Study on the Photo-alignment Performance of Liquid Crystalline Polymers with Photosensitive Groups

Abstract

The liquid crystalline polymers with photosensitive groups can self-assemble like the low-molar-mass liquid crystals. Also when the polymer film is exposed to linearly polarized (LP) light, it can react a polarization-axis selective photoreaction. Upon irradiating, a small negative optical anisotropy results from an axis-selective photoreaction of the photosensitive groups, while annealing in the LC temperature range leads a large positive optical anisotropic change of the polymer film. Photo-alignment in polymeric film is a promising technique applicable to the photo-alignment layer of liquid crystal displays, birefringent optical devices, information records and holographic data storage devices.In this paper, a series of liquid crystalline polymers with photosensitive group were synthesized and photo-alignment performance was systematically investigated. The results showed that the photo-induced optical anisotropy ΔA increase with the exposure dose increase, and then became stable quickly, though A// and A⊥ continued increasing. What's more, the photo-induced optical anisotropy ΔA was thermally enhanced after annealing. The stability of coumain-containing polymers was better than cinnamate-containing polymers, because the former polymer materials only undergo an [2+2] photo-cross-linking reaction.