Synthesis and characterization of semi-alicyclic poly(amic acid) varnishes via bis-spironobornane dianhydride and the derived polyimide alignment layers for potential applications in TFT-LCDs

Abstract

A series of semi-alicyclic poly(amic acid) varnishes designed for potential applications as the alignment layers for thin-film transistor driven liquid crystal display devices (TFT-LCDs) were prepared from an alicyclic dianhydride, norbornane-2-spiro-α- cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (CpODA) and aromatic diamines. Then, the liquid crystal (LC) minicells were fabricated by using the polyimide (PI) as the alignment layers, which were prepared by thermally dehydrating the PAA varnishes at elevated temperatures. The derived PI alignment layers exhibited good thermal stability with the 5% weight loss temperatures higher than 470 °C. In addition, the PI layers showed excellent optical transparency with the transmittances higher than 94.0% at the wavelength of 550 nm with a thickness around 100 nm. The LC cells fabricated with the CpODA-PI alignment layers exhibited good optoelectronic features. The rubbing PI layers could induce the effective alignment of the LC molecules with the pretilt angles in the range of 1.62–2.14°. The voltage holding ratios of the LC cells were higher than 92.00%, and the residual direct voltage values were all lower than 300 mV.