UV-irradiation cured organic-inorganic hybrid nanocomposite initiated by ethoxysilane-modified multifunctional polymeric photoinitiator through sol-gel process

Article abstract of DOI:10.1002/cjoc.201180341

The UV-cured organic-inorganic hybrid nanocomposite (nano-Si-m-PI) was prepared through the photopolymerization of acrylic resin initiated by ethoxysilane-modified multifunctional oligomeric photoinitiator (Si-m-PI). The esterification reaction of 2-hydro

Full text of DOI:10.1002/cjoc.201180341

FULL PAPER
UV-Irradiation Cured Organic-inorganic Hybrid Nanocomposite
Initiated by Ethoxysilane-modified Multifunctional Polymeric
Photoinitiator through Sol-gel Process
Hu, Lihua(胡丽华)
Shi, Wenfang*(施文芳)
Chinese Academy of Sciences Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and
Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China
The UV-cured organic-inorganic hybrid nanocomposite (nano-Si-m-PI) was prepared through the photopolymeri-
zation of acrylic resin initiated by ethoxysilane-modified multifunctional oligomeric photoinitiator (Si-m-PI). The es-
terification reaction of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) with thioglycolic acid,
and the following addition reactions with dipentaerythritol hexaacrylate and then 3-aminopropyltriethoxysilane were
carried out for preparing the Si-m-PI. The Si-m-PI exhibits the similar UV absorption and molar extinction coefficient
with Irgacure 2959. The photoinitiating activity study by photo-DSC analysis showed that the Si-m-PI possesses high
max
p
f
photopolymerization rate at the peak maximum (R
) and final unsaturation conversion (P ) in the cured hybrid
films. From the scanning electron microscope (SEM) observation, the SiO nanoparticles dispersed uniformly in the
2
formed nano-Si-m-PI, whereas the aggregation of nanoparticals occurred in nano-Irg, which was prepared through the
photopolymerization of acrylic resin initiated by Irgacure 2959. Moreover, compared with the UV-cured pure polymer
and nano-Irg, the nano-Si-m-PI showed remarkably enhanced thermal stability and mechanical properties.
Keywords polymer-matrix composites, sol-gel process, mechanical property, UV-curing
1
6,17
Introduction
from the cured films.
However, the photoinitiating
activity was usually affected by the reduced chromo-
phore percentage in a UV-curable formulation.
Numerous studies have recently been reported on
organic-inorganic hybrid nanocomposite coatings due to
In this study, we proposed a method to prepare the
1
-6
the good mechanical and optical properties. They are
usually prepared utilizing a sol-gel process by incorpo-
rating organic polymers or oligomers with metal alkox-
hybrid nanocomposite (Nano-Si-m-PI) by combining the
18,19
sol-gel procedure with UV curing.
A sol-gel precursor,
tetraethylorthosilicate (TEOS), was used to form the
7-10
ides.
The covalent bonds between organic and inor-
20-22
crosslinked organic-inorganic.
The photopolymeriza-
ganic components occur via suitable coupling agents
such as organofunctional silanes, which prevent the
macroscopic phase from separation, resulting in the
tion of acrylic resin was initiated by ethoxysilane-
modified multifunctional oligomeric photoinitiator
(
2
(
Si-m-PI) which was synthesized by the esterification of
-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone
Irgacure 2959) with thioglycolic acid, followed by the
addition reactions with dipentaerythritol hexaacrylate
EM265) and then 3-aminopropyltriethoxysilane (KH-
50). For comparison, the UV-cured hybrid composite
nano-Irg) initiated by Irgacure 2959 was also prepared.
1
1,12
formation of well-dispersed nanostructured phase.
The UV-curing technology has been widely used in
various industries owing to its advantages such as “100%
solid” formulation, low energy consumption, effectively
(
5
(
13,14
curing.
Photoinitiators play an important role in cur-
ing kinetics and properties of end products even though at
a small percentage loading in formulations. However,
traditional low molecular weight photoinitiators have
many intrinsic defects such as compatibility problem,
toxicity and odor because of the migration of decomposed
The photoinitiating efficiency of Si-m-PI, the thermal
and mechanical properties, and microstructure of the
obtained hybrid nanocomposites were investigated.
15
species from cured films. This is disadvantageous to
apply the UV-curing approach to tobacco and food pack-
aging. The commonly used method to solve this problem
is the use of polymeric or polymerisable photoinitiators,
in which the chemically bonded radical fragments to
polymer chains could reduce the tendency to migrate
Experimental
Materials
2-Hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophe-
none (Irgacure 2959) was supplied by Insight High
Technology Co. Ltd. (China). Thioglycolic acid was
*
E-mail: wfshi@ustc.edu; Tel.: 0086-0551-3606084; Fax: 0086-0551-3606630
Received March 28, 2011; revised May 7, 2011; accepted May 19, 2011.
Project supported by the National Natural Science Foundation of China (No. 50973100).
Chin. J. Chem. 2011, 29, 1961— 1968 © 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1961

Hu & Shi
FULL PAPER
purchased from Aldrich Chemical Co. Dipentaerythritol
hexaacrylate (EM265) was offered by Eternal Chemical
Co., Taiwan. EB605, which is a commercial resin con-
sisting of 75% standard bisphenol A epoxy diacrylate and
The pendulum and pencil hardness were respectively
determined using a QBY pendulum and QHQ-A pencil
hardness apparatus (Tianjin Instrument Co., China).
Synthesis
25% tripropylene glycol diacrylate (TPGDA), was of-
fered by Cytec Industries Inc., USA. Tetraethylorthosili-
cate (TEOS) and 3-aminopropyltriethoxysilane (KH-550)
were purchased from Nanjing Yudeheng Chemical Co.
Thioglycolic acetate-modified photoinitiator (TA-
m-PI)
4-Dimethylaminopyridine p-toluenesulfonate
(DPTS) was used as a catalyst for the esterification re-
action of thioglycolic acid with Irgacure 2959, and was
prepared according to the literature reported by Moore
(
China).
p-Toluene
sulphonic
acid
(PTSA),
4
-dimethylamino pyridine (DMAP) and other chemicals
2
4
were purchased from Shanghai First Reagent Co. All
chemicals were used as received without further purifi-
cation except for KH-550 and triethylamine, which were
purified before uses.
and Stupp. The equivalent amount of PTSA and
DMAP were, respectively, dissolved into hot toluene,
then mixed and cooled to room temperature. After fil-
trated and dried under vacuum, DPTS was obtained as a
white needle-like powder (yield 99%).
Thioglycolic acid (11.04 g, 0.12 mol), Irgacure 2959
(22.4 g, 0.1 mol), and DPTS (0.672 g) were mixed into
50 mL of toluene, and stirred overnight under refluxing
Measurements
1
The H NMR spectra were recorded with a
DMX-300MHz spectrometer (Bruker, Germany) using
CDCl
3
as a solvent. The FT-IR spectra were recorded
at 125 ℃ in N
2
atmosphere. Then toluene was removed
from the reactant by rotary evaporation under reduced
pressure. The crude product was diluted with 60 mL of
with a Nicolet MAGNA-IR 750 spectrometer. The UV
spectra were recorded with a SHIMADZU UV-2401 PC
instrument.
2 2 3
CH Cl , then washed with saturated NaHCO aq. (100
The photopolymerization kinetics analysis was per-
formed on a modified CDR-1 DSC apparatus (Shanghai
Balance Instrument Co., China) equipped with a UV
spotcure system BHG-250 (Mejiro Precision Co., Japan).
The incident light intensity at the sample pan was meas-
mL×5) and distilled water (100 mL×3). The organic
4
phase was dried with anhydrous MgSO overnight. After
the filtration of MgSO and removal of CH Cl , the
4 2 2
product, thioglycolic acetate-modified photoinitiator,
named TA-m-PI, was obtained as a yellowish liquid
－
2
1
ured to be 2.4 mW•cm by a UV power meter. The
with a yield of 90%. H NMR (CDCl
3
, 300 MHz) δ:
f
unsaturation conversion (P ) was calculated by the for-
8.04—7.98 (m, 2H), 6.93—6.87 (m, 2H), 4.45 (t, J＝4.8
Hz, 2H), 4.20 (t, J＝4.8 Hz, 2H), 3.25 (d, J＝8.3 Hz,
2H), 1.97 (t, J＝8.3 Hz, 1H), 1.57 (s, 6H); IR (NaCl
f
mula, P ＝H
t
/H
∞
t
, where H is the heat effect within t
seconds, H
∞
is the heat effect of 100% unsaturation
－
1
conversion. The DSC curve was normalized by the
weight of a sample (g). The polymerization rate is de-
fined by J•g •s , namely, the heat of polymerization
per second for 1 g samples. For calculating the polym-
erization rate and unsaturation conversion, the value of
polymerization heat ∆H
ble bond was taken.
The fracture surface morphological characters of hy-
brid films were examined by a SEM Amray1000B in-
strument (Amray Co., USA). The thermogravimetric
analysis (TGA) was carried out on a Shimadzu
plate) ν: 3600—3100, 2576, 1735, 1667, 1600 cm .
Ethoxysilane-modified multifunctional oligomeric
photoinitiator (Si-m-PI) The ethoxysilane-modified
multifunctional oligomeric photoinitiator (Si-m-PI) with
average four photoinitiator chromophores and two
triethoxysilane groups was prepared by two stages.
Firstly, TA-m-PI (5.97 g, 0.02 mol), EM265 (2.89 g,
0.005 mol) and triethylamine (0.17 g) were mixed into
－
1
－
1
－
1
0
＝86 J•mmol per acrylic dou-
2
3
40 mL of CH
2
Cl
2
, and stirred at 40 ℃ until the charac-
－
1
teristic SH peak at 2576 cm in the FT-IR spectrum
disappeared. The obtained oligomeric TA-m-PI (oligo-
TA-m-PI, 8.85 g, 0.005 mol) with average four
photoinitiator chromophores as an intermediate product
TGA-50H thermoanalyzer under a N
2
flow rate of 8×
－
5
3
－
1
1
0
m •min . In each case, a 5-mg sample was exam-
－
1
ined at a heating rate of 10 ℃•min from room tem-
perature to 800 ℃.
after evaporating CH
further reacted with KH-550 (2.21 g, 0.01 mol) under
the presence of triethylamine (0.07 g) in CH Cl at 45
2 2
Cl under reduced pressure was
The tensile storage modulus (E′) and tensile loss
factors (tan δ) were measured by a dynamic mechanical
thermal analyzer (Diamond DMA, PE Co., USA) at a
2
2
℃ until the characteristic peak of acrylate double bond
－
1
at 810 cm in the FT-IR spectrum disappeared. After
－
1
frequency of 2 Hz and a heating rate of 5 ℃•min in
2 2
evaporating CH Cl under reduced pressure, the ethoxy-
the range of －20 to 200 ℃ with the sheet of 25 mm
silane-modified multifunctional oligomeric photoinitia-
tor, named Si-m-PI, was obtained as a yellowish liquid
×
5 mm×1 mm. The mechanical properties were
measured with an Instron Universal tester (model 1185,
with a yield of 95%.
－
1
1
Japan) at 25 ℃ with a crosshead speed of 25 mm•min .
The dumb-bell-shaped specimens were prepared ac-
cording to ASTM D412-87. Five samples were analyzed
to determine an average value in order to obtain the re-
producible result.
For oligo-TA-m-PI, H NMR (CDCl
3
, 300 MHz) δ:
8.04—7.98 (m, 8H), 6.93—6.87 (m, 8H), 6.45—5.78 (m,
6H), 4.61—1.03 (m, 80H); IR (NaCl plate) ν: 3600—
－
1
3100, 1735, 1667, 1600, 810 cm .
1
For Si-m-PI, H NMR (CDCl
3
, 300 MHz) δ: 8.04—
1
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UV-Irradiation Cured Organic-inorganic Hybrid Nanocomposite
7
1
3
.98 (m, 8H), 6.93—6.87 (m, 8H), 4.58—0.93 (m,
systems, USA), and then immersed into distilled water
at 50 ℃ for 3 h for facilitating the hydrolysis, follow-
ing by heating in an oven at 80 ℃ for 2 h, 90 ℃ for 1
h for postcuring the silanol group. Finally, the UV-cured
hybrid nanocomposites with different organic and inor-
ganic domains, named Nano-Si-m-PI2, Nano-Si-m-PI4
and Nano-Si-m-PI6, were obtained according to the dif-
ferent Si-m-PI loadings.
For comparison, the corresponding UV-cured hybrid
nanocomposites initiated by Irgacure 2959, named
nano-Irg2, nano-Irg4 and nano-Irg6, were also prepared.
And the acrylic resin without oligo-TEOS addition was
UV-irradiated in the presence of 4% Irgacure 2959 to
form pure polymer.
26H), 0.64—0.54 (m, 4H); IR (NaCl plate) ν: 3600—
－
1
100, 1735, 1667, 1600 cm .
Oligomeric TEOS (oligo-TEOS) 5.19 g (288.3
mmol) water, 20 g (96.2 mmol) TEOS, and 8.85 g
ethanol were mixed in a round-bottom flask. After the
mixture became homogenous, hydrochloric acid (2
mmol) was added slowly under stirring, and kept the
reaction overnight at room temperature, resulting in
formation of an oligomeric TEOS (oligo-TEOS). For
measuring the FT-IR spectrum, the NaCl plate coated
with oligo-TEOS was heated in an oven at 75 ℃ for 2
－
1
h. IR (NaCl plate) ν: 3399, 1077, 958, 798 cm .
Preparation of hybrid coatings The formulations
utilized in this study for preparing the hybrid coatings
consisted of EB605, oligo-TEOS, and either Si-m-PI or
Irgacure 2959. The compositions are listed in Table 1.
The photoinitiating chromophoric group contents in the
formulations were set as 2 wt%, 4 wt% and 6 wt%, re-
spectively. The formulation was adequately stirred until
the homogenous solution was formed, and then kept un-
der vacuum for 10 min at 50 ℃ to remove the air bub-
bles formed during stirring. The sample was irradiated by
a medium pressure mercury lamp (1 kW, Fusion UV
Results and discussion
Synthesis and characterization
Scheme 1 depicts the synthetic route of Si-m-PI. The
esterification reaction of Irgacure 2959 with thioglycolic
acid was carried out effectively in the presence of DPTS
as a catalyst to form TA-m-PI. As shown in Figure 1,
1
the peaks at δ 2.0—1.94 in the H NMR spectrum of
TA-m-PI are assigned to the proton of SH, while other
Table 1 Photoinitiator contents of the UV-curable acrylate formulations based on EB605 resin
Irgacure 2959/wt% Si-m-PI/wt% oligo-TEOS/wt% Irgacure 2959 moiety/wt%
Sample
Pure polymer
Nano-Irg2
4
—
—
4
2
4
6
2
4
6
2
4
6
—
2
4
6
2
4
6
Nano-Irg4
—
Nano-Irg6
—
Nano-Si-m-PI2
Nano-Si-m-PI4
Nano-Si-m-PI6
—
—
—
3.7
7.4
11.1
Scheme 1 Synthetic route of Si-m-PI
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1963

Hu & Shi
FULL PAPER
proton-corresponding peaks can also be distinguished
clearly. In order to obtain the oligomeric photoinitiator
with four photoinitiator chromophoric end-groups the
addition reaction took place between SH bond of
TA-m-PI and double bond of EM265. From the H NMR
spectrum for oligo-TA-m-PI in Figure 1, the peaks at δ
the molecular structures of TA-m-PI, oligo-TA-m-PI
and Si-m-PI.
The UV absorption spectra of Irgacure 2959 and
2 2
Si-m-PI were determined in CH Cl with the concentra-
1
－
5
－
1
tion of 3.1×10 g•L in terms of Irgacure 2959 moi-
ety, as shown in Figure 3. It can be seen that the Si-m-PI
possesses the similar UV spectrum and molar extinction
coefficient compared with Irgacure 2959. This indicates
that the macromolecular structure of Si-m-PI has no
effect on the light absorption capacity of chromophoric
group. As well known, the maximum absorption wave-
length range and the molar extinction coefficient are the
most important characters for a photoinitiator, which
determine the photoinitiating efficiency and photopoly-
merization behaviors. Therefore, the Si-m-PI is very
attractive as a photoinitiator for free radical UV-curing
systems.
2
.0—1.94 disappeared completely, indicating the entire
consumption of SH group. The average functionality of
oligo-TA-m-PI was defined according to the calculated
number of photoinitiating chromophoric group from the
1
H NMR spectrum. Finally, the residual double bonds in
2
oligo-TA-m-PI further addition reacted with NH of
KH-550 for the introduction of trimethoxysilane group,
leading to the formation of Si-m-PI. As seen from the
1
H NMR spectrum of Si-m-PI in Figure 1, the peaks at δ
6
.45—5.78 for the acrylate double bond protons disap-
peared completely and the new peaks at δ 0.64—0.54
for the protons abutted on the Si atom appeared, denot-
ing the formation of Si-m-PI. Figure 2 represents the
FT-IR spectra of TA-m-PI, oligo-TA-m-PI and Si-m-PI.
Compared with the FT-IR spectrum of TA-m-PI, the
－
1
peak at 2576 cm for SH group in the oligo-TA-m-PI
spectrum disappeared. Contrariwise, the peaks at 810
－
1
cm for the C＝C bond of acrylate group appeared.
Moreover, in the FT-IR spectrum of Si-m-PI, the peak
－
1
for the C＝C bond of acrylate group at 810 cm disap-
peared completely. These results further confirmed
2 2
Figure 3 UV spectra of Irgacure 2959 and Si-m-PI (CH Cl ,
－
5
－
1
3
.1× 10 g•L in terms of Irgacure 2959 moieties).
Figure 4 shows the FT-IR spectrum of oligo-TEOS.
－
1
The peaks at 1077 and 798 cm are the characteristic
peaks of the asymmetric stretch vibration and symmetric
stretch vibration for the Si-O-Si group, respectively.
－
1
While the absorption at 958 cm is assigned to the
2
2
Si-OH group. The existence of these peaks indicated
the occurrences of hydrolysis and condensation of
TEOS.
1
Figure 1 H NMR spectra of TA-m-PI, oligo-TA-m-PI and
Si-m-PI.
Photoinitiating behavior of Si-m-PI
The photolysis of Irgacure 2959 results in the forma-
tion of benzoyl and hydroxyalkyl radicals, which can
effectively initiate the polymerization of vinyl mono-
mers and oligomers. In the hybrid Si-m-PI, the hy-
droxyl-2-methylpropiophenone group of Irgacure 2959
is incorporated together with the triethoxysilane group
of KH-550 at the terminals. Figure 5 shows the photo-
max
polymerization rates at the peak maximum (Rp ) and
f
the final unsaturation conversion (P ) in the cured
Nano-Irg films with oligo-TEOS addition initiated by
Irgacure 2959 in different contents in comparison with
the pure acrylic resin in the presence of 4 wt% Irgacure
2
959. All the data measured by photo-DSC method are
Figure 2 FT-IR spectra of TA-m-PI, oligo-TA-m-PI and
Si-m-PI.
listed in Table 2. It can be seen that the Nano-Irg sys-
tems possesses the lower Rp
max
f
and P compared
1
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UV-Irradiation Cured Organic-inorganic Hybrid Nanocomposite
max
Table 2 Photopolymerization rates at peak maximum (R
p
)
f a
and final unsaturation conversion (P ) in the UV-cured films
obtained by Photo-DSC method
max
p
－
1
－
1
f
Sample
R
/( J•g •s )
P /%
Pure polymer
Nano-Irg2
5.8
4.2
5.0
5.5
4.8
6.2
6.8
66.8
59.0
64.1
67.9
69.2
71.5
78.4
Nano-Irg4
Nano-Irg6
Nano-Si-m-PI2
Nano-Si-m-PI4
Nano-Si-m-PI6
Figure 4 FTIR spectrum of oligo-TEOS.
a
f
The irradiation time for the final unsaturation conversion (P ) is
f
with the pure acrylic resin except for the almost same P
300 s.
of Nano-Irg6 sample. This is due to the fact that the
concentration of double bond in the Nano-Irg systems
was diluted by the addition of oligo-TEOS. However,
max
f
both Rp
and P increase successively with increasing
Irgacure 2959 loading.
On the other hand, for the Nano-Si-m-PI systems
with the Irgacure 2959 segment content of over 2 wt%,
max
the higher Rp
than that of pure acrylic resin is ob-
served (Figure 6 and Table 2). Moreover, the much
f
higher P values in the cured Nano-Si-m-PI films are
obtained than that in the pure polymer as well Nano-Irg
films. There are mainly two competitive factors which
max
f
affect the Rp
and P . On the one hand, the triethoxy-
silane group in Si-m-PI reacts with oligo-TEOS to form
the crosslinking network, which restricts the remotion of
formed benzoyl radicals, and the concentration of
Figure 6 (a) Photopolymerization rates and (b) unsaturation
conversion in the cured hybrid films initiated by Si-m-PI in dif-
ferent contents in comparison with acrylic resin.
double bond is diluted by the addition of oligo-TEOS,
max
f
both leading to the decrease of Rp
and P in the
cured film; on the other hand, the concentration of local
radicals generated by the multifunctional Si-m-PI was
higher than that of Irgacure 2959, resulting in the in-
max
f
creases of Rp
and P . As a result, the significant ef-
fect of increased local radical concentration counteracts
the influence of reduced concentration of double bond
max
p
and restricted remotion of benzoyl radicals on the R
and P .
f
Morphology of the UV-cured nanacomposites
Figure 5 (a) Photopolymerization rates and (b) unsaturation
conversion in the cured hybrid films initiated by Irgacure 2959 in
different contents in comparison with acrylic resin.
Figure 7 shows the SEM micrographs of UV-cured
hybrid nanocomposites (Nano-Irg6 and Nano-Si-m-PI6)
Chin. J. Chem. 2011, 29, 1961— 1968
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1965

Hu & Shi
FULL PAPER
and pure polymer initiated by 6 wt% either Irgacure
Thermal properties of the UV-cured nanocomposites
2
2959, or Si-m-PI. The formed SiO nanoparticles
The TGA thermograms of Nano-Irgs and Nano-Si-
through sol-gel procedure can be found from both im-
ages of hybrid nanocomposites. However, the aggrega-
tion of nanoparticles, and phase separation phenomenon
are obviously observed from Figure 7(b). This is due to
the poor compatibility between the inorganic domains
formed from the oligo-TEOS and the polymer matrix.
Whereas, as shown in Figure 7(c), the SiO nanoparti-
2
cles dispersed uniformly in the polymer matrix, causing
the interface between the organic and inorganic phases
m-PIs measured from room temperature to 800 ℃ in
2
N atmosphere are shown in Figure 8 and Figure 9. The
specific degradation temperatures and the final char
yields at 800 ℃ are listed in Table 3. It can be obvi-
ously found from the data that the thermal stability of
cured hybrid nanocomposite films is improved by the
incorporation of inorganic component into the polymer
matrix. And the enhancement is much more remarkable
for Nano-Si-m-PIs than Nano-Irgs because of the uni-
2
unclear. Additionally, the size of formed SiO nanopar-
2
form dispersion of SiO nanoparticles in the polymer
ticles with near-round shape was estimated to be mostly
in the range of 15—30 nm. This can be explained that
the formed benzoyl and hydroxyalkyl radicals from
Si-m-PI initiate the photopolymerization of acrylic dou-
ble bonds when exposed to an UV lamp, forming the
organic domains; on the other hand, the triethoxysilane
end-groups of Si-m-PI react with oligo-TEOS, forming
the inorganic domains. The chemically bonding took
place between the organic and inorganic domains. Con-
sequently, the compatibility between the organic and
inorganic phases was improved by the chemical connec-
tion at a molecular level. Therefore, the Si-m-PI can be
considered as an effective coupling agent, except for
acting as an oligomeric photoinitiator in the preparation
of hybrid nanocomposites.
matrix for the former, and thus effectively preventing
the polymer chains from thermal degradation. The in-
crease in decomposition temperature of over 22 ℃ for
Nano-Si-m-PI6 was obtained at 10% weight loss,
whereas for Nano-Irg6, there was only an increase of 12
℃
, compared with the pure polymer. Moreover, the
thermal stability and the char residue of both samples
increase along with increasing photoinitiator and
oligo-TEOS loadings.
The thermal mechanical properties were investigated
by the dynamic mechanical thermal analysis (DMTA).
The storage modulus (E′) and loss factor (tan δ) curves
are depicted in Figure 10 and Figure 11, and the data are
listed in Table 4. The temperature associated with the
peak position of tan δ curve is defined as the glass tran-
Figure 8 TGA curves of UV-cured pure polymer and Nano-Irgs
under N flow.
2
Figure 7 SEM micrographs of (a) pure polymer, (b) Nano-Irg6
Figure 9
TGA curves of UV-cured pure polymer and
and (c) Nano-Si-m-PI6.
Nano-Si-m-PIs under N flow.
2
1
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UV-Irradiation Cured Organic-inorganic Hybrid Nanocomposite
Table 3 TGA data of the UV-cured pure polymer and hybrid
nanocomposites
Temperature recorded at the
Residue/%
Sample
specific weight loss/℃
(
800 ℃)
1
0%
50%
401.7
397.0
404.8
405.9
401.8
402.4
413.9
Pure polymer
Nano-Irg2
310.9
302.2
313.4
322.0
306.4
322.3
332.3
0.1
0.8
1.5
2.3
2.6
5.6
7.3
Nano-Irg4
Nano-Irg6
Nano-Si-m-PI2
Nano-Si-m-PI4
Nano-Si-m-PI6
Figure 10 DMTA curves of UV-cured pure polymer and
Nano-Irgs.
sition temperature (T ). E′ can be used to provide the
g
information regarding the degree of cure and
cross-linking density. It is interesting to note that the
rubbery storage modulus E′rubb first increases and then
decreases with increasing Si-m-PI content. This can be
interpreted to be mainly two competitive factors, that is,
2
the nanoreinforcement effect from the SiO nanoparticle
dispersed in the polymer matrix, and the decreased
crosslinking density per unit volume caused by the addi-
tion of inorganic component. However, for the systems
with the Si-m-PI and oligo-TEOS contents of both be-
low 4 wt%, the significant nanoreinforcement effect
counteracts the influence of reduced crosslinking den-
sity on the rubbery storage modulus. With continuing to
increase both the Si-m-PI and oligo-TEOS contents to 6
wt%, the reduced crosslinking density dominates the
negative effect, leading to the decrease in E′rubb. More-
Figure 11 DMTA curves of UV-cured pure polymer and
Nano-Si-m-PIs.
Table 4 E′rubb and T of the UV-cured pure polymer and hybrid
g
nanocomposites obtained from DMTA
Sample
E′rubb/MPa
71.8
T
g
/℃
over, the T
nanoreinforcement effect on T
films with the Si-m-PI and oligo-TEOS contents of both
below 4 wt%. The bulky SiO inorganic core might re-
g
follows the same trend with the E′rubb. The
dominates for the hybrid
Pure polymer
Nano-Irg2
88.3
91.4
g
74.2
2
Nano-Irg4
85.6
94.9
strict the segmental motion of polymer chain, resulting
in the requirement of higher temperature to provide the
requisite thermal energy for the occurrence of glass
transition in the nanocomposite. As the hybrid compos-
ite contains 6 wt% Si-m-PI and oligo-TEOS contents,
the decrease in crosslinking density dominants, resulting
Nano-Irg6
79.7
92.0
Nano-Si-m-PI2
Nano-Si-m-PI4
Nano-Si-m-PI6
89.9
93.6
100.6
95.6
111.2
102.2
in the decrease of T
g
.
UV cured nanocomposites initiated by Si-m-PI is higher
than that by Irgacure 2959. This is consistent with the
results obtained by DMTA. However, the elongation at
break of all the hybrid samples decreases compared with
that of the pure polymer. This can be attributed to that
the polymer chains in the hybrids are restricted by the
inorganic network, resulting in the decreased degree of
freedom. The Pendulum and pencil hardness for both
series samples increase with increasing photoinitiator
and oligo-TEOS loadings due to the nanoreinforcement
The similar trend was obtained for the UV-cured hy-
brid nanocomposites initiated by Irgacure 2959, while
possessing the lower values (Figure 10) than that by
Si-m-PI due to the poor compatibility between the or-
ganic and inorganic domains.
Mechanical and physical properties of the UV-cured
nanocomposites
The mechanical properties of UV-cured hybrid films
were measured and the data are listed in Table 5. The
tensile strength first increases and then decreases along
with the increase of either Si-m-PI or Irgacure 2959
loading owing to the competitive effects by the nanore-
2
effect of SiO nanoparticles.
Conclusions
inforcement of the SiO
crosslinking density. Furthermore, the tensile strength of
2
core and the decrease of
The homogeneous UV-cured hybrid nanocomposite
was prepared through the photopolymerization of
Chin. J. Chem. 2011, 29, 1961— 1968
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
1967

Hu & Shi
FULL PAPER
Table 5 Mechanical properties and hardness of UV-cured pure polymer and hybrid nanocomposites
Sample
Pure polymer
Nano-Irg2
Tensile strength/MPa
Elongation at break/%
Persoz hardness/s
Pencil hardness/H
32.6
34.5
38.7
36.3
40.5
45.8
43.1
10.2
9.7
9.3
8.4
8.0
7.2
6.5
323
329
335
341
339
350
368
2
2
3
3
3
4
4
Nano-Irg4
Nano-Irg6
Nano-Si-m-PI2
Nano-Si-m-PI4
Nano-Si-m-PI6
acrylic resin initiated by silanized multifunctional oli-
gomeric photoinitiator (Si-m-PI). Compared with Ir-
gacure 2959, the Si-m-PI possesses the higher photoini-
tiating activity based on the photopolymerization kinet-
7
8
9
Teng, G. H.; Wegner, J. R.; Hurtt, G. J.; Soucek, M. D.
Prog. Org. Coat. 2001, 42, 29.
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2
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cles in the polymer matrix was achieved through a
sol-gel process by using the oligo-TEOS. Whereas, the
UV-cured hybrid nanocomposite initiated by Irgacure
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2
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Chin. J. Chem. 2011, 29, 1961— 1968