Archived measurements of urethane rheology undergoing crosslinking at 45, 55, and 65 degrees C were reanalyzed by a sigmoidal mathematical model. The phenomenological sigmoidal model, with two kinetic parameters associated with cure advancement coupled with parameters for the initial viscosity and the terminal viscosity of the network, captures the nonlinearities in dynamic viscosity during polymerization and were similarly compared with a power law model. The interpretation of the gel time was determined using both models, with the sigmoidal model interpretation of the gel time being defined in terms of the other kinetic constants. The takeaway message is that there is very little difference in the quality of the fit between the power law model and the sigmoidal model and the experimental dynamic viscosity data. One would need a more comprehensive dataset to make a larger comparison as to which model actually represents viscosity more accurately. POLYM. ENG. SCI., 50:499-503, 2010. (C) 2009 Society of Plastics Engineers