Uniaxial stress, strain, strain rate and temperature relations for polymers are formulated and generalized to the multiaxial stress system. A full axisylnmetric finite-element method with thermo-elasto-viscoplastic constitutive model is employed to analyze the deformation behavior of polymeric bars subjected to tension. The effects of environmental temperature, deformation-induced heating and strain rate sensitivity on neck propagation are clarified. The results include load-elongation behavior, triaxiality factor, evolution of specimen profiles and temperature distributions.