The rheological behavior during bulk polymerization of epsilon-caprolactone with titanium tetrapropoxide as the initiator was studied in connection with the kinetics of the reaction (conversion rate and molecular weight variations). The viscoelastic properties of the melt polycaprolactone performed by this reactive system was predicted reasonably well using phenomenological models such as the Yasuda-Carreau or relaxation spectrum models and a molecular dynamic model based on a blending law of the relaxation function. The evolution of these viscoelastic properties during bulk polymerization was calculated by combining these viscoelastic models with the kinetic laws of the system. By taking into account the dilution effect caused by the presence of a monomer, a global rheological predictive model was then achieved. It was shown to give a reasonably good depiction of the viscoelastic properties [parallel to eta*(t)parallel to, G＇(t) and G "(t)] whatever the processing conditions (temperature, frequency, initiator concentration, etc.) are. (C) 2000 The Society of Rheology. [S0148-6055(00)00903-2].