Melt Rheology of Poly Vinilydene Fluoride: Evidence of Long Chain Branching and Microgel Formation

Rheological measurements are used to study the influence of molecular weights and molecular weight distributions (MWD) on the melt behavior of poly(vinylidene fluoride) (PVDF). Six commercial PVDF samples with weight‐average molecular weight ranging from 139 to 263 kg/mol and polydispersity index ranging from 2.3 to 4 are investigated. The use of van Gurp‐Palmen (vGP) plots reveals the presence of long‐chain branching (LCB) in three of the samples. They furthermore allow for a qualitative classification of these samples by their LCB degree. The Mark‐Houwink relationship between the intrinsic viscosity and weight‐average molecular weight is determined and shows no dependence on a low degree of LCB. A similar effect is observed for the flow activation energy which increases linearly with increasing weight‐average molecular weight with the exception of the flow activation energy for the highly branched PVDF sample. Samples known to contain microgels are also identifiable by extending the vGP analysis. The generality of this approach is substantiated by removal of the microgel fraction from these samples, which then exhibit conventional melt behavior.