EFFECTS OF TEMPERATURE AND MOLECULAR-STRUCTURE ON RHEOLOGICAL PROPERTIES OF TLCP WITH FLEXIBLE UNITS IN A MAIN-CHAIN

Abstract

Three kind of thermotropic liquid crystalline (TLC) polyesters with two flexible spacers of decamethylene and hexamethylene in a main chain were synthesized. The homopolymer with decamethylene groups in a main chain (H10) showed two peaks of light intensity in the nematic state during heating and different textures on the temperature in the nematic state. Melting and crystallization transition temperatures by Rheometrics dynamic spectrometer (RDS) and polarized optical microscope (POM) was higher than those by differential scanning calorimetry (DSC). The TLC polyesters showed the dependence of theological properties on the thermal history at a temperature between the melting temperature measured by DSC and the theological transition temperature by RDS but above the theological transition temperature they showed almost the same properties affected negligibly by thermal history. The dependence on thermal history might be caused by both the presence of crystallites in the nematic phase and the effect of supercooling. The existence of crystallites was confirmed by the abrupt decrease of yield stress with temperature. Below the theological transition temperature spin-drawing was difficult because of fiber breakage and the free-fall fiber showed low orientation, tensile strength, and initial modulus. On the other hand, above it the free-fall fiber had better orientation and higher tensile strength and initial modulus. It was recognized that the theological transition temperature needed to be defined to determine the temperature for the polymer processing.