Sulfur vulcanisation model studies

The technology of sulfur vulcanisation of unsaturated elastomers has evolved since Goodyear s invention in 1839. Scientific studies into the chemistry of sulfur vulcanisation started to appear in the late 1950s (for reviews see References [14-18]). Two experimental approaches can be distinguished the analysis of rubber vulcanisates themselves and the so-called low-molecular-weight model studies. 

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... 

After these early studies an extensive FT-Raman study [77] was performed to bridge the gap between the low-molecular-weight ENBH model vulcanisation studies and the vulcanisation studies using high-molecular-weight EPDM. These studies will be presented in detail. First, a series of low-molecular-weight dialkenylsulfides will be discussed in order to determine the effect of sulfur vulcanisation on Raman spectra of olefins. Subsequently, the attachment of the sulfur crosslinks at the allylic positions, the conversion of ENB, the length of sulfur crosslinks and the network structure will be addressed for unfilled sulfur vulcanisates of amorphous EPDM. Some preliminary network structure/ properties relationships will also be presented. 

Model compounds based on 2-methyl-2-pentene were studied to supplement the 13C chemical shift assignments of the products from accelerated sulfur vulcanisation of NR. It is observed in the model compound data that it may not be possible to distinguish between a 13C NMR resonance which is due to disulfidic crosslinks and a peak due to pendent accelerator groups, while a large chemical shift difference ( 3 ppm) is observed for the monosulfidic bonds. The MBS-accelerated sample shows similar new resonances as seen in the TMTD accelerated systems. In this comparison however, the quantitative aspects of the data might be obscured due to the differences in the state of cure among the different formulations. 

Vulcanisation of EPDM with sulfur systems was studied by H-NMR using ethylidene norbornane (ENBH) as a model of ENB [62]. The use of ENBH was also effective to elucidate the curing reaction of EPDM with phenol-formaldehyde resin [63]. Similarly, halogenation reaction of HR was studied by H-NMR using 2,2,4,8,8-pentamethyl-4-nonene as a model [64],... 

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