Identifying smectic I phase of main-chain PB-10 polyester consisting of 4,4′-biphenol and 1,10-dodecanoic acid by fibre X-ray diffraction

Spinnable main-chain PB-10 liquid crystal (LC) polyester was obtained for the first time by solid state polymerization after conventional melt condensation of 4,4′-biphenol and 1,10-dodecanoic acid. The smectic LC phase oriented uniaxially in the fibre and exhibited an X-ray diffraction pattern attributable to a C-centred monoclinic unit cell with a = 0.64 nm, b = 0.90 nm, c = 2.31 nm and β = 126° with the c-axis parallel to the fibre axis. The type of mesophase can thus be identified as smectic I rather than smectic H, as speculated previously. Polymer chains are thus packed laterally into a hexagonal lattice and pass diagonally across the smectic layers. In the smaller angle region, the fibre exhibited a series of diffraction peaks attributed to lamellae stacking along the fibre direction with a spacing of 41 nm. The lamellae are thus perpendicular to the polymer chain axis and inclined to the smectic layer.