Morphology control of polybenzimidazole by using reaction-induced phase separation of oligomers during solution polymerization

This paper deals with a new finding on the morphology control of poly[2,2′-(p-phenylene)-5,5′-bibenzimidazole] (PBI) by using the reaction-induced crystallization of oligomers during solution polymerization. Polymerizations of 3,3′-diaminobenzidine and diphenyl terephthalate or terephthalic acid were carried out at 350°C for 6 hours in poor solvent such as dibenzyl toluene mixture to induce the crystallization of oligomers. Bundle-like aggregates of PBI nanofibers and plate-like PBI crystals were prepared with high yields. The values of inherent viscosity of FBI were 0.49 - 0.58 dL/g. Obtained crystals possessed high crystallinity measured on WAXS and good thermal stability. The morphology of the products was drastically influenced by the end-group structure of phase separated oligomers.