Investigating the Effect of Chain Extender on the Phase Separation and Mechanical Properties of Polybutadiene-Based Polyurethane.

The thermodynamic incompatibility between the soft and hard segments of thermoplastic polyurethane (TPU) results in a microphase-separated behavior and excellent mechanical properties. However, the effect of the chain extender on the degree of microphase separation (DMS) and the resultant mechanical properties of TPU have not been well studied because of the complex interactions between the soft and hard segments. Herein, hydroxyl-terminated polybutadiene-based TPUs(HTPB-TPUs) without hydrogen bonding between the soft and hard segments are synthesized using hydroxyl-terminated polybutadiene, toluene diisocyanate, and four different chain extenders, and the effect of the chain extender structure on DMS is analyzed experimentally using a combination of analytical techniques. Furthermore, the solubility parameters of the soft and hard segments, glass transition temperatures, and hydrogen-bond density of the HTPB-TPUs, are computed using all-atom molecular dynamics simulations. The results clearly reveal that the chain extender significantly affects the DMS and thus the mechanical properties of HTPB-TPUs. This study paves the way for studying the relationship between the structure and properties of TPU.

Preparation and Performance Study of HTPB-g-(PNIPAM/PEG) Thermoresponsive Polymer Brush.

In recent years, a great deal of work has been devoted to the development of thermoresponsive polymers that can be made into new types of smart materials. In this paper, a branched polymer, HTPB-g-(PNIPAM/PEG), with polyolefin chain segments as the backbone and having polyethylene glycol (PEG) and poly(N-isopropylacrylamide) (PNIPAM) as side chains was synthesized by ATRP and click reactions using N3-HTPB-Br as the macroinitiator. This initiator was designed and synthesized using hydroxyl-terminated polybutadiene (HTPB) as the substrate. The temperature-responsive behavior of the branched polymer was investigated. The lower critical solution temperature (LCST) of the branched polymer was determined by ultraviolet and visible spectrophotometry (UV-vis) and was found to be 35.2 °C. The relationship between the diameter size of micelles and temperature was determined by dynamic light scattering (DLS). It was found that the diameter size changed at 36 °C, which was nearly consistent with the result obtained by UV-vis. The results of the study indicate that HTPB-g-(PNIPAM/PEG) is a temperature-responsive polymer. At room temperature, the polymer can self-assemble into composite micelles, with the main chain as the core and the branched chain as the shell. When the temperature was increased beyond LCST, the polyolefin main chain along with the PNIPAM branched chain assembled to form the nucleus, and the PEG branched chain constituted the shell.

Preparation and Characterization of Soft-Hard Block Copolymer of 3,4-IP-b-s-1,2-PBD Using a Robust Iron-Based Catalyst System.

A series of well-defined diblock copolymers, namely, 3,4-polyisoprene-block-syndiotactic-1,2-polybutadiene (3,4-PI-b-s-1,2-PBD), with a soft-hard block sequence were synthesized via an in situ sequential polymerization process using a robust iron-based catalytic system Fe(acac)3/(isocyanoimino) triptenylphosphorane (IITP)/AliBu3. This catalyst exhibits vigorous activity and temperature tolerance, achieving a polymerization activity of 5.41 × 106 g mol(Fe)-1 h-1 at 70 °C with a [IP]/[Fe] ratio of 15,000. Moreover, the quasi-living polymerization characteristics of the catalyst were verified through kinetic experiments. The first-stage polymerization of isoprene (IP) is performed at 30 °C to give a soft 3,4-PI block, and then a quantitative amount of 1,3-butadiene was added in situ to the quasi-living polymerization system to produce a second hard s-1,2-PBD. The s-1,2-PBD segments in block copolymers display a rodlike morphology contrasting with the spherulitic morphology characteristic of s-1,2-PBD homopolymers. The precise tunability of the length of the soft and hard chain segments of these novel elastic materials with the feed ratio of IP and BD, endowing them with outstanding mechanical properties and excellent dynamic mechanical properties, which are expected to be promising high-performance rubber materials.

Rheological and Mechanical Characterization of 3D-Printable Solid Propellant Slurry.

This study delves into the rheological and mechanical properties of a 3D-printable composite solid propellant with 80% wt solids loading. Polybutadiene is used as a binder with ammonium sulfate, which is added as an inert replacement for the ammonium perchlorate oxidizer. Further additives are introduced to allow for UV curing. An in-house illumination system made of four UV-A LEDs (385 nm) is employed to cure the resulting slurry. Rheological and mechanical tests are conducted to evaluate the viscosity, ultimate tensile strength and strain, and compression behavior. Viscosity tests are performed for both pure resin and complete propellant composition. A viscosity reduction factor is obtained for the tested formulations when pre-heating slurry. Uniaxial tensile and compression tests reveal that the mechanical properties are consistent with previous research. Results emphasize the critical role of temperature and solid loading percentage. Pre-heating resin composites may grant a proper viscosity reduction while keeping mechanical properties in the applicability range. Overall, these findings pave the way for the development of a 3D printer prototype for composite solid propellants.

Ultraconformable Capacitive Strain Sensor Utilizing Network Structure of Single-Walled Carbon Nanotubes for Wireless Body Sensing.

Capture and real-time recording of precise body movements using strain sensors provide personal information for healthcare monitoring and management. To acquire this information, a sensor that conforms to curved irregular surfaces, including biological tissue, is desired to record complex body movements while acting like a second skin to avoid interference with the movements. In this study, we developed a thin-film-type capacitive strain sensor that is flexible and stretchable on the surface of a living body. We fabricated conductive polymeric ultrathin films ("nanosheets") comprising polystyrene-block-polybutadiene (SB) elastomers and single-walled carbon nanotubes (SWCNTs) (i.e., SWCNT-SB nanosheets) via gravure coating; the SWCNT-SB-coated nanosheets were used as the flexible electrode in a capacitive strain sensor. The dielectric (DE) layer was then prepared using the silicone elastomer Ecoflex 00-30 because its Young's modulus is comparable to that of the epidermis. The normalized capacitance changes (ΔC/C0) in the sensor increased with increasing tensile strain over a range from 0-100%, indicating that the proposed sensor can measure the strain of biological movements, including those of skin and blood vessels. To improve sensor conformability further, the effect of sensor thickness on the gauge factor (GF) was investigated using thinner DE layers by focusing on their flexural rigidity. As a result, the GF increased from 0.64 to 1.13 as the DE layer thickness decreased from 260 to 40 µm. Finally, we evaluated the fabricated sensor's signal stability and mechanical durability, including during wireless sensing when applied to human skin and a vascular model. The ΔC/C0 values varied in response to the bending motion of a finger, dilation of a blood vessel, and the swallowing movement of the throat. These results indicate that our capacitive strain sensor is conformable and functional on biological tissue to enable monitoring of dynamic biological movements (e.g., pulse rate and arterial dilation) without wearer discomfort.

Glass Transition Temperatures and Thermal Conductivities of Polybutadiene Crosslinked with Randomly Distributed Sulfur Chains Using Molecular Dynamic Simulation.

The thermal conductivities and glass transition temperatures of polybutadiene crosslinked with randomly distributed sulfur chains having different lengths from mono-sulfur (S1) to octa-sulfur (S8) were investigated. The thermal conductivities of the related models as a function of the heat flux autocorrelation function, applying an equilibrium molecular dynamic (EMD) simulation and the Green-Kubo method, were studied for a wide range of temperatures. The influence of the length of sulfur chains, degree of crosslinking, and molar mass of the crosslinker on the glass transition temperature and final values of thermal conductivities were studied. First, the degree of crosslinking is considered constant for the eight simulation models, from mono-sulfur (S1) to octa-sulfur (S8), while the molar mass of the sulfur is increases. The results show that the thermal conductivities of the crosslinked structure decrease with increasing temperature for each model. Moreover, by increasing the lengths of the sulfur chains and the molar weight of the crosslinker, thermal conductivity increases at a constant temperature. The MD simulation demonstrates that the glass transition temperature and density of the crosslinked structure enhance as the length of the sulfur chains and molar mass of the sulfur increase. Second, the molar weight of sulfur is considered constant in these eight models; therefore, the degree of crosslinking decreases with the increase in the lengths of the sulfur chains. The results show that the thermal conductivities of the crosslinked structure decrease with the increase in the temperature for each model. Moreover, by increasing the lengths of sulfur chains and thus decreasing the degree of crosslinking, the trend in changes in thermal conductivities are almost the same for all of these models, so thermal conductivity is constant for a specific temperature. In addition, the glass transition temperature and density of the crosslinked structure decrease.

Enhanced gas and plasticizer barrier HTPB composite liner implanted with parallel orientation Fe3O4/RGO nanosheets by an ultrasound/magnet-coassisted method.

It is of great significance to prepare liners with excellent inhibition of energetic plasticizer migration and gas barrier properties. Here, we have successfully prepared magnetic iron oxide decorated reduced-graphene-oxide nanosheets (MRGO) by using ultrasound-assisted method. The obtained MRGO nanosheet-fillers were filled into hydroxyl-terminated polybutadiene (HTPB) which was exposed to a magnetic field (200 mT) to achieve ordered orientation of MRGO in the HTPB matrix (Ordered MRGO/HTPB). The laser confocal microscopy demonstrates that MRGO exhibit ordered orientation structure in HTPB matrix with good dispersion, which renders the HTPB composite liners exhibiting high gas and plasticizer barrier capability, with a reduction of 18.9 % in water vapor permeability and a decrease of 14.1 % in dibutyl phthalate (DBP) migration equilibrium concentration as compared with those of random MRGO embedded HTPB composite liners (Random MRGO/HTPB). Moreover, a theoretical model accounting for such enhanced gas/plasticizer barrier performance of HTPB due to the implantation of order aligned MRGO was established, which shows that the effective diffusion pathways of plasticizer/gas for liner penetration would be significantly enhanced when the MRGO nanosheets are oriented within the HTPB matrix. This work provides an effective and facile strategy toward the design and development of composite liners with high plasticizer/gas barrier performance for industrial applications.

Ladder-like Poly(methacryloxypropyl) silsesquioxane-Al2O3-polybutadiene Flexible Nanocomposites with High Thermal Conductivity.

Ladder-like poly(methacryloxypropyl)-silsesquioxanes (LPMASQ) are photocurable Si-based gels characterized by a double-stranded structure that ensures superior thermal stability and mechanical properties than common organic polymers. In this work, these attractive features were exploited to produce, in combination with alumina nanoparticles (NPs), both unmodified and functionalized with methacryloxypropyl-trimethoxysilane (MPTMS), LPMASQ/Al2O3 composites displaying remarkable thermal conductivity. Additionally, we combined LPMASQ with polybutadiene (PB) to produce hybrid nanocomposites with the addition of functionalized Al2O3 NPs. The materials underwent thermal stability, structural, and morphological evaluations via thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR). Both blending PB with LPMASQ and surface functionalization of nanoparticles proved to be effective strategies for incorporating a higher ceramic filler amount in the matrices, resulting in significant increases in thermal conductivity. Specifically, a 113.6% increase in comparison to the bare matrix was achieved at relatively low filler content (11.2 vol%) in the presence of 40 wt% LPMASQ. Results highlight the potential of ladder-like silsesquioxanes in the field of thermally conductive polymers and their applications in heat dissipation for flexible electronic devices.

Convolution Neural Networks for Motion Detection with Electrospun Reversibly-Cross-linkable Polymers and Encapsulated Ag Nanowires.

This paper presents the design, fabrication, and implementation of a novel composite film, a polybutadiene-based urethane (PBU)/AgNW/PBU sensor (PAPS), demonstrating remarkable mechanical stability and precision in motion detection. The sensor capitalizes on the integration of Ag nanowire (AgNW) electrodes into a neutral plane, embedded within a reversibly cross-linkable PBU polymer. The meticulous arrangement confers pore-free and interfaceless sensor formation, resulting in an enhanced mechanical robustness, reproducibility, and long-term reliability. The PBU polymer is subjected to an electrospinning process, followed by sequential Diels-Alder (DA) and retro-DA reactions to produce a planarized encapsulation layer. This pioneering technology, based on electrospinning, allows for more flawless engineering of the neutral plane as compared to conventional film lamination or layer-by-layer spin-coating processes. This encapsulation, matching the thickness of the preformed PBU film, effectively houses the AgNW electrodes. The PAPS outperforms conventional AgNW/PBU sensors (APS) in terms of mechanical stability and bending insensitivity. When affixed to various body parts, the PAPS generates distinctive signal curves, reflecting the specific body part and degree of motion involved. The PAPS sensor's utility is further magnified by the application of machine learning and deep learning algorithms for signal interpretation. K-means clustering algorithm authenticated the superior reproducibility and consistency of the signals derived from the PAPS over the APS. Deep learning algorithms, including a singular 1D convolutional neural network (1D CNN), long short-term memory (LSTM) network, and dual-layered combinations of 1D CNN + LSTM and LSTM + 1D CNN, were deployed for signal classification. The singular 1D CNN model displayed a classification accuracy exceeding 98%. The PAPS sensor signifies a pivotal development in the field of intelligent motion sensors.

Cross-Linking Characteristics, Morphology, Dynamics, and Mechanical and Thermal Properties of Polychloroprene/Polybutadiene/Nano-Zinc (CR/BR/nZn) Compositions with Reduced Fire Hazard.

The properties of unconventional blends of crystallizable and thermo-cross-linkable polychloroprene (CR) with polybutadiene (BR) were investigated in this study. The compositions were prepared using the method of reactive processing and cross-linking in the presence of nano-sized zinc (nZn). The purpose of the research was to assess the efficacy of nano-zinc as a curing agent of polychloroprene and polybutadiene (CR/BR) composites and to obtain rubber goods characterized by increased flame resistance. The blends were filled with nano-silica (aerosil) and fillers of natural origin (chalcedonite or silitin). The cross-linking process was characterized by determining the kinetics curves, the equilibrium swelling, and the Mooney-Rivlin elasticity constants. The morphology of the vulcanizate surface was specified by scanning electron microscopy (SEM). The dynamic and mechanical properties, flammability, and toxicity of gaseous substances involved in thermal decomposition were determined. Mass changes and thermal effects were studied using simultaneous thermal analysis (STA). It was confirmed that nano-zinc is an efficient curing agent for the polychloroprene and polybutadiene compositions, with a satisfactory degree of cross-linking (αc = 0.10, CRI = 4.11 min-1), good mechanical strength (TSb = 5 MPa), satisfactory tear resistance (Ts = 2.9 N/mm), and very high flame resistance (OI = 30%, HRRmax = 283 kW/m2). Filled products could be used as non-combustible materials, confirming the low fire hazard (1/tflashover = 3.5-6.4 kW/m2∙s). The most effective filler of the tested composites was nano-sized silica.

Synthesis and Comparative Study of Polyether-b-polybutadiene-b-polyether Triblock Copolymers for Use as Polyurethanes.

In this paper, the effects of HTPBs with different main-chain microstructures on their triblock copolymers and polyurethane properties were investigated. Three polyether-modified HTPB triblock copolymers were successfully synthesized via a cationic ring-opening copolymerization reaction using three HTPBs with different microstructures prepared via three different polymerization methods as the macromolecular chain transfer agents and tetrahydrofuran (THF) and propylene oxide (PO) as the copolymerization monomers. Finally, the corresponding polyurethane elastomers were prepared using the three triblock copolymers as soft segments and toluene diisocyanate (TDI) as hard segments. The results of an analysis of the triblock copolymers showed that the triblock copolymers had lower viscosity and glass transition temperature (Tg) values as the HTPB 1,2 structure content decreased, although the effect on the thermal decomposition temperature was not significant. An analysis of the polyurethane elastomers revealed that as the content of the 1,2 structure in HTPB increased, its corresponding polyurethane elastomers showed a gradual increase in breaking strength and a gradual decrease in elongation at break. In addition, PU-1 had stronger crystallization properties compared to PU-2 and PU-3. However, the differences in the microstructures of the HTPBs did not seem to have much effect on the surface properties of the polyurethane elastomers.

Traditional vs. Energetic and Perchlorate vs. "Green": A Comparative Study of the Choice of Binders and Oxidising Agents.

The aim of this article is to compare rocket propellants containing a traditional binder (hydroxyl-terminated polybutadiene) and an energetic binder (glycidyl azide polymer), as well as a perchlorate oxidising agent and a "green" one, i.e., ammonium perchlorate and phase-stabilised ammonium nitrate. We have outlined the effects of individual substances on the sensitivity parameters and decomposition temperature of the produced solid propellants. The linear combustion velocity was determined using electrical methods. Heats of combustion for the propellant samples and the thermal decomposition features of the utilised binders were investigated via differential scanning calorimetry (DSC). Activation energy values for the energetic decomposition of the propellants were determined via the Kissinger method, based on DSC measurements at varied heating rates.

Amorphous cis-1,4-polybutadiene P-V-T properties from atomistic simulations.

CONTEXT: As a result of the diversity of microstructures encountered in cis-1,4-polybutadiene and the variety of measurement methods used, experimental values of variation of glass transition temperature (Tg) with pressure are relatively dispersed. However, atomistic simulations enable access to valuable information for very well-controlled chemistry and structures with a well-defined and systematic acquisition protocol. By varying the temperature and pressure, the specific volume of the melt was computed, yielding results that deviated by only 2% from experimental data. A linear relationship between Tg and pressure was observed, with Tg predicted to be 162 K at zero pressure and a rate of change of Tg with respect to pressure (dTg/dP) of 0.24 K/MPa. METHOD: The atomistic dilatometry experiments were conducted on a model of amorphous cis-1,4 polybutadiene with an approximate molecular weight of 5400 g/mol using the LAMMPS code and the all-atom forcefield pcff + . The dilatometry process involved cooling and heating at a rate of 9 × 1012 K/min. The specific volume was calculated by averaging over seven independent configurations for each temperature. The Tait equation was employed to fit the specific volume evolution within the temperature range of 10 to 700 K under different pressures of 0, 60, and 100 MPa.

Self-Repairing and Energy-Harvesting Triboelectric Sensor for Tracking Limb Motion and Identifying Breathing Patterns.

The increasing prevalence of health problems stemming from sedentary lifestyles and evolving workplace cultures has placed a substantial burden on healthcare systems. Consequently, remote health wearable monitoring systems have emerged as essential tools to track individuals' health and well-being. Self-powered triboelectric nanogenerators (TENGs) have exhibited significant potential for use as emerging detection devices capable of recognizing body movements and monitoring breathing patterns. However, several challenges remain to be addressed in order to fulfill the requirements for self-healing ability, air permeability, energy harvesting, and suitable sensing materials. These materials must possess high flexibility, be lightweight, and have excellent triboelectric charging effects in both electropositive and electronegative layers. In this work, we investigated self-healable electrospun polybutadiene-based urethane (PBU) as a positive triboelectric layer and titanium carbide (Ti3C2Tx) MXene as a negative triboelectric layer for the fabrication of an energy-harvesting TENG device. PBU consists of maleimide and furfuryl components as well as hydrogen bonds that trigger the Diels-Alder reaction, contributing to its self-healing properties. Moreover, this urethane incorporates a multitude of carbonyl and amine groups, which create dipole moments in both the stiff and the flexible segments of the polymer. This characteristic positively influences the triboelectric qualities of PBU by facilitating electron transfer between contacting materials, ultimately resulting in high output performance. We employed this device for sensing applications to monitor human motion and breathing pattern recognition. The soft and fibrous-structured TENG generates a high and stable open-circuit voltage of up to 30 V and a short-circuit current of 4 µA at an operation frequency of 4.0 Hz, demonstrating remarkable cyclic stability. A significant feature of our TENG is its self-healing ability, which allows for the restoration of its functionality and performance after sustaining damage. This characteristic has been achieved through the utilization of the self-healable PBU fibers, which can be repaired via a simple vapor solvent method. This innovative approach enables the TENG device to maintain optimal performance and continue functioning effectively even after multiple uses. After integration with a rectifier, the TENG can charge various capacitors and power 120 LEDs. Moreover, we employed the TENG as a self-powered active motion sensor, attaching it to the human body to monitor various body movements for energy-harvesting and sensing purposes. Additionally, the device demonstrates the capability to recognize breathing patterns in real time, offering valuable insights into an individual's respiratory health.

Thermal Conductivities of Uniform and Random Sulfur Crosslinking in Polybutadiene by Molecular Dynamic Simulation.

Thermal conductivities of polybutadiene crosslinked with sulfur as a function of the heat flux autocorrelation function by using an equilibrium molecular dynamic (EMD) simulation were investigated. The Green-Kubo method was used to calculate thermal conductivities. All simulations were performed by applying the LAMMPS software (version 3 Mar 2020) package. The united-atom force field (OPLS-UA) from the Moltemplate software (version 2.20.3) was applied in the simulations. The influence of uniform and random distributions of sulfur in polybutadiene on the final value of thermal conductivities was studied by polymeric model structures with similar and variable degrees of crosslinking. The results showed that for identical degrees of crosslinking, the distribution of crosslinkers in the polymeric model structures significantly influenced the final value of thermal conductivity. Moreover, the influence of the crosslinking degree on the final value of thermal conductivity was studied by considering polymeric model structures with different degrees of crosslinking. The results demonstrate that by having a random distribution of sulfur, the thermal conductivity will be enhanced. However, by increasing the degree of crosslinking to the higher percentage in random crosslinked model structures, the value of thermal conductivity drops significantly due to possible higher crystallization of the model structures, which decrease the degree of freedom for phonon contributions.

DFT and ONIOM Simulation of 1,3-Butadiene Polymerization Catalyzed by Neodymium-Based Ziegler-Natta System.

Using modern methods of quantum chemistry, a theoretical substantiation of the high cis-stereospecificity of 1,3-butadiene polymerization catalyzed by the neodymium-based Ziegler-Natta system was carried out. For DFT and ONIOM simulation, the most cis-stereospecific active site of the catalytic system was used. By analyzing the total energy, as well as the enthalpy and Gibbs free energy of the simulated catalytically active centers, it was found that the coordination of 1,3-butadiene in the trans-form was more favorable than in the cis-form by 11 kJ/mol. However, as a result of π-allylic insertion mechanism modeling, it was found that the activation energy of cis-1,3-butadiene insertion into the π-allylic neodymium-carbon bond of the terminal group on the reactive growing chain was 10-15 kJ/mol lower than the activation energy of trans-1,3-butadiene insertion. The activation energies did not change when both trans-1,4-butadiene and cis-1,4-butadiene were used for modeling. That is, 1,4-cis-regulation was due not to the primary coordination of 1,3-butadiene in its cis-configuration, but to its lower energy of attachment to the active site. The obtained results allowed us to clarify the mechanism of the high cis-stereospecificity of 1,3-butadiene polymerization by the neodymium-based Ziegler-Natta system.

Simulating Stress-Strain Behavior by Using Individual Chains: Uniaxial Deformation of Amorphous Cis- and Trans-1,4-Polybutadiene.

This work develops a probability-based numerical method for quantifying mechanical properties of non-Gaussian chains subject to uniaxial deformation, with the intention of being able to incorporate polymer-polymer and polymer-filler interactions. The numerical method arises from a probabilistic approach for evaluating the elastic free energy change of chain end-to-end vectors under deformation. The elastic free energy change, force, and stress computed by applying the numerical method to uniaxial deformation of an ensemble of Gaussian chains were in excellent agreement with analytical solutions that were obtained with a Gaussian chain model. Next, the method was applied to configurations of cis- and trans-1,4-polybutadiene chains of various molecular weights that were generated under unperturbed conditions over a range of temperatures with a Rotational Isomeric State (RIS) approach in previous work (Polymer2015, 62, 129-138). Forces and stresses increased with deformation, and further dependences on chain molecular weight and temperature were confirmed. Compression forces normal to the imposed deformation were much larger than tension forces on chains. Smaller molecular weight chains represent the equivalent of a much more tightly cross-linked network, resulting in greater moduli than larger chains. Young's moduli computed from the coarse-grained numerical model were in good agreement with experimental results.

Structure-Property Relationships of Shape Memory, Semicrystalline Polymers Fabricated by In Situ Polymerization and Crosslinking of Octadecyl Acrylate/Polybutadiene Blends.

The current work presents the study of a semicrystalline, shape memory polymer synthesized by simultaneous free radical polymerization and crosslinking in a blend of polybutadiene (PB) and octadecyl acrylate. Blending elastomers and phase change materials provide a modular method for new smart materials, such as shape memory polymers. In this system, grafted, side-chain crystalline poly(octadecyl acrylate) (PODA) fixes a programmed shape in the shape memory cycle, while crosslinked polybutadiene drives shape recovery. This work focuses on improving material parameters important for shape memory (crystallinity, gel fraction, melting temperature) by tuning the processing and formulation parameters (amount of crosslinker and PB weight fraction). The result is a shape memory PB-PODA copolymer that can be fabricated by melt processing and programmed without cooling below ambient temperature. It is found that good shape memory (i.e., high shape fixity and recovery) is obtained at a low PB weight fraction where a percolating PODA crystal network is formed at room temperature. The optimized sample shows excellent shape memory properties (fixity > 99%, recovery = 96%). It is shown that it is possible to mold this material into complex 3D shapes or topography with potential use in anticounterfeiting and antitampering applications.

Establishment of a NIR-based methodology for tracking the blend homogeneity of HTPB propellant slurry in the mixing process.

The hydroxyl-terminated polybutadiene (HTPB) propellants with high level of solid loadings from 80 wt% to 90 wt% consist of aluminum (Al) powder, ammonium perchlorate (AP) and HTPB. The Al/AP/HTPB adhesive system full of solid grains appears high viscosity against flow. Therefore, the mixing is a crucial procedure in the production as it directly affects the structural integrity of the finished product. This work focused on the feasibility of tracking the blend homogeneity of Al/AP/HTPB adhesive system in the mixing process through using the near-infrared (NIR) spectroscopy and orthogonal partial least squares discrimination analysis (OPLS-DA). The OPLS-DA classification models were created by variable selection, spectral pretreatment and latent variables (LVs) optimization. It had been demonstrated that the developed models presented an excellent predictability with the root mean square error of cross-validation (RMSECV) for slurries in Ⅰ, Ⅱ groups of 0.1261 and 0.0789, respectively. Meanwhile, the well-fitted models for slurries in Ⅰ, Ⅱ groups with the squared correlation coefficient (R2) of 0.806 and 0.980, exhibited separately an acceptable predictive capability with the predictive squared correlation coefficient (Q2) > 0.5. Furthermore, Euclidean distance and move block standard deviation (MBSD) as reference methods were used to validate the predictive performance of the developed models with respect to the blend homogeneity of HTPB propellant slurry. The experimental results showed that the terminal time for each batch of slurry reaching to ideal uniformity predicted by Euclidean distance/MBSD and OPLS-DA were both at 26-30 min. Therefore, it had been proved that the method we proposed was a potential tool to monitor the variation of the uniform state of HTPB propellant slurry in the mixing process.

Effect of Dilution on the Crystallization Kinetics of Neodymium-Based Rare Earth Polybutadiene Rubber.

The crystallization behavior of neodymium-based rare earth polybutadiene rubber (Nd-BR) is studied in the presence of small-molecule treated distillate aromatic extract (TDAE) and high-molecular-weight polybutadiene-isoprene copolymer rubber (BIR). Pronounced inhibitory effects on the crystallization of Nd-BR are exhibited by both materials, as evidenced by reductions in the crystallization temperature (Tc), melting point (Tm), and corresponding enthalpy change. It is found that, at equal concentrations, a greater influence on the crystallization rate is exerted by TDAE oils, whereas nucleation inhibition is more potently affected by BIR. Incomplete crystallization during cooling is exhibited by Nd-BR when the TDAE oil concentration reaches 40 parts per hundreds of rubber (PHR) (31 wt.%), or BIR achieves a 60 wt.% concentration; subsequently, a noticeable cold crystallization phenomenon is observed upon heating. Insights into the isothermal crystallization kinetics are offered by the data, which reveal that the Avrami index n value for Nd-BR predominantly ranges between 2.5 and 3.0. A decrease in the n value is induced by a small amount of TDAE oil, while a noticeable decline in the n value is observed only when the BIR concentration is 60 wt.%. A correlation between the crystallization activation energy, the concentration of TDAE oil and BIR, and the crystallization temperature is established; a negative activation energy is recorded, and a decrease in the crystallization rate is noted when both concentrations are low and the crystallization temperature exceeds -50 °C. In contrast, positive activation energy and an increase in the crystallization rate are observed when the BIR concentration reaches 60%, and the crystallization temperature resides between -50 °C and -70 °C.