Bleaching of polyene structures

Polyene structures formed during the photodehydrochlorination of poly(vinyl chloride) samples are bleached in the dark as well under UV/VIS irradiation. Bleaching in the dark is a much slower process that in the presence of light. Oxygen plays an important role in bleaching processes in the dark and during light irradiation [771, 1674, 1791, 1881, 1882]. 

The polymer alkoxy allyl radicals (3.58) produced in reaction 3.245 may initiate some new degradation chains. 

Another possible reaction would be the internal rearrangement of polymer alkoxy allyl biradical (3.58) leading to the formation of a,) -unsaturated aldehydes (3.59) and ketones (3.60)  

In the dark bleaching mechanism, the consumption of polyenes is faster for long conjugated sequences, since the probability of oxygen attack is enhanced as the sequence length increases. 

Bleaching in the presence of light (photobleaching) may occur by different mechanisms  

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