Abstract: A novel biphenyl side-chained diamine with alkyloxy spacer and alkyloxy tail, 4′-butoxy-4-(3,5-diami- nobenzoyloxy)hexyloxybiphenyl(C6BBC4), was synthesized and characterized by FTIR and 1H NMR. A series of polyimide(PI) films with different side chain contents was synthesized from biphenyltetracarboxylicdianhydride (BPDA), 4,4′-oxydianiline(ODA) and C6BBC4, and their thermal properties, optical transparency and liquid crystal alignment property, and so on, were investigated by thermogravimetric analysis(TGA), differential scanning calorimetry(DSC), crystal rotation method, polarizing microscopy and UV-Vis spectra. With the content of side chained diamine increasing from 0 to 100%, the η_inh of poly(amide acid)(PAA) decreased rapidly from 3.0 to 0.51, the glass transition temperature(T_g) of polyimides(PIs) decreased from 274 °C to 203 °C and the Vis-light transmittance of alignment films substantially increased. As for the alignment properties, the pretilt angle of PI alignment films wi- thout rubbing could reach 90° when the content of C6BBC4 was 60% or more. At the same time, the alignment stability could meet the industrial requirements. It was considered that the alkoxy spacer, the biphenyl unit and the alkoxy tail may all play important roles in achieving a large pretilt angle even up to 90°, and the introduction of only the alkoxy spacer or alkoxy tail can also improve the pretilt angle, but not by much.

Key words: Polyimide, Alignment film, Liquid crystal, Biphenyl side chain