Synthesis and characterization of alkaline-soluble triazine-based poly(phenylene sulfide)s with high refractive index and low birefringence

Article abstract of DOI:10.1002/pola.28945

High-refractive-index (high-n) polymers (HRIPs) with a high optical transparency are highly needed in advanced optoelectronic devices. In this work, we report the synthesis and characterization of a series of high-n, transparent, totally colorless, and hi

Full text of DOI:10.1002/pola.28945

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Synthesis and Characterization of Alkaline-Soluble Triazine-Based
Poly(phenylene sulfide)s with High Refractive Index and Low
Birefringence
1
Mao-Chun Fu,1 Yoshitaka Murakami,2 Mitsuru Ueda,1 Shinji Ando,3 Tomoya Higashihara
1Department of Organic Materials Science, Yamagata University, Yonezawa, Yamagata 992-8510, Japan
2JSR Corporation, 1-9-2, Higashi-Shinbashi, Minato-ku, Tokyo 105-8640, Japan
3Department of Chemical Science and Engineering, Tokyo Institute of Technology, Ookayama 2-12-1-E4-5, Meguro-ku, Tokyo
152-8552, Japan
Correspondence to: T. Higashihara (E-mail: thigashihara@yz.yamagata-u.ac.jp)
Received 27 November 2017; accepted 15 December 2017; published online 00 Month 2018
DOI: 10.1002/pola.28945
ABSTRACT: High-refractive-index (high-n) polymers (HRIPs) with
a high optical transparency are highly needed in advanced
optoelectronic devices. In this work, we report the synthesis
and characterization of a series of high-n, transparent, totally
colorless, and high-sulfur-containing poly(phenylene sulfide)s
(PPSs) bearing a triazine unit. Two new triazine monomers T1
and T2 with hydroxyl and tert-butyl acetate side chains, respec-
tively, were designed and synthesized to develop PPSs with
high-n and high alkaline solubility. These PPSs were prepared
by the single-phase polycondensation from T1/T2 and
commercial aromatic dithiols such as 4,40-thiobisbenzenethiol
(TBT) and benzene-1,3-dithiol (BDT), achieving very high-n up
to 1.7530 at 633 nm, a high optical transparency (T% > 90%
@400 nm) and low birefringence (Dn 5 0.0014–0.0080), and
exhibiting high potential on the application of high-n photore-
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sists.
2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A:
Polym. Chem. 2018, 00, 000–000
KEYWORDS: birefringence; optoelectronic; photoresist; poly(phe-
nylene sulfide); refractive index
INTRODUCTION High-refractive-index
(high-n)
polymers
However, polymers have relatively low n values in the
(HRIPs) with a high optical transparency have been widely
used in daily life. A very high-n over 1.7 or even 1.8 is fre-
quently desired for advanced optical device applications
(e.g., thermoplastic lenses, high-performance substrates for
display devices, optical adhesives, encapsulates for light
emitting diode (LED) and organic light emitting diode
(OLED), antireflective coatings, or microlens components for
CMOS or CCD image sensors).1–7 Therefore, HRIPs with
high-n values, high transparency and low birefringence have
received considerable attention in the past few decades.
The general approach to improve n values in polymers
involves the introduction of substituents with high molar
refraction and low molar volume according to the Lorentz–
Lorenz equation.8 Thus, aromatic rings, heavy halogens (Cl,
Br, and I, except for F), sulfur, and metallic elements have
been introduced in polymers to enhance their n values.9
Therefore, many conventional sulfur-containing high-n poly-
mers with high optical transparency have been reported for
optical device applications, such as epoxy resins,10 polyur-
ethanes,11 polymethacrylates,12 and poly(arylene sulfide)s.13
range of 1.5–1.7 at the sodium-D line (589 nm) or 633 nm.
In the past few decades, our group has developed a series of
sulfur-containing aromatic polyimides (PIs) for optical appli-
cations because PIs have several advantages such as high
thermal, oxidative, chemical, and mechanical stabilities.14–21
These PIs showed high-n values in the range of 1.74–1.77
and low birefringence values of less than 0.0093, but the
optical transparency in approximately 400 nm of 10 lm-
thick films was lower than 80% due to the coloration origi-
nating from the inter/intra-charge transfer (CT) interactions
between the electron-donating and electron-accepting moie-
ties in the PIs. These problems limited the progress in opti-
cal applications of the aromatic PIs.
Alternatively, poly(aryl ether)s and poly(aryl thioether)s,
such as poly(arylene ether ketone)s, poly(arylene ether sul-
fone)s, and poly(phenylene sulfide)s, are well-known high-
performance engineering thermoplastics. Such polymers
have several advantages of not only high thermal, oxidative,
and chemical stabilities but also high stiffness and
Additional Supporting Information may be found in the online version of this article.
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toughness.22 Recently, poly(thioether ketones) and poly(aryl
thioether)s containing fluorene, sulfone, and oxadiazole sub-
stituents have been developed for optical applica-
tions.13,23–26 Most of the polymers showed high thermal
stability and excellent optical transparency with low bire-
fringence. However, the n values of these polymers are in
the range of 1.65–1.72 at the sodium-D line (589 nm). The
relatively low refractive indices are mainly attributed to two
factors. One is the low sulfur content because the n values
of sulfur-containing polymers mainly depend on the sulfur
content in the repeating unit.27 The other is that the steri-
cally bulky substituents such as fluorene and sulfone groups
endow large free volumes among polymer chains, which
lowers the n values. Therefore, a breakthrough in the trade-
off between the refractive index and optical transparency is
an important topic. To enhance the n values, heteroaromatic
rings containing AC@NA bonding in place of the phenyl
rings can be effective because the ACAN@CA bonds pos-
sess a higher molar refraction (4.10) compared to the
AC@CA bond (1.73).28,29 On the basis of this finding, we
were interested in triazine dichloride with various alkylsul-
fanyl side chains as monomers and reported a highly refrac-
tive and transparent poly(phenylene sulfide)s (PPSs)
containing a triazine unit, which were obtained by the poly-
condensation of the aromatic dithiols (4,40-thiobisbenzene-
thiol (TBT), benzene-1,3-dithiol (BDT) and thianthrene-2,7-
dithiol (TDT)) and triazine dichloride derivatives (2,4-
dichloro-6-methylthio-1,3,5-triazine (DMT) and 2,4-dichloro-
6-butylthio-1,3,5-triazine (DBT)). These polymers exhibited
high-n values (nav 5 1.7222–1.7720 at 633 nm), excellent
transmittance in the visible region (T > 80% @400 nm) and
low birefringence values (Dn 5 0.0013–0.0051).30,31 These
results provide a new concept to develop HRIPs, prompting
the development of a high-n polymer matrix for photoresists
by employing sulfur-containing triazine-based poly(pheny-
lene sulfide)s. In the application of positive-type photore-
solubility of the polymer by the introduction of a pendant
phenolic and tert-butyl ester moieties. The obtained PPSs
exhibited high-n values in the range of 1.6486–1.7530, low
birefringence values in the range of 0.0014–0.0080, a high
optical transparency over 400 nm and good solubility in
2.38 wt% tetramethylammonium hydroxide (TMAH)(aq) after
the deprotection of the tert-butyl ester groups in case of
PPS-3 and PPS-4.
EXPERIMENTAL
Materials
The materials were used without further purification unless
otherwise noted. The thermal acid generator (TAG), isopropyl
methanesulfonate (IMS), was prepared through a previous
reference.36 TBT and BDT were purified by recrystallization
from toluene and a mixed solution of toluene/n-hexane,
respectively.
Synthesis of tert-Butyl 2-((4-Hydroxyphenyl)sulfanyl)acetate
A 20 mL round flask was charged with 4-hydroxybenzenethiol
(0.505 g, 4.00 mmol), tert-butyl bromoacetate (0.835 g, 4.28
mmol), potassium carbonate (0.354 g, 2.56 mmol), and N,N-
dimethylformamide (DMF) (5 mL). The solution was stirred at
room temperature for 24 h, extracted with ethyl acetate and
then washed with deionized water. The organic fractions were
combined, and the solvent was dried over MgSO4. Then, the sol-
vent was removed under reduced pressure. Further purifica-
tion by flash column chromatography (silica gel, n-hexane/
ethyl acetate, 5/1, v/v) yielded 0.865 g (90%) of tert-butyl 2-
((4-hydroxyphenyl)sulfanyl)acetate as a white solid. 1H NMR
(400 MHz, CDCl3-d1, d, 25 8C): 7.40 (d, J 5 9.20 Hz, 2H; ArH),
6.82 (d, J 5 9.20 Hz, 2H; ArH), 4.48 (s, 1H; ArOH), 3.43 (s, 2H),
1.38 (s, 9H).
General Synthetic Procedures of the Triazine Monomer
Cyanuric chloride (30 mmol) was mixed with 100 mL of
THF at different temperatures. The resulting solution was
dropwise added to a solution of aromatic thiol or phenol
derivatives (20 mmol) and triethylamine (TEA) (20 mmol) in
25 mL of tetrahydrofuran (THF). After stirring at 240 8C
overnight, the reaction mixture was washed once with satu-
rated NH4Cl(aq) and 3 times with NaCl(aq). The organic frac-
tions were combined and the solvent was dried over MgSO4,
then the solvent was removed under reduced pressure. The
crude compound was further purified by flash column chro-
matography, yielding a white solid.
sists,
a
dissolution inhibitor (DI) system employing
diazonaphthoquinone (DNQ) has been widely used. In this
system, an alkaline soluble polymer matrix is needed. After
the exposure of UV light, DNQs changed structures generat-
ing carboxylic acid groups, working as dissolution pro-
moters to increase the dissolution rate of the exposed area.
However, the DNQs in the unexposed area could work as
dissolution inhibitors to generate the dissolution contrast
between the exposed and unexposed areas and the clear
positive-tone patterns could be obtained. Therefore, the
polymer matrices with a good alkaline solubility are highly
32
R
Synthesis of 2,6-Dichloro-4-(4-hydroxyphenyl)sulfanyl-
1,3,5-triazine (T1)
V
desired in this area (e.g., Novolac resin, poly (amic acid)s
(PAAs),33 and poly(hydroxyl amide)s (PHAs)34).
The general synthetic procedures for the triazine monomer
were followed using 4-mercaptophenol as the aromatic thiol
derivative. The reaction was carried out at 240 8C. The
purification was performed by flash column chromatogra-
phy (silica gel, n-hexane/ethyl acetate, 5/1, v/v), yielding a
white solid (4.44 g, 80%). 1H NMR (400 MHz, CDCl3-d1, d,
25 8C): 7.41 (d, J 5 8.00 Hz, 2H; ArH), 6.91 (d, J 5 8.00 Hz,
2H; ArH), 5.43 (s, 1H; ArOH). 13C NMR (100 MHz, CDCl3-
d1, d, 25 8C): 187.18 (1 carbon), 170.60 (2 carbons),
Therefore, in this work, we focused on the development of
alkaline-soluble high-n triazine-based poly(phenylene sul-
fide)s from triazine derivatives and aromatic dithiols. The tri-
azine units together with sulfur atoms generally lead to a
high transmittance in the visible region and high-n values. In
addition, the chemoselectivity of each chloride toward the
substitution reaction of cyanuric chloride facilitates the
design of a monomer side chain,35 providing the alkaline
2
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157.94 (1 carbon), 137.20 (1 carbon), 116.97 (2 carbons),
116.06 (2 carbons). Anal calcd. for C9H5Cl2N3OS: C, 39.44;
H, 1.84; N, 15.33; S, 11.70. Found: C, 40.41; H, 1.95; N,
15.70; S, 11.75.
C15H11N3OS3: C, 52.46; H, 2.64; N, 12.24; S, 28.01. Found: C,
53.28; H, 3.04; N, 11.33; S, 26.17.
PPS-3 (T2/TBT)
The general synthetic procedures for poly(phenylene sul-
fide)s were followed, yielding PPS-3 (0.47 g, 85%) as a
white fiber. 1H NMR (400 MHz, CDCl3-d1, d, 25 8C): 7.31 (d,
J 5 8.00 Hz, 4H; ArH), 7.28 (d, J 5 8.40 Hz, 2H; ArH), 7.24 (d,
J 5 8.00 Hz, 4H; ArH), 6.91 (d, J 5 8.40 Hz, 2H; ArH), 3.54 (s,
2H), 1.37 (s, 9H). 13C NMR (100 MHz, CDCl3-d1, d, 25 8C):
183.40 (2 carbons), 168.72 (1 carbon), 168.06 (1 carbon),
150.47 (1 carbon), 137.49 (2 carbons), 135.79 (2 carbons),
132.76 (1 carbons), 131.34 (4 carbons), 130.66 (4 carbons),
126.08 (2 carbons), 122.04 (2 carbons), 82.11 (1 carbon),
38.20 (1 carbon), 28.02 (3 carbons). Anal calcd. for
Synthesis of 4-[(4-(tert-Butoxycarbonyl)methylsulfanyl)
phenoxyl]-2,6-dichloro-1,3,5-triazine (T2)
The general synthetic procedures for the triazine monomer
were followed with tert-butyl 2-((4-hydroxyphenyl)sulfany-
l)acetate as the aromatic thiol derivative. The reaction was
carried out at 0 8C. The purification was performed by
flash column chromatography (silica gel, n-hexane/ethyl
acetate, 5/1, v/v), yielding a white solid (5.44 g, 70%). 1H
NMR (400 MHz, CDCl3-d1, d, 25 8C): 7.49 (d, J 5 8.40 Hz,
2H; ArH), 7.11 (d, J 5 8.40 Hz, 2H; ArH), 3.57 (s, 2H),
1.39 (s, 9H). 13C NMR (100 MHz, CDCl3-d1, d, 25 8C):
173.22 (1 carbon), 171.12 (2 carbons), 168.63 (1 carbon),
149.88 (1 carbon), 134.27 (1 carbon), 131.55 (2 carbons),
121.68 (2 carbons), 82.33 (1 carbon), 37.98 (1 carbon),
27.99 (3 carbons). Anal calcd. for C15H15Cl2N3O3S: C,
46.40; H, 3.89; N, 10.82; S, 8.26. Found: C, 46.46; H, 3.91;
N, 10.70; S, 7.71.
C27H23N3O3S4: C, 57.32; H, 4.10; N, 7.43; S, 22.67. Found: C,
57.21; H, 3.87; N, 7.34; S, 22.38.
PPS-4 (T2/BDT)
The general synthetic procedures for poly(phenylene sul-
fide)s were followed, yielding PPS-4 (0.38 g, 84%) as a
white fiber. 1H NMR (400 MHz, CDCl3-d1, d, 25 8C): 7.34 (d,
J 5 8.00 Hz, 2H; ArH), 7.33 (s, 1H; ArH), 7.25 (d, J 5 8.40 Hz,
2H; ArH), 7.14 (t, J 5 8.00 Hz, 1H; ArH), 6.84 (d, J 5 8.40 Hz,
2H; ArH) 3.53 (s, 2H), 1.40 (s, 9H). 13C NMR (100 MHz,
CDCl3-d1, d, 25 8C): 183.26 (2 carbons), 168.70 (1 carbon),
168.08 (1 carbon), 150.38 (1 carbon), 141.40 (2 carbons),
136.59 (1 carbon), 132.73 (1 carbon), 131.08 (2 carbons),
129.81 (2 carbons), 127.71 (1 carbon), 122.00 (2 carbons),
82.16 (1 carbon), 38.12 (1 carbon), 28.02 (3 carbons). Anal
calcd. for C21H19N3O3S3: C, 55.12; H, 4.19; N, 9.18; S, 21.02.
Found: C, 54.77; H, 3.95; N, 9.03; S, 21.21.
General Synthetic Procedures for Poly(phenylene
Sulfide)s
The triazine monomer (1 mmol), aromatic dithiols (1 mmol),
and 2 mL of THF were placed in a 10 mL round flask. TEA
(2.2 mmol) was dropwise added to the solution at 0 8C with
vigorous stirring. After stirring at room temperature over-
night, the solution was poured into methanol. Then, the pre-
cipitate was filtered and dried under vacuum at 70 8C,
yielding a white polymer.
Film Preparation
PPS-1 (T1/TBT)
All of the polymer films were prepared by solution casting in
DMAc, followed by heating on a hot plate from 25 to 100 8C
under a nitrogen atmosphere. Films with a thickness of 20–
60 lm were obtained.
The general synthetic procedures for the poly(phenylene sul-
fide)s were followed, yielding PPS-1 (0.36 g, 80%) as a
white precipitate. H NMR (400 MHz, THF-d8, d, 25 8C): 8.81
1
(s, 1H; ArOH), 7.33 (d, J 5 8.40 Hz, 4H; ArH), 7.24 (d,
J 5 8.40 Hz, 4H; ArH), 7.16 (d, J 5 8.40 Hz, 2H; ArH), 6.69 (d,
J 5 8.40 Hz, 2H; ArH). 13C NMR (100 MHz, THF-d8, d, 25 8C):
181.54 (2 carbon), 179.67 (1 carbon), 159.43 (1 carbon),
137.20 (1 carbon), 136.90 (1 carbon), 135.74 (1 carbon),
131.21 (4 carbons), 126.56 (4 carbons), 116.20 (2 carbon),
115.71 (2 carbons). Anal calcd. for C21H13N3OS4: C, 55.85; H,
2.90; N, 9.31; S, 28.40. Found: C, 55.36; H, 3.02; N, 8.46; S,
28.34.
Solubility Tests
The solubility tests using organic solvents are carried out in
the bulk samples at the concentration of 10 mg/mL. The
alkaline solubility is checked by the film samples that were
prepared from DMAc solutions through spin coating on sili-
con wafers. For PPS-3 and PPS-4, 10 wt% of the thermal
acid generator (TAG) was first blended with PPSs after spin
coating on the silicon substrates. The resulting films were
heated on a hot plate at 150 8C for 2 min to catalyze the
deprotection reactions of t-butyl ester groups.
PPS-2 (T1/BDT)
The general synthetic procedures for poly(phenylene sul-
fide)s were followed, yielding PPS-2 (0.24 g, 70%) as a
white precipitate. 1H NMR (400 MHz, THF-d8, d, 25 8C):
10.00 (s, 1H; ArOH), 7.40 (d, J 5 8.00 Hz, 2H; ArH), 7.35 (s,
1H; ArH), 7.10 (t, J 5 8.40 Hz, 1H; ArH), 6.83 (d, J 5 8.40 Hz,
2H; ArH), 6.65 (d, J 5 8.40 Hz, 2H; ArH). 13C NMR (100 MHz,
THF-d8, d, 25 8C): 181.54 (2 carbons), 179.71 (1 carbon),
159.15 (1 carbon), 140.77 (1 carbon), 136.73 (2 carbons),
136.14 (1 carbon), 129.67 (1 carbon), 127.88 (2 carbons),
116.22 (2 carbons), 115.41 (2 carbons). Anal calcd. for
Measurements
1
The H and 13C NMR spectra were recorded on a JEOL JNM-
ECX400 spectrometer at resonant frequencies of 400 MHz
for 1H and 100 MHz for 13C nuclei using CDCl3 and THF-d8
as the solvents and tetramethylsilane as the reference. FTIR
spectra were measured by a Nicolet iS5 Fourier transform
spectrophotometer. Mn and Mw values were measured by
SEC on a JASCO GULLIVER 1500 system equipped with two
polystyrene gel columns (Plegel 5 lm MIXED-C) that were
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TABLE 1 Basic Properties of PPSs
b
c
Yield
(%)
Tg
Td5%
(oC)
a
a
-
D
Mn
(oC)
PPS-1
PPS-2
PPS-3
PPS-4
30,000
11,000
21,000
20,800
2.55
2.43
1.80
1.88
80
70
85
84
180
185
150
140
265
255
220
210
a
Determined by SEC eluted with chloroform using polystyrene standards.
Determined by TGA at a heating rate of 10 8C/min.
b
c
Determined by DSC in the first heating scan at a heating rate of 10 8C/min.
SCHEME 1 Synthesis of the triazine monomers T1 and T2.
performed using the software package of Gaussian-03 (Rev.
C02 and D01). A typical packing coefficient (Kp) of 0.60 was
used for evaluating the intrinsic molecular volumes of mod-
els to predict the refractive indices.9
eluted with chloroform at a flow rate of 1.0 mL/min and cal-
ibrated by polystyrene standard samples. Thermogravimetry
(TG) measurements were performed on a Seiko EXSTAR
6000 TG/DTA 6300 thermal analysis system at a heating
rate of 10 8C/min. DSC analysis was conducted on a DSC
6200 at a heating rate of 10 8C/min under nitrogen. The in-
plane (nTE) and out-of-plane (nTM) refractive indices of PPS
films were measured using a prism coupler (Metricon, model
RESULTS AND DISCUSSION
Synthesis of the Triazine Monomer
In the synthesis of the triazine monomer, the chemoselectiv-
ity of each chloride toward the substitution reaction of cya-
nuric chloride generally facilitates the design of a monomer
side chain.35 In the synthesis of T1, due to the strong
electron-donating effect of a hydroxyl group on the para
position, the nucleophilic property of thiol group increased.
This situation caused a multisubstitution reaction to occur;
therefore, an optimization of the reaction conditions (drop-
wise-addition method, low concentration, and temperature
(240 8C)) was required to obtain the monosubstituted target
compound T1. However, this is not the case for T2 due to
the lower nucleophilicity of the phenol group compared with
the thiol group. Therefore, the reaction was carried out at
0 8C and the mono-substituted target compound T2 could be
obtained. After optimizing the conditions, both monomers
PC-2000) equipped with
a He–Ne laser (wavelength:
633 nm) and a half-waveplate in the light-path. The in-
plane/out-of-plane birefringences (Dn) were estimated as
the difference between nTE and nTM, and the average refrac-
tive indices were calculated according to the following equa-
tion: nav 5 [(2n2TE 1 nT2M)/3]1/2
.
The refractive indices of PPSs synthesized in this study were
calculated based on the Lorentz–Lorenz theory using the cor-
responding model compounds (see Fig. S11 in supporting
information) as reported previously.9 One-electron transition
energies and the corresponding oscillator strengths of the PI
models were also calculated using the time-dependent den-
sity functional theory (TD-DFT) to predict the optical
absorption in the UV–vis region.8 The 6–311G(d) basis set
was used for geometry optimizations under no constraints,
and the 6–31111G(d,p) was used for calculating linear
polarizabilities, transition energies, and oscillator strengths.
The three-parameter Becke-style hybrid functional (B3LYP)
was adopted as a function and all the calculations were
SCHEME 2 Synthesis of triazine-containing PPSs.
FIGURE 1 FTIR spectra of PPSs.
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FIGURE 4 DSC traces of PPSs.
Synthesis and Characterization of Triazine-Containing
PPSs
The synthetic route for the triazine-containing PPSs is shown
in Scheme 2. All the triazine-containing PPSs were prepared
by the single-phase polycondensation of T1 and T2 with aro-
matic dithiols TBT and BDT. A single-phase polycondensa-
tion was carried out in THF in the presence of TEA as an
HCl scavenger at 0 8C to room temperature. The polyconden-
sation proceeded smoothly to give PPSs with Mn values from
11,000 to 30,000. The results are summarized in Table 1.
The structures of the PPSs were characterized by 1H, 13C
NMR, and FTIR spectroscopies. The characteristic IR absorp-
tion peaks were observed at 1473 and 1245 cm21, which
are attributable to the AC@NA groups in the triazine and
thioether units, respectively. For PPS-1 and 2, the broad Ph-
OH peaks were observed at 3500–3000 cm21 (Fig. 1). In the
1H NMR spectrum of PPS-1 (Fig. 2), the signals that reso-
nated at 7.33, 7.24, 7.16, and 6.69 ppm are assigned to the
aromatic and Ph-OH protons (8.81 ppm). In the 1H NMR
spectrum of PPS-4 (Fig. 2), the signals that resonated at
3.51 and 1.38 ppm are assigned to the methylene and tert-
FIGURE 2 1HNMR spectra of PPS-1 and PPS-4.
(T1 and T2) were successfully synthesized in good yields
over 70% (Scheme 1). The 1H and 13C NMR spectra of T1
and T2 are shown in supporting information (Figs. S1–S4).
1
butyl protons, respectively. Other H and 13C NMR spectra of
PPSs are shown in supporting information (Figs. S5–S10).
TABLE 2 Optical Properties of PPSs
S (wt%)a
nTE
nTM
nav
Dne
koff
b
c
d
f
PPS-1
PPS-2
PPS-3
PPS-4
28.27
27.84
22.59
20.93
1.7550
1.7430
1.6784
1.6490
1.7480
1.7390
1.6741
1.6476
1.7530
1.7420
1.6769
1.6486
0.0080
0.0040
0.0043
0.0014
363
357
350
329
a
Sulfur content.
b
c
d
e
f
In-plane refractive index.
Out-of-plane refractive index.
Average refractive index at 633 nm.
Birefringence (5nTE–nTM).
Cut-off wavelength.
FIGURE 3 TGA traces of PPSs.
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FIGURE 6 Calculated refractive indices of PPSs.
FIGURE 5 UV–vis spectra of PPSs.
Optical Properties
The optical properties of the PPS films are summarized in
Table 2. Figure 5 displays representative UV–visible trans-
mission spectra of the PPS films. All films exhibit short cutoff
wavelengths (koff) of 320–370 nm, and the optical transmit-
tance are as high as 90% at 400 nm. The high optical trans-
parency is consistent with the calculated absorption spectra
as shown in Figure S12, in which all PPSs show no absorp-
tion peaks in the visible region (400–800 nm). The excellent
colorlessness is probably due to the meta-substituted tri-
azine and thio groups in the triazine unit, which efficiently
suppresses the localization of the p-electrons and CT interac-
tions in PPSs as well as the prevention of interchain packing.
These results clearly indicate that the optical transparency is
not reduced by the introduction of a triazine unit into the
polymer chains.
Thermal Properties
The thermal stability, that is, the glass transition tempera-
tures (Tg) and thermal decomposition temperatures of the
high-n polymers, plays a critical role in optical device fabri-
cation. The thermal requirement mainly comes from a con-
sideration of the servicing circumstance of the optical
devices and the thermal-releasing problem caused by the
miniaturization of the opto-integrated assembly. The ther-
mal stabilities of the PPSs investigated by TGA and DSC are
summarized in Table 1. In Figure 3, PPSs show a relatively
good thermal stability, such as a 5% weight loss tempera-
ture (T5%) above 250 8C for both PPS-1 and PPS-2 in a
nitrogen atmosphere. For PPS-3 and PPS-4, due to the t-
butyl ester side-chain as the carboxyl acid protection group,
the first degradation stages were observed at approximately
200 8C, and the first-stage weight losses were 9% and
14%, respectively, which were in a good agreement with
the weight percentage of departing t-butyl ester groups in
PPS-3 and PPS-4. Therefore, these first-stage weight losses
can be assigned as the elimination of t-butyl ester groups.
Figure 4 shows the DSC thermograms of the PPSs. The
PPSs derived from T1 (PPS-1 and PPS-2) show high Tg
over 180 8C. However, the PPSs prepared from T2 (PPS-3
and PPS-4) exhibit lower Tg, which are derived from the
flexible t-butyl ester groups.
The in-plane (nTE) and out-of-plane (nTM) refractive indices
of the PPS films show the range of 1.649–1.755 and 1.648–
1.748, respectively. The fact that the values of nTE are
slightly higher than those of nTM for all the PPS films might
reflect the preferential orientation of the main chains parallel
to the film plane. The average refractive indices (nav) range
between 1.649 and 1.753. Therefore, PPS-1 with the highest
sulfur content (28.3 wt%) showed the highest nav of 1.753.
This trend is also consistent with the calculated refractive
indices by TD-DFT as shown in Figure 6. The lower nav of
TABLE 3 Solubility of PPSsa
2.38 wt%
THF
CHCl3
TCE
DMAc
DMSO
PGMEc
PGMEAd
MMPe
EDMf
TMAH(aq)
PPS-1
PPS-2
PPS-3
PPS-4
11
11
11
11
22
22
11
11
22
22
11
11
11
11
11
11
1
2
2
2
2
2
11
11
11
11
11
11
1
11
11
11
11
11
11
2
11
11
1b
11b
a
d
e
f
Key: (2) partially dissolved, (1) dissolved after heating, (11) dis-
Propylene glycol monomethyl ether acetate.
Methyl 3-methoxypropionate.
solved at room temperature, Conc. 10 mg / 1 mL.
b
Measured after deprotection by TAG.
Propylene glycol monomethyl ether.
Ethylene glycol dimethyl ether.
c
6
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ACKNOWLEDGMENTS
PPS-3 compared with PPS-1 is explainable by the lower sul-
fur content (22.6 wt%), and the substitution of tert-butyl
ester moieties lower the refractive indices of PPS-2 and
PPS-4. The calculated Abbe numbers for PPS-224 are 15.7,
17.7, 18.5, 21.2, respectively, which are relatively high, indi-
cating lower wavelength dispersion of refractive indices, as
high-n polymers. Furthermore, the flexible thioether and
meta-linkages in the PPS chains provide very small birefrin-
gence (Dn) values in the range of 0.0014–0.0080. Moreover,
the PPSs prepared from BDT (PPS-2 and PPS-4) exhibited
lower Dn compared with those of PPS-1 and PPS-3 derived
from TBT due to the meta-linkage of BDT allowing more
three-dimensional and isotropic structures of the main
chains. All these results indicate that the introduction of the
triazine moiety together with multiple sulfur atoms is an
effective way to provide PPSs with high-n values, low bire-
fringence, and high transparency in the visible region.
This work was mainly supported by JSR Corporation. M. C., Fu
thanks Innovative Flex Course for Frontier Organic Material
Systems (iFront) at Yamagata University for financial support.
REFERENCES AND NOTES
1 H. Dislich, Angew. Chem. Int. Ed. Engl. 1979, 18, 49.
2 T. Matsuda, Y. Funae, M. Yoshida, T. Yamamoto, T. Takaya,
J. Appl. Polym. Sci. 2000, 76, 50.
3 A. Nebioglu, J. A. Leon, I. V. Khudyakov, Ind. Eng. Chem.
Res. 2008, 47, 2155.
4 J-g. Liu, M. Ueda, J. Mater. Chem. 2009, 19, 8907.
5 J.-P. Kim, W.-Y. Lee, J.-W. Kang, S.-K. Kwon, J.-J. Kim, J.-S.
Lee, Macromolecules 2001, 34, 7817.
6 K.-S. Lee, J.-S. Lee, Chem. Mater. 2006, 18, 4519.
7 T. Higashihara, M. Ueda, Macromolecules 2015, 48, 1915.
8 S. Ando, T. Fujigaya, M. Ueda, Jpn. J. Appl. Phys. 2 2002, 41, L105.
Solubility Tests
9 J-g. Liu, Y. Nakamura, T. Ogura, Y. Shibasaki, S. Ando, M.
Ueda, Chem. Mater. 2008, 20, 273.
The solubilities of PPSs are summarized in Table 3. PPS-2
and PPS-4 with BDT units showed a higher solubility in
green solvents or alkaline solution compared to PPS-1 and
PPS-3 with TBT units. The meta-linkage structure in the
BDT may provide the main-chain flexibility and thereby
increasing the solubility. However, PPS-3 and PPS-4 showed
better solubility in common solvents and therefore preferred
processability due to the ester protection groups. To achieve
a highly photosensitive system, a polymer matrix with high
alkaline solubility is needed. The hydroxyl groups were
introduced in the side chain of PPS-1 and PPS-2 to increase
the alkaline solubility; however, PPS-1 and PPS-2 were
insoluble in 2.38 wt% TMAH(aq), even after heating, which is
probably due to the highly hydrophobic main-chain struc-
ture. In contrast, the blended films of PPS-3 and PPS-4 with
10 wt% of the thermal base generator (TAG) after deprotec-
tion at 150 8C for 2 min could be dissolved after heating and
at room temperature, respectively. The TAG could catalyze
the deprotection reaction from the ester to the carboxyl acid
group, resulting in a balanced solubility between common,
green, and alkaline solutions.
€
10 C. Lu, Z. Cui, Y. Wang, B. Yang, J. Shen, J. Appl. Polym.
Sci. 2003, 89, 2426.
€
11 C. Lu, Z. Cui, Y. Wang, Z. Li, C. Guan, B. Yang, J. Shen, J.
Mater. Chem. 2003, 13, 526.
12 L.-H. Lee, W.-C. Chen, Chem. Mater. 2001, 13, 1137.
13 S. Seesukphronrarak, S. Kawasaki, K. Kobori, T. Takata, J.
Polym. Sci. Part A: Polym. Chem. 2007, 45, 3073.
14 J-g. Liu, Y. Nakamura, Y. Shibasaki, S. Ando, M. Ueda,
Polym. J. 2007, 39, 543.
15 J-g. Liu, Y. Nakamura, Y. Shibasaki, S. Ando, M. Ueda, Mac-
romolecules 2007, 40, 4614.
16 C. A. Terraza, J.-G. Liu, Y. Nakamura, Y. Shibasaki, S. Ando,
M. Ueda, J. Polym. Sci. Part A: Polym. Chem. 2008, 46, 1510.
17 N.-H. You, Y. Suzuki, D. Yorifuji, S. Ando, M. Ueda, Macro-
molecules 2008, 41, 6361.
18 N.-H. You, Y. Suzuki, T. Higashihara, S. Ando, M. Ueda,
Polymer 2009, 50, 789.
19 N.-H. You, N. Fukuzaki, Y. Suzuki, Y. Nakamura, T.
Higashihara, S. Ando, M. Ueda, J. Polym. Sci. Part A: Polym.
Chem. 2009, 47, 4428.
20 N.-H. You, Y. Nakamura, Y. Suzuki, T. Higashihara, S. Ando,
M. Ueda, J. Polym. Sci. Part A: Polym. Chem. 2009, 47, 4886.
21 N.-H. You, T. Higashihara, S. Ando, M. Ueda, J. Polym. Sci.
Part A: Polym. Chem. 2010, 48, 656.
CONCLUSIONS
22 P. M. Hergenrother, B. J. Jensen, S. J. Havens, Polymer
1988, 29, 358.
Two new triazine monomers (T1 and T2) and corresponding
poly(phenylene sulfide)s (PPSs) have been successfully syn-
thesized. PPSs with high sulfur contents and the combination
of triazine groups exhibited high-n values (1.6448–1.7530),
high transparency (T% > 90% @400 nm), and low birefrin-
gence (Dn 5 0.0014–0.0080). PPSs exhibited relatively good
thermal stabilities (Td5%: 210–265 8C and Tg: 140–180 8C),
which could facilitate opto-electrical device manufacturing
processes. For PPS-3 and PPS-4, after deprotection by TAG,
the blended polymer films were soluble in 2.38 wt% TMA-
H(aq). All results produced valuable information to develop
high-n and alkaline-soluble photosensitive triazine-based pol-
y(phenylene sulfide) materials. The investigation of photo-
lithographic applications is ongoing.
23 S. Matsumura, N. Kihara, T. Takata, J. Appl. Polym. Sci.
2004, 92, 1869.
24 S. Kawasaki, M. Yamada, K. Kobori, F. Jin, Y. Kondo, H.
Hayashi, Y. Suzuki, T. Takata, Macromolecules 2007, 40, 5284.
25 K. Nakabayashi, T. Imai, M.-C. Fu, S. Ando, T. Higashihara,
M. Ueda, J. Mater. Chem. C 2015, 3, 7081.
26 K. Nakabayashi, T. Imai, M.-C. Fu, S. Ando, T. Higashihara,
M. Ueda, Macromolecules 2016, 49, 5849.
27 C. Paquet, P. W. Cyr, E. Kumacheva, I. Manners, Chem.
Mater. 2004, 16, 5205.
28 Chemical Handbook Basic II, 1979, 520
29 N. Nishimura, Y. Shibasaki, M. Ozawa, Y. Oishi, J. Photopo-
lym. Sci. Technol. 2012, 25, 355.
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2018, 00, 000–000
7

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
30 N.-H. You, T. Higashihara, Y. Oishi, S. Ando, M. Ueda, Mac-
romolecules 2010, 43, 4613.
33 Y. Inoue, Y. Saito, T. Higashihara, M. Ueda, J. Mater. Chem.
C 2013, 1, 2553.
31 Y. Nakagawa, Y. Suzuki, T. Higashihara, S. Ando, M. Ueda,
Macromolecules 2011, 44, 9180.
34 K. Ebara, Y. Shibasaki, M. Ueda, J. Polym. Sci. Part A:
Polym. Chem. 2002, 40, 3399.
32 C. G. Willson, In Introduction to Microlithography; L. F.,
Thompson, C. G., Willson, M. J., Bowden, Eds.; ACS: Washing-
ton, DC, 1983; p 87.
35 P. Gamez, J. Reedijk, Eur. J. Inorg. Chem. 2006, 2006, 29.
36 P. N. Culshaw, J. C. Walton, Tetrahedron Lett. 1990, 31,
2457.
8
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