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N. Oh et al.
Polymer165(2019)191–197
sulfur contents and rigid structure, the polymers have relatively low
solubility in common organic solvents, low transparency, and tedious
(80.6%). The number-average molecular weight (Mn) and weight-
average molecular weight (Mw) estimated by gel permeation chroma-
tography (GPC) were 14.99 × 103 and 27.68 × 103, respectively, and
the dispersity index (PDI = Mw/Mn) was 1.59.
In this work, we report the synthesis and characterization of new
solution-processed polymers containing pyrimidine, benzonitrile units,
and sulfur to achieve good optical properties such as a high refractive
index and optical transparency and a low birefringence in the visible
region. All of the poly(phenylene thioether ether)s (PPTEs) such as
DPTT–DFBN and DPTT–DCMP have high refractive indices in the range
of 1.7188–1.7204 with low birefringence values in the range of
0.0114–0.0106 and a high thermal stability (> 360 °C) and optical
transparency. The effects of the structure on the optical and thermal
properties of the polymers are discussed in detail.
2.5. Measurements
The 1H (600 MHz) and 13C (150 MHz) nuclear magnetic resonance
(NMR) spectra were measured on an Agilent 600 MHz Premium
COMPACT in dimethyl sulfoxide-d6 (DMSO‑d6) or chloroform-d (CDCl3)
using tetramethylsilane (TMS) as an internal standard. Gel permeation
chromatography (GPC, Tosoh HLC-8320GPC EcoSEC) measured the
number-average molecular weights (Mn), weight-average molecular
weights (Mw), and polydispersities (Mw/Mn) with tetrahydrofuran
(preservative-free HPLC grade, Fisher or Daejung Chemical Company)
at 40 °C at 1.0 mL/min and were calibrated with 14 monodisperse
polystyrene standards (purchased from Alfa Aesar). Fourier transform-
infrared (FT-IR) spectra were obtained with a Nicolet IS10 with 32
scans per spectrum at a 2 cm−1 resolution. Thermogravimetric analysis
(TGA) was carried out with a Q50 TA Instruments at a heating rate of
20 °C/min under a nitrogen gas flow. The glass transition temperature
(Tg) was taken by differential scanning calorimetry (DSC) analysis with
a Q10 (TA Instruments) at a heating rate of 10 °C/min under a nitrogen
atmosphere. Dynamic mechanical thermal analysis (DMA) was ex-
amined using a Q800 (TA Instruments) at a scanning rate of 3 °C/min
with a load frequency of 1 Hz in air. The specimens were prepared in
film form (30 mm length, 5 mm width, and ca. 20 μm thickness).
Thermogravimetric analysis (TGA) was performed under a nitrogen gas
flow using a Q50 (TA Instruments) at a heating rate of 10 °C/min.
Ultraviolet–visible (UV–vis) spectra were recorded on a JASCO V-670
2. Experiments
2.1. Materials
4-Fluoro-benzenthiol, 4-hdroxybenzenethiol, 2,6-difluorobenzonitrile,
and 4,6-dichloro-2-(methylthio)pyrimidine, 2,6-difluoro-benzoic acid, and
2,6-difluoro-pyridine were purchased from Tokyo Chemical Industry Co.
Ltd. N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP)
were purified by a two-column solid-state purification system (Glass
contour system, Joerg Meyer, Irvine, CA). All commercial reagents and
organic solvents were used as received without further purification.
2.2. 2,7-(4,4′-diphenol)thiothianthrene (DPTT)
2,7-Difluorothianthrene was prepared as previously described [31].
4-Hydroxybenzenethiol (2.20 g, 17.44 mmol) was added to a solution of
2,7-difluorothianthrene (2.00 g, 7.93 mmol) and K2CO3 (2.89 g,
20.91 mmol) in dehydrated DMF under a nitrogen atmosphere. The
resulting solution was refluxed at 150 °C for a day. The excess K2CO3
was filtered. The filtrate was removed using a rotary evaporator. After
the removal of the solvents, the product was separated by column
chromatography using silica gel followed by recrystallization with ethyl
acetate and hexane. The pale yellow powder was dried at 80 °C under a
vacuum. Yield: 2.06 g (56%); pale yellow solid; mp 161–162 °C. 1H
NMR (600 MHz, DMSO‑d6) MS (–ESI): calculated for C24H16O2S4eH+:
463.63; found: 463.10. 1H NMR (600 MHz, DMSO‑d6) δ = 9.99 (s, 2H),
δ = 7.44 (s, 1H), δ = 7.42 (s,1H) δ = 7.36–7.33 (m, 4H) δ = 7.15 (d,
J = 2H) δ = 7.02–7.00 (dd, 2H) δ = 6.87–6.85 (m, 4H).
spectrometer in transmittance mode at
a wavelength range of
250–800 nm, a resolution of 1 nm, and a scanning rate of 400 nm/min.
The refractive indices of the samples such as in-plane (nTE) and out-of-
plane (nTM) were measured by a prism coupler (Metricon PC-2000), and
the wavelength was a 637 nm HeeNe laser light source. The bi-
refringence (Δn) was calculated between the nTE and nTM, and the
average refractive index (nav) was calculated by the following equation:
n
av = [(2nTE + nTM2)/3]1/2
.
2
3. Results and discussion
3.1. Synthesis of DPTT
2.3. Synthesis of DPTT–DFBN
The novel 4,4′-diol aromatic monomer, 2,7-(4,4′-diphenol)thio-
2,6-difluorobenzonitrile (0.15 g, 1.08 mmol) was added to a solu-
tion of DPTT (0.50 g, 1.08 mmol) K2CO3 (0.59 g, 4.30 mmol) in dehy-
drated NMP under a nitrogen atmosphere. The reaction solution was
refluxed at 130 °C for a day. The resulting solution was poured into
water/methanol to precipitate the product. The obtained polymer was
collected by filtration and washed with methanol. The final product was
dried at 150 °C under a vacuum. Yield: 0.501 g (82.4%). The number-
average molecular weight (Mn) and weight-average molecular weight
(Mw) estimated by gel permeation chromatography (GPC) were
11.55 × 103 and 26.34 × 103, respectively, and the dispersity index
(PDI = Mw/Mn) was 2.28.
thianthrene (DPTT), which contains a thianthrene unit with 4 sulfur
atoms, was synthesized by
a two-step procedure with 2,7-di-
fluorothianthrene as the starting material (Scheme 1). First, the inter-
described [26]. Then, DFT was reacted with 4-hydroxybenzenethiol to
give the final compound DPTT with a yield of 56%. The thermal
properties of the synthesized compound DPTT were measured by TGA
and DSC shown in Fig. S1. The onset decomposition temperature (Td) of
DPTT in a nitrogen flow was 203 °C, and its melting temperature (Tm)
was about 159 °C.
The chemical structure of DPTT was characterized by FT-IR and
NMR spectroscopy. In the FT-IR spectrum (Fig. 1), the band from the
OeH of both terminal hydroxyl groups of DPTT appears at around
3550–3200 cm−1. The characteristic absorption from the CeSeC bond
of the thioether group was observed at 817 cm−1. The 1H and 13C NMR
spectra of the model compound DPTT are presented in Fig. 2 along with
the assignments of all the signals. In the 1H NMR spectrum (Fig. 2(a)),
the characteristic proton of the hydroxyl group was observed at
9.88 ppm. In the 13C NMR spectrum (Fig. 2(b)), 9 carbon signals were
observed in the range of 39–160 ppm which are consistent with the
expected molecular structure of DPTT.
2.4. Synthesis of DPTT–DCMP
4,6-dichloro-2-(methylthio)pyrimidine (0.21 g, 1.08 mmol) was
added to
a solution of DPTT (0.50 g, 1.08 mmol) K2CO3 (0.59 g,
4.30 mmol) in dehydrated NMP under a nitrogen atmosphere. The re-
action solution was refluxed at 100 °C for a day. The resulting solution
was poured into water/methanol to precipitate the product. The ob-
tained polymer was collected by filtration and washed with methanol.
The final product was dried at 150 °C under a vacuum. Yield: 0.510 g
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