Synthesis and characterization of mesogenic disklike benzenetricarboxylates containing diacetylenic groups and their polymerization

Polymerizable disklike compounds that have a benzene ring core and three rigid diacetylenic units were prepared. The diacetylenic units were attached to the benzene ring via ester linkages. By varying number of alkoxy tail carbons and benzene rings of the disk, the morphological change of the compounds and their polymerization were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy, infrared spectroscopy (IR), and powder X-ray diffraction (XRD). Compound 7 with no alkoxy tail was glassy or small crystals at room temperature and showed crystal-to-crystal phase transition when heated. Compounds 8 with butyloxy tails, 9 with hexyloxy tails, and 10 with octyloxy tails showed monotropic transitions. When the compounds were cooled from the isotropic liquid states, birefringent phases with mosaic textures were observed. XRD study showed that compounds 9 and 10 had hexagonal columnar structures in their liquid crystalline (LC) states. The diacetylene compounds were polymerized by irradiation with UV in solid states or LC states. IR and UV-vis studies showed that the polymerization proceeded by 1,4-addition.