Preparation and properties of novel cyclophosphazenes containing cyanato groups

Article abstract of DOI:10.1080/10426507.2012.710677

Novel cyclotriphosphazenes containing cyanato group (PZCN) derivatives were synthesized by a substitution reaction of 4-hydroxyphenoxycyclotriphosphazenes and cyanogen bromide (BrCN) in the presence of triethylamine (TEA). The PZCNs were characterized by FT-IR, liquid chromatography-mass spectrometry (LC-MS), ¹H NMR, ¹³C NMR, and ³¹P NMR spectroscopy. Curing reactions of the PZCNs were evaluated by FT-IR spectroscopy, thermogravimetry/differential thermal analysis (TG/DTA), and differential scanning, calorimetry (DSC). The PZCNs exhibited an exothermic peak due to curing within the temperature range of 140-300C by DSC. The PZCNs were completely cured at 220C. The cured PZCNs exhibited high thermal stability up to 350C, a high char-forming capability, and electrical properties, such as dielectric constants (Dks) between 2.68 and 2.87, and dissipation factors (Dfs) between 0.008 and 0.013 at 1MHz. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426507.2012.710677

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Preparation and Properties of Novel
Cyclophosphazenes Containing Cyanato
Groups
Yuji Tada a , Narimasa Moriya a , Takashi Inoue a , Atsuko Suzuki a &
Shigeto Koyama a
a Research and Development Department , Fushimi Pharmaceutical
Co., Ltd. , Marugame , Japan
Accepted author version posted online: 17 Jul 2012.Published
online: 10 Sep 2012.
To cite this article: Yuji Tada , Narimasa Moriya , Takashi Inoue , Atsuko Suzuki & Shigeto
Koyama (2012) Preparation and Properties of Novel Cyclophosphazenes Containing Cyanato
Groups, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:12, 1555-1567, DOI:
10.1080/10426507.2012.710677
To link to this article: http://dx.doi.org/10.1080/10426507.2012.710677
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Phosphorus, Sulfur, and Silicon, 187:1555–1567, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.710677
PREPARATION AND PROPERTIES OF NOVEL
CYCLOPHOSPHAZENES CONTAINING CYANATO GROUPS
Yuji Tada, Narimasa Moriya, Takashi Inoue, Atsuko Suzuki,
and Shigeto Koyama
Research and Development Department, Fushimi Pharmaceutical Co., Ltd.,
Marugame, Japan
GRAPHICAL ABSTRACT
NCO
OCN
NCO
O
O
O O
P
P
N
N
N
N
P
O
O
P
O
O
OCN
O
O
P
P
O
O
OCN
NCO
N
N
O
∆
O
O
∆
OCN
NCO
NCO
PZCN (IV)
PZCN (VII)
O
O
O
O
N
N
N
N
N
P
P
N
O
O
O
P
P
O
O
N
N
N
P
N
N
N
N
O
O
P
O
O
O
N
O
O
N
O
O
O
O
O
O
O
O
O
N
O
P
P
N
N
P
N
N
P
N
N
N
N
N
N
N
N
N
O
O
P
O
O
N
O
N
O
O
O
P
O
O
O
N
N
O
O
O
O
O
O
O
O
O
N
P
P
N
N
P
N
N
N
P
N
P
N
O
O
O
P
O
O
O
O
O
O
N
O
O
N
N
N
Cured PZCN (VII)
Cured PZCN (IV)
O
O
O
Abstract Novel cyclotriphosphazenes containing cyanato group (PZCN) derivatives
were synthesized by substitution reaction of 4-hydroxyphenoxycyclotriphosphazenes
a
and cyanogen bromide (BrCN) in the presence of triethylamine (TEA). The PZCNs were
characterized by FT-IR, liquid chromatography–mass spectrometry (LC-MS), 1H NMR,
13C NMR, and 31P NMR spectroscopy. Curing reactions of the PZCNs were evaluated
by FT-IR spectroscopy, thermogravimetry/differential thermal analysis (TG/DTA), and
differential scanning, calorimetry (DSC). The PZCNs exhibited an exothermic peak due to
curing within the temperature range of 140–300◦C by DSC. The PZCNs were completely
cured at 220◦C. The cured PZCNs exhibited high thermal stability up to 350◦C, a high
char-forming capability, and electrical properties, such as dielectric constants (Dks)
between 2.68 and 2.87, and dissipation factors (Dfs) between 0.008 and 0.013 at 1 MHz.
Received 8 May 2012; accepted 6 July 2012.
The authors would like to thank Ms. Tomoko WATO for TGA and DSC measurements and Kagawa
Prefectural Industrial Technology Research Center for the use of their LCR meter.
Address correspondence to Yuji Tada, Research and Development Department, Fushimi Pharmaceutical
Co., Ltd., Marugame, Japan. E-mail: ytada@fushimi.co.jp
1555

1556
Y. TADA ET AL.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords Cyclophosphazenes; cyanates; dielectric properties; thermal properties
INTRODUCTION
Cyanate resins (CRs) are a category of thermoset resins in which cyanate ester
monomers polymerize by a cyclotrimerization reaction to a cyanurate (often referred to as
an s-triazine)-linked network polymer. The CRs have attracted commercial and scientific
interest due to their thermal, mechanical, and processing properties, especially their di-
electric properties, such as the dielectric constant (Dk) and the dissipation factor (Df). The
CRs have been applied to products ranging from composites for aerospace to insulating
materials for electronics.1–6
In particular, CR applications in reinforced circuit boards and in the thin-film insula-
tion of high-density interconnect devices, termed multi-chip modules (MCMs), are driven
by the benefits of faster operating speeds, smaller sizes, reduced crosstalk, reduced power
requirements, and reduced heat production (inversely related to the square root of the Dk).
Lower Dfs are known to proportionally reduce power loss and heat production.1
Phosphazenes have been investigated as forms of cyclic monomers or linear polymers
over wide ranges. Many phosphazene derivatives with reactive functional groups (e.g.,
amino, hydroxyl, glycidyl, isocyanato, vinyl, etc.) or without reactive functional groups have
been prepared and evaluated in the literature.7–9 It is well known that phenoxyphosphazenes,
without reactive functional groups, exhibit high resistances to hydrolysis, high thermal
stability, and high flame retardancy as an alternative halogen-free flame retardant.10,11
Phenoxyphosphazene derivatives are proposed as candidates for applications as additives,
coatings, adhesives, composites, and electronic materials.
Mathew et al.12 reported hydroxyphenyl-substituted cyclotriphosphazenes prepared
from hexachlorocyclotriphosphazene with phenol and bisphenol-A. These cyclotriphosp-
hazenes were converted to their corresponding cyanate-functional compounds for applica-
tions in stringent fire resistance norms, such as in aircraft interiors and in the transporta-
tion industry. However, the phenol-functionalized cyclotriphosphazenes possess multiply
linked structures because bisphenol-A, having bi-functionality, was directly reacted to hex-
achlorocyclotriphosphazene. The cyanato-density of the resulting cyanato-functionalized
cyclotriphosphazenes is lower than that of the compound without the structure multiply
linked with bisphenol-A. The flame retardancy and the char-yielding properties of the
polymer improved with increased crosslinking, the Dk and Df performance of the polymer
constructed simply with phosphazene and triazine rings, however, was not obtained with
the multiply linked structure that resulted from the reaction method.
In this paper, we have synthesized novel cyclophosphazenes with cyanato groups
that do not have a cross-linked structure. The synthesis was achieved by the reaction of
a cyclophosphazene containing a hydroxyphenoxy group with cyanogen bromide (BrCN)
and triethylamine (TEA), and the thermal and electrical properties of the phosphazenes
were evaluated.

CYCLOPHOSPHAZENES CONTAINING CYANATO GROUPS
1557
RESULTS AND DISCUSSION
Synthesis and Characterization
Cyclophosphazenes containing cyanato groups (PZCN, IV and VII) were synthe-
sized by the reaction of 4-hydroxyphenoxycyclotriphosphazenes (III and VI) with BrCN
in the presence of a base. The phosphazenes (III) and (VI) were prepared from hexachloro-
cyclotriphosphazene (I) via 4-methoxyphenoxycyclophosphazenes (II) or (V) as shown in
Scheme 1, according to methods reported in the literature.13–15
The 4-methoxyphenoxyphosphazenes (II) or (V) were first prepared by substitution
of (I) with an alkaline metal salt of 4-methoxyphenol or a mixture of 4-methoxyphenol
and phenol in yields of 87.3–96.4%. Subsequently, the methyl group of (II) and (V) was
deprotected by pyridine-hydrochloride (instead of BBr3 as reported by Medici et al.15)
to give 4-hydroxyphenoxyphosphazenes (III) and (VI) in yields of 98.7% and 88.9%,
respectively. The tris(4-hydroxyphenoxy)tris(phenoxy)cyclotriphosphazene (VI) has been
confirmed to be substituted with phenoxy and 4-hydroxyphenoxy in the position of germinal
and nongeminal, mainly nongeminal, by the 31P NMR spectroscopy.
The PZCNs (IV) or (VII) were prepared by reaction of the corresponding 4-
hydroxyphenoxyphosphazenes (III) or (VI) and BrCN in the presence of TEA under
moisture-free conditions. The cyanation reaction with BrCN and TEA gave rise to diethyl-
cyanamide as a side product. However, the diethylcyanamide and other impurities were
completely eliminated from the PZCNs by recrystallization or reprecipitation with the con-
firmation of gas chromatography (GC) and 1H NMR such that trace impurities did not affect
the curing reaction with the cyanato group of the PZCNs. The resulting PZCNs (IV) and
(VII) were obtained in yields of 90.8% and 72.5%, respectively, and were characterized by
the 13C and 31P NMR, FT-IR, and liquid chromatography–mass spectrometry (LC-MS).
The formation of PZCN (IV) from 4-hydroxyphenoxyphosphazene (III) can be ob-
served characteristically by the IR spectroscopy. Absorption based on the hydroxy group
disappeared at 3292 cm−1 for (III), and the characteristic absorption of the cyanato group
appeared at 2272 and 2237 cm−1 for (IV), which was split into partially resolved bands.
Five signals were observed in the 13C NMR spectrum for PZCN (IV) as shown in Figure 1,
of which four signals at 117.8, 123.6, 149.1, and 150.9 ppm were based on the carbon of
the phenylene group and one signal, at 109.2 ppm, was based on the carbon of the cyanato
group, as supported by the work of Fyfe et al.16 Further, the structure of PZCN (IV) was
elucidated to be substituted with six of the 4-cyanatophenoxy groups on the phosphazene
ring by LC-MS analysis. The cyanato equivalent weight of PZCN (IV) was calculated to
be 157 g/eq based on this analysis.
The formation of PZCN (VII) from 4-hydroxyphenoxyphosphazene (VI) was also
confirmed by the IR spectroscopy. Absorption based on the hydroxy bond disappeared
at 3325 cm−1 for (VI), and an alternative new absorption based on the cyanato bond
appeared at 2270 and 2236 cm−1 with resolved bands for (VII). Nine signals were
observed in the 13C NMR spectrum of PZCN (VII) as shown in Figure 2, with eight
signals at 117.5, 121.6, 123.6, 126.3, 130.6, 149.4, 150.5, and 151.1 ppm attributed
to the carbon of the phenyl and phenylene groups, and one signal at 109.3 ppm
attributed to the carbon of the cyanato group. The PZCN (VII) is determined to
be a mixture of N3P3(OC6H4OCN)2(OC6H5)4, N3P3(OC6H4OCN)3(OC6H5)3, and
N3P3(OC6H4OCN)4(OC6H5)2 whose protonated molecule ions were observed at m/z

1558
Y. TADA ET AL.
Scheme 1
776, 817, and 858, respectively, by LC-MS. Furthermore, the PZCN (VII) is estimated
1
to have a mean structure of N3P3(OC6H4OCN)3(OC6H5)3 by the H NMR spectroscopy,
and the cyanato equivalent weight of the PZCN (VII) was calculated to be 272 g/eq
based on this analysis. As a result, the PZCNs (IV) and (VII) were confirmed to possess

CYCLOPHOSPHAZENES CONTAINING CYANATO GROUPS
1559
Figure 1 13C NMR of spectrum of PZCN (IV).
cyanato groups on molecules that are able to form triazine rings with trimerization by
heating.
In addition, ionic impurities in the PZCNs (IV) and (VII) were detected at concen-
trations less than 10 ppm by IEC; therefore, the prepared PZCNs (IV) and (VII) were
determined to be suitable for the evaluation of their electrical properties.
Curing Study
The thermal aspects of the PZCNs (IV) and (VII) were investigated by differential
scanning calorimetry (DSC). PZCN (IV) exhibited a sharp endothermic peak due to its
melting point at 150◦C, followed by a broad exothermic peak due to the curing reaction in
the temperature range of 160–280◦C, with a maximum at 233◦C in the thermogram. PZCN
(VII) exhibited only a broad exothermic peak due to the curing reaction in the temperature
range of 140–300◦C, with a peak at 255◦C. Because PZCN (VII) consists of a mixture of
substituted di-, tri-, and tetra-cyanatophenoxy groups, including stero and regio isomers
substituted in geminal and nongeminal positions, resulting in PZCN (VII) having a viscous
oily nature.

1560
Y. TADA ET AL.
i
h
c
b
e
OCN
c
d
b
a
O
P N
3
h
O
f
g
i
g
e
a
f
d
160
150
140
130
110
100
120
(ppm)
Figure 2 13C NMR spectrum of PZCN (VII) (Color figure available online).
After the PZCNs (IV) and (VII) were heated to 280◦C and 300◦C, respectively,
the samples were cooled to room temperature in a nitrogen atmosphere. The structure of
the samples was determined using the IR spectroscopy, and their spectra compared with
starting samples are shown in Figure 3. The IR spectra of the PZCNs (IV) and (VII)
showed absorptions based on the phosphazene rings and the phenoxy groups at 1593, 1495,
1169, and 954 cm−1. Additionally, the characteristic absorptions of the C–N triple bond
showed up at both 2270–2272 cm−1 and 2235–2237 cm−1. After the PZCNs (IV) and (VII)
were heated up to 280◦C and 300◦C, respectively, the absorptions based on the C–N triple
bond disappeared completely, and the characteristic absorptions based on the triazine rings
appeared at 1570 cm−1 for N C N and at 1374 cm−1 for N–C–O. Hence, the cyanate
group of the PZCNs (IV) or (VII) cyclotrimerized exothermically to form triazine ring
structures, resulting in a tightly cross-linked structure as shown in Scheme 1.
Thermal Properties of PZCNs
The properties of the cured PZCNs (IV) and (VII) were evaluated after precuring
treatments at 140◦C for 2 h and 2 h, respectively, and following postcuring at 220◦C for 14 h
and 3 h, respectively. After the PZCNs (IV) and (VII) were postcured, the PZCNs turned
from tacky liquids to dimensionally stable solids. At the same time, the conformational

CYCLOPHOSPHAZENES CONTAINING CYANATO GROUPS
1561
Figure 3 IR spectra of PZCNs and cured PZCNs (Color figure available online).
transition from the cyanates to the triazines was confirmed by the IR spectroscopy as shown
in Figure 3.
Figure 4 shows thermogravimetry curves of the cured PZCNs (IV) and (VII) taken in
a nitrogen atmosphere. The results are summarized in Table 1. The cured PZCNs (IV) and
(VII) were stable up to 350◦C without weight loss. The 5% weight loss temperature of the
Table 1 Thermal and electrical properties of cured PZCN (IV), (VII), and BPACN
Td5%
(◦C)
Td10%
(◦C)
Residue at
600◦C (%)
Dielectric
constant (Dk)
Dissipation
factor (Df)
Cured
PZCN (IV)
PZCN (VII)
BPACN
424
436
425
461
467
438
75.0
71.0
47.5
2.87
2.68
2.91a
0.013
0.008
0.005a
aDk: 2.91, Df: 0.005 in literature.

1562
Y. TADA ET AL.
100
IV
VII
50
BPACN
0
0
200
400
600
Temperature/°C
Figure 4 TG analysis of cured PZCNs (IV), (VII), and BPACN (Color figure available online).
cured PZCNs (IV) and (VII) was determined to be 424◦C and 436◦C, respectively. More-
over, the cured PZCNs (IV) and (VII) had high char residues, including 75.0% and 71.0%
at 600◦C, respectively. The cured PZCNs (IV) and (VII) were compared with 2,2-bis(4-
cyanatophenyl)propane (BPACN) that was a commercially available simple cyanate com-
pound. Although, the cured PZCNs (IV) and (VII) showed initial weight loss temperatures
similar to the cured BPACN, the cured PZCNs (IV) and (VII) exhibited characteristically
larger char residues than the cured BPACN at 600◦C.
The cyanate-functionalized cyclotriphosphazenes consisting of cyclotriphosphazene,
phenol, and bisphenol-A reported in the literature had weight losses beginning at 200◦C and
had ca. 50% char residue at 600◦C.12 The PZCN (IV) substituted with six cyanatophenoxy
groups showed a particularly high char residue at 600◦C. The PZCNs (IV) and (VII) were
of high purity with high phosphazene content. While the reported cyclotriphosphazenes
included cross-linked structures, they were difficult to purify to low impurity levels. The
PZCNs (IV) and (VII) have a high phosphazene ring because the PZCNs (IV) and (VII)
derive from (IV) and (VII) with six and three hydroxyphenoxy groups, respectively, instead
of isopropylidene diphenoxy groups.
Electrical Properties of PZCNs
Novel phosphazenes containing cyanato groups, PZCNs (IV) and (VII), with high
phosphazene content were prepared without a multiply linked structure. The Dk and Df of
the cured PZCNs were measured at a 1 MHz frequency at room temperature, as summarized
in Table 2. Although, the cured PZCNs (IV) and (VII) showed Dk values less than 3, similar
to the cured BPACN, the Dk values of the cured PZCNs (IV) and (VII) were slightly higher
than that of the cured BPACN. The phosphazene and triazine rings that consist of a plain

CYCLOPHOSPHAZENES CONTAINING CYANATO GROUPS
1563
six-membered cyclic structure are irrelevant to both the Dk and Df values of the PZCNs.
Thus, the electrical properties of the PZCNs maintain low Dk and Df values with high
phosphazene and triazine rings content.
Additionally, where difunctional phenols are reacted with hexachlorocyclotriphos-
phazene, the resulting products include cross-linked structures that are difficult to make
soluble in common solvents. Consequently, these cross-linked compounds are difficult to
purify to low levels of ionic impurities based on a substitution reaction (in which the
leaving group is an alkali metal halide) by using the alkali metal of the phenols with the
hexachlorocyclotriphosphazene. Therefore, the phosphazenes obtained in our process are
able to achieve a low ionic impurity level by purification, as needed to attain high dielectric
properties.
The PZCNs may become good candidates for electric or electronic applications due
to their low Dk and high flame retardancy.
Flame Retardancy of PZCNs
The flame retardancy of the cured PZCNs was evaluated by the UL-94 vertical
test method. The cured PZCNs showed V–0 rating at 0.8 mm thickness, but the cured
BPACN burned at the same thickness. The cured PZCNs showed excellent flame-retardancy
compared with the cured BPACN. The PZCNs will be able to enhance the flame retardancy
of other matrix polymers, such as epoxy and CRs.
The resulting PZCNs can be used as candidates for flame-retardant additives, as
needed in the electric industry because of their low dielectric properties, in addition to their
application in stringent fire resistant norms, such as in aircraft interiors and the transport
industry.
CONCLUSIONS
Novel PZCN derivatives were synthesized by a substitution reaction of 4-
hydroxyphenoxycyclophosphazene and BrCN with TEA in high yield. After the PZCNs
were postcured at 220◦C, the resulting cured PZCNs exhibited high thermal stabilities of
up to 350◦C, high char-forming capabilities, and electrical properties, such as dielectric
constants (Dks) of 2.68–2.87 and dissipation factors (Dfs) of 0.008–0.013 at 1 MHz. Hence,
the PZCN derivatives exhibited properties well suited for high-speed and high-density
multi-layer boards in the microelectronics industry.
EXPERIMENTAL
Materials
Hexachlorocyclotriphosphazene (I) (NPCl2)3 was purified by recrystalliza-
tion from hexane and dried under reduced pressure. BrCN was purchased from
Sigma–Aldrich Co., Saint Louis, MO, USA, and used as received. Solvents were
purified by conventional methods, and other reagents were of reagent grade and
used without further purification. All reactions were carried out in a nitrogen atmo-
sphere. Hexakis(4-hydroxyphenoxy)cyclotriphosphazene (III) was prepared by the
reaction of (NPCl2)3 (I) with the sodium salt of 4-methoxyphenol to form hexakis(4-
methoxyphenoxy)cyclotriphosphazene (II) and then by demethylating (II) with an excess of
pyridine-hydrochloride instead of BBr3, as reported in the literature.13–15 The melting point

1564
Y. TADA ET AL.
was 241–242◦C experimentally and 241–243◦C in the literature.15 BPACN was purchased
ꢀR
as PRIMASET BADCy from LONZA Ltd., Basel, Switzerland, and used as received.
Measurements
1
The H NMR, 13C NMR, and 31P NMR spectra were recorded on a Varian Unity
300 FT-NMR spectrometer at 300 MHz, 75 MHz, and 121 MHz, respectively. Deuterated
chloroform (CDCl3) and deuterated acetone (acetone-d6) were used as solvents. Tetram-
1
ethylsilane (TMS) was used as an internal standard for the H NMR and 13C NMR, and
85% phosphoric acid was used as an external standard for the 31P NMR. LC–MS mea-
surements were conducted on a Thermo Finnigan LCQ Advantage MAX ion-trap mass
spectrometer (ESI+) coupled to a Surveyor HPLC system (Thermo Fisher Scientific, Inc.,
Waltham, MA) equipped with a C18 (Inertsil ODS-2, 4.6 mm D, 250 mm L, 5 µm particle
size, GL Sciences Inc., Tokyo, Japan) analytical column and buffers A: acetonitrile and
B: 0.1% aq. formic acid. Thermogravimetric analysis (TGA) and DSC were performed
using a Shimadzu DTG 60 and DSC 60 analyzer (Shimadzu Corporation, Kyoto, Japan),
respectively, at a heating rate of 10◦C min−1 under a nitrogen flow of 50 mL min−1. Both
Dk and Df were measured at 1 MHz at room temperature using an Agilent 4284A Precision
LCR Meter (Agilent Technologies, Inc., Santa Clara, CA). Additional experimental details
are found in the Supplemental Materials (available online).
Synthesis of Cyclophosphazenes Containing Cyanato Groups;
Synthesis of Hexakis(4-cyanatophenoxy)cyclotriphosphazene (IV)
A solution of hexakis(4-hydroxyphenoxy)cyclotriphosphazene (III) (450.0 g, 1.71
unit mol), BrCN (444.9 g, 4.20 mol), and acetonitrile (5750 mL) was cooled to −10◦C,
and TEA (425.0 g, 4.20 mol) in acetonitrile (640 mL) was added dropwise with stirring
below 0◦C, and then stirred at the same temperature for 30 min. Water (2500 mL) was
added to the reaction mixture and stirred for 30 min. The resulting precipitate was collected
and washed with water (800 mL) and toluene (570 mL) to give a wet 655 g of crude
product as a pale-brownish solid. The crude product was purified by recrystallization from
acetone/heptane (1:1) to give 486.0 g of hexakis(4-cyanatophenoxy)cyclotriphosphazene
(IV) as a white solid with a yield of 90.8%.
Melting point: 150◦C. 1H NMR (300 MHz, CDCl3, δ, ppm): 7.03 (d, 2H, J = 12.4 Hz,
H of aromatic ring), 7.15 (d, 2H, J = 12.4 Hz, H of aromatic ring), 13C NMR (75 MHz,
acetone-d6, δ, ppm): 109.2, 117.8, 123.6 (q), 149.1 (q), 150.9, 31P NMR (121 MHz, CDCl3,
δ, ppm): 9.2 (s, phosphorous of cyclophosphazene); IR (KBr, pellet, ν, cm−1): 2272 and
2237 (s, νC–N), 1495 (vs, νC–C), 1169 (s, νP–N–P), 954 (s, νP–O–C), 883 (m, νP–N–P), 833
(m); LC-MS (positive-ESI, m/z): 941 (M+H+), 963 (M+Na+).Cyanato equivalent weight:
940(M+)/6 = 157 g/eq.
Synthesis of Tris(4-methoxyphenoxy)tris(phenoxy)cyclotriphosphazene
(V)
A mixture of phenol (purity: 99%, 585.6 g, 6.16 mol), toluene (3550 mL), and
44% NaOH aq. solution (549.1 g, 241.6 g as NaOH, 6.04 mol) was heated to 110◦C.
The mixture was stirred while refluxing, and the water was removed from azeotropically
distilled toluene–water until the water content of the mixture was less than 100 ppm. The

CYCLOPHOSPHAZENES CONTAINING CYANATO GROUPS
1565
mixture was concentrated and dissolved in tetrahydrofuran (THF; 1560 mL). The resulting
solution was added to hexachlorocyclotriphosphazene (I) (700.0 g, 6.04 unit mol) in toluene
(11660 mL) while stirring for 8 h at 10◦C or below. The reaction mixture was stirred for 1 h at
the same temperature, and then warmed up to 25◦C to give intermediate. The composition
of the intermediate was calculated as nongeminal P3N3(OC6H5)3Cl3 65.8%, germinal
P3N3(OC6H5)3Cl3 16.9%, P3N3(OC6H5)2Cl4 :10.3%, and P3N3(OC6H5)4Cl2 7.0% from
the integrals of the 31P NMR spectrum. Mean structure estimated from the 31P NMR:
N3P3(OC6H5)3.0Cl3.0 (see Figure S1 available online in the Supplemental Materials).
A mixture of 4-methoxyphenol (purity: 99%, 988.1 g, 7.88 mol), toluene (7600 mL),
and 44% KOH aq. solution (994.5 g, 437.6 g as KOH, 7.80 mol) was heated to 110◦C,
and the water was removed from azeotropically distilled toluene–water until the water
content of the mixture was less than 100 ppm. The reaction mixture was cooled to below
40◦C, and the toluene solution of the trichlorotriphenoxycyclotriphosphazenes was added.
The mixture was heated, and the THF was distilled off. After the mixture was stirred
at 110◦C for 12 h, the mixture was cooled to room temperature, and a 2% NaOH aq.
solution (3000 mL) was added. The organic layer was washed with 5% NaOH aq. solution
(3000 mL). Water (3000 mL) was then added to the organic layer, and the pH of the
aqueous layer was adjusted to 3 by addition of a 4% HCl aq. solution. The organic layer
was concentrated under a reduced pressure to give 1521.0 g of tris(4-methoxyphenoxy)-
tris(phenoxy)cyclotriphosphazene (V) as a dark brown viscous liquid with a yield of 96.4%.
Mean structure estimated from the 1H NMR: N3P3(OC6H4OCH3)3.0(OC6H5)3.0
.
1H NMR (300 MHz, CDCl3, δ, ppm): 3.76 (s, 3H, OCH3), 6.8–7.3 (m, 9H, aromatic
ring), 31P NMR (121 MHz, CDCl3, δ, ppm): 10.7 (s, phosphorus of cyclophosphazene).
Synthesis of Tris(4-hydroxyphenoxy)tris(phenoxy)cyclotriphosphazene
(VI)
To a solution of pyridine (556.9 g, 7.04 mol) in toluene (1630 mL),
gaseous hydrogen chloride (295.0 g, 8.09 mol) was introduced at less than
10◦C. After the preparation of the pyridine-hydrochloride/toluene mixture, tris(4-
methoxyphenoxy)tris(phenoxy)cyclotriphosphazene (V) (1413.2 g, 5.41 unit mol) was
added. The mixture was heated, and the toluene was distilled off. Finally, the mixture
was heated to 200–205◦C and stirred for 3 h at this temperature. The reaction mixture was
cooled to less than 40◦C, and 4-methylpentan-2-one (MIBK, 2570 mL) and 3% HCl aq.
solution (2160 mL) were added. The organic layer was washed with 3% HCl aq. solution
(2170 mL). Moreover, water (1060 mL) was added to the organic layer, and the pH of
the aqueous layer was adjusted to 6 by addition of 10% NaOH aq. solution. The organic
layer was washed with water (2000 mL) and was concentrated under a reduced pressure to
give 1189.4 g of tris(4-hydroxyphenoxy)tris(phenoxy)cyclotriphosphazene (VI) as a dark
brown viscous liquid with a yield of 88.9%.
Mean structure estimated from the 1H NMR: N3P3(OC6H4OH)3.0(OC6H5)3.0
.
1H NMR (300 MHz, acetone-d6, δ, ppm): 6.7 (m, 4 H, H2 and H6 of quinone, and H3
and H5 of phenoxy), 6.94 (dd, 2 H, H3 and H5 of quinone), 7.18 (m, 1 H, H4 of phenoxy),
7.27 (m, 2 H, H2 and H6 of phenoxy), 8.35 (brs, 1H, OH), 31P NMR (121 MHz, acetone-d6,
δ, ppm): 10.7 (s, phosphorus of cyclophosphazene).
IR (KBr, pellet, ν, cm−1): 3325 (b, νO–H,), 1593 (m, νC–C), 1508 (s, νC–C), 1489
(s, νC–C), 1188 (s, νP–N–P), 1176 (s, νP–O–C), 956 (s, νP–O–C), 877 (m, νP–N–P), 835 (m);

1566
Y. TADA ET AL.
LC-MS (positive-ESI, m/z).
N3P3(OC6H4OH)2(OC6H5)4 : 726 (M + H+), 748 (M + Na+),
N3P3(OC6H4OH)3(OC6H5)3 : 742 (M + H+), 764 (M + Na+),
N3P3(OC6H4OH)4(OC6H5)2 : 758 (M + H+), 780 (M + Na+).
Synthesis of Tris(4-cyanatophenoxy)tris(phenoxy)cyclotriphosphazene
(VII)
A
solution of tris(4-hydroxyphenoxy)tris(phenoxy)cyclotriphosphazene (VI)
(500.0 g, 2.02 unit mol), BrCN (251.0 g, 2.37 mol), and MIBK (1030 mL) was cooled
to −10◦C, and a TEA (239.8 g, 2.37 mol) in acetonitrile (1750 mL) solution was added
dropwise with stirring below 0◦C, followed by stirring at this temperature for 30 min. Into
this reaction mixture, toluene (3500 mL) and water (1750 mL) were added and stirred for
30 min. The organic layer was washed with water (1750 mL) and concentrated under a
reduced pressure below 40◦C to give 638.9 g of the crude product as a brownish viscous
oil. The crude product was purified by reprecipitation with toluene–heptane seven times
to give 398.6 g of tris(4-cyanatophenoxy)tris(phenoxy)cyclotriphosphazene (VII) as a
brownish viscous oil with a yield of 72.5%.
1H NMR (300 MHz, CDCl3, δ, ppm): 6.80–7.08 (m, 4H, aromatic ring), 7.10–7.28
(m, 5H, aromatic ring), 13C NMR (75 MHz, acetone-d6, δ, ppm): 109.3, 117.5 (q), 121.6,
123.6, 126.3, 130.6, 149.4 (q), 150.5, 151.1, 31P NMR (121 MHz, CDCl3, δ, ppm): 9.7 (s,
phosphorous of phosphazene ring).
IR (KBr, pellet, ν, cm−1): 2270 and 2235 (s, νC–N), 1591 (s, νC = C), 1496 (vs, νC = C),
1182 (s, νP–N–P), 1163 (s, νP–O–C), 953 (s, νP–O–C), 883 (m, νP–N–P), 840 (m).
LC-MS (positive-ESI, m/z): N3P3(OC6H4OCN)2(OC6H5)4 : 776 (M + H+),
798 (M + Na+),
N3P3(OC6H4OCN)3(OC6H5)3 : 817(M + H+), 839 (M + Na+),
N3P3(OC6H4OCN)4(OC6H5)2 : 858 (M + H+), 880 (M + Na+).
Curing conditions for Hexakis(4-cyanatophenoxy)cyclotriphosphazene
(IV) and Tris(4-cyanatophenoxy)tris(phenoxy)cyclotriphosphazene (VII)
The PZCN (IV) was dissolved at a concentration of 50% by weight in 1-methoxy-2-
(2-methoxyethoxy)ethane (Diglyme) and then preheated to 140◦C for 30 min. The PZCN
(VII) was preheated at 140◦C for 45 min.
The preheated PZCNs (IV) or (VII) were poured and spread on polyethylene tereph-
thalate (PET) films that were preheated to 140◦C and were then precured at 140◦C for 2 h.

CYCLOPHOSPHAZENES CONTAINING CYANATO GROUPS
1567
The resulting films were separated from the PET films and were postcured at 220◦C for
14 h and 3 h, respectively, to give the films for measurement.
As a reference, after the BPACN was precured at 140◦C for 40 h and postcured at
250◦C for 4 h and 285◦C for 2 h, the cured BPACN was evaluated.
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