COOPERATIVE MODEL FOR MECHANICAL DEFORMATION OF POLYMERS

A model for the mechanical behavior of solid polymers is proposed in the form of a linear elastic network with transitions. A simplified version of the model involving a single column of two-site activated processes is found to be a mean-field system. The failings of this system as a description of yield and glass transition relaxation behavior lead to two extensions to the system: that of many available sites in each activated process, and that of a finite number of such processes in the whole system. These extensions reduce the properties of the system to those of a single activated flow process with a temperature-dependent activation energy. Agreement is found between this result and time-temperature shift measurements in the alpha transition region of several polymers, together with an explanation of the dependence of yield stress on temperature for one of these polymers that is physically more reasonable than the usual constant activation energy proposal.