A study of the rate of formation of polysulfides of tetramethylthiuram disulfide

Geyser, M.; McGill, W. J.

doi:10.1002/app.1995.070550204

Cited by 37 publications

(68 citation statements)

References 20 publications

(4 reference statements)

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“…However, an alternative mechanism for sulfur activation is indicated by the experimental results of Geyser and McGill 59 on the formation of thiuram polysulfides (TMTPs) from the reaction of TMTD and sulfur and the studies of Gradwell et al 46 on the formation of MBTPs via the reaction of MBTS and sulfur. The experimental results of Geyser and McGill 59 are shown in Figure 6, where TMTPs with lower sulfur length are produced in higher concentrations than TMTPs with higher sulfur lengths. Similar trends in the production of MBTPs of different polysulfidic lengths were also observed by Gradwell et al 45 A careful examination of the data in Figure 6 indicates that early in the reaction (i.e.…”

Section: Sulfur Vulcanizaton Of Natural Rubber For Benzothiazole 609mentioning

confidence: 99%

Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model

Ghosh

Katare

Patkar

et al. 2003

Rubber Chemistry and Technology

204

221

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The chemistry of accelerated sulfur vulcanization is reviewed and a fundamental kinetic model for the vulcanization process is developed. The vulcanization of natural rubber by the benzothiazolesulfenamide class of accelerators is studied, where 2-(morpholinothio) benzothiazole (MBS) has been chosen as the representative accelerator. The reaction mechanisms that have been proposed for the different steps in vulcanization chemistry are critically evaluated with the objective of developing a holistic description of the governing chemistry, where the mechanisms are consistent for all reaction steps in the vulcanization process. A fundamental kinetic model has been developed for accelerated sulfur vulcanization, using population balance methods that explicitly acknowledge the polysulfidic nature of the crosslinks and various reactive intermediates. The kinetic model can accurately describe the complete cure response including the scorch delay, curing and the reversion for a wide range of compositions, using a single set of rate constants. In addition, the concentration profiles of all the reaction intermediates as a function of polysulfidic lengths are predicted. This detailed information obtained from the population balance model is used to critically examine various mechanisms that have been proposed to describe accelerated sulfur vulcanization. The population balance model provides a quantitative framework for explicitly incorporating mechanistically reasonable chemistry of the vulcanization process.

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Section: Sulfur Vulcanizaton Of Natural Rubber For Benzothiazole 609mentioning

confidence: 99%

Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model

Ghosh

Katare

Patkar

et al. 2003

Rubber Chemistry and Technology

204

221

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“…No such breakdown has been observed at vulcanization temperatures in the absence of rubber in any studies in these laboratories. 11,12 Versloot et al, 2 also, did not report TMTU formation on heating TMTD. The addition of dimethylamine to TMTD leads to the production 13 of dimethylammonium dimethyldithiocarbamate (dma.dmtc) and TMTU, and it has been suggested 5 that differences in TMTU formation may be ascribed to the presence of an impurity, such as an amine, that may or may not be trapped in the system, depending on the experimental setup employed.…”

Section: Rs X C(s)n(ch 3 ) 2 ϩ Rs Ymentioning

confidence: 98%

“…Within 5 min equilibrium had been established between sulfur, TMTD, and the various TMTP species. 12 The addition of a small amount of Hdmtc solution and reheating at 150°C for 5 min, changed the HPLC product spectrum, the TMTM and TMTD concentrations increasing at the expense of TMTP. This is attributed to an exchange between Hdmtc and TMTP as depicted in eq.…”

Section: Mechanism Of Tmtd Accelerated Sulfur Vulcanizationmentioning

confidence: 99%

The role of dimethyldithiocarbamic acid in accelerated sulfur vulcanization

Shelver

Shumane

Gradwell

et al. 1999

J. Appl. Polym. Sci.

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Polyisoprene/tetramethylthiuram disulfide (TMTD)/sulfur compounds were vulcanized under a variety of conditions. TMTD does not decompose to tetramethylthiourea (TMTU) at vulcanization temperatures as has been suggested, neither is it formed as an integral part of the crosslinking process. Instead, it results from the attack of dimethylamine, released on decomposition of dimethyldithiocarbamic acid (Hdmtc), on TMTD. It is demonstrated that the formation of TMTU in vulcanizates may be overlooked, as it is readily lost in the work-up for HPLC analysis. Hdmtc is shown to play an essential role in the crosslinking process in polyisoprene/TMTD/sulfur formulations, and its removal from the system during vulcanization severely impedes crosslinking. Polysulfidic thiuram-terminated pendent groups are formed, in part, by the interaction of tetramethylthiuram polysulfides with the polymer chain, but largely by an exchange between Hdmtc and polysulfidic thiol pendent groups. The latter are formed when sulfurated Hdmtc reacts with the polymer chain. Crosslinking of thiuramterminated pendent groups is slow, and in the absence of ZnO crosslinking results from reaction between polysulfidic thiuram pendent groups and thiols. Crosslinking is delayed until the bulk of the accelerator is bound to the polymer chain, at which point the concentration of free thiuram groups, in the form of Hdmtc, is low, and exchanges between newly formed thiol pendent groups and Hdmtc is less frequent, permitting crosslinking of thiuram pendent groups with these newly formed thiol pendent groups. Data to support the proposed reaction mechanism is presented. Hdmtc on its own accelerates sulfur vulcanization and acts as a catalyst for the reaction, being regenerated in the crosslinking process.

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“…Tagged TMTD and Zn 2 (dmtc) 4 exchange at elevated temperatures, 14 which is under conditions where tetramethylthiuram polysulfides (TMTPs) can form. [2][3][4]15,16 McCleverty et al 17 also reported ligand exchange at elevated temperatures. Recent evidence for sulfur-rich zinc(II) complexes was demonstrated in theoretical density functional calculations, where it was also shown that the addition of further sulfur atoms to the zinc dithiocarbamate chelate ring is energetically more favorable than insertion of the first sulfur.…”

Section: Introductionmentioning

confidence: 99%

Effect of water and hydrogen sulfide in zinc dimethyldithiocarbamate accelerated sulfur vulcanization

Shumane

Gradwell

McGill

2002

J of Applied Polymer Sci

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Rubber and the model compound 2,3-dimethyl-2-butene (TME) are vulcanized with zinc dimethyldithiocarbamate [Zn 2 (dmtc) 4 ] accelerated sulfur formulations. When heated in dry nitrogen, Zn 2 (dmtc) 4 is stable at vulcanization temperatures. However, it shows a mass increase when heated in moist nitrogen, indicating strong coordination with water; in a nitrogen/H 2 S atmosphere rapid degradation to dimethyldithiocarbamic acid (Hdmtc) and ZnS occurs. Model compound studies show that crosslinked sulfides are essentially bis(alkenyl) and confirm the absence of accelerator terminated pendant groups in the vulcanizates, while the ease with which rubber vulcanizates crystallize on cooling in a density column also suggests that pendant groups are largely absent. However, the rates of crystallization, measured as the time for the crystallization process to go to 50% completion, are slower in lightly crosslinked gels than in peroxide cures of similar crosslink density, particularly in the vulcanizates cured in a vacuum; this is interpreted as an indication that some residual pendant groups are present in Zn 2 (dmtc) 4 vulcanizates. Water promotes the rate of crosslink formation in both rubber and TME systems, and it is suggested that the strong coordination of water with zinc in Zn 2 (dmtc) 4 promotes its reactivity. The H 2 S liberated in the vulcanization process promotes decomposition of Zn 2 (dmtc) 4 to Hdmtc, and this reaction makes an important contribution to the amount of Hdmtc that is formed in situ. The importance of Hdmtc as an accelerator and its role in providing alternative routes to crosslink formation in Zn 2 (dmtc) 4 accelerated sulfur vulcanization are discussed. It is suggested that water, which is liberated when Hdmtc reacts with ZnO to form Zn 2 (dmtc) 4 , activates newly formed Zn 2 (dmtc) 4 molecules; and this accounts for the beneficial influence of ZnO in Zn 2 (dmtc) 4 formulations.

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A study of the rate of formation of polysulfides of tetramethylthiuram disulfide

Cited by 37 publications

References 20 publications

Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model

Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction Mechanisms to a Rational Kinetic Model

The role of dimethyldithiocarbamic acid in accelerated sulfur vulcanization

Effect of water and hydrogen sulfide in zinc dimethyldithiocarbamate accelerated sulfur vulcanization

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