Mixed crosslinking system with electron beam irradiation as one of the crosslinkers in rubber has been developed for the first time. This paper describes some unique features of dynamic mechanical properties of the electron beam irradiated nitrile rubber vulcanizates at varying levels of sulphur in the network. Dynamic mechanical thermal analysis ( DMTA) was performed on these vulcanizates over a range of temperatures (- 80 degrees C to + 80 degrees C), frequencies (0.032 to 32 Hz) and strains (0.001 to 10%). The results showed that there were significant changes in tan delta peak temperature and storage modulus on irradiation of these vulcanizates. The vulcanizates containing higher amount of sulphur formed intense crosslinked networks and crosslink rearrangements, which were supported by the increase in the storage modulus and shift in tan delta towards higher temperature as compared to their control counterpart. There is also an increase in the peak height due to chain scission and subsequent plasticization. A concept of network distribution using the plots of the storage modulus ratio divided by frequency against inverse of frequency was introduced. This contravening nature was also affirmed with the help of these curves showing broader network distribution for irradiated samples having lower amount of sulphur. This was also supported from the crossover frequency values estimated from the plot of storage and loss modulii against frequencies observed. (C) 2005 Springer Science + Business Media, Inc.