Rheological Behavior of Thermotropic Liquid-Crystalline Polymers: Effects of Thermal and Deformation Histories

Abstract The effects of thermal and deformation histories on the rheological behavior of thermotropic liquid-crystalline polymers (TLCPs) were investigated using a cone-and-plate rheometer. For the study, two TLCPs were used: (1) the copolyester consisting of 73 mol % hydroxybenzoic acid (HBA) and 27 mol % 6-hydroxy-2-naphthoic acid (HNA) (Vectra A900) having the clearing temperature (Tcl) close to or above thermal degradation temperature (ca. 350°C) and (2) an aromatic polyester, poly [(phenylsulfonyl)-p-phenylene 1,10-decamethylene-bis(4- oxybenzoate)] (PSHQ10) having a Tcl of 175°C, which was synthesized in our laboratory. In the use of PSHQ10, we were able to control the initial conditions of the specimens before being subjected to shear flow in the nematic region by first heating a solvent-cast specimen to the isotropic state and then cooling slowly to the nematic region. This was not possible, however, for Vectra A900. We found that the first normal stress difference (N1) of PSHQ10 in the nematic st...