Photo-oxidative degradation of polypropylene and stabilization by hindered amines

Abstract

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 polypropy— lene 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