AN INVESTIGATION OF RADIATION-INDUCED STRUCTURAL-CHANGES IN NITRILE RUBBER

The mechanism of radiation-induced structural changes in nitrile rubbe r with different acrylonitrile contents were investigated by ESR, NMR, and FTIR. To investigate new structures solid-state NMR methods had t o be used due to crosslinking of the irradiated rubbers, and higher pr obe temperatures were used to obtain better resolution. The radicals g enerated on the acrylonitrile groups were found to abstract hydrogen f rom the adjacent butadiene units resulting in the formation of allylic radicals. These allylic radicals reacted to form intermolecular cross links and cyclisation. Cyclisation of the butadiene units were found t o occur in the initial stages of the irradiation. Radiation yields of radicals increased with acrylonitrile content from 1.42, 1.58, to 2.42 for 18, 30, and 45% acrylonitrile rubbers. The radiation yields for i ntermolecular crosslinking were higher in rubbers with higher acryloni trile contents, giving G values of 17.8, 21.3, and 24.5 for 18, 30, an d 45% acrylonitrile rubbers, respectively. However, the crosslink clus tering was found to be less in the rubbers with a higher acrylonitrile content. (C) 1996 John Wiley & Sons, Inc.