Abstract: The liquid crystal alignment layer plays a critical role in the liquid crystal display. In order to prepare liquid crystal alignment layer with excellent properties, three kinds of 3,5-diaminobiphenyls with different terminal groups were synthesized by Suzuki coupling reaction, and three polyimides were prepared by polymerization of the three diamines with 1,2,3,4-cyclobutanetetracarboxylic dianhydride. The structures of monomers and polymers were characterized by proton nuclear magnetic resonance (¹H NMR) spectroscopy. The solubility, thermal stability and properties of the polymers as liquid crystal alignment layer were studied. The resulting polyimides show good solubility and thermal stability. After rubbing, the polyimide with methoxy as terminal group can align the liquid crystal molecules parallel to the rubbing direction. On the contrary, the polyimides with phenoxycarbonyl and biphenoxycarbonyl as terminal groups align the liquid crystal molecules perpendicular to the rubbing direction. This kind of soluble polyimide liquid crystal alignment film will simplify the preparation process and present great application value in flexible display devices.

Key words: polyimide, alignment layer, solubility, thermal stability