Luminescent two-way reversible shape memory polymers prepared by hydroxyl-yne click polymerization

Article abstract of DOI:10.1039/d0tc03888a

Two-way reversible shape memory polymers (2W-SMPs), capable of changing their shape reversibly, are highly desirable for many potential applications. However, the polymerization reactions used for preparing 2W-SMPs always require harsh conditions, such as

Full text of DOI:10.1039/d0tc03888a

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Page 1 of 9
J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
View Article Online
DOI: 10.1039/D0TC03888A
ARTICLE
Luminescent two-way reversible shape memory polymers
prepared by the hydroxyl-yne click polymerization
a†
a†
a
a
a
a,b
Kaojin Wang, Han Si, Qing Wan, Zhiming Wang, Anjun Qin, * Ben Zhong Tang *
Received 00th January 20xx,
Accepted 00th January 20xx
Two-way reversible shape memory polymers (2W-SMPs), capable of changing their shapes reversibly, are highly desirable
for many potential applications. However, the polymerization reactions used for preparing 2W-SMPs always require harsh
conditions, such as metal catalysts, light irradiation and elevated temperature. Furthermore, there are rare reports on SMPs
integrating with other functions, such as luminescence. Herein, luminescent 2W-SMPs of semi-crystalline PCL-based
networks bearing aggregation-induced emission (AIE) moiety of tetraphenylethylene (TPE) are designed and prepared via
an organobase-catalyzed hydroxyl-yne click polymerization under mild reaction conditions. For comparison, a TPE-free
polymer network is also prepared through the same polymerization. The TPE-containing polymer network shows stronger
emission than that of TPE-containing monomer because of the activation of restriction of intramolecular rotation. Both the
polymer networks are able to perform excellent reversible shape motions, such as bending-unbending, coiling-uncoiling,
and closing-blooming, when they are exposed to cold and warm water. By taking advantages of the shape memory and
luminescence properties, the TPE-containing polymer network is used to construct a luminescent robotic gripper, which can
grab and release weights with payload-to-weight ratio much higher than that of many industrial robotic grippers. Moreover,
it could also be used to realize double anti-counterfeiting function. This work represents the first example of luminescent
DOI: 10.1039/x0xx00000x
2
W-SMPs, which might be widely applied in diverse areas.
actuators,24 switches, artificial muscles,26,27 microrobots,5,28
25
2
9,30
Introduction
flexible electronics,
and so on. However, to date, most of
the investigation is focused on the design and synthesis of 2W-
SMPs with single function, i.e., reversible shape changes,
limiting their broad applications.
Thus, endowing the 2W-SMPs with additional functions, such
as luminescence, may greatly expand their applications. For
example, when using the SMPs with NIR-II emission as
intravascular stent inside our body, we can observe where they
are by their luminescence due to their excellent tissue
Shape memory polymers (SMPs) are a kind of intelligent
materials that are capable of fixing their deformation shape and
recovering their original one when exposed to external stimuli,
1
-4
5,6
7
8
such as heat,
light,
electric field, magnetic field,
microwave,9 ultrasound, solvent,
10
11-13
ion,14 and pH.
14,15
Different from conventional one-way SMPs, which cannot
reverse their permanent shape to the temporary one unless
they are programmed by imposing an external force,
two-way shape memory polymers (2W-SMPs) can automatically
change between two distinguished shape upon exposure to two
external stimuli.5
1
6-20
the
3
1
penetration depth (>1.0 cm), which is hard to be observed by
3
2,33
other technique.
Another example is the anti-counterfeiting
application. Although the SMPs have been commercialized in
this field, they are still easily counterfeited due to the single
,21-23
Thus, such polymers can extend the
applications of SMPs in diverse areas including biomimetic
3
4
anti-counterfeiting manner. Luminescent SMPs might provide
an alternative toward this problem, and more complicated dual
anti-counterfeit purpose can be realized. Unfortunately, there
is no report on semi-crystalline 2W-SMP that integrates the
reversible shape deformation and luminescence ability in one
system though structural color materials have been reported
One of the reasons may be that conventional
organic fluorophores usually suffer from the aggregation-
caused quenching (ACQ) effect, which makes this target
a. State Key Laboratory of Luminescent Materials and Devices, Guangdong Provincial
Key Laboratory of Luminescence from Molecular Aggregates, SCUT-HKUST Joint
Research Institute, AIE Institute, Center for Aggregation-Induced Emission, South
China University of Technology (SCUT), Guangzhou 510640, China
b.
Department of Chemistry, Hong Kong Branch of Chinese National Engineering
Research Center for Tissue Restoration and Reconstruction, The Hong Kong
3
5-37
University of Science & Technology (HKUST), Clear Water Bay, Kowloon, Hong Kong, recently.
China
†K.W. and H.S. contributed equally to this work.
Electronic Supplementary Information (ESI) available: Synthetic routes to
dipropiolates and PCL-4OH prepolymers, structure characterization (Figures S1-S8), challengeable.
properties of PCL prepolymers, Thermal properties of monomers, PCL-4OH, and PCL-
Exactly opposite to the ACQ effect, aggregation-induced
based networks, and the structure of used AIEgen with red emission).
Movie S1, coiling and uncoiling shape changes of PCL3600 network
Movie S2, coiling and uncoiling shape changes of PCL5800-TPE network
Movie S3, luminescent closing and blooming shape changes of PCL5800-TPE network
Movie S4, luminescent grasping and releasing actions of a robotic gripper
See DOI: 10.1039/x0xx00000x
emission (AIE), conceptually coined by Tang et al. in 2001, refers
to a unique phenomenon that the luminogens show weak or
non-emission in solution but emit intensely in their aggregate
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Page 2 of 9
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DOI: 10.1039/D0TC03888A
ARTICLE
through the 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyzed
hydroxyl-yne click polymerization under mild reaction
conditions (Scheme 1). Thanks to their dual functions, the
resultant luminescent 2W-SMP could be fabricated into robotic
grippers and realize double anti-counterfeiting. This work not
only provides a new synthetic strategy for 2W-SMPs and
enriches their family but also expands their applications by
combining luminescence property.
Results and discussion
Scheme 1. Synthesis of PCL3600 network (A) and PCL5800-TPE
network (B) via DABCO-catalyzed hydroxyl-yne click
polymerizations.
Preparation of monomers and polymer networks
TPE-free and TPE-containing dipropiolates 1 and 2 could be
facilely synthesized via esterification reactions of propiolic acid
and
1,6-hexanediol
or
1,2-bis(4-hydroxylphenyl)-1,2-
state.38 Thus, the luminogens featuring AIE characteristics
diphenylethene, respectively. PCL prepolymers with 4 terminal
hydroxyl groups and number-average molecular weights (M
(
AIEgens) are promisingly applicable in luminescent 2W-SMPs.
n
) of
3
9,40
Among the reported AIEgens,
tetraphenylethene (TPE) has
1
2
200, 3600, 4500 and 5800 g/mol, determined by H NMR
drawn much attention because of its simple synthetic
analyses, were prepared by the ring opening polymerizations
Scheme S1 and Table S1, ESI†). The resultant prepolymers are
denoted as PCL-4OH with M values in the subscript. For
example, PCL3600-4OH indicates a PCL prepolymer with M of
600. Furthermore, both PCL networks were facile prepared by
DABCO-catalyzed hydroxyl-yne click polymerizations of PCL-
OH prepolymers and dipropiolates 1 or 2 under mild reaction
4
1,42
procedures and high fluorescence quantum yield.
Herein,
(
TPE was used as the AIE unit to design and prepare luminescent
n
2
W-SMPs.
n
In addition, to facilely prepare 2W-SMPs, efficient
3
polymerization reactions are essential. However, most of them
require harsh reaction conditions. For example, semi-crystalline
polyurethane networks that show reversible shape changes
were prepared by the polymerization of sensitive diisocyanates
4
conditions (Scheme 1).
Characterization of polymer networks
The molecular structures of dipropiolate 1, TPE-containing
4
3,44
and alcohol monomers in the presence of metal catalyst.
Furthermore, free radical polymerization of methacrylates or
1
dipropiolate 2 and PCL-4OH prepolymers were confirmed by H
acrylates4
5,46
and thiol-ene reaction
21,47
were also utilized to
1
3
and C NMR, and FT-IR spectroscopies, and satisfactory results
were obtained (Figures S1-S8, ESI†). The ethynyl protons of both
dipropiolates are detected at δ 2.87 and 3.04, respectively
construct semi-crystalline polymer networks, where photo-
irradiation is a necessary condition. Moreover, the use of
dicumyl peroxide as cross-linker to synthesize 2W-SMPs
(Figures S1 and S2, ESI†). The resonance of methylene protons
4
8,49
requires elevated temperature at a high pressure.
To
assigned to −CH CO− and −OCH − of the CL unit appear at δ 4.07
2
2
expand the application of 2W-SMPs, robust and powerful
polymerizations, which could be performed in a meal-free
manner under very mild reaction conditions, are highly needed.
Our groups have been working on the development of new
polymerization reactions based on triple-bond building
blocks.5 Recently, we succeeded in establishing many robust
alkyne-based click polymerizations, such as spontaneous thiol-
and 2.30, respectively (Figure S3, ESI†). The peak at δ 3.64 is
assignable to methylene protons next to the hydroxyl group.
The methylene protons of the pentaerythritol unit adjacent to
reacted and unreacted hydroxyl groups are resonated at δ 4.11,
and 3.59 and 3.51, respectively.
Their molecular structures were further confirmed by 13C
NMR spectra. Dipropiolate 1 show C≡C carbon resonances at δ
0-52
5
3,54
50,55-57
yne,
spontaneous amino-yne
and organobase-
7
4.86 and 74.69 (Figure S5, ESI†), and those of TPE-containing
5
8,59
catalyzed hydroxyl-yne
click polymerizations, which could
dipropiolate 2 at δ 74.11, 76.64 (Z-configuration) and 76.84 (E-
configuration), respectively (Figure S6, ESI†). The resonance
peaks of carbon atoms of carbonyl group appear at δ 173.58,
while that of the carbons adjacent to the hydroxyl groups
emerge at δ 62.60 in the spectrum of PCL3600-4OH (Figure S7,
ESI†). These results indicate that the above monomers and
prepolymers were synthesized successfully.
be carried out under very mild reaction conditions.
Given that the ε-caprolactone (CL) is gernally used to prepare
SMPs via the ring-opening polymerization, and the resultant
poly(ε-caprolactone) (PCL) is terminated by the aliphatic
hydroxyl groups,60 we thus used them to react with TPE-
containing dipropiolate to prepare luminescent 2W-SMPs
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ARTICLE
A
A
B
PCL3600 network
View Article Online
DOI: 10.1039/D0TC03888A
PCL5800-TPE network
C
C
H
H
C
C
C
C
PCL3600-4OH
PCL5800-4OH
OH
C
D
C
O
-50
0
50
100
150
C
C
Temperature (C)
C
O
B
E
C
C
C
O
4000
3000
2000
1600
1200
800
400
-1
Wavenumber (cm )
PCL5800-4OH
PCL3600-4OH
Figure 1. FT-IR spectra of dipropiolate 1 (A), TPE-containing
dipropiolate 2 (B), PCL3600-OH prepolymer (C), PCL3600 network
PCL5800-TPE network
PCL3600 network
(D), and PCL5800-TPE network (E).
Polymer networks were only characterized by FT-IR
-50
0
50
100
150
Temperature (C)
spectroscopy because they cannot be dissolved in any organic
solvents. As shown in Figure 1, the absorption peaks of
dipropiolates associated with C≡C and ≡C−H stretching
Figure 2. DSC curves of heating (A) and cooling (B) processes of
PCL-4OH prepolymers and PCL-based networks.
-1
vibrations are observed at 2111 and 3229 cm , respectively,
-1
surface of PCL crystals, thus slowing down the arrangement rate
of PCL chains into lattice.
and the absorption at 3545 cm is assignable to the stretching
vibrations of -OH group in PCL-4OH prepolymers. In the
networks, the absorption peaks associated with the stretching
vibrations of -OH and C≡C groups almost disappear and that of
4
1
Photophysical properties
-1
C=C appears at 1624 cm , indicative of the occurrence of Thanks to their containing TPE units, the photoluminescence
hydroxyl-yne click polymerization.
(PL) of TPE-containing dipropiolate 2 and PCL5800-TPE network
were studied. As shown in Figure 3, 2 shows an emission peak
at 470 nm, whereas, PCL5800-TPE network exhibits a slightly red-
shifted peak at 475 nm. Moreover, the absolute PL quantum
Thermal properties of PCL-4OH prepolymers and networks
The thermal stabilities of PCL-4OH prepolymers and networks
were measured by TGA. As indicated in Figure S9 (ESI†), the
yields (Φ
network in their film states were measured to be 4.5, 1.5 and
.4%, respectively. The higher Φ value of PCL5800-TPE network
F
) values of PCL5800-TPE network, 2, and PCL3600
decomposition temperatures (T
are above 300 °C. Moreover, all polymer residues are very low
below 2 wt%) except PCL5800-TPE network because of its
d
, 5% weight loss) of all samples
0
F
(
than that of 2 is probably because TPE units are covalently
incorporated in the polymer chains, which lead to the
restriction of the intramolecular rotation of their phenyl rings
and activation of more radiative transition.
containing aromatic TPE units.
The melting and crystallization behaviors of PCL-4OH
prepolymers and networks were investigated by DSC analysis,
and their curves are depicted in Figures 2, S10 and S11 (ESI†).
Both of melting temperatures (T
temperatures (T ) of PCL-4OH prepolymers increase with an
increase in their molecular weights. T values of PCL3600-4OH
and PCL5800-4OH were recorded to be 43 and 48 °C, while their
values are 21 and 25 °C, respectively. Compared with PCL-
OH prepolymers, T values of PCL3600 and PCL5800-TPE networks
m
) and crystallization
c
m
T
c
4
c
are decreased to -9 and -12 °C, respectively, due to the
constrained polymer chain diffusion and conformational
rearrangement. Moreover, the T
m
values decreased to 33 and
PCL5800-TPE network
TPE-containing dipropiolate 2
4
1 °C, respectively, because of lower crystal size and more
6
1
defects. It is worth noting that a weak crystallization peak at -
9.5 °C was observed in the heating curve of PCL5800-TPE,
400
450
500
550
600
1
Wavelength (nm)
indicating that TPE slows down the crystallization rate of PCL
chains. The reason might be that during crystallization of PCL
chains, TPE units are expelled out to the surface of the crystal
lamellae and finally resided on the
Figure 3. Photoluminescence spectra of the films of TPE-
containing dipropiolate 2 and PCL5800-TPE network (λex = 280
nm).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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ARTICLE
Journal Name
Reversible shape memory behaviours and luminescent properties
View Article Online
DOI: 10.1039/D0TC03888A
The thermal property measurement shows that PCL2200 network
exhibits weak crystallization peak, while the degree of
crystallinity of PCL4500 and PCL5800 networks is too high, thus,
PCL3600 network manifests the best shape memory effect due to
4
4,46
its suitable crystallinity degree.
Notabley, when TPE units
are incorporated, PCL5800-TPE network possess a better
reversible shape change than PCL3600-TPE network. The reason
is that the TPE units are expelled out of lamellar of polymer
crystals,41 thus inhibiting the crystallization of polymers and
leading to a slower crystallization rate and a lower crystallinity
degree of the former. Thus, PCL5800-TPE network was selected
to show its luminescent two-way reversible shape memory
effect (2W-SME) and PCL3600 network was used as comparison.
The 2W-SMEs under stress-free condition of PCL3600 and
PCL5800-TPE networks are shown in Figure 4 and Movies S1-S3
(
ESI†) in water baths. Based on the results of thermal property
measurement, 33 and 39 °C were selected as actuation
temperatures (T s) for PCL3600 and PCL5800-TPE networks,
A
respectively, because they are in the range of melting
temperatures. while 0 °C was used to cool them for
2
1
c
crystallization, which is below their T s. As shown in Figure 4A,
different original shapes of PCL3600 network were programmed
into V and flower ones in 70 °C water bath for melting crystals
of PCL networks and then placed into an ice-water bath to fix
them. Once the samples were heated to 33 °C and cooled to 0
°
C, different reversible shape transformations, such as bending-
unbending, coiling-uncoiling, and closing-blooming shape
changes, were realized. PCL5800-TPE network behaves similarly
to PCL3600 network between 0 and 39 °C (Figure 4B) and strong Figure 4. Photograph illustration of various reversible shape changes
bending-unbending, coiling-uncoiling, and blooming-closing) in
(
emission was also observed under 365 nm UV light irradiation
Figure 4C).
water baths with different temperatures. (A) PCL3600 network and (B)
PCL5800-TPE network under bright field, and (C) PCL5800-TPE network
under irradiation of a 365 nm UV lamp. Scale bar: 1.0 cm.
(
Soft robotic gripper for grasping and releasing capability
The luminescent 2W-SMPs might have potential applications
owing to their dual functions of luminescence and reversible branch unbented due to the partial melting of PCL crystals
shape memory properties. For example, the coiling-uncoiling (Figure 5B and Movie S4, ESI†). Next, when the gripper was
shape changes of the luminescent 2W-SMPs incorporated NIR II placed in an ice-water bath, it bended and grasped the screw
fluorophores with deep tissue penetration might be used as owing to the recrystallization of PCL chains. Afterward, the
intravascular stent. The sample would uncoil when it is system was lifted and put in a warm water bath to make the
implanted into blood vessel and can be traced by its gripper unbent again and release the screw. Repeating this
luminescence. It would coil and thus can also be removed easily process, another crew could be grasped and released. The same
by cooling blood vessel.
processes of PCL5800-TPE network were also demonstrated
Furthermore, they could also be used to fabricate nanorobots under bright field as a control, which is shown in Figure 5C. Ti is
to perform complex operations by their reversible shape worth noting the gripper with the weight of 0.25 g can grasp and
changes, and their position can also be traced through detecting release various screws with weights up to 37 g, which is 148-
its luminescence. To address this possible application, we fold higher than that of the polymer gripper. Moreover, this
designed a micro-gripper from two long strips of PCL5800-TPE payload-to-weight ratio is much higher than many industrial
6
3
network. The strips were first placed in a 70 °C water bath and robotic grippers.
programmed to a closed bending shape. The gripper was used
Double anti-counterfeiting
to grasp screws, which are pre-coated with a red-emissive
6
2
SMPs have been used in the field of anti-counterfeiting because
of their shape changing ability upon heating. For example, an
injected film sheet with convex-concave patterns or words is
pressed into the plane at the temperature above its transition
temperature, which become invisible under such temperature.
AIEgen (the structure is shown in Figure S12, ESI†), in an ice-
water beaker (0 °C) and release them to a warm water beaker
(39 °C). Under the irradiation of 365 nm UV light, the gripper
gives a blue emission, and the screws are red emissive (Figure
5
A). When the gripper was immersed in warm water, each
4
| J. Name., 2012, 00, 1-3
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DOI: 10.1039/D0TC03888A
Figure 5. (A) Schematic and (B and C) photograph illustration of a robotic gripper made of PCL5800-TPE network showing grasping and releasing
capability. The photos in panel B were taken under a 365 nm UV lamp irradiation. Scale bar: 1.0 cm.
reversible shape transformation under UV light irradiation. A
robotic gripper made of PCL5800-TPE network can grasp a crew
which weight could be 148-fold higher than itself, in cool water
and release in warm water automatically. Moreover, PCL5800
-
TPE network demonstrated dual anti-counterfeiting
a
properties of luminescence and shape change. Thus, this work
offers a new strategy to develop smart materials by integrating
more functions into one system.
Experimental Section
Figure 6. Photographs showing the double anti-counterfeiting
capability of a luminescent SMP. (A, C) After sealing with an SMP Materials. 1,4-Diazabicyclo[2.2.2]octane (DABCO), N,N'-
o
word; (B, D) After heating using a heating gun at 50 C. Scale bar, 0.5
cm.
dicyclohexylcarbodiimide (DCC), pentaerythritol, and 1,6-
hexanediol were purchased from TCI. 4-
Methoxybenzophenone, ε-caprolactone (CL), and 4-
dimethylaminopyridine (DMAP) were purchased from Energy.
TiCl , BBr , and stannous octoate were bought from Aladdin.
4 3
Propiolic acid and TsOH were purchased from Macklin and
HWRK Chem, respectively. Tetrahydrofuran (THF) was distilled
under nitrogen at normal pressure from sodium benzophenone
ketyl immediately prior to use. Dichloromethane (DCM), N,N-
dimethylformamide (DMF) and dimethylsulfoxide (DMSO) are
ultra-dry reagents purchased from Energy.
The patterns or words would reappear again when the system
is heated to above its transition temperature. However, such
technique is still easily counterfeited due to the single anti-
counterfeiting way.64
If another parameter is furnished to the anti-counterfeiting
system, the safety will be enhanced. Thanks to the
luminescence and shape memory property of PCL5800-TPE
network, we tried to apply it in dual anti-counterfeiting area. As
shown in Figure 6, its film was first sealed with the characters of
Characterization
“SMP” in a 70 °C water bath, followed by placing in an ice-water
bath to fix the patterns. As expected, this sealed film shows dual Thermogravimetric analysis (TGA) was performed on a Netzsch
anti-counterfeit capability. It is emissive upon UV irradiation, STA 449 F3 at a heating rate of 20 °C/min under nitrogen.
and the sealed characters would disappear upon heating by a Differential scanning calorimetry (DSC) measurements were
o
heat gun at about 50 C. Thus, PCL5800-TPE shows great carried out on a DSC Q800 (TA Instruments) at a heating rate of
advantages over traditional single anti-counterfeit materials.
10 °C/min. Fourier transform infrared spectroscopy (FT-IR) was
used to confirm the reaction of dipropiolate and hydroxyl
groups using a Bruker Vector 33 FTIR spectrometer with an ATR
Conclusions
The first examples of luminescent PCL-based 2W-SMPs, which (attenuated total reflectance) mode. All spectra were scanned
−
1
−1
1
were prepared by the organobase-catalyzed hydroxyl-yne click 32 times in the range 400 − 4000 cm at a 4 cm resolution. H
1
3
polymerization under mild reaction conditions, are presented. and C spectra were performed on a Bruker Avance 500 MHz
Compared with PCL-4OH prepolymers, PCL-based networks NMR spectrometer using CDCl3 as solvent and
show reduced T s and crystallinity degrees. The introduction of tetramethylsilane (TMS, δ = 0) as an internal reference. SEC
m
TPE units into polymer network can further reduce the coupled with successively connected refractive index and UV
crystallinity degree and enhance the emission compared with detectors was conducted in THF at 35 °C using two identical PL
-1
its monomer 2. The PCL3600 network is able to perform gel columns (5 μm, MIXED-C) at a flow rate of 1.0 mL min and
reversible bending-unbending, coiling-uncoiling, and closing- polystyrenes with different molcular weights were used as
blooming motions. Whereas, PCL5800-TPE network can not only standards. Photoluminescence spectra were recorded on a
behave the same as PCL3600 network but also shows luminescent Horiba Fluoromax-4 fluorescence spectrophotometer. Absolute
This journal is © The Royal Society of Chemistry 20xx
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ARTICLE
fluorescence quantum yields were performed on a Hamamatsu dried over MgSO
Journal Name
4
and removing the solvent by rotary
View Article Online
DOI: 10.1039/D0TC03888A
C11347-11 Quantaurus-QY.
evaporation, the crude product was purified by column
chromatography on silica gel using petroleum ether/ethyl
acetate (10:1, v/v) as eluent. TPE-containing dipropiolate 2 was
obtained as white powders in 37.2% yield (0.95 g). FT-IR (KBr
disk), υ (cm ): 3265, 3242, 2987, 2350, 2124, 1719, 1501, 1214,
1076, 1018, 915, 811, 750, 699. H NMR (500 MHz, CDCl ) δ
Synthesis of monomers (Scheme S1, ESI†)
1
,6-Hexanediol dipropiolate
-1
1
,6-Hexanediol dipropiolate (dipropiolate 1) was synthesized
1
6
5
according to the procedures in our previously reported work.
3
(TMS, ppm): 7.14 – 7.07 (m, 6H), 7.06 – 6.98 (m, 8H), 6.94 – 6.87
1
,6-Hexanediol (3.54 g, 30 mmol), propiolic acid (5,6 mL, 90
1
3
(
m, 4H), 3.04 (d, 2H). C NMR (125 MHz, CDCl
3
) δ (TMS, ppm):
50.68, 148.42, 143.00, 141.74, 140.41, 132.42, 131.26, 127.95,
27.81, 120.59, 120.42.
mmol), TsOH (1.03 g, 6mmol), and 100 mL of dry toluene were
successively added in a 250 mL round-bottom flask equipped
with a Dean–Stark apparatus. The mixture was refluxed for 12
h. After stopping the reaction, the solution was concentrated by
a rotary evaporator and then extracted with DCM three times.
The organic layer was dried overnight with anhydrous
1
1
Synthesis of PCL-4OH prepolymers
n
A typical synthetic protocol of PCL-4OH prepolymer (M = 3600
g/mol) is addressed here. Pentaerythritol (0.204 g, 1.5 mmol)
was added into a Schlenk tube equipped with a magnetic stir
bar. The tube was stoppered with rubber septa, and an
exhausting-refilling process was repeated three times. CL (2.91
mL, 25.50 mmol) was subsequently added via a syringe under
nitrogen into the reaction vials. The vials were then placed into
4
magnesium sulfate (MgSO ) and then filtered. After solvent
evaporation, the crude product was purified by column
chromatography on silica gel (petroleum ether/ethyl acetate =
1
%
2
0:1 v/v). Dipropiolate 1 was obtained as white powders in 78.5
-1
yield (5.24 g). FT-IR (KBr disk), υ (cm ): 3228, 2946, 2874,
1
112, 1698, 1477, 1250, 1077, 965, 904, 773, 713, 606, 424. H
2
a preheated oil bath at 130 °C. After 5 min, Sn(Oct) (0.02 mL)
NMR (500 MHz, CDCl
.70 (m, 4H), 1.42 (m, 4H). 13C NMR (125 MHz, CDCl
3
) δ (TMS, ppm): 4.19 (t, 4H), 2.88 (s, 2H),
was injected into the mixture, which was stirred for 12 h. The
polymerization was terminated by exposing to air and adding
excess of chloroform. The crude polymer solution was
precipitated from methanol and dried under vacuum at 30 °C
for 24 h. The product was obtained as white powders in 49.9%
yield (1.60 g). PCL2200-OH (1.56 g), PCL4500-OH (2.14 g), and
PCL5800-OH (2.44 g) prepolymers were obtained with yields of
1
3
) δ (TMS,
ppm): 152.92, 74.69, 66.30, 28.31, 25.55.
1
,2-Bis(4-hydroxyphenyl)-1,2-diphenylethene (compound 3)
This compound was synthesized via a McMurry coupling. 4-
Hydroxy-benzophenone (4.95 g, 25.0 mmol) and zinc powder
(
6.54 g, 100.0 mmol) were placed into a flask equipped with a
condenser. Anhydrous THF (70 mL) was added into the flask
after exhausting-refilling process for three times. TiCl (4.1 ml,
7.5 mmol) was added dropwise into the mixture after being
4
7.7%, 68.3%, and 69.1%, respectively, by the same synthetic
procedures.
4
n
The number-average molecular weight (M ) of PCL-4OH
3
6
0
prepolymers is calculated by using the following expressions:
placed in an ice-water bath. The mixture was refluxed
overnight. Afterward, the reaction was quenched by the
S
4 i
N =
addition of 10% aqueous solution of NaHCO
filtered and then extracted with DCM for three times. The
organic layer was dried with anhydrous MgSO overnight and
3
. The mixture was
S + S + S
i
o
p
(1)
Sm + Sn
4
Ln =
Sn
then filtered. After solvent evaporation, the crude product was
purified by a silica gel column using petroleum ether/ethyl
acetate (3:1, v/v) as eluent. The product was obtained after
drying under vacuum overnight. The compound 3 was obtained
(2)
3)
where S denotes the integral area of proton signal, N is the
average arm number, L is the average number of CL units for
each arm. Four PCL prepolymers with different molecular
weights were obtained. Moreover, M and polydispersity index
Ð) were also measured by size exclusion chromatography
SEC). The results are summarized in Table S1 (ESI†). PCL3600-OH
M = 114.14  N  L + 136
n
n
(
n
-
as white powders in 54.0% yield (2.46 g). FT-IR (KBr disk), υ (cm
1
)
: 3530, 3401, 3024, 1608, 1509, 1438, 1334, 1256, 1170, 823,
n
1
7
01. H NMR (500 MHz, CDCl
3
) δ (TMS, ppm): 7.13 – 7.10 (m,
(
(
1
3
6
H), 7.05 – 7.01 (m, 8H), 6.93 – 6.89 (m, 4H), 3.03 (d, 1.79H). C
NMR (125 MHz, CDCl ) δ (TMS, ppm): 150.82, 148.45, 143.14,
41.94, 140.55, 132.53, 131.42, 128.09, 127.02, 120.55.
3
-1
prepolymer: FT-IR ATR mode, υ (cm ): 3544, 2944, 2863, 1721,
1
1
470, 1418, 1398, 1366, 1294, 1240, 1175, 1107, 1044, 961,
1
4
,4’-(1,2-Diphenylethenylene)diphenyl dipropiolate (TPE-
934, 840, 730. H NMR (500 MHz, CDCl
3
) δ (TMS, ppm): 4.14 –
containing dipropiolate 2)
4.09 (d, 6H), 4.09 – 4.02 (t, 57H), 3.69 – 3.60 (t, 6H), 3.60 – 3.55
(
1
d, 1H), 3.58 – 3.47 (d, 1H), 2.40 – 2.25 (m, 63H), 1.74 – 1.50 (m,
33H), 1.46 – 1.30 (m, 63H). C NMR (125 MHz, CDCl ) δ (TMS,
3
Compound 3 (2.0 g, 5.5mmol), DCC (5.78 g, 28 mmol), DMAP
1
3
(0.56 g, 28 mmol), and TsOH (1.03 g, 6mmol) were added to 20
ppm): 64.16, 62.63, 34.15, 32.35, 28.37, 25.55, 24.60.
mL DCM in a round-bottom flask equipped with a magnetic stir
bar and placed in an ice-water bath. Propiolic acid (1.1 mL, 16.5
mmol) in 20 mL of DCM was added dropwise to the system
under vigorous stirring. The reaction was carried out at room
Preparation of polymer networks via hydroxyl-yne click
polymerization reaction
temperature for 12 h. Afterward, the reacted mixture was PCL3600-4OH (500 mg, 0.139 mmol,), dipropiolate 1 (61.7 mg,
filtered and extracted with DCM. After the organic layer was 0.277 mmol), and 2.4 mL THF were mixed in a dry vial under
6
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ARTICLE
vigorous stirring. DABCO (3.1 mg, 0.027mmol) in 100 μL THF 12. H. Venkatesan, J. Chen, H. Liu, Y. Kim, S. Na, W. VLieiuw AarnticdleJO. nHlinue,
Mater. Chem. Front., 2019, 3, 2472-2482D.OI: 10.1039/D0TC03888A
3. Y. Han, J. Hu and X. Chen, Mater. Chem. Front., 2019, 3, 1128-
solution was added into the mixture. The vial was stirred for 30
s and then poured into Teflon molds (rectangular shape: 2.0 ×
1
1
1
1
1
138.
6
.0 cm, flower shape with five petals). The system was allowed
4. X. Le, W. Lu, H. Xiao, L. Wang, C. Ma, J. Zhang, Y. Huang and T.
Chen, ACS Appl. Mater. Interfaces, 2017, 9, 9038-9044.
5. Y. Li, H. Chen, D. Liu, W. Wang, Y. Liu and S. Zhou, ACS Appl.
Mater. Interfaces, 2015, 7, 12988-12999.
to set in a fume hood for 2 days and then removed from the
mold. The obtained polymer is denoted as PCL3600 network. FT-
-1
IR ATR mode, υ (cm ): 2942, 2864, 1729, 1623, 1463, 1391,
1
357, 1326, 1158, 1129, 1038, 965, 819, 736.
6. K. Wang, Y.-G. Jia, C. Zhao and X. X. Zhu, Prog. Mater. Sci., 2019,
PCL5800-4OH prepolymer was used to prepare a TPE-
1
05, 100572.
containing polymer network (denoted as PCL5800-TPE network). 17. K. Wang, S. Strandman and X. X. Zhu, Front. Chem. Sci. Eng.,
The procedures are similar with those of PCL3600 network,
2017, 11, 143-153.
except that the mixture was stirred only for 10 s and then 18. H. M. Chen, L. Wang and S. B. Zhou, Chinese J. Polym. Sci., 2018,
3
6, 905-917.
poured into Telfon molds due to the higher reactivity of TPE-
1
2
9. Q. Zhao, H. J. Qi and T. Xie, Prog. Polym. Sci., 2015, 49-50, 79-120.
0. K. Wang, K. Amin, Z. An, Z. Cai, H. Chen, H. Chen, Y. Dong, X. Feng,
W. Fu, J. Gu, Y. Han, D. Hu, R. Hu, D. Huang, F. Huang, F. Huang,
Y. Huang, J. Jin, X. Jin, Q. Li, T. Li, Z. Li, Z. Li, J. Liu, J. Liu, S. Liu, H.
Peng, A. Qin, X. Qing, Y. Shen, J. Shi, X. Sun, B. Tong, B. Wang, H.
Wang, L. Wang, S. Wang, Z. Wei, T. Xie, C. Xu, H. Xu, Z.-K. Xu, B.
Yang, Y. Yu, X. Zeng, X. Zhan, G. Zhang, J. Zhang, M. Q. Zhang, X.-
Z. Zhang, X. Zhang, Y. Zhang, Y. Zhang, C. Zhao, W. Zhao, Y. Zhou,
Z. Zhou, J. Zhu, X. Zhu and B. Z. Tang, Mater. Chem. Front., 2020,
containing dipropiolate 2. The structures of the polymer
-1
networks are shown in Figure 1. FT-IR ATR mode, υ (cm ): 2942,
2
1
863, 1728, 1623, 1504, 1462, 1391, 1358, 1261, 1234, 1159,
095, 806, 734, 701.
Conflicts of interest
There are no conflicts to declare.
4
, 1803-1915.
1. K. Wang, Y.-G. Jia and X. X. Zhu, Macromolecules, 2017, 50, 8570-
579.
2
2
8
Acknowledgements
This work was financially supported by the National Natural
2. Y. Yao, T. Zhou, J. Wang, Z. Li, H. Lu, Y. Liu and J. Leng, Compos.
Part A: Appl. Sci. Manuf., 2016, 90, 502-509.
Science Foundation of China (21788102 and 21525417), the 23. L. Du, Z. Y. Xu, C. J. Fan, G. Xiang, K. K. Yang and Y. Z. Wang,
Natural Science Foundation of Guangdong Province
Macromolecules, 2018, 51, 705-715.
(
2019B030301003, 2016A030312002 and 2019A1515011585), 24. C. Ma, W. Lu, X. Yang, J. He, X. Le, L. Wang, J. Zhang, M. J. Serpe,
Y. Huang and T. Chen, Adv. Funct. Mater., 2018, 28, 1704568.
5. F. Ge, X. Lu, J. Xiang, X. Tong and Y. Zhao, Angew. Chem. Int. Ed.,
the Fundamental Research Funds for the Central Universities
2
2
(2019MS007), and the Innovation and Technology Commission
2
017, 56, 6126-6130.
6. Q. X. Yang, J. Z. Fan and G. Q. Li, Appl. Phys. Lett., 2016, 109,
83701.
7. S. Zhu and J. Hu, Mater. Chem. Front., 2019, 3, 2463-2471.
8. Q. Peng, H. Wei, Y. Qin, Z. Lin, X. Zhao, F. Xu, J. Leng, X. He, A. Cao
and Y. Li, Nanoscale, 2016, 8, 18042-18049.
9. H. Gao, J. Li, F. Zhang, Y. Liu and J. Leng, Mater. Horiz., 2019, 6,
931-944.
30. X. Du, H. Cui, Y. Wang, J. Wang and Q. Zhao, Natl. Sci. Rev., 2020,
7, 629-643.
31. J. Zhao, D. Zhong and S. Zhou, J. Mater. Chem. B, 2018, 6, 349-
365.
32. Y. Yu, C. Feng, Y. Hong, J. Liu, S. Chen, K. M. Ng, K. Q. Luo and B.
Z. Tang, Adv. Mater., 2011, 23, 3298-3302.
of Hong Kong (ITC-CNERC14S01). K. Wang thanks the support
from the China Postdoctoral Science Foundation
1
(
2019M662902).
2
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Table of Content
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