The impact of the flexibility of photosensitive polyimide backbone on the properties of liquid-crystal alignment under non-polarised ultraviolet light

In order to study the impact of the flexibility of photosensitive polyimide (PI) backbone on the properties of liquid crystal (LC) alignment under non-polarised ultraviolet light (NPUVL), two kinds of photosensitive PI with different backbone structures were synthesised through the polymerisation of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (AHHFP) with 4,4MODIFIER LETTER PRIME-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4,4MODIFIER LETTER PRIME-oxydiphthalic anhydride (ODPA) respectively. Polarising optical microscope showed that the irradiation time for ODPA-PI-CA is shorter that for 6FDA-PI-CA in order to induce uniform LC alignment. The reason was investigated in detail with the UV-Vis spectra and reaction kinetics of the photosensitive group.