Aromatic polyimides containing pendant alkyl groups for liquid crystal alignment layers

A series of polyimides has been synthesized by polycondensation reaction of 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride (BPDA) and correspondi ng diamines with various alkyl side chains via polyamic acid formation. The inherent viscosities of the polyamic acids measured in N-methyl-2-pyrrolid one (NMP) were in the range of 0.45 to 1.19 dL/g, which was decreased with the increase of alkyl chain length. The glass transition temperatures of th e polyimides were in the range of 247.6-291.4 degrees C. The effect of curi ng temperature on the pretilt angle of liquid crystals (BL-002. Merck Ltd.) with polyimides having alkyl side chains was investigated, which revealed that the increase of degree of imidization resulted in higher pretilt angle s. On the other hand. the pretilt angles were decreased by the curing react ion above the temperature of 300 degrees C due to decomposition reaction of alkyl side chains. It was also found that the pretilt angles were Varied w ith the length of alkyl side chains.