A thermomechanical viscoelastic material model for isotropic materials is developed based on the free
volume theory by [Ferry, 1980] and [Krawietz, 1986]. Thermodynamic consistency of the constitutive
and evolution equations is ensured by evaluation of the Clausius-Duhem inequality. The material
model is numerically implemented in the programming language Python. Polypropylene and unsatu-
rated polyester polyurethane hybrid resin are characterized by means of dynamic mechanical analysis
with the GABO Eplexor 500N. The material parameters for both materials are determined by min-
imizing numerically the error between experimental and simulated data. To this end, the MIDACO
software is used.