Hyperbranched thermotropic liquid crystalline polyesters composed of aromatic ester type mesogens and polymethylene spacers

Two pairs of new isomeric hyperbranched polyesters composed of aromatic ester type mesogenic units and penta- or decamethylene spacers were prepared and their liquid crystallinity was studied. Branch points in these polymers are connected to each other through the nonmesogenic spacers. All the polyesters were found to be amorphous, but thermotropic, regardless whether the terminal groups are esters or free carboxylic acid or phenolic groups. Although these polymers form nematic phases, their apparent melt viscosity appears to be much higher than those of conventional nematic liquid crystalline polyesters (LCPs), indicating that linear alignment of the mesogens in these polymers may not be as readily achieved as in the common LCPs that are known to have very low melt viscosities in nematic state. Thermal and LC properties were studied by differential scanning calorimetry and X-ray diffractometry and by the observation of the optical textures on a polarizing microscope.