Comparative study of different bis-citraconimides as anti-reversion agents in natural rubber

Sulfur-cured natural rubber (NR) commonly accompanies reversion, which severely impacts the properties as well as service life of NR products. Introducing anti-reversion agents is one of the most effective ways to counteract reversion. In this work, five structurally different bis-citraconimides have been synthesized and used as anti-reversion agents for sulfur-cured NR. In detail, the differences of anti-reversion agents in the cure characteristics, cross-linked structure, physical-mechanical properties, heat build-up, and dynamic mechanical properties of sulfur-cured NR are investigated in order to elaborate on the differences in reactivity and cross-linking chemistry of anti-reversion agents. The results show that N,N′-p-phenylene-biscitraconimide (BCmB) provides the best anti-reversion performance for compound cured at 150°C, with N,N′-p-phenylene-biscitraconimide (BCpB) following closely behind. Although Perkalink 900 (1,3-bis(citraconimidomethyl)benzene: BCDB), 1,3-bis(citraconimido)isobutane (BIB), and 1,6-bis(citraconimido)hexane (BCH) are less effective than BCmB and BCpB in improving the anti-reversion performance of compound cured for a short period of time or cured at 150°C, they show better anti-reversion performance of compound cured for a longer time or cured at higher vulcanization temperature.