Early-stage photodegradation of polyamide 6 probed by low- and high-frequency Raman mapping

Low- and high-frequency Raman spectroscopy combined with Raman mapping was employed to investigate the structural evolution of annealed polyamide 6 (PA6) films during heating and photo degradation. Temperature-dependent Raman measurements revealed systematic changes in both low-wavenumber modes associated with molecular chain dynamics and high-wavenumber bands related to crystalline conformations and hydrogen-bonded functional groups. Complementary intensity variations were observed between low-wavenumber bands at ∼60 and ∼105 cm^-1, as well as between the amide III and amide I modes in the high-wavenumber region, reflecting their distinct vibrational directions relative to hydrogen bonding. Raman mapping was further employed to visualize spatially resolved structural evolution during the photodegradation simulation. While complementary spatial patterns were observed between low- and high-wavenumber vibrational modes, the carbonyl index exhibited a markedly different distribution from that of the crystallinity-related bands, suggesting a spatial decoupling between chemical oxidation and higher-order structural evolution. The present study demonstrates that low-frequency Raman mapping provides a sensitive and non-destructive approach for detecting subtle early-stage degradation processes that are difficult to resolve using conventional spectroscopic methods, offering new mechanistic insight into polymer degradation behavior.