Synthesis, characterization, and thermally activated polymerization behavior of bisphenol-S/aniline based benzoxazine

Article abstract of DOI:10.1016/j.polymer.2010.06.009

A difunctional benzoxazine monomer, 6,6'-bis(3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazinyl) sulfone (BS-a), was synthesized via a solution method from bisphenol-S, aniline and formaldehyde. The chemical structure of the benzoxazine was confirmed by ¹

Full text of DOI:10.1016/j.polymer.2010.06.009

Polymer 51 (2010) 3722e3729
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis, characterization, and thermally activated polymerization behavior of
bisphenol-S/aniline based benzoxazine
*
Yanfang Liu , Zaiqin Yue, Jungang Gao
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
A difunctional benzoxazine monomer, 6,60-bis(3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazinyl) sulfone
(BS-a), was synthesized via a solution method from bisphenol-S, aniline and formaldehyde. The chemical
structure of the benzoxazine was confirmed by 1H and 13C nuclear magnetic resonance spectroscopy,
Fourier transform infrared (FTIR) spectroscopy, elemental analysis, and size exclusion chromatography.
The ring-opening polymerization of BS-a monomer was investigated with FTIR under air and nitrogen
atmospheres, and with differential scanning calorimetry (DSC) in both dynamic and isothermal condi-
tions. The FTIR results show that the absorption intensities of CeOeC, CeNeC, and oxazine ring decrease
gradually with temperature and time rising during the polymerization reaction. The change rates of
some absorption intensities of oxazine ring are affected by different atmospheric environments, and
a higher degree of conversion is obtained in nitrogen than that in air at the same reaction temperature
and in equal time. Kinetic parameters of the dynamic polymerization DSC results were evaluated with
Kissinger and Ozawa methods, respectively. The isothermal DSC results show that the polymerization
reaction of BS-a monomer follows an autocatalytic mechanism.
Article history:
Received 24 February 2010
Received in revised form
25 May 2010
Accepted 2 June 2010
Available online 9 June 2010
Keywords:
Benzoxazine
Bisphenol-S
Ring-opening polymerization
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
composites, especially in microelectronics, aerospace and pack-
aging industry [15e17].
Benzoxazine is a newly developed thermosetting phenolic resin,
and it can be synthesized via Mannich condensation from phenol,
amine and formaldehyde [1,2]. Various phenols and amines offer
enormous flexibility in molecular-design for benzoxazine, and
a few number of benzoxazine monomers with different structures
have been synthesized [3e10]. The benzoxazine monomer can be
polymerized by a thermally activated ring-opening polymerization
reaction with no reaction byproducts released and no catalyst
required [10e16]. During the self-crosslinking polymerization
reaction, the Mannich bridge structure (eCH2eNReCH2e) was
formed between benzoxazine molecules through the ring-opening
reaction of oxazine rings. So, with the polymerization proceeding,
benzoxazine gradually convert into a three-dimension network of
polybenzoxazine. The benzoxazine-based materials possess excel-
lent mechanical and thermal properties, high dimensional stability,
low water absorption, and high char yield, which make benzox-
The properties of the polybenzoxazine materials depend on
benzoxazine monomer molecular structure and the polymerization
processing conditions, and it is essential to understand the poly-
merization behavior of different benzoxazine resins to define the
actual processing conditions. In recent years, the majority of studies
were reported on synthesis methods [3,18], polymerization
[19e22], blending and composites [23e28], modification
[16,29e31], properties [32e34], and degradation [35] of benzox-
azine monomers and the resultant polymers. Most research articles
were concerned with the studies of the popular bisphenol-A based
difunctional benzoxazine, while the bisphenol-S based benzox-
azine was seldom studied [5,12]. Different from the isopropyl in
bisphenol-A, the sulfone (eSO2e) moiety in bisphenol-S is a strong
electron-withdrawing group with high rigidity. Introducing sulfone
moiety into benzoxazine can enhance its rigidity and improve its
thermal stability. In the literatures, sulfone-based benzoxazine was
briefly mentioned as part of many compound study [5], and
synthesis and structure prediction of benzoxazine based on
bisphenol-S and methylamine was reported [12].
azine
a promising matrices candidate for high performance
The objective of this paper is to perform a comprehensive study
for the polymerization reaction of a benzoxazine monomer based
on bisphenol-S and aniline, and to understand the polymerization
* Corresponding author. Fax: þ86 312 5079525.
E-mail address: liuyanfang@msn.com (Y. Liu).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.06.009

Y. Liu et al. / Polymer 51 (2010) 3722e3729
3723
behavior and reaction mechanism of the benzoxazine. In the paper,
the difunctional benzoxazine monomer, 6,60-bis(3-phenyl-3,4-
dihydro-2H-benzo[e][1,3]oxazinyl) sulfone (abbreviated as BS-a),
was synthesized via a solution method from bisphenol-S, aniline
and formaldehyde. The ring-opening polymerization of BS-
a monomer was investigated with Fourier transform infrared (FTIR)
spectroscopy in both air and nitrogen atmospheres, and with
differential scanning calorimetry (DSC) in both dynamic and
isothermal conditions.
The dynamic and isothermal polymerization reactions of BS-
a monomer were monitored with a Shimadzu DSC-41 differential
scanning calorimeter operating in a nitrogen atmosphere. The DSC
instrument was calibrated with high purity indium. a-Al2O3 was
used as the reference material. The amount of BS-a used was about
6.5 mg. In the dynamic analyses, the samples were scanned at
different heating rates of 5, 7.5, 10, 12.5, and 15 ꢀC/min, respectively.
Isothermal analyses were performed at temperatures of 172, 176,
182,187,191, and 197 ꢀC, respectively. Before loading the sample, the
furnace was first heated up to a desired temperature and kept for
a certain period of time. When the system reached an equilibrium
state, the sample cell was quickly set on the calorimetric detector
plate. The reaction was considered complete when the rate curve
leveled off to a baseline. After each isothermal run, the sample was
rapidly cooled to 10 ꢀC and then reheated at 10 ꢀC/min to 280 ꢀC to
2. Experimental
2.1. Materials
Bisphenol-S (4,40-dihydroxydiphenyl sulfone) (99%), was
purchased from Shanghai Chemical Reagent Co. (China). Formal-
dehyde (37% aqueous), aniline, dioxane and chloroform were
obtained from Tianjin Chemical Reagent Co. (China). All chemicals
were used as received.
determine the residual heatof reaction, DHr. Therefore, the total heat
evolved during the polymerization reaction is
D
H0 ¼
D
Hi þ
DHr.
3. Results and discussion
3.1. Synthesis and characterization
2.2. Synthesis of 6,60-bis(3-phenyl-3,4-dihydro-2H-benzo[e][1,3]
oxazinyl) sulfone
BS-a was synthesized via a solution method [2], and the
synthesis reaction mechanism is shown in Scheme 1. The chemical
structure of BS-a was confirmed with 1H and 13C NMR, FTIR,
element analysis, and SEC.
To a 100 mL three-necked round bottom flask equipped with
a mechanical stirrer, a thermometer, and a reflux condenser, 4.5 mL
aniline, 8.1 g formaldehyde, and 20 mL dioxane were added,
keeping the temperature below 10 ꢀC in an ice bath. The mixture
was stirred for 15 min before adding the solution of 6.26 g
bisphenol-S in 15 mL dioxane. The temperature was then gradually
raised to 92 ꢀC, and the mixture was allowed to reflux for 6 h.
Subsequently, the solvent was removed by distillation under
reduced pressure, and the residue was dissolved in 20 mL chloro-
form. The chloroform solution was washed several times with
3 mol Lꢁ1 NaOH aqueous solution and de-ionized water, respec-
tively. 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 7 h and then at 70 ꢀC in an air circulated
oven for 8 h, and a pale yellow powder was obtained.
Fig. 1 shows the 1H NMR spectrum of BS-a. Resonances
appearing at 4.75 ppm and 5.52 ppm are assigned to the methylene
protons of AreCH2eN and OeCH2eN of the oxazine ring, respec-
tively. The multiplets at 6.79e6.89, 7.08e7.22, 7.63e7.72 ppm are
assigned to the aromatic protons.
In the corresponding 13C NMR spectrum in Fig. 2, resonances
appearing at 50.3 ppm and 80.7 ppm are assigned to the methylene
carbons (C5 and C6) of AreCH2eN and OeCH2eN of the oxazine
ring, respectively. Other chemical shifts (ppm) are assigned to the
aromatic carbon resonances: 118.2 (C3), 118.9 (C8), 122.2 (C1), 123.1
(C11), 127.8 (C12), 128.3 (C9), 129.8 (C2), 130.0 (C2), 135.0 (C10),
148.7 (C4), 159.2 (C7).
The FTIR spectrum of BS-a is shown in Fig. 3A. The characteristic
absorptions at 1078, 1118 and 1194 cmꢁ1 are assigned to the
asymmetric stretching of CeNeC, while the absorption peak at
792 cmꢁ1 is assigned to the symmetric stretching of CeNeC [36].
The characteristic absorptions at 1030 and 1238 cmꢁ1 are due to the
symmetric and asymmetric stretching of CeOeC [36], respectively.
The peak at 1329 cmꢁ1 is due to CH2 wagging mode in benzoxazine
structure [15e17]. The absorption at 971 cmꢁ1 is attributed to the
benzene with an attached oxazine ring [37], and the peaks at 722
and 664 cmꢁ1 are due to the absorptions of oxazine ring. In addi-
tion, the absorption at 1600 cmꢁ1 is assigned to C]C stretching of
benzene ring. The absorptions at 1483 and 1493 cmꢁ1 are due to the
2.3. Measurements
Both proton (1H) and carbon (13C) nuclear magnetic resonance
(NMR) spectra were recorded using a Bruker Avance 600 NMR
spectrometer at a proton frequency of 600 MHz and the corre-
sponding carbon frequency. Deuterated acetone was used as
a solvent and tetramethylsilane as an internal standard.
FTIR spectra were obtained with a Nicolet 380 FTIR spectrom-
eter at a resolution of 4 cmꢁ1. BS-a sample was finely ground with
KBr powder and pressed into disk. For polymerization study, the
BS-a monomer in KBr disk was isothermally polymerized in an
oven under either circulating air or nitrogen atmosphere. During
the polymerization reaction, the disk was repeatedly withdrawn at
a regular time interval for measurement.
The quantitative analyses of C, H, N, O and S were carried out on
an Exeter Analytical CE-440 elemental analyzer.
Size exclusion chromatography (SEC) was performed on a Waters
workstation equipped with a 515 HPLC pump, a 717 auto sample
injector and a 2410 refractive index detector. Three styragel columns
(HT3, HT5, and HT6E, with pore sizes of 100 nm, 10,000 nm, and
100,000 nm, respectively) were connected in series. The measure-
ments were performed at a column temperature of 25 ꢀC with
tetrahydrofuran as an eluent and at a flow rate of 1.0 mL/min. The
concentration of BS-a was 2 mg/mL in tetrahydrofuran, and the
injecting amount for measurement was 50
m
L.
Scheme 1. Chemical reaction of BS-a monomer synthesis.

3724
Y. Liu et al. / Polymer 51 (2010) 3722e3729
Fig. 1. 1H NMR spectrum of BS-a monomer.
stretching vibrations of the benzene ring attached to oxazine ring,
and the out-of-plane bending mode can be found at 919 cmꢁ1
[38,39], while the in-plane bending mode is at 577 cmꢁ1 [36].
Moreover, the peak at 825 cmꢁ1 is assigned to CeH out-of-plane
bending vibrations of 1,4-substituted benzene ring, and the
absorption bands characteristic of CeH out-of-plane deformation
vibration of meta-disubstituted benzene ring appeared at 693 and
756 cmꢁ1. Besides, CeH stretching vibrations of benzene ring
appeared at 3020 cmꢁ1, and the peaks at 2923 and 2850 cmꢁ1 are
assigned to the asymmetric and symmetric stretching vibrations of
CH2 of oxazine ring, respectively. The absorption at 1097 cmꢁ1 is
due to the stretching vibrations of aromatic CeS, and the peaks at
1140 and 1297 cmꢁ1 are assigned to the symmetric and asymmetric
stretching vibrations of O]S]O group, respectively.
Elemental analysis of BS-a shows that the experimental results
(C, 68.67%; H, 5.05%; N, 6.25%; O, 13.43; S, 6.58%) are in reasonable
agreement with the calculated value (C, 69.40%; H, 4.99%; N, 5.78%;
O, 13.21%; S, 6.62%).
The SEC chromatogram is shown in Fig. 4, and the weight-average
molecular weigh is 500. Comparing the SEC results with the calculated
molecular weight value, 484.6, it can be deduced that no oligomeric
fraction exists in the initial BS-a monomer, which is in good agreement
with 1H and 13C NMR spectra, indicating that no protons or carbons exist
from the methylene groups as a resultof the ring-openingof oxazine ring.
Fig. 3. FTIR spectra of: (A) BS-a monomer, and polymerized at 170 ꢀC in air for: (B)
30 min, (C) 60 min, and (D) 180 min.
reaction proceeding, chemical structure changes can be traced from
the FTIR spectra. Some obvious changes are located at 1238, 1194,
1118, 1078, 1030, 722, 664 cmꢁ1, and the intensities of these bands
decreased with the reaction time increasing, which are associated
with the variations of the absorption intensities of CeOeC, CeNeC,
and oxazine ring, owing to the ring-opening reaction of BS-a.
Meanwhile, corresponding to the decrease of these absorption
intensities, some new absorption bands appeared. Among these,
the new band at 3350e3390 cmꢁ1 is assigned to the stretching of
OH group formed through oxazine ring-opening reaction, and the
new absorption at 1650 cmꢁ1 may be attributed to Schiff base, N]
CH, a possible intermediate of oxazine ring-opening polymeriza-
tion [20,38,40]. With reaction time rising, these new peaks became
wider and their absorption intensities increased. Moreover, other
obvious changes located at 1618, 1600, 1587, 1512, 1493, 1483, 1456,
3.2. Structure changes during the ring-opening polymerization
reaction
Fig. 3BeD are the FTIR spectra of BS-a polymerized under air
atmosphere at 170 ꢀC for different times. With the polymerization
Fig. 2. 13C NMR spectrum of BS-a monomer.
Fig. 4. SEC chromatogram of BS-a monomer.

Y. Liu et al. / Polymer 51 (2010) 3722e3729
3725
1452, 971, 919, 825, 693, 577 cmꢁ1 are the absorptions associated
with benzene ring. Corresponding to the intensities decreasing of
CeOeC, CeNeC, and oxazine ring, the absorption intensities at
1600, 1493, 1483, 919, 825, 693 cmꢁ1 also reduced, while the
intensities at 1618, 1587, 1512, 1456, 1452 cmꢁ1 increased, which is
attributed to the variation of the numbers of the substituted groups
attached to benzene ring, namely tri-substituted benzene ring
converts into tetra-substituted. According to the structure changes
during BS-a polymerization, the ring-opening polymerization
reaction can be described as in Scheme 2.
To evaluate the effect of the atmospheric environments on the
polymerization reaction, the polymerization of BS-a in nitrogen
atmosphere was also monitored by FTIR, and some FTIR spectra are
shown in Fig. 5. Comparing the FTIR spectra with that in Fig. 3, some
difference of absorption changes can be discerned.
In order to analyze quantitatively the absorption intensity
changes in the FTIR spectra, some absorptions were normalized and
their relative conversions (a) at various isothermal polymerization
temperatures were determined as follow [13,20,26]:
ðAi=ArÞT;t
ðAi=ArÞT;t¼0
a
¼ 1 ꢁ
(1)
where T is the polymerization temperature and t is the polymeri-
zation time, ðAi=ArÞT;t and ðAi=ArÞT;t¼0 are the ratios of integrated
intensity of the specified band to the integrated intensity of the
internal standard band at time t and at starting time, respectively.
The band at 756 cmꢁ1 is used as an internal standard.
Fig. 5. FTIR spectra of: (A) BS-a monomer, and polymerized at 170 ꢀC in nitrogen for:
According to equation (1), the conversions of different absorp-
tion bands were calculated in air and nitrogen at different
temperatures for various times. And some plots of conversion
against reaction time are shown in Fig. 6. It is apparent that poly-
merization environment (temperature and atmosphere) greatly
affected the thermally activated polymerization process. On one
hand, the effect of temperature is significant on the conversion
change rates of various absorption bands in air and nitrogen. For
a selected band, in the same reaction time, a higher conversion was
gained at a higher reaction temperature. On the other hand, it is
obvious that under air condition the polymerization proceeds
slower than that in nitrogen, and the degree of changes in air for
a selected band was lower than that in nitrogen at the same reac-
tion temperature and in equal time, which may be ascribed to the
decreased catalytic effect of phenolic hydroxyl groups partly
oxidized in air.
(B) 10 min, (C) 30 min, and (D) 60 min.
electron-withdrawing sulfone group (eSO2e), which makes BS-
a polymerization proceed slower in air than that in nitrogen.
However, different reaction trends were earlier observed with FTIR
and DSC in air and nitrogen in other type benzoxazines polymeri-
zation, respectively [20,38].
In addition, it would be observed that at the same reaction
temperature the reaction rates of these selected bands were
different, which can in some extent indicate the reaction sequence
or activity for various chemical reaction sites during the polymer-
ization. Among these selected bands, the intensity change rates of
bands at 1238, 1118, 722 cmꢁ1 are higher than those of other bands,
and the change rate of band at 1030 cmꢁ1 is the lowest.
3.3. Ring-opening polymerization kinetics
Generally, the reaction is considered to be cationic polymeri-
zation, and the oxazine ring-opening is catalyzed by phenolic
hydroxyl groups formed during the early stages of heating [19,41].
In BS-a monomer polymerization, the phenolic hydroxyl groups are
liable to be oxidized in air due to the electronic effects of the
The polymerization kinetic analysis for thermosetting resins can
be performed using several techniques based on different
measurement principles, such as, DSC [19,42,43], FTIR [44], NMR
[45], and rheology [22]. Among these techniques, DSC is based on
a phenomenological method, with which kinetic analysis only need
to calculate the heat variation for a whole reaction process with
temperature or time, and not to distinguish individual reaction in
the process. So DSC is the most utilized technique to determine
kinetic parameters and rate equation of benzoxazine polymeriza-
tion [19,28,46], and both dynamic and isothermal DSC modes can
be used to characterize the polymerization process.
In this study, a multiple-heating-rate method for dynamic mode
was used to evaluate the polymerization reaction kinetic parameters
by measuring the exothermic peak temperatures (Tps) at several
heating rates. Fig. 7 shows the DSC curves of BS-a dynamic poly-
merization. During the heating process, an endothermic peak
appearedatabout100ꢀC,whichcorrespondstothemeltingprocesses
of BS-a. With the temperature rising, an exothermic reaction process
covered a wide temperature range, which corresponds to the poly-
merization of BS-a. Based on the difference of the exothermic peak
Scheme 2. Thermally activated ring-opening polymerization of BS-a monomer.

3726
Y. Liu et al. / Polymer 51 (2010) 3722e3729
Fig. 6. Plots of conversion versus reaction time for different absorption bands at different temperatures in air and nitrogen.
temperatures of the DSC curves, the kinetic parameters can be
determined by Kissinger and FlynneWalleOzawa methods [47e49].
Kissinger’s technique assumes that the maximum reaction rate
where b is the linear heating rate, A is the pre-exponential factor, E
is the activation energy and R is the universal gas constant.
Therefore, a plot of lnð
b
=Tp2Þ versus 1=Tp gives the values of E and A.
occurs at peak temperatures, where d2
expressed as
a
=dt2 ¼ 0, it can be
FlynneWalleOzawa method assumes that the degree of
conversation at peak temperatures for different heating rates is
constant, and it can be expressed as
!
ꢀ
ꢁ
b
Tp2
AR
E
E
RTp
ln
¼ ln
ꢁ
(2)
E
RT
ln
b
¼ ꢁ1:052 þ C
(3)

Y. Liu et al. / Polymer 51 (2010) 3722e3729
3727
Fig. 9. Plots of conversion versus reaction time at different temperatures.
Fig. 7. DSC curves of BS-a dynamic polymerization at different heating rates.
Table 1
Table 2
Peak temperatures and kinetic parameter values obtained from dynamic DSC scans.
Kinetic parameter values obtained from isothermal DSC scans.
Heating rate
(ꢀC/min)
Tp (ꢀC)
Kissinger
FlynneWalleOzawa
Temperature (ꢀC)
k (10ꢁ3, sꢁ1
)
m
n
E (kJ molꢁ1
)
A (sꢁ1
)
5.02 ꢂ 1013
E (kJ/mol)
A (sꢁ1
1.07 ꢂ 1016
)
E (kJ/mol)
172
176
182
187
191
197
1.57
2.10
3.50
5.40
7.38
11.50
0.22
0.23
0.30
0.36
0.41
0.46
2.66
1.96
2.01
2.05
1.87
1.90
140.7
5
204.0
208.0
211.0
213.5
215.5
176.8
175.7
7.5
10
12.5
15
where C is a constant, T is the iso-conversion temperature, and the
other parameters are the same as described previously. E can be
b
obtained from the slope of the plot of ln versus 1=Tp.
D
Ht
a
¼
(4)
D
H0
According to the equations (2) and (3), the polymerization
kinetic parameters were calculated and the results are listed in
Table 1. It can be noticed that the activation energy values obtained
by the two methods are very close.
In isothermal DSC mode, the polymerization reaction kinetics
can be characterized by measuring the heat released during the
reaction with temperature and time. It is assumed that the heat
evolution recorded by DSC is proportional to the extent of
d
a
1
dH
¼
ꢂ
(5)
dt
D
H0 dt
where
of heat, and
D
Ht is the reaction heat within time t, dH/dt is the flow rate
H0 is the total reaction heat, which is the maximum
D
heat value determined among all the isothermal and dynamic
polymerization reactions.
Fig. 8 shows the DSC curves of BS-a isothermal polymerization
at different temperatures. It is clearly seen that the heat flow rate is
a function of the polymerization temperature and time. The total
exothermic reaction heat of BS-a is 305.3 J gꢁ1. According to
consumption of the reactive groups. So, the extent of reaction (a)
and the reaction rate (da/dt) during polymerization can be
described as follows:
Fig. 8. DSC curves of BS-a isothermal polymerization at different temperatures.
Fig. 10. Plots of reaction rate versus conversion at different temperatures.

3728
Y. Liu et al. / Polymer 51 (2010) 3722e3729
Fig. 11. Comparisons of the experimental results with the kinetic model data.
ꢀ
ꢁ
E
RT
equations (4) and (5),
a
and d
at different temperatures are shown in
Figs. 9 and 10, respectively.
a/dt were calculated, and the plots of
k ¼ Aexp ꢁ
(7)
a
versus t, da/dt versus a
where all parameters have usual Arrhenius significance.
The forgoing studies with FTIR show that the individual band
conversion is affected by temperature and time. Also, it can be
seen in Fig. 9 that the extent of the whole reaction process is
affected by temperature and time. Here, it should be noted that
the meanings of conversions given by FTIR and DSC methods are
different, and the effects of temperature or time on conversions
appear different. In FTIR, the conversions are obtained from the
changes of absorption intensities of each selected group with an
internal band as standard, while the conversions in DSC are
obtained from the heat variation of all the reaction groups with
the total exothermic reaction heat as quantitative standard. In
addition, it can be noticed that the temperature ranges selected
in the study are different for FTIR and DSC methods. In FTIR
Based on the experimental data, kinetic parameters, k, m and n,
can be obtained by fitting the experimental data to the equation (6)
with nonlinear regression. Then, according to Arrhenius equation,
activation energy (E) and pre-exponential factor (A) can be calcu-
lated via least squares linear regression. The results are listed in
Table 2, and the comparisons of the experimental data with the
kinetic model are shown in Fig. 11. The activation energy value is
lower than the results obtained in dynamic mode.
In addition, comparing the kinetic results of BS-a with that of
bisphenol-A based benzoxazine (BA-a) reported by Ishida and
Rodriguez [19], it can be noticed that the activation energy values of
BS-a are higher than that of BA-a. In the dynamic polymerization
mode, the activation energy values of BS-a are 176.8 kJ/mol by
Kissinger’s method and 175.7 kJ/mol by Ozawa’s method, respec-
tively, while those of BA-a are 116 kJ/mol by Kissinger’s method and
107 kJ/mol by Ozawa’s method, respectively. In isothermal poly-
merization mode, the activation energy values of BS-a and BA-a are
140.7 kJ/mol and 102 kJ/mol, respectively. This may be ascribed to
the structure difference between BS-a and BA-a monomers,
namely, one is the rigid sulfone moiety e electron-withdrawing
group, and the other is the flexible isopropyl e electron-donating
group. In additon, it can also be noted that the reaction rate of BS-
a is higher than that of BA-a at the same isothermal polymerization
temperature. According to Arrhenius relationship (7), the reaction
rate depends on the pre-exponential factor (A) and the activation
energy (E) at the same temperature.
method,
a relatively low temperature range was chosen to
capture the small changes of the absorption intensities at a slow
reaction rate. In DSC method, a relatively high temperature
range was selected to determine sensitively the heat released
during the reaction. Naturally, temperatures cannot be set too
low or too high in DSC, at which the reaction heat cannot be
measured effectively.
Fig. 10 shows that the reaction rate varied with the polymeri-
zation temperature and conversion, which phenomenologically
shows the autocatalytic characteristics, and the reaction rate can be
described by the following autocatalytic kinetic equation [50]:
d
a
n
¼ kamð1 ꢁ
a
Þ
(6)
dt
4. Conclusions
where m and n are the reaction orders, k is the rate constant at
temperature T, following Arrhenius equation (7):
Bisphenol-S and aniline based benzoxazine monomer was
synthesized with
a solution method. The FTIR absorption

Y. Liu et al. / Polymer 51 (2010) 3722e3729
3729
[22] Kumar S, Reghunadhan Nair CP, Ninan KN. Thermochim Acta 2006;441:150.
[23] Chozhan CK, Alagar M, Gnanasundaram P. Acta Mater 2009;57:782.
[24] Velez-Herrera P, Ishida H. J Polym Sci Part A Polym Chem 2009;47:5871.
[25] Garea SA, Iovu H, Nicolescu A, Deleanu C. Polym Test 2009;28:338.
intensities of CeOeC, CeNeC, and oxazine ring decrease gradually
with the temperature and time rising during the polymerization.
The change rates of some absorption intensities of oxazine ring are
affected by different atmosphere environments (air and nitrogen),
and a higher degree of conversion is obtained in nitrogen than that
in air at the same reaction temperature and in equal time. The
polymerization reaction follows an autocatalytic mechanism.
[26] Santhosh Kumar KS, Reghunadhan Nair CP, Ninan KN. Eur Polym
2009;45:494.
J
[27] Takeichi T, Saito Y, Agag T, Muto H, Kawauchi T. Polymer 2008;49:1173.
[28] Santhosh Kumar KS, Reghunadhan Nair CP, Sadhana R, Ninan KN. Eur Polym J
2007;43:5084.
[29] Kiskan B, Demiray G, Yagci Y.
2008;46:3512.
J Polym Sci Part A Polym Chem
References
[30] Kiskan B, Yagci Y, Ishida H. J Polym Sci Part A Polym Chem 2008;46:414.
[31] Cacal B, Cianga L, Agag T, Takeichi T, Yagci Y. J Polym Sci Part A Polym Chem
2007;45:2774.
[32] Ning X, Ishida H. J Polym Sci Part B Polym Phys 1994;32:921.
[33] Lin CH, Chang SL, Lee HH, Chang HC, Hwang KY, Tu PA, et al. J Polym Sci Part A
Polym Chem 2008;46:4970.
[34] Allen DJ, Ishida H. J Appl Polym Sci 2006;101:2798.
[35] Macko JA, Ishida H. Macromol Chem Phys 2001;202:2351.
[36] Dunkers J, Ishida H. Spectrochim Acta Part A 1995;51A:1061.
[37] Allen DJ, Ishida H. Polymer 2009;50:613.
[1] Holly FW, Cope AC. J Am Chem Soc 1944;66:1875.
[2] Ning X, Ishida H. J Polym Sci Part A Polym Chem 1994;32:1121.
[3] Agag T, Jin L, Ishida H. Polymer 2009;50:5940.
[4] Lin CH, Chang SL, Hsieh CW, Lee HH. Polymer 2008;49:1220.
[5] Kim HJ, Brunovska Z, Ishida H. Polymer 1999;40:6565.
[6] Santhosh Kumar KS, Reghunadhan Nair CP, Radhakrishnan TS, Ninan KN. Eur
Polym J 2007;43:2504.
[7] Andreu R, Espinosa MA, Galia M, Cadiz V, Ronda JC, Reina JA. J Polym Sci Part A
Polym Chem 2006;44:1529.
[8] Sponton M, Larrechi MS, Ronda JC, Galia M, Diz VC. J Polym Sci Part A Polym
Chem 2008;46:7162.
[38] Allen DJ, Ishida H. Polymer 2007;48:6763.
[39] Jin L, Agag T, Ishida H. Eur Polym J 2010;46:354.
[40] Shen SB, Ishida H. J Appl Polym Sci 1996;61:1595.
[9] Kiskan B, Koz B, Yagci Y. J Polym Sci Part A Polym Chem 2009;47:6955.
[10] Ishida H, Ohba S. Polymer 2005;46:5588.
[41] Andreu R, Reina JA, Ronda JC.
2008;46:3353.
J Polym Sci Part A Polym Chem
[11] Agag T, Takeichi T. Macromolecules 2003;36:6010.
[12] Hamerton I, Howlin BJ, Mitchell AL. React Funct Polym 2006;66:21.
[13] Kim HJ, Brunovska Z, Ishida H. J Appl Polym Sci 1999;73:857.
[14] Shen SB, Ishida H. J Polym Sci Part B Polym Phys 1999;37:3257.
[15] Garea SA, Iovu H, Nicolescu A, Deleanu C. Polym Test 2007;26:162.
[16] Kiskan B, Aydogan B, Yagci Y. J Polym Sci Part A Polym Chem 2009;47:804.
[17] Jin L, Agag T, Ishida H. Eur Polym J 2010;46:354.
[18] Ishida H, Heights S. US Patent. US5543516; 1996.
[19] Ishida H, Rodriguez Y. Polymer 1995;36:3151.
[42] Rosu D, Cascaval CN, Mustata F, Ciobanu C. Thermochim Acta
2002;383:119.
[43] Shi ZX, Yu DS, Wang YZ, Xu RW. Eur Polym J 2002;38:727.
[44] Bartolomeo P, Chailan JF, Vernet JL. Eur Polym J 2001;37:659.
[45] Russell VM, Koenig JL, Low HY, Ishida H. J Appl Polym Sci 1998;70:1413.
[46] Yei DR, Fu HK, Chen WY, Chang FC.
2006;44:347.
J Polym Sci Part B Polym Phys
[47] Kissinger HE. Anal Chem 1957;29:1702.
[48] Flynn JH, Wall LA. Polym Sci Part B Polym Lett 1966;4:323.
[49] Ozawa T. Bull Chem Soc Jpn 1965;38:1881.
[50] Kamal MR. Polym Eng Sci 1974;14:231.
[20] Kim HJ, Brunovska Z, Ishida H. Polymer 1999;40:1815.
[21] Kasapoglu F, Cianga I, Yagci Y, Takeichi T. J Polym Sci Part A Polym Chem
2003;41:3320.