In‐situ small‐angle studies of microstructural changes in polymers

A series of experiments in which small‐angle x‐ray scattering (SAXS) is used to follow microstructural changes in situ is reviewed. The work relates to primary and secondary crystallization, to melting and to physical aging. SAXS curve shapes are used to define whether primary crystallization occurs through the growth of “skeletal” or of “dense” spherulites. The integrated intensity is used to establish whether primary and secondary crystallization occur simultaneously. The ratio of second‐ to first‐order peak intensities, the absolute intensity, and reversible peak shifts are used to study the nature of secondary crystallization in polyethylene, poly(vinylidene fluoride) and a polysiloxane. The last two of these exhibit reversible peak shifts which are not consistent with simple models and it is concluded that thorough replacement of existing structures occurs during this process. SAXS peak shape changes in PE indicate that melting occurs by the random loss of crystals throughout the material. Finally, it is shown that SAXS can be a useful tool for monitoring physical aging in semicrystalline polymers.