最新刊期
卷 ， 期 12 ， 2017
-
Controlling Cellular Structure of Polypropylene Foams through Heat of Phase Transition of Water 增强出版
摘要：At present, a problem in the field of polymer foaming is how to efficiently prepare polymer foamed products with large size, especially for semi-crystalline polymers (for example, polypropylene (PP)). A difficulty is that the polymer melt inside the foam samples cannot be quickly cooled after the formation of foam structure, resulting in collapse and merging of the cell structure, which may lead to form the gradient cellular structure between inside and outer layers. This problem severely restricts the development of polymer foaming technology and the application of foam products. In this work, we use PP as an example to demonstrate a novel foaming method with water as an in situ cooling medium for the first time. PP/hydrophilic polyethylene glycol (PP/PEG) blends are prepared by melt mixing, and then the blends are subjected to moulding physical foaming using CO2 as a foaming agent and water as an assistant foaming agent. The temperatures in the surface and core of the foamed samples are measured by the infrared imager. The results show that the addition of PEG makes PP has an ability to absorb water in the saturation stage. Owing to the water penetrating into the PP/PEG samples, the adsorption amount (μ) of foaming agent for PP/PEG blends is significantly higher than that for pure PP. In the foaming processing, water can quickly vaporize as a co-foaming agent. At the same time, the vaporization of water absorbs a lot of heat, which leads to the temperature drop in the inside of foam samples. Therefore the foam structures are cooled and shaped. As a result, under the same foaming conditions, the internal temperature of the PP/PEG foam is quickly fallen, and the foaming materials with higher expansion ratio are obtained compared with the case of pure PP. The mechanism of the obvious reduction in internal temperature of PP/PEG foam is discussed. This method has a universality, which can be applied in different polymer systems and different foaming processes such as moulding foaming, extrusion foaming and batch foaming.关键词：Polypropylene foam;Foaming agent;In situ cooling;Structural control- 47
- |
- 17
- |
- 0
发布时间：2021-01-26
Rapid Communications
- 摘要：All-polymer solar cells (all-PSCs) use blend of polymer electron donor and polymer electron acceptor as active layer. There are much less polymer electron acceptors than polymer electron donors. In contrast to the molecular design of typical polymer acceptors using imide structure, we proposed in 2015 to design polymer acceptors using boron-nitrogen coordination bond (B←N). This paper summarizes our recent progress on polymer acceptors containing B←N unit. At first, we elucidate the principle of B←N unit to downshift LUMO/HOMO energy levels of conjugated polymers. Then we disclose the three effects of B←N unit on the opto-electronic properties of the repeating units of conjugated polymers, i.e. downshifting the LUMO/HOMO energy levels, redshifting the absorption spectra and fixing the planar configuration. We discuss the two molecular design approaches to develop polymer electron acceptors containing B←N unit. One is to copolymerize a building block containing one B←N unit with another electron-deficient building block to develop A-A type conjugated polymers. The other is to copolymerize a building block containing two B←N units with another electron-rich building block to develop D-A type conjugated polymers. The feature of the polymer acceptors containing B←N unit is their delocalized LUMO and tunable LUMO energy levels, which lead to all-PSC devices with high open-circuit voltage. We also show how to use molecular design to tune the key opto-electronic properties of the polymer acceptors containing B←N unit. The UV-Vis absorption spectra can be tuned by copolymerizing with some narrow bandgap units. The LUMO/HOMO energy levels can be tuned by changing the electron-donating/withdrawing substitutes on the copolymerization unit. The electron mobilities can be enhanced by decreasing theπ-π stacking distance or using pseudo-straight configuration of the polymer backbone. These molecular designs lead to an improvement of all-PSC power conversion efficiency from 0.15% in 2015 to > 6% in 2017. Finally, we outlook the future of high efficiency all-PSC devices based on polymer acceptors containing B←N unit.关键词：All-polymer solar cells;Electron acceptor;Boron-nitrogen coordination bond;Energy levels;Electron mobility
- 86
- |
- 29
- |
- 1
发布时间：2021-01-26 - 摘要：Anti-icing polymeric materials have attracted extensive interest and concerns, as undesired ice accumulation always leads to inconvenience and disasters, in extreme cases even loss of lives of human beings. To deal with the icing problem, molecular mechanisms of ice formation have to be unravelled, which have been pending for more than one hundred years. In this review, we firstly introduce basic instruments for investigating ice formation. In order to reliably evaluate the capability of surfaces on tuning ice nucleation, propagation and adhesion, instruments with controlled environmental conditions, such as humidity and surface temperature, are required. We discuss the set-ups built in our lab for investigating the properties of anti-icing materials. Then we summarize our recent research progress on polymeric materials that can tune ice nucleation, control ice propagation, and reduce ice adhesion. The initial and control step for ice formation is ice nucleation, which often starts on foreign surfaces,i.e., heterogeneous nucleation, and different surfaces possess distinct capabilities in tuning ice nucleation. Via. investigating and mimicking the mechanism of antifreeze proteins in the body of organisms living in cold environments, we fabricated polymeric surfaces for regulating the ice nucleation temperature. When ice nucleation triggers freezing of water droplets, ice propagation from frozen water droplets to unfrozen ones follows. In this case, polymeric materials with the functionality of trapping different amount of free water was developed and applied to inhibit ice propagation. Once ice accumulates on solid surfaces, one of the anti-icing strategies is to minimize ice adhesion for easy de-icing. Polymeric materials with aqueous lubricating layer have been prepared and ice on the surface could be blown off under a strong breeze. In addition, solid organogel material with a regenerable solid surface layer is proposed to improve the durability of the materials.关键词：Anti-icing;Polymeric functional material;Ice nucleation;Ice propagation;Ice adhesion
- 206
- |
- 61
- |
- 6
发布时间：2021-01-26 - 摘要：Since gene therapy has the potential to alter expression of any gene of interest, itoffers tremendous promise for treating various human diseases including genetic disorders, cancers, viral infections, and cardiovascular diseases. To construct a suitable vector for transferring the therapeutic gene into the target cells of patients is important for achieving successful gene therapy. Cationic polymers have become one of the most promising synthetic vectors for gene transfection in biotechnology over the past two decades because of their advantages of simple preparation and modification. However, they have failed to enter clinical trials due to their low gene transfection efficacy by far. This review highlights some research work on developing Michael addition reaction, thiol-coupling reaction and thiol-exchange reaction for the preparation of stimuli-responsive polymers for helping the release of DNA inside cell and enhancing gene transfection; the fabrication of bioreducible cationic polymers with different topologies (linear structure, branched structure, and hyperbranched structure) via Michael addition reaction for tuning the morphology of the formed polymer/DNA polyplex to increase the cell-uptake and gene transfection; the design of newmethods for making the formed polyplex stable in blood system and for long blood circulation time, which can highly increase gene transfection in vivo. On the other hand, for most of the cationic polymers, their binding affinity with plasmid DNA is very weak. Therefore, a large excess of cationic polymer is typically required to achieve a complete DNA condensation, which results in high cytotoxicity and instability of the blood system. Herein, we also highlight the methods for the preparation of a novel class of bioreducible cationic nanomicelles with high surface charge using disulfide bonds to connect the cationic shells to the hydrophobic cores, and the bioreducible nanomicelles thus formed with very high binding affinity to DNA, and they can completely condense DNA even at N/P ratio of 1. The resulting nanomicelles/DNA polyplexes exhibit high biocompatibility and perform very effectively as an efficient gene delivery system, so its gene transfection efficiency is close to that of virus. Therefore, the new bioreducible cationic polymer nanomicelles have many potential applications in gene therapy.关键词：Cationic polymer;Responsibility;Nanomicelles;Gene delivery
- 130
- |
- 24
- |
- 3
发布时间：2021-01-26
Feature Articles
- 摘要：Nanofiltration membranes occupy a crucial position in membrane technology due to their superiority of high separation efficiency and low energy cost, which are therefore widely applied in the field of water treatment, food and medicine, membrane bioreactor and petro chemistry. Most nanofiltration membranes are made from polymeric materials with composite structure containing a thin selective layer and a porous support layer. As the key of this structure, the selective layer can be fabricatedvia various methods such as interfacial polymerization, layer-by-layer assembly, surface coating and graft polymerization followed with crosslinking. However, it still remains a big challenge to precisely control the skin layer structures during interfacial polymerization process ascribed to its very fast reaction. We demonstrate that the interfacial property and the interfacial reactions can be well tuned via controlled surface/interface engineering, thus to control the fabrication and performance of the composite nanofiltration membranes. This review is aimed to summarize the most recent advances on polymeric composite nanofiltration membranes based on controlled surface/interface engineering mainly conducted in our group. On one hand, a tunable polymerization-deposition strategy is proposed to realize novel or functional selective layer. In these cases, dopamine and derivative polyphenol are employed to fabricate the selective layer with self-polymerization and deposition process tuned by additives, oxidant and contra-diffusion operation. Novel nanofiltration membranes with photocatalytic function are further achieved owing to the reactive moieties in the co-deposition layer. On the other hand, an interfacial property tailoring interfacial polymerization strategy is proved to obtain ultrathin and high-performance nanofiltration membranes. An intermediate layer is fabricated prior to traditional interfacial polymerization with excellent hydrophilicity and uniform structure, which help to homogenize the monomer concentration on substrate surface and control the release of monomers to achieve ultrathin polyamide layer. We believe that these advances will provide reliable methodological and theoretical foundation for the controllable fabrication of high performance composite nanofiltration membranes. Moreover, the challenges remained in this area are also presented, such as details of chemical reactions, reaction-structure-function relationship, optimization of methodology and development of basic theory, to point out the future research direction with the aim to push forward the studies in this area.关键词：Nanofiltration membrane;Composite membrane;Surface/Interface engineering;Co-deposition;Interfacial polymerization
- 195
- |
- 98
- |
- 1
发布时间：2021-01-26
Reviews
- 摘要：A new type of the SalenCo(Ⅲ) with CN as the co-ligand is developed to catalyze the copolymerization of CO2 with propylene oxide (PO) to afford poly(propylene carbonate) (PPC). The co-ligand (X) is the initiating group during the reaction and becomes the site at which the growing polymer chain is proposed to propagate. The copolymerization rate, selectivity of the polymer to the cyclic carbonate, stereoselectivity, and regioselectivity of the polycarbonate exhibit a pronounced dependence on the nature of the axial ligand. Compared with the SalenCo(Ⅲ)Cl and SalenCo(Ⅲ)Br catalysts, the PPC obtained by SalenCo(Ⅲ)CN catalyst at 25℃ presented 98% head-to-tail (HT) connectivity, and without head-to-head linkage. Further increasing the reaction temperature from 25℃ to 75℃, the polymerization activity over SalenCo(Ⅲ)CN catalysts increased, and the product still maintained a high selectivity for carbonate linkages. The PPC achieved using the SalenCo(Ⅲ)CN/PPNCl (PPNCl=bis(triphenylphosphino)iminium chloride) catalyst systems at 50℃ within 2 h with TOF=379 mol PO·mol-1 Co·h-1 was highly regioregular (HT up to 95%) and had carbonate linkages of up to 99% with a narrow molecular weight distribution (MWD). The SalenCo(Ⅲ)CN catalyst showed good stability and polymer chain control ability even at 75℃. This novel catalyst efficiently terpolymerized CO2, PO, and two other kinds of epoxide monomers. When the quantity of the third epoxide was added gradually, the MWD of the generated polymers was broader, indicating the epoxide was incorporated into the PPC chain successfully. The third epoxide monomer not only acted as an interlinkage in the terpolymerization of CO2 and PO, which increased the MW of the resultant terpolymer to a value that increased the glass transition temperature (Tg), but also strongly influenced the productivity of PPC and the selectivity. Introducing the dicyclopentadiene dioxide (EP1) could greatly increase the activity of the catalyst system to TOF=624 h-1, with a slight effect on Tg. For the case of 1, 3, 5-triglycidyl isocyanurate (EP2), it increased MW of the resultant copolymer and the Tg up to 45℃.关键词：Carbon dioxide;Polycarbonate;SalenCo(Ⅲ)CN;Polymerization temperature;Molecular weight
- 60
- |
- 21
- |
- 1
发布时间：2021-01-26 - 摘要：Syndiotactic polymerization of p-fluorostyrene and its copolymerization with ethylene catalyzed by half-sandwich scandium complex (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2(1) and (C5Me4SiMe3)Sc(CH2Si-Me3)2(THF) (2) have been examined. The microstructures and thermal properties of the obtained polymers were characterized by 1H-NMR, 13C-NMR, GPC and DSC. Scandium complex 1 showed syndiotactic selectivity for the polymerization of p-fluorostyrene with low activity (103 g polymer molSc-1h-1). Scandium complex 2 proved to be a high activity catalyst for the polymerization of p-fluorostyrene to afford syndiotactic or atactic poly(p-fluorostyrene) by controlling the type and the volume of the solvent. When the concentration of p-fluorostyrene in chlorobenzene was below 2.4 mol/L, the syndiotactic poly(p-fluorostyrene) (rrrr > 99%) was obtained with scandium complex 2 possessing high activity (105 g polymer molSc-1 h-1). The melting point (Tm) of syndiotactic poly(p-fluorostyrene) reached up to 324℃, suggesting the semicrystalline morphology of this polymer. The molecular weight of the syndiotactic poly(p-fluorostyrene) (Mn=3.10×104-2.08×105) was easily controlled by changing the feed ratio of p-fluorostyrene to catalyst. When the concentration of p-fluorostyrene in chlorobenzene was above 4.8 mol/L or fluorobenzene used as solvent, atactic poly(p-fluorostyrene) with controllable molecular weight (3.80×104 -1.88×105) was obtained. Moreover, the copolymerizations of p-fluorostyrene with ethylene catalyzed by complexes 1 or 2 have also been prepared, leading to novel copolymers with controlled composition (p-fluorostyrene content:41 mol% -88 mol%) and molecular weight (3.10×104 -1.84×105), and with high activity (up to 106 g polymer molSc-1 h-1). When ethylene content in the copolymer is higher than that of p-fluorostyrene, the copolymers showed a Tm around 119 -126℃ owing to polyethylene blocks. When p-fluorostyrene content in the copolymer is higher than that of ethylene, the obtained copolymers with syndiotactic poly(p-fluorostyrene) blocks, prepared by scandium complex 1, showed a Tm around 269 -282℃ and a Tg around 79 -82℃; In contrast, the copolymers with atactic poly(p-fluorostyrene) blocks prepared by scandium complex 2 showed their Tg around 94 -96℃.关键词：Scandium;p-Fluorostyrene;Syndiotactic polymerization;Ethylene;Copolymerization
- 39
- |
- 13
- |
- 2
发布时间：2021-01-26 - 摘要：Taking highcis-1, 4 hydroxyl-terminated polybutadiene (HTPB) as a starting material, two kinds of triblock copolymers were successfully synthesized by polymerization ofε-caprolactone (ε-CL) and styrene. Polycaprolactone-b-polybutadiene-b-polycaprolactone triblock copolymer (CLBCL) was synthesizedvia the ring-opening polymerization ofε-CL with stannous octanoate[Sn(Oct)2] as the catalyst and HTPB as the macroinitiator. The length of PCL segments was controlled by changing the reaction time based on the living property of the ring-opening polymerization. Besides, the reaction between HTPB and 2-bromoisobutyryl bromide yielded the Atom Transfer Radical Polymerization (ATRP) macroinitiator (BiB-PB-BiB), which was used for the preparation of the polystyrene-b-polybutadiene-b-polystyrenetriblock copolymers (SBS)via the Activators Regenerated by Electron Transfer for ATRP (ARGET ATRP) of styrene. The ARGET ATRP reaction was controllable and the molecular weight distribution of the copolymers was narrow. The structure of these triblock copolymers was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H-NMR and 13C-NMR), gel permeation chromatography (GPC), and their thermal properties were tested by thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA analysis indicated that the thermal stability of the CLBCL triblock copolymers increased with the increase in PCL content in the copolymers. Only one thermal degradation stage was observed for the SBS triblock copolymers from the TGA curves and the thermal stability of copolymers was slightly better than HTPB precursors. In the DSC curves of CLBCL copolymers, the glass transition temperature at -106.0℃ for the PB segments and the melting temperature at 54.4℃ for the PCL segments were detected. The results of DSC analysis for the SBS triblock copolymers indicated that there were two glass transition temperatures at -104.1 and 102.4℃, which corresponded to the PB and the PS segments, respectively.关键词：Hydroxyl-terminated polybutadiene;ε-Caprolactone;Styrene;Macroinitiator;Ring-opening polymerization (ROP);Activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP)
- 54
- |
- 12
- |
- 1
发布时间：2021-01-26 -
Photo-and Chemo-Degradable Polystyrene Containing
o -Nitrobenzyl Ester and Trithiocarbonate Moieties 增强出版摘要：The extensive use of polystyrenes led to the accumulation of plastic waste because of the non-degradability in natural circumstance, which has caused serious environmental impacts, dubbed "white pollution". Therefore, it is highly desirable to design and prepare degradable polystyrenes. A new macromolecular chain transfer agent was designed and synthesized by polyesterfication of the monomer with dicarboxylic groups, S, S'-bis(α, α'-dimethyl-α"-acetic acid)-trithiocarbonate, and the monomer with diiodine groups, 1, 3-bis(iodo-methyl)-2-nitrobenzene. Then, multiblock polystyrenes (PS) containing o-nitrobenzyl ester and trithiocarbonate moieties as photosensitive units in the main chain weresuccessfully synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene in the presence of the macromolecular chain transfer agent. Moreover, the photodegradation behavior of the multiblock PS in tetrahydrofuran and in solid state was examined under ultravioletray (UV) irradiation at room temperature in air atmosphere. The structure and molecular weight of the macromolecular chain transfer agent and the block polymer were characterized by nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC). The molecular weight and molecular weight distribution of the macromolecular chain transfer agent were 8400 and 1.8, respectively. The kinetics of RAFT polymerization of styrene was studied, and it was found that the polymerization was a first-order reaction with respect to monomer concentration. The photodegradation and chemical degradation behaviour were investigated through1H-NMR, ultraviolet-visible spectroscopy (UV-Vis) and GPC analyses. The results demonstrated that the multiblock polystyrenes could be degraded into separate PS blocks, not only by UV light, but also by hydrolysis or amiolysis of the ester and trithiocarbonate groups. In addition, thermal properties of the multiblock PS were measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) under a nitrogenatmosphere. The glass transition temperature and the maximum rate of the decomposition of the multiblock PS appeared respectively at 97 and 385℃. The result of thermal analysis indicated that the thermal properties of the multiblock PS are very similar to those of conventional polystyrene.关键词：Photodegradable;Polystyrene;Polyesterification;RAFT polymerization- 60
- |
- 15
- |
- 0
发布时间：2021-01-26 - 摘要：Redox-responsive microparticles with core-shell structure were prepared by the coaxial electrospray technique. Poly(ether urethane) (PEU) with multiple-disulfide bonds in the main chain was synthesized via a facile one-pot method. It was found that the number average molecular weight of the resultant polymer decreased from 3.1×107 to 6.6×106 in 8 h in the presence of DL-dithiothreitol (DTT). The microparticles with PEU as the core and polyethylene glycol (PEG) as the shell were prepared by the coaxial electrospray technique. The results of the microscopies (the scanning electron microscopy and laser scanning confocal microscopy) showed that the constructed microparticles were spherical, uniform and with a distinct core-shell structure. It was also found that the mean diameter of the prepared microparticles decreased to less than 100 nm when the PEG shell was removed. Dynamic light scattering results showed that the hydrodynamic mean diameter of the particles after PEG template removal was about 112 nm. The spherical nanoparticles could be completely decomposed when they were placed in phosphate buffer saline (PBS) solution at pH=7.4 + 10 mmol/L L-glutathione (GSH) for 24 h at 37℃. In contrast, the shape of the spherical nanoparticles remained unchanged in PBS without GSH after 24 h. The doxorubicin (DOX) loaded nanoparticles were also prepared with the coaxial electrospray technique, and the results showed that the drug-loading efficiency was nearly 100%. Meanwhile, under the condition of GSH, the content of the cumulative drug release could be up to 80% within 12 h at 37℃, in contrast to the case that only 50% of the loaded DOX could release within 12 h in the absence of GSH. This study shows that the prepared nano drug delivery system has the characteristics of significant GHS response and controlled drug release.关键词：Electrospray;Redox responsive;Core-shell structure microparticle
- 31
- |
- 11
- |
- 0
发布时间：2021-01-26 - 摘要：Based on the biological properties of saccharides, saccharide-protein interaction, self-assembling ability and high quantum yield of perylene bisimide derivatives, glucose functionalized water-soluble perylene bisimide derivatives were designed. Tri-block glycopolymers with different sugar units, 1-linked glucose (1-Glc) and 6-linked glucose (6-Glc), were synthesized by atom transfer radical polymerization (ATRP) and click reaction, using perylene bisimide (PBI) as the initiator. Dynamic light scattering (DLS), transmission electron microscopy (TEM) and ultraviolet-visible absorption spectra (UV-Vis) were used to characterize the morphology, size and optical property of the glycopolymers in aqueous solution. The results show that the polymers had high absorption in the near IR region. In addition, the photoacoustic property of the polymers was studied by photoacoustic imaging. The results showed that the glycopolymers had strong photoacoustic signals. Moreover, a variety of characterizations including UV-Vis and DLS were conducted to observe the interaction between the two glycopolymers and Con A in order to study glyco-regioisomerism effect on lectin-binding. It was found that the turbidity and particle size of PBI-1-Glc solution increased significantly with the addition of Con A lectin, while PBI-6-Glc solution showed little change. Further more, photoacoustic imaging was also applied to study the recognition of glycopolymers and lectin. The results indicated that Con A could increase the photoacoustic signal of PBI-1-Glc solution, and photoacoustic technology could also be used to identify the interaction between two polymers and lectins effectively. In conclusion, the experimental results showed that PBI-1-Glc had a strong interaction with lectin Con A, whereas PBI-6-Glc did not, confirming that the monosaccharide isomerization effect on their biological function of glycopolymers had universality in a certain degree.关键词：Glycopolymer;Perylene bisimide;Photoacoustic imaging;Protein
- 29
- |
- 14
- |
- 2
发布时间：2021-01-26 - 摘要：Thecrown ethers show good efficiency for lithium isotope separation due to their high affinity and size selectivity for lithium ions. A chitosan (CTS) graft 4'-formoxylbenzo-15-crown-5-ether (FB15C5) (CTS-g-FB15C5) film was synthesized from chitosan and FB15C5 via Schiff reaction. The structure of CTS-g-FB15C5 film was analyzed through XPS analysis. The solid-liquid extraction was used to study the lithium ion adsorption kinetics, adsorption thermodynamics and lithium isotope separation effect of the CTS-g-FB15C5 films. Meanwhile, the effect of immobilization amount of crown ether on CTS and extraction temperature on single stage separation factor were also explored. The results showed that pseudo-second-order kinetic model and Langmuir isotherm model were more favorable to describe the process of lithium ions adsorption on CTS-g-FB15C5 film with the immobilization amount of crown ether of 2.98 mmol/g. It indicated that the Li+ ions adsorption carried out with CTS-g-FB15C5 film exhibited the typical chemical adsorption and the monolayer adsorption. The thermodynamics parameters, such as Gibbs free energy (△G), enthalpy change (△H) and entropy change (△S), indicated that Li+ ions adsorption on the film was spontaneous, exothermic and random. Furthermore, the single stage separation factor decreased from (1.053 ±0.002) to (1.012 ±0.001) with the increase of extraction temperature from 10℃ to 30℃ during the solid-liquid extraction for lithium isotopes separation using CTS-g-FB15C5 film. The single stage separation factor increased from (1.042 ±0.002) to (1.053 ±0.002) with the increasing immobilization amount of crown ether from 1.10 mmol/g to 2.98 mmol/g. The maximum value of single stage separation factor obtained from the extraction system of H2O-LiI/CTS-g-FB15C5 film at 10℃ was up to (1.053 ±0.002), which was higher than an acceptable single stage separation factor of 1.03 in a large scale. In addition, it was found that light isotope (6Li) was concentrated in the film, whereas the heavy isotope, 7Li, was enriched in the solution. In sum, the produced CTS-g-FB15C5 films have a good potential prospect in lithium isotope adsorptive separation.关键词：Lithium isotope separation;4'-Formylbenzo-15-crown-5-ether;Chitosan;CTS-g-FB15C5;Solid-liquid extraction
- 72
- |
- 22
- |
- 0
发布时间：2021-01-26 - 摘要：Controlled polycondensation of decafluorobiphenyl and bisphenol A at low temperature gave a highly linear polymer with its main chain consisting of octafluoro benzene moiety, which acted as grafting reaction position for post-functionalization at higher temperature. 3, 5-dimethylphenol grafted onto the main chain of the mother polymer by partial elimination of the fluorine atoms in the octafluoro benzene moiety to form the ionomers precursor with side chain benzyl groups. The precursor transformed then into a series of partly fluorinated anion exchange membranes containing side chain benzyl quaternary ammonium groups with varying IEC values by bromination and quaternization. The participation of the ortho-and meta-fluorine atoms to the polycondensation, leading to the cross linking gelation, was successfully avoided through this method. Moreover, the method could achieve the controllable degree of functionalization by controlling the feed ratio of NBS to the benzyl groups in the precursor polymer. In addition, two benzyl groups on the side chains could be brominated and quaternized to form local domains of high density ionization, which could form ion clusters of microphase separation to increase the ion conductivity. The molecular structure and aggregation structure of the membranes were characterized by GPC, 1H-NMR, 19F-NMR, IR and SASX. The results confirmed that the precursor polymer of the partly fluorinated anion exchange membranes had a linear skeleton, adjustable functionality and the obtained membranes showed obvious microphase separation aggregation morphology. The results of the property evaluation indicated that the swelling ratio, ion conductivity and alkaline stability were greatly improved by the designed structure of the partly fluorinated main chain and the aromatic side chain ionic group. QFPAE-95 had the highest ion conductivity and appropriate swelling ratio with the values of 108.6 mS cm-1 and 42.6% at 80℃ respectively. QFPAE-55 possessed the highest tensile strength of 21.01 MPa. Moreover, the series of membranes also showed excellent alkaline stability. The ion conductivity and IEC value of QFPAE-55 remained 82.3% and 84.2% of the values in the original membrane after being immersed into 1 mol/L NaOH solution at 60℃ for 20 days. The membranes are promising anion exchange membranes for alkaline fuel cells.关键词：Post-functionalization;Partly fluorinated;Side chain benzyl quaternary ammonium groups;Anion exchange membranes;Alkaline membrane fuel cells
- 58
- |
- 11
- |
- 0
发布时间：2021-01-26 - 摘要：The conformational change of polyelectrolyte chains under external stimuli such as temperature, solvent quality, pulling force, or salt, is of critical importance to numerous biological and synthetic processes, as well as to their potential applications. The conformation transition and ion condensation of a strongly charged polyelectrolyte chain in solvent with added salt are studied using parallel tempering Monte-Carlo simulation on a lattice model, focusing on the effects of salt concentration and valence. The variation of the mean-square radius of gyration (<Rg2>) with Bjerrum length (lB) is obtained in different salt concentrations and for salts of different valence. It is shown that the chain expands first with increased lB, and then it shrinks and finally the chain assumes a collapse globule conformation. The chain size is related to both the concentration and the valence of the salt. In intermediate range of lB, upon addition of monovalent salt, < Rg2> gradually decreases. By contrast, the addition of a multivalent salt leads to a more pronounced decrease in <Rg2> and a relatively lowlB value for the chain collapse transition. When lB is appropriate, the chain re-expansion is observed with increased concentration of the multivalent salt. In the high multivalent salt solution, condensation of both multivalent counterions and co-ions happens when the charge of total multivalent counterions is greater than that of the chain segments, whereas the univalent counterions hardly condense. For the monovalent salt, the effective charge of chain decreases with increased salt concentration at a givenlB. For the multivalent salt, overcompensation of multivalent counterions is observed in appropriate range of lB when salt concentration exceeds a specific value, leading to inversion of effective charge of the chain. The overcompensation of multivalent counterions also leads to condensation of the co-ions. The charge reversal and condensation of co-ions lead to the re-expansion of the chain at a high salt concentration. By comparing the chain size with the Debye length at NS ≈ 64 and lB=1.2, it is concluded that the condensation of multivalent counterions is the major reason for the chain collapsing, rather than the Debye screening in case with multivalent salt.关键词：Polyelectrolyte;Collapse;Multivalent salt;Parallel tempering;Monte Carlo
- 25
- |
- 9
- |
- 0
发布时间：2021-01-26 - 摘要：The response of DNA origami nanostructures to pH is systematically investigated from two aspects in this work. At first, self-assembly of DNA origami triangle in different pH buffer was tested by putting M13 scaffold and staple strands into a series of sodium citrate buffer (10 mmol/L with 12.5 mmol/L Mg2+), the as-prepared sample was characterized by AFM. The formation of the origami structure was affected by pH and the structure was observed only in the pH range of 6-9. Tolerance of DNA origami to pH in the external environment was investigated by immersing them (pH=8) into acidic and basic solutions for 2 h at room temperature, followed by characterization of the samples by AFM and 0.5% agarose gel respectively. The AFM results showed that the DNA origami triangle maintained the original structure at pH range of 5-10, and the structure was broken at higher or lower pH. The agarose gel suggested that the most stable state of DNA origami triangle was in pH range of 7-8, where the intensity and mobility of the sample band remained the same. Compared with the origami self-assembled in different pH buffers, the pre-prepared origami showed better resistance to acidic and alkali environments. In order to test the long time-stability of DNA origami, pH value of the prepared triangle origami was adjusted in the range of 5-10 and the reaction time was extended to 12 h. AFM test results indicated that the DNA origami could maintain its original structure for at least 12 h. Another common origami nanostructure was also tested; like origami triangle, rectangle structure showed a similar pH tolerance which could keep the stability at pH range of 5-10 for at least 12 h. The long time pH stability experiment of the triangle and the rectangle structures indicated that the origami structure based on M13 owned a relatively high pH tolerance. Based on the above results, possible mechanism of pH effect on DNA origami stability was also proposed. In the process of the origami preparation, excess H+ or OH- will affect the formation of the hydrogen bond thus affecting the hybridization of DNA double helixes. In the pH tolerance experiment, excessive H+ or OH- will attack the formed hydrogen bonds and make the origami structure floppy. In both aspects, more H+ or OH- will undermine the primary structure of DNA, and eventually affect the formation and stability of DNA origami structures.关键词：DNA origami;Self-assembly;Stability;pH
- 137
- |
- 34
- |
- 3
发布时间：2021-01-26
Research Article
- Postal code：100190
- Tel：010-62588927 Email：gfzxb@iccas.ac.cn
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备05002797号-8
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0