The morphology and thermal response of high-temperature–crystallized poly(vinylidene fluoride)

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Abstract
In this study, optical microscopy, differential scanning calorimetry, and infrared spectroscopy are used to study the high‐temperature isothermal crystallization of high‐molecular‐weight poly(vinylidene fluoride). It is shown that there exists a temperature domain in which both the α and β phases of PVF2 can be grown concurrently and in competition with each other to form two distinct populations of spherulites which are characterized by different diameters, band periods, and melting points. In addition, a time‐ and temperature‐dependent crystal‐crystal transition from the α phase to the γ form can be induced in this high‐temperature crystallization region to produce spherulites which melt 15–20 ° above the melting point of the original α phase. This transformation exhibits nucleation and propagation characteristics which in some regions can compete with the normal growth of the α phase to produce unique ’’wagon‐wheel’’ spherulitic structures.