Structure of Poly-2, 5-benzoxazole (ABPBO) and Poly-2, 6-benzothiazole (ABPBT) Fibers by X-Ray Diffraction

摘要

The determination of the crystalline structure of oriented fibers of poly-2, 5-benzoxazole (ABPBO) and poly-2, 6-benzothiazole (ABPBT) is described. Both unit cells are metrically orthorhombic with the parameters: a=6.061 (17), b=3.384 (13), c(fiber axis)=11.575 (6) A for ABPBO; and a=6.044(6), b=3.417 (7), c(fiber axis) =12.194 (18) A for ABPBT. The fiber repeat consists in each structure of two fused ring groups arranged in a planar, zigzag conformation. The conformational torsion angle and orientation of chains within the unit cells are derived from a link-atom least squares refinement technique. Polymer chains pack laterally through va n der Waals interactions. A plausible disorder model which involves defects in chain direction is presented. Refinement of a static disorder model for ABPBO in which 50% of the chains have their chain directions reversed leads to a lower R residual and sum of constraints.