Determination of the α, β, and γ crystalline phases of poly(vinylidene fluoride) films prepared at different conditions

Samples containing the three crystalline phases of poly(vinylidene fluoride), alpha, beta, and gamma, have been obtained under distinct crystallization conditions. Samples containing exclusively unoriented beta phase have been obtained by crystallization from dimethylformamide (DMF) solution at 60 degrees C. Oriented beta phase has been obtained by uniaxial drawing, at 80 degrees C, of an originally a phase sample. Samples containing exclusively alpha phase have been obtained by melting and posterior cooling at room temperature. Samples containing both alpha and gamma phases have been obtained by melt crystallization at 164 degrees C for 16 and 36 h. Presence of the crystalline phases in each sample were confirmed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXD), polarized light optical microscopy (PLOM), and scanning electron microscopy (SEM). Infrared absorption bands identifying unequivocally the presence of beta and gamma phases in a sample are presented. It is shown that solution crystallization at T < 70 degrees C always results in the beta phase, regardless of the solvent used. Melt temperatures of the respective phases have also been determined. (c) 2006 Wiley Periodicals, Inc.