Solid State C-13 NMR Studies of Vulcanized Elastomers. XII. Accelerated Sulfur-Vulcanized High-Vinyl Polybutadiene

Abstract

Abstract Solid state 13C NMR measurements were made on accelerated sulfur-vulcanized polybutadiene with a high vinyl content (70%). The systems studied included conventional, semi-efficient and efficient formulated with N-t-butyl benzothiazole sulfenamide (TBHS) as the accelerator. The kinetics of the three vulcanization systems were different, but the final levels of cure were similar. The resonances due to TBBS disappear as the vulcanization proceeds. The ratio of monosulfidic to polysulfidic crosslinks as a function of accelerator to sulfur ratio initially decreases rapidly and then increases in favor of the monosulfidic component. A variety of sulfur-bonded accelerator fragments was found in the system. This reinforces the polar-radical mechanism.