Abstract
A main-chain non-racemic chiral liquid crystalline polymer has been synthesized from (R)-(−)-4′-{ω-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-nonyloxy}-4-biphenyl carboxylic acid, abbreviated PET(R∗)-9. Based on differential scanning calorimetry, wide angle X-ray diffraction (WAXD) and polarized light microscopy experiments, this polymer undergoes at least three liquid crystalline (LC) transitions in addition to crystallization. The LC transition sequence isI↔3.21kJ/mol185°CTGBA∗↔1.27kJ/mol175°CSA∗↔0.35kJ/mol130°CSC∗↔37°CTgThe transition sequence is reversible since they are LC phases, which are close to thermodynamic equilibrium. Among these phases, the twisted grain boundary smectic A (TGBA∗) phase is, for the first time, found in a main-chain LC polymer. The TGBA∗ is only stable within a temperature region of 10°C between the Smectic A∗ (S∗A) phase and the isotropic melt. Crystallization that takes place in the (S∗A) phase can form both flat-elongated and double-twist helical single lamellar crystals, as observed by transmission electron microscopy (TEM). Analysis of the WAXD fiber patterns of this polymer indicates that the crystal structure of PET(R∗)-9 in the bulk is orthorhombic, identical with that determined using selective area electron diffraction in TEM [Macromolecules 32 (1999) 524; Phys Rev B 60 (1999) 12 675].
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