Fully rodlike polyimides containing flexible side chains with various lengths and their ability to align liquid-crystals on the rubbed surface

Abstract

Rodlike poly(p-phenylene pyromellitimide)s with various side chains (Cm-PMDA-PDA PIs) were newly prepared in a good quality of films. The polyimide films were rubbed, and used in constructing liquid-crystal (LC) cells which were filled with a nematic LC containing a dichroic dye. For the LC cell, both pretilt angle and alignment director of LCs were dependent strongly on the side chain length as well as the rubbing density. On the polymer film, both homogeneous and homeotropic LC alignments were achievable by either changing the side chain length or varying rubbing density. Unlike polymers reported previously as a LC alignment layer material, the Cm-PMDA-PDA P1 induced LCs to pretilt with a negative angle rather than a positive angle: this is a unique property characteristic of the Cm-PMDA-PDA PIs, In addition, film properties were measured.