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Polymeric materials play critical role in many current technologies. Among them, adaptive polymeric materials with dynamic (reversible) bonds exhibit unique properties and provide exciting opportunities for various future technologies. Dynamic bonds enable structural rearrangements in polymer networks in specific conditions. Replacement of a few covalent bonds by dynamic bonds can enhance polymeric properties, e.g., strongly improve the toughness and the adhesive properties of polymers. Moreover, they provide recyclability and enable new properties, such as self-healing and shape memory effects. We briefly overview new developments in the field of polymers with dynamic bonds and current understanding of their dynamic properties. We further highlight several examples of unique properties of polymers with dynamic bonds and provide our perspectives for them to be used in many current and future applications.

Binder Jet Additive Manufacturing (BJAM) is a versatile AM technique that can form parts from a variety of powdered materials including metals, ceramics, and polymers. BJAM utilizes inkjet printing to selectively bind these powder particles together to form complex geometries. Adoption of BJAM has been limited due to its inability to form strong green parts using conventional binders. We report the discovery of a versatile polyethyleneimine (PEI) binder for silica sand that doubled the flexural strength of parts to 6.28 MPa compared with that of the conventional binder, making it stronger than unreinforced concrete (~4.5 MPa) in flexural loading. Furthermore, we demonstrate that PEI in the printed parts can be reacted with ethyl cyanoacrylate through a secondary infiltration, resulting in an increase in flexural strength to 52.7 MPa. The strong printed parts coupled with the ability for sacrificial washout presents potential to revolutionize AM in various applications including construction and tooling. The limited strength of green parts have been a major hurdle in the Binder Jet Additive Manufacturing. Here the authors apply polyethyleneimine binder to print silica sand structures with double the flexural strength of green parts and 8-fold increase in the strength upon reactive infiltration. [ABSTRACT FROM AUTHOR]

Self‐healable elastomers are extremely attractive due to their ability to prolong product lifetime. An additional function that could further expand their applications is strong adhesion force to clean and dusty surfaces. This study reports a series of autonomous self‐healable and highly adhesive elastomers (ASHA‐Elastomer) that are fabricated via a simple, efficient, and scalable process. The obtained elastomers exhibit outstanding mechanical properties with elongation at break up to 2102% and toughness (modulus of toughness) of 1.73 MJ m–3. The damaged ASHA‐Elastomer can autonomously self‐heal with full recovery of functionalities, and the healing process is not affected by the presence of water. The elastomers are found to possess an ultrahigh adhesion force up to 3488 N m−1, greatly outperforming previously reported self‐healing adhesive elastomers. Furthermore, the adhesion force of the ASHA‐Elastomer is negligibly affected by dust on the surface, in stark contrast with regular adhesive polymers that have adhesion strengths extremely sensitive to dust. The successful development of high‐toughness, autonomous self‐healable, and ultra‐adhesive elastomers will enable a wide range of applications with enhanced longevity and versatility, including their use in sealants, adhesives, and stretchable devices. [ABSTRACT FROM AUTHOR]

The effect of polymer infiltration and pyrolysis (PIP) cycles with polycarbosiloxane on the microstructure, air leak rate, and properties of SiC composites manufactured by a combination of binder jet 3D printing and PIP is reported. The density, Young's modulus and flexural strength of disk‐shaped components increased with the number of PIP cycles. In the case of density, it increased from 2.05 g/cm3 in one PIP cycle to 2.33 g/cm3 after three PIP cycles, while values of flexural strength and Young's modulus at room temperature after three PIP cycles reached 66.8 ± 2.5 MPa and 69.5 ± 2.8 GPa, respectively. Conversely, the air leak rate was found to decrease with number of PIP cycles, and it reached a value of 4 mbar‐L/s after three cycles. The instantaneous coefficient of thermal expansion of the composite was found to change minimally with the number of PIP cycles and had a value of 4 ± 1.2 ppm/°C between 200°C and 1000°C. Thermal conductivity was found to increase with number of PIP cycles and to decrease with temperature. For example, after three PIP cycles it was found to change from 6.72 ± 0.08 to 6.98 ± 0.08 W/mK at 25°C and 7.36 ± 0.08 to 7.96 ± 0.08 W/mK at 300°C. These values were lower than those of crystalline SiC because of the amorphous nature of the matrix and the presence of pores and cracks. [ABSTRACT FROM AUTHOR]

The development of high-performance materials for carbon dioxide separation and capture will significantly contribute to a solution for climate change. Herein, (bicycloheptenyl)ethyl-terminated polydimethylsiloxane (PDMSPNB) membranes with varied cross-link densities were synthesized via ring-opening metathesis polymerization. The developed polymer membranes show higher permeability and better selectivity than those of conventional cross-linked PDMS membrane. The achieved performance (CO2 permeability≈6800 Barrer; CO2/N2 selectivity≈14) is very promising for practical applications. The key to achieving this high performance is the use of an in situ cross-linking method for difunctional PDMS macromonomers, which provides lightly cross-linked membranes. By combining positron annihilation lifetime spectroscopy, broadband dielectric spectroscopy, and gas solubility measurements, key parameters necessary for achieving excellent performance have been elucidated. [ABSTRACT FROM AUTHOR]

Barriers to charge transfer at electrode-semiconductor contacts are ubiquitous and limit the applicability of organic semiconductors in electronic devices. Molecular or ionic doping near contacts can alleviate charge injection or extraction problems by enabling charge tunneling through contact barriers, but the soft nature of organic materials allows for small molecule dopants to diffuse and migrate, degrading the performance of the device and limiting effective interfacial doping. Here, it is demonstrated that contact doping in organic electronics is possible through ionic polymer dopants, which resist diffusion or migration due to their large size. Sub-monolayer deposition of non-conjugated strong polyelectrolytes, e.g., sulfonated poly(sulfone)s, at the anode-semiconductor interface of organic photovoltaics enables efficient hole extraction at the anode. The performance of contact-doped organic photo­voltaics nearly matches the performance of devices composed of traditional hole transport layers such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The degree of sulfonation of the dopant polymer and the thickness of the ionic dopant layer is shown to be critical for optimizing doping and the efficiency of the device. [ABSTRACT FROM AUTHOR]

The development of technologies to tune lignin properties for high-performance lignin-based materials is crucial for the utilization of lignin in various applications. Here, the effect of methanol (MeOH) fractionation on the molecular weight, molecular weight distribution, glass transition temperature ( Tg), thermal decomposition, and chemical structure of lignin were investigated. Repeated MeOH fractionation of softwood Kraft lignin successfully removed the low-molecular-weight fraction. The separated high-molecular-weight lignin showed a Tg of 211 °C and a char yield of 47 %, much higher than those of as-received lignin ( Tg 153 °C, char yield 41 %). The MeOH-soluble fraction of lignin showed an increased low-molecular-weight fraction and a lower Tg (117 °C) and char yield (32 %). The amount of low-molecular-weight fraction showed a quantitative correlation with both 1/ Tg and char yield in a linear regression. This study demonstrated the efficient purification or fractionation technology for lignin; it also established a theoretical and empirical correlation between the physical characteristics of fractionated lignins. [ABSTRACT FROM AUTHOR]

The recovery of uranium (U) from seawater has been investigated for over six decades in efforts to secure uranium sources for future energy production. The majority of the research activities have focused on inorganic materials, chelating polymers, and nanomaterials. Previous studies of uranium adsorption from aqueous solutions, mainly seawater, are reviewed here with a focus on various adsorbent materials, adsorption parameters, adsorption characterization, and marine studies. Continuous progress has been made over several decades, with adsorbent loadings approaching 3.2 mg U/g adsorbent in equilibrium with seawater. Further research is needed to improve first, the viability including improved capacity, selectivity, and kinetics, and second, the sorbent regeneration for multicycle use. An overview of the status of the uranium adsorption technology is provided and future research needs to make this technology commercially competitive are discussed. [ABSTRACT FROM PUBLISHER]

Due to their outstanding mechanical properties and high aspect ratios, carbon nanotubes (CNTs) are envisioned as attractive nanofillers in polymer composites. However, due to strong van der Waals interactions, deleterious aggregation of CNTs is typically observed in polymer nanocomposites. Moreover, due to low stress transfer between the matrix polymer and the nanotube filler, only limited reinforcement is obtained. We report here a novel functionalization strategy to obtain CNTs with pendant self-complementary hydrogen bonding groups in order to address these limitations. Multi-walled CNTs were functionalized with ureidopyrimidinone (UPy) groups, which display multiple hydrogen bonding. The functionalized CNTs were blended with acrylic copolymers containing pendant UPy moieties and significant enhancement in tensile performance of the nanocomposites was observed. [ABSTRACT FROM AUTHOR]

Abstract: Membrane separators reduce oxygen flux from the cathode into the anolyte in microbial fuel cells (MFCs), but water accumulation and pH gradients between the separator and cathode reduces performance. Air cathodes were spray-coated (water-facing side) with anion exchange, cation exchange, and neutral polymer coatings of different thicknesses to incorporate the separator into the cathode. The anion exchange polymer coating resulted in greater power density (1167±135mWm−2) than a cation exchange coating (439±2mWm−2). This power output was similar to that produced by a Nafion-coated cathode (1114±174mWm−2), and slightly lower than the uncoated cathode (1384±82mWm−2). Thicker coatings reduced oxygen diffusion into the electrolyte and increased coulombic efficiency (CE=56–64%) relative to an uncoated cathode (29±8%), but decreased power production (255–574mWm−2). Electrochemical characterization of the cathodes ex situ to the MFC showed that the cathodes with the lowest charge transfer resistance and the highest oxygen reduction activity produced the most power in MFC tests. The results on hydrophilic cathode separator layers revealed a trade off between power and CE. Cathodes coated with a thin coating of anion exchange polymer show promise for controlling oxygen transfer while minimally affecting power production. [ABSTRACT FROM AUTHOR]

A polyol–ligand-containing porous hollow-fiber membrane for the recovery of antimony(III) was prepared by radiation-induced graft polymerization of an epoxy-group-containing vinyl monomer, glycidyl methacrylate (GMA), and by subsequent functionalization with N-methylglucamine (NMG) and 3-amino-1,2-propanediol (APD), that form a coordination complex with Sb(III). The structure of NMG–Sb(III) and APD–Sb(III) complexes in aqueous solution were determined by electron ionization-time-of-flight mass spectrometer (ESI-TOF-MS), and the binding ratio of NMG or APD to Sb(III) is 2:1. An antimony(III) oxide solution (10 mg Sb/l, pH 11.4) was forced to permeate through the submicron-diameter pores of the polyol–ligand-containing porous hollow-fiber membranes. The equilibrium binding capacity for antimony(III) to the NMG–ligand-containing porous hollow-fiber membrane, 96 g Sb/kg, was 10 times higher than that of the APD membrane. In a further study of the NMG membrane, the equilibrium binding ratios for antimony(III) to NMG groups were all approximately 0.5, illustrating that the NMG–Sb(III) complex on the fibers was in the ratio of 2:1. The results of computational structural analysis of the NMG–Sb(III) complex were in agreement with the experimental results of binding ratio. It was verified that an antimony(III) ion formed a coordination complex with two adjacent hydroxyl groups of two NMG moieties. The length of a functional group and the distance between functional groups on the polymer brush were significant factors to bind antimony(III) through the computational simulation. [Copyright &y& Elsevier]

The cover picture illustrates reduction of CO2 emission from a power plant by using a high‐performance passive polymer membrane. Designing new membranes with high permeability and efficient CO2 separation performance is imperative for treating the large volume of flue gas with minimum energy costs. This work reports the design, synthesis, and performance of newly developed lightly cross‐linked polydimethylsiloxane–norbornene membranes that show excellent CO2 permeability and CO2/N2 selectivity. This finding can open up a new approach to enhance performance for gas separation and could elucidate additional factors important for the selective gas permeation mechanisms in rubbery polymers. More details can be found in the Full Paper by Hong et al. on page 3595 in Issue 21, 2015 (DOI: 10.1002/cssc.201500903). [ABSTRACT FROM AUTHOR]