Thermal and mechanical properties of poly(glycidyl azide)/polycaprolactone copolyol-based energetic thermoplastic polyurethanes

To examine the addition effect of polycaprolactone (PCL) on poly(glycidyl azide) (GAP)-based energetic thermoplastic polyurethanes (ETPUs) (GAP ETPUs), a series of poly(glycidyl azide)/polycarprolactone copolyolbased ETPUs (GAP/PCL ETPUs) with different copolyol wt% ratios was synthesized with 4,4′-diphenylmethane diisocyanate (MDI) and 1,5-pentanediol (1,5-PD) by solution polymerization in dimethyl formamide (DMF). The thermal and mechanical properties were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and a universal testing machine (UTM). DSC showed that the GAP segment did not interact with the PCL segment and the existence of PCL melting. DMA showed that the presence of a PCL segment in ETPUs improved the storage modulus below the Tm of the PCL block. UTM revealed improvement in the tensile strength and elongation at breaks of the ETPUs with increasing PCL content. From the above results, this enhancement of the mechanical properties is due to the crystalline PCL segment-induced phase separation. The crystalline PCL segment helps impart extensibility and reinforces the ETPUs in a similar manner as a hard domain.