Kinetics and rheological studies were carried out on polyurethane reactions involving a new polyol and TDL Conversion of isocyanate by uncatalyzed polymerization under isothermal conditions was monitored by IR spectrometry and titration. Viscosity changes of the reaction mixture were followed by a digital cone-and-plate viscometer under identical conditions. Conversion and viscosity were found to follow a power relationship. A relationship involving the order of the reactionnthat connects the viscosity with time was derived. This provides a new viscometric method to find the order of the reaction. The order of the reaction determined by this method was very close to the values obtained by a fractional-life method already reported.