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Polyisoprene and model compound, 2,3‐dimethyl‐2‐butene, were vulcanized with N,N′‐dipentamethylenethiuram disulfide (CPTD), CPTD/sulfur and N,N′‐dipentamethylenethiuram hexasulfide (CPTP6) in the absence of ZnO and residual extractable curatives and reaction intermediates analyzed by HPLC at various stages of the reaction. Accelerator polysulfides, required for the formation of accelerator‐terminated polysulfidic pendent groups, form rapidly, or are present from the outset in the case of CPTP6. Model compounds confirm the formation of thiuram‐terminated polysulfidic pendent groups as intermediates in the vulcanization process. Removal of pentamethylenedithiocarbamic acid (Hpmtc) from the system during heating delays the onset of vulcanization and leads to very low crosslink densities. Rubbers heated under vacuum can subsequently be crosslinked by the addition of zinc stearate, pointing to the presence in the compound of thiuram‐terminated pendent groups. However, such pendent groups do not readily crosslink on their own, and hydrogen‐terminated polysulfidic pendent groups, formed by the reaction of sulfurated Hpmtc with the polymer, are suggested to be involved in the crosslink formation. N,N′‐Pentamethylenethiurea forms in the vulcanizate, but is not as product of crosslinking reactions, rather of CPTD degradation. The data are discussed with respect to mechanisms proposed in the literature for crosslinking, and it is concluded that the data support recently formulated mechanisms in which crosslinking involves reaction between thiuram and thiol‐terminated pendent groups, with Hmptc playing and essential role in the overall process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1100–1111, 2000

Polyisoprene and model compound, 2,3‐dimethyl‐2‐butene, were vulcanized with N,N′‐dipentamethylenethiuram disulfide (CPTD), CPTD/sulfur and N,N′‐dipentamethylenethiuram hexasulfide (CPTP6) in the presence of ZnO and zinc (bispentamethylenedithiocarbamate) (ZPD), and residual extractable curatives and reaction intermediates analyzed by HPLC at various stages of the reaction. CPTD and ZnO do not react at vulcanization temperatures and, as in zinc‐free systems, the reaction is initiated by accelerator polysulfides that lead to the formation of thiuram terminated pendent groups. Pentamethylenedithiocarbamic acid, liberated in the process, is trapped by ZnO as ZPD. Crosslinking is more rapid than in the absence of ZnO. ZPD catalyzes the crosslinking of thiuram pendent groups, and high crosslink densities are achieved because the ZPD catalyzed crosslinking of thiuram crosslink pendent groups is more efficient than when thiuram pendent groups crosslink, mainly via a reaction with thiol pendent groups, as is suggested in the absence of zinc. When free sulfur is available in the system, ZPD acts as an accelerator in its own right. Thiuram pendent groups were not detected in ZPD/sulfur formulations with model compounds, but their formation or the formation of thiol pendent groups, either of which may form via sulfurated ZPD, cannot be excluded. ZPD promoted the rapid crosslinking of such pendent groups. Overall, the reaction mechanism with zinc‐containing formulations is similar to those for the corresponding TMTD systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1112–1120, 2000