Synthesis of organosoluble copolyimide and preparation of fibers by dry-spinning process on a large scale

An organosoluble copolyimide (co-PI) was synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 1,4-bis-(4-aimino-2-triflupromethyl-phenoxy)-benzene (p-6FAPB), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) via the one-step polymerization using N-methyl-2-pyrrolidone (NMP) as the solvent, and high-performance co-PI fibers were directly prepared by the dry-spinning process on a large scale. Scanning electron microscopic images show that all formulations of as-spun fibers exhibit elliptical cross sections as well as dense morphologies. The structural evolution of the co-PI fiber induced by the high rolling speed and post-heat-drawing treatment was studied by means of thermogravimetric analysis, dynamic thermomechanical analysis, and two-dimensional wide-angle X-ray diffraction (2D WAXD). With increasing rolling speeds, glass transition temperatures (T _gs) and thermal stabilities of as-spun fibers slightly decrease, which may be resulted from the disentanglement of entangled molecular chains under the large deformation and high-temperature heating atmosphere in the spinning column. 2D WAXD data indicate that both increasing rolling speeds and post-heat-drawing treatment are beneficial for getting a highly ordered structure along the meridian direction of the fibers. The fibers treated at 430°C exhibit outstanding mechanical properties, and the tensile strength and modulus reach 1.44 GPa and 48.69 GPa, respectively, at a drawing ratio of 2.8.