Morphology of polypropylene crystallized from the melt

Polypropylene was oxidized with nitric acid in a manner contrived to remove its amorphous component. Concurrent with the loss in weight there was an increase in crystallinity, a decrease in molecular weight, a drop in melting point, and a change in visible structure. The crystalline component, which survived from polymer which had orginally crystallized isothermally, consisted of separated spherulites. These spherulites could be broken apart into lamellae which gave electron diffraction patterns like those now associated with a variety of solution‐grown single crystals. As opposed to the high molecular weight of the unoxidized parents, the lamellae which survived the acid treatment consisted of short chains whose length depended on the temperature at which the parents had crystallized. If, as diffraction studies indicate, these short molecules are lined up in rank and file, then the length of the molecules and the height of the lamellae should correspond. The heights of the lamellae could not be measured precisely enough to establish an exact correlation, but the variations in average chain length calculated from viscosity data at least approximated the heights of the lamellae which were observed visually.