Controlled insertion reaction of thiirane into carbamothioate: Novel synthesis of well-defined polysulfide

Article abstract of DOI:10.1021/ma101969r

The insertion reaction of propylene sulfide (PS) into p-tolylcarbamothioate (PTCT) was examined in the presence of tetrabutylammonium chloride (TBAC) in 1-methyl-2-pyrrolidinone at 60°Cin the feed ratio of PTCT/PS = 1/1 - 1/40, affording the corresponding

Full text of DOI:10.1021/ma101969r

Macromolecules 2010, 43, 9655–9659 9655
DOI: 10.1021/ma101969r
Controlled Insertion Reaction of Thiirane into Carbamothioate: Novel
Synthesis of Well-Defined Polysulfide
Hiroto Kudo, Kenichiro Sato, and Tadatomi Nishikubo*
Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, Rokkakubashi,
Kanagawa-ku, Yokohama, 221-8686, Japan
Received January 27, 2010; Revised Manuscript Received October 6, 2010
ABSTRACT: The insertion reaction of propylene sulfide (PS) into p-tolylcarbamothioate (PTCT) was
examined in the presence of tetrabutylammonium chloride (TBAC) in 1-methyl-2-pyrrolidinone at 60 °C in
the feed ratio of PTCT/PS = 1/1-1/40, affording the corresponding polysulfides in satisfactory yields. It was
0
found that the molecular weights (Mn s) coincided with the feed ratios PS and molecular dispersity ratios
(Mw/Mn) were very narrow (Mw/Mn <1.10). i.e., this insertion reaction could be performed under the living
system. Furthermore, the insertion living reaction of PS using tricarbamothioate was examined to give the
controlled three-arms star-shaped polysulfides.
Introduction
Experimental Section
Materials. 1,2-Dichloroethane, triethylamine, and 1-methyl-
2-pyrrolidinone (NMP) were dried over CaH2 and purified by
distillation before use. n-Hexane sodium azide, 1,3,5-benzene-
tricarbonyl trichloride, p-toluenethiol, dibutyltin dilaurate, pro-
pylene sulfide (PS), and tetrabutylammonium chloride (TBAC)
were used without further purification.
The characteristic physical properties of sulfur-containing poly-
mers, such as polysulfides, polysulfoxides, polysulfones, poly-
disulfides, and polythioesters, have led to the application of these
polymers in various functional materials, including high-refractive-
index materials, conductive materials, coatings, sealants, and
adhesives.1 Polysulfides can be synthesized by ring-opening poly-
merization and polyaddition. Well-defined linear and star-shaped
polysulfides have been synthesized by the living ring-opening
polymerization of propylene sulfide (PS).2 Recently, we also
achieved the controlled acyl transfer polymerization (CAT) of
thiirane using aryl thioester as an initiator, obtaining well-defined
star-shaped polysulfides.3 The refractive-index values of these star-
shaped polysulfides were consistent with the structures, i.e., the
value of refractive-index increased with increasing number of arms,
length of arms, and sulfur content, and with decreasing size of the
core structure.4 Furthermore, the insertion reaction of thiirane into
cyclic thioester as an initiator was examined in the CAT system
for the synthesis of cyclic polysulfide, and it was found that the
ring-expansion polymerization (REP) proceeded to give the cyclic
polysulfides quantitatively.5 However, the size of the cyclic poly-
sulfides could not be controlled because both intra- and intermole-
cular thioester exchange reaction occurred during REP, i.e., living
REP could not be achieved because the thioester bond is a dynamic
covalent bond.6 Very recently, we investigated a new REP system,
utilizing the insertion reaction of thiirane into cyclic carbamothioate
as an initiator.7 We had expected that the size of the cyclic
polysulfide might be controlled by the feed ratio, because the car-
bamothioate is not a dynamic covalent bond. However, the size of
larger cyclic polysulfides could not be controlled. If the contin-
uous insertion reaction of thiirane into carbamothioate could be
performed in a living fashion, a living REP system would be
possible. In this paper, we describe the results of a detailed exami-
nation of the reaction of carbamothioate and thiirane, and
we present a new living system for the synthesis of well-defined
polysulfides.
Measurements. Infrared (IR) spectra were measured on a
Jasco Model IR-420 spectrometer. The proton nuclear magnetic
resonance (1H NMR) spectra were recorded on JEOL Model
JNM R-600 (600 MHz for 1H NMR) instruments in deuterated
chloroform (CDCl3) using Me4Si (TMS) as an internal standard
1
for H NMR. The number-average molecular weight (Mn) and
molecular weight distribution (Mw/Mn) of the polymers were esti-
mated by size exclusion chromatography (SEC) with the use of a
Tosoh HLC-8220 SEC equipped with refractive index and ultra-
violet detectors, using TSK gel columns [eluent: THF] cali-
brated with narrow-molecular-weight polystyrene standards.
Synthesis of p-Tolylcarbamothioate (PTCT). The solution of
p-tolyl isocyanate (1.2 mL, 10 mmol) and benzenethiol (1.0 mL,
10 mmol) in 1,2-dichloroethane (10 mL) was prepared, and then
triethylamine (1.00 mL, 10 mmol) was added. The resulting
solution was stirred at 25 °C for 15 min. After that, the solution
was poured into large amount of n-hexane to precipitate the
white solid. The obtained solid was purified by the recrystalliza-
tion from the mix solvent of n-hexane:chloroform =3:1. The
obtained solid was collected by filtration and dried in vacuo at
25 °C for 12 h to obtain p-tolylcarbamothioate (PTCT). Yield =
76% (1.79 g). Mp = 124.2-124.7 °C. 1H NMR (600 MZ, CDCl3):
δ = 2.30 (s, 3.0 H, -CH3), 6.99 (s, 1.0 H, -NH-), 7.10 (d, J =
8.4 Hz, 2.0 H, aromatic H), 7.25 (d, J = 4.8 Hz, 2.0 H, aromatic H),
7.43-7.48 (m, 3.0 H, aromatic H), 7.60 - 7.62 (m, 2.0 H, aromatic
H). IR (KBr, cm-1):814(νC-S), 1513 and 1602 (νCdCaromatic),
1665 (ν CdO), and 3226 (ν aromatic C-H).
The Insertion Reaction of PTCT and PS (PTCT/PS = 1/40).
Typical procedure for the synthesis of PTCT-poly(PS)40. PTCT
(0.064 g, 0.026 mmol), PS (0.078 g, 1.05 mmol), and TBAC (13.9
mg, 0.05 mmol) were dissolved in NMP (1.05 mL) in a poly-
merization tube. The tube was cooled, degassed, and sealed,
then heated at 60 °C for 24 h. The resulting reaction mixture was
poured into methanol to precipitate a polymer, which was dried
in vacuo at room temperature for 72 h, affording a highly viscous
*To whom all correspondence should be addressed. E-mail: nishikubot@
kanagawa-u.ac.jp.
r 2010 American Chemical Society
Published on Web 11/04/2010
pubs.acs.org/Macromolecules

9656 Macromolecules, Vol. 43, No. 23, 2010
Kudo et al.
Table 1. Reaction of PTCT and PS a
run
feed ratios PTCT/PS
solvent
catalyst
reaction temperature, °C
convn,b %
yield, %
Mn(Mw/ Mn)c
DP(1HNMR)d
1
2
3
4
5
6
7
8
1/1
1/5
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
DMSO
o-DC
TBAC
TBAC
TBAC
TBAC
TBAC
TBAC
none
TBAC
TBAC
TBAC
TBAC
60
60
60
60
60
60
60
40
50
60
60
>99
>99
>99
>99
>99
>99
24
>99
>99
85
94e
87e
86e
65f
92 f
95 f
g
95
87
44
g
300 (1.02)
590 (1.06)
1000 (1.09)
1940 (1.09)
2560 (1.10)
3400 (1.08)
g
2940 (1.16)
3210 (1.11)
2610 (1.23)
g
1
5
1/10
1/20
1/30
1/40
1/40
1/40
1/40
1/40
1/40
10
20
30
40
g
40
42
47
g
9
10
11
<3
a Conditions; total monomer concentration =1.0 mol/L, reaction time 24 h. b Calculated from 1H NMR signals. c Estimated by SEC based on
polystyrene standards in THF. d Calculated from H NMR signals. e Separated by silica gel column chromatography. f Insoluble part in methanol.
1
g Not determined.
Scheme 1
colorless oil. The yield was 95% (0.135 g). Mn = 3400, Mw/
Mn = 1.08 (run 6 in Table 1). 1H NMR (600 MHz, CDCl3): δ =
1.32-1.45 (m, 124H, CH3 of thiirane moiety), 2.32 (s, 3.0H,
-CH3), 2.56-3.74 (m, 123H, methine and methylene protons),
7.10-7.13 (m, 2.0H, aromatic H), 7.20-7.22 (m, 2.0H, aromatic
H), 7.26-7.32 (m. 4.0H, aromatic H), 7.36- 7.38 (m, 2.0H,
aromatic H). IR (KBr, cm-1): 815 (ν C-S), 1514 and 1595 (ν
CdC aromatic), 1688 (ν CdO), 2959 (ν aromatic C-H), and
3306 (ν N-H).
The Insertion Reaction of PTCT and PS (PTCT/PS = 1/1).
The reaction PTCT (2.58 g, 1.05 mmol), PS (0.078 g, 1.05 mmol),
and TBAC (13.9 mg, 0.05 mmol) was performed in the same
method for the synthesis of PTCT-poly(PS)40. Yield = 94%
(2.45 g). Mn= 300, Mw/Mn=1.02. 1H NMR (600 MHz, CDCl3):
δ = 1.47 (d, 3.0H, J = 7.2 Hz, -CH3 of thiirane moiety), 2.31 (s,
3.0H, -CH3), 3.04 (dd, 1.0H, methylene proton, J = 9.0 Hz,
J = 13.2 Hz), 3.48 (dd, 1.0H, methylene proton, J = 9.0 Hz, J =
13.2 Hz), 3.75-3.80 (m, 1.0H, methine proton), 6.93 (s, 1.0 H,
-NH), 7.12 (d, 2.0H, J = 18.6 Hz, aromatic H), 7.18 (t, 1.0H,
J = 6.6 Hz, aromatic H), 7.25-7.30 (m, 4.0H, aromatic H),
7.43 (d, 2.0H, J = 7.8 Hz, aromatic H). IR (KBr, cm-1): 812(ν
C-S), 1594 (ν CdC of aromatic), 1653 (ν CdO ester), 3317(ν
-NH-).
The Reaction of PS in the Absence of PTCT. PS (0.078 g, 1.05
mmol) and TBAC (13.9 mg, 0.05 mmol) were dissolved in NMP
(1.05 mL) in a polymerization tube. The reaction was performed
Figure 1. 1H NMR spectra. (a) PTCT. (b) PTCT-poly(PS)1 (run 1 in
Table 1). (c) PTCT-poly(PS)40 (run 6 in Table 1).
as the same manner for the synthesis of PTCT-poly(PS)40. Yield =
81% (0.063 g). Mn =30 000, Mw/Mn = 1.32. 1H NMR (600 MHz,
CDCl3): δ = 1.38 (s, -CH3 of thiirane moiety), 2.60-2.72 (m,
methine protons), 2.84-3.02 (m, methine protons). IR (KBr, cm-1):
824 (ν C-S), 2920 and 2960 (ν C-H).
The Reaction of PS and S-Phenyl Methyl(p-tolyl)carbamothio-
ate (PMCT). The reaction of PMCT (0.067 g, 0.026 mmol), PS
(0.078 g, 1.05 mmol), and TBAC (13.9 mg, 0.05 mmol) was
examined in the same manner for the synthesis of PTCT-poly-
(PS)40. Poly(PS) with Mn = 28 000 and Mw/Mn = 1.36 was
obtained in 82% yield.
Synthesis of S-p-Tolyl Benzene-1,3,5-triyltricarbamothioate
(TBTTC). The solution of sodium azide (0.54 g, 8.3 mmol) in water
(5 mL) was prepared, and then the solution of 1,3,5-benzenetricar-
bonyl trichloride (0.67 g, 2.5 mmol) in 1,2-dichloroethane (10 mL)

Article
Macromolecules, Vol. 43, No. 23, 2010 9657
Scheme 2
Scheme 3
was examined under various conditions (Scheme 1 and Table 1).
When this reaction was carried out with feed ratios of PTCT/
PS = 1/1 to 1/40 in NMP at 60 °C using tetrabutylammonium
chloride (TBAC) as a catalyst for 24 h, the SEC profiles of all
the products showed unimodal peaks. This means that the
corresponding oligomers and polymers were obtained with a
number-average molecular weight (Mn) in the range between
300 and 3400, and with a narrow polydispersity ratio (Mw/Mn)
in the range between 1.02 and 1.08 (runs 1-6).
The structures of the products were confirmed by 1H NMR
and IR spectroscopy. Figure 1 depicts the 1H NMR spectra of
oligomer (run 1) and polymer (run 6), along with that of PTCT.
As shown in Figure 1(b), the 1: 1 adduct PTCT-poly(PS)1 was
obtained in the case of an equimolar feed of PTCT and PS in
94% yield (run 1). As shown in Figure 1(c), the extent of the
continuous insertion reaction (DI) of PS into the carbamothio-
ate moiety could be calculated based on the signals of the
aromatic protons at 7.10-7.13 ppm and the methyl protons of
thiirane moieties produced by the insertion reaction of PS at
1.32-1.45 ppm, and it was found that the DI value coincided
well with the feed ratio of PS, i.e., PTCT-poly(PS)40 was
obtained in 95% yield (run 6). Furthermore, at all feed ratios
examined, the DI value of PS was precisely controlled and the
corresponding PTCT-poly(PS)n (n = 5, 10, 20, and 30) could
be synthesized in satisfactory yield with a narrow molecular
weight distribution (runs 2-5).
In the absence of TBAC, it was observed that 24% of PS was
converted after the reaction, and the polymer was not obtained
(run 7). When this reaction was performed at other tempera-
tures, such as 40 and 50 °C, >99% of PS was converted to the
corresponding polysulfides with Mn = 2140 (Mw/Mn = 1.16)
at 40 °C and Mn = 3210 (Mw/Mn = 1.11) at 50 °C (runs 8 and
9). Furthermore, in dimethyl sulfoxide (DMSO) the reaction
afforded a polymer with Mn = 2610 (Mw/Mn = 1.23), while no
polymer was obtained in o-dichlorobenzene (o-DC) (runs 10
and 11). Thus, the insertion reaction of PS into PTCT pro-
ceeded smoothly with TBAC as a catalyst in NMP at 60 °C for
24 h.
Figure 2. Relationship of number-average molecular weight (Mn), feed
ratioofPS and PTCT, and conversionofPS. [A] Mn and feed ratioofPS
and PTCT. [B] Mn and conversion of PS. [C] ln([PS]0/[PS]) vs time.
was added slowly at 0 °C. The resulting mixture was stirred at 25 °C
for 1 h. After that, the organic part was extracted and dried over
using MgSO4. Next the resulting solution was heated at 90 °C for
125 min, and then p-toluenethiol (1.02 g, 8.3 mmol) and dibutyltin
dilaurate (0.5 mL) were added. The obtained solution was stirred at
90 °C for 1 h. After that the solution was cooled at 0 °C and CHCl3
was added to obtain the white solid. The obtained solid was purified
by recrystallization from 1,2-dichloroethane and was dried in vacuo
to obtain S-p-tolyl benzene-1,3,5-triyltricarbamothioate (TBTTC).
Yield = 85% (1.22 g). Mp = 94.5 °C (decomposition). 1H NMR
(600MZ,CDCl3):δ= 2.39 (s, 9.0H, -CH3),7.06(s,3.0H,aromatic
H), 7.23-7.27 (m, 6.0H, aromatic H), 7.42-7.44 (m, 6.0H, aromatic
H). IR (KBr, cm-1): 807 (ν C-S), 1528 and 1613 (ν CdC of
aromatic), 1653 (ν CdO), 1708 (ν -NdC = O), 3072 (νCH3).
The Insertion Reaction of PS into TBTTC. The typical
procedure follows. The reaction of PS (0.083 mL, 1.05 mmol),
TBTTC (0.005 g, 0.0088 mmol), and TBAC (0.015 g, 0.0525
mmol) in NMP (1.05 mL) was performed in the same fashion for
the syntheis of PTCT-poly(PS)40. Yield = 83%. Mn = 9160,
Mw/ Mn=1.21.
Results and Discussion
The reaction of PTCT and PS. The reaction of S-phenyl
p-tolylcarbamothioate (PTCT) and propylene sulfide (PS)

9658 Macromolecules, Vol. 43, No. 23, 2010
Kudo et al.
Scheme 4
Table 2. Reaction of TBTTC and PS a
run
feed ratios PTCT/3 ꢀ PS
1/1
1/5
convn,b %
yield, %
Mn(Mw/ Mn)e
DP(1H NMR)b
1
2
3
4
5
>99
>99
>99
94
93c
36c
65c
82d
83d
850 (1.02)
2010 (1.13)
2900 (1.14)
5210 (1.15)
9160 (1.21)
1
5
10
21
42
1/10
1/21
1/40
97
a Conditions; total monomer concentration =1.0 mol/L, reaction time 24 h. b Calculated from 1H NMR signals. c Separated by silica gel column
chromatography. d Methanol-insoluble part. Calculated from 1H NMR signals. e Estimated by SEC based on polystyrene standards in THF. Separated
by silica gel column chromatography.
To confirm the living character in the present polymeri-
zation, we examined the relationships among the values of
conversion of PS, Mn, and Mw/Mn of PTCT-poly(PS)n. The
relationships among Mn, Mw/Mn, and feed ratio are also
illustrated in Figure 2A. As shown in Figure 2B, it was found
that the value of Mn increased linearly with increasing conversion
until about >99%, while the value of Mw/Mn remained un-
changed (1.01). Furthermore, Figure 2C shows the straight line
of ln([PS]0/[PS]) vs time ([PS]0 and [PS] mean molecular-weight-
values of propylene sulfide (PS) before and after insertion
reaction, respectively), indicating the constant concentration of
active species during the polymerization until the conversion
reached 99%. These show that the continuous insertion reaction
of PS into PTCT proceeded in a living fashion.
Furthermore, when the reaction of PS in the absence of
PTCT was carried out under the same conditions, using
TBAC as catalyst at 60 °C in NMP for 24 h, it was observed
that anionic ring-opening polymerization of PS proceeded to
afford the corresponding polysulfide poly(PS) with Mn =
30 000 and Mw/Mn = 1.32 in 81% yield (Scheme 2).
We also synthesized the carbamothioate which the -NH-
proton was replaced with a methyl group, S-phenyl methyl-
( p-tolyl)carbamothioate (PMCT),8 and examined the inser-
tion reaction of PS using PMCT as an initiator under the
same conditions with a feed ratio of PMCT/PS=1/40. In this
case, insertion polymerization of PS did not proceed and
anionic ring-opening polymerization of PS occurred to give
the corresponding poly(PS) with Mn = 28 000 and Mw/
Mn = 1.36 in 82% yield (Scheme 3). This means that the
proton of carbamothioate is necessary for the insertion
reaction of PS into carbamothioate. It might be indicated
that an intermediate product is constructed by the combina-
tion of carbamothioate, quaternary onium salt, and thiirane.
Furthermore, the insertion reaction of PS into PTCT was
also examined in the case of feed ratio of PMCT/PS = 1/50
and 1/60, and it was observed that their SEC profiles showed
bimodal peaks. This means that the anionic polymerization
of PS proceeded during insertion reaction of PS into PTCT;
i.e., higher molecular weight polysulfides could not be ob-
tained in this insertion reaction.
Next, the insertion reaction of PS using tricarbamothioate
as initiators was examined in the same fashion for the
synthesis of PTCT-poly(PS)n to afford the corresponding
polymers with Mns in the range between 800 and 10,010
(Scheme 4 and Table 2). The structures of the polymers were
confirmed by 1H NMR and IR spectroscopy. The values of
DPn were almost coincided with the feeds of PS. As the
result, the continuous insertion reaction of PS into tricarba-
mothioate proceeded to give the corresponding controlled
three-arm star-shaped polysulfides.
In summary, the insertion reaction of propylene sulfide
(PS) into p-tolylcarbamothioate (PTCT) using TBAC as a
catalyst in NMP at 60 °C for 24 h proceeded in a living
fashion, yielding corresponding polysulfides with narrow
molecular dispersity ratios in satisfactory yields. The living
character of the insertion reaction of PS into PTCT was
supported by the following evidence: constant concentration
of propagation species reached >99% conversion, narrow
molecular weight distribution (Mw/Mn < 1.10), and molecular
weight (Mn) could be controlled by the feed monomer con-
centration in the range of PTCT/PS=1/1 to 1/40. Further-
more, the insertion reaction of PS into tricarbamothioate was

Article
Macromolecules, Vol. 43, No. 23, 2010 9659
performed to give the controlled three-arms star-shaped
polysulfides. This living insertion polymerization system
should be applicable for the living expansion polymeriza-
tion, and further investigation is in progress.
Krivokuca, M. R. J. Polym. Sci. Part A. Polym. Chem. 1997, 35, 1369–
1373. (f ) Todorova, D.; Kostov, G.; Popov, A.; Todorov, S. J. Appl.
Polym. Sci. 2000, 75, 1205–1209. (g) Quan, Y.; Wang, Q.; Dong, W.;
Chen, Q. J. Appl. Polym. Sci. 2003, 89, 2672–2675. (h) Ruiz, J.;
Quesada, R.; Riera, V.; Vivanco, M.; Garcia-Granda, S.; Diaz, M. R.
Angew. Chem. 2003, 115, 2494–2497.
Supporting Information Available: Scheme showing the
synthesis of PMCT and text giving experimental procedures and
spectroscopic data of S-phenyl methyl( p-tolyl)carbamothioate
(PMCT). This material is available free of charge via the
Internet at http://pubs.acs.org.
(2) (a) Nicol, E.; Plaisance, C. B.; Dony, P.; Levesque, G. Macromol.
Chem. Phys. 2001, 202, 2843–2852. (b) Nicol, E.; Plaisance, C. B.;
Levesque, G. Macromolecules 1999, 32, 4485–4487.
(3) Kudo, H.; Inoue, H.; Nishikubo, T.; Anada, T. Polym. J. 2006, 36,
289–297.
(4) Kudo, H.; Inoue, H.; Inagaki, T.; Nishikubo, T. Macromolecules
2009, 42, 1051–1057.
(5) Kudo, H.; Makino, M.; Kameyama, A.; Nishikubo, T. Macromolecules
2005, 38, 5964–5969.
(6) Kudo, H.; Makino, S.; Nishikubo, T. J. Polym. Sci. Part A. Polym.
References and Notes
(1) For example: (a) Kameyama, A.; Murakami, Y.; Nishikubo, T.
Macromolecules 1996, 29, 6676–6678. (b) Hara, A.; Ohishi, Y.;
Kakimoto, M.; Imai, Y. J. Polym. Sci., Part A: Polym. Chem. 1991,
29, 1933–1940. (c) Koyama, E.; Sanda, F.; Endo, T. Macromolecules
1998, 31, 1495–1500. (d) Tenc-popovic, M. E.; Bogunovic, L. J.;
Jankovic, D. D.; Velickovic, A. D. J . Polym. Sci., Part A: Polym.
Chem. 1997, 35, 1363–1367. (e) Tenc-popovic, M. E.; Bogunovic, L. J.;
Chem. 2007, 45, 680–687.
(7) Kudo, H.; Sato, M.; Wakai, R.; Iwamoto, T.; Nishikubo, T.
Macromolecules 2008, 41, 521–523.
(8) Synthesis and spectroscopic date are presented in the Supporting
Information.