Aspects of the mechanism of zinc dimethyldithiocarbamate (ZDMC)‐accelerated sulfur vulcanization were discussed. The trends in the efficiency parameter E, confirmed that crosslinking is preceded by the formation of pendent groups RSxSX [R = polyisoprenyl, X = Me2NC(S)] in ZDMC‐based systems. The index x in RSxX was calculated as 5.82 in the cis‐1,4‐polyisoprene (IR)/sulfur/ZDMC/ZnO compound at the initial stages of curing, compared to 3.23 in the absence of ZnO. The high value of x supports the postulation that elemental sulfur and ZDMC react at the early stages of vulcanization, to form the active sulphurating agent XSxSZnSSX. Crosslinks form by either a disproportionation reaction between two α‐methylic or α‐methylenic pendent groups RSxX, or a reaction between a pendent group RSxX and the rubber chain—these routes are the same as that suggested for the IR/tetramethylthiuram disulfide (TMTD)/ZnO compound. The beneficial role of ZnO and zinc stearate is shown, as in the case of ZnO in the IR/TMTD/ZnO system, to be related to their ability to trap dimethyldithiocarbamic acid, which formed in the generation of pendent groups and crosslinks. ZnS is inactive in this regard. The formation of ZnS is characteristic of natural rubber/sulfur/ZDMC/ZnO systems, as opposed to IR/TMTD/ZnO mixtures where little ZnS forms.
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Krüger et al. (1992) studied this question.
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