| Abstract: | A thermotropic liquid crystalline copolyester (LCP) based on p-acetoxy-benzoic acid (49.9 mol%), 2,7-diacetoxynaphthalene (22.3 mol%), terephthalic acid (22.3%) and Q-resin (polyethylene 2,6-naphthalene, 5.5%) was prepared via melt transesterification, and then a blend was prepared by physically mixing 40% thermotropic liquid crystallline copolyester and 60% polyethlene terephthalate (PET). The thermal properties of both-the LCP and the blend were studied by DSC and the result showed that the various transition temperatures for the blend were rather close to those for pure PET. The thermal stability of LCP, blend and PET was characterized by TGA. The dynamic rheological properties of LCP and the blend were studied by the oscillation test on a rheometric mechanical spectrometer( Instron RM32SO) with parallel plate disk. The results showed that the rheological behavious of the blend melt exhibit as conventional polymeric melt in the whole experimental frequency range (0.02-12 Hz). However, for the melt of pure LCP, an interesting phenomenon was observed: in the low frequency regions, G'> G" and in the moderate and high frequency regions, G'< G". This phenomenon can be an evidence of the presence of domains or locally ordered supramolecular aggregate (crystalline network) for thermotropic liquid crystalline polymer melt at low shear rate or frequency regions. An another result of this work was that a mesophase transition was clearly observed in the plot of complex viscosity of the LCP versus temperature. |
