Strong Liquid Crystal Anchoring on Photo-Alignment Copolymer Films Containing ω-(4-chalconyloxy)alkyl Side Groups

One order of magnitude enhancement of the liquid crystal anchoring strength can be realized on photo-aligned copolymer films containing ω-(4-chalconyloxy)alkyl side groups, when the photo-dimerization of chalconyl units by linearly polarized near ultraviolet light is carried out at a temperature above the glass transition of the start polymer. Under the optimal condition, the polar anchoring strength was found to become comparable with that of rubbed polyimide alignment films, thereby allowing a stable electro-optical performance. Based on the behavior of the photo-induced optical anisotropy, we argue that the enhanced anchoring results from a cooperative relaxation of polymer main chains that assists further photo-crosslinking of chalconyl units via a “zipper-closing” mechanism.