最新刊期
卷 51 ， 期 6 ， 2020
- 摘要：Sequence-controlled polymers have been regarded as a great challenging holy grail to be ultimately achieved in polymer science. However, its synthesis is just like a Pandora’s box that is impossible to be reopened due to the lack of efficient synthetic methodologies. More recently, Yuetao Zhang’s group at Jilin University has made a big breakthrough in the synthesis of sequence-controlled polymers by using living/controlled frustrated Lewis pair (FLP) polymerization system. FLP composed of organophosphorus superbase and organoaluminum Lewis acid can rapidly incoporate four methacrylic monomers into a tripentacontablock copolymers, which is by far the world’s highest record for block numbers (about 2.5 times of the previous record) and the degree of polymerization is 50 per block. This synthetic strategy has several remarkable features such as room-temperature synthesis and easily scale-up to high multigram experiment over 110 grams; simple procedure: no additional initiator or catalyst but only sequential addition of monomer is required for per block copolymerization. It only took 30 min to synthesize such a tripentacontablock copolymers. All these features indicated the very promising prospects of this FLP polymerization system in industry, inspiring the polymer chemists’ enthusiasm to reopen the pandora’s box.关键词：Sequence-controlled multiblock copolymers;Frustrated Lewis pair;Living polymerization;Organophosphorus superbase;Pandora’ box
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发布时间：2021-01-26 - 摘要：Lightweight polymer nanocomposites with excellent processability and chemical resistance have been becoming research focus of electromagnetic interference (EMI) shielding materials. The EMI shielding performance of polymer nanocomposites greatly depends on electrical conductivity, which is in turn determined by the transport efficiency through the conducting network. However, it still remains a great challenge to construct high-quality conducting pathway in polymer matrices with least filler content by matrix-filler interface and rational structural design. Research on the key scientific issues of polymer nanocomposites was conducted, and some interesting results were achieved, including: (1) Several approaches for the design and tailoring of filler dispersion and matrix-filler interfaces were developed and a series of high-performance electrically conductive polymer nanocomposites with low percolation threshold were successfully prepared; (2) Some routes for constructing preformed three-dimensional architectures for conductance/shielding were proposed, facilitating the structural and functional integration design of polymer nanocomposites; (3) The construction of multi-interface structures in polymer nanocomposite enables the balance of high EMI shielding performance and lightweight feature. This perspective summarizes our recent research advances, and forecasts the future challenges and opportunities of polymer nanocomposites for electromagnetic shielding.关键词：Nanocomposite;Graphene;MXene;Electromagnetic interference shielding;Structure design
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发布时间：2021-01-26 - 摘要：Cellulose, the most abundant and sustainable natural polymer material in nature, is mainly contained in plants. The structures of plants are quite complex and all the plants exhibit multiple hierarchical structures. In micro-scale, plants are organized by various types of cells. The main matters of the cells exist at cell walls. For most plants, composite structures with cellulose nanofibrils and matrix such as hemicellulose and lignin were formed during the cell synthesis and growth, which play a critical role on the performance and function of plants. Nanofibrils in the plant cell walls can be individualized through chemical purification combined with nanofibrillation strategy. The as-extracted nanofibrillated cellulose exhibits one-dimensional nanofiber structure, high relative crystallinity, and excellent mechanical and thermal properties. Nanofibrillated cellulose is recognized as a promising novel polymer nanomaterial, which has been widely exploited for applications in catalysis, adsorbents, elastic conductors, optoelectronic devices, energy storage, conversion and harvest, as well as desalination. Herein, the recent progress of our group is introduced, with specific focuses on the multiple hierarchical structures of plants, cells, the biosynthesis of cell walls, nanostructures of cell walls, and the research advances of the isolation of nanofibrillated cellulose by chemical purification treatment combined with mechanical nanofibrillation strategy. The nanofibrilaltion of the cellulose pulps using a high-intensity ultrasonicator, high-speed blender and high-pressure homogenizer is discussed in detail. The main challenges and future research directions are summarized and prospected.关键词：Plant;Cell wall;Nanostructure;Nanocellulose;Nanofibrillation
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发布时间：2021-01-26 - 摘要：Macroscopic supramolecular assembly (MSA), which is mainly focused on the interfacial assembly of building blocks with a size exceeding ten micro-meter, has been a recent progress of supramolecular science. A typical MSA process resembles many interfacial phenomena such as underwater adhesion, self-healing, bio-adhesion etc.; MSA is flexible in the design, fabrication and assembly of building blocks and thus is promising to prepare 3D ordered structures of various purposes such as tissue scaffolds, flexible devices and so on. To facilitate the application of MSA, much efforts have been dedicated to understanding the assembly mechanism. The intrinsic feature of MSA is an interfacial assembly event between two macroscopic building blocks modified with massive supramolecular interactive motifs. Because of increased groups and interactive area, MSA assembly normally results in a few thermodynamic metastable structures, leading to many imprecise assemblies and less ordered final structures, which is not favourable for high performance of bulk supramolecular materials and corresponding applications. Therefore, developing strategies to achieve precise MSA for the construction of ordered supramolecular structures, has remained as a challenge of further development of MSA. In this feature article, we have briefly introduced the concept of MSA by comparing the similarity and difference with supramolecular assembly of molecular level or nano-scale, which thus relies on further insight into assembly mechanism of MSA. With further analysis of the energy landscape of MSA, we have elaborated the low-precision problem of MSA towards the formation of ordered structure, which is a new issue different from molecular assembly. More than the situation of similar components leading to different assembly geometry, MSA has an extra low-precision phenomenon of meta-stable assemblies, i.e. the matching degree of even the same assembly geometry could be diverse, due to the increasing interactive area and surface groups in an MSA event. Until now, several strategies have been reported to increase the precision of MSA structures. We have summarized two general idea from the point of thermodynamic and kinetic features of MSA. (1) The thermodynamic stability of precise and imprecise assemblies differs dramatically, which provides design room for selective assembly of precise structures. For example, fabricating anisotropic building blocks could increase the selectivity of targeted assembly geometry; applying a self-correction methodology based on a dynamic assembly/disassembly principle could efficiently convert meta-stable assemblies into stable ones. (2) Assembly kinetics and pathways could be well controlled through engineering of building blocks. Self-propulsion methods could make macroscopic building blocks to locomote similar to molecules, thus providing collision and interactive chances. Long-ranged forces (e.g. curvature forces at immiscible phases) could pre-align the matching degree of macroscopic surfaces before assembly. Efficient interfacial assembly upon contact could stabilize precise assemblies by applying a ‘flexible spacing coating’ beneath the supramolecular groups. Finally, we envisioned potential applications of precise MSA structures in fabricating complex tissue scaffolds, which requires integration of multiple materials, diverse chemical/biological factors etc.关键词：Precise macroscopic supramolecular assembly;Dynamic assembly/disassembly;Self-correction;Anisotropic building blocks;Principle of minimization of interfacial free energy
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发布时间：2021-01-26 - 摘要：Molecular bottlebrushes (MBB), as a special kind of grafted polymers, have densely grafted with side chains along a linear polymer backbone that often show a wormlike single chain morphology, representing a promising one-dimensional unimolecular nanomaterial. MBB attracts much attention from material scientists on account of its unique structure as well as unique properties. Benefited from the development of controlled living polymerization and click chemistry over the years, it allows excellent control over their synthesis and structural compositions, showing the great diversity of its structure and functionality. As compared with nanomaterials based on self-assembly, brush polymers have lots of advantages, including favorable stability, tunable sizes and morphologies, facile synthesis, and flexible compositions, that make them promising nanocarriers and capable of loading more and multiple “cargos” within one molecule. In addition, by adjusting the relative length of the backbone and side chain of molecular bottlebrush, that is, adjusting the ratio of length to diameter, nanomaterials with the shape of sphere, rod and worm can be obtained, providing a research platform for studying the physiological behavior of nanomaterials with the same chemical composition but different morphologies. Herein, this review aims to summarize the recent research progress in the application of molecular bottlebrush in the field of nanomedicine, such as small molecule drug delivery, gene loading and biological imaging, and the future development and challenges of molecular bottlebrush in nanomedicine field have also been discussed.关键词：Molecular bottlebrush;Unimolecular nanoparticle;Nanomedicine;Drug delivery system;Biological imaging
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发布时间：2021-01-26 - 摘要：In this contribution, we report a set of wide bandgap conjugated polymers (PB3TCN-C32, PB3TCN-C36, PB3TCN-C36-R, PB3TCN-C40) based on 3,4-dicyanothiophene (DCT) for use as electron donors in organic solar cells (OSCs). The polymers exhibit wide optical bandgaps (> 1.8 eV) and deep highest occupied molecular orbital (HOMO) levels due to the high electron affinity of DCT unit. The optoelectronic properties, active layer morphology, and device performance of the polymers can be tuned by side chains. As a result, high-performance solar cells with a decent power conversion efficiency (PCE) of 11.2% have been achieved by PB3TCN-C40 when using IT-4F as the electron acceptor. Noticeably, the polymers afforded a high open circuit voltage (Voc) of up to 0.92 V and an energy loss (Eloss) as low as 0.6 eV even though there is not any additional withdrawing groups such as F, Cl, or S atom on the polymers, which is superior to the leading polymer donors in the field of OSCs. These results suggest that the DCT unit hold big room for further increasing Voc and decreasing Eloss of OSCs via rational polymer design, which is desirable for application in tandem devices and in-door photovoltaics. Overall, this work demonstrated that DCT is a promising building block for constructing wide bandgap conjugated polymer with deep HOMO level for highly efficient OSCs.关键词：Organic solar cells;Conjugated polymers;Wide bandgap;Donor materials;3,4-Dicyanothiophene
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发布时间：2021-01-26 -
Influence of Grafting Point Distribution on Self-assembly Morphology of ABA Triblock Copolymer Brush
摘要：The simulated annealing method was used to study the self-assembly morphology of the symmetrical ABA triblock copolymer brush formed with one end of the A-blocks tethered onto a planar surface. The copolymer brush was immersed in a selective solvent which is poor for the A-blocks but good for the middle B-blocks. Taking the system at high grafting density as an example, the morphology of the copolymer brush aggregates during uniformal grafting, local random grafting and global random grafting were investigated, and the phase diagram was constructed. The simulation studies showed that the position distribution of the grafting point mainly affect the morphology of aggregates near the bottom layer for ABA triblock copolymer brushes. A similar self-assembled morphology could be formed during uniformal grafting, region random grafting, and global random grafting. However, the density fluctuation of the grafting point caused the micelle morphology formed under random grafting, which did not have the regular shape as that formed under uniformal grafting, and the long-range order in the microphase-segregated structures is reduced. The self-assembled morphologies of homopolymer brushes in poor solvent and AB diblock copolymer brushes in the solvent which is selective for the tethered A-blocks but poor for the top B-blocks were also investigated to further understand the results mentioned above.关键词：Triblock copolymer brush;Simulated annealing;Self-assembly;Grafting point- 81
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发布时间：2021-01-26 - 摘要：Heterophasic copolymerization of propylene based on Ziegler-Natta catalyst is one of the major methods for preparing polypropylene/ethylene propylene rubber (PP/EPR) heterophasic copolymer. Compared with traditional physical blending method, PP/EPR heterophasic copolymer can achieve even dispersion of EPR phase in PP matrix with smaller phase domain size. However, for linear EPR, it is prone to flow and aggregate during polymerization, resulting in adhesion between/among polymer particles. In addition, the PP/EPR heterophasic copolymer will undergo significant phase separation during melt processing, and the EPR droplets will aggregate into larger rubber particles. Moreover, the longer the melting processing time, the more serious the phase separation of PP phase and EPR phase, and the larger the size of rubber particles. Therefore, it is very important to control the particle morphology and EPR phase morphology of propylene heterophasic copolymer. In this study, a dichlorosilane functionalized nonconjugatedα,ω-diolefin, di(5-hexenyl)dichlorosilane, was introduced into the polymerization and participated in the random copolymerization of ethylene/propylene to prompt cross-linking of EPR. The results showed that the dichlorosilane functionalized nonconjugated α,ω-diolefin rendered the formation of cross-linked EPR, and the flow and aggregation of EPR droplets were effectively controlled. The surface morphology of PP/EPR copolymer particles was observed by SEM, which showed that all samples had good particle morphology. TEM and AFM results showed that EPR was evenly dispersed in the PP matrix with a small phase domain size. Moreover, the condensation reaction of the Si―Cl group in the presence of water further enhanced the branching/cross-linking of the copolymer, which led to a greater extent stabilized the phase morphology of the copolymer. As a result, the mechanical properties of PP/EPR copolymer were greatly improved.关键词：Ziegler-Natta catalyst;Di(5-hexenyl)dichlorosilane;Propylene heterophasic copolymer;Phase morphology
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发布时间：2021-01-26 - 摘要：Dense and uniform arrays of ZnO nanorods were successfully formed on the surface of ultra high molecular weight polyethylene (UHMWPE) fiber via low temperature hydrothermal method. The resultant microstructure could effectively enhance the interfacial bonding strength between the fiber and the resin due to its ability to form a mechanical meshing structure with the resin. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) were used to analyze the structure and properties of UHMWPE fibers before and after modification, and the monofilament pull-out experiment was performed to characterize the interfacial shear strength (IFSS) between the fiber and epoxy resin, exploring the effects of reaction time and precursor concentration on interface properties. The results showed that this gentle modification process had little effect on the intrinsic properties of the fiber, and the IFSS could be 58% higher than that of the unmodified fiber. In addition, the UHMWPE fabric was modified by the similar method, and the puncture work was improved by 20% for the UHMWPE@ZnO fabric. The puncture work was further improved by 42% when tannic acid was introduced at the interface to enhance the binding force between ZnO nanorods and fiber surface.关键词：Ultra-high molecular weight polyethylene;ZnO nanorods;Interfacial shear strength;Puncture work
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发布时间：2021-01-26 - 摘要：Silicone elastomer with self-healability can be developed by effectively constructing reversible dynamic bonds (i.e., covalent and non-covalent). Due to the low bond energy of dynamic bonds, the mechanical properties of the silicone elastomers are generally poor. Besides, the self-healing silicone elastomers are usually not transparent due to their compatibility. To solve this problem, colourless and transparent sulfhydryl silicone oils (PDMS-SH) are firstly prepared by the hydrolysis-condensation reaction. Then a transparent silicone elastomer with fast UV curing rate and excellent self-healability can be achieved by the reversible-irreversible hybrid dual-crosslinked networks, constructed by the photo-induced click reaction of PDMS-SH and vinyl-terminated silicone oil (VPS), as well as the thermal reversible dynamic cross-linked network of carboxyl- and amino-modified silicone oil. If the irradiation intensity is 70 mW/cm2, the dosage of Darocur1173 is 1.0 wt% and the molar ratio of ―SH/―Vi is 1.5/1, the thiol-ene photopolymerization has high gel content, conversion rate and polymerization rate, and will not be affected by ion cross-linked network. The formation of ionic crosslinking network and improvement of physical properties can be promoted via further heating. Moreover, the dynamic ionic crosslinking network is uniformly distributed in silicone elastomers. The increase of ion cross-linked network can effectively reduce the activation energy Ea, which is beneficial to the stress relaxation. Meanwhile, movement, dissociation and recombination of dynamic ion reversible network, as well as the formation of dual network structure can benefit from the heat treatment, so the improvement of healing efficiency will be more easily achieved. Importantly, the prepared silicone elastomer with a transmittance of 93% in visible light and healing efficiency over ~ 90% after multiple healing cycles can be acquired, Therefore, a feasible approach is provided to impart reversible ionic association induced self-healing silicone materials.关键词：Thiol-ene photopolymerization;Dynamic ion cross-linked network;Hybrid dual-crosslinked network;Self-healing silicone elastomer;Thiol-modified silicone oil
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发布时间：2021-01-26 - 摘要：Dynamic reversible covalent bonds introduced into the polymer networks enable the materials to undergo structural rearrangement and obtain processability under suitable conditions, endowing it with considerable applications in polymeric materials. In this work, particle-crosslinked vitrimer and molecular cross-linked vitrimer were obtained through the crosslinking reaction between carboxy-terminated liquid polybutadiene rubber and epoxy-containing crosslinkers (molecular crosslinker and nano-particle crosslinker). The reversibility and reprocessability of crosslinked polymer were proved by stress relaxation and melt remolding. Furthermore, linear and nonlinear dynamic rheology were used to study the influences of the size differences of crosslinker on the dynamic characteristics of vitrimer composites. In linear rheology, the double relaxation processes in dynamically cross-linked systems were observed, where fast relaxation process at high frequencies could be attributed to the contribution of the pendant chain. In contrast to the molecular cross-linked system, whose terminal relaxation was determined by the scission of active network strands, the terminal relaxation of particle cross-linked system was due to particle diffusion out of particles cage. The reversible covalent network had a weaker contribution to the modulus as compared to the particles’ contribution, but greatly slowed down the particle diffusion. In nonlinear oscillatory rheology, the comparison of Lissajous curves and strain overshoot of loss modulus among particle-crosslinked vitrimer, molecular crosslinked vitrimer and particle-filled polymer composites also verified the above results.关键词：Vitrimer;Nanoparticles;Dynamic rheology;Double relaxation
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发布时间：2021-01-26
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