Thermal aging of nitroplasticized Estane 5703

In support of the Lifetime Prediction modeling effort, we have been investigating the aging processes that could impact the lifetime of PBX 9501. PBX 9501 is composed of 95% HMX and 5% polymeric binder. The polymeric binder is composed of 50% nitroplasticizer (NP) and 50% Estane{reg_sign} 5703 with a small quantity of stabilizer. Estane{reg_sign} 5703 is a segmented poly(ester urethane) with mechanical properties derived from phase separation of hard and soft segments along the polymer backbone. Since the binder has a significant effect on the composite mechanical properties, it is essential to know how the binder changes with time. Typically, polymer lifetime predictions are determined from extrapolation of properties after the material has been exposed to elevated temperatures and/or reactive environments for varying periods of time. For multiphase polymers, this accelerated aging methodology is very difficult to interpret since elevated temperatures alter the physical structure of the polymer, as well as, accelerate the chemical degradation reactions. Accelerated aging studies of nitroplasticized Estane have shown an increase in the molecular weight. The increase in molecular weight is most likely due to polymer chain branching reactions that eventually leads to formation an insoluble cross-linked gel. The decreased chain mobility caused by branching may also affect phase separation, which in turn, may change the mechanical properties. In this paper we report results of thermal aging studies on the properties, morphology and chemistry of nitroplasticized Estane