Catalyst-free thiol-yne click polymerization: A powerful and facile tool for preparation of functional poly(vinylene sulfide)s

Article abstract of DOI:10.1021/ma402559a

The thio-click polymerization is a well-expanded concept of click polymerization. Among the click polymerizations, the thiol-yne click polymerization is less developed and still in its infancy stage. In general, UV light, elevated temperature, amine, or transition metal complexes is needed to catalyze the thiol-yne click polymerization, which greatly complicates the experimental operation and limits its application. In this work, a facile and powerful thiol-yne click polymerization was developed, which could be carried out under very mild conditions without using external catalyst. Simply mixing the aromatic diynes (1a-1e) and dithiols (2-4) with equivalent molar ratio in THF at 30 C will readily produce soluble and regioregular functional poly(vinylene sulfide)s (PIa-PIe, PII, and PIII) with high molecular weights (M_w up to 85 200) in excellent yields (up to 97%) after as short as 2 h. Furthermore, no double addition product of an ethynyl group was found. This catalyst-free thiol-yne click polymerization has remarkably simplified the reaction conditions and will facilitate the preparation of functional materials applied in diverse areas.

Full text of DOI:10.1021/ma402559a

Article
pubs.acs.org/Macromolecules
Catalyst-Free Thiol−Yne Click Polymerization: A Powerful and Facile
Tool for Preparation of Functional Poly(vinylene sulfide)s
Bicheng Yao,† Ju Mei,† Jie Li,§ Jian Wang,† Haiqiang Wu,† Jing Zhi Sun,† Anjun Qin,*,†,‡
and Ben Zhong Tang*,†,‡,§
†MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering,
Zhejiang University, Hangzhou 310027, China
‡Guangdong Innovative Research Team, State Key Laboratory of Luminescent Materials and Devices, South China University of
Technology, Guangzhou 510640, China
§Department of Chemistry, Institute for Advanced Study, Institute of Molecular Functional Materials, and State Key Laboratory of
Molecular Neuroscience, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong China
S
* Supporting Information
ABSTRACT: The “thio-click” polymerization is a well-expanded concept of
click polymerization. Among the click polymerizations, the thiol−yne click
polymerization is less developed and still in its infancy stage. In general, UV
light, elevated temperature, amine, or transition metal complexes is needed to
catalyze the thiol−yne click polymerization, which greatly complicates the
experimental operation and limits its application. In this work, a facile and
powerful thiol−yne click polymerization was developed, which could be carried
out under very mild conditions without using external catalyst. Simply mixing
the aromatic diynes (1a−1e) and dithiols (2−4) with equivalent molar ratio in
THF at 30 °C will readily produce soluble and regioregular functional
poly(vinylene sulfide)s (PIa−PIe, PII, and PIII) with high molecular weights
(Mw up to 85 200) in excellent yields (up to 97%) after as short as 2 h.
Furthermore, no double addition product of an ethynyl group was found. This
catalyst-free thiol−yne click polymerization has remarkably simplified the reaction conditions and will facilitate the preparation of
functional materials applied in diverse areas.
ization.3,4 Recently, great progress has also been made in the
INTRODUCTION
■
development of other type click polymerizations, for example,
The development of powerful and facile polymerization
reactions is of vital importance to polymer science, through
which materials with advanced properties could be facilely
prepared. In general, most, if not all, polymerization processes
are developed from known organic reactions of small
molecules. However, it is not an easy task to develop an
organic reaction into a successful polymerization technique
the metal-free azide−alkyne,5 the Diels−Alder,6 and thiol−ene
click polymerizations.7
Although there are tremendous reports on the azide−alkyne
click polymerizations, the research on the “thio-click” polymer-
izations, especially the thiol−yne click polymerization, is still in
its infancy stage.8,9 New type reactions, novel catalyst systems
other than the dominated ones, i.e. photon, heat, organic base,
because several important issues should be taken into account
and transition-metal complexes, as well as new functionalities of
seriously, for example, the efficiency of catalyst system, the
the resultant polymers are waiting for further development.
scope and availability of monomer, the tolerance of functional
Our research groups have been working on the development
group, the optimization of the polymerization conditions, the
of new polymerizations based on triple-bond building blocks
control of molecular weights, and regio- and stereo-structures
for years.10 As a natural extension of our research, we have
as well as the solubility and processability of the resultant
expanded our efforts to develop the alkyne-based click reactions
polymers. Thus, an ideal organic reaction for this specific
into powerful polymerization techniques. We have succeeded in
establishing the Cu(I)-catalyzed and metal-free azide−alkyne
click polymerizations and preparing functional polytriazoles
with linear and hyperbranched structures.11 Attracted by the
purpose must be highly efficient and could be carried out under
mild conditions. Among the reported organic reactions, the
click chemistry, proposed by Sharpless and co-workers in
2001,1 was found to meet such requirements and thus
considered to be a promising candidate to be developed into
a powerful polymerization technique. Indeed, the Cu(I)-
catalyzed azide−alkyne cycloaddition,2 an archetypal click
reaction, has been developed into an efficient click polymer-
Received: December 15, 2013
Revised: January 28, 2014
Published: February 5, 2014
© 2014 American Chemical Society
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Scheme 1. Synthetic Route to Monomer 1a
versatility and efficiency of the thiol−yne click reactions, we
embarked on a project in this emerging area. The Rh-catalyzed
thiol−yne and secondary amine-mediated thiol-activated alkyne
click polymerizations have been developed, and functional
poly(vinylene sulfide)s (PVSs) have been prepared in our
group.12 Inspired by these exciting results, we further explored
other catalyst systems for the thiol−yne click polymerization.
Most recently, Zhang and co-workers reported an elegant
copper-catalyzed thiol−yne reaction.13 Interestingly, the stereo-
selectivity of this reaction could be fine-tuned by the CO2
atmosphere. Since such reaction system is efficient and robust,
we are interested in testing its possibility to be developed into a
Cu(I)-catalyzed thiol−yne click polymerization. The prelimi-
nary results showed that the polymerization of diyne (1a)
which was synthesized according to the routes shown in
Scheme 1, and 4,4′-thiodibenzenethiol (2) in the presence of
CuI at 60 °C for 10 h in N,N-dimethylformamide (DMF) or
tetrahydrofuran (THF) furnished products with weight-
averaged molecular weights (Mw) mostly less than 7000 and
yields lower than 77%. When we changed the catalyst system
from CuI to organosoluble Cu(PPh3)3Br, elevated the reaction
temperature to 70 °C, replaced the solvents DMF or THF with
toluene, and prolonged the reaction time to 12 h, the Mw values
of the resulting products were slightly increased but still less
than 10 000. Moreover, further lengthening the reaction time to
24 h in toluene could produce polymer with Mw of 16 900 in
85% yield.
Scheme 2. Syntheses of Poly(vinylene sulfide)s by Catalyst-
Free Thiol−Yne Click Polymerizations of Diynes 1 and
Dithiols 2 or 3
temperature (Table 1). While the Mw of the polymer produced
at 30 °C was almost doubled (52 600) but the PDI increased
Encouraged by these preliminary results, we further
optimized the catalyst system. For the purpose of comparison,
we carried out a control polymerization of 1a and 2 under the
same reaction conditions but without addition of the Cu(I)
catalyst. To our surprise, this polymerization furnished product
with Mw of 17 300 in moderate yield (55%). We thus changed
our strategy to conduct a systematically investigation on this
special thiol−yne polymerization.
In this paper, we report the first example of a new type of
thiol−yne click polymerization. This polymerization could be
carried out under mild reaction conditions without addition of
any catalysts. Mixing the dithiols and diynes in THF at 30 °C
will produce PVSs with high molecular weights (Mw up to 85
200) in excellent yields (up to 97%) after as short as 2 h.
Table 1. Effect of Temperature on the Thiol−Yne
a
Polymerization of 1a and 2
b
c
c
entry
T (°C)
yield (%)
S
Mw
Mw/Mn
1
2
3
4
25
30
50
70
92
93
98
93
√
√
√
Δ
27 500
52 600
90 600
85 700
1.54
1.77
2.22
2.16
a
Carried out in THF under nitrogen for 4 h; [M]0 = 50 mM.
Solubility (S) tested in common used organic solvents such as THF
b
and chloroform; √ = completely soluble, Δ = partially soluble.
c
Estimated by gel-permeation chromatography (GPC) in THF on the
basis of a polystyrene calibration; Mw = weight-average molecular
weight; Mw/Mn = polydispersity index (PDI); Mn = number-average
molecular weight.
RESULTS AND DISCUSSION
■
Catalyst-Free Thiol−Yne Click Polymerization. We first
studied the effect of temperature on the polymerization using
1a and 2 as monomers (Scheme 2). The Mw and polydispersity
(PDI) values of the products decreased with gradually lowering
the reaction temperatures from 70 to 25 °C while the yields
remained almost unchanged (>92%). Delightfully, the polymers
with Mw of 27 500 and PDI of 1.54 could be obtained in 92%
yields even when the reactions were conducted at room
slightly to 1.77 compared to those at 25 °C, we thus chose 30
°C as the preferable polymerization temperature.
Next, we carried out the polymerizations in toluene, 1,4-
dioxane, chloroform, THF, and DMF to optimize the reaction
solvent. Partially soluble products were obtained in toluene and
DMF after 1 and 4 h, respectively, and the Mw values of soluble
parts were moderate (<10 300) (Table 2). It is worth noting
that the polymer with quite low Mw was yielded in chloroform,
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Table 2. Effect of Solvent on the Thiol−Yne Polymerization
Table 4. Effect of Monomer Concentration on the Thiol−
a
a
of 1a and 2
Yne Click Polymerization of 1a and 2
b
c
c
b
c
c
entry
solvent
t (h) yield (%)
S
Mw
Mw/Mn
entry
[M]0 (mM)
yield (%)
S
Mw
Mw/Mn
1
2
3
4
5
toluene
dioxane
chloroform
THF
1
4
4
4
4
56
91
80
93
73
Δ
5 400
58 300
9 300
2.08
1.83
2.10
1.77
2.02
1
2
3
25
50
88
93
95
√
√
√
33 400
60 100
59 600
1.51
1.85
1.95
√
√
√
Δ
100
a
b
52 600
Carried out in THF at 30 °C under nitrogen for 2 h. Solubility (S)
tested in common organic solvents such as THF and chloroform; √ =
completely soluble. Estimated by gel-permeation chromatography
(GPC) in THF on the basis of a polystyrene calibration; Mw = weight-
average molecular weight; Mw/Mn = polydispersity index (PDI); Mn =
number-average molecular weight.
DMF
10 300
c
a
b
Carried out at 30 °C under nitrogen; [M]0 = 50 mM. Solubility (S)
tested in common organic solvents such as THF and chloroform; √ =
completely soluble, Δ = partially soluble. Estimated by gel-
permeation chromatography (GPC) in THF on the basis of a
polystyrene calibration; Mw = weight-average molecular weight; Mw/
Mn = polydispersity index (PDI); Mn = number-average molecular
weight.
c
Table 5. Click Polymerizations of Diynes 1 with Dithiols 2−
a
4
b
b
entry
1
monomers
polymer
yield (%)
Mw
Mw/Mn
implying the radical mechanism of such reaction. The results of
the polymerizations carried out in 1,4-dioxane and THF are
similar; we thus assigned the THF as the optimal solvent
because it is a popular solvent used in the laboratory.
Afterward, we followed the time course of the polymer-
ization. Unexpectedly, the polymerization of 1a and 2 is so
efficient that a polymer with Mw of 38 300 was yielded even
after as short as 1 h (Table 3), which is also more efficient than
1a + 2
1a + 2
1a + 2
1b + 2
1c + 2
1d + 2
1e + 2
1a + 3
PIa
PIa
PIa
PIb
PIc
PId
PIe
PII
PIII
93
91
96
92
78
90
97
95
75
60 100
84 800
85 200
17 600
29 900
53 900
9 100
1.85
2.05
2.15
2.74
3.11
2.40
2.48
1.49
1.65
c
2
d
3
4
5
6
7
8
9
21 300
6 200
e
1a + 4
Table 3. Time Course on the Thiol−Yne Polymerization of
a
a
Carried out in THF at 30 °C under nitrogen for 2 h; [M]0 = 50 mM.
Estimated by gel-permeation chromatography (GPC) in THF on the
1a and 2
b
b
c
c
entry
t (h)
yield (%)
S
Mw
Mw/Mn
basis of a polystyrene calibration; Mw = weight-average molecular
weight; Mw/Mn = polydispersity index (PDI); Mn = number-average
1
2
3
4
5
6
1
2
93
93
√
√
√
√
√
√
38 300
60 100
60 300
52 600
59 500
60 000
1.65
1.85
1.84
1.77
1.87
1.93
c
d
molecular weight. Reacted in darkness. Reacted with UV irradiation.
e
4 = 1,5-pentanedithiol.
3
87
4
93
6
100
95
12
which could be widely applied in diverse areas. Interestingly,
the polymerization also propagated smoothly in darkness, and
no obvious difference was observed as compared to those in
daylight (entry 2, Table 5). In addition, the UV light also exerts
negligible impact on the polymerization results (entry 3, Table
5). More importantly, the polymerization could also be
performed between 1a and electron-withdrawing sulfone-
containing aromatic dithiol of 3 and aliphatic 1,5-pentanedithiol
(4), and polymers with high Mw (21 300 and 6200,
respectively) could be successfully obtained in satisfactory
yields (95 and 75%, respectively), further proving the
universality of such polymerization.
Structural Characterization. The obtained PIa-PIe, PII,
and PIII are soluble in commonly used organic solvents such as
THF and chloroform. Thanks to their excellent solubility, the
polymer structures of PIa-PIe, PII, and PIII could be
characterized spectroscopically by “wet” methods. As the
spectral profiles of PIa−PIe and PII are similar (Figure 1 and
Figures S1−S5), the FTIR spectra of PIa and its monomers 1a
and 2 were discussed here as an example (Figure 1). The
stretching vibrations of C−H and S−H in 1a and 2 were
observed at 3275 and 2557 cm−1, respectively. These
characteristic peaks, however, disappeared in the spectrum of
PIa, indicating that the triple bonds of 1a and the mercapto
groups of 2 have been reacted by the polymerization reaction.
The 1H NMR spectroscopy could offer more detailed
information about the polymer structures. To facilitate the
structure characterization of PIa−PIe and PII, model reaction
of aromatic monoyne of phenylacetylene (5) and monothiol of
a
Carried out in THF at 30 °C under nitrogen; [M]0 = 50 mM.
Solubility (S) tested in common organic solvents such as THF and
chloroform; √ = completely soluble. Estimated by gel-permeation
chromatography (GPC) in THF on the basis of a polystyrene
calibration; Mw = weight-average molecular weight; Mw/Mn
polydispersity index (PDI); Mn = number-average molecular weight.
b
c
=
those with other catalyzed systems. Since the Mw, PDI, and
yield of the resultant polymer reacted for more than 2 h remain
almost unchanged, we prefer 2 h as the reaction time.
Finally, we investigated the effect of monomer concentration
on the polymerizations, and the experiments showed that the
best results (Mw: 60 100; yield: 93%) were recorded with the
monomer concentration of 50 mM (Table 4), which was, thus,
adopted for further polymerizations.
With the optimized reaction conditions in hand, we
performed the polymerizations using other aromatic diynes
1b−1e with the dithiol 2 (Scheme 2). All the polymerization
reactions propagated smoothly, and the polymers of PIb−PIe
with high Mw (up to 53 900) in excellent yields (up to 97%)
were produced, manifesting the universality of this powerful
and efficient polymerization (Table 5).
As far as we know, the predominant thiol−yne polymer-
izations are initiated or catalyzed by the UV light, thermal,
organic base, or transition metal complexes, but no catalyst-free
system has ever been reported. It is no doubt that such a
polymerization reaction will remarkably simplify the reaction
conditions and facilitate the preparation of functional materials
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Figure 1. FTIR spectra of monomers (A) 1a and (B) 2 and (C)
polymer PIa.
Figure 2. 1H NMR spectra of (A) compound 7 and (B) crude product
of model reaction with equimolar of 5 and 6 in CDCl3. The solvent
peaks are marked with asterisks.
p-thiocresol (6) was performed under the same reaction
conditions as the polymerization ones (Scheme 3).
Theoretically, the reaction of alkyne and thiols could proceed
through Markovnikov and anti-Markovnikov addition routes to
yield regioisomers with branched and linear structures,
units of vinyl sulfides could be observed and be readily assigned
due to the difference in their coupling constants. The
resonances at δ 6.45 and 6.58 are assigned to the Z-isomeric
units, whereas the peak at δ 6.76 is the resonance of one of the
E-vinylene protons (another is seriously overlapped with the
aryl protons). The E/Z ratio of PIa thus could be calculated
from their integrals, which is 44/56. Similar results were also
respectively.14 Figure 2 shows the H NMR spectra of the
1
crude product which was obtained by merely evaporating THF
after reaction and the purified compound. After carefully
analyzing these spectra, we found that solely anti-Markovnikov
product of 7, in which the vinyl protons presented as two
singlet peaks below δ 6.0, was obtained.12 The GC-MS
measurement of the crude product also excluded the formation
of 8 and other theoretically possible disulfide derivatives
(Figure S6). These results suggest the catalyst-free thiol−yne
reaction could furnish regioregular product and thus could be
regarded as a kind of click reaction. Furthermore, as can be seen
1
observed in the H NMR spectra of other PVSs (Figures S7−
S12).
The 13C NMR spectrum of polymer PIa shows no resonance
peaks of the ethynyl carbon atoms of monomer 1a at δ 83.7 and
77.7 (Figure 4). Furthermore, new peaks corresponding to the
resonances of the olefinic carbons were observed at downfield.
These results again indicate the conversion of the CC triple
bonds of 1a into the CC double bonds in PIa. Similar results
were observed for PIb-PIe, PII, and PIII as well (Figures S13−
S18).
1
from the H NMR spectrum of 7 that there are no resonances
of double addition products existed probably due to the
aromatic conjugation effect of formed vinyl sulfides.12b
On the basis of the above results, we characterized our PVSs
1
by NMR techniques. Figure 3 shows the H NMR spectra of
PIa and its monomers 1a and 2 in chloroform-d as an example.
The ethynyl and mercapto protons of 1a and 2 resonate at δ
3.09 and 3.46, respectively, which almost disappear in the
spectrum of PIa, further substantiating the conclusion drawn
from the IR analysis. As suggested by the 1H NMR spectrum of
7, we could readily assign the resonances at δ 6.45, 6.58, and
6.76 to the linear vinyl sulfide units. Furthermore, two isomeric
Proposed Mechanism. In general, the UV light or elevated
temperature initiated free-radical, amine-mediated nucleophilic
addition, and transition-metal involved migratory insertion are
the mostly studied mechanisms for the thiol−yne reaction-
s.12,14a,15 As aforementioned, the polymerization results of 1a
and 2 in chloroform which is a chain transfer reactant in a
radical polymerization have suggested a free-radical mechanism
Scheme 3. Model Reaction of Phenylacetylene (5) and p-Thiocresol (6)
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1
Figure 3. H NMR spectra of monomers (A) 1a and (B) 2 and (C)
polymer PIa in CDCl3. The solvent peaks are marked with asterisks.
for this click polymerization.14a,c,16 To confirm it, we carried
out a series of controlled experiments.
Figure 4. 13C NMR spectra of monomers (A) 1a and (B) 2 and (C)
polymer PIa in CDCl3.
It is well-known that γ-terpinene (1-isopropyl-4-methylcy-
clohexa-1,4-diene) could serve as a radical trapper. We thus
added this compound to the polymerization system of 1a and 2
before the reaction. As expected, the Mw of yielded polymers
greatly decreased from 60 900 to 1000 (Table 6). We thus
could draw a conclusion that the dominant mechanism of our
reported catalyst-free thiol−yne click polymerizations are free-
radical processes but no catalyst, light source, or heating is
needed, showing the advantage of spontaneity.
Thermal Stability. The thermal properties of the PVSs of
PIa−PIe and PII were evaluated by thermogravimetric analysis
(TGA) under nitrogen. The 5% weight losses of these polymers
are at temperatures higher than 303 °C (Figure 5). It is worth
noting that the char yields of PId and PIe are as high as 60%
probably due to the conjugated aromatic structures, whereas
the relatively low char yields of PIa−PIc are likely ascribed to
their containing alkyl chains.
Light Refractivity. With a detailed survey on the polymer
structures, we can find that PVSs of PIa−PIe and PIIa are rich
in aromatic rings and sulfur atoms, making them possible to
possess high refractive index (RI) and find broad applications in
the areas of lenses, prisms, optical waveguides, memories, and
holographic image recording systems, etc.8c,17 Indeed, all the
PVSs exhibit high RI values (n). Wavelength-dependent
refractivity measurement reveals that the RI values of these
PVSs are higher than 1.63 in the wavelength region of 400−
1600 nm (Figure 6). It is worth noting that these RI values are
much higher than those of commercially important optical
plastics, such as polycarbonate (n = 1.581 at 632.8 nm) and
Table 6. Polymerization of 1a with 2 in the Presence of γ-
Terpinene
a
b
c
d
d
entry
[add] (mM)
yield (%)
S
Mw
Mw/Mn
1
2
3
0
50
97
63
53
√
√
√
60900
1400
1000
1.98
1.50
1.36
100
a
Carried out in THF at 30 °C under nitrogen for 2 h; [M]0 = 50 mM.
b
c
add = γ-terpinene. Solubility (S) tested in common organic solvents
d
such as THF and chloroform; √ = completely soluble. Estimated by
gel-permeation chromatography (GPC) in THF on the basis of a
polystyrene calibration; Mw = weight-average molecular weight; Mw/
Mn = polydispersity index (PDI); Mn = number-average molecular
weight.
polystyrene (n = 1.587 at 632.8 nm).18 Among these PVSs, PId
shows the best light refractivity (n = 1.771 at 632.8 nm and
1.702 at 1550 nm) probably due to the higher conjugation and
stronger polarizability as well as higher content of hetero atoms.
In addition, no or little birefringence for PVSs was detected,
indicative of the amorphous nature of their thin solid films.
Aggregation-Induced Emission. PIe contains the moiety
of tetraphenylethene (TPE), an archetypical luminogen
featured the unique aggregation-induced emission (AIE)
characteristics: it is virtually nonluminescent when molecularly
dissolved in its good solvents but emits intensely when
aggregated in its poor solvents or fabricated into thin solid
films.19 Does PIe behave in a similar way? To answer this
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Figure 5. TGA thermograms of polymers PIa−PIe and PII. Td
represents the temperature of 5% weight loss.
Figure 6. Light refraction spectra of thin solid films of polymers PIa−
PIe and PII.
Figure 7. (a) PL spectra of PIe in THF and THF/water mixtures.
Polymer concentration: 10 μM. Excitation wavelength: 330 nm. (b)
Plot of relative PL intensity versus water fraction in THF/water
mixtures, where I = peak intensity and I0 = peak intensity in pure THF.
Inset: fluorescent images of PIe in THF and THF/water fractions
taken under a hand-held UV lamp.
question, we studied its photoluminescence (PL) behaviors in
the solution and aggregated states.
Figure 7 shows the PL spectra of PIe in THF and THF/
water mixtures with different water fractions. When excited at
330 nm, the PL spectrum of the diluted solution of polymer
gives almost a flat line parallel to the abscissa, manifesting that
PIe is weakly emissive when molecularly dissolved. As shown in
the inset of Figure 7b, a faint green emission was observed in
the THF/water mixture with 20% water fraction under UV
light. Afterward, the emission gradually intensified and the
strongest emission was recorded in THF/water mixture with
90% water fraction, which is 66-fold higher than that in pure
THF. It is worthy to note that the maximum emission peaks at
∼520 nm remain unchanged with addition of water, which is
similar to the behaviors of TPE but with ∼50 nm red-shift as a
result of the extended conjugation in PIe.
Instruments. FT-IR spectra were recorded on a Bruker Vector 22
1
spectrometer as thin films on KBr pellets. H and 13C NMR spectra
were measured on a Bruker AV 500, Bruker AV 400 or Varian NMR
300 spectrometer in chloroform-d using tetramethylsilane (TMS; δ =
0) as internal reference. Elemental analysis was performed on a
ThermoFinnigan Flash EA 1112. High-resolution mass spectra
(HRMS) were recorded on a GCT premier CAB048 mass
spectrometer operated in MALDI-TOF mode. Gas chromatogra-
phy−mass spectrometry (GC-MS) was performed on an Agilent GC-
6890/MS-5973. Relative molecular weights (Mw and Mn) and
polydispersity indices (PDI, Mw/Mn) of the polymers were estimated
by a Waters PL-GPC-50 gel permeation chromatography (GPC)
system equipped with refractive index (RI) detector, using a set of
monodisperse polystyrenes as calibration standards and THF as the
eluent at a flow rate of 1.0 mL/min. Thermal stabilities were evaluated
by measuring thermogravimetric analysis (TGA) thermograms on a
PerkinElmer TGA 7 under dry nitrogen at a heating rate of 10 °C/
min. Refractive index (RI) values were determined on a Metricon
Models 2010 and 2010/M prism coupler thin film thickness/refractive
index measurement system. UV−vis spectra were measured on a
Varian VARY 100 Bio UV−vis spectrophotometer. Photolumines-
cence (PL) spectra were recorded on a Shimadzu RF-5301PC
spectrofluorophotometer.
EXPERIMENTAL SECTION
■
Materials. 4,4′-Thiobisbenzenethiol (2) was purified before use by
standard method. 1,5-Pentanedithiol (4), phenylacetylene (5), p-
thiocresol (6), and other chemicals and reagents were purchased from
Sigma-Aldrich or Alfa and used as received without further
purification. Tetrahydrofuran (THF), toluene, and dioxane were
distilled under nitrogen at normal pressure from sodium benzophe-
none ketyl immediately prior to use. Triethylamine (Et3N) was
distilled and dried over potassium hydroxide. DMF was extra-dry
grade.
For the AIE measurement, a stock solution of PIe in THF (1 × 10−4
M) was first prepared. Aliquots of this stock solution were transferred
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into volumetric flasks (10 mL), into which appropriate volumes of
THF and water were added dropwise under vigorous stirring to
furnish 1 × 10−5 M solutions with different water contents (0−90 vol
%). UV and PL spectra were measured immediately after the solutions
were prepared.
Monomer Preparation. The synthetic route of model monomer
1a is shown in Scheme 1. The other monomers were prepared
according to previously published procedures, and the detailed
synthetic routes are given in the Supporting Information. Detailed
experimental procedures for the synthesis of 1a are given below as an
example.
polymer was washed with hexane and dried under vacuum at room
temperature to a constant weight.
The control polymerizations for mechanism study were performed
with similar procedures except that the γ-terpinene was injected into
the reaction system using a syringe before the addition of solvent.
Preparation of Model Compound. The synthetic route to
model compound 7 is shown in Scheme 3. Into a 10 mL Schlenk tube
were placed phenylacetylene (5, 102 mg, 1.0 mmol) and p-thiocresol
(6, 124 mg, 1.0 mmol). After being evacuated and refilled with
nitrogen for three times, THF (1.0 mL) was injected into the tube
using a hypodermic syringe. The mixture was stirred at 30 °C for 4 h.
After solvent evaporation, the crude product was purified by a silica gel
column chromatography using PE as eluent. Light yellow oily product
of 7 was obtained in 89% yield (202 mg). 1H NMR (300 MHz,
CDCl3), δ (TMS, ppm): 7.57−7.17 (Ar−H), 6.91 (d, J = 15.3 Hz, 
C−H from the E-vinylene unit), 6.70 (d, J = 15.3 Hz, C−H from
the E-vinylene unit), 6.55 (d, J = 10.8 Hz, C−H from the Z-vinylene
unit), 6.50 (d, J = 10.8 Hz, C−H from the Z-vinylene unit), 2.38 (s,
CH3).
4,4′-(Isopropylidenediphenyl)-bis(4-bromobenzyl) ether (11). To a
solution of bisphenol A (1.694 g, 7.4 mmol) and 1-bromo-4-
(bromomethyl)benzene (4.081 g, 16.3 mmol) in acetone (60 mL)
was added 2.557 g of potassium carbonate (18.5 mmol). The resulted
suspension was heated with refluxing overnight and then cooled to
room temperature. After filtration and solvent evaporation, the crude
product was purified by a silica gel column chromatography using
petroleum ether (PE) as eluent. A white needle-like product 11 was
1
obtained in 99% yield (4.128 g). H NMR (400 MHz, CDCl3), δ
Characterization Data of PIa. White powder; yield: 93%. Mw 60
(TMS, ppm): 7.50 (d, 4H, Ar−H), 7.30 (d, 4H, Ar−H), 7.14 (d, 4H,
Ar−H), 6.85 (d, 4H, Ar−H), 4.99 (s, 4H, CH2), 1.64 (s, 6H,
CH3CCH3).
100; Mw/Mn 1.85. IR (thin film), ν (cm−1): 2960, 1606, 1510, 1475,
1
1383, 1302, 1242, 1182, 1099, 1065, 1010, 939, 827, 559, 495. H
NMR (400 MHz, CDCl3), δ (TMS, ppm): 7.58−7.17 (Ar−H), 6.90
(Ar-H and C−H from the E-vinylene unit), 6.82 (d, J = 14.8 Hz, 
C−H from the E-vinylene unit), 6.64 (d, J = 10.4 Hz, C−H from
the Z-vinylene unit), 6.51 (d, J = 10.4 Hz, C−H from the Z-vinylene
unit), 5.06 (CH2), 3.10 (C−H), 1.66 (CH3). 13C NMR (100 MHz,
CDCl3), δ (ppm): 157.2, 144.0, 136.6−123.4, 114.8, 70.3, 42.4, 31.7.
Characterization Data of PIb. White powder; yield: 92%. Mw 17
600; Mw/Mn 2.74. IR (thin film), ν (cm−1): 2956, 1593, 1473, 1390,
4,4′-(Isopropylidenediphenyl)-bis{[4-(2,2-trimethylsilyl)ethynyl]-
benzyl} ether (13). Into a 250 mL round-bottom flask were added
PdCl2(PPh3)2 (197 mg, 0.28 mmol), CuI (107 mg, 0.56 mmol), PPh3
(220 mg, 0.84 mmol), 11 (3.964 g, 7 mmol), and a mixture of THF/
TEA/piperidine (60:30:10 v/v/v) (100 mL) under nitrogen. After the
catalysts were completely dissolved, trimethylsilylacetylene (12, 3.0
mL, 21 mmol) was injected. The solution was stirred at 50 °C for 2
days, and then the formed precipitates were removed by filtration and
washed with diethyl ether. The filtrate was concentrated by a rotary
evaporator under reduced pressure, and the crude product was purified
by a silica gel column chromatography using PE/dichloromethane
(DCM) (10:1 v/v) as eluent. White powder of 13 was obtained in
1
1250, 1105, 1068, 1010, 939, 810, 775, 683, 528, 492. H NMR (400
MHz, CDCl3), δ (TMS, ppm): 7.57−7.32 (Ar−H), 6.89 (d, J = 15.2
Hz, C−H from the E-vinylene unit), 6.80 (d, J = 15.2 Hz, C−H
from the E-vinylene unit), 6.62 (d, J = 10.0 Hz, C−H from the Z-
vinylene unit), 6.51 (d, J = 10.0 Hz, C−H from the Z-vinylene unit),
0.58 (CH3). 13C NMR (75 MHz, CDCl3), δ (ppm): 137.2, 134.8,
134.5, 132.9, 131.9, 130.4, 128.3, 125.7, 123.3, −2.1.
1
95% yield (3.980 g). H NMR (400 MHz, CDCl3), δ (TMS, ppm):
7.47 (d, 4H, Ar−H), 7.35 (d, 4H, Ar−H), 7.13 (d, 4H, Ar−H), 6.84
(d, 4H, Ar−H), 5.02 (s, 4H, CH2), 1.63 [s, 6H, C(CH3)2], 0.26 [s,
18H, Si(CH3)3].
Characterization Data of PIc. Yellow powder; yield: 78%. Mw 29
900; Mw/Mn 3.11. IR (thin film), ν (cm−1): 2954, 1575, 1493, 1475,
1
4,4′-(Isopropylidenediphenyl)-bis(4-ethynylbenzyl) ether (1a). Into
a 250 mL round-bottom flask was added 13 (3.305 g, 5.5 mmol) and
THF (60 mL). Then KOH (2.468 g, 44 mmol) dissolved in methanol
(80 mL) was added. The mixture was stirred at room temperature
overnight. After most of the solvent was evaporated, 1 M HCl solution
(50 mL) was added. The aqueous solution was extracted with DCM
for three times. The organic phases were combined and washed with
water and brine and then dried over MgSO4 for an hour. After
filtration and solvent evaporation, the crude product was purified by a
silica gel column chromatography using PE/DCM (10:1 v/v) as
eluent. White powdery product of 1a was obtained in 91% yield (2.275
g). IR (thin film), ν (cm−1): 3275 (C−H stretching), 2108 (weak
CC stretching). 1H NMR (300 MHz, CDCl3), δ (TMS, ppm): 7.50
(m, 4H, Ar−H), 7.38 (m, 4H, Ar−H), 7.14 (m, 4H, Ar−H), 6.85 (m,
4H, Ar−H), 5.03 (s, 4H, CH2), 3.09 (s, 2H, CH), 1.64 [s, 6H,
C(CH3)2]. 13C NMR (75 MHz, CDCl3), δ (ppm): 156.6, 143.8, 138.2,
132.6, 128.0, 127.5, 121.8, 114.4, 83.7, 77.7, 69.7, 42.0, 31.3. Anal.
Calcd for C33H28O2: C, 86.81; H, 6.18. Found: C, 86.88; H, 5.83.
Polymer Synthesis. All the polymerization reactions were carried
out under nitrogen atmosphere using a standard Schlenk technique. A
typical procedure for the polymerization of 1a and 2 is given below as
an example.
1419, 1388, 1205, 1099, 1070, 1030, 1010, 953, 814, 746, 490. H
NMR (400 MHz, CDCl3), δ (TMS, ppm): 7.41−7.28 (Ar−H), 7.05−
6.94 (Ar−H and C−H), 6.87 (C−H), 6.49 (d, J = 10.4 Hz, C−
H from the Z-vinylene unit), 4.06 (CH2), 1.80 (CH2), 1.52 (CH2),
1.01 (CH3). 13C NMR (100 MHz, CDCl3), δ (ppm): 151.1, 135.9−
123.3, 113.8, 111.5, 69.5, 32.1, 20.1, 14.6.
Characterization Data of PId. Pale yellow powder; yield: 90%. Mw
53 900; Mw/Mn 2.40. IR (thin film), ν (cm−1): 2918, 1593, 1504, 1473,
1325, 1278, 1178, 1095, 1068, 1010, 953, 812, 756, 694, 525. 1H NMR
(400 MHz, CDCl3), δ (TMS, ppm): 7.41−7.00 (Ar−H), 6.72 (d, J =
16.0 Hz, C−H from the E-vinylene unit), 6.70 (d, J = 16.0 Hz, 
C−H from the E-vinylene unit), 6.53 (d, J = 9.6 Hz, C−H from the
Z-vinylene unit), 6.34 (d, J = 9.6 Hz, C−H from the Z-vinylene
unit). 13C NMR (100 MHz, CDCl3), δ (ppm): 147.1, 146.5, 135.6,
133.4, 132.0−129.4, 127.8, 127.1, 125.0, 123.6, 120.1.
Characterization Data of PIe. Yellow powder; yield: 97%. Mw
9100; Mw/Mn 2.48. IR (thin film), ν (cm−1): 3292, 2974, 1597, 1574,
1473, 1442, 1388, 1180, 1099, 1068, 1010, 939, 914, 848, 816, 758,
1
700, 628, 491. H NMR (400 MHz, CDCl3), δ (TMS, ppm): 7.26−
7.01 (Ar−H), 6.71 (C−H), 6.65 (C−H), 6.46 (C−H), 6.37
(C−H). 13C NMR (100 MHz, CDCl3), δ (ppm): 143.5, 142.7,
140.8, 134.5, 131.5, 130.4, 128.2, 126.6, 125.5.
Thiol−Yne Click Polymerization. Into a 10 mL Schlenk tube
were placed 1a (22.8 mg, 0.05 mmol) and 2 (12.5 mg, 0.05 mmol).
After being evacuated and refilled with nitrogen for three times, THF
(1.0 mL) was injected into the tube to dissolve the monomers. The
mixture was stirred at 30 °C for 2 h. Then, the resultant solution was
diluted with THF (2.0 mL) and added dropwise into 300 mL of
hexane through a cotton filter under stirring. The precipitate was
allowed to stand overnight and then collected by filtration. The
Characterization Data of PII. White powder; yield: 95%. Mw 21
300; Mw/Mn 1.49. IR (thin film), ν (cm−1): 2966, 1606, 1575, 1508,
1319, 1240, 1180, 1157, 1084, 1012, 829, 766, 630, 580, 509. 1H NMR
(400 MHz, CDCl3), δ (TMS, ppm): 7.83 (Ar−H), 7.50−7.37 (Ar−
H), 7.12 (Ar−H), 6.90 (d, J = 15.6 Hz, C−H from the E-vinylene
unit), 6.84 (Ar−H and C−H from the E-vinylene unit), 6.74 (d, J =
10.4 Hz, C−H from the Z-vinylene unit), 6.44 (d, J = 10.4 Hz, 
C−H from the Z-vinylene unit), 5.01 (CH2), 1.62 (CH3). 13C NMR
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(100 MHz, CDCl3), δ (ppm): 156.5, 143.4, 136.8, 135.3, 132.3,
130.7−126.5, 121.6, 119.0, 114.1, 69.5, 41.7, 31.0.
1. (e) Binder, W. H.; Sachsenhofer, R. Macromol. Rapid Commun.
2007, 28, 15. (f) Lo, C. N.; Hsu, C. S. J. Polym. Sci., Part A: Polym.
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H. Macromol. Chem. Phys. 2011, 211, 2464. (h) Schwartz, E.;
Breitenkamp, K.; Fokin, V. V. Macromolecules 2011, 44, 4735. (i) Li,
D.; Wang, X.; Jia, Y.; Wang, A.; Wu, Y. Chin. J. Chem. 2012, 30, 861.
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Junkers, T.; Schlaad, H.; Camp, W. V. Angew. Chem., Int. Ed. 2011, 50,
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Liu, Y.; Qin, J.; Li, Z. Chem.Eur. J. 2012, 18, 4426. (f) Plietzsch, O.;
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Characterization Data of PIII. White powder; yield: 75%. Mw
1
6200; Mw/Mn 1.65. H NMR (500 MHz, CDCl3), δ (TMS, ppm):
7.48−7.28 (Ar−H), 7.12 (Ar−H), 6.85 (Ar−H), 6.69 (d, J = 16.0 Hz,
C−H from the E-vinylene unit), 6.47 (C−H from the E-vinylene
unit), 6.44 (d, J = 10.5 Hz, C−H from the Z-vinylene unit), 6.23 (d,
J = 10.5 Hz, C−H from the Z-vinylene unit), 5.00 (CH2), 3.07 (
C−H), 2.78 (S−CH2−), 1.71 (CH2), 1.62 (CH3), 1.56 (CH2), 1.33
(−SH). 13C NMR (125 MHz, CDCl3), δ (ppm): 156.7, 143.4, 138.1,
136.7, 135.5, 132.4, 128.8−125.2, 114.2, 69.8, 41.7, 35.7, 31.1, 29.9.
CONCLUSION
■
In summary, we have developed a facile and efficient catalyst-
free thiol−yne click polymerization. The polymerization of
aromatic diynes and dithiols could be carried out under very
mild reaction conditions without any external stimulus and
readily furnished PVSs of PIa−PIe, PII, and PIII in high yields
with high Mw values at 30 °C after 2 h. Furthermore, this
catalyst-free thiol−yne click polymerization is regioselective,
and solely anti-Markovnikov addition products were obtained.
The PVSs enjoy good solubility, thermal stability, and film-
forming ability. Thin solid films of PVSs exhibit higher RI
values (n > 1.63) than commercially important optical plastics.
The AIE-active TPE moiety containing PVS of PIe also
possesses the AIE feature. Thus, this catalyst-free thiol−yne
click polymerization provides a powerful tool for the
preparation of functional materials for the application in
diverse areas.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Detailed synthetic routes of monomer 1b−1e and 3; FTIR, 1H
NMR, and 13C NMR spectra of PVSs PIb−PIe, PII, and PIII;
GC-MS spectrum of crude product from the model reaction.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*E-mail qinaj@zju.edu.cn (A.J.Q.).
*E-mail tangbenz@ust.hk (B.Z.T).
■
(h) Turunc,̧ O.; Meier, M. A. R. J. Polym. Sci., Part A: Polym. Chem.
̈
̈
2012, 50, 1689. (i) Konkolewicz, D.; Gray-Wealeb, A.; Perrier, S. J.
Am. Chem. Soc. 2009, 131, 18075. (j) Chen, G.; Kumar, J.; Gregory, A.;
Stenzel, M. H. Chem. Commun. 2009, 6291. (k) Naik, S. S.; Chan, J.
W.; Comer, C.; Hoyle, C. E.; Savin, D. A. Polym. Chem. 2011, 2, 303.
(l) Potzsch, R.; Komber, H.; Stahl, B. C.; Hawker, C. J.; Voit, B. I.
Macromol. Rapid Commun. 2013, 34, 1772.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by the National Science
Foundation of China (21222402 and 21174120); the key
project of the Ministry of Science and Technology of China
(2013CB834702), and the Research Grants Council of Hong
Kong (604711, 602212 and HKUST2/CRF/10). A.Q. and
B.Z.T. thank the support from Guangdong Innovative Research
Team Program (201101C0105067115).
(10) (a) Liu, J.; Lam, J. W. Y.; Tang, B. Z. Chem. Rev. 2009, 109,
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2013, 214, 175.
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Z. Macromolecules 2013, 46, 3907. (b) Wei, Q.; Wang, J.; Shen, X.;
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