Evolution process of regular structure in isothermal crystallization phenomena of crystalline polymers viewed from synchrotron small-and wide-angle x-ray scatterings and vibrational spectroscopy

The evolution processes of regular structure in isothermal crystallization phenomena of crystalline polymers have been investigated from the viewpoints of molecular level, crystal lattice, and higher-order structure on the basis of time- dependent infrared spectral data and synchrotron small- (SAXS) and wide-angle X-ray scattering (WAXD) data. The polymers treated here were isotactic polypropylene (iPP), nylon 10/10 and polyoxymethylene (POM). In the case of iPP, the formation and growing processes of regular helical segments in the molten state are described by utilizing the concept of critical sequential length for infrared bands. Combination of these spectroscopic data with the SAXS and WAXD data clarifies the formation process of domains consisting of regular helical segments, the increment of correlation of neighboring domains, and the development of stacked lamellar structure, during which the remarkable growth of crystal lattices consisting of regular helices occurs in parallel. In the case of nylon 10/10, weak hydrogen bonds are formed between amide groups even in the molten state. Once the isothermal crystallization starts to occur, these more-or-less correlated domains built up by the hydrogen bonds are formed followed by the formation of crystal lattices consisting of relatively regular methylene segments. Such growth is quite different from the case of iPP crystallization. The study of POM is based on the observation of infrared bands intrinsic to the folded chain crystals (FCC) and extended chain crystals (ECC). From the time-resolved measurements of these infrared bands as well as the SAXS and WAXD in the isothermal crystallization process of POM, we clarified that the lamellar structure of FCC morphology is formed at first. Then some new lamellae are formed in between these original lamellae, resulting in the formation of ECC parts in which the regular helices pass through the several neighboring lamellae as taut tie chains.