A model of cooperative relaxation in finite viscoelasticity of amorphous polymers

Constitutive equations are derived for amorphous rubbery polymers at finite strains. A polymer is treated as an ensemble of flow units. The viscoelastic response is modeled as rearrangements of relaxing regions occurring at random times. The kinetics of rearrangement is described by the Eyring concept of thermally activated processes. Several phenomenological expressions are proposed for material functions. Adjustable parameters are found by fitting observations for polydienes functionalized by benzoic units, polyisobutylene and polystyrene in tensile and shear relaxation tests. Fair agreement is demonstrated between experimental data and results of numerical analysis. (C) 2000 Elsevier Science Ltd. All rights reserved.