Synthesis and characterization of colorless polyimides for liquid crystal alignment layer

A series of soluble polyimides has been synthesized by polycondensation rea ction of 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexane-1,2-dicarboxylic anhydride (DOCDA) and the mixture of p-phenylenediamine(p-PDA) and the new ly prepared diamine with pendant hexadecaoxy group(DA-L-160) via one step p olymerization in m-cresol at high temperature. The inherent viscosities of the resulting polymers measured in NMP were in the range of 0.27 to 1.41 dL /g, which was decreased with the increase of the content of the diamine wit h the pendant hexadecaoxy group. The obtained polyimides were highly solubl e in common aprotic polar solvents and some of them were even soluble in co mmon organic solvents such as tetrahydrofuran, cyclohexanone, chloroform. T he glass transition temperatures of the polyimides were in the range of 186 similar to 327 degreesC and most of the polyimides had good transparency i n the wavelength of 400 similar to 700nm. The pretilt angle of liquid cryst als (BL-002, Merck Ltd.) with polyimides having alkoxy side chain was inves tigated, which revealed that the increase of alkoxy side chain in polyimide resulted in higher pretilt angles.