Characterization of the structure and organization of β‐form crystals in type III and type IV isotactic polypropylene spherulites

Abstract

Abstract Anisotropic growth of β‐form crystals of isotactic polypropylene in type III and type IV spherulites has made possible microanalysis of the unit cell structure, optical properties, and crystal arrangement within the spherulites. Micro x‐ray studies of the type III and type IV spherulites show that interspherulitic β‐form crystals have a hexagonal unit cell with dimensions; a = 19.08 Å and c = 6.49 Å. The intrinsic refractive indices of these β‐form crystals are 1.506 along the a axis and 1.536 along the c axis. The organization of the crystals within the spherulites and the optical properties of the spherulites are also quantitatively evaluated. Both the type III and type IV spherulites have the a axis of the crystal radial while the crystals rotate randomly around the type III spherulite radii and periodically around the type IV spherulite radii. The radial refractive index for both the type III and type IV spherulites has the same value of 1.496. The tangential refractive index of the type III spherulite has a constant value of 1.509; it varies periodically between a minimum of 1.496 and a maximum of 1.519 in the type IV spherulite. Microtechniques such as micro x‐ray diffraction, interference microscopy, birefringence, and optical microscopy were required for acquisition of the data.