The properties of co-oligomerized mesophase pitch from methylnaphthalene and naphthalene catalyzed by HF/BF₃

Co-oligomerized mesophase pitch from naphthalene and methylnaphthalene at mixing ratio of 7:3 by aid of HF/BF₃ was studied in terms of its structure, flow behavior and stabilization reactivity as well as microstructure and mechanical properties of the resultant fiber. The molecular structure of co-oligomerized mesophase pitch was rather similar to that of naphthalene pitch because of major content and higher reactivity of naphthalene at the oligomerization, however, the pitch exhibited higher stacking height, preferred orientation and stabilization reactivity than the naphthalene pitch, which certainly reflect the methylnaphthalene units. The resultant fiber showed very high tensile strength and Young's modulus, the former of which was much higher than those of naphthalene and methylnaphthalene pitches, while the latter was comparable to that of methylnaphthalene pitch. The high strength appeared to reflect no crack in the radial alignment of multi-bent domains in the transverse section, while the fiber from methylnaphthalene pitch carried a wide open wedge when both pitches were spun under similar conditions. Such structure of the present fiber may reflect the flow properties of the present pitch which are governed by the molecular stacking of the co-oligomerized mesogens in the liquid crystal state. The little pleats were also observed aligned irregularly on the surface of the present fiber after the graphitization, probably contributing to the high strength.