Synthesis of transparent and thermally stable polycyanurates and their thermal rearrangement

Article abstract of DOI:10.1002/pola.26803

Transparent and thermally stable polycyanurates, whose solubility can be changed by thermal rearrangement, have been synthesized as functional films used in the multilayer coating process. Before the synthesis of polycyanurates, the model compound, 2,6-bis(4-methoxyphenyl)-6-methoxy-1,3,5-triazine as a cyanurate is prepared and rearranged to an isocyanurate, 1,3-bis(4-methoxyphenyl)-5- methyl-1,3,5-triazinane-2,4,6-trione in an excellent yield by thermal treatment. Based on this result, polycyanurates are prepared by the phase-transfer- catalyzed polycondensation of 2,4-dichloro-6-methoxy-1,3,5-triazine with bisphenol monomers in the presence of quaternary ammonium salts. The polycyanurate obtained from 9,9-bis(hydroxyphenyl)fluorene exhibits a high glass transition temperature at 251°C. The solubility of polycyanurate films containing 1 wt % of tetrabutylammonium bromide can be changed by thermal rearrangement. The partially rearranged films keep high transparency and low birefringence. Copyright

Full text of DOI:10.1002/pola.26803

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Synthesis of Transparent and Thermally Stable Polycyanurates
and Their Thermal Rearrangement
Yoshitaka Saito, Hidetoshi Matsumoto, Tomoya Higashihara, Mitsuru Ueda
Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology,
2–12-1 H120 O-okayama, Meguro-ku, Tokyo 152-8550, Japan
Correspondence to: M. Ueda (E-mail: ueda.m.ad@m.titech.ac.jp)
Received 25 March 2013; accepted 25 May 2013; published online 22 June 2013
DOI: 10.1002/pola.26803
ABSTRACT: Transparent and thermally stable polycyanurates,
whose solubility can be changed by thermal rearrangement,
have been synthesized as functional films used in the multilayer
coating process. Before the synthesis of polycyanurates, the
model compound, 2,6-bis(4-methoxyphenyl)26-methoxy-1,3,5-
triazine as a cyanurate is prepared and rearranged to an isocya-
nurate, 1,3-bis(4-methoxyphenyl)25-methyl-1,3,5-triazinane-2,4,
6-trione in an excellent yield by thermal treatment. Based on this
result, polycyanurates are prepared by the phase-transfer-
catalyzed polycondensation of 2,4-dichloro-6-methoxy-1,3,5-tria-
zine with bisphenol monomers in the presence of quaternary
ammonium salts. The polycyanurate obtained from 9,9-
bis(hydroxyphenyl)fluorene exhibits a high glass transition tem-
perature at 251 ꢀC. The solubility of polycyanurate films contain-
ing 1 wt % of tetrabutylammonium bromide can be changed by
thermal rearrangement. The partially rearranged films keep high
C
V
transparency and low birefringence.
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KEYWORDS: change of solubility; high performance polymers;
phase transfer polycondensation; polycyanurate; polyisocyanu-
rate; tetrabutylammonium bromide; thermal properties; ther-
mal rearrangement; transparency; transparent and thermally
stable polymers
were required as described above. Aromatic s-triazine-based
polymers have attracted much interest academically and
industrially, due to their unique properties, such as excellent
thermal resistance, good chemical resistance, and high tensile
strengths and moduli.6–8 These properties may be attributed
to the rigid s-triazine units and the strong charge-transfer
interactions between the s-triazine rings and the aromatic
rings. Furthermore, triallyl cyanurate has been reported to
rearrange to triallyl isocyanurate by thermal treatment.9,10
INTRODUCTION The development of flexible displays is a fast
growing field due to the possibility of cost effective process-
ing. Flexible displays consist of many functional transparent
films, which are required for the multilayer coating process
and environmental stabilities. Thus, a postcuring procedure is
necessary for the film to prevent each layer from mixing by
applying the crosslinking reactions. For example, poly(ary-
lether-ketone)s with ethynyl as crosslinkable groups were
cured at a very high temperature.1,2 Poly(arylether-ketone)s
containing carboxylic acids were used to react with poly(vinyl
alcohol) or bisphenols to prepare crosslinked polymers.3,4
Another postcuring procedure is an intramolecular cyclization.
Poly(amic acid)s are soluble in aprotic solvents and converted
to polyimides (PIs) by thermal treatment. The resulting PIs
become insoluble in common organic solvents.5
Based on these findings, we report the synthesis of polycya-
nurates by the polycondensation of 2,4-dichloro-6-methoxy-
1,3,5-triazine with bisphenols and their thermal rearrange-
ment to the corresponding polyisocyanurates. It is found
that this thermal rearrangement of polymers is one of the
best methods to change the solubility of cast films.
Rearrangement, which is an intramolecular isomerization, is
also a potential tool to alter the solubility of polymers. It
induces the polarity change of the polymer, which means
that the solubility of the resulting polymers will be different
from that of the original polymers.
EXPERIMENTAL
Materials
The materials were used without further purification unless
otherwise noted. Bisphenol A and 9,9-bis(hydroxyphenyl)fluor-
ene were purified by recrystallization from acetone/hexane.
2,4-Dichloro-6-methoxy-1,3,5-triazine (1) was donated by San-
kyo Chemical, and was recrystallized from hexane.
Recently, thermally stable and transparent films, whose solu-
bility can be changed by thermal treatment or UV irradiation,
Additional Supporting Information may be found in the online version of this article.
C
V
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Synthesis of 2,6-Bis(4-methoxyphenyl)26-methoxy-1,3,5-
triazine (2)
in 1,1,2,2-tetrachloroethane (21.2 mL) was stirred vigorously
45 ꢀC for 2 h. The resulting solution was poured into the
solution of acetone/methanol (2/1, v/v), giving the end-
capped polymer 4a (1.26 g, 76%). The number average
molecular weight (Mn) and weight average molecular weight
(Mw) values estimated from size exclusion chromatography
(SEC) were 6.28 3 104 and 17.9 3 104, respectively, with
2.85 of the polydispersity index (PDI 5 Mw/Mn).
A solution of 4-methoxyphenol (1.20 g, 9.60 mmol), tetrabu-
tylammonium bromide (TBAB) (0.162 g, 0.504 mmol), and
sodium hydroxide (0.480 g, 12.0 mmol) in water was added
to a solution of 1 (0.720 g, 4.00 mmol) in chloroform (9.6
mL). The mixture was stirred vigorously for 3 h at room
temperature. To this mixture, water (10 mL) and chloroform
(10 mL) was added, and then the mixture was transferred to
a separatory funnel, mixed thoroughly, and the organic layer
was separated, dried over MgSO4, and concentrated under
reduced pressure with a rotary evaporator. The residue was
recrystallized from cyclohexane to produce 1.14 g (80%) of
2 as a white crystal.
IR (KBr), m (cm21): 1566 (C@C), 1504 (C@C), 1361 (C@N),
1211 (CAOAC). 1H NMR (300 MHz, CDCl3, d, 25 ꢀC): 7.25
(dd, J 5 6.75 and 1.80 Hz, 4H, ArH), 7.08 (dd, J 5 6.90 and
1.80 Hz, 4H, ArH), 3.94 (s, 3H, OACH3), 1.68 (s, 6H, CACH3).
13C NMR (75 MHz, CDCl3, d, 25 ꢀC): 174.06 (2 carbons),
173.60, 149.71 (2 carbons), 148.07 (2 carbons), 128.08 (4
carbons), 120.98 (4 carbons), 55.75, 42.68 (2 carbons),
31.14. Anal calcd. for C19H18N3O3: C, 67.84; H, 5.39; N,
12.49. Found: C, 67.97; H, 5.20; N, 12.42.
M.p. 106.5–107.0 ꢀC. IR (KBr), m (cm21): 1566 (C@C), 1504
(C@C), 1369 (C@N), 1203 (CAOAC). 1H NMR (300 MHz,
CDCl3, d, 25 ꢀC): 7.08 (dd, J 5 6.90 and 2.40 Hz, 4H; ArH),
6.89 (dd, J 5 6.75 and 2.40 Hz, 4H; ArH), 3.93 (s, 3H;
OACH3), 3.80 (s, 6H; OACH3). 13C NMR (75 MHz, CDCl3, d,
25 ꢀC): 174.09, 173.96 (2 carbons), 157.49 (2 carbons),
145.36 (2 carbons), 122.38 (4 carbons), 114.63 (4 carbons),
55.72 (2 carbons), 55.68. Anal calcd. for C18H17N3O5: C,
60.84; H, 4.82; N, 11.82. Found: C, 61.07; H, 4.93; N, 11.79.
Synthesis of Polycyanurate 4b
The polymer 4b was prepared by the same procedure of 4a
using monomer 1 with 9,9-bis(hydroxyphenyl)fluorene as
described above except for using TBAB as a phase transfer
catalyst (1.27 g, 81%). The Mn and Mw values estimated
from SEC were 3.82 3 104 and 8.21 3 104, respectively,
with 2.15 of PDI.
Synthesis of 1,3-Bis(4-methoxyphenyl)25-methyl-1,3,5-
triazinane-2,4,6-trione (3)
IR (KBr), m (cm21): 1566 (C@C), 1500 (C@C), 1369 (C@N),
1211 (CAOAC). 1H NMR (300 MHz, CDCl3, d, 25 ꢀC): 7.76–
7.01 (m, 16H, ArH), 3.88 (s, 3H, OACH3). 13C NMR (75 MHz,
CDCl3, d, 25 ꢀC): 173.95 (2 carbons), 173.46, 150.8 (2 car-
bons), 150.52 (2 carbons), 143.49 (2 carbons), 140.17 (2
carbons), 129.41 (4 carbons), 128.01 (2 carbons), 127.09 (2
carbons), 126.32 (2 carbons), 121.31 (2 carbons), 120.42 (2
carbons), 64.74, 55.76. Anal calcd. for C29H20N3O3: C, 75.97;
H, 4.40; N, 9.16. Found: C, 75.97; H, 4.53; N, 9.01.
A test tube charged with the compound 2 (0.164 g, 0.464
mmol) was heated at 260 ꢀC for 10 min under nitrogen
atmosphere. The product was purified by silica gel column
chromatography (eluent: ethyl acetate/hexane (6/4, v/v)) to
give the compound 3 (yield: 0.135 g, 82%). Recrystallization
from toluene yielded a white crystal.
M.p. 161.4–162.6 ꢀC. IR (KBr), m (cm21): 1720 (C@O), 1547
(C@C), 1500 (C@C), 1211 (CAOAC). 1H NMR (300 MHz,
CDCl3, d, 25 ꢀC): 7.14–6.82 (m, 8H, ArH), 3.82 (s, 3H,
OACH3), 3.77 (s, 3H, OACH3), 3.59 (s, 3H, NACH3). 13C NMR
(75 MHz, CDCl3, d, 25 ꢀC): 169.75, 164.16 (2 carbons),
158.26–156.63 (2 carbons), 145.20–144.08 (2 carbons),
122.37–122.17 (4 carbons), 114.98–114.56 (4 carbons),
55.79–55.71 (2 carbons), 29.68. Anal calcd. for C18H17N3O5:
C, 60.84; H, 4.82; N, 11.82. Found: C, 60.99; H, 5.04; N,
11.79.
Measurement
The 1H and 13C NMR spectra were recorded on a BRUKER
DPX-300S spectrometer at resonant frequencies of 300 MHz
1
for H and 75 MHz for 13C nuclei using CDCl3 as the solvent
and tetramethylsilane as the reference. The FTIR spectra
were measured by a Horiba FT-120 Fourier transform spec-
trophotometer. Mn and Mw values were measured by SEC on
a JASCO GULLIVER 1500 system equipped with two polysty-
rene gel columns (Plegel 5 lm MIXED-C) eluted with chloro-
Synthesis of Polycyanurate 4a
A solution of bisphenol A (1.14 g, 5.00 mmol), benzylcetyldi-
methylammonium chloride hydrate (BCDMAC) (0.250 g,
0.631 mmol), and sodium hydroxide (0.600 g, 15.0 mmol) in
water was added to a solution of 1 (0.900 g, 5.00 mmol) in
chloroform (13 mL). The mixture was stirred vigorously at 0
ꢀC for 2 h. To this mixture was added 4-methoxyphenol
(1.24 mg, 0.100 mmol), and then this mixture was stirred
form at a
flow rate of 1.0 mL min21 calibrated by
polystyrene standard samples. The UV–visible optical absorp-
tion spectra were recorded on a Hitachi U-3210 spectropho-
tometer at room temperature. The absorbance of polymer
solutions was evaluated in the wavelength range of 200–800
nm. Elemental analyses were performed on a Yanaco MT-6
CHN recorder elemental analysis instrument. Thermal analy-
sis was performed on a Seiko EXSTAR 6000 TG/DTA 6300
ꢀ
vigorously at 0 C for 30 min. The organic layer was washed
21
ꢀ
with water and poured into acetone. The fibrous polymer
was obtained in good yield (1.31 g, 78%). Next, the obtained
polymer was end-capped with acetic anhydride. A solution of
the polycyanurate 4a (1.31 g, 3.91 mmol), acetic anhydride
(3.84 mL, 40.6 mmol), and pyridine (0.490 mL, 6.09 mmol)
thermal analysis system at a heating rate of 10 C min for
thermogravimetry (TG) and on a differential scanning calo-
rimetry (DSC) 6200 a heating rate of 10 ꢀC min21 for DSC
under nitrogen. The in-plane (nTE) and out-of-plane (nTM
)
refractive indices of polycyanurate films with more than 3
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SCHEME 1 Synthesis of model compound 2 and its thermal rearrangement to the corresponding isocyanurate 3.
lm thickness were measured with using a prism coupler
(Metricon, model PC-2000) equipped with a He-Ne laser
light source (wavelength: 632.8 nm). The in-plane/out-of-
plane birefringence (Dn) was calculated as the difference
between nTE and nTM. The average refractive index (nav) was
calculated using eq 1:
13C NMR spectra of 3 are presented in Figure 1 with assign-
ments of all signals. The signal at 3.59 ppm in Figure 1(A) is
assignable to the methyl group. Two singlet signals for
methoxy protons attached to the aromatic ring are observed
at 3.82 and 3.77 ppm, probably due to the boat and the chair
conformations. In the 13C NMR spectrum [Fig. 1(B)], each aro-
matic and methoxy carbon exhibits two signals, which is also
explained by the existence of two conformers as described
above.12 Elemental analyses also supported the formation of
compound 3.
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
n
AV 5 ð2nTE 212nTM Þ=3
(1)
RESULTS AND DISCUSSION
Synthesis of Polycyanurates
Model Reaction
Nakamura et al. reported the synthesis of polycyanurates
by the interfacial polycondensation of 2,4-dichloro-6-substi-
tuted-1,3,5-triazines with various aromatic diols in the
presence of cationic emulsifiers.9 According to this report,
the phase-transfer-catalyzed polycondensation of compound
1 with bisphenol monomers, bisphenol A, and 9,9-bis(hy-
droxyphenyl)fluorine was carried out in a chloroform-
aqueous alkaline solution at room temperature to afford
polycyanurates 4. Quaternary ammonium salts such as
BCDMAC and TBAB were employed as a phase-transfer cat-
alyst. The polycondensations proceeded smoothly and gave
polycyanurates 4 with high molecular weights (Scheme 2).
The end-cap of polymers was carried out by adding 4-
methoxyphenol at the chloro-1,3,5-triazine end polymers,
followed by acetylation of the hydroxy end polymers with
acetic anhydride. The results are summarized in Table 1.
The BCDMAC with a long alkyl group is very effective for
the polymerization using bisphenol A, on the other hand,
TBAB with short alkyl chains is suitable for the polymeriza-
tion using 9,9-bis(hydroxyphenyl)fluorene. These results
may be explained by the different characteristics of
BCDMAC and TBAB, which act as an emulsifier and a phase
transfer catalyst, respectively. The more organic structure
of 9,9-bis(hydroxyphenyl)fluorene compared to bisphenol A
favors a phase transfer catalyst to transfer the anion in the
water phase to the organic phase.10 The Mns and PDI of
polycyanurates 4a and 4b are 62.8 3 103 and 2.85, and
38.2 3 103 and 2.15, respectively, determined by SEC using
a polystyrene standard.
As described in the Introduction, triallyl cyanurate thermally
rearranges to triallyl isocyanurate.9,10 However, no studies on
the thermal rearrangement of polycyanurates have been pub-
lished. Therefore, before the synthesis of polycyanurates, the
model compound, 2,6-bis(4-methoxyphenyl)26-methoxy-
1,3,5-triazine (2) was prepared by the interfacial reaction of
2,4-dichloro-6-methoxy-1,3,5-triazine (1) in chloroform with
4-methoxyphenol in an aqueous alkaline solution (Scheme 1),
and its thermal rearrangement was studied. Thermal
treatment of compound 2 was carried out in a test tube at
260 ꢀC for 10 min, producing the isocyanurate, 1,3-bis
(4-methoxyphenyl)25-methyl-1,3,5-triazinane-2,4,6-trione (3),
in good yield (Scheme 1). The chemical structure of 3 was
1
assigned on the basis of FTIR, H and 13C NMR spectroscopy,
and elemental analysis. The FTIR spectrum exhibited strong
carbonyl absorption at 1712 cm21 and no trace of a C@N
1
stretching absorption was detected at 1369 cm21. The H and
1
The structures of polycyanurates 4 were characterized by H
and 13C NMR and FTIR spectroscopy. The characteristic
peaks of polycyanutrates 4a and 4b were observed at 1361
and 1369 cm21, respectively, which are attributable to the
1
C@N stretching. Figure 2(A) shows the H NMR spectrum of
polycyanutrate 4b. The resonances at 7.76–7.01 and 3.88
ppm are assignable to the aromatic and methoxy protons.
The assignments of all carbon signals in the 13C NMR spec-
trum for polycyanutrate 4b are summarized in Figure 2(B).
FIGURE 1 The (A) 1H and (B) 13C NMR spectra of 3.
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SCHEME 2 Synthesis of polycyanurates 4 from compound 1 with bisphenol monomers.
TABLE 1 Synthesis of Polycyanurates 4
Polymer
Catalyst
Temperature (ꢀC)
Time (h)
Mn (SEC)a (kg mol21
)
PDI (SEC)a
Mn (NMR)b (kg mol21
)
Yield (%)
4a
BCDMACc
TBABd
0
2.5
3
62.8
1.08
5.64
38.2
2.85
1.68
1.84
2.15
85.2
–
75.5
11.4
14.9
81.2
0
4b
BCDMAC
TBAB
r.t.
r.t.
7
–
9.5
34.2
a
Determined by SEC.
Determined by 1H NMR.
b
c
BCDMAC: benzylcetyldimethylammonium chloride hydrate.
TBAB: tetrabutylammonium bromide.
d
The 4-methoxy phenyl and acetyl protons of both terminal
ends were observed at 3.79 and 2.28 ppm, respectively, in
the magnified 1H NMR spectrum of polycyanutrate 4a.
Furthermore, the elemental analysis also supported the for-
mation of polycyanutrates 4.
Thermal Rearrangement
The thermal stabilities of polymers, such as high degradation
temperature and high glass transition temperature, are one
of the most important requirements for manufacturing opti-
cal films. The thermal properties of polycyanurates 4 were
evaluated by TG and DSC. As shown in Figure 3, polycyanu-
rates 4a and 4b exhibit 5% weight loss temperatures at 380
Polycyanurates are white solids and soluble in dichlorome-
thane, chloroform, and NMP. A white transparent film was
obtained by casting from a chloroform solution of 4.
ꢀ
ꢀC and 394 C, respectively under nitrogen. Their glass tran-
sition temperatures (Tgs) determined by DSC measurements
are 165 and 251 ꢀC, respectively. Polycyanurate 4b exhibits
high Tg due to a bulky cardo structure (Fig. 4). Moreover,
large exothermic peaks for polycyanurates 4a and 4b are
ꢀ
found at 279 and 302 C, respectively, where no weight loss
is observed, suggesting the rearrangement of
4
to
FIGURE 2 The (A) 1H and (B) 13C NMR spectra for polycyanu-
rate 4b.
FIGURE 3 TGA curves of polycyanurates 4 under nitrogen at a
heating rate of 10 ꢀC min21
.
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TABLE 2 Solubility of Polycyanurates 4 and Partially Rear-
ranged Polycuanurate 5
Polymer
CHCl3
CH2Cl2
NMP
DMAc
THF
4a
5a
4b
5b
11
2
11
2
1
2
2
2
2
2
2
2
2
1
11
2
11
1
11
11
11: Soluble, 1: partially soluble, 2: insoluble.
required. In fact, the 4a film containing 1 wt % of TBAB
became insoluble in chloroform after thermal treatment at
180 ꢀC for 30 min. The degree of rearrangement was esti-
mated from the decrease of relative intensity of the absorp-
tion band at 1361 cm21 corresponding to the C@N
stretching as 15%. Similarly, the changes of IR spectra in the
thermally treated polycyanurate 4b indicate that the degree
of rearrangement from 4b to polyisocyanurate also increases
with increasing the amount of TBAB (Fig. 5). The 4b film
containing 1 wt % of TBAB became insoluble in chloroform
at 200 ꢀC for 10 min, and its degree of rearrangement was
8.5% estimated by the method described above using the
absorption band at 1369 cm21. These resulting polymers are
referred to as partially rearranged polyisocyanurates 5a and
5b, respectively. The solubility of all polymers is listed in
Table 2. The inherent viscosity of 4a and 5a (before and
after thermal rearrangement) has been investigated. Unfortu-
FIGURE 4 DSC curves of polycyanurates 4 under nitrogen at a
heating rate of 10 ꢀC min21
.
polyisocyanurate 5. Based on these findings, the thermal
rearrangement of polycyanurate 4a was investigated at 260
ꢀC for 10 min under nitrogen. After thermal treatment, the
flexible film became brittle likely due to the decrease of the
molecular weight, indicating that some side reactions
occurred during the rearrangement. To avoid this problem, a
thermal rearrangement of polycyanurate 4 at a lower tem-
perature in the presence of catalysts would be effective.
Grosu et al. reported that isocyanurate derivatives were
obtained by the rearrangement reaction from cyanurate
derivatives in a process catalyzed by TBAB or tetrabutylpho-
11
ꢀ
nately, the ginh value decreased from 0.96 to 0.27 dL g21
,
phonium bromide at 120 C without any solvent. Thus, the
thermal rearrangement of polycyanurate 4a was carried out
at various temperatures in the presence of TBAB, and it was
found that the thermal rearrangement proceeded at 180 ꢀC.
which indicates that the degradation of main chains occurred
to some extent. However, the solubility of polymers in CHCl3
and CH2Cl2 reduced enough almost without scarifying their
film property after the thermal rearrangement.
ꢀ
As a result, the Tg value of 4a increased to 237 C (5a) (Sup-
porting Information Fig. S1). The effect of TBAB loading on
the thermal rearrangement was studied, and the changes of
the FTIR spectra in the thermally treated polycyanutate 4a
are shown in Figure 5. The intensity of the characteristic car-
bonyl absorption peak of polyisocyanurate increases with
increasing the amount of TBAB. To change the solubility of
polycyanurates, a complete rearrangement would not be
Optical Properties
Figure 6 shows the UV–vis absorption spectra of polycyanu-
rate 4 and partially rearranged polycyanurate 5 after the
thermal treatment. All polymers exhibit high transparency in
the visible region (k: 400–800 nm) with transmittance over
90% at 400 nm even after thermal rearrangement. The high
FIGURE 5 FTIR spectra on the thermally treated polycyanurate (A) 4a and (B) 4b in the presence of various amounts of TBAB.
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TABLE 3 Optical Properties of Polycyanurates 4 and Partially
Rearranged Polycyanurates 5
Dnc
nAV
ee
a
b
d
Polymer
nTE
nTM
4a
5a
4b
5b
1.5964
1.5985
1.6368
1.6424
1.5924
1.5937
1.6356
1.6416
0.0041
0.0048
0.0012
0.0008
1.5951
1.5969
1.6364
1.6421
2.54
2.55
2.68
2.70
a
The in-plane refractive indices at 633 nm.
The out-of-plane refractive indices at 633 nm.
b
c
Birefringence: Dn 5 nTE 2 nTE
.
d
e
Average refractive index: nAV 5 [(2nTE2 1 nTE2)/3]1/2
.
2
Dielectric constant: e 5 1.0 nAV
.
FIGURE 6 The UV–vis absorption spectra of polycyanurates 4
and partially rearranged polycyanurates
treatment.
5
after thermal
ACKNOWLEDGMENTS
This work is supported by the JSR Corporation. The authors
gratefully thank Masaru Mizoroki and Shinji Ando in the
Department of Chemistry and Materials Science, Tokyo Insti-
tute of Technology, for the assistance of the measurement for
refractive indices.
transparency may originate from the isolated aromatic rings.
No coloration in the films after thermal rearrangement was
observed (Fig. 6).
The refractive indices and their birefringence for polymers
are summarized in Table 3. All polymers have relatively high
refractive indices due to the aromatic units, and show low
birefringence. In fact, the birefringence values of the poly-
mers 4b and 5b are very low due to a bulky cardo structure,
which prevents in-plane orientation of the molecular chains.
These results indicate that polycyanurate 4b is promising for
high Tg and transparent materials whose solubility can be
changed by thermal treatment.
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CONCLUSIONS
4 H. Yu, L. Wang, Z. Wang, X. Han, M. Zhao, Polymer 2010, 51,
3269–3276.
High-molecular-weight polycyanurate 4 had been success-
5 M. K. Ghosh, K. L. Mittal, Polyimides: Fundamentals and
Applications; M. Dekker: New York, 1996.
fully prepared by the phase-transfer-catalyzed polycondensa-
tion of monomer
1 with bisphenol monomers in the
6 J. Verborgt, C. S. Marvel, J. Polym. Sci. Polym. Chem. 1973,
11, 261–273.
presence of quaternary ammonium salts. Polymer 4b exhib-
ited a 5% weight loss temperature and Tg at 394 and 251
ꢀC, respectively. Polycyanurate 4 partially rearranged to poly-
isocyanurate by thermal treatment. The solubility of polymer
4 films containing 1 wt % of TBAB could be changed by
thermal rearrangement. The partially rearranged films 5
kept high transparency and low birefringence. Therefore, pol-
ycyanurate 4 is one of the candidates for functional trans-
parent films, which require a multilayer coating process and
environmental stabilities. Furthermore, the rearrangement of
polymers by thermal treatment is one of the best methods
to prevent mixing of each layer for the multilayer coating
process.
7 D. R. Anderson, J. M. Holovka, J. Polym. Sci. Polym. Chem.
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9 Y. Nakamura, K. Mori, K. Tamura, Y. Saito, J. Polym. Sci.
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