A model for the nonlinear rheology of associating polymers

Theories for transient networks formed by associating telechelic polymers r equire that the kinetics of chain detachment and reattachment processes are somehow specified. We propose here very simple choices for such kinetics, that are nevertheless based on plausible molecular mechanisms. Specific evo lution equations are then formulated for the populations of both elasticall y-active chains and chains temporarily detached from the network. By using typical closure approximations, the rheological model is finally elaborated into a set of ordinary differential equations. For steady shear flows, the se nonlinear equations predict shear thickening at moderate shear rates fol lowed by shear thinning at higher shear rates, in agreement with observatio ns. In the limit of slow flows, analytical expressions for the viscosity an d the relaxation times are also obtained. (C) 2000 Elsevier Science B.V. Al l rights reserved.