The missing link between the extensional dynamics of polymer melts and solutions

•The extensional flow of oligomer diluted monodisperse (MD) polystyrenes is studied.•The flow dynamics depends on the size (e.g. Kuhn steps) of the polystyrene oligomer.•In the use of oligomers of less than two Kuhn steps the dilution flows as a solution.•In the use of two or more Kuhn steps it flows neither as a solution nor as a MD melt.•The flow dynamics of these dilutions are currently unresolved.

Based on extensional viscosities measured on narrow molecular weight distributed (NMMD) polystyrenes and polystyrene oligomer dilutions thereof, we discuss the relation between the flow physics of polymer solutions and melts. A polymer solution is here characterized as a dilution where the diluent contains less than two Kuhn steps. At the same entanglement number (e.g. concentrations) its extensional viscosities are up to about 300% higher than the corresponding viscosities for polymer blends. A blend is understood as a polymer system diluted with polymer/oligomer containing active chain in term of Kuhn steps, e.g. at least two Kuhn steps. A similar disagreement is observed between blends and pure NMMD melts, both containing the same entanglement number.