MALDI investigation of the photooxidation of nylon-66

Matrix-assisted laser desorption ionization mass spectrometry (MALDI) was used to determine the structure of the molecules produced in the photooxidative degradation of nylon-66 at 60 degreesC in air. The MALDI spectra of the photooxidized nylon-66 (Ny66) show the presence of nearly 40 compounds, as compared to only four in the original Ny66 sample, and provide information on the structure and end groups of the oligomers produced in the oxidation. The structural analysis of the photooxidized species provided by the MALDI spectra allowed drawing a detailed map of the photodecomposition mechanisms of Ny66. Our results extend the currently accepted picture for the photooxidation mechanisms of Ny66, confirming previous insights into the hydrogen abstraction and subsequent formation of a hydroperoxide intermediate, but also reveal that Norrish I and Norrish II chain cleavage reactions play an important role in the photooxidation process of Ny66. Ny66 films exposed for 12 h show the appearance of only photooxidation products generated by the hydrogen peroxide decomposition, indicating that the chain photocleavage reactions Norrish I and Norrish II type do occur at a later stage of irradiation. An explanation is offered for the appearance of this induction period. It is expected that future MALDI studies may have an impact on the current views on photooxidation processes of other polymer systems.