Synthesis and properties of polyacetylenes containing bis(4-alkylphenyl)terephthalate as pendant and methyleneoxy as spacer

Monosubstituted polyacetylenes containing lateral pendants of bis(p-alkylphenyl)terephthalate with spacer and alkyl tails [R, where R is H, CH3 and C3H7] were synthesized, and the effects of the backbone structure and alkyl tails on the properties were investigated. The monomer with alkyl tails (p-methyl and p-propyl) formed a smectic mesophase upon heating above the melting temperature, but the other one without tails could not exhibit liquid crystallinity at elevated temperatures. The lower melting temperature and wider mesomorphic temperature range of 2-propargyloxy-bis(p-propylphenyl)terephthalate (k 91.6 SmB 102.6 i) than 2-propargyloxy-bis(p-methylphenyl)terephthalate (k 134.3 SmB 143.7 i) indicated that the long tail in mesogen played an important role in the packing order and stability of their liquid crystalline phase. The polymerization of acetylene monomers were carried out with [Rh(nbd)Cl]2 as a catalyst in toluene. The structures and properties of the monosubstituted polyacetylenes were characterized by the means of nuclear magnetic resonance, polarized optical microscopy, infrared spectroscopy, ultraviolet spectroscopy, photoluminescence, thermogravimetry and differential scanning calorimetry. The molecular weights of the polymers were measured by gel permeation chromatograph. The polymers could not exhibit liquid crystallinity at elevated temperatures. The steric effect of bulky liquid-crystallinity mesogens prevented the coplanar conformation of the polyene backbone, and thus, led to the lower absorption and emission of the polymers.