Miscibility, structure and properties of PP/PIB blends

Polypropylene/polyisobutylene (PP/PIB) blends were prepared in the entire composition range in an internal mixer. The miscibility of the components was estimated by various methods including model calculations, using melting and crystallization characteristics, glass transition temperature, and solvent uptake experiments. The structure was characterized by microscopy, while the mechanical properties of the blends were studied by tensile tests. PP and PIB form heterogeneous two-phase blends in the entire range of composition, but dissolution of some PIB in the amorphous phase of PP is revealed by the composition dependence of various characteristics. The Flory-Huggins interaction parameters derived by the group contribution approach of Small, from the melting temperature of the PP phase, by dynamic mechanical (DMTA) analysis and solvent uptake experiments indicate partial miscibility of PP and PIB, which is further supported by the morphology of the blends, and the composition dependence of mechanical properties. The glass transition temperature of the elastomer phase decreases with increasing PP content because of the development of thermal stresses as a result of good adhesion and different thermal expansion of the two polymers.