Fibers drawn form poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (PBI) were studied by DSC and DMA. PBI is a high temperature polymer Tg is between 387 and450C depending on the measurement technique used. The as-spun fiber is free of orientation. The oriented
fiber exhibits considerable dependence on whether the DSC measurements were carried out in free-to-shrink or fixed-length
modes. The β-relaxation is at 290C, and was associated with loss of water. The γ-transition at 20C was not identified, while
theδ-transition at –90C seems to correspond to rotation of the m-phenylene ring.