A facile synthetic route to novel thermotropic liquid crystalline polymers and characterization of their mesophases

Abstract

A novel method for the synthesis of a new class of thermotropic liquid crystalline polymers has been developed: it proceeds via a polyaddition reaction involving diepoxy-containing mesogene groups and a monoamine (aniline). The reaction between the epoxy ring and the primary amine produces an intermediate containing a secondary amine which undergoes further reaction with an epoxy ring of another molecule in the melt to generate a thermotropic liquid crystalline polymer. This polymerization process is one step. The two new thermotropic liquid crystalline polymers prepared with this method have high molecular weights. Both polymers were found to exhibit nematic mesophase characteristics. The prepared polymers exhibit high thermal stabilities (degradation temperatures above 350 °C) but low melting temperatures (lower than 250 °C). When examined with polarized optical microscopy in the melt state, the nematic phases of the polymers produce characteristic textures. The liquid crystalline structures of the two polymers were confirmed by performing 2D X-ray diffraction measurements. Scanning electron microscopy images of drawn polymer fibers reveal a strong orientation on the surface along the flow direction and many microfibrillar structures extruding out of the fractured surfaces normal to the direction of flow. These results demonstrate the potential for the facile mass production of novel thermotropic liquid crystalline polymers for high performance composites or fibers of high mechanical strength.