Invited Article. X-ray diffraction by mesomorphic comb-like polymers

This article presents a survey of the literature on X-ray diffraction by mesomorphic comb-like polymers. Special emphasis is placed upon two points: it is often possible to study the localization of the backbone in the smectic phases by considering the intensities of the Bragg reflections from the layers. It is also possible to observe different kinds of short range order and localized defects through their contribution to the X-ray diffuse scattering. For instance, the average S_A structure may be affected by layer undulations or disturbed by edge dislocations. By examining the many X-ray diffraction studies already published, it can be shown that the backbones have an ambiguous influence upon the molecular organization. They sometimes tend, for entropic reasons, to lessen the positional long range order or to create defects, whereas they sometimes promote short range order because they induce correlations among the mesogenic cores chemically linked to them.