Copolymerization of 3,3-bis (nitratomethyl) oxetane and 3-azidomethyl-3-methyloxetane was carried out in the presence of the triisobutyl-aluminum-water catalyst system. The structure of synthesized high-molecular copolymers was proven with C-13 and H-1 NMR, IR-Fourier spectroscopy, GPC, and elemental analysis. The data on relaxation and phase transitions as well as the thermal decomposition of copolymers were obtained using the DSC method.