A New Class of Poly(ester hydrazide) Copolymers with Liquid Crystalline Properties. Synthesis and Characterization

A series of copolyesters (PE) of low molecular weight containing propyloxy-substituted aromatic ring and/or ethylenic sequences between aromatic units were prepared by melt polycondensation between corresponding diacids and diacetates, and used as precursor of poly(ester-co-polyhydrazide) (PEH) new copolymers. The PEs showed to have thermotropic properties, with transition temperatures which depend on the chemical composition and with a good interval of stability of the mesophase. The corresponding PEHs were obtained by high-temperature polycondensation of carboxyl-terminated PEs with terephthalic dihydrazide. The PEHs showed as well a stable mesophase in the melt, and improved thermal stability respect to polyesters. All the polymers were characterized by elemental analysis, inherent viscosity, infrared and 13 C solid state NMR spectroscopy, thermal and thermogravimetric analysis and optical microscopy. Fibers of PEHs were obtained by melt-spinning and characterized by WAXS analysis.