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Photoalignment and Holographic Properties of Azobenzene-Containing Block Copolymers with Oxyethylene and Alkyl Spacers

Two azobenzene-containing block copolymers with an oxyethylene (P1) or an alkyl (P2) spacer in the side chain were prepared by atom transfer radical polymerization (ATRP). Neither of the block copolymers with a low azobenzene content showed a liquid-crystalline phase. However, their glass transition temperatures (T gs) were lowered by introducing flexible spacers. In particular, T g was lowered by about 30°C in P1. Their photoalignment and holographic behavior was investigated at various temperatures in thin films. Rapid changes in refractive index were induced in the P1 films upon irradiation at a temperature below T g. But the photoinduced birefringence in the P1 film was lower than that in the P2 films. Similar results were obtained in holographic recording. The azobenzene-containing block copolymer with the oxyethylene spacer (P1) used in this study has potential application for dynamic hologram.