Solid‐state 13C NMR studies of vulcanized elastomers, 4. Sulfur‐vulcanized polybutadiene

Abstract The sulfur vulcanization of cis‐1,4‐polybutadiene was studied by solid‐state 13C NMR spectroscopy. Polybutadiene is cured with several different formulations including sulfur and accelerators in order to determine the network structure of the resulting vulcanizates. Polysulfidic crosslinks bound to the methylene carbons of the polybutadiene repeating unit were observed in the rubber network. Cyclic sulfide structures were detected in the network structure in addition to cis‐to‐trans chain isomerization. Two different pulse sequences were used for the NMR experiments of the sulfur‐vulcanized cis‐polybutadiene. The gated high power decoupling NMR experiment reflects the mobile regions of the vulcanizate sample while the cross polarization pulse sequence reflects the regions of the sample which are inherently more rigid. The cross polarization spectra of the samples cured with high sulfur levels showed that a considerable amount of rigidity is found in the vulcanized cis‐polybutadiene network. It was also possible to obtain cross polarization spectra of the lightly crosslinked polybutadiene vulcanizates. This is in contrast to the NMR results of the vulcanized natural rubber systems which generally tended to have considerably more mobility.