Neutron Structure Analysis and Structural Disorder of Poly(p-phenylene benzobisoxazole)

Abstract

On the X-ray fiber diagram of poly(p-phenylene benzobisoxazole) (PBO), the diffuse streak scatterings are observed along the first and third layer lines, while Laue spots can be observed on the second and fourth layer lines. This shows that the molecular heights of PBO are disordered by a half of the fiber period. Therefore, the cell parameter c reduces to a half of the fiber period, 12.05 A. Furthermore, all the reflections observed on the X-ray fiber diagram can be indexed by the one-chain unit cell with parameters a = 5.651 A, b = 3.570 A, and γ = 101.4° (at 295 K). Neutron diffraction measurements were made on the equator at 17, 100, 200, and 295 K, and the structure analyses were made. The half-widths of the reflections do not depend on the temperature. This shows that the crystallite size and lattice distortion are independent of the temperature. The temperature dependences of the unit cell dimensions and temperature parameter are small in comparison with those of polyethylene, one of the flexible polymers. This may reflect the rigidity of the PBO molecule.