| Liquid crystal device(LCD) has attracted more interest due to flatness portability, lower power consumption and eyesight protection .The share of LCD in the international display field will close to that of CRT and keep increasing tendency. The surface rubbing technique has been commonly used for fabricating liquid crystal display panels by LCD industry. However, the rubbing process may cause electrostatic charge, dust or scratches that tend to destroy the display quality. Non-rubbing technique, photoalignment technique attracts more people's attention. Photoalignment is promising for overcoming the drawbacks caused by the rubbing process and providing multi-domain structure for widening the viewing angle and a new way for liquid crystal optic devices.The mechanism of photoalignment is that the selective photoreaction broke out on the surface of the polymer under the irradiation of linearly polarized ultraviolet light (LPUV). The orientational alignment of molecular chains induces LC alignment in a certain direction. Poor thermal stability as a bottleneck has limited the development of liquid crystal photo-alignment technique. The intrinsic reason is that the photosensitive polymer has large space resistance and decreases the reaction degree of the directional photo-polymerization. The effective solution is focused in the increase of orientational order of photo-alignment film. In this paper, the alignment method of Four-center linear polymerization using cinnamate monomers was put forward and the photoalignment technique was searched in details and renovated.The monomer structures were designed. Biphenyldicinnamate ester (BPDE) , bisphenol A dicinnamate ester (BADE) , and hexafluorobiphenol A dicinnamate ester (6F-BADE) were synthesized in our laboratory. Changing the rigidity of molecular structure solved the crystallizing problem in the process of spin-coated monomer films and a good film in quality was fabricated. The photochemical reaction rate and degree were measured by UV-visible and infrared absorbance spectra. When the fluorine atoms were grafted in the monomer structure, the reaction degree as well as the reaction rate was enhanced obviously. The photo-crosslinking films of BPDE and BADE can induce homogeneous alignment of liquid crystals. Uniform alignment was kept even curing at 90℃ for 30 minutes and the thermal stability was suit to the general fabrication of liquid crystal devices. Photo polymerized films of 6F-BADE can align liquid crystal in homeotropic alignment and the thermal stability reaches 120℃. It suggests that the photo polymerized 6F-BADE was fitted to fabricate multi-domain vertical alignment, a LC display mode with broad viewing angles. The orientational orders of the photoaligned polymer films were analyzed by polarized Fourier transition infrared (FT-IR) spectra. The quantitative calculation was made by the infrared dichroic absorption. The results indicate that the orientational orders of monomer photoalignment films of BPDE, BADE were much larger than that of polymer (cinnamate) photoalignment films.In summery, this work was successfully performed based' on the elementary knowledge of physics and chemistry. It has a valuable contribution to the improvement and the application of the photo-alignment technique.
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