Design, synthesis and properties of polyimide alignment materials

Polyimide has been applied to the alignment of liquid crystals (LCs) since 1970. It is desirable that polyimide has a stable conformation for control of the pretilt angle of LCs. Low pretilt angle (1-2 degrees) of LCs is the key issue for high duty TN-LCDs. In this paper we report the design, synthesis and properties of a series of polyimide alignment materials for LCs. The LC cells exhibit stable pretilt angle (less than 2 degrees) irrespective of curing temperature and rubbing treatment, and also show no reverse tilt disclination after thermal annealing treatment. We suggest that rigid biphenyl skeletons are the key factor for the stable conformation of polyimide alignment materials