THE INFLUENCE OF SUBSTITUENTS ON THE PHOTO-STABILIZING EFFICIENCY OF HINDERED AMINE STABILIZERS IN POLYPROPYLENE

The following series of 4-benzoyloxy and 4-stearoyloxy 2,2,6,6-tetramethyl-piperidine derivatives substituted at the nitrogen atom were prepared: H, OH, OCOCH3, COCH3 and O•. The photo-stabilizing efficiency in these series depends on the method of incorporation of stabilizer into isotactic polypropylene. The N-O• and N-OH derivatives were usually the most efficient. ESR spectroscopy revealed that during processing in a Brabender, the concentration of the NO•-radicals decreased. On the other hand, an increasing NO•-radical concentration was observed and a maximum was reached in the first stages of irradiation. Some mechanistic aspects of these observations are discussed. 4-Stearoyloxy-derivatives were found to be substantially more effective than 4-benzoyloxy derivatives. © 1990.