Neodymium-Mediated Coordinative Chain Transfer Polymerization of Isoprene in the Presence of External Donors.

Nd-based polydiene elastomers, including NdIR and NdBR, are regarded as indispensable key raw materials in preparing green tires with excellent performance capabilities, but their wide application is still limited by the relative higher cost of Nd precatalysts. Nd-mediated coordinative chain transfer polymerization (CCTP) of diene provides an effective strategy to reduce the precatalyst cost, because this method involves very high atom economy, i.e., each Nd molecule can generate multiple polymer chains. Nevertheless, all possible factors that could influence such CCTP behaviors are still mostly unexplored to date. In this report, the basic chemistry on the influence of external donors on the overall CCTP behaviors of isoprene was established for the first time. It was found that increasing the amount of external donors had a negative influence on the chain transfer efficiencies, resulting in gradually decreasing atom economies. Catalyst addition order studies revealed that the coordination of donors with cationic Nd active species, rather than alkylaluminium CTAs, contributed mostly to such decreased efficiencies. Moreover, it was found that when the ratio of donors and Nd compounds was higher than 1.0, the CCTP behaviors were corrupted, resulting in polymers with broad distributions, as well as resulting in low atom economies; nevertheless, when the ratio was lower than 0.5, the system still displayed CCTP characteristics, implying that the critical ratio for maintaining the CCTP was 0.5. Additionally, when such a ratio was 0.01, the high atom economy was almost the same as donor-free CCTP systems. Detailed kinetic studies at such a ratio demonstrated that the donor-contained system proceeded in a well-controlled manner, as concluded from the good linear relationship between the Mn of the PIps against the polymer yields, as well as the good linearity between the Mn against the (IP)/(Nd) ratios. Such maintained CCTP properties also allowed for seeding two-step polymerizations to prepare diblock copolymers with precisely controlled molecular weights. Expanding the types of donors to more phosphine, oxygen, and nitrogen containing compounds showed that they also affected the CCTP behaviors depending on their steric and electronic properties.

Synthesis of PNIPAAm-g-P4VP Microgel as Draw Agent in Forward Osmosis by RAFT Polymerization and Reverse Suspension Polymerization to Improve Water Flux.

Microgels have unique and versatile properties allowing their use in forward osmosis areas as a draw agent. In this contribution, poly(4-vinylpyridine) (P4VP) was synthesized via RAFT polymerization and then grafted to a poly(N-Isopropylacrylamide) (PNIPAAm) crosslinking network by reverse suspension polymerization. P4VP was successfully obtained by the quasiliving polymerization with the result of nuclear magnetic resonance and gel permeation chromatography characterization. The particle size and particle size distribution of the PNIPAAm-g-P4VP microgels containing 0, 5, 10, 15 and 20 wt% P4VP were measured by means of a laser particle size analyzer. It was found that all the microgels were of micrometer scale and the particle size was increased with the P4VP load. Inter/intra-molecular-specific interactions, i.e., hydrogen bond interactions were then investigated by Fourier infrared spectroscopy. In addition, the water flux measurements showed that all the PNIPAAm-g-P4VP microgels can draw water more effectively than a blank PNIPAAm microgel. For the copolymer microgel incorporating 20 wt% P4VP, the water flux was measured to be 7.48 L∙m-2∙h-1.

A Dual-Surface Amidoximated Halloysite Nanotube for High-Efficiency Economical Uranium Extraction from Seawater.

By chemical cross-linking the amidoxime group onto dual-surfaces of natural ore materials, namely halloysite nanotubes (HNTs), an efficient adsorbent, AO-HNTs, is developed. AO-HNTs show high uranium adsorption capacity of 456.24 mg g-1 in 32 ppm uranium-spiked simulated seawater. In natural seawater, AO-HNTs reach the high uranium extraction capacity of 9.01 mg g-1 after 30 days' field test. The dual-surface amidoximated hollow nanotubular AO-HNTs exhibit more coordination active sites for uranium adsorption, which is attributed to the high and fast uranium adsorption capacity. Because of the stable natural ore structure, AO-HNTs also show long service life. Benefiting from the low cost of HNTs, the cost for uranium extraction from seawater is close to the uranium price in the spot uranium market, suggesting that AO-HNTs could be used for economical extraction of uranium from the oceans.

Graphene networks and their influence on free-volume properties of graphene-epoxidized natural rubber composites with a segregated structure: rheological and positron annihilation studies.

Epoxidized natural rubber-graphene (ENR-GE) composites with segregated GE networks were successfully fabricated using the latex mixing combined in situ reduced technology. The rheological behavior and electrical conductivity of ENR-GE composites were investigated. At low frequencies, the storage modulus (G') became frequency-independent suggesting a solid-like rheological behavior and the formation of GE networks. According to the percolation theory, the rheological threshold of ENR-GE composites was calculated to be 0.17 vol%, which was lower than the electrical threshold of 0.23 vol%. Both percolation thresholds depended on the evolution of the GE networks in the composites. At low GE concentrations (<0.17 vol%), GE existed as individual units, while a "polymer-bridged GE network" was constructed in the composites when GE concentrations exceeded 0.17 vol%. Finally, a "three-dimensional GE network" with percolation conductive paths was formed with a GE concentration of 0.23 vol%, where a remarkable increase in the conductivity of ENR-GE composites was observed. The effect of GE on the atom scale free-volume properties of composites was further studied by positron annihilation lifetime spectroscopy and positron age momentum correlation measurements. The motion of ENR chains was retarded by the geometric confinement of "GE networks", producing a high-density interfacial region in the vicinity of GE nanoplatelets, which led to a lower ortho-positronium lifetime intensity and smaller free-volume hole size.

Rapid Synthesis of Functions-Integrated Hydrogel as a Self-Powered Wound Dressing for Real-Time Drug Release and Health Monitoring.

A bio-hydrogel is prepared via a low-cost and time-saving strategy and is studied as a self-powered wound dressing for precision medicine and health monitoring. Promoted by a dual self-catalytic pair composed of Fe3+ and catechol, gelation time is dramatically accelerated to 15 s and the hydrogel can be freely modeled at -18 °C without losing flexibility. As smart wound dressing, the required properties such as self-healing, self-adhesion, antibacterial, and sensing stability, are integrated into one hydrogel. TA@CNC offers abundant hydrogen bond and metal-ligand coordination which facilitate the hydrogel with a self-healing efficiency of 91.6%. Owing to the catechol in TA@CNC, hydrogel can adhere to multiple substrates including skin, and show good antibacterial activity. Inspired by a fruit battery, a self-powered wound dressing is fabricated, which exhibits excellent correlation and efficiency in real-time monitoring of body activity and drug release. In vivo experiments prove that efficient drug release of hydrogel dressing significantly accelerate wound healing. Additionally, the dressing exhibits excellent biocompatibility and has no negative impacts on organs. Herein, a smart wound dressing that is different from the traditional way is proposed. As a self-powered device, it can be integrated with wireless devices and is expected to participate in promising applications.

Transparent Silica Aerogels: Optical and Chemical Design, Controlled Synthesis, and Emerging Applications.

Transparent silica aerogel, serving as one typical porous and transparent material, possesses various unique features (e. g., large amounts of pores and interfaces, super-lightweight, super thermal insulation, low refractive index similar to gas), and it has attracted great attention in the fields of science, technology, engineering, art, and others. Transparency is one important evaluation index of transparent silica aerogel, and it was influenced by various factors such as raw materials, sol-gel reactions, phase separation, and drying methods. The structure design and fabrication of transparent silica aerogel is one huge and fine engineering. In this review, the optical/chemical guidance and design for the preparation of transparent silica aerogels are discussed, and typical applications, such as Cherenkov detectors, solar energy collection, lighting systems, and transparent fabric, were also discussed. Finally, a future outlook on the opportunities and challenges of transparent silica aerogels was proposed.

Design and Optimization of NR-Based Stretchable Conductive Composites Filled with MoSi2 Nanoparticles and MWCNTs: Perspectives from Experimental Characterization and Molecular Dynamics Simulations.

Stretchable conductive composites play a pivotal role in the development of personalized electronic devices, electronic skins, and artificial implant devices. This article explores the fabrication and characterization of stretchable composites based on natural rubber (NR) filled with molybdenum disilicide (MoSi2) nanoparticles and multi-walled carbon nanotubes (MWCNTs). Experimental characterization and molecular dynamics (MD) simulations are employed to investigate the static and dynamic properties of the composites, including morphology, glass transition temperature (Tg), electrical conductivity, and mechanical behavior. Results show that the addition of MoSi2 nanoparticles enhances the dispersion of MWCNTs within the NR matrix, optimizing the formation of a conductive network. Dynamic mechanical analysis (DMA) confirms the Tg reduction with the addition of MWCNTs and the influence of MoSi2 content on Tg. Mechanical testing reveals that the tensile strength increases with MoSi2 content, with an optimal ratio of 4:1 MoSi2:MWCNTs. Electrical conductivity measurements demonstrate that the MoSi2/MWCNTs/NR composites exhibit enhanced conductivity, reaching optimal values at specific filler ratios. MD simulations further support experimental findings, highlighting the role of MoSi2 in improving dispersion and mechanical properties. Overall, the study elucidates the synergistic effects of nanoparticles and nanotubes in enhancing the properties of stretchable conductive composites.

Donor-acceptor conjugated polymers based on a pentacyclic aromatic lactam acceptor unit for polymer solar cells.

A series of donor­acceptor (D­A) conjugated polymers P1­P4 was synthesized by copolymerization of a novel pentacyclic aromatic lactam acceptor unit, thieno[20,30:5,6]pyrido[3,4-g]thieno[3,2-c]-isoquinoline-5,11(4H,10H)-dione (TPTI), with a donor unit, benzo-[1,2-b:4,5-b0]dithiophene (BDT) or dithieno[3,2-b:20,30-d]silole (DTS). The effect of the donor units and the side chains on TPTI on polymer properties and solar cell performance was investigated. Bulk heterojunction solar cells based on P1 and PC71BM afforded the highest power conversion efficiency (PCE) of 5.30%.

Molecular Dynamic and Dissipative Particle Dynamic Simulation on the Miscibility of NR/CR Blends.

Natural rubber (NR) exhibits good elasticity, flexural resistance, wear resistance, and excellent mechanical properties, and it has been widely used in aerospace, transportation, medical, and health fields. For NR, however, the resistance to thermal-oxidation and ozone aging is fairly poor. Although aging properties of NR can be significantly improved with the incorporation of chloroprene rubber (CR) according to some references, the miscibility between NR and CR, the morphologies of the binary blends, and so on are revealed ambiguously. In this work, molecular dynamics simulation (MD) and dissipative particle dynamics (DPD) simulation were carried out to predict the compatibility between natural rubber and chloroprene rubber in view of Flory-Huggins parameters. The morphologies of the blends were obtained with the use of the DPD method. The simulation results were furtherly examined by means of Fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical analysis (DMA). It was found that the miscibility between NR and CR is poor. Nevertheless, the miscibility could be improved when the content of CR is 50% or 90%. In addition, spinodal decomposition with a critical temperature of 390 K would take place according to the phase diagram. Microphase structure such as spherical, lamellar, and bicontinuous phases can be found with different contents of CR in the blends with the results of morphologies analysis.

Combination strategy of large interlayer spacing and active basal planes for regulating the microwave absorption performance of MoS2/MWCNT composites at thin absorber level.

Recently, molybdenum disulfide (MoS2)/carbon has become a promising candidate for efficient microwave absorption. However, it is still challenging to simultaneously optimize the synergy of impedance matching and loss capability at the level of a thin absorber. Here, a new adjustment strategy is proposed by changing the concentration of precursor l-cysteine for MoS2/multi-walled carbon nanotubes (MWCNT) composites to unlock the basal plane of MoS2 and expand the interlayer spacing from 0.62 nm to 0.99 nm, leading to improved packing of MoS2 nanosheets and more active sites. Therefore, the tailored MoS2 nanosheets exhibit abundant sulfur-vacancies, lattice-oxygen, more metallic 1T-phase, and higher surface area. Such sulfur-vacancies and lattice-oxygen promote the electronic asymmetric distribution at the solid-air interface of MoS2 crystals and induce stronger microwave attenuation through interface/dipole polarization, which is further verified by first-principles calculations. In addition, the expansion of the interlayer spacing induces more MoS2 to deposit on the MWCNT surface and increases the roughness, improving the impedance matching and multiple scattering. Overall, the advantage of this adjustment method is that while optimizing impedance matching at the thin absorber level, composite still maintains a high attenuation capacity, which means enhancing the attenuation performance of MoS2 itself offsets the weakening of the composite's attenuation ability caused by the decrease in the relative content of MWCNT components. Most importantly, adjusting impedance matching and attenuation ability can be easily implemented by separate control of l-cysteine content. As a result, the MoS2/MWCNT composites achieve a minimum reflection loss value of -49.38 dB and an effective absorption bandwidth of 4.64 GHz at a thickness of only 1.7 mm. This work provides a new vision for the fabrication of thin MoS2-carbon absorbers.