Thermal measurements on poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] fibers

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 and 450°C 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 290°C, and was associated with loss of water. The γ-transition at 20°C was not identified, while the δ-transition at -90°C seems to correspond to rotation of the m-phenylene ring.