Sulfur Vulcanisation of Polydiene Rubbers

Coleman of the Koenig group identified the reaction products obtained after heating various mixtures of sulfur, TMTD, tetramethyl thiurammonosulfide, ZDMC and/or ZnO in the absence of elastomer or olefin using Raman spectroscopy. This enabled the 

Chen and co-workers tentatively assigned new signals in the FT-IR spectra of accelerated sulfur-vulcanised NR to the formation of C-S and S-S bonds corresponding to monosulfides, disulfides and polysulfides [68]. The vulcanisation of NR was retarded when clay was added to the NR compound. 

Recently, it was shown using FT-IR that the decrease of vulcanisation rate and final crosslink density of sulfur vulcanised NR upon increasing silica content may be related to increased absorption of zinc stearate onto the silica surface [69]. 

Schotman and co-workers tentatively assigned the new Raman peaks at 1625 and 1592 cm 1 observed during sulfur vulcanisation of squalene, to the formation of conjugated dienes and trienes, respectively [70]. When vulcanisation was carried out in the presence of l,3-di(citraconimidomethyl)benzene, this resulted in a reduced intensity of these two new peaks, corroborating that conjugated dienes and trienes, formed as a result of reversion, react with the diimide. Obviously, the diimide is not an anti-reversion agent in the sense that it prevents reversion, but it is in the sense that it repairs crosslinks when reversion has occurred. 

S3 + accelerator + ZnO + stearic acid-- soluble sulphurated zinc complex 

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The results of the optical spectroscopy studies into sulfur vulcanisation of polydiene rubbers correspond well with the results obtained via low molecular weight model olefin studies and solid state 13C NMR studies. From all these studies the mechanism for accelerated sulfur vulcanisation as shown in Figure 6.2 has emerged [14-18], which is... 

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