Disulfide crosslinks introduced into an ENR matrix enable the thermo-activated reprocessing of the chemically crosslinked rubber, studied in terms of stress relaxation and adhesion experiments.

The crosslinking of epoxidized natural rubber with dodecanedioic acid and the mechanism of its acceleration by 1,2-dimethylimidazole (DMI) are investigated using nuclear magnetic resonance spectroscopy. Solid-state NMR experiments (¹H, ¹H → ¹³C cross-polarization and ¹³C direct polarization) are used to analyse crosslinked samples, whereas ¹³C solution NMR provides information about liquid epoxidized rubber species. ¹³C solid-state NMR demonstrates the ester nature of the crosslinks, and confirms that DMI acts through the formation of imidazolium dicarboxylate species, well dispersed in the elastomeric matrix. After synthesis of a low molecular weight epoxidized rubber and subsequent reaction with a monofunctional carboxylic acid in the presence of DMI, a solution NMR study reveals that the imidazolium dicarboxylate would react preferentially at the less substituted side of the epoxy site.

The work focuses on crosslinking epoxidised natural rubber by dicarboxylic acids which react with the epoxy sites along the chain. The crosslinking reaction at 180 °C is followed in a rheometer, and the cured materials are characterised by stress–strain experiments. The cure process is tremendously accelerated (from 3 h to 20 min) in the presence of an equimolar amount of 1,2-dimethylimidazole. Thermal stability and fatigue life experiments were carried out on samples charged with carbon black and antioxidants. The results are found in between the ones obtained with standard sulphur or peroxide crosslinked samples.