The antioxidant role of u.v. stabilisers

The mechantsrns of action of the more important classes of uv stabtltsers for polyoleftns are considered in the light of present views on the mechanisms of antioxidant behaviour.The metal thiolate catalytic peroxide decomposers (PD-C) are seen to be effective uv stabilisers in their own right and as synergtsts with 'uv absorbers' .Chain-breaking antioxidants (CB-A), of which the hindered nttroxyl radicals are the most Important, are very effective as slngle component uv stabilisers but their precursors, the hindered amines, are thermal pro-oxidants .Donor chain-breaking antioxidants (CB-D), as ttfted by the hindered phenols, are weak photostabilisers with only a small concentration gradient .Their radical scavenging effect, Is augmented when they are used In conjunction with the 'uv absorbers ' but they antagonise with the peroxide decomposers.The 'uv absorbers' appear to function at least in part by a CB-D mechanism and their effectiveness is due mainly to their uv stability.They are destroyed by both hydroperoxides and by excited carbonyl chromophores and their synergism with the peroxide decomposers (PD-C) Is to a large extent due to their protection by this class of uv stabiliser.