Synthesis, polymerization, and thermal properties of benzoxazine based on p-aminobenzonitrile

Article abstract of DOI:10.1016/j.tca.2012.09.017

The 6,6′-bis(3-benzonitrile-3,4-dihydro-2H-benzo[e][1,3]oxazinyl) isopropane (BA-PABN) was synthesized from bisphenol-A, p-aminobenzonitrile and paraformaldehyde via solventless method. The chemical structure of BA-PABN was confirmed by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis, and the polymerization of BA-PABN was investigated by FTIR, solid-state ¹³C NMR, and differential scanning calorimetry. BA-PABN undergoes the oxazine ring-opening polymerization and the cyclotrimerization of cyano groups with the formation of the corresponding polybenzoxazine (PBA-PABN). Dynamic mechanical analysis results show the storage modulus of PBA-PABN at 25°C is about 2.7 GPa, and the glass transition temperature is 190°C. The 5% and 10% weight loss temperatures of PBA-PABN are 300 and 325°C in both air and nitrogen, respectively. The char yield is about 43% at 800°C in nitrogen, whereas almost no degradation residue is remained at 750°C in air.

Full text of DOI:10.1016/j.tca.2012.09.017

Thermochimica Acta 549 (2012) 42–48
Contents lists available at SciVerse ScienceDirect
Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Synthesis, polymerization, and thermal properties of benzoxazine based on
p-aminobenzonitrile
Yanfang Liu∗, Shasha Zhao, Haili Zhang, Man Wang, Mingtao Run
College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China
a r t i c l e i n f o
a b s t r a c t
The 6,6ꢀ-bis(3-benzonitrile-3,4-dihydro-2H-benzo[e][1,3]oxazinyl) isopropane (BA-PABN) was synthe-
sized from bisphenol-A, p-aminobenzonitrile and paraformaldehyde via solventless method. The
chemical structure of BA-PABN was confirmed by 1H and 13C nuclear magnetic resonance (NMR) spec-
troscopy, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis, and the polymerization
of BA-PABN was investigated by FTIR, solid-state 13C NMR, and differential scanning calorimetry. BA-
PABN undergoes the oxazine ring-opening polymerization and the cyclotrimerization of cyano groups
with the formation of the corresponding polybenzoxazine (PBA-PABN). Dynamic mechanical analysis
results show the storage modulus of PBA-PABN at 25 ◦C is about 2.7 GPa, and the glass transition temper-
ature is 190 ◦C. The 5% and 10% weight loss temperatures of PBA-PABN are 300 and 325 ◦C in both air and
nitrogen, respectively. The char yield is about 43% at 800 ◦C in nitrogen, whereas almost no degradation
residue is remained at 750 ◦C in air.
Article history:
Received 19 May 2012
Received in revised form 6 September 2012
Accepted 7 September 2012
Available online 25 September 2012
Keywords:
Benzoxazine
Ring-opening polymerization
Cyclotrimerization
Dynamic mechanical properties
Thermal stability
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
such as acetylene [9,10], nitrile [11–15], allyl [16], propargyl [17],
and the resultant polybenzoxazines exhibit higher mechanical
Benzoxazines are oxygen- and nitrogen-containing hetero-
cyclic compounds synthesized from phenols, primary amines, and
formaldehyde through Mannich condensation. The first benzox-
azine compound was synthesized by Holly and Cope [1], and then
the benzoxazine chemistry was developed in synthesis and ring-
opening polymerization reaction [2–6]. These developments are
based on mono-functional benzoxazines, and establish the basis
for the following study on bifunctional benzoxazines. The first
bifunctional benzoxazine was synthesized by Ning and Ishida [7],
then it was recognized that bifunctional benzoxazines can be ther-
mally polymerized into polybenzoxazines with many outstanding
properties, such as excellent mechanical properties, high thermal
stability, low water absorption [8]. Thereafter, more attention has
been paid to the research on bifunctional benzoxazines, and various
bifunctional benzoxazines have been synthesized.
properties and thermal stability than the corresponding analogues
without functional groups.
Generally, the functional benzoxazines can be synthesized
from various phenols and primary amines with different groups.
However, the steric hindrance or the electron effect from some
functional groups on phenols or primary amines will increase the
difficulty of the synthesis reaction. If an electron withdrawing
functional group is on phenols or primary amines, the reaction
temperature will increase, whereas the product yield will decrease,
even no product can be formed. In addition, in the synthesis of some
benzoxazines, the reaction may well proceed, but it may be difficult
to purify the products, because the starting materials, intermedi-
ates, or solvents cannot be removed effectively.
In the previous reports, nitrile-functional benzoxazines
were well synthesized from o-aminobenzonitrile, (m,p)-
aminobenzonitrile, and p-aminophenoxylphthalonitrile, with
several phenols employing melt or solution methods [11–15],
but no study has been reported on the bisphenol-A and
p-aminobenzonitrile (PABN) based benzoxazine (BA-PABN).
PABN is a push–pull molecule, with amino ( NH2, an electron
donor group) and cyano ( CN, an electron acceptor group) in para
In practical application, benzoxazines are used as resin matrices
for high performance composite in electrics and aerospace indus-
tries, and the mechanical properties and thermal stability of the
corresponding polybenzoxazines are the major aspects to be con-
cerned. To enhance the properties of polybenzoxazines, different
functional groups were introduced into benzoxazine molecules,
position on a benzene ring. In PABN molecule,
C N group and
benzene ring form a more rigid and highly conjugated ␲-electron
system. Owing to the electronic effect, the charge density on the
nitrogen and hydrogen atoms of the amino group is lower than
∗
Corresponding author. Tel.: +86 312 5079359; fax: +86 312 5079525.
E-mail address: liuyanfang@msn.com (Y. Liu).
0040-6031/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.tca.2012.09.017

Y. Liu et al. / Thermochimica Acta 549 (2012) 42–48
43
that of the counterpart in aniline. Therefore, the cyano group in
PABN will reduce the reaction activity in comparison to aniline in
the synthesis of benzoxazines.
In
this
study,
6,6ꢀ-bis(3-benzonitrile-3,4-dihydro-2H-
benzo[e][1,3]oxazinyl) isopropane (BA-PABN) was synthesized
from bisphenol-A, p-aminobenzonitrile and paraformaldehyde via
solventless method. The structure of BA-PABN was characterized
by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy,
Fourier transform infrared (FTIR) spectroscopy, and elemental
analysis. The thermally activated polymerization of BA-PABN was
studied by FTIR, solid-state 13C NMR, and differential scanning
calorimetry (DSC). In addition, the dynamic mechanical properties
and the thermal stability of the corresponding polybenzaoxazine
(PBA-PABN) were investigated.
2. Experimental
2.1. Materials
Bisphenol-A (4,4ꢀ-isopropylidenediphenol) (99%), was pur-
chased from Shanghai Chemical Reagent Co., China. PABN was
supplied by Sanheyuan Chemical Co., Ltd., China. Paraformalde-
hyde, dioxane, chloroform, and diethyl ether were obtained from
Tianjin Chemical Reagent Co., China. All chemicals were used as
received.
Scheme 1. Chemical reaction of BA-PABN synthesis.
The FTIR spectra were obtained with a Nicolet 380 FTIR spec-
trometer by 32 scans at a resolution of 4 cm−1. BA-PABN was
dispersed in KBr and pressed the mixture into a disk. After scanned
by the FTIR spectrometer, the disk was placed in an oven with a
fixed temperature under air atmosphere. During the polymeriza-
tion reaction, the disk was repeatedly removed at different times
for measurement.
2.2. Preparation of BA-PABN
The quantitative analyses of C, H, N, and O were carried out on
an Exeter Analytical CE-440 elemental analyzer.
In a 100 mL three-necked round bottom flask equipped with
a mechanical stirrer, a thermometer, and a reflux condenser,
bisphenol-A (5.7 g), PABN (5.9 g), and paraformaldehyde (3.6 g)
were added. The mixture was heated to about 140 ◦C and kept
stirring for 60 min. Subsequently, the viscous liquid was cooled to
about 50 ◦C, and about 30 mL chloroform was introduced into the
flask. Then, the chloroform solution was poured into a separatory
funnel and washed several times with 3 mol/L NaOH aqueous solu-
tion and deionized water, respectively. Thereafter, the chloroform
was removed by distillation under reduced pressure, and the prod-
uct was dried at 70 ◦C in a vacuum oven for 12 h, then it was washed
with diethyl ether and dried at 120 ◦C in the vacuum oven. Finally,
a pale yellow powder was obtained. The yield was about 50%.
The non-isothermal polymerization reaction of BA-PABN was
monitored by a Shimadzu DSC-41 differential scanning calorime-
ter operating in a nitrogen atmosphere. The DSC instrument was
calibrated with high purity indium, and ␣-Al2O3 was used as the
reference material. BA-PABN samples of about 6.5 mg were scanned
at five heating rates: 5, 7.5, 10, 12.5, and 15 ◦C/min, respectively.
A Perkin-Elmer DMA-8000 dynamic mechanical analyzer was
used to determine the dynamic storage modulus (Eꢀ), loss mod-
ulus (Eꢀꢀ), and loss factor (tan ı) of PBA-PABN by using the single
cantilever bending mode. Measurement was performed from 25 to
about 250 ◦C at a heating rate of 2 ◦C/min in static air atmosphere,
and the testing frequency was set at 1 Hz. The dimension of the
specimen was approximately 10.0 mm × 3.7 mm × 2.0 mm.
A Shimadzu TGA-40 thermogravimeter was used to determine
the weight loss behavior of PBA-PABN. The PBA-PABN fine pow-
der samples of about 3.0 mg were heated to 800 ◦C at a heating
rate of 10 ◦C/min in dynamic nitrogen and static air atmospheres,
respectively.
2.3. Preparation of PBA-PABN
First, BA-PABN was put into a steel mold, and the mold was
put into a vacuum oven. Then the vacuum oven was step-heated
to 120, 140, 160, and 180 ◦C and hold at each temperature for 1 h,
thereafter, hold at 220 ◦C for 6 h.
3. Results and discussion
2.4. Measurements
3.1. Synthesis and characterization of BA-PABN
Both proton (1H) and carbon (13C) NMR spectra were recorded
with a Bruker Avance III 600 NMR spectrometer at a proton
frequency of 600 MHz and the corresponding carbon frequency.
Deuterated chloroform (CDCl3) was used as a solvent and tetram-
ethylsilane (TMS) as an internal reference. Solid state NMR
experiments were carried out at room temperature (25 ◦C) on a
Bruker Avance III 400 NMR spectrometer operating at a 13C reso-
nance frequency of 100.568 MHz. Samples were analyzed under
cross-polarization/magic-angle spinning (CP/MAS) conditions by
using 4-mm zirconia rotors at a spinning frequency of 5 kHz. A 90◦
pulse width of 4 ms was employed, and the CP HartmanneHahn
contact time was set at 3.0 ms. The chemical shifts of 13C spectra
were externally referenced to the carbon signal of solid adamantane
(38.48 ppm relative to TMS).
BA-PABN
was
synthesized
from
bisphenol-A,
p-
aminobenzonitrile and paraformaldehyde via solventless method
[18]. The synthesis reaction mechanism is shown in Scheme 1. The
chemical structure of BA-PABN was confirmed by 1H and 13C NMR,
FTIR, and element analysis.
Fig. 1 shows the 1H NMR spectrum of BA-PABN. The resonances
at 4.66 and 5.37 ppm correspond to the methylene protons (C6 and
C7) of Ar CH2 N and O CH2 N of the oxazine ring, respectively.
The chemical shifts (ppm) at 1.62 (6H, H15) are assigned to the
aliphatic protons in the methyl, and 6.77 (2H, H9), 6.90 (4H, H4),
6.98 (2H, H10), and 7.09 (2H, H12) 7.54 (4H, H3) are assigned to the
aromatic protons. The ratio of the corresponding integration area
of the eight protons (H3, H4, H6, H7, H9, H10, H12, and H15) was

44
Y. Liu et al. / Thermochimica Acta 549 (2012) 42–48
Fig. 1. 1H NMR spectrum of BA-PABN.
determined roughly to be 2:2:2:2:1:1:1:3, which is well coincident
with the theoretical proton ratio based on the chemical structure.
In the corresponding 13C NMR spectrum in Fig. 2, the resonances
at 77.10 and 49.79 ppm correspond to the methylene carbons (C7
and C6) of O CH2 N and Ar CH2 N of the oxazine ring, respec-
tively. Other chemical shifts (ppm) are assigned to the resonances
of the carbons: 30.02 (C15), 41.89 (C14), 102.71 (C2), 116.21 (C9),
116.77 (C4), 119.49 (C13), 124.63 (C1), 126.87 (C12, C10), 133.66
(C3), 143.74 (C11), 151.30 (C5), 151.96 (C8).
Elemental analysis of BA-PABN shows that the experimental
results (C, 76.90%; H, 5.32%; N, 11.04%; O, 6.74%) are consistent with
the theoretical values (C, 77.32%; H, 5.51%; N, 10.93%; O, 6.24%).
The FTIR spectrum of BA-PABN is shown in Fig. 3a. The char-
acteristic absorption of the benzoxazine structure at 1232 cm−1
Fig. 3. FTIR spectra of (a) BA-PABN and (b)–(f) polymerization products obtained at
220 ◦C in air for different times.
C
H out-of-plane bending of the aromatic ring, whereas the band
at 750 cm−1 is ascribed to the benzoxazine ring breathing [19]. The
peak at 3042 cm−1 is due to the C H stretching vibration of the
aromatic ring, and the peaks at 2964 and 2868 cm−1 are the C
H
is assigned to the asymmetric stretching vibration of C
O C of
the oxazine ring [19], and the symmetric stretching vibration of
asymmetric and symmetric stretching vibrations of CH3, respec-
tively. The absorption peaks at bands of 1449, 1384, and 1259 cm−1
are attributed to the CH2 bending, wagging, and twisting vibrations
of the oxazine ring, respectively. The absorptions at 1605, 1514,
and 1500 cm−1 are associated with the C C stretching vibrations
of the aromatic ring. The absorption at 1178 cm−1 is related to the
C
O
C is observed at 1028 cm−1 [19]. The absorptions at 974 and
959 cm−1 are the characteristic mode of the benzene ring with an
oxazine ring attached. The absorptions at 2217 and 544 cm−1 are
belong to the stretching and the in-plane bending vibrations of C
[20], respectively. The band at 823 cm−1 corresponds to the sym-
metric stretching vibration of C C of the oxazine ring and the
N
Ar
C
Ar stretching vibration. The peak at 1122 cm−1 is assigned to
N
the C H in plane deformation vibration, whereas the C H out-of-
plane bending of the aromatic ring is found at 906 cm−1. The FTIR
spectrum of BA-PABN is consistent with the proposed structure.
3.2. Structure changes
The structure changes of BA-PABN in thermally activated poly-
merization were studied by FTIR, and the FTIR spectra of the
polymerized product obtained at 220 ◦C for different times in air
are shown in Fig. 3b–f. As can be seen, the absorption intensity of
the characteristic peaks at 1384, 1232, 1028, 974, 959, 823, and
750 cm−1 decreased rapidly in the early reaction stage, and most
of them disappeared in 180 min, indicating that the oxazine ring-
opening reaction is complete. With the polymerization proceeding,
the tri-substituted benzene ring-mode at band of 1500 cm−1
decreased gradually. Consequently, the tetra-substituted benzene
ring-mode at band of 1484 cm−1 appeared and increased for the
ortho-substituted (methylene-amine-methylene bridge) phenolic
structure formed by the reaction between the oxazine ring and
the free ortho position of a phenol structure. At the same time,
the intensity of the peak at 1605 cm−1 decreased, and two absorp-
tion peaks appeared at 1665 and 1581 cm−1 due to the C
N
Fig. 2. 13C NMR spectrum of BA-PABN.

Y. Liu et al. / Thermochimica Acta 549 (2012) 42–48
45
Scheme 2. Structure change from BA-PABN to PBA-PABN.
with the C H stretching vibration at 2964 cm−1 as the internal ref-
erence, for the intensity of the absorption at 2964 cm−1 remained
almost unchanged in the polymerization. The conversion of some
absorption bands was calculated according to Eq. (1), and the plots
of conversion against reaction time are shown in Fig. 4. As can be
seen, the reaction temperature and time have a profound effect on
the conversion degree of these absorption bands, and the conver-
sion degrees of these characteristic absorption bands are different
at the same temperature in an equal time interval. The difference
in conversion degree comes from the difference in reaction activity
between the groups. In addition, the conversion degree of bands of
1382, 1233, and 959 cm−1 gain relatively high values in the reac-
tion, whereas that at the band of 823 cm−1 reaches a low value
even at the end of polymerization. Here, it should be noted that the
absorption intensity of the peak at 823 cm−1 is contributed by the
stretching vibrations of the triazine ring formed in the polymeriza-
tion [11–13]. Correspondingly, the intensity of the C N absorption
peaks at 2217 and 544 cm−1 decreased. Moreover, due to the phe-
nol hydroxyl formed in the reaction, the absorption peak at around
3390 cm−1 increased with the time rising. Besides, with the dis-
appearing of the peak at 906 cm−1, another peak appeared at
880 cm−1 and increased, due to the C H out-of-plane vibrations
of aromatic ring. These FTIR spectra reflect the structure changes in
the reaction, which indicates that BA-PABN undergoes the oxazine
ring-opening polymerization and the cyclotrimerization of cyano
groups in the reaction. With the general polymerization reaction
mechanism of benzoxazines, the structure changes from BA-PABN
to PBA-PABN can be described by Scheme 2.
Based on the FTIR spectra, the intensities of some absorption
peaks were normalized and their relative conversions (˛) were
determined as follows [9,21,22]:
C
C
N
C symmetric stretching vibration of the oxazine ring and the
H out-of-plane bending of the aromatic ring, but the variation in
(Ai/Ar)T,t
the absorption intensity only involves the former in the reaction.
Fig. 5 shows the solid-state 13C CP/MAS NMR spectra of BA-
PABN and PBA-PABN, and the peaks in the 13C CP/MAS NMR spectra
are assigned on the basis of the calculated chemical shifts and the
comparison with the peak assignments for the deuterium chloro-
form solution-state NMR spectrum in Fig. 2. As shown in Fig. 5a,
the peaks at 76.86 and 48.54 ppm correspond to the resonances of
˛ = 1 −
(1)
(Ai/Ar)T,t=0
where T is the polymerization temperature, t is the polymeriza-
tion time, (Ai/Ar)T,t and (Ai/Ar)T,t=0 are the ratios of the integrated
intensity of a specified band to the integrated intensity of an inter-
nal reference at the time t and at the starting time, respectively.
The absorption intensity of the associated groups was normalized
Fig. 4. Plots of conversion versus reaction time for some absorption bands at different temperatures in air.

46
Y. Liu et al. / Thermochimica Acta 549 (2012) 42–48
Fig. 6. DSC curves of BA-PABN at several heating rates.
where ꢀHT is the reaction heat released from beginning of poly-
merization up to the temperature T, and ꢀHr is the total reaction
heat obtained at a certain heating rate.
According to the isoconversional principle that the reaction rate
at constant extent of conversion is only a function of tempera-
ture [23], the reaction activation energy can be determined by
Kissinger–Akahira–Sunose equation from the non-isothermal DSC
curves obtained at several heating rates, which can be expressed as
follows [23–25]:
Fig. 5. Solid-state 13C NMR spectra of BA-PABN and PBA-PABN.
ꢀ
ꢁ
ˇi
T˛2,i
E˛
ln
= Const −
(3)
RT˛,i
methylene carbons (C7 and C6) of O CH2 N and Ar CH2 N of the
oxazine ring, respectively. Some chemical shifts (ppm) are assigned
as follows: 152.20 (C8, C5), 144.80 (C11), 133.61 (C3), 103.15 (C2),
42.43 (C14), and 32.82 (C15), and the other resonances of C12, C10,
C1, C13, C4, and C9 are highly overlapped in the chemical shift
rang of 114.35–120.28 ppm. With the identification of these reso-
nances native to the carbons in BA-PABN, the assignments of the
peaks for carbons in PBA-PABN are shown in Fig. 5b. Though the
resonance peaks of most carbons in BA-PABN and PBA-PABN are
overlapped, some characteristic changes in chemical shift for cer-
tain carbons can be obviously traced in the variation from BA-PABN
to PBA-PABN. The chemical shift changes of C6 and C7 indicate that
the ring-opening polymerization is complete. In addition, the peak
at around 166.39 ppm is assigned to the resonance of the triazine
carbon formed in the polymerization, whereas the other peak at
17.31 ppm may be due to the resonance of the terminal carbon of
PBA-PABN molecule. These chemical shifts of the carbons confirm
the proposed structure of PBA-PABN.
where ˇ is the linear heating rate, E˛ is the activation energy at
˛, R is the universal gas constant, and T˛ is the absolute tempera-
ture at ˛. The E˛ values can be obtained from the slope of the plot
of ln(ˇ/T˛2) versus 1/T␣ through a least squares linear regression
method. Fig. 7 shows the dependence of the activation energy on
conversion for the polymerization of BA-PABN.
The E˛ values in Fig. 7 show an initial rapid increase with ˛ up to
∼0.2 and maintain almost constant in the ˛ range of 0.2–0.6, then
increase gradually and reach a maximum at ˛ ∼ 0.86, and decrease
quickly thereafter. The variation in E˛ with ˛ indicates that the
polymerization of BA-PABN proceeds through a multi-step reac-
tion mechanism. As mentioned above, the reaction involves the
3.3. Polymerization activation energy
Fig. 6 shows the non-isothermal DSC curves of BA-PABN, and
each DSC curve gives one endothermic peak at around 76 ◦C due to
the melting of BA-PABN, and one exothermic peak corresponding
to the polymerization, including the oxazine ring-opening poly-
merization and the cyclotrimerization of cyano groups. With the
general principle of the heat is proportional to the extent of the
reaction, the extent of conversion (˛) for polymerization at any
temperature can be calculated by integrating the exothermic peak,
and it is expressed as:
ꢀHT
˛ =
(2)
Fig. 7. Dependence of the activation energy on conversion for the polymerization
of BA-PABN.
ꢀHr

Y. Liu et al. / Thermochimica Acta 549 (2012) 42–48
47
Fig. 8. Dynamic mechanical curves of PBA-PABN.
oxazine ring-opening polymerization and the cyclotrimerization of
CN groups, and the difference in the reactive activity between the
two groups may enhance the complexity in the reaction. Moreover,
the changes in molecular structure during the polymerization may
affect the E˛ values. In the initial stage, with the triazine structure
forming, the further cyclotrimerization of CN groups may become
difficult due to the steric hindrance, and the E˛ value increases.
With the polymerization temperature rising, the mobility of the
molecular chain is enhanced, and the reaction can proceed steadily
with a constant E˛ value. However, when the cross-linking density
increases to a certain extent, the mobility of the molecular chain
decreases, which reduces the reaction chance and enhance the E˛
value.
Fig. 9. TG and DTG curves of PBA-PABN in air and in nitrogen at a heating rate of
10 ◦C/min.
3.4. Dynamic mechanical properties
Fig. 8 shows the temperature dependence of Eꢀ, Eꢀꢀ, and tan ı
for PBA-PABN. At room temperature (25 ◦C), the Eꢀ is about
2.7 GPa, indicating higher stiffness than those of phenylnitrile and
phthalonitrile-functional polybenzoxazines (about 1.5–2 GPa) and
the analogues on the basis of bisphenol-A/aniline and methamine
(PB-a and PB-m) (2.2 and 1.8 GPa) [8,12–14], which may be
attributed to the higher cross-linking density and more prevalent
hydrogen bonding in PBA-PABN network [8]. With the temperature
rising, some segments get the ability to move, correspondingly,
Eꢀꢀ and tan ı increase gradually, and a weak broad peak appears
in their curves, which corresponds to the ␤-relaxation transition.
With the temperature continuously rising, Eꢀ decreases signifi-
cantly at about 156 ◦C due to energy dissipation, whereas Eꢀꢀ and
tan ı are close to their second peak values. The glass transition
temperature is 190 ◦C determined from the peak temperature on
the tan ı curve, which is higher than those of PB-a and PB-m (150
and 180 ◦C) and significantly lower than those of phenylnitrile
and phthalonitrile-functional polybenzoxazines (340 ◦C). Besides,
the magnitude of tan ı is lower than those of PB-a and PB-m and
significantly higher than those of phenylnitrile and phthalonitrile-
functional polybenzoxazines [8,12–14], which indicating that the
flexibility of the PBA-PABN molecular chain is lower than those
of PB-a and PB-m and higher than those of phenylnitrile and
phthalonitrile-functional polybenzoxazines in the glass transition
region.
the same as that in nitrogen in the initial stage, indicating that the
degradation in this stage is not affected by oxidation. The 5% and
10% weight loss temperatures are about 300 and 325 ◦C in both air
and nitrogen, respectively. However, the amount of the weight loss
in air is less than that in nitrogen at the same temperature in the
range of 412–629 ◦C, whereas the case reverses when temperature
above 629 ◦C due to the effect of oxidation. In addition, the char
yield is about 43% at 800 ◦C in nitrogen, and the element analysis
results for the residue show that the contents of carbon, hydrogen,
nitrogen, and oxygen are 79.07, 2.34, 3.70, and 14.89%, respectively.
However, almost no degradation residue is remained at 750 ◦C in
air, implying that the degradation reaction is accelerated in the
presence of oxygen in the high temperature range. Compared with
the previous studies on phenylnitrile and phthalonitrile-functional
polybenzoxazines [11–14], the 5% and 10% weight loss tempera-
tures and the char yield at 800 ◦C in nitrogen of PBA-PABN are lower,
indicating a lower thermal stability.
4. Conclusion
The BA-PABN was synthesized from bisphenol-A, p-
aminobenzonitrile and paraformaldehyde, and the chemical
structure was confirmed. The BA-PABN underwent the oxazine
ring-opening polymerization and the cyclotrimerization of cyano
groups with the formation of PBA-PABN. The storage modulus
of PBA-PABN at 25 ◦C is about 2.7 GPa, and the glass transition
temperature is 190 ◦C. The 5% and 10% weight loss temperatures of
PBA-PABN are 300 and 325 ◦C in both air and nitrogen, respectively.
The char yield is about 43% at 800 ◦C in nitrogen, whereas almost
no degradation residue is remained at 750 ◦C in air.
3.5. Thermal stability
Fig. 9 shows the thermogravimetry (TG) and the correspond-
ing derivative thermogravimetry (DTG) curves of PBA-PABN in air
and in nitrogen. As can be seen, the weight loss behavior in air is

48
Y. Liu et al. / Thermochimica Acta 549 (2012) 42–48
Acknowledgement
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This work was financially supported by the Natural Science
Foundation of Hebei University (2011YY06).
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