Synthesis of 9,9-bis(4-aminophenyl)fluorene-based benzoxazine and properties of its high-performance thermoset

Article abstract of DOI:10.1002/pola.25993

A benzoxazine (P-bapf) based on 9,9-bis(4-aminophenyl)fluorene (BAPF), phenol, and formaldehyde was successfully prepared using two-pot and one-pot procedures. In the two-pot approach, BAPF initially reacted with 2-hydroxybenzaldehyde, leading to 9,9-bis(4-(2-hydroxybenzylideneimino)phenyl) fluorene. The imine linkages of 9,9-bis(4-(2-hydroxybenzylideneimino)phenyl) fluorene were then reduced by sodium borohydride, forming 9,9-bis(4-(2- hydroxybenzylamino)phenyl)fluorene. Finally, paraformaldehyde was added to induce ring closure condensation, forming benzoxazine (P-bapf). In the one-pot approach, P-bapf was obtained directly by reacting BAPF, phenol, and paraformaldehyde in various solvents. Among the solvents, we found that using toluene/ethanol (2/1, v/v) as a solvent leads to the best purity and yield. No gelation was observed in the preparation. The structure of the resulting benzoxazine was confirmed by ¹H, ¹³C, ¹Hi￡¹H and ¹Hi￡¹³C NMR spectra. P-bapf exhibits a photoluminescent emission at 395 nm under an excitation of 275 nm. After curing, the resulting P-bapf thermoset exhibits T_g as high as 236 °C, and the T_g can be further increased to 260 °C by copolymerization with an equal equivalent of cresol novolac epoxy. The 5% degradation temperature of the P-bapf thermoset reaches as high as 413 °C (N ₂) and 431 °C (air). The refractive index at 589 nm is as high as 1.70, demonstrating a high refractive index characteristic of fluorene linkage. 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 A 9,9-bis(4-aminophenyl)fluorene-based benzoxazine was successfully prepared using two-pot and one-pot procedures. After curing, a thermoset with high T _g, good thermal stability, and a high refractive index was achieved. The fluorene structure is responsible for these special properties. Copyright

Full text of DOI:10.1002/pola.25993

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Synthesis of 9,9-Bis(4-aminophenyl)fluorene-Based Benzoxazine and
Properties of Its High-Performance Thermoset
Hou Chien Chang,1 Ching Hsuan Lin,1 Yu Wei Tian,1 Yu Ren Feng,1 Li Hsin Chan2
1Department of Chemical Engineering, National Chung Hsing University, Taichung 402, Taiwan
2Department of Applied Materials and Optoelectronic Engineering, National Chi Nan University, Puli, Taiwan
Correspondence to: C. H. Lin (E-mail: linch@nchu.edu.tw)
Received 4 November 2011; accepted 22 December 2011; published online 28 February 2012
DOI: 10.1002/pola.25993
ABSTRACT: A benzoxazine (P-bapf) based on 9,9-bis(4-amino-
phenyl)fluorene (BAPF), phenol, and formaldehyde was suc-
cessfully prepared using two-pot and one-pot procedures. In
the two-pot approach, BAPF initially reacted with 2-hydroxy-
benzaldehyde, leading to 9,9-bis(4-(2-hydroxybenzylideneimi-
no)phenyl)fluorene. The imine linkages of 9,9-bis(4-(2-
hydroxybenzylideneimino)phenyl)fluorene were then reduced
by sodium borohydride, forming 9,9-bis(4-(2-hydroxybenzyla-
mino)phenyl)fluorene. Finally, paraformaldehyde was added to
induce ring closure condensation, forming benzoxazine (P-
bapf). In the one-pot approach, P-bapf was obtained directly
by reacting BAPF, phenol, and paraformaldehyde in various
solvents. Among the solvents, we found that using toluene/
ethanol (2/1, v/v) as a solvent leads to the best purity and
yield. No gelation was observed in the preparation. The struc-
ture of the resulting benzoxazine was confirmed by 1H, 13C,
1HA1H and 1HA13C NMR spectra. P-bapf exhibits a photolumi-
nescent emission at 395 nm under an excitation of 275 nm. Af-
ter curing, the resulting P-bapf thermoset exhibits Tg as high
as 236 ꢀC, and the Tg can be further increased to 260 ꢀC by
copolymerization with an equal equivalent of cresol novolac
epoxy. The 5% degradation temperature of the P-bapf thermo-
set reaches as high as 413 ꢀC (N2) and 431 ꢀC (air). The refrac-
tive index at 589 nm is as high as 1.70, demonstrating a high
C
V
refractive index characteristic of fluorene linkage. 2012 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 2201–
2210, 2012
KEYWORDS: thermosets; ring-opening polymerization; refractive
index
INTRODUCTION Benzoxazines are resins that can be poly-
merized to thermosets by means of thermally activated ring-
opening reactions.1 Thermosets with low water absorption,
superior electrical properties,2 and low surface energy3 can
be obtained after curing. Benzoxazines can be monofunc-
tional, difunctional, or multifunctional. Among them, difunc-
tional benzoxazines have received the most attention due to
their balanced processability and thermal properties after
curing. There are two types of difunctional benzoxazines,
including bisphenol-based benzoxazines and diamine-based
benzoxazines (Fig. 1). Bisphenol-based benzoxazines are pre-
pared by the condensation of bisphenol, primary mono-
amine, and formaldehyde [Fig. 1(a)]. The wide variety of aro-
matic bisphenols and monoamines allow for the considerable
molecule-design flexibility of benzoxazines. Some special
functional groups, such as acetylene,4,5 furan,6 allyl,7 propar-
gyl,8 maleimide,9 carboxylic acid,10 methacrylol,11 and
amine12 have been incorporated into benzoxazines to pro-
vide some desired properties. Diamine-based benzoxazines
are prepared by the condensation of diamine, formaldehyde,
and monophenol [Fig. 1(b)]. Unlike bisphenol-based benzoxa-
zines, aromatic diamine-based benzoxazines have rarely been
using a one-pot procedure.12–15 In addition, to the best of
our knowledge, most reported diamine-based benzoxazines
prepared using the one-pot procedure have generally been
based on diaminodiphenylmethane, although benzoxazine
based on diaminodiphenylsulfone has also been reported.13
Recently, we proposed a three-step procedure to prepare
aromatic diamine-based benzoxazines.16,17 Almost simultane-
ously, Ronda and coworker prepared deuterated benzoxa-
zines to prove the mechanism.18 Endo and coworkers
also applied a similar approach to prepare poly(allylamine)-
based benzoxazine.19 Liu and coworkers used the same
approach to prepare phosphazine-containing benzoxa-
zines.20,21 Although the approach is time consuming, it can
be applied in preparing various diamine or multifunctional
amine-based benzoxazines.
The fluorene group contains two benzene rings that are con-
nected via a carbonAcarbon bond and an adjacent methyl-
ene bridge.22 The methylene bridge forces the two phenyl
rings to be planar, thereby providing high overlaps of
Additional Supporting Information may be found in the online version of this article.
C
V
2012 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210
2201

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
properties with those of BHPF-based polybenzoxazines. In
this work, we use two approaches to prepare a benzoxazine
(P-bapf) based on BAPF, phenol, and formaldehyde. The first
is a two-pot procedure based on a modified procedure of
our previous work,16,17 and the second is a one-pot proce-
dure using a special cosolvent. The resulting BAPF-based
benzoxazine displays a photoluminescent peak at 395ꢀnm.
The resulting polybenzoxazine shows Tg as high as 236 C, a
coefficient of thermal expansion as low as 36 ppm/ꢀC, and
5% degradation temperature as high as 416 ꢀC (N2), and
431 ꢀC (air). The refractive index is as high as 1.70
(589 nm). Detailed synthesis and properties of the resulting
thermosets are provided in this work.
EXPERIMENTAL
Materials
BAPF (from TCI), paraformaldehyde (from TCI), 2-hydroxy-
benzaldehyde (from Showa), and sodium borohydride
(NaBH4, from Acros) were used as received. Cresol novolac
epoxy (CNE) with epoxy equivalent weight 200 g/equiv. was
kindly supplied by Chang Chun Plastics, Taiwan under the
trade name CNE-200ELD. N,N-Dimethylacetamide (DMAc)
was purchased from TEDIA, purified by distillation under
reduced pressure over calcium hydride (from Acros), and
stored over molecular sieves. 1,4-Dioxane, toluene, xylene,
chloroform, and ethanol (99.5%) were purchased from
TEDIA and used without further purification.
FIGURE 1 Synthesis of (a) bisphenol-based and (b) diamine-
based benzoxazines.
p
orbitals. Fluorene-based conjugated polymers have
received much attention in polymer light-emitting
diodes.23,24 9,9-Bis(4-hydroxyphenyl)fluorene (BHPF) has
two phenol linkages at the bridge position of fluorene. The
four phenyl rings of BHPF are connected to a quaternary
carbon, leading to a severe rotational hindrance of the
phenyl rings. Therefore, incorporating the rigid and bulky
fluorenyl moiety to polymers leads to enhanced thermal
properties, solubility, and refractive index.25–27 Recently, Liu
and coworkers prepared fluorene-containing benzoxazines
based on BHPF, primary amines, and formaldehyde.28 The
fluorene-based polybenzoxazines show remarkably higher Tg
and better thermal stability than the thermoset of B-a, which
is a benzoxazine based on bisphenol A, aniline, and formal-
dehyde. Liu et al. prepared fluorene-containing benzoxazine
based on BHPF, furfurylamine, and formaldehyde.29 The
resulting polybenzoxazine exhibits high Tg, high modulus,
good thermal stability, and a high refractive index. In
addition, the resulting benzoxazine displays high photo-
luminescent intensity in the blue-light band.
Characterization
Differential scanning calorimetry (DSC) scans were obtained
using a Perkin-Elmer DSC 7 in a nitrogen atmosphere at a
heating rate of 20 ꢀC/min. Thermal gravimetric analysis
(TGA) was performed with a Perkin-Elmer Pyris1 at a heat-
ing rate of 20 ꢀC/min in an atmosphere of nitrogen or air.
Dynamic mechanical analysis (DMA) was performed with a
Perkin-Elmer Pyris Diamond DMA with a sample size of 5.0
cm ꢁ 1.0 cm ꢁ 0.2 cm. The storage modulus E0 and tan d
were determined as the sample was subjected to the temper-
ature scan mode at a programmed heating rate of 5 ꢀC/min
at a frequency of 1 Hz. The test was performed by a bending
mode with an amplitude of 5 lm. Thermal mechanical analy-
sis (TMA) was performed with a Perkin-Elmer Pyris Dia-
mond TMA at a heating rate of 5 ꢀC/min. NMR measure-
ments were performed using a Varian Inova 600 NMR in
DMSO-d6, and the chemical shift was calibrated by setting
the chemical shift of DMSO-d6 as 2.49 ppm. IR Spectra were
obtained from at least 32 scans in the standard wavenumber
range of 400–4000 cmꢂ1 using a Perkin-Elmer RX1 infrared
spectrophotometer. UV–vis spectra were recorded with a Var-
ian Cary 50 in the standard wavenumber range of 200–800
9,9-Bis(4-aminophenyl)fluorene (BAPF) has a similar struc-
ture to BHPF except that the hydroxyl moiety is replaced by
aniline moiety. Because of the unusual rotational hindrance
of the four phenyl rings, BAPF and its derivatives have been
used in polyimides,30,31 sulfonated polyimides,32 polyimine,33
and epoxy.34 In our previous paper, we reported that dia-
mine-based polybenzoxazines exhibited better thermal stabil-
ity than biphenol-based polybenzoxazines. For example, ther-
moset of diaminodiphenylmethane-based benzoxazine (P-
cmꢂ1
. Photoluminescence spectra were measured on a
Hitach4500 florescence spectrophotometer at a concentra-
tion of 10ꢂ5 M. The excitation wavelength is 275 nm. Refrac-
tive index was obtained by an ellipsometer SOPRA, GES-5E.
ꢀ
ꢀ
ddm) exhibits 53 C higher in Tg, and 120 C higher in 5 wt
% decomposition temperature than the thermoset of bisphe-
nol F-based benzoxazine (F-a), although P-ddm and F-a are
constitutional isomers.16 Therefore, it would be interesting
to prepare a BAPF-based polybenzoxazine and compare its
Two-Pot Synthesis of BAPF-Based Benzoxazine
In the first procedure of this approach, 2-hydroxybenzal-
dehyde 3.68 g (30.13 mmol), BAPF 5.00 g (14.35 mmol),
and DMAc/toluene (2/1, v/v) 45 mL were introduced into a
2202
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
100-mL glass flask equipped with a nitrogen inlet, a magnetic
stirrer, and a Dean–Stark trap. The reaction mixture was
stirred at reflux temperature for 12 h. After the reaction so-
lution was cooled to room temperature, NaBH4 1.74 g (45.92
mmol) was added, and the reaction mixture was stirred for
an additional 12 h at room temperature. The mixture was
then poured into water. The precipitate was filtrated and
then dried in a vacuum oven. Yellow powder (88% yield)
was obtained. In the second procedure of this approach, (2)
5.0 g (8.90 mmol), paraformaldehyde 0.84 g (28.6 mmol),
and chloroform 100 mL were introduced into a 250-mL glass
flask equipped with a nitrogen inlet, a condenser, and a mag-
netic stirrer. The mixture was stirred at reflux temperature
for 8 h. After that, the solution was poured into n-hexane.
The precipitate was filtrated and then dried in a vacuum
oven. Light yellow powder (85% yield) was obtained.
1H NMR (DMSO-d6), d ¼ 4.60 (2H, H12), 5.40 (2H, H19), 6.70
(2H, H17), 6.82 (2H, H15), 6.90–7.0 (4H, H9, H10), 7.06 (2H,
H14, H16), 7.24 (2H, H4), 7.30–7.40 (4H, H3, H5). 13C NMR
(DMSO-d6), d ¼ 13C NMR (DMSO-d6), d ¼ 116.3 (C17), 117.1
(C9), 120–121(C13, C15), 121.5 (C2), 126.0 (C3), 127.1–128.7
(C4, C5, C14, C16), 128.3 (C10), 137.5 (C8), 139.3 (C6), 146.2
(C1), 151 (C11), 154 (C18). ELEM. ANAL: calculated C, 84.22%;
H, 5.52%; N, 4.79% for C41H32N2O2 Found C, 84.10%; H,
5.62%; N, 4.70%. FTIR (KBr): 945 cmꢂ1 (NACAO stretch),
1039 cmꢂ1 (ArAOAC symmetric stretch), 1223 cmꢂ1
(ArAOAC asymmetric stretch), 1377 cmꢂ1 (CAN stretch).
The BAPF-based benzoxazine prepared using this two-pot
procedure is referred to as P-bapf-2.
SCHEME 1 Synthesis of P-bapf-2.
ꢀ
for 2 h at each of 180, 200, and 220 C in an air-circulating
oven. Thereafter, samples were allowed to cool slowly to
room temperature to prevent cracking. For P-bapf and CNE
copolymer, mixtures of (P-bapf-2)/CNE with equal equiva-
lency were melted, stirred, and transferred to an aluminum
mold and then cured under the same condition used for as
P-bapf-2.
RESULTS AND DISCUSSION
Two-Pot Synthesis of BAPF-Based Benzoxazine
The BAPF-based benzoxazine was successfully synthesized
using a modified two-pot procedure.16,17 The resulting ben-
zoxazine is referred to as P-bapf-2. In the first procedure of
this approach, 2-hydroxybenzaldehyde reacted with BAPF,
yielding an intermediate with an o-hydroxyl phenylimine
linkage. Sodium borohydride was then used to reduce the
imine linkage, yielding 9,9-bis(4-(2-hydroxybenzylamino))-
fluorene. In the second pot, paraformaldehyde was added to
the chloroform solution of 9,9-bis(4-(2-hydroxybenzylamino)
phenyl)fluorene to induce ring closure condensation, forming
P-bapf-2 (Scheme 1).
One-Pot Synthesis of BAPF-Based Benzoxazine
BAPF 5.0 g (92.45 mmol), phenol 2.71 g (184.9 mmol), para-
formaldehyde 1.72 g (57.4 mmol), and a mixed solvent of
toluene/ethanol 150 mL (2/1, v/v) were introduced into a
round-bottomed 250-mL glass flask equipped with a nitro-
gen inlet, a condenser, anꢀd a magnetic stirrer. The reaction
mixture was stirred at 80 C for 12 h. After that, the solution
was poured into n-hexane. The precipitate was filtered and
then dried in a vacuum oven. Yellow powder (65% yield)
was obtained. ELEM. ANAL: calculated C, 84.22%; H, 5.52%; N,
4.79% for C41H32N2O2 Found C, 83.98%; H, 5.72%; N,
4.69%. The BAPF-based benzoxazine prepared using this
one-pot procedure is referred to as P-bapf-1.
1
Figure 2 shows the H NMR spectrum of P-bapf-2. The char-
acteristic peaks of benzoxazines, OACH2AN, and phACH2AN
at 5.4 and 4.6 ppm confirm the structure of benzoxazines.
No signal was observed at around 4.0 ppm corresponding to
the NACH2Aph as a result of the ring opening of benzoxa-
zine, revealing the purity of the synthesized benzoxazine.
Figure 3 shows the 13C NMR spectra of P-bapf-2. The char-
acteristic peaks of benzoxazines, OACH2AN, and
phACH2AN, at 48.9 and 78.5 ppm confirm the structure of
benzoxazines. The detailed assignment of each peak in Fig-
ures 2 and 3, assisted by the correlation in 1HA1H and
1HA13C spectra (Figs. S1 and S2, Supporting Information),
confirms the structure of P-bapf-2.
Preparation of Polybenzoxazines
As P-bapf-2 has better purity than P-bapf-1 (as discussed
later), the curing of benzoxazine was based on P-bapf-2. The
UV–vis, photoluminescence (PL), and IR analysis are all
based on P-bapf-2. In the curing process, P-bapf-2 was ini-
ꢀ
tially stirred at 160 C in an aluminum mold and then cured
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210
2203

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 2 1H NMR spectrum of P-bapf-2 in DMSO-d6.
One-Pot Synthesis of BAPF-Based Benzoxazine
because diamine and formaldehyde are tetrafunctional and
difunctional, respectively. In our previous work involved
with the preparation of diamine/bisphenol A/formaldehyde-
based polybenzoxazines,36 we proposed that competition
between R1 and R2 plays a key role in polybenzoxazine syn-
thesis. If R1 ꢃ R2, gelation will occur. On the other hand, if
R1 < R2, a soluble product will be produced. In that work,
we found that toluene/ethanol (2/1, v/v) is an effective
cosolvent in reducing R1. Based on the finding, we examine
According to the literature, synthesis of bisphenol-based ben-
zoxazine can be divided into two steps: the formation of tria-
zine and the dissociation of the resulting triazine.35 Based on
this knowledge, the diamine-based benzoxazine is expected
to proceed according to the similar steps. The first step
involves the formation of a triazine network (R1), and the
second step is the dissociation of the resulting triazine net-
work (R2; Scheme 2). Note that a network will be formed
FIGURE 3 13C NMR spectrum of P-bapf-2 in DMSO-d6.
2204
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 2 Proposed reaction procedure for the preparation of a diamine-based benzoxazine. The first step involves with the for-
mation of a triazine network (R1) and the second step is the dissociation of the triazine network (R2).
the solvent effect on the one-pot synthesis of P-bapf in this
work. The P-bapf prepared by the one-pot procedure is
referred to as P-bapf-1.
NMR spectrum for P-bapf-1 prepared by run 11. The pat-
terns shown in Figure 4 are similar to those in Figure 2,
except for the small peaks at 6.4, 7.6, and 8.9 ppm. Although
the purity of P-bapf-1 is not as high as P-bapf-2, the ratio
of the integral area of OACH2AN, phACH2AN, and H2 in P-
bapf-1 is very close to 2:2:1, suggesting a reasonable purity.
Table 1 lists the solvent effect on the synthesis of P-bapf-1.
Using homosolvents, such as 1,4-dioxane (run 1), xylene
(run 5), and toluene (run 9) led to some insoluble gelation.
However, the degree of gelation was significantly reduced
using toluene/alcohol (runs 2–4, 6–8, and 10–12) as a reac-
tion solvent. Among these solvents, toluene/ethanol (2/1, v/
v; run 11) gave the best purity and yield. Figure 4 shows the
UV and PL Spectra
As the purity of P-bapf-2 is higher than that of P-bapf-1, the
measurements UV–vis absorption and photoluminescent data
are based on P-bapf-2. Figure 5 shows the UV–vis absorp-
tion and photoluminescent spectra of BAPF and P-bapf. In
the UV–vis spectra (10ꢂ5 M in ethanol), the absorption peaks
are 245, 275, and 315 nm for BAPF, and 245, 260, and 315
nm for P-bapf-2. The spectra are nearly identical because
the absorptions are determined mainly by the spin-allowed
TABLE 1 Solvent Effect on the Synthesis of P-bapf-1
Reaction Status and
Purity of Productb
Runa Solvent
1
1,4-Dioxane
Some gelatin, some impurity
2
1,4-Dioxane/methanol(2:1) Homogeneity, poor purity
3
1,4-Dioxane/ethanol(2:1)
1,4-Dioxane /IPA(2:1)
Xylene
Homogeneity, poor purity
Few gelatin, poor impurity
Some gelatin, some impurity
Few gelatin, some impurity
Homogeneity, some impurity
Few gelatin, some impurity
Some gelatin, some impurity
Homogeneity, some impurity
Homogeneity, little impurity
Few gelatin, some impurity
4
5
6
Xylene/methanol(2:1)
Xylene/ethanol(2:1)
Xylene/IPA(2:1)
7
8
9
Toluene
10
11
12
a
Toluene/methanol(2:1)
Toluene/ethanol(2:1)
Toluene/IPA(2:1)
The reaction time is 12 h, and the reaction temperature is 80 ꢀC for all
runs.
b 1H NMR spectra of reaction product prepared in runs 1–12 are shown
in Supporting Information Figures S3(a)–S3(l).
FIGURE 4 1H NMR spectrum of P-bapf-1 in DMSO-d6.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210
2205

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Further study of the potential application of P-bapf in the
blue emission is required.
DSC Thermograms of Benzoxazines
Figure 6 shows the DSC thermograms of P-bapf-2 and P-
bapf-1. The initial exothermic temperature of P-bapf-2 is
higher than that of P-bapf-1. In addition, the exothermic
enthalpy of P-bapf-2 is 246 J/g, which is larger than that
(175 J/g) of P-bapf-1. It is known that a small amount of
phenolic OH present in the precursor catalyzes the ring
opening of oxazine, and consequently shifts the exothermic
peak to a lower temperature. The higher initial exothermic
temperature and the larger exothermic enthalpy suggest that
the purity of P-bapf-2 is better than that of P-bapf-1. This
result is consistent with the NMR measurement.
Curing of Benzoxazines Probed by IR
Benzoxazine can be thermally cured into a cross-linked poly-
benzoxazine through the ring opening of the benzoxazine
linkages. Figure 7 shows the IR spectra of P-bapf after accu-
mulative curing for 20 min at each temperature. After curiꢂn1g
ꢀ
at 220 C, the ArAOAC absorptions at 1039 and 1225 cm
,
and the oxazine absorption 1377 cmꢂ1 disappeared. The
absorptions of the characteristic mode of benzene with an
attached oxazine ring at 945 cmꢂ1 also disappeared. In con-
trast, a 1,2,3-trisubstituted benzene absorption appeared at
1619 cmꢂ1. The structure of the P-bapf thermoset was pro-
posed according to the IR analysis, as shown in Scheme 3.
For structure–property comparisons (to be discussed later),
the structure of P-ddm is also listed in Scheme 3. Note that
P-ddm is a benzoxazine prepared from the condensation of
diaminodiphenylmethane, phenol, and formaldehyde.39
Thermal Properties of Polybenzoxazines
A dynamic mechanical analyzer was applied to measure the
dynamic mechanical properties of the resultant thermosets.
Figure 8 shows the DMA thermograms of the P-bapf thermo-
set. The Tg of the P-bapf thermoset measured by the DMA is
236 ꢀC, which is 36 ꢀC higher than that of the P-ddm ther-
moset (Table 2).39 As shown in Scheme 3, the P-bapf and P-
ddm thermosets show similar structure except for the fluo-
rene linkages. Therefore, the higher Tg of the P-bapf thermo-
set may probably be attributed to the higher rigidity of the
fluorene skeleton in the chain backbone. In addition, the
Tg value of the P-bapf thermoset is 16 ꢀC higher than that
of the thermoset of BHPF-f, which is a benzoxazine based
on 9,9-bis(4-hydroxyphenyl)fluorine/furfurylamine/formalde-
hyde.29 The result demonstrates the high Tg characteristic of
the P-bapf thermoset. The high Tg characteristic of fluorene
structure can also be confirmed by TMA measurements. As
FIGURE 5 (a) UV–vis absorption and (b) PL spectra of BAPF
and P-bapf.
p–p* transitions involving the fluorene and phenyl structure.
Compared with the absorption spectra in the range from
250 to 280 nm, the relative absorption intensity of P-bapf is
higher than that of BAPF. The absorption is probably
assigned to the absorption of the benzoxazine group. The
absorption intensity of BAPF above 280 nm is higher than
that of P-bapf. This phenomenon can likely be attributed to
that the intermolecular interaction between BAPF and etha-
nol being stronger than it is between P-babf and etha-
nol.37,38 In the PL spectra, BAPF shows an emission at 325
nm, while P-bapf shows an emission at 395 nm. The BAPF
presented only one emission peak that belongs to the back-
bone of aminophenylfluorene. However, a bathochromic shift
is observed in the case of P-bapf, indicating an enhanced
conjugation due to the presence of benzoxazine moiety. The
location of the maximum emission wavelength around 290
nm indicates the emission of benzoxazine chromophore, and
the emission wavelength located at 395 nm may be attrib-
uted to the extended conjugated length from the nitrogen of
the benzoxazine group to the phenyl ring of the fluorene.
ꢀ
listed in Table 2, Tg value of the P-bapf thermoset is 217 C,
ꢀ
which is 34 C higher than the P-ddm thermoset. The coeffi-
cient of thermal expansion (CTE) value of P-bapf thermoset
is 36 ppm/ꢀC, while the CTE value of the P-ddm thermoset
is 57 ppm/ꢀC. The result demonstrates the dimensional sta-
bility of fluorene skeleton.
Figure 8 also shows the DMA thermogram of the P-bapf/
CNE copolymer. Only one tan d peak was observed, indicat-
ing that a homogeneous copolymer was obtained. As seen in
2206
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 6 DSC thermograms of P-bapf-2 and P-bapf-1.
Figure 8, the Tg of the P-bapf/CNE thermoset is as high as
260 ꢀC, which is 24 ꢀC higher than that of the P-bapf ther-
moset.28 This indicates that the crosslinking density of the
P-bapf thermoset was enhanced by the incorporation of
CNE. It is thought that the phenolic groups, resulting from
ring-opening polymerization of benzoxazine, reacted with the
oxirane of CNE and thus tighten the network structure. This
speculation can be confirmed by the tan d curves of the P-
bapf and P-bapf/CNE thermosets. The height of tan d for
the P-bapf/CNE thermoset is much lower than that of the P-
bapf thermoset, confirming the higher crosslinking density
of the P-bapf/CNE thermoset. As shown in Table 2, the Tg of
the P-bapf/CNE copolymer is 17 ꢀC higher than that of the
P-ddm/CNE copolymer in the DMA data, further demonstrat-
ing the high Tg characteristic of fluorene linkage. However,
almost the same Tg data were detected for the P-bapf/CNE
and P-ddm/CNE copolymers in the TMA measurement.
Detailed analysis might be required to explain the
phenomenon.
Figure 9 shows the TGA thermograms of the P-bapf and P-
bapf/CNE thermosets, with the results listed in Table 2. The
5% degradation temperature of the P-bapfꢀthermoset is 416
ꢀC, which is slightly higher than that (413 C) of the P-ddm
thermoset. In addition, it is 82 ꢀC higher than that of the
thermoset of BHPF-a, which is a benzoxazine based on 9,9-
bis(4-hydroxyphenyl)fluorine/aniline/formaldehyde.28
The
value of 416 ꢀC is even higher than the 10% degradation
SCHEME 3 Propose structures of P-bapf, P-ddm, P-bapf/CNE,
and P-ddm/CNE thermosets.
FIGURE 7 IR spectra of P-bapf after accumulative curing for 20
min at each temperature.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210
2207

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
finding that fluorene linkage effectively enhances the thermal
resistance and char formation of polymers.25–27 As listed in
Table 2, the thermal stability of the P-bapf/CNE thermoset
is slightly lower than that of the P-bapf thermoset, but the
5% degradation temperature and char yield are still as high
as 402 ꢀC and 43%, respectively. However, it is known that
thermal properties (e.g., Tg, decomposition temperature) of
all thermosets are pretty much dependent on extent of cross-
linking. The thermal property data in Table 2 are not abso-
lute as no optimal curing procedure was researched in this
work.
Refractive Index
Fluorene-containing polymers, such as polyimides,25,41 poly-
ether,27 poly(ether ether ketone),42 have been proven to ex-
hibit high refractive indices due to their high aromatic con-
tents. Figure 10 shows the refractive index of the P-bapf
thermoset. The refractive index at 589 nm is 1.70, which is
much higher than that (1.58) of the bis(3-furfuryl-3,4-dihy-
dro-2H-1,3-benzoxazinyl)isopropane thermoset.43 The value
is also higher than that (1.65) of BHPF-f29 and that (1.646)
of fluorene-containing poly(ether ether ketone).42 The result
demonstrates the high-refractive-index characteristic of the
P-bapf thermoset. The high refractive-index characteristic
makes P-bapf thermoset a potential candidate in antireflec-
tive coating.
FIGURE 8 DMA thermograms of P-bapf and P-bapf/CNE
thermosets.
temperature (384 ꢀC) of BHPF-f thermoset.29 According to
the previous study, the 5% degradation temperature of
biphenol/aniline/formaldehyde
benzoxazine
thermosets
ꢀ
rarely exceeds 350 C, and the release of aniline fragments is
responsible for the low thermal stability of polybenzoxa-
zines.40 The nitrogen linkage of the BHPF-a thermoset is
linked to a phenyl pendant, which leads to fragmentation of
40
ꢀ
aniline at temperatures higher than 300 C. In contrast, as
shown in Scheme 3, the nitrogen linkage in the P-bapf ther-
moset is bonded to the other repeating unit. This makes the
release of aniline fragments difficult, and thus causes the P-
bapf thermoset to be thermally more stable than the BHPF-
a thermoset. This result demonstrates that diamine-based
benzoxazine thermosets display better thermal stability than
bisphenol-based benzoxazine thermosets, as has been
reported in our previous work.16 As listed in Table 2, the
5% degradation temperature of the P-bapf thermoset in air
is higher than it is in nitrogen, demonstrating the outstand-
ing antioxidative resistance of the P-bapf thermoset. The
char yield of the P-bapf thermoset in nitrogen atmosphere is
53%, which is also higher than that (46%) of the P-ddm
thermoset. In Scheme 3, we show that the P-bapf and P-
ddm thermosets have a similar structure, with the exception
of the fluorene linkage. The result is consistent with the
CONCLUSIONS
A 9,9-bis(4-aminophenyl)fluorine/phenol/formaldehyde-based
benzoxazine, P-bapf, was successfully prepared by a one-pot
and a two-pot approach, respectively. We found that the
reaction solvent had a profound effect on the purity and
yield of benzoxazine synthesis in the one-pot approach.
Using toluene/ethanol (2/1, v/v) as a cosolvent leads to the
best purity and yield. We also found that benzoxazine P-bapf
prepared by the two-pot approach has a better purity,
although the approach is relatively time consuming and
more expensive in the raw materials. After curing, the P-
bapf thermoset exhibits higher Tg (236 ꢀC) than the P-ddm
thermoset (200 ꢀC). This result may probably be attributed
to the higher rigidity of the fluorene skeleton as the P-bapf
and P-ddm thermosets have similar structures except for
the fluorene linkage. Compared with the bisphenol-based
TABLE 2 Thermal Properties of the P-bapf and P-bapf/CNE Thermosets
Char
Char
Thermoset
Based on
E0
(GPa)a
Tg DMA
(ꢀC)b
Tg TMA
(ꢀC)c
CTE
(ppm/ꢀC)d
Td
(N2; ꢀC)e
Td
(air; ꢀC)f
Yield
(wt %)g
Yield
(wt %)h
P-bapf
2.2
236
260
200
243
217
223
183
225
36
49
57
54
f
416
402
413
406
431
409
–
53
43
46
40
22
4.0
–
P-bapf/CNE
3.3
i
P-ddm
2.28
3.19
i
P-ddm/CNE
–
–
a
Storage modulus (E0) at 50 ꢀC.
Five percentage degradation temperature in air.
Residual weight percentage at 800 ꢀC in nitrogen.
Residual weight percentage at 800 ꢀC in air.
Data from reference.39
b
c
g
h
i
Measured by DMA at a heating rate of 5 ꢀC/min.
Measured by TMA at a heating rate of 5 ꢀC/min.
Coefficient of thermal expansion before Tg.
d
e
Five percentage degradation temperature in a nitrogen atmosphere.
2208
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
4 Chernykh, A.; Agag, T.; Ishida, H. Macromolecules 2009, 42,
5121–5127.
5 Dogan Demir, K.; Kiskan, B.; Yagci, Y. Macromolecules 2011,
44, 1801–1807.
6 Liu, Y.-L.; Chou, C.-I. J. Polym. Sci. Part A: Polym. Chem.
2005, 43, 5267–5282.
7 Agag, T.; Takeichi, T. Macromolecules 2003, 36, 6010–
6017.
8 Agag, T.; Takeichi, T. Macromolecules 2001, 34, 7257–7263.
9 Liu, Y.-L.; Yu, J.-M. J. Polym. Sci. Part A: Polym. Chem. 2006,
44, 1890–1899.
10 Andreu, R.; Reina, J. A.; Ronda, J. C. J. Polym. Sci. Part A:
Polym. Chem. 2008, 46, 6091–6101.
11 Jin, L.; Agag, T.; Yagci, Y.; Ishida, H. Macromolecules 2011,
44, 767–772.
12 Agag, T.; Arza, C. R.; Maurer, F. H. J.; Ishida, H. Macromole-
cules 2010, 43, 2748–2758.
FIGURE 9 TGA thermograms of the P-bapf and P-bapf/CNE
13 Agag, T.; Jin, L.; Ishida, H. Polymer 2009, 50, 5940–5944.
thermosets in (a) N2 and (b) air.
14 Baqar, M.; Agag, T.; Ishida, H.; Qutubuddin, S. Polymer
2011, 52, 307–317.
15 Chernykh, A.; Agag, T.; Ishida, H. Polymer 2009, 50,
382–390.
16 Lin, C. H.; Chang, S. L.; Hsieh, C. W.; Lee, H. H. Polymer
2008, 49, 1220–1229.
17 Lin, C. H.; Chang, S. L.; Lee, H. H.; Chang, H. C.; Hwang, K.
Y.; Tu, A. P.; Su, W. C. J. Polym. Sci. Part A: Polym. Chem.
2008, 46, 4970–4983.
18 Andreu, R.; Ronda, J. C. Synth. Commun. 2008, 38,
2316–2329.
19 Oie, H.; Sudo, A.; Endo, T. J. Polym. Sci. Part A: Polym.
Chem. 2011, 49, 3174–3183.
20 Wu, X.; Zhou, Y.; Liu, S.-Z.; Guo, Y.-N.; Qiu, J.-J.; Liu, C.-M.
Polymer 2011, 52, 1004–1012.
21 Wu, X.; Liu, S.-Z.; Tian, D.-T.; Qiu, J.-J.; Liu, C.-M. Polymer
2011, 52, 4235–4245.
22 Abbel, R.; Schenning, A. P. H. J.; Meijer, E. W. J. Polym.
Sci. Part A: Polym. Chem. 2009, 47, 4215–4233.
23 Leni, A. Prog. Polym. Sci. 2003, 28, 875–962.
FIGURE 10 Refractive index of the P-bapf thermoset at various
wavenumbers.
24 Kim, D. Y.; Cho, H. N.; Kim, C. Y. Prog. Polym. Sci. 2000, 25,
1089–1139.
25 Terraza, C. A.; Liu, J.-G.; Nakamura, Y.; Shibasaki, Y.; Ando,
S.; Ueda, M. J. Polym. Sci. Part A: Polym. Chem. 2008, 46,
1510–1520.
BHPF-a thermoset, the diamine-based P-bapf thermoset dis-
plays much better thermal stability and a higher refractive
index. The combination of high Tg, good thermal stability,
higher char yield, and a high refractive index makes the P-
bapf thermoset attractive in electronic applications.
26 Seesukphronrarak, S.; Kawasaki, S.; Kobori, K.; Takata, T.
J. Polym. Sci. Part A: Polym. Chem. 2008, 46, 2549–2556.
27 Seesukphronrarak, S.; Kawasaki, S.; Kobori, K.; Takata, T. J.
Polym. Sci. Part A: Polym. Chem. 2007, 45, 3073–3082.
The authors thank the National Science Council of the Republic
of China, Taiwan, for financial support. Partial sponsorship by
the Green Chemistry Project (NCHU), funded by the Ministry of
Education, is also gratefully acknowledged.
28 Wang, J.; Wu, M.-Q.; Liu, W.-B.; Yang, S.-W.; Bai, J.-W.;
Ding, Q.-Q.; Li, Y. Eur. Polym. J. 2010, 46, 1024–1031.
29 Liu, Y.-L.; Chang, C.-Y.; Hsu, C.-Y.; Tseng, M.-C.; Chou,
C.-I. J. Polym. Sci. Part A: Polym. Chem. 2010, 48, 4020–
4026.
~
30 Maya, E. M.; Munoz, D. M.; Lozano, A. E.; de Abajo, J.; de la
Campa, J. G. J. Polym. Sci. Part A: Polym. Chem. 2008, 46,
8170–8178.
REFERENCES AND NOTES
1 Ghosh, N. N.; Kiskan, B.; Yagci, Y. Prog. Polym. Sci. 2007, 32,
1344–1391.
31 Wang, C.; Zhao, X.; Li, G.; Jiang, J. Polym. Degrad. Stab.
2009, 94, 1746–1753.
32 Guo, X.; Fang, J.; Watari, T.; Tanaka, K.; Kita, H.; Okamoto,
K.-I. Macromolecules 2002, 35, 6707–6713.
2 Ning, X.; Ishida, H. J. Polym. Sci. Part A: Polym. Chem. 1994,
32, 1121–1129.
_
33 Kaya, I.; Yıldırım, M.; Aydın, A.; Sꢀenol, D. React. Funct.
3 Wang, C.-F.; Su, Y.-C.; Kuo, S.-W.; Huang, C.-F.; Sheen, Y.-C.;
Chang, F.-C. Angew. Chem. Int. Ed. 2006, 45, 2248–2251.
Polym. 2010, 70, 815–826.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210
2209

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
34 Liu, W.; Qiu, Q.; Wang, J.; Huo, Z.; Sun, H. Polymer 2008,
49, 4399–4405.
39 Chang, S. L.; Lin, C. H. J. Polym. Sci. Part A: Polym.Chem.
2010, 48, 2430–2437.
35 Brunovska, Z.; Liu, J. P.; Ishida, H. Macromol. Chem. Phys.
1999, 200, 1745–1752.
40 Hemvichian, K.; Ishida, H. Polymer 2002, 43, 4391–4402.
41 Hsiao, S.-H.; Li, C.-T. J. Polym. Sci. Part A: Polym. Chem.
1999, 37, 1403–1412.
36 Lin, C. H.; Chang, S. L.; Shen, T. Y.; Shih, Y. S.; Lin, H. T.;
Wang, C. F. Polym. Chem. 2012, DOI: 10.1039/c2py00449f.
42 Kawasaki, S.; Yamada, M.; Kobori, K.; Jin, F.; Kondo, Y.;
Hayashi, H.; Suzuki, Y.; Takata, T. Macromolecules 2007, 40,
5284–5289.
37 Dey, J. K.; Dogra, S. K. Chem. Phys. 1990, 143, 97–107.
38 El-Sayed, M.; Blaudeck, T.; Cichos, F.; Spange, S. J. Photo-
chem. Photobiol. A: Chem. 2007, 185, 44–50.
43 Tseng, M.-C.; Liu, Y.-L. Polymer 2010, 51, 5567–5575.
2210
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2201–2210