Synthesis, mesomorphism, isomerization, and aromatization of stereoregularpoly{[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}carbon (1), are effected by molybdenum and tungsten halides and rhodium-diene complexes. The. rhodi um-initiated polymerizations produce polymers (2) of high molecular weights (M-n up to 1.2 x 10(5)) in high yields (up to 93%). IR, UV, and NMR analys es confirm that 2 possesses a stereoregular alternating-double-bond backbon e with a predominant cia conformation. DSC, POM, and XRD measurements revea l that 2 is liquid crystalline: it shows smectic A mesophase in the tempera ture range 135-146 degrees C. The cis-rich 2 undergoes active isomerization to the trans conformation at 170 degrees C. Intrachain cyclization followe d by chain scission at ca. 200 degrees C releases 1,3,5-trisubstituted benz ene as the sole aromatization product, proving that the repeat units of the polymer chains are linked in a regular head-to-tail fashion.