Synthesis and characterization of colorless polyimides for liquid crystal alignment layer

A series of soluble polyimides has been synthesized by polycondensation reaction of 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexane-1,2-dicarboxylic anhydride (DOCDA) and the mixture of p-phenylenediamine(p-PDA) and the newly prepared diamine with pendant hexadecaoxy group(DA-L-160) via one step polymerization 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 with the pendant hexadecaoxy group. The obtained polyimides were highly soluble in common aprotic polar solvents and some of them were even soluble in common organic solvents such as tetrahydrofuran, cyclohexanone, chloroform. The glass transition temperatures of the polyimides were in the range of 186 similar to 327 degreesC and most of the polyimides had good transparency in the wavelength of 400 similar to 700nm. The pretilt angle of liquid crystals (BL-002, Merck Ltd.) with polyimides having alkoxy side chain was investigated, which revealed that the increase of alkoxy side chain in polyimide resulted in higher pretilt angles.