Suzuki reaction within the core-corona nanoreactor of
poly(N-isopropylacrylamide)-grafted Pd nanoparticle in water
Guanwei Wei, Wangqing Zhang*, Fei Wen, Yao Wang, and Minchao Zhang
Key Laboratory of Functional Polymer Materials of Ministry of Education, Institute of
Polymer
Chemistry,
Nankai
University,
Tianjin,
300071,
China.
Email:
[email protected]. Tel: 86-22-23509794, Fax: 86-22-23503510.
1.
Synthesis of poly(N-isopropylacrylamide) (PNIPAM) by reversible addition
fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide.
The chain transfer reagent of S-benzyl dithiobenzoate (BDTB) was synthesized
according to ref.1S. The nearly monodispersed PNIPAM (Mn=5.7×103 g/mol,
Mw/Mn=1.14) was synthesized by RAFT employing 2,2’-Azobisisobutyronitrile
(AIBN) as the primary source of radicals and DBTB as the chain transfer reagent in
N,N-dimethylformamide (DMF). In a typical run, 10.0 g of NIPAM, 0.32 g of BDTB,
and 0.073 g of AIBN were charged in a glass tube at the molar ratio of 200:3:1 and
then 20 mL of DMF was added. After the mixture was degassed three times, the tube
was sealed under vacuum, and then kept in an oil bath for 36 hours at 65 oC. Then 40
mL of THF was added into the tube to halt the polymerization. The resultant polymer
of PNIPAM was precipitated by dropping the solution into large amount of diethyl
ether. This precipitation procedure was repeated three times. The powdery polymer
with light pink color was dried for three days under vacuum at 40 oC. The yield of the
polymer is 6.5 g. Figure 1s shows the GPC chromatogram of the synthesized PNIPAM,
wherein the GPC measurement was performed on a Waters 600E gel permeation
chromatography
(GPC)
analysis
system
using THF
was
narrow-polydispersity polystyrene was used as calibration standard.
1
as
eluent
and
Figure 1s. The GPC chromatogram of the Synthesized PNIPAM.
2. Synthesis of the thiol-terminated PNIPAM (PNIPAM-SH).
PNIPAM-SH was synthesized by hydrazinolysis of the synthesized PNIPAM
according to ref.2s. 2.0 g of PNIPAM was firstly dissolved in 100 mL of ethanol in a
two-neck round-bottom flask with stirring. Then, 1.0 mL of 80 wt. % hydrazine was
injected dropwisely with a syringe; the hydrazinolysis started immediately indicated
by the rapid fading of the pink color of the solution. The hydrazinolysis was allowed to
continue for 1 h at room temperature under nitrogen. The progress of the reaction was
monitored by a TU-8110 UV-vis spectrometry until the absorbance maximum of
dithiobenzoate group at 498.6 nm disappeared. The pH of the resulting mixture was
adjusted to 3 using 0.1 M HCl aqueous solution, and then the solvent was removed
with a rotary evaporator. The resultant polymer was purified by firstly being dissolved
in THF, and then filtrated, and further precipitated in diethyl ether, and lastly washing
2
with hot water to yield a primrose yellow powder of PNIPAM-SH.
3. Synthesis of PNIPAM-grafted Pd Nanoparticles of Pd@PNIPAM in Water.
PNIPAM-SH was firstly dissolved in water at room temperature to make 5.0
mmol/L aqueous solution. Subsequently, a given volume of 0.010 mol/L PdCl2
aqueous solution was added to keep the molar ratio of PNIPAM/Pd equal to 1/6. The
mixture was kept at room temperature for 30 min and then 10-fold excess of 0.50
mol/L NaBH4 aqueous solution was added dropwisely with vigorously stirring. The
mixture turned immediately into brown and was kept at room temperature with
vigorously stirring for 4 h. The colloidal dispersion of Pd@PNIPAM nanoaprticles
was dialyzed against water at room temperature for 4 days.
Figure 2s shows the XRD patterns of the synthesized Pd@PNIPAM nanoparticles.
Figure 2s. The XRD patterns of the Pd@PNIPAM nanoparticles.
4. The Suzuki reaction of a binary mixture of the hydrophobic 4-bromoanisole
and the hydrophilic 4-bromophenol (1:1 by mole number) within the
Pd@PNIPAM nanoreactor in water.
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Table 1s shows the competition Suzuki reaction of a binary mixture of
4-bromoanisole and 4-bromophenol within the Pd@PNIPAM nanoreactor. To
compare the efficiency of the Suzuki reaction of the hydrophilic 4-bromophenol with
those of the hydrophobic 4-bromoanisole within the Pd@PNIPAM nanoreactor, the
molar ratio of 4-bromophenol to 4-bromoanisole is set at 1:1.
Table 1s. Competition Suzuki reaction of a binary mixture of 4-bromoanisole and
4-bromophenol within the Pd@PNIPAM nanoreactor in water.a
Br
OH
Pd@PNIPAM
B(OH)2
Br
a
OCH3
OH
OCH3
K2CO3, H2O, 25 ~ 90 0C
Yield (%)b
Entry
Temperature
(oC)
1
25
42
2
2
50
60
5
3
70
71
8
4
90
75
17
OCH3
OH
Reaction conditions: 4-bromophenol (1.0 mmol), 4-bromoanisole (1.0 mmol),
benzeneboronic acid (3.0 mmol), K2CO3 (6.0 mmol), 8.0 mL of water containing
4.0×10-3 mmol of Pd@PNIPAM nanoparticles, 1 h.
b
The yield was determined by 1H NMR analysis of the crude extracted powder using
DMSO as solvent.
Reference.
[1s]. Zhu, M.-Q.; Wang, L.-Q.; Exarhos, G. J.; Li, A. D. Q. J. Am. Chem. Soc. 2004,
126, 2656.
[2s]. Shan, J.; Nuopponen, M.; Jiang, H.; Kauppinen, E.; Tenhu, H. Macromolecules
2003, 36, 4526.
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