MORPHOLOGY OF SYNDIOTACTIC POLYPROPYLENE

The morphology of syndiotactic polypropylene (s-PP), containing 91% ra cemic pentads, isothermally crystallized from the melt has been invest igated by means of light microscopy, atomic force microscopy (AFM), an d small-angle X-ray scattering (SAXS). Light microscopy shows a typica l needle-like structure of crystalline entities at crystallization tem peratures ranging from 115 to 150 degrees C. Large bundles of lamellae and rectangular entities with single crystal character were the main morphological structures observed by AFM. These single crystal-like en tities exhibit two typical fracture types; (i) transverse straight fra ctures with an average distance between the cracks of approximately 2 mu m, and (ii) irregular fractures which yield a small mosaic-like str ucture. A lamellar thickness of 10 nm and a long period of 20 nm of s- PP crystallized isothermally at 135 degrees C were obtained from the t wo-dimensional correlation function of SAXS measurements. This long pe riod is in good agreement with that measured by AFM. Rare structures s uch as spherulites, hedrites and aggregates having a clear lateral per iodicity perpendicular to the growth direction can be observed. Light microscopy of s-PP crystallized at 126 degrees C and 3.5 kbar shows ma inly spherulitic growth with an irregular banding structure.