最新刊期
卷 51 ， 期 11 ， 2020
- 摘要：Covalent thermosets generally exhibit robust mechanical properties and dimensional stability, but suffer from fragility, intractability and lack of recyclability. After the end-of-life usage, most thermosets are discarded, leading to severe wastes of resources and causing environmental problems. Recently, Xu, Zhang and co-workers proposed a new strategy of incorporating low-content noncovalent bonds into polymer main chains to construct tough and multi-recyclable cross-linked supramolecular polyureas. The polyureas were prepared via the copolymerization of quadruple hydrogen-bonded supramonomers and covalent monomers/crosslinkers. It was shown that the remarkable mechanical properties of covalent cross-linked polymers and excellent multiple recyclability of supramolecular polymers were well combined in the cross-linked supramolecular polyureas. The molecular design is simple but elegant. It is anticipated that the similar methodology can be used for making various cross-linked supramolecular polymer materials with superior recyclability and mechanical properties, thus providing a new and general strategy for the preparation of reprocessible and recyclable cross-linked materials.关键词：Recyclable polymer;Supramolecular polymer;Cross-linked polyurea;Quadruple hydrogen bonds;Supramonomer
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发布时间：2021-01-26 - 摘要：The dynamic covalent bond (DCB) is a kind of special bond that can cleave, reform, and exchange under external stimulus. DCBs have been evolved in a wide range of polymers like self-healing materials, shape memory materials and so on. Selenium is an essential element in human bodies. Our research group pioneered in the research of Se-containing dynamic polymers, and discovered that many Se-containing bonds are dynamic covalent bonds with very mild responsive conditions due to selenium’s unique chemical properties. This feature article is aimed to summarize the recent progress in the field of selenium-containing dynamic covalent bonds and their applications in dynamic polymeric materials. We started from the discovery of several Se-containing DCBs and the introduction of their distinct responsive features, including visible light responsive Se―Se bond and Se―Te bond, UV light responsive Se―S bond and sonication responsive Se―N bond. Then we exhibited how integrating Se-containing DCBs into polymers could produce dynamic features in materials. For instance, based on the visible light responsive diselenide dynamic exchange reaction, the diselenide bond containing polymers can achieve remote self-healing, shape memory, light plasticity and information storage. By employing the balance of swelling and strain relaxation for polymers in solvent, diselenide bond containing polyurethane could achieve 3D patterning. Apart from dynamic bulk materials, selenium-containing polymer could also serve as biomaterials. We designed a Se―N bond containing polymer assembly, which showed impressive anti-cancer effect via the transformation of Se, S based DCBs.关键词：Selenium;Dynamic covalent bond;Dynamic polymeric materials
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发布时间：2021-01-26 - 摘要：Utilizing photocatalytic materials to convert solar energy into sustainable chemical fuels is a promising route to address the global energy crisis and environmental issues. Recently, conjugated polymer-based semiconductor materials have gradually emerged as a new class of materials in photocatalysis due to their highly controllable chemical structures with tunable electronic structures. Especially, their surface active sites can be rationally constructed. Systematic investigations into the reaction pathways and the associated regulating methodologies are highly desirable to enhance the reaction efficiency and selectivity. Although it has been more than 30 years since the first report of using polymer photocatalysts for photocatalytic water splitting, the intrinsic activity of polymer photocatalysts is still very low and elucidating the reaction mechanisms is still challenging. This feature article summarizes the recent progress in characterizing surface active sites and corresponding reaction pathways in photocatalytic reactions using metal-free polymer photocatalysts. Meanwhile, future opportunities and challenges in developing polymer photocatalysts for photocatalytic energy conversion are included. It is expected to provide crucial and significant insights for designing novel polymer photocatalysts with high activity and stability in the near future.关键词：Conjugated polymers;Photocatalysis;Active sites;Reaction pathways;Solar energy conversion
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发布时间：2021-01-26 - 摘要：Fused deposition modeling (FDM) as the most common additive manufacturing technique, is a revolutionary processing method for polymer materials. FDM technique can build complicated and multifunctional components by selectively depositing one or two kinds of polymer materials layer-by-layer according to the predetermined paths. Further, the recent development of polymer nanocomposites and printing devices has broadened the applicability of FDM technique to fabricate lightweight, customized and multifunctional products for medical, electronics, aerospace and automotive areas. Although the ability to fabricate end-use products is expanding, the evolution of FDM into a fully manufacture tool is limited by several challenges including narrow material selection, weak interlayer bond and poor surface quality. In order to acquire a good knowledge of the processing-structure-performance relationship for polymer parts fabricated by FDM technique, this review firstly analyses the stringent requirements for polymer materials compatible with FDM platform, then provides a comprehensive overview on the crystallization kinetics, hierarchical structures as well as the mechanical performance of FDM-printed parts. For semicrystalline polymer materials, high shear and extension field in the nozzle is found to accelerate the crystallization kinetics and induce oriented structures and shish-kebab morphology. In this sense, FDM-printed parts can achieve mechanical properties superior to their counterparts by means of injection molding. However, the intrinsic layer-wise deposition in conjunction with non-isothermal profile during a typical FDM process tend to introduce weak bond interfaces as well as residual stresses in FDM-printed parts, leading to anisotropic mechanical properties and serious dimensional errors. This in turn puts complicated requirements for polymer materials for FDM platform, including good feeding properties (e.g. elastic modulus E/melt viscosity η larger than 3.24 × 105 s−1) and excellent printing properties (e.g. low coefficient of thermal expansion and appropriate melt viscosity). Recent efforts suggest that adding organic/inorganic additives to physically modified polymer materials is a simple and effective way to overcome both limited variety of semicrystalline materials and weak interlayer bond issues for FDM technique. In the near future, polymer composites should be well designed and screened to fit for FDM platform and also the processing-structure-property relationship for FDM-printed parts should be explored in detail so as to obtain polymer articles with excellent properties and meet the growing requirements from various areas.关键词：Fused deposition modeling;Semi-crystalline polymers;Hierarchical structures;Mechanical anisotropy
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发布时间：2021-01-26 - 摘要：Gold nanoparticles (AuNPs) with unique optothermal, catalysis and biocompatibility properties have been widely used for biosensors, catalysts, disease diagnosis and other fields. However, AuNPs are prone to aggregation during preparation due to high surface energy, which limits their practical application. Fabrication of AuNPs-polymer hybrid composites not only prevents AuNPs aggregation, but also takes advantage of both polymer and AuNPs through synergistic effect. As the most famous thermo-responsive polymer, the combination between poly(N-isopropylacrylamide) (PNIPAM) and AuNPs has been well reported. This paper summarizes the technologies for PNIPAM/AuNPs composite particles preparation through surface grafting, in situ reduction, layer-by-layer assembling and physical mixing. The temperature responsiveness and localized surface plasmon resonance (LSPR) performance of the composite particles can be modulated by controlling the size of AuNPs, the molecular weight of PNIPAM, and the ratio of PNIPAM to AuNPs. PNIPAM/AuNPs composite particles with various configurations such as core-shell, core-satellite, yolk-shell, hollow microsphere, random filled, and surface covered have been reviewed. In addition, the development prospects, and applications of PNIPAM/AuNPs composite particles in various types of sensors, nanoreactors for catalysis, optical devices, biological and other fields applications have also been discussed. Researchers can combine with advanced colorimetric analysis methods to improve the temperature response sensitivity of the composite particles, and make efforts to improve its cycle efficiency by increasing magnetic properties when the composite particles are used as catalysts.关键词：Poly(N-isopropylacrylamide);Gold nanoparticles;Composite particles;Preparation;Configuration;Application
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发布时间：2021-01-26 - 摘要：Microparticles that are capable of sustained release of nanoparticles have been widely used as drug delivery carriers for pulmonary delivery, oral delivery and intratumoral delivery, with the advantages of local retention and sustained release of nanoparticles to promote tissue penetration and cellular uptake of drugs. Herein, a strategy to prepare microparticles capable of sustainably releasing nanoparticles by droplet-based microfluidic approach was reported. Biodegradable amphiphilic polymers PCL-Dlinkm-PAMAMs were first synthesized through the reaction of 2-propionic-3-methylmaleic anhydride (CDM) modified poly( ε-caprolactone) (PCL) and poly(amidoamine) dendrimer (PAMAM), generating labile amide bonds. By tuning the feed ratio, a series of amphiphilic polymers with different PCL conjugates (PCL-Dlinkm)n-PAMAM (n = 1 − 5) were synthesized. With droplet-based microfluidic approach, these polymers were assembled into microparticles by the hydrophobic interaction of PCL segments. The size of microparticles was well-controlled by adjusting the ratio of flow rates of continuous phase and dispersed phase. It was found that regularly spherical microparticles (imCluster) were formed only when more than two PCL segments were conjugated on the amphiphilic polymer. These imCluster could sustainably release PAMAM nanoparticles after the cleavage of amide bonds in the aqueous solution. This study developed a class of microparticles with controlled size and capability of sustained release of nanoparticles.关键词：Nanoparticle release;Microparticles;Microfluidics;Controlled preparation;Biodegradable polymer
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发布时间：2021-01-26 - 摘要：Surface grafting of hydrophilic polymer brushes is an important strategy to endow the biomedical polymer materials with anti-fouling property. Immobilization of initiator is the core procedure of this strategy, which is expected to be fast and versatile. In this study, a new UV-fixable initiator is designed, which is universal for a wide range of polymeric substrates and monomers to polymerize. The initiator contains a benzophenone structure for UV immobilization on various polymeric substrates, and two bromine initiator termini, which have the potent to graft high-density polymer brushes through the single electron transfer living radical polymerization (SET-LRP). The method was first carried out by grafting poly(oligo(ethylene glycol) methyl ether acrylate) (POEGA) brush on the poly(vinyl chloride) (PVC) surface. Fibrinogen (Fg) adsorption results showed that the modified surface has good protein-resistant properties. The POEGA brush with the polymerization time of 2 hours has the lowest amount of Fg adsorption. The results of cell adhesion experiments showed that the modified surface can effectively inhibit the adhesion of Hela cells and Staphylococcus aureus. The universality of the method was further studied on different substrates and using different hydrophilic monomers. It was showed that the UV-fixable initiator can be applied to polydimethylsiloxane (PDMS), polyurethane (PU) and poly(ethylene terephthalate) (PET), and is universal to other hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA),N-acrylamide (NIPAAm) and sulfobetaine methacrylate (SBMA). Protein resistant property of these modified surfaces was comparable to that of the PVC-POEGA surface.关键词：Photo-fixable initiator;Hydrophilic polymer brush;Antifouling surface;Protein adsorption
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发布时间：2021-01-26 -
Computational Investigation on the Superstructures of Micelles from Amphiphilic DNA Block Copolymers
摘要：Amphiphilic DNA block copolymers, which are composed of DNA and polymeric blocks linked by covalent bonds, are regared as novel building units for creating hierarchically self-assembled superstructures at the mesoscales. However, insufficient understanding of the formation mechanisms and the regulation rules of self-assembled superstructures seriously impedes their potential utility in the field of nanomedicines. In this work, we build a coarse-grained model for amphiphilic block copolymers consisting of DNA blocks in selective solution, and propose a stepwise self-assembly strategy of DNA block copolymers on the basis of Brownian dynamics simulations. It is computationally demonstrated that the amphiphilic DNA block copolymers self-assemble into spherical micelles due to the solvophobic effect of polymeric blocks in the first-step of coarse-grained simulations. Driven by the hybridization of complementary DNA blocks, the binary mixtures of nano-sized micelles in the second-step of simulations are programmed to co-assemble into a series of hierarchical superstructures such as network-like, branched-like, star-like and linear topologies. The DNA-programmed superstructures of micelles can be regulated by finely tuning the sequence of DNA blocks, the stoichiometric ratio of binary mixtures of micelles and the reduced temperature of simulation system. The simulation results turn out to be in agreement with the available experimental findings. Furthermore, it is corroborated that the DNA-programmed superstructures of micelles have a close connection with the coordination number of micelles and the hybridization fraction of DNA blocks at the microscopic level.关键词：DNA;Superstructures;Block copolymers;Coarse-grained model- 95
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发布时间：2021-01-26 - 摘要：The optical polarization inversion phenomena of spherulite growth of bio-based polyamide 56 (PA56) under isothermal and non-isothermal crystallization conditions were studied. The results of isothermal crystallization by “one step procedure” indicate that the morphology and optical properties of PA56 strongly depended on the temperature. At a low temperature as 220 °C, PA56 spherulites are optically positive which have clear boundaries and bright brightness with regular shape. At a medium temperature as 235 °C, PA56 spherulites show morphological features obviously with unclear boundary, dark field of vision, belonging to the mixed spherulites type. At a high temperature as 245 °C, PA56 spherulites are positive and negative mixed petal type spherulites. The morphology and optical properties of PA56 spherulites are strongly dependent on the temperature of the isothermal crystallization, demonstated by both “two step procedure” and “three step procedure”. During the non-isothermal crystallization with a cooling rate of 10 and 30 °C/min, respectively, the birefringence characteristics of PA56 spherulites show the positive optical property. However, PA56 spherulites undergo a transition of positive ones into negative ones through a higher cooling rate (60 °C/min). High isothermal crystallization temperature and high cooling rate will lead to the acceleration of molecular chain movement during spherulite growth. The direction of the hydrogen bonding plane between the chain parallels to the spherulite radius direction and the chain becomes vertical, making the positive optical spherulite transformation negative optical characteristics.关键词：Polyamide 56;Spherulites;Crystallization kinetics;Optical polarization inversion
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发布时间：2021-01-26 - 摘要：Fluorescence imaging in the second near-infrared window (NIR-II) holds promise for real-time deep tissue imaging. In this work, we design a low-band gap conjugated polymers(pTB) with donor-acceptor (D-A) structures by Stille cross-coupling reaction, which can improve the quality of fluorescence imaging and effectiveness of photothermal therapy. In order to improve the water solubility and biocompatibility of pTB, we adopted nano-deposition technology to envelop the hydrophobic polymer pTB into amphiphilic copolymer (1,2-distearoyl-phosphatidylethanolamine-methyl-polyethyleneglycol conjugate (DSPE-mPEG)) shells for NIR-II water-soluble nanoparticles (pTB-PEG). The structure, properties and morphology of the polymer were analyzed by 1H-NMR, UV-Vis, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results show that the conjugated polymer nanoparticles have not only a good absorption peak at 831 nm, but also a large Stokes shift of 206 nm. In addition, the average hydrodynamic radius of pTB-PEG NPs was around 69 nm and spherical morphology was observed from TEM. And the nanoparticles also possess excellent photostability and good biocompatibility in physiological environment such as phosphate buffer saline (PBS), Dulbecco's Modified Eagle Medium (DMEM) and fetal bovine serum (FBS), indicating the potential for further in vivo application. More importantly, we used MTT assay to analyze photothermal treatment toward human breast cancer (4T1) cellsin vitro, and confocal laser scanning microscopy (CLSM) tests further indicated that this material has a good photothermal therapeutic effect. To study the NIR-II fluorescence characters, we firstly detected the maximum imaging depth of pTB-PEG NPsin vitro. With the help of long-wavelength emission (>1000 nm), the imaging depth is 6 mm, far exceeding the traditional near-infrared region (NIR-I) reagents. Under 808 nm laser irradiation, the high-resolution second near-infrared window (NIR-II) fluorescence imaging of healthy mouses’ blood vascular system and tumor-bearing mice was effectively achieved. In general, conjugated polymer nanoparticles (pTB-PEG) have a good biocompatibility, excellent light stability and good optical properties. It is a promising NIR-II imaging probe with a wide range of the potential for clinical imaging and live tumor imaging.关键词：Conjugated polymer;Photothermal therapeutic effect;Blood vascular system;Second near-infrared window fluorecence imaging
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发布时间：2021-01-26 - 摘要：A series of novel zirconium complexes containing bis(β-ketiminato) ligands with cyclic skeleton were efficiently synthesized through the coordination reaction of β-ketimine salt with ZrCl4. The structures of bis(β-ketiminato) zirconium chloride were characterized in detail by 1H, 13C and 19F-NMR and single crystal X-ray diffraction. Under the activation of dried methylaluminoxane (dMAO), they can efficiently catalyze ethylene oligomerization to produce linear α-olefins with high molecular weight. Its catalytic performance was much better than that of the corresponding dibenzylzirconium catalyst. The electronic effect and steric hindrance of ligand substituents have a significant effect on the catalytic performance for ethylene oligomerization. When chlorine atom was introduced into 4-position of the benzene imine ring, the withdrawing electron effect remarkably improved the catalytic activity; when tertbutyl was introduced into 4-position of the benzene imine ring, the remote steric hindrance effect of tertbutyl could greatly increase the molecular weight of oligomers while maintaining high catalytic activity. The amount of dMAO, reaction temperature, ethylene pressure and reaction time also greatly influenced the oligomerization of ethylene. Thus, changing the structure ofβ-ketiminato ligands and oligomerization conditions, the catalytic efficiency, molecular weight and molecular weight distribution of oligomers could be adjusted in a wide range.关键词：Ethylene oligomerization;Non-zirconocene catalyst;High α-olefins
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发布时间：2021-01-26
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