The rheological behavior during the bulk polymerization of urethane systems made from diphenyl methane 4,4' diisocyanate (MDI) and poyether macro diol was studied in connection with the kinetics of the reaction. The linear viscoelastic behavior in the terminal zone has been reasonably predicted using the molecular weight distribution obtained from size exclusion chromatography (SEC) and owing to only a few rheological parameters, namely, the scaling law relating the zero shear viscosity to the average weight molecular weight and the plateau modulus. These parameters were previously determined from oscillatory shear experiments performed on model samples of various molecular weights. The combination of this predictive model together with a reasonable kinetic scheme for such systems, enables to calculate the evolution of the viscoelastic parameters (storage and loss moduli) during bulk polymerization. The overall calculation was shown to give a reasonable depiction of the viscosity function. However, some discrepancies were noted as far as the elasticity of the melt is concerned. This was attributed to an additional relaxation mechanisms in the earliest stage of the polymerization connected to hydrogen bonding. Nevertheless, the procedure remains fundamental for apprehending some aspects of the viscoelastic changes of the material during a reactive processing technique such as extrusion for example.