Synthesis and characterization of chiral liquid-crystalline polyesters containing sugar-based diols via melt polymerization

Liquid-crystalline (LC) polyesters based on hexanediol or butanediol, dimethyl 4,4′-biphenyldicarboxylate, and a sugar-based diol, isosorbide or isomanide, were prepared with conventional melt polymerization. ¹H NMR spectroscopy confirmed that 50 mol% of the charged sugar diol was successfully incorporated into various copolyesters. Modest molecular weights were obtained, although they were typically lower than those of polyester analogues that did not contain sugar-based diols. Thermogravimetric analysis demonstrated that the incorporation of isosorbide or isomanide units did not reduce the thermal stability in a nitrogen atmosphere. Melting points that ranged from 190 to 270°C were achieved as a function of the copolyester composition. The lined focal conic fan textures, typical indications of a chiral smectic C LC phase, were observed upon the shearing of the LC melt under polarized light microscopy. Atomic force microscopy revealed that the twisted molecular orientation in the chiral LC phase induced periodically soft lamellar structures.