ABSTRACT:We investigated photo-alignment properties of main-chain polyimides prepared from acid anhydrides [4,4 0 -(hexafluoro-isopropylidene) diphthalic anhydride (6FDA) or 4,4 0 -biphthalic anhydride (BPDA)] and diamine derivatives containing a chalcone group. The polyimides in the film state were irradiated with linearly polarized UV (LPUV) light under different conditions. The liquid-crystalline (LC) cell was fabricated from the polyimide film irradiated with LPUV light. A mixture of a low molecular liquid crystal (4-cyano-4 0 -n-pentylbiphenyl: 5CB) and a dichroic dye was filled in the LC cell. 5CB in the LC cell was easily aligned perpendicular to the electric vector of the incident LPUV light. [DOI 10.1295/polymj.37.162] KEY WORDS Chalcone / Liquid-Crystalline Polymer / Photo-alignment / Polyimide / Alignment of liquid-crystalline (LC) molecules is important for liquid-crystalline displays (LCDs). Rubbing has been mainly employed for the uniaxial orientation of the LC molecules. However, rubbing has many disadvantages for LCDs such as generation of electrostatic charge and dust. Therefore, many methods of alignment technique for LC molecules focus on rubbing free methods. Photo-alignment procedure is a rubbing free method and is investigated as one of candidates that overcome the generation of electrostatic charge and dust for the rubbing process. 1,2The photo-alignment procedure is based on photochemical reactions such as photo-isomerization, photo-dimerization (photo-crosslinking) and photodecomposition.3-5 Photo-dimerization of photosensitive groups in polymers is employed to obtain a stable alignment of LC molecules. 2,[6][7][8][9][10][11][12] It is desirable that photo-dimerization occurs by the exposure of relatively longer wavelength of the UV light to avoid partial degradation of polymers by the irradiation.13 Photoreaction of chalcone moieties takes place by the irradiation with relatively longer wavelength of the UV light. Non-mesogenic photosensitive polymers containing chalcone derivatives have been studied for the photo-alignment film. 13-19The alignment of LC molecules is easily improved by the surface of LC polymers that exhibit a mesophase. This idea arises from the simple role of solubility for organic compounds, that is, like dissolves like. We already investigated thermal and photo-alignment properties of side-chain LC methacrylate polymers and side-chain polyimides bearing the chalcone derivative in the side chain. [20][21][22] Generally, main-chain polyimides demonstrate good thermal and mechanical properties based upon the rigid rod-like chemical structure of the polymer backbone. Therefore, main-chain polyimides would be suitable candidates for the polymeric materials applied to the photo-alignment film, because many polyimide derivatives have been used as an alignment film of LCDs owing to excellent thermal and mechanical properties.In this study, we investigate the extent of photoreaction of the chalcone-based main-chain polyimides prepared from two anhydride compounds [4,4 0 -(...

ABSTRACT:We synthesized main chain polyimides containing photosensitive chalcone moiety and investigated thermal properties of the polyimides. The polyimides were prepared by acid anhydrides [4,4 0 -(hexafluoro-isopropylidene) diphthalic anhydride (6FDA) or 4,4 0 -biphthalic anhydride (BPDA)] and diamine derivatives containing a chalcone group. The polyimides with 6FDA derivative were soluble in organic solvents such as tetrahydrofuran, chloroform and N,N-dimethylformamide. On the other hand, the polyimides with BPDA derivative were insoluble in common organic solvents. The polyimides with 6FDA derivative did not exhibit any mesophases, while the polyimides with BPDA derivative displayed a smectic phase.