Photodecomposition of hydroperoxide groups

Carbonyl groups present in a virgin polymer or formed during photo-oxidative degradation of a polymer after absorption of light can give two types of reaction  

Norrish Type I reaction, during which carbon monoxide and two end-macro-radicals are formed  

Norrish type II reaction, a non-radical, intramolecular process which occurs with the formation of a six-membered cyclic intermediate (2.8). Abstraction of a hydrogen from the y-carbon results in its subsequent decomposition into an unsaturated polymer chain end, and a polymer chain with an end carbonyl group  

In polymers, the Type II reaction may also involve an intramolecular process with a longer chain segment. 

The Norrish I and II reactions may occur from the excited singlet (S ) or triplet (T ) states however the triplet state is much more favoured because of its longer lifetime (Table 1.1). Both Norrish reactions are responsible for the photodegradation of polymeric ketones (cf. section 3.2.1) and polymers containing main chain carbonyl groups. 

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UV wavelengths which damage certain polymers. The absorbed photons raise electrons to an excited state and cause bond dissociation reactions. An example is the photodecomposition of hydroperoxide groups introduced during melt processing. 

Acetophenone end-groups, which develop as a result of thermal and/or photodecomposition of hydroperoxide groups (cf. section 3.11.1.6) ... 

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