The composition and properties of raw materials play a crucial role in determining the outcomes of spinnable pitch preparation. This study investigated the effects of copolymerizing synthetic pitch (CT) with coal liquefaction pitch on the properties of the resulting product, which exhibited 100% mesophase content. The addition of an appropriate amount of CT increased the soluble components in the mesophase pitch, and thus promoted the enrichment of mesophase. The CT with principally condensed aromatic structure reduced the alkyl side chains, and resulted in a more uniform molecular weight distribution, as indicated by a decreased polymer dispersity index. Consequently, the mesophase domain size of the product increased significantly, along with a higher content of naphthenic components, leading to a remarkable improvement in spinnability. The single-filament length of the resulting carbon fiber increased from 3,296 m to 11,536 m. Additionally, the incorporation of CT reduced the aromatization degree (C/H ratio) of the mesophase pitch and enhanced its fluidity during melt spinning. The cross section of the carbon fiber transformed from a radial to a vortex structure. This vortex configuration effectively dissipated the contraction stress within the fiber, thereby preventing splitting. The resulting carbon fiber, with a more complete and ordered structure, exhibited superior mechanical properties, achieving a tensile strength of 1,631 MPa and a tensile modulus of 272 GPa

Coal liquefaction pitch, Mesophase pitch, Copolymerization, Spinnability, Carbon fiber