Synthesis and Characterization of Main Chain Polyimides Containing Chalcone Derivatives for LC Alignment

Abstract

Two soluble polyimides containing chalcone derivatives in the main chains were successfully prepared using the Mitsunobu reaction at room temperature, reacting diols with diimides. With this reaction procedure the high temperature imidization step normally needed for the synthesis of polyimides is avoided and the polymers can be used for temperature sensitive applications. The main chain polyimides were characterized with FT-IR, NMR and DSC and the extent of the photoreaction was measured with FT-IR and UV-vis spectroscopy. Isobestic points were observed in the absorption spectral changes at the early stage of UV irradiation as a result of a single photochemical process. Further photoirradiation is accompanied by deviation from the isobestic points, implying that another photochemical process has started. With FT-IR investigations it was concluded that photodimerization is the process occurring at low UV exposure doses and that trans-cis isomerization is starting simultaneously at higher doses. The optical anisotropic properties were investigated upon exposure of the polymers as thin films to linearly polarized UV (LPUV) light of different doses. Selected crosslinking in the parallel direction relative to the direction of the LPUV light and subsequent optical anisotropy in the film were achieved.