Synthesis and characterization of novel polyimides with 1-octadecyl side chains for liquid crystal alignment layers

A series of poly(amic acid)s have been synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), a functional diamine, 1-(3,5-diaminophenyl)-3-(1-octadecyl)-succinicimide and 4,4-diaminodiphenylmethane (DDM) to give liquid crystal alignment layers with high pretilt angle after a rubbing process for vertically aligned liquid crystal display devices. Inherent viscosities of the poly(amic acid)s measured were in the range 0.2-1.56 dl/g, which decreased with an increase of content of 1-(3,5-diaminophenyl)-3-(1-octadecyl)-succinicimide. The cured polyimide films had good transparency, which was above 95% at 400 nm. Surface energies of all the polyimide films prepared from 1-(3,5-diaminophenyl)-3-(1-octadecyl)-succinicimide were below 40.7 dyn/cm before the rubbing process, which resulted in very high pretilt angles above 89 degrees. By a rubbing process, the surface energy of the polyimide prepared from diamine mixture with 10 mol% of 1-(3,5-diaminophenyl)-3-(1-octadecyl)-succinicimide and 90% of DDM increased from 40.7 to 42.7 dyn/cm. Copyright (C) 2007 John Wiley & Sons, Ltd.