Synthesis and properties of monopolyacetylenes with terphenyl mesogens groups linked at waist position

Abstract

Side-on-fixed monosubstituted polyacetylene P(1) containing lateral pendants of terpheny mesogens linked at the waist position with flexible spacers and methoxy tail was synthesized successfully by polymerization of 5-{[2,5-bis(4′-methyloxyphenyl)carbonyl]oxy}-1-pentyne (M(1)) using the Rh complex catalyst. However, polymerization of the similar structure acetylene monomer 5-{[2,5-bis(4′-hexyloxyphenyl)carbonyl]oxy}-1-pentyne (M(6)) with hexyloxy tail was not successful. This is probably due to the steric hindrance of too long and bulky mesogenic groups. The structures and properties of the monomers and polymers 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 polymer were measured by gel permeation chromatography. The monomers formed smectic A phases in the heating and cooling processes. In sharp comparison to the monomers, the P(1) could not exhibit liquid crystallinity at elevated temperatures. This suggested that the short spacer and tail limited the mesogens to undergo thermal transitions in a relatively fashion. The polymer was stable and soluble in common solvents. The terphenyl mesogenic core contributes to the monomers and polymer with strong UV absorption. The polymer can emit blue light at 460 nm.