Preparation and properties of novel low dielectric constant benzoxazole-based polybenzoxazine

Article abstract of DOI:10.1002/pola.26344

A novel benzoxazine monomer containing a benzoxazole group was synthesized using a nonsolvent method and then named DAROH-a. The structure of DAROH-a was confirmed by FTIR, ¹H NMR, elemental analysis, and mass spectrometry. The curing reaction activation energy was calculated at 140 kJ/mol. Its corresponding crosslinked polybenzoxazines, poly(DAROH-a), displayed a higher glass transition temperature at 402°C, a 9% weight loss at the said temperature, and a high char yield of 42 wt % (800°C, in nitrogen). Moreover, the dielectric constants of poly(DAROH-a) were low and changed only slightly at different temperatures. Furthermore, the dielectric constants and dielectric loss of poly(DAROH-a) at the same frequency barely changed from room temperature to 150°C. The photophysical properties of poly(DAROH-a) film were also investigated. Poly(DAROH-a) showed an absorption peak at 280 nm. The photoluminescent emission spectrum of poly(DAROH-a) film displayed predominant emission peaks at 521 nm. It might have potential application as high-performance materials because of its excellent dielectric constants stability and thermal stability under high temperature.

Full text of DOI:10.1002/pola.26344

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Preparation and Properties of Novel Low Dielectric Constant
Benzoxazole-Based Polybenzoxazine
Kan Zhang, Qixin Zhuang, Yunchao Zhou, Xiaoyun Liu, Guang Yang, Zhewen Han
Key Laboratory for Specially Functional Polymeric Materials and Related Technology of the Ministry of Education,
East China University of Science and Technology, Shanghai 200237, China
Correspondence to: X. Liu (E-mail: liuxiaoyun@ecust.edu.cn)
Received 28 April 2012; accepted 12 August 2012; published online
DOI: 10.1002/pola.26344
ABSTRACT: A novel benzoxazine monomer containing a ben-
zoxazole group was synthesized using a nonsolvent method
and then named DAROH-a. The structure of DAROH-a was con-
firmed by FTIR, 1H NMR, elemental analysis, and mass spec-
trometry. The curing reaction activation energy was calculated
at 140 kJ/mol. Its corresponding crosslinked polybenzoxazines,
poly(DAROH-a), displayed a higher glass transition temperature
at 402 ꢀC, a 9% weight loss at the said temperature, and a high
char yield of 42 wt % (800 ꢀC, in nitrogen). Moreover, the
dielectric constants of poly(DAROH-a) were low and changed
only slightly at different temperatures. Furthermore, the dielec-
tric constants and dielectric loss of poly(DAROH-a) at the same
frequency barely changed from room temperature to 150 ꢀC.
The photophysical properties of poly(DAROH-a) film were also
investigated. Poly(DAROH-a) showed an absorption peak at 280
nm. The photoluminescent emission spectrum of poly(DAROH-
a) film displayed predominant emission peaks at 521 nm. It
might have potential application as high-performance materials
because of its excellent dielectric constants stability and ther-
C
V
mal stability under high temperature. 2012 Wiley Periodicals,
Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2012
KEYWORDS: benzoxazine; benzoxazole; dielectric properties; high-
performance polymers; thermal properties
INTRODUCTION Phenolic resin is widely used because of its
good heat resistance, flame resistance, mechanical strength,
corrosion resistance, and electrical insulation. However,
strong acid catalyst is often required and reaction byprod-
ucts are released in the curing process, thereby limiting its
application. Benzoxazine is a newly developed thermosetting
phenolic resin that can be synthesized via Mannich conden-
sation from phenol, amine, and formaldehyde.1,2 The molecu-
lar structural design of benzoxazine is very flexible. Various
phenols and amines offer enormous flexibility, and many
benzoxazines with different structures have been synthesized
for various applications. The benzoxazine monomer can be
polymerized by thermal-activated ring-opening polymeriza-
tion reaction to form a spatial network structure. During the
self-crosslinking polymerization reaction, no reaction byprod-
ucts are released and no catalyst is required.3–5 Benzoxazine
resin has good mechanical properties and thermal proper-
ties, low water absorption, high carbon residue, and low sur-
face energy,6–14 which make benzoxazine a promising matrix
for composite materials, especially for use in microelec-
tronics, aerospace, and packaging industries.8,15
posites,17–19 properties,20,21 and reaction mechanisms22,23 of
benzoxazine monomers and the resultant polymers. Many
chemical groups have been incorporated in benzoxazine
monomers to improve the properties of benzoxazines and
polybenzoxazines. For example, a benzoxazine compound
possessing a fluorene group and two terminal furan groups
has been reported. The photoluminescent intensity of this
benzoxazine reaches sixfold of the intensity recorded with
4,40-(9-fluorenylidene) diphenol, which is the phenol for
benzoxazine.24 Poly(siloxane) segments increase the tough-
ness or decrease the dielectric constants of the resulting
benzoxazine-based polymers.25–27 Polymers and oligomers
containing benzoxazine in the main chains have also caught
the attention of numerous researchers.28,29
Polybenzoxazole is a class of high-performance liquid crystal
polymers.30,31 Among these benzoxazole polymers, poly(ben-
zobisoxazole) (PBO) exhibits high tensile strength, high mod-
ulus, and excellent thermal and environmental stability. PBO
has been used in protection and insulation layers for very
large-scale integration circuits and multichip modules for
computers owing to their high thermal stability and excellent
mechanical property.32 Moreover, PBO are considered rela-
tively lower dielectric materials because of the absence of
carbonyl groups in their structure.33 Lower dielectric
Many reports on benzoxazine have been published in recent
years. The majority of studies reported have focused on
synthesis methods,5 polymerization,15,16 blending and com-
C
V
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constants are required to increase the circuit speed, so many
studies have been focused on lowering the dielectric con-
stant of PBO.
The above features inspired the idea to incorporate benzoxa-
zine and benzoxazole groups into one compound. In this
study, a novel benzoxazole-based benzoxazine monomer
named DAROH-a was synthesized and characterized. The
ring-opening polymerization of the DAROH-a monomer was
investigated with differential scanning calorimetry (DSC) in
dynamic conditions. The polymerization behavior, network
structure, and thermal properties of the monomers and the
polybenzoxazines were investigated. Moreover, the liquid
crystalline structure was studied by polarized optical micro-
scopy (POM). Finally, the dielectric and photophysical
properties of polybenzoxazine were investigated.
EXPERIMENTAL
Materials
The polymerization medium, poly(phosphoric acid) (PPA)
with a phosphorus pentoxide (P2O5) content of 80.8%, was
freshly prepared using phosphoric acid and P2O5 (Shanghai
1st Chemical), which was used as received.
SCHEME 1 Chemical
reaction
of
DAROH-a
monomer
synthesis.
ꢀ
dried at 120 C under vacuum for 8 h before measurements.
A sample of 20 mm in diameter and 1 mm in thickness was
placed between the two copper electrodes; thus, a parallel
plate capacitor was formed. The dependence of the dielectric
constant and dielectric loss on the frequency of the applied
Other reagents and solvents, including p-hydroxybenzoic
acid, paraformaldehyde, 4,6-diaminobenzene-1,3-diol dihy-
drochloride (DAR), and aniline, were obtained from Aldrich
and used as received.
ꢀ
field was studied in the temperature range of 25–200 C and
within the frequency range of 10 Hz–5 MHz. Optical observa-
tions were made with a POM (model WETZLAR).
Measurements
FTIR spectra were obtained with a Nicolet 5700 FTIR Spec-
trometer at a resolution of 4 cmꢁ1. All samples were finely
ground with KBr powder and pressed into disk. 1H NMR
spectra were recorded with ArANCEIII (400 MHz) using
dimethylsulfoxide (DMSO-d6) as solvent and tetramethylsi-
lane as an internal standard. Mass spectra were recorded
with an IonSpec HIResMALDI high-resolution mass spec-
trometer with matrix-assisted laser desorption ionization.
The matrix 2,5-dihydroxybenzoic acid was dissolved in
DMSO (10 mg/mL) and mixed with the sample solution (1
mg/mL) in 1:1 v/v ratio. Samples were spotted onto the tar-
get and dried in air. DSC measurements were conducted
with a DSC Q2000 V24.9 Build 121 using N2 as a purge gas
Synthesis of DAROH
The synthesis reaction route of DAROH is shown in Scheme 1.
Five grams of DAR, 6.48 g of p-hydroxybenzoic acid, and 75
g of PPA were mixed together in a glass reactor vessel. The
dehydrochlorination was performed at 90–110 ꢀC for 12 h.
The reaction temperature was raised to 130 ꢀC for 12 h,
then to 150 ꢀC for 12 h, and finally to 180 ꢀC, which was
maintained for 8 h. The highly viscous light-yellow dope was
placed in water. The solution was washed several times with
water to remove the PPA completely. At last, the solution
ꢀ
was dried at 60 C in a vacuum oven for 12 h, and a brown
ꢀ
(100 mL/min) at scanning rate of 10 C/min. Samples of 3–
powder was obtained.
5 mg were placed in aluminum pans with pierced lids. In
the dynamic analyses, the samples were ꢀscanned at different
heating rates of 5, 7.5, 10, 12.5, and 15 C/min, respectively.
Thermogravimetry analysis (TGA) was undertaken using a
NETZSCH STA 409 PC/PG thermogravimetric analyzer.
Experiments were carried out on ꢂ7 mg samples heated in
flowing nitrogen or air (20 mL/min) at a heating rate of 10
ꢀC/min. Elemental analyses were run in a VARIO ELIII ana-
lyzer with 4-nitroaniline as a standard. UV–vis absorption
spectra were recorded with a Shimadzu UV-2550 spectros-
copy. Photoluminescent (PL) emission spectra were meas-
ured on a Jobin Yvon Fluorolog-3-p spectrofluorometer.
Dielectric constant measurement was carried out using a
Concept 40 broadband dielectric spectrometer (Novocontrol
Technologies GmbH & Co., KG, Germany). The films were
The chemical structure of DAROH was confirmed with 1H
NMR, FTIR, and elemental analysis.
1
Figure 1 shows the H NMR spectrum of DAROH. The peaks
at 6.98 to ꢁ7.00 ppm, 7.40–7.42 ppm, and 8.04–8.26 ppm
are assigned to the aromatic protons. Resonance appearing
at 10.4 ppm is assigned to the hydroxybenzene protons.
The FTIR spectrum of DAROH is shown in Figure 2. The
bands at 1608 and 989 cmꢁ1 are related to the absorption
of C¼¼N and CAO in the benzoxazole ring, respectively. The
band at 3448 cmꢁ1 is attributed to the hydroxyl of
hydroxybenzene.
Elemental analysis of DAROH shows that the experimental
results (C, 68.67%; H, 3.22%; N, 7.65%) are in reasonable
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FIGURE 1 1H NMR spectrum of DAROH.
FIGURE 3 1H NMR spectrum of DAROH-a.
agreement with the calculated value (C, 69.77%; H, 3.51%;
N, 8.13%).
ized with the resonance peaks at 4.58 (Ar-CH2AN) and 5.75
ppm (OACH2AN), and the intensity ratio of these two peaks
is 1:1.02. The intensity ratio results and no other major
Synthesis of DAROH-a
DAROH-a was synthesized according to Scheme 1. Parafor-
maldehyde (1.39 g) and aniline (2.16 g) were mixed in a
100-mL three-necked round-bottom flask equipped with a
mechanical stirrer, a thermometer, and a reflux condenser.
The mixture was stirred for 15 min before adding DAROH
1
peaks in the H NMR spectrum, indicating that DAROH-a has
high purity. The resonance peaks at 4.58 (Ar-CH2AN) and
5.75 ppm (OACH2AN) separate more than 1 ppm. No other
benzoxazines have been reported to show this phenomenon.
The possible reason is that the p inductive effect by benzoxa-
zole groups, which have stronger deshielding effect to
OACH2AN than Ar-CH2AN.
ꢀ
(4 g). The temperature was then gradually raised to 110 C.
Subsequently, the yellow product was washed several times
with 1 mol/L sodium hydroxide aqueous solution and deion-
ized water, respectively. During the purification process, the
product was precipitated and filtered out in a separatory
funnel. Thereafter, it was dried at 60 ꢀC in a vacuum oven
for 12 h, and a yellow powder was obtained.
The FTIR spectrum of DAROH-a is shown in Figure 4. The
benzoxazine ring of DAROH-a displays characteristic absorp-
tion at 1234 cmꢁ1 (asymmetric stretching of CAOAC), 1007
cmꢁ1 (symmetric stretching of CAOAC), and 1351 cmꢁ1
(CH2 wagging). The disubstituted benzene groups of DAROH-
a exhibit an absorption peak at 1514 cmꢁ1. The absorption
bands at 938 cmꢁ1 corresponding to the out-of-plane bend-
ing vibration of CAH are due to the characteristic mode of
benzene with an attached oxazine ring.24 The band at 1611
The chemical structure of DAROH-a was confirmed with 1H
NMR, FTIR, elemental analysis, and mass spectrometry.
The 1H NMR spectrum of DAROH-a is shown in Figure 3.
The peaks at 6.60–8.42 ppm are assigned to the aromatic
protons. The benzoxazine rings of DAROH-a are character-
FIGURE 2 FTIR spectrum of DAROH.
FIGURE 4 FTIR spectrum of DAROH-a.
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FIGURE 5 Mass spectrometry of DAROH-a.
cmꢁ1 is related to the absorption of C¼¼N in the benzoxazole
at a heating rate of 10 ꢀC/min. The endotꢀhermal peak with an
ꢀ
ring.
onset at 145 C and a maximum at 175 C is believed as the
melting phase of DAROH-a. The exothermal peak in the range
of 192–223 C is assigned to the curing reaction of DAROH-a.
The curing temperature observed is slightly lower compared
with other benzoxazines, which generally exhibit exothermic
ring-opening reaction at ꢂ220–260 ꢀC.
Figure 5 shows the mass spectrum of DAROH-a. A peak at
578.3 is observed, which is in accord with the empirical
formula of DAROH-a. This result is in good agreement with
the structural data obtained from 1H NMR and FTIR
spectroscopy.
ꢀ
Elemental analysis of DAROH-a shows that the experimental
results (C, 73.06%; H, 4.39%; N, 9.89%) are in reasonable
agreement with the calculated values (C, 74.73%; H, 4.53%;
N, 9.68%).
RESULTS AND DISCUSSION
Polymerization Behavior of DAROH-a Monomer
The polymerization behavior of DAROH-a was studied by
DSC and FTIR. The corresponding in situ FTIR spectra are
shown in Figure 6. The peak at 938 cmꢁ1 corresponds to
the out-of-plane bending vibration of CAH.24 The new band
at 3417 cmꢁ1 is assigned to the stretching of OH group.16
The disappearance of 938 cmꢁ1 and the appearance of 3417
cmꢁ1 indicate the occurrence of ring-opening polymerization
of DAROH-a (Scheme 2).
The curing behavior of the monomer DAROH-a was monitored
by DSC. Figure 7 shows the DSC plots for DAROH-a recorded
FIGURE 6 FTIR spectra during the ring-opening reaction of
DAROH-a at 190 ꢀC (0–120 min).
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FIGURE 8 DSC thermograms of the cured polybenzoxazine.
Figures 9 and 10 show the DSC plots of DAROH-a and the
conversion versus temperature at different heating rates. Fig-
ure 9 also shows the initial curing temperature (Ti) and
peak temperature (Tp) at different heating rates. The figures
indicate that the exothermic peak shifts to a higher tempera-
ture with the increase of heating rate. The data are summar-
ized in Table 1.
The curing reaction activation energy was investigated using
the well-known Kissinger and Ozawa methods.33,34
SCHEME 2 Ring-opening polymerization of DAROH-a.
According to the Kissinger method, the activation energy can
be calculated by eq 1 as follows:
In the second scan (Fig. 8), poly(DAROH-a), the correspond-
ing crosslinked polymer from DAROH-a, did not show any
exothermic peaks in the DSC thermogram. The curing
reaction of the DAROH-a benzoxazine groups was carried
out, and the degree of conversion was found to be high.
Poly(DAROH-a) showing a high glass transition temperature
of about 400 ꢀC, higher than common polybenzoxazine, was
a notable finding. The possible reasons include the formation
of additional physical crosslinks via hydrogen bonds and the
existence of a rigid benzobisoxazole group.
ꢀ
ꢁ
ꢀ
ꢁ
b
Tp2
AR
E
E
ln
¼ ln
ꢁ
;
(1)
RTp
where b is the heating rate, A is the frequency factor, Tp is
the temperature of the exothermic peak, Ea is the activation
energy, and R is the gas constant. If the plot of ln(b/Tp2)
FIGURE 7 DSC thermograms of the DAROH-a monomer.
FIGURE 9 DSC curves of DAROH-a at different heating rates.
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FIGURE 11 Representations of Kissinger and Ozawa methods
for the calculation of activation energy from nonisothermal
data for the benzoxazine monomer.
FIGURE 10 Conversion versus temperature for DAROH-a cured
at different heating rates.
against 1/Tp is linear, Ea can be obtained from the slope of
the corresponding straight line.
Liquid Crystalline Property of Crosslinked
Poly(DAROH-a)
The POM photos in Figure 12 demonstrate the ordered tex-
ture of the polymer poly(DAROH-a). At room temperature,
the appearance of a fine birefringence pattern suggests the
liquid crystalline structure of poly(DAROH-a), which means
that the poly(DAROH-a) is in the lyotropic liquid crystal
phase at room temperature.
Another theoretical treatment, namely, the Ozawa method,
can also be applied to the thermal data using eq 2 as follows:
E
ln b ¼ ꢁ1:052
þ C;
(2)
RTp
where C is a constant.
Thermal Stability of Crosslinked Poly(DAROH-a)
TGA was carried out under nitrogen atmospheres to deter-
mine the thermal stability and the decomposition behavior.
Figure 13 shows the TGA curves and the first derivative
curves, and Table 2 summarizes the TGA data.
Figure 11 shows the plot of ln(b/Tp2) and ln(b) against 1/Tp
for the DAROH-A according to Kissinger and Ozawa methods.
The Ea value is estimated to be ꢂ140 kJ/mol and is listed in
Table 1.
In addition, comparing the kinetic results of DAROH-a with
that of bisphenol-A-based benzoxazine (BA-a) reported by
Ishida and Rodriguez,35 it can be found that the activation
energy values of DAROH-a are higher than that of BA-a. In
the dynamic polymerization mode, the activation energy val-
ues of DAROH-a are 140.6 kJ/mol by Kissinger’s method and
142.6 kJ/mol by Ozawa’s method, whereas those of BA-a are
116 kJ/mol by Kissinger’s method and 107 kJ/mol by
Ozawa’s method. This may be ascribed to the structural
difference between DAROH-a and BA-a monomers. The
benzoxazole groups in DAROH-a are highly rigid, whereas
the isopropyl groups in BA-a are flexible.
Two weight-loss stages in the TGA curve of poly(DAROH-a)
were observed in Figure 13. The first weight-loss stage that
occurred at 260 ꢀC and ended at 430 ꢀC is probably attrib-
uted to the weight loss of alkyl. The second stage that
occurred at 603 ꢀC is believed to be the thermal
TABLE 1 Cure Characteristics of DAROH-a
Heating
Rate
(ꢀC/min)
Flynn-Wall-
Ozawa
Ti
(ꢀC)
Tp
(ꢀC)
Tf
(ꢀC)
Kissinger
E (kJ/mol)
E (kJ/mol)
5
184.0
190.0
192.6
192.9
195.5
196.2
200.1
205.5
207.9
209.1
212.7
218.2
223.4
226.0
241.2
7.5
10
140.6
142.6
12.5
15
FIGURE 12 Polarized optical micrographs for poly(DAROH-a) at
room temperature.
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FIGURE 13 TGA thermograms of the crosslinked polybenzoxa-
FIGURE 14 Dielectric constant versus frequency of poly-
zines poly(DAROH-a).
(DAROH-a) at different temperatures.
decomposition of benzobisoxazole. The weight loss of the
ꢀ
first stage is about 8% and the char yield at 800 C is 42%.
zine, which strongly depends on temperature,37 the dielectric
constants of poly(DAROH-a) at the same ꢀfrequency barely
change under low temperatures up to 150 C.
TGA results indicated that the thermal stability of poly-
(DAROH-a) was a little lower than that of PBO, which is very
stable below 600 ꢀC under air.36 However, this thermal
decomposition temperature is higher than most other
polybenzoxazines.
The dependence curve of dielectric loss on frequency at dif-
ferent temperatures is shown in Figure 15. These curves
suggest that the dielectric loss also depends on the fre-
quency of the applied field and barely changes under low
temperatures up to 150 ꢀC at the same frequency, which is
similar to the phenomenon with the dielectric constant of
poly(DAROH-a) (Fig. 14). The dielectric loss decreases from
0.015 to 0.01 at 25 ꢀC, whereas it decreases from 0.17 to
0.02 at high temperature (200 ꢀC) as the frequency of the
applied AC field is increased from 10 Hz to 5 MHz. Dielectric
loss decreases very little with the increase in frequency at
lower temperature and appears to achieve saturation at the
higher frequency range of 1 kHz and above at temperatures
Dielectric Property Analysis of Crosslinked
Poly(DAROH-a)
The dependence of dielectric constant and dielectric loss on
the frequency of the applied field was studied in the temper-
ature range of 25–200 C and within the frequency range of
ꢀ
10 Hz–5 MHz. The variation of the dielectric constant with
the frequency of the applied field is shown in Figure 14. The
dielectric constant was observed to vary from 2.1 to 2.3 at
room temperature within the frequency range of 10 Hz–5
MHz. The dielectric constants of poly(DAROH-a) are fairly
low, especially in the high-frequency range, which suggests
its potential application as microelectronic packaging mate-
rial. The dielectric constant has a higher value within the
lower frequency region, after which it decreases with
increase in frequency and remains practically constant. At a
slightly higher temperature (i.e., 200 ꢀC), the value of the
dielectric constant decreases from a maximum value of 3.9
at 10 Hz to a value of 2.4 at 10 MHz and remains almost
constant beyond 100 kHz. These data imply that the poly-
(DAROH-a) crystal exhibits normal dielectric behavior. In
normal dielectric behavior, the dielectric constant decreases
with the increase in frequency and reaches a constant value
beyond a certain frequency on the electric field. The dipole
does not follow the alternating field. Figure 14 also suggests
that unlike the dielectric constant of common polybenzoxa-
ꢀ
ranging from 25 to 150 C.
TABLE 2 Thermal Properties of Crosslinked Polybenzoxazines
Poly(DAROH-a)
Sample
T5%
375
T10%
416
Yc (%)
FIGURE 15 Dielectric loss versus frequency of poly(DAROH-a)
poly(DAROH-a)
42
at different temperatures.
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FIGURE 18 Normalized absorbance spectra of poly(DAROH-a)
FIGURE 16 Dielectric constant of poly(DAROH-a) versus
film.
temperature.
mophore units.37 The possible reason for this red shift is the
incorporation of benzoxazine rings to benzobisoxazole, which
might hinder the aggregation of benzobisoxazole groups. The
application potential of the poly(DAROH-a) film in PL and EL
fields is worthy of further studies.
Figures 16 and 17 show the dependence curves of the
dielectric constant and dielectric loss on temperature for the
frequency range of 1 MHz. The curves show that the effect
of temperature on the dielectric properties of poly(DAROH-
a) is weak until 150 ꢀC. A low, steady dielectric loss at high
frequency for a broad range of temperatures mainly charac-
terizes poly(DAROH-a).
CONCLUSIONS
A
novel benzoxazine containing a benzoxazole group,
DAROH-a, was synthesized. DSC indicates that the curing
reaction occurred at 205 ꢀC. The curing reaction activation
energy was 140 kJ/mol. POM photos of corresponding cross-
linked polybenzoxazines from DAROH-a showed an ordered
texture, suggesting the existence of liquid crystal.
Photophysical Properties of Crosslinked Poly(DAROH-a)
Figure 18 shows the absorbance spectra of the poly(DAROH-
a) films. The spectrum of poly(DAROH-a) film shows a
absorption peak at 280 nm. The absorption band of benzobi-
soxazole chromophore appears in a lower energy range with
the maxima at 402 and 426 nm,38 so the absorption of poly-
(DAROH-a) shows blue shift. The PL emission spectrum of
the poly(DAROH-a) film is exhibited in Figure 19. The excita-
tion wavelength is 353 nm. The poly(DAROH-a) film displays
a strong PL emission peak at 521 nm, which has a slight red
shift compared with the emission of benzobisoxazole chro-
Poly(DAROH-a) behaved at a higher glass transition tempera-
ture of 402 ꢀC after 9% weight loss, which was ascribed to
the highly crosslinked polybenzoxazine networks and the
existence of the benzoxazole structure. Poly(DAROH-a)
also showed good thermal stability. The 10% weight-loss
FIGURE 17 Dielectric
loss
of
poly(DAROH-a)
versus
FIGURE 19 PL spectra of poly(DAROH-a) film at excitation
temperature.
wavelength of 353 nm.
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ꢀ
14 Andreu, R.; Reina, J. A.; Ronda, J. C. J. Polym. Sci. Part A:
Polym. Chem. 2008, 46, 6091–6101.
temperature obtained was 416 C and the char yield at 800
ꢀC was 42%. The dielectric constants of poly(DAROH-a) at
different temperatures were low. Meanwhile, the dielectric
constants and dielectric loss of poly(DAROH-a) at the same
15 Jin, L.; Agag, T.; Ishida, H. Eur. Polym. J. 2010, 46, 354–363.
16 Liu, Y. F.; Yue, Z. Q.; Gao, J. G. Polymer 2010, 51,
3722–3729.
ꢀ
frequency barely changed from room temperature to 150 C.
Furthermore, poly(DAROH-a) film showed an absorption
peak at 280 nm. The PL emission spectrum of the poly-
(DAROH-a) film showed predominant emission peaks at 521
nm. It might have potential application as high-performance
materials because of its excellent dielectric constants stabil-
ity and thermal stability under high temperature.
17 Kubra, D. D.; Mehmet, A. T.; Tamer, U.; Awei, W. K.;
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20 Hwang, H. J.; Lin, C. Y.; Wang, C. S. J. Appl. Polym. Sci.
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The authors express their gratitude to the National Natural Sci-
ence Foundation of China (NSFC) for their financial support
(contract grant numbers 50703010 and 50973028). This
project is also supported by Innovation Program of Shanghai
Municipal Education Commission (12ZZ049) and the Funda-
mental Research Funds for the Central Universities.
21 Qu, L.; Xin, Z. Langmuir 2011, 27, 8365–8370.
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