Precise Synthesis of Poly(thioester)s with Diverse Structures by Copolymerization of Cyclic Thioanhydrides and Episulfides Mediated by Organic Ammonium Salts

Article abstract of DOI:10.1002/anie.201812135

The precise synthesis of poly(thioester)s with diverse structures is still a significant challenge in the polymeric materials field. Herein, we report a novel approach to the synthesis of well-defined poly(thioester)s by the controlled alternating copolymerization of cyclic thioanhydrides and episulfides induced by simple organic ammonium salts. Both the cation and anion have strong effects on the copolymerization. [PPN]OAc ([PPN]=bis(triphenylphosphine)iminium) with a bulky cation was proven to be efficient in initiating this polymerization, yielding poly(thioester)s with a completely alternating structure, controlled molecular weight, and narrow polydispersity. The poly(thioester) obtained from succinic thioanhydride and propylene sulfide is a typical semicrystalline material, possessing a high refractive index of up to 1.78. Because it uses readily available monomers, this method is expected to open up a new route to poly(thioester)s with diverse structures and properties.

Full text of DOI:10.1002/anie.201812135

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Accepted Article
Title: Precise Synthesis of Poly(thioester)s with Diverse Structures
by Copolymerization of Cyclic Thioanhydrides and Episulfides
Mediated by Organic Ammonium Salts
Authors: Xiao-Bing Lu, Yue-Tian Jun, Ming-Chao Zhang, Ge-Ge Gu,
Li-Yang Wang, and Wei-Min Ren
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201812135
Angew. Chem. 10.1002/ange.201812135
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COMMUNICATION
Precise Synthesis of Poly(thioester)s with Diverse Structures by
Copolymerization of Cyclic Thioanhydrides and Episulfides
Mediated by Organic Ammonium Salts
†
†
Tian-Jun Yue, Ming-Chao Zhang, Ge-Ge Gu, Li-Yang Wang, Wei-Min Ren,* and Xiao-Bing Lu*
Abstract: Precise synthesis of poly(thioester)s with diverse structures
the polycondensation of mercaptoalkanoic acids, affording
poly(thioester)s with a high molecular weight.[ Although this
technique is an environmentally benign method for meeting the
green polymer chemistry requirements, it is difficult to be adopted
in the practical applications because the biological process still
10]
is still a significant challenge in the polymeric materials field. Herein,
we report
a novel approach to the synthesis of well-defined
poly(thioester)s by the controlled alternating copolymerization of
cyclic thioanhydrides and episulfides induced by simple organic
ammonium salts. Both the cation and anion have strong effects on the
[11]
seems not cheap enough for the products. A more common
method for poly(thioester) synthesis is the ring-opening
[
12,13]
copolymerization.
[PPN]OAc
([PPN]
=
polymerization of thiolactone or thionolactone (Scheme 1b),
which can be traced back to the 1960s;[ however, the lack of
structurally diverse monomers significantly limits its application.
Therefore, the development of an efficient synthetic route to
poly(thioester)s with versatile functionality is highly desirable for
improving the properties and expanding the applications of this
important class of materials. In this communication, we report a
new method for the highly efficient synthesis of poly(thioester)s
with diverse structures by the alternating copolymerization of
cyclic thioanhydrides and episulfides induced by simple organic
ammonium salts under mild conditions (Scheme 1c). The
resultant aliphatic poly(thioester)s show a completely alternating
structure, controlled molecular weight, and narrow polydispersity.
12]
bis(triphenylphosphine)iminium) with a bulky cation was proven to be
efficient in initiating this polymerization, yielding poly(thioester)s with
a completely alternating structure, controlled molecular weight, and
narrow polydispersity. The poly(thioester) obtained from succinic
thioanhydride and propylene sulfide is a typical semi-crystalline
material, possessing a high refractive index of up to 1.78. Because it
uses readily available monomers, this method is expected to open up
a new route to poly(thioester)s with diverse structures and properties.
The introduction of sulfur atom(s) onto target molecules is a
significant area of research, particularly in the synthesis of
[1]
pharmaceutical drugs, while substitution of some oxygen atoms
with sulfur atoms in the backbone of a polymer can result in
enhanced electrical, mechanical, thermal, and optical features, as
well as chemical resistance and heavy-metal-recognition ability.[
As a consequence, various sulfur-containing polymers including
2]
poly(thioether)s,
poly(thiourethane)s,
poly(thiocarbonate)s,
poly(thioester)s, and poly(sulfur-random-styrene) have been
[3]
produced. For example, the alternating copolymerization of
carbonyl sulfide with epoxides was developed to give
poly(thiocarbonate)s with enhanced thermal properties compared
2
to the corresponding polycarbonates obtained from CO and
[4]
epoxides. Prior to these studies, the copolymerization of
episulfides with carbon disulfide was reported by Nozaki and
coworkers, affording a sulfur-rich polymer with a high refractive
[5]
index.
In addition to poly(thiocarbonate)s, aliphatic poly(thioester)s
are a promising class of polymers because the analogous
polyesters have a wide range of applications in drug delivery
Scheme 1. Comparison of synthetic routes to aliphatic poly(thioester)s.
[
6]
systems, artificial tissues, and commodity materials. Historically,
poly(thioester)s were prepared by the polycondensation of
[
7]
mercaptoacetic acid; however, this method is energy intensive,
requiring high temperatures and removal of the water byproduct.
As an alternative approach, Steinbuchel and coworkers reported
the biosynthesis of poly(thioester)s using an engineered
Succinic thioanhydride (STA), prepared by reacting succinic
[
14]
anhydride and sodium sulfide,
is easily ring-opened by a
nucleophile to give a thiocarboxylate moiety[ while propylene
15]
sulfide (PS) is well-known to be polymerized by an anionic or
[8]
[9]
[16]
Escherichia coli or a recombinant strain of E. coli cultured with
mercaptoalkanoic acids (Scheme 1a). In a subsequent study,
Matsumura et al. utilized an immobilized lipase as a catalyst for
coordination anionic mechanism. On the basis of these facts,
we envisioned that the STA/PS copolymerization could proceed
smoothly in an anionic manner once triggered by a nucleophilic
initiator. Initially, we focused on the copolymerization using DBU
(
1,8-diazabicyclo[5.4.0]undec-7-ene), an effective initiator for the
living episulfide ring-opening polymerization.[
17]
With
a
[
a]
[*] T.-J. Yue, M.-C. Zhang, G.-G. Gu, L.-Y. Wang, Prof. Dr. W.-M.
Ren, Prof. Dr. X.-B. Lu
State Key Laboratory of Fine Chemicals, Dalian University of
Technology,
PS/STA/DBU feed ratio of 1000/250/1 at 25 °C, the
copolymerization can proceed with an STA conversion of 30%
within 1 h (Table 1, entry 1). However, the formed poly(thioester)
2
Linggong Road, Dalian, 116024, China.
was an oligomer with a number-average molecular weight (M
n
) of
E-mail: wmren@dlut.edu.cn; xblu@dlut.edu.cn
4
.6 kg/mol, which was dramatically lower than the theoretical
theo
Supporting information for this article is given via a link at the end
of the document.
number-average molecular weight (M
increase in STA conversion on prolonging the reaction time had
little effect on the M of the resulting copolymer (entry 2). A similar
n
, 14.3 kg/mol). The
n
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COMMUNICATION
Table 1: Ring-Opening Copolymerization of STA and PS.a
b
theo c
d
PDId
1.46
1.56
1.24
1.72
1.23
1.27
1.24
1.28
1.23
entry
initiator (I)
DBU
DBU
[PPN]Cl
[PPN]Cl
[PPN]Cl
[PS]/[STA]/[I]
1000/250/1
1000/250/1
1000/250/1
1000/250/1
250/300/1
1000/250/1
1000/250/1
1000/250/1
1000/250/1
time [h]
1.0
4.0
0.5
1.0
48.0
2.0
24.0
24.0
0.2
conv. [%]
M
n
[kg/mol]
14.3
M
n
[kg/mol]
4.6
4.8
35.2
43.7
44.3
35.9
30.5
28.8
26.3
1
2
3
4
30
85
78
>99
99f
70
66
69
63
40.4
37.1
47.5
47.0
33.3
31.4
32.8
29.9
e
5
6
7
8
9
[Et
[Me
[PPN]NO
[PPN]OAc
4
N]Cl
4
N]Cl
3
a
Reactions were performed in neat PS (20 mmol) at 25 °C, with a PS/STA/I molar ratio of 1000/250/1 unless noted otherwise. The selectivities for the thioester over
the thioether unit in the resulting copolymer are all >99%, determined by 1H NMR spectroscopy. b Conversion of STA, determined by H NMR spectroscopy. c
=
Conversion of PS, determined by H NMR spectroscopy.
1
M
theo
n
190.01 × 250 × Conv. d Determined by using gel permeation chromatography in THF, calibrated with polystyrene. Toluene (1 mL) was added as solvent. f
e
1
situation
dimethylamino)pyridine)
triazabicyclododecene) was employed as an initiator (see
Supporting Information, Table S1). The low M is attributed to the
organic bases mediated PS/STA copolymerization through
triggering the nucleophilic ring-opening of both propylene sulfide
and cyclic thioanhydride. The latter path normally yields a
Zwitterion including an iminium moiety and a thiocarboxylate or
polythiocarboxylate moiety, which easily forms cyclic
was
observed
or
when
MTBD
DMAP
(4-(N,N-
h, STA was fully consumed and the resultant polymer had a
broader PDI (1.72 vs. 1.24) (entry 4). Since the copolymerization
reaction was conducted in excess PS, the active species at the
end of the propagating polymer chain is proposed to be an alkyl
sulfide anion, which may cause a polymer transesterification.
Indeed, when the copolymerization was performed in toluene with
an excess of STA relative to PS, the transesterification was
suppressed effectively even after full conversion of the PS (entry
5). However, the use of the solvent resulted in a very slow reaction
rate.
(N-methyl-1,5,7-
n
poly(thioester)s with low
n
M s through the intramolecularly
nucleophilic attack of the propagating polymer anion at the
carbonyl group linked to iminium cation, along with the release of
the organic base.
We next examined the effect of the cation and anion of the
organic ammonium salt on the STA/PS copolymerization, and
found that replacement of [PPN]Cl with [Et N]Cl or [Me N]Cl
4 4
As well as organic bases, organic ammonium salts have also
been widely used as initiators or cocatalysts in the
resulted in notable decreases in the polymerization rate (Table 1,
entries 6 and 7; Supporting Information, Figure S2). In order to
copolymerization of epoxides with
cyclic anhydrides.[
18]
Thus, we
decided to use [PPN]Cl ([PPN] =
bis(triphenylphosphine)iminium),
one of the most common organic
ammonium salts, as the initiator to
induce
copolymerization. Gratifyingly, the
copolymerization yielded
the
STA/PS
a
unimodal polymer with a narrow
polydispersity index (PDI) of 1.24
n
and a high M of 35.2 kg/mol (entry
3
), which is in good agreement with
theo
the M
n
(37.1 kg/mol). No signal
assigned to thioether units was
1
observed in the H NMR spectrum
of the resultant copolymer (see
Supporting Information, Figure
S1), indicating
a
completely
Figure 1. Free-energy profiles for the ring-expansion addition of STA to ethylene sulfide initiated by different
alternating structure. When the
reaction time was extended to 1.0
organic ammonium salts.
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COMMUNICATION
shed light on the relationship between the cation of the organic
ammonium salt and the polymerization rate, a density-functional-
conversion and narrow PDIs (<1.3) even at high monomer
conversion (Figure 3A). The controlled character was also
theory (DFT) study was undertaken. To simplify the calculation,
n
supported by a second-feed experiment. A copolymer with M =
−
ethylene sulfide and 2-chloroethylane-1-thioate (ClCH
CH
2 2
S )
18.1 kg/mol and PDI = 1.27 was first prepared by nearly complete
consumption of 100 equiv of STA with [PPN]OAc in excess PS.
Copolymerization was then restarted by subsequent addition of
were substituted for PS and the propagating polymer chain,
respectively. The Gibbs-free-energy profiles (including key
transition states) were calculated for the complete enchainment
reaction (Figure 1). These energy profiles clearly show that the
rate-determining step is episulfide ring-opening, and the barriers
n
100 equiv of STA to afford a poly(thioester) with M = 35.7 kg/mol
and PDI = 1.30 at an STA conversion of 97% (Figure 3B). The
copolymerization was further studied with the addition of a chain
transfer agent. Unexpectedly, the addition of benzyl alcohol
(BnOH) had little effect on the reaction rate and polymer
molecular weight (see Supporting Information, Table S2, entries
are 13.5, 16.1 and 20.9 kcal/mol for [PPN]Cl, [Et
Me N]Cl, respectively. Substitution of [PPN]NO for [PPN]Cl led
to a dramatic decrease in the reaction rate (entry 8), but the salt
PPN]OAc was found to be more efficient for this reaction (entry
; see Supporting Information, Figure S3). To compare the
4
N]Cl and
[
4
3
[
1−4). Indeed, the proton cannot be exchanged between the
−
9
propagating polymer chain end-capped with –CH
BnOH since the –CH CH(CH
2
CH(CH
3
)S and
reaction kinetics of various initiator systems for the PS/STA
copolymerization, we performed a kinetic study of this process as
a function of time using in-situ FTIR spectroscopy with a probe
fitted to a modified stainless-steel Parr reactor, monitoring the
2
3
)SH end group has a higher acidity
than BnOH. A similar result was observed when using other
alcohols as the chain transfer agent (Table S2, entries 5 and 6).
In contrast, when using benzyl mercaptan (BnSH) as the chain
−1
intense absorbance at 1692 cm for the νC=O stretch of the formed
transfer agent, the molecular weights determined by GPC (M
n
)
[19]
theo
poly(thioester). It can be seen from Figure 2 that when utilizing
PPN]OAc with a highly nucleophilic anion, no induction period
was observed, which is different from when [PPN]Cl or [PPN]NO
were in good agreement with the calculated
Supporting Information, Figure S6).
M
n
(see
[
3
2.0
4
5
(A)
Mn
was used as the initiator. The structure of the polymer chain end-
1
.9
.8
PDI
capped with an OAc group was confirmed by ESI-TOF
40
1
[20]
spectroscopy
(see Supporting Information Figure S5). In
3
3
5
0
2
R = 0.99783
1.7
1.6
general, an organic ammonium salt consisting of a bulky cation
and a nucleophilic anion as the initiator is more effective at
improving the copolymerization rate. Since the copolymerization
of propylene sulfide and cyclic thioanhydride mediated by organic
quaternary ammonium salts predominantly proceeds in an
anionic manner, both the nucleophilicity and free degree of the
anion of the quaternary ammonium salt have critical influences on
the induction period and initiation efficiency, which significantly
affect the copolymerization rate. The Coulombic interaction
between the anion and cation of a quaternary ammonium salt is
inversely proportional to the distance of the ion pair. As a result,
25
1
.5
.4
2
1
0
5
1
1.3
10
2
1.2
0
30 40 50 60 70 80 90 100
STA Conversion (%)
(B)
(b) (a)
(b): M : 35.7
Mntheo : 36.9
(a): Mn: 18.1
Mntheo : 18.6
PDI : 1.27
n
+
a bulky cation (such as PPN ) combining with a nucleophilic anion
-
with large ionic radius (such as OAc ) is beneficial to weaken the
PDI : 1.30
interaction, and thus enhancing the nucleophilicity of the anion.
0
0
0
0
0
0
0
0
0
.8
.7
.6
.5
.4
.3
.2
.1
.0
[
PPN]OAc
[PPN]Cl
PPN]NO3
[
1
1
12 13 14 15 16 17 18
Retention Time (min)
Figure 3. Controlled character of the STA/PS copolymerization induced by
PPN]OAc. (A) Plots of the copolymer molecular weight and distribution versus
the conversion of STA; (B) GPC traces of the STA/PS copolymers obtained after
the first (a) and second (b) feeds of STA, M values are given in kg/mol.
[
n
The thermal properties of the resultant poly(thioester)s were
studied by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC). The TGA indicated that the STA/PS
n
0
.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (h)
copolymer (M = 26.3 kg/mol, PDI = 1.23) had a temperature at
5
% weight loss (T
Figure S7). The DSC thermograms showed that this copolymer
had a melting temperature (T ) of 80.1 °C with a melting enthalpy
ΔH ) of 15.1 J/g (see Supporting Information, Figure S8A).
Interestingly, a higher T of up to 91.0 °C along with a ΔH of 47.3
d
) of 275.1 °C (see Supporting Information,
Figure 2. Comparison of poly(thioester) vC=O peak height measured by in-situ
FTIR spectroscopy (1692 cm−1) of copolymers produced from PS and STA
utilizing different initiators. Reaction conditions: [PS]/[STA]/[I] = 10000/2500/1,
m
(
m
25 °C.
m
m
J/g (Figure S8B) was observed for the copolymer resulting from
the copolymerization of STA and (R)-PS.[ The powder X-ray
diffraction (XRD) analysis confirmed the crystallization behavior
of these copolymers (see Supporting Information, Figure S9).
Additionally, the STA/PS copolymer was measured to have a
21]
Furthermore, the controlled character of the STA/PS
copolymerization induced by [PPN]OAc was clearly evidenced by
the linear increase in M of the resulting poly(thioester)s with STA
n
D
refractive index (n ) of 1.78 (measured on an Abbe refractometer,
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COMMUNICATION
cast film, 20 °C), which is one of the largest values among those
post-polymerization modification (entry 4). One of the advantages
of cyclic thioanhydride/episulfide copolymerization is that the
polymer’s properties can be tuned not only by changing the
episulfide but also by changing the cyclic thioanhydride. When
glutaric thioanhydride (GTA) was employed in the
copolymerization with PS, the resultant poly(thioester) has only a
[
22]
reported for sulfur-containing polymers.
In contrast, the
corresponding polyester from succinic anhydride and propylene
o
oxide has a very low glass transition temperature of -2.1 C.
To explore the substrate scope of this copolymerization, we first
screened a variety of episulfides, which can be easily obtained
from the sulfuration reaction of the corresponding epoxides and
T
g
of 49.9 °C (entry 5). The other poly(thioester)s produced with
[
23]
thiourea with a yield of >90%. All the formed poly(thioester)s
GTA showed decreased T s compared with the corresponding
g
1
had completely alternating structures as determined by H NMR
copolymers from STA (entries 6 and 7). Notably, all the resultant
copolymers exhibited a good transmittance.
spectroscopy (Table 2, entries 1−4). Of importance, incorporation
of vinyl cyclohexene sulfide (VCHS) offers the opportunity for
Table 2: Alternating Copolymerization of Cyclic Thioanhydrides and Episulfides.a
b
c
PDIc
1.29
d
e
entry
1
monomers
STA/PrOS
time [h]
2.0
conv [%]
84
M
n
[kg/mol]
48.4
T
g
[°C]
0.4
d
T [°C]
i
264.3
276.5
262.2
232.4
269.4
299.6
254.4
2
3
4
5
6
7
STA/HS
STA/CHS
STA/VCHS
GTA/PS
1.0
0.5
0.5
0.5
2.0
0.5
96
87
85
95
90
94
44.8
42.3
45.0
46.5
48.8
53.6
1.30
1.28
1.35
1.25
1.27
1.26
−11.5
44.7
60.2
49.9
−22.1
5.7
i
GTA/PrOS
GTA/CHS
a
Reactions were performed in neat episulfides (20 mmol) with a [PPN]OAc/cyclic thioanhydride/episulfide molar ratio of 1/250/1000 at 25 °C. The selectivity for
thioester over thioether units in the resulting copolymer are all >99%, determined by H NMR spectroscopy. b Conversion of cyclic thioanhydrides, determined by
1
1
c
d
H NMR spectroscopy. Determined using gel permeation chromatography in THF, calibrated with polystyrene. Glass transition temperature, determined by
e
differential scanning calorimetry (DSC). 5% weight loss decomposition temperature.
formation was detected by the shifted GPC trace
relative to the STA/PS copolymer trace. Based
on the 1H NMR analysis, the resulting block
copolymer showed an alternating degree
of >99% (see Supporting Information, Figure
S10). The thermal behavior of the block
copolymer was studied by DSC in a nitrogen flow.
The DSC thermogram of the block copolymer
(
b)(a)
(
b): M : 35.9
Mntheo : 37.2
(a): Mn: 18.4
Mntheo : 18.6
PDI : 1.27
n
PDI : 1.30
g m
showed a T of 35.7 °C and a T of 80.3 °C (see
Supporting Information, Figure S11), attributed
to the GTA/PS and STA/PS segments,
respectively. The TGA analysis showed that the
1
1
12 13 14 15 16 17 18
Retention Time (min)
block copolymer had
a 5% weight loss
decomposition temperature of 243 °C with a
broader range than that of the STA/PS and
GTA/PS
copolymers
(see
Supporting
Information, Figure S12).
In conclusion, we have demonstrated an
efficient approach to well-defined, structurally
diverse poly(thioester)s prepared by the
alternating copolymerization of a variety of cyclic
Scheme 2. Synthesis and characterization of the block copolymer from PS, STA and GTA. M
values in the inset are given in kg/mol.
n
To take advantage of the well-controlled features of this
copolymerization process, we were interested in synthesizing
block copolymers by stepwise addition of different monomers.
Scheme 2 shows our strategy for the preparation of a block
copolymer comprising PS, STA, and GTA. Almost quantitative
conversion of STA was achieved in excess PS, and then addition
of GTA restarted the copolymerization. The block copolymer
thioanhydrides and episulfides induced by simple organic
ammonium salts. Both monomers can be easily prepared from
available cyclic anhydrides and epoxides in the presence of a
cheap sulfur transferring agent. Moreover, the use of two distinct
monomer sets allows the facile tuning of the properties of the
resultant polymers as well as post-polymerization modification.
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COMMUNICATION
These features along with the strategy being metal-free,[24] give
these poly(thioester)s the potential to be utilized as high-
performance engineering plastics, as well as optical,
optoelectronic, and photochemical materials. Studies focused
on further expanding the monomer scope and controlling the
stereochemistry are currently in progress.
Bourissou, Chem. Rev. 2004, 104, 6147 – 6176; d) Longo, J. M.; Sanford,
M. J.; Coates, G. W. Chem. Rev. 2016, 116, 15167 – 15197.
[7] H. R. Kricheldorf, G. Schwarz, J. Macromol. Sci. A 2007, 44, 625 – 649.
[8] a) T. Lutke-Eversloh, K. Bergander, H. Luftmann, A. Steinbuchel,
Biomacromolecules 2001, 2, 1061 – 1065; b) T. Lutke-Eversloh, J. Kawada,
R. H. Marchessault, A. Steinbuchel, Biomacromolecules 2002, 3, 159 – 166.
[
25]
[
9] T. Lutke-Eversloh, A. Fischer, U. Remminghorst, J. Kawada, R. H.
Marchessault, A. Bogershausen, M. Kalwei, H. Eckert, R. Reichelt, S. J. Liu,
A. Steinbuchel, Nature Materials 2002, 1, 236 – 240.
Experimental Section
[
10] a) M. Kato, K. Toshima, S. Matsumura, Biomacromolecules 2005, 6, 2275
–
2280; b) M. Kato, K. Toshima, S. Matsumura, Biomacromolecules 2007,
An oven-dried flask equipped with a side arm and a magnetic stirrer bar
was charged with the initiator (0.01 mmol, 1 equiv), cyclic thioanhydride
8, 3590 – 3596.
[
[
[
11] S. Shoda, H. Uyama, J. Kadokawa, S. Kimura, S. Kobayashi, Chem. Rev.
016, 116, 2307 – 2413.
(
2.5 mmol, 250 equiv) and episulfide (10 mmol, 1000 equiv) in an argon
2
atmosphere. The reaction vessel was sealed and then stirred at 25 °C .
After an appropriate time, a small amount of the resultant mixture was
12] a) C. G. Overberg, J. K. Weise, J. Am. Chem. Soc. 1968, 90, 3533 – 3537;
b) C. G. Overberg, J. K. Weise, J. Am. Chem. Soc. 1968, 90, 3538 – 3543.
13] a) F. Sanda, D. Jirakanjana, M. Hitomi, T. Endo, Macromolecules 1999, 32,
1
removed from the flask for H NMR analysis to quantitatively determine the
conversion of cyclic thioanhydride, as well as the selectivity of
poly(thioester) to polythioether. The crude polymer was dissolved in 10 mL
CH Cl , and then, the solution was precipitated with excess methanol. This
2 2
process was repeated 2 or 3 times to completely remove the residual
episulfide. A white polymer was obtained by vacuum-drying. A small
amount of solid was used for the DSC and TGA analyses.
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Gratitude is expressed to the National Natural Science
Foundation of China (NSFC, Grant 21674015, 21722402,
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Author Contributions
T.-J. Yue and M.-C. Zhang contributed equally to this work.
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infrared spectra (see Supporting Information, Figure S4).
Conflict of interest
[20] Some attempts were made to confirm the copolymer chain structure end-
capped with a acetic group by MALDI-TOF spectroscopy, however, we
didn't obtain the polymer chain-growth species due to the serious
interference of [PPN] cation.
The authors declare no competing financial interests.
Keywords: poly(thioester)s • cyclic thioanhydrides • episulfides •
controlled synthesis • diverse structure
[
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Tian-Jun Yue, Ming-Chao Zhang, Ge-Ge
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Precise Synthesis of Poly(thioester)s
with Diverse Structures by
Copolymerization of Cyclic
Thioanhydrides and Episulfides
Mediated by Organic Ammonium
Salts
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