A study of molecular architectural dynamics of crosslinked urethane during photo-aging by two-dimensional infrared correlation spectroscopy

Abstract The molecular architecture changes of crosslinked urethane during photo-oxidation was investigated by Fourier transform infrared spectroscopy (FTIR) in combination with two-dimensional (2D) correlation analysis. The 2D correlation FTIR spectroscopy provided insight into molecular architectural dynamics during photo-aging, where the sequential order of peak changes was determined upon perturbation with photo-aging. Photo-oxidation was monitored from the decrease in the peak intensity at 1537 cm−1 (attributed to the urethane group) and the generation of the hydrogen bonded C =O groups at 1698 cm−1 immediately after urethane decomposition. Several notable peaks appeared (1712, 1650, and 1750 cm−1) in the later stages, which were attributed to the free photo-oxidative product. In summary, photo-oxidation involved a cleavage of urethane crosslink and generation of end groups that formed hydrogen bonds with surrounding hydrogen bonding sites. Further degradation of the free photo-products was observed likely because of the small number of accessible hydrogen bonding sites due to the increasing heterogeneity of the internal structure.