Paracrystalline Nature of Poly (p-Phenylene)

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Abstract
The electron diffraction pattern of oriented, annealed poly (p-phenylene) is explained on the basis of an orthorhombic unit cell: a = 0.7781, b = 0.5520 and c(fiber axis) = 0.4300 nm. and exhibits the following features: (1)The reflections on the equator and meridian are sharp. Only a few weak diagonal reflections can be observed. (2) Strong diffuse scattering is seen on the third layer line. (3)The reflections on the meridian (00l-reflections) have a characteristic line profile. in which the intensity increases suddenly at the Bragg angle and decreases gradually. From (1) to (3), it can be concluded that the material is paracrystalline like a nematic structure in liquid crystals. Molecular chains are laterally packed in a rather regular way. However, the disorder by the shift of chains in the direction parallel to their axes is remarkable.