To reduce the sensitivity of explosive compositions, inert polymers and plasticisers have been incorporated. The polymers bind the explosive crystals together whilst the plasticisers reduce the rigidity of the compositions. In order to improve the performance of these compositions without compromising on safety, energetic polymers and energetic plasticisers are now being investigated. While energetic plasticisers have been successfully developed energetic polymers are still very much in the research and development phase. The UK have for the past decade been concentrating on polyNIMMO and to a lesser extent, polyGLYNN. In order to understand the stability of these polymers to ageing, a study was conducted to investigate the effect of ultra-violet (UV) and thermal radiation on polyNIMMO. PolyNIMMO was found to thermally degrade in the presence and absence of oxygen at temperatures of 70, 100 and 130 degreesC. DSC and FTIR results indicate that polyNIMMO undergoes degradation by three different mechanisms, namely homolytic scission of the O-NO2 bond, scission of the polyether backbone and crosslinking of the polymer chains. PolyNIMMO was also found to degrade when subjected to W radiation at ambient temperature. Evidence from analyses indicates that only two of the degradation mechanisms are taking place namely homolytic scission of the O-NO2 bond, and scission of the polyether backbone. PolyNIMMO will only undergo crosslinking when subjected to W at higher temperatures (i.e. 100 degreesC).