  A constitutive model is developed to predict the viscoelastic response of
polyimide resins that are used in high temperature applications. This model is
based on a thermodynamic framework that uses the notion that the `natural
configuration' of a body evolves as the body undergoes a process and the
evolution is determined by maximizing the rate of entropy production in general
and the rate of dissipation within purely mechanical considerations. We
constitutively prescribe forms for the specific Helmholtz potential and the
rate of dissipation (which is the product of density, temperature and the rate
of entropy production), and the model is derived by maximizing the rate of
dissipation with the constraint of incompressibility, and the reduced energy
dissipation equation is also regarded as a constraint in that it is required to
be met in every process that the body undergoes. The efficacy of the model is
ascertained by comparing the predictions of the model with the experimental
data for PMR-15 and HFPE-II-52 polyimide resins.
