Synthesis and thermal properties of silicon-containing epoxy resin used for UV-curable flame-retardant coatings

Article abstract of DOI:10.1007/s10973-010-1053-9

A novel silicon-containing trifunctional cycloaliphatic epoxide resin tri(3,4-epoxycyclohexylmethyloxy) phenyl silane (TEMPS) was synthesized and characterized by FTIR, ¹H NMR, ¹³C NMR, and ²⁹Si NMR spectroscopic analysis. A series of flame-retardant formulations by blending TEMPS with a commercial epoxide resin DGEBA (EP828) in different ratios were prepared, and exposed to a medium pressure lamp to form the cured films in the presence of diaryliodonium hexafluorophosphate salt as a cationic photoinitiator. The thermal degradation behaviors of the cured films were evaluated by thermogravimetric analysis. The char yields under nitrogen and air atmospheres increased along with the TEMPS content. The limiting oxygen index (LOI) value increased from 22 for EP828 to 30 for TEMPS80, demonstrating the improved flame retardancy. The data from the dynamic mechanical thermal analysis showed that TEMPS had good miscibility with EP828. The T _s and T _g both decreased from 93 and 138 to 78 and 118 °C, respectively. The crosslinking density (ν _e) increased along with the TEMPS content. The mechanical property measurements indicated that the addition of TEMPS led to a decrease in the tensile strength and an increase in the elongation-at-break.

Full text of DOI:10.1007/s10973-010-1053-9

J Therm Anal Calorim (2011) 103:303–310
DOI 10.1007/s10973-010-1053-9
Synthesis and thermal properties of silicon-containing epoxy resin
used for UV-curable flame-retardant coatings
•
Xi-e Cheng Wenfang Shi
Received: 23 March 2010 / Accepted: 13 September 2010 / Published online: 7 October 2010
´
´
Ó Akademiai Kiado, Budapest, Hungary 2010
Abstract A novel silicon-containing trifunctional cyclo-
aliphatic epoxide resin tri(3,4-epoxycyclohexylmethyloxy)
phenyl silane (TEMPS) was synthesized and characterized
by FTIR, 1H NMR, 13C NMR, and 29Si NMR spectroscopic
analysis. A series of flame-retardant formulations by
blending TEMPS with a commercial epoxide resin
DGEBA (EP828) in different ratios were prepared, and
exposed to a medium pressure lamp to form the cured films
in the presence of diaryliodonium hexafluorophosphate salt
as a cationic photoinitiator. The thermal degradation
behaviors of the cured films were evaluated by thermo-
gravimetric analysis. The char yields under nitrogen and air
atmospheres increased along with the TEMPS content. The
limiting oxygen index (LOI) value increased from 22 for
EP828 to 30 for TEMPS80, demonstrating the improved
flame retardancy. The data from the dynamic mechanical
thermal analysis showed that TEMPS had good miscibility
with EP828. The Ts and Tg both decreased from 93 and 138
to 78 and 118 °C, respectively. The crosslinking density
(me) increased along with the TEMPS content. The
mechanical property measurements indicated that the
addition of TEMPS led to a decrease in the tensile strength
and an increase in the elongation-at-break.
Introduction
Since the introduction in the 1940s, epoxy resins have been
widely used on a large scale for adhesives, coatings, cast-
ings, and advanced composites in aerospace and electronic
industries due to their excellent thermal and chemical
resistance, superior mechanical properties, and high adhe-
sion to many substrates [1–3]. However, to meet some
application requirements, the flammability of epoxy resins
is a major disadvantage in the use. Moreover, most thermo-
curing epoxy resins are used as mutually reactive compo-
nent mixtures. Owing to their poor handling characteristics,
epoxy resins cannot be easily used in automated assembly-
line processes. Therefore, it is worth to develop one-com-
ponent, shelf-stable flame-retardant epoxy resins.
As an alternative to halogenated flame retardants, which
release toxic gases and corrosive smoke during combustion
[4], silicon-containing flame retardants have been consid-
ered environmental friendly because it can reduce the
harmful impact on the environment compared with the
existing materials. Two approaches for preparing epoxy
resins with silicon covalently bonded to the final epoxy
network have been reported. One is to synthesize the sili-
con-containing epoxides, which can be thermo-cured on
their own or blended with other epoxy comonomers in the
presence of curing agents [5–11]. Another is to synthesize
diamino-terminated siloxanes, which can be used as curing
agents to effectively introduce silicon into thermo-curing
epoxy resins [6, 11, 12].
Keywords Cycloaliphatic epoxide resin ꢀ Silicon ꢀ
Flame-retardant ꢀ UV-curing
However, apart from thermally curing systems, UV-
curing systems, which can be classified into free-radical
and cationic systems, have been successfully introduced
into many applications, such as printing inks, electronics,
activating adhesives, and coatings [13, 14]. Although many
interests have been focused on free-radical systems due to
X. Cheng ꢀ W. Shi (&)
CAS Key Laboratory of Soft Matter Chemistry, Department of
Polymer Science and Engineering, University of Science and
Technology of China, Hefei, Anhui 230026, People’s Republic
of China
e-mail: wfshi@ustc.edu
123

304
X. Cheng, W. Shi
their high photopolymerization activity, the less utilized
cationic curing, based on the photo-generation of acid and
consecutive cationic polymerization, still presents a num-
ber of advantages. First, the epoxide resins used in cationic
photopolymerization systems are characterized by being
less toxic and irritant with respect to acrylates largely used
in radical photopolymerization. Second, the cationic pho-
topolymerization is not inhibited by oxygen, whereas the
free-radical photopolymerization is usually inhibited by
oxygen and even sometimes must be carried out in inert
atmosphere [15, 16]. Third, there is low shrinkage during
UV-curing of cationic curable materials, thereby resulting
in good adhesion to substrates. More importantly, the cat-
ionic systems containing epoxide resins are usually one-
component formulations and possess good shelf stability at
room temperature in dark, compared with two-component
mixtures used in thermo-curing systems.
Phenyltrimethoxy silane (9.92 g; 0.050 mol), CM
(33.65 g; 0.30 mol), and titanium tetraisopropoxide
(0.30 g; 0.001 mol) were added into a 250-mL flask, and
stirred at 60 °C in vacuo to remove the formed methanol.
1
The progress of the reaction was monitored by H NMR
analysis until complete disappearance of the peak for Si–
O–Me group. The unreacted CM was removed under
reduced pressure at higher temperature. Then the reaction
mixture was washed twice with 5 wt% tartaric acid, three
times with 5 wt% NaHCO3, and then with water and brine.
The organic layer was dried over Na2SO4 and filtered.
Then the solvent was evaporated under vacuum, obtaining
a liquid product with a yield of 86%, named TCMPS.
1H NMR (300 MHz, CDCl3, ppm) d: 1.10–1.43 (CH2CH-
CH2CH2), 1.55–2.26 (CH2CHCH2CH2), 3.48–3.83 (OCH2-
CH), 5.55–5.81 (CH2CH=CHCH2), 7.18–7.86 (SiC6H5).
13C NMR (300 MHz, CDCl3, ppm) d: 24.8 (CH2CH-
CH2CH2), 25.4 (CH2CHCH2CH2), 28.2 (CH2CHCH2CH2),
36.2 (CH2CHCH2CH2), 67.8 (OCH2CH), 126.2 (CHCH2-
CH=), 127.9 (=CHCH2CH2), 127.1, 130.4 and 134.9
(SiC6H5).
There has been little work performed to prepare silicon-
containing epoxide resins as flame-retardant components
used for cationically UV-curing systems. In this study, we
synthesized a trifunctional silicon-containing cycloaliphatic
epoxide, tri(3,4-epoxycyclohexylmethyloxy) phenyl silane
(TEMPS), used as a new reactive-type flame retardant.
TEMPS monomer has good miscibility with different ratios
of commercial DGEBA resin (EP828). The flame retardan-
cy, thermal and mechanical properties, and the dynamic
mechanical thermal behavior were investigated in detail.
29Si NMR (300 MHz, CDCl3, ppm) d: -58.1.
Synthesis of tri(3,4-epoxycyclohexylmethyloxy) phenyl
silane (TEMPS)
mCPBA (34.5 g, 0.20 mol) was dissolved in 300 mL of
dichloromethane in a three-necked flask. TCMPS (21.9 g,
0.050 mol) dissolved in 100 mL of dichloromethane was
then added dropwise into above solution at 0 °C using an
ice bath, and reacted at room temperature for 24 h. After
precipitation and filtration, the suspension was washed by
0.1 M aqueous Na2S2O3, saturated aqueous NaHCO3, and
then distilled water. The obtained organic layer was dried
by anhydrous Na2SO4. After filtration and evaporation to
remove Na2SO4 and dichloromethane, the transparent
liquid obtained was further purified by flash chromatogra-
phy (hexane/ethyl acetate = 5:2), obtaining the final
product in a yield of 74%, named TEMPS.
Experimental
Materials
Phenyltrimethoxyl silane and titanium tetraisopropoxide
were supplied by Fluka. 3-Cyclohexene-1-carboxaldehyde
and m-chloroperoxybenzoic acid (mCPBA) were purchased
from Aldrich Chemical Co. NaBH4, Na2SO4, NaHCO3,
Na2S2O3, tartaric acid, methanol, and toluene were pur-
chased from the First Reagent Co. of Shanghai, China.
DGEBA resin (EP828) was obtained from Shell Chemical
Co. USA. Diaryliodonium hexafluorophosphate salt (Irga-
cure 250) was supplied as a gift by BASF (Ciba-Geigy) and
used as a cationic photoinitiator.
1H NMR (300 MHz, CDCl3, ppm) d: 0.82–2.27 (CH2CH-
CH2CH2), 3.05–3.26 (CH2CHCHCH2), 3.48–3.63 (OCH2
CH), 7.34–7.64 (SiC6H5).
13C NMR (300 MHz, CDCl3, ppm) d: 20.5–34.7 (CH2CH-
CH2CH2), 51.2 (CHCH2CH), 52.2 (CHCH2CH2), 66.9
(OCH2CH), 127.5, 130.1 and 134.2 (SiC6H5).
Synthesis
29Si NMR (300 MHz, CDCl3, ppm) d: -58.4.
Synthesis of tri(cyclohex-3-enylmethoxy) phenyl silane
(TCMPS)
UV cationic curing
3-Cyclohexenyl-l-methanol (CM) was prepared in a high
yield by the reduction of 3-cyclohexene-1-carboxaldehyde
with NaBH4 in methanol according to the literature
reported elsewhere [17].
The mixtures of TEMPS with DGEBA in different ratios
(Table 1) were stirred until the homogenous blends
formed. TEMPS and the mixtures in the presence of 4 wt%
Irgacure 250 exposed to a medium pressure mercury lamp
123

Synthesis and thermal properties of silicon-containing epoxy resin
305
(2 kW, Fusion UV systems, USA) for 2 min and then
thermally cured at 120 °C for 150 min to obtain the cured
films.
frequency of 2 Hz and a heating rate of 5 °C min-1 in the
range from -50 to 200 °C with the sheet of 25 9 5 9
1 mm3.
The mechanical properties were measured with an In-
stron Universal tester (model 1185, Japan) at 25 °C with a
crosshead speed of 25 mm min-1. The dumb-bell-shaped
specimens were prepared according to ASTM D412-87.
Five samples were analyzed to determine an average value
in order to obtain the reproducible result.
Measurements
The Fourier transfer infrared (FTIR) spectra were recorded
using a Nicolet MAGNA-IR 750 spectrometer. The liquid
samples were filmed on the surface of NaCl crystal.
1
The H NMR, 13C NMR, and 29Si NMR spectra were
recorded with an AVANCE 300 Bruker spectrometer using
tetramethylsilane as an internal reference and CDCl3 as a
solvent.
Results and discussion
The thermogravimetric analysis (TG) was carried out
with the sample of 3–5 mg on a Shimadzu TG-50 instru-
ment using a heating rate of 10 °C min-1 in nitrogen or air
atmosphere.
Synthesis and characterization
In this study, the silicon-containing cycloaliphatic epoxide
resin (TEMPS) was prepared in three steps, as presented
Fig. 1, including the synthesis of unsaturated alcohol by
the reduction of 3-cyclohexene-1-carboxaldehyde, the
Lewis acid-catalyzed transesterification of trimethoxy-
phenyl silane with unsaturated alcohol, and then the
epoxidation of double bond. In the titanium tetraisoprop-
oxide-catalyzed transesterification, an excess of CM was
used and the generated methanol was removed under
reduced pressure during the reaction in order to enhance
the reaction rate and achieve a higher yield. mCPBA was
used to epoxidize the unsaturated intermediate, TCMPS,
which gives almost complete conversion of double bond.
The obtained TCMPS and TEMPS were characterized
by FTIR, 1H NMR, 13C NMR, and 29Si NMR spectroscopy.
The FTIR spectra in Fig. 2 show the strong absorptions
around 1068 and 1130 cm-1, which correspond to the Si–
O–C and Si–C6H5 stretching, respectively. In the TCMPS
spectrum, the absorption peaks around 1653 and
3021 cm-1 can be attributed to the vibration of alkene C=C
and =C–H bonds in the cyclohexyl ring. In the TEMPS
spectrum, the disappearance of peaks for alkene C=C and
=C–H groups and the appearance of absorption peak at
The limiting oxygen index (LOI) values were measured
using a ZRY-type instrument (made in Jiangning, China)
with the sheet of 120 9 6.5 9 3 mm3 according to ASTM
D635-77.
The tensile storage modulus (E0) and tensile loss factors
(tan d) were measured using a dynamic mechanical ther-
mal analyzer (Diamond DMA, PE Co., USA) at a
Table 1 Compositions of the resins and the flame retardancy of the
cured films
Sample
Composition/wt%
Silicon
contenta/wt%
LOI
EP828
TEMPS
EP828
100
80
60
40
20
0
0
20
0
22
24
26
29
30
32
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS100
a
1.15
2.30
3.46
4.61
5.76
40
60
80
100
Theoretical value
Fig. 1 Synthetic route of
TEMPS
OCH3
CH3O Si OCH3
NaBH4
OH
CHO
CM
catalyst
O
O
O
O
mCPBA
O
O
Si O
O
Si O
TEMPS
TCMPS
123

306
X. Cheng, W. Shi
a
1653
TCMPS
TEMPS
3021
b
808
3000
2400
1800
1200
600
50
0
–50
–100
–150
Wavenumber/cm–1
ppm
Fig. 2 FTIR spectra of (a) TCMPS, and (b) TEMPS
Fig. 5 29Si NMR spectra of TCMPS and TEMPS in CDCl3
1
3.03–3.26 ppm in the H NMR spectrum and at 51.2 and
h
i
52.2 ppm in the 13C NMR spectrum. Moreover, the inte-
O
d
d
1
grated values of these peaks in the H NMR spectra match
i
f + g + j
j
O
Si
O
h
e
d
c
b
a
well to the numbers of hydrogen atoms in the TCMPS and
TEMPS structures. It can be also observed that the number
of peak in the 13C NMR spectrum for TEMPS is more than
the number of carbon, which may be interpreted that dif-
ferent isomers of the epoxycyclohexyl rings are present in
TEMPS. The details will be studied in the future. The
further confirmation for the molecular structures was made
by means of the 29Si NMR spectra. The single absorption
bands with chemical shifts for the silane structure are
shown in Fig. 5, indicating the expected structures both for
TCMPS and TEMPS, as well their high purity.
g
f
a
e
b
c
O
h
i
c
O
b
O
e + f + g + j
i
a
j
O
O
Si
O
h
d
e
a
g
f
b
c
8
6
4
2
0
ppm
Fig. 3 1H NMR spectra of TCMPS and TEMPS in CDCl3
g
Thermal degradation behavior
j
f
d
d
O
b
i
i
j
O
Si
O
h
e
e
d
a
h
a
g
f
Thermogravimetric analysis (TG) is one of the commonly
used techniques for rapid evaluation in comparing and
ranking the thermal stability of various polymers. To
examine the effect of silicon content on the thermal sta-
bility and decomposition behavior, TG data under nitrogen
and air atmospheres were determined and analyzed. The
resin compositions and the silicon contents were listed in
Table 1.
c
b
c
e+f+g+j
a
O
b
h
i
O
O
i
j
O
c
O
Si
O
h
d
e
a
g
f
b
c
140
120 100
80
ppm
60
40
20
Figures 6 and 7 show the mass loss thermograms (TG)
and the differential mass loss (DTG) curves of UV-cured
samples from room temperature to 850 °C recorded in
nitrogen atmosphere, respectively. The specific degradation
temperatures and the final char yields at 850 °C are listed
in Table 2. The onset decomposition temperature, T5%, of
UV-cured film decreases along with the addition of
TEMPS, from 280 °C for pure EP828 to 250 °C for
TEMPS80 sample. From the DTG curves, it can be
observed that all the UV-cured films mainly give a one-
stage mass loss behavior. The sample with higher TEMPS
content began to degrade at a lower temperature and show
Fig. 4 13C NMR spectra of TCMPS and TEMPS in CDCl3
808 cm-1 for epoxy group both confirm the expected
structures of TCMPS and TEMPS.
Figures 3 and 4 show the 1H and 13C NMR spectra with
1
their signal assignments. The chemical shifts of H NMR
signals at 5.48–5.89 ppm and 13C NMR signals at 126.2
and 127.9 ppm indicate the presence of alkene in TCMPS,
which are not present in TEMPS. After the epoxidation,
new signals of the formed epoxide ring are observed at
123

Synthesis and thermal properties of silicon-containing epoxy resin
307
a broader mass loss temperature range. The temperatures at
the maximum mass loss rate (Tmax1) decreases from 407 °C
for the silicon-free resin to 373 °C for the resin containing
4.61% silicon. So the thermal stability decreases as the
silicon content increases at a lower temperature. This can
be ascribed to the presence of decomposable Si–O groups
at lower temperature in the resins, as reported elsewhere
[9]. However, the final char yield at 850 °C is significantly
enhanced from 14 for EP828 to 25 for TEMPS80, as listed
in Table 2. It can be explained by the fact that the
decomposition of Si–O group at lower temperature resulted
in the formation of silicone-containing group which will
participate in the crosslinked carbonization and effectively
retard the decomposition at higher temperature.
The TG and the DTG curves of the UV-cured samples
recorded in air atmosphere are also investigated, as shown
in Figs. 8 and 9. The onset decomposition temperatures,
100
T5%, decrease along with the increase of TEMPS content,
EP828
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS100
showing a similar trend to the one mentioned above. The
difference in degradation behavior of epoxy resins con-
taining different contents of silicon can be observed from
their DTG curves. The degradation of all the cationically
UV-cured samples exhibits a two-step process based on the
number of peaks in the DTG curves. For the first stage of
decomposition, the temperature of the maximum mass loss
rate, Tmax1, decreases slightly with the increase of TEMPS
content, from 346 °C for EP828 to 334 °C for TEMPS.
Moreover, the Tmax1 of TEMPS occurs at 26 °C lower than
that in nitrogen atmosphere, which further indicates that
the oxidation in breaking off the Si–O group results in the
80
60
40
20
200
400
600
800
Temperature/°C
Fig. 6 TG curves of the UV-cured TEMPS/EP828 films in N2
atmosphere
100
1.2
EP828
EP828
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS100
80
60
40
20
0
0.9
TEMPS100
0.6
0.3
0.0
200
400
600
800
200
400
600
800
Temperature/°C
Temperature/°C
Fig. 7 DTG curves of the UV-cured TEMPS/EP828 films in N2
atmosphere
Fig. 8 TG curves of the UV-cured TEMPS/EP828 films in air
atmosphere
Table 2 TG and DTG analysis data of the cured films
Sample
N2
Air
T
5%/°C
T
max1/°C
Char/wt%
T5%/°C
Tmax1/°C
T
max2/°C
Char/wt%
EP828
280
273
260
255
250
244
407
395
389
382
373
360
14
18
20
22
25
27
266
261
257
250
244
231
346
344
342
340
336
334
514
517
523
536
558
590
0
5
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS100
7
10
14
16
123

308
X. Cheng, W. Shi
0.8
EP828
109
108
107
106
1.2
0.8
0.4
0.0
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS100
0.6
EP828
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS100
δ
0.4
0.2
0.0
200
400
600
800
0
50
100
150
200
Temperature/°C
Temperature/°C
Fig. 9 DTG curves of the UV-cured TEMPS/EP828 films in air
atmosphere
Fig. 10 DMTA curves of the UV-cured TEMPS/EP828 films
EP828 to 30 for TEMPS80. It is concluded that the addition
of TEMPS can efficiently enhance the flame retardancy of
EP828. The silicon-containing compounds are a family of
condensed-phase flame retardants [9]. Their flame-retar-
dant performance arise partly from the dilution function to
more combustible organic gases, and partly from the bar-
rier effect by the silicaceous residues formed in an
advancing flame. While heating, the low surface energy of
silicon migrates to the surface of coated film, following by
the formation of a protective layer with high heat resis-
tance. The high-performance char acts as an insulator and
mass transport barrier, which can cut off the heat and
oxygen transfer, and thus effectively improve the flame
retardance of UV-cured resin.
decomposition of TEMPS at a lower temperature. How-
ever, the Si–O unit was reported to absorb more thermal
energy and its vibration can dissipate the thermal decom-
position energy [18]. The decomposition of Si–O groups
generates a silicon-containing residue, which slows down
the decomposition in the second stage. Therefore, the
second stage of mass loss temperature increases with the
addition of TEMPS content. The temperature of the max-
imum mass loss rate, Tmax2, for TEMPS is observed at
590 °C, compared with the 514 °C for EP828. It can also
be seen that the mass loss of the silicon-containing resins at
high temperature region is less than that of cured EP828.
The final char yield at 850 °C in air atmosphere also
increases with increasing silicon content.
Dynamic mechanical thermal properties
To sum up, the T5% and Tmax1 both decrease with
increasing TEMPS content either in air or nitrogen atmo-
sphere due to the decomposition of Si–O unit. In the second
process of decomposition, the Tmax2 increases with
increasing TEMPS content because the silicon-containing
group participates in the crosslinked carbonization and
effectively retards the flame formation at higher tempera-
ture. The observed higher char yield for TEMPS further
indicates that the mechanism of improved fire performance
via silicon modification indeed plays an important role in
flame retardation.
The dynamic mechanical thermal analysis (DMTA) was
utilized to investigate the dynamic mechanical behavior in
order to further acquire the microstructure information of a
UV-cured film. Figure 10 shows the variation in the stor-
age modulus and the relaxation peaks of loss factors as a
function of temperature beginning from the glassy state to
the rubbery plateau of cured films. The crosslinking density
of the highly crosslinked UV-cured films can be estimated
with the formula [19]: ve = E0/3RT, where E0 is the storage
modulus in the rubbery state, R is the ideal gas constant,
and T is the absolute temperature at Tg ? 50 °C. From the
Table 3, it can be seen that the crosslink density increases
from 4.18 for pure EP828 to 10.28 mmol cm-3 for pure
TEMPS. As far as the chemical structures of these net-
works are concerned, this behavior is to be expected since
the relative concentration of epoxy group in TEMPS is
6.20 mmol g-1, higher than that in EP828. Moreover,
TEMPS is a trifunctional cycloaliphatic epoxide, while
EP828 has only two glycidyl ether type epoxy groups per
molecule with lower reactivity.
Flame retardance
The flame-retardant properties of UV-cured epoxy resins
were further evaluated by measuring the LOI values. The
LOI, as a qualitative method to rank the flammability of a
material, is the minimum fraction of oxygen in an oxygen/
nitrogen mixture that will just support the combustion. The
LOI values of UV-cured TEMPS, EP828, and their blends
are listed in Table 1. It can be observed that the LOI value
increases with increasing silicon content from 22 for
123

Synthesis and thermal properties of silicon-containing epoxy resin
309
Table 3 DMTA results and mechanical properties of the cured films with different TEMPS contents
Sample
Ts/°C
Tg/°C
Ts/Tg
me/mmol cm-3
Tensile strength/MPa
Elongation-at-break/%
EP828
93
92
90
81
79
78
138
133
130
125
122
118
0.89
0.90
0.90
0.89
0.89
0.90
4.18
4.84
5.62
6.83
8.75
10.28
49.4
41.5
36.4
24.8
22.1
19.8
3.3
3.7
4.2
4.5
4.9
5.1
TEMPS20
TEMPS40
TEMPS60
TEMPS80
TEMPS100
The glass transition temperature (Tg) can be determined
as the a relaxation peak of loss factor. The softening point
(Ts) is detected as the extrapolated onset of the drop of
storage modulus. According to the theory reported else-
where [19], the meaning of the crosslinking density is the
molar number of elastically effective network chains per
cube centimeter. A higher ve value means that the chains
are highly restricted, which makes the chain motion pos-
sible at higher temperature. However, both the Tg and Ts of
UV-cured films decrease with increasing TEMPS content,
as listed in Table 3. This can be explained by the incor-
poration of more Si–O and Si–C bonds, resulting in the
reduction in the rigidity of polymeric network, although the
crosslinking density increased with the addition of TEMPS.
The width of relaxation peak of the loss factor indicates
the homogeneity of UV-cured network, which can be
expressed by Tg/Ts values of the cured sample. A little
change is observed in Tg/Ts ratio after the addition of
TEMPS, and the values of all samples are higher than 0.89.
This uniformity of the tan d peak indicates the absence of
any network heterogeneity, which implies the good mis-
cibility between EP828 and TEMPS.
as a reactive-type flame retardant in cationic UV-curable
systems. The flame retardancy was efficiently improved
with the addition of TEMPS into the commercial epoxide
resin EP828. The onset decomposition temperature and the
temperature of maximum mass loss rate in the first stage
decrease with increasing TEMPS content either in air or in
nitrogen atmosphere. In the second process of decompo-
sition, the temperature of maximum mass loss rate
increases with the increase of TEMPS content. The silicon-
containing group decomposes at lower temperature and
participates in the crosslinked carbonization at higher
temperature. The char yields under nitrogen and air
atmospheres increased along with the silicon content. The
LOI value increased from 22 for the commercial epoxide
resin EP828 to 30 for the blend with 80% TEMPS.
Moreover, TEMPS had good miscibility with EP828. The
addition of TEMPS led to a decrease in tensile strength and
an increase in elongation-at-break.
Acknowledgements The authors gratefully acknowledge the
financial support of the National Natural Science Foundation of China
(No. 50633010).
Mechanical properties
References
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The tensile strength and elongation-at-break are also listed
in Table 3. With increasing TEMPS content, the tensile
strength decreases from 49.4 MPa for EP828 to 22.1 MPa
for TEMPS80, while the elongation-at-break slightly
increases from 3.3% for EP828 to 4.9% for TEMPS80. In
other words, with increasing the TEMPS content, the
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Conclusions
A novel silicon-containing cycloaliphatic epoxide resin
was successfully synthesized by a simple method and used
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