FTIR Characterization of Moisture Cured Polyurethane

The urethane prepolymer product and its microstructure produced throughout the curing process were investigated by Fourier Transform Infrared (FTIR) spectroscopy. The coating process was adapted from one-component polyurethane coating system, where prepolymer was applied as the undercoat layer. The obtained infrared spectrum confirmed that both urethane and urea carbonyl groups existed with small portion of isocyanate remained unreacted in the system. The depreciation trend of isocyanate peak and shifting pattern of other absorption bands such as NH and carbonyl group were observed and explained in this paper. Peak area measurement confirmed that isocyanate content decreased with the progress of curing reaction. The FTIR results showed that the urethane C=0 band shifted to lower frequency while the urea C=0 shifted slightly to the higher frequency. The study also found that the polymer microstructure became more disordered at the end of curing reaction, which was indicated by the decrease of the ordered C=0 peak intensity as the disordered peak increased.