The anisotropic development is studied of mesophase pitches prepared from modified ethylene tar (ETP) using AlCl3, of fractions separated by benzene, tetrahydrofuran (THF) and pyridine, and of mixed fractions, to find structural factors affecting fusibility and optical anisotropy of mesophase pitch. Annealing was carried out at 360° C for 10 min. Each fraction developed a unique optical anisotropy quite different from that of the parent mesophase pitch. The lightest fraction (soluble in benzene) was highly fusible with small numbers of small anisotropic spheres. The heaviest fraction (insoluble in pyridine) was infusible and exhibited a total mosaic anisotropy. In contrast, mixed fractions behaved like the parent mesophase pitch in terms of liquid crystal behaviour. The extent of anisotropy and fusibility after annealing were strongly dependent on the preparatory conditions of the parent mesophase pitch. The fusibility of mixed fractions is ascribed to the dissolving ability of the fusible fraction and the solubility of the infusible fraction at the annealing temperature. Small molecules in the lighter fractions also contribute to anisotropy when they are located in interlayer positions between the larger aromatic molecules which constitute liquid crystals. Such co-operative properties of constituent molecules of the mesophase pitch can be described in terms of a practical compatibility.
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