The crystallization behaviour and phase diagram of extended-chain crystals of poly(vinylidene fluoride) under high pressure

In order to obtain the pressure-temperature (P—T) phase diagram of poly(vinylidene fluoride) (PVDF), the melting and crystallization behaviours under high pressure were investigated as a function of temperature and pressure. A corrected P—T phase diagram, in which the triple point (orthorhombic, hexagonal and melt) exists at 320 MPa and 300°C, is proposed. A film mainly consisting of extended-chain lamellar crystals of β-form can be obtained by crystallization in the metastable hexagonal phase, which appears when increasing pressure is applied on the melt. This crystallization method provides good-quality β-form films without thermal degradation.