The isotropic pitches as the materials for carbon fibers were prepared from various tars. The quality of the material pitches was evaluated by observing fiber continuity, infusibility in the processing and strength of the product fibers. The pitches were also characterized by means of elemental analysis, solvent fractionation analysis, NMR and ESR spectroscopies. It was confirmed that pitches with higher spin concentrations, larger aliphatic carbon amounts and higher mobilities show higher qualities. The desirable condition of the air-blowing reaction was found to be at lower temperature and pressure.
