Azidated oxetanic polymers such as poly(3-azidomethyl-3-methyl oxetane). are under investigation as "energetic" binder to be used as an alternative to polybutadiene in solid rocket propellants. The classic synthetic route for the production of the polymer is through an azidated monomer where the N-3(-) functionality has been previously introduced by nucleophilic displacement of a suitable, usually a halogen, leaving group. However, this could involve critical steps with manipulation of a highly unstable liquid monomer. Here it is shown that the azidation can be performed as the final step of the preparation by substitution of the tosyl group in a preformed polymer. The procedure assures good yield and purity of the product and satisfactory rate of reaction, being the energetic functionality always kept in a safe form, which shows low shock and friction sensitivity. Poly (3-azidomethyl-3-methyl oxetane) was prepared by azidation of poly(3-tosyloxymethyl-3-methyl oxetane) in dimethylsulfoxide, testing several operating conditions. Moreover, hypothesizing a second order kinetics, the rate constant and the activation energy for the azidation step have been estimated.