MALDI Investigation of the Photooxidation of Nylon-66

Matrix-assisted laser desorption ionization mass spectrometry (MALDI) was used to det. the structure of the mols. produced in the photooxidative degrdn. of nylon-66 at 60 °C in air. The MALDI spectra of the photooxidized nylon-66 (Ny66) show the presence of nearly 40 compds., 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 oxidn. The structural anal. of the photooxidized species provided by the MALDI spectra allowed drawing a detailed map of the photodecompn. mechanisms of Ny66. Our results extend the currently accepted picture for the photooxidn. 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 photooxidn. process of Ny66. Ny66 films exposed for 12 h show the appearance of only photooxidn. products generated by the hydrogen peroxide decompn., indicating that the chain photocleavage reactions Norrish I and Norrish II type do occur at a later stage of irradn. 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 photooxidn. processes of other polymer systems.