Preparation of phosphinated bisphenol from acid-fragmentation of 1,1,1-tris(4-hydroxyphenyl)ethane and its application in high-performance cyanate esters

Article abstract of DOI:10.1002/pola.24936

We reveal a route for the preparation of phosphinated bisphenol, 1,1-bis(4-hydroxyphenyl)-1-(6-oxido-6H-dibenz <1,2> oxaphosphorin-6-yl)ethane (2), via a one-pot reaction of 1,1,1-tris(4- hydroxyphenyl)ethane and 9,10-dihydro-9-oxa-10-phosphaphenant

Full text of DOI:10.1002/pola.24936

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ARTICLE
Preparation of Phosphinated Bisphenol from Acid-Fragmentation
of 1,1,1-Tris(4-hydroxyphenyl)ethane and Its Application in
High-Performance Cyanate Esters
Ching Hsuan Lin,1 Hung Tse Lin,1 Yu Wei Tian,1 Shenghong A. Dai,1 Wen Chiung Su2
1Department of Chemical Engineering, National Chung Hsing University, Taichung, Taiwan
2Department of Chemistry and Chemical Engineering, Chung Shan Institute and Technology, Lungtan, Tauyuan, Taiwan
Correspondence to: C. H. Lin (E-mail: linch@nchu.edu.tw)
Received 8 June 2011; accepted 6 August 2011; published online 7 September 2011
DOI: 10.1002/pola.24936
ABSTRACT: We reveal a route for the preparation of phosphi-
nated bisphenol, 1,1-bis(4-hydroxyphenyl)-1-(6-oxido-6H-dibenz
<c,e> <1,2> oxaphosphorin-6-yl)ethane (2), via a one-pot reac-
tion of 1,1,1-tris(4-hydroxyphenyl)ethane and 9,10-dihydro-9-
oxa-10-phosphaphenanthrene 10-oxide (DOPO) in the catalysis
bisphenol A (BACY). Experimental data show that incorporat-
ing (3) into BACY enhances the flame retardancy and dielectric
properties with little penalty to the thermal properties. A ther-
moset with Tg 274 ꢀC, coefficient of thermal expansion (CTE)
49 ppm/ꢀC, Dk 3.04 (1 GHz), Td (5%,) N2: 435 ꢀC, air: 424 ꢀC, and
C
V
of p-toluenesulfonic acid.
A
two-step reaction mechanism,
UL-94 V-0 rating can be achieved via this approach.
2011
acid-fragmentation of 1,1,1-tris(4-hydroxyphenyl)ethane fol-
lowed by nucleophilic addition of DOPO, is proposed for the
synthesis. Based on (2), a dicyanate ester derivative, 1,1-bis(4-
cyanatophenyl)-1-(6-oxido-6H-dibenz <c,e> <1,2> oxaphos-
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:
4851–4860, 2011
KEYWORDS: cyanate ester; dielectric constant; DOPO; fragmen-
tation of trisphenol; flame retardancy; flame retardant; synthe-
sis; thermosets
phorin-6-yl)ethane (3) was prepared and co-cured with
a
commercially available dicyanate ester, the dicyanate ester of
INTRODUCTION Cyanate esters have received considerable
attention because of their exceptional properties, such as
good thermal stability, low water absorption, and low dielec-
tric properties. They have been found to be particularly useful
in the preparation of electrical and structural laminates, pot-
ting formulations, molding formulations, and so forth. Dicya-
nate esters are generally prepared by the reaction of bisphe-
nol and cyanogen bromide in the presence of triethylamine at
low temperature. The cyanate group undergoes trimerization
to form the s-triazine ring and generates a thermoset with
high cross-linking density. A large variety of cyanate esters
with different backbone structures and properties have been
synthesized and are summarized by Shimp and coworker1
and Lin and Pearce,2 respectively. Over the past decade, many
new cyanate esters were developed. For example, Guenthner
et al. prepared a silicon-containing dicyanate ester in which
isopropylidene of dicyanate ester of bisphenol A (BACY) is
replaced by a quaternary silicon.3 The silane-based poly(cya-
nate ester) exhibits improved thermal oxidation and moisture
resistance. Snow and coworkers prepared oligodimethylsilox-
anes linked cyanate esters with low dielectric characteristic.4
Davis and coworkers used racemic/diastereomeric concept to
prepare a liquid-type tricyanate ester for favorable processing
characteristic and enhanced thermomechanical performance
in wet environments.5 Wang and coworkers prepared phenol-
phthalein-based cyanate esters with high-Tg for higher temper-
ature applications.6 Snow and Buckley prepared fluoromethy-
lene cyanate ester with lower Tg, dielectric constant, critical
surface tension, and water absorption.7 Lin et al. prepared a
dipentene-containing cyanate ester with low moisture absorp-
tions and low dielectric properties due to the hydrophobic
character of the aliphatic dipentene structure.8 Although pol-
y(cyanate esters) display promising properties, the lack of
flame retardancy is a drawback of cyanate ester for electronic
applications, where meeting a flame retardancy standard, UL-
94 V-0, is required. Literatures have reported that the flame
retardancy of cyanate esters can be greatly enhanced by the
incorporation of phosphorus element.5,9–18
It has been reported that bisphenol A undergoes acid- or
base-catalyzed fragmentation to phenol and 4-isopropenyl-
phenol.19–21 According to the fragmentation chemistry of
bisphenol
A and our knowledge in conjugate addition
chemistry of 9,10-dihydro-9-oxa-10-phosphaphenanthrene
10-oxide (DOPO),22,23 we speculated that DOPO might react
with the resulting 4-isopropenylphenol via a conjugate addi-
tion. To prove our speculation, we reacted the bisphenol A
Additional Supporting Information may be found in the online version of this article.
C
V
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and DOPO in the catalysis p-toluenesulfonic acid (p-TSA) as
a model reaction. A model compound, phosphinate monophe-
nol (1), was successfully prepared. On the basis of successful
model reaction, we prepared a phosphinated bisphenol (2)
via a one-pot reaction of 1,1,1-tris(4-hydroxyphenyl)ethane
and DOPO in the catalysis of p-TSA. Then a dicyanate ester
derivative (3) was prepared from (2) and co-cured with
BACY to enhance the flame retardancy. Thermal properties,
dielectric properties, and flame retardancy of these co-ther-
mosets were evaluated and discussed. The successful prepa-
ration of (1–2) via the combination of nucleophilic addition
of DOPO and acid-fragmentation of bisphenol A or 1,1,1-
tris(4-hydroxyphenyl)ethane expands the chemistry of DOPO.
Detailed synthesis, characterization, and proposed mecha-
nisms were reported in this work.
recorded. Five specimens were measured, and the average
burning time was recorded. If t1 plus t2 is less than 10 s with
no dripping, it is considered to be a V-0 grade, an industrial
standard for flame retardancy. If t1 plus t2 is in the range of
10–30 s without any dripping, the polymer is considered to
be a V-1 material. If t1 plus t2 is in the range of 10–30 s with
dripping that ignites a cotton indicator located below the sam-
ple, the polymer is considered to be a V-2 material. Dielectric
measurements were performed with an Agilent E4991A mea-
surement system at a temperature of 20 ꢀC in an air atmos-
phere by the two parallel plate modes at 1 GHz. The applied
voltage was 1 V. Before testing, samples (1 cm ꢁ1 cm and 0.2
ꢀ
cm thickness) were dried under vacuum at 120 C for 3 h.
Synthesis of Monophenol (1)
To a 100-mL round-bottom flask equipped with a nitrogen
inlet and magnetic stirrer, 4.38 mmol (1.00 g) of bisphenol
A, 4.7345 g (21.9 mmol) of DOPO, and 0.1894 g (4% based
on DOPO) of p-TSA were added. The reaction mixture was
EXPERIMENTAL
Materials
ꢀ
DOPO was purchased from TCI (Tokyo Chemical Industry
Co., Ltd.). BACY, B-10, was kindly supplied by Rhone-Pou-
lence. Bisphenol A, p-TSA, and 1,1,1-tris(4-hydroxyphenyl)-
ethane were purchased from Acros. All solvents used are
commercial products (High-performance liquid chromatogra-
phy (HPLC) grade) and used without further purification.
gradually heated to 130 C and maintained at that tempera-
ture for 12 h. After the reaction was complete, the product
was crushed to powder and poured into ethanol to remove
excess DOPO. 1.228 g of white powder (80% yield) with a
ꢀ
melting point of 244 C (DSC) was obtained.
High-resolution mass spectrometry (HR-MS) fast atomic bom-
bardment (FABþ) m/z: calcd. for C21H19O3P 350.1072; anal.,
Characterization
351.1016 [Mþ1]þ C21, H20, O3, P. 1H NMR (DMSO-d6), d ¼
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 or air atmosphere. Dynamic mechanical
analysis (DMA) was performed with a Perkin-Elmer Pyris Dia-
mond 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 temperature scan mode at a pro-
grammed heating rate of 5 ꢀC/min at a frequency of 1 Hz.
The test was performed by a bending mode with an ampli-
tude of 5 lm. Thermal mechanical analysis (TMA) was per-
formed with a Perkin-Elmer Pyris Diamond TMA at a heating
rate of 5 ꢀC/min. NMR measurements were performed using
a Varian Inova 600 NMR in Dimethyl Sulfoxide (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 powder
form. High resolution mass spectra were obtained by a Finni-
gan/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 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 would be noted if polymer drip-
ping occurred during the test. After cooling, the second igni-
tion was performed on the same sample. The self-extinguish-
ing time (t2) and dripping characteristics were again
0
1.36–1.48 (6H, H6, H6 ), 6.54 (2H, H2), 6.98 (2H, H3), 7.21
(2H, H15, and H17), 7.30 (1H, H11), 7.40 (1H, H16), 7.45 (1H,
H10), 7.71 (1H, H9), 8.00 (1H, H14), 8.11 (1H, H8), 9.31 ( 1H,
0
OH). 13C NMR (DMSO-d6), d ¼ 21.88–23.01 (C6, C6 ), 41.38–
41.98 (C5), 114.43 (C2), 119.14 (C17), 121.02 (C12), 121.26
and 121.98 (C7), 123.46 (C8), 123.93 (C15), 125.32 (C14),
127.03 (C10), 128.75 (C3), 129.28 (C13), 130.64 (C16),131.63
(C11), 133.46 (C9), 136.07 (C4), 150.72 (C18), 156.13 (C1).
Synthesis of Bisphenol (2)
To a 100-mL round-bottom flask equipped with a nitrogen
inlet and magnetic stirrer, 32.6 mmol (10 g) of 1,1,1-tris(4-
hydroxyphenyl)ethane, 163 mmol (35.2 g) of DOPO, and 1.41
g (4% based on DOPO) of p-TSA were ꢀadded. The reaction
mixture was gradually increased to 130 C and maintained at
that temperature for 12 h. After the reaction was complete,
the product was crushed to powder and poured into ethanol
to remove excess DOPO. About 12.03 g of white powder (86%
yield) with a melting point of 298 ꢀC (DSC) was obtained.
HR-MS (FABþ) m/z: calcd. for C26H21O4P 428.1177; anal.,
429.1266 [Mþ1]þ C26, H22, O4, P. 1H NMR (DMSO-d6), d ¼
0
1.58 (3H, H6), 6.59 (2H, H2), 6.61 (2H, H2 ), 7.09–7.22 (7H, H3,
0
H17, H11, H15, H3 ), 7.33–7.36 (2H, H16, H10), 7.67 (1H, H9),
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TABLE 1 Thermal Properties of P0–P2 and P(3)
Td5% (ꢀC)e
Char Yieldf
P
Tan d
(ꢀC)a
Tg (ꢀC)
(DSC)b
Tg (ꢀC)
(TMA)c
CTE
(ppm/ꢀC)d
Thermoset
(wt %)
N2
air
N2
air
P0
0
279
278
276
275
275
274
268
276
278
277
275
275
273
263
266
240
237
237
236
235
226
e
57
53
53
55
54
49
53
455
441
437
438
438
435
426
454
444
445
433
428
424
417
41
40
40
39
39
40
48
20
23
27
27
28
32
41
P0.75
P1
0.75
1.00
1.25
1.50
2.00
6.48
P1.25
P1.5
P2
P(3)
a
Measured by DMA at a heating rate of 5 ꢀC/min.
Temperature corresponding to 5% weight loss by TGA at a
heating rate of 20 ꢀC/min.
Residual wt % at 800 ꢀC.
b
Measured by the second DSC heating scan at a heating rate
f
of 20 ꢀC/min.
c
Measured by TMA at a heating rate of 5 ꢀC/min.
d
Coefficient of thermal expansion are recorded from 100 to
200 ꢀC.
7.98 (1H, H14), 8.08 (1H, H8), 9.35 (2H, OH). 130C NMR (DMSO-
filtration. After the precipitate was dried, 4.9 g (85% yield)
of white powder was obtained. Then the yellow powder was
recrystallized from hexane/Acetonitrile (ACN) and then dried
d6), d ¼ 24.22 (C6), 51.48 (C5), 114.51 (C2 ), 114.73 (C2),
119.02 (C11), 120.83 (C12), 121.98 (C7), 123.33 (C8), 123.94
0
(C15), 125.34 (C14), 127.83 (C16), 129.51 (C3 ), 130.60 (C3,10),
in a vacuum oven at 100 C. Light ꢀwhite powder (3.4 g, 70%
ꢀ
131.87 (C17), 132.93 (C13), 133.36 (C9), 136.04 (C4), 136.22
yield) with a melting point of 158 C (DSC) was obtained.
0
0
(C4 ), 150.75 (C18), 155.86 (C1 ), 156.33 (C1).
R-MS (FAB) m/z: calcd. for C28H19O4N2P 478.1082; anal.,
479.1178 for C28, H20, O4, N2, P [Mþ1]þ. FTIR (KBr): 920
cmꢂ1 (PAOAPh), 1203 cmꢂ1 (P¼¼O), 2267 cmꢂ1, and 2235
cmꢂ1 (cyanate stretch). 1H NMR (ppm, DMSO-d6), d ¼ 1.76–
1.79 (3H, H6), 7.14 (1H, H18), 7.15 (1H, H16), 7.28–7.30 (4H, H3,
0
0
and H3 ), 7.34 (1H, H17), 7.36 (1H, H12), 7.43 (2H, H4 ), 7.46 (1H,
H11), 7.52 (2H, H4), 7.75 (1H, H10),7.92 (1H, H15), 8.09 (1H, H9).
13C NMR (ppm, DMSO-d6), d ¼ 23.96 (C6), 52.45 and 53.05
0
0
(C7), 108.41 (C1,1 ), 115.10 (C3), 115.28 (C3 ), 119.06 (C18),
120.22 and 120.99 (C8), 120.62 (C13), 123.60 (C9), 124.17 (C16),
125.33 (C15), 128.40 (C11), 130.78 (C12), 131.03 (C4), 131.94
0
0
(C4 ), 132.05 (C17), 134.17 (C10), 136.43 (C14), 138.32 (C5 ),
0
140.95 (C5), 150.80 (C19), 151.13 (C2 ), 151.54 (C2).
Synthesis of (3)
To a 100-mL round-bottom flask equipped with a nitrogen
inlet and magnetic stirrer, 20 mL dry DMAc was added. The
reaction mixture was gradually cooled to ꢂ15 ꢀC, and then
30 mmol (3.17 g) of BrCN was added. A mixture containing
12 mmol (5.14 g) of (2), 30 mmol (3.09 g) of triethylamine,
and 20 mL of dry DMAc was added gradually in 2 h. The
mixture was kept at that temperature for another 2 h. After
the reaction was complete, the white Et3NꢃHBr salt was fil-
tered. The filtrate solution was then poured into water (500
mL) with stirring, yielding a precipitate that was isolated by
SCHEME 1 One-pot synthesis of phosphinated monophenol (1). [Color figure can be viewed in the online issue, which is available
at wileyonlinelibrary.com.]
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SCHEME 2 Proposed reaction mechanism for the synthesis of (1). According to 1H and 13C NMR data, path A is the only reaction
route of this reaction.
FIGURE 1 (a) 1H and (b) 13C NMR spectra of (1).
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SCHEME 3 One-pot synthesis of phosphinated bisphenol (2). [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
SCHEME 4 Proposed reaction mechanism for the synthesis of (2). [Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
RESULTS AND DISCUSSION
Curing Procedure
(3)/BACY with various ratios (the phosphorus content was
Synthesis of Monomer
controlled from 0.75 to 2 wt %) were mixed well in a hot
By combining the acid-fragmentation of bisphenol A19–21 and
plateꢀ at 160 ꢀC. The mixtures were cured at 180 ꢀC for 4 h,
conjugate addition of DOPO,22–24 we prepared a model
ꢀ
ꢀ
200 C for 4 h, 220 C for 4 h, and 240 C for 4 h. After that,
samples were allowed to cool slowly to room temperature to
prevent cracking. The relation between sample ID and the con-
tent of phosphorus was listed in Table 1. The number after P is
the phosphorus content in the co-thermoset. Therefore, P0
means neat BACY thermoset, while P1.25 means the (3)/BACY
thermoset with a phosphorus content of 1.25 wt %, and P2
means (3)/BACY thermoset with a phosphorus content of 2 wt
%. The homopolymer of (3) is named as P(3).
compound, phosphinated monophenol (1), from a one-pot
reaction of DOPO and bisphenol A in the catalysis of p-TSA
(Scheme 1).
A reaction mechanism for the synthesis is proposed in
Scheme 2. In that mechanism, Compound 1(b), generated
from the acid-fragmentation of bisphenol A, reacted with
DOPO via a conjugate addition. According to the addition
position, two possible addition paths might occur. Path A is
SCHEME 5 Synthesis of dicyanate ester (3). [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
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FIGURE 2 (a) 1H and (b) 13C NMR spectra of (3).
the same mechanism as that for DOPO and rosolic acid,22
whereas path B is the same mechanism as that for DOPO
and benzoquinone.23,24
Figure 1(b) shows 1H NMR spectrum of (1). For carbon C5
1
and C7, due to JPAC coupling, the peak is split into doublets
with a coupling constant of 90 (JPAC5) and 121 Hz (JPAC7),
respectively. The patterns ArAC also support the structure of
(1). These spectroscopic data remind us that path A is the
only addition route. In addition, literature has reported that
4-isopropenylphenol is unstable and tends to dimerize to
dimmer.19–21 In this case, the resulting 4-isopropynylphenol
reacted with DOPO quickly, so no 4-isopropenylphenol
dimmer was detected in the product.
If path B is the reaction route, signals corresponding to CH3
and CH should be observed, respectively. However, according
1
to the H NMR spectrum of the product shown in Figure 1(a),
only two doublets corresponding to methyl groups (H6 and
0
H6 ) are observed at 1.4 ppm. The splitting of methyl peak is
3
due to the JPAH coupling, and the coupling constant is 16.2
Hz. The assignment of each ArAH is detailed in Figure 1(a).
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FIGURE 3 DSC thermograms of (2), (3), and (BACY). [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
On the basis of this success of the model reaction, we then
prepared a phosphinated bisphenol (2) from a one-pot reac-
tion of DOPO and 1,1,1-tris(4-hydroxyphenyl)ethane in the
catalysis of p-TSA (Scheme 3).
A similar reaction mechanism is proposed in Scheme 4. In
that mechanism, Compound 2(b), generated from the acid-
fragmentation of 1,1,1-tris(4-hydroxyphenyl)ethane, reacted
with DOPO via a conjugate addition. The structure of (2)
FIGURE 4 (a) DSC, (b) DMA, (c) TMA, and (d) TGA thermograms of P(3).
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Thermal Properties of Homopolymer
Figure 4(a) shows theꢀDSC thermogram of P(3) homopoly-
mer. A Tg value of 263 C was observed for P(3). Figure 4(b)
shows the DMA thermogram of P(3). A Tg value of 268 ꢀC
was obtained from the peak temperature of tan d. TMA mea-
surement shows P(3) exhibits a Tg value of 226 ꢀC, and a
coefficient of thermal expansion of 53 ppm/ꢀC [Fig. 4(c)].
TGA measurement shows the 5% decomposition tempera-
ture of P(3) is 426 (in N2) and 4ꢀ17 ꢀC (in air), respectively
[Fig. 4(d)]. The char yield at 800 C is 48 (in N2) and 41 wt
% (in air), respectively. DSC, DMA, TMA, and TGA data dem-
onstrate P(3) exhibits high Tg and moderate to high thermal
stability.
Thermal Properties of Copolymer
Figure 5 shows the DMA thermograms of BACY homopoly-
mer (P0) and (3)/BACY copolymers (P0.75–P2). The
detailed results are presented in Table 1. DMA thermograms
of (3)/BACY co-thermosets are almost the same as those of
P0, suggesting very little penalty to the Tg value after incor-
poration of the bulky phosphinate pendant. Theoretically, a
bulky pendant that separates the polymer chains should lead
to loose networks of thermosets. Therefore, it is thought that
the effect of restricted segmental mobility, caused by the po-
lar P¼¼O bond and the rigid biphenylene phosphinate pend-
ant, compensates for the loss of crosslinking density, and
maintains high Tg.
FIGURE 5 DMA thermograms of P0–P2. [Color figure can
be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
was confirmed by the 1H, 13C, and 31P NMR spectra
(Supporting Information Fig. S1). Although bisphenol (2)
has been prepared by a different procedure in our previ-
ous article,25 the strategy revealed in the work expands
the chemistry of DOPO. On the basis of this strategy, prep-
aration of multifunctional phosphinated phenols is in
progress.
Phosphinated dicyanate ester (3) was prepared from the
reaction of cyanogen bromide and (2) in the presence of
triethylamine at low temperature (Scheme 5). There are two
common side reactions in the preparation of cyanate ester.26
The first is the formation of imidocarbonate when the phe-
nol group is excess, and the second is the formation of dieth-
ylcyanamide when the reaction temperature is higher than
The thermal dimensional stability of all thermosets was
measured by TMA. The results are detailed in Table 1. Figure
6 shows the TMA curve of P2 and P0. Although no reduction
in Tg is observed in DMA measurement, a small decrease in
Tg is observed in the TMA measurement. Tgs defined by the
onset of the TMA curve are 266 and 235 ꢀC for P0 and P2
and CTEs are 57 and 49 ppm, respectively. The CTE data
demonstrate better dimensional stability of co-thermosets.
The restricted segmental mobility caused by the bulky phos-
phinate pendant might be responsible for the improved CTE
values.
0
ꢀC. To prevent side reactions, bisphenol and triethylamine
were added dropwise into the cyanogen bromide/DMAc so-
ꢀ
lution, and the temperature is maintained at about ꢂ15 C.
Figure 2(a) shows the 1H NMR spectrum of (3). The disap-
pearance of phenolic OH suggests the transformation of phe-
nolic groups of (2). The assignment of each ArAH is detailed
in Figure 2(a) to confirm the structure and purity. Figure
2(b) shows the 13C NMR spectrum of (3). The characteristic
signals of cyanate ester appear at d ¼ 108.4 ppm. The
detailed assignment of each ArAC is detailed in Figure 2b to
confirm the structure and purity.
Figure 3 shows the DSC thermograms of (2), (3), and BACY.
Because of the disappearance of intermolecular hydrogen
bonding induced by the phenolic groups, the melting point
of (3) is much lower than that of (2). An exothermic peak
corresponding to trimerization of cyanate esters starts at
around 240 ꢀC. The exothermic peak temperature is 305 ꢀC
with an exothermic enthalpy of 481 J/g. The wide tempera-
ture difference between melting point and exothermic peak
temperature demonstrates a reasonable processing window.
As shown in Figure 3, the melting points of (3) and BACY
are 158 and 80 ꢀC, respectively, ꢀsuggesting they can easily
be blended on a hot plate at 160 C, and mixed well.
FIGURE 6 TMA curve of P0 and P2. [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.
com.]
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FIGURE 7 TGA curves of P0–P2 in (a) N2 and (b) air atmosphere. [Color figure can be viewed in the online issue, which is available
at wileyonlinelibrary.com.]
Figure 7 shows the TGA thermograms of P0–P2, and the
results are detailed in Table 1. In an N2 atmosphere, the 5%
degradation temperatures are 455ꢀ and 435 ꢀC for P0 and
P2, respectively. The value of 435 C is relatively high when
compared with that of other phosphorus-containing poly-
mers. The PAC chain has a lower bonding energy, so the ini-
tial degradation of the polymer occurs at that chain. In our
previous studies,25,27,28 we reported that the thermal stabil-
ity of phosphorus-containing thermosets is related to the
electron density of the carbon adjacent to the phosphorus
(C7, in this case). The lower the electron density of the car-
bon is, the lower its thermal stability. In this case, the methyl
group, an electron-donating group, increases the electron
density of C7, increasing the thermal stability of the PAC
bond. As listed in Table 1, high thermal stability (Td5) and
improved char yield of (3)/BACY thermosets are also
observed in an air atmosphere.
lyzer, and the results are in Table 2. The dielectric constant
at 1 GHz decreases from 3.14 for P0 to 3.04 for P2.
Hougham et al. reported that the dielectric constant can be
reduced by increasing molecule’s hydrophobicity and free
volume, and by decreasing polarization.26,29,30 Therefore, it is
thought that the increased free volume due to the bulky
phosphinate pendant might be responsible for the reduced
dielectric constant.
CONCLUSIONS
By combining the acid-fragmentation of bisphenol19–21 and
conjugate addition of DOPO,22–24 we first report the synthesis
of a phosphinated bisphenol (2) from a one-pot reaction of
DOPO and 1,1,1-tris(4-hydroxyphenyl) ethane in the catalysis
of p-TSA. A two-step mechanism, an acid-fragmentation of
1,1,1-tris(4-hydroxyphenyl)ethane followed by nucleophilic
addition of DOPO is proposed. On the basis of this strategy,
preparation of multifunctional phosphinated phenols is in pro-
gress. Experimental data show that incorporating phosphi-
nated dicyanate ester (3) into BACY enhances the flame retard-
ancy and reduces dielectric properties with little penalty to the
thermal properties. The combination of high Tg, good thermal
stability, low dielectric, and high flame retardancy makes (3)/
BACY co-thermosets attractive in electronic applications like
high-performance, halogen-free printed circuit boards.
Table 2 also lists the UL-94 data for BACY and (3)/BACY co-
thermosets. Neat BACY thermoset belongs to burning grade,
whereas phosphinated thermosets can reach V-0 grade if the
phosphorus content is higher than 1.50 wt %. This result shows
the good flame retardancy of the phosphinated cyanate esters.
Dielectric Properties
The dielectric constant and dissipation factor of P0–P2 were
measured by an Agilent E4991A RF Impedance Material Ana-
TABLE 2 Dielectric Properties and UL-94 Data for P0–P2
First Burning
Time (s)a
Second Burning
Time (s)a
a
Thermoset
Dk
Dfb
Dripping
UL-94 Grade
P0
3.14 6 0.005
3.13 6 0.003
3.08 6 0.003
3.06 6 0.004
3.05 6 0.003
3.04 6 0.004
4.52 6 0.05
4.59 6 0.01
4.75 6 0.15
4.65 6 0.15
4.65 6 0.05
4.40 6 0.11
>60
–
No
No
No
No
No
No
Burning
Burning
Burning
V-1
P0.75
P1
49.6
40.6
23.3
8.5
–
0.1
3.1
1.4
1.2
P1.25
P1.5
P2
V-0
4.6
V-0
a
b
Dielectric constant at 1 GHz at room temperature.
Dissipation factor at 1 GHz at room temperature.
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13 Yagci, Y.; Kiskan, B.; Ghosh, N. N. J Polym Sci Part A:
Polym Chem 2009, 47, 5565–5576.
The authors thank the National Science Council of the Republic
of China for financial support. Partially sponsorship by the
Green Chemistry Project (NCHU), as funded by the Ministry of
Education is also gratefully acknowledged.
14 Espinosa, L. M. D.; Ronda, J. C.; Galia`, M.; Ca´diz, V.; Meier,
M. A. R. J Polym Sci Part A: Polym Chem 2009, 47, 5760–5771.
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16 Bian, X. C.; Chen, L.; Wang, J. S.; Wang, Y. Z. J Polym Sci
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