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8444122 
Journal Article 
Some aspects of stabilization of polymers against light 
Heller, HJ; Blattmann, HR 
1973 
1 
Pure and Applied Chemistry
ISSN: 0033-4545
EISSN: 1365-3075 
36 
1-2 
141-162 
English 
Different mechanisms for the protection of polymers against photodegradation are discussed. (1) The u.v.-absorbers of the 2-(2-hydroxypheny1)-benzo-triazole and the o-hydroxybenzophenone type have rates of internal conversion much higher than the rate of intersystem crossing and of fluorescence decay. Evidence is presented that this rapid non-radiativc deactivation cannot be explained very satisfactorily by a simple `enol-keto ‘-equilibrium in the first excited singlet state only. (2) At the concentrations used in practice the quenching rate of light stabilizers is so low that quenching cannot compete successfully with other deactivation processes of triplet states, while excited singlet states of primary sensitizers can be quenched efficiently only by additives with extinction coefficients of more than 5000 to 10000. (3) The derivatives of 2,2,6, 6-tetramethyl-piperidines of the structures I to IV cannot quench excited singlet states in the apolar solvent heptane. The corresponding N-oxyls inhibit the Norrish reaction of aralkylketones. Specific N-oxyl- and N-methyl-2,2,6, 6-tetramethyl-piperidines as well as certain nickel chelates decelerate the singlet oxygen induced photo-oxygenation of rubrene and 9, 10-dimethoxy anthracene. © 1973, Walter de Gruyter. All rights reserved.