Radical ring-opening polymerization of five-membered cyclic vinyl sulfone using p-toluenesulfonyl halides

Article abstract of DOI:10.1002/pola.26378

Radical ring-opening polymerizations of a five-membered cyclic vinyl sulfone monomer, 2-vinylthiolane-1,1-dioxide (VTDO), was carried out by using p-toluenesulfonyl iodide (TosI) and bromide (TosBr) as radical initiators, and the corresponding ring-opened polymer (PVTDO) was obtained. Both TosI and TosBr were found to work as the radical initiators for the polymerization of VTDO in bulk. The use of TosI gave PVTDOs with a broad, multimodal distribution of molecular weight in low yields. When 10 mol % of TosBr was employed, the isolated yield of PVTDO reached 49%, and the obtained PVTDO had a relatively narrow, monomodal molecular weight distribution of 1.8 with an M_n of 4100.

Full text of DOI:10.1002/pola.26378

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Radical Ring-Opening Polymerization of Five-Membered Cyclic Vinyl
Sulfone Using p-Toluenesulfonyl Halides
Shimon Tanaka, Yoshio Furusho, Takeshi Endo
Molecular Engineering Institute, Kinki University, Fukuoka 820-8555, Japan
Correspondence to: T. Endo (E-mail: tendo@moleng.fuk.kindai.ac.jp)
Received 20 June 2012; accepted 6 September 2012; published online 5 October 2012
DOI: 10.1002/pola.26378
ABSTRACT: Radical ring-opening polymerizations of a five-mem-
bered cyclic vinyl sulfone monomer, 2-vinylthiolane-1,1-dioxide
(VTDO), was carried out by using p-toluenesulfonyl iodide (TosI)
and bromide (TosBr) as radical initiators, and the corresponding
ring-opened polymer (PVTDO) was obtained. Both TosI and TosBr
were found to work as the radical initiators for the polymerization
of VTDO in bulk. The use of TosI gave PVTDOs with a broad, mul-
timodal distribution of molecular weight in low yields. When 10
mol % of TosBr was employed, the isolated yield of PVTDO
reached 49%, and the obtained PVTDO had a relatively narrow,
monomodal molecular weight distribution of 1.8 with an Mn of
C
V
4100.
2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym
Chem 51: 222–227, 2013
KEYWORDS: cyclic vinyl sulfone; heteroatom-containing poly-
mers; living polymerization; polyolefin sulfone; polyolefins; p-
toluenesulfonyl halide; radical polymerization; radical ring-
opening polymerization
INTRODUCTION Polysulfones are defined as the polymers
that include sulfonyl groups connected to aliphatic or aro-
matic groups in main chain.1 Aromatic polysulfones, an im-
portant class of engineering plastics, are prepared by poly-
condensation and are used in a wide range of applications.
Aliphatic polysulfones such as polyolefin sulfone and polyal-
kylene sulfone contain weak sulfur–carbon bond in the main
chain that is readily cleaved under extreme ultraviolet irradi-
ation, so that they have been utilized as resist material.2,3 In
general, polyolefin sulfones have been synthesized by the
radical copolymerization of olefins with sulfur dioxide.4–9
Another synthetic method of polyolefin sulfones is radical
ring-opening polymerization of cyclic vinyl sulfone mono-
mers, which is quite attractive from viewpoint of polymer
synthesis as well as material science, because it permits
copolymerization with various vinyl monomers, allowing a
wide range of design of polysulfones so as to meet various
requirements.10–12 The radical ring-opening polymerization
produces polymers with functional groups, such as ether,
esters, amides, and carbonates, incorporated into the back-
bone of the polymer chains, which cannot be achieved by
the conventional radical polymerization of vinyl monomers.13
trile occurs readily at room temperature under argon atmos-
phere to give 1:1 adducts, b-iodosulfones. Percec reported
that metal-catalyzed living radical polymerization of common
vinyl monomers, such as methacrylates and styrenes, can be
realized by using the systems composed of p-toluenesulfonyl
halides, cupper halides, and bipyridines.27–29 The initiation
step of the metal-catalyzed polymerization of these vinyl
monomers using tosyl halides is the attack of a sulfonyl radi-
cal to the vinyl group of a monomer, and the resulting car-
bon radical works as a propagating radical that is in equilib-
rium with a dormant halide species. On the other hand,
sulfonyl radical works as a propagating radical in the ring-
opening polymerization of cyclic vinyl sulfone monomers.
Based on this mechanism in combination with the fact that
TosI is radically added to olefins, we hypothesized that TosI
per se could operate as radical initiator without any other
reagents, leading to the radical ring-opening polymerization
of cyclic vinyl sulfones. In this article, we report the radical
ring-opening polymerization of a five-membered cyclic vinyl
sulfone, 2-vinylthiolane-1,1-dioxide (VTDO), using p-toluene-
sulfonyl halide initiators.
EXPERIMENTAL
Aryl- and alkylsulfonyl halides undergo bond homolysis,14
and the resulting sulfonyl radicals are subsequently added to
substituted and unsubstituted olefins.15–24 Percec pointed
out that the homolysis of the sulfonyl halide can be initiated
thermally.25 Edwards reported radical addition of p-toluene-
sulfonyl iodide (TosI) to unsaturated alcohols and ethers.26
The addition of TosI to the unsaturated alcohols in acetoni-
Materials
1,3-Dibromopropane, sodium sulfide nonahydrate, allyl bromide,
diisopropylamine, sodium periodate, sodium p-toluenesufinate
tetrahydrate, and iodine were purchased from Wako Pure
Chemical Industries (Japan). p-Toluenesulfonyl hydrazide,
p-toluenesulfonyl chloride, and bromine were purchased
C
V
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SCHEME 1 Synthesis of 2-vinylthiolane-1,1-dioxide (4, VTDO).
from Tokyo Chemical Industry (Japan). n-Butyllithium (1.57
M in hexane) was purchased from Kanto Chemical (Japan).
Dimethyl sulfoxide (DMSO), acetonitrile, tetrahydrofuran
(THF), and N, N-dimethylformamide (DMF) were purchased
from Wako Pure Chemical Industries and distilled before
use. 2,2-Azobisisobutyronitrile (AIBN) was purchased from
Wako Pure Chemical Industries (Japan) and recrystallized
from acetone. VTDO was prepared according to the literature
(Scheme 1).10,30,31 p-Toluenesufonyl bromide (TosBr) and
TosI were prepared according to the literature.27,28
2H; SACH2ACH2), 5.10–5.14 (m, 2H; CH¼¼CH2), 5.76–5.82 (m,
1H; CH¼¼CH2); 13C NMR d (ppm) 28.79 (BrACH2ACH2), 32.05
(BrACH2), 32.17 (SACH2ACH2), 34.73 (SACH2ACH¼¼CH2),
117.2 (CH¼¼CH2), 134.2 (CH¼¼CH2).
Synthesis of 2-Vinylthiolane (3)31
To diisopropylamine (5.8 mL, 41 mmol) was added dropwise
to a hexane solution of n-butyllithium (1.57 M, 26 mL, 41
ꢀ
mmol) at ꢁ70 C. An argon stream was maintained through-
out the experiment. Dry THF (30 mL) was added. To this
rapidly stirred solution was then added dropwise a solution
of 2 (4.6 mL, 31 mmol) in THF (20ꢀ mL) over a 30-min pe-
riod. Stirring was continued at ꢁ70 C for a further 1 h, and
the mixture was then quenched with water. After the mixture
had warmed to room temperature, it was washed with 5%
HCl and then with saturated NaHCO3 aqueous solution, dried
over Na2SO4, and filtered. The hexane was removed at
atmospheric pressure and the residue was distilled under
reduced pressure to give 3 (2.97 g, 26 mmol, 84%). Bp
Measurements
1H and 13C NMR spectra were recorded on a JEOL JNM-
1
ECS400 (400 and 100 MHz for H and 13C, respectively, with
tetramethylsilane as an internal standard). Number average
molecular weight (Mn) and weight average molecular weight
(Mw) were estimated by size exclusion chromatography
(SEC) using DMF solution of lithium bromꢀide (10 mM) as an
eluent at a flow rate of 0.6 mL/min at 40 C, performed on a
Tosoh chromatograph model HLC-8220 system equipped
with three consecutive polystyrene gel columns (Super-
AW4000, Super-AW3000, and Super-AW2500) and a refrac-
tive index detector at 40 ꢀC. The molecular weight calibra-
tion curve was obtained with polystyrene standards. Ther-
mogravimetric analysis (TGA) was conducted with a Seiko
Instruments. TG/DTA6200 at a heating rate of 10 ꢀC/min
under nitrogen flow (20 mL/min).
ꢀ
55–58 C (16 mmHg).
1H NMR (CDCl3, 400 MHz): d (ppm) 1.6–2.2 (m, 4H;
CHACH2ACH2ACH2), 2.94 (m, 2H; SACH2), 3.92 (m, 1H;
SACH), 4.9A5.2 (m, 2H; CH¼¼CH2), 5.7–5.9 (m, 1H;
CH¼¼CH2); 13C NMR d (ppm) 30.87 (CH2ACH2ACH2), 33.27
(CH2ACH2ACH), 38.01 (SACH2), 51.63 (SACH), 114.6
(CH¼¼CH2), 140.3 (CH¼¼CH2).
Synthesis of 2-Vinylthiolane-1,1-dioxide (4, VTDO)10
Monomer Synthesis
To a solution of sodium periodate (14.0 g, 65.5 mmol) in dis-
tilled water (130 mL) and methanol (100 mL), a solution of
3 (3.26 mL, 28.5 mmol) in methanol (30 mL) was added
dropwise over a 30-min period. The mixture was stirred for
Synthesis of Thietane (1)30
Sodium sulfide nonahydrate (60.1 g, 250 mmol) was added
to a solution of 1,3-dibromopropane (50.5 g, 250 mmol) in
DMSO (100 mL) in small portions at 5 ꢀC. Then, steam was
introduced to the mixture, which was heated at 150 ꢀC for
20 min with vigorous stirring and the steam distillate was
collected. The aqueous layer of the distillate was saturated
with NaCl, and the organic layer was separated, dried, and
distilled to give pure thietane (1) (10.3 g, 139 mmol, 56%).
ꢀ
a further 12 h at 60 C. The precipitated solid was removed
by filtration and then methanol was evaporated under
reduced pressure. The aqueous solution was extracted with
dichloromethane. The extract was dried over MgSO4, and the
solvent was removed under reduced pressure. The residue
was purified by silica gel chromatography (eluent: dichloro-
methane) to afford crude 4, which was distilled under
reduced pressure in the presence of active carbon and hy-
droquinone to give pure 4 (2.46 g, 16.8 mmol, 59%) as a
ꢀ
Bp 96–98 C.
1H NMR (CDCl3, 400 MHz): d (ppm) 2.92–2.99 (m, 2H;
CH2ACH2ACH2), 3.25 (t, 4H; SACH2); 13C NMR (CDCl3,
100MHz): d (ppm) 26.0 (CH2ACH2ACH2), 27.86 (SACH2).
ꢀ
light yellow liquid. Bp 110–113 C (4 mmHg).
1H NMR (CDCl3, 400 MHz): d (ppm) 2.0–2.4 (m, 4H;
CH2ACH2ACH2ACH), 3.0–3.25 (m, 2H; SO2ACH2ACH2), 3.61
(m, 1H; CHACH¼¼CH2), 5.40–5.47 (m, 2H; CHACH¼¼CH2),
5.75–5.85 (m, 2H; CH¼¼CH2); 13C NMR d (ppm) 24.81
(CH2ACH2ACH2), 30.12 (CH2ACH2ACH), 51.0 (SO2ACH2),
65.0 (SO2ACH), 122.8 (CH¼¼CH2), 128.5 (CH¼¼CH2).
Polymerization of VTDO
The following procedure is a typical method for the polymer-
ization of VTDO (Scheme 2). A mixture of VTDO (0.52 g, 3.6
Synthesis of Allyl 3-Bromopropyl Sulfide (2)31
To a solution of thietane (1) (23.6 g, 318 mmol) in acetoni-
trile (120 mL) was added allyl bromide (38.5 g, 318 mmol)
at room temperature. The mixture was stirred at 40 ꢀC for
12 h. The solvent was evaporated at reduced pressure, and
the residue was distilled to give 2 (52.6 g, 270 mmol, 85%).
ꢀ
Bp 60–63 C (4 mmHg).
1H NMR (CDCl3, 400 MHz): d (ppm) 2.10 (m, 2H; BrACH2ACH2),
2.61 (t, 2H; BrACH2), 3.13 (d, 2H; SACH2ACH¼¼CH2), 3.51 (t,
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SCHEME 2 Radical ring-opening polymerization of VTDO.
mmol) and TosBr (84 mg, 0.36 mmol) in a glass ampoule
was degassed through three freeze–pump–thaw cycles. The
ꢀ
ampoule was sealed under vacuum and heated at 100 C for
24 h. The polymerization was quenched by rapid cooling
with liquid nitrogen and an excess of methanol was added to
the reaction mixture. A polymeric product was washed with
methanol for several times, collected by suction filtration,
and dried under vacuum at 60 ꢀC. The polymer yield was
gravimetrically determined from the weight of the methanol-
insoluble product.
FIGURE 2 TG curves for the pristine PVTDO (a: Td5 ¼ 241 ꢀC)
and the hydrogenated PVTDO (b: Td5 ¼ 308 ꢀC (2-h hydrogena-
tion)), (c Td5 ¼ 336 ꢀC (12-h hydrogenation)).
insoluble in most common organic solvents, such as DMF,
DMAc, DMSO, and NMP, so that the hydrogenation conver-
sion could not be determined by 1H NMR. Figure 3 shows
DSC thermograms of the pristine PVTDO and the hydrogen-
ated PVTDO (12-h hydrogenation). The pristine PVTDO
showed endothermic peaks above 150 ꢀC, which suggested
partial crystallinity of the pristine PVTDO. However, as
shown in Figure 2, thermal decomposition of the pristine
PVDTO began near the onset temperature of the endother-
mic peak, thus hampering further investigation. On the other
hand, the hydrogenated PVTDO exhibited endothermic peaks
in a higher temperature range from 180 to 220 ꢀC, which
were attributable to the melt of the crystalline region. Fur-
thermore, a slope change of the DSC curve owing to the glass
transition of amorphous region was not observed. Thus, the
DSC results of the hydrogenated PVTDO suggested that
hydrogenated PVTDO consisted mainly of crystalline region
and the insolubility of the hydrogenated PVTDO in organic
solvents was owing to the high crystallinity. Matsumoto and
coworkers5 examined the solubility of some polydiene sul-
fones and pointed out that a symmetric polymer chain struc-
ture is favored for partial crystallization, resulting in the
poor solubility of the polydiene sulfones. By the same token,
RESULTS AND DISCUSSION
Free Radical Ring-Opening Polymerization of VTDO and
Hydrogenation of PVTDO
First, the free radical ring-opening polymerization of VTDO
was carried out by using AIBN (4 mol % to monomer) as a
ꢀ
radical initiator at 60 C for 25 h in DMF according to the lit-
erature.10–12 The PVTDO was obtained in 88% yield and the
number average molecular weights (Mn) of obtained VTDO
were estimated by means of SEC to be 31,000 with a molec-
ular weight distribution (Mw/Mn) of 2.5. The 1H NMR spec-
ꢀ
trum of the PVTDO prepared using ꢀAIBN initiator at 60 C in
DMF (measured in DMSO-d6 at 90 C) is shown in Figure 1.
The NMR result indicated that the radical polymerization of
VTDO proceeded clearly via a ring-opening process. The
obtained PVTDO was soluble in polar organic solvents such
as DMF, dimethylacetamide (DMAc), DMSO, and nitroxide-
mediated polymerization (NMP)ꢀ in low polymer concentra-
tion (about 0.1 wt %) above 80 C.
The hydrogenation of the carbon–carbon double bond in
PVTDO was carried out by using p-toluenesulfonyl hydrazide
in DMF at 100 ꢀC.6 The TGA data showed that the 5%
weight-loss temperature (Td5) of the pristine PVTDO was
241 ꢀC, indicating that the PVTDO is not thermally stable
probably because of the C¼¼C bond in the main chain [Fig.
2(a)]. A drastic increase in the thermal decomposition tem-
perature was observed for the hydrogenated PVTDO [Figure
ꢀ
2(b, c)] of which the Td5 values were 308 and 336 C for the
hydrogenated PVTDO samples obtained by 2 and 12 h of
hydrogenation, respectively. The hydrogenated PVTDOs were
FIGURE 3 DSC thermographs for the hydrogenated PVTDO
(a: 12-h hydrogenation, 5 K/min heating, first scan) and the
pristine PVTDO (b: 10 K/min heating, first scan).
FIGURE 1 1H NMR spectrum of PVTDO synthesized from AIBN
at 60 ꢀC in DMF.
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TABLE 1 Results of Polymerization of VTDO Using TosI
TosI
Temp.
(ꢀC)
Time
(h)
Yield
(%)
a
Run
(mol %)
Mn (g/mol)
1
2
3
4
5
6
a
2
80
60
40
80
80
80
2
2
2
3
3
2
28
15
9
3,100, 1,000
4,300, 1,000
3,100, 1,000
6,500
2
2
0.5
1
16
29
26
5,400, 900
2,500, 900
FIGURE 5 1H NMR spectrum of PVTDO prepared from 2 mol %
of TosI initiator at 80 ꢀC in bulk.
10
Measured by means of SEC using polystyrene standards in DMF (LiBr,
10 mM).
two refractive intensity peaks at high and low-molecular-
weight part of the PVTDO prepared with 2 mol % of TosI
were estimated to be 3100 and 1000, respectively [Fig.
4(a)]. The use of a smaller amount of TosI (0.5 mol %)
increased the Mn to 6500. However, the molecular weight
distribution of the PVTDO remained broad [Fig. 4(b)].
the hydrogenated PVTDO had more crystallinity as well as
less solubility than the pristine PVTDO that contained a mix-
ture of cis- and trans-olefin units as evidenced by the 1H
NMR spectrum shown in Figure 1.
The 1H NMR spectrum of the PVTDO prepared using TosI
initiator at 80 C (Run 1, Table 1) is shown in Figure 5. The
Polymerization of VTDO Using p-Toluenesulfonyl Halides
We investigated the ring-opening polymerization of VTDO
using p-toluenesulfonyl halides, such as TosI and TosBr, as
initiators. Under the conditions studied herein, no polymer-
ization of VTDO proceeded without the tosyl halide initiator.
The experimental conditions and the results with TosI initia-
tor are summarized in Table 1. When 2 mol % of TosI was
used, polymerization of VTDO proceeded at the reaction tem-
ꢀ
spectral pattern was quite similar to that of the PVTDO pre-
pared using AIBN initiator shown in Figure 1, except for the
tosyl region. The characteristic proton signals of the tosyl
group at the polymer chain ends were observed at 7.4 and
7.8 ppm for the aromatic protons and 2.4 ppm for the
methyl protons. The NMR result suggested that TosI oper-
ated as a radical initiator and the polymerization of VTDO
proceeded via ring-opening process. The polymerization of
VTDO with TosI was inhibited in the presence of a radical
scavenger, 2,2,6,6-tetramethylpiperidinyl-oxy radical (TEMPO).
This inhibition strongly supported the radical mechanism of
the ring-opening polymerization.
ꢀ
peratures above 40 C to afford the polymeric products after
2 h (Runs 1–3). However, the yields of PVTDO remained low
as 9–28% and could not be increased by prolongation of the
ꢀ
time or elevating the temperature above 80 C. Similarly, the
PVTDO yield did not exceed 30% when the amount of TosI
was changed from 0.5 to 10 mol % (Runs 4–6). In all cases,
the unreacted monomer was recovered in filtrates after puri-
fication of PVTDO. This suggests that the polymerization was
terminated by combination of two active chain ends or radi-
cal disproportionation.
We have thus confirmed our working hypothesis that the
polymerization initiated by thermal dissociation of TosI at
elevated temperature to generate the toluenesulfonyl and
halide radicals, which attack the vinyl group in VTDO mono-
mer and form an open-chain sulfonyl radical via the ring open-
ing, which further attacks the vinyl group of another monomer
to constitute the propagation step of the polymerization.
Figure 4 shows the SEC curves of PVTDO synthesized using
TosI initiator (Runs 1 and 4, Table 1). Both curves exhibited
broad, multimodal distributions of molecular weight. The
We next examined the polymerization of VTDO using TosBr.
The polymerization conditions and the results are summar-
ized in Table 2. When compared with the TosI cases, longer
reaction time and higher reaction temperature were needed
for polymerizing VTDO with TosBr, as can be expected from
the lower reactivity of TosBr. When the polymerization was
ꢀ
conducted with 2 mol % of TosBr at 100 C for 24 h, PVTDO
was obtained in 38% yield (Run 1, Table 2). The Mn and
Mw/Mn of the obtained polymer were estimated to be 5300
and 2.5, respectively. The isolated yield of PVTDO reached
49% when 10 mol % of TosBr was employed, and its Mn
and Mw/Mn were determined to be 4100 and 1.8, respec-
tively (Run 2, Table 2). The yield value could not be
increased on prolonging the polymerization time to 48 h and
ꢀ
elevating the temperature up to 120 C. As a whole, the iso-
lated yields of PVTDO using TosBr were higher than those
with TosI. It should be noted here that the polymerization
FIGURE 4 SEC profiles of PVTDO prepared using TosI (a: 2
mol %; b: 0.5 mol %) at 80 ꢀC.
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TABLE 2 Results of Polymerization of VTDO Using p-
Toluenesulfonyl Halides
a
TosBr
TosI
Temp. Time Yield Mn
a
Run (mol %) (mol %) (ꢀC)
(h)
(%)
(g/mol) Mw/Mn
1
2
3
4
5
a
2
–
–
2
5
1
100
100
80
24
24
24
24
16
38
49
30
32
23
5,300
4,100
4,600
2,600
4,100
2.5
1.8
1.7
1.6
1.7
10
2
SCHEME 3 Plausible mechanism for the radical ring-opening
5
80
polymerization of VTDO.
3
80
Measured by means of SEC using polystyrene standards in DMF (LiBr,
tion of the sulfonyl halides on the vinyl groups of the VTDO,
resulting in formation of the b-iodosulfone (path b).26 The
CAX bond is sufficiently stable at the temperatures examined
in this study, thereby undergoing no dissociation of the CAX
bond in the absence of amines32 or metal catalysts28 and
constituting a termination step. The halogen radical could
also initiate the polymerization, rendering the polymerization
mechanism complicated (path c). Last but not least, it is
worth mentioning that this could be developed as a living
radical polymerization system if the side reactions such as
the 1,2-addition are sufficiently suppressed somehow or
other.
10 mM).
using 10 mol % of TosBr afforded PVTDO with an Mn of
4100 (Run 2, Table 2), which exhibited a relatively narrow,
monomodal molecular weight distribution of 1.8 (Fig. 6). We
also examined the mixed initiator systems of TosBr and TosI
(Runs 3–5, Table 2), which afforded PVTDO in lower yields
around 30%. The molecular weight distributions were as
narrow as those with 10 mol % of TosBr although the SEC
curves showed some small peaks and shoulders in the low-
molecular-weight part.
Based on the results thus obtained, we speculate the plausi-
ble mechanism of the radical ring-opening polymerization of
VTDO using the sulfonyl halides as initiators as shown in
Scheme 3 although quantitative discussion is impossible as
the produced PVTDO was separated from the polymerization
mixture during the polymerization owing to its poor solubil-
ity as already mentioned. The polymerization is initiated by
the thermal homolysis of the SAX bond of TosX (X ¼ Br and
I)14 to give the sulfonyl and halogen radicals. The sulfonyl
radical first attacks the vinyl group of the VTDO monomer,
forming a carbon radical, which rearranges immediately to
the more stable open-chain sulfonyl radical as the propagat-
ing radical via ring opening, which further attacks the vinyl
groups of another monomer to constitute the propagating
step of the polymerization (path a). Besides recombination
and disproportionation of the propagating sulfonyl radical, a
possible termination reaction could be the 1,2-radical addi-
CONCLUSIONS
The polyolefin sulfone (PVTDO) was prepared by the radi-
cal ring-opening polymerization of VTDO with p-toluenesul-
fonyl halides as an initiator in bulk. When TosI was
employed, polymeric products with a broad, multimodal
distribution of molecular weight were obtained in low
1
yields. The H NMR analysis of the PVTDO synthesized with
TosI along with the inhibition of the polymerization with
TEMPO indicated that TosI operated as a radical initiator
and the polymerization proceeded via ring-opening process.
In contrast to TosI, the use of TosBr as an initiator resulted
in high yields up to 49%. Furthermore, the PVTDO synthe-
sized with TosBr initiator had a monomodal distribution of
molecular weight of 1.8 with an Mn of 4100. To the best of
our knowledge, this is the first example of p-toluenesulfonyl
halides (TosI and TosBr) initiated radical ring-opening poly-
merization of cyclic vinyl sulfone monomer instead of com-
mon radical initiators such as AIBN and benzoyl peroxide.
Another hypothesis concerning this system is that a con-
trolled radical polymerization would be achieved if the
propagating sulfonyl radical is stabilized as a dormant
species and the side reactions are sufficiently suppressed
by changing the polymerization conditions, such as use of
solvents or metal complexes,33–35 which is ongoing in our
group.
ACKNOWLEDGMENT
This work was financially supported by JSR Corporation.
REFERENCES AND NOTES
FIGURE 6 SEC curve of the PVTDO prepared with 10 mol % of
TosBr at 100 ꢀC for 24 h.
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