Room Temperature One-Step Conversion from Elemental Sulfur to Functional Polythioureas through Catalyst-Free Multicomponent Polymerizations

Article abstract of DOI:10.1021/jacs.8b02886

The utilization of sulfur is a global concern, considering the abundant and cheap source of sulfur from nature and petroleum industry, its limited consumption, and the safety/environmental problems caused during storage. The economic and efficient transformation of sulfur remains to be a great challenge for both academia and industry. Herein, a room temperature conversion from sulfur to functional polythioureas was reported through a catalyst-free multicomponent polymerization of sulfur, aliphatic diamines, and diisocyanides in air with 100% atom economy. The polymerization enjoys quick reaction and wide monomer scope, which affords 16 polythioureas with well-defined structures, high molecular weights (M_ws up to 242 500 g/mol), and excellent yields (up to 95%). The polythioureas can be utilized to detect mercury pollution with high sensitivity (K_sv = 224 900 L/mol) and high selectivity, clean Hg²⁺ with high removal efficiency (>99.99%) to achieve drinking water standard, and monitor the real-time removal process by fluorescence.

Full text of DOI:10.1021/jacs.8b02886

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Room Temperature One-Step Conversion from Elemental Sulfur to Functional
Polythioureas through Catalyst-Free Multicomponent Polymerizations
Tian Tian, Rongrong Hu, and Ben Zhong Tang
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 23 Apr 2018
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Page 1 of 11
Journal of the American Chemical Society
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Room Temperature One-Step Conversion from Elemental Sulfur to
Functional Polythioureas through Catalyst-Free Multicomponent
Polymerizations
7
8
9
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0
†
,†
,†,‡
Tian Tian, Rongrong Hu,* and Ben Zhong Tang*
†
State Key Laboratory of Luminescent Materials and Devices, Center for Aggregation-Induced Emission, South Chi-
na University of Technology, Guangzhou 510640, China.
‡
Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Resto-
ration and Reconstruction, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong
Kong, China.
ABSTRACT: The utilization of sulfur is a global concern, considering the abundant and cheap source of sulfur from na-
ture and petroleum industry, its limited consumption and the safety/environmental problems caused during storage. The
economic and efficient transformation of sulfur remains to be a great challenge for both academia and industry. Herein, a
room temperature conversion from sulfur to functional polythioureas was reported through a catalyst-free multicompo-
nent polymerization of sulfur, aliphatic diamines, and diisocyanides in air with 100% atom economy. The polymerization
enjoys quick reaction and wide monomer scope, which affords 16 polythioureas with well-defined structures, high molec-
ular weights (M s up to 242 500 g/mol), and excellent yields (up to 95%). The polythioureas can be utilized to detect mer-
w
2+
cury pollution with high sensitivity (K = 224 900 L/mol) and high selectivity, clean Hg with high removal efficiency (>
sv
99.99%) to achieve drinking water standard, and monitor the real-time removal process by fluorescence.
19,20
soluble polymers with well-defined structures.
Among
INTRODUCTION
that, multicomponent polymerizations (MCPs) with fas-
cinating features such as high efficiency, simple opera-
tion, high atom economy, great structural diversity, and
Sulfur, as the third most abundant element in the fossils,
has become one of the major byproducts from worldwide
petroleum industry. Compared with its large surplus from
over 70 million tons annual production, the consump-
tion of sulfur is quite small, which is mainly used in the
mild conditions, provide great opportunity for the direct
1
,2
21-25
utilization of sulfur.
For example, the MCP of diamine,
o
dialdehyde and sulfur at 115 C was reported to synthesis
3
26,27
production of sulfuric acid, resulting in rapidly growing
polythioamides.
In these approaches, high tempera-
mountains of sulfur on the oil sands. While the dispose of
sulfur is costly, the storage of sulfur has also been proved
to be a challenging issue, considering the flammable na-
ture is generally required for the polymerization of sulfur.
New methods with concerns of environmental friendli-
ness and energy saving are desired.
ture of sulfur and its slow transformation to SO which
Recently, we have reported a catalyst-free MCP of sul-
fur, alkynes, and aliphatic amines to afford a series of pol-
ythioamides with well-defined structures, high yields,
high molecular weights, and high refractive indices at 100
x
might cause serious environmental problems such as acid
4
rain. It is hence urgently demanded to develop economic
and efficient method for the utilization of elemental sul-
fur in the preparation of functional materials.
o
28
C. It can be expected that when alkynes are replaced by
Sulfur-containing polymers have attracted much at-
tention because of their outstanding characteristics such
more reactive isocyanides, the polymerization reactivity
could be enhanced, which might decrease the polymeri-
zation temperature. Indeed, an autocatalytic multicom-
ponent reaction of isocyanides, aliphatic amines, and sul-
fur was reported to afford a library of asymmetric thiou-
5
,6
7
as high refractive indices, high transparency, metal
8
9,10
coordination ability, self-healing capability,
electro-
1
1,12
13
chemical properties, and photocatalytic activity. Mas-
sive effort has been devoted to investigate the direct utili-
zation of elemental sulfur in the preparation of sulfur-
containing functional polymers such as vulcanized rub-
29
reas. In this reaction, cyclic S first reacts with an ali-
8
phatic amine to yield a zwitterionic ammonium polysul-
fide chain A. The negatively charged sulfur terminus of A
then attacks the carbenoid carbon of the isocyanide to
yield an isothiocyanate intermediate C, which then reacts
with another amine molecule to produce a thiourea D
14
15-17
bers, polysulfides,
and high sulfur-content copoly-
2
mers, which generally involve high temperature, ambig-
18
uous structure, and poor solubility of products. Few ex-
29,30
(Scheme S1).
ample has been reported to directly use sulfur to produce
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Page 2 of 11
Inspired by the advantages of this MCR such as low finished rapidly in air in 2 h at room temperature or 10
o
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
reaction temperature, catalyst-free, high atom economy,
and procedure simplicity, in this work, the polymeriza-
tion of elemental sulfur, aliphatic diamines, and diisocya-
nides was investigated to produce polythioureas. Among
the sulfur-containing polymers, polythioureas possess
min at 100 C, respectively, suggesting its fast polymeriza-
tion speed and high efficiency of sulfur conversion. To the
best of our knowledge, this is the first example demon-
strating room temperature polymerization with elemental
sulfur. Moreover, the thiourea groups endow the poly-
9
2+
great potential in self-healing materials, heat-resistant
mers sensitive and selective coordination with Hg with
their potential applications as fluorescent chemosensors
and removal adsorbents for mercury.
3
1
32
materials, extraction of heavy metal ions, and dielectric
3
3
materials, which are usually prepared by polycondensa-
tion of toxic monomers such as carbon disulfide, isothio-
3
4-37
RESULTS AND DISCUSSION
cyanates, or thiophosgene.
Herein, this MCP can be
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
carried out smoothly at room temperature under nitrogen
or in air, affording 16 polythioureas with great structural
diversity, high molecular weights in high yields. The anal-
ysis of in situ IR spectra suggests that the MCP can be
Catalyst-Free MCPs of Sulfur, Aliphatic Diamines,
and Diisocyanides. To develop multicomponent
polymerizations of sulfur, aliphatic diamines, and diisocy-
anides, sublimed sulfur 1 was selected because of its low
Figure 1. (A) Catalyst-free multicomponent polymerization of sulfur 1, diamines 2a-d, and diisocyanides 3a-d. (B) Chemical
structures and polymerization results of P1/2a-d/3a-d. M s are determined by GPC in DMF based on polystyrene standard
w
samples.
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Journal of the American Chemical Society
series of commercially available primary and secondary
cost among the various existence forms of elemental sul-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
fur,
and
commercially
2a
available
well
1,4-
1,4-
aliphatic diamines 2a-d, aliphatic diisocyanides 3a-b, and
facilely available aromatic diisocyanides 3c-d are selected
phenylenedimethanamine
bis(isocyanomethyl)benzene 3a prepared from 2a are se-
lected as the representative monomers (Scheme S2). The
polymerization of 1, 2a, and 3a was first conducted in tol-
uene at 50 C for 4 h under nitrogen without catalyst, giv-
ing an insoluble product in toluene with a molecular
weight (M ) of 17 400 g/mol in 72% yield (Figure 1A).
Polar solvents such as DMF, DMSO, and toluene/DMF
mixed solvents were investigated and the best polymeri-
zation result was obtained in toluene/DMF (v/v, 1/2), fur-
as
as
3
9
as monomers (Figure 1A). The MCPs of all the 16 combi-
nations of four diamines and four diisocyanides were car-
3
8
o
ried out in toluene/DMF (v/v, 1/2) at 100 C under nitro-
o
gen. All the polymerizations proceeded smoothly and
rapidly to produce soluble polymers in 1 h with satisfacto-
ry yields of 64-95% and high M s of up to 242 500 g/mol,
w
w
demonstrating general monomer applicability and high
efficiency (Figure 1B). In particular, primary amines 2a-c
can afford better polymerization results compared with
secondary amine 2d, owing to their higher reactivity.
Among all the combinations, aromatic diisocyanide 3c
with good solubility affords the highest Mw upon
polymerization with sulfur and 2c, despite of its steric
hindrance.
Room Temperature MCPs of Sulfur, Aliphatic Di-
amines, and Diisocyanides in Air. To further enhance
the potential of this MCP, the polymerizations were op-
timized at room temperature (Table 1). The MCPs of eight
monomer combinations among primary/secondary dia-
mines 2a-d, and aliphatic/aromatic diisocyanides 3a-c
were conducted as examples at room temperature for 1 h
under nitrogen, generating satisfactory results with up to
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
nishing polymer with an improved M of 37 900 g/mol in
w
82% yield (Table S1). The potential hydrogen bonds be-
tween thiourea groups and polar solvent molecules might
have facilitated the polymer dissolution process. When
the temperature was optimized from room temperature
to 100 C, the yield was increased from 53% to 85%, and
the M of product was increased from 27 000 to 73 900
g/mol (Table S2). The monomer loading ratio and con-
centration are also crucial for the MCP. When strict theo-
retical monomer loading ratio of [1]: [2a]: [3a] = 2: 1: 1 was
adopted, polymer with a M of 42 200 g/mol was obtained
in 75% yield. Increasing the amount of sulfur benefits
o
w
w
both yields and M s (Table S3). Based on the optimized
ratio of [1]: [2a]: [3a] = 4: 1: 1, the concentrations of 2a and
w
79% yields and M s of up to 44 500 g/mol. Compared
w
o
3
a were then increased from 0.1 M to 1.0 M. The M was
with the above-mentioned optimal condition at 100 C,
w
increased from 28 700 to 77 100 g/mol, while the yield was
not affected much. Further increase of the monomer con-
centration led to highly viscous polymerization solution,
which was terminated in 1 h to afford similar result (Table
S4). Interestingly, neat polymerization can be realized at
100 C, which proceeds smoothly and provides satisfactory
results in 1 h with the M of 22 100 g/mol, indicating po-
tential economic impact of this catalyst- and solvent-free
approach. The study of polymerization time from 1 to 8 h
does not show obvious influence on yield and M of the
the reaction time was then prolonged to 4 h and the con-
centration of diamine was increased to 1.1 M, considering
that amine was less reactive at room temperature than at
o
100 C. Eight polymers were obtained with good to excel-
lent yields of 67-94% and high M s of 30 500-116 100
w
o
g/mol, demonstrating excellent polymerization results at
room temperature.
Furthermore, the room temperature MCP was investi-
gated in air, considering that no air-sensitive monomer or
catalyst was involved. All the eight MCPs provide satisfac-
w
w
product, indicating that this MCP is quite fast and effi-
cient (Table S5).
To explore the monomer scope of this catalyst-free
MCP and enrich the structural diversity of products, a
tory results in air with M s ranging from 21 300 to 99 000
w
g/mol in 56-87% yields, proving that the MCP of sulfur,
aliphatic diamines and diisocyanides is quite robust. The
mild condition at room temperature in air, general ap-
a
Table 1. Polymerization Results of Room Temperature MCPs of 1, 2a-d, and 3a-c.
b
c
c
1 h, N2
4 h, N2
4 h, air
polymer
Mw
d
yield
%)
Mw
d
yield
(%)
d
d
yield (%)
PDI
d
PDI
M (g/mol)
w
PDI
d
(
(g/mol)
(
g/mol)
P1/2a/3a
P1/2b/3a
P1/2c/3a
P1/2d/3a
P1/2a/3b
P1/2a/3c
P1/2b/3c
P1/2c/3c
79
55
78
trace
79
33
24 500
24 900
30 800
16 500
30 800
41 600
36 400
44 500
1.34
1.54
1.51
1.87
1.45
1.64
1.38
1.40
94
79
87
67
87
76
89
87
35 200
1.68
1.51
81
72
87
57
60
71
26 700
21 300
37 400
23 400
25 700
60 600
33 800
99 000
1.41
1.37
1.69
1.27
1.57
1.69
1.32
1.53
40 500
33 700
30 500
32 200
61 400
48 600
116 100
1.67
1.34
1.64
1.69
1.41
35
44
56
82
1.84
a
b
c
Carried out at room temperature in toluene/DMF (v/v, 1/2). [1] = 4.0 M, [2a-d] = [3a-c] = 1.0 M. [1] = 4.0 M,
2a-d] = 1.1 M, [3a-c] = 1.0 M. M s are determined by GPC in DMF based on polystyrene standard samples.
d
[
w
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Page 4 of 11
plicability, high efficiency, high convenience, and low cost in the IR spectra of the other 15 polymers, strong -NH-
-
1
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
of this catalyst-free MCP may bring it great potential in
industrial development.
stretching vibration peaks at 3174-3276 cm and C=S
-
1
stretching vibration peaks at 1502-1553 cm emerged, con-
firming their expected thiourea structures (Figure S2-5).
The reaction progress of the MCP of 1, 2a, and 3a was
Kinetic Study of the MCP by In Situ IR Spectrom-
etry. To reveal the kinetic process of this MCP, in situ IR
spectrometry was used to monitor the formation of poly-
thiourea. Model compound 9 was synthesized to assist
the characterization of the polymer structure (Scheme
S2). The regular IR spectra of 2a, 3a, 9, and P1/2a/3a were
compared in Figure S1. The -N≡C stretching vibration of
o
then monitored as an example in air at both 100 C and
room temperature. The in situ IR spectra of the tolu-
ene/DMF (v/v, 1/2) solutions of 2a, 3a, P1/2a/3a, and the
o
polymerization solutions after reaction at 100 C for 4 h or
at room temperature for 8 h, respectively, were compared
in Figure 2A. It is clear that two new peaks emerged at
~1540 cm and 1340 cm in the spectra of both polymeri-
zation solutions, which can be assigned as the stretching
vibrations of C=S and C-N bonds of the thiourea moiety,
respectively (Figure S6). The time-dependent peak in-
tensity and the kinetic variation of the 3D-FTIR profiles at
~1540 cm were recorded to follow the track of the gener-
ation of thiourea moieties at both 100 C and room tem-
-
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3a at 2149 cm was disappeared, and the -NH stretching
2
-
1
-1
-1
vibration of 2a at 3312 cm was converted to -NH- stretch-
-
1
ing vibration at 3250 and 3267 cm in the spectra of 9 and
P1/2a/3a, respectively. Most importantly, new strong
-
1
40
peaks emerged at 1563 and 1544 cm in the spectra of 9
and P1/2a/3a, respectively, which were in accordance with
the stretching vibration of the newly formed C=S bonds,
confirming the formation of thiourea moieties. Similarly,
-
1
o
2
3a
a
A
o
P1/2a/3a
+2a+3a, 100 C
+2a+3a, r.t.
1
00 C
B
o
1
1
r.t.
C=S
C-N
0
1
2
3
4
5
Reaction time (min)
1600
1450
1300
1150
1000 0
40
80
120
240
-1
Wavenumber (cm )
Reaction time (min)
D
C
Figure 2. (A) The in situ IR spectra of 2a, 3a, and P1/2a/3a in toluene/DMF (v/v, 1/2), and the polymerization solutions of 1,
a, and 3a after reaction at 100 C for 4 h or at room temperature for 8 h, respectively. (B) The time-dependent peak intensi-
ty at 1540 cm (100 C) or 1544 cm (room temperature). Three-dimensional Fourier transform IR profiles of the peaks at ~
o
2
-
1
o
-1
-
1
o
1540 cm for the MCP (C) at 100 C and (D) at room temperature, respectively.
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Journal of the American Chemical Society
perature, which clearly suggested the quick initiation and
completion of the MCP (Figure 2B-D). The peak intensity
4.88, respectively, have combined into a single peak at δ
4.64-4.67, owing to the similar chemical environment of
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
-
1
at ~1540 cm increased rapidly to reach saturation after 5
these two -CH - groups in 9 and P1/2a/3a. Most im-
2
o
min at 100 C, or after 1 h at room temperature, suggesting
portantly, new peaks emerged at δ 7.92 and 7.89 in the
spectra of 9 and P1/2a/3a, respectively, corresponding to
the -NH- proton from the newly formed thiourea group
the fast rate and high efficiency of this MCP.
Under the guidance of the in situ IR analysis, the time
of the MCPs of 1, 2a, and 3a can be further optimized. The
1
3
(Figure 3A-D). Similarly, in the C NMR spectra of 9 and
P1/2a/3a, the isocyanide peak of 3a at δ 156.7 has disap-
peared and new thiourea peaks emerge at δ 183.0 and
o
polymerizations at 100 C were conducted in air for 3, 5,
10, and 60 min. The yields have already reached 81% in 3
min, while the M s of the polymer are gradually increased
183.5, respectively. Meanwhile, the -CH - peaks of 2a at δ
w
2
from 30 200 to 47 600 g/mol in 10 min, which do not
change much afterwards (Table S6). For room tempera-
45.5 and 3a at δ 44.5 have combined into a single peak at
δ 47.4 in the spectrum of P1/2a/3a (Figure 3E-H). For all
the 16 polythioureas, the characteristic -NH- peaks at δ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ture polymerization, both yields and M s of product were
w
1
increased upon elongation of the reaction time, and poly-
9.55-7.05 all emerged in their H NMR spectra, and the
thiourea with a M of 24 400 g/mol can be obtained in
characteristic C=S peaks at δ 179.6-183.6 all emerged in
w
1
3
82% yield in 2 h.
their C NMR spectra, confirming their polythiourea
structures (Figure S7-14).
Characterization of the Polythioureas. The well-
defined structure of the polythioureas are confirmed by
Solubility and Thermal Stability. The polythioureas
possess excellent solubility in polar solvents such as DMF
and DMSO, while they generally show poor solubility in
THF, chloroform and dichloromethane. Thermogravimet-
1
13
1
their H and C NMR spectra. In the H NMR spectra of 9
and P1/2a/3a, the resonance of -NH of 2a at δ 1.68 has
2
disappeared; the -CH - peaks of 2a and 3a at δ 3.67 and
2
Hb
2
Ha
NH2
H N
Hb
Ha
A
E
Hc
N
C
C
Hc
N
C1
B
C
F
C1
S
Hd
H '
d
He
H '
e
N
H
N
H
H
C2
H
N
N
H + H '
d
d
S
H + H '
e
e
G
C2
S
Hf
N
H
Hg
N
H
C3
H
N
H
N
n
Hf
S
Hg
D
H
C3
8.4
7.6
4.9
4.2
3.5 2.0
1.5
180
160
140
120
50
45
Chemical Shift (ppm)
Chemical Shift (ppm)
1
13
Figure 3. H NMR spectra of (A) 2a, (B) 3a, (C) 9, and (D) P1/2a/3a. C NMR spectra of (E) 2a, (F) 3a, (G) 9, and (H)
P1/2a/3a in DMSO-d6.
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2
+
ric analysis suggests that these polythioureas enjoy good
thermal resistance with their decomposition tempera-
tures at 5 wt% weight loss ranging from 209 to 279 C,
owing to the intramolecular and intermolecular hydrogen
bonds among the abundant thiourea moieties (Figure
S15).
can reach 224 900 L/mol and the detection limit of Hg
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
can reach 0.1 ppm, demonstrating high sensitivity of mer-
cury detection (Figure 4 inset). Moreover, a large variety
o
+
+
2+
2+
3+
2+
of metal ions including Na , K , Mg , Ca , Al , Pb ,
2+
2+
3+
3+
2+
3+
2+
2+
+
2+
2+
Mn , Fe , Fe , Ru , Co , Ir , Ni , Cu , Ag , Zn , Cd ,
3
+
3+
Ce , and Sm were tested with the same aqueous mixture
of P1/2b/3d. While negligible change on PL intensity and
fluorescence image was observed for the other metal ions,
only Hg exhibits dramatic fluorescence quenching,
demonstrating high specificity of mercury detection (Fig-
ure 4).
Application of Polythioureas in Mercury Detec-
tion and Removal. Thiourea compounds are well-known
ligands for heavy metal ions with strong binding to mer-
2+
4
1
2+
cury ion. The detection and removal of Hg are highly
2
+
desired considering that Hg is a commonly found toxic
heavy metal ion extensively distributed in water and soil,
causing lethal effects on living organisms and neurologi-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
It is observed that when HgCl solution and DMF so-
2
lution of polythiourea were mixed, white precipitate was
4
2
2+
cal systems. Currently, clays and zeolites, activated car-
bon, biomaterials, nanoparticles, and covalent organic
formed due to the poor solubility of the polymer-Hg
complex. The polythioureas were hence utilized for the
removal of Hg from aqueous solutions (Figure 5A,B). For
4
3-35
2+
frameworks are utilized as mercury adsorbents,
with
their performance regarding to removal efficiency, affinity
and capacity, stability, or availability to be further im-
proved. The polythioureas prepared from this economic
and facile MCP of sulfur are hence ideal candidates as
mercury sensors and adsorbents.
example, the DMF solution or solid powder of P1/2a/3a
were added into 2 mL of HgCl solution and stirred at
2
room temperature for 1 h or 40 min, respectively. After
the precipitate was removed by centrifugation, the re-
2+
maining [Hg ] in the filtrate was measured by F732-VJ
Cold-atomic Absorption Spectroscopy. The DMF solution
Of all the 16 polythioureas, P1/2a-d/3d prepared from
2+
tetraphenylethene-containing diisocyanide 3d enjoy ag-
of P1/2a/3a can reduce [Hg ] sharply from 60 mg/L to 20
46,47
gregation-induced emission characteristics.
Their
μg/L using 9.6 mg polymer, which is lower than the
standard of the discharge limit of the industrial waste (50
DMF solutions absorb at 328-336 nm and emit weakly at
92-498 nm (Figure S16 and S17). Their photolumines-
50
4
μg/L); or to 1.6 μg/L with 99.99% removal efficiency
cence (PL) spectra suggest that in DMF/water mixtures
with more than 40 vol% water as poor solvent, the poly-
mers form nanoaggregates to emit brightly. The
DMF/water mixture of P1/2b/3d with 50 vol% water frac-
using 24 mg polythiourea, reaching the standard limit for
45
drinking water (2 μg/L). Three precipitation-filtration
cycles with 2.4 mg/mL polymer can also clean the aque-
ous solution to drinking water standard (Figure 5C). The
solid powder of P1/2a/3a showed better performance with
the standard limit for drinking water achieved when 12
2+
tion was selected to detect Hg , owing to its high fluores-
cence quantum efficiency of 13.3% (Table S7). Upon addi-
2+
2+
tion of Hg from 0 to 10 μM, the emission of the aqueous
mg polymer was used to decrease the [Hg ] to 0.9 μg/L.
suspension of P1/2b/3d gradually decreased, attributing
The high removal efficiency of 99.99% also applies to var-
2+
2+
to the formation of polythiourea-Hg complexes (Figure
ious initial [Hg ] such as 10 mg/L and 0.05 mg/L.
0
4
8,49
S18).
The Stern-Volmer plot of the relative PL intensity
2+
(I /I) versus [Hg ] suggests that the quenching constant
0
30
12
Ksv,I = 11 500 L/mol
24
Ksv,II = 57 300 L/mol
H
N
9
Ksv,III = 224 900 L/mol
III
6
18
S
S
12
II
3
0
N
N
N
n
H
H
H
I
6
0
2
4
6
8
10
2+
[
Hg ] (µM)
0
2+
+
+
2+
2+
3+
2+
2+
2+
3+
3+
2+
3+
2+
2+
+
2+
2+
3+
3+
blank Hg Na K Mg Ca Al Pb Mn Fe Fe Ru Co Ir Ni Cu Ag Zn Cd Ce Sm
Figure 4. Fluorescence detection of mercury ion with polythiourea. Relative intensity (I /I) at 493 nm of P1/2b/3d in DMF/H O
mixture (v/v, 1/1, 10 μM) in the presence of different metal ions (10 μM) and the corresponding fluorescence photos taken under
0
2
UV irradiation. I = fluorescence intensity in the absence of metal ions. Inset: Stern-Volmer plot of relative intensity (I /I) of
0
0
2
+
2+
P1/2b/3d in DMF/H O mixtures (v/v, 1/1, 10 μM) versus [Hg ]. I = PL intensity in the absence of Hg . Excitation wavelength:
2
0
336 nm.
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Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
A
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
emissive, soluble
non-emissive, insoluble
B
C
2
+
D
15.0
99.85%
µ
g/L
E
1.0
0.8
[
Hg ]
0
0
0
10 20 40 60 80 100
0.6 4.8 16 33 190 270
(mg/2L+)
H
N
1
5
0
5
0
[Hg ]
S
(µg/L)
S
N
N
N
H
n
H
H
1
0.6
0.4
0.2
6
9
.6
µg/L
9.93%
5.0
> 99.99%
1.6
µg/L
µg/L
> 99.99%
0
>
.8
µ
g/L
99.99%
0.09
0.18
0.27
0.36
0.45
0
10
20
30 180
µg/L)
270
2+
mP1/2b/3d (mg)
[Hg ] (
Figure 5. (A) Schematic diagram of facile mercury removal process. (B) The proposed mechanism for mercury removal
with polythioureas. (C) The mercury removal efficiencies of both DMF solution and solid powder of P1/2a/3a with 2 mL of
Hg solution (60 mg/L). 20 mL of Hg solution was used for three precipitation-filtration cycles. n.d. = not detectable.
(D) The mercury removal efficiencies of different amount of P1/2b/3d in DMF solution with 2 mL of Hg solution ([Hg ]0
= 10 mg/L). (E) The plot of relative emission intensity (I/I ) versus [Hg ] when DMF solution of P1/2b/3d (0.27 mg/mL)
2+
†
2+
2+
2+
2+
0
2+
2+
was mixed with HgCl solutions with [Hg ] ranging from 10 to 100 mg/L. I = PL intensity in the absence of Hg . Excita-
tion wavelength: 336 nm. Inset: fluorescence photographs of the resultant solutions taken upon UV irradiation.
2
0
0
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The mercury sensing and removal functionalities can
CONCLUSIONS
Page 8 of 11
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
be further combined in fluorescent polythioureas which
serve both as fluorescent indicators and removal adsor-
bents. In fact, fluorescent P1/2b/3d prepared from aro-
matic isocyanide possesses better performance than
P1/2a/3a. When DMF solutions of 0.09-0.45 mg P1/2b/3d
In this work, the first example of room temperature one-
step conversion from elemental sulfur to functional poly-
thioureas is demonstrated through a catalyst-free multi-
component polymerization of sulfur, dialiphatic amines,
and diisocyanides. This MCP enjoys unique advantages of
mild condition at room temperature under nitrogen or in
air, cheap monomers and no catalyst, high efficiency and
convenience, high atom economy and wide monomer
scope, which can be applied to versatile primary amines,
secondary amines, aliphatic isocyanides, and aromatic
isocyanides, producing soluble polythioureas with high
2+
were added to 2 mL of HgCl solution with the [Hg ] of
2
0
2
+
10 mg/L, the remaining [Hg ] is gradually decreased to
0.8 μg/L below the standard limit of drinking water, with
the removal efficiency higher than 99.99% (Figure 5D).
Alternatively, when polymer solution was added into
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2+
HgCl solutions with [Hg ] ranging from 10 to 100 mg/L,
2
0
2+
the remaining [Hg ] lay between 0.6 to 270 μg/L, accom-
panying with gradual fluorescence decrease (Figure 5E
yields, large M s, and great diversity of well-defined pol-
w
ymer structures. The real-time kinetic process of this
MCP suggests rapid completion of the polymerization in
2+
and Figure S19). The [Hg ] can hence be correlated with
the fluorescence intensity, enabling real time monitoring
of removal process of mercury contaminants.
o
10 min at 100 C or in 2 h at room temperature. The poly-
thioureas can serve both as mercury sensors with high
sensitivity and high selectivity, and efficient mercury re-
moval adsorbents for polluted water with the cleaning
process monitored simultaneously by fluorescence
change. It is anticipated that the MCP can provide an
economic, convenient, and efficient tool for the direct
conversion of elemental sulfur to functional materials,
solving problems regarding to sulfur hoarding and sul-
fur/mercury pollution, which kills two birds with one
stone and may eventually benefit industry and environ-
ment.
EXPERIMENTAL SECTION
General procedure of the multicomponent
o
polymerization at 100 C. The typical procedure for the
o
MCP of 1, 2a, and 3a at 100 C was given below as an ex-
ample. Elemental sulfur 1 (77 mg, 2.40 mmol), 1,4-
benzenedimethanamine 2a (82 mg, 0.60 mmol), and 1,4-
benzenedimethanisocyanide 3a (94 mg, 0.60 mmol) were
added into a 10 mL Schlenk tube equipped with a magnet-
ic stir bar under nitrogen or in air. 0.4 mL of DMF and 0.2
mL of toluene were then injected into the tube and stirred
o
at 100 C for 1 h. The polymerization solution was then
ASSOCIATED CONTENT
cooled to room temperature and diluted with 4.0 mL of
DMF, which was then precipitated by adding the mixture
dropwise into 80 mL of methanol through a cotton filter.
The precipitates were filtrated and washed with methanol
for three times (3 × 20 mL), and dried under vacuum to a
constant weight to afford polymer P1/2a/3a as a white
solid in 88% yield. M = 73 800 g/mol, M /M = 2.52. IR
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website. Materials/instrumentation, syn-
thetic procedures, in situ IR and mercury removal proce-
dures, and characterization data; effect of solvent, reaction
temperature, loading ratio of sulfur, monomer concentra-
tion, and time course on the polymerization; stacked in situ
w
w
n
-
1
o
1
(
KBr disk), ν (cm ): 3267, 3053, 2918, 1544 (C=S), 1423,
IR profiles at 100 C and room temperature; IR spectra, H
1
3
1
NMR and C NMR spectra of the model compound 9 and
polythioureas P1/2a-d/3a-d; all the original HRMS spectra,
H NMR, and C NMR spectra; TGA spectra of the polymers
1
375, 1341, 1280, 1223. H NMR (500 MHz, DMSO-d ), δ
6
1
3
(
TMS, ppm): 7.89 (s, 4H), 7.23 (s, 8H), 4.64 (s, 8H). C
1
13
NMR (125 MHz, DMSO-d ), δ (TMS, ppm): 183.5 (C=S),
6
P1/2a-d/3a-d; UV-vis and PL spectra of the polythioureas
138.3, 127.7, 47.4 (CH2).
P1/2a-d/3a-d; and PL spectra of P1/2b/3d in DMF and H O
2
General procedure of the room temperature mul-
ticomponent polymerization. The typical procedure for
the MCP of 1, 2a, and 3a at room temperature was given
below as an example. Elemental sulfur 1 (77 mg, 2.4
mmol), 1,4-benzenedimethanamine 2a (90 mg, 0.66
mmol), and 1,4-benzenedimethanisocyanide 3a (94 mg,
mixture with mercury ion.
AUTHOR INFORMATION
Corresponding Author
*
*
(R. H.) msrrhu@scut.edu.cn
(B. Z. T.) tangbenz@ust.hk
0
.60 mmol) were added into a 10 mL Schlenk tube
Notes
equipped with a magnetic stir bar under nitrogen or in
air. 0.4 mL of DMF and 0.2 mL of toluene were then in-
jected into the tube and stirred at room temperature for 4
h. The polymerization solution was then diluted with 4.0
mL of DMF, which was then precipitated by adding the
mixture dropwise into 80 mL of methanol through a cot-
ton filter. The precipitates were filtered and washed with
methanol for three times (3 × 20 mL), and dried under
vacuum to a constant weight to afford polymer P1/2a/3a
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was partially supported by the National Science
Foundation of China (21774034, 21490573, 21490574, and
21788102), the Young Elite Scientist Sponsorship Program of
the China Association of Science and Technology
(
2015QNRC001), the Natural Science Foundation of Guang-
dong Province (2016A030306045 and 2016A030312002), the
Innovation and Technology Commission of Hong Kong (ITC-
CNERC14SC01).
as a white solid in 94% yield. M = 35 200 g/mol, M /M =
w
w
n
1
.68.
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