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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.

Synthesis, chemical and chemical-physical characterisation of new thermotropic copolymers containing ester and hydrazidic units are reported. The polymers consist of polyester blocks linked together through p-phenylenhydrazidic units. By varying the nature and the relative percentage of the comonomers in the polyester block, it is possible to obtain thermotropic copolymers with melting temperatures well below the degradation, with a good range of stability of the mesophase, and with heat resistance properties similar to those of homopolymeric polyhydrazides.