Polyurethane copolymers of 3,3-bis (azidomethyl)oxetane (BAMO) and 3-azidomethyl-3-methyloxetane (AMMO) with molecular structures of types B(AB)n, A(AB)n, (BB) n and ABn with different ratios of oligomeric units were investigated, where A is the non-crystallizable "soft" block of oligoAMMO and B is the "hard" block of oligoBAMO and the included urethane diol fragments. The amorphous-crystalline structures of copolymers BAMO and AMMO were elucidated by wide angle X-ray diffraction measurements. The influences of the molecular structure and the ratio of oligomeric units on the structural parameters were identified. The degree of crystallinity is in a range from 8 to 22% and sizes of the crystallites were determined. The defectivenesses of first and second kind in the structure were evaluated, which show high values of the first kind defectiveness (approx. 20%), which describes the displacement of theoretical lattice sites and the existence of unequal sizes of the lattice sites, and minor values for the second kind defectiveness (approx. 3%), which describes the lattice site disorder in large distances. Small-angle X-ray diffraction measurements were used to investigate the domain structures of copolymers BAMO and AMMO. The distribution and sizes of the crystallites in the structures of the copolymers were calculated.