MORPHOLOGY AND PHASE-BEHAVIOR OF BLENDS OF SYNDIOTACTIC AND ISOTACTICPOLYPROPYLENE .1. X-RAY-SCATTERING, LIGHT-MICROSCOPY, ATOMIC-FORCE MICROSCOPY, AND SCANNING ELECTRON-MICROSCOPY

Blends of isotactic and syndiotactic polypropylene were studied by wid e angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS), light microscopy, scanning electron microscopy and atomic force micros copy. WAXS measurements show that both polymers crystallize in differe nt 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 degrees C as revealed by SAXS. From the crystallization morphology, it can be concluded that the crystalli zation of isotactic and syndiotactic polypropylene after isothermal an nealing in the melt occurs always in large, macroscopic domains. Isota ctic polypropylene crystallizes preferably in different spherulitic fo rms which can usually not be detected for syndiotactic polypropylene c rystallizing preferably as needle-like entities. The crystalline morph ology of the blends is very complex and depends strongly on the therma l history in the melt, the crystallization temperature and blend compo sition. It can clearly be seen that the blends undergo liquid-liquid p hase 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 ne arly symmetric blends. Copyright (C) 1996 Elsevier Science Ltd.