Dynamic rheology and dielectric relaxation of poly(vinylidene fluoride)/poly(methyl methacrylate) blends

The molecular relaxations in melt-extruded poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blends with less than 40 wt% PMMA were investigated using dynamic rheological measurement and broadband dielectric spectroscopy. According to dynamic rheology, the total chain entanglement density of the blend melts increased with adding PMMA, and the dissimilar chains were more likely to entangle with each other than similar ones. Furthermore, PMMA facilitated the relaxation process. The dielectric temperature spectra revealed strong structural heterogeneity in the semicrystalline blends whose αa and αc relaxations were accelerated by increasing PMMA content. The αa and αc relaxations were shown to follow the Vogel-Fulcher-Tamman and Arrhenius equations, which allows assigning their molecular origins clearly to amorphous PVDF interphase and the amorphous portions within the crystalline PVDF phase, respectively. However, there exist structural heterogeneities in amorphous PVDF/PMMA mixture phase associated to intermolecular entanglement between dissimilar chains, giving rise to one or two αm relaxations in the dielectric temperature spectra depending on the PMMA content.