Photosensitive Polyimides with Rigid Side Chain and Their Thermal Stable Liquid-Crystal Alignment Properties

Thermally stable polyimide (PI), which has a photoreactive p-phenylenediacryloyl (PDA) moiety in the main chain with a rigid biphenyl as a side group, was prepared from a poly(amic acid) (PAA) solution using a thermal imidization process. PAA was synthesized successfully with a reasonably high molecular weight and gave high quality films with relatively good thermal stability. The photoreactions and photoalignments of PI were analyzed by ultraviolet-visible spectroscopy, and their liquid crystal (LC) alignment properties were examined. The PI in the film showed good photoreactivity to UV light irradiation. Linearly-polarized ultra-violet light (LPUVL) irradiation induced anisotropic reorientation of the polymer chains in the film due to a direction-selective photoreaction of the PDA moieties. All the films irradiated with LPUVL aligned the LCs in a direction perpendicular to the electric vector of the LPUVL. The pretilt angles of the LC molecules on the LPUVL irradiated film surfaces were controlled by th...