Photostability of polypropylene

On account of the high internal viscosity of the polymer the combination of the two macro-radicals formed in reactions of type IA probably predominates over the RO 2 formation, especially when the concentration of the dissolved oxygen, and hence its permeability, is low. Radical combination according to reaction type IB is unlikely, since CH3CO or CH3 may diffuse from the reaction site before recapture. Other isolated macro-radicals may also be formed by hydrogen abstraction by CH3 or CH3CO. Consequently the photolysis of polypropylene ketones according to type I seems to be an important factor in the photostability of polypropylene [124]. The tentative mechanism may be summarized as... 

Many pigments, particularly organic yellow, orange, and red, have negative effects on the photostability of polypropylene. 

Iron and chromium ions show negative influence in the photostability of polypropylene, whereas copper ions act as antioxidants [448]. 

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