Thermally stable and flame retardant low dielectric polymers based on cyclotriphosphazenes

Article abstract of DOI:10.1039/b920203j

We prepared thermally stable, low dielectric polymers by thermal polymerization of cyclotriphosphazenes bearing acetylene or styrene groups. Homosubstituted cyclotriphosphazene 1, containing acetylene groups, was synthesized by reaction of hexachlorocyclotriphosphazene with sodium salts of 4′-trimethylsilylethynyl-1,1′-biphenyl-4-ol and subsequent removal of trimethylsilyl groups under basic conditions. Heterosubstituted cyclotriphosphazene 2 was prepared using 4-phenylphenol as a cosubstituent. Cyclotriphosphazene 3 with styrene groups was prepared by reaction of hexachlorocyclotriphosphazene with sodium salts of 4-hydroxystyrene. Highly cross-linked polymers were obtained by thermal polymerization of the cyclotriphosphazenes at 200 °C for 1 and 2 and at 150 °C for 3. The 5% weight loss temperatures of the cross-linked polymers of compounds 1-3, measured by TGA, were above 470 °C. The flame-retardant property of the polymers was evaluated by measuring LOI (limiting oxygen index) values. The polymers of cyclotriphosphazenes 1-3 showed very high LOI values of 52, 50 and 49, respectively. We also prepared copolymers of cyclotriphosphazene 3 with styrene by UV irradiation in the presence of a photoinitiator (2,2-dimethoxy-2- phenylacetophenone). In the TGA thermograms, the copolymers showed good thermal stability, nearly comparable to the homopolymer of 3 when the composition of 3 was higher than 60%. The dielectric properties of the polymers were measured by a metal-insulator-metal method. The polymer obtained from acetylene-containing cyclotriphosphazene 1 showed dielectric constant and dielectric loss values of about 3.12 and 0.0016, respectively, at 1 GHz. The polymer of cyclotriphosphazene 3 showed a dielectric constant of 2.4 and a dielectric loss of 0.0014 at 1 GHz.

Full text of DOI:10.1039/b920203j

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Thermally stable and flame retardant low dielectric polymers based on
cyclotriphosphazenes
*
Ho Lim and Ji Young Chang
Received 28th September 2009, Accepted 22nd October 2009
First published as an Advance Article on the web 23rd November 2009
DOI: 10.1039/b920203j
We prepared thermally stable, low dielectric polymers by thermal polymerization of
cyclotriphosphazenes bearing acetylene or styrene groups. Homosubstituted cyclotriphosphazene 1,
containing acetylene groups, was synthesized by reaction of hexachlorocyclotriphosphazene with
sodium salts of 40-trimethylsilylethynyl-1,10-biphenyl-4-ol and subsequent removal of trimethylsilyl
groups under basic conditions. Heterosubstituted cyclotriphosphazene 2 was prepared using 4-
phenylphenol as a cosubstituent. Cyclotriphosphazene 3 with styrene groups was prepared by reaction
of hexachlorocyclotriphosphazene with sodium salts of 4-hydroxystyrene. Highly cross-linked
polymers were obtained by thermal polymerization of the cyclotriphosphazenes at 200 ꢀC for 1 and 2
and at 150 ꢀC for 3. The 5% weight loss temperatures of the cross-linked polymers of compounds 1–3,
measured by TGA, were above 470 ꢀC. The flame-retardant property of the polymers was evaluated by
measuring LOI (limiting oxygen index) values. The polymers of cyclotriphosphazenes 1–3 showed very
high LOI values of 52, 50 and 49, respectively. We also prepared copolymers of cyclotriphosphazene 3
with styrene by UV irradiation in the presence of a photoinitiator (2,2-dimethoxy-2-
phenylacetophenone). In the TGA thermograms, the copolymers showed good thermal stability, nearly
comparable to the homopolymer of 3 when the composition of 3 was higher than 60%. The dielectric
properties of the polymers were measured by a metal–insulator–metal method. The polymer obtained
from acetylene-containing cyclotriphosphazene 1 showed dielectric constant and dielectric loss values
of about 3.12 and 0.0016, respectively, at 1 GHz. The polymer of cyclotriphosphazene 3 showed
a dielectric constant of 2.4 and a dielectric loss of 0.0014 at 1 GHz.
(propylene oxide)-b-poly(ethylene oxide) (PEO-b-PPO-b-PEO)
Introduction
as a template to generate nanoporous structures.5 However, the
SSQs generally suffer from drawbacks, such as a lack of sufficient
toughness and the difficulty of pore structure control. The latter
is closely related to reliability issues.
Over the past few decades, the number of components on an
integrated circuit (IC) has been dramatically increased along with
the continual miniaturization of the devices. As a result, the IC
has now become heavily populated with transistors and
connection wires. The performance of the IC was mainly
dependent on the transistor population in the past. However, as
the complexity of the IC has increased, the interconnect signal
delay (RC delay), wire cross-talk and dissipation of energy
become major problems for its further improvement.1 In this
context, there has been a growing need for the development of
new insulating materials replacing silicon dioxide to overcome
these interconnect performance limitations.2
A number of organic polymers have been proposed as future
generation dielectric materials.1,10–13 The most thoroughly eval-
uated polymer is SiLK (Dow Chemical Co.).1 SiLK is an
aromatic thermosetting polymer, having cyclopentadienone and
acetylene moieties as reactive groups. SiLK has good dielectric
and mechanical properties, but some disadvantages such as its
high curing temperature of above 400 ꢀC and synthetic difficulty.
Film shrinkage was observed after cross-linking reaction at such
a high temperature.14,15 Poly(binaphthylene ether)s,10,11 polymers
having triptycene units12 and aromatic polymers having ethynyl
units13 have been also reported as low dielectric polymers.
In the present study, we report novel low dielectric materials
based on cyclotriphosphazenes. The cyclotriphosphazenes with
skeletal nitrogen and phosphorus atoms exhibit unusual thermal
properties such as flame retardancy and self-extinguishibility.16
Flame retardants are indispensable in the fabrication of elec-
tronic devices. Halogen free fire resistant materials for printed
circuit boards and IC encapsulators have already become a big
issue in the industry.17,18 Since most organic polymers produce
toxic chemicals under fire in a different way from inorganic
materials, the flame retardancy of low dielectric constant poly-
mers could be another challenge for their practical application.
Among the low dielectric materials developed for interconnect
fabrication, the most notable are silsesquioxane based materials
and organic polymers. Polysilsesquioxanes (SSQ) are organo-
silicates, in which the organic groups provide a low density and
low dielectric properties to the silicate. The dielectric property
can be further improved by introducing pores into the organo-
silicate. Porous SSQs have been prepared by using organic
polymer templates.3–9 For example, Yang and coworkers used
amphiphilic triblock copolymers, poly(ethylene oxide)-b-poly-
Department of Materials Science and Engineering, College of Engineering,
Seoul National University, Seoul, 151-744, Korea. E-mail: jichang@snu.ac.
kr; Fax: +82- (0)2 885 1748; Tel: +82 (0)2 880 7190
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Cyclotriphosphazenes have been incorporated into organic
polymers as additives or pendants to improve their thermal
properties.19–22 Thermally curable cyclotriphosphazenes bearing
acetylenic,23 maleimido,24 and nadic25 were also reported to
produce cross-linked polymer matrices. However, there are few
reports concerning dielectric properties of the polymers based on
cyclotriphosphazenes. In one early study, a cyclotriphosphazene
bearing acryloyloxyethyleneoxy and trifluoroethoxy groups as
polymerizable groups and cosubstituents, respectively, was
investigated, but the resulting cross-linked polymer showed
a very high dielectric constant and poor thermal stability,
probably due to its polar and flexible organic groups.26 Polar
polymers have an asymmetric charge distribution, and thus
higher dielectric constant and dielectric loss values.
4-phenylphenol as a cosubstituent. Substitution mole percentage
of the acetylene compound was controlled to be about 40%. In
the similar manner, 4-hydroxystyrene was introduced to the
cyclotriphosphazene ring to result in compound 3. All six chloro
groups of hexachlorocyclotriphosphazene were substituted by
the sodium salt of 4-hydroxystyrene.
Thermal polymerization
Thermal polymerization of compounds 1–3 was examined by
DSC. Thꢀermogramꢀs were obtained by scanning tꢀhe sample twice
from 30 C to 350 C with a heating rate of 10 C minꢁ1 under
nitrogen atmosphere. Homosubstituted cyclotriphosphazene 1
showed strong exotherms for the thermal reaction of acetylene
groups above 175 ꢀC, while heterosubstituted cyclo-
triphosphazene 2 showed a sharp endotherm for melt transition
at 200 ꢀC, immediately followed by a strong exotherm. In the
second scan, no significant exothermic peaks appeared, indi-
cating that most acetylene groups were thermally reacted in the
first scan (Fig. 1a). Highly cross-linked polymers were obtained
by thermal polymerization of cyclotriphosphazenes 1 and 2 at
200 ꢀC for 2 h. They showed excellent thermal stability. The 5%
weight loss temperatures (Td5) of the cross-linked polymers of
compounds 1 and 2, measured by TGA under nitrogen, were 523
and 480 ꢀC, respectively (Fig. 1b). The IR spectra of compounds
1 and 2 showed the peaks for C–H and C–C triple bond
stretching modes of the acetylene groups at 3293 and 2107 cmꢁl,
respectively. After polymerization, these peaks almost dis-
appeared. The acetylene group has been widely used as a cure site
Results and discussion
Monomer synthesis
We prepared thermally curable cyclotriphosphazenes containing
acetylene and styrene groups according to Scheme 1. 40-Trime-
thylsilylethynyl-1,10-biphenyl-4-ol was synthesized by reaction of
40-bromo-1,10-biphenyl-4-ol
with
(trimethylsilyl)acetylene
using a palladium catalyst. Six chloro groups of hexa-
chlorocyclotriphosphazene were replaced by reaction with
sodium salts of 40-trimethylsilylethynyl-1,10-biphenyl-4-ol. Tri-
methylsilyl groups were removed under basic conditions to
give cyclotriphosphazene
1 containing acetylene groups.
Heterosubstituted cyclotriphosphazene 2 was prepared using
Scheme 1 Synthesis of thermally curable cyclotriphosphazenes.
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Fig. 1 (a) DSC and (b) TGA thermograms of 1 and 2.
because it is thermally curable without the evolution of volati1es.
It has been proposed that several reactions are involved in the
curing process, including cyclotrimerization to an aromatic ring
structure, biradical reaction to form linear or cyclic conjugated
linkages, coupling reaction to form diyne structures and Diels–
Alder reactions to form condensed polycyclic aromatic
structures.27,28
cannot tolerate elevated temperatures. The polymerization was
carried out by UV irradiation (a high pressure mercury arc lamp,
3 mW cmꢁ2) in the presence of a photoinitiator (2,2-dimethoxy-2-
phenylacetophenone) at room temperature, resulting in the
highly cross-linked, thermally stable cyclotriphosphazene
embedded polystyrene. Thermal properties of the copolymers
were investigated by DSC and TGA (Fig. 2c and 2d). As the
proportion of compound 3 was increased from 5 to 20 wt%, the
Tg of the copolymer was also increased. When the content of
compound 3 was above 20 wt%, no discernible glass transition
was found. In the TGA thermograms, the copolymers showed
good thermal stability nearly comparable to the homopolymer of
compound 3 when its composition was higher than 60%.
The IR spectrum of compound 3 showed the C]C stretching
vibration peak of the styrene units at 1629 cmꢁ1. Based on the
peak intensity decrease, the conversions were estimated to be
about 70% in the homopolymerization of compound 3 and
nearly 100% in the copolymerization of compound 3 and styrene.
The high conversion in the copolymerization was attributable to
the fact that the reaction of the styrene units of compound 3 with
styrene monomers occurred in addition to the inter- and intra-
molecular reactions between themselves.
Styrene containing cyclotriphosphazene 3 showed a sharp melt
transition peak around 100 ꢀC and a broad exothermic peak for
the thermal polymerization of styrene groups above 150 ꢀC in the
DSC thermogram. No peak appeared in the second scan
(Fig. 2a). The spontaneous thermal polymerization of styrene
has been well known for many years. Although the mechanism of
the polymerization has not been fully understood, it is generally
accepted that the dimerization of styrene is involved in the
initiation step.29 The dimerization may proceed via a Diels–Alder
type [2 + 4] addition or an addition between two vinyl groups.
Both reactions produce radicals, which will initiate the poly-
merization of styrene. Six membered or four membered cyclic
adducts can be also formed by the reactions. The polymer
obtained by thermal polymerization of cyclotriphosphazene 3 at
150 ꢀC for 2 h also showed good thermal stability with a Td5 of
472 ꢀC (Fig. 2b).
We prepared copolymers of cyclotriphosphazene 3 with
styrene. Polystyrene is known as an excellent insulator but
Flame-retardant property. The flame-retardant property of the
polymers was evaluated by measuring LOI (limiting oxygen
Fig. 2 (a) DSC and (b) TGA thermograms of 3 and (c) DSC and (d) TGA thermograms of the copolymers of 3 and styrene.
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Table 1 The dielectric and thermal properties of the polymersa
Monomer
Dielectric constant (at 1 GHz)
Dielectric Loss (at 1 GHz)
Tg/ꢀC
Td5/ꢀC
LOI (%)
Char yield (%)b
1
2
3
3.12
3.07
2.40
2.55
2.53
2.58
2.58
0.0016
0.0020
0.0014
0.0041
0.0038
0.0019
0.0015
—
—
—
109
139
—
523
480
472
310
353
364
388
52
50
49
21
22
24
27
85
74
63
8
16
31
42
Styrene/3 (10 wt%)
Styrene/3 (20 wt%)
Styrene/3 (40 wt%)
Styrene/3 (60 wt%)
—
a
DSC and TGA were carried out at a heating rate of 10 ꢀC minꢁ1. The Td5 indicates a 5% weight loss temperature. b Measured at 700 ꢀC under nitrogen.
index) values according to an ASTM D2863 method. The poly-
mers of cyclotriphosphazene 1 containing six acetylene groups
and cyclotriphosphazene 2 having mixed substituents of acety-
lene (40%) and phenylphenoxy (60%) groups showed very high
LOI values of 52 and 50, respectively. The polymer of compound
3 with styrene groups also exhibited a high LOI value of 49. The
copolymers of compound 3 and styrene showed an improved
flame retardancy compared with polystyrene (LOI ¼ 18.8).30
Their LOI values increased in accordance with the increase of the
content of compound 3. Char yields of the polymers showed
a similar trend to the LOI values. The polymer of compound 1
had the highest char yield of 85% at 700 ꢀC under nitrogen, while
the polymers of compounds 2 and 3 showed a little lower char
yields of 74% and 63%, respectively. Thermal properties of the
polymers are summarized in Table 1.
dielectric constant of about 3.12 and 3.07, respectively, at 1 GHz.
Much improved dielectric properties were obtained from the
styrene containing cyclotriphosphazene systems. The polymer of
cyclotriphosphazene 3 showed a dielectric constant of 2.40 and
a dielectric loss of 0.0014 at 1 GHz. This dielectric constant value
is lower than those of SiLK (2.65)1 and polystyrene (2.6).32 We
presume that the hypercross-linked network structure increased
the free volume of the polymer and lowered the dielectric
constant.33 The dielectric properties of the polymers are
summarized in Table 1. The polymer of compound 3 showed
hardness of 0.31 GPa, which was similar to that of SiLK
(0.38 GPa).1
Fig. 4 shows dielectric constants and dielectric losses of the
homo and copolymers of compound 3 having different compo-
sitions, measured according to electric frequency. In proportion
to the amount of compound 3 in the copolymers, dielectric
constants did not change significantly, but dielectric losses
decreased. It showed an especially sharp fall of a dielectric loss
when the content of compound 3 was larger than 20 wt% in the
copolymer. The dielectric constant and dielectric loss values of
the homopolymer and the copolymers of compound 3 were
almost constant from 0.1 to 1 GHz.
Dielectric properties
Polymer pellets with a thickness of 1–2.5 mm were prepared for
dielectric constant and dielectric loss measurements. Compounds
1–3 were placed in a Teflon molder and polymerized thermally or
photochemically as described above. Air was removed from the
pellet by applying gentle pressure during the polymerization. No
macro pores were found in the cross-section, which was exam-
ined by SEM (Fig. 3). The pore structure will decrease the
dielectric constant but also cause problems such as intercon-
nection and deterioration of the mechanical property.
Conclusions
We developed curable cyclotriphosphazenes as low dielectric
materials. In particular, the polymers of compound 3 bearing
styrene groups showed excellent dielectric properties; low
dielectric constant and dielectric loss over the range of 0.1 to 1
GHz. The dielectric and physical properties of the polymers
could be controlled without sacrificing much thermal stability
through the copolymerization with styrene. We expect these
cyclotriphosphazenes will be useful as future low dielectric
materials.
The dielectric properties of the polymers were measured by
a metal–insulator–metal method.31 The polymer obtained from
acetylene containing cyclotriphosphazene 1 and 2 showed
Experimental
Measurements
1H, 13C and 31P nuclear magnetic resonance (NMR) spectra were
measured by a Bruker Avance DPX-300 (300 MHz for 1H NMR)
spectrometer and a Bruker Avance DPX-500 (200 MHz for 31P
NMR) spectrometer. All chemical shifts were listed in ppm
downfield from tetramethylsilane (1H NMR) and phosphoric
acid (31P NMR). Fourier transform infrared (FT-IR) measure-
ments were recorded on a PERKIN ELMER Spectrum GX I
using KBr pellets. Elemental analyses were performed by an EA
Fig. 3 SEM image of cross-section of the specimen prepared by poly-
merization of compound 3.
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Fig. 4 (a) Dielectric constants and (b) dielectric losses of the polymer of compound 3 and the copolymers of compound 3 and styrene.
1110 (CE Instrument) and a Flash 1112 (Thermo Electron
corporation). Dielectric constant and dielectric loss were
measured by a metal–insulator–metal method using an E4991A
RF impedance/material analyzer (Agilent Technology). The
frequency ranged from 1 MHz to 1 GHz. Thermogravimetric
analysis (TGA) was performed on a TA modulated TGA2050
128.1, 126.7, 121.7, 115.9, 105.3, 94.8. 31P NMR (CDCl3): d 9.79.
Anal. calcd for C102H102N3O6P3Si6: C, 70.92; H, 5.95; N, 2.43.
Found C, 71.01; H, 5.53; N, 2.47%.
N3P3(OC6H4C6H4ChCH)6 (1). To a solution of hexakis(40-
trimethylsilylethynyl-1,10-biphenyl-4-oxy)cyclotriphosphazene
(4.25 g, 2.40 mmol) in tetrahydrofuran (100 ml) and methanol
(30 ml), potassium hydroxide (1.30 g, 22.0 mmol) was added.
After stirring for 3 h at room temperature, the solvents were
removed by evaporation. The resulting residue was dissolved in
ethyl acetate (50 ml). The solution was washed with water
(50 ml) and dried over anhydrous magnesium sulfate. After
filtration and evaporation, the product was isolated by column
chromatography on silica gel (50% tetrahydrofuran in hexane)
(3.0 g, 97%). 1H NMR (CDCl3): d 7.46–7.49 (d, 12H, Ar), 7.25–
7.32 (m, 24H, Ar), 6.94–7.05 (d, 12H, Ar), 3.15 (s, 3H,
–ChCH). 13C NMR (CDCl3): d 150.4, 140.2, 137.1, 132.9,
128.1, 126.7, 121.7, 115.9, 83.5, 78.3. 31P NMR (CDCl3): d 9.79.
Anal. calcd for C84H54N3O6P3: C, 77.95; H, 4.21; N, 3.25.
Found C, 77.68; H, 4.20; N, 2.99%.
with a heating rate of 10 C minꢁ1 under nitrogen. Differential
ꢀ
scanning calorimetry (DSC) measurement was perfoꢀrmed by
a TA modulated DSC Q10 with a scanning rate of 10 C minꢁ1
under nitrogen. SEM images were obtained by using a JEOL
JSM-6330F microscope. Hardness was determined with a nano-
indenter (AIS2100, Frontics. Inc.) according to the reported
procedure.34 LOI (limiting oxygen index) values were measured
by a Fire Testing Technology instrument at a flow rate of 10.6 L
minꢁ1 with test specimen bars of 80 mm in length, 10 mm in width
and about 4.0 mm in thickness. The testing was performed
according to American Society for Testing and Materials
(ASTM) test D2863.
Synthesis and characterization
40-Trimethylsilylethynyl-1,10-biphenyl-4-ol.
40-Bromo-1,10-
N3P3(OC6H4C6H4ChCSiMe3)2.4(OC6H4C6H5)3.6
.
Sodium
biphenyl-4-ol (10.0 g, 40.5 mmol) was dissolved in TEA (200 ml).
To the solution dichlorobis(triphenylphosphine)palladium
(1.13 g, 1.62 mmol) and copper iodide (0.153 g, 0.81 mmol) were
added. After stirring for 1 h at room temperature, (trimethylsi-
lyl)acetylene (4.70 g, 0.48 mmol) was added and the resulting
solution was stirred for 20 h at 40 ꢀC. After filtration and
evaporation, the product was isolated by column chromatog-
raphy on silica gel (9% ethyl acetate in hexane) (8.90 g, 84%). 1H
NMR (CDCl3): d 7.38–7.54 (m, 6H, Ar), 6.89 (d, 2H, Ar), 0.24
(s, 9H, -Si(CH3)3). 13C NMR (CDCl3): d 156.0, 140.9, 132.5,
128.5, 126.5, 121.6, 115.9, 105.3, 94.8. IR (KBr): 3400, 2160,
1610, 1495, 1250. Anal. calcd for C17H18OSi: C, 76.64; H, 6.81.
Found: C, 76.78; H, 6.53%.
hydride (0.41 g, 17.40 mmol) was added to a solution of 4-phe-
nylphenol (3.00 g, 17.40 mmol) in 1,4-dioxane (50 ml). After
stirring for 1 h at room temperature, a solution of hexa-
chlorocyclotriphosphazene (2.00 g, 5.75 mmol) in 1,4-dioxane
(50 ml) was added dropwise. After refluxing for 24 h,
a solution of sodium 40-trimethylsilylethynyl-1,10-biphenyl-4-
oxide, prepared from 40-trimethylsilylethynyl-1,10-biphenyl-4-ol
(5.60 g, 20.1 mmol) and sodium hydride (0.50 g, 20.1 mmol) in
1,4-dioxane (50 ml), was added to the solution and refluxed for
48 h. After filtration and evaporation, the product was isolated
by column chromatography on silica gel (15% ethyl acetate in
1
hexane) (5.29 g, 64%). H NMR (CDCl3): d 7.44–7.47 (overlap,
7H, Ar), 7.26–7.36 (overlap, 43H, Ar), 6.99–7.03 (m, 15H, Ar),
0.24 (s, 27H, –Si(CH3) 3). 13C NMR (CDCl3): d 150.2, 141.5,
132.8, 128.3, 127.6, 127.0, 126.8, 121.6, 83.6, 78.3. 31P NMR
(CDCl3): d 9.82.
N3P3(OC6H4C6H4ChCSiMe3)6. Sodium hydride (0.50 g, 21.0
mmol) was added to a solution of 40-trimethylsilylethynyl-1,10-
biphenyl-4-ol (5.50 g, 21.0 mmol) in tetrahydrofuran (100 ml).
After stirring for 1 h at room temperature, a solution of hexa-
chlorocyclotriphsphazene (1.00 g, 2.88 mmol) in tetrahydrofuran
(50 ml) was added dropwise and refluxed for 48 h. The solvent
was removed by evaporation and the product was isolated by
column chromatography on silica gel (50% tetrahydrofuran in
N3P3(OC6H4C6H4ChCH)2.4(OC6H4C6H5)3.6 (2). This com-
pound was prepared by following the procedure for the prepa-
ration of compound 1. The product was isolated by column
chromatography on silica gel (15% ethyl acetate in hexane)
(3.82 g, 92%). 1H NMR (CDCl3): d 7.44–7.47 (overlap, 7H, Ar),
7.26–7.36 (overlap, 43H, Ar), 6.99–7.03 (m, 15H, Ar), 3.15
(s, 3H, –ChCH). 31P NMR (CDCl3): d 9.82.
1
hexane) (4.25 g, 85%). H NMR (CDCl3): d 7.46–7.49 (d, 12H,
Ar), 7.25–7.32 (m, 24H, Ar), 6.94–7.05 (d, 12H, Ar), 0.24 (s, 54H,
-Si(CH3) 3). 13C NMR (CDCl3): d 150.4, 140.2, 137.1, 132.9,
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1,1,3,3,5,5-Hexakisstyreneoxycyclotriphosphazene
(3). 4-
Hydroxystyrene was prepared according to the literature
procedure.35 To a solution of 4-hydroxystyrene (8.16 g, 68.0
mmol) in tetrahydrofuran (100 ml), sodiumhydride (1.63 g, 68.0
mmol) was added. After stirring 1 h at room temperature,
a solution of hexachlorocyclotriphsphazene (2.60 g, 7.47 mmol)
in tetrahydrofuran (50 ml) was added dropwise and stirred for 48
h at 50 ꢀC. After evaporation, the product was purified by
recrystallization from methanol (4.72 g, 73%). 1H NMR
(CDCl3): d 7.16 (d, 2H), 6.83 (d, 2H), 6.60–6.66 (q, 1H), 5.66
(d, 1H), 5.23 (d, 1H). 31P NMR (CDCl3): d 9.40. IR (KBr): 3080,
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4.94. Found C, 67.80; H, 4.97; N, 4.94%.
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Polymerization. Cyclotriphosphazene compounds were placed
in a Teflon mold and heated at 200 ꢀC (for 1 and 2) or at 150 ꢀC
(for 3) for 2 h under gentle pressure. The typical procedure of the
copolymerization of compound 3 with styrene is as follows:
compound 3 (0.056 g, 6.60 ꢂ 10ꢁ2 mmol) was dissolved in styrene
(1.0 g, 8.3 mmol). After addition of 2,2-dimethoxy-2-phenyl-
acetophenone (1.70 mg, 6.64 ꢂ 10ꢁ2 mmol), the resulting solu-
tion was irradiated by a UV lamp (a high pressure mercury arc
lamp, 3 mW cmꢁ2) for 2 h at room temperature.
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Commun., 1990, 11, 467.
22 K. Inoue, H. Nakamura, S. Ariyoshi, M. Takagi and T. Tanigaki,
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Acknowledgements
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This research was supported by a grant from the Fundamental
R&D Program for Core Technology of Materials funded by the
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754 | J. Mater. Chem., 2010, 20, 749–754
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