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Chemistry Letters Vol.33, No.1 (2004)
Synthesizing Hyperbranched Azo Polymer through Azo-coupling Reaction
Pengchao Che, Yaning He, Yue Zhang, and Xiaogong Wangꢀ
Department of Chemical Engineering, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, P. R. China
(Received September 26, 2003; CL-030911)
An AB2 monomer N,N-bis[2-(4-aminobenzoyloxy)ethyl]-
aniline was synthesized by nucleophilic substitution reaction be-
tween N,N-bis(2-chloroethyl)aniline and 4-aminobenzonic acid.
Based on the monomer, the azo-coupling reaction was explored
for the first time to prepare a hyperbranched azo polymer. The
results showed that the scheme was a feasible way to synthesize
hyperbranched azo polymers under extremely mild conditions.
Hyperbranched polymers (HBPs) have attracted considera-
ble attention in recent years.1 HBPs possess unique properties
of dendritic polymers such as high solubility, low solution and
melt viscosity compared to linear analogues, and amorphous na-
ture in solid state. Existence of a large number of end functional
groups enables HBPs to react with other reactive groups and to
significantly modify properties of the polymers. HBPs are gener-
ally prepared from ABx (where x is usually 2 or 3) monomers
through a one-step polymerization process.2 Polycondensation
reactions have been widely used for preparing HBPs, in which
strict reaction conditions such as high temperature and vacuum
are required.3 Linear azo polymers have been extensively stud-
Scheme 1.
ied in recent years for a wide range of applications such as rever-
sible optical storage systems, EO modulators, holographic grat-
1
vacuum at 70 ꢁC for 24 h. Yield: 80%, mp = 160 ꢁC. The H
NMR spectrum (DMSO-d6) of the compound and assignment
are given in Figure 1a.
ings and sensors. However, up to now, only few hyperbranched
azo polymers have been synthesized.4 In a previous paper, we re-
ported a way to obtain azobenzene-containing HBPs through the
esterification reaction.5 In this letter, we further report that azo
coupling reaction was used to synthesize an azobenzene-con-
taining HBP. To our knowledge, no HBPs or even linear poly-
mers have been prepared through this route.
The hyperbranched polymer was prepared by azo coupling
reaction. The N,N-bis[2-(4-aminobenzoyloxy)ethyl]aniline
(0.520 g 1.4 mmol) was dissolved in a homogeneous mixture
of glacial acetic acid (11.2 mL) and sulfuric acid (1.0 mL).
Aqueous solution of sodium nitride (0.242 g 3.5 mmol in
0.6 mL of water) was added dropwise into the solution at 0 ꢁC.
Then the clear solution of diazonium salt was added into DMF
(40 mL) and stirred at 0 ꢁC for 8 h. After the reaction, a solution
of N,N-bis(2-hydroxyethyl)aniline (0.253 g 1.4 mmol in 10 mL
of DMF) was added into the solution and kept in 0 ꢁC with stir-
ring for 5 h, which enabled the remaining diazonium salt groups
on the periphery to be completely reacted through azo coupling
reaction. The mixture was then poured into an excessive amount
of water. The precipitate was collected by filtration, washed re-
peatedly with water, and dried. The product was dissolved in
DMF (20 mL) and then dropped into ethanol slowly with stir-
ring. The precipitate was collected by filtration, washed repeat-
edly with ethanol, and dried under vacuum at 70 ꢁC for 48 h.
Yield: 60%.
The hyperbranched polymer was prepared through the route
shown in Scheme 1. N,N-bis(2-chloroethyl)aniline was synthe-
sized by the reaction between N,N-bis(2-hydroxyethyl)aniline
and phosphorus oxycholride. In the reaction, N,N-bis(2-hydrox-
yethyl)aniline (10 g, 0.055 mol) was added slowly into phospho-
rus oxychloride (10.2 mL, 0.11 mol) under ice-bath cooling. Af-
ter the addition was completed, the mixture was heated to 110 ꢁC
and reacted at that temperature for 1 h. The solution was then
poured into benzene (50 mL). After repeatedly washed with wa-
ter and then dried by using anhydrous magnesium sulfate, the
product was finally obtained by removing the benzene. Yield:
1
82%. H NMR (DMSO-d6), ꢀ ¼ 7:20 (2H, m), 6.67 (3H, m),
3.72 (8H, t). mp: 43 ꢁC.
N,N-Bis[2-(4-aminobenzoyloxy)ethyl]aniline was prepared
by nucleophilic substitution reaction between N,N-bis(2-chlor-
oethyl)aniline and 4-aminobenzonic acid. In the reaction, N,N-
bis(2-chloroethyl)aniline (1.308 g, 6 mmol) and 4-aminobenzon-
ic acid (2.888 g 2.4 mmol) were dissolved in DMSO (80 mL).
Potassium carbonate (8 g) and potassium iodide (2 g) were added
into the DMSO solution. The mixture was reacted at 110 ꢁC for
7 h with stirring and then precipitated into an excessive amount
of water. The product was collected by filtration and dried under
1
The H NMR spectrum of the hyperbranched azo polymer
and assignment are shown in Figure 1b. The resonance
(ꢀ ¼ 6:62 ppm, Figure 1a) corresponding to anilino moieties at
1
the focal points can no longer be observed from the H NMR
spectra of the final products, which indicates a high reaction
yield. The UV–vis spectrum of the hyperbranched azo polymer
in DMF solution is shown in Figure 2. The spectrum shows typi-
cal absorption behavior of the pseudo-stilbene type of azo chro-
Copyright Ó 2004 The Chemical Society of Japan
Che, Pengchao
