Correlations between pyroelectricity, thermal transitions and dielectric relaxations in PVDF and related copolymers

The temperature dependence of the pyroelectric coefficient of PVDF and P(VDF-TrFE)75/25 has been correlated with thermal transitions and dielectric relaxations as revealed by DSC and TSC. For both polymers, three changes in slope have been found: the lower temperature one corresponds to the glass transition of the free amorphous phase of the polymers. An upper component of the glass transition, Tgu(10/20°C) has been ascribed to the glass transition of the amorphous phase constrained by crystallites. The α process occurs at 40/50°C. It has been associated with conformational reorganizations related to the crystalline phase. It plays a key role in ageing of electroactive properties. Above Tα, cooperative movements are liberated. They are precursors of the Curie transition