Synthesis of macromolecular antioxidants containing thioether and aromatic secondary amine to improve the anti-oxidation properties of EPDM

A macromolecular antioxidant PM containing thioether and aromatic secondary amine was synthesized by the thiol-ene click reaction between the antioxidant N-(4-aminophenyl)maleimide (MC) and pentaerythritol tetra(3mercapto propionate) (PETPM). Then, the curing properties and anti-oxidation properties of PM in EPDM were investigated. The results showed that PM reduced the negative effect of the coexisted of PETPM and MC (PETPM+MC) on rubber curing and improved the crosslinking density of the rubber. PM also exhibited high anti volatility and anti-migration properties due to its high molecular mass. Moreover, the aromatic secondary amine group in PM was able to capture aging radicals and inhibit the occurrence of oxidation reactions, while the thioether group effectively decomposed hydroperoxides and inhibited the occurrence of autocatalytic oxidation reactions. The combination of these two groups improved the anti-oxidation properties of EPDM. As a result, PM/ EPDM demonstrated the lowest crosslinking density change rate and carbonyl index, as well as the largest aging coefficient K when compared to the EPDM containing low molecular weight antioxidants (PETPM/EPDM, MC/ EPDM, MC+PETPM/EPDM).