POLYMER PHOTOSTABILIZATION BY PIPERIDINE DERIVATIVES - ROLE OF NITROXIDE-HYDROPEROXIDE COMPLEXING

Hindered amines derived from piperidine are a relatively new class of highly effective light stabilizers for polyolefins, polystyrene, unsaturated polymers, etc. Their effectiveness is suggested to result from their conversion to nitroxide radicals, which then scavenge the alkyl radicals involved in the oxidative deterioration of polymers. However, alkyl radical generation in photooxidizing polymer results predominantly from the photolysis of these hydroperoxides. In addition hydroperoxides are well known to form quite strong hydrogen bonds. Thus it is possible that nitrooxide-hydroperoxide association could occur. and so raise the local nitroxide radical concentration in the regions where alkyl radicals are generated. In the reported experiments, the authors studied the extent of nitrogen oxide ion association with hydroperoxides in liquid-phase systems that are models of the oxidized polymer. Experimental data are presented and evaluated in terms of reaction kinetics and its mechanisms.