Coagents
Coagents protect the already cross-linked bonds between the polymer and vulcanizing agent from being torn apart. This assures that bonds are not broken as fast as new bonds are generated.
There are two types of coagents: type I and type II. Type I coagents increase the cure rate (speed) and cure state (stiffness) of the compound. Type II coagents increase the cure state but do not effect cure rate.