Showing papers in "Macromolecular Rapid Communications in 2018"
TL;DR: Using 3D printing, stimuli-responsive liquid crystalline elastomeric structures are created here, offering a new paradigm for active polymer system preparation and overcoming the current limitations of actuation energy available from thin-films.
Abstract: Soft matter elements undergoing programed, reversible shape change can contribute to fundamental advance in areas such as optics, medicine, microfluidics, and robotics. Crosslinked liquid crystalline polymers have demonstrated huge potential to implement soft responsive elements; however, the complexity and size of the actuators are limited by the current dominant thin-film geometry processing toolbox. Using 3D printing, stimuli-responsive liquid crystalline elastomeric structures are created here. The printing process prescribes a reversible shape-morphing behavior, offering a new paradigm for active polymer system preparation. The additive character of this technology also leads to unprecedented geometries, complex functions, and sizes beyond those of typical thin-films. The fundamental concepts and devices presented therefore overcome the current limitations of actuation energy available from thin-films, thereby narrowing the gap between materials and practical applications.
236 citations
TL;DR: This article focuses on the relationship between thermoelectric properties and the materials structure, including chemical structure, microstructure, dopants, and doping levels, which can be further improved to be comparable to inorganic counterparts in the near future.
Abstract: Thermoelectric materials can be used as the active materials in thermoelectric generators and as Peltier coolers for direct energy conversion between heat and electricity. Apart from inorganic thermoelectric materials, thermoelectric polymers have been receiving great attention due to their unique advantages including low cost, high mechanical flexibility, light weight, low or no toxicity, and intrinsically low thermal conductivity. The power factor of thermoelectric polymers has been continuously rising, and the highest ZT value is more than 0.25 at room temperature. The power factor can be further improved by forming composites with nanomaterials. This article provides a review of recent developments on thermoelectric polymers and polymer composites. It focuses on the relationship between thermoelectric properties and the materials structure, including chemical structure, microstructure, dopants, and doping levels. Their thermoelectric properties can be further improved to be comparable to inorganic counterparts in the near future.
208 citations
TL;DR: Basic physicochemical aspects as well as new material developments in the field are described, published after a recent review in Macromolecular Rapid Communications in 2013.
Abstract: Adaption and self-healing are two major principles in material science, often coupled with the placement of supramolecular moieties within a material. Proper molecular design can enable self-healing within such materials, displaying enormous potential in technology and application. Here, basic physicochemical aspects as well as new material developments in the field are described, published after a recent review in Macromolecular Rapid Communications in 2013.
171 citations
TL;DR: A miniature inching robot fabricated from a monolithic liquid crystal elastomer film, which upon visible-light excitation is capable of mimicking caterpillar locomotion on different substrates like a blazed grating and a paper surface, paving the way toward light-driven, soft, mobile microdevices capable of operating in various environments, including the close proximity of humans.
Abstract: Liquid crystal elastomers are among the best candidates for artificial muscles, and the materials of choice when constructing microscale robotic systems. Recently, significant efforts are dedicated to designing stimuli-responsive actuators that can reproduce the shape-change of soft bodies of animals by means of proper external energy source. However, transferring material deformation efficiently into autonomous robotic locomotion remains a challenge. This paper reports on a miniature inching robot fabricated from a monolithic liquid crystal elastomer film, which upon visible-light excitation is capable of mimicking caterpillar locomotion on different substrates like a blazed grating and a paper surface. The motion is driven by spatially uniform visible light with relatively low intensity, rendering the robot “human-friendly,” i.e., operational also on human skin. The design paves the way toward light-driven, soft, mobile microdevices capable of operating in various environments, including the close proximity of humans.
165 citations
TL;DR: The new 3D printing method via two-stage curing combines the attributes of outstanding printing speed, high resolution, low volume shrinkage, and excellent mechanical properties, and provides a new avenue to fabricate 3D thermosetting composites with excellent mechanical Properties and high efficiency toward high-performance and functional applications.
Abstract: Design and direct fabrication of high-performance thermosets and composites via 3D printing are highly desirable in engineering applications. Most 3D printed thermosetting polymers to date suffer from poor mechanical properties and low printing speed. Here, a novel ink for high-speed 3D printing of high-performance epoxy thermosets via a two-stage curing approach is presented. The ink containing photocurable resin and thermally curable epoxy resin is used for the digital light processing (DLP) 3D printing. After printing, the part is thermally cured at elevated temperature to yield an interpenetrating polymer network epoxy composite, whose mechanical properties are comparable to engineering epoxy. The printing speed is accelerated by the continuous liquid interface production assisted DLP 3D printing method, achieving a printing speed as high as 216 mm h-1 . It is also demonstrated that 3D printing structural electronics can be achieved by combining the 3D printed epoxy composites with infilled silver ink in the hollow channels. The new 3D printing method via two-stage curing combines the attributes of outstanding printing speed, high resolution, low volume shrinkage, and excellent mechanical properties, and provides a new avenue to fabricate 3D thermosetting composites with excellent mechanical properties and high efficiency toward high-performance and functional applications.
129 citations
TL;DR: The strategies for constructing visible and near-infrared (NIR) light-responsive azo-macromolecules are reviewed, and the potential applications of visible- and NIR-light-responsiveAzo-Macromolecule in biomedicine and solar energy conversion are highlighted.
Abstract: Azobenzene-containing macromolecules (azo-macromolecules) such as azobenzene-containing polymers (azopolymers) and azobenzene-functionalized biomacromolecules are photoswitchable macromolecules. Trans-to-cis photoisomerization in conventional azo-macromolecules is induced by ultraviolet (UV) light. However, UV light cannot penetrate deeply into issue and has a very small fraction in sunlight. Therefore, conventional azo-macromolecules are problematic for biomedical and solar-energy-related applications. In this Feature Article, the strategies for constructing visible and near-infrared (NIR) light-responsive azo-macromolecules are reviewed, and the potential applications of visible- and NIR-light-responsive azo-macromolecules in biomedicine and solar energy conversion are highlighted. The remaining challenges in the field of photoswitchable azo-macromolecules are discussed.
129 citations
TL;DR: Both nonaromatic compound of xylitol and polymers of PEG and F127 are studied and are found to be emissive in concentrated solutions and solids, verifying the rationality of the CTE mechanism and suggesting the possibility to discover and design new luminophores according to it.
Abstract: Nonaromatic luminophores without remarkable conjugates have aroused great attention Their emission mechanism, however, remains an open question Meanwhile, previous studies generally focus on aliphatic amine and/or carbonyl-containing systems; those with merely oxygen moieties (ie, ether, hydroxyl) are scarcely touched Recently, the clustering-triggered emission (CTE) mechanism is proposed to rationalize the emission of nonconventional luminophores, according to which compounds bearing purely oxygen moieties can also be emissive To check this conjecture, herein, both nonaromatic compound of xylitol and polymers of PEG and F127 are studied, which are found to be emissive in concentrated solutions and solids Furthermore, cryogenic-persistent phosphorescence of the compounds and even persistent room temperature phosphorescence of xylitol crystals are observed Additionally, their potential application as Fe3+ sensors is demonstrated These results not only verify the rationality of the CTE mechanism but also suggest the possibility to discover and design new luminophores according to it
107 citations
TL;DR: Recent progress in ionic-gel-based electronic skin (pressure/strain sensors, electric double-layer transistors, etc.), flexible displays, energy storage devices, and soft actuators are summarized.
Abstract: Ionic gels represent a novel class of stretchable materials where ionic conducting liquid is immobilized in a polymer matrix. This review focuses on the design of ionic gel materials and device fabrication of ionic-gel-based stretchable electronics. In particular, recent progress in ionic-gel-based electronic skin (pressure/strain sensors, electric double-layer transistors, etc.), flexible displays, energy storage devices, and soft actuators are summarized, followed by a discussion of challenges in developing ionic-gel-based electronics and suggestions for future research directions that might overcome those challenges.
103 citations
TL;DR: It is demonstrated that dual-crosslinked polysaccharide hydrogels are promising in wound care management and can promote cell proliferation and accelerate wound healing.
Abstract: Development of advanced wound dressing materials with rapid healing rates is in urgent demand for wound cares. A suitable microenvironment will promote cell proliferation and migration, which benefits to early wound healing and prevents inflammations and scars. In this work, N-carboxymethyl chitosan- and alginate-based hydrogels are prepared via both electrostatic interaction and divalent chelation with epidermal growth factor (EGF) payload to promote the cell proliferation and wound healing. The dual-crosslinked hydrogels are investigated in terms of rheology, water retention ability, and the release rate of EGF. Moreover, such amorphous hydrogel can promote cell proliferation and accelerate wound healing. The present study demonstrates that dual-crosslinked polysaccharide hydrogels are promising in wound care management.
100 citations
TL;DR: A new poly(dimethylsiloxane) elastomer with high stretchability, room-temperature self-healability, repeatable reprocessability, and controlled degradability is reported by incorporating an aromatic disulfide bond and imine bond.
Abstract: It is a challenge to synthesize materials that possess the properties of high stretchability and self-healability. Herein a new poly(dimethylsiloxane) elastomer with high stretchability, room-temperature self-healability, repeatable reprocessability, and controlled degradability is reported by incorporating an aromatic disulfide bond and imine bond. The as-prepared elastomer can be stretched to over 2200% of its original length. Without external stimuli, a damaged sheet can completely heal in 4 h. In addition, the elastomer can be reprocessed multiple times without obvious performance degradation and degraded controllably by three ways. All these properties of the elastomer can be ascribed to the unique dual-dynamic-covalent sacrificial system.
93 citations
TL;DR: A facile template-free thermally impacted water-induced phase separation approach for the fabrication of skin-free Thermoplastic polyurethane foam with high efficiency of oil recovery and excellent compressibility is proposed, which makes this method a promising prospect for environmental applications.
Abstract: Developing a facile large-scale strategy to fabricate polymer foams with excellent wettability and recycling its counterpart for oil-water separation is in urgent demand. Here, a facile template-free thermally impacted water-induced phase separation approach for the fabrication of skin-free thermoplastic polyurethane foam with a water contact angle of 147°, porosity more than 90%, density less than 14 mg cm-3 , and excellent compressibility (>1000 cycles) is proposed. The foams show high efficiency of oil recovery (>98%) during the squeezing and pumping oil-water separation test. Moreover, the used foams could be recycled and reused to form refresh foams without sacrificing their high performance, which makes this method a promising prospect for environmental applications.
TL;DR: In-situ attenuated total reflectance Fourier transform infrared spectroscopy reveals that the metal-ligand bond is cleaved during the damage process while metal ion is still coordinated with the ligand by stronger metal-pyridyl interaction.
Abstract: A metal-ligand crosslinked internal self-healing polyurethane is developed using low-cost and commercially available compounds. The mechanical, photoluminescent, and self-healing properties can be governed by incorporating multiple metal-ligand crosslinks with weak and strong coordination bonds and varying the metal ion. In-situ attenuated total reflectance Fourier transform infrared spectroscopy reveals that the metal-ligand bond is cleaved during the damage process while metal ion is still coordinated with the ligand by stronger metal-pyridyl interaction. The multiple metal-ligand coordination facilitates the crosslinks to be fully reformed during the repairing process, leading to the superior self-healing property.
TL;DR: PNT1 is employed as the electron acceptor in solution-processed bulk heterojunction organic solar cells, demonstrating the potential of this new type of materials for optoelectronic applications.
Abstract: The efficient synthesis of a new solution-processable n-type conjugated polymer network (PNT1) is reported through palladium-catalyzed Stille cross-coupling reaction conditions following the A3 + B2 synthetic approach. A benzo[1,2-b:3,4-b':5,6-b″]trithiophene derivative is used as the A3 knot and an alkyl functionalized naphthalenediimide is utilized as the B2 linker. The thermal, optical, and electrochemical properties are examined in detail, showing high thermal stability, absorbance in the visible part of the solar spectrum, and reversible reduction characteristics similar to those of the fullerene derivative [6,6]-phenyl-C71 -butyric acid methyl ester (PC71 BM). PNT1 is employed as the electron acceptor in solution-processed bulk heterojunction organic solar cells, demonstrating the potential of this new type of materials for optoelectronic applications.
TL;DR: A particular focus of this review is the effect of the azobenzene photoswitching on the host-guest interaction, enabling smart applications of the material.
Abstract: Metal-organic frameworks (MOFs) are nanoporous, crystalline hybrid materials, which enable various functionalities by incorporating functional organic molecules. By using organic linker molecules that possess photoswitchable azobenzene side groups, the remote control over certain properties was introduced to MOFs. Different MOF materials in the form of powders and thin films have been used to demonstrate the photoswitching. The applications of these stimuli-responsive nanoporous solids range from switching the adsorption capacity of various gases over remote-controlled release of guest molecules to continuously tunable membrane separation of molecular mixtures. A particular focus of this review is the effect of the azobenzene photoswitching on the host-guest interaction, enabling smart applications of the material. Steric hindrance, which may suppress the photoswitching in some MOF structures, is also discussed.
TL;DR: The structural design and properties of nanocomposite hydrogels are summarized, and the novel stimuli-responsive properties induced by the synergies between functional NPs and polymeric networks are reviewed.
Abstract: Hydrogels are an important class of soft materials with high water retention that exhibit intelligent and elastic properties and have promising applications in the fields of biomaterials, soft machines, and artificial tissue. However, the low mechanical strength and limited functions of traditional chemically cross-linked hydrogels restrict their further applications. Natural materials that consist of stiff and soft components exhibit high mechanical strength and functionality. Among artificial soft materials, nanocomposite hydrogels are analogous to these natural materials because of the synergistic effects of nanoparticle (NP) polymers in hydrogels construction. In this article, the structural design and properties of nanocomposite hydrogels are summarized. Furthermore, along with the development of nanocomposite hydrogel-based devices, the shaping and potential applications of hydrogel devices in recent years are highlighted. The influence of the interactions between NPs and polymers on the dispersion as well as the structural stability of nanocomposite hydrogels is discussed, and the novel stimuli-responsive properties induced by the synergies between functional NPs and polymeric networks are reviewed. Finally, recent progress in the preparation and applications of nanocomposite hydrogels is highlighted. Interest in this field is growing, and the future and prospects of nanocomposite hydrogels are also reviewed.
TL;DR: A versatile double-network (DN) hydrogel with two noncovalent crosslinked networks is synthesized by multiple hydrogen bonding (H-bonding) interactions, which enables the hydrogels high self-healing efficiency, good shape memory ability, and high mechanical strength.
Abstract: A versatile double-network (DN) hydrogel with two noncovalent crosslinked networks is synthesized by multiple hydrogen bonding (H-bonding) interactions. The DN hydrogels are synthesized via a heating-cooling photopolymerization process by adding all reactants of agar, N-acryloyl glycinamide (NAGA) and N-benzylacrylamide (NBAA) monomers, UV initiators to a single water pot. Poly(N-acryloyl glycinamide-co-N-benzyl acrylamide) (P(NAGA-co-NBAA)) with a triple amide in one side group is synthesized via UV-light polymerization between NAGA and NBAA, forming a strong intermolecular H-bonding network. Meanwhile, the intramolecular H-bonding network is formed between P(NAGA-co-NBAA) and agars. The sol-gel phase transition of agars at 86 °C generates the molecular entanglement network. Such a double network enables the hydrogel high self-healing efficiency (about 95%), good shape memory ability, and high mechanical strength (1.1 MPa). Additionally, the DN hydrogel is completely crosslinked by multiple hydrogen bonds (H-bonds) and the physical crosslinking of agar without extra potential toxic chemical crosslinker. The DN hydrogels find extensive applications in the biomedical materials due to their excellent biocompatibility.
TL;DR: A first insight into this rigid, fibrous, light-responsive hydrogel is provided, allowing the fabrication of a novel drug delivery system for controlled release of large molecules.
Abstract: Low-molecular-weight self-assembled peptides may serve as promising hydrogelators for drug delivery applications by changing their structural network in response to external stimuli. Herein, inspired by the well-studied low-molecular-weight peptide hydrogelator, fluorenyl-methoxycarbonyl-diphenylalanine (Fmoc-FF), a novel peptide is designed and synthesized to include an ultraviolet (UV)-sensitive phototrigger. Similar to Fmoc-FF, 6-nitroveratryloxycarbonyl-diphenylalanine (Nvoc-FF) self-assembles to form a 3D, self-supporting, nanofibrous hydrogel. The Nvoc-FF hydrogel exhibits good mechanical properties with a storage modulus of 40 kPa. UV irradiation of the Nvoc-FF hydrogel encapsulating insulin-fluorescein isothiocyanate (insulin-FITC) results in the cleavage of Nvoc-FF peptide to produce unmasked FF, thereby facilitating the degradation of the hydrogel and the release of insulin-FITC. This release is in linear correlation to the irradiation time. In the present study, a first insight into this rigid, fibrous, light-responsive hydrogel is provided, allowing the fabrication of a novel drug delivery system for controlled release of large molecules.
TL;DR: P pseudo free-standing tensile testing is used to obtain a comprehensive understanding of the viscoelastic properties of conjugated D-A polymers by thickness-dependent, strain rate dependent, hysteresis tests, and stress-relaxation tests, highlighting the importance of Tg for designing intrinsically stretchable conjugation polymers.
Abstract: The understanding of the structure-mechanical property relationship for semiconducting polymers is essential for the application of flexible organic electronics. Herein pseudo free-standing tensile testing, a technique that measures the mechanical property of thin films floating on the surface of water, is used to obtain the stress-strain behaviors of two semiconducting polymers, poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(2-decyltetradecyl)-3,6-di(thiophen-2-yl)diketopyrrolo[3,4-c]pyrrole-1,4-dione-alt-thienovinylthiophene (DPP-TVT) donor-acceptor (D-A) polymer. To our surprise, DPP-TVT shows similar viscoelastic behavior to P3HT, despite DPP-TVT possessing a larger conjugated backbone and much higher charge carrier mobility. The viscoelastic behavior of these polymers is due to sub room temperature glass transition temperatures (Tg ), as shown by AC chip calorimetry. These results provide a comprehensive understanding of the viscoelastic properties of conjugated D-A polymers by thickness-dependent, strain rate dependent, hysteresis tests, and stress-relaxation tests, highlighting the importance of Tg for designing intrinsically stretchable conjugated polymers.
TL;DR: A very promising material toward tissue engineering applications and more specifically, biofabrication, is presented, which maintains the excellent biocompatibility and cell interactivity of gelatin.
Abstract: In the present work, gelatin type B is modified with highly reactive norbornene functionalities (Gel-NB) following a one-pot synthesis approach to enable subsequent thiol-ene photo-click crosslinking. The modification strategy displays close control over the amount of introduced functionalities. Additionally, Gel-NB exhibits considerably improved processing capabilities in terms of two-photon polymerization when benchmarked to earlier-reported crosslinkable gelatin derivatives (e.g., gelatin-methacrylamide (Gel-MOD) and gelatin-methacrylamide-aminoethylmethacrylate (Gel-MOD-AEMA)). The improvement is especially apparent in terms of minimally required laser power (20 mW vs >= 60 mW (Gel-MOD) vs >= 40 mW (Gel-MOD-AEMA) at 100 mm s(-1) scan speed) and processable concentration range (>= 5 w/v% vs >= 10 w/v% (Gel-MOD/Gel-MOD-AEMA)). Furthermore, the proposed functionalization scheme maintains the excellent biocompatibility and cell interactivity of gelatin. Additionally, the norbornene functionalities have potential for straightforward postprocessing thiol-ene surface grafting of active molecules. As a consequence, a very promising material toward tissue engineering applications and more specifically, biofabrication, is presented.
TL;DR: This review aims to provide a critical analysis of PB-mediated ROP systems and a useful guide for the further design of organocatalysts applied to polymer synthesis.
Abstract: Over the past several years, organocatalyzed polymerization reactions have attracted considerable attention, and these efforts have led to major advances. A large number of organic compounds have been proven active for the polymerization of a large variety of monomers. In particular, phosphazene bases (PBs) are a family of extremely strong, non-nucleophilic, and uncharged auxiliary bases, and have shown their remarkable potential as organocatalysts for the ring-opening polymerization (ROP) of cyclic monomers. By deprotonation of weak acids or in combination with lithium cation, PBs significantly enhance the nucleophilicity of the initiator/chain-end, thus allowing fast and usually controlled anionic polymerization. In this feature article, the recent advances in phosphazene-catalyzed ROP of cyclic esters are summarized. This review is divided into three sections, including general features, design and synthesis, and catalytic applications. It aims to provide a critical analysis of PB-mediated ROP systems and a useful guide for the further design of organocatalysts applied to polymer synthesis. An outlook is given at the end.
TL;DR: It is hoped that this review will help stimulate more interest towards the development of light-reversible materials for energy harvesting and conversion, and their successful incorporation into a wide variety of current and future high-tech applications in devices.
Abstract: The development of stimuli-responsive polymers is among the key goals of modern materials science. The structure and properties of such switchable materials can be designed to be controlled via various stimuli, among which light is frequently the most powerful trigger. Light is a gentle energy source that can target materials remotely, and with extremely high spatial and temporal resolution easily and cheaply. Reversible light-control over molecular mechanical properties in particular has in recent years attracted great interest due to potential applications as optical-to-mechanical conversion actuators and 'devices', enabling 'molecular robotic machines'. In this review, some recent examples and emerging trends in this exciting field of research are highlighted, covering a wide variety of polymer hosts that contain azobenzene photo-reversible switches. It is hoped that this review will help stimulate more interest towards the development of light-reversible materials for energy harvesting and conversion, and their successful incorporation into a wide variety of current and future high-tech applications in devices.
TL;DR: Recent advances in PDT development are described, including therapeutic mechanisms of PDT in cancer treatments, light excitation methods, and especially recent advances of conjugated polyelectrolytes and conjugate polymer nanoparticles as photosensitizers.
Abstract: Conjugated polymers have recently attracted a great deal of attention for applications in photodynamic therapy (PDT) because of their light-harvesting capability, efficient energy transfer, and singlet oxygen generation properties. This review describes recent advances in PDT development, including therapeutic mechanisms of PDT in cancer treatments, light excitation methods, and especially recent advances of conjugated polyelectrolytes and conjugated polymer nanoparticles as photosensitizers. The future direction on PDT and further development of conjugated polymer photosensitizers are discussed. The aim of this review is to stimulate innovative ideas to synthesize a new generation of conjugated polymer photosensitizers and promote their translation to clinical applications of PDT.
TL;DR: The resultant hydrogels are responsive to multiple external stimuli, such as temperature, pH, and ion; therefore, they show the thermal-induced dual and metal ion-induced triple shape memory behaviors.
Abstract: Constructing dual or multiple noncovalent crosslinks is highly effective to improve the mechanical and stimuli-responsive properties of supramolecular physical hydrogels, due to the synergistic effects of different noncovalent bonds. Herein, a series of tough physical hydrogels are prepared by solution casting and subsequently swelling the films of poly(ureidopyrimidone methacrylate-co-stearyl acrylate-co-acrylic acid). The hydrophobic interactions between crystallizable alkyl chains and the quadruple hydrogen bonds between ureidopyrimidone (UPy) motifs serve as the dual crosslinks of hydrogels. Synergistic effects between the hydrophobic interactions and hydrogen bonds render the hydrogels excellent mechanical properties, with tensile breaking stress up to 4.6 MPa and breaking strain up to 680%. The UPy motifs promote the crystallization of alkyl chains and the hydrophobic alkyl chains also stabilize UPy-UPy hydrogen bonding. The resultant hydrogels are responsive to multiple external stimuli, such as temperature, pH, and ion; therefore, they show the thermal-induced dual and metal ion-induced triple shape memory behaviors.
TL;DR: In this review, recent research progress on nonfullerene acceptors, including small molecules and polymers, are sorted and summarized on the basis of the different characteristics.
Abstract: Recently, research on nonfullerene acceptors in organic solar cells has gradually become a hot topic due to such superior characteristics of light absorption and energy-level-convenient manipulation, multiformity of the photoactive material structures, as well as the extensive area in production compared to the fullerene derivatives. However, the nonfullerene acceptors evolved slowly before 2012 and, as a matter of fact, the power conversion efficiency values could only bear 2.0%. Strikingly, nonfullerene acceptors have developed at a fast pace since 2013, with the best device performance of 13.1% now. In this review, recent research progress on nonfullerene acceptors, including small molecules and polymers, are sorted and summarized on the basis of the different characteristics.
TL;DR: A novel enzyme-catalysis-induced reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization for preparing AB diblock copolymer nano-objects with complex morphologies at room temperature is described.
Abstract: Enzyme catalysis is a mild, efficient, and selective technique that has many applications in organic synthesis as well as polymer synthesis. Here, a novel enzyme-catalysis-induced reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization for preparing AB diblock copolymer nano-objects with complex morphologies at room temperature is described. Taking advantage of the room-temperature feature, it is shown that pure, worm-like polymer nano-objects can be readily prepared by just monitoring the viscosity. Moreover, it is demonstrated that inorganic nanoparticles and proteins can be loaded in situ into vesicles by this method. Finally, a novel oxygen-tolerant RAFT-mediated dispersion polymerization initiated by enzyme cascade reaction that can be carried out in open vessels is developed. The enzyme-initiated RAFT dispersion polymerization provides a facile platform for the synthesis of various functional polymer nano-objects under mild conditions.
TL;DR: In this review, recent research progress in the fabrication, properties, and applications of PNAs is summarized and typical applications in supercapacitors, electrocatalysts for oxygen reduction reaction, flexible electrodes, oil absorbents, adsorbents, tissue engineering, stimuli-responsive materials, and catalyst carriers are presented.
Abstract: Aerogels are gels in which the solvent is supplanted by air while the pores and networks are largely maintained. Owing to their low bulk density, high porosity, and large specific surface area (SSA), aerogels are promising for many applications. Various inorganic aerogels, e.g., silica aerogels, are intensively studied. However, the mechanical brittleness of common inorganic aerogels has seriously restricted their applications. In the past decade, nanofibers have been developed as building blocks for the construction of aerogels to improve their mechanical property. Unlike traditional frameworks constructed by interconnected particles, nanofibers can form chemically cross-linked and/or physically entangled 3D skeletons, thus showing flexibility instead of brittleness. Therefore, excellent elasticity and toughness, ultralow density, high SSA, and tunable chemical composition can be expected for the polymer nanofiber-derived aerogels (PNAs). In this review, recent research progress in the fabrication, properties, and applications of PNAs is summarized. Various nanofibers, including nanocelluloses, nanochitins, and electrospun nanofibers are included, as well as carbon nanofibers from the corresponding organic precursors. Typical applications in supercapacitors, electrocatalysts for oxygen reduction reaction, flexible electrodes, oil absorbents, adsorbents, tissue engineering, stimuli-responsive materials, and catalyst carriers, are presented. Finally, the challenges and future development of PNAs are discussed.
TL;DR: Highly stable 3D PNIPAM sponges that show a sufficiently low density and high specific pore volume, required for maximizing the amount and rate of water absorption-desorption, are presented.
Abstract: Poly(N-isopropyl acrylamide) (PNIPAM) hydrogels are well known for their temperature-dependent water uptake and release. Hence, they are ideal candidates for water management applications. However, efficiency and rate of water uptake and release, respectively, have to be optimized. Here, highly stable 3D PNIPAM sponges that show a sufficiently low density and high specific pore volume, required for maximizing the amount and rate of water absorption-desorption, are presented. They are prepared by a top-down approach based on freeze-drying a dispersion of short crosslinked PNIPAM fibers coated with crosslinked PNIPAM. The sponges have low densities (4.10-21.04 mg cm-3 ), high porosities >98%, and high specific pore volumes in the range of 47-243 cm3 g-1 depending on the concentration of the dispersions. The sponges absorb high amounts of water (≈7000%) at temperatures below the lower critical solution temperature (LCST) of PNIPAM and can release more than 80% of the absorbed water above the LCST in less than 2 min. Moreover, the water-swollen sponges are reversibly foldable, can be confined to different shapes, and have compressive elastic modulus below 10 Pa. Hence, these spongy materials are of interest not only for water management but also for biomedical applications, smart textiles, and catalysis.
TL;DR: Poly(N-isopropylacrylamide)/Laponite (PNIPAM) gradient nanocomposite hydrogel actuators are developed as temperature-controlled actuators with excellent performance using a facile electrophoresis method, showing an interesting water-promoted effect.
Abstract: Poly(N-isopropylacrylamide)/Laponite (PNIPAM/Laponite) gradient nanocomposite hydrogel actuators are developed as temperature-controlled actuators with excellent performance using a facile electrophoresis method. The actuators exhibit a rapid (20 s response time) and reversible response, as well as large deformation (bending angle of 231°), which is due to the graded forces generated by the thermo-induced anisotropic shrinkage and extension of the gradient hydrogels. A good linear relationship is observed between the maximum bending angles and the corresponding temperatures for the actuators with fixed sizes. Moreover, the gradient hydrogel with high water content achieved larger actuation angles and shorter response time than the one with low water content, showing an interesting water-promoted effect. Meanwhile, different types of actuators are designed to suit for more specific scenarios, and may be used for various applications, such as biosensing, artificial organization, and transportation of targeted objects.
TL;DR: The syntheses, characterizations, and unique properties of conjugated molecules/polymers involving a variety of bridging noncovalent bonds are disussed in the context of coplanar backbone conformation.
Abstract: Torsional conformation of the backbone of a π-conjugated molecule or macromolecule shapes its solubility, optoelectronic characteristics, rheological behaviors, and ultimately solid-state functions. In order to tailor these molecular, supramolecular, and materials properties, the desired coplanar conformation in π-conjugated systems can be locked by using dynamic noncovalent bonds. In this article, the syntheses, characterizations, and unique properties of conjugated molecules/polymers involving a variety of bridging noncovalent bonds are disussed in the context of coplanar backbone conformation. In addition, challenges in this specific field are identified and discussed for future breakthroughs in exploiting the promising potential of noncovalent-bond-bridged, π-conjugated organic materials.
TL;DR: The recent representative developments in the synthesis of sequence-controlled polymers by multicomponent reactions are highlighted to give insight on the design of novel sequence- controlled polymers with sufficient molecular diversity and complexity.
Abstract: Control over the monomer sequence during polymerization has attracted great attention in polymer science, but it remains a serious challenge. Recently, multicomponent reactions have been playing a significant role in the synthesis of sequence-controlled polymers due to their inherent advantage of combining three or more starting materials in time-saving, one-pot operations to afford complex microstructures. In this feature article, the recent representative developments in the synthesis of sequence-controlled polymers by multicomponent reactions are highlighted to give insight on the design of novel sequence-controlled polymers with sufficient molecular diversity and complexity. The main part of this article is divided into three sections according to the different polymerization strategies using multicomponent reactions: direct multicomponent polymerization, multicomponent cascade polymerization, and iterative multicomponent reaction, respectively. It is anticipated that this feature article may provide some guidance for the fabrication of sequence-controlled polymers by multicomponent reactions.