A thermodynamically admissible reptation model for fast flows of entangledpolymers

The primary purpose of this paper is to introduce the effect of chain stret ching into a previously developed, thermodynamically admissible reptation m odel incorporating anisotropic tube cross sections, double reptation, and c onvective constraint release, while avoiding the independent alignment appr oximation. A second goal is the detailed illustration of the thermodynamic modeling approach. Two versions of the model with different stretching mech anisms are proposed, and the simpler one sheds new light on thermodynamical ly admissible reptation models without independent alignment. The stochasti c reformulation of the new model, its simulation, its linear viscoelastic p roperties, its predictions for rapid double-step shear strains, and the mod el parameters are discussed in detail. (C) 1999 The Society of Rheology. [S 0148-6055(99)00806-8].