Entangled Melts of BranchedPS Behave Like LinearPS in the Steady State of Fast Elongational Flows.

The classical Doi–Edwards theory for the steady-statestressof entangled linear polymers in uniaxial elongational flow is hereextended to entangled branched polymers, specifically to stars andpompoms, both symmetric and asymmetric. The arm withdrawal idea advancedlong ago by McLeish and Larson is also fully exploited. Non-Gaussiancorrections are considered. Aside from quantitative details, the theoryfor branched polymers predicts that they behave similarly to linearones in the steady state (as opposed to the startup stage) of fastelongational flows. The theoretical predictions are then successfullycompared, both qualitatively and quantitatively, to data collectedby Hassager and co-workers on polystyrene (PS) melts of a pompom andof an asymmetric star. These are, to the authors’ knowledge,the only published data for branched polymers of known architecturethat, during startup of the elongational flow, extend in time longenough to allow determination of steady-state values of the elongationalstress. [ABSTRACT FROM AUTHOR]