Polymer conformation in elongational flow

The elongational-flow-induced deformation of a polymer segment of arbitrary length and location along the contour of a macromolecule is calculated neglecting excluded-volume and nondraining effects. The resulting expression is valid for arbitrary flow strain rates in both steady-state and transient regimes of extension. For strain rates approaching a critical value at which a steady-state solution ceases to exist, the center of the macromolecule becomes much more stretched than its ends and it is argued that as a result of this nonuniform elongation, the stretching cannot be characterized by a single time scale corresponding to the uniform deformation of the polymer. The emerging picture of the process agrees with earlier conjectures made by the author and with Ryskin's "yo-yo" model of polymer stretching in elongational flow.