Preparation of polybenzimidazole nanofibers by using reaction-induced crystallization of oligomers during solution polymerization

This paper deals with our new finding on the fabrication of poly[2,2'-(p-phenylene)-5,5'-bibenzimidazole] (PBI) nanofibers by using the crystallization of oligomers during solution polymerization. Polymerizations of 3,3'-diaminobenzidine and diphenyl terephthalate were carried out at 320 and 350°C for 6 hours in poor solvents to induce the crystallization of oligomers. The solvents used in this study were liquid paraffin (LPF) and Barrel Therm 400 (BT4, Matsumura Oil Co., Ltd.), which is the mixture of dibenzyl toluene. In the polymerizations in LPF, plate-like crystals of PBI were obtained and their inherent viscosities (ηinh) were 0.21 - 0.27 dL/g. On the other hand, in the polymerization in BT4, the bundle-like aggregates of PBI nanofibers were prepared with quantitative yields. The diameter of each nanofibers was 20 - 100 nm. The values of ηrinh of PBI nanofibers were 0.35 - 0.58 dL/g and they were higher than those in LPF. These nanofibers possessed extremely high crystallinity measured on WAXS and good thermal stability. The morphology was drastically influenced by the solvent, and the control of miscibility is of great importance for the fabrication of PBI nanofibers.