The samples of PUU polymers were characterized by In-situ FTIR in a temperature-controlled cell. The spectra of FTIR showed that the absorbance of ordered hydrogen-bonded urea carbonyl group (1643 cm(-1)) became stronger with increasing thermal process time (at 100 degrees C), then changed little after a certain time. The rate of change for absorbance of ordered hydrogen-bonded urea link, attributed to microphase separation kinetics, was enhanced with increasing thermal process temperature. In carbonyl region of FTIR spectra, absorbance for various carbonyls available in PUU polymers, associated with micro-hard domain, was observed before process. However, after the process, only the absorbance of free urethane, hydrogen-bonded urethane and ordered urea became obvious. At 100 degrees C, the longer the process time (beyond 8 h), the worse the mechanical properties obtained. The PUU polymers processed at 100 degrees C with the identical process time exhibited the best mechanical properties.