New Vistas in the Photo-Oxidation of Nylon 6

Abstract

Matrix-assisted laser desorption ionization mass spectrometry (MALDI) is an excellent method to use in determining the structure of the molecules produced in the photo-oxidative degradation of nylon 6 at 60°C in air. The MALDI spectra of photo-oxidized nylon 6 (Ny6) show the presence of over 40 compounds, as compared to only 3 in the blank Ny6 sample. The extremely favorable event here is that the MALDI spectra present so many new well-resolved peaks, which provide information on the structure and end groups of the oxidation products. The structural analysis of the photo-oxidation products provided by the MALDI spectra allowed us to draw a detailed map of the photo-oxidation mechanisms of Ny6 (Schemes 1-4). The presence of the majority of the oligomers listed in Table 1 had not been revealed before. Our results extend and modify the currently accepted picture for the photo-oxidation mechanisms of Ny6. In fact, our results confirm previous insights that the hydrogen abstraction and subsequent formation of a hydroperoxide intermediate actually occur but also reveal that Norrish I and Norrish II chain-cleavage reactions play an important role in the photo-oxidation process of Ny6. This essential feature of the process had been missed in previous studies focused on UV and IR techniques. The peculiarity of our approach consists of using a high-sensitivity and nonaveraging technique such as mass spectrometry, which allows the detection and monitoring of each new oligomers formed during the oxidation process. This is a remarkable result, and it should be expected that future MALDI studies may have an impact on the current views of photo-oxidation processes of other polymer systems.

Comparative investigation of photo- and thermal-oxidation processes in poly(butylene terephthalate)

“…Applications of MALDI to the study of polymer photo-and thermooxidation are quite recent [10][11][12][13][14][15][16] and involve the collection of MALDI spectra at different irradiation times and/or temperature to observe the structural changes induced by heat or light under an oxidizing atmosphere. The polymer sample can be directly analyzed and the recorded MALDI spectrum arises from a mixture of nonoxidized and oxidized chains.…”

“…The polymer sample can be directly analyzed and the recorded MALDI spectrum arises from a mixture of nonoxidized and oxidized chains. The results obtained for the systems so far investigated by MALDI [10][11][12][13][14][15][16] are remarkably highly informative, in comparison with previous studies based on conventional techniques, yielding precise information on the size, structure and end groups of molecules originated in the oxidation process.…”

Surface modification of polyamide 12 angioplasty balloons by photochemical reaction with an aromatic azide

“…In order to achieve the best compromise between maximization of reaction yield and minimization of PA12 degradation, preliminary irradiation experiments were carried out at 254 nm using 3 irradiation distances (2, 5, and 10 cm). As shown in Figure , in the UV‐vis spectra of irradiated balloons, a new peak appeared in the region above 250 nm; its intensity increased with the decrease of the irradiation distance, denoting increasing levels of photooxidation probably due to the formation of carbonyl or carboxylated groups on methylenes adjacent to the nitrogen atoms …”

Photoinduced synthesis of polyester networks from methacrylate functionalized precursors: analysis of side reactions

“…The possible influences of such irradiation on poly( ε ‐caprolactone) (PCL) chains in the context of network formation and alterations of their properties have not been discussed in the literature to our knowledge. Some previous investigations reported on the influence of UV light on polymethylmethacrylate, polylactide, polycaprolactam, or PCL regarding the initiation of polymerization, degradation, and ablation behavior, also considering the impact of oxygen, dopants, and different intensity regimes of light . Especially radical photolysis of ester groups upon exposure to light with wavelength smaller than 308 nm has been described repeatedly, and reaction schemes for photolysis and Norrish type II rearrangements were reported .…”