Synthesis and radical polymerization of styrene-based monomer having a five-membered cyclic dithiocarbonate structure

Article abstract of DOI:10.1002/pola.26508

A styrene-based monomer having a five-membered cyclic dithiocarbonate structure, 4-vinylbenzyl 1,3-oxathiolane-2-thione-5-ylmethyl ether (VBTE), was synthesized from 4-vinylbenzyl glycidyl ether (VBGE) and carbon disulfide in the presence of lithium bromide in 86% yield. Radical polymerization of VBTE in dimethyl sulfoxide by 2,2′-azobisisobutyronitrile was carried out at 60 °C to afford the corresponding the polymer, polyVBTE, in 64% yield. PolyVBTE with number-averaged molecular weight higher than 31,000 was obtained. The glass transition temperature (T_g) and 5 wt % decomposition temperature (T_d5) of the polyVBTE were evaluated to be 66 and 264 °C under nitrogen atmosphere by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBTE repeating unit could also be obtained via polymer reaction, that is, a lithium bromide-catalyzed addition of carbon disulfide to a polyVBGE prepared from a radical polymerization of VBGE. Copolymerization of VBTE and styrene with various compositions efficiently gave copolymers of VBTE and styrene.

Full text of DOI:10.1002/pola.26508

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Synthesis and Radical Polymerization of Styrene-Based Monomer Having
a Five-Membered Cyclic Dithiocarbonate Structure
Takahiro Miyata,1 Kozo Matsumoto,1 Takeshi Endo,1 Shigeaki Yonemori,2 Shoji Watanabe2
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DOI: 10.1002/pola.26508
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INTRODUCTION Sulfur-containing materials have been widely
applied for optical materials,1ꢁ3 metal absorbents,4–7 and
reactive polymers8–14 owing to their high refractive indices,
high metal coordination ability, and specific reactivity. Among
various sulfur-derived functional groups, cyclic dithiocarbon-
ate15–18 have attracted much attention because they exhibit
low dielectric constants, high refractive indices, high metal
coordination abilities, and specific reactivities toward amines.
Our research group has already studied the synthesis of
polymers having the five-membered cyclic dithiocarbonate
structures, and revealed their unique properties.10,11,13 How-
ever, styrenic polymers having five-membered dithiocarbonate
groups have not been synthesized so far.
into a dithiocarbonate structure. Five-membered cyclic
dithiocarbonate could be readily prepared in a mild condi-
tion by insertion of carbon disulfide into epoxides, which is
catalyzed lithium bromide.18 Carbon disulfide is an abundant
low-cost carbon resource, and VBGE is an industrially avail-
able compound, which is effectively prepared from 4-chloro-
methyl styrene and epichlorohydrin. Therefore, the styrenic
monomer shown in Scheme 1 may be a convenient and
attracting monomer to produce the targeted functional
polymers.
In this study, we synthesized a new styrenic monomer hav-
ing a five-membered cyclic dithiocarbonate structure as a
pendant group, VBTE, by lithium bromide-catalyzed addition
of carbon disulfide to an epoxy group of VBGE, and investi-
gated its radical polymerization under various conditions,
including radical copolymerization with styrene to prepare
polystyrene derivatives having a five-membered cyclic dithio-
carbonate moiety in the side group (Scheme 1). Fundamental
properties such as glass transition temperature and thermal
decomposition temperature of the obtained polymers were
examined. We also investigated another synthetic route to
prepare a polymer composed of the same chemical structure
by a chemical modification of a polymer; addition of carbon
Recently, we reported that a styrene-based monomer having
a five-membered cyclic carbonate structure can be easily
synthesized from 4-vinylbenzyl glycidyl ether (VBGE) and
carbon dioxide in the presence of lithium bromide, and that
it could be radically polymerized to give the corresponding
polymer having five-membered cyclic carbonate structures.19
Five-membered cyclic carbonates have interesting properties
such as high polarity, high refractive index, and high reactiv-
ity. More characteristic properties derived from the sulfur
atom can be expected by substituting the carbonate moiety
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JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
was carried out with a Seiko Instrument DSC-6200 using an
aluminum pan under a 20-mL minꢁ1 N2 flow at the heating
rate of 5 ꢀC minꢁ1. Thermal gravimetric analysis (TGA) was
performed with a Seiko Instrument TG-DTA 6200 using an
alumina pan ꢁu1nder a 50-mL minꢁ1 N2 flow at a heating rate
ꢀ
of 10 C min
.
4-Vinylbenzyl 1,3-Oxathiolane-2-thione-5-ylmethyl Ether
In a 100-mL round-bottomed flask equipped with a magnetic
stirring bar, three-way stopcock, and 5-L rubber balloon,
were added lithium bromide (220 mg, 2.5 mmol), THF (30
mL), VBGE (9.45 g, 50.0 mmol), and carbon disulfide (4.67 g,
ꢀ
62.5 mmol), and the mixture was stirred at 0 C for 2 h. Af-
ter stirring at room temperature for three more times, the
mixture was cooled to room temperature and poured into
water. The products were extracted with ethyl acetate (100
mL), dried over Na2SO4, concentrated in vacuo to give a
crude yellow liquid (11.6 g, 86% yield). Then a part of the
crude product was purified by a silica gel column chroma-
tography (hexane/ethyl acetate ¼ 3/1) to give 81% total
yield from VBGE of the pure title compound (yellow liquid).
SCHEME 1
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disulfide to a polymer having an epoxy moiety in the repeat-
ing unit.
EXPERIMENTAL
Materials
VBGE, derived from 4-(chloromethyl)styrene, was provided
from AGC Seimi Chemical (Kanagawa, Japan) and distilled in
the presence of 3,5-dinitrotoluene under reduced pressure.
Styrene was purchased from Wako Pure Chemical Industry
(Osaka, Japan) and washed three times with 1-M NaOH
aqueous solution, and distilled water, dried over anhydrous
Na2SO4, and distilled over CaH2 under reduced pressure
before use. CS2 was purchased from Wako Pure Chemical
Industry. Lithium bromide (anhydrous) was purcꢀhased from
Kanto Chemical (Tokyo, Japan) and dried at 120 C in vacuo
for 2 h before use. 2,20-Azobisisobutyronitrile (AIBN) was
purchased from Wako Pure Chemical Industry and purified
by recrystallization from methanol. N,N-Dimethylformamide
(DMF), N,N-dimethylacetamide (DMAC), methyl ethyl ketone
(MEK), dimethyl sulfoxide (DMSO), and tetrahydrofuran
(THF), chlorobenzene were purchased from Wako Pure
Chemical Industry (Osaka, Japan) and distilled before use.
IR (ATR) 822, 905, 984, 1031, 1181, 1225, 1510, 1624, 2859
cmꢁ1
.
1H NMR d (CDCl3) 3.61 (dd, J ¼ 7.3, 11.1 Hz, 1H),
3.70 (dd, J ¼ 8.2, 11.1 Hz, 1H), 3.78 (dd, J ¼ 4.4, 10.6 Hz,
1H), 3.85 (dd, 5.1, 10.6 Hz, 1H), 4.59 (d, J ¼ 11.9 Hz, 1H),
4.64 (d, J ¼ 11.9 Hz, 1H), 5.25 (dddd, J ¼ 4.4, 5.1, 7.3, 8.2
Hz, 1H), 5.26 (d, J ¼ 11.0 Hz, 1H), 5.77 (d, J ¼ 17.7 Hz, 1H),
6.73 (dd, J ¼ 11.0 Hz, 1H), 7.31 (d, J ¼ 8.1 Hz, 2H), 7.43 (d,
J ¼ 8.1 Hz, 2H). 13C NMR d (CDCl3) 36.13, 68.57, 73.46,
89.20, 114.2, 126.4, 128.1, 136.4, 136.7, 137.4, 212.0. HRMS:
Calcd. [Mþ1] For C13H15O2S2: 267.0513, Found: 267.0513.
Polymerization of VBTE
A typical solution polymerization procedure is as follows. A
mixture of VBTE (810 mg, 3.00 mmol), AIBN (14.7 mg,
0.090 mmol), and DMSO (6 mL) was placed in a 20-mL
Schlenk tube equipped with a magnetic stirring bar and a
three-way stopcock. After the mixture was degassed under
reduced pressure, the flask was filled with nitrogen. The
Characterization
ꢀ
mixture was heated at 60 C for 24 h with stirring. A portion
IR spectra were recorded on a Thermo Scientific Nicolet iS10
spectrometer equipped with a Smart iTR Sampling Accessory.
1H (300 MHz) and 13C (75 MHz) NMR spectra were recorded
on a JEOL AL300 NMR spectrometer in CDCl3 or DMSO-d6.
Chemical shifts were determined using tetramethylsilane or
the residual protons as the internal standards. High-resolu-
tion fast atom bombardment (FAB) mass spectra were
obtained on a JEOL JSM-700 spectrometer. Number-averaged
molecular weight (Mn) and weight-averaged molecular
weight (Mw) were estimated by size exclusion chromatogra-
phy on a TOSOH HLC-8220 system equipped with refractive
index and ultraviolet (k ¼ 254 nm) detectors, and three con-
secutive polystyrene gel columns [TSK gels (bead size, exclu-
sion limited molecular weight); super-AW4000 (6 lm, >4 ꢂ
105), super-AW3000 (4 lm, >6 ꢂ 104), and super-AW2500
(4 lm, >2 ꢂ 103). The system was operated at a flow rate
of 0.5 mL minꢁ1, using a DMF solution of lithium bromide
(10 mM) as an eluent at 40 ꢀC. Polystyrene standards were
used for calibration. Differential scanning calorimetry (DSC)
of the polymerization solution was taken for 1H NMR analy-
sis, and the monomer conversion (74%) was determined
from an integral ratio of a signal at 5.8 ppm of the vinyl CH
proton in VBCE to a signal at 5.6 ppm of the dithiocarbonate
CH protons in both VBTE and polyVBTE. Precipitation of the
product with methanol, followed by vacuum drying, gave a
white solid of polyVBTE (518 mg, 1.95 mmol) in 64% yield.
IR (ATR) 808, 831, 1034, 1088, 1184, 1223, 1337, 1507,
2845, 2909 cmꢁ1 1H NMR d (DMSO-d6) 0.60–2.30 (m, 3H),
.
3.42–3.78 (m, 2H), 4.10–4.35 (m, 1H), 4.35–4.65 (m, 3H),
4.82–5.05 (m, 1H), 6.18–6.80 (m, 2H), 6.80–7.25 (m, 2H). Mn
¼ 31,000, Mw ¼ 203,000, Mw/Mn ¼ 6.55.
Polymerization of VBGE
A mixture of VBGE (567 mg, 3.00 mmol), AIBN (4.9 mg,
0.030 mmol), and DMF (3 mL) was placed in a 20-mL
Schlenk tube equipped with a magnetic stirring bar and a
three-way stopcock. After the mixture was degassed under
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0
,
0
0
0
–
0
0
0

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1
FIGURE 1
H N MR s p e c tr u m i n C D C l o f V BT E p u r i fi e d b y a s i li c a - g e l c o lu m n c h r o m at o g r a p h y .
3
reduced pressure, the flask was filled with nitrogen. The
mixture was heated at 60 C for 12 h with stirring. A portion
magnetic stirring bar and a three-way stopcock was
ꢀ
degassed by three melt and thaw cycles under vacuum; then
the flask was filled with nitrogen. The mixture was heated at
60 ꢀC for 72 h with stirring. Precipitation of the product
with methanol followed by filtration and then by vacuum
drying gave a white solid of poly(VBTE-co-styrene) (440 mg)
in 78 wt % yield. The copolymer composition was deter-
of the polymerization solution was taken for 1H NMR analy-
sis, and the monomer conversion (67%) was determined
from an integral ratio of a signal at 5.8 ppm of the vinyl CH
proton in VBGE to a signal at 4.6 ppm of the benzyl CH2
protons in both VBGE and polyVBGE. Precipitation of the
product with methanol, followed by vacuum drying, gave a
white solid of polyVBGE (244 mg, 1.29 mmol) in 43% yield.
1
mined from an integral ratio of a H NMR signal at 5.4 ppm
of five-membered cyclic dithiocarbonate CH proton in VBTE
unit to a signal at 6.2–7.3 ppm of aromatic CH protons in
styrene unit. Copolymer composition in mol % (VBTE/sty-
rene) ¼ 48/52, Mn ¼ 15,000, Mw ¼52,000, Mw/Mn ¼ 3.48.
FTIR (ATR) 752, 809, 826, 896, 1009, 1077, 1244, 1415,
1507, 2839, 2902 cmꢁ1 1H NMR d (CDCl3) 0.78–2.30
.
(m, 3H), 2.60–2.90 (m, 1H), 3.05–3.15 (m, 1H), 3.15–3.60
(m, 2H), 3.60–3.80 (m, 1H), 4.25–4.65 (m, 2H), 6.20–6.80
(m, 2H), 6.80–7.25 (m, 2H). Mn ¼ 25,700, Mw ¼ 43,300, Mw/
Mn ¼ 1.68.
RESULTS AND DISCUSSION
Monomer Synthesis
A styrenic monomer having a five-membered cyclic dithio-
carbonate moiety (VBTE) was successfully synthesized by
the reaction of VBGE and carbon disulfide in the presence of
lithium bromide in THF at 0 ꢀC for 1.5 h and then at room
temperature for 3 h (Scheme 1). An analytically pure VBTE
was obtained in 78% yield after purification by silica gel col-
Transformation of PolyVBGE to PolyVBTE
A mixture of polyVBGE (189 mg, 1.0 mmol/monomer unit),
lithium bromide (4.4 mg, 0.05 mmol), THF (3 mL), and car-
bon disulfide (4.67 g, 62.5 mmol) was placed in a 100-mL
round-bottomed flask equipped with a magnetic stirring bar,
a three-way stopcock, and a rubber balloon. The mixture
was stirred at 0 ꢀC for 2 h, and then at room temperature
for 3 h. The mixture was poured into methanol to precipitate
the polymeric products. The products were collected and
dried in vacuo to provide a white solid polyVBTE (205 mg,
0.76 mmol/monomer unit) in 76% yield. Mn ¼ 56,600, Mw
¼ 264,000.
1
umn chromatography. Figure 1 shows the H NMR spectrum
of the desired VBTE purified by silica gel column chromatog-
raphy. Three protons in the vinyl group of the styrenic
moiety were clearly observed at 5.26, 5.77, and 6.73 ppm
along with the three protons of the five-membered cyclic
dithiocarbonate moiety at 3.61, 3.73, and 5.25 ppm, indicat-
ing the selective insertion of carbon disulfide to the epoxy
ring. This reaction proceed via nucleophilic attack of halide
anion at the less substituted position of epoxides and cycli-
zation of the resulting dithiocarbonate anion as reported
previously.14,18 Figure 2 shows the FTIR spectrum of the
obtained VBTE. The strong absorption at 1180 cmꢁ1 was
attributed to the C¼¼S stretching band of the cyclic dithiocar-
bonate moiety, whereas a weak absorption at 1510 cmꢁ1
was attributed to the C¼¼C stretching band of the vinyl group
in the styrenic moiety. The crude product in Scheme 1 before
FTIR and 1H NMR spectra of the obtained compound were
identical to those of the polymer previously prepared by the
polymerization of VBTE.
Copolymerization of VBTE and Styrene
A typical procedure for copolymerization of VBTE and sty-
rene is as follows. A mixture of VBTE (405 mg, 1.50 mmol),
styrene (156 mg, 1.50 mmol), AIBN (14.4 mg, 0.090 mmol),
and DMF (3 mL) in a 20-mL Schlenk tube equipped with a
W
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T
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2
0
1
2
,
0
00
,
0
0
0
–
0
0
0
3

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FIGURE 2 F T I R s p e c tr u m o f V BT E p u r i fi ed b y a s i li c a g e l c o lu m n c h r o m at o g r a p h y.
silica gel column chromatography was slightly yellow, but its
1H NMR spectrum was similar to that of the purified VBTE,
indicating that the crude product had few impurities. There-
fore, the crude VBTE was used without further purification
for the following polymerization experiments.
the C¼¼S stretching of the five-membered cyclic dithiocarbon-
ate structure is clearly observed, while the weak absorption
at 1625 cmꢁ1 of C¼¼C stretching at the styrenic part of VBTE
monomer disappeared. These observations also revealed the
chemical structure of the obtained polyVBTE. It should be
worth noting that the obtained polymer (run 5 in Table 1)
had rather high polydispersity (Mw/Mn ¼ 6.50). This is pre-
sumably because of a kind of chain transfer, which some-
times occurs in dithiocarbonate compounds. However, the
chemical structure generated by side reactions could not be
Homopolymerization
Homopolymerization of VBTE in various solutions was car-
ꢀ
ried out at 60 C using AIBN as an initiator (Scheme 1). The
polymerization results are summarized in Table 1. The
monomer conversion was estimated by 1H NMR analysis of
the polymerization mixture. The polymeric products were
corrected by precipitation with methanol, and the isolated
yield was determined. Polymers insoluble to organic solvent
were obtained by polymerization in DMF, DMAC, and MEK.
Polymers soluble in organic solvent were obtained only
when the polymerization was conducted in diluted DMSO
(run 5). Figure 3 shows the 1H NMR spectrum of the
obtained polyVBTE. Two signals at 3.42–3.78 and 5.30–5.55
ppm assigned to proton on the five-membered cyclic dithio-
carbonate structure are clearly observed, and the broad sig-
nals around 0.60–2.30 ppm assigned to the methyne and
methylene protons in the main chain are also observed,
which indicate that the vinyl polymerization occurred with
the five-membered cyclic dithiocarbonate structure remain-
ing intact. Figure 4 shows the FTIR spectrum of the obtained
polyVBTE. The strong absorption at 1180 cmꢁ1 attributed to
1
detected by HNMR and FTIR spectroscopies.
Chemical Modification of an Epoxy-Based Polymer
The VBTE homopolymer thus obtained could be synthesized
by another route as shown in Scheme 2. The epoxide VBGE,
which is the starting material of VBTE, was first polymerized
using AIBN as a radical initiator and DMF as a solvent to
provide polyVBGE (Mn ¼ 25,700, Mw ¼ 43,300) in 43%
yield. This polymer could be transformed to the polymer
consisting of VBTE as the repeating unit by an addition of
carbon disulfide to the epoxy group in the repeating unit of
polyVBGE. One hundred percent conversion of the epoxy
pendant groups to the five-membered dithiocarbonate moi-
eties was achieved, which implies that this reaction pro-
ceeded effectively. The isolated yield of the polymer was
76%. The obtained polymer showed the same 1H NMR and
FTIR spectra as those of the polyVBTE prepared by the
TABLE 1
R
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JOURNAL OF
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ARTICLE
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1
FIGURE 3
H N M R s p ec t r u m o f p o ly V BT E i n D M S O -d6.
polymerization of VBTE. We consider that the polymer reac-
tion process is useful for various applications such as carbon
disulfide absorbing materials.
of the polymer was clearly observed, and the glass transition
temperature (Tg) was determined to be 66 ꢀC. The glass
transition temperature of the polyVBGE was a little higher
than the corresponding polymer having a carbonate struc-
ture19 (52 ꢀC) and far lower than a usual polystyrene pre-
Thermal Properties
ꢀ
Thermal stability of polyVBTE prepared by polymerization of
VBTE was examined by TGA. Figure 5 shows the TGA curve
obtained at a heating rate of 10 ꢀC minꢁ1 under a nitrogen
flow. The polyVBTE was thermally stable under 200 ꢀC and
showed no decomposition at all. The 5-wt % decomposition
temperature (Td5) was determined to be 264 ꢀC. Compared
with the corresponding cyclic carbonates (Td5 ¼ 329 ꢀC),19
heat stability of the cyclic dithiocarbonates is rather low, this
may be explained from the higher reactivity of the cyclic
dithiocarbonate. Thermal phase transition of polyVBTE pre-
pared by radical polymerization of VBTE was examined by
DSC. Figure 6 shows the DSC curve obtained at the second
pared by radical polymerization (Tg ¼ ꢃ100 C), which may
be due to the increase of the free volume around the main
chain by introduction of the large pendant groups.
Copolymerization
Copolymerization of VBTE with styrene was examined in
DMF using AIBN as a radical initiator (Scheme 3). Table 2
shows the results of the copolymerization with various
monomer
compositions.
Copolymerization
proceeded
smoothly to give the corresponding copolymers with almost
the same composition as the monomer feed ratios in a high
yield. The copolymer compositions were determined by 1H
NMR analysis of the obtained polymers. The integral ratio of
heating scan (heating rate: 5 C minꢁ1). The glass transition
ꢀ
FIGURE 4
F
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5

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SCHEME 3
C
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.
SCHEME 2
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v
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.
also evidenced a formation of copolymers. The copolymeriza-
tion results in Table 2 suggest that VBGE is will be useful as
a key monomer to obtain various functional materials having
cyclic dithiocarbonate structures by radical copolymerization
with conventional vinylic monomers.
CONCLUSIONS
We demonstrated that a styrene-based monomer having a
five-membered cyclic dithiocarbonate structure can be syn-
thesized easily and efficiently under a mild condition, and
that the monomer can be readily polymerized to afford poly-
mers having a five-membered dithiocarbonate structure in
every repeating unit. The same polymer can be easily pre-
pared by adding carbon disulfide to a polymer having an
epoxide group under a very mild reaction condition. This fac-
ile polymer reaction under a mild condition may be impor-
tant when practical applications as functional materials are
considered. The new styrenic monomer synthesized here can
be copolymerized with usual vinyl monomers such as sty-
rene, which implies that the monomer has high applicability
to various purposes. The polymeric materials having five-
membered dithiocarbonate structures are expected to be
useful as new functional materials, such as heavy metal
absorbents, polymer electrolytes, resists, optical materials
with high refractive index, adhesives, coatings, paints,
and reactive polymers constructing three-dimensionally
crosslinked networked materials. Further studies for these
applications are currently in progress.
FIGURE 5
T
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A
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p
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.
methyne proton of VBTE unit at 5.25 ppm to the aromatic
protons of VBTE and styrene unit at 6.2–7.4 ppm was used
for the determination. Although the styrene homopolymer is
insoluble in DMSO, the products of polymerization with
monomer feed ratio of VBTE/styrene ¼ 75/25, 50/50, and
75/25 (Table 2) were completely soluble in DMSO. This is a
clear evidence for formation of the VBTE and styrene copoly-
mer. In addition, the copolymerization products (Table 2)
showed only one glass transition temperature between Tg of
polyVBTE (66 ꢀC) and Tg of polystyrene (ca. 100 ꢀC), which
a
TABLE 2
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FIGURE 6
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JOURNAL OF
POLYMER SCIENCE
ARTICLE
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8
F
.
S
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a
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T
.
S
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.
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T
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, Macromol. Rapid
ACKNOWLEDGMENTS
Commun. 2001, 22, 3 63 – 3 6 6.
High-resolution mass spectra were measured under the Coop-
erative Research Program of ‘‘Network Joint Research Center
for Materials and Devices.’’
9
T
.
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.
Part A: Polym. Chem. 2007, 45, 1 17 0 – 1 17 5 .
11
N
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, J. Polym. Sci. Part A: Polym.
Macromolecules 2009, 42
, J. Polym. Sci. Part A: Polym.
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0
0
5
–
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.
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.
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,
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o
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15
Y
.
T
a
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u
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i
,
I
.
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,
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7
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7
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–
i
7
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0
,
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.
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a
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,
,
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a
,
B
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C
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4
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.
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.
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b
,
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.
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e
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,
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.
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,
,
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.
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i
2
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e
6
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4
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.
,
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.
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