Investigation of the curing process of spray polyurea elastomer by FTIR, DSC, and DMA

The curing process of a typically formulated spray polyurea elastomer (SPUA) system has been thoroughly investigated with the help of a combined analysis of Fourier transform infrared spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis. The evolvement of the microstructure and mechanical responses of the SPUA system during the curing process have been described in detail. The experimental results indicated that the fast curing property of SPUA, which mainly based on the reaction between the primary amine groups and the isocyanate groups, led to the formation of the unstable hard segments in the interphase. After the tack‐free time, the residual isocyanate groups continued to react with the rest of the secondary amine groups of the chain extenders for several hours and caused the increase of the molecular weight of the hard segment in SPUA. Furthermore, during the curing process, the “disordered” hydrogen bond formed by one CO and one nearby NH (secondary amine) reconstructed to “ordered” bond, which contributed to the increase of the content of the hard segment and ultimately, improved the mechanical properties of the SPUA system greatly.