APPLICATIONS OF FOURIER-TRANSFORM INFRARED MICROSPECTROSCOPY TO THE ANALYSIS OF MICROSCOPIC ORIENTATION IN LIQUID-CRYSTALLINE POLYMER SHEETS

Fourier transform infrared (FTi.r.) microspectroscopy was applied to evaluate the microscopic orientation of extrusion moulded sheets of a thermotropic liquid crystalline polymer, consisting of 4-hydroxybenzoic acid units, biphenol units and benzene dicarboxylic acid units. The polarized i.r. spectra were measured in the microscopic area down to 40-mu-m using a redundantly apertured i.r. microscope equipped with a wire-grid polarizer. It was shown that Beer's law held in the absorbance range below 2.5, and the polarization properties of oriented samples were accurately measured by FTi.r. microspectroscopy. The orientation profiles of the polymer sheets were obtained by plotting the dichroic ratio of the 1602 cm-1 band against distance from the centres of sheets. In the case of the sheet 0.68 mm thick, the central region is nearly isotropic, but the dichroic ratio increases markedly toward the surface of the sheet. In the thinner sheet (0.255 mm), the polymer chains in both surface and central regions are highly oriented in the extrusion direction, and the dichroic ratio gradually increases on approaching the surface. At the same sheet thickness, the degree of orientation decreases as the extrusion temperature is lowered. The orientation profiles obtained by polarized FTi.r. microspectroscopy are in accordance with the morphological structures studied by scanning electron microscopy.