Hyperbranched Poly(ester-enamine) from Spontaneous Amino-yne Click Reaction for Stabilization of Gold Nanoparticle Catalysts

Article abstract of DOI:10.1002/asia.202000621

Hyperbranched polymers have garnered much attention due to attractive properties and wide applications, such as drug-controlled release, stimuli-responsive nano-objects, photosensitive materials and catalysts. Herein, two types of novel hyperbranched poly(ester-enamine) (hb-PEEa) were designed and synthesized via the spontaneous amino-yne click reaction of A₂ monomer (1, 3-bis(4-piperidyl)-propane (A_2a) or piperazine (A_2b)) and B₃ monomer (trimethylolpropanetripropiolate). According to Flory's hypothesis, gelation is an intrinsic problem in an ideal A₂+B₃ polymerization system. By controlling the polymerization conditions, such as monomer concentration, molar ratio and rate of addition, a non-ideal A₂+B₃ polymerization system can be established to avoid gelation and to synthesize soluble hb-PEEa. Due to abundant unreacted alkynyl groups in periphery, the hb-PEEa can be further functionalized by different amino compounds or their derivates. The as-prepared amphiphilic PEG-hb-PEEa copolymer can readily self-assemble into micelles in water, which can be used as surfactant to stabilize Au nanoparticles (AuNPs) during reduction of NaBH₄ in aqueous solution. As a demonstration, the as-prepared PEG-hb-PEEa-supported AuNPs demonstrate good dispersion in water, solvent stability and remarkable catalytic activity for reduction of nitrobenzene compounds.

Full text of DOI:10.1002/asia.202000621

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Hyperbranched Poly(ester-enamine) from Spontaneous Amino-
yne Click Reaction for Stabilization of Gold Nanoparticle
Catalysts
Authors: Dong Yang, Pei Liu, Wanran Lin, Shanglin Sui, Long-Biao
Huang, Ben Bin Xu, and Jie Kong
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To be cited as: Chem. Asian J. 10.1002/asia.202000621
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10.1002/asia.202000621
Chemistry - An Asian Journal
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Hyperbranched Poly(ester-enamine) from Spontaneous Amino-
yne Click Reaction for Stabilization of Gold Nanoparticle
Catalysts
Dong Yang[a]#, Pei Liu[a]#, Wanran Lin[a], Shanglin Sui[a], Long-Biao Huang[b]*, Ben Bin Xu[c] and Jie
Kong[a]*
[a]
D. Yang, Dr. P. Liu, W. Lin, S. Sui, Prof. J. Kong
MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, Shaanxi Key Laboratory of Macromolecular Science and
Technology
School of Chemistry and Chemical Engineering
Northwestern Polytechnical University
Xi’an 710072, P. R. China
E-mail: kongjie@nwpu.edu.cn (J.K.)
Dr. L.B. Huang
College of Physics and Optoelectronic Engineering
Shenzhen University
Shenzhen, 518060, P. R. China
E-mail: huanglb@szu.edu.cn (L.H.)
Prof. B. B. Xu
[b]
[c]
Mechanical and Construction Engineering, Faculty of Engineering and Environment
University of Northumbria
Newcastle upon Tyne, NE1 8ST, UK
#Equal contribution
Abstract: Hyperbranched polymers have attracted much attention
due to attractive properties and wide applications, such as drug
controlled release, stimuli-responsive nano-objects, photosensitive
materials and catalysts. Herein, Two types of novel hyperbranched
poly(ester-enamine) (hb-PEEa) were designed and synthesized via
the spontaneous amino-yne click reaction of A2 monomer (1, 3-bis(4-
piperidyl)-propane (A2a) or piperazine (A2b)) and B3 monomer
(trimethylolpropanetripropiolate). According to Flory’s hypothesis,
gelation is an intrinsic problem in an ideal A2 + B3 polymerization
system. By controlling the polymerization conditions, such as
monomer concentration, molar ratio and rate of addition, a non ideal
A2 + B3 polymerization system can be established to avoid gelation
and to synthesize soluble hb-PEEa. Due to abundant unreacted
alkynyl groups in periphery, the hb-PEEa can be further
functionalized by different amino compounds or their derivates. The
as-prepared amphiphilic PEG-hb-PEEa copolymer can readily self-
assemble into micelles in water, which can be used as surfactant to
stabilize Au nanoparticles (AuNPs) during reduction of NaBH4 in
aqueous solution. As a demonstration, the as-prepared PEG-hb-
PEEa-supported AuNPs demonstrate good dispersion in water,
solvent stability and remarkable catalytic activity for reduction of
nitrobenzene compounds.
2001, the click polymerizations had been widely utilized as a
powerful technique in synthesis and modification of functional
HBPs. For example, transition-metal catalyzed azide-alkyne
click polymerizations (AACPs) have been widely used to
synthesize hyperbranched polytriazoles.[16-21] In addition, the
thiol-based click polymerizations have also been igniting great
interesting in the preparation of sulfur-rich HBPs.[22-24] However,
some aspects still need further enhancement in this field, i.e.,
the safety of azide monomers and the residue of metal catalysts
in AACPs, the unpleasant smell and the limited types of thiol
monomers in thiol-based click polymerizations.[25] As a result, it
is challenging and very attractive to synthesize more novel
functional HBPs using new click polymerizations in a mild
condition.
In the past few years, Tang’s group had developed several
spontaneous click polymerizations including spontaneous
thiol−yne click polymerization,[26] spontaneous amine−yne click
polymerization,[27]
polymerization.[28]
and
These
spontaneous
phenol−yne
click
amine−yne
polymerization
demonstrated obvious advantages in a catalyst-free system with
high efficiency, regioselectivity, 100% atom efficiency and mild
conditions. Ni et al. synthesized polymer−doxorubicin prodrug
via spontaneous amino−yne click reaction.[29] The prepared
polymer shows good water solubility, biocompatibility, pH
response and the potential in cancer therapy. Langer et al.
synthesized the water-compatible β-aminoacrylate hydrogel
platforms via the click polymerization between alkynoates and
secondary amines.[30] However, merely reports are relative to the
synthesis of functional HBPs via this click polymerization. In the
meanwhile, multi-functional HPBs can be used as templates to
control the size, stability, and dispersion of metal nanoparticles
(metal NPs).[31-36] For the most part, HBPs-encapsulated metal
NPs are prepared by sequestering metal ions within HBPs
followed by chemical reduction to yield metal NPs. The particle
size of metal NPs depends on the number of metal ions initially
Introduction
Hyperbranched polymers (HBPs), as nano-sized highly-
branched three-dimensional macromolecular architectures, have
been broadly investigated and utilized in various applications
including controlling drug delivery,[1-5] sensing,[6,7] and
catalysis,[8-10] as well as materials science.[11-15] Because of the
attractive properties and wide applications of HBPs, the
development of new efficient and selective polymerizations to
prepare functional HBPs is an invariably theme in polymer
science. Since the concept of click chemistry was proposed in
1
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10.1002/asia.202000621
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loaded into HBPs.[37,38] In addition, HBPs with highly branched
and globular structure and multiple functional groups provide
tremendous active sites and spatial constraint for aggregation of
metal NPs, which are beneficial to improving efficiency in
catalysis.[38-42] The terminal groups on the HBPs periphery can
be tailored to control dispersion of the hybrid nanocomposites to
realize homogeneous catalysis of metal nanocomposites in
water or organic solvents.
can be further functionalized by NH2-PEG. The structure of B3
monomer was characterized by FT-IR and NMR spectroscopy
(Figure S1). The as-prepared amphiphilic PEG-hb-PEEa can
effectively stabilize AuNPs. The resultant AuNPs@PEG-hb-
PEEa composites efficiently catalyze reduction of nitrobenzene
compounds in the presence of NaBH4.
In this study, the A2 + B3 monomers polymerization strategy is
applied to the synthesis of HBPs. According to Flory’s
hypothesis, gelation is an intrinsic problem in an ideal A2 + B3
polymerization system.[43-46] During the polymerization of A2 with
B3 monomers, the gelated products take place when monomer
solids are directly added or the addition of monomer solution is
too quick. Besides the monomer concentration, other factors,
such as slow addition of one monomer to another, monomer
molar ratio, also account for avoiding gelation. Because of the
high activity and efficiency of the amino-yne click reaction, the
total monomer concentration should be lower and higher
monomer concentration leads to insoluble products. Through
slow addition approach to avoid any high local concentration,
Herein, Two types of novel hyperbranched poly(ester-enamine)
(hb-PEEa) with regional and stereo regular structure were
designed and successfully synthesized by the spontaneous
amino-yne click polymerization. As a demonstration, they were
utilized as surfactant to synthesis AuNPs with remarkable
catalytic activity for nitrobenzene compounds. First, the A2 + B3
monomers polymerization strategy including the A2-type
monomer (1, 3-bis(4-piperidyl)-propane (A2a) or piperazine (A2b))
and the B3-type monomer (trimethylolpropanetripropiolate) was
chosen to synthesize hb-PEEa. By controlling monomer
concentration, molar ratio and rate of addition, the resultant hb-
PEEa without gelation present good solubility in organic solvents. fully soluble hb-PEEa-1 (Entry 2-5, Table 1) could be
Abundant unreacted alkynyl groups on the periphery of hb-PEEa
can be further functionalized by different amino compounds,
such as n-butylamine, diethyamine and NH2-PEG (polyethylene
glycol monomethyl ether). Second, the as-prepared amphiphilic
PEG-hb-PEEa synthesized through modification of NH2-PEG
containing a large number of amino and ester functions can
capture gold ions and lead to the nucleation and growth of
AuNPs. Therefore, PEG-hb-PEEa can be used as surfactant to
synthesize AuNPs via in-situ reduction of Au ions using NaBH4.
synthesized by polymerization of A2a and B3 monomers at
different molar ratios. As increasing the molar ratio of B3
monomer, the average molecular weight (Mn and Mw) and
polydispersity index (PDI) decreased accordingly. hb-PEEa-1
(Entry 5) with Mn = 8940 g mol-1 and PDI = 2.88 was synthesized
at the molar ratio of 1.0/1.2. On the contrary, severe gelation
quickly occurred at A2a/B3 molar ratio of 1.5/1.0 (equal molar
concentration of functional groups) under the same
polymerization conditions (Entry 1). Furthermore, hb-PEEa-2
(Entry 6) with Mn = 5080 g mol-1 and PDI = 3.02 was obtained
via the polymerization of A2b and B3 monomer at the molar ratio
of 1.0/1.2. Therefore, by controlling the polymerization
conditions, a non ideal A2 + B3 polymerization system was
established to avoid gelation and to synthesize soluble hb-PEEa
via the spontaneous amino-yne click reaction. The synthesis
strategy of hb-PEEa provides a helpful reference for the design
and synthesis of HBPs via A2 + B3 monomers polymerization.
The
as-prepared
PEG-hb-PEEa-supported
AuNPs
(AuNPs@PEG-hb-PEEa) show good dispersion in water and
solvent stability, and remarkable catalytic activity for reduction of
nitrobenzene compounds. The synthesis strategy of
AuNPs@PEG-hb-PEEa provides new insight into the design and
synthesis of functional metal nanocomposites.
Results and Discussion
Table 1. Polymerization condition for hyperbranched poly(ester-enamine) via
spontaneous amino-yne click reaction.
The synthesis process and structure of AuNPs@PEG-hb-PEEa
are schematically shown in Figure 1. The hb-PEEa is
synthesized via the spontaneous amino-yne click polymerization
of A2 monomer (1,3-bis(4-piperidyl)-propane (A2a) or piperazine
(A2b)) and B3 monomer (trimethylolpropanetripropiolate), which
[b]
[b]
A2 : B3
(molar ratio)
Mw
Mn
Entry[a]
PDI[b]
[g mol-1]
[g mol-1]
1[c]
2[d]
3
4
5
A2a : B3 = 1.5 : 1.0
A2a : B3 = 1.0 : 1.0
A2a : B3 = 1.0 : 1.0
A2a : B3 = 1.0 : 1.1
A2a : B3 = 1.0 : 1.2
A2b : B3 = 1.0 : 1.2
insoluble
36,270
197,610
80,580
25,780
15,360
insoluble
6,990
33,280
25,550
8,940
insoluble
5.19
5.94
3.16
2.88
6
5,080
3.02
[a] Carried out in THF under nitrogen for 24 h; monomer concentration (A2
=
20 mM); all yields over 90% by precipitation from hexane. [b] Molecular weight
(g mol−1) determined by gel-permeation chromatography (GPC) in THF on the
basis of a polystyrene calibration: Mw = weight-average molecular weight, Mn =
number-average molecular weight, PDI = Mw/Mn. [c] Molecular weight could
not be obtained because the polymer was not soluble in common solvents. [d]
Reaction time is for 12 h.
By optimizing the polymerization conditions, hb-PEEa can be
rapidly and effectively synthesized. The resultant hb-PEEa is
soluble in common organic solvents such as dichloromethane,
acetone, ethanol, and tetrahydrofuran. The molecular structure
Figure 1. Schematic synthesis process and structure of AuNPs@PEG-hb-
PEEa and application in catalytic reduction of nitrobenzene compounds.
2
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of hb-PEEa was identified by FT-IR and NMR spectroscopy. By
analyzing the FT-IR spectra of A2a monomer, B3 monomer, and
hb-PEEa-1 (Figure S2a), the N−H vibration of A2a monomer
occurs at 3190.0 cm−1, which disappears completely after
polymerization. The characteristic absorptions of B3 monomer at
3242.2 and 2119.7 cm−1 can be assigned to the ≡C-H and C≡
C stretching vibrations, which weak in the hb-PEEa-1. The key
absorption of new C=C is at 1609.1 cm−1 in the hb-PEEa-1.
These results reveal the occurrence of the polymerization and
there are many unreacted alkynyl groups in its periphery. From
the 1H NMR spectrum (Figure 2a), two new peaks (l and m)
assigned to the resonances of the vinylene protons appear at
7.4 and 4.6 ppm in the spectra of hb-PEEa-1. The ≡C-H (n) of
B3 monomer at 2.9 ppm was shifted to 4.21 ppm in hb-PEEa-1.
And the intensity of the alkynyl units becomes weaker after
polymerization, which also indicates alkynyl units as terminal
units. Furthermore, the hb-PEEa-1 was investigated by 13C NMR
spectroscopy (Figure S3). There are some characteristic signals
at 169.8, 152.7, 151.2 and 83.4 ppm, which represent the
carbon atoms of the ester carbonyl units and the vinylene
groups, respectively. The molecular structure of hb-PEEa-2 was
also characterised by FT-IR (Figure S2b) and NMR (Figure 2b
and S4). The analysis results show that hb-PEEa-2 can be
successfully synthesized by the amino-yne click reaction of A2
and B3 monomers.
The amphiphilic PEG-hb-PEEa contains a large number of
amino and ester functions, which can be used to capture metal
ions, guide the nucleation and growth of metal NPs, and
enhance the non-covalent interaction between support and
loaded metal NPs. Therefore, PEG-hb-PEEa can be used as
organic templates to stabilize AuNPs in water. AuNPs@PEG-hb-
PEEa is synthesized by mixing PEG-hb-PEEa and HAuCl4•3H2O
in deionized water under vigorous stirring. During the process,
Au(III) ions are sequestered into PEG-hb-PEEa. A freshly
prepared NaBH4 solution is then added dropwise into the as-
prepared solution. Then Au (III) ions are reduced by NaBH4, and
the Au(0) atoms gather together to form stable AuNPs inside the
PEG-hb-PEEa. The color of the solution gradually becomes
purple with the formation of AuNPs. The size and morphology of
AuNPs are determined by typical transmission electron
microscope (TEM) (Figure 3a and 3b). The DLS analysis
displays the hydrodynamic behavior, and AuNPs@PEG-hb-
PEEa has a narrow dispersion in aqueous solution by the DLS
measurement (Figure 3c). Moreover, UV−vis spectra reveal the
plasmonic properties of AuNPs, with the change of the surface
plasmon band (SPB) along with the variety of sizes. The surface
plasmon band (SPB) is observed at 531 nm for AuNPs@PEG-
hb-PEEa-1, 524 nm for AuNPs@PEG-hb-PEEa-2 (Figure 3d).
Furthermore, we found that the micelle size and color in
aqueous solution do not change under environmental conditions
for several weeks, which indicated AuNPs@PEG-hb-PEEa has
good solvent stability. The final content of gold is 1.2 wt%
(AuNPs@PEG-hb-PEEa-1) and 1.8 wt% (AuNPs@PEG-hb-
PEEa-2) from ICP analysis, respectively. In a word, the as-
prepared amphiphilic PEG-hb-PEEa copolymer can readily self-
assemble into micelles in water. And the heteroatom-rich PEG-
hb-PEEa also provides an extra support for the formation and
stabilization of Au NPs through its non-covalent interaction with
Au ions or NPs. These advantages are beneficial to the
synthesis of metal nanocomposites. AuNPs@PEG-hb-PEEa can
be synthesized via infiltration of HAuCl4•3H2O and in situ
reduction using NaBH4. AuNPs@PEG-hb-PEEa with good
dispersion in water and solvent stability suggests promising
applications in aqueous media.
Figure 2. 1H NMR spectra in CDCl3: (a) A2a, B3 and hb-PEEa-1; (b) A2b, B3 and
hb-PEEa-2.
According to structure analysis of hb-PEEa, there are a large
number of unreacted alkynyl groups in the periphery of hb-PEEa,
which can be further functionalized via spontaneous amino-yne
reaction. By simply mixing the hb-PEEa and the different amines
such as n-butylamine, diethyamine and NH2-PEG (polyethylene
glycolmonomethyl ether, Mn = 2000 g mol-1) in THF at room
temperature for 12 h, the quantitative reaction of the terminal
alkynyl groups was observed by FT-IR and 1H NMR
spectroscopy. The vibration of ≡C−H completely disappears
and the absorption of C=C enhances after post-polymerization in
the FT-IR spectrum (Figure S5). By analyzing the 1H NMR
spectra (Figure S6 and S7), we can observe some peaks of
new vinylene protons with the disappearance of the alkynyl
groups. As indicated by the GPC measurement, the Mn of PEG-
hb-PEEa-1 (78670 g mol-1) and PEG-hb-PEEa-2 (30430 g mol-1)
are enhanced compared with that of hb-PEEa-1 (8940 g mol-1)
and hb-PEEa-2 (5080 g mol-1), respectively, Meanwhile, the
PEG-modified hb-PEEa (PEG-hb-PEEa) is soluble in water in
contrast to hb-PEEa.
Figure 3. TEM images of Au NPs: (a) AuNPs@PEG-hb-PEEa-1 and (b)
AuNPs@PEG-hb-PEEa-2; (c) DLS size distribution; (d) UV-vis spectra.
3
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Nitrobenzene compounds are toxic and hazardous pollutants in
industrial and agricultural waste water. They have high stability
and low solubility in water, so their degradation in nature has
always been difficult and challenging.[47,48] In general, p-
nitrophenol (4-NP) reduction in the presence of NaBH4 is a
versatile reaction to evaluate the catalytic activity of various
metal NPs, and this reaction can also be readily monitored by
UV−vis spectroscopy. The as-prepared AuNPs@PEG-hb-PEEa
has good dispersion in water and solvent stability, and its
application in catalysis was explored. The reduction of 4-NP in
the excess presence of NaBH4 was chosen as a model reaction
to evaluate the catalytic activity of AuNPs@PEG-hb-PEEa and
show that AuNPs@PEG-hb-PEEa exhibits remarkable catalytic
activity toward the reduction of a series of nitrobenzene
compounds. The synthesis and application of AuNPs@PEG-hb-
PEEa provide great opportunities to prepare functional metal
nanocatalysts with potential in the homogeneous catalysis field.
Conclusion
In summary, Two types of novel hyperbranched poly(ester-
enamine) were successfully synthesized via the spontaneous
amino-yne click polymerization of A2 monomer (1,3-bis(4-
piperidyl)-propane (A2a) or piperazine (A2b)) and B3 monomer
monitored dynamically by UV-Vis spectra. As
a control
experiment, the reaction did not occur when using only PEG-hb-
PEEa as catalyst. The intensity of the absorption peak at 400
nm, a characteristic peak of 4-NP and NaBH4, remains almost
unchanged in the presence of PEG-hb-PEEa at a prolonged
period. This means that the PEG-hb-PEEa alone does not have
catalytic activity. By adding AuNPs@PEG-hb-PEEa as a catalyst,
the reduction was initiated immediately, showing the rapid
decrease of the absorption at 400 nm and the related increase
of the characteristic peak of p-aminophenol (Figure 4a and 4b).
And the color of the solution gradually changed from bright
yellow to colorless (Figure 4c, inset image). Since NaBH4 was
used in excess compared to the 4-NP in the system, the
reduction of 4-NP can be considered as a pseudo-first order
reaction to evaluate the kinetic reaction rate of the catalytic
reaction. Herein, Figure 4d show a linear correlation of ln(At/A0)
versus time at any instant. Kapp (the apparent rate constant) is
12.80×10-3 s-1 for AuNPs@PEG-hb-PEEa-1 and 21.78×10-3 s-1
for AuNPs@PEG-hb-PEEa-2. In order to ensure the universal
applicability of AuNPs@PEG-hb-PEEa, other nitrobenzene
compounds with different substituent groups were also
considered (Figure S8). The results illustrate that the
AuNPs@PEG-hb-PEEa exhibit efficient catalytic activity for the
reduction of other nitrobenzene compounds. The substituent has
a great influence on the rate of reduction reaction, and the
electron withdrawing groups (Br or F) have a faster reaction,
compared with the electron donating groups.[49] These results
(trimethylolpropanetripropiolate).
By
optimizing
the
polymerization conditions, gelation can be successfully avoided
and the resultant hb-PEEa shows good solubility in common
organic solvents. The hb-PEEa can be further functionalized via
amine−yne click reactions. PEG-modified hb-PEEa (PEG-hb-
PEEa) can readily self-assemble into micelles in water, which
can be used as surfactant to stabilize AuNPs. The as-prepared
AuNPs@PEG-hb-PEEa shows good catalytic activity for efficient
reduction of nitrobenzene compounds under mild conditions.
Experimental Section
Materials
All reagents and solvents were purchased from J.&K. Scientific Ltd
(Beijing, China). Tetrahydrofuran (THF) was distilled through sodium
under dry nitrogen before using. Other solvents were used without further
purification. Reactions were followed with TLC (0.254 mm silica gel 60-F
plates). Flash chromatography was carried out on silica gel of 200–300
mesh.
Synthesis of trimethylolpropanetripropiolate (B3 monomer).
Trimethylolpropane (40.25 g, 0.30 mol) and Propiolic acid (70.05 g, 1.0
mol) were added to the benzene (250 mL) with 5 mol% P-toluenesulfonic
acid used as catalyst. A Dean-stark trap and a condenser were attached,
and the reaction was protected under nitrogen. The mixture was heated
to reflux for 24 h. Then the mixture was allowed to reach room
temperature and diluted with EtOAc (250 mL), washed with 5 wt%
Na2CO3 aqueous solution and brine and dried over anhydrous MgSO4.
The solvent was removed under reduced pressure and the purification of
the reaction mixture by silica gel column chromatography eluting with
EtOAc/petroleum (1/3) was performed to afford the product. IR (KBr, v,
cm−1): 3292.34, 3242.19, 2985.67, 2119.67, 1718.50, 1217.03, 983.65,
756.06, 707.84. 1H NMR (400 MHz, CDCl3) δ 4.19 (s, 6H), 2.93 (s, 3H),
1.56 (t, J = 8.0 Hz, 2H), 0.92 (t, J = 8.0 Hz, 3H). 13C NMR (100 MHz,
CDCl3) δ 152.4, 75.9, 74.2, 66.3, 40.8, 22.9, 7.4.
Synthesis of hyperbranched poly(ester-enamine) (hb-PEEa). The
polymerization of A2a and B3 monomers at the molar ratio of 1/1.2 is
given below as an example. A single-necked 25 mL flask equipped with a
magnetic stir bar was added 1, 3-bis(4-piperidyl)-propane (A2a momomer)
(42 mg, 0.2 mmol) and tetrahydrofuran (THF,
4
mL).
Trimethylolpropanetripropiolate (B3 monomer) (70 mg, 0.24 mmol) in 4
mL THF was injected into the above solution by syringe over 0.5 h. The
mixture was stirred under dry nitrogen for 24 h at room temperature, and
then the solution was poured slowly into an excess amount of hexane.
The precipitate was collected and dried at room temperature under
vacuum.
Figure 4. Time-dependent UV-vis spectra of the reduction of p-nitrophenol
(0.9 μmol) and 0.09 mmol NaBH4 catalyzed by 60 μL AuNPs@PEG-hb-PEEa
solution (1 mg/mL), (a) AuNPs@PEG-hb-PEEa-1 solution; (b) AuNPs@PEG-
hb-PEEa-2 solution; (c) At/A0 as a function of reaction time, Inset images:
Characterization data for hb-PEEa-1 synthesized through the
polymerization A2a and B3 monomers. IR (KBr, v, cm−1): 2926.67,
2845.77, 2117.78, 1688.44, 1609.11, 1455.11, 1237.33, 1123.77. 1H
NMR (400 MHz, CDCl3) δ 7.39-7.36 (d, 1H), 4.64-4.61 (d, 1H), 4.21 (s,
typical optical images of reaction mixtures at
relationship of ln(At/A0) as a function of time.
0 and 4 min; (d) linear
4
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0.8H), 4.08 (s, 2.1H), 3.50-3.47 (m, 2.1H), 2.94-2.91 (m, 2.4H), 1.71 (s,
2.8H), 1.54-1.17(m, 7.6H), 0.92 (s, 1.7H).
Acknowledgements
This work was supported by the funding of the National Natural
Science Foundation of China (21901206/51973119), Joint
Foundation of Shaanxi Province Natural Science Basic
Research Program and Shaanxi Coal Chemical Group Co., Ltd.
(2019JLM-46) and Polymer Electromagnetic Functional
Materials Innovation Team of Shaanxi Sanqin Scholars.
Characterization data for hb-PEEa-2 synthesized through the
polymerization A2b and B3 monomers. IR (KBr, v, cm−1): 3253.33,
2968.67, 2113.11, 1697.78, 1602.89, 1448.89, 1349.33, 1224.89,
1142.44, 1004.00. 1H NMR (400 MHz, CDCl3) δ 7.40-7.29 (m, 1.0H),
4.73 (d, 1.0H), 4.21 (s, 1.4H), 4.09 (s, 2.0H), 3.31 (s, 4.0H), 2.95-2.92 (m,
0.7H), 1.80 (s, 0.6H), 1.58-1.51 (m, 1.1H), 1.28 (s, 0.5H), 0.95-0.88 (m,
2.0H).
Modification of hb-PEEa by amino-yne reaction. A solution of amine
compound (n-butylamine (7.3 mg) or diethyamine (7.3 mg) or NH2-PEG
(polyethylene glycolmonomethyl ether, Mn = 2000 g mol-1, 200 mg) in 2
Conflict of interest
mL THF was added dropwise to a solution of hb-PEEa-1 (50 mg, Mn
=
8940 g mol-1, PDI = 2.88) or hb-PEEa-2 (38 mg, Mn = 5080 g mol-1, PDI =
3.02) in THF (4 mL). The mixture was stirred under dry nitrogen at room
temperature for 12 h, and then added dropwise into hexane. The
precipitate was collected by filtration and dried at room temperature
under vacuum.
The authors declare no competing financial interest.
Keywords: hyperbranched polymers • amino-yne click reaction •
nanocatalyst • reduction reaction
Preparation of AuNPs@ PEG-hb-PEEa. AuNPs@PEG-hb-PEEa was
synthesized by mixing PEG-hb-PEEa-1 (10 mg, Mn = 78670 g mol-1) or
PEG-hb-PEEa-2 (10 mg, Mn = 30430 g mol-1) and HAuCl4•3H2O (3 mg,
0.008 mmol) in deionized water (10 mL) under vigorous stirring for 1h.
Then a freshly-prepared NaBH4 (40 mg in 2 mL water) aqueous solution
was added dropwise into the as-prepared solution. The obtained solution
was continuously stirred for another 2 h. The AuNPs@PEG-hb-PEEa
was purified by dialysis against a large volume of water (3 × 100 mL).
The AuNPs@PEG-hb-PEEa was collected by freeze-drying.
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Entry for the Table of Contents
Novel hyperbranched poly(ester-enamine) (hb-PEEa) was synthesized by the spontaneous amino-yne click reaction of A2 + B3
monomers. The amphiphilic PEG-hb-PEEa was used as surfactant for stabilization of Au nanoparticles (AuNPs). The PEG-hb-PEEa-
supported AuNPs nanocomposites (AuNPs@PEG-hb-PEEa) showed remarkable catalytic activity for catalytic reduction of
nitrobenzene compounds.
7
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