Synthesis and characterization of novel polyimides containing stilbene unit in the side chain and their controllability of nematic liquid crystal alignment on the rubbed surfaces

Four polyimides containing hexylene spacer and a fluorostilbene unit in the side chains were prepared in thin-film form by two-step condensation of 3,3'-bis[(4'-fluoro-4-stilbenyl)oxyhexyloxy]-4,4'-biphenyldiamine (FS6B) with pyromellitic dianhydride (PMDA), benzophenone-3,3',4,4'-tetracarboxylic dianydride (BTDA), 4,4'-oxydi(phthalic anhydride) (ODPA), and 4,4'-hexafluoroisopropylidenedi(phthalic anhydride) (6FDA), respectively, and their controllability of liquid crystal (LC) alignment on rubbed surfaces was investigated. Pretilt angles of LCs were achieved in the 2-9 degrees range, depending on the rubbing density and backbone structures. The effect of the mesogenic stilbene group on the pretilting of LCs was distinctive in FS6B-PMDA. Contact-angle measurements on thin films annealed at 120 degreesC revealed that FS6B-PMDA potentially had the better alignment stability than FS6B-6FDA. (C) 2001 John Wiley & Sons, Inc.