Abstract
The effect of flexible spacer length on the phase transitions and mesophase structures of main-chain thermotropic liquid-crystalline polyesters having bulky pendent side groups was investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarizing optical microscopy (POM). For the investigation, a homologous series of poly[(phenylsulfonyl)-p-phenylene alkylenebis(4-oxybenzoate)]s (PSHQn) having varying lengths (n) of methylene groups of flexible spacers (n = 3−12) were synthesized in our laboratory. Using POM we observed that all PSHQn synthesized, with the exception of PSHQ3, have only a schlieren-textured nematic mesophase at temperatures between a glass transition temperature (or melting point) and the isotropization temperature; the nematic−isotropic transition temperature exhibits odd−even fluctuation with the number of methylene groups of the flexible spacer. We found that the isotropization enthalpy and isotropization entropy for PSHQn do not follow a li...
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