The complex shear moduli of the segmented polyurethane Estane 5703p, Livermore explosive (LX)-14, and plastic bonded explosive (PBX)-9501, which use this polymer as a binder, have been investigated. Segmented polyurethanes, such as Estane 5703, contain microphase-separated hard segments in a rubbery matrix of soft segments. LX-14 is composed of 95.5% 1,3,5,7-tetranitroazacyclooctane (HMX) explosive with 4.5% Estane 5703 binder. PBX-9501 is composed of 94.9% HMX, 2.5% Estane 5703p binder, 2.5% nitroplasticizer (NP), and about 0.1% antioxidant Irganox 1010. In the temperature range from -150 to 120 degreesC, two relaxations were observed as peaks in the loss modulus and tangent delta in Estane 5703p and LX-14. A third relaxation was found in PBX-9501. The low temperature relaxation associated with vitrification of the poly(ester urethane) soft segment occurred in the shear loss modulus (G ") at -29 and -26 degreesC in Estane and LX-14, respectively, at 1 Hz. In PBX-9501 the Estane soft segment glass transition peak, T-g(SS), in the loss modulus occurred at -40 +/- 3 degreesC at 1 Hz. The reduction in soft segment glass transition in PBX-9501 is clear evidence of plasticization of the soft segment by NP. The apparent activation energy of the maximum in the loss modulus for LX-14 and PBX-9501 over the frequency range from 0.1 to 10 Hz was 230 kJ/mole (55 kcal/mole). The hard segment glass transition, T-g(HS), was observed as a peak in the loss modulus at about 70 degreesC. In LX-14 the transition was observed at lower temperatures (56-58 degreesC at I Hz) depending on thermal history. There was a low temperature shoulder on the T-g(HS) of Estane 5703 associated with soft segment crystallinity. Modulated differential scanning calorimetry (MDSC) was used to verify the T-g(HS) in Estane and 50/50 mixtures of Estane with NP. In PBX-9501 the hard segment glass transition occurred between 65 and 72 degreesC. The presence of NP in PBX-9501 gave rise to a new transition, T-eu(NP), between 8 and 15 degreesC. This peak is believed to be associated with the eutectic melting of the plasticizer. Returns of fielded PBX-9501 that were 6 and 11 years old were also measured, Small variations in T-g(SS) and the rubber plateau modulus were observed in these aged samples, consistent with migration of plasticizer and/or very low levels of chain scission.