Energetic polymers have been synthesised by the introduction of picryl groups onto linear polyethylenimine and polyvinylamine. The degree of substitution was 70-97% for polyethylenimine, depending upon the molecular weight of the polymer, and around 70% for polyvinylamine. N-Picrylation of low molecular weight, model compounds was also studied. The results illustrate the influence of molecular weight on the chemical accessibility of a reaction site and reflect the difficulty of modelling polymer modification reactions using small molecules.