SOLID-STATE C-13-NMR STUDIES OF CHANGES IN CROSS-LINKED CARBON STRUCTURE OF NATURAL-RUBBER DURING HEATING UNDER AIR AND NITROGEN ENVIRONMENTS

The chemical changes that occur in thermal degradation of sulfur-cured natural rubber were investigated using C-13-NMR analysis. The crossli nked carbons formed during the vulcanization process appear in the NMR spectra as peaks representing the various structures formed. Samples of vulcanized rubber were heat-aged at 100 and 150 degrees C under bot h air (oxidative) and nitrogen (inert) environments to assess both tem perature and oxidative effects. Changes were observed by measuring pea k areas under the crosslinked carbon peaks. A- and B-type cis monolink ages were found to decompose much faster by oxidative factors at both 100 and 150 degrees C than under nitrogen at either temperature. The p olylinkages, however, showed the opposite result of thermal degradatio n predominating over oxidative factors. Cis-trans isomerization of the main chain carbons was observed at the higher temperature while absen t at 100 degrees C. (C) 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1371-1383, 1998.