HIGH-RESOLUTION SOLID-STATE C-13 NMR-STUDIES OF THE CROSS-LINK STRUCTURE IN ACCELERATED SULFUR VULCANIZED NATURAL-RUBBER

An improved assignment of the signals of polysulfidic and monosulfidic crosslinks in the C-13 NMR solid state spectra of accelerated sulfur vulcanized NR is presented. The assignment of monosulfidic sulfur bridges is accomplished by analysis of the spectrum of a NR model vulcanizate cured with tetramethylthiuram disulfide (TMTI) where different isomers of monosulfidic crosslinks were detected for the first time. The NMR results of a real normal cure vulcanizate are compared to the results of model compound vulcanization studies.