Morphology and phase behaviour of blends of syndiotactic and isotactic polypropylene: 1. X-ray scattering, light microscopy, atomic force microscopy, and scanning electron microscopy

Abstract Blends of isotactic and syndiotactic polypropylene were studied by wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS), light microscopy, scanning electron microscopy and atomic force microscopy. WAXS measurements show that both polymers crystallize in different unit cells already during precipitation from a common solvent. Both polymers have a very similar long period and lamella thickness after isothermal crystallization at 135°C as revealed by SAXS. From the crystallization morphology, it can be concluded that the crystallization of isotactic and syndiotactic polypropylene after isothermal annealing in the melt occurs always in large, macroscopic domains. Isotactic polypropylene crystallizes preferably in different spherulitic forms which can usually not be detected for syndiotactic polypropylene crystallizing preferably as needle-like entities. The crystalline morphology of the blends is very complex and depends strongly on the thermal history in the melt, the crystallization temperature and blend composition. It can clearly be seen that the blends undergo liquid-liquid phase separation in the melt which yields isotactic polypropylene in a matrix of syndiotactic polypropylene; syndiotactic polypropylene in a matrix of isotactic polypropylene or a co-continuous morphology for nearly symmetric blends.