最新刊期
卷 ， 期 7 ， 2017
- 摘要：Catalyst design for single-site olefin polymerization is of great scientific and industrial importance, and has attracted much attention since the pioneering work of Ziegle-Natta. "Sidearm strategy" developed in the last decades has been used successfully for designing homogenous catalyst. By which, a "sidearm" group is introduced to a basic unit, and the performance of the active center could be improved readily by modulate its shape and/or the electronic properties. This review article discloses the application of sidearm strategy in olefin polymerization catalyst design. Modification of a simple bidentate salicylaldeminate by a coordination group (OR, SR, SeR, PPh2) induced the coordination pattern variation. Of the newly-designed salicylaldiminato titanium trichlorides, both steric and electronic properties of the active species were proved to be readily tunable. Sidearm effect was obviously seen. For example, hard and small oxygen as a donor atom in sidearm induced moderate catalytic activity (104 gPE/mol(Ti)·h·atm) when it was used to polymerize ethylene in the presence of MMAO, whereas the complexes with soft and large S, Se, and P atoms as donor atom showed much higher activity (106 gPE/mol(Ti)·h·atm). The sidearm effect on thermostability of the complexes was also observed. In addition, the capability of catalyzing ethylene/comonomers (α-olefin, cycloolefin) copolymerization was also sidearm dependent. Both the activity and the incorporation of a comonomer could be improved by replacing the sidearm from bulky-SiPr to-SnPr. The newly designed titanium trichloride complexes was proved to have good polar group tolerance. Consequently, ω-alkenol, ω-alkenoic acid, and ω-alkenoic ester etc. could be incorporated into PE backbone efficiently. By this way, PPh2-and AsPh2-were zipped on polyethylene efficiently, which was proved to be efficient in catalytic[3 + 2] cycloaddition and Wittig reaction, separately. This is a simple way for the preparation of readily recovered and reused PE-supported organocatalyst. The strategy was also extended to the modification of SHOP-type catalysts, and nickel complexes bearing an alkyloxyl group as a sidearm were synthesized. The distance between Ni and O(R) is shorter than the sum of van der Waals radii of Ni and O (2.985 Å versus 3.15 Å), indicating a weak interaction between O(R) and Ni atoms. Further studies showed that the introduction of alkoxyl group improved the activity and thermostability. Based on the optimized metal complex, heterogeneous titanium catalyst was developed and used in production of ultra-high molecular weight polyethylene (UHMWPE), which is highly linear and readily processible.关键词：Sidearm strategy;Metal complexes;Polyolefin catalyst;Ethylene polymerization;Polar comonomers
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发布时间：2021-01-26 - 摘要：The conformation of a mesogen-jacketed liquid crystalline polymer (MJLCP) chain can be a supramolecular rod or sheet. Therefore, MJLCPs can serve as supramolecular mesogens to form various liquid crystalline (LC) phases, such as hexagonal columnar, columnar nematic, hexatic columnar nematic, and smectic phases. By introducing nanobuilding blocks such as one-dimensional biphenyl, two-dimensional triphenylene and three-dimensional polyhedral oligomeric silsesquioxane (POSS) into MJLCPs, the resultant polymers can self-assemble into hierarchical structures on the sub-10 nm and close-to-1 nm length scales, as proven by a combination of experimental techniques including differential scanning calorimetry, polarized light microscopy, wide-angle and small-angle X-ray scattering, and transmission electron microscopy. In general, polymers form hierarchical structures at low temperatures. With increasing temperature, the ordered structure of the nanobuilding blocks in the side chain becomes disordered first. When the temperature is further elevated, the nano-sized LC phase of the polymer as a whole will transform to another structure or become isotropic. For some polymers, a re-entrant isotropic phase exists at intermediate temperatures. Because the hierarchical structures of these polymers have the advantages of controllable sizes and monodispersity and LC polymers are capable of being aligned by external fields and forming large-scale ordered domains, such polymers have wide potential applications in organic opto-electronics, nanoporous membranes, nanolithography, and so on. This paper reviews research works on the design, synthesis, and hierarchical self-assembly of MJLCP-based homopolymers containing biphenyl, azobenzene, calamitic multi-benzene structure, triphenylene, and POSS units in the side chains.关键词：Mesogen-jacketed liquid crystalline polymer;Nanobuilding block;Biphenyl;Triphenylene;Polyhedral oligomeric silsesquioxane (POSS)
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发布时间：2021-01-26 - 摘要：Cationic polymerization is one of the most important polymerization methods in polymer science. Polyisobutylene (PIB) and butyl rubber (ⅡR) with excellent properties in gas barrier, chemical and thermal stability, and resistance to oxidation are useful materials for automotive manufacture and medical equipment. These polymers can be merely produced by cationic polymerization of isobutylene or its copolymerization with a small amount of isoprene under strictly anhydrous conditions. The living cationic polymerizations of olefins, such as isobutylene, styrene and its derivatives, have been achieved to synthesize the corresponding polymes with theoretical molecular weight and chlorine terminal groups by using BCl3 or TiCl4 as coinitiator since 1980's. This feature article is aimed to summarize the novel initiating systems for the controlled/living cationic polymerizations, transformation of polymerization character, cationic polymerization in aqueous medium with high efficiency, cationic polymerization in rotating packed bed reactor and their applications. A simple but effective FeCl3-based initiating system with low toxicity has been developed to achieve living cationic polymerization of isobutylene in the presence of isopropanol at -80℃ at much lower coinitiator concentration. It has been recognized that the living cationic polymerization could be converted to the chain-transfer dominated process, in which the rate of β-proton elimination from-CH3 groups in the growing chain ends and the chain transfer reaction to monomer were dependent on the concentrations of the complex of Lewis acid with nucleophiles or free nucleophile molecules and polymerization temperature. Based on this observation, a series of initiating systems have been developed for direct synthesis of highly reactive polyisobutylenes with more than 90 mol% of exo-olefin terminal groups. On the other hand, the cationic stereospecific polymerization of styrene and p-methylstyrene has been achieved by mediating the tightness of the growing ion pair, conformation of the last two units of the propagating polymer segment and the approaching direction of the incoming monomer, leading to formation of high molecular weight polymers with predominant isotacticity of more than 80% for meso dyad (m). The long-chain branched isotactic-rich polystyrene was in situ synthesized via cationic stereospecific polymerization of styrene by introducing a small amount of isoprene as a comonomer and branching sites as well. The environmental problems demand clean reaction processes and do use environmental friendly reaction media, in which water is no doubt the most valuable green medium. We presented the first example of highly effective cationic polymerization of IB using classic Lewis acid-based initiating systems in aqueous medium. The new continuous process of cationic polymerization in aqueous medium has been further scaled up for preparing high molecular weight PIB or butyl rubber. The cationic polymerization in the high-gravity environment generated by a rotating packed bed reactor has been successfully conducted for the first time to produce high molecular weight butyl rubber. The controlled/living cationic polymerization provides a cost-effective method to synthesize polymers with designed architecture and will be beneficial for the resulting polymer product engineering, including new chemical structure and topology, new functionality, high performance and high quality.关键词：Cationic polymerization;Controlled/Living polymerization;Polyisobutylene;Butyl rubber
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发布时间：2021-01-26 - 摘要：As the most abundant natural polymer on the earth, cellulose has been considered as the sustainable raw material of energy and chemical engineering in the future. However, because of the strong hydrogen bonding network, cellulose is unmeltable and insoluble in conventional solvents, which limits its wide utilization. Effective utilization of cellulose-based resources is becoming a hot spot in chemistry, chemical engineering and material science fields. Recently, certain ionic liquids exhibited excellent dissolving capability for cellulose, which provides a new and versatile platform for cellulose processing and functionalization. By using ionic liquids as the solvents, a variety of cellulose-based materials, including fibers, films, hydrogels, aerogels and composites have been fabricated successfully and efficiently. Among them, regenerated cellulose fibers and films with outstanding mechanical properties are being produced on the pilot scale. In addition, almost all conventional cellulose esters, a variety of novel and functional cellulose esters, especially partially and regioselectively substituted cellulose esters, and cellulose graft copolymers have been successfully synthesized using ionic liquids as reaction media. In this review article, we will summarize our research work on cellulose dissolution, processing, homogeneous derivatization and graft copolymerization with ionic liquids. We first introduce the ionic liquids with good capability for dissolving cellulose. Then, the dissolution mechanism and dissolution process of cellulose in ionic liquids, and the physical properties of cellulose/ionic liquidssolutions are also discussed. Based on the understanding of the dissolution and regeneration process of cellulose in ionic liquids, our research progress on preparation of various regenerated cellulose-based materials in ionic liquids are described. The homogeneous derivatization and graft copolymerization of cellulose to make novel functional cellulose materials are also summarized. Finally, a brief outlook for future opportunities in advancing this area is also depicted. It is hoped that this review will draw more attention of scientists and engineers to this relatively new and exciting research field.关键词：Cellulose;Ionic liquids;Dissolution;Regeneration;Derivatization
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发布时间：2021-01-26 - 摘要：Polypropylene (PP) is still one of the most important general plastics, and it is of great significance to achieve high-performance PP materials. As a semicrystalline polymer, PP is essentially polymorphism. At least five polymorphs have been identified,i.e., α, β, γ, δ and quasi-hexagonal form. Among them, β form is highly desirable, due to its excellent physical properties. However, β crystals are hard to be obtained via common crystalline condition. The polymorphic modification by adding β-nucleator (β-NA) is a powerful method for achieving dominant β form and thus tailoring the toughness and thermal stability of PP. In contrast to many past researches which focused on the roles of crystallinity and β-phase content, a new methodology has been recently suggested which optimized the physical properties of PP by controlling β-crystalline morphology. Some relevant studies include:(1) to assess the solubility and self-assembly behavior of β-NA by using temperature gradient (g-T) field; (2) to control the β-crystalline morphology by processing varables and β-NA content, and receive super-high toughness and good heat stability; (3) to reveal the rule of stretching-induced porosity in the β-PP films with different crystalline morphologies. β-NA of low-molecular-weight is soluble in the melt of PP, which will self-assemble into supermolecular structures prior to the primary crystallization of PP during the cooling process. Such supermolecular structures act as templates for the guidance of PP crystallization, resulting in special crystalline morphologies. By using the g-T technique, the dependence of β-NA solubility on molten temperature and nucleator loading could be clarified readily. Thus the crystalline morphology of β-PP is controllable, and different morphologies, such as spherulite, transcrystallinity and flower-like aggregations, are achievable through adjusting the solubility and self-assembly behavior ofβ-NA. Special crystalline morphology leads to a significant increase in the tensile ductility of β-PP. Meanwhile, the heat distortion temperature and homogeneity of microporosity are also strongly dependent on β-crystalline morphology. Obviously, the manipulation of crystalline morphology is a promising pathway to realize high-performance in crystalline polymers.关键词：Polypropylene;Polymorphs;β-Crystalline morphology;Toughness;Microporous membranep
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发布时间：2021-01-26
Feature Articles
- 摘要：In recent years, much attention has been paid to organic field-effect transistors (OFETs) due to their potential applications in flexible and wearable electronic devices. Especially for OFETs based on donor-acceptor (D-A) conjugated polymers, significant progress has been made. It is crucial to design and synthesize novel high-mobility polymers, the key components of OFETs. In this review, the recent progress of these novel polymeric materials is summarized to show the systematic effect of molecular structure on the mobility. The development, design and corresponding OFET performance are systematically summarized according to the different types of the polymers. These polymers are introduced based on the types of conventional acceptors, which include diketopyrrolopyrrole (DPP), isoindigo (ⅡD), benzodifurandione-based oligo (p-phenylene vinylene) (BDOPV), naphthalenediimide (NDI) and other novel moieties. These acceptors have been proven to be promising building blocks for high-mobility polymers due to their planar backbones, electron-deficient property, and facile chemical modifications. Based on these acceptors, p-type, ambipolar or n-type polymers can be achieved by using different donors or by introducing electron withdrawing groups onto the acceptor unit. Generally, DPP and ⅡD based polymers are p-type or ambipolar materials. In contrast, n-type transport characteristics are observed in most of the polymers based on BDOPV and NDI. To date, a high hole mobility of up to 17.8 cm2V-1s-1 has been achieved by a DPP-based polymer, while the reported highest electron mobility is of 8.5 cm2V-1s-1 in a NDI-based polymer. Here, we have summarized some key points for high-performance polymers by investigating the relationship among molecular structure, aggregation type and device performance. In detail, high-mobility polymers generally show some features including fine-tuned highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, good main-chain π-conjugation, planar backbone, high crystallinity etc. It is really crucial to develop novel building blocks to accelerate the development of this field. This review may give a helpful guide to the design and the synthesis of other novel high-mobility polymers in the future.关键词：Organic field-effect transistors;Novel semiconducting polymers;Molecular design
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发布时间：2021-01-26
Reviews
- 摘要：A new method is reported in this paper that the toughness, stiffness and heat resistance of impact polypropylene copolymer (IPC) resin could be increased simultaneously by adding a small amount of hydrophobic nano-SiO2. According to the results of scanning electron microscopy (SEM) and polarized optical microscopy (POM), a small amount of nano-SiO2 can significantly reduce both the particle size of ethylene-propylene rubber and the spherulite size of polypropylene matrix in IPC; therefore, the stiffness, the heat resistance and the toughness of IPC at room temperature and low temperature can be improved simultaneously. Energy dispersive spectroscopy (EDS) results of the composite material indicate that the nano-SiO2 particles are distributed uniformly in IPC resin. Tested in accordance with ASTM standard, the new composite material prepared in this new way shows that the flexural modulus and heat distortion temperature of IPC/nano-SiO2 composite can gain a monotonical increase as much as 8% and 9.6%. It is also found that the nano-SiO2 and the nucleating agent have synergy effect on IPC modification. When the content of nanoparticles reaches 0.7%, the impact strength gets an increase of 16.5%, the best performance among all samples. The particle sizes of ethylene-propylene rubber and spherulite size of polypropylene matrix in IPC are further reduced when nano-SiO2 and nucleating agent are added into IPC together, which improve further the properties of IPC. The flexural modulus, flexural strength, Izod notched impact strength and heat distortion temperature of IPC are increased by 18%, 15%, 10% and 20% when 0.7% of SiO2 and 0.3% of nucleating agent VP-101B are added into IPC resin. The experimental results show that, to modify IPC, use of the nano-particles and the nucleating agent together is a promising method to produce high performance IPC with high toughness, high stiffness and high heat resistance.关键词：Nano SiO2;Impact polypropylene copolymer;Structure;Property;Nucleating agent
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发布时间：2021-01-26 - 摘要：To fabricate hydrophilic/underwater superaerophobic coatings on various transparent materials, such as polystyrene (PS), polypropylene (PP), polymethylmethacrylate (PMMA), polyimide (PI) and polyethylene terephthalate (PET), a co-deposition method of polydopamine (PDA) and polyethyleneimine (PEI) is developed in this work. This method enables one to overcome the obstacle of the bubble adhesion phenomenon in the transparent materials used in underwater devices such as swim goggles and submarine windows. By adding PDA and PEI, a hydrophilic cross-linking network is formed on the material surface via Michael addition or Schiff-base reaction. The modified surface demonstrates improved hydrophilicity, and the water contact angle decreases from 80° to 66° while the submerged gas contact angle increases from 100° to 146°, exhibiting extremely low gas adhesion under water. All these materials are immersed into water during a continuous bubbling process, the PDA/PEI modified surfaces show great gas repellent ability in water on which no obvious bubbles are observed. XPS results and ellipsometer tests show that, with extended deposition time, the amount of the PDA/PEI coating and the thickness of the PDA/PEI coating grow. Meanwhile, the absorption of substrates increases slightly in the visible region with a deposition time below 6 h, which meets the requirements in high transparency and light transmittance. At the same time, the stability of the PDA/PEI coating is measured. After 10 days of submerging and shaking under water, the transparent materials maintain their hydrophilicity and underwater superaerophobicity after deposition, and the sheets exhibit extremely low gas adhesion during underwater bubbling process. Such coating can be applied on various transparent polymer materials such as PP, PMMA, PI and PET (all the submerged gas contact angles are above 140°), which are promising to be used in many submerged devices such as swim goggles, submarine windows, underwater optical lens and transparent shields.关键词：Transparent;Low bubble adhesion;Dopamine;Surface modification;Hydrophilicity
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发布时间：2021-01-26 - 摘要：The interaction between sugar and protein occurs in many important biological processes. Several methods can be used to investigate this interaction. Compared to other methods, especially those in solution, quartz crystal microbalance (QCM) can detect interactions on liquid-solid interface, which might be more useful because the proteins are usually mobilized on the chip surface by covalent bond. However, most proteins used in this study belong to plant lectins with high molecular weight and less modification sites. The efficiency of covalent modification of lectins is quite low. In this paper, we propose a new method based on dynamic covalent bond between sugar and phenylboronic acid, which dramatically increases the modification efficiency on surface. On a gold chip of QCM, block copolymer PtBMA-co-PBOB was first coated by spin-coating, glycopolymers (PMan, PGal, PGlc) was then deposited on the surface via the dynamic covalent bond between benzoboroxole (BOB) and sugars. The three glycopolymers did not show much differences due to their relatively similar binding ability to BOB-containing polymers. Control experiments proved that the coating of glycopolymers was driven by the dynamic covalent bond. The glycopolymer coating was quite stable even at low pH and high concentration corresponding to monosaccharides. The lectin Concanavalin A (Con A) was immobilized via the interaction between Con A and mannopyranoside. It was found that the amount of Con A coated on gold chip, via the above-mentioned non-covalent method, was much higher than that by the traditional covalent method. By Sauerbrey equation, the amount of Con A deposited via non-covalent method was calculated to be 2832 ng/cm2, while that of Con A via covalent method was only 424.8 ng/cm2. Moreover, on the glycopolymer surface built by non-covalent method, Con A and glyco-micelles could be deposited layer-by-layer continuously, showing the robustness of this non-covalent method. We hope that this method could be further utilized to deposit sugar-coating nanomaterials and even cells with glycocalyx on certain surfaces.关键词：Lectin;Molecular self-assembly;Dynamic covalent bond;Quartz crystal microbalance
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发布时间：2021-01-26 - 摘要：Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a biodegradable bio-based polyester, has a limited application in fibers because of its slow crystallization rate and large spherulite size. Therefore, the key to expand applications of PHBV fibers is to control its crystallization behavior. In consideration that the characteristics of the original bio-based materials PHBV will be changed after chemical modification, nano-hybrid technology is applied in this study to regulate heterogeneous nucleation behavior of PHBV after introducing nano-tungsten sulfide into PHBV system. In addition, drawing induced during melt crystallization process tends to change the crystalline structure of the polymers and thus to change the mechanical properties of PHBV fibers. Hence, effects of heterogeneous nucleation and draft induction on the crystal structure and the mechanical properties of the fibers were studied in this paper via differential scanning calorimeter (DSC), polarizing microscope (POM) equipped with hot stage, two-dimensional wide-angle X-ray diffraction (2D-WXRD) and fiber strength tester. It was found that the crystallization temperature of PHBV increased obviously with the induction of WS2 nanoparticle. When the content of WS2 was 2 wt%, the crystallization temperature of the composite materials increased to 115-130℃, about 25℃ higher than that of neat PHBV. When WS2 component was induced, the nucleation density of PHBV/WS2 composite materials was enhanced significantly and the nucleation activity Φ of the resultant composite decreased from 1.0 to 0.49 without influencing the radial growth rate of PHBV spherulites. With the increase in draft rate and WS2 content, the tensile strength of fibers increased first and then decreased. When the addition of WS2 content was 1 wt% and a uniaxial draw of 3.8 times was adapted, the crystal orientation of the fibers was enhanced, and the β-form crystal structure was produced, and thus the tensile strength of composite fibers increased from 37 MPa for pure PHBV to 155 MPa and the elongation at break increased from 2.4% to 45%.关键词：Biopolyester;PHBV;Tungsten disulfide;Heterogeneous nucleation;Draw ratio;Mechanical property
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发布时间：2021-01-26 - 摘要：Sulfur-vulcanized natural rubber is constructed by three-dimensional crosslinked networks containing plenty of monosulfidic, disulfide and polysulfide linkages, which is insoluble and infusible and hence difficult to be reprocessed. Considering that disulfide bonds possess dynamic reversibility under certain circumstances, however, we might impart rehabilitation power and processibility to vulcanized natural rubber if disulfide exchange among different disulfide and polysulfide bonds were activated. Model disulfide metathesis between equimolar small-molecule disulfides and stress relaxation of vulcanized natural rubber reveal that copper(Ⅱ) methacrylate (MA-Cu) is an effective catalyst of disulfide metathesis. Compared with CuCl 2, MA-Cu is more suitable for working with vulcanized natural rubber from the view point of environmental polarity and activation energy involved in stress relaxation. By incorporating MA-Cu during compounding of natural rubber and other ingredients as defined by industrial formulation, built-in sulfur-crosslinked networks are created after vulcanization and become dynamically reversible at or above 120℃ under the action of MA-Cu. Accordingly, rearrangement of the crosslinked networks is enabled as a result of reversible exchange of the sulfur bonds, which not only provides thermal deformability like linear polymers, but also helps to re-establish covalent bonding across cracked surfaces. Based on this finding, the vulcanized natural rubber is successfully coupled with multiple arbitrarily reshaping, intrinsic self -healing and solid-state recycling capabilities. Either the cracked or the reprocessed vulcanized natural rubber can restore mechanical properties of the original version to a great extent (~80%). Because disulfide metathesis is triggered at temperature ≥ 120℃, above the working temperatures for most natural rubber products, the materials are allowed to keep their structure and properties stability in the course of the operation. The approach proposed here has nothing to do with conventional measures of rubber reclaiming via de-crosslinking, and is eco-friendly and energy-saving. Moreover, the sulfur-crosslinked networks are not intentionally introduced into the vulcanized natural rubber but present following traditional technique. All these factors benefit popularization of the concept in practical applications.关键词：Vulcanized natural rubber;Dynamic covalent bond;Disulfide metathesis;Intrinsic self-healing;Solid-state recycling
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发布时间：2021-01-26 - 摘要：Three alternating conjugated polymers of isoindigo[7, 6-g]isoindigo (DⅡD) and vinylene,i.e., P0F, P2F and P4F, in which DⅡD units contain 0, 2 and 4 fluorine (F) atoms, respectively, were synthesized via Stille polycondensation. The number-average molecular weights (Mn) were 3.94×104, 4.45×104 and 1.93×104 for P0F, P2F and P4F, respectively. All these three polymers are largely planar and their frontier molecular orbitals are well-delocalized along conjugated backbones as revealed by density functional theory (DFT) calculation. Their 5 wt% weight loss temperatures are above 360℃. They all have very broad absorption spectra in the range of 400~1000 nm and their optical band-gaps are ca. 1.25 eV. With an increase of F atoms, both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels decreased, from -5.26 and -3.57 eV for P0F to -5.48 and -3.68 eV for P2F, and further to -5.62 and -3.82 eV for P4F. Thin films of the polymers were characterized by X-ray diffraction and atomic force microscopy (AFM). All these polymers formed ordered structure in their films with conjugated backbone adopting an edge-on arrangement. The portion of the ordered structure in the films increased from P0F to P4F, along with the increase in F-atoms in DⅡD unit. Top-gate and bottom-contact (TGBC) organic field-effect transistors (OFETs) of the polymers were fabricated with poly(methylmethacrylate) as dielectric via solution spin casting with o-dichlorobenzene. The device performance was measured under ambient conditions. With increasing the number of F atoms, the transfer behaviour of the devices based on the polymers changed from ambipolar to unipolar n-type. P0F and P2F were ambipolar polymers. Their hole mobility was 0.11 and 0.30 cm2 V-1s-1, respectively, and the electron mobility was 0.22 and 1.19 cm2 V-1s-1, respectively. P4F was a typical unipolar n-type semiconductor and its electron mobility was up to 0.18 cm2 V-1s-1. The relatively lower mobility ofP4F was attributed to its lower molecular weight. This study shows that DⅡD is a promising building block for conjugated polymers with high mobility and low band-gap.关键词：Fluorination;Isoindigo[7, 6-g]isoindigo;Conjugated polymers;Organic field-effect transistors
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发布时间：2021-01-26 - 摘要：pH responsivenanogels (DD-NGs) with different degrees of crosslinking were synthesized through dispersion polymerization. In this polymerization, dextran modified with acrylic acid (Dex-AA) served as the crosslinker. 2-(Dimethylamino) ethyl methacrylate (DMAEMA) was the monomer, thus the nanogels changed the particle size at different pH values. Ammonium persulfate (APS) and tetramethylethylenediamine (TEMED) were the initiator and the promoter, respectively. The structure and ability of mediating siRNA transfection of the DD-NGs were characterized. Also, for the DD-NGs/siRNA complexes, their particle size, zeta potential, TEM assay, pH sensitive cellular uptake (by confocal laser scan microscopy and flow cytometry) were investigated. The results indicated that the DD-NGs/siRNA complexes were positively charged and DD-NGs could mediate siRNA into tumor cells. Both in HeLa-Luc cells and Huh7-Luc cells, the complexes of the two kinds of DD-NGs and siRNA downregulated about 50% luciferase reporter gene, indicating an excellent efficiency of gene silencing. Moreover, the cellular cytotoxicity assay was performed, and both DD-NGs showed non-cytotoxicity compared with PEI25k toward HeLa-Luc cells and Huh7-Luc cells, achieving 70% cell viability at the concentration of 0.1 mg/mL. The DD-NGs/siRNA complexes showed positive charge (13-15 mV), and suitable particle size (50-100 nm) for systemic circulation at physiological pH (pH=7.4), but the complexes swelled to a much larger particle size (150-250 nm) at tumor matrix (pH=6.8), revealing a particle size changeable property with pH. Particle size measurement and TEM assay accurately supported this conclusion. Finally, flow cytometry assay was conducted to measure quantitatively the cellular uptake ability of the DD-NGs/siRNA complexes by HeLa-Luc cells at pH=7.4 and 6.8. Because of the variation in particle size, an enhanced cellular uptake at tumor matrix (pH=6.8) was obtained compared with the physiological condition at pH=7.4. CLSM images redefined this result. A much brighter fluorescence intensity generated by Cy5-labeled-RNA was observed. The as-prepared nanogels exhibited pH-enhanced tumor targeting ability and cellular uptake without introducing any targeting molecules.关键词：Dextran;Nanogels;Gene delivery;pH sensitive
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发布时间：2021-01-26 - 摘要：Polyoxometalates (abbreviated as POM), are a class of anionic metal-oxygen clusters, which consist of early transition metals in their highest oxidation states. Thus they show excellent catalytic function. In the past years we have concentrated on synthesizing POM-containing polymers, so-called poly(polyoxometalate)s, to obtain a class of novel organic-inorganic hybrid materails with good processabililty and mechnical properties of organic polymers and catalytic function of inorganic POM clusters. We connected an organic-functionalized Wells-Dawson POM with norbornene to prepare a POM-containing norbornene monomer. Then, using the ring-opening metathesis polymerization (ROMP) approach, hybrid block and random copolymers of poly(POM norbornene) and poly(hexanoic acid norbornene) (denoted as Poly(POM)m-b-Poly(COOH)n) and Poly(POM)m-r-Poly(COOH)n) were synthesized in the presence of Grubbs 3rd catalyst. These copolymers thus prepared included block copolymers with m=5 and n=50, 100, 200 and 300, as well as a random copolymer with m=5 and n=100, i.e., Poly(POM)5-r-Poly(COOH)100. The chemical structures of these hybrid copolymers were characterized by 1H-NMR, 31P-NMR and FTIR. The characterization results indicated that all the copolymers were successfully synthesized. Their absolut molecular weights and polydispersity indexes were determined by size exclusion chromatography (SEC) equipped with light scattering and infrared detectors. The results indicated that the molecular weights of the obtained hybrid copolymers were well-controlled with narrow molecular weight distribution coefficient. These hybrid copolymers were solution-processable. Their solid samples, prepared from their solution, were flexible. These hybrid copolymers also demonstrtated the catalytic activity of the parent POM cluster. The study on their capacity in catalytic oxidation of tetrahydrothiophene (THT) into cyclobutylsulfoxide (THTO) showed that their catalytic efficiencies were lower than that the hybrid homopolymer, poly(polyoxometalate) and decreased with increasing length of Poly(COOH) blocks. The findings obtained in this study offer a competitive strategy for developing novel hybrid materials with both functions of inorgnaic compnents and mechanical properties and pocessebility of the organic polymers.关键词：Polyoxometalates;Poly (polyoxometalate)s;Copolymers;ROMP;Catalytic activity
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发布时间：2021-01-26 - 摘要：One of the most challenging tasks in the fabrication of multilayer polymer light-emitting diodes (PLEDs) by solution process is to avoid the interfacial mixing between different layers. To overcome this challenge, extensive efforts have been made in developing crosslinkable materials for PLEDs. However, considering the unfavorable effects of their harsh crosslinking conditions on device performance, it is still desirable to design crosslinkable materials with moderate cured condition to satisfy the requirements of printing device in large scale in the future. Herein, a crosslinkable conjugated polymer with hole-transporting property, poly[9, 9-bis(6-furfuryloxyhexyl)-9H-fluorene-co-4, 4'-(4″-butyltriphenylamine)] (P1) with furan pendant side chains, and a small molecule crosslinker, N, N'-bis[4-(6-maleimidohexyl) phenyl]-N, N'-di-phenylbenzidine (M1) with maleimide functional group, were developed. Due to the fast Diels-Alder reaction between the maleimide in M1 and the furan group in P1, the blend films of P1 and M1 can be quickly crosslinked in extremely short time, resulting in robust hole transporting layer (HTL) films with good solvent resistance, which can overcome the interface mixing problem in solution processed multilayer PLEDs. Such a moderate cured condition (heated at 150℃ for~1 min) can decrease negative effects and the optoelectronic property of the resulting HTL film can be tuned also by changing the ratio of the small molecular crosslinker (5%-100%; maleimide/furan). The PLEDs, with the structure of ITO/poly(3, 4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/P1 + M1/emmisive layer/Ba/Al, were fabricated to investigate the effects of the crosslinker ratio on device performance. The device study results indicated that the HTLs based on P1 + M1 exhibited excellent hole-transporting/electron blocking properties and can prevent emission quenching caused by PEDOT:PSS in the traditional PEDOT:PSS based PLEDs. When M1 content is below 10%, the device displayed lower Von, higher Bmax and LEmax, and the device with HTL based on P1 + 10% M1 exhibited the best performance with LEmax of 9.0 cdA-1, Bmax of 35681 cd m-2 and Von of 3.2 V, with a higher brightness of 5000 cd m-2. Our results indicated that the Diels-Alder reaction between the maleimide and the furan groups can be used to prepare optoelectronic materials for solution processed multilayer engineering of optoelectronic devices, such as PLEDs, polymer solar cells etc..关键词：Polymer light-emitting diodes;Crosslink;Hole transporting;Click reaction
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发布时间：2021-01-26 - 摘要：The optimization of the efficacy of currently available antibiotics by taking advantage of drug delivery systems has emerged as an alternative methodology to combat the severe threat of antimicrobial resistance, which can in part bypass the challenges for developing brand new antimicrobial agents. Herein, we report a new strategy to design and fabricate bacterial enzyme-responsive polymersomes as "smart" antimicrobial delivery carriers. Lipase (Lip)-and nitroreductase (NTR)-responsive amphiphilic block copolymers (BCPs), poly(ethylene glycol)-b-poly(2-((((4-acetoxybenzyl)oxy)carbonyl)amino)ethyl methacrylate) (PEG-b-PA) and poly(ethylene glycol)-bpoly(2-((((4-nitrobenzyl)oxy)carbonyl)amino)ethyl methacrylate) (PEG-b-PN), consisting of enzyme-reactive pendent chains, were synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. The resultant BCPs self-assembled into vesicles with hydrophilic PEG coronas and hydrophobic enzyme-reactive bilayers. The as-assembled vesicles were relatively stable in aqueous solution but they underwent enzymatic degradation with the formation of core cross-linked (CCL) micelles through aminolysis reaction from decaged carbamate linkages. Several antimicrobial agents, including hydrophobic triclosan (TCN), hydrophilic antibacterial peptide (Parasin Ⅰ), and therapeutic protein lysozyme (Lyz), were encapsulated into the enzymeresponsive polymersomes either within the aqueous interiors or hydrophobic bilayer membranes. We demonstrated that the enhanced release of encapsulated antibacterial agents as well as antimicribial activities against Gram-negative (E.coli), Gram-positive (S.aureus) bacteria, and fungi (C.albicans), could be achieved when triggered by Lip or NTR.关键词：Vesicles;Enzyme-responsive;Drug nanocarriers;Bacterial drug resistance;Antimicrobial agents
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发布时间：2021-01-26 - 摘要：Here, we reported two cyclic peptide fluorescent probes for simultaneous glutathione (GSH) and Caspase-3 imaging. The cyclic peptide fluorescent probes were composed of 5(6)-carboxylfluorescein (FAM)/4-(dimethylaminoazo)benzene-4-carboxylic acid (dabcyl) fluorescence resonance energy transfer (FRET) pair, Caspase-3 specific peptide sequence Asp-Glu-Val-Asp (DEVD), glutathione (GSH) responsive disulfide bond, with Arg-Arg-Arg-Arg (RRRR) cell penetration peptide unit (short as cpCP) or without cell penetration peptide (short as CP). Due to the FRET effect between FAM and Dabcyl in CP and cpCP, the FAM fluorescence was quenched with high efficiency. GSH could cleave the disulfide bond in the probes, but it would not terminate the intracellular FRET effect. And then, Caspase-3 would further recognise and cleave the DEVD peptide sequence, which would terminate the FRET process and subsequently induce dramatically fluorescence enhancement. The fluorescence recovery of the cyclic fluorescent probe was studied with or without the presence of GSH and/or Caspase-3. The fluorescent probe exhibited good stability in cell culture medium including DMEM, MEM, RMPI1640 and trypsin. And also, the cell cytotoxicity of CP and cpCP was measured against Hela cells using MTT assay. Benefitting from the RRRR cell penetration peptide sequence, cpCP could efficiently penetrate into cells. Using staurosporine (STS) as the cell apoptosis inducer, the Caspase-3 related cell apoptosis could be observed and the real time cell apoptosis was monitoredin situ using the fluorescence recovery of cpCP. And also, doxorubicin (DOX) and cisplatin induced cell apoptosis could be monitored using cpCP as the reporter, which indicated that cpCP could be used as a tool for therapeutic efficacy evaluation. This dual-locked fluorescent probe design could extensively improve the precision for disease diagnose. Moreover, this type of cyclic peptide fluorescent probe is a versatile platform for multi-analyte imaging just by changing the response unit, which would faciliate the development of more sophisticated fluorescent probes for biological applications in the near future.关键词：Fluorescent probe;Cyclic peptide;FRET;Precise diagnosis
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发布时间：2021-01-26 - 摘要：Polymer carbon nano dots (PCNDs) have recently emerged as important nanomaterials. Although they have many attractive luminescence properties, most of them show intense emissions at short blue or green wavelengths. In this work, we designed a facile, high-output method for fabricating orange-red emissive PCNDs (centered at 604 nm, PLQY 30.64%) with two-photon fluorescence. The PCNDs were no crystal lattice polymer dots with an average diameter of 20 nm, which were detected by TEM and HRTEM. And the XPS findings indicated that C=O and graphitic N play important roles in the red emission. UV-Vis absorption spectrum of PCNDs exhibited several absorption maxima/bands at 277, 386, 541 and 575 nm (though the absorption at 541 and 575 nm was very weak), and a maximum emission wavelength of 600 nm with excitation-wavelengthindependent PL. At lower temperatures, dopamine and o-phenylenediamine underwent a dehydration reaction to form intertwined polymer chains with benzene rings and heterocycles in the backbone. Inside the PCNDs, large molecules or crosslinked polymer chains were dominant rather than carbonized structures. The PL mechanisms of the PCNDs were mainly molecule state emission or crosslink-enhanced emission. Moreover, the QY of the PCNDs was 30.64%, which was the highest value recorded for red emissive CNDs. To assess the prospects of the PCNDs as a bioimaging material, KB human oral squamous carcinoma cells were used to evaluate the cytocompatibility of the PCNDs. The cell viability of the PCNDs was determined by a methyl thiazole terazolium (MTT) assay. The MTT assays of cell viability studies suggested that the PCNDs demonstrated low cytotoxicity and were not found to pose any significant toxic effects. This result concluded that PCNDs can be used in a high concentration for imaging or other biomedical applications. Then, the luminescence stability of these PCNDs was examined by irradiating with a UV lamp for 8 h. The results turned out that almost no PL attenuation was observed. For bioimaging, PCNDs were subcutaneously injected into the back of a nude mouse, resulting in a strong fluorescence signal with good signal-to-noise ratio at excitation and emission wavelengths of 540 and 600 nm, respectively, which indicated a promising potential applicabilityin vivo imaging.关键词：Polymer carbon nano dots;Luminescence;Red luminescence;Two-photon fluorescence;Bioimaging
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发布时间：2021-01-26 - 摘要：A phenylimide-containing monomer was first introduced into PET backbone by bulk copolymerization, and a series of inherently flame-retardant, anti-dripping and smoke-suppressed copolyesters, P(ET-co-BN)n, where n denotes the molar part of BN per hundred mole of dimethyl terephthalate (DMT) (namely, BN:DMT=n:100), were successfully synthesized. Thermogravimetric analysis (TGA) indicated that the introduction of the phenylimide group not only increased the char residue of the copolyesters at high temperatures, but also greatly decreased the thermal decomposition rate of the copolyesters. The initial decomposing temperature (T5%) of the copolyesters showed a slight increase compared with that of PET, indicating that the original thermal stability was maintained. With increasing the proportion of phenylimide, the copolyesters exhibited higher glass transition temperature (Tg). Further more, the higher was the phenylimide content, the higher was the limiting oxygen index (LOI). When P(ET-co-BN)20 was tested at a high oxygen concentration of 29%, flame propagation was obviously slowed and extinguished within 52 s. After LOI test, the top zone of P(ET-co-BN)20 specimen was covered by intumescent char layer, and no dripping was observed. Compared with those of neat PET, the peak heat release rate (p-HRR), peak release smoke rate (p-RSR) and total smoke release (TSR) of P(ET-co-BN)20, obtained from cone calorimetry, were reduced by 51.5%, 44.7% and 31.1%, respectively, indicating its inherently low flammability and smoke suppression. Raman spectroscopy indicated that the formation of a thermally stable graphitic structure was promoted by the phenylimide at high temperatures. It could also be proved by SEM that the char layer of the copolyester was compact and coherent, which took an active part in isolating the unburned polymer from heat source, cutting off oxygen and preventing the volatilization of flammable fragments, resulting in excellent inherent flame retardancy and smoke suppression. Without traditional flame retardant elements, such as chloride, bromine and phosphorus, this high-performance copolyester was only composed of carbon, nitrogen, hydrogen and oxygen, which would be really eco-friendly.关键词：Phenylimide;PET Copolyester;Flame retardance;Smoke suppression;Char-forming
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发布时间：2021-01-26
Research Article
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