Does the interchain pressure effect exist in flow of polymer melt?

Based on the uniaxial extension of monodisperse polystyrenes presented by Bach et al. (Macromolecules, 2003) Marrucci and Ianniruberto (Macromolecules, 2004) formulated the 'interchain pressure' concept, based on ideas going back to Doi and Edwards. For a theory to be valid id needs the ability to quantitatively to predict experiments observation. Here we critically evaluate the 'interchain pressure' concept within the MSF model as suggested by Wagner er al. (J.Rheol. 2005). The experiments are startup of uni-axial elongational flow until steady flow, followed by stress relaxation or reversed bi-axial flow. The measurements are all performed on a filament stretching rheometer and narrow molar mass distribution polystyrened; controlled architecture branched as well as linear polymers.