Abstract
The morphology of syndiotactic polypropylene (s-PP), containing 91% racemic pentads, isothermally crystallized from the melt has been investigated by means of light microscopy, atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). Light microscopy shows a typical needle-like structure of crystalline entities at crystallization temperatures ranging from 115 to 150°C. Large bundles of lamellae and rectangular entities with single crystal character were the main morphological structures observed by AFM. These single crystal-like entities exhibit two typical fracture types; (i) transverse straight fractures with an average distance between the cracks of approximately 2 μm, and (ii) irregular fractures which yield a small mosaic-like structure. A lamellar thickness of 10 nm and a long period of 20 nm of s-PP crystallized isothermally at 135°C were obtained from the two-dimensional correlation function of SAXS measurements. This long period is in good agreement with that measured by AFM. Rare structures such as spherulites, hedrites and aggregates having a clear lateral periodicity perpendicular to the growth direction can be observed. Light microscopy of s-PP crystallized at 126°C and 3.5 kbar shows mainly spherulitic growth with an irregular banding structure.
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