Torsional Braid and Infrared analysis were used to examine the curing behavior of a model Polyurethane prepolymer (reaction product of polyethylene adipate glycol and 2 4-toluene diisocyanate) with a triol (tnmethylol propane) and an amine (MOCA). These analytical methods were used to follow the mechanical and chemical conversion of the curing system. The results were interpreted in terms of the formation of "physical" and chemical cross-links. It was concluded that with the triol cure, both chemical and physical cross-links characterize the mechanical conversion of the polymer; with the amine cure, a two-step mechanical conversion mechanism is proposed.