Soft Segment Matrix Research Articles

Recent Developments in Polyurea Research for Enhanced Impact Penetration Resistance and Blast Mitigation.

Polyurea has gained significant attention in recent years as a functional polymer material, specifically regarding blast and impact protection. The molecular structure of polyurea is characterized by the rapid reaction between isocyanate and the terminal amine component, and forms an elastomeric copolymer that enhances substrate protection against blast impact and fragmentation penetration. At the nanoscale, a phase-separated microstructure emerges, with dispersed hard segment microregions within a continuous matrix of soft segments. This unique microstructure contributes to the remarkable mechanical properties of polyurea. To maximize these properties, it is crucial to analyze the molecular structure and explore methods like formulation optimization and the incorporation of reinforcing materials or fibers. Current research efforts in polyurea applications for protective purposes primarily concentrate on construction, infrastructure, military, transportation and industrial products and facilities. Future research directions should encompass deliberate formulation design and modification, systematic exploration of factors influencing protective performance across various applications and the integration of numerical simulations and experiments to reveal the protective mechanisms of polyurea. This paper provides an extensive literature review that specifically examines the utilization of polyurea for blast and impact protection. It encompasses discussions on material optimization, protective mechanisms and its applications in blast and impact protection.

Temperature-dependent pyrolysis behavior of polyurethane elastomers with different hard- and soft-segment compositions

The pyrolysis behaviors of seven kinds of polyurethane elastomers (PUEs) with different ratios between the hard segment (HS) and soft segment (SS) were investigated for both fast pyrolysis (300, 350, 450, 850 °C) and slow pyrolysis at the heating rate of 10 °C min–1 by thermogravimetric analysis (TG), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and evolved gas analysis-mass spectrometry (EGA-MS). These PUEs were synthesized from 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BD), and poly(oxytetramethylene glycol) (PTMG). Atomic force microscopy measurements found that the HS domains were formed in PUEs containing HS, and these domains were aggregated at extremely high HS ratio. The main pyrolysate derived from HS was MDI under all conditions. In fast pyrolysis tests, the decomposition of SS proceeded sufficiently at 450 °C, and a lot of low molecular weight compounds were produced at 850 °C. In slow pyrolysis tests, three-step degradation was observed, and this degradation behavior was influenced by the HS domain and SS matrix structures. The first step is the HS pyrolysis inside the HS domain, then the HS surrounded by SS is pyrolyzed. Finally, the SS matrix is pyrolyzed. The HS pyrolysates changed from isocyanate to amine with increasing temperature. We believe that the newly found pyrolysis behavior of PUEs with different ratios between the HS and SS will promote future studies on the characterization of PUE materials and the pyrolytic recovery of chemical feedstock from PUE wastes.

Silicone-urea copolymer as a basis for self-organized multiphase nanomaterials

We discuss the results of atomistic molecular dynamics simulations of both unfilled and nanosilica filled silicone-urea copolymers consisting of soft poly (dimethylsiloxane) and hard bis(4-isocyanatocyclohexyl)methane segments (SS and HS, respectively). The simulations show that due to hydrogen bonding between the urea groups, the polymer segments tend to microphase separate into soft and hard domains. Using an approach based on the numerical analysis of spatially coarse-grained density fields calculated from time-averaged scattering amplitudes, we observe the formation of an irregular bicontinuous structure that can be pictured as an intertwisted sponge-like network where two effectively infinite HS-rich and SS-rich domains are present simultaneously. The HS-rich regions act as physical (reversible) crosslinks, functionally similar to those in chemically crosslinked elastomers, and at the same time as a pseudo-reinforcing filler of the rubbery soft segment matrix. Thus, the phase segregated copolymer itself can be regarded as a spontaneously occurring nanocomposite with hard inclusions embedded in a soft (elastically compliant) phase. The incorporation of silica nanoparticles results in slight improvement of the thermophysical and mechanical properties of the copolymer. The nanoparticles are mainly located in the amorphous phase, in which the soft segments dominate, and do not show a tendency to aggregate.

Structure and deformation recovery of the thermoplastic polyurethane spherulite

ABSTRACTWe investigated the structure and deformation behavior of the thermoplastic polyurethane (TPU) spherulite by optical microscopy, tensile testing, Hv light scattering, and small angle X‐ray scattering. The TPU spherulite structure obtained by melt crystallization was coarse consisting of bundle‐like structure containing hard segment (HS) lamellar domain in which the HS domains were stacked and the HS chain direction was perpendicular to the longitudinal axis of the HS domain. By stretching, the spherulite was deformed to ellipsoidal one and the stacked HS lamellar domains were tilted in the stretching direction. The deformed spherulite and the tilted HS domain in the spherulite were recovered to the unstretched state by retraction. The recovery of the structure is ascribed to the characteristic spherulite structure consisting of rubbery soft segment matrix physically cross‐linked with the stacked HS domain. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1585–1594

Electrospinning-induced shape memory effect in thermoplastic polyurethane characterization and thermoviscoelastic modeling

Electrospun thermoplastic polyurethane (TPU) nanofibers are known to contract considerably (∼40%) on heating up to ∼90 °C. This study investigates this thermomechanical behavior and the TPU shape memory capabilities. The shape memory effect was first studied in TPU films as a model system by applying classical thermomechanical cycles (programming and recovery). The films were able to fix the applied deformation during long-term storage at room temperature, well above the material's calorimetric glass transition temperature and in the absence of a percolated structure of hard domains. Structural analysis (Fourier transform infrared, differential scanning calorimeter, and dynamic mechanical analysis) revealed broad thermal transitions indicating the presence of a mixed phase of hard segments dispersed in the soft segment matrix. Using a linear viscoelastic model together with time–temperature superposition, the shape memory effect was attributed to the thermoviscoelastic properties of TPU. In particular, the mixed phase was found to give rise to a very broad relaxation spectrum dominated by long relaxation times, which explains the suppression of strain recovery at room temperature. Finally, the electrospinning process was examined and was found to be similar to a programming cycle characterized by the strong elongation flow accompanied by massive solvent evaporation, whereas the contraction effect was interpreted as the recovery phase in a shape memory perspective. Thus, the contraction of electrospun TPU mats may be considered to be an electrospinning-induced shape memory effect. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1590–1602

Thermoplastic polyurethanes with controlled morphology based on methylenediphenyldiisocyanate/isosorbide/butanediol hard segments

Isosorbide, a cyclic, rigid and renewable diol, was used as a chain extender in two series of thermoplastic polyurethanes (PUs). Isosorbide was used alone or in combination with butanediol to examine the effects on the morphology of PU. Two series of materials were prepared – one with dispersed hard domains in a matrix of polytetramethylene ether glycol soft segments of molecular weight 1400 g mol−1 (at 70 wt% soft segment concentration, SSC) and the other with co-continuous soft and hard phases at 50 wt% SSC. We investigated the detailed morphology of these materials with optical and atomic force microscopy, as well as ultra-small-angle X-ray scattering. The atomic force microscopy measurements confirmed the different morphologies in PUs with 50 wt% SSC and with 70 wt% SSC. Small-angle X-ray scattering data showed that in PU with 70 wt% SSC, the hard domain size varied between 2.4 and 2.9 nm, and decreased with increasing isosorbide content. In PU with 70 wt% SSC, we found that the correlation length and average repeat distances became smaller with increasing isosorbide content. We estimated the thickness of the diffuse phase boundary for PU with 70 wt% SSC to be ca 0.5 nm, decreasing slightly with increasing isosorbide content. © 2015 Society of Chemical Industry

Soft segment composition and its influence on phase-separated morphology of PCL/PEG-based poly(urethane urea)s

A composition-dependent microphase separation of segmented poly(urethane urea)s (PUUs), based on a mixture of two hydrophobic (polycaprolactone) and hydrophilic (polyethylene glycol) polyols, is investigated. Synthesis of PUUs was carried out through the reaction of in situ generated AB-type macromonomers, prepared from the reaction of NCO-terminated urethane prepolymers, with benzoic acid in dimethyl sulfoxide as solvent/reagent at 40–80 °C. The segmented PUUs were characterized by different methods including FTIR and NMR spectroscopies, gel permeation chromatography, differential scanning calorimetry and dynamic mechanical analysis. Microphase separation in the synthesized PUUs was monitored using atomic force microscopy (AFM) to find a better insight into structure–property relationship of PUUs consisting of mixed polyols. Thermal analysis of the polymers revealed that by introducing poly(ethylene glycol) (PEG) in PUU backbone, a well-defined glass transition was obtained. The results of AFM showed that PCL-based poly(urethane urea) has a morphology in which hard segment domains were homogeneously distributed in the soft segment matrix. In the samples based on PCL/PEG, the hard segment domains aggregates were connected to each other and were inhomogeneously distributed in the matrix. Comparison of the overall data revealed that the differences in soft segment compositions had a marked effect on the molecular structure and the mechanical properties of PUUs.

Shape memory polyurethanes based on recycled polyvinyl butyral. I. Synthesis and morphology

Abstract Shape memory polyurethanes (SMPUs) were synthesized by 4,4′-diphenylmethane diisocyanate (MDI), hexane-1,6-diol (HD), polypropylene glycol (PPG), and recycled polyvinyl butyral (PVB). Dynamic mechanical analysis, differential scanning calorimetry and Fourier transformation infrared attenuated total reflection spectroscopy was used to characterize the poly (vinylbutyral-urethanes). Micro-phase domain separation of hard and soft segments and phase inversion were investigated. Increasing the hard segment content, i.e., average hard segment molecular weight, leads to an increase in the degree of micro-phase separation, hard domain order and crystallinity. The crystalline hard segment structures combined with the elastic nature of soft segment matrix provide enough physical and chemical crosslinks to have shape memory effect.

Structure formation and hydrogen bonding in all-aliphatic segmented copolymers with uniform hard segments

Fully aliphatic segmented poly(ether ester amide) copolymers with uniform hard segments prepared by melt polycondensation of α,ω-hydroxyl end-functionalized polytetrahydrofuran and short glycine or β-alanine bisester–bisoxalamide units hold promise for biomedical applications. For polymers with the hard block contents varying from 10% to 27%, differential scanning calorimetry and atomic force microscopy reveal a highly phase-separated morphology, with ribbon-like nanocrystals dispersed in the soft segment matrix. To relate the polymer properties to the structure of the hard segment, the monomers were prepared and studied by optical and X-ray diffraction measurements. It was shown that the glycine and β-alanine carbonyl ester groups are tilted away from the oxalamide plane, which can affect the degradation rate via hydrolysis of the ester bond.

Synthesis and characterization of novel h -HTBN/PEG PU copolymers for tissue engineering: degradation, phase behavior, and mechanical properties

The phase behavior of the as-prepared polyether polyurethane (PU) elastomers was investigated by dynamic mechanical analysis (DMA), polarized optical microscope (POM), and atomic force microscopy (AFM). This PU copolymers were composed of different compositions of two soft segments, poly(ethylene glycol) (PEG) and hydrolytically modified hydroxyl-terminated poly(butadiene-co-acrylonitrile) (h-HTBN) oligomers. The microphase separation behavior is confirmed to occur between soft and hard segments as well as soft and soft segments as the h-HTBN is incorporated into the PU system, depending on soft-soft and/or soft-hard microdomain composition, molecular weight (MW) of PEG, and hydrolysis time of HTBN. The driving force for this phase separation is mainly due to the formation of inter- and intramolecular hydrogen bonding interaction. The PU-70, PU-50 samples with non-reciprocal composition seem to exhibit larger microphase separation than any other PU ones. The hydrolysis degradation, thermal stability, and mechanical properties of the copolymers were assessed by gravimetry, scanning electron microscope (SEM), thermal gravity analysis (TGA), and tensile test, respectively. The experimental results indicated that the incorporation of h-HTBN soft segment into PEG as well as low MW of PEG leads to increased thermal and degradable stability based on the intermolecular hydrogen bond interaction. The PU-70 and PU-50 copolymers exhibit better mechanical properties such as high flexibility and high ductility because of their larger microphase separation architecture with the hard domains acting as reinforcing fillers and/or physical crosslinking agents dispersed in the soft segment matrix. Copyright © 2009 John Wiley & Sons, Ltd.

Chain and mirophase-separated structures of ultrathin polyurethane films

Measurements are presented how chain and microphase-separated structures of ultrathin polyurethane (PU) films are controlled by the thickness. The film thickness is varied by a solution concentration for spin coating. The systems are PUs prepared from commercial raw materials. Fourier-transform infrared spectroscopic measurement revealed that the degree of hydrogen bonding among hard segment chains decreased and increased with decreasing film thickness for strong and weak microphase separation systems, respectively. The microphase-separated structure, which is formed from hard segment domains and a surrounding soft segment matrix, were observed by atomic force microscopy. The size of hard segment domains decreased with decreasing film thickness, and possibility of specific orientation of the hard segment chains was exhibited for both systems. These results are due to decreasing space for the formation of the microphase-separated structure.

Segmental Orientation in Well-Defined Thermoplastic Elastomers Containing Supramolecular Fillers

The mechanical behavior of segmented block copolymers is studied by unraveling the deformation mechanisms on both a macroscopic and a molecular level. Small-angle X-ray scattering and infrared dichroism are used to study the deformation of a thermoplastic elastomer with bisureidobutylene hard segments (PCLU4U) containing various amounts of perfectly fitting supramolecular filler (U4U) incorporated. The pristine PCLU4U and polymers containing filler amounts up to 25 mol % show predominantly a shear type of deformation. The hard segment stacks tend to align parallel to the strain axis upon uniaxial deformation up to the yield point. Permanent deformation is caused by fragmenting of the stacks, which then start to reorient perpendicular to the strain axis. When >25 mol % of filler is added to PCLU4U, two hard phases are present: the first hard phase consists of polymer hard segments containing a maximum amount of filler incorporated and the second hard phase consists of filler aggregates only. In this case, all urea groups orient parallel to the strain axis when such a sample is uniaxially loaded up to the yield point. At the yield point, the first hard phase shows the same shear type of deformation as the pure PCLU4U polymer. The filler aggregates, however, are not connected to the soft segment matrix, and stress transfer to the soft matrix does not occur. Therefore, we propose that they remain parallel to the strain axis. All of these data support the unique character of the supramolecular fillers used in well-defined thermoplastic elastomers.

The Microphase-separated Structure of Polyurethane Bulk and Thin Films

The microphase-separated structure of polyurethane bulk and thin films were investigated using atomic force microscopy (AFM). The polyurethane (PUs) were synthesized with poly(oxytetramethylene) glycol (PTMG), 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) by a prepolymer method. The hard segment contents were 34 and 45wt%. Polarized optical microscopy (POM) revealed that the 34wt% PUE is homogeneous at a macroscopic level, while the 45wt% one is macrophase-separated into two phases. One phase forms spherulites of ca. 2–5 μm in diameter. AFM observation for the 34wt% PUE showed the microphase-separated structure, consisting of hard segment domains and a soft segment matrix. In contrast, for the 45 wt% PUE, a lot of the hard segment domains were observed in the spherulite region, indicating that spherulites include much amount of hard segment component, in contrast, outside of spherulite exhibited similar structure to that of 34 wt% one. For the PU bulk, the different microphase-separated structure in the inside and outside of spherulite was successfully observed for the first time. Also, the microphase-separated structure of PU films was investigated as a function of the film thickness. The PU films exhibited similar microphase-separated structure. For the thicker film (∼200nm), the interdomain spacing almost corresponded to bulk one. On the other hand, that for the film thickness below 7nm dramatically decreased. This seems to be simply related to a decreasing space. We obtained the experimental data, which the phase-separated domain size of multiblock copolymer decreased with decreasing film thickness.

Microphase Separation of Bulk and Ultrathin Films of Polyurethane Elastomers

AbstractSurmmary: Polyurethane elastomers (PUEs) were synthesized with poly(oxytetramethylene) glycol (PTMG), 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butanediol (BD)/1,1,1‐trimethylol propane (TMP) by a prepolymer method. The degree of microphase separation of bulk and ultrathin films for these PUEs was confirmed by Fourier transform infrared (FT‐IR) spectroscopy, differential scanning calorimetry (DSC) and atomic force microscopy (AFM). In the bulk films, FT‐IR and DSC measurements revealed that the degree of micro‐phase separation strengthened with increasing BD content. AFM observation of the BD‐PUE showed hard segment domains surrounded by a soft segment matrix. The domains ranged in size from 10‐20 nm, while BD/TMP‐ and TMP PUEs did not have clear domains. On the other hand, AFM observation was carried out on thin films (200 mm in thickness) and ultrathin films (approximately 8‐5 nm) prepared by spin‐coating the different concentrations of PUE solutions. The microphase separated strucuture under 10 nm in thickness showed marked decreases in the size of the microphase‐separated domain.

Novel Polyurethane Gels: The Effect of Structure on Gelation

AbstractNovel polyurethane gels have been reported in common solvent like dimethyl formamide (DMF). Polyurethanes have been synthesized from diisocyanates, diols and rigid chain extenders. We have illustrated the influence of chemical structure of the chain extenders on gelation rate, thermal property and morphology of the gels in DMF. Gelation rate increases significantly with the rigidity of the chain extender. Introduction of more rigid chain extender molecules in polyurethane prepolymer enhanced the thermal stability of the pure polymer. On the contrary, the solvent retention power of the gels gradually decreases with increasing rigidity of chain extender presumably because of the poor dispersion/greater aggregation of the hard segments in the soft segment matrix. Morphology and formation of gelation have been discussed.

Relationship between nanoscale deformation processes and elastic behavior of polyurethane elastomers

The cyclic deformation of two polyurethane elastomers that differed in soft segment content and molecular weight was investigated. The microphase-separated morphology of the polyurethane with higher soft segment content consisted of hard segment domains dispersed in a soft segment matrix. In the polyurethane with lower soft segment content, the hard segment domains appeared to be partially cocontinuous. Following an initial ‘conditioning’ cycle, both polyurethanes exhibited reversible elastomeric behavior. Structural changes that occurred during conditioning were investigated using atomic force microscopy and Fourier transform infrared dichroism. The results provided the basis of a structural model for the deformation behavior. Yielding and reorganization of hard domains resulted in a highly oriented microfibrous morphology. Subsequent unloading and reloading were associated with reversible relaxation and reformation of the microfibrous entities. The elastic behavior of the conditioned polyurethanes was satisfactorily described by classical rubber theory with inextensibility. The structural model proposed here extended previous efforts to describe the deformation processes of polyurethanes during cyclic loading.

Structure–property behavior of segmented polyurethaneurea copolymers based on an ethylene–butylene soft segment

Novel segmented polyurethaneurea copolymers were synthesized using a poly(ethylene–butylene) glycol based soft segment and either hydrogenated diphenyl methane diisocyanate (HMDI) or hexamethylene diisocyanate (HDI) in addition to either ethylene diamine (EDA) or 2-methyl-1,5-diaminopentane (DY) as the chain extender. Dynamic mechanical analysis (DMA), small angle X-ray scattering (SAXS) and in some cases atomic force microscopy (AFM) established the presence of a microphase-separated structure in which hard microdomains are dispersed throughout a soft segment matrix. Wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) imply that the materials are amorphous. Samples that are made with HMDI/DY and have hard segment contents in the range of 16–23 wt% surprisingly exhibit near-linear mechanical deformation behavior in excess of 600% elongation. They also show very high levels of recoverability even though their hysteresis is also considerable. The materials have all proven to be melt processable in addition to solution processable.

MORPHOLOGY OF POLYURETHANES REVISITED BY COMPLEMENTARY AFM AND TEM

Cast, segmented polyetherurethanes with 30 and 50% hard-segment content (HSC), respectively, were studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Multi-phase segregation was observed in both samples on two levels (micro and nano) of structural organization. Spherulites with a prominent radial structure, built of branched fibrils and globules, were captured on the micrometer level. The use of AFM enabled us to investigate the nanostructure in the polyurethanes studied here. In the sample with low (30%) HSC, nano-scale phase separation was observed by AFM in areas outside the crystalline aggregates. The morphology in these domains exhibited short, rodlike hard domains embedded in the matrix of the soft segments. The other sample (50% HSC) contained four identifiable morphological features. These included spherulites, globules, bundles of lamellae, and nanophase-separated, rodlike hard domains, embedded in the soft-segment matrix. The globules did not have any internal structure visible by AFM down to the nanometer scale. We speculate that the globules form as a result of macro-phase segregation, due to incompatibility of the reactants, during synthesis and may thus be identified as pockets of free hard segments. The AFM phase imaging has been very useful to observe the bundles of lamellae and the nanoscale phase-separated structures, which were not captured by TEM, due to large differences in AFM phase signal contrast between the hard and the soft domains. †On leave from Technical University of Gdańsk.

Solvent-influenced mesostructures in polyurethane-based membranes of different transport parameters using SAXS synchrotron method

The state of solvent in a membrane and the membrane mesostructure are of prime importance for the understanding of membrane transport phenomena. In our last SAXS (small angle X-ray scattering) study we have given evidence that the model of permeation with the permeate phase transition level is not correct for the polyurethane membrane. Instead, inside the membrane, a structure of the system polymer-solvent is formed, which changes gradually from structure of dry polymer to the one saturated with solvent, depending on the depth in the permeating membrane [1]. This result confirmed the correctness of models of permeation, taking into account “anomalous diffusion.” The anomalous diffusion can be caused by some physical parameters such as entrapping effects due to geometric constraints on the pathway of the solvent molecules [2–5]. Also modelling of the diffusion process in heterogeneous media containing impermeable domains (liquid crystal type) was carried out using a random-walk simulation [6]. The domains acts as obstructions in the diffusional path and the solvent molecules diffuse through the amorphous polymer matrix via tortuous path around the domains. Segmented polyurethanes are regarded as multiblock copolymers of the (AB)n type, in which A and B are the hardand soft-segment repeat units respectively. Microphase separation in this type of materials, due to thermodynamic incompatibility between segments of both types and formation of impermeable hard-segment domains dispersed in the rubbery soft-segment matrix, was observed. The structure of the microphase was assumed to be lamellar [7]. So, the structure of these lamellar systems and its change upon a solvent action should have a real influence on the transport parameters. The aim of this work was to find a change caused by solvent in the structure of the previous lamellar system in membranes differing in transport parameters. The segmented polyurethanes studied in this work were prepared using a prepolymer method in DMF solution. In the case of PU-P-1, a prepolymer consisting of PTMO (hydroxy-terminated polytetramethylene oxide, M = 1000) and TDI (2,4-tolylene diisocyanate) was obtained, which was followed by a chain extension with PP (4,4′-diaminodiphenylmethane). PU-B-1 was obtained in a similar manner using PBD (hydroxyterminated polybutadiene with a similar molecular weight) as a macrodiol component. The details of the synthesis have been described previously [8]. The schematic representation of the molecular structure of the obtained polyurethanes is given in Fig. 1. They are denoted as PU-X-x , where X describes type of macrodiol used (P as PTMO, B as PBD), and x is a number of repeat units in the hard segment (Fig. 1). The overall compositions of the investigated PUs and their physicochemical characteristics are given in Table I. Films of the PUs were obtained by casting a 15% DMF solution of the polymer onto a glass plate and evaporating the solvent in an oven. The densities of the polyurethane films were measured by buoyancy in water. The molecular weights of the synthesized PUs and the polydispersity index were determined using gel-permeation chromatography (GPC). The measurements were carried out in DMF solutions at 80 ◦C with a Knauer apparatus based on polystyrene standards. Differential scanning calorimetry (DSC), used for the determination of the glass transition temperatures, was conducted with a Rheometric Scientific DSC plus apparatus at a heating rate 10◦/min. Sorption experiments were carried out at 25 ◦C by placing the PU samples in solvent. The liquid uptake was monitored gravimetrically by weighing the PU samples until equilibrium weight was attained. The sorption equilbrium values given in Table II were determined as the moles of liquid sorbed in 100 g of a dry sample.

Dynamic mechanical signatures of a polyester‐urethane and plastic‐bonded explosives based on this polymer

AbstractThe 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°C, 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°C in Estane and LX‐14, respectively, at 1 Hz. In PBX‐9501 the Estane soft segment glass transition peak, Tg(SS), in the loss modulus occurred at −40 ± 3°C 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, Tg(HS), was observed as a peak in the loss modulus at about 70°C. In LX‐14 the transition was observed at lower temperatures (56–58°C at 1 Hz) depending on thermal history. There was a low temperature shoulder on the Tg(HS) of Estane 5703 associated with soft segment crystallinity. Modulated differential scanning calorimetry (MDSC) was used to verify the Tg(HS) in Estane and 50/50 mixtures of Estane with NP. In PBX‐9501 the hard segment glass transition occurred between 65 and 72°C. The presence of NP in PBX‐9501 gave rise to a new transition, Teu(NP), between 8 and 15°C. 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 Tg(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. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1009–1024, 2002