The present work is outlined for the model-free isoconversion rheo-kinetics of 2-oxazolidone modified novolac epoxy film adhesive through rheological assessment under isothermal condition at different temperatures viz. 160, 165, 170, and 175 °C during its curing process. Effect of polyethersulfone (PES), which is used for toughening the film adhesive, on the isothermal curing reaction of film adhesive is also studied. Model-free isothermal isoconversion rheo-kinetic analysis is attempted while curing reaction via both integral and differential methods of Vyazovkin and Friedman, respectively. Curing behavior is predicted and compared with experimental data at each temperature. It is found that the prediction is > 90% and > 85% accurate for integral and differential method, respectively. Activation energy obtained in both approaches is showing the dependency on the extent of conversion, and it is seen in the range of 165–132 kJ mol−1 for WO-PES and 188–141 kJ mol−1 for W-PES in integral method and 114–90 kJ mol−1 for WO-PES and 108–78 kJ mol−1 for W-PES in differential approach. Contradictory behavior of activation energy in these approaches is attributed to the presence of non-reactive PES.