FLASH-PHOTOLYSIS AND TIME-RESOLVED ELECTRON-SPIN-RESONANCE STUDIES OFTRIPLET BENZOPHENONE QUENCHING BY HINDERED AMINE LIGHT STABILIZERS (HALS) - A COMPARISON OF HALS AMINES AND AMINOETHERS AS ELECTRON AND HYDROGEN-ATOM DONORS

Transient absorption spectroscopy and time-resolved electron spin reso nance (TR-ESR) were employed to understand the electron and hydrogen a tom transfer quenching of triplet benzophenone ((BP)-B-3) in acetonitr ile and benzene by amine and aminoether derivatives of 2,2,6,6-tetrame thylpiperidine (hindered amine light stabilizers, HALS). The amines (I and II) are efficient quenchers of (BP)-B-3. The observed quenching r ate constants were found to be in the range 6X10(8)-6X10(9) M(-1) s(-1 ) and depend on the structure of the amine and the solvent. On the oth er hand, the aminoethers (III and IV) do not exhibit any quenching at all. Reactions of 3BP with amines I and II in benzene yield ketyl radi cals (detected by transient absorption spectroscopy) and the correspon ding aminyl or aminomethyl radicals (detected by TR-ESR). Neither expe rimental method provided any evidence for products of the reactions of 3BP with aminoethers III and IV. The experimental results are discuss ed from the viewpoint of the mechanism of polymer stabilization by HAL S.