Preparation and photoinduced isomerization study of a homopolymer and a copolymer based on 4′-(6-acryloxy)hexyloxy-4-methoxyazobenzene and acrylic acid

Abstract

The synthesis and characterization of a copolymer based on 4′-(6-acryloxy)hexyloxy-4-methoxyazobenzene (MAB6) and acrylic acid (AA) are reported. A reaction was carried out by free-radical polymerization, yielding an MAB6 homopolymer and an AA-MAB6 copolymer with an MAB6 concentration of 16-80%. A nematic phase was observed in the copolymer when the MAB6 content was 44% or higher. Both nematic and smectic phases were observed in the MAB6 homopolymer. All of the polymers were investigated for trans-cis-trans isomerization in a solid film. The samples were irradiated with nonpolarized ultraviolet light (385 nm) before absorption measurements were taken with an ultraviolet-visible spectrometer. The copolymer and homopolymer exhibited a thermal cis-trans isomerization, which could be described by a double-exponential relaxation process (fast and slow). The relaxation experiment suggested that the hydrogen bonding may have hindered the slow process but had no effect on the fast process. A film of a copolymer sample with a high MAB6 content could be optically aligned by the exposure of the sample to polarized light (385 nm).