For highly unsaturated rubbers, usually Type II coagents provide no increase in cross-link density because of the relative ease of allylic hydrogen abstraction from the polymer chain compared with the vinylic group of coagent.
The polymer macroradical formed by allylic hydrogen abstraction added to the coagent, generating a new radical; combined with another polymer radical to form a C–C cross-link; or abstracted hydrogen from the coagent. Some peroxide radicals also initiate isomerization of TAC to triallylisocyanurate (TAIC; Scheme 2)
The former two reactions will increase cross-link density. This might be the reason for increased cross-link density at lower concentrations of TAC.