A rigid-rod copolymer, poly(p-phenylene benzobisoxazole)-block-poly(pyridobisimidazole) (PBO-b-PIPD), was synthesized, and the effect of hydration on the structures and performance of the block copolymer fibers was evaluated. PBO and PBO-b-PIPD as-spun fibers (AS-fibers) were prepared by dry-jet wet spinning, and subsequent thermal treatment in a nitrogen atmosphere was performed. Fourier transform infrared and wide-angle X-ray diffraction were used to characterize the structures of the thermally treated fibers. Mechanical properties of both the AS-fibers and thermally treated fibers were tested, and scanning electronic microscopy was used to observe the fracture surfaces of the fibers from tensile testing. It has been revealed that heat treatment is an effective method to remove the absorbed water to improve the orderly arrangement of chains along the fiber direction, which resulted in enhancement of the tensile modulus of the block copolymer fibers.
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