Photo-alignment of azobenzene polymers with both thermotropic liquid crystallinity and proton conductivity in thin films

Abstract

By RAFT polymerization, we prepared side-chain liquid crystalline block copolymers, PHMA-b-P(Az-co-AA), connected P(Az-co-AA) to poly(hexyl methacrylate) (PHMA). Evaluating the synthesized block copolymers of the composition by NMR, we could obtain PHMA100-b-P(Az34-co-AA52) and PHMA50-b-P(Az36-co-AA84). The volume fractions of P(Az-co-AA) block (ΦAz-AA) in two block copolymers were 0.53 and 0.75, respectively. The LC orientations of two block copolymer thin films were analyzed by UV-vis absorption spectroscopy. After annealing, the absorption band due to the mesogenic Az decreased in PHMA50-b-P(Az36-co-AA84) film. This indicates the homeotropic orientation of the mesogenic group in thin films. On the other hand, in PHMA100-b-P(Az34-co-AA52) film, the absorbance of the band was almost unchanged, suggesting that PHMA100-b-P(Az34-co-AA52) adopts the random planar orientation in a thin film.