We outline a model to describe the rheology and the nonlinear response of layered materials. Explicitly, the focus is on cases wherein the system possesses internal states whose relative populations undergo a change upon the application of a stress. The objective of the model is to describe the mutual interplay between stress-induced transformations and the macroscopic rheological response of the materials. We focus on the specific case of multiblock copolymers, wherein the bridge and loop conformations of the chain constitute the internal states. The numerical results of our model for different polymeric architectures and different rheological constraints indicate a rich variety of phenomena including strain localization and shear banding. We derive an explicit constitutive equation that explains the origin of the inhomogeneous rheological response of the model. (C) 2001 The Society of Rheology.