Isomeric effects on liquid crystal alignment behaviors of polystyrene derivatives

We synthesized a series of 4-ethylphenoxymethyl (P4EP) and 3ethylphenoxymethyl (P3EP) and 2-ethylphenoxymethyl-substituted polystyrenes (P2EP), using polymer analogous reactions, in order to study the isomeric effect of the ethylphenoxymethyl side groups on the liquid crystal (LC) alignment properties. The LC cells fabricated with the unrubbed P4EP, P3EP, and P2EP films exhibited uniform vertical, partial vertical, and random planar LC alignment. A high pretilt angle of about 90 degrees was observed from the LC cell prepared from the rubbed film of P4EP at number of rubbing of 1. On the contrary, the LC cells prepared from the rubbed films of P3EP and P2EP showed pretilt angles of approximately 30 degrees and 0 degrees at number of rubbing of 1, respectively. Therefore, the position of ethyl group attached to phenyl group in the side chain was found to LC alignment behavior of the polystyrene derivatives. The LC alignment behavior was well correlated with the wettability of the polymer films. These polystyrene derivatives having good solubility in many organic solvents and their films having low process temperature can be candidates for LC alignment layer in the flexible display. This study contributes to the latest efforts to develop new alignment layers for pretilt angle control.