CHARACTERIZATION OF LIQUID CRYSTALLINE POLYESTER MORPHOLOGY

J.J. Pasatta and T.E. Long

Novel thermotropic liquid crystalline polyesters were characterized using differential scanning calorimetry (DSC), polarized light microscopy (PLM), and melt rheology (MR). The control liquid crystal polyester, poly(hexamethylene 4,4Õ-bibenzoate) (B6) was then modified with four different monomers: sulfonated dimethyl isopthalate (SDMI), dimethyl isopthalate (DMI), cyclohexane dimethanol (CHDM), and trans and cis isosorbide (ISB and ISM respectively). Each modifier was selectively chosen to induce certain characteristics in the liquid crystal. SDMI was chosen to introduce ionic intermolecular attractions and thus maintain liquid crystalline structure, although it also introduces a kinked effect because of its meta-substitution on the phenyl ring. The DMI was chosen to investigate this kink effect and serves as a control for the SDMI. The SDMI modified B6 was found to have a maximum effect of intermolecular attractions somewhere between 5 and 20 mole percent SDMI, and a comparison between 10% SDMI modified B6 and 10% DMI modified B6 showed a much greater degree of liquid crystallinity in the 10% SDMI modified B6. SDMI modified copolymers also generally formed a smectic A (Sa) phase as observed in PLM. CHDM modified B6 was found to raise the isotropic temperature (Ti) because it contains a more rigid spacer than the hexamethylene diol of B6. Addition of the ISB and ISM produced very interesting optical textures, either a chiral smectic C (Sc*) or a smectic E (Se) phase, although the region between the melting point (Tm) and the isotropic point was narrowed with increasing concentration of the isosorbide. Preliminary melt rheology studies of the liquid crystalline polyesters demonstrate transitions at temperatures indicated by corresponding DSC experiments.