Influence of sensitisers on the photostabilising action of a hindered piperidine compound in polypropylene

Abstract

AbstractThe influence of prior thermally generated hydroperoxides and added anthraquinone have been examined on the photostabilising action of a hindered piperidine compound, bis(2,2,6,6‐tetramethyl‐4‐piperidinyl) sebacate, in polypropylene film using ESR spectroscopy and flash photolysis techniques. The hindered piperidine compound was found to effectively inhibit both the hydroperoxide and carbonyl group sensitised photooxidation of the polymer. Using ESR spectroscopy evidence is presented to show that the hindered piperidine compound reacts stoichiometrically with the hydroperoxide groups generated by thermal oxidation to give a stable nitroxyl radical. On flash photolysis of anthraquinone in hexane transient formation due to the semi‐quinone radical and subsequent formation of the hydroquinone were found to be effectively inhibited by a stable N‐oxyl radical compound but not the amine. It is concluded that the nitroxyl radical is the effective stabilising species and operates by a radical scavenging mechanism to form the hydroxylamine.