Impurity Effect of the Dielectric Properties of Isotactic Polypropylene

Two dielectric relaxation peaks, the crystalline and the primary relaxations, were observed in the temperature-dielectric loss curves in isotactic polypropylene. Among them the primary relaxation ß was studied in detail using different kinds of polypropylene films and their films purified with acetone. It was found that ß-relaxation consists of two peaks, denoted ß1 and ß2, being consistent with the dynamic mechanical characteristics. The lower temperature peak ß1 is assigned to the amorphous phase, which is rich in atactic chains, and the upper temperature peak ß2 is ascribed to an antioxidant contained in the amorphous phase which is rich in isotactic chains. The antioxidant also causes an increase in dielectric loss in the higher temperature region. The extraction of impurities from polypropylene films with acetone reduces the magnitude of the primary relaxation peaks.