Search

Highly regioselective conjugate addition of isoxazol-5-ones to ESF gave N2-/C4-alkylated isoxazol-5-ones with a sulfonyl fluoride group in good to excellent yields.

Enantioselective conjugate addition of azlactones to ethylene sulfonyl fluoride has been achieved via the cooperative catalysis with (DHQD)2PHAL and a hydrogen-bond donor (HBD). This approach furnishes a facile access to a range of structurally diverse azlactone sulfonyl fluoride derivatives with good to excellent yields and enantioselectivities. The combination of azlactone and sulfonyl fluoride group produces valuable unnatural α-quaternary amino acid derivatives for the drug discovery.

An enantioselective Michael addition between N-2,2,2-trifluoroethylisatin ketimines and ethylene sulfonyl fluoride has been disclosed. This method provides a facile strategy to access a range of structurally diverse isatin-derived α-(trifluoromethyl)imine derivatives with excellent yields and enantioselectivities. The intriguing combination of α-(trifluoromethyl)amine and sulfonyl fluoride groups leads to the valuable candidates for the drug discovery.

Implantable and wearable materials, which are usually used in/on a biological body, are mostly needed with biomimetic self-healing function. To enable repeatable large-wound self-healing and volume/structure recovery, we verified a proof-of-concept approach in this work. We design a polymer hydrogel that combines temperature responsiveness with an intrinsic self-healing ability through host-guest orthogonal self-assembly between two types of poly(N-isopropylacrylamide) (PNIPAM) oligomers. The result is thermosensitive, capable of fast self-repair of microcracks based on reversible host-guest assembly. More importantly, when a large open wound appears, the hydrogel can first close the wound via volume swelling and then completely self-repair the damage in terms of intrinsic self-healing. Meanwhile, its original volume can be easily recovered by subsequent contraction. As demonstrated by the experimental data, such millimeter-level wound self-healing and volume recovery can be repeatedly carried out in response to the short-term cooling stimulus. With low cytotoxicity and good biocompatibility, moreover, this highly intelligent hydrogel is greatly promising for practical large-wound self-healing in wound dressing, electronic skins, wearable biosensors, and humanoid robotics, which can tolerate large-scale human motions.

Severe skin injuries are hard to repair and susceptible to bacterial infection. Development of a versatile antimicrobial anti-inflammatory hydrogel dressing that eliminates concern over antibiotic resistance is urgently needed but remains an elusive goal. Our research, described herein, the design and fabrication of a new family of supramolecular hydrogels based on hydroxypropyl chitosan (HPCS) and poly(N-isopropylacrylamide) (PNIPAM) may prove to be that goal. Employing the reversible cross-linking by β-cyclodextrin (β-CD) and adamantyl (AD) pre-assembly, the hydrogels can be formed in a facile one-pot method. Additionally, the structure and performance of the hydrogels can be controlled by a simple adjustment of the AD content. The obtained hydrogels exhibit an abundance of desired properties; they are injectable, thermosensitive, highly ductile, self-healable (will self-heal recurring damage to the hydrogel bandage of up to several millimeters wide), biocompatible, and have antimicrobial activity against Staphylococcus aureus when infused with dipotassium glycyrrhizinate (DG). Using a mouse full-thickness skin defect model, in vivo wound healing evaluations revealed that the DG-loaded hydrogels (HP-3/DG10) applied to the wound resulted in rapid wound closure. The hydrogels promoted efficient tissue remolding, collagen deposition, decreased inflammation and performed better than the control groups of commercial Tegaderm

An enantioselective Michael addition between

Thermoresponsive hydrogels, as a type of intelligent materials, have great potential for applications in the biomedical field. However, it is still a great challenge to develop hydrogels with regularly arranged networks and combination of high intelligence, multifunction, and good biocompatibility. Herein, we present a new family of supramolecular hydrogels constructed through the orthogonal assembly of well-defined star and linear polymer units. These units were synthesized by combining atom transfer radical polymerization (ATRP) and click reaction. The obtained hydrogels are injectable, processable and cytocompatible with thermoresponsiveness and self-healing properties. This work demonstrates the great potential of reticular design and orthogonal host–guest assembly towards the creation of highly-intelligent and multifunctional hydrogel materials.

Recent progress has seen significant advances in the mechanical performances of synthetic hydrogels. However, the mechanics of hydrogels usually suffer drastic degradation under repetitive mechanical and complicated environmental loadings. Here, we fabricate a class of biocompatible layered poly(vinyl alcohol) hydrogels by simply soaking a preformed poly(vinyl alcohol) gel in sodium silicate. The resulting hydrogels exhibit a combination of superior mechanical performances and good biocompatibility, along with exceptional chemical robustness. The layered structure is composed of a compact cover layer and a porous center layer. Both layers are composed of poly(vinyl alcohol). The network in the cover is crosslinked by ordered polarized H-bonds with swelling stability, while the porous center confines a large volume of interstitial water. The structural and crosslinking metric confers the hydrogels with capabilities to tolerate complicated mechanical and environmental loads. The optimized gel is tough (fracture energy >10 kJ m−2) and strong (fracture stress ≈ 5 MPa). The strengthening mechanism can be correlated to the layered structure, which causes the impeded flow of interstitial water. Their mechanical performance is maintained in strong acidic/alkaline, and concentrated electrolytes, and in the presence of salting-in and H-bond-breaking reagents even at elevated temperatures. We speculate that the dipole–dipole pairings of Oδ−–Hδ+⋯ Oδ−–Hδ+ in the cover layer probably generate hydrophobic microdomains. This swelling-resistant interaction may protect the hydrogels from swelling in complex aqueous envrionments. We also discuss the possible mechanism of the formation of layered structures and their crosslinkings.

Multidrug-resistant biofilms are highly resistant to current antimicrobial therapies. We have developed an antimicrobial platform that integrates the bacteria-killing phytochemical carvacrol into dynamically crosslinked polymer nanocomposites (DCPNs). Taking advantage of a reversibly crosslinked Schiff-base scaffold throughout the engineered emulsions, DCPNs exhibited long-term shelf-life and good stability in serum, while readily disassembling in acidic microenvironments. Furthermore, we demonstrated that DCPNs efficiently penetrate the biofilm matrix, eradicating both Gram-negative/positive bacteria enclosed within. Moreover, DCPNs showed no observable toxicity to fibroblast mammalian cells within the same antimicrobial concentrations necessary to eradicate MDR biofilms. Given their potent antimicrobial and stimuli-responsive dissociation characteristics in a biofilm setting, DCPNs are a suitable therapeutic platform for combating MDR bacterial infections.

In order to find a more environmentally friendly flame retardant, we have designed a novel halogen-free flame-retardant (FR) system consisting of ternary and quaternary sulfonates centered on adamantane. They are named 1,3,5-tri(phenyl-4-sodium sulfonate)adamantane (AS3) and 1,3,5,7-tetrakis(phenyl-4-sodium sulfonate)adamantane (AS4), respectively. Both kinds of FRs were synthesized and compounded with polycarbonate (PC) to study their effects on the properties of PC composites. The results show that the new FR system can improve PC flame retardancy efficiently, and has mechanical strength advantages as well. The PC composites with only 0.1 wt% AS3 or 0.08 wt% AS4 can pass vertical burning tests (UL-94) V-0 level, with increasing the value of limiting oxygen index (LOI) to 31.2% or 32.3%. Moreover, they can maintain ideal mechanical properties compared to neat PC simultaneously. Finally, the flame retardant mechanism of this system was verified via thermal analysis, morphology and chemical structure analysis of the char residues.

A series of chiral polysulfonate cyclohexyldiamine-Ni(II) catalysts were prepared via sulfur (VI) fluoride exchange click-reactions. The catalysts exhibited good catalytic activity and enantioselectivity in the Michael addition of malonates to nitroalkenes. The excellent recyclability of the catalysts was demonstrated via the reuse of the privileged catalyst 7a for ten times. The results provide a new strategy for the immobilization of chiral homogeneous catalysts.

Section 1. Icing does harm to the aerodynamic performance of aircraft and it is necessary to evaluate the aerodynamic performance of the aircraft in icing conditions. Icing wind tunnel test is the main method to study icing and anti/de-icing at present, but limited by icing wind tunnel test section size, sometimes it is impossible to carry out full scale model test in it. Instead of scaling the whole airfoil, a designed hybrid airfoil with a shorter chord length is usually used in icing wind tunnel which is composed of a leading edge geometry identical to that of the full scale leading edge and a shorter aft section. The aft section is usually designed to provide full scale flow field and droplet impingement on the leading edge. A newly developed method is to design the aft section to provide full scale airfoil surface pressure coefficient. This paper examined the “same surface pressure coefficient” design method based on icing similarity.

Inspired by naturally occurring species that allow for self-healing of nonfatal harm, self-healing polymeric materials have been prepared and represent a component of the intelligent materials family. These materials possess the inherent ability to rehabilitate damage produced during manufacturing and/or usage. The self-healing methodologies developed to date can be classified as intrinsic or extrinsic according to the method used to deliver the healing components to the target site in the material. Intrinsic self-healing operates through inter- or intra-macromolecular interactions, whereas extrinsic self-healing makes use of a pre-embedded healing agent. Extrinsic self-healing can be more easily realized in commercially available polymers because no structural modification of the matrix molecules is required. In recent years, extrinsic self-healing based on microencapsulated healing agents has attracted growing interest. Extrinsic self-healing in a variety of materials (including thermosets, thermoplastics, rigid, and elastomeric materials) has been demonstrated and offers recovery of both mechanical and non-structural functional properties. Self-healing based on microcapsules can deliver further results if combined with intrinsic self-healing. Using a bottom-up perspective, the current article presents a comprehensive review of recent progress in this field from the viewpoint of material design and preparation. The topics presented include (i) a basic overview of self-healing systems, (ii) microencapsulation techniques (e.g., in situ polymerization, interfacial polymerization, Pickering emulsion templating, miniemulsion polymerization, solvent evaporation/solvent extraction, sol–gel reaction, etc.), (iii) crack response of microcapsules, and (iv) healing chemistries (e.g., ring-opening metathesis polymerization, polycondensation, anionic ring opening polymerization, cationic polymerization, free radical polymerization, addition reaction, etc.). The strengths and weaknesses of each microencapsulation technique and type of healing chemistry are analyzed and compared. Additionally, formulation optimization (including species of healing agent and wall substance of capsules), processing, structure and property relationship, healing mechanisms, and stability are discussed. Trends and challenges are summarized at the end of the review. The scope of this review is to provide the reader with an overview of achievements to date and insight into future development for engineering applications.

Commercially available polystyrene is coupled with self-healability by exploiting a novel healing chemistry of redox cationic polymerization. In this system, iodonium bis(4-methylphenyl) hexafluorophosphate (IBH)/glycidyl methacrylate (GMA) loaded microcapsules and NaBH4 particles are embedded in the matrix through compression molding. The healant is oxygen insensitive and heat resistant so that it meets the requirement of remendable thermoplastics.

In this work, a multilayered microcapsule is proposed and prepared for use in self-healing polymers. Reactants for atom transfer radical polymerization (ATRP) are separately introduced into different places of the microcapsule to construct a latent ATRP reactor. When a polymer containing these capsules is damaged, crack induced breakage of the tiny vessels would lead to contact of the aforesaid reactants and hence autonomous polymerization of the released monomer, so that the damaged portions are re-bonded. The formation of the microcapsules goes through four steps. Optimum synthetic conditions for each step are carefully explored. The experimental results indicate that the components included in the multilayered microcapsules maintain their room temperature reactivity within the time of interest. The single microcapsule-type microreactor is provided with broad applicability as it can work alone with no need for additional chemicals and can be tailor-made according to the requirements of different polymers to be repaired.

In the past few years, extrinsic self-healing based on microencapsulated healing agents has received more and more research interest. Self-healing of a variety of materials (including thermosets and thermoplastics, rigid and elastomeric) has been demonstrated by using this technique, which enables recovery of not only mechanical properties but also nonstructural functional properties. This chapter presents a comprehensive review of the recent progress in this field from the viewpoint of material design and preparation. The trends and challenges are presented at the end of the chapter. It is hoped that the reader will be provided with an understanding of the achievements to date and an insight into future developments.

Here in this work we propose a thermally molded self-healing thermoplastic polymer containing a multilayer microcapsule-type microreactor. The latter consists of an isolated monomer and catalyst system. As the first proof-of-concept composites, commercial plastics polystyrene (PS) filled with glycidyl methacrylate (GMA)-loaded microreactors are reported. The specially designed structure of the microreactors enables them to be robust enough to survive the thermal processing already widely used in the plastics industry, like melt mixing under shear and compression molding. Upon damage of the composites and microreactors, the GMA monomer is released to the cracks and its atom transfer radical polymerization is triggered when it passes by the catalyst layer. The polymerized GMA serves as a macromolecular adhesive, which not only fills up the interstitial gap of the cracks but also is anchored to the sub-surface of the matrix forming mechanical interlocking, offering satisfactory healing efficiency at room temperature. By changing the species of healing monomer, catalyst and wall substances, the microreactors can meet the versatile requirements of different polymers, so that the approach is provided with broad applicability.