Synthesis and characterization of carbon-13 labelled 2-ethylidene-5-norbornene containing EPDM rubber. Observation of crosslinking and oxidation

[2,8-C-13(2)] ENB was synthesized from labelled acetic acid and terpolymeri zed in a batch reactor to [2,8-C-13(2)] ENB-EPDM rubber (M-w = 4.8 x 10(5), d = 3, ENB content similar to 8 wt.%, ethene to propene ratio similar to 1 .8). Labelled ENB, its precursors and the EPDM were characterized by NMR sp ectroscopy. ENB is incorporated in the polymer chain through the endo cycli c double bond. Upon high temperature exposure to air of an NMR sample, the number of double bonds decreases due to crosslinking via addition of backbo ne radicals to double bonds. Some oxidation of double bonds occurs, giving rise to acetyl norbornene units. No significant cleavage of double bonds ta kes place. The labelling/NMR approach provides an excellent tool for studyi ng (minor) chemical conversions in EPDM rubber. (C) 1999 Published by Elsev ier Science Ltd. All rights reserved.