Synthesis and characterization of a soluble polyimide containing a photoreactive 4-styrylpyridine derivative as the side group

Abstract

An aromatic polyimide bearing photoreactive 4-(2-(4-oxyethylenyloxyphenyl)vinyl)pyridine side groups was synthesized and characterized. The polymer is stable up to 300 degreesC and soluble in organic solvents, giving thin films in good quality. When exposed to UV light, it reorients favorably with an angle of 98 degrees with respect to the electric vector of linearly polarized UV light. UV-exposed films align liquid-crystals (LCs) homogeneously along the preferential orientation of the polymer chains on the surface. The pretilt angle of the LCs is 0.32-0.92 degrees, depending on the exposure dose and annealing. LC alignment is retained up to 210 degreesC. Based on the optical retardation behavior and spectroscopic measurements, a photoalignment mechanism is proposed.