Solid-State C-13 NMR Studies of Vulcanized Elastomers X. N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75.5 MHz

Abstract

Abstract Accelerated sulfur vulcanized cis-polyisoprene was analyzed using C-13 solid-state NMR to determine the chemical microstructure of the network. Three formulations were analyzed consisting of varying accelerator/sulfur ratios. All formulations yielded similar network structures, but the amount of sulfurization varied with sulfur concentration. At low percent cure, only polysulfidic A-type cis-structures were found. For longer cure times, the A-type structures shortened to monosulfldic, and B-type polysulfidic structures, both cis and trans, were formed. The amount of trans-sulfurized product was constant with cure once this resonance appeared. No isomerization, chain scission, saturation, or double bond migration was detected. The NMR measurements appeared to show fairly good agreement with equilibrium swelling measurements.