Preparation of a novel ternary photosensitive polyimide for liquid crystal alignment films

Abstract

In order to obtain liquid crystal alignment films with better photosensitivity, transmittance and solubility, a ternary copolymer polyimide (BFB-PI-CA) is synthesised by benzophenone-3, 3′, 4, 4′-tetracarboxylic dianhydride (BTDA), 4,4ʹ-hexafluoroisopropyl phthalic anhydride (6FDA) and 2,2-bis (3-amino-4-hydroxyphenyl) propane (BAP). The initial thermal decomposition temperature (Td5) of the BFB-PI-CA is 371°C. And it shows good solubility. The BFB-PI-CA film has excellent optical transparency in the visible region (400–700 nm) after UV irradiation, which transmittance at 400 nm is 95.3%. In addition, after irradiated by non-polarised ultraviolet light (NPUVL) for 15 min, the film can show excellent alignment performance which remains unchanged after 24 h at 100°C. The pretilt angle is 0.4°C, which can meet the use of liquid crystal display (LCD) in parallel mode.