Influence of Polymer End Groups on Crystallization and Morphology of Poly(vinylidene fluoride) Synthesized in Homogeneous Phase with Supercritical Carbon Dioxide

Abstract

Poly(vinylidene fluoride) (PVDF) samples from homogeneous phase polymerizations in supercritical CO2 and subsequent expansion to ambient conditions were analyzed with respect to polymer end groups, crystallinity, type of polymorphs, and morphology. Upon expansion the polymer was obtained as white particles. Scanning electron microscopy showed that DTBP (di-tert-butyl peroxide) derived polymer end groups lead to stack-type particles whereas sponge- or rose-type particles were obtained in case of chain transfer agent fragments as end groups. FTIR (Fourier-transform infrared spectroscopy) and WAXD (wide-angle X-ray diffraction) indicated that the type of polymorph, α or β crystal phase, is significantly affected by the type of end group. In addition, the crystallinity of the material, as determined via differential scanning calorimetry, is affected by the end groups and polymer molecular weights. For example, with Mn around 6700 g·mol−1 crystallinity ranges from 29% for DTBP-derived endgroups to a maximum of 64% for end groups originating from perfluorinated hexyl iodide used as chain transfer agent during polymerization.