Morphology of melt-crystallized poly(vinylidene fluoride): influence of chain structure and polydispersity

Abstract

The morphology of melt-crystallized poly(vinylidene fluoride) (PVF₂) fractions and whole polymers is presented for a wide range of crystallization temperatures (T_c). In both cases, at each isothermal T_c an increase in size of α-spherulites with increase in head-to-head (H-H) defects of the chain was observed. However, at the same T_c, for some fractions with a higher concentration of defects (> 5.27% defects) the spherulitic radius decreased with increasing defect concentration, and in some cases a disordered morphology was also observed. Possible explanations are offered for these exceptions. When quenching from the melt to room temperature, a decrease in spherulitic size with increasing H-H defect content was found for both the fractions and the whole polymers. When comparing isothermally crystallized samples under the same undercooling, similar deterioration of spherulitic size and morphology with increasing defect structure in the chain was found. A general explanation involving the inclusion of H-H defects into the lamellae is suggested. The spherulites of whole polymers are larger than those of the fractions and a possible explanation for this is offered.