N,N?-Pentamethylenethiuram disulfide- andN,N?-pentamethylenethiuram hexasulfide-accelerated sulfur vulcanization. I. Interaction of curatives in the absence of rubber

N,N?-Pentamethylenethiuram disulfide- andN,N?-pentamethylenethiuram hexasulfide-accelerated sulfur vulcanization. II. Relative stability ofN,N?-pentamethylenethiuram disulfide and tetramethylthiuram disulfide with respect to amine formation

“…9 In the figures and tables, the concentrations of the reactants, intermediates, and products are expressed in terms of the initial concentration of the reactant. Acronyms are listed in Table I.…”

“…By contrast, it was shown in the first article in this series 9 that CPTU is one of the major decomposition products of N,NЈ-dipentamethylenethiuram monosulfide (CPTM), CPTD, and CPTP6 at 140°C, the accelerators being stable only below 120°C. DSC studies 9 showed the accelerated formation of CPTU above 150°C, indicating the lower stability of CPTD compared to TMTD. The presence of ZnO in CPTD and CPTP6 mixtures suppressed the formation of CPTU, and DSC studies showed no CPTU even at 195°C and no degradation of N,NЈ-dipentamethylenethiuram polysulfides (CPTP), leading to CPTU, was found in isothermal studies at 140°C over a 25-min period.…”

“…The presence of ZnO in CPTD and CPTP6 mixtures suppressed the formation of CPTU, and DSC studies showed no CPTU even at 195°C and no degradation of N,NЈ-dipentamethylenethiuram polysulfides (CPTP), leading to CPTU, was found in isothermal studies at 140°C over a 25-min period. 9 A comparison of TMTU formation in the absence and presence of ZnO was made by heating 8 TMTD was also found to decompose quantitatively into TMTU under the same conditions. Zinc bis(pentamethylenedithiocarbamate) (ZPD) may be added to compounds as an accelerator or it may form in situ during vulcanization, where it results from the interaction of pentamethylenedithiocarbamic acid (Hpmtc) with ZnO, as will be discussed in a later article in this series.…”

“…7 In the presence of ZnO, thiourea does not form, even at 200°C, [3][4][5] although on heating TMTD/ZnO for 16 h at 140°C, TMTU was reported. 8 In a previous article in this series, 9 it was shown that N,NЈ-dipentamethylenethiuram disulfide (CPTD) and N,NЈ-dipentamethylenethiuram hexasulfide (CPTP6) are much less stable than is TMTD and that complete decomposition to N,NЈ-dipentamethylenethiourea (CPTU) and CS 2 occurs at vulcanization temperatures (140°C). ZnO prevents degradation.…”

“…ZnO prevents degradation. 9 On vulcanization, thioureas are commonly found in the extractable by-products of the reaction. This has been interpreted 10 as resulting from the attack by dimethylamine, formed on the decomposition of dimethyldithiocarbamic acid (Hdmtc) on TMTD, although it has also been suggested that TMTU may result from the vulcanization process itself.…”