Our objective is to extend the population balance equation model for vulcanization of natural rubber in the presence of N-t-butylbenzothiazole-2-sulfenamide (TBBS) as an accelerator and N-(cyclohexylthio)phthalimide (CTP) as a retarder. The experiments performed by using the oscillating disk rheometer are used to track the evolution of crosslink density in natural rubber. The model quantitatively predicts the trends observed in the vulcanization mixture at various temperatures, including capturing the effects of changing the initial amounts of TBBS and CTP. This model is able to capture all the key trends involved in the retarder chemistry. Specifically, both experiments and model show that addition of CTP delays the scorching time by a few minutes, without affecting the final crosslink concentration. The model qualitatively predicts trends in the major species reported in the literature. The model can reliably predict and explain the trends of monosulfidic, disulfidic, and polysulfidic crosslinks in a conventional and efficient TBBS-accelerated system. Finally, reaction path analysis is performed for the vulcanization process, which is able to clearly identify the key reaction mechanisms in the induction, crosslinking, and postcrosslink zones during the curing process.