Photodegradation radical initiators

Lopez JL, Garcia Einschlag FS, Gonzalez MC, Capparelli AL, Oliveros E, Hashem TM, Braun AM (2000) Hydroxyl Radical Initiated Photodegradation of 4-Chloro-3,5-dinitrobenzoic Acid in Aqueous Solution, J Photochem. Photobiol. A Chem. 137 177-184. 

Another pathway implied in the obtaining of photodegradable polymers consists in the blending of light responsive radical initiators. A very often used compound in... 

The final possible mode of action for an antioxidant is as a peroxide decomposer. In the sequences that lead to photodegradation of a polymer the ready fragmentation of the hydroperoxide groups to free radicals is the important step. If this step is interfered with because the peroxide has undergone an alternative decomposition this major source of initiation is removed. The additives which act by decomposing hydroperoxide groups include compounds containing either divalent sulfur or trivalent phosphorus. The mechanism involves... 

Another mechanism for alkanone-sensitized photodehydrochlorination comprises Norrish type I scission of the ketone, followed by ground-state reactions of radicals (19). However, the evidence for such a mechanism is based on experiments that were carried out in the vapor phase (19). Initiation of the photodegradation of PVC by hexachloroacetone has been suggested to involve the abstraction of hydrogen from the polymer by radicals resulting from the photolysis of the ketone s carbon-chlorine bonds (22). 

Both of these general anaesthetics have long been known to oxidize in the presence of air and sunlight. Chloroform was shown to photo-oxidize to a peroxide of uncertain structure which collapsed to the poison gas phosgene. Anaesthetic chloroform is protected by the addition of ethanol, which intercepts the initial free radical and prevents the photodegradation [17]. Diethyl ether... 

Radiation initiated or photodegradation - free radical reactions (see Chapter 18 on photodegradation and photostabilization of poly (ethylene terephthalate)). 

In the photodegradation process of PVC, the involvement of free radicals has been extensively documented. The applications of electron spin resonance, ESR, spectroscopy have revealed some details in the degradation mechanism (5, 6). However, the potential applications of ESR spectroscopy in this area are far from being exhaustively exploited. For instance, in the initial step of the photodegradation of PVC, one would expect "Radical I" to be a predominant radical (8) ... 

This phenomenon was explained by the existence of two distinct mechanisms of H2O2 photodegradation a chain mechanism at low incident photon flow and a non-chain mechanism at higher photon flows. The suppression of high quantum yields at high incident Op is possibly due to high concentrations of initial hydroxyl and hydroperoxyl radicals, which effectively terminate the radical chain reaction of the Haher-Weiss cycle (see Fig. 6-8). 

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