To improve the mechanical performance of poly(glycidyl azide) (GAP)-based thermoplastic elastomers (TPEs), poly(oxytetramethylene glycol) (PTMG) which has flexible polymer backbone was introduced into their chemical structure by polyaddition. The effects of crystalline PTMG segment on the macro morphology, microphase separation, local hydrogen bonding, and mechanical performance of GAP-based TPEs were investigated. These obtained elastomers have a transparent and homogeneous phase structure, indicating that no macroscopic phase separation occurred. Meanwhile, the small-angle X-ray scattering (SAXS) demonstrated that the long-range ordered microstructures formed by the crystallization of flexible PTMG segments was existed in the elastomers and the phase separated microstructure was enhanced with increasing the content of PTMG. These results were also confirmed by the investigation of crystalline behavior by wide-angle X-ray diffraction (WAXD) and loss factor curves by dynamic mechanical analyzer (DMA). The enhancement of microphase separated structure leads to the significant improvement of tensile properties, modulus, and creep resistance. These GAP/PTMG-based TPEs with enhanced mechanical performance imply potential applications in propellant formulations. POLYM. ENG. SCI., 58:E167-E173, 2018. (c) 2018 Society of Plastics Engineers