Simulation study on the liquid-crystalline ordering and fluidity of energetic diblock copolymers based on poly[3,3-bis(azidomethyl) oxetane]

The liquid-crystalline ordering and fluidity of energetic diblock copolymers based on poly[3,3-bis(azidomethyl) oxetane] (BAMO) and 3-nitratomethyl-3′-methyloxetane (NMMO) were investigated by the dissipative particle dynamics method. The results show that these copolymers, with moderate BAMO block lengths (x's), experienced the disorder, nematic, and smectic phases with decreasing temperature. The nematic phase was suppressed when the rod length was too long or short. After the formation of the smectic phase, the fluidity had a sharp decline. The temperature forming the smectic phase was defined as the order-disorder transition temperature (T_ODT) and depended strongly on x. A simple scaling rule, T_ODT ≈ e ^-x, between T_ODT and x was constructed. The effect of the soft NMMO block fraction on the fluidity emerged before the formation of the smectic phase. These results can help researchers design and synthesize new energetic copolymers with an appropriate melting temperature range for use as binders of solid propellants.