AbstractThe mechanism of the antioxidative effect of thiobisphenols in the inhibition of autoxidation of polyolefins initiated by the decomposition of hydroperoxides was studied by means of a model reaction of 4,4′‐thiobis(2‐methyl‐6‐tert‐butylphenol) (I) with tert‐butylhydroperoxide in the presence CO(II)acetyl acetonate. Products isolated from the reaction mixture prove that in the inhibition of autoxidation, thiobisphenols break as phenols the propagation chains of radical autoxidation, while they decompose as sulphides the hydroperoxides into nonrad