High-Tg and low-dielectric epoxy thermosets based on a propargyl ether-containing phosphinated benzoxazine

Article abstract of DOI:10.1002/pola.27125

A propargyl ether-containing benzoxazine (4) was prepared from a potassium carbonate-catalyzed nucleophilic substitution of propargyl bromide and a phenolic OH-containing benzoxazine (3), which was prepared from 1-(4-hydroxyphenyl)-1-(4-aminophenyl)-1-(6-

Full text of DOI:10.1002/pola.27125

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High-Tg and Low-Dielectric Epoxy Thermosets Based on a Propargyl
Ether-Containing Phosphinated Benzoxazine
Ching Hsuan Lin,1 Chu Ming Huang,1 Tung I. Wong,1 Hou Chien Chang,1 Tzong Yuan Juang,2
Wen Chiung Su3
1Department of Chemical Engineering, National Chung Hsing University, Taichung, Taiwan
2Department of Applied Chemistry, National Chiayi University, Chiayi, Taiwan
3Department of Chemistry and Chemical Engineering, Chung Shan Institute and Technology, Lungtan, Tauyuan, Taiwan
Correspondence to: C.-H. Lin (E-mail: linch@dragon.nchu.edu.tw) or H.-C Chang (E-mail: hchang@dragon.nchu.edu.tw)
Received 26 November 2013; accepted 23 January 2014; published online 24 February 2014
DOI: 10.1002/pola.27125
ABSTRACT: A propargyl ether-containing benzoxazine (4) was
prepared from potassium carbonate-catalyzed nucleophilic
in (4)-cured epoxy thermosets afforded higher crosslinking den-
sity, and led to higher thermal properties. In addition, the (4)-
cured epoxy thermosets possess half the amount of highly polar
hydroxyl groups than those of the (3)-cured epoxy thermosets,
a
substitution of propargyl bromide and a phenolic OH-containing
benzoxazine (3), which was prepared from 1-(4-hydroxyphenyl)-
1-(4-aminophenyl)-1-(6-oxido-6H -dibenz <c,e><1,2> oxaphos-
phorin-6-yl)ethane (1) by a three-step procedure. The curing
reactions of (4) were monitored by IR and DSC. A reaction
mechanism was proposed based on the observation. Benzoxa-
zines (3) and (4) were applied as epoxy curing agents. The
microstructure and the structure-property relationship of the
resulting thermosets are discussed. The double-strand structure
resulting in a lower dielectric constant, dissipation factor, and
C
V
water absorption.
2014 Wiley Periodicals, Inc. J. Polym. Sci.,
Part A: Polym. Chem. 2014, 52, 1359–1367
KEYWORDS: benzoxazine; high performance polymer; propargyl;
structure-property relations; thermal properties; thermosets
with FR4 epoxy thermosets and bismaleimides. The advant-
age of incorporating fluoro element in reducing dielectric
constant has also been observed by other groups. For exam-
ple, Su and Chang prepared a low-dielectric polybenzoxazine
based on a hexafluorobisphenol A and 4-(trifluoromethyl)a-
niline-based benzoxazine.4 Lin et al. prepared low-dielectric
polybenzoxazines from fluorinated diamines and phenol-
based benzoxazines.5 Velez-Herrera et al. prepared low-
dielectric polybenzoxazines from highly fluorinated aliphatic
diamines and 4-fluorophenol-based benzoxazines, and fluori-
nated aromatic diamines and hexafluorobisphenol A-based
benzoxazines.6 The incorporation of polyhedral oligomeric
silsesquioxane (POSS) has been proven to be an effective
approach in reducing the dielectric constant.7–10 Low-
dielectric polybenzoxazines based on octa(maleimido phe-
nyl)silsesquioxane (OMPS), and found that the dielectric
decreased from 3.62 for neat polybenzoxazine to 2.42 with
10 wt % OMPS. Tseng and Liu prepared a nanocomposite
based on a furan-containing benzoxazine and methyl methac-
rylate terminated polyhedral oligomeric silsesquioxane
(MMA-POSS).11 They found that the dielectric constant was
reduced with the content of MMA-POSS. Furthermore, the
INTRODUCTION Benzoxazines are resins that can be poly-
merized to phenolic-type thermosets via the thermally acti-
vated ring-opening of the oxazine linkage.1,2 The epoxy/
benzoxazine system has recently been used in the industry
of copper clad laminates (CCL) due to the characteristic of
higher Tg, better adhesion to glass fiber, and better tough-
ness than the epoxy/phenol novolac system. With the trends
of increased circuit density, material with a low dielectric
constant is preferred since the signal propagating speed in
integrated circuits is inversely proportional to the square
root of the dielectric constant, and the signal propagation
loss is proportional to the square root of the dielectric con-
stant. Therefore, preparing benzoxazines with the low-
dielectric constant is attractive for the CCL industry.
Works on developing low-dielectric polybenzoxazines have
been done by various groups. Hamerton et al. prepared a
series of bis-benzoxazines from various bisphenols, and found
that bisphenol A and hexafluorobisphenol A-based polyben-
zoxazines exhibit the lowest dielectric constant.3 They also
found that the dielectric constant of polybenzoxazines is
higher than cured commercial cyanate esters, but comparable
Additional Supporting Information may be found in the online version of this article.
C
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dielectric constant of the composites can further be reduced
via the orientation of POSS into the lamellar structure. Low-
dielectric polybenzoxazines can also be prepared from a
porous structure. For example, Chang et al. prepared benzox-
azine with labile poly(3-caprolactone) linkage.12 Low-
dielectric polybenzoxazine can be achieved after the labile
polycaprolactone was decomposed. The introduction of low-
polar linkages has also been demonstrated as an effective
approach to reduce the dielectric constant. Huang et al. com-
pared three benzoxazines from dicyclopentadiene-phenol
adduct, bisphenol A, and 4,40-biphenol, respectively.5,13 They
found that polybenzoxazine based on dicyclopentadiene-
phenol adduct exhibits the lowest dielectric constant.
Recently, Yang and Gu14 and Zhang et al.15 prepared low
ether-dielectric polybenzoxazines with benzoxazole moieties
since polybenzoxazoles are considered to be relatively low-
dielectric materials. Hougham et al.16,17 reported that the
dielectric constant could be reduced by increasing molecule’s
hydrophobicity, free volume, and by decreasing polarization.
Recently, we successfully prepared phosphinated cyanate
ester thermoset based on the bulky phosphinate pendant
that increased free volume of thermoset.18
Synthesis of (2)
Ten grams (0.012 mol) of (1), 2-hydroxybenzaldehyde 3.09 g
(0.025 mol), and 50 mL of ethanol were introduced into a
100 mL round-bottom glass flask equipped with a condenser
and a magnetic stirrer. The mixture was reacted at room
temperature for 12 h. Then, 1.392 g (0.042 mol) NaBH4 was
added. The reaction mixture was stirred at room tempera-
ture for 12 h. The mixture was then poured into methanol/
water (1/1, V/V). The precipitate was isolated by filtration.
After drying, 10.94 g of (2) (82% yield) was obtained. HR-
MS (FAB1) m/z: calcd. for C33H28O4NP 533.1756; anal.,
534.1761 (M11)1.
ELEM ANAL CALCD: C, 74.29 %; H, 5.29%; N, 2.63%. Found: C,
72.13%; H, 5.42%, 2.59%.1H-NMR (ppm, DMSO-d6), d 5 1.5
(CH3), 4.2 (CH2), 5.9 (NH), 6.4-8.1 (Ar-H), 9.5 (OH).
Synthesis of (3)
Exactly 7.73 g (0.014 mol) of (2), 0.696 g (0.023 mol) of
paraformaldehyde, and 50 mL of THF were introduced into a
100 mL round-bottom glass flask equipped with a condenser
and a magnetic stirrer. The mixture was stirred at room tem-
perature for 4 h, and then further stirred at 50 ꢀC for 12 h.
The precipitate was filtered and washed with DI water. After
drying, white powder 6.26 g (82% yield) with a melting
point of 239 ꢀC (DSC) and an exothermic peak temperature
of 245 ꢀC was obtained. HR-MS(FAB1) m/z: calcd. for
Aryl propargyl ether is known to undergo Claisen type rear-
rangement to benzopyran with thermal treatment, and sub-
sequently polymerize via the curing of the C5C bond in the
benzopyran structure.19–26 Preparation of propargyl ether-
containing benzoxazine has been reported by Agag and Take-
ichi,27 Kiskan et al.,28 Chernykh et al,29,30 and Chang et al.31
However, no dielectric properties of the propargyl-containing
benzoxazine have been discussed in the literature. In this
work, we report our strategy in preparing a propargyl ether-
containing benzoxazine (4) from a nucleophilic substitution
of propargyl bromide and a phenolic OH-containing benzoxa-
zine (3). Benzoxazines (3) and (4) were applied as epoxy
curing agents. Experimental data show that (4)-cured epoxy
thermosets show higher thermal properties and a lower
dielectric constant than (3)-cured epoxy thermosets. The
detailed synthesis, curing behavior, and structure-property
relationship of the resulting thermosets are reported in this
work.
C
34H28O4NP 545.1755; anal., 546.1762, (M11)1.
ELEM ANAL CALCD: C, 74.85 %; H, 5.17%; N, 2.57%. Found: C,
74.53%; H, 5.43%, 2.49%. H-NMR (ppm, DMSO-d6), d 5 1.5
(CH3), 4.6 (N-CH2-ph), 5.4 (N-CH2-O), 6.6-8.0 (Ar-H), 9.5
(OH).
1
Synthesis of (4)
Exactly 2.73 g (0.005 mol) of (3), 0.892 g (0.006 mol) of
potassium carbonate, 0.892 g (0.006 mol) of propargyl bro-
mide, and 30 mL of acetone were introduced into a 100 mL
round-bottom glass flask equipped with a condenser and a
magnetic stirrer. The mixture was stirred at reflux for 24 h.
After that, the mixture was filtered (to remove KBr) and the
filtrate was poured into DI water. The precipitate was fil-
tered and dried (60% yield). An exothermic peak at 252 ꢀC
with enthalpy of 319 J/g was observed in the DSC thermo-
gram. HR-MS(FAB1) m/z: calcd. for C37H30O4NP 583.1912;
anal., 584.1919, (M11)1.
EXPERIMENTAL
Materials
Potassium carbonate, 2-hydroxybenzaldehyde, and propargyl
bromide were purchased from Acros; 1-(4-hydroxyphenyl)-1-
(4-aminophenyl)-1-(6-oxido-6H -dibenz <c,e><1,2> oxa-
phosphorin-6-yl)ethane (1) was prepared according to the
literature.32 Diglycidyl ether of bisphenol A (DGEBA) with an
epoxy equivalent weight (EEW) of 187 g/eq and cresol novo-
lac epoxy (CNE) with an EEW of 200 g/eq were kindly sup-
plied by Chang Chun Plastics, N,N-dimethylacetamide
(DMAc) was purchased from Tedia and purified by distilla-
tion under reduced pressure over calcium hydride (Acros)
and stored over molecular sieves. The other solvents used
are commercial products and were used without further
purification.
ELEM ANAL CALCD: C, 76.15 %; H, 5.18%; N, 2.40%. Found: C,
74.83%; H, 5.83%, 2.18%. H-NMR (ppm, DMSO-d6), d 5 1.8
1
(CH3), 2.5 (HCꢁC-), 4.5 (O-CH2-ph), 4.6 (CꢁC-CH2-O), 5.3
(N-CH2-O), 6.6-8.0 (Ar-H).
Preparation of the Epoxy Thermosets
The epoxy thermosets were obtained via the thermal curing
of (3) and (4) with commercially-available epoxy resins:
DGEBA and CNE. The curing agent and epoxy with 1/1
equivalent ratio were mixed and stirred homogeneously in
an aluminum mold at 140 ꢀC, and then cumulatively cured
at 160, 200 and 220 ꢀC for 2 h each in an air-circulating
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oven. Three types of samples were prepared: 12.7 3 1.27 3
0.127 cm3 for UL-94 measurement, 5.0 3 1.0 3 0.2 cm3 for
DMA measurement and 1.0 3 1.0 3 0.2 cm3 for TMA, dielec-
tric and water absorption measurements. The sample IDs for
(3)-cured DGEBA and CNE are named (3)/DGEBA and (3)/
CNE, respectively. The sample IDs for (4)-cured DGEBA and
CNE are named (4)/DGEBA and (4)/CNE, respectively.
was subjected to two 10-s ignitions. After the first ignition,
the flame was removed and the time for the polymer to self-
extinguish (t1) was recorded. Cotton ignition was noted if
polymer dripping occurred during the test. After cooling, the
second ignition was performed on the same sample. The
self-extinguishing time (t2) and dripping characteristics were
again recorded. Five specimens were measured and the aver-
age burning time was recorded. If t1 plus t2 was less than
10 s with no dripping, it was considered to be a V-0 grade,
an industrial standard for flame-retardancy. If t1 plus t2 was
in the range of 10 to 30 s without any dripping, the polymer
was considered to be a V-1 material. If t1 plus t2 was in the
range of 10 to 30 s with dripping that ignited a cotton indi-
cator located below the sample, the polymer was considered
to be a V-2 material.
Characterization
Differential scanning calorimetry (DSC) was performed with
a Perkin-Elmer DSC 7 in a nitrogen atmosphere at a heating
rate of 10 min/ꢀC. Thermal gravimetric analysis (TGA) was
performed with a Perkin-Elmer Pyris1 at a heating rate of
20 ꢀC/min in a nitrogen atmosphere. Dynamic mechanical
analysis (DMA) was performed with a Perkin-Elmer Pyris
Diamond DMA with a sample size of 5.0 3 1.0 3 0.2 cm3.
The storage modulus E0 and tan d were determined as the
sample was subjected to the temperature 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 analysis (TMA) was
performed with a Perkin-Elmer Pyris Diamond TMA at a
RESULTS AND DISCUSSION
Synthesis and Characterization of (4)
A propargyl ether-containing benzoxazine (4) was prepared
from the nucleophilic substitution of
a phenolic OH-
containing benzoxazine (3) with propargyl bromide in the
presence of potassium carbonate (Scheme 1). The precursor
(3) was prepared from the condensation of (1) with 2-
hydroxybenzaldehyde, followed by the reduction of the imine
linkage by NaBH4, and ring closure condensation of (2) with
formaldehyde.
ꢀ
heating rate of 5 C/min with a sample size of 1.0 3 1.0 3
0.2 cm3 in a penetration mode. NMR measurements 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 measured by
a Perkin-Elmer RX1 infrared spectrophotometer in KBr pow-
der form. High resolution mass spectra were obtained by a
Finnigan/Thermo Quest MAT 95XL mass spectrometer. The
UL-94 vertical test was performed according to the testing
procedure of FMVSS 302/ZSO 3975 with a test specimen bar
of 127 mm in length, 12.7 mm in width and about 1.27 mm
in thickness. The height of the burner flame was 25 mm and
the height from the top of the burner to the bottom of the
test bar was 10 mm. During the test, the polymer specimen
1
Supporting Information Figure S1 shows the H-NMR spectra
of (2). The disappearance of the amino signal of (1) at 5.0
ppm, and the appearance of the methylene signal at 4.2 ppm
and secondary amine signal at 6.0 ppm support the success-
ful preparation of (2). Figure 1 shows the 1H-NMR spectra
of (3-4). The disappearance of the phenolic OH signal of (3)
and the appearance of propargyl ether peaks at 2.5 (Ha) and
4.6 (Hc) ppm support the transformation of phenolic OH to
SCHEME 1 Synthesis of benzoxazine (4).
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FIGURE 1 1H-NMR spectrum of (3) and (4).
propargyl ether. In addition, the oxazine signals at 4.5 (Hc)
and 5.3 (Hd) ppm indicates the stability of the oxazine link-
age in this potassium carbonate-catalyzed reaction.
high as 319 J/g, which is much higher than that (134 J/g) of
analogous benzoxazine (4), which is a difunctional phosphi-
nated benzoxazine without the propargyl ether linkage. Com-
pared with the peak patterns of (4) and (40), we proposed
that the second exothermic peak of (4) is related to the cur-
ing propargyl ether linkage. The curing of (4) was monitored
by IR spectra and discussed below to prove the proposal.
DSC Thermograms
Figure 2 shows the DSC thermograms of (3), (4), and (40),
which was prepared from the Mannich condensation of 1,1-
bis(4-aminophenyl)-1-(6-oxido-6H-dibenz <c,e> <1,2> oxa-
phosphorin-6-yl)ethane, paraformaldehyde, and phenol.33
A
Microstructure
ꢀ
melting point at 239 C and a rapid exothermic peak at 244
ꢀC were observed for (3). The rapid exotherm after melting
indicates (3) is difficult to process. For (4), an exotherm
with two peaks at 252 ꢀC and 270 ꢀC, respectively, were
observed. The total enthalpy of the exothermic peak is as
Figure 3 shows the IR spectra of (4) after accumulative cur-
ing. The curing temperature and curing time are marked in
Figure 3. The characteristic absorptions of benzene with an
attached oxazine ring at 975 cm21, oxazine at 1376 and
1032 cm21, and propargyl ether at 2120 cm21 decreased
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FIGURE 2 DSC thermograms of (3), (4) and (40). [Color figure can be viewed in the online issue, which is available at wileyonlineli-
brary.com.]
gradually with the progress of curing. A C5C absorption of
benzopyran at 1680 cm21, which resulted from the Claisen
type rearrangement of propargyl ether, appeared after curing
polymerization mechanism of (4) was proposed in Scheme 2.
This first stage is related to the ring opening of the oxazine
and Claisen type rearrangement of propargyl ether, and the
second stage is the polymerization of the C5C bond of benzo-
pyran. This observation is consistent with data reported in
previous studies.19–26
ꢀ
at 180 C, but decreased gradually with the progress of cur-
ing, and disappeared after curing at 240 ꢀC. Figure 4 shows
the DSC thermogram of (4) after accumulative curing (the
same thermal history as in Fig. 3). The first exothermic
enthalpy decreased obviously with the progress of curing. IR
and DSC data suggest that the ring opening of oxazine and
the formation of benzopyran are correlated with the first
DSC exotherm. The second exothermic peak decreased obvi-
Properties of Epoxy Thermosets
We initially used (1), (3) and (4) as epoxy curing agents.
However, the melting point of (1) was as high as 294 ꢀC
(Supporting Information Fig. S2), hindering the processing
and preparation of the epoxy thermoset. Supporting Informa-
tion Figure S3 shows the DSC thermograms of powder mix-
tures of (3)/DGEBA and (4)/DGEBA. The onset exothermic
temperature of (3)/DGEBA starts at 160 ꢀC, which is much
lower than self-curing of (3). The nucleophilic addition of
phenolic OH of (3) on epoxy resin is thought to be responsi-
ble for the exothermic peak. However, the exothermic
enthalpy is not high. We speculate that the melting enthalpy
of (3), which is 239 ꢀC as shown in Figure 2, compensates
the exothermic peak. The onset exothermic temperature of
(4)/DGEBA is similar to that of (4). If some ring-opened
structures exist in (4), the onset exothermic temperature
will reduce remarkably. This result indicates that no or little
ring-opened structures exist in (4), supporting the purity of
(4). Figure 5 shows DMA thermograms of the resulting
epoxy thermosets. The Tg value of the (4)/CNE is 227 ꢀC,
which is 31 ꢀC higher than that of the (3)/CNE. A similar
trend was observed for (3)/DGEBA and (4)/DGEBA (Table
1). Moreover, as shown in Figure (5 and 3)-cured thermosets
display higher modulus than 4-cured thermosets. It is
thought that the modulus is strongly related with the inter-
molecular interaction. The 3-cured thermoset exhibits more
second alcohol for intermolecular interaction. In addition,
the 4-cured thermosets exhibits higher free volume due to
the double-strain structure (Scheme 3, to be discussed later).
Figure 6 shows the TMA thermograms of the resuꢀlting epoxy
thermosets. The Tg value defined by TMA is 212 C for (4)/
CNE, which is 45 ꢀC higher than that of (3)/CNE. The
ꢀ
ously after curing at 220 C, and disappeared after curing at
240 ꢀC. From IR and DSC data, the second exotherm is
related to the polymerization of the C5C bond of benzo-
pyran. According to the data in Figures 3 and 4, a two-stage
FIGURE 3 IR spectra (4) after accumulative curing. The curing
temperature and curing time are marked in the Figure. [Color
figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
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FIGURE 4 DSC thermograms of (4) after accumulative curing (the same thermal history as in Fig. 3). [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.com.]
SCHEME 2 Proposed polymerization mechanism of (4). [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
coefficient of thermal expansion (CTE) of (4)/CNE is 47
ppm/ꢀC, which is smaller than that (56 ppm/ꢀC) of (3)/CNE.
A similar trend was observed for (3)/DGEBA and (4)/
DGEBA (Table 1). The 5 wt % degradation temperature is
393 ꢀC for (4)/CNE, while the value reduces to 348 ꢀC for
(3)/CNE (Fig. 7). The char yield also reduces from 40 for
(4)/CNE to 33 for (3)/CNE. A similar result was observed
for (3)/DGEBA and (4)/DGEBA (Table 1). DMA, TMA and
TGA data demonstrate the advantage of the propargyl ether
linkage in thermal properties over phenolic OH as an epoxy
curing agent. Table 1 also lists the UL-94 result of the result-
ing epoxy thermosets. UL-94 V-0 grade can be achieved for
all systems. This result demonstrates the good flame retard-
ancy of the phosphinate pendant.
Dielectric Properties
The advantage of propargyl ether in the dielectric constant
(Dk) and dissipation factor (Df) can be supported by the
dielectric values of the epoxy thermosets (Table 2). Dk and
Df of (4)/CNE at 1 GHz are 2.62 U and 4.6 mU, respectively,
which are much lower than those (3.60 U and 26.7 mU) of
(3)/CNE. A similar trend was observed for (3)/DGEBA and
(4)/DGEBA (Table 2). Hougham et al.16,17 reported that the
dielectric constant could be reduced by increasing molecule’s
hydrophobicity, free volume, and by decreasing polarization.
According to the data shown in Figures 2 to 4, the curing of
the benzopyran leads to a low-polar aliphatic cycloether
structure (Scheme 3), which can result in a low-dielectric
FIGURE 5 DMA thermograms of the resulting epoxy thermo-
sets. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
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TABLE 1 Thermal Properties of the Resulting Epoxy Thermosets
Thermoset ID
Tg (ꢀC)a
Tg (ꢀC)b
CTE (ppm/ꢀC)c
Td5% (ꢀC)d
Char yield (wt %)e
Dripping
UL-94 Grade
(3)/DGEBA
(4)/DGEBA
(3)/CNE
173
202
196
227
159
190
167
212
56
47
56
47
341
388
348
393
27
33
33
40
No
No
No
No
V-0
V-0
V-0
V-0
(4)/CNE
a
d
Peak temperature of tan(delta) measured by DMA at a heating rate of
ꢀC/min.
Measured by TMA at a heating rate of 5 ꢀC/min.
Coefficient of thermal expansion are recorded from 50 ꢀC to 150 ꢀC.
Temperature corresponding to 5% weight loss by thermogravimetry
at a heating rate of 20 ꢀC/min in the atmosphere of nitrogen.
5
b
e
Residual weight % at 800 ꢀC in the atmosphere of nitrogen.
c
SCHEME 3 Proposed structure of the (a) (3)/CNE and (b) (4)/CNE thermosets. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
FIGURE 7 TGA thermograms of the resulting epoxy thermo-
sets. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
FIGURE 6 TMA thermograms of the resulting epoxy thermo-
sets. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
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TABLE 2 Dielectric Properties and Water Absorption of the Resulting Epoxy Thermosets
k(U) Df (mU)
D
Water Absorption at 100 ꢀC (25 ꢀC)a
Thermoset ID
1 GHz
100 MHz
1 GHz
100 MHz
12 h
24 h
48 h
(3)/DGEBA
(4)/DGEBA
(3)/CNE
3.32 6 0.01
2.77 6 0.01
3.60 6 0.01
2.62 6 0.01
3.43 6 0.02
2.81 6 0.02
3.79 6 0.02
2.65 6 0.01
17.57 6 0.02
6.76 6 0.01
26.73 6 0.02
4.62 6 0.01
20.66 6 0.03
6.94 6 0.02
30.55 6 0.03
5.27 6 0.02
2.22(0.50)
0.27(0.12)
3.14(0.86)
1.04(0.54)
2.38(0.74)
1.31(0.25)
3.47(1.60)
1.73(0.72)
3.10(1.12)
1.95(0.37)
3.63(1.84)
2.79(1.26)
(4)/CNE
a
The value in parentheses is the water absorption at 25 ꢀC.
ACKNOWLEDGMENTS
value. In addition, the bulky cycloether structure that increases
the free volume of the thermoset might also be responsible for
the low Dk and Df. Particularly, as shown in Scheme 3(a), two
secondary alcohols were formed for each (3) curing with
epoxy. However, as shown in Scheme 3(b), only one secondary
alcohol was formed for each (4) curing with epoxy. It is known
that secondary alcohol in the epoxy thermosets is a highly
polar linkage that leads to increased Dk and Df. Therefore, the
formation of aliphatic cycloether and half amounts of second-
ary alcohol in the (4)-cured epoxy thermoset are thought to
partially be responsible for the lower dielectric Dk and Df. It is
known that aryl esterized phenol compounds, active esters,
have been used as epoxy curing agents to eliminate the forma-
tion of secondary alcohol.34,35 However, thermosets cured by
active esters usually display a lower Tg than those cured by
their phenol precursors. In this case, an enhancement in Tg
and reduction in dielectric properties was simultaneously
achieved, which is rarely seen in the literature. Table 2 lists
the water absorption of the resulting epoxy thermosets. (4)/
CNE and (4)/DGEBA display much lower absorption values
than (3)/CNE and (3)/DGEBA, no matter at 100 ꢀC or at 25
ꢀC. The trend is consistent with that of the dielectric proper-
ties. The formation of half amounts of highly polar secondary
alcohol is thought to be responsible for the result.
The authors thank the National Science Council of the
Republic of China for financial support. Partial sponsorship
by the Green Chemistry Project (NCHU), as funded by the
Ministry of Education, is also gratefully acknowledged.
REFERENCES AND NOTES
1 X. Ning, H. Ishida, J. Polym. Sci. Part A: Polym. Chem. 1994,
32, 1121–1129.
2 Y. Yagci, B. Kiskan, N. N. Ghosh, J. Polym. Sci. Part A:
Polym. Chem. 2009, 47, 5565–5576.
3 I. Hamerton, B. J. Howlin, A. L. Mitchell, L. T. McNamara, S.
Takeda, React. Funct. Polym. 2012, 72, 736–744.
4 Y.-C. Su, F.-C. Chang, Polymer 2003, 44, 7989–7996.
5 C. H. Lin, S. L. Chang, H. H. Lee, H. C. Chang, K. Y. Hwang,
A. P. Tu, W. C. Su, J. Polym. Sci. Part A: Polym. Chem. 2008,
46, 4970–4983.
6 P. Velez-Herrera, K. Doyama, H. Abe, H. Ishida, Macromole-
cules 2008, 41, 9704–9714.
7 M. R. Vengatesan, S. Devaraju, A. A. Kumar, M. Alagar, High
Perform. Polym. 2011, 23, 441–456.
8 Y.-J. Lee, J.-M. Huang, S.-W. Kuo, J.-K. Chen, F.-C. Chang,
Polymer 2005, 46, 2320–2330.
9 Y.-J. Lee, S.-W. Kuo, C.-F. Huang, F.-C. Chang, Polymer 2006,
47, 4378–4386.
CONCLUSIONS
10 Y.-J. Lee, S.-W. Kuo, Y.-C. Su, J.-K. Chen, C.-W. Tu, F.-C.
Chang, Polymer 2004, 45, 6321–6331.
We have successfully prepared a propargyl ether-containing
benzoxazine (4) by a four-step procedure from (1). According
to the IR and DSC data, a two-stage polymerization mechanism
was proposed: the first stage is related to the ring opening of
the oxazine and Claisen rearrangement of propargyl ether, and
the second stage is the polymerization of the C5C bond of
benzopyran. Epoxy thermosets cured by (4) display better
properties than those cured by (3) in Tg, dimensional stability,
thermal stability, dielectric properties, and water absorption. In
particular, thermosets cured by (4) show low-dielectric charac-
teristic, which should be attractive for application in high-
frequency printed circuit boards. We proposed that the forma-
tion of aliphatic cycloether and half the amount of secondary
alcohol in the (4)-cured epoxy thermoset are responsible for
the lower dielectric Dk and Df. The high-Tg characteristic of
propargyl ether-containing has been reported in the literature;
however, to the best of our knowledge, this is the first article
reporting the low-dielectric characteristic of propargyl
ether-containing benzoxazines as epoxy curing agents.
11 M.-C. Tseng, Y.-L. Liu, Polymer 2010, 51, 5567–5575.
12 Y.-C. Su, W.-C. Chen, K.-L. Ou, F.-C. Chang, Polymer 2005,
46, 3758–3766.
13 J.-Y. Shieh, C.-Y.; Lin, C.-L. Huang, C.-S. Wang, J. Appl.
Polym. Sci. 2006, 101, 342–347.
14 P. Yang, Y. Gu, J. Appl. Polym. Sci. 2012, 124, 2415–2422.
15 K. Zhang, Q. Zhuang, Y. Zhou, X. Liu, G. Yang, Z. Han,
J. Polym. Sci. Part A: Polym. Chem. 2012, 50, 5115–5123.
16 G. Hougham, G. Tesoro, J. Shaw, The synthesis and proper-
ties of polyimides made from perfluoro aromatic diamines.
Polym. Mater. Sci. Eng. 1989, 61, 369.
17 G. Hougham, G. Tesoro, J. Shaw, Macromolecules 1994, 27,
3642–3649.
18 H. C. Chang, H. T. Lin, C. H. Lin, Polym. Chem. 2012, 3, 970–
978.
19 M. F. Grenier-Loustalot, V. Denizot, D. Beziers, High
Perform. Polym. 1995, 7, 157–180.
20 M. F. Genier-Loustalot, C. Sanglar, High Perform. Polym.
1996, 8, 315–339.
1366
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1359–1367

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
21 M. F. Grenier-Loustalot, C. Sanglar, High Perform. Polym.
1996, 8, 341–361.
29 A. Chernykh, T. Agag, H. Ishida, Polymer 2009, 50, 382–390.
30 A. Chernykh, T. Agag, H. Ishida, Macromolecules 2009, 42,
22 M. F. Grenier-Loustalot, C. Sanglar, High Perform. Polym.
1996, 8, 533–554.
5121–5127.
31 H. C. Chang, C. H. Lin, H. T. Lin, S. A. Dai, J. Polym. Sci.
Part A: Polym. Chem. 2012, 50, 1008–1017.
23 M. F. Grenier–Loustalot, C. Sanglar, High Perform. Polym.
1996, 8, 555–578.
32 C. H. Lin, S. L. Chang, P. W. Cheng, J. Polym. Sci. Part A:
Polym. Chem. 2011, 49, 1331–1340.
24 W. E. Douglas, A. S. Overend, Eur. Polym. J. 1991, 27, 1279–
1287.
33 C. H. Lin, unpublished work.
25 C. P. R. Nair, R. L. Bindu, K. Krishnan, K. N. Ninan, Eur.
Polym. J. 1999, 35, 235–246.
34 T. Kan, S. Etsuko, M. Kunihiro, A. Kazuo, Active ester resin,
method for producing same, thermosetting resin composition,
cured product thereof, semiconductor sealing material, pre-
preg, circuit board, and build-up film. 2012.
26 S. Prieto, M. Galia, V. Cadiz, Macromol. Chem. Phys. 1998,
199, 1291–1300.
27 T. Agag, T. Takeichi, Macromolecules 2001, 34, 7257–7263.
35 A. Kazuo, S. Etsuko, Thermosetting resin composition, cured
product thereof, active ester resin, semiconductor sealing mate-
rial, prepreg, printed circuit board, and build-up film. 2012.
28 B. Kiskan, G. Demiray, Y. Yagci, J. Polym. Sci. Part A:
Polym. Chem. 2008, 46, 3512–3518.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1359–1367
1367