Supermolecular mobility and new concept of supermolecular organization in oriented semicrystalline polymers

Abstract

The study of highly oriented films from a low-density polyethylene and other semicrystalline polymers by methods of small-angle and wide-angle x-ray scattering in a broad temperature range has been carried out. A new idea connecting the temperature of “a supermolecular mobility” T _h (strictly speaking, about a range of temperatures) is introduced. After heating a polymer up to T _h and higher temperatures, a sharp increase in the mobility of large supermolecular aggregates (such as crystallites and fibrils) can be observed by x-ray methods. Simultaneously, in the same temperature region, a wide spectrum of structure–mechanical property relationships changes their character. The nature of small-angle x-ray scattering reflections and the concept of supermolecular organization of oriented semicrystalline polymers are revised in light of these results.

Keywords:

• Highly oriented polymer films
• Semicrystalline polymers
• Supermolecular organization
• Small-angle x-ray scattering
• Wide-angle x-ray scattering
• Structure–mechanical property correlations
• Polyethylene
• Polyamide 6
• Long period
• Fibril
• Microdeformation
• Slip

Acknowledgments

The authors are grateful to Prof. P. H. Geil for reading the manuscript and making helpful remarks.

Notes

^*Recently in [15], Sauer et al. obtained similar results for heating of nonoriented samples of poly(oxymethylene): after some sufficiently high temperature the invariant Q of SAXS started to drop, whereas the values of long period and longitudinal sizes of the crystallites continued to grow; it was concluded that the decrease of Q is due by the melting of thin lamellae inserted into the initial stacks, and then by the melting of basic stacks (decrease of crystallinity).