Triazine functionalized hydroxyl terminated polybutadiene polyurethane: Influence of triazine structure

Comparative Study on Thermal Response Mechanism of Two Binders during Slow Cook-Off

The HTPE (hydroxyl-terminated polyether) propellant had a lower ignition temperature (150 °C vs. 240 °C) than the HTPB (hydroxy-terminated polybutadiene) propellant in the slow cook-off test. The reactions of the two propellants were combustion and explosion, respectively. A series of experiments including the changes of colors and the intensity of infrared characteristic peaks were designed to characterize the differences in the thermal response mechanisms of the HTPB and HTPE binder systems. As a solid phase filler to accidental ignition, the weight loss and microscopic morphology of AP (30~230 °C) were observed by TG and SEM. The defects of the propellant caused by the cook-off were quantitatively analyzed by the box counting method. Above 120 °C, the HTPE propellant began to melt and disperse in the holes, filling the cracks, which generated during the decomposition of AP at a low temperature. Melting products were called the “high-temperature self-repair body”. A series of analyses proved that the different thermal responses of the two binders were the main cause of the slow cook-off results, which were likewise verified in the propellant mechanical properties and gel fraction test. From the microscopic point of view, the mechanism of HTPE’s slow cook-off performance superior to HTPB was revealed in this article.

Bioinspired modified graphene oxide/polyurethane composites with rapid self-healing performance and excellent mechanical properties

Self-healing efficiency and mechanical strength are always a pair of mechanical contradictions of a polymer. Herein, a series of novel mussel-inspired modified graphene oxide/polyurethane composites were successfully fabricated via rational molecular design and introducing hyperbranched polymer-modified graphene oxide. The composites exhibit outstanding self-healing performances with a self-healing efficiency of 87.9%. Especially, their self-healing properties possess exceptional water-insensitivity, which presents a high self-healing efficiency of 92.5% under 60 °C water for 2 h and 74.6% under 25 °C water for 6 h. Furthermore, the tensile strength of the composites increased by 107.7% with a high strain of 2170%. In addition, the composites show a remarkable recovery capability of 76.3% and 83.7% under tensile and compression loading, respectively, after 20 cycles. This strategy shows prominent application potential in high-performance solid propellants, protective coating, electronic skin, soft sensors and other water-insensitive devices.

We successfully modified graphene oxide with amino-terminated hyperbranched polyamide(MGO), and obtained novel mussel-inspired MGO/polyurethane composites with outstanding self-healing and mechanical performances via rational molecular design.

Hyperbranched polyamide modified graphene oxide-reinforced polyurethane nanocomposites with enhanced mechanical properties

As is well known, it is difficult to simultaneously improve both the strength and elongation at break of polymers filled with nanomaterials. This work obtained high-performance composites with enhanced strength and elongation at break via cross-linking hydroxyl-terminated polybutadiene (HTPB) chains with hyperbranched-polyamide-modified graphene oxide (HGO), and the preparation, characterization, and mechanical properties of the composites serving as a composite solid-propellant binder have been described in detail. Compared with pure HTPB polyurethane (P-HTPB), the tensile strength and elastic modulus of the composite containing 0.1 wt% HGO (H-0.1/HTPB) increase by 57.8% and 65.3%, respectively. Notably, the elongation at break of the H-0.1/HTPB composite can reach up to 1292.6%, which is even higher than that of P-HTPB. Moreover, the capabilities of the composites to resist deformation have also been enhanced significantly. The glass transition temperatures of the composites are still extremely low (∼-73 °C), which is beneficial for their applications. It can be expected that this study can provide an effective fabrication approach and strategy for preparing high-performance polyurethane composites.

Mussel-inspired and aromatic disulfide-mediated polyurea-urethane with rapid self-healing performance and water-resistance

Although lots of methods have been developed for self-healing materials, it remains a formidable challenge to achieve a thermosetting material with water-insensitive and self-healing properties at room temperature. Nature always provides intelligent strategies for developing advanced materials with superior properties. Herein, a novel self-healable polyurea-urethane was rationally designed by combining mussel adhesive protein-mimetic structure and dynamic aromatic disulfide bonds. It achieves high self-healing efficiency of 98.4% at room temperature for only 6 h and 90% at 60℃ for only 30 min without any external stimuli. Impressively, this self-healing capability possesses exceptional water-resistance, which presents high self-healing efficiency of 98.1% for 2 h and 82.1% for 6 h in 60℃ and 25℃ water, respectively. Besides, the designed polyurea-urethane exhibits excellent mechanical properties such as high elongation at break of 2400%, notch-insensitive stretching elongation of 1500% and notable recovery capability. This strategy shows promising application potential in solid propellants, protective coating, electronic skin, soft sensors and other water-resistant devices.

Mechanochemical Cellular Membrane Internalization of Nanohydrogels: A Large-Scale Mesoscopic Simulation

By combining large-scale dissipative particle dynamics and steered molecular dynamics simulations, we investigate the mechanochemical cellular internalization pathways of homogeneous and heterogeneous nanohydrogels and demonstrate that membrane internalization is determined by the crosslink density and encapsulation ability of nanohydrogels. The homogeneous nanohydrogels with a high crosslink density and low encapsulation ability behave as soft nanoparticles partially wrapped by the membrane, while those with a low crosslink density and high encapsulation ability permeate into the membrane. Regardless of the crosslink density, the homogeneous nanohydrogels undergo typical dual morphological deformations. The local lipid nanodomains are identified at the contacting region between the membrane and nanohydrogels because of different diffusion behaviors between lipid and receptor molecules during the internalization process. The yolk@shell heterogeneous nanohydrogels present a different mechanochemical cellular internalization pathway. The yolk with strong affinity is directly in contact with the membrane, resulting in partial membrane wrapping, and the contacting area is much reduced when compared to homogenous nanohydrogels, leading to a smaller lipid nanodomain and thus avoiding related cellular toxicity. Our findings provide a critical mechanism understanding of the biological pathways of nanohydrogels and may guide the molecular design of the hydrogel-based materials for controlled release drug delivery, tissue engineering, and cell culture.

Review of novel energetic polymers and binders - high energy propellant ingredients for the new space race

Current solid rocket propellant formulations still employ traditional ingredients utilized since the 1960s, such as hydroxyl terminated polybutadiene (HTPB). Recent advances in energetic polymer see many binders capable of providing higher specific impulse and burn rates over HTPB. As shown by calculations, even slight increases in specific impulse can drastically increase the maximum payload of a launch system. Therefore, replacing HTPB with energetic binders could provide heavy space missions the needed extra boost. Energetic binders could also be paired with chlorine-free energetic oxidizers to synergistically provide a specific impulse exceedingly higher than the current formulation while reducing pollution. A comprehensive evaluation of the synthesis, mechanical properties, and performance of various trending and overlooked energetic polymers is described. Several outstanding candidates show promising properties to replace HTPB.

Properties related to linear and branched network structure of hydroxyl terminated polybutadiene

The correlation between properties and the network structure of hydroxyl terminated polybutadiene (HTPB) based polyurethanes (PUs) was studied through linear and branched structure polymer matrixes formed by toluene diisocyanate (TDI) and an aliphatic polyisocyanate curing agent (N100). The curing reactions were monitored using differential scanning calorimetry (DSC) and viscosity build-up. The swelling capacity of PUs decreased with the increase of crosslink density with a stable solubility parameter according to the equilibrium swelling test. Tensile properties of PUs cured by TDI and N100 in different stoichiometric ratios of NCO/OH groups were tested. Both breaking elongation and tensile strength were remarkably improved by N100. The thermal decomposition processes of HTPB/TDI and HTPB/N100 indicated that a branched structure has higher depolymerization temperature, and hence, improved thermal stability. In addition, PU with a branched network prevented the migration of the plasticizer during isothermal accelerated aging due to the higher crosslink density.

Effect of Solvent and Functionality on the Physical Properties of Hydroxyl-Terminated Polybutadiene (HTPB)-Based Polyurethane

The present article reports the investigation on the effects of solvent and position of functionality on various physical properties of polyurethanes (PUs) based on hydroxyl-terminated polybutadiene (HTPB). The PU films (curative)  were prepared by coupling HTPB (P0) with isophorone diisocyanate (IPDI) in various solvent media. The PUs obtained in different solvent media displayed similar thermal profile and glass transition temperature (T _g), but their tensile properties varied significantly. Optimized tensile properties were observed when tetrahydrofuran was used as the solvent media. In the course, the investigation of the functionality effect, tetrazole (M1, M2, and M3) were covalently attached at the terminal carbon of HTPB to obtain three modified HTPBs (P1, P2, and P3), thereby coupling with IPDI to obtain the corresponding tetrazole functional PUs films. Pristine (P0-PU) and functional PU (P1-PU, P2-PU, and P3-PU) films have similar thermal profile and T _g (-76 °C), but they have a notable enhancement in tensile properties; for example, tensile strength and elongation at break of P0-PU were found to be 3.21 MPa and 727%, respectively, whereas these values were 4.84 MPa and 958%, respectively, in the case of P3-PU. It was observed that on increasing the number of methylene group from 1 to 3 between HTPB and tetrazole moiety, the strength of hydrogen bonding increases, which facilitates better packing of urethane network in the PU and hence improves the tensile properties. Also, modification of pristine HTPB with tetrazole derivatives enhanced the calorific values of the resulting PUs.

Nanostructured polyurethane perylene bisimide ester assemblies with tuneable morphology and enhanced stability

Size control has been successfully achieved in inorganic materials, but it remains a challenge in polymer nanomaterials due to their polydispersity. Here, we report a facile approach to tailor the diameters of polyurethane (PU) nanoparticles (490 nm, 820 nm and 2.1 µm) via perylene bisimide (PBI) assisted self-assembly. The formed morphologies such as spindle, spherical and core-shell structures depend on the ratio of PBI and polymer concentrations. It is shown that the formation of PU nanoparticles is directed by π-π stacking of PBI and the morphology transition is not only affected by the amount of PBI incorporated, but also influenced by solvent, which controls the initial evaporation balance. Furthermore, the prepared PUs exhibit retained optical stability and enhanced thermal stability. The PUs, designed to have conjugated PBI segments in backbones, were synthesized via ring-opening and condensation reactions. Compared with the neat PU, gel permeation chromatography shows narrower molecular weight distribution. Fluorescence spectra and ultraviolet-visible spectra indicate retained maximum emission wavelength of PBI at 574 nm and 5.2% quantum yields. Thermo-gravimetric analysis and differential scanning calorimetry reveal 79°C higher decomposition temperature and 22°C higher glass transition temperature. This study provides a new way to fabricate well-defined nanostructures of functionalized PUs.

Influence of mono-lithium based initiators with different steric volumes on 1,4 unit content of hydroxyl terminated polybutadiene using anionic polymerization

The influence of steric structural factors of mono-lithium based anionic initiators on 1,4 unit content of hydroxyl terminated polybutadiene was investigated.

Synthesis and properties of polyurethane urea with pyridine-2,6-dicarboxamide moieties in their structure

The inclusion of 2,6-pyridinedicarboxamide into polyurethanes structure strongly influenced their morphology, surface and thermo-mechanical properties. The 2,6-pyridinedicarboxamide units adopt syn-syn conformations into polyurethane matrix.