Formation of the gamma phase in oriented isotactic polypropylene with varying stereoregularity

Structural transformations have been studied in oriented samples of isotactic polypropylene with various contents of stereodefects. With the use of small- and wide-angle X-ray diffraction, it was found that a stretched film of polypropylene contains small and defective crystallites of the α phase with an axial orienta tion. The γ phase is formed in oriented polypropylene with a significant amount of stereodefects during high-temperature annealing near the melting point owing to epitaxial crystallization of the partial melt on residual oriented crystallites. The clearer this process is expressed, the lower the degree of crystallinity and/or the higher the degree of stretching of the samples. An increase in the amount of stereodefects in the initial material is expressed in the appearance of the second long period, which is associated with the formation of lamellar crystallites of the γ phase.