Glycidyl azide-r-(3,3-bis(azidomethyl)oxetane) copolymers were synthesized by cationic copolymerization of epichlorohydrin and 3,3-bis(bromomethyl)oxetane, using butane-1,4-diol as initiator and boron trifluoride etherate as catalyst, followed by azidation of the halogenated copolymer. The main objective of this work is the preparation of an amorphous polymer with energetic content higher than that of the well known glycidyl azide homopolymer. The effect of experimental conditions, like i.e. the rate of monomer feeding, on the final molecular weight and functionality of the copolymer has also been investigated. The obtained copolymers were extensively characterized to determine their composition and thermal stability. The heat of reaction for the polymerisation of the halogenated key precursors has also been measured.