p-Phenylenediamine (PPD) antioxidants play a vital role in protecting diene rubbers from oxidative degradation. However, their strong polarity often leads to migration from the bulk to the surface, adversely affecting product appearance and reducing long-term anti-aging performance, which limits their wider use. To address this, a novel antioxidant, EMA2-PPDA (designated E2P), was synthesized by attaching two 3,4-epoxycyclohexylmethyl acrylate (EMA) units to an N-phenyl-p-phenylenediamine (PPDA) core via an epoxy-amine reaction. E2P exhibits a notable capacity to react during vulcanization. This characteristic can improve its retention within diene rubber matrices, making it less prone to migration compared to the conventional antioxidant 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine). Results show that E2P provides excellent anti-aging protection in both natural rubber (NR) and butadiene rubber (BR), with the best overall thermal-oxidative stability observed at 3 phr (parts per hundred rubber). In addition, E2P exhibits a markedly improved resistance to migration compared to 6PPD under the investigated conditions. These findings indicate that introducing acrylate groups represents a promising strategy for improving the migration resistance of PPD-type antioxidants in vulcanizates, without compromising their antioxidative activity.
Chen et al. (Tue,) studied this question.