Studies on polymer stabilizers: Part II. A new concept of a synergistic mechanism between phenolic and thiopropionate type antioxidants

3,9-Bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1, 1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5] undecane (Sumitomo's new antioxidant: Sumilizer GA-80) is shown to have a very effective synergistic stabilizing effect in combination with thiopropionate type antioxidants. For synergistic stabilization, association of phenolic antioxidants with thiopropionate type antioxidants through hydrogen bonding is shown, by IR analyses and estimation of association equilibrium constant of a model system, to be an important factor.