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30
Published on the web April 4, 2012
Synthesis of Hyperbranched Azo-polymer-grafted Graphene Oxide Hybrid
Yang Wang, Renbo Wei, Yaning He,* and Xiaogong Wang
Department of Chemical Engineering, Laboratory for Advanced Materials, Tsinghua University,
Beijing 100084, P. R. China
(
Received January 13, 2012; CL-120033; E-mail: heyaning@mail.tsinghua.edu.cn)
O
O
Hyperbranched azo-polymer-grafted graphene oxide (GO)
O
O
O
O
i
OH
O
OH
hybrid was synthesized. Epoxy-based precursor polymer was
first covalently attached to GO through an ester linkage. Then
the hyperbranched azo-polymer-grafted graphene oxide hybrid
can be obtained by azo-coupling reaction between the epoxy-
based precursor-polymer-functionalized GO and hyperbranched
diazonium salts under extremely mild conditions.
O
O
O
OH
O
OH
O
OH OH
O
(
GO)
O
OH
O
O
O
N
O
OH
n
iii
O
(
GO-BPAN)
O
O
N
n
O
O
N n
OH
OH
N
OH
(
BPAN)
O
C
O
N
N
O
C
O
C
N
O
N
NH2
O
O
N N
ii
m
O
C
O
N
N
m
O
C
O
NH2
C
O
N2
(HB-DAS)
(GO-HBAZO)
AB2 Monomer
Graphene, the first isolated monolayer of carbon atoms
arranged in a two-dimensional network, has attracted much
attention due to its intrinsic properties, such as electrical
transport capacity and intrinsic tensile strength.1 As a tradi-
tional precursor for graphene, chemically derived graphene
oxide (GO) has received increasing attention for its own
Scheme 1. Synthetic route of GOHBAZO. Reaction con-
ditions: (i) BPAN, DMF, r.t.; (ii) HOAc, H SO , NaNO , 0 °C,
DMF; (iii) DMF, 0 °C.
2
4
2
4
Scheme 1 shows the synthetic route of hyperbranched azo-
polymer-functionalized GO (GOHBAZO). GO was prepared
from natural graphite powder by a modification of Hummers
5
characteristics. The oxygen-containing functional groups such
as carboxy, hydroxy, and epoxy groups on the basal plane or the
sheet edge allow GO to interact with various materials to easily
prepare functional hybrids and composites.5
2
0
method. Sodium nitrate, sulfuric acid, potassium persulfate,
phosphoric anhydride, and potassium permanganate were used as
oxidants. After exhaustive washing with deionized water until
the pH was 7, the resulting GO sheets were purified by dialysis
for one week and finally were dried in air. Then GO powder was
dispersed in dry dimethylformamide (DMF), and a solution of
BPAN, N-ethyl-N¤-(3-dimethylaminopropyl)carbodiimide hy-
drochloride (EDC¢HCl), and 4-dimethylaminopyridine (DMAP)
in DMF were added, and the solution was stirred at room
temperature for two days. The resulting GOBPAN was filtered,
and rinsed with DMF several times. An AB2 monomer N,N-
bis[2-(4-aminobenzoyloxy)ethyl]aniline was synthesized accord-
7
It is well known that photochromic azobenzene derivatives
exhibit diverse photoresponsive properties for their transcis
photoisomerization upon light irradiation. On the basis of the
photoisomerization, materials containing azobenzene chromo-
phores show potential applications in areas such as holographic
information storage, photoswitching, sensors, and many oth-
812
ers.
Hyperbranched azo polymers with a highly branched
backbone and a large number of terminal functional groups have
received great attention during the past decade.1
3,14
Hyper-
branched azo polymers with different structures have been
reported to show many interesting photoresponsive properties
such as good surface relief grating properties and enhanced
second-order nonlinear optical properties.1
2
1
ing to our previous report. The hyperbranched azo polymer
bearing peripheral diazonium groups (HBDAS) was obtained
through the azo-coupling reaction of above AB2 monomer in
416
2
1
Recently, GO containing low-molecular-weight azobenzene
moieties (GOAZO) has been reported to show some attractive
properties such as tunable electronic properties.17 The con-
ductance of the GOAZO film can be optically modulated by
irradiating with UV light. We recently reported that graphene
nanosheet grafted with azo polymer brushes prepared via a
DMF. Then GOBPAN and HBDAS DMF solution were
mixed in DMF and stirred for 3 days under 0 °C. The resulting
GOHBAZO was filtered, and rinsed with DMF several times.
2
2
The exact experimental details are shown in the ESI.
The UVvis spectrum of GOHBAZO in DMF is shown in
Figure 1. The maximum absorbance of GOHBAZO in DMF
appears at about 484 nm, which is related to the ³³* transition
of the trans isomers of the azobenzene units. The spectrum
shows typical absorption behavior of the pseudo-stilbene type
of azo chromophores, which confirms the hyperbranched azo
polymer has been successfully attached to the GO sheets.
The FTIR spectra of GO and GOHBAZO are shown in
Figure 2. For GOHBAZO the new peaks at about 2960, 2872,
“
grafting-from” approach could significantly increase the surface
relief grating diffraction efficiency growth rate and the saturated
1
8
level. However, a study of the preparation of GO grafted with
hyperbranched azo polymer has not appeared in the literature yet.
Functionalizing GO with hyperbranched azo polymers can
combine the interesting properties of graphene and the unique
photoresponsive properties of hyperbranched azo polymers. In
this paper, hyperbranched azo-polymer-grafted GO hybrid was
synthesized. Precursor polymer (BPAN)19 was first covalently
attached to GO through an ester linkage. Then the hyperbranched
azo-polymer-grafted GO hybrid can be obtained by azo-coupling
reaction between the BPAN-functionalized GO and hyper-
branched diazonium salts under extremely mild condition.
¹
1
and 2927 cm can be attributed to the CH3 and CH2 in the
¹1
azo polymers. The strong peaks at 1600 and 1510 cm can be
attributed to the benzene rings of the polymer. The peak at
¹
1
1716 cm corresponds to the C=O stretching vibration of the
aromatic ester bond. XPS was also used to confirm that the azo
polymer has been attached to the GO sheets (Figure 3). The
Chem. Lett. 2012, 41, 430431
© 2012 The Chemical Society of Japan