Discotic liquid crystals: synthesis and mesomorphic properties of polyacetylenes carrying triphenylene pendant groups

Triphenylene-containing poly(1-decyne)s with different alkyl chain lengths are synthesized and the effects of the structural variables on their mesomorphic properties are investigated. The monomers [HC≡C(CH₂) ₈CO₂C₁₈H₆(OC_m _H2m+1)₅; m = 4-9] are prepared by consecutive etherization, coupling, and esterification reactions. The monomers form columnar phases at room temperature. The polymerizations of the monomers are effected by [Rh(nbd)Cl]₂, producing soluble polymers in high yields (up to 84%). The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, DSC, POM, and XRD analyses. All the polymers are thermally stable, losing little of their weights when heated to 300°C. The isotropization temperature of the polymers increases initially with the length of alkyl chain but decreases on further extension. Whilst the polymers with shorter and longer alkyl chain lengths adopt a homogeneous hexagonal columnar structure, those with intermediate ones form mesophases with mixed structures.