Thermotropic liquid crystalline polyesters($LCP_s$) were prepared by melt polymerization and they have flexible spacers(-(-$CH_2-)-_{6.10}$) inserted between mesogen units. Their thermal properties as well as mesophasic behaviors were investigated by using differential scanning calorimetry and polarizing microscope. They had nematic mesophase between melting and isotropic transition temperature. Their rheological properties of nematic melts were measured with rheometric dynamic spectrometer at low shear rate and capillary rheometer at high shear rate. The dynamic data of the liquid crystalline homopolymer and copolymer showed that LCP melts were different from flexible chain polymers in a sense of having a quite long relaxation time, strongly shear thinning and apparent yield stress at low frequency. In their blends with isotropic polymers(PET, PA-6), the spherical or ellipsoidal domains of LCP in the matrix were formed and deformed to fibrous structure by the elongational flow.
The melt viscosities of the blends measured by capillary rheometer were significantly reduced since the oriented liquid crystalline domain lubricated the melt. Especially, in a high shear rate the viscosity was sharply decreased between 10 and 30wt% of LCP. Also, the morphological changes of LCP domain in the matrix polymer according to various shear rates and blend ratios were investigated by using scanning electron microscopy.
We could observe the deformed structure of LCP domain. In a high shear rate the change to fibrous structure of LCP domain occurred between 10 and 30wt% of LCP supported the viscosity behavior which was sharply decreased near the blend ratio.
