Preparation and properties of polyimide-silica hybrid films with conjugation of the polyimide and silica by a sol-gel process using 3-(triethoxysilyl)propyl succinic anhydride

Article abstract of DOI:10.1016/j.reactfunctpolym.2010.11.015

New polyimide-silica hybrid materials were prepared using the polyamic acid synthesized by copolymerization of 3,3′,4,4′- benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-oxydianiline (ODA) and an A₂A′-type tri-functional amine, 1,1-bis(4-(

Full text of DOI:10.1016/j.reactfunctpolym.2010.11.015

Reactive & Functional Polymers 71 (2011) 85–94
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Reactive & Functional Polymers
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Preparation and properties of polyimide–silica hybrid films with conjugation
of the polyimide and silica by a sol–gel process using 3-(triethoxysilyl)propyl
succinic anhydride
⇑
Yoshikatsu Shiina, Atsushi Morikawa
Department of Biomolecular Functional Engineering, Ibaraki University, Hitachi, Ibaraki 316-8511, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
New polyimide–silica hybrid materials were prepared using the polyamic acid synthesized by copoly-
merization of 3,30,4,40-benzophenonetetracarboxylic dianhydride (BTDA), 4,40-oxydianiline (ODA) and
an A2A0-type tri-functional amine, 1,1-bis(4-(aminophenoxy)phenyl)-1-(4-(4-amino-2-trifluoromethyl-
phenoxy)phenyl)ethane (1) (BTDA:ODA:1 = 7:6:1 in the molar). 3-(Triethoxysilyl)propyl succinic anhy-
dride(TESSA) was reacted with amino groups in polyamic acid to introduce ethoxysilyl moiety which
act as conjugation site for silica. The polyimide–silica hybrid films were prepared by a sol–gel reaction
of tetraethoxysilane (TEOS) in a solution of the polyamic acid, followed by thermal imidation. Self-stand-
ing films were obtained with up to 50 wt.% silica, and transparent films were obtained at up to 40 wt.%
silica. Dynamic-mechanical and mechanical analyses were carried out to examine the properties of
hybrid films.
Received 21 September 2010
Received in revised form 10 November 2010
Accepted 11 November 2010
Available online 16 November 2010
Keywords:
Polyimide–silica hybrid
Sol–gel reaction
A2A0-type tri-functional amine
3-(Triethoxysilyl)propyl succinic anhydride
Conjugation site
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
acids with the alkoxysilyl group, which acted as conjugation site
for silica [16,17,19,22,23]. These polyamic acids with the alkoxysi-
Polyimides are known to be reliable at high temperature poly-
mers that exhibit superior mechanical and electrical properties
[1]. Because of these excellent characteristic, polyimide have been
used in aerospace, electronic and high-tech industries [2,3].
Organic–inorganic hybrids are attractive materials because they
generally possess desirable characteristics that are associated with
organic and inorganic compounds, such as heat, mechanical and
electrical advantage. In particular, thermal stability of organic
compound is enhanced through the incorporation of inorganic
moiety in the hybrid material. In this regard, hybridizations of
organic materials with inorganic compounds have also focused
on the modification of polyimides to improve their properties
[4–11]. One attractive method for hybridization with inorganic
compounds is the sol–gel process [12–15]. Polyimide–silica hybrid
materials were prepared by the hydrolysis and polycondensation
of tetraalkoxysilane in a polyamic acid solution, followed by ther-
mal treatment [16–23]. Preparation using polyamic acids without
conjugation for silica, resulted in films with high silica content that
were opaque due to the phase separation; additionally, these hy-
brid films exhibited poorer mechanical properties relative to pris-
tine polyimide [18]. Transparent and tough hybrid films with high
silica contents were prepared by a sol–gel reaction using polyamic
lyl groups were prepared by the reaction of diamines having alk-
oxysilyl groups with dianhydrides and the reaction of polyamic
acid with commercially available coupling agents. As the synthesis
of diamines having ethoxysilyl group is complicated due to the
necessity of multi-step reactions [19], polyamic acids having the
alkoxysilyl group have been more frequently prepared with
commercially available coupling agents, such as 3-aminopropyltri-
methoxysilane(APrTMS), 3-aminopropyltriethoxysilane(APrTEOS)
and p-aminophenyltrimethoxysilane(APTMS) [16,17,22,23]. The
polyimide–silica hybrid materials with conjugation between the
polyimide and the silica were prepared by a sol–gel reaction in a
solution of polyamic acid terminated with APTMS and APrTEOS
[16,17] and hyperbranched polyamic acid modified with APrTEOS
[22,23].
In this study, polyimide–silica hybrid films were prepared using
polyamic acid from BTDA, ODA and the A2A0-type tri-functional
amine 1 (BTDA:ODA:1 = 7:6:1 in the molar). As the ratio between
anhydride and amino groups in the monomers was 14/15, free
amino groups existed in the polyamic acids. The A2A0-type tri-func-
tional amine 1 was used to avoid gelation during polycondensa-
tion. Triethoxysilyl groups, which acted as conjugation site for
silica, were introduced into the polyamic acid by reaction of the
amino groups with TESSA. Polyimide–silica hybrid films were pre-
pared by a sol–gel reaction with TEOS in the polyamic acid solu-
tion, and by heating the resulting film at 300 °C. The polyimide
⇑
Corresponding author. Tel.: +81 294 38 5070; fax: +81 294 38 5078.
E-mail address: morikawa@mx.ibaraki.ac.jp (A. Morikawa).
1381-5148/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2010.11.015

86
Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
based on BTDA–ODA has five carbonyl groups in the repeating
units, and was thought to be suitable for hybridization with hydro-
philic silica.
evaporated under a reduced pressure of 15–25 torr. After 150 ml
of water was added to the residue, the mixture was extracted twice
with 160 ml of dichloromethane. The combined extract was dried
over anhydrous magnesium sulfate, and the solvent was evapo-
rated. After the residue was purified by silica gel chromatography
with dichloromethane as the eluent, pure 6 was obtained as an
amorphous compound. Yield: 9.40 g (85%).
2. Experimental
2.1. Materials
The IR spectrum exhibited absorption bands at 1520 cmꢀ1
(NO2), 1340 cmꢀ1 (NO2), 1250 cmꢀ1 (Ar–O–Ar) and 1210 cmꢀ1
(C–F).
1,1,1-tris(4-hydroxyphenly)ethane (2), 4-fluoro-nitrobenzene
(3) and 2-fluoro-5-nitrobenzotrifluoride (5) were purchased from
Tokyo Kasei Kogyo and used without purification. TESSA was pur-
chased from AZmax Co., and used without purification. Potassium
carbonate, N,N-dimethylformamide (DMF) and N-Methyl-2-pyrrol-
idone (NMP) were purchased from Kanto Kagaku Co., (Japan).
Potassium carbonate and DMF were used without purification
and NMP was purified by vacuum distillation over calcium hydride.
BTDA and ODA were obtained commercially and purified by subli-
mation under reduced pressure. Tetrahydrofuran, ethanol and tet-
raethoxysilane (TEOS) were purchased from Kanto Kagaku Co.,
(Japan) and used without purification.
1
2
3
4
O2N
O
O
NO2
5
6
O
CF3
7
8
9
NO2
2.2. Monomer synthesis
The 1H NMR spectrum [d in CDCl3] showed signals at 2.21 (s, 3H,
CH3–), 7.02 (d, 1H, J = 8.8 Hz, 7), 7.04 (d, 4H, J = 8.8 Hz, 3), 7.05 (d,
4H, J = 8.8 Hz, 2 and 6), 7.18 (d, 2H, J = 8.8 Hz, 4), 7.23 (d, 4H,
J = 8.8 Hz, 5), 8.20 (d, 4H, J = 8.8 Hz, 1), 8.30 (dd, 4H, J = 8.8 Hz,
J = 2.1 Hz, 8), and 8.60 (d, 4H, J = 2.1 Hz, 9) ppm. The 13C NMR spec-
trum [d in CDCl3] showed signals at 30.78, 51.21, 114.21, 117.06,
119.80, 119.90, 121.40 (q, J = 273 Hz), 123.26 (q, J = 33.5 Hz),
124.13 (q, J = 4.8 Hz), 125.82, 127.33, 129.08, 130.28, 136.80,
140.55, 143.88, 146.09, 152.70, 157.08, 157.09 and 162.96 ppm.
Anal. Calcd for C39H26N3O9F3: C, 63.50%; H, 3.55%; N, 5.70%.
Found: C, 63.31%; H, 3.61%; N, 5.58%.
2.2.1. 1,1-bis[4-(4-nitrophenoxy)phenyl]-1-(4-hydroxyphenyl)ethane
(4)
In a flask, a mixture of 12.25 g (40 mmol) of 1,1,1-tris(4-hydrox-
yphenly)ethane (2), 11.29 g (80 mmol) of p-fluoronitrobenzene (3),
11.04 g (80 mmol) of potassium carbonate, and 150 ml of DMF was
stirred at 130 °C for 12 h. The reaction mixture was cooled to 80 °C,
and the solvent was evaporated under a reduced pressure of 15–
25 torr. After 250 ml of water was added to the residue, the mix-
ture was extracted twice with 200 ml of dichloromethane. The
combined extract was dried over anhydrous magnesium sulfate,
and the solvent was evaporated. After the residue was purified
by silica gel chromatography with dichloromethane as the eluent,
pure 4 was obtained as an amorphous compound. Yield: 9.87 g
(45%).
2.2.3. 1,1-bis(4-(aminophenoxy)phenyl)-1-(4-(4-amino-2-
trifluoromethylphenoxy)phenyl)ethane (1)
A mixture of 7.38 g (10 mmol) of 6 and 0.3 g of 10% Pd/C in
60 ml of tetrahydrofuran and 40 ml of ethanol was stirred at room
temperature for 15 h under a hydrogen atmosphere. After the Pd/C
was removed by filtration, the solvent was evaporated under a re-
duced pressure of 15–20 torr. After the residue was purified by sil-
ica gel chromatography with dichloromethane as the eluent, pure 1
was obtained as an amorphous compound. Yield: 5.96 g (92%).
The IR spectrum exhibited absorption bands at 3460 cmꢀ1
The IR spectrum exhibited absorption bands at 3650–
3150 cmꢀ1 (OH), 1520 cmꢀ1 (NO2), 1340 cmꢀ1 (NO2) and 1250
cmꢀ1 (Ar–O–Ar).
1
2
3
4
O2N
O
O
NO2
5
6
(NH2), 3370 cmꢀ1 (NH2), 1230 cmꢀ1 (Ar–O–Ar) and 1210 cmꢀ1
.
OH
1
2
3
4
H2N
O
O
NH2
The 1H NMR spectrum [d in CDCl3] showed signals at 2.21 (s, 3H,
CH3–), 6.71 (d, 2H, J = 8.4 Hz, 6), 6.95 (d, 2H, J = 8.4 Hz, 5), 7.00 (d,
2H, J = 8.8 Hz, 2), 7.04 (d, 4H, J = 8.8 Hz, 3), 7.16 (4H, J = 8.8 Hz, 4)
and 8.21 (d, 4H, J = 8.8 Hz, 1) ppm. The 13C NMR spectrum [d in
CDCl3] showed signals at 30.78, 51.22, 114.20, 117.06, 119.90,
125.80, 127.34, 130.26, 136.80, 140.55, 146.07, 152.68, 157.07
and 162.98 ppm.
5
6
O
CF3
7
8
9
Anal. Calcd for C32H24N2O7: C, 70.07%; H, 4.41%; N, 5.11%.
Found: C, 69.82%; H, 4.67%; N, 4.95%.
NH2
The 1H NMR spectrum [d in DMSO-d6] showed signals at 2.20 (s,
3H, CH3–), 4.95 (broad s, 4H, –NH2), 5.41 (broad s, 2H, –NH2), 6.57
(d, 4H, J = 8.8 Hz, 1), 6.75 (d, 4H, J = 8.8 Hz, 2), 6.76 (d, 4H,
J = 8.8 Hz, 3), 6.78 (d, 4H, J = 8.8 Hz, 6), 6.80 (dd, 1H, J = 8.8 Hz,
J = 2.9 Hz, 8), 6.87 (d, 1H, J = 8.8 Hz, 7), 6.90 (d, 1H, J = 2.9 Hz, 9),
6.94 (d, 4H, J = 8.8 Hz, 4) and 6.97 (d, 2H, J = 8.8 Hz, 5) ppm. The
13C NMR spectrum [d in DMSO-d6] showed signals at 30.86,
2.2.2. 1,1-bis(4-(nitrophenoxy)phenyl)-1-(4-(4-nitro-2-
trifluoromethylphenoxy)phenyl)ethane(6)
In a flask, a mixture of 8.23 g (15 mmol) of 4, 3.14 g (15 mmol)
of 2-fluoro-5nitrobenzotrifluoride (5), 2.07 g (15 mmol) of potas-
sium carbonate, and 80 ml of DMF was stirred at 130 °C for 12 h.
The reaction mixture was cooled to 80 °C, and the solvent was

Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
87
50.74, 100.08, 112.89 (q, J = 4.8 Hz), 114.46, 116.18, 119.12, 120.49,
121.15, 121.96 (q, J = 33.5 Hz), 123.04 (q, J = 272.5 Hz), 129.61,
129.77, 141.60, 141.82, 142.47, 142.96, 145.68, 145.88, 153.44
and 156.76 ppm.
(d, 12H, J = 8.8 Hz, 2 and 3) and 6.94 (d, 4H, J = 8.8 Hz, 4) ppm. The
13C NMR spectrum [d in DMSO-d6] showed signals at 30.84, 50.72,
100.08, 114.45, 116.20, 121.14, 129.62, 141.81, 145.84 and
156.73 ppm.
Anal. Calcd for C39H32N3O3F3: C, 72.32%; H, 4.98%; N, 6.49%.
Found: C, 72.08%; H, 5.10%; N, 6.34%.
Anal. Calcd for C38H33N3O3: C, 78.73%; H, 5.74%; N, 7.25%.
Found: C, 78.55%; H, 5.61%; N, 7.17%.
2.2.4. 1,1,1-tris[4-(4-nitrophenoxy)phenyl]ethane(7)
2.3. Preparation of polyimide–silica hybrid films
In a flask, a mixture of 3.06 g (10 mmol) of 1,1,1-tris(4-hydrox-
yphenly)ethane (2), 4.23 g (30 mmol) of p-fluoronitrobenzene (3),
4.14 g (30 mmol) of potassium carbonate and 100 ml of DMF was
stirred at 130 °C for 12 h. The reaction mixture was cooled to
80 °C, and the solvent was evaporated under a reduced pressure
of 15–25 torr. After 150 ml of water was added to the residue,
the mixture was extracted twice with 100 ml of dichloromethane.
The combined extract was dried over anhydrous magnesium sul-
fate, and the solvent was evaporated. Pure 7 was obtained by crys-
tallization from acetic acid. Yield: 5.94 g (82%).
In a three necked flask, 0.563 g (1.75 mmol) of BTDA was added
to a solution of 0.161 g (0.25 mmol) of 1 and 0.300 g (1.5 mmol) of
ODA in 15.0 ml of NMP at 0 °C. The mixture was stirred at 0 °C for
6 h under nitrogen until a viscous solution of polyamic acid
formed. The inherent viscosity was approximately 0.95 dlgꢀ1
.
A polyimide–silica hybrid film containing 20 wt.% silica is de-
scribed below. To the polyamic acid solution, 0.076 g (0.25 mmol)
of TESSA was added and stirred at room temperature for 1 h. Sub-
sequently, 0.861 g (4.14 mmol) of TEOS and 0.312 g (17.3 mmol) of
water were added to the polyamic acid solution, which was stirred
at room temperature until the mixture was homogeneous (ꢁ1 h).
After stirring the resulting homogeneous solution for an additional
24 h, the solution was cast onto a glass plate and dried at 80 °C. The
thermal cyclodehydration of the polyamic acid was performed by
successive heating 100 °C for 1 h, 200 °C for 1 h and 300 °C for
1 h under vacuum.
The IR spectrum exhibited absorption bands at 1520 cmꢀ1
(NO2), 1340 cmꢀ1 (NO2) and 1250 cmꢀ1 (Ar–O–Ar).
1
2
3
4
O2N
O
O
NO2
IR spectrum exhibited absorption bands at 1780 cmꢀ1 (C@O),
1720 cmꢀ1 (C@O), 1375 cmꢀ1 (CAN), 1100–1000 cmꢀ1 (SiAO)
and 830 cmꢀ1 (SiAO).
O
2.4. Measurement
NO2
1H and 13C NMR were recorded on a JNM-GSX400 FT NMR spec-
trometer, and IR spectra were recorded on a SHIMADZU spectro-
photometer IR 435. For thermogravimetry (TG), a Rigaku thermal
analysis station TG 8110 was used and measurements were made
at a heating rate of 10 °C minꢀ1 in air. Scanning electron micros-
copy (SEM) studies were performed using a JEOL JSM-5600LV.
Fractured surfaces of hybrid films were fixed by carbon tape, and
The 1H NMR spectrum [d in CDCl3] showed signals at 2.21 (s, 3H,
CH3–), 7.03 (d, 6H, J = 8.8 Hz, 3), 7.06 (d, 6H, J = 8.8 Hz, 3), 7.19 (6H,
J = 8.8 Hz, 4) and 8.22 (d, 6H, J = 8.8 Hz, 1) ppm. The 13C NMR spec-
trum [d in CDCl3] showed signals at 30.78, 51.22, 117.03, 119.90,
125.78, 130.24, 142.55, 146.07, 152.65, and 162.96 ppm.
Anal. Calcd for C38H27N3O9: C, 68.16%; H, 4.06%; N, 6.28%.
Found: C, 68.01%; H, 3.95%; N, 6.12%.
1
2
3
4
H2N
O
O
NH2
2.2.5. 1,1, 1-tris(4-(aminophenoxy)phenyl)ethane (8)
A1
5
6
A mixture of 5.36 g (8 mmol) of 7 and 0.3 g of 10% Pd/C in 40 ml
of tetrahydrofuran and 27 ml of ethanol was stirred at room tem-
perature for 15 h under a hydrogen atmosphere. After the Pd/C
was removed by filtration, the solvent was evaporated under re-
duced pressure of 15–20 torr. Pure 1 was obtained by crystalliza-
tion from toluene. Yield: 3.85 g (83%).
O
CF3
7
8
9
A1
A2 NH2
The IR spectrum exhibited absorption bands at 3460 cmꢀ1
(NH2), 3370 cmꢀ1 (NH2) and 1230 cmꢀ1 (Ar–O–Ar).
A2
1
2
3
4
7.0
6.5
6.0
5.5
5.0 (ppm)
H2N
O
O
NH2
2
3
1
O
4
6
8
5
9
7
NH2
7.0
6.9
6.8
6.7
6.6 (ppm)
The 1H NMR spectrum [d in DMSO-d6] showed signals at 2.20 (s,
3H, CH3–), 4.95 (broad s, 6H, –NH2), 6.57 (d, 6H, J = 8.8 Hz, 1), 6.75
Fig. 1. 1H NMR spectrum of 1.

88
Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
ODA
H2N
O
NH2
O
6
1
O
O
O
0
O
O
+
NMP
H2N
O
O
NH2
O
BTDA
O
CF3
1
NH2
O
O
O H
N
O H
N
H O
N
H O
N
O
O
O
OH
OH
HO
HO
O
O
O
O
O
CF3
NH2
n
6n
H2N
O
NH2
O
6
O
O
O
ODA
0
O
O
+
NMP
1
H2N
O
O
NH2
O
BTDA
O
8
NH2
Gelation
Scheme 1. Synthesis of polyamic acid from tri-functional amine.
sputter-coated with Au under an electric current of 20 mA at 6 Pa
for 60 s. Dynamic mechanical analysis (DMA) was performed with
the Advanced Rheometric Expansion System at 1.0 Hz at
5 °C minꢀ1. Mechanical properties were measured with Shimadzu
characteristic of trifluoromethyl groups. The 1H NMR spectrum of
1 was assigned in Fig. 1. The signal of protons in amino group A2
was observed in downfield (5.41 ppm) of that of A1 (4.95 ppm).
The signals of protons H8 and H9 on the ortho-position of the ami-
no group A2 were also observed in downfield (6.80 ppm and
6.90 ppm, respectively) of those of H1 on the ortho-position of
amino group A1 (6.57 ppm). The effect of the electron withdrawing
trifluoromethyl group caused the differences in these chemical
shifts in 1H NMR spectrum.
AUTOGRAPH at a strain rate 10% minꢀ1
.
3. Results and discussion
3.1. Synthesis of A2A0-type tri-functional amine (1)
In the 13C NMR spectrum, spin–spin coupling with fluorine
atoms was observed, and the signals were complicated. However,
the signals were classified into 21 groups, all of which indicate
the formation of the postulated diamine.
1,1-bis(4-(aminophenoxy)phenyl)-1-(4-(4-amino-2-trifluorom-
ethylphenoxy)phenyl)ethane (1), an A2A0-type tri-functional amine,
was synthesized in three steps from 1,1,1-tris(4-hydroxy-
phenyl)ethane (2). The reaction of 2 with 4-fluoronitrobenzene (3)
yielded 1,1-bis[4-(4-nitrophenoxy)phenyl]-1-(4-hydroxyphenyl)
ethane (4), and the subsequent reaction of 4 with 2-fluoro-5nitro-
benzotrifluoride (5) afforded 1,1-bis(4-(nitrophenoxy)phenyl)-1-
3.2. Synthesis of polyamic acid using A2A0-type tri-functional amine (1)
Polycondensation using tri-functional compounds yields poly-
mers with a greater ratio of cross-linking units if the reactivity of
the functional groups is equal. In such a polycondensation reaction,
the polymer solution shows large inherent viscosity and eventually
undergoes gelation. Hence, the preparation of hybrid materials
from such a solution is difficult. The amino group A2 was expected
(4-(4-nitro-2-trifluoromethylphenoxy)phenyl)ethane (6).
obtained by the hydrogenation of 6 using Pd/C as a catalyst.
1 was
Chemical structures were confirmed by IR and NMR spectra.
Compound 1 showed IR absorption at 3380 cmꢀ1 and 3360 cmꢀ1
characteristic of amino groups and 1340 cmꢀ1
which was
,
,

Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
89
O
O
O
O
H
N
O
O
H
N
H
N
O
O
H
N
O
O
O
O
O
O
O
O
OH
OH
HO
HO
O
CF3
C2H5O Si OC2H5
OC2H5
NH2
TESSA
TESSA
O
O
O
O
H
N
O
O
H
N
H
N
O
O
H
N
O
O
O
O
O
OH
OH
HO
HO
O
N
CF3
OH
H
O
O
C2H5O Si OC2H5
OC2H5
TEOS, H2O
O
O
O
O
H
N
O
O
H
N
H
N
O
O
H
N
O
O
O
O
O
OH
OH
HO
HO
O
CF3
OH
N
H
O
O
Si O Si O Si O Si
O
O
O
O
Si O Si O Si O Si
100 -1h, 200 -1h, 300 -1h
O
O
O
O
O
O
O
O
N
O
O
N
N
O
N
O
O
O
CF3
N
O
O
Si O Si O Si O Si
O
O
O
O
Si O Si O Si O Si
Scheme 2. Preparation of polyimide–silica hybrid films.
to react slower with anhydride than amine A1 in polycondensation
due to the electron-withdrawing effect of the trifluoromethyl
group on amino group A2, leading to reduction of the formation
of cross-linking sites.

90
Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
Table 1
Preparation of polyimide–silica hybrid films.
Code
Polyamic acid/g
TESSA/g (mmol)
H2O/g (mmol)
TEOS/g (mmol)
Silica/wt.%
Remarks
PI
PIS-0
16.0
16.0
16.0
16.0
16.0
16.0
16.0
16.0
16.0
–
–
–
–
–
–
T
T
T
T
T
T
O
O
O
0.0761 (0.25)
0.0761 (0.25)
0.0761 (0.25)
0.0761 (0.25)
0.0761 (0.25)
0.0761 (0.25)
0.0761 (0.25)
–
0.0135 (0.75)
0.146 (8.12)
0.312 (17.3)
0.525 (29.2)
0.809 (44.9)
1.206 (67.0)
1.800 (100)
0.289 (16.0)
PIS-10
PIS-20
PIS-30
PIS-40
PIS-50
PIS-60
PIS-200
0.383 (1.84)
0.861 (4.14)
1.477 (7.10)
2.297 (11.0)
3.445 (16.6)
5.169 (24.9)
0.835 (4.01)
10
20
30
40
50
60
20
(a) 6.4 wt.% NMP solution. (b) Calculated silica content in the hybrid films. (c) T: Transparent, O: Opaque.
Polyamic acid was prepared from BTDA, ODA and 1 (BTDA:O-
DA:1 = 7:6:1 M equivalents) as shown in Scheme 1. BTDA was
added to a solution of ODA and 1 in NMP at 0 °C, and the solution
was then stirred. The viscous polyamic acid solution was obtained
without gelation. For comparison, a polyamic acid was prepared
from 1,1,1-tris(4-(aminophenoxy)phenyl)ethane (8) instead of 1.
Hyperbranched polyimides were reported to be prepared from an
A3-type triamine and a tetracarboxylic dianhydride without gela-
tion [24–27]; however, gelation could not be avoided in the poly-
Fig. 3 shows of the thermogravimetric curves of PI and the hy-
brid films under an atmosphere of air. The onset of weight loss
was observed at 410 °C for PI, and at approximately 395 °C for
the hybrid films. As the weight loss at 440 °C was larger with
increasing silica contents, and the weight loss near 395 °C in
the hybrid films was thought to be due to the loss of ethanol
and water by continuation of the sol–gel reaction during heating.
The weight of the residues at 800 °C was almost proportional to
the silica contents.
condensation using
literature results.
8 when attempting to recreate those
100
PI-20
3.3. Preparation of polyimide–silica hybrid films by sol–gel process
PI
80
PI-40
Polyimide–silica hybrid films were prepared as shown in
Scheme 2. First, 3-(triethoxysilyl)propyl succinic anhydride was re-
acted with the amino group in the polyamic acid that was synthe-
sized from 1 to introduce triethoxysilyl groups. Second, TEOS and
water were added to the polyamic acid solution, which was then
stirred to form a homogeneous solution. The resulting homoge-
neous mixture was additionally stirred for 24 h to advance the
sol–gel reaction. The solution was cast onto a glass plate and dried
to reach final product of silica-containing polyamic acid films. Fi-
nally, polyimide–silica hybrid films were obtained by heating the
silica-containing polyamic acid films at 100 °C for 1 h, 200 °C for
1 h, and 300 °C for 1 h under vacuum. For comparison, hybrid film
(PIS-200) containing 20 wt.% silica was prepared without using
TESSA.
60
40
20
0
PI-50
PI-20’
400
500
600
700
800
Wavelength / nm
Fig. 2. UV–Vis spectra of PI, and the hybrid films (PIS-20, PIS-40, PIS-50 and PIS-
200).
Table 1 summarizes the results of the preparation of polyimide–
silica hybrid films. The silica content in the Table 1 denotes the va-
lue calculated under the assumption that the sol–gel reaction pro-
ceeded completely. Sample codes are abbreviated using silica
content. For example, PIS-30 stands for the hybrid films containing
30 wt.% of silica. The hybrid films containing up to 50 wt.% silica
were obtained as free standing. Fig. 2 shows UV–Vis spectra of
the hybrid films. The hybrid films containing up to 40 wt.% silica
showed good transparency with transmittance higher than 70%
at 700 nm, while the hybrid film containing 50 wt.% silica content
was opaque. The transparent–opaque barrier was approximately
the same as that of the films prepared from triethoxysilane-termi-
nated polyamic acid [16]. The film PIS-200 prepared without using
TESSA was opaque, and significant improvements in the optical
transparency could be achieved by the introduction of ethoxysilyl
groups in the matrix polyimides.
100
PIS-60
PI
PIS-50
PIS-40
PIS-10
PIS-20
PIS-30
50
PIS-60
PIS-40
PIS-30
PIS-20
PIS-50
360
380
400
420 440
PIS-10
The chemical structure of polyimide–silica hybrid film was con-
firmed by IR spectroscopy. Absorptions at 1780 cmꢀ1 (C@O),
1725 cmꢀ1 (C@O) and 1375 cmꢀ1 (CAN) are characteristic of imide
group confirmed the formation of polyimide. In addition, absorp-
tions at 1100–1000 cmꢀ1 (SiAO) and 830 cmꢀ1 (SiAO) were ob-
served in PIS-20, and indicated that silica had formed the
polyimide matrix.
PI
0
0
200
400
Temperature (ºC)
600
800
Fig. 3. Thermogravimetric curves of PI, and the hybrid films with various silica
contents under an atmosphere of air at a heating rate of 10 °C/min.

Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
91
2 m
2 m
PI
PIS-20
PIS-50
PIS-20’
2 m
PIS-40
2 m
2 m
2 m
PIS-60
Fig. 4. SEM photograph of PI, and the hybrid films (PIS-20, PIS-40, PIS-50, PIS-60 and PIS-200).
3.4. Morphology of silica in the polyimide–silica hybrid films
the silica particles were clearly observed as beads having diameter
1.0–2.0
TESSA.
l
m in the hybrid film PIS-200 that was prepared without
The fractured surfaces of the hybrid films were observed di-
rectly by SEM (Fig. 4). The fracture morphology of the hybrid films
containing up to 40 wt.% silica showed smooth surfaces. In the
films with larger silica contents (PIS-50 and PIS-60), spherical
phases were observed as agglomerates formed by being covered
with polyimide. The diameters of the particles were approximately
3.5. Dynamic-mechanical and mechanical properties of the polyimide–
silica hybrid films
Dynamic mechanical analysis (DMA) was carried out to exam-
ine the effect of the silica contents and the introduction of ethoxy-
silyl group on the dynamic mechanical properties of hybrid films.
In tan d curves, single peaks corresponding to the Tg of the polyi-
mides were observed around 280–322 °C.
0.50 0.20 lm and 0.8 0.20 lm in PIS-50 and PIS-60, respec-
tively. This result indicated that phase separation at submicrome-
ter-scale occurred in the hybrids. Such particles were not observed
in hybrid films having less than 40 wt.% silica. On the other hand,

92
Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
10
280
1.0
9
8
7
320
PI
PIS-0
0
6
10
280
1.0
9
8
298
7
6
PIS-20
PIS-20’
100
0
0
300
Temperature (
400
100
200
0
300
Temperature (
400
200
)
)
Fig. 5. DMA results of PI, PIS-0, and the hybrid films (PIS-20 and PIS-200).
Fig. 5 shows DMA curves of pristine PI, PIS-0, and the hybrid
the polyimide and the silica had an influence on the mechanical
properties. The hybrid films in the present study showed higher
tensile strengths and moduli than those of the films prepared from
triethoxysilane-terminated polyamic acid [16] when the silica con-
tent was constant. However, PI-50 was brittle due to the phase
separation.
films (PIS-20 and PIS-200). The Tg values of PI and PIS-0 were
280 °C and 320 °C, respectively. The higher Tg of PIS-0 suggested
the formation of cross-linking by sol–gel reaction among trieth-
oxysilyl groups introduced in the polyimide matrix. Despite the
same silica content, for PIS-20, the Tg value was higher, the inten-
sity of tan d maximum was less, and the decrement in the storage
modulus at the glass transition was lower than those of PIS-200.
These results indicated that the movement of polyimide chain in
the hybrid films was restricted by the conjugation between the
polyimide and the silica.
4. Conclusions
New polyimide–silica hybrid films with conjugation of the poly-
imide chains and the silica particles were successfully prepared by
a sol–gel process using 3-(triethoxysilyl)propyl succinic anhydride
(TESSA) as the coupling agent. The polyamic acid, which contains
free amino groups, was synthesized by the copolymerization of
3,30,4,40-benzophenonetetracarboxylic dianhydride (BTDA), 4,40-
oxydianiline (ODA) and the tri-functional amine, 1,1-bis(4-(amino-
phenoxy)phenyl)-1-(4-(4-amino-2-trifluoromethylphenoxy)phenyl)
ethane (1) (BTDA:ODA:1 = 7:6:1 M equivalents). The A2A0-type tri-
amine (1) was used to avoid cross-linking during polycondensa-
tion. TESSA was reacted with the amino group in the polyamic
acid to introduce ethoxysilyl moieties that allow for conjugation
to silica. The polyimide–silica hybrid films were prepared by sol–
gel reaction with tetraethoxysilane in the polyamic acid solution,
and thermal imidation. The prepared hybrid films were transpar-
ent with silica contents up to 40 wt.%, whereas the hybrid films
Fig. 6 shows DMA curves of PIS-10, PIS-20, PIS-30, PIS-4 and PIS-
50. The values of the storage modulus were greater and the decre-
ments in the storage modulus at the glass transition were lower
with increasing silica content due to the increased stiffness. Tg val-
ues of the hybrid films were higher with increasing silica content,
and the data support the hypothesis that the degree of conjugation
between polyimide chains and silica increased with silica content.
The tensile properties of the hybrid films were examined, and
results are summarized in Table 2. The elongation at the break de-
creased and the tensile modulus increased with increasing silica
content. As the content of silica increased up to 40 wt.%, the tensile
strength did not decreased significantly, and for PIS-40, the tensile
strength and the tensile modulus were 100 MPa and 5.3 GPa,
respectively. The tensile strength and the tensile modulus of PIS-
20 were higher than those of PIS-200, and the conjugation between

Y. Shiina, A. Morikawa / Reactive & Functional Polymers 71 (2011) 85–94
93
10
280
288
1.0
9
8
7
PI
PIS-10
0
6
10
1.0
9
8
7
6
298
307
PIS-20
PIS-30
0
10
1.0
9
8
7
6
315
300
321
PIS-40
100
PIS-50
100
0
0
200
300
400
400
0
200
Temperature (
)
Temperature (
)
Fig. 6. DMA results of PI, and the hybrid films (PIS-10, PIS-20, PIS-30, PIS-40 and PIS-50).
film was higher than that in the hybrid prepared without TESSA.
The values of Tg increased with increasing silica contents in hybrid
films and indicated that movement of polyimide chains were re-
stricted by conjugation of the polyimide and silica.
Table 2
Tensile properties of polyimide and polyimide–silica hybrids.
Code
Silica/wt.%
Strength (MPa)
Elongation
Modulus (GPa)
at break (%)
PI
0
10
20
30
40
50
20
120
112
118
113
100
75
11
8
6.1
4
3.2
1.7
7
2.5
3.3
3.9
4.5
5.3
5.8
3.1
PIS-10
PIS-20
PIS-30
PIS-40
PIS-50
PIS-200
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