C for 1 h under an air
atmosphere.
Silica gel powder was prepared by heating the fully concentrated
coating solution in an electrical furnace at 100–700 ◦ C for 1 h under
an air atmosphere.
Measurements
Gel permeation chromatography was carried out using a Shimadzu
LD-10AD with two Polymer Laboratory Mixed-D 250 × 20 mm
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2010, 24, 545–550
Polyhedral oligomeric silsesquioxane/polysiloxane copolymers
H
Si
O
Si OO
Si
O
Si H
O
O H
O Si
Si O
O
O
Si
O Si
H
X
H
H H
O Si
O
O Si
Si O Si
O
O
+ HO
O
O
Si
Si
O O
O
Si O Si
H
H H
H
H
T8H
R
(1) Et2NOH/ THF
Si O
R
H
n
(2) Me3SiCl, Et3N
H
DPS (R=Ph, n = 1)
O
O Si
O Si
O
O
Si O Si HO
OH
O Si
Si O
O
Si O Si O H
H
H
H
H
O Si
O Si
O H
Si O Si O
O
OH
O Si
O Si O
H
Si O Si O
X
X
X = -O(SiR2O)n-
H
1 (DPS/T8 )
TPDD (R=Ph, n = 2)
2 (TPDD/T8H)
STDMS (R=Me, n = 6, 13, 55)
3 (STDMS (MW 550)/T8H)
4 (STDMS (MW 1100)/T8H)
5 (STDMS (MW 4200)/T8H)
Scheme 1. Schematic figure for the synthesis of polyhedral oligomeric silsesquioxane–polysiloxane copolymers.
columns and a refractive index detector. Tetrahydrofuran was
used as an eluent.
The 29 Si NMR spectra were recorded using a Jeol ECP-500 (29 Si
at 99 MHz) spectrometer. Chemical shifts were reported as δ units
(ppm) relative to SiMe4 , and the residual solvent peaks were used
as the standard.
The Fourier transform infrared (FTIR) spectra were measured
using a Jasco FT/IR-6100 IR spectrophotometer using the KBr disk
method or CCl4 solution method. Differential thermogravimetric
analysis (TG-DTA) was performed by using MAC Science TGDTA2020S under an air atmosphere.
BET surface area was measured using a Shimadzu Gemini 2360.
Samples were degassed by heating under an nitrogen atmosphere
to 100 ◦ C for 1 h and then cooling to the room temperature before
the measurement.
The pencil-hardness was tested using the Yasuda Seiki
Seisakusho electric system pencil hardness tester no. 533-M1
according to Japanese Industrial Standard JIS-K5400. The hardness was evaluated in the increasing order of 6B, 5B, 4B, 3B, 2B, B,
HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H and 9H using the Mitsubishi
Pencil Uni series.
Results and Discussion
Results of the Synthesis of 1 and 2
Appl. Organometal. Chem. 2010, 24, 545–550
Molecular weight by GPCc
Compound
Molar ratiob
Yield (%)
Mw
Mw /Mn
2
4
2
4
93
42
84
54
45 000
11 000
27 000
9000
2.0
1.5
1.8
1.6
1
2
a Scale of operation: T H 0.25 g (0.59 mmol), THF 50 ml, Et NOH (8 µl,
8
2
80 µmol); time, 2 h; temperature, r.t. Silylation: Me3 SiCl (7.1 mmol,
14 mmol), Et3 N (7.1 mmol, 14 mmol). Time, 1 h. Temperature, r.t.
b
Molar ratio of DPS–T8 H or TPDD–T8 H .
c Calculated based on standard polystyrene.
ether, chloroform, carbon tetrachloride, benzene and acetone, but
insoluble in hexane and methanol.
The FTIR spectra of T8 H , DPS, and 1 are shown in Fig. 1.
Comparing the spectra of T8 H with 1, the decrease in the
absorption intensity due to νSi−H (2294 cm−1 ) and the broadening
of the absorption band due to νSi−O−Si (ca 1100 cm−1 ) support
the progress of the dehydrogenative reaction to form siloxane
networks. Moreover, comparing the spectra of DPS with 1, the
disappearance of the absorption band due to νO−H (3213 cm−1 )
suggests the formation of a siloxane network and the progress of
the trimethylsilylation of silanols.
The 29 Si NMR spectra of 1 and 2 are shown in Fig. 2. The
signals at around 12, −45, −83 and −109 ppm were assigned
to the Me3 SiO (M), Ph2 SiO2 (DPh ), HSiO3 (T), and SiO4 (Q) units,
respectively. The appearance of the signal due to the Q unit
supports the progress of the dehydrogenative reaction to form a
siloxane network, while the signal due to the T unit suggests the
presence of a remaining hydrosilyl group in 1. The peak areas of
M, DPh , T and Q signals were calculated to be 9, 7, 16 and 68%,
respectively, when the molar ratio was 2. The composition of T8 H
to DPS was calculated to be 0.62, which suggests that the siloxane
formation occurred by two pathways: the reaction between T8 H
and DPS and the reaction between two T8 H molecules, as shown
in Scheme 1.
The composition of the DPS and T8 H units was increased to 0.81
when the molar ratio of DPS to T8 H was increased to 4. Although
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
547
The results of the synthesis of 1 and 2 are summarized in Table 1.
Compounds 1 and 2 were synthesized by the same procedure
by changing the molar ratios of DPS or TPDD to T8 H to 2 or 4.
The progress of the dehydrogenative reaction was monitored by
the evolution of hydrogen gas when diethylhydroxylamine was
added to the system. Compound 1 was isolated as a white solid by
reprecipitation from methanol. When the molar ratio of DPS to T8 H
was 2, the yield of 1 was 93% and the weight-averaged molecular
weight (Mw ) was 45 000 Da. Both the yield and Mw decreased to
42% and 11 000 Da, respectively, when the molar ratio was 4. The
same behavior was observed for 2, which was isolated as a white
powder. The yield and Mw were 84% and 27 000 Da, respectively,
when the molar ratio of TPDD to T8 H was 2. The yield and Mw
decreased to 54% and 9000 Da, respectively, when the molar
ratio was 4. Compounds 1 and 2 were soluble in THF, diethyl
Table 1. Results for the preparation of DPS–T8 H and TPDD–T8 Ha
T. Gunji et al.
Table 2. Results for the preparation of STPDMS–T8 Ha
H
T8
Molecular weight by GPCb
HO(SiMe2 O)n H THF
Compound
(ml)
(Mn /n)
νSiH
3
4
5
DPS
νSiPh
νSiOH
νSiOSi
3000
2000
40
50
60
Mw
Mw /Mn
0.29/40
0.92/74
1.86/89
45 000
41 000
38 000
2.3
3.2
2.7
a
Scale in operation: T8 H 0.20 g (0.47 mmol), Et2 NOH 4 µl (40 µmol).
Molar ratio of STPDMS–T8 H = 2; time, 1 h; temperature, 80 ◦ C.
Silylation: Me3 SiCl 0.61 g (5.6 mmol), Et3 N 0.57 g (5.6 mmol); time,
2 h; temperature, 80 ◦ C.
b Calculated based on standard polystyrene.
1
4000
550/6
1100/13
4200/55
Yield
(g/%)
1000
Wavenumber/cm-1
Figure 1. FTIR spectra of T8 H , DPS, and DPS–T8 H (1) copolymer.
T8H
νSiH
Q
M
1
DPh
STDMS
T
TMS
νSiOH
δSiOMe
2
2
20
0
-20 -40 -60 -80 -100 -120
Chemical shift / ppm
νSiOSi
Figure 2. 29 Si NMR spectra of DPS–T8 H (1) and TPDD–T8 H (2) copolymers.
4000
we expected there to be complete consumption of the hydrosilyl
groups in T8 H by DPS or TPDD units, the yield and Mw decreased
by increasing the molar ratios of these diols. The reaction between
the hydrosilyl groups and silanol groups probably became less
favorable in response to increasing steric hindrance due to the
diphenylsilanoxyl or tetraphenyldisiloxanoxyl groups on the T8 H
unit. In addition, the reaction between two silanols is not favored
in the presence of diethylhydroxylamine to decrease Mw . The
same feature was also observed for the 29 Si NMR spectra of 2. The
compositions of the TPDD and T8 H units were calculated to be 0.54
and 0.92 when the TPDD to T8 H ratios were 2 and 4, respectively.
Results of the Synthesis of 3, 4, and 5
548
The results of the synthesis of 3, 4, and 5 are summarized in
Table 2. Compounds 3, 4 and 5 were synthesized by the same
procedure by changing the average length of the siloxane unit.
Compound 3 was isolated as a white solid by reprecipitation in
40% yield with a Mw of 45 000. Compound 4 was isolated as a
colorless highly viscous liquid in 74% yield with a Mw of 41 000.
Compound 5 was isolated as a colorless highly viscous liquid in
89% yield with a Mw of 38 000. Compounds 3–5 were soluble in
THF, diethyl ether, chloroform, carbon tetrachloride, acetone and
hexane but insoluble in methanol.
The FTIR spectra of T8 H , STPDMS (MW 550), and 3 are shown
in Fig. 3. Comparing the spectrum of T8 H with that of 3, the
www.interscience.wiley.com/journal/aoc
3000
2000
1000
Wavenumber/cm-1
Figure 3. FTIR spectra of T8 H , STDMS, and STPDMS–T8 H (3) copolymer.
decrease in the absorption intensity due to νSi−H (2276 cm−1 )
and the broadening of the absorption bond due to νSi−O−Si (ca
1100 cm−1 ) indicate the progress of a dehydrogenative reaction
to form siloxane networks. Moreover, comparing the spectrum
of STPDMS (MW 550) with that of 3, the disappearance of the
absorption peak due to νO−H (3327 cm−1 ) suggests the formation
of a siloxane network and the progress of trimethylsilylation of
silanols.
The 29 Si NMR spectrum of 3 is shown in Fig. 4. The signals at
around 13, −22, −83 and −109 ppm were assigned to the M,
DMe , T and Q units, respectively. The appearance of the signal
due to the Q unit supports the progress of the dehydrogenative
reaction to form a siloxane network, while the signal due to the
T unit suggests the presence of a remaining hydrosilyl group in
3. The peak areas of the M, DMe , T and Q signals were calculated
to be 7, 48, 19, and 26%, respectively. The composition of T8 H
and STPDMS (MW 550) was calculated to be 1 : 1.4, which implies
that the siloxane formation occurred by two different pathways:
the reaction between T8 H and STPDMS (MW 550) and the reaction
between two T8 H molecules, as shown in Scheme 1.
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2010, 24, 545–550
Polyhedral oligomeric silsesquioxane/polysiloxane copolymers
Table 3. BET surface area of gels
BET surface area (m2 /g)
DMe
Temperature
(◦ C)
Q
TMS
M
20
T
0
-20 -40 -60 -80 -100 -120 -140
Chemical shift / ppm
Figure 4. 29 Si
100
200
400
650
800
DPS/T8 H
TPDD–T8 H
<1
<1
2
449
8
<1
<1
1
294
3
NMR spectra of STPDMS–T8 H (3) copolymer.
100 °C
200 °C
300 °C
400 °C
500 °C
νSiOH
600 °C
700 °C
δSiOSi
νSiOSi
4000
3000
2000
1000
Wavenumber/cm-1
Figure 5. FTIR spectra of DPS–T8 H (1) silica gels on heat treatment.
Results of the Preparation of Films and Silica Gels
Appl. Organometal. Chem. 2010, 24, 545–550
Conclusions
All siloxane-type siloxane–polyhedral oligomeric silsesquioxane
copolymers were synthesized by the dehydrogenative condensation reaction of T8 H with diphenylsilanediol, tetraphenyldisiloxane1,3-diol or silanol-terminated polydimethylsiloxanes in the presence of diethylhydroxylamine followed by trimethylsilylation. The
progress of the dehydrogenative reaction was confirmed by infrared spectroscopy and 29 Si nuclear magnetic resonance of the
copolymers.
Coating films were prepared by spin-coating of the polymer
solutions, which were prepared by the dehydrogenative condensation of T8 H with diphenylsilanediol or tetraphenyldisiloxane1,3-diol. The hardness of the coating films was evaluated by a
scratching test, with the hardness increasing to 6H with increases
in the sintering temperature. In contrast, silica gels were prepared
by sintering the products, which were prepared by concentrating
the coating solution. These silica gels showed a small surface area
below 400 ◦ C, then a maximum surface area at 650 ◦ C, followed
by a decrease at 850 ◦ C. The surface area trend upon sintering
showed good agreement with the formation of a siloxane network
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
549
Films were prepared by using the reaction mixture of T8 H with
DPS or TPDD. Therefore, unreacted or remaining DPS or TPDD
would contribute to the formation of the films. Starting from both
the DPS–T8 H and –TPDD–T8 H systems, transparent coating films
were prepared with a sub-micrometer thickness.
The pencil-hardness of DPS–T8 H and –TPDD–T8 H films was
evaluated by pencil hardness tests. In the DPS–T8 H system, the
pencil hardness changed in the order of HB, 2H, 4H, 4H, 6H, 6H,
and 6H by heating at 100, 200, 300, 400, 500, 600, and 700 ◦ C,
respectively, with a maximum hardness of 6H. In the TPDD–T8 H
system, the pencil hardness changed in the order of B, H, 4H, 4H,
6H, 6H and 6H by heating at 100, 200, 300, 400, 500, 600 and
700 ◦ C, respectively, also with a maximum hardness of 6H. The
TPDD–T8 H films were softer than those of DPS–T8 H because of the
higher carbon contents of TPDD–T8 H compared with DPS–T8 H .
The FTIR spectrum of DPS–T8 H film is shown in Fig. 5. After
heating at 100 ◦ C, some characteristic absorption bands were
observed due to νSiOH , νCH , νSiH , νSi−Ph and νSi−O−Si . The absorption
band due to νSiOH disappeared, and the intensity of the absorption
band due to νSiH was decreased after heating at 300 ◦ C. The
absorption bands due to νCH and νSiH disappeared, and a
weak absorption band due to δSi−O−Si appeared at 500 ◦ C. The
absorption band due to νSiOH appeared again, and the intensity of
the absorption band due to δSiOSi was increased at 600 ◦ C. These
spectral changes correspond to the pencil-hardness of the coating
films, which is based on the thermal behavior of functional groups:
the increase of the pencil hardness at 300 ◦ C compared with that
of 200 ◦ C can be ascribed to the condensation of silanol groups
to form siloxane networks, while the increase at 500 ◦ C is due to
the elimination of phenyl groups and the subsequent siloxane
network formation. The same trend was observed for TPDD–T8 H
coating films on heating.
Silica gels were prepared by drying and heating the DPS–T8 H
and TPDD–T8 H coating solutions. The BET surface areas of the
DPS–T8 H silica gels are summarized in Table 3. The BET surface
areas were under the detectable limit at 100 and 200 ◦ C, 2 m2 /g at
400 ◦ C, 449 m2 /g at 650 ◦ C, and 8 m2 /g sintered at 800 ◦ C. The BET
surface areas of TPDD–T8 H silica gels were under the detectable
limit at 100 and 200 ◦ C, 1 m2 /g at 400 ◦ C, 294 m2 /g at 650 ◦ C and
3 m2 /g sintered at 800 ◦ C. In both systems, the maximum was
observed at 650 ◦ C. In both systems, the small surface areas below
400 ◦ C suggest the coagulation of T8 H and DPS or TPDD units
to form a dense material due to the relatively easy molding of
phenylsiloxane chains. On heating at 650 ◦ C, the phenyl group
was burned out to form a stiff silica network, which resulted in the
formation of porous silica gels. When the silica gels were sintered
at 800 ◦ C, it probably allowed the newly formed siloxane bridges
to densify and form a dense silica network.
T. Gunji et al.
in response to the combustion of phenyl groups and the formation
of a dense silica network on heating.
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