Synthesis of cyclic polymers: Ring-expansion reaction of cyclic s-dithioester with thiiranes

Article abstract of DOI:10.1021/ma047642h

The ring-expansion reaction of equimolar cyclic dithioester 1 with 3-phenoxypropyrene sulfide (PPS) (cyclic dithioester 1/PPS = 1/2) was examined in the presence of TBAC as a catalyst in NMP for 24 h, It was found that intermodular ester-exchange reaction

Full text of DOI:10.1021/ma047642h

5964
Macromolecules 2005, 38, 5964-5969
Synthesis of Cyclic Polymers: Ring-Expansion Reaction of Cyclic
S-Dithioester with Thiiranes
Hiroto Kudo, Shinya Makino, Atsushi Kameyama, and Tadatomi Nishikubo*
Department of Applied Chemistry, Faculty of Engineering, Kanagawa University,
Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
Received November 15, 2004; Revised Manuscript Received April 28, 2005
ABSTRACT: The ring-expansion reaction of equimolar cyclic dithioester 1 with 3-phenoxypropyrene
sulfide (PPS) (cyclic dithioester 1/PPS ) 1/2) was examined in the presence of TBAC as a catalyst in
NMP for 24 h. It was found that intermolecular ester-exchange reaction occurred during the insertion
reaction of PPS into cyclic dithioesters, and cyclic polymers with Mns ) 3600-8900 were obtained in
80-96% yields. The structures of the obtained cyclic polymers were confirmed by the 1H NMR, 13C NMR
IR, and MALDI TOF-MS spectroscopy. The continuous insertion reaction of excess PPS into cyclic
dithioester (cyclic dithioester 1/PPS ) 1 /50) was also examined, and it was found that the insertion
reaction proceeded quantitatively to afford the corresponding cyclic polysulfide with Mn ) 42 000 and
Mw/Mn ) 4.50 in a 96% yield.
Introduction
fides by the acyl transfer polymerization of thiiranes
with thioesters (Scheme 1).13
Nonlinear compounds, such as cyclic polymers, star
polymers, hyperbranched polymers, dendrimers, cat-
enanes, and rotaxanes, have attracted much attention.
This is because their unique structures often result in
unusual physical behavior such as extreme thermal or
viscoelastic behavior, high densities, and unique solubil-
ity characteristics. As a result, new applications are
expected to arise from these materials. Furthermore, a
variety of synthetic methods for these materials have
been reported. In the case of cyclic polymers, two
strategies for their syntheses are well-known. One is
the ring-closure reaction of linear compounds with
difunctional groups at the ends. Hocker1 and To-
porowski et al.2 reported independently the first syn-
thesis of the cyclic polystyrenes by the ring-closure
reaction of a living R,ω-dicarbanionic polystyrene with
dibromo-p-xylene and dimethyldichlorosilane, respec-
tively, under highly diluted conditions. Recently, Tezuka
et al.3-5 reported the highly selective synthesis of
multicyclic polymers by the reliant on electrostatic self-
assembly. The another method for the synthesis of cyclic
polymers is the ring-expansion polymerization of cyclic
compounds. Kricheldorf et al.6,7 succeeded the synthesis
of the cyclic polyesters by the insertion reaction of
lactones with cyclic compounds containing stannum.
Shea et al.8,9 also examined the synthesis of cyclic
polymers by the polyhomologation reaction of cyclic
compounds containing borane atoms. More recently,
Grubbs et al.10,11 reported the synthesis of the ring-
expanded cyclic polymers by the ring-closing metathesis
reaction. Furthermore, comparison of the physical prop-
erties of the cyclic and linear polymers was examined.11
In this system, the continuous insertion reaction of
thiiranes into thioester moieties proceeded in living like
fashion, affording the corresponding polysulfides with
narrow molecular weight distribution.
Therefore, in this time, we designed and examined a
new approach for the synthesis of cyclic polymers with
controlled the ring size by the ring-expansion reaction
of the cyclic dithioester 1 with 3-phenoxypropyrene
sulfide (PPS) as shown in Scheme 2. Through this ring-
expansion reaction, we provided a foundation for syn-
thesizing cyclic polymers.
Experimental Section
Materials. 1-Methyl-2-pyrrolidone (NMP) was dried with
CaH2 and was purified by distillation before use. Tetrabutyl-
ammonium bromide (TBAB) was recrystallized from dried
ethyl acetate. Tetrabutylammonium chloride (TBAC) and
tetraphenylphosphonium chloride (TPPC) were used without
further purification. Cesium carbonate (Cs2CO3), tetrahydro-
furan (THF), ethyl acetate, chloroform (CHCl3), and n-hexane
were used without further purification.
Measurements. Infrared (IR) spectra were measured on a
1
Jasco model IR-420 spectrometer. The H NMR spectra were
1
recorded on JEOL model JNM R-500 (500 MHz for H NMR
and 125 MHz for 13C NMR) instruments in CDCl3 and DMSO-
d6 using Me4Si (TMS) as an internal standard reagent for 1H
NMR. Matrix-assisted laser desorption ionization time-of flight
mass (MALDI-TOF-MS) experiments were performed on a
Shimazu/Kratos MALDI-TOF-MS using dihydroxybenzoic
acid as matrix and chloroform as solvent. The number-average
molecular weight (MnSEC) and molecular weight distribution
[weight-average molecular weight/number-average molecular
weight (Mw/Mn)] of the polymers were estimated by size
exclusion chromatography (SEC) with a Toso HLC-8220 SEC
instrument equipped with refractive index and ultraviolet
detectors with TSK gel columns [with a solution of LiBr and
phosphoric acid (20 mM) in DMF as an eluent] and calibrated
with narrow molecular weight polystyrene standards.
Meanwhile, Nishikubo et al.12 have developed the
ring-opening reaction of thiiranes with esters. These
reactions proceeded smoothly and regioselectively in the
presence of quaternary onium salts as catalysts to afford
the corresponding thioesters in high yields.12 Further-
more, they achieved the synthesis of the linear polysul-
The Equivalent Reaction of Cyclic Dithioester 1 with
PPS. A Typical Procedure: Cyclic dithioester (0.073 g, 0.2
mmol as dithioester groups), PPS (0.033 g, 0.2 mmol), and
TBAC (0.003 g, 0.002 mmol) were dissolved in NMP (0.25 mL)
in a polymerization tube. The tube was cooled, degassed, and
* To whom all correspondence should be addressed. E-mail:
nishikubot@kanagawa-u.ac.jp.
10.1021/ma047642h CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/11/2005

Macromolecules, Vol. 38, No. 14, 2005
Synthesis of Cyclic Polymers 5965
Scheme 1
Scheme 2
Table 1. Reaction of Cyclic Dithioester 1 with PPSa
(1.65 g). Mn ) 42 000; Mw/Mn ) 4.50. IR (film, cm-1): 3019 (ν
C-H aromatic), 2923 (ν C-H aliphatic), 1681 (ν CdO thioester),
1595 and 1576 (ν CdC aromatic), 1285 (ν C-O-C ether), 756
(ν C-S-C sulfide). 1H NMR (500 MHz, CDCl3, TMS) δ (ppm):
2.97-3.15 (m, 4.0 H, -CH2-S-), 4.16-4.22 (m, 100.0 H, -
CH2-O-Ph), 5.16 (s, 4.0 H, Ph-CH2-O-Ph), 6.83-7.93 (m,
274.0 H, aromatic H).
temp concn
run (°C) (M)
DI yield Mn,SEC
×
catalyst (%)b (%)c
10-3 d
Mw/Mn
d
e
e
e
1
2
3
4
5
6
7
8
30 0.1
TBAC
TBAC
TBAC
TBAC
TBAC
TBAC
TBAC
TPPC
0
32
e
e
e
50 0.1
70 0.1
50 1.0
70 1.0
90 1.0
120 1.0
150 bulk
>99
>99
>99
>99
>99
>99
80
92
90
96
90
91
5
3.1
4.2
4.1
4.6
9.8
2.3
6.1
6.5
5.7
8.9
3.6
Results and Discussion
The Equivalent Reaction of Cyclic Dithioester
1 with PPS. We examined the reaction of cyclic
dithioester 1 (1 mmol) with PPS (2 mmol) in the
presence of quaternary onium salts tetrabutylammo-
nium chloride (TBAC) or tetraphenylphosphonium bro-
mide (TPPC) as catalysts for 24 h in NMP (Scheme 3).
The reaction conditions and results are summarized in
Table 1.
a The reaction of dithioester 1 (0.1 mmol) with PPS (0.2 mmol)
in the solvent (0.25 mL) in the presense of catalyst (5 mol %) for
24 h. b The degree of insertion of PPS into cyclic dithioester (DI)
was calculated by 1H NMR. c Methanol-insoluble parts. d Esti-
mated by SEC based on polystyrene standards; eluent: solution
of LiBr and phosphoric acid (20 mM) in DMF. e Not observed.
sealed off, and then the reaction was carried out at 90 °C for
24 h. The reaction mixture was diluted by the addition of
CHCl3 and poured into methanol to precipitate a polymer; it
was reprecipitated twice from CHCl3 into methanol and dried
in vacuo at 60 °C for 24 h. The yield was 96% (0.102 g). Mn )
6500; Mw/Mn ) 4.10 (run 5 in Table 1). IR (film, cm-1): 3068
(ν C-H aromatic), 2927 (ν C-H aliphatic), 1671 (ν CdO
thioester), 1597 (ν C-C aromatic), 1298 (ν C-O-C ether), 756
(ν C-S-C sulfide). 1H NMR (500 MHz, CDCl3, TMS) δ (ppm):
3.31-3.40 (m, 4.0 H, -CH2-S), 4.12-4.23 (m, 4.0 H, -CH2-
O-, side chain), 4.44 (s, 2.0 H, CH-), 5.17 (s, 4.0 H, -CH2-
O-, main chain), 6.83-7.93 (m, 34.0 H, aromatic H).
The Equivalent Reaction of Linear Dithioester with
PPS. Linear dithioester (0.05 g, 0.2 mmol as thioester groups),
PPS (0.033 g, 0.2 mmol), and TBAC (0.003 g, 0.002 mmol) were
dissolved in NMP (0.25 mL) in a polymerization tube. The tube
was cooled, degassed, and sealed off, and then the reaction
was carried out at 70 °C for 24 h. The reaction mixture was
diluted by the addition of CHCl3 and poured into methanol to
precipitate a reaction product; it was reprecipitated twice from
CHCl3 into methanol and dried in vacuo at 60 °C for 24 h.
The yield was 90% (0.071 g). IR (film, cm-1): 3068 (ν C-H
aromatic), 2927 (ν C-H aliphatic), 1671 (ν CdO thioester),
1597 (ν C-C aromatic), 1298 (ν C-O-C ether), 756 (ν C-S-C
sulfide). 1H NMR (500 MHz, CDCl3, TMS) δ (ppm): 3.31-3.40
(m, 4.0 H, -CH2-S), 4.12-4.23 (m, 4.0 H, -CH2-O-, side
chain), 4.44 (s, 2.0 H, CH-), 5.17 (s, 4.0 H, -CH2-O-, main
chain), 6.83-7.93 (m, 34.0 H, aromatic H).
When the reaction was performed at 30 °C under
highly diluted conditions (0.1 M), no product was
obtained (run 1 in Table 1). The degree of insertion (DI)
of PPS into cyclic dithioester was only 32% on the
reaction at 50 °C (run 2 in Table 1). However, the
insertion reaction proceeded smoothly and completely
at 70 °C, and a polymer with Mn ) 5000 was obtained
in a 80% yield (run 3 in Table 1). Furthermore, we
examined the reaction under 1.0 M concentration at the
temperatures in the range between 50 and 120 °C, and
it was found that the corresponding polymers with Mns
) 5700-8900 were obtained in 90-96% yields. These
results show that the Mns of the resulting polymers
increased with the reaction temperature in most cases.
It was also observed that the molecular weight distribu-
tion (Mw/Mn) of the resulting polymers was broader with
increasing the reaction temperatures (runs 4-7 in Table
1). The polymer with Mn ) 3600 (Mw/Mn ) 2.3) was also
obtained in a 90% yield in bulk (run 8 in Table 1). The
SEC curves of these polymers showed unimodal peaks.
The structures of the resulting polymers were confirmed
by IR, 1H NMR, 13C NMR, and MALDI-TOF mass
spectroscopy.
Figure 1 illustrates the 1H NMR spectrum of the
obtained polymer (Mn,SEC ) 6500, run 5 in Table 1),
which shows the signals assignable to the methylene
protons of the sulfide moieties, methylene protons of the
ether moieties, and methine protons produced by the
insertion reaction of PPS at 3.31-3.42, 4.12-4.23, and
4.44 ppm, respectively. However, any proton signals of
end groups of the polymers were not observed.
The Continuous Insertion Reaction of Excess PPS
into Cyclic Dithioester 1. The reaction of cyclic dithioester
(0.073 g, 0.2 mmol as thioester groups), PPS (1.65 g, 10.0
mmol), and TBAC (0.003 g, 0.002 mmol) was carried out in
NMP (5.2 mL) at 90 °C for 24 h by the similar method for the
reaction of cyclic dithioester 1 with PPS. The yield was 96%

5966 Kudo et al.
Macromolecules, Vol. 38, No. 14, 2005
Scheme 3. Cyclic Products Obtained by the Reaction of Cyclic Dithioester 1 (1 mmol) with PPS (2 mmol)
Table 2. Data of the MALDI-TOF Mass Spectra
Figure 2 depicts the MALDI-TOF mass spectra of
cyclic products
m/z (calcd)
m/z (found)
the obtained polymer with Mn ) 6500 (run 5 in Table
1) with Na+ doping.
C1 (n ) 1, DP(PPS) ) 2)
C2 (n ) 1, DP(PPS) ) 3)
C3 (n ) 2, DP(PPS) ) 1)
C4 (n ) 2, DP(PPS) ) 2)
C5 (n ) 2, DP(PPS) ) 3)
C6 (n ) 2, DP(PPS) ) 4)
C7 (n ) 2, DP(PPS) ) 5)
C8 (n ) 3, DP(PPS) ) 5)
C9 (n ) 3, DP(PPS) ) 6)
(C58H48O6S6 + Na): 1088.39
(C67H58O7S7 + Na): 1254.63
(C89H66O9S9 + Na): 1655.06
(C98H76O10S10 + Na): 1821.30
(C107H86O11S11 + Na): 1987.54
(C116H96O12S12 + Na): 2153.78
(C125H106O13S13 + Na): 2320.02 2319.50
(C165H134O17S17 + Na): 3052.93 3052.43
(C174H144O18S18 + Na): 3219.17 3218.67
1088.11
1254.35
1654.44
1820.68
1986.92
2153.16
In this figure, two mass differences patterns in peaks
were observed to be exactly the molar mass of PPS
(M ) 166.24) and cyclic(thioester-alt-sulfide) C1 (M )
1065.39). C1 was the cyclic compound obtained by the
insertion reaction of two equivalent PPS into cyclic
thioester 1. Therefore, the cyclic size (n) and the degree
of polymerization of PPS (DP(PPS)) of C1 were 1 and 2,
respectively, as shown in Scheme 3. C2 was formed by
the insertion reaction of PPS into synthesized C1, and
its n and DP(PPS) were 1 and 3, respectively. Further-
more, C3-C7 (n ) 3) with DP(PPS) ) 1-5, C8-C10 (n
) 3) with DP(PPS) ) 5-7, C11 (n ) 4) with DP(PPS) ) 8,
and C12 (n ) 5) with DP(PPS) ) 10 were also observed.
This means that the obtained polymer contained many
cycles C1-C12 with different Mns; the values of m/z are
listed in Table 2. In addition MnSEC was not same to
that of Mn measured by MALDI-TOF mass spectros-
copy. This result might be caused by the structures of
the obtained cyclic polymers.
C10 (n ) 3, DP(PPS) ) 7) (C183H154O19S19 + Na): 3385.41 3384.91
C11 (n ) 4DP(PPS) ) 8)
C12 (n ) 5, DP(PPS) ) 10) (C290H240O30S30 + Na): 5349.95 5349.38
(C232H192O24S24 + Na): 4284.56 4284.09
evidence of linear polymers in all samples (runs 3-8 in
Table 1).
If controlled insertion reaction of PPS into thioester
moieties of cyclic compounds could be achieved, well-
defined low-molecular-weight cyclic compound 1:1 ad-
duct C1 could be only obtained. However, in this
reaction system, cyclic polymers with different Mns were
obtained. These results mean that intermolecular ester-
exchange reaction occurred between the thioester moi-
eties of the cyclic compounds during the insertion
reaction of PPS into cyclic dithioesters (Scheme 3).
MALDI-TOF mass spectra also revealed the exist-
ence of the cyclic polymers but did not show any

Macromolecules, Vol. 38, No. 14, 2005
Synthesis of Cyclic Polymers 5967
nary onium halide (Q+X-) to form a complex 1, and then
1 reacts with cyclic thioester to form an intermediate
2. After that, the intramolecular and intermolecular
ester-exchange reactions of 2 proceed to afford the ring-
expanded cyclic compounds.
Although the intermolecular ester-exchange reaction
occurred during the insertion reaction of thiirane into
thioester moieties of both linear and cyclic thioester with
thiirane in the presence of the quaternary onium salt
as the catalyst, the ring-expansion reaction could be only
confirmed on the intermolecular ester-exchange reaction
of the cyclic thioester, affording the cyclic polymers with
high molecular weights in high yields. It is noteworthy
that the insertion reaction and intermolecular ester-
exchange reaction occurred successively at the same
time; that is, this reaction system might be a novel ring-
expansion reaction to give larger cyclic polymer.
Therefore, the insertion reaction of excess PPS into
cyclic dithioester (PPS/cyclic dithioester ) 50 /1) was
examined in the presence of TBAC as a catalyst at 90
°C for 24 h in NMP, and it was observed that the
insertion reaction proceeded quantitatively (96% yield)
to afford the corresponding cyclic polymer, in which the
main structure was composed from polysulfide units as
shown in Scheme 6. The degree of the insertion reaction
of PPS into thioester was calculated by 1H NMR
integration of the signal for methylene protons (-CH2-
O-) of cyclic dithioesters at 5.16 ppm and methylene
protons ( CH2-O-) of PPS at 4.16-4.22 ppm. As the
Figure 1. 1H NMR (500 MHz, CDCl3) spectrum of the cyclic
polymer (Mn,SEC ) 6500, Mw/Mn ) 4.10, run 5 in Table 1)
obtained by the insertion reaction of PPS into cyclic dithioester
1.
1
result, the molecular weight calculated from H NMR
was to be 9000. However, the molecular weight (Mn,SEC
)
and polydispersity ratios (Mw/Mn) of resulting polymer
estimated by SEC were 42 000 and 4.50, respectively.
This means that the intermolecular ester-exchange
reaction proceeded during continuous insertion reaction
of PPS into thioester moieties to afford the larger cyclic
polymer cyclic poly(sulfide) in high yield.
In summary, we examined the insertion reaction of
PPS into cyclic dithioester 1 in the presence of TBAC
as the catalyst. As a result, it was found that the
intermolecular reaction occurred between thioester
moieties during the insertion reaction of PPS to produce
the cyclic polymers in high yields. That is, the ring-
Furthermore, we examined the insertion reaction of
linear dithioester 2 with PPS to confirm the inter-
molecular reaction in this reaction system and discuss
the polymerization mechanism (Scheme 4). This reac-
tion was carried out under the same condition as the
reaction of cyclic dithioester 1 with PPS, and it was
found that only the corresponding 1:1 adduct, linear
thioester-sulfide, was obtained in a 90% yield, and any
evidence of the polymerization was not observed.
Furthermore, Scheme 5 shows the reaction mecha-
nism of the insertion reaction of cyclic dithioester with
PPS. In the first step, thiirane is activated by quater-
Figure 2. MALDI-TOF MS spectrum of cyclic polymer (Mn,SEC ) 6500, Mw/Mn ) 4.10, run 5 in Table 1) obtained by the insertion
reaction of PPS into cyclic dithioester 1.

5968 Kudo et al.
Macromolecules, Vol. 38, No. 14, 2005
Scheme 4
Scheme 5. Reaction Mechanism of the Insertion Reaction of Cyclic Dithioester with PPS
Scheme 6
Supporting Information Available: Experimental pro-
cedure, 1H NMR, 13C NMR, IR, and MAS data of cyclic
dithioester and linear dithioester. This material is available
free of charge via the Internet at http://pubs.acs.org.
expansition reaction of excess PPS with cyclic dithioester
is useful synthetic strategy to obtain large cyclic mac-
romolecules. Furthermore, the synthesis and the prop-
erties such as glass transition temperature (Tg), thermal
stability, solubility, film-forming ability, and refractive
index value of the cyclic macromolecules are also
particularly interesting due to their structures and are
now under investigation.
References and Notes
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(4) Tezuka, Y.; Oike, H. J. Am. Chem. Soc. 2001, 123, 11570.
(5) Tezuka, Y.; Oike, H. Macromol. Rapid Commun. 2001, 22,
1017.
Acknowledgment. This work was supported by a
Grant-in-Aid for Scientific Research, in Japan (No.
15750107) from the Ministry of Education, culture,
Sports, Science and Technology, which is gratefully
acknowledged.
(6) Kricheldorf, H. R.; Lee, S. R.; Schittenhelm, N. Macromol.
Chem. Phys. 1998, 199, 273.

Macromolecules, Vol. 38, No. 14, 2005
Synthesis of Cyclic Polymers 5969
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