Liquid crystal alignment property of polystyrene derivatives containing dual photoreactive side groups

We synthesized a series of polystyrene derivatives having the dual photoreactive side moieties, 4-(4-cyanophenylazo)phenoxymethyl and methyl cinnamate-4-oxymethyl, for the application of photoalignment materials. Stable and homogeneous planar LC cells having pretilt angles adjustable from 0.5° to 5° were obtained from these polymer films having molar contents of cinnamate and azobenzene groups in the ranges of 100–80 and 0–20 mol%, respectively, through the irradiation of linearly polarized ultraviolet (LP-UV) light to crosslink the cinnamate groups, followed by the irradiation of linearly polarized visible (LP-Vis) light to induce the isomerization of the azobenzene groups. The electro-optical and LC alignment properties of the LC cells were found to be affected by the molar composition of the photoreactive side groups and the exposure energies of LP-UV and LP-Vis light.