Liquid crystalline polyesters based on hexanediol, dimethyl 4,4′-biphenyldicarboxylate, and various levels of dimethyl 5-sodiosulfoisophthalate (0-20 mol%) were prepared using a conventional melt polymerization process. The presence and quantification of the ionic functionality was surveyed using 1H NMR spectroscopy. Solution viscosities and corresponding molecular weights decreased when the ionic monomer concentration exceeded a critical value (higher than 3 mol%). Differential scanning calorimetry indicated a maximum in the isotropic transition temperature versus ionic modification at approximately 10 mol%. Dynamic mechanical analysis indicated that the glass transition temperature was suppressed due to ionic association at high concentrations (greater than 3 mol%) of ionic functionality. Polarized light microscopy and wide-angle X-ray diffraction were used to identify the smectic liquid crystalline and crystalline phases.
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