Abstract
Three organo-soluble polyimide powders have been synthesized. Their imidization was verified by Fourier transform infrared (FTIR) and thermal gravimetric analysis (TGA) techniques. The amorphous morphology of their thin films were confirmed by X-ray diffraction. Polyimide thin films were prepared by solution casting or spin coating. UV–visible transmission spectra of thin films revealed that they are almost transparent in the range of visible light. With in-plane orientation, revealed by FTIR spectra, negative birefringence (Δ n) of thin films were observed, and refractive indices of the thin films along the film plane ( n TE) and normal to the plane ( n TM) were measured by a prism coupler. Because of negative birefringence of the thin films, they can be substituted for the compensation films for twisted nematic liquid crystal displays (TN-LCDs) to extend their viewing angles. In this paper, a 90 °C TN-LCD and 120 °C TN-LCD were taken as examples to show the compensation effect of thin films of a qualified polyimide.
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