We demonstrated that the crosslinking of epoxidized natural
rubber with carboxylic diacids could be tremendously accelerated
using 1,2-dimethylimidazole. Among usual accelerators of the acid/
epoxy reaction, DMI was the only one able to activate in bulk the
crosslinking of the high molecular weight elastomer. Not catalytic,
the mechanism of acceleration involves the quantitative formation
of an imidazolium carboxylate. Indeed, an equimolar amount of
accelerator and carboxylic functions is required to optimize the rate
of the reaction as well as the tensile properties of the cured
systems. Whereas the usual role of imidazoles in the acceleration of
epoxy/acid reaction is catalytic, here DMI is an accelerator acting
through the formation of an imidazolium dicarboxylate that
enables the solubilization and the activation of the crosslinking
agent. Further studies on model systems will investigate the
mechanism of the acceleration reaction.