Synthesis and properties of polyacetylenes with directly attached bis(4-alkoxyphenyl)terephthalate mesogens as pendants

Liquid-crystalline, monosubstituted polyacetylenes containing lateral pendants of bis(4-alkoxyphenyl)terephthalate with no flexible spacers and alkoxy tails {RO, where R is CH3 [P(1)] or C6H13 [P(6)]} were synthesized, and the effects of the backbone structure and alkoxy tails on the properties of the polymers were investigated. The polymerizations of acetylene monomers were carried out with chloronorbornadiene rhodium(I) dimer as a 1,2-insertion catalyst in toluene. The structures and properties of the monosubstituted polyacetylenes were characterized and evaluated with nuclear magnetic resonance, infrared spectroscopy, thermogravimetry, differential scanning calorimetry, polarized optical microscopy, ultraviolet spectroscopy, and photoluminescence analyses. The molecular weights of the polymers were measured by gel permeation chromatography. The polymer with long tails (p-hexyloxy), that is, P(6), formed a smectic mesophase upon heating above the melting temperature, but the other one with short tails (p-methoxy), that is, P(1), could not exhibit liquid crystallinity at elevated temperatures. The steric effect of bulky, liquid-crystal line mesogens and a direct connection with the main chain prevented the planar conformation of the polyene backbone and, therefore, led to the lower absorption and emission wavelength of the polymers. (c) 2006 Wiley Periodicals, Inc.