Side-Chain Azobenzene Polymers: Synthesis and Properties 117=[349]
bath for 10 min. A solution of distilled methacryloyl chloride (1.15 g, 0.011 mol) in
THF (10 mL) was added slowly to the reaction mixture. After the addition of
methacryloyl chloride, the solution was stirred for 12 h at ambient temperature.
The solvent was removed by the rotary evaporation, and the residue was washed
with a solution of sodium carbonate (0.8 g) in water (40 mL). After removing the
solvent, the resulting material was purified by column chromatography (silica gel,
ethyl acetate=hexane 1=8). Red solid residue, yield: 87%. 1H NMR (CDCl3), d
(ppm): 7.89, 7.87 (d, 4H, Ar), 7.75, 7.73 (d, 2H, Ar), 6.82, 6.8 (d, 2H, Ar), 6.1
(s, 1H, CH2), 5.6 (s, 1H, CH2), 4.36 (m, 2H, OCH2), 3.7 (m, 2H, NCH2), 3.55
(m, 2H, NCH2), 1.94 (s, 3H, CH3), 1.25 (m, 3H, NCH2CH3).
40-[(2-Methacryloyloxyethyl)ethylamino]-azobenzene (M2). Azomonomer M2 was
synthesized using the above procedure for azomonomer M1. The product was purified
by column chromatography (silica gel, ethyl acetate=hexane 1=8). Orange solid
1
residue, yield 75%. H NMR (CDCl3), d (ppm): 7.83, 7.85 (d, 4H, Ar), 7.48 (t, 2H,
Ar), 7.38 (t, 1H, Ar), 6.8 (d, 2H, Ar), 6.11 (s, 1H, CH2), 5.6 (s, 1H, CH2), 4.36 (m, 2H,
OCH2), 3.71 (m, 2H, NCH2), 3.51 (m, 2H, NCH2), 1.95 (s, 3H, CH3), 1.24 (m, 3H, CH3).
40-[(2-Methacryloyloxyethyl)ethylamino]-4-nitroazobenzene (M3). Azomonomer
M3 was synthesized in the same way as azomonomer M1. The solid was
1
recrystallized from methanol. Dark red crystals, yield 80%. H NMR (CDCl3), d
(ppm): 8.33, 8.31 (d, 2H, Ar), 7.92 (t, 4H, Ar), 6.83, 6.81 (d, 2H, Ar), 6.1 (s, 1H,
CH2), 5.6 (s, 1H, CH2), 4.37 (m, 2H, OCH2), 3.74 (m, 2H, NCH2), 3.56 (m, 2H,
NCH2), 1.94 (s, 3H, CH3), 1.24 (m, 3H, CH3).
Polymerization. Polymers were synthesized by free-radical polymerization in toluene. The
homo-polymerization was carried out in a 10-wt. % dry toluene solution of a monomer
with AIBN as a free radical initiator (1 wt.% of monomer) at 80ꢀC 35h in the argon
atmosphere. Previously, the initial mixture was degassed with repeated freeze-pump-taw
cycles. The polymerization was stopped by pouring the reaction mixture into methanol.
The polymer was redissolved in THF and then precipitated in methanol. This procedure
was repeated several times to ensure the removal of the unreacted methacrylic
monomer, and finally the homo-polymer (P3) was dried under vacuum at 50ꢀC
overnight. The synthesis of copolymers based on azobenzene methacrylic monomers
M1, M2, M3, and MMA was a typical polymerization procedure [21]. The
copolymerization ratios in the corresponding polymers P1-MMA (1:1), P1-MMA (1:3),
P2-MMA (1:1), P2-MMA (1:3), P3-MMA (1:1), and P3-MMA (1:3) were calculated on
the basis of the integrated peak areas of 1H NMR spectra in DMSO-d6.
3. Results and Discussion
The 40-[(2-hydroxyethyl)ethylamino]-4-cyanoazobenzene and 40-[(2-hydroxyethyl)-
ethylamino]azobenzene were prepared by coupling the diazonium salt of 4-amino-
benzonitrile or aniline correspondingly with 2-(N-ethylanilino)ethanol according to
the procedure published previously [22]. The 40-[(2-hydroxyethyl)ethylamino]-4-
nitroazobenzene is commercially available (Aldrich). The azobenzene methacrylate
monomers were synthesized by the reaction of azobenzene alcohols with methacry-
loyl chloride in the presence of triethylamine as a nucleophilic catalyst and a hydro-
chloric acid acceptor. The polymers were synthesized by the radical polymerization
using AIBN as a radical initiator.