RANGE OF VALIDITY OF THE ENTROPIC SPRING CONCEPT IN POLYMER MELT RELAXATION

Computer simulations of stress relaxation in a model polymer melt demonstrate that the entropic spring concept and the Rouse model greatly underestimate the stress in the glassy and transition regimes and become accurate only in the rubbery and terminal regimes. The time-dependent segment orientation in a time-dependent elongational deformation of this model is also studied. The ratio of orientation to stress is smaller (by a factor of approximately 35) in the glassy regime than in the rubbery and terminal regimes.