Melting and crystallization behavior of syndiotactic poly(propylene) homopolymer mixtures with atactic poly(propylene)

摘要

The melting and crystallization behavior of syndiotactic (sPP) poly(propylene) homopolymer mixtures with atactic (aPP) poly(propylene) are investigated by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The tacticity microstructure of sPP homopolymer polymerized with metallocene catalysts varies with polymerization temperature. The resultant sPP microstructure is strongly coupled to the DSC melting behavior. Multiple endotherms are observed which are sensitive to heating rate, consistent with a melting-recrystallization-remelting (MRM) mechanism as a contributing factor to the higher temperature endotherm (Endotherm II). Reduced sPP tacticity and molecular weight promote the reorganization. The multiple melting response is a useful probe of aPP "diluent" segregation within the sPP/aPP blend morphology. The addition of aPP leads to a suppression of crystallization temperature, and promotion of Endotherm II on heating which is sensitive to both the "host" sPP and "diluent" aPP molecular weight. Both behaviors suggest a degree of "local" mixing of diluent within the morphology.