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RSC Advances
purication methods, or are very expensive and toxic. Therefore,
The polyvinylamine/SBA-15 (PVAm/SBA-15) composite was
from both the environmental and economic points of view, synthesized in two steps without using any organosilica
using organic–inorganic hybrid composites, instead of orga- precursors via an in situ polymerization method.36 At rst, SBA-
noalkoxysilane compounds as supports for the supporting of 15 (0.5 g) and acrylamide (0.25 g) in THF (7 mL) were placed in a
dendrimers is highly desirable.
round bottom ask. Benzoyl peroxide (0.025 g) was added and
In continuing our efforts towards the development of efficient the mixture was heated to 70–75 ꢁC for 5 h, while being stirred.
and environmentally benign heterogeneous catalysts,32–34 The solvent was removed and the precipitate was dried at 60 ꢁC
herein, hyperbranched polyamidoamine–polyvinylamine/SBA- overnight under a vacuum to gain 0.7 g of a white powder of a
15 containing Ni nanoparticles was prepared as a heterogeneous polyacrylamide/SBA-15 (PAA/SBA-15) composite. In the second
catalyst, without using organosilane precursors. The obtained step, Hoffmann degradation on the PAA/SBA-15 was carried out
catalyst was used as an efficient heterogeneous catalyst for the by Ca(OCl)2 in order to prepare PVAm/SBA-15 composite
rapid reduction of aromatic nitro compounds to the corre- (conversion of the amide groups into amines).36 PAA/SBA-15 (0.1
sponding aromatic amino compounds in the presence of sodium g), H2O (15 mL) and Ca(OCl)2 (0.4 g) were placed into a round
borohydride (NaBH4) as a mild reducing agent. In addition, the bottom ask and reuxed for 6 h under vigorous stirring. Then,
catalytic activity of this hybrid hyperbranched polymeric catalyst the mixture was ltered, washed with water, then n-hexane and
in the reduction reaction was compared with Ni nanoparticle- nally dried at 60 ꢁC overnight under a vacuum, to yield the
polyvinylamine/SBA-15, which was reported in our previous yellow PVAm/SBA-15 composite (the reaction of calcium dihy-
work,32 in order to investigate the effect of hyperbranched poly- pochlorite (Ca(OCl)2) with polyacrylamide, transforms the
mer material on the activity and stability of the catalyst.
primary amide into an isocyanate intermediate. Then, the
isocyanate intermediate is hydrolyzed to a primary amine,
giving off carbon dioxide).
2.3.2. Preparation of hyperbranched polyamidoamine–
polyvinylamine/SBA-15 (PAMAM–PVAm/SBA-15). The graing
reaction and propagation of hyperbranched polyamidoamine
from the PVAm/SBA-15 surface was achieved in two steps:37,38 (1)
Michael addition of methyl acrylate (MA) to the amino groups
on the surface; and (2) amidation of the terminal ester groups
by ethylenediamine (EDA).
2. Experimental
2.1. Chemicals supply
All the chemicals were obtained from Sigma-Aldrich and Merck,
and were used without further purication.
2.2. Instruments and characterization
The samples were analyzed using FT-IR spectroscopy (using a
Perkin Elmer 65 in a KBr matrix in the range 4000–400 cmꢀ1).
The BET specic surface areas and BJH pore size distribution of
the samples were determined by the adsorption–desorption of
nitrogen at the liquid nitrogen temperature, using a Series BEL
SORP 18. The X-ray powder diffraction (XRD) of the catalyst was
carried out on a Bruker D8Advance X-ray diffractometer, using
nickel ltered Cu Ka radiation at 40 kV and 20 mA. The scanning
electron microscope (SEM) studies were performed on a Philips,
XL30, SE detector. The transmission electron microscope (TEM)
observations were performed on a Phillips CM10 microscope at
an accelerating voltage of 150 kV, in order to obtain information
on the size of the Ni nanoparticles and the X-ray photoelectron
spectra (XPS) were recorded on an ESCA SSX-100 (Shimadzu)
using a non-monochromatized Mg Ka X-ray as the excitation
source.
The Michael addition of MA to the amino groups on the
surface was carried out as follows. At rst, 0.42 g of PVAm/SBA-
15, 7 mL of methanol and 0.84 g (9.7 mmol) of MA were placed
in a round bottom ask. Then, the mixture was stirred with a
magnetic stirrer at 50 ꢁC. Aer 24 h, the resulting powder (MA–
PVAm/SBA-15) was separated, washed several times with
methanol and dried at room temperature (Scheme 1a).
The amidation of the resulting terminal ester groups of the
composite was carried out as follows. At rst, the obtained MA–
PVAm/SBA-15 powder, 7 mL of methanol and 0.84 g (13.9 mmol)
of EDA were placed in a round bottom ask. Then, the mixture
was stirred with a magnetic stirrer at 50 ꢁC. Aer 24 h, the
resulting powder (EDA–MA–PVAm/SBA-15) was separated,
washed several times with methanol and dried at room
temperature (Scheme 1b).
The two reactions of Michael addition and amidation were
repeated for the propagation of the hyperbranched poly-
amidoamine from the PVAm/SBA-15 surface, in order to yield
PAMAM–PVAm/SBA-15 (Scheme 1c).
2.3.3. Preparation of Ni nanoparticle-hyperbranched poly-
amidoamine–polyvinylamine/SBA-15. 1 mL aqueous solution of
NiCl2$6H2O (1 M) was added to the obtained PAMAM–PVAm/
SBA-15 (0.1 g) together with 3 mL of H2O and the solution pH
was adjusted to 3, by the addition of 0.1 M HCl aqueous solu-
tion. The mixture was stirred at 80 ꢁC for 5 h. Then, a solution of
NaBH4 (0.23 g, 6 mmol) dissolved in 5 mL methanol was added
1
The products were characterized by H NMR and 13C NMR
spectroscopy (Bruker DRX-500 Avance spectrometer at 400 and
100 MHz, respectively). The melting points were measured on
an Electrothermal 9100 apparatus and they were uncorrected.
All the products were known compounds and they were char-
acterized by FT-IR, 1H NMR and 13C NMR. All the melting points
were compared satisfactorily with those reported in the
literature.
2.3. Catalyst preparation
2.3.1. Preparation of polyvinylamine/SBA-15 composite. to the mixture drop by drop over 20–30 min. Aer that, the
Mesoporous silica SBA-15 was prepared through the method solution was stirred for 3 h. Then, the addition of the same
described in the literature recently.35
amount of NaBH4 was repeated and again the mixture was
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RSC Adv., 2014, 4, 7444–7453 | 7445