Liquid crystalline compounds with various rigid siloxane frameworks

Novel oligosiloxanes with mesogenic group were synthesized from tetrakis(dimethylsiloxy)silane (cross-structured), 1,3,5,7-tetramethylcyclotetrasiloxane (cubic-structured), tetraphenyltetrahydroxycyclotetrasiloxane (cyclic-structured, having bulky phenyl group), tetrakis(dimethylsilyl)octaphenylsilsesquioxane (double-decker type), and hydride Q resin (branch structured) as cores and 4-allyloxy-4′-cyanobiphenyl (M1) and cholesteryl-10-undecenoate (M2) as mesogenic derivatives via hydrosilylation reaction catalyzed by Karstedt's catalyst. The phase behaviors of these oligomeric compounds with various structures of the mesogenic group and the core were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD) measurements. Liquid crystalline properties were observed for almost all of the synthesized oligomers in a wide temperature range.