Microstructural Change of Poly(1-butene) during Crystallization, Phase Transition, and Melting Revealed by Synchrotron Small-Angle X-ray Scattering

For a long time, polymer lamellar crystals were hard to characterize accurately and comprehensively. The main reason is that the small-angle X-ray scattering (SAXS) mechanism of semicrystalline polymers has not been elucidated thoroughly. In recent years, we examined SAXS in semicrystalline polymers carefully, finding that SAXS in semicrystalline polymers probably is from a new physical mechanism, that is, evanescent wave-induced scattering. Based on the finding, a full set of new characterization methodologies for lamellar stack were proposed. In this study, to help more researchers to understand the new theory and methodologies, we introduce our new theory and methodologies systematically, with poly(1-butene) as an example. Results indicate that the new methods can extract effectively the structural information during the isothermal crystallization, phase transition, and melting of poly(1-butene), i.e., the lamellar thickness, long period, and lateral size. With the methods, it was found that the lamellar crystal as a whole can contract by 20% ± 4.5% in the lateral size and elongate by 12% along the chain direction during the phase transition, in agreement with the theoretical prediction. This conversely indicates the validation of the new theory. Initial evidence for the existence of the evanescent wave was also given. It is expected that, with this study, more researchers can better employ synchrotron SAXS to study polymer crystallization issues.