  We introduce an entropic network model for copolymer elastomers based on the
evolution of microscopic chain conformations during deformation. We show that
the stress results from additive contributions due to chain stretch at the
global as well as entanglement level. When these parameters are computed with
molecular simulations, the theory quantitatively predicts the macroscopic
stress response. The model requires only one elastic modulus to describe both
physically crosslinked triblock networks and uncrosslinked homopolymers.
