The hindered amine‐induced decomposition of polypropylene hydroperoxide was studied in the solid state and in the presence of a liquid solvent and the polymer was compared with model hydroperoxides. The high reactivity of the macrohydroperoxides appears to be related to the adjacent, hydrogen‐bonded hydroperoxide groups that occur in the polymer. The hindered amines are converted to nitroxides in the reaction via hydroxylamine intermediates. Amine‐induced decomposition of polypropylene hydroperoxide is faster in the absence of a liquid solvent for the amine than in the presence of the solvent, probably because of the strong amine‐hydroperoxide association that occurs in the solid state. The decomposition process in the solid state is sufficiently rapid for the reaction to contribute to the effectiveness of hindered amines in the light stabilization of polymers.

-From a consideration of oxidative free radical reactions in solid polypropylene, it is concluded that only a small fraction of the peroxy radicals is expected to cause the bulk of the oxidation and need be scavenged for effective photo-stabilization. Most peroxy radicals terminate after only a few propagation steps with another peroxy radi cal descended from the same initiation event. The few that escape this "secondary cage" recombination produce long lived chains of very high kinetic length, which are easily scavenged. Tetramethylpiperidines and their products (nitroxides and substituted hydroxylamines) appear to photo-stabilize polypropylene by acting as inefficient scavengers of macroalkyl and macroperoxy radicals. In addition nitroxide association with oxidized domains is possible, together with decomposition of the grafted, substituted hydroxylamines in these oxidized regions.

No abstract

of a dipolar transition state8 consisting of diphenoquinone and benzene in place of 4 cannot be ruled out at present.