Specific features of the force and thermal elastic deformations of chain molecules and their energetics in polymer crystals

In polymer crystals (in particular, polyethylene), changes in the axial and contour lengths of skeletal interatomic bonds in chain molecules under mechanical loading (stretching) and heat treatment (heating) were measured using X-ray diffractometry and Raman spectrometry. The performed analysis of the measured force and temperature dependences gave theoretical descriptions of the deformation of a polymer crystal (the confirmation of the data available in the literature for mechanical loading and an original development for heating). The components of the potential energy of a deformed polymer crystal were determined both for stretching of skeletal bonds and for bending of chain molecules. It was found that there is a significant difference in the ratios of these components for a deformed polymer crystal under mechanical loading and during heating.