Bisphenol-1,2,3-triazole (BPT) epoxies and cyanate esters: Synthesis and self-catalyzed curing

Article abstract of DOI:10.1021/ma200767j

Novel bisphenol-1,2,3-triazole (BPT) resins, including epoxy (DGE-BPT) and cyanate ester (BPTCE) systems, were prepared and used in curing chemistry with no added reagents or catalysts. The materials were characterized relative to conventional epoxies and

Full text of DOI:10.1021/ma200767j

ARTICLE
pubs.acs.org/Macromolecules
Bisphenol-1,2,3-triazole (BPT) Epoxies and Cyanate Esters:
Synthesis and Self-Catalyzed Curing
Beom-Young Ryu and Todd Emrick*
Polymer Science and Engineering Department, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003,
United States
ABSTRACT: Novel bisphenol-1,2,3-triazole (BPT) resins,
including epoxy (DGE-BPT) and cyanate ester (BPTCE)
systems, were prepared and used in curing chemistry with no
added reagents or catalysts. The materials were characterized
relative to conventional epoxies and cyanate esters, in terms of
curing and thermal properties, and the curing process and products were characterized by differential scanning calorimetry (DSC),
thermogravimetric analysis (TGA), pyrolysis combustion flow calorimetry (PCFC), and small scale flame tests. These novel BPT-
based resins cure in the absence of added catalysts and exhibit exceptionally low heat release and high char residue. Despite the
absence of antiflammable additives (either halogenated or inorganic compounds), BPTCE itself was found to be nonignitable, with
extremely high char residue value (67%) and extraordinarily low heat release capacity (HRC of ∼10 J/(g K)).
’ INTRODUCTION
of curing catalysts, such as imidazoles or transition metal com-
plexes.24ꢀ27
Polymer matrix composites such as blends and filled systems
are exceptionally useful for a wide range of industrial applications
that require high performance-to-weight ratio and corrosion
resistance, such as in transportation, construction, and electronic
materials. Because of their excellent adhesive properties, proces-
sability, and low cost, epoxy and cyanate ester resins are used
prominently as the polymer matrix in such composites.1ꢀ4 For
example, bisphenol A (BPA) epoxy formulations dominate the
epoxy resin market but generally contain fillers, curing agents,
and flame retardants (FRs).5 The inherent flammability of such
materials is particularly problematic in settings that require flame
resistance, such as vehicles and electronic and construction
materials. Brominated FR small molecules such as polybromi-
nated diphenyl ethers, hexabromocyclododecane, and tetrabro-
mobisphenol A (TBBPA) have been implemented widely to
reduce flammability.6,7 However, many brominated FRs were
recently classed together with halogenated FRs and face legisla-
tive restrictions in Europe and the United States due to health
and environmental concerns, such as bioaccumulation and
associated carcinogenicity.8ꢀ19 Potential negative effects of such
molecules on the environment, and in animals and humans,
remain controversial and under continued investigation.20ꢀ23
While most epoxy resins require added curing agents (e.g.,
multifunctional amines), cyanate ester (CE) resins cure ther-
mally by cyclotrimerization to give polycyanurates (Figure 1).
Polycyanurates exhibit high glass transition temperatures, tough-
ness, and low dielectric properties, making them useful in high-
performance structural and electronics applications.24 Halogen-
free CE resins (e.g., BPA, bisphenol-E, and bisphenol-M CE
resin) exhibit undesirably high flammability, with a heat release
capacity (HRC) of 240ꢀ320 J/(g K), total heat release (THR) of
15ꢀ23 kJ/g, and char yield of 26ꢀ42%.25 Moreover, the long
gelation time of CE resins is frequently adjusted by the addition
We recently reported the preparation of novel polymers cont-
aining bisphenol-1,2,3-triazole (BPT) moieties, which undergo
a thermally induced triazole-to-phenylindole rearrangement,28ꢀ31
releasing nitrogen gas and giving high levels of char with little
burning.32 For example, BPT-containing aromatic polyesters
were prepared and found to exhibit exceptionally low heat release
properties. BPT-polyesters gave a heat release capacity (HRC) of
<50 J/(g K), total heat release (THR) of ∼7 kJ/g, and char yields
of 47ꢀ56%. HRC, an inherent materials property, is defined as
the maximum specific heat release divided by the heating rate
during a controlled thermal decomposition and is now a well-
established method for evaluating flammability characteristics of
combustible materials.33ꢀ36 We measured HRC by a standard
oxygen combustion calorimetry technique37 and judged self-
extinguishing properties in small scale flame tests.
Here we describe an effort designed to test whether BPT units
could be integrated successfully into cross-linked epoxy and cyanate
ester networks and, if so, whether the resulting materials would repre-
sent any potential advantage over existing materials. As described
below, we found that these novel BPT-epoxies function effectively as
one-component resins (i.e., requiring no curing catalyst) and that
BPT-cyanate ester resins exhibit a markedly reduced gelation time
(5 min at 170 °C) relative to more conventional versions.
’ RESULTS AND DISCUSSION
BPT-Diglycidyl Ether Synthesis. Bisphenol-1,2,3-triazoles 1
and 2, containing meta- and para-substitution patterns, respectively,
Received: April 1, 2011
Revised:
June 3, 2011
Published: June 21, 2011
r
2011 American Chemical Society
5693
dx.doi.org/10.1021/ma200767j Macromolecules 2011, 44, 5693–5700
|

Macromolecules
ARTICLE
Figure 1. Curing networks based on bisphenol A epoxy (top) and bisphenol A cyanate ester (bottom).
337.13 m/z of [M ꢀ N2]þ was observed, due to the loss of N2
from triazole under these ionization conditions.
As the postcured BPT-containing products are insoluble, and
thus difficult to characterize by standard solution spectroscopy,
we prepared the dimethyl ester version of BPT, shown as
compound 5 in Scheme 2, for the purpose of examining its
reaction with the aromatic monoglycidyl ether 6. A mixture of
5 and 6 was heated to 180 C for 1.5 h, and the resulting reaction
mixture was readily soluble and could be characterized by
1H NMR spectroscopy. The glycidyl ether methylene and meth-
yne resonances were absent, indicating the anticipated epoxide
ring-opening, and new resonances from 4.43 to 4.05 ppm reflect
the formation of an oligomeric ethylene oxide structure. The
broadening of the triazole proton peak (from 8.22 ppm of 5 to
8.23ꢀ8.14 ppm in the product) suggests its reaction with the
glycidyl ethers that might lead to a zwitterionic structure, as
shown in Scheme 2. As for curing with tertiary amines and
imidazoles,38ꢀ40 the triazole moiety can react with the electron-
poor methylene of the epoxide and then propagate further to an
oligomeric product. While this experiment confirms participa-
tion of the triazole in the curing mechanism, we note that
concurrent participation of adventitious nucleophilic initiators
(water, base, etc.) cannot be ruled out, despite our efforts to
purify BPT and the other reagents used.
We found that these novel DGE-BPT epoxy resins can be used
alone in curing chemistry or as a component of blends with other
epoxides. Blends of DGE-BPT with BPA-based epoxy (DGE-
BPA) and deoxybenzoin-based epoxy (DGE-BHDB)41 were
prepared to determine the properties of these mixtures. By
DSC, each blend showed a large exotherm in the temperature
range 160ꢀ320 °C (Figure 3) due to catalytic curing at over
160 °C (regardless of para- or meta-substitution) under homo-
geneous melt conditions.
Figure 2. DSC thermograms of 3-DGE-BPT (—) and 4-DGE-BPT
(---) resins.
were prepared by the click cycloaddition reactions that we
reported previously.32 Then, the corresponding diglycidyl ether
derivatives (DGE-BPTs) were prepared by reaction of the
phenols with epichlorohydrin in a sodium hydroxide solution
in water/isopropanol. 3-DGE-BPT, compound 3, was obtained
as a yellow solid in 82% yield and 4-DGE-BPT, compound 4, as a
pale brown solid in 62% yield. Nuclear magnetic resonance
(NMR) spectroscopy confirmed the desired structure of 3 and
4, as seen for example in the 1H NMR spectrum of 4 showing the
characteristic glycidyl ether resonances centered at 4.35, 3.41,
2.97, and 2.82 ppm. Differential scanning calorimetry (DSC)
analysis of 4-DGE-BPT showed a small endotherm from 190 to
195 °C, and a large exotherm at 195ꢀ250 °C (Figure 2),
reflecting an initial melting that is followed immediately by
self-curing. In contrast, 3-DGE-BPT 3 did not exhibit a clear
melting point, showing only a glass transition at ∼20 °C, likely an
effect of the meta-substitution. However, 3-DGE-BPT also
showed a large exotherm from 160 to 280 °C upon self-curing.
High-resolution mass spectroscopy of 3 (366.1462 m/z of [M þ
H]þ) and 4 (366.1426 m/z of [M þ H]þ) (calculated 366.1454
m/z) confirmed the expected molecular weight of each com-
pound in fast atom bombardment (HRMS-FAB) mode. Inter-
estingly, in electron impact mode (HRMS-EI), the expected
signal at 365.14 m/z of [M]þ was absent, but instead a signal at
The heat release and char properties of self-cured DGE-BPT
resins and their blends with other diglycidyl ethers were char-
acterized by pyrolysis combustion flow calorimetry (PCFC) and
thermogravimetric analysis (TGA). Samples for PCFC and TGA
were prepared by curing the homogeneous mixture (in the
melted state) for 2 h at 160 °C and for 1 h at 180 °C, followed
by a 1 h postcure at 200 °C in a Teflon mold. The data obtained
from these formulations are listed in Table 1. DGE-BHDB resins
5694
dx.doi.org/10.1021/ma200767j |Macromolecules 2011, 44, 5693–5700

Macromolecules
ARTICLE
Scheme 1
Scheme 2
Figure 3. DSC thermograms of DGE-BPA/3-DGEBPT (1/1, w/w, —) and DGE-BEDB/4-DGE-BPT (4/1, w/w, ---) blend.
cured with the aromatic diamines diaminodiphenyl sulfone (DDS)
and diaminodiphenylmethane (DDM) (Table 1, entries 3 and 4)
exhibited moderately lower heat release properties than those
of the BPA version (entry 1) due to the known char-forming
properties of the deoxybenzoin moiety41ꢀ43 (increasing from
12% to 30ꢀ35%). Impressively, despite the significant aliphatic
character inherent to diglycidyl ethers, the HRC and THR values
of the blended triazole containing resins (entries 2, 5, 6, and 7)
5695
dx.doi.org/10.1021/ma200767j |Macromolecules 2011, 44, 5693–5700

Macromolecules
ARTICLE
Table 1. Heat Release and Char Properties of Epoxy Formulations
entry
formulation
DGE-BPA/DDSa
HRC (J/(g K))
THR (kJ/g)
char (%)b
1
2
3
4
5
6
7
513 ( 10
408 ( 10
420 ( 14
439 ( 7
265 ( 5
222 ( 5
200 ( 7
25.3 ( 0.2
16.9 ( 0.2
17.2 ( 0.2
17.6 ( 0.2
16.6 ( 0.4
12.5 ( 0.2
10.9 ( 0.3
12
26
30
35
35
43
45
DGE-BPA/3-DGE-BPT (1/1, w/w)
DGE-BHDB/DDSa
DGE-BHDB/DDMa
DGE-BHDB/4-DGE-BPT (4/1, w/w)
DGE-BHDB/3-DGE-BPT (1/1, w/w)
3-DGE-BPT (self-cured)
a Equivalent amount of aromatic diamine (DDS: diaminodiphenyl sulfone; DDM: diaminodiphenylmethane) was used (data taken from the ref 41).
b Data obtained from TGA at 850 °C in a nitrogen atmosphere (heating rate 10 °C/min).
Scheme 3
Figure 4. Adhesion demonstration using the 3-DGE-BPT resin ((a)
before loading additional weight and (b) after loading 700 g of metal
weight).
decreased significantly with increasing DGE-BPT content. The
self-cured 3-DGE-BPT resin was most impressive in this regard,
with a HRC of only 200 ( 7 J/(g K), and an impressively high
char value of 45%.
Figure 5. Measured gelation time of BPACE, 3-BPTCE, and BPACE/
BPTCE blends.
The adhesive properties of self-cured BPT-containing epoxies
were confirmed by demonstrating adhesion of a metal alloy rod
(30 g, 1 cm diameter) on a glass surface. The adhesion of the self-
cured 3-DGE-BPT specimen was sufficiently robust to bear an
additional 700 g loading (see Figure 4). Quantitative adhesive
studies (i.e., lap shear tests) of BPT-epoxy will be possible
following development of these experimental scale materials into
a larger scale process.
Bisphenol-1,2,3-triazole Cyanate Ester (BPTCE). We antici-
pated that combining the benefits of BPT with aryl cyanurate
structures into a resin formulation would improve these conven-
tional systems by reducing curing time and their enhancing flame
resistance, even in the absence of added catalyst. The cyanate
ester of 3-BPT (3-BPTCE, 7) was prepared in the good yield by
reaction of 3-BPT with cyanogen bromide in the presence of
triethylamine (Scheme 3). 3-BPTCE was obtained as a pale
brown solid and seen to have a significantly higher melting point
(155ꢀ160 °C) than the BPA version (78ꢀ82 °C). The 13C
NMR spectrum of cyanate ester 7 showed signals at 108.6 and
108.9 ppm, in the expected regions for cyanate esters, with the
two separate peaks arising as a consequence of the unsymmetrical
nature of BPT (i.e., having a nonequivalent electronic environ-
ment around the two cyanate ester carbon atoms). Mass spectro-
metry analysis confirmed the desired structure, with BPTCE 7
giving a mass of 275.1 m/z by HRMS-EI ([M ꢀ N2]þ) and
304.0822 m/z by HRMS-FAB ([M þ H]þ, calculated 304.0834
m/z).
Unlike BPA cyanate ester (BPACE), which requires imple-
mentation of heating cycles to achieve curing in the absence of
added catalysts (e.g., 18 h at 150 °C, 4 h 200 °C, and 4 h
240 °C),20 BPTCE gelled rapidly after melting. This rapid
gelation of BPTCE allowed the curing reaction to be completed
within 30 min by heating the material from 160 to 280 °C at
5 °C/min. Anticipating that BPTCE might be most useful in
blends with commercially available BPACE, the effect of blend
ratios on curing was investigated, in BPACE-to-BPTCE weight
ratios of 9:1, 8:2, 7:3, and 1:1. Gelation times were measured
using a magnetic stir bar (1 cm) in 100 mg of sample at 170 °C,
noting the time required for a mixture stirring initially at 200 rpm
to stop completely (Figure 5). At 170 °C, BPACE alone showed
5696
dx.doi.org/10.1021/ma200767j |Macromolecules 2011, 44, 5693–5700

Macromolecules
ARTICLE
Figure 6. Left: diagram of a small scale flame test; middle: the specimens (a) before test and (bꢀd) after test; right: flame test results as a function of
cyanate ester composition.
Table 2. Heat Release and Char Properties of Cured BPACE,
BPTCE, and Blend Resins
entry
composition (w/w)
HRC (J/(g K)) THR (kJ/g) char (%)a
8
9
BPACE
332 ( 10
285 ( 14
280 ( 15
261 ( 12
200 ( 15
10 ( 2
14.5 ( 0.2
13.4 ( 0.3
12.5 ( 0.2
11.2 ( 0.4
9.2 ( 0.2
2.0 ( 0.2
44
44
46
48
53
67
BPACE/BPTCE (9/1)
10 BPACE/BPTCE (8/2)
11 BPACE/BPTCE (7/3)
12 BPACE/BPTCE (5/5)
13 BPTCE
a Data obtained from TGA at 850 °C in nitrogen (heating rate 10 °C/min).
no reduction in rpm for 6 h. However, for 9:1 and 7:3 BPACE:
BPTCE blends, gelation time decreased dramatically from 230 to
55 min, likely due to catalysis of the cyclotrimerization by the
triazole group.4,24 Such mixtures may prove convenient for
processes that require rapid online wetting or continuous fiber
reinforcement such as wet filament winding, resin transfer
molding, and pultrusion.44
Figure 7. TGA thermograms of cured BPACE (black), BPTCE (red),
As a precursor to small scale flame tests, PCFC, and TGA
experiments, BPACE/BPTCE blends were prepared by curing a
homogeneous mixture of the two cyanate esters for 4 h at 170 °C,
then for 4 h at 240 °C, followed by postcuring at 280 °C for 1 h.
BPACE samples were cured for 18 h at 150 °C, then for 4 h at
200 °C, 4 h at 240 °C, and finally postcured at 280 °C for 1 h. In
the case of 3-BPTCE, samples were cured for 30 min at 170 °C
and then heated to 280 at 5 °C/min. Small scale flame tests were
conducted by placing a sample specimen (∼1 ꢁ 0.35 ꢁ 0.1 cm)
in a propane torch flame at a 45° angle for 3 s, noting the time
required for the sample to self-extinguish following removal from
the flame (Figure 6).45 Striking differences were observed among
these samples as a function of BPTCE content. BPACE exhibited
self-sustained burning in air following removal from the flame,
with moderate visible smoke. In the blended materials, intumes-
cence increased with the BPTCE content, possibly due to N2 gas
evolution upon burning. Such intumescence can provide an
effective barrier to release of fuel from the material surface.
The specimens containing 50 wt % BPTCE (entry 12) burned for
only 1ꢀ2 s, while BPTCE samples (entry 13) were seen to
extinguish immediately after removal from the flame, with little
noticeable smoke evolution. We also note that BPTCE exhibited an
impressive char volume, expanding outward from the specimen in
the flame (Figure 6c,d). Such char formation is exceptionally useful
as it contributes further to effective suppression of flame spread.
The PCFC and TGA results of BPACE/BPTCE materials are
listed in Table 2. Heat release values (HRC and THR values) of
the cured blends decreased with increasing BPTCE weight
and BPACE/BPTCE (5/5, w/w, blue).
percent, approximately following the rule of mixtures. Notably,
the cured BPTCE exhibited miniscule HRC (10 J/(g K)) and
THR (2 kJ/g), extraordinary low values, even lower than
halogen-containing CE resins such as hexafluorobisphenol A
(62 J/(g K) HRC and 4.6 kJ/g THR) and bisphenol C contain-
ing CE resins (24 J/(g K) HRC and 4.2 kJ/g THR).25 TGA of
BPTCE showed a two-step weight loss curve (about 10% weight
loss at 330ꢀ430 °C), which would be expected from the loss of
N2, and a 67% char yield at 850 °C (Figure 7). With increasing of
BPT content in the blends, the slope of weight loss decreased and
the residual mass (char) increased, indicating an enhanced flame-
retardancy through char by aromatization during combustion.
In summary, we have described the synthesis of novel bi-
sphenol-1,2,3-triazole epoxy and cyanate ester resins as self-
catalyzed, self-extinguishing systems. BPT epoxy resins and their
blends with BHDB epoxy are self-curable in the absence of
aromatic diamines and have significantly lower heat release
properties than conventional non-halogenated versions. The
presence of the BPT moiety in cyanate ester resins dramatically
reduced the gelation time of blends relative to the conventional
BPA version and suppressed heat release properties and flamm-
ability. Most importantly, BPTCE, though halogen-free, clearly
possesses ultralow heat release properties even lower than
halogenated resins and as such opens another opportunity for
replacing halogenated molecules in many settings.
5697
dx.doi.org/10.1021/ma200767j |Macromolecules 2011, 44, 5693–5700

Macromolecules
ARTICLE
’ EXPERIMENTAL SECTION
(95% yield) of a brown oil. 1H NMR (acetone-d6, 300 MHz, ppm): 8.57
(s, 1H, ArꢀOH), 7.02 (m, 1H, ArꢀH), 6.96ꢀ6.86 (m, 3H, ArꢀH), 0.23
(s, 9H, TMS). 13C NMR (CDCl3, 75 MHz, ppm): 155.5, 129.8, 124.8,
124.4, 118.8, 116.3, 105.0, 94.5, 0.1.
4-(2-Trimethylsilylethynyl)phenol (4-TMSE-phenol). 4-TMSE-
phenol was prepared in a similar manner as 3-TMSE-phenol, using
4-iodophenol (5.0 g) instead of 3-iodophenol. This gave 3.5 g (82% yield) of
a brown oil. 1H NMR (acetone-d6, 300 MHz, ppm): 8.80 (s, 1H, ArꢀOH),
7.34 (d, 2H, J= 8.4 Hz, ArꢀH), 6.85 (d, 2H, J =8.4 Hz, ArꢀH), 0.21(s, 9H,
TMS). 13CNMR(CDCl3, 75 MHz, ppm): 156.1, 133.9, 115.6, 115.5, 105.3,
92.7, 0.2.
1,4-Bis(3-hydroxyphenyl)-1,2,3-triazole (3-BPT). To 3-TMSE-
phenol (4.0 g, 21.02 mmol) in 35 mL of DMF were added 3-azidophenol
(3.41 g, 25.2 mmol), CuBr (153 mg, 1.05 mmol), and 2,20-bipyridyl
(328 mg, 2.10 mmol). The mixture was heated at 80 °C for 24 h, cooled to
room temperature, and then diluted with 250 mL of EtOAc. The combined
organic mixture washed with water and dried over MgSO4. Solvents were
removed by rotary evaporation, and the residue was recrystallized in acetic
acid/water to give 3.70 g (70% yield) of a brown crystalline solid. 1H NMR
(MeOD-d4, 300 MHz, ppm): 8.80 (s, 1H, triazolꢀH), 7.43ꢀ7.26 (m, 6H,
ArꢀH), 6.95ꢀ6.91 (m, 1H, ArꢀH), 6.84ꢀ6.83 (m, 1H, ArꢀH). 13C
NMR (MeOD-d4, 75 MHz, ppm): 158.6, 157.7, 148.1, 137.9, 131.1, 130.4,
129.7, 118.8, 116.7, 115.6, 115.1, 112.1, 110.7, 107.1.
1,4-Bis(4-hyroxyphenyl)-1,2,3-triazole (4-BPT). 4-BPT was
prepared in a similar manner as 3-BPT, using 4-TMSE-phenol (3.50 g,
18.4 mmol) and 4-azidophenol (3.73 g, 27.9 mmol) instead of 3-TMSE-
phenol and 3-azidophenol. This gave 2.79 g (60% yield) of a purple
crystal. 1H NMR (MeOD-d4, 300 MHz, ppm): 8.62 (s, 1H, triazolꢀH),
7.75ꢀ7.68 (m, 4H, ArꢀH), 6.99 (d, 2H, J = 9.0 Hz, ArꢀH), 6.90 (d, 2H,
J = 8.7 Hz, ArꢀH). 13C NMR (MeOD-d4, 75 MHz, ppm): 159.7, 159.3,
149.8, 131.0, 128.4, 123.4, 123.0, 119.4, 117.3, 116.9.
Materials. Ethynyltrimethylsilane (ETMS), pyridine, 4-iodophenol,
4-aminophenol, 3-iodophenol, 3-aminophenol, 2,20-bipyridyl, sodium
azide, sodium nitrite, N,N-diisopropylethylamine (DIPEA), copper
bromide (CuBr), copper iodide (CuI), bis(triphenylphosphine)pal-
ladium(II) dichloride (PdCl2(PPh3)2), deoxyanisoin, pyridine hydro-
chloride, epichlorohydrin, and cyanogen bromide were purchased from
Sigma-Aldrich and used without further purification. Bisphenol A
cyanate ester (BPACE) was obtained from Lonza and used as received.
Toluene, dichloromethane, and triethylamine were distilled prior to use.
Silica gel (60 Å, 40ꢀ63 μm) was purchased from Sorbent Technologies.
Characterization. 1H and 13C nuclear magnetic resonance (NMR)
spectra were obtained on a Bruker DPX300 NMR spectrometer.
Fourier transform infrared spectroscopy (FT-IR) was conducted on a
Perkin-Elmer Spectrum One FT-IR spectrometer equipped with ATR
accessory. High-resolution mass spectroscopy data (HRMS) of the final
products were obtained on a JEOL JMS 700 mass spectrometer.
Thermogravimetric analysis (TGA) was performed in a nitrogen atmo-
sphere on a DuPont TGA 2950 at a heating rate of 10 °C/min. Char
yields were determined by TGA from the mass residue at 850 °C.
Specific heat release rate (HRR, W/g), heat release capacity (HRC,
J/(g K)), and total heat release (THR, kJ/g) were measured by pyrolysis
combustion flow calorimetry (PCFC) on 3ꢀ5 mg samples of cured
resins. PCFC was conducted from 100 to 900 °C at a heating rate of
1 °C/s in an 80 cm3/min stream of nitrogen. The anaerobic thermal
degradation products in the nitrogen gas stream were mixed with a
20 cm3/min stream of oxygen prior to entering the combustion furnace
(900 °C). The heat is determined by standard oxygen consumption
methods. During the test, HRR is obtained by dividing dQ/dt, at each
time interval, by the initial sample mass, and HRC is obtained by dividing
the maximum value of HRR by the heating rate. Three to five sample
runs were conducted for each sample.
4,40-Bishydroxydeoxybenzoin (BHDB). Desoxyanisoin (5.00 g,
19.5 mmol) and pyridine hydrochloride (9.02 g, 78.0 mmol) were added to
a round-bottom flask equipped with a condenser. The mixture was refluxed
for 5 h at 200 °C, cooled to room temperature, and poured into water. The
precipitate was filtered and recrystallized from acetic acid to give 3.8 g (85%
yield) of a pale yellow crystalline solid. 1H NMR (DMSO-d4, 300 MHz,
ppm): 10.35 (s, 1H, HOꢀArꢀCO), 9.28 (s, 1H, HOꢀArꢀCH2), 7.91
(d, 2H, J = 8.7 Hz, ArꢀH), 7.04 (d, 2H, J = 8.5 Hz, ArꢀH), 6.84 (d, 2H, J =
8.7 Hz, ArꢀH), 6.68 (d, 2H, J = 8.5 Hz, ArꢀH), 4.11 (s, 2H,
ArꢀCOꢀCH2ꢀAr). 13C NMR (DMSO-d6, 75 MHz, ppm): 196.5,
162.3, 156.2, 131.3, 130.7, 128.1, 125.9, 115.5, 115.4, 43.7.
Synthesis of BPT-Based Resins and BHDB-Based Epoxy
Resin (DGEBHDB). 1,4-Bis(3-hydroxyphenyl)-1,2,3-triazole (3-BPT),
1,4-bis(4-hydroxyphenyl)-1,2,3-triazole (4-BPT), and diglycidyl ether of
4,40-bishydroxydeoxybenzoin (DGE-BHDB) were prepared by following
the literature procedures.32,41ꢀ43
3-Azidophenol. An aqueous solution (15 mL) of NaNO2 (3.79 g,
54.9 mmol) was added dropwise to 3-aminophenol (5.0 g, 45 mmol) in 2
N HCl (100 mL) at 0ꢀ5 °C. The solution was stirred for 30 min,
followed by addition of an aqueous solution of sodium azide (4.5 g,
69 mmol, in 35 mL of water). The mixture was stirred at room
temperature for 24 h and extracted with 300 mL of ethyl acetate. The
combined organic layer was washed with water and dried over MgSO4.
Solvents were removed by rotary evaporation, and the residue was
purified by column chromatography (EtOAc/hexanes, 1/4) to give the
desired product as a dark red oil (4.52 g, 73% yield). 1H NMR (acetone-
d6, 300 MHz, ppm): 8.69 (s, 1H, ArꢀOH), 7.24 (t, 1H, J = 8.1 Hz,
ArꢀH), 6.70ꢀ6.53 (m, 3H, ArꢀH). 13C NMR (CDCl3, 75 MHz, ppm):
157.2, 141.6, 130.9, 112.4, 111.5, 106.5. FT-IR (cmꢀ1): 3348, 2109.
4-Azidophenol. 4-Azidophenol was prepared similarly to 3-azido-
phenol, using 4-aminophenol (5.0 g) instead of 3-aminophenol. This
Diglycidyl Ether of 4,40-Bishydroxydeoxybenzoin (DGE-
BHDB). Epichlorohydrin (5.0 g, 54 mmol), BHDB (1.24 g, 5.43 mmol),
2-propanol (2.7 g, 4.5 mmol), and water (0.43 mL) were added to a
round-bottom flask and stirred at 65 °C. A 20% aqueous sodium
hydroxide solution (1.95 g) was added dropwise over 45 min, and
stirring was continued for 30 min. The mixture was cooled to room
temperature, and chloroform (50 mL) was added. The organic layer was
washed extensively with water, and the combined organic extract was
dried over magnesium sulfate. Solvents were removed by rotary eva-
poration, and the residue was dissolved in chloroform then precipitated
into hexanes to give 1.48 g (80% yield) of the product as a pale yellow
1
1
solid. H NMR (CDCl3, 300 MHz, ppm): 7.99 (d, 2H, J = 8.8 Hz,
gave 5.27 g (85% yield) of a dark red oil. H NMR (acetone-d6, 300
MHz, ppm): 8.48 (s, 1H, ArꢀOH), 6.94 (m, 4H, ArꢀH). 13C NMR
(MeOD-d4, 75 MHz, ppm): 156.4, 132.4, 121.1, 117.7. FT-IR (cmꢀ1):
3372, 2113, 2072.
ArꢀH), 7.18 (d, 2H, J = 8.4 Hz ArꢀH), 6.91 (d, 2H, J = 8.8 Hz, ArꢀH),
6.88 (d, 2H, J= 8.4 Hz, ArꢀH), 4.32ꢀ4.17 (m, 2H, 2(ꢀOꢀCH2ꢀoxirane)),
4.17 (s, 2H, ArꢀCOꢀCH2ꢀAr), 4.01ꢀ3.92 (m, 2H, 2(ꢀOꢀCH2ꢀ
oxirane)), 3.39ꢀ3.32 (m, 2H, 2(oxirane CH)), 2.94ꢀ2.88 (m, 2H,
2(oxirane CH2)), 2.78ꢀ2.74 (m, 2H, 2(oxirane CH2)). 13C NMR
(CDCl3, 75 MHz, ppm): 196.5, 162.3, 157.4, 130.9, 130.5, 130.0,
127.5, 114.8, 114.4, 68.9, 68.8, 50.2, 49.9, 44.7, 44.6, 44.4. HRMS-EI
m/z [M]þ calcd: 340.1311; found: 340.1293.
3-(2-Trimethylsilylethynyl)phenol (3-TMSE-phenol). To
3-iodophenol (5.0 g, 23 mmol) in 50 mL of toluene were added
PdCl2(PPh3)2 (479 mg, 689 μmol), CuI (432 mg, 2.27 mmol), DIPEA
(4.8 mL, 27 mmol), and ETMS (3.90 mL, 27.3 mmol). The mixture was
stirred at 30 °C for 24 h and then cooled to room temperature. After
filtering, solvents were removed by rotary evaporation. The residue was
purified by column chromatography (EtOAc/hexane, 1/9) to give 4.1 g
Diglycidyl Ether of 1,4-Bis(3-hydroxyphenyl)-1,2,3-tria-
zole (3-DGE-BPT). 3-DGE-BPT was prepared in a similar manner
5698
dx.doi.org/10.1021/ma200767j |Macromolecules 2011, 44, 5693–5700

Macromolecules
ARTICLE
as DGE-BHDB, using 3-BPT (1.00 g, 39.5 mmol) instead of BHDB.
This gave 1.18 g (82% yield) of a yellow amorphous solid. H NMR
(4) Nair, C. P. R.; Mathew, D.; Ninan, K. N. Adv. Polym. Sci. 2001,
155, 1–99.
1
(5) Pham, H. Q.; Marks, M. J. Epoxy Resins. Kirk-Othmer Encyclopedia
of Chemical Technology; Wiley: New York, 2004; Vol. 10, pp 347ꢀ461.
(6) Levchik, S. V.; Weil, E. D. Polym. Int. 2004, 53, 1901–1929.
(7) Guerra, P.; Alaee, M.; Eljarrat, E.; Barcelꢀo, D. In The Handbook of
Environmental Chemistry: Brominated Flame Retardants; Eljarrat, E.,
Barcelꢀo, D., Eds.; Springer: Berlin, 2011; Vol. 16, pp 1ꢀ17.
(8) Blum, A.; Amen, B. N. Science 1977, 195, 17–23.
(9) Gold, M. D.; Blum, A.; Ames, B. N. Science 1978, 200, 785–787.
(10) Fishbein, L. Carcinog. Mutagens Envron. 1985, 5, 75–93.
(11) de Boer, J.; Wester, P. G.; Klamer, H. J. C.; Lewis, W. E.; Boon,
J. P. Nature 1998, 394, 28–29.
(12) Hale, R. C.; La Guardia, M. J.; Harvey, E. P.; Gaylor, M. O.;
Mainor, T. M.; Duff, W. H. Nature 2001, 412, 140–141.
(13) Toxic Flame Retardant Prohibition Act; HR 4076, U.S. House
of Representatives, 18th Congress, 2nd Session, 2004.
(14) Rahman, M.; Brazel, C. S. Prog. Polym. Sci. 2004, 29, 1223–
1248.
(CDCl3, 300 MHz, ppm): 8.19 (s, 1H, triazolꢀH), 7.55ꢀ7.36 (m, 6H,
ArꢀH), 7.05ꢀ6.94 (m, 2H, ArꢀH), 4.41ꢀ4.33 (m, 2H, 2(ꢀOꢀCH2ꢀ
oxirane)), 4.05ꢀ4.01 (m, 2H, 2(ꢀOꢀCH2ꢀoxirane)), 3.42ꢀ3.41
(m, 2H, 2(oxirane CH)), 2.96ꢀ2.95 (m, 2H, 2(oxirane CH2)),
2.82ꢀ2.81 (m, 2H, 2(oxirane CH2)). 13C NMR (CDCl3, 75 MHz,
ppm): 161.1, 160.6, 149.7, 139.6, 133.1, 132.3, 131.7, 120.3, 119.4,
116.8, 114.5, 113.2, 108.6, 70.8, 70.4, 51.7, 51.6, 46.3, 46.2. HRMS-FAB
m/z [M þ H]þ calcd: 366.1454; found: 366.1462.
Diglycidyl Ether of 1,4-Bis(4-hydroxyphenyl)-1,2,3-tria-
zole (4-DGE-BPT). 4-DGE-BPT was prepared in a similar manner
as DGE-BHDB, using 4-BPT (1.00 g, 39.5 mmol) instead of BHDB.
This gave 890 mg (62% yield) of a pale purple solid. 1H NMR (CDCl3,
300 MHz, ppm): 8.06 (s, 1H, triazolꢀH), 7.86 (d, 2H, J = 8.7 Hz,
ArꢀH), 7.72 (d, 2H, J = 9.0 Hz, ArꢀH), 7.11 (d, 2H, J = 9.0 Hz, ArꢀH),
7.05 (d, 2H, J = 8.7 Hz, ArꢀH), 4.38ꢀ4.29 (m, 2H, 2(ꢀOꢀCH2ꢀ
oxirane)), 4.06ꢀ3.99 (m, 2H, 2(ꢀOꢀCH2ꢀoxirane)), 3.42ꢀ3.41
(m, 2H, 2(oxirane CH)), 2.99ꢀ2.95 (m, 2H, 2(oxirane CH2)),
2.84ꢀ2.81 (m, 2H, 2(oxirane CH2)). 13C NMR (CDCl3, 75 MHz,
ppm): 158.7, 158.6, 147.9, 130.9, 127.3, 123.5, 122.3, 117.4, 115.7,
115.2, 69.2, 68.9, 50.3, 50.2, 44.8, 44.7. HRMS-FAB m/z [M þ H]þ
calcd: 366.1454; found: 366.1426.
(15) Gomara, B.; Herrero, L.; Ramos, J. J.; Mateo, J. R.; Fernandez,
M. A.; Garcia, J. F.; Gonzalez, M. J. Environ. Sci. Technol. 2007,
41, 6961–6968.
(16) Blum, A. Science 2007, 18, 194.
(17) An Act to Protect Pregnant Women and Children from Toxic
Chemicals Released into Home; HP 1167, LD 1658, 123rd Maine State
Legislature, 2007.
(18) Toxicological Profile for Decabromodiphenyl Ether (BDE-209)
Integrated Risk Information; U.S. Environmental Protection Agency, 2008.
(19) Toxicological Profile for Pentabromodiphenyl Ether (BDE-99)
Integrated Risk Information; U.S. Environmental Protection Agency,
2008.
Dicyanate Ester of 1,4-Bis(3-hydroxyphenyl)-1,2,3-tria-
zole (3-BPTCE). 1.89 mL of an acetonitrile solution of cyanogen
bromide (1.00 g, 94.8 mmol) was added to 3-BPT (1.00 g, 39.5 mmol) in
60 mL of acetone at 0ꢀ5 °C. After stirring for 20 min, triethylamine
(1.16 mL, 82.9 mmol) was added dropwise at 0ꢀ5 °C. The mixture was
stirred for 1 h and diluted with 200 mL of dichloromethane. The
combined organic mixture was washed with 10% aqueous Na2CO3
solution and water. Solvents in the organic extract were removed by
rotary evaporation, and the precipitate was washed with methanol to
give 1.08 g (90% yield) of the desired product as a pale brown solid.
1H NMR (DMSO-d6, 300 MHz, ppm): 9.36 (s, 1H, triazolꢀH), 8.05
(m, 4H, ArꢀH), 7.88 (m, 1H, ArꢀH), 7.71 (m, 1H, ArꢀH), 7.63ꢀ7.59
(m, 1H, ArꢀH) 7.46ꢀ7.42(m, 1H, ArꢀH). 13C NMR (DMSO-d6, 75
MHz, ppm): 153.5, 153.4, 146.3, 138.2, 133.1, 133.0, 132.2, 124.3, 121.5,
118.7, 116.1, 115.7, 112.2, 108.9, 108.6, 108.1. HRMS-FAB m/z
[M þ H]þ calcd: 304.0834; found: 304.0822.
(20) Communication from the Commission on the Risk Evaluation
and the Risk Reduction Strategies for the Substances; C152, Official
Journal of the European Union, 2008.
(21) Debenst, T.; Gagꢀne, F.; Petit, A.-N.; Kohli, M.; Eullafroy, P.;
Blaise, C. J. Environ. Monit. 2010, 12, 1918–1923.
(22) McCormick, J. M.; Paiva, M. S.; H€aggblom, M. M.; Cooper,
K. R.; White, L. A. Aquat. Toxicol. 2010, 100, 255–262.
(23) de Wit, C. A.; Kierkegaard, A.; Ricklund, N.; Sellstr€om, U. In
The Handbook of Environmental Chemistry: Brominated Flame Retar-
dants; Eljarrat, E., Barcelꢀo, D., Eds.; Springer: Berlin, 2011; Vol. 16,
pp 241ꢀ286.
(24) Bauer, M.; Bauer, J. In Chemistry and Technology of Cyanate
Ester Resins; Hamerton, I., Ed.; Blackie Academic and Professional:
London, 1994; pp 58ꢀ86.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: tsemrick@mail.pse.umass.edu.
(25) Lyon, R. E.; Walters, R. N.; Gandhi, S. Fire Mater. 2006,
30, 89–106.
(26) Fang, T.; Shimp, D. A. Prog. Polym. Sci. 1995, 20, 61–118.
(27) Liu, H.; George, G. A. Polymer 1996, 37, 3675–3682.
(28) Gilchrist, T. L.; Gymer, G. E.; Rees, C. W. J. Chem. Soc., Perkin
Trans. 1 1975, 1–8.
(29) Gilchrist, T. L.; Rees, C. W.; Thomas, C. J. Chem. Soc., Perkin
Trans. 1 1975, 8–11.
(30) Burgess, E. M.; Carithers, R.; McCullagh, L. J. Am. Chem. Soc.
1968, 90, 1923–1924.
(31) Kirmse, W. Eur. J. Org. Chem. 2002, 2193–2256.
(32) Ryu, B.-Y.; Emrick, T. Angew. Chem., Int. Ed. 2010, 49, 9644–9647.
(33) Walters, R. N.; Lyon, R. E. J. Appl. Polym. Sci. 2003,
87, 548–563.
’ ACKNOWLEDGMENT
The authors acknowledge the financial support of the Federal
Aviation Administration (FAA-09-G-013) and the member
companies and organizations of the Center for UMass-Industry
Research on Polymers (CUMIRP) that support antiflammable
polymer research, including Boeing, SABIC, Sekisui, Solvay
Advanced Polymers, and the U.S. Army. Facilities support from
the Materials Research Science and Engineering Center
(MRSEC) (DMR-0820506) is also acknowledged.
(34) Lyon, R. E.; Walters, R. N. J. Anal. Appl. Pyrolysis 2004,
71, 27–46.
(35) Lyon, R. E.; Walters, R. N.; Stoliarov., S. I. J. ASTM Int. 2006, 3
(4), 1–18.
’ REFERENCES
(1) Pilato, L. A.; Michno, J. Advanced Composite Materials; Springer:
Berlin, 1994.
(36) Wilkie, C. A.; Chigwada, G.; Gilman, J. W.; Lyon, R. E. J. Mater.
Chem. 2006, 16, 2023–2030.
(2) Lee, H.; Neville, K. Handbook of Epoxy Resins; McGraw-Hill:
New York, 1967.
(3) McAdams, L. V.; Gannon, J. A. Epoxy Resins. Encyclopedia
of Polymer Science and Engineering, 2nd ed.; Wiley: New York, 1986;
pp 322ꢀ382.
(37) Standard Test Method for Determining Flammability Char-
acteristics of Plastics and Other Solid Materials Using Microscale
Combustion Calorimetry; ASTM D7309-07.
5699
dx.doi.org/10.1021/ma200767j |Macromolecules 2011, 44, 5693–5700

Macromolecules
ARTICLE
(38) Rozenberg, B. A. Adv. Polym. Sci. 1986, 75, 146–156.
(39) Ricciardi, F.; Romanchick, W. A.; Joullie, M. M. J. Polym. Sci.,
Polym. Chem. Ed. 1983, 21, 1475–1490.
(40) Heise, M. S.; Martin, G. C. Macromolecules 1989, 22, 99–104.
(41) Ryu, B.-Y.; Moon, S.; Kosif, I.; Ranganathan, T.; Farris, R. J.;
Emrick, T. Polymer 2009, 50, 767–774.
(42) Ellzey, K. A.; Ranganathan, T.; Zilberman, J.; Coughlin, E. B.;
Farris, R. J.; Emrick, T. Macromolecules 2006, 39, 3553–3558.
(43) Ranganathan, T.; Zilberman, J.; Farris, R. J.; Coughlin, E. B.;
Emrick, T. Macromolecules 2006, 39, 5974–5975.
(44) Wallace, M.; Craig, Jr. Bis(4-cyanatophenyl)-1,1-ethane.
US Pat. 5,162,574, 1992.
(45) Hergenrother, P. M.; Thompson, C. M.; Smith, J. G., Jr.;
Connell, J. W.; Hinkley, J. A.; Lyon, R. E.; Moulton, R. Polymer 2005,
46, 5012–5024.
5700
dx.doi.org/10.1021/ma200767j |Macromolecules 2011, 44, 5693–5700