Synthesis of cyclic polysulfides: Controlled ring-expansion polymerization of cyclic tetrathioester with thiirane

Article abstract of DOI:10.1002/pola.27068

We synthesized cyclic tetrathioesters containing thioester moieties at the o-position (o-CTE) and m-position (m-CTE) of an aromatic skeleton. The reaction of phenoxy propylenesulfide (PPS) with o-CTE and m-CTE was examined using tetrabutylammonium chlorid

Full text of DOI:10.1002/pola.27068

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Synthesis of Cyclic Polysulfides: Controlled Ring-Expansion
Polymerization of Cyclic Tetrathioester with Thiirane
Hiroto Kudo,1 Yuki Takeshi2
1Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University,
3-3-35, Yamate-cho, Suita-shi, Osaka, 564-8680, Japan
2Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1, Rokkakubashi, Kanagawa-ku,
Yokohama, 221-8686, Japan
Correspondence to: H. Kudo (E-mail: kudoh@kansai-u.ac.jp)
Received 31 July 2013; accepted 10 December 2013; published online 27 December 2013
DOI: 10.1002/pola.27068
ABSTRACT: We synthesized cyclic tetrathioesters containing
thioester moieties at the o-position (o-CTE) and m-position (m-
CTE) of an aromatic skeleton. The reaction of phenoxy propyle-
nesulfide (PPS) with o-CTE and m-CTE was examined using
controlled by the feed ratios of PPS and reaction temperature.
Furthermore, the glass transition temperature (Tg) and thermal
i
decomposition temperature (Td ) of poly[m-CTE(PPS)n] increased
C
V
with decreasing molecular weights.
2013 Wiley Periodicals,
tetrabutylammonium chloride as
a
catalyst in 1-methyl-2-
Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 857–866
pyrrolidinone, yielding the corresponding cyclic polysulfides
poly[o-CTE(PPS)n] with Mn’s 5 37,000–54,000 at 34–61% yields
and poly[m-CTE(PPS)n] with Mn’s 5 46,600–107,200 at 63–>99%
yields. Although the molecular weights of poly[o-CTE(PPS)n]
could not be controlled, those of poly[m-CTE(PPS)n] could be
KEYWORDS: cyclic polymer; cyclopolymerization; insertion reac-
tion; macrocycles; polysulfides; ring-expansion polymerization;
synthesis
lar radical coupling reaction using a nitroso radical trap at a
high yield. Grayson7 succeeded in the synthesis of narrow
polydispersity cyclic poly(caprolactone) by the cyclic cou-
pling reaction of a-akynyl-x-azido heterodifunctional poly-
mers. Kricheldorf and coworker8,9 reported ring-expansion
polymerization by the insertion of lactones into cyclic com-
pounds, yielding cyclic polyesters. Waymouth and
coworkers10 reported the synthesis of cyclic polyesters by
the ring-expansion polymerization of b-lactone. Shea et al.11
also examined the synthesis of cyclic polymers using the
ring-expansion polymerization of cyclic borane by the inser-
tion of a methylene unit. Grubbs and coworkers12,13 reported
the synthesis of ring-expanded cyclic polymers by a ring-
closing metathesis reaction and the physical properties of
the cyclic polymers were compared with those of linear poly-
mers. Furthermore, Sanders and coworkers and Otto et al.14–17
showed that a dynamic covalent chemistry (DCC) system is a
very useful approach for the synthesis of well-defined mac-
rocycles at excellent yields. Otsuka and coworkers18 reported
the synthesis of cyclic polyesters by the reversible radical
ring-crossover polymerization of a cyclic monomer contain-
ing an alkoxyamine bond as a dynamic covalent bond.
INTRODUCTION The synthetic strategies of polymers are
usually classified into two categories: chain-growth and step-
growth polymerization. However, the synthetic strategies of
cyclic polymers cannot belong to either of these categories,
because cyclic polymers have no end group. Although the
physical properties, such as thermal stability, glass transition
temperature, and viscoelastic behavior of cyclic polymers
have attractive much attention compared to linear poly-
mers,1 their detailed examinations have been restricted by
the synthetic limitations. Three strategies for the synthesis
of cyclic polymers are well known:2 (1) ring-closure reaction
of linear polymers, (2) ring-expansion polymerization of
cyclic monomers, and (3) ring-crossover polymerization
(ring–ring equilibration) of cyclic monomers. Hocker and
Geiser3 and Toporowski and Roovers4 independently
reported the first synthesis of cyclic polystyrenes by the
ring-closure reaction using living polystyrenes containing
two reactive end groups. Barner-Kowollik and coworker5
reported the synthesis of cyclic poly(alkyl acrylates) by the
Diels–Alder coupling reaction of two end groups of linear
polymers. Recently, Tillman and coworker6 also reported
that cyclic polystyrenes were synthesized by an intramolecu-
Additional Supporting Information may be found in the online version of this article.
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Endo and Yamanaka19 also reported the synthesis of inter-
locking cyclic polymers by the thermal ring-crossover poly-
merization of cyclic disulfide.
(mp) was determined by a YANAKO micromelting point
apparatus.
Synthesis of Cyclic Tetrathioester (o-CTE)
Meanwhile, Nishikubo and coworkers reported that the
insertion of thiirane into thiocarbamate or thioester pro-
ceeded in a living-like fashion, yielding well-defined linear
polysulfides, respectively.20–22 Furthermore, these insertion
reaction systems were applicable to ring-expansion polymer-
ization for the synthesis of cyclic polymers. The insertion of
thiirane into cyclic dithioester23 or monothiocarbamate24
was performed, selectively yielding cyclic polysulfides. In the
case of cyclic monothiocarbamate,24 well-defined cyclic poly-
sulfides could be obtained with a narrow polydispersity ratio
and a number average molecular weight (Mn) 5 8000. How-
ever, Vana and Schuetz25,26 reported that the ratios of poly-
dispersities increased with increasing Mn’s by the continuous
insertion of thiirane. In the case of cyclic dithioester, various
sizes of cyclic polysulfide were obtained due to both the
insertion reaction and ring-crossover polymerization. Ring-
crossover polymerization is due to the thioester bond as a
dynamic covalent bond; that is, the ring size of the cyclic pol-
ysulfides is related to the DCC system.27
A mixture of hexadecyl trimethylammonium bromide (HTAB)
(0.0240 g, 0.0659 mmol) in water (50 mL) and CHCl3 (300
mL) was prepared. Two solutions of o-phthaloyl dichloride
(2.01 g, 9.90 mmol) in CHCl3 (66 mL) and 4,4’-thiobisbenze-
nedithiol (TBBT) (2.48 g, 9.90 mmol) in NaOH (0.810 g,
20.25 mmol) alkaline aqueous solution water (66 mL) were
added to the resulting mixture slowly and stirred at 25 ꢀC
for 12 h. The organic layer was dried over MgSO4, and con-
centrated in a rotary evaporator to obtain a solid. The
obtained solid was purified by recrystallization from the mix-
ture of CHCl3 and n-hexane to obtain a colorless solid (cyclic
tetrathioester at o-poistion, o-CTE).
Yield 5 1.25 g (38%). Mp 5 289.4–291.3 ꢀC. IR (film, cm21):
3018 (m CAH aromatic), 1680 (m C@O thioester), 1572 and
1475 (m C@C aromatic), 700 and 659 (m CASAC). 1H NMR
(500 MHz, CDCl3, TMS) d (ppm): 7.44 (d, J 5 8.5 Hz, 8.0 H,
aromatic protons of AS-Ar-SA), 7.49 (d, Jab 5 8.5 Hz, 8.0 H,
aromatic protons of AS-Ar-SA), 7.65–7.67 (m, 4.0 H, aro-
matic protons of A(O)C-Ar-C(O)A), 7.84–7.87 (m, 4.0 H, aro-
matic protons of A(O)C-Ar-C(O)A). 13C NMR (125 MHz,
CDCl3, TMS) d (ppm): 126.3, 128.4, 131.3, 131.8, 135.2, and
137.0 (aromatic C). MALDI-TOF mass: calcd. for [o-CTE
(C40H24O4S6) 1 Na]1: 782.99, found: 783.10.
In this article, we focused on the ring-expansion polymeriza-
tion behavior of thiirane using cyclic tetrathioester com-
pounds for the synthesis of cyclic polysulfides.
EXPERIMENTAL
Reaction on Insertion of PPS into o-CTE
A Typical Procedure
Materials
1-Methyl-2-pyrrolidinone (NMP) was dried with CaH2 and
purified by distillation before use. Tetrabutylammonium
chloride (TBAC), tetraphenylphosphonium chloride (TPPC),
magnesium sulfoxide (MgSO4), phthaloyl dichloride, chloro-
form (CHCl3), methanol, benzene thiol (BT), and triethyl
amine were used without further purification.
o-CTE (0.0761 g, 0.1 mmol), TBAC (0.0013 g, 0.0046 mmol),
and PPS (0.0673 g, 0.405 mmol) were dissolved in NMP (1.0
mL) in
a polymerization tube. The tube was cooled,
degassed, and sealed, and then the reaction was carried out
at 50 ꢀC for 24 h. The reaction mixture was diluted by the
addition of CHCl3, poured into methanol to precipitate the
solid, and dried in vacuo at 25 ꢀC for 24 h. The polymer
poly[o-CTE(PPS)n] and oligomer o-CTE(PPS)4 were separated
by HPLC and their structures were confirmed by 1H NMR,
13C NMR, and IR spectroscopies, beside MALDI-TOF mass
spectroscopy.
Measurements
Infrared (IR) ray spectra were taken with a Nicolet 380 FTIR
(Thermo Fisher Scientific). The 1H NMR spectra were
recorded on JEOL Model JNM a-500 (500 MHz for 1H NMR
and 125 MHz for 13C NMR) instruments in CDCl3 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 with
AXIMA-CFRplus (Shimazu/Kratos) using dihydroxy benzoic
acid as a matrix and CHCl3 as a solvent. The number-average
molecular weight (Mn) and molecular weight distribution
[weight-average molecular weight/number-average molecu-
lar weight (Mw/Mn)] of the polymers were estimated by size
exclusion chromatography (SEC) with a Tosoh HLC-8220 SEC
instrument equipped with refractive-index and ultraviolet
detectors with TSK gel columns (Tskgel SuperHzM-M 3 3)
in THF as an eluent and calibrated with narrow molecular
weight polystyrene standards. The reaction products were
separated by preparative HPLC (Nihon Bunseki Kogyo)
equipped with two polystyrene gel columns (JAIGEL 1H-40
and 2H-40) using CHCl3 as an eluent. The melting point
Poly[o-CTE(PPS)n]
Mn 5 52,000, Mw/Mn 5 1.71. IR (film, cm21): 3062 (m CAH
aromatic), 2928 and 2871 (m CAH aliphatic), 1783 (m C@O
lactone), 1684 (m C@O thioester), 1598 and 1495 (m C@C
aromatic), 1241 and 1214 (m CAOAC), 1097 (m CAOAPh),
754 (m CASAC sulfide). 1H NMR (500 MHz, CDCl3, TMS) d
(ppm): 3.13–3.44 (broad m, ACH2AOA), 4.08–4.20 (broad
m, ACH2ASA), 4.44 (broad s, @CHA), 6.70–7.73 (m, aro-
matic protons).
o-CTE(PPS)4
IR (film, cm21): 3062 (m CAH aromatic), 2924 and 2866
(m CAH aliphatic), 1663 (m C@O thioester), 1598 and 1496
(m C@C aromatic), 1239 and 1215 (m CAOAC), 1098 (m
CAOAPh), 754 (m CASAC sulfide). 1H NMR (500 MHz,
CDCl3, TMS) d (ppm): 3.38–3.51 (m, 8.0H, ACH2AOA), 4.09–
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4.22 (m, 8.0H, ACH2ASA), 4.52 (d, J 5 10.0 Hz, 4.0 H,
@CHA), 6.85–6.88 (m, 4.0H, aromatic H), 6.95 (t, J 5 7.5 Hz,
8.0H, aromatic H), 7.13–7.16 (m, 8.0 H, aromatic H), 7.24–
7.26 (m, 8.0H, aromatic H), 7.33 (t, J 5 3.5 Hz, 8.0H, aromatic
H), 7.55 and 7.57 (dd, J 5 5.0 Hz, 4.0H, aromatic H), 7.71 (d,
J 5 4.5 Hz, 4.0H, aromatic H). MALDI-TOF mass: calcd for
[Oligomer (C76H64O8S10) 1 Na]1: 1447.17, found: 1447.66.
matic protons of AS-Ar), 7.62 and 7.65 (dd, J 5 7.5 Hz, 1.0 H,
aromatic protons of AS-Ar), 8.23 and 8.27 (dd, J 5 1.5 Hz,
2.0 H, aromatic protons of A(O)C-Ar-C(O)A), 8.67 and 8.68
(dd, J 5 1.5 Hz, aromatic protons of A(O)C-Ar-C(O) A). 13C
NMR (125 MHz, CDCl3, TMS) d (ppm): 126.4, 126.7, 129.4,
129.8, 132.0, 135.0, 137.2, and 189.4 (aromatic C).
Model Reaction of 1,2-Bis(phenyl thioester)benzene and
1,3-Bis(phenyl thioester)benzene
Ring-Crossover Polymerization of o-CTE
A Typical Procedure
A Typical Procedure
o-CTE (0.0761 g, 0.1 mmol) and TPPC (0.0018 g, 0.005
mmol) were dissolved in NMP (1.0 mL) in a polymerization
tube. The tube was cooled, degassed, and sealed, and then
The reaction of o-PTB (0.0349 g, 0.202 mmol) was carried
out at 120 C using TPPC as a catalyst for 24 h in the same
way as the ring-crossover polymerization of o-CTE.
ꢀ
ꢀ
the reaction was carried out at 180 C for 24 h. The reaction
Yield 5 0.022 g (64%). 1H NMR (500 MHz, CDCl3, TMS) d
(ppm): 7.13–7.80 (m, aromatic protons). 13C NMR (125 MHz,
CDCl3, TMS) d (ppm): 10.9, 22.8, 23.6, 29.5, 30.2, 38.5, 68.0,
99.1 (aliphtatich carbon), 123.3–148.6 (aromatic C), 167.1
(C@O of lactone moiety), 190.9 (C@O of thioester moiety).
mixture was diluted by the addition of CHCl3, poured into
methanol to precipitate a polymer, and dried in vacuo at 25
ꢀC for 24 h. The polymer yield was 68%. Mn and Mw/Mn of
the obtained polymer were 7400 and 1.06, respectively (Run
5 in Table 2). The structure of the obtained polymer was
1
confirmed by H NMR, 13C NMR, and IR spectroscopies.
Synthesis of (5-tert-Buthyl)isophythaloyl Dichloride (TID)
The mixture of (5-tert-buthyl)isophythalic (2.22 g, 10.0
mmol) acid, SOCl2 (4.77 g, 40.1ꢀmmol), and DMF (0.0156 g,
0.216 mmol) was stirred at 60 C for 2 h, and then refluxed
for 3 h. The resulting mixture was concentrated by a rotary
evaporator to obtain a viscous yellow liquid. The obtained
residue was purified by recrystallization from n-hexane to
obtain a colorless solid (TID).
1H NMR (500 MHz, CDCl3, TMS) d (ppm): 6.72–7.90 (m, aro-
matic H). 13C NMR (125 MHz, CDCl3, TMS) d (ppm): 14.2–
30.9 (m, quaternary carbon), 126.3–137.1 (m, aromatic car-
bon), 171.1 (carbonyl of lactone), and 190.4 (carbonyl thio-
ester). IR (film, cm21): 3013 (m CAH aromatic), 1772 (m C@O
lactone), 1683 (m C@O thioester), 1473 (m C@C aromatic),
741 (m CASAC sulfide).
IR (film, cm21): 2969 (m CAH aromatic), 2874 (m CAH ali-
phatic), 1765 (m C@O), 1587 (m C@C aromatic), 689 (m
CACl). H NMR (600 MHz, CDCl3, TMS) d (ppm): 1.42 (s, 9.0
H, ACH3), 8.41 (s, 2.0 H, aromatic protons), 8.70 (s, 1.0 H,
aromatic proton). 13C NMR (150 MHz, CDCl3, TMS) d (ppm):
31.0 (ACH3), 35.3 (@C@), 131.7, 134.1, 134.2, and 153.9
(aromatic carbon), 167.6 (C@O).
Synthesis of 1,2-Bis(phenyl thioester)benzene
A mixture of BT (2.21 g, 20.1 mmol) and triethylamine (2.02
g, 20.0 mmol) in CHCl3 (40 mL) was prepared. The solution
of o-phthaloyl dichloride (2.07 g, 10.2 mmol) in CHCl3 (20
mL) was added to the resulting mixture slowly and stirred
1
ꢀ
at 25 C for 12 h. Then, the mixture was washed with citric
acid aqueous solution (0.1 mol/L), saturated NaHCO3 aque-
ous solution, and water twice, respectively. The separated
organic layer was dried over MgSO4, and concentrated in a
rotary evaporator to obtain a colorless solid. The obtained
solid was purified by recrystallization from the mixture of
Synthesis of Cyclic Tetrathioester m-CTE
A mixture of triethyl amine (0.608 g, 6.01 mmol) in CH2Cl2
(2.9 L) was prepared. Two solutions of TID (0.779 g, 3.01
mmol) in CH2Cl2 (40 mL) and TBBT (0.753 g, 3.01 mmol) in
CH2Cl2 (40 mL) were added to the resulting mixture slowly
CHCl3 and n-hexane to obtain
a colorless solid (1,2-
bis(phenyl thioester)benzene, o-PTB).
ꢀ
and stirred at 25 C for 40 h. The mixture was then concen-
Yield 5 2.74 g (77%). IR (film, cm21): 3052 (m CAH aromatic),
1692 and 1675 (m C@O thioester), 1475 (m C@C aromatic),
and 745 (m CASAC). 1H NMR (500 MHz, CDCl3, TMS) d
(ppm): 7.42–7.44 (m, 6.0 H, aromatic protons of AS-Ar), 7.51–
7.55 (m, 4.0 H, aromatic protons of AS-Ar), 7.60 and 7.64 (dd,
J 5 7.5 Hz, 2.0 H, aromatic protons of A(O)C-Ar-C(O) A), 7.82
and 7.86 (dd, J 5 7.5 Hz, aromatic protons of A(O)C-Ar-C(O)
A). 13C NMR (125 MHz, CDCl3, TMS) d (ppm): 127.4, 128.4,
129.3, 129.6, 131.6, 134.7, 137.2, and 191.1 (aromatic C).
trated in a rotary evaporator and washed with water. The
organic layer was dried over MgSO4, and then concentrated
in a rotary evaporator to obtain a white solid.
Yield 5 0.25 g (25%). IR (film, cm21): 2955 (m CAH ali-
phatic), 1696 and 1673 (m C@O thioester), 1476 (m C@C aro-
matic), 731 (m CASAC). 1H NMR (600 MHz, CDCl3, TMS) d
(ppm): 1.56 (s, 18.0H, ACH3), 7.26–7.44 (m, 16.0 H, aromatic
protons), 8.13 (s, 4.0 H, aromatic proton), 8.27 (s, 2.0 H, aro-
matic proton). MALDI-TOF mass: calcd. for [m-CTE
(C48H40O4S6) 1 Na]1: 895.13, found: 894.67.
Synthesis of 1,3-Bis(phenyl thioester)benzene
The reaction of isophthaloyl chloride and BT was carried out
in the same way as the synthesis of o-PTB. Yield 5 27.6%. IR
(film, cm21): 3064 (m CAH aromatic), 1673 (m C@O thio-
ester), 1478 (m C@C aromatic) and 750 (m CASAC). H NMR
(500 MHz, CDCl3, TMS) d (ppm): 7.47–7.54 (m, 10.0 H, aro-
Ring-Crossover Polymerization of m-CTE
A Typical Procedure
m-CTE (0.0342 g, 0.0392 mmol) and TBAC (0.0013 g, 0.0046
mmol), were dissolved in NMP (0.5 mL) in a polymerization
1
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tube. The tube was cooled, degassed, and sealed, and then
ꢀ
the reaction was carried out at 50 C for 24 h. The reaction
mixture was diluted by the addition of CHCl3, poured into
methanol to precipitate a polymer, and dried in vacuo at 25
ꢀC for 24 h. The polymer yield was 93%. Mn and Mw/Mn of
the obtained polymer were 6990 and 1.93, respectively. The
structure of the obtained polymer was confirmed by 1H
NMR and IR spectroscopies.
1H NMR (600 MHz, CDCl3, TMS) d (ppm): 1.40–1.52 (m,
ACH3), 7.39–7.57 and 8.13–8.51 (m, aromatic H). IR (film,
cm21): 3077 (m CAH aromatic), 2956 and 2904 (m CAH ali-
phatic), 1695 and 1672 (m C@O thioester), 1475 (m C@C aro-
matic), 731 (m CASAC sulfide).
Reaction of PPS on Insertion into m-CTE
A Typical Procedure
m-CTE (0.0349 g, 0.0399 mmol), TBAC (0.0013 g, 0.0046
mmol), and PPS (0.0265 g, 0.159 mmol) were dissolved in
NMP (0.2 mL) in a polymerization tube. The tube was
cooled, degassed, and sealed, and then the reaction was car-
SCHEME 1 Reaction of o-CTE and PPS.
Figure 1. The conversion of PPS was calculated by 1H
NMR spectroscopy to be 53%.
ried out at 50 oC for 24 h. The reaction mixture was diluted
ꢀ
by the addition of CHCl3 and poured into methanol to pre-
cipitate a polymer and dried in vacuo at 25 C for 24 h. The
The synthesized polymer and oligomer were separated by
HPLC and each structure was confirmed by IR, H NMR, and
ꢀ
1
structure of the obtained polymer was confirmed by 1H
NMR, 13C NMR, and IR spectroscopies. Yield 5 0.0436 g
(71%). Mn 5 46,700, Mw/Mn 5 1.78. IR (film, cm21): 3063 (m
CAH aromatic), 2964 and 2871 (m CAH aliphatic), 1661 (m
C@C thioester), 1496 (m C@C aromatic), 1239 (m CAOAC),
752 (m CAS-C). 1H NMR (600 MHz, CDCl3, TMS) d(ppm):
1.36 (s, -CH3), 3.45–3.48 (m, methylene proton of -CH2-OPh),
4.16–4.28 (m, methylene proton of -CH2-S), 4.50–4.51 (m,
methine proton of >CH-), 6.88–7.37 (m, aromatic proton),
8.15 (s, aromatic proton), 8.35 (aromatic proton).
MALDI-TOF mass spectroscopies. From 1H NMR spectra of
the separated polymer, the peaks at 3.13–3.44 and 4.08–4.20
ppm assignable to methylene protons of AOACH2A and
ASACH2A moieties were seen, indicating these are produced
by the insertion of PPS into thioester moieties [Supporting
Information Fig. S1(a,b)]. The degree of insertion of PPS into
cyclic o-CTE could be calculated by the integration ratios of
aromatic protons and methylene protons to be 95%
(DI 5 95). In IR spectra of this polymer, a new peak was
seen at 1783 cm21. Except for this peak, the other peaks of
the separated polymer were almost the same as those of o-
CTE [Supporting Information Fig. S2(a,b)]. The peak at 1783
cm21 might be assignable to the ester moiety. This means
that an intracyclization reaction might proceed during the
insertion of PPS into o-CTE to produce cyclic lactone moi-
eties in the corresponding polymer poly[o-CTE(PPS)n], as
shown in Scheme 1.
RESULT AND DISCUSSION
Reaction of Thiirane on Insertion into Cyclic
Tetrathioester o-CTE
Equivalent Reaction of PPS and o-CTE
A cyclic tetrathioester (o-CTE) was synthesized by the con-
densation reaction of phthaloyl dichloride and 4,4’-thiobis-
benzenedithiol, and its structure was confirmed by 1H NMR,
13C NMR, IR, and MALDI-TOF mass spectroscopies. o-CTE has
a cyclic skeleton and four thioester moieties in a molecule. If
the continuous insertion of PPS into o-CTE can proceed in a
living-like fashion, well-defined cyclic polysulfides can be
synthesized.
At first, we examined the reaction on the insertion of PPS
(4 mmol) into o-CTE (1 mmol) with an equivalent feed
ratio in the presence of TBAC as a catalyst for 24 h in
NMP at 50 ꢀC (Scheme 1). SEC profiles of the obtained
products showed multimodal peaks, and a corresponding
polymer at a retention time 5 7–9 min with Mn 5 52,000
(Mw/Mn 5 1.71) and an oligomer with Mn 5 910 (Mw/
Mn 5 1.07) at a retention time 5 10.5 min as shown in
FIGURE 1 SEC profiles (elution; THF) of the products by the
insertion of 4 equiv of PPS into o-CTE.
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TABLE 1 Insertion Reaction of PPS with Cyclic o-CTEa
Feed Ratio
Polymerc
Run
PPS/o-CTE
Conv. (%)b
Yield (%)
Mn (Mw/Mn)d
DI (%)e
1
2
3
4
5
4
53
34
51
52
51
61
54,000 (1.67)
37,000 (1.63)
33,000 (1.64)
38,000 (1.60)
47,000 (1.72)
95
8
>99
83
>99
>99
>99
>99
12
24
32
34
35
a
d
The reaction of PPS and o-CTE was carried out using TBAC as a cata-
Estimated by SEC based on polystyrene standards; eluent: a solution
lyst in NMP at 50 ꢀC for 24 h.
b
of LiBr and phosphoric acid (20 mM) in DMF.
e
Calculated by 1H NMR.
Methanol insoluble part.
The degree of insertion of PPS into o-CTE (DI) was calculated from 1H
c
NMR data (see text).
Furthermore, in the case of a separated oligomer, the 1H
NMR spectrum showed peaks at 3.38–3.51, 4.09–4.22, and
4.52 ppm assignable to methylene protons of ACH2OA,
methylene protons of ACH2ASA, and methine protons of
@CHA, respectively [Supporting Information Fig. S1(c)]. In
IR analysis, no peak assignable to cyclic lactone moieties was
seen [Supporting Information Fig. S2(c)]. The MALDI-TOF
mass spectrum of this oligomer after Na1 doping showed a
mass parent peak at 1447.66 which correspond to the mass
of a cyclic tetra(thioester-sulfide) o-CTE(PPS)4, as shown in
Scheme 1 (Supporting Information Fig. S3). These indicate
that, although o-CTE(PPS)4 was synthesized by the insertion
of 4 equiv of PPS into 1 equiv of o-CTE, another reaction
occurred to produce cyclic polysulfide poly[o-CTE(PPS)n]
containing cyclic lactone moieties in the main chain.
increase in the feed-ratios of PPS. 1H NMR and IR spectros-
copies of the corresponding polymers also indicated that
cyclic polymers poly[o-CTE(PPS)n] contained cyclic lactone
moieties in the main chain. This might be because intracycli-
zation occurred during the insertion reaction of PPS to pro-
duce the cyclic lactone moieties, and then the insertion
reaction with PPS could not proceed. As a result, the values
of Mn’s of the obtained cyclic polysulfides were independent
of the feeds ratios of PPS and could not be controlled.
Ring-Crossover Polymerization of o-CTE
To confirm the intracyclization of thioester moieties in o-
CTE, the ring-crossover polymerization of o-CTE was exam-
ined (Scheme 2). When the reaction of PPS was carried out
in the presence of quaternary onium salts as catalysts in
NMP at temperatures in the range between 50 and 180 ꢀC,
the corresponding oligomers and polymers with Mn’s 5 910–
Insertion Reaction of PPS and o-CTE in the Certain Feeds
Ratios
ꢀ
7,400 were obtained at 64–78% yields more than at 120 C
Based on the aforementioned results, another reaction might
proceed in the equivalent insertion of PPS with o-CTE to
give cyclic polysulfides. We examined the effects of feeds
ratios in the insertion reaction of PPS with o-CTE. These con-
ditions and results are summarized in Table 1.
(Runs 3–5 in Table 2). However, no reaction proceeded at
lower reaction temperatures (Runs 1–2 in Table 2). These
results are summarized in Table 2.
The structures of the obtained products were confirmed by
1
1
IR and H NMR spectroscopies. Although their H NMR spec-
tra mostly coincided with that of o-CTE, their IR spectra
showed peaks around 1780 cm21 [Supporting Information
Figs. S1(d) and S2(d)] assignable to cyclic lactone moieties.
These indicate that the intracyclization of thioester moieties
The corresponding polymers with Mns 5 33,000–47,000
were obtained at 51–61% yields (Runs 2–5 in Table 1).
Although almost all thioester moieties in o-CTE converted in
all cases (>99%), the conversions of PPS decreased with an
TABLE 2 Ring-Crossover Polymerization of o-CTEa
Run
Temperature (ꢀC)
Catalyst
Yield (%)b
Mn (Mw/Mn)c
1
2
3
4
5
50
TBAC
TBAC
TPPC
TPPC
TPPC
2d
2d
64
78
68
2d
2d
70
120
150
180
1,220 (1.58)
910 (1.77)
7,400 (1.06)
a
c
The reaction of o-CTE was carried out in NMP for 24 h.
Methanol-insoluble part.
Estimated by SEC based on polystyrene standards; eluent: a solution
b
of LiBr and phosphoric acid (20 mM) in DMF.
d
Not determined.
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However, in the case of m-diphenyl thioester m-PTB, no reac-
tion proceeded. These mean that the cyclic lactone moiety
was produced by the intracyclization of neighboring thio-
ester groups as shown in Scheme 3.
Ring-Crossover Polymerization of m-CTE
To avoid the intracyclization of thioester groups, we
designed and synthesized a new cyclic tetrathioester (m-
CTE) containing thioester moieties at the m-position of the
aromatic moiety. The ring-crossover polymerization of m-
CTE was carried out in the presence of TBAC as a catalyst in
NMP at 50 ꢀC for 24 h, yielding the corresponding polymer
poly(m-CTE) with Mn 5 6990 (Mw/Mn 5 1.93) at 51% yield.
1
The structure of poly(m-CTE) was confirmed by H NMR and
IR spectroscopies. The 1H NMR spectrum of poly(m-CTE)
showed that poly(m-CTE) had the same repeating unit of m-
CTE. In the IR spectra, no peak at about 1780 cm21 was
seen, indicating that the product had no cyclic lactone moi-
ety. This means that intracyclization between thioester moi-
eties did not occur and only thioester-exchanging reactions
proceeded, yielding corresponding cyclic polythioester
poly(m-CTE), as shown in Scheme 4.
SCHEME 2 Ring-crossover polymerization of o-CTE.
proceeded to yield cyclic lactone moieties during ring-
crossover polymerization as shown in Scheme 2. After the
cyclic lactone moieties were produced, ring-crossover poly-
merization could not proceed. In our previous report, the
ring-crossover polymerization of cyclic-dithioester afforded
the corresponding cyclic polythioester and their molecular
weights were consistent with the reaction temperatures.24
However, in the case of o-CTE, Mn could not be controlled
due to intracyclization occurring during ring-crossover
polymerization.
Insertion Reaction of PPS and m-CTE
Furthermore, the insertion reaction of PPS with m-CTE was
examined at the various feed ratios in the range of m-CTE /
PPS 5 1/4–1/34, yielding polymers with Mn 5 46,700–
100,500 and Mw/Mn 5 1.78–2.48 (Scheme 5). These condi-
tions and results are summarized in Table 3. The SEC pro-
files of these polymers showed unimodal peaks, as presented
in Figure 2.
Model Reaction of 1,2-Bis(phenyl thioester)benzene and
1,3-bis(phenyl thioester)benzene
Their structures were also confirmed by IR and 1H NMR
spectroscopies. Figures 3 and 4 depict the 1H NMR and IR
spectra of the obtained polymer with Mn 5 46,700 (Run 1 in
Table 3) along with m-CTE. 1H NMR spectra showed the
peaks at 3.45–3.48 and 4.16–4.28 ppm assignable to methyl-
ene protons of AOACH2A and ASACH2A moieties, and the
peaks at 4.51 ppm assignable to methine protons of @CHA
(Fig. 3). Furthermore, its IR spectrum showed no peak at
about 1780 cm21 assignable to the cyclic lactone moiety
Next, we examined the model reaction using o-PTB and 1,3-
bis(phenyl thioester)benzene (m-PTB) under the same reac-
tion conditions for the insertion reaction of PPS with o-CTE
(Scheme 3). In the case of o-diphenyl dithioester o-PTB,
intracyclization proceeded to produce a cyclic lactone moiety.
SCHEME 3 Model reaction of o-PTB and m-PTB.
SCHEME 4 Ring-crossover polymerization of m-CTE.
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SCHEME 5 Reaction of m-CTE and PPS.
FIGURE 2 SEC profiles (elution; THF) of the products by the
insertion of PPS into m-CTE.
(Fig. 4). These indicate that the intraexchange reaction of
thioester moieties to produce cyclic lactone moieties did not
occur on the insertion of PPS into m-CTE. Thus, cyclic poly-
sulfide poly[m-CTE(PPS)n] with a unimodal peak, as shown
in SEC, could be obtained by the ring crossover polymeriza-
tion and insertion reaction of PPS.
Furthermore, the effect of reaction times and temperatures
on the ring-expansion polymerization of PPS into m-CTE in
the feed ratios of m-CTE/PPS 5 1/4 and 1/32. These condi-
tions and results are summarized in Table 4.
Figure 5 also depicts the relationships among Mn, DI, and
feed ratios on the continuous insertion of PPS into m-CTE.
Although DI values were consistent with the feed ratios of
PPS, the values of Mn’s were almost the same, at 50,000 in
the feed ratios of PPS/m-CTE 5 1/1–16/1 (Runs 1–3 in Table
3), and then increased with increasing feed ratios of PPS
(Runs 3–5 in Table 3). When the feed ratios of PPS were
lower, ring-crossover polymerization occurred frequently
under thermodynamic control. After that, its molecular
weight increased with increasing feed ratios of PPS, indicat-
ing that the cyclic polymers could be synthesized under
kinetic control. These mean that the ring-expansion polymer-
ization of m-CTE with PPS could be controlled by the feed
ratios.
When its ring-expansion polymerization was performed at
temperatures in the range between 50 and 90 C, the molec-
ꢀ
ular weights of poly[(m-CTE(PPS)n] decreased with increas-
ing reaction temperatures (Runs 1–6 in Table 4). This
suggests that ring-crossover polymerization proceeded under
thermodynamic control to give more stable cyclic polysul-
fides. Furthermore, this ring expansion polymerization was
examined at 50 ꢀC for a longer reaction time. As the result,
the corresponding poly[m-CTE(PPS)n] (n 5 5.2) could be
obtained with Mn 5 48,700 at 75% yield (Run 7 in Table 4),
that is, Mn could not be markedly increased by the longer
reaction time. Consequently, higher molecular weight
poly[m-CTE(PPS)n] could be obtained at lower reaction
temperatures.
TABLE 3 Insertion Reaction of PPS with m-CTE at 50 ꢀC for 24 h at Various Feeds Ratiosa
Conv.b (%)
Yieldc (%)
Mn (Mw/Mn)d
DPn
e
Run
PPS/m-CTE
1
2
3
4
5
4
98
73
72
88
91
71
63
67
85
91
46,700 (1.78)
46,600 (1.91)
50,400 (2.17)
85,100 (2.24)
100,500 (2.48)
4.4
8.0
8
16
24
34
13.6
24.4
37.2
a
d
The reaction of PPS and m-CTE was carried out using TBAC as a cata-
Estimated by SEC based on polystyrene standards; eluent: a solution
lyst in NMP.
of LiBr and phosphoric acid (20 mM) in DMF.
b
e
Calculated by SEC.
The degree of insertion of PPS into m-CTE (DI) was calculated from 1H
c
Methanol-insoluble part.
NMR data (see text).
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FIGURE 5 Relationships of DI (degree of insertion of PPS), Mn,
and feed ratios of PPS on ring-expansion polymerization of
PPS with m-CTE.
with linear polymers.28
A linear polysulfide containing
similar units of poly[m-CTE(PPS)n] can be synthesized easily
by the anionic polymerization of PPS. We examined the reac-
tion of PPS in the presence of TBAC in NMP at 90 ꢀC for
24 h, yielding corresponding polysulfide polyPPS with
Mn 5 102,600 and Mw/Mn 5 2.66 at 70% yield. The weight
average molecular weights [Mw(MALLS)] of polyPPS, poly[m-
CTE(PPS)4.4], and poly[m-CTE(PPS)30.8] were also measured
by MALLS. Table 5 summarizes the results regarding the
molecular weights of these polymers and their thermal prop-
erties. The Mw(MALLS) was in the range between 173,100 and
380,700. The ratios of Mw(SEC)/Mw(MALLS) of poly[m-CTE
(PPS)4.4], poly[m-CTE(PPS)30.8], and polyPPS were 0.48, 0.68,
and 0.83, respectively. These values depended on the
excluded volume effect in the synthesized polymers, that is,
a lower molecular weight cyclic polymer has a larger
excluded volume effect due to its cyclic structure. Further-
more, the glass transition temperature (Tg) and initial
FIGURE 3 1H NMR spectra of m-CTE and poly[m-CTE(PPS)n].
Physical Properties of Cyclic and Linear Polysulfides
Cyclic polymers have no end group and are expected to
show some characteristic physical properties in comparison
i
decomposition temperature (Td ) were also determined. The
i
values of Tg and Td of poly[m-CTE(PPS)4.4] were larger than
those of poly[m-CTE(PPS)30.8] and polyPPS (Table 5). These
results might be because the degree of PPS in poly[m-
CTE(PPS)30.8] is too long, and its morphological properties
might be similar to those of linear polysulfide polyPPS. This
means that the characteristic physical properties based on
cyclic structures might be consistent with the molecular
weight.
CONCLUSIONS
We examined the reaction on the insertion of PPS into the
cyclic tetrathioesters o-CTE and m-CTE. When the insertion
of PPS into o-CTE was performed using TBAC as a catalyst in
ꢀ
NMP at 50 C for 24 h, both the intracyclization of thioester
groups and ring-crossover polymerization proceeded, and
cyclic polysulfides poly[o-CTE(PPS)n] containing cyclic lac-
tone moieties with Mn’s 5 37,000–54,000 were synthesized
FIGURE 4 IR spectra of [A] m-CTE and [B] poly[m-CTE(PPS)n].
864
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TABLE 4 Effect of the Reaction Time and Temperature on Insertion Reaction of PPS with m-CTEa
Feed ratio
Reaction
Run
Reaction Time (h)
24
Temperature (ꢀC)
m-CTE/PPS
Conv.b (%)
Yieldc (%)a)
Mn (Mw/Mn)d
DPn
e
1
2
3
4
5
6
7
50
70
90
50
70
90
50
1/4
98
71
72
78
91
90
91
75
46,700 (1.78)
45,700 (1.76)
36,200 (2.18)
100,500 (2.48)
107,200 (2.44)
61100 (5.00)
48,700 (1.81)
4.4
>99
>99
91
5.2
4.8
24
1/32
1/4
37.2
30.8
38.0
5.2
90
>99
>99
192
a
d
The reaction of PPS and m-CTE was carried out using TBAC as a cata-
Estimated by SEC based on polystyrene standards; eluent: a solution
lyst in NMP.
of LiBr and phosphoric acid (20 mM) in DMF.
b
e
Calculated by SEC.
The degree of insertion of PPS into m-CTE (DI) was calculated from 1H
c
Methanol-insoluble part.
NMR data (see text).
TABLE 5 Molecular Weight and Thermal Properties of Poly[m-CTE(PPS)n] and PolyPPS
c
d
e
if
Run
Polymers
Morphology
Mw (SEC)
Mw (MALLS)
M
w(SEC)/Mw (MALLS)
Tg (ꢀC)
Td (ꢀC)
a
1
2
3
Poly[m-CTE(PPS)4.4
]
Cyclic
Cyclic
Linear
82,830
173,100
380,700
328,100
0.48
0.68
0.83
81
28
20
231
199
208
b
Poly[m-CTE(PPS)30.8
]
257,910
272,770
PolyPPS
a
d
e
f
Poly[m-CTE(PPS)4.4] was obtained in run 1 in Table 3.
Poly[m-CTE(PPS)30.8] was obtained in run 5 in Table 4.
Estimated by SEC based on polystyrene standards; eluent: a solution
Determined by MALLS.
Measured by DSC.
Measured by TGA.
b
c
of LiBr and phosphoric acid (20 mM) in DMF.
4 J. Roovers, P. M. Toporowski, Macromolecules 1983, 16,
843–849.
at 34–61% yields, and their molecular weights could not be
controlled. In the case of the reaction of PPS and m-CTE,
insertion reaction of PPS into m-CTE proceeded smoothly
without intracyclization of thioester groups. With the supply
of PPS and m-CTE, the molecular weight of the correspond-
ing polysulfides could be controlled, yielding poly[m-
CTE(PPS)n] with Mn’s 5 46,600–107,200 in 63–>99% yields.
The absolute molecular weights (Mw(MALLS)) of the cyclic pol-
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