Epoxy groups responsible for crosslinking in natural rubber

Abstract

STORAGE hardening in natural rubber, which is of considerable industrial interest, has been ascribed to the crosslinking of carbonyl groups present in the rubber chain¹. Supporting evidence is that the crosslinking reaction can be prevented or accelerated by the addition of monofunctional or difunctional amines, respectively. These observations may be explained if the monofunctional amine is regarded as condensing with, and hence destroying, the carbonyl group, whereas the difunctional reagent is capable of reaction with carbonyl groups on separate chains, thus effecting a crosslink. The ability of dimedone (5,5-dimethylcyclohexane-1,3-dione) to inhibit the crosslinking reaction led to the conclusion that the groups were aldehydic¹.