ABSTRACT

X-ray diffraction from single crystals is the most direct and powerful experimental tool available to date to determine molecular structures and intermolecular interactions at atomic resolution. A fiber diffraction pattern is normally recorded on a flat-film camera in which the fiber-to-photographic film distance is typically in the range of 3 to 4 cm. The nature of a diffraction pattern is largely governed by the extent of molecular organization in the fiber, the building block of which is the unit cell of dimensions a, b and c in Å and interaxial angles α, ß and γ in degrees. In the case of helix-forming polymers, the individual microcrystallites are large with sufficient lateral ordering, but rotated differently about their long axes which are nearly parallel to the fiber axis. The distance of each reflection from the center of the pattern is a function of the fiber-to-film distance as well as the unit cell dimensions.