THERMOTROPIC LIQUID-CRYSTALLINE POLYMERS HAVING 5-MEMBERED HETEROCYCLES AS MESOGENS .2. HOMOPOLYMERS AND COPOLYMERS COMPOSED OF 1,3-PHENYLENEBIS(1,3,4-THIADIAZOLE-2,5-DIYL) UNIT OR 1,4-PHENYLENEBIS(1,3,4-THIADIAZOLE-2,5-DIYL) UNIT

New home- and copolyhydrocarbons composed of 1,3- and/or 1,4-phenylene bis(1,3,4-thiadiazole-2,5-diyl) units were successfully prepared by in tramolecular cyclization of the corresponding polyhydrazides, which we re synthesized by direct polycondensation of terephthalhydrazide and/o r isophthalhydrazide with 1,18-octadecanedicarboxylic acid, with dipho sphorus pentasulphide in pyridine. Spectroscopical measurements, eleme ntal analysis data and thermogravimetric analyses (TGA) suggested that the intramolecular cyclization completely proceeded. Differential sca nning calorimetry (DSC) measurements, optical texture observation by m eans of polarizing microscope and powder X-ray analyses indicated that only the 1,4-phenylenebis(1,3,4-thiadiazole-2,5-diyl) unit-rich copol ymer (80 mol.%) formed thermotropic liquid-crystalline smectic phase, but the others had birefringent or normal melts. The phase transition temperatures (melting and isotropization) had a tendency to change non -linearly with the 1,4-phenylenebisthiadiazole composition.