Mechanism of photostabilization of polypropylene by nickel oxime chelates

Recent work has shown that certain nickel oxime chelates act as effective light stabilizers for polypropylene. The mechanism of their protective action was examined by spectrophosphorimetry and flash photolysis. Examination of the phosphorescence from the commercial polymer shows that it is due to aldehydic carbonyl groups. From flash photolysis observations of the triplet quenching action of a range of nickel chelates it is suggested that stabilization by the oxime chelates is achieved by a mechanism of efficient energy transfer from the photoreactive carbonyl group to the chelate, where the energy is harmlessly dissipated. The efficiency of this quenching action is primarily dependent on the spatial configuration of the ligand around the central metal atom in the chelate.