Sacrificial consumption and depletion of stabilizers

This relates, for example, to coatings, in which stabilizer molecules may migrate from the clearcoat to the basecoat or plastic substrate. These problems may be alleviated by the use of physically persistent stabilizers. High molar mass stabilizers (M 500gmor ), including oligomers with appropriate molecular structures (M=3500-5000 g mol ), are sufficiently physically persistent and do not evaporate at the elevated temperatures of curing [87]. 

In the case of UV absorbers forming intramolecular hydrogen bonds, the loss of stabilizer efficiency may be due to the interruption of intramolecular hydrogen bonds and the formation of intermolecular hydrogen bonds with H-acceptors (carbonyl groups) generated by photooxidation of the polymer matrix. Thus, the 

Chart 9.16 Nitroso (a) and nitro compounds (b), and nitrogen-free compounds ((c) and (d)) formed during the photolysis of hindered amines [117]. 

ESIPTmechanism (see Section 93.2.2) can no longer be repeated. Regarding hindered amine stabilizers, depletion is caused by the reaction of acyl radicals, stemming from Norrish reactions, with nitroxyl radicals. Nitroso and nitro compounds (see Chart 9.16) are formed when nitroxyl radicals are photolyzed (117]. 

1 Semiconductor Industry Association, The International Roadmap for Semiconductors, International SEMATECH, Austin TX 

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