A series of polyurethanes based on 2,4-toluenediisocyanate (TDI), with different amounts of 3-chloro-1,2-propanediol (CPDO), have been prepared. The process of thermal degradation was monitored by thermogravimetric analysis (TGA) alone or coupled with infrared spectroscopy (TGA/FTIR) and differential scanning calorimetry (DSC). Flammability of the polymers was determined using the oxygen index (OI) method. The influence of CPDO on the thermal decomposition parameters [e.g., initial decomposition temperature (IDT), char residue at 500 degrees C, and DTG-max-temperature] and on the OI values have been discussed. Some correlations between thermogravimetric data and OI values were found, thus making it possible to apply the TGA method for certain flammability predictions of modified polyurethanes.