PolyNIMMO is regarded as an energetic polymer. It consists of a nitrate ester group and an ether linkage, which are known to degrade naturally with time, a process which is increased drastically with heat and/or light. The general mechanism for heat ageing of polyesters is the homolytic scission of the CH2O-NO2 bond to produce CH2O. and (NO2)-N-. radicals. Often at low temperatures the (NO2)-N-. radicals can initiate autoxidation, reacting with oxygen resulting in chain scission of the polyether backbone. In this investigation polyNIMMO was subjected to gamma radiation which is a more aggressive form of radiation. Gamma irradiation of a polymer generally produces radicals, which in turn may produce more radicals through chain scission, chain transfer or quench radicals through recombination or crosslinking. Gamma radiation may also lead to internal plasticisation of the polymer. This is achieved by breaking the polymer backbone into smaller chain lengths, providing compatible, small molecules to plasticise the polymer. Thermal ageing of polyNIMMO tends to induce degradation, however, and surprisingly this was not observed in the bulk irradiation of polyNIMMO. Gamma radiation did not break down the polymeric chains into smaller lengths and therefore internal plasticisation did not occur. (C) 2003 Elsevier Ltd. All rights reserved.