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

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 CO 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. •Photo-aging process of crosslinked urethane was studied.•Two-dimensional correlation analysis enables to investigate morphological evolution.•Change of spectral features is discussed in combination with oxidation reactions.•Hydrogen bonding state of carbonyl species was investigated using infrared spectrum.•Increasing heterogeneity is implied from association state of photo-products.