THERMOTROPIC HYDROCARBON MAIN-CHAIN LIQUID-CRYSTALLINE POLYMERS BASED ON A TOLAN MESOGEN - SYNTHESIS AND CHARACTERIZATION

A series of thermotropic hydrocarbon liquid-crystalline oligomers contained a tolan mesogenic unit connected by a flexible polymethylene spacer were prepared. The oligomers were synthesized by a palladium-catalyzed carbon-carbon coupling reaction between aryl iodide and aryl acetylene monomers. Polymers with number-average molecular weights in the range of 3000-4000 have been obtained. Four tolan polymers with 6, 8, 10, and 12 methylene spacers were prepared and characterized by DSC, polarized light optical microscopy, X-ray diffraction, and solid-state C-13 NMR. The polymers were liquid-crystalline, but their mesophases could not be definitively characterized. Lengthening the polymethylene spacers between the tolan mesogenic groups decreased both the melting points and the isotropization temperatures and also narrowed the mesomorphic ranges.