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

An aromatic polyimide bearing photoreactive 4-(2-(4-oxyethylenyloxyphenyl)v inyl)pyridine side groups was synthesized and characterized. The polymer is stable up to 300 degreesC and soluble in organic solvents, giving thin fil ms in good quality. When exposed to UV light, it reorients favorably with a n angle of 98 degrees with respect to the electric vector of linearly polar ized UV light. UV-exposed films align liquid-crystals (LCs) homogeneously a long 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 d ose and annealing. LC alignment is retained up to 210 degreesC. Based on th e optical retardation behavior and spectroscopic measurements, a photoalign ment mechanism is proposed.