Synthesis, Mesomorphism, Isomerization, and Aromatization of Stereoregular Poly{[4-({[6-({[4‘-(heptyl)oxy-4-biphenylyl]carbonyl}oxy)- hexyl]oxy}carbonyl)phenyl]acetylene}

The polymerizations of a functional phenylacetylene derivative, [4-({[6-({[4‘-(heptyl)oxy-4-biphenylyl]carbonyl}oxy)hexyl]oxy}carbonyl)phenyl]acetylene (1), are effected by molybdenum and tungsten halides and rhodium−diene complexes. The rhodium-initiated polymerizations produce polymers (2) of high molecular weights (Mn up to 1.2 × 105) in high yields (up to 93%). IR, UV, and NMR analyses confirm that 2 possesses a stereoregular alternating-double-bond backbone with a predominant cis conformation. DSC, POM, and XRD measurements reveal that 2 is liquid crystalline: it shows smectic A mesophase in the temperature range 135−146 °C. The cis-rich 2 undergoes active isomerization to the trans conformation at 170 °C. Intrachain cyclization followed by chain scission at ca. 200 °C releases 1,3,5-trisubstituted benzene as the sole aromatization product, proving that the repeat units of the polymer chains are linked in a regular head-to-tail fashion.