Synthesis and characterization of cardanol containing tetra-functional fluorene-based benzoxazine resin having two different oxazine ring structures

Article abstract of DOI:10.1016/j.polymer.2019.121620

A new cardanol containing tetra-functional fluorene-based (t-BF-a-c) benzoxazine resins has been successfully synthesized via two-stage Mannich condensation reaction. The monomer contains simultaneous diamine- and bisphenol-type oxazine rings. The FTIR, <

Full text of DOI:10.1016/j.polymer.2019.121620

Accepted Manuscript
Synthesis and characterization of cardanol containing tetra-functional fluorene-
based benzoxazine resin having two different oxazine ring structures
Yu-Peng Chen, Xuan-Yu He, Abdul Qadeer Dayo, Jun-Yi Wang, Wen-bin Liu, Jun
Wang, Tao Tang
PII:
S0032-3861(19)30604-4
10.1016/j.polymer.2019.121620
121620
DOI:
Article Number:
Reference:
JPOL 121620
To appear in:
Polymer
Received Date:
Accepted Date:
10 April 2019
29 June 2019
Please cite this article as: Yu-Peng Chen, Xuan-Yu He, Abdul Qadeer Dayo, Jun-Yi Wang, Wen-
bin Liu, Jun Wang, Tao Tang, Synthesis and characterization of cardanol containing tetra-functional
fluorene-based benzoxazine resin having two different oxazine ring structures, Polymer (2019), doi:
10.1016/j.polymer.2019.121620
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ACCEPTED MANUSCRIPT
Synthesis and characterization of cardanol containing tetra-functional
fluorene-based benzoxazine resin having two different oxazine ring structures
a
a,b
a,d
a
Yu-Peng Chen , Xuan-Yu He , Abdul Qadeer Dayo , Jun-Yi Wang , Wen-bin Liu
a,*, Jun Wang , Tao Tang
a,*
c,*
a
Key Laboratory of Superlight Material and Surface Technology of Ministry of
Education, College of Materials Science and Chemical Engineering, Harbin
Engineering University, Harbin 150001, China.
b
Xi'an Aerospace Composites Research Institute，Xi’an 710025, China.
c
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Science, Changchun 130022, PR China.
d
Department of Chemical Engineering, Balochistan University of Information
Technology, Engineering and Management Sciences, Quetta 87300, Pakistan.
*
Corresponding author E-mail:
Wen-bin Liu (wjlwb@163.com),
Jun Wang (wj6267@sina.com),
T. Tang (ttang@ciac.jl.cn).

ACCEPTED MANUSCRIPT
Abstract
A
new cardanol containing tetra-functional fluorene-based (t-BF-a-c)
benzoxazine resins has been successfully synthesized via two-stage Mannich
condensation reaction. The monomer contains simultaneous diamine- and bisphenol-
1
13
type oxazine rings. The FTIR, H and C NMR tests were performed to confirm the
structure of intermediates and t-BF-a-c benzoxazine. The rheological properties and
curing behavior of the resin and thermal and thermomechanical properties of the
corresponding polymer (poly(t-BF-a-c)) were evaluated by rheometer, differential
scanning calorimeter, thermogravimetric analysis, and dynamic mechanical analyzer.
The synthesized benzoxazine resin displays good processability and wide process
window due to the incorporation of cardanol. Poly(t-BF-a-c) exhibits much higher
glass transition temperature (373 °C) than corresponding bi-functional
polybenzoxazines and better thermal stability than mono- and bi-functional
cardanol-based polybenzoxazines. With the introduction of the flexible long alkyl
chain of cardanol, the brittleness of fluorene-based polybenzoxazine is greatly
modified without sacrificing thermal properties of the polymer.
Keywords: Tetra-functional benzoxazine; cardanol; thermomechanical properties.

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1
. Introduction
st
Since the start of the 21 century, the growing environmental concerns and the
rapid fluctuation in the petrochemical prices diverted the attention of researchers
towards the synthesis of monomers and polymers from bio-based resources [1, 2]. The
cellulose, lignin, tannins, starch, castor oil, cashew nut shell oil, chitin, and chitosan
are the most widely used bio-based materials [3]. The cardanol is a pale yellow
phenolic oil obtained as a byproduct from the cashew nut processing industry. The
cardanol having a long alkyl side chain has attracted the attention of researchers
working on the high performance polymers. A variety of high performance polymers
have been synthesized from the cardanol, which includes polybenzoxazine (PBz),
polynaphthols, phthalonitrile, alkyds, melamines, polyesters, etc, are successfully
synthesized from the cardanol [4]. However, the cardanol based polymers exhibit
higher flexibility as compared to the simple phenol based polymers due to internal
plasticization due to the presence of long alkyl side-chain, this chain also reduces the
thermal and thermomechanical properties of the polymers [5].
The PBz resins provide some outstanding characteristics such as no generation of
by-products, excellent flame retardancy and higher thermal stability, near zero
shrinkage upon polymerization, and low moisture absorption. The extraordinary
molecular design flexibility of PBz resins as compared to other polymers and brings a
wide range of properties [6-9]. The synthesis of fluorene-based polymers attracted the
researchers due to the reduced segmental activity, and significant enhancements in the
glass transition temperature (T ) and thermal stabilities. Several types of
g
fluorene-based high performance polymers are successfully synthesized such as PBz,
polyimides, poly(ether imide), and epoxy [10-19]. However, the low toughness and
high fragility of the fluorenyl containing polymers limit their further application. In

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our previous studies, we introduced the aryl ether and aryl ester in the monomer
structure to improve the toughness of the polybenzoxazines [20, 21].
In the current study, keeping in view the higher fragility of the fluorenyl
containing polymers and flexibility of the cardanol based polymers, we successfully
synthesized a new cardanol containing tetra-functional fluorene-based benzoxazine
monomer (t-BF-a-c). A single molecule of the monomer contains diamine- and
bisphenol- type oxazine rings. The detailed synthesis, polymerization behavior, and
properties of poly(t-BF-a-c) are investigated.
2
2
. Experimental
.1. Materials
Shanghai Jingchun Reagent Co., Ltd. Shanghai, China supplied the
2
4
,7-Dihydroxy-9-fluorenone,
p-formaldehyde,
trifluoroacetic
anhydride,
-chlorobenzene, sodium borohydride, and methyl sulfonic acid. Cardanol, distilled
technical grade, was kindly obtained from Shandong Haobo Co. Ltd. Shandong,
China. Aniline and all the solvents used in the current study were supplied by Tianjin
Kermel Chemical Reagent Co., Ltd. Tianjin, China. All the materials were used
without further purification.
2
.2. Synthesis of monomer
The condensation reaction of bisphenol or diamine with formaldehyde and
primary amine or phenol produced the benzoxazine monomer as a product. In the
current study, the simultaneous presence of bisphenol and diamine functional groups
in 9,9-bis(4-aminophenyl)-2,7-dihydroxyindole (b-AHF) (intermediate monomer)
make it difficult to obtain a monomer with two different oxazine ring structure.
Therefore, we utilize a two-stage Mannich condensation reaction to synthesize
t-BF-a-c benzoxazine resin (Scheme 1). Firstly, diamine in the b-AHF was protected

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by using the trifluoroacetic anhydride to afford amine-protected 9,9-bis(4-trifluoro-
acetamidophenyl)-2,7-dihydroxy-fluorene (b-pAHF). Later, the amine-protected
biphenol-type benzoxazine (b-pABF-a) was obtained via the first Mannich
condensation reaction of b-pAHF with aniline and paraformaldehyde. Subsequently,
b-pABF-a was deprotected with sodium borohydride in ethyl acetate/ethanol solution
to liberate amine. Finally, the t-BF-a-c benzoxazine resin was prepared by the second
Mannich condensation reaction of amine-liberated biphenol-type benzoxazine
(b-ABF-a) with paraformaldehyde and cardanol. The details of each step are provided
below, Scheme 1 shows the followed synthesis route.
Scheme 1.
2
.2.1. Preparation of b-AHF
The 2,7-dihydroxy-9-fluorenone and aniline were reacted by following the
method as described by Wang et al; [22]. The yield of a yellow powder (compound 1)
1
was 86%. H NMR (500 MHz, DMSO-d , ppm): 9.24 (s, 2H, –OH), 6.40-7.45 (m,
6
-1
1
4H, Ar–H), 4.93 (s, 4H, –NH ). FTIR (KBr, cm ): ν = 3375 (N-H stretching), 3308
2
(
–OH stretching), 1610 and 1445 (aromatic stretching vibration), 1484
1,2,4-trisubstituted characteristic absorption), 1182 (C–N asymmetric stretching).
(
2
.2.2. Preparation of b-PAHF
Compound 1 (19.0 g, 0.05 mol) and THF (200 mL) were added into a 250 mL
round flask and cooled for 30 min in an ice bath. Afterward, trifluoroacetic anhydride
23.1 g, 0.11 mol) was added dropwise in 30 min during the mixture stirring; later, the
(
mixture was stirred for 2 h in an ice bath. The solvent was removed by a rotary
evaporator, followed by dissolving the residue in ethyl acetate. The solution was
washed five times with saturated aqueous Na CO solution and three times with
2
3
distilled water. The solution was dried with sodium sulfate, filtered, and concentrated

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under vacuum. The product was precipitated in hexane (500 mL), filtered, and
overnight dried under vacuum. The yield of yellowish powder (compound 2) was 92%.
1
H NMR (500 MHz, DMSO-d , ppm): 11.31 (s, 2H, –NH), 9.44 (s, 2H, –OH),
6
-1
6
.71-7.58 (m, 14H, Ar–H). IR (KBr, cm ): ν = 3600-3100 (N–H and O–H stretching
overlap), 1704 (C=O stretching).
2
.2.3. Preparation of b-PABF-a
A 100 mL neck round-bottomed flask was connected with reflux condenser,
thermometer, and magnetic stirrer, and compound 2 (5.72 g, 0.01 mol), aniline (1.86 g,
0
.02 mol), p-formaldehyde (1.20 g, 0.04 mol) and 30 mL of chlorobenzene/xylenes
o
(
1:1) were added and mixed for 4 h at 130 C, and cooled to room temperature. Later,
the hexane was mixed in the cooled mixture, and produced precipitated were
separated by the filtration. The yellowish powder was thoroughly washed with ethanol
o
and vacuum dried at 60 C for one night. Afterward, the crude product was dissolved
in dichloromethane (100 mL), and three times washed with 100 mL each of 5 wt %
aqueous Na CO solution and water. The white powder (compound 3, with 83% yield )
2
3
was obtained after the solution drying over anhydrous sodium sulfate, followed by
1
evaporation of the solvent under vacuum. H NMR (500 MHz, DMSO-d , ppm):
6
1
1.24 (s, 2H, –NH), 6.73-7.53 (m, 22H, Ar–H), 4.74 (s, 4H, Ar–CH –N), 5.44 (s, 4H,
2
-1
O–CH –N). IR (KBr, cm ): ν = 3297 (N–H stretching), 1711 (carbonyl stretching),
2
1
478 (stretching of 1,2,4,5-tetrasubstituted benzene ring), 1244 (asymmetric
stretching of C–O–C), 950 (the oxazine ring stretching mode with a minor
contribution of CH out-of-plane bending).
2
.2.4. Preparation of b-ABF-a
Compound 3 (8.06 g, 0.01 mol) was dissolved in a 200 mL mixture of methanol/
ethyl acetate at a ratio of 1:100 in a 500 mL flask. The NaBH (3.78 g, 0.10 mol) was
4

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added in the solution, and the nitrogen atmosphere was adjusted and stirred for 5 h at
room temperature. Later, the mixture was three times washed with brine and water.
After that, ethyl acetate was withdrawn by using a rotary evaporator, and vacuum
o
1
dried at 60 C for 24 h. The yield of the final product (compound 4) was 71%. H
NMR (500 MHz, DMSO-d , ppm): 4.70 (s, 4H, Ar–CH –N), 4.89 (s, NH ), 5.41 (s,
6
2
2
-1
4
H, O–CH –N), 6.35-7.41 (22H Ar). IR (KBr, cm ): ν = 3363 (N–H stretching), 1478
2
(stretching of 1,2,4,5-tetrasubstituted benzene ring), 1225 (asymmetric stretching of
C–O–C), 1182 (asymmetric stretching of C–N–C), 941 (the oxazine ring stretching
mode with minor contribution of CH out-of-plane bending).
2
.2.5. Preparation of t-BF-a-c
In a 250 mL flask, compound 4 (3.07 g, 0.005 mol), cardanol (3.05 g, 0.01 mol),
p-formaldehyde (0.90 g, 0.03 mol) and 20 mL of toluene were manually mixed till the
o
uniformity of solution. Later, the solution was stirred for 12 h at 90 C and cooled
down to room temperature. Afterward, the hexane was poured in the mixture, and the
product (yellowish precipitates) were obtained after the filtration and 24 h vacuum
1
drying, the yield of product was 79%. H NMR (500 MHz, CDCl -d , ppm):
3
1
6
5
.48–7.45 (m, 28H, Ar–H), 5.32-5.40 (vinyl double bond), 5.33 (s, 4H, O–CH –N),
2
.25 (s, 4H, O–CH –N), 4.69 (s, 4H, Ar–CH –N), 4.52 (s, 4H, Ar–CH –N). FTIR
2
2
2
–
1
(
KBr, cm ): 1654, 992 (C=C stretching), 1367 (CH wagging), 1214, 1261 (C–O–C
2
asymmetric stretching), 1110-1190 (C–N–C asymmetric stretching), 1032, 1073
C–O–C symmetric stretching), 929-962 (C–H out-of-plane bending), 919 (the
oxazine ring stretching mode with minor contribution of CH out-of-plane bending).
(
2
.3. Curing of benzoxazine monomers
The t-BF-a-c benzoxazine resin was polymerized without the added initiator or
catalyst. The monomer was isothermally cured in an air-circulating oven by keeping

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theme at 150, 180, and 210 °C for 2 h at each stage. The polymer was post-cured for 1
h at 240 °C in an air-circulating oven.
2
.4. Characterization
A Perkin Elmer Spectrum-100 spectrometer was used to record the Fourier
−
1
−1
transform infrared (FTIR) spectra in the range of 4000-500 cm , at a 4 cm
resolution, after averaging two scans. The sample (monomers or cured) was blended
with KBr powder, a thin KBr pellet was prepared, and the spectrum of the pellet was
recorded in the presence of deuterated triglycine sulfate (DTGS) detector. The Bruker
1
13
AVANCE-500 NMR spectrometer was used to test the H and C NMR. The average
1
13
number of transients for H and C NMR is 32 and 1024, respectively. The tests were
performed after dissolving the samples in deuterated DMSO (DMSO-d ) and CDCl ,
6
3
while tetramethylsilane (TMS) was used as an internal standard. A TA Q200
differential scanning calorimeter was used to evaluate the differential scanning
calorimetry (DSC) measurements at a heating rate of 20 °C/min, from 30 to 350 °C,
under a constant (50 mL/min) flow of nitrogen gas. Prior to the samples testing, the
DSC machine was calibrated with a high-purity indium standard. A 5 mg of sample
was weighed into a hermetic aluminum sample pan at room temperature (24 °C),
which was then sealed, and tested immediately. The TA Instruments AR-2000ex
Rheology was used to evaluate the dynamic rheological measurements. The tests were
o
performed on a 6.283 rad/s angular frequency and 4 C/min heating rates. Thermal
stability of the polymer was evaluated by analyzing the thermogravimetric analysis
(TGA) under a nitrogen atmosphere (50 mL/min), performed on a TA Instruments
o
o
Q50 from 25 to 820 C at a 20 C/min heating rate. The thermomechanical properties
of the polymer were obtained by evaluating a rectangular (35×5×2 mm3)
polybenzoxazine sample on a dynamic mechanical analyzer (DMA) TA-Q800, USA.

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The sample was loaded in single cantilever mode, and tested at 3°C/min heating rate
from 30 to 390 °C, with a 1 Hz frequency of air atmosphere.
3
3
. Results and discussion
.1. Benzoxazine monomers structure
1
The H NMR spectra intermediates compounds (b-AHF, b-pAHF, b-pABF-a, and
b-ABF-a) and final t-BF-a-c benzoxazine resin are plotted as Figure 1. We can easily
observe from Figure 1(A) that the –OH protons shift from 9.26 to 9.44 ppm, and the
–
NH protons located at 4.92 ppm disappear before and after amine protection for
2
b-AHF. The new protons peak of CF CONH– at 11.24 ppm was observed. After the
3
first Mannich condensation and amine deprotection, the typical resonances of
bisphenol-type benzoxazine and deprotected amine groups appear at 4.70, 5.41, and
4
.89 ppm, respectively. The methylene protons of diamine-type benzoxazine were
located (at 4.52 and 5.25 ppm) after the second Mannich condensation reaction
Figure 1(B)). The disappearance of the deprotected amine group peak confirms the
(
formation of two different kinds of oxazine rings connected with phenyl and fluorene
rings, respectively. The peaks at 5.36 and 5.43 ppm, and 4.97-5.06 and 5.78-5.81 ppm
weak peaks can be ascribed to the –CH=, CH =CH–, and –CH=CH protons of
2
2
cardanol, respectively. These resonances are in agreement to the long alkyl side chain
of cardanol [23]. In addition, the integral ratio of the methylene protons is nearly
1
:1:1:1, indicating that the t-BF-a-c benzoxazine resin is successfully synthesized.
Figure 1
1
3
The C NMR spectra intermediate monomers (b-ABF-a and b-pABF-a) and final
t-BF-a-c benzoxazine monomers are displayed in Figure 2. The carbon atom
resonances of O–CH –N and Ar–CH –N oxazine ring were observed at 49.27-50.55
2
2
and 78.84-79.43 ppm, respectively. In particular, there were four kinds of oxazine

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rings carbon atom resonances in t-BF-a-c benzoxazine monomer backbone,
bisphenol-type oxazine rings (50.55 and 79.42 ppm) and diamine-type oxazine rings
(
50.11 and 79.32 ppm). The quaternary carbon atom of the fluorene ring was recorded
at around 63.8 ppm. The b-pABF-a intermediate showed multiple new peaks around
54.6 and 153.44 ppm, these peaks can be attributed to the resonance of carbon atom
of –CF and –CO–, respectively.
1
3
Figure 2
The FTIR spectrum of t-BF-a-c benzoxazine monomer (Figure 3) showed the
−
1
out-of-plane bending of C–H at 962 and 929 cm , which can be corresponded to the
phenyl and fluorene with an oxazine ring attached, respectively. The asymmetric
−
1
−1
stretching of C–O–C (1214 and 1261 cm ) and C–N–C (1110-1190 cm ), symmetric
−
1
−1
stretching of C–O–C (1073 and 1032 cm ), and CH wagging (1367 cm ) of oxazine
2
ring connected with benzene and fluorene, respectively, are also observed.
Additionally, the C=C stretching and out-of-plane deformation of =C–H in the
–
1
unsaturated moiety of cardanol were observed at 1654, and 992 cm the characteristic
1
13
absorption, respectively. These FTIR, H and C NMR spectra indicate the successful
synthesis of targeted cardanol containing tetra-functional fluorene-based benzoxazine
monomer.
3
.2. Polymerization behavior of benzoxazine monomer
The polymerization behavior of the synthesized t-BF-a-c benzoxazine monomer
was investigated by FTIR and DSC. The FTIR spectra of neat t-BF-a-c benzoxazine
o
monomer before and after cumulative curing at 180, 210, and 240 C are plotted as
Figure 3. The absorption band intensities ascribed to oxazine ring, symmetric
stretching of C–O–C, CH wagging, asymmetric stretching of C–N–C and C–O–C,
2
and out-of-plane bending of C–H gradually decrease as the curing temperature

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increases and curing proceeds. The similar phenomena were also recorded for the
olefinic bond peaks due to the C=C stretching and out-of-plane deformation of =C–H,
and completely disappear on the completion of the curing process. These results
indicate that high-temperature ring-opening polymerization can further carry out the
cross-linking reaction and increase the cross-linking density of polybenzoxazine.
Meanwhile, the FTIR spectrum of poly(t-BF-a-c) confirmed the hydrogen bonding
−
1
(
intramolecular and intermolecular) by the broad peak at 3382 cm with a shoulder.
The hydrogen bonding was recorded due to the ring-opening of benzoxazine, the
shoulder confirmed the overlapping in the crosslinked network structure of
polybenzoxazine [24].
Figure 3
The dynamic DSC plot of the t-BF-a- benzoxazine monomer before and after
each curing stage were evaluated, produced curves are illustrated in Figure 4. The
o
t-BF-a-c benzoxazine monomer only exhibits an exothermal peak at 277 C with
1
21.4 J/g of enthalpy value. The exotherm peak was slightly wide as compared to the
traditional benzoxazine monomers; this can be due to the overlap of oxazine
ring-opening and addition polymerization of double bonds in the alkyl side chain of
cardanol. In addition, the small value (121.4 J/g) for the heat of polymerization was
observed due to the dilution effect of cardanol having long alkyl chains in the
structure [25]. In addition to this, the t-BF-a-c benzoxazine monomer does not show
the very wide peak or shoulders, even though the single molecule contains two
different oxazine rings as recorded for the other fluorene-based benzoxazine [22],
may be due to the addition of alkyl side chain of cardanol. This confirms that the
steric hindrance was not observed during the polymerization.
Moreover, from the produced curves we can easily observe that the exothermic

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peak temperature moves to a higher temperature as the curing process moves on from
one to another curing stage. This can be dedicated to the formed network structures
and increased curing degree, which reduced the system viscosity, polymerization rate,
and activity of the functional group in the system. In addition to these, the reactivity
of functional groups can be increased by increasing the curing temperature, which
ultimately completes the curing of the monomer [20, 21]. After the complete curing
procedure, DSC curves did not show any exothermic peak, and the T was not
g
observed in the studied temperature range.
Figure 4
The rheological properties provide a basic understanding of the polymer’s
processability because it produces the melting point, gel point, and processing
window of the monomer. The melting point corresponds to the conversion of the solid
to liquid, while, the gel point corresponds to the conversion of the liquid to the solid
(conversion of the monomers to polymer). The processing window is very useful for
the polymer compounding or processing, it is the temperature range in between
melting point and gel point [26, 27].
The viscoelastic response of t-BF-a-c benzoxazine resin against the temperature
is plotted as Figure 5. For keeping the consistency in the study, the liquefying and gel
point temperatures value of t-BF-a-c benzoxazine monomer was defined at 1000 Pa·s
o
viscosity, the corresponding recorded values were 116 and 176 C. This shows a
o
processing window of 60 C, which is good enough for the processing of polymer.
Figure 5
The time at which the evolving dynamic storage (G’) and loss (G”) moduli
intersect during the isothermal polymerization is known as gelation point [28]. The
o
viscoelastic properties of t-BF-a-c benzoxazine monomer against time at 160 C

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isothermal polymerization are illustrated as Figure 6. The t-BF-a-c benzoxazine resin
achieves a gelled state in approximately 7 min.
Figure 6
3
.3. Thermomechanical and thermal properties
The thermomechanical properties of poly(t-BF-a-c) were evaluated by DMA, the
produced results are plotted as Figure 7. The T of poly(t-BF-a-c) was dramatically
g
improved as compared to the bi-functional fluorene-based polybenzoxazine
o
o
(
poly(BF-p), 256 C by DMA; poly(B-pbf), 229 C by DSC [12, 15] in spite the
o
incorporation of long alkyl side groups, the T was recorded at 373 C from the tan δ
g
peak height. As discussed earlier each t-BF-a-c benzoxazine resin molecule possesses
four oxazine rings and olefinic double bonds, resulting in a higher crosslinking density
of polybenzoxazine. In the bi-functional fluorene-based polybenzoxazines, the
fluorene molecules protrude vertically from the main chain of the polymer. In the
current study, the fluorene molecule exists in the backbone of molecule structure, due
to this the internal rotations and thermal motions of polymer segments are prevented.
o
However, a significant decline in the stiffness value (storage modulus at 50 C) was
recorded for the poly(t-BF-a-c). The recorded value was about 1.9 GPa, which around
0
.7 GPa lower than the stiffness value recorded for poly(BF-p) (2.6 GPa) [15]. This
decline in the stiffness value can be devoted to the introduction of a flexible alkyl side
chain of Cardanol, which reduced the rigidity of polybenzoxazine and improved the
toughness of fluorene-containing polybenzoxazine.
Figure 7
The TGA under a nitrogen atmosphere of poly(t-BF-a-c) was performed to
evaluate the thermal stability of polymer, Figure 8 shows the produced TGA curve.
The initial decomposition temperatures corresponding to 5% and 10% weight loss

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o
temperatures (T5% and T10%) and char yield (Y ) at 800 C are summarized in Table 1.
c
The initial decomposition temperature values of poly(t-BF-a-c) were recorded as
o
3
64 and 405 C, for the T and T10%, respectively. These values are lower than the
5
%
earlier recorded values for poly(BF-p), but much higher than those of poly(B-pbf) and
reported cardanol-based polybenzoxazines. In addition to this, similar behavior was
recorded for the Y value, the recorded value was 14 and 16% lower than the Y value
c
c
observed for poly(BF-p) and poly(B-pbf), respectively. A 35% Y value was recorded
c
for the poly(t-BF-a-c). However, this Y value is much higher than the corresponding
c
values recorded in 12-29% range for mono and bi-functional cardanol-based
polybenzoxazines [12, 15, 29]. These enhancements in the thermal stabilities values
can be attributed to the high aromatic content and tighter packing density because of
the higher crosslinking density for poly(t-BF-a-c). It reflects that cardanol containing
tetra-functional fluorene-based polybenzoxazine has excellent processability and
thermal stability, and thermomechanical properties. The produced polymer can be an
ideal material for electronic packaging materials, laminate materials, and high
performance composite substrates.
Figure 8 and Table 1.
4
. Conclusions
In this work, a novel cardanol containing tetra-functional fluorene-based t-BF-a-c
benzoxazine having both diamine and bisphenol-type oxazine rings have been
successfully prepared. The curing characteristic of t-BF-a-c benzoxazine was studied
by DSC and FTIR analysis and found similar to di-functional benzoxazine monomers.
In addition to this, the t-BF-a-c benzoxazine showed better processability. The
poly(t-BF-a-c) exhibits higher Tg and better thermal stability than those of
mono-functional and bi-functional cardanol-based polybenzoxazines due to the rigid

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backbone. The cross-linking of the polymer was improved due to the cardanol flexible
long alkyl groups. The incorporation of flexible long alkyl groups reduced the
stiffness of the poly(t-BF-a-c), which will have positive impacts on the toughness and
mechanical properties without sacrificing thermal properties compared to
bi-functional polybenzoxazines.
Acknowledgments
This work is financially sponsored by the National Natural Science Foundation of
China (Project No.51773048), Natural Science Foundation of Heilongjiang Province
(
Project No.E2017022), and Fundamental Research Funds for the Central Universities
Project No.HEUCFP201724).
(
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Scheme 1. Synthetic route of t-BF-a-c benzoxazine resin.

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1
Figure 1. H NMR spectra of t-BF-a- c benzoxazine intermediates (A) and final
monomer (B).

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1
3
Figure 2. C NMR spectra of novel t-BF-a-c benzoxazine monomer and their
intermediates.
Figure 3. The FTIR spectra of t-BF-a-c benzoxazine monomer after different
isothermal curing stages, and poly(t-BF-a-c).

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Figure 4. The DSC curves of neat t-BF-a-c benzoxazine monomer after different
isothermal curing stages.
Figure 5. The relationship between dynamic viscosity and temperature of t-BF-a-c
monomer.

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Figure 6. The evolution of the storage (G’) and loss (G’’) moduli of t-BF-a-c
o
monomer as a function of time at 160 C.
Figure 7. Storage modulus and loss tangent as a function of temperature for
poly(t-BF-a-c).

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Figure 8. TGA curve of poly(t-BF-a-c) under a nitrogen atmosphere.
Table 1. Comparison of the glass transition and TGA parameters of poly(t-BF-a-c)
with other polybenzoxazine matrices.
o
o
Sample
T ( C) T5% (oC) T10% (oC) Y (%, 800 C)
Reference
Current study
[12]
g
c
Poly(t-BF-a-c)
Poly(B-pbf)
373
364
334
401
355
348
354
292
323
405
364
432
389
377
377
350
374
35
51
229
256
104
–
Poly(BF-p)
49
[15]
Poly(Bzc-A)
Poly(Bzc-HP)
Poly(Bzc-HM)
Poly(Bzc-dds)
Poly(Bzc-BA)
12*
29*
19*
12*
18*
–
[29]
–
–
o
*
Y recorded at 700 C
c

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Highlights



Synthesis of a new cardanol containing tetra-functional benzoxazine monomer (t-BF-a-c).
The t-BF-a-c monomer showed good processability.
The poly(t-BF-a-c) showed much better thermal properties than the other bi-functional
cardanol based polybenzoxazines.