Abstract

To study the network structure generated by the polysulfide polymer [[(CH₂)₂S₄]_p as a crosslinking agent, model compound vulcanization with 2,3-dimethyl-2-butene as the model alkene was carried out. It was found that the polysulfide polymer generates hybrid bridges of the general constitution S_n−(CH₂CH₂−S_m)_k(n=1−4,m=1−4,k=1−6). To a lesser extent the polysulfide polymer behaves as a sulfur donor generating conventional sulfur bridges S_x(x=1−5). Polysulfidic bridges (x=4, 5) were only detected in the very early stage of network formation. The process of network formation and the development of the bridges during prolonged heating was monitored by ¹H NMR spectroscopy and compared with that of a sulfur cure. In the case of the polysulfide polymer cure the early network contained a relatively high amount of mono-and disulfidic bridges and a stable network was formed after at least 60 min of heating (150 °C). This effect results from the higher thermal stability of hybrid bridges in comparison to conventional sulfur bridges. The higher stability of the hybrid bridges also leads to a suppression of the formation of 3,4-dimethylthiophene which has been identified in the sulfur cure as a product of reversion processes. Thus, the increased reversion stability of polysulfide polymer cures, which has been claimed earlier, can be related to the formation and the increased stability of the hybrid bridges.