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

A series of thermotropic hydrocarbon liquid-crystalline oligomers cont ained a tolan mesogenic unit connected by a flexible polymethylene spa cer were prepared. The oligomers were synthesized by a palladium-catal yzed carbon-carbon coupling reaction between aryl iodide and aryl acet ylene 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, p olarized light optical microscopy, X-ray diffraction, and solid-state C-13 NMR. The polymers were liquid-crystalline, but their mesophases c ould 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 mesom orphic ranges.