The practical application of emerging rechargeable aqueous zinc(Zn)batteries is challenged by the poor reversibility and cycling stability of Zn anodes,primarily due to parasitic side reactions.While numerous strategi...The practical application of emerging rechargeable aqueous zinc(Zn)batteries is challenged by the poor reversibility and cycling stability of Zn anodes,primarily due to parasitic side reactions.While numerous strategies have been proposed,balancing the suppression of side reactions with the maintenance of fast Zn plating/stripping kinetics remains a significant challenge.In this study,sucrose,a sterically-hindered organic molecule with abundant hydroxyl groups,is employed to suppress the side reactions and maintain the moderate kinetics of Zn plating/stripping by modulating the hydrogen bond network without altering the Zn^(2+)solvation structure.Its steric hindrance effect further impedes the lateral diffusion of Zn atoms on the electrode surface within the electric double layer,effectively mitigating dendrite growth and stabilizing the electrodeposition process.Consequently,the formulated Suc/ZnSO_(4)electrolyte achieves a remarkably Coulombic efficiency of 99.90% over 2600 cycles at 3 mA cm^(-2)for 1 mAh cm^(-2)in Zn‖Cu cells.The enhanced Zn anode reversibility leads to excellent cycling stability in Zn‖LiFePO_(4)cells and Zn‖β-MnO_(2)cells.This study underscores the potential of sterically-hindered organic molecule strategies to enhance Zn anode stability while maintaining favorable Zn deposition/stripping dynamics in aqueous Zn batteries.展开更多
Multiple donor-acceptor(D-A) combinations represent a promising category of thermally activated delayed fiuorescence(TADF) materials, offering potential for superior efficiency and stability. However, current systems ...Multiple donor-acceptor(D-A) combinations represent a promising category of thermally activated delayed fiuorescence(TADF) materials, offering potential for superior efficiency and stability. However, current systems are predominantly composed of limited donor groups, primarily carbazole-based derivatives. In this work, we developed a series of D-A type materials incorporating helical π-expanded carbazole(Cz Naph) and 7H-dinaphtho[1,8-bc:1,8-ef]azepine(Az Naph), alongside traditional carbazole, ranging from mono-to tetra-substituted configurations(D_(n)-A). Through systematic investigation of geometric and electronic structures, the number and positioning of multiple donors are confirmed with significant manipulations on charge transfer characteristics and the S_(1) state via steric effects. Density functional theory(DFT) calculations reveal that varying the number of π-extended donors within the acceptor framework produces emission colors from ultraviolet to red, providing a diverse range of emitters. Furthermore, the reduced reorganization energy of S1observed in tetra-substituted Cz and Cz Naph, as well as Mono Az N, indicates lower structural relaxation, highlighting these materials' potential as stable luminescent candidates. This study underscores the importance of diverse composing units in achieving efficient and stable TADF emitters with multiple and hetero-donor configurations.展开更多
A series of“half-sandwich”bis(imino)pyridyl iron complexes with a substituted 8-(p-Xphenyl)naphthylamine(X=OMe,Me,CF3)was designed and synthesized by combining weakπ-πinteraction with steric and electronic tunings...A series of“half-sandwich”bis(imino)pyridyl iron complexes with a substituted 8-(p-Xphenyl)naphthylamine(X=OMe,Me,CF3)was designed and synthesized by combining weakπ-πinteraction with steric and electronic tunings.The weak noncovalentπ-πinteraction as well as the steric and electronic effects of bis(imino)pyridyl iron complexes were identified by experimental analyses and calculations.The roles of weakπ-πinteraction,steric bulk,and electronic tuning on the ethylene polymerization performance of bis(imino)pyridyl iron catalysts were studied in detail.The combination ofπ-πinteraction with steric and electronic tunings can access to thermally stable bis(imino)pyridyl iron at 130°C.展开更多
LiMnxFe1-xPO_(4) is a promising cathode candidate due to its high security and the availability of a high 4.1 V operating voltage and high energy density.However,the poor electrochemical kinetics and structural instab...LiMnxFe1-xPO_(4) is a promising cathode candidate due to its high security and the availability of a high 4.1 V operating voltage and high energy density.However,the poor electrochemical kinetics and structural instability currently hinder its broader application.Herein,inspired by the hydrogen-bonded cross-linking and steric hindrance effect between short-chain polymer molecules(polyethylene glycol-400,PEG-400),the pomegranate-type LiMn_(0.5)Fe_(0.5)PO_(4)-0.5@C(P-LMFP@C)cathode materials with 3D ion/electron dual-conductive network structure were constructed through ball mill-assisted spray-drying method.The intermolecular effects of PEG-400 promote the spheroidization and uniform PEG coating of LMFP precursor,which prevents agglomeration during sintering.The 3D ion/electron dual-conductive network structure in P-LMFP@C accelerates the Li^(+)transport kinetics,improving the rate performance and cycling stability.As a result,the designed P-LMFP@C has remarkable electrochemical behavior,boasting excellent capacity retention(98%after 100 cycles at the 1C rate)and rate capability(91 mAh·g^(-1)at 20C).Such strategy introduces a novel window for designing high-performance olivine cathodes and offers compatibility with a range of energy storage materials for diverse applications.展开更多
Li metal batteries(LMBs)offer signifi-cant potential as high energy density alternatives;nev-ertheless,their performance is hindered by the slow desolvation process of electrolytes,particularly at low temperatures(LT)...Li metal batteries(LMBs)offer signifi-cant potential as high energy density alternatives;nev-ertheless,their performance is hindered by the slow desolvation process of electrolytes,particularly at low temperatures(LT),leading to low coulombic efficiency and limited cycle stability.Thus,it is essential to opti-mize the solvation structure thereby achieving a rapid desolvation process in LMBs at LT.Herein,we introduce branch chain-rich diisopropyl ether(DIPE)into a 2.5 M Li bis(fluorosulfonyl)imide dipropyl ether(DPE)elec-trolyte as a co-solvent for high-performance LMBs at-20℃.The incorporation of DIPE not only enhances the disorder within the electrolyte,but also induces a steric hindrance effect form DIPE’s branch chain,excluding other solvent molecules from Li+solvation sheath.Both of these factors contribute to the weak interactions between Li^(+)and solvent molecules,effectively reducing the desolvation energy of the electrolyte.Consequently,Li(50μm)||LFP(mass loading~10 mg cm^(-2))cells in DPE/DIPE based electrolyte demonstrate stable performance over 650 cycles at-20℃,delivering 87.2 mAh g^(-1),and over 255 cycles at 25℃ with 124.8 mAh g^(-1).DIPE broadens the electrolyte design from molecular structure considera-tions,offering a promising avenue for highly stable LMBs at LT.展开更多
Viologens known as a kind of promising negolyte materials for aqueous organic redox flow batteries,face a critical stability challenge due to the S_N2 nucleophilic attack by hydroxide ions(OH-)during the battery cycli...Viologens known as a kind of promising negolyte materials for aqueous organic redox flow batteries,face a critical stability challenge due to the S_N2 nucleophilic attack by hydroxide ions(OH-)during the battery cycling.In this work,a N-cyclic quaternary ammonium-grafted viologen molecule,viz.1,1'-bis(4,4'-dime thylpiperidiniumyl)-4,4'-bipyridinium tetrachloride((DBPPy)Cl_(4)),is developed by the molecular engineering strategy.The obtained(DBPPy)Cl_(4) molecule shows a decent solubility of 1.84 M and a redox potential of-0.52 V vs.Ag/AgCl,Experimental and theoretical results reveal that the grafted N-cyclic quaternary ammonium groups act as the steric hindrance to prevent nucleophilic attack by OH~-,increasing the alkali resistance of the electroactive molecule.The symmetrical battery with 0.50 M(DBPPy)Cl4shows negligible decay during the 13-day cycling test.As demonstration,the flow battery utilizing 1.0 M(DBPPy)Cl_(4) as the negolyte and 1-(1-oxyl-2,2',6,6'-tetramethylpiperidin-4-yl)-1'-(3-(trimethylammonio)propyl)-4,4'-bipyridinium trichloride as the posolyte exhibits a high capacity retention rate of 99.99%per cycle at 60 mA cm^(-2).展开更多
α-Diimide catalysts have attracted widespread attention due to their unique chain walking characteristics.A series ofα-diimide nickel/palladium catalysts with different electronic effects and steric hindrances were ...α-Diimide catalysts have attracted widespread attention due to their unique chain walking characteristics.A series ofα-diimide nickel/palladium catalysts with different electronic effects and steric hindrances were designed and synthesized for olefin polymerization.In this work,we synthesized a series of asymmetricα-diimide nickel complexes with different steric hindrances and used them for ethylene polymerization.These nickel catalysts have high ethylene polymerization activity,up to 6.51×10^(6)g·mol^(−1)·h^(−1),and the prepared polyethylene has a moderate melting point and high molecular weight(up to 38.2×10^(4)g·mol^(−1)),with a branching density distribution between 7 and 94 branches per 1000 carbons.More importantly,the polyethylene prepared by these catalysts exhibits excellent tensile properties,with strain and stress reaching 800%and 30 MPa,respectively.展开更多
The relative contributions of surface temperature and salinity to steric sea-level variations are investigated using satellite observations and reanalysis datasets.By defi ning a contribution factor,the relative roles...The relative contributions of surface temperature and salinity to steric sea-level variations are investigated using satellite observations and reanalysis datasets.By defi ning a contribution factor,the relative roles of thermal and haline steric height variations are quantifi ed over the South China Sea(SCS).The thermosteric height dominates the steric sea level variation in the northern SCS deep basin,while the contribution of the halosteric height increases southward.Further investigation reveals that this transition is related to the meridional imbalance of surface heat flux and precipitation variations.The revealed steric constitution distribution is not confi ned to the surface but extends within the upper layer to approximately 50m depth,and then the thermosteric component dominates from the depth underneath.The results of this study clarify the steric sea level constitution over the SCS,benefit the understanding of sea-level variations at the regional scale,and may further facilitate multisensor remote sensing data mining studies.展开更多
Naphthyl-α-diimine nickel complexes with systematically varied ligand sterics, activated by modified methylaluminoxane（MMAO）, were tested in the polymerization of higher α-olefin（1-hexene, 1-decene and 1-hexadec...Naphthyl-α-diimine nickel complexes with systematically varied ligand sterics, activated by modified methylaluminoxane（MMAO）, were tested in the polymerization of higher α-olefin（1-hexene, 1-decene and 1-hexadecene） under suitable conditions. The polymerization results indicated the possibility of precise microstructure control, depending on catalyst structure, polymerization temperature, monomer concentration and types of monomers, which in turn strongly affects the resultant polymer properties. Naphthyl-α-diimine nickel complex bearing chiral bulky sec-phenethyl groups in the o-naphthyl position showed good catalytic activity, and resulted in branched polymers（42-88/1000 C） with high molecular weights（Mn：（4.3-15.2） × 10^4 g·mol^-1） and narrow molecular weight distribution（Mw/Mn = 1.13-1.29, RT）, which suggested a living polymerization. The increasing steric hindrance of catalyst leads to enhance insertion for 2,1-insertion of α-olefin and the chain-walking reaction.展开更多
The rare earth complexes Tb（o-BrBA）3,Tb（m-BrBA）3 and Tb（p-BrBA）3 were synthesized using o-,m-,p-bromo benzoic acids（2-bromo benzoic acid,3-bromo benzoic acid and 4-bromo benzoic acid） as ligand,respectively.Th...The rare earth complexes Tb（o-BrBA）3,Tb（m-BrBA）3 and Tb（p-BrBA）3 were synthesized using o-,m-,p-bromo benzoic acids（2-bromo benzoic acid,3-bromo benzoic acid and 4-bromo benzoic acid） as ligand,respectively.The UV spectra showed that the absorption ability of Tb（m-BrBA）3 was the strongest.However,the fluorescent intensity of Tb（o-BrBA）3 was the weakest.The effect of the molecular structure,the energy level of Tb3＋ and energy transfer efficiency from ligands to Tb3＋ were discussed to explain the experimental results.The results indicated that,due to the large atomic radius of bromine,the steric effect caused by the different substitution bromine on the benzene ring might strongly affect the bond length formed by the coordination atoms and Tb3＋.The longer the bond length was,the lower the efficiency of energy transfer was,and the weaker the fluorescent intensity was.展开更多
The exchange action of six types of organic phenols on clay surfaces in seawater is systematically studied in this work. The following significant conclusions are drawn from the experiments. (1) The interaction of org...The exchange action of six types of organic phenols on clay surfaces in seawater is systematically studied in this work. The following significant conclusions are drawn from the experiments. (1) The interaction of organic phenols with montmorillonite, illite and kaolinite in seawater is monovalent anion exchage.(2) Their isotherms of stepwise exchage on clay surfaces belong to the Langmuir type or stepwise type.(3) The discovery of the"steric hindrance effects of stepwise exchange of organic phenols on clays surfaces", and revelation of an exchange mechanisrn diffeient from that in references are the greatest achieverments in this work.展开更多
Aluminum porphyrin complexes are heavy-metal-free and soil-tolerant green catalysts for the copolymerization of CO2 and propylene oxide（PO）, but they suffer from relatively poor poly（propylene carbonate）（PPC） se...Aluminum porphyrin complexes are heavy-metal-free and soil-tolerant green catalysts for the copolymerization of CO2 and propylene oxide（PO）, but they suffer from relatively poor poly（propylene carbonate）（PPC） selectivity. Herein, steric hindrance porphyrin ligand was used to enhance the PPC selectivity. Typically, a bulky anthracene-like group was incorporated into the porphyrin ring to form 5,10,15,20-tetra（1,2,3,4,5,6,7,8-octahydro-1,4：5,8-dimethanoanthracen-9-yl）porphyrin, the aluminum porphyrin complex with this ligand, in combination with bis（triphenylphosphine）iminium chloride as a co-catalyst, produced completely alternate PPC. Additionally, the obtained PPC showed high regioselectivity, with a head-to-tail linkage content（HT） of 92%. Therefore, we demonstrated that introduction of bulky steric ligand into the porphyrin ring could reduce the propylene oxide homopolymerization activity leading to excellent PPC selectivity, and improve regioselectivity for the PO ring-opening during the copolymerization.展开更多
Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we pres...Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we present our progress in the design of fluorene-based bulky semiconductors with a fractal four-element pattern. Firstly, we established one-pot methods to spirofluorenes, especially spiro[fluorene-9,9＇-xanthene] （SFX） serving as the next-generation spiro-based semiconductors. Secondly, we observed the supramolecular forces at the bulky groups and discovered the supramolecular steric hindrance （SSH） effect on polymorphisms, nanocrystals as well as device performance. Thus, a synergistically molecular attractor-repulsor theory （SMART） was proposed for the control of nanocrystal morphology, thin film phase and morphology. Thirdly, the third possible type of defects has been identified to generate green band （g-band） emission in wide- bandgap semiconductors by the introduction of molecular strain design of cyclofluorene. Finally, the first bulky polydiarylfluorene with highly crystalline and β conformation was achieved by an attractor-repulsor design of tadpole-shape monomer, which offered an effective platform to fabricate stable wide-bandgap semiconducting devices. All the discoveries offer the solid basis to break through bottlenecks of organic/polymer wide-bandgap semiconductors by the improvements of overall performances.展开更多
The self-assembly reactions between mixed-ligand and tetrahydrate dysprosium acetate in the presence of mixed organic solvents lead to two structural similar dinuclear dysprosium complexes with composition formulas of...The self-assembly reactions between mixed-ligand and tetrahydrate dysprosium acetate in the presence of mixed organic solvents lead to two structural similar dinuclear dysprosium complexes with composition formulas of Dy_(2)(L_1)_(2)(L_(2))_(2)(CH_(3)OH)_(2)·CH_(2)Cl_(2)·CH_(3)OH(1) and Dy_(2)(L_1)_(2)(L_(3))_(2)(CH_(3)OH)_(2)·CH_(3)CN(2),where L_1,L_(2) and L_(3) represent the deprotonated form of 4-tert-butyl-2-(7-methoxybenzo[d]oxazol-2-yl)phenol,(E)-1-(((3,5-di-tert-butyI-2-hydroxyphenyI)imino)methyl)naphthalen-2-ol and(E)-2,4-di-tertbutyl-6-((2-hydroxybenzylidene)amino)phenol.The tiny difference of the core structure of 1 and 2 is derived from the steric hindrance of Schiff base ligands L_(2) and L_(3).Dynamic magnetic measurements reveal that 1 and 2 show frequency-dependent out-of-phase alternating-current susceptibility signal peaks at different temperatures under zero dc field,diagnostic of single-molecule magnet behavior.The experimental derived energy barrier to magnetization reversal for 1 and 2 is 108(1),47(2) and 33(3) K.Ab initio CASSCF calculations performed on 1 and 2 suggest that the origin of the difference in magnetic properties originates from the variation in the single-ion anisotropy that arises due to minor structural variation.Further,the equation to calculate the effective energy barrier for Dy_(2) proposed earlier is found to yield an excellent agreement with the experimental results.Solid state fluorescence measurements performed on 1 and 2 demonstrate that both exhibit two ligands centered components of fluorescent emissive,in addition,with different emitting colors and chromaticity coordinates.The discrepancy of fluorescence and single molecule magnet behavior showed by 1 and 2 can be attributed to the steric hindrance effect of Schiff base ligands.展开更多
In this study the steric height anomaly which is calculated from the hydrological data （EN3） is compared with the sea level anomaly derived from satellite altimetry in the Nordic Seas. The overall pattern of steric ...In this study the steric height anomaly which is calculated from the hydrological data （EN3） is compared with the sea level anomaly derived from satellite altimetry in the Nordic Seas. The overall pattern of steric height is that it is higher in the margin area and lower in the middle area. The extreme values of steric height linear change from 1993 to 2010 occur in the Lofoten Basin and off the Norwegian coast, respectively. Such a distribution may be partly attributed to the freshening trend of the Nordic Seas. The correlation between SLA （sea level anomaly） and SHA （steric height anomaly） is not uniform over the Nordic Seas. The time series of SLA and SHA agree well in the Lofoten Basin and northern Norwegian Basin, and worse in the northern Norwegian Sea, implying that the baroclinic effect plays a dominant role in most areas in the Norwegian Sea and the barotropic effect plays a dominant role in the northern Norwegian Sea. The weaker correlations between SLA and SHA in the Greenland and Iceland Seas lead a conclusion that the barotropic contribution is significant in these areas. The area-mean SHA over the entire Nordic Seas has similar amplitudes compared with the SLA during 1996-2002, but SHA has become lower than SLA, being less than half of SLA since 2006.展开更多
Rare earth catalysts possessing characteristics of cation-anion ion pair show advantages of adjusting electronegativity and steric hindrance of metal active sites, which can control the catalytic performance and stere...Rare earth catalysts possessing characteristics of cation-anion ion pair show advantages of adjusting electronegativity and steric hindrance of metal active sites, which can control the catalytic performance and stereoselectivity better than those of traditional metallocene and Ziegler-Natta catalysts in diene polymerization. In this work, a series of neodymium organic sulfonate complexes,Nd(CF_3SO_3)_3·x H_2O·y L(x, y: the coordination number; L refers to an organic electron donating ligand, such as acetylacetone(acac), isooctyl alcohol(IAOH), tributyl phosphate(TBP), etc.), have been synthesized to form the cationic active species in the presence of alkylaluminum such as Al(i-Bu)_3, AlEt_3, and Al(i-Bu)_2H, which display high activities and distinguishing cis-1,4 selectivities(up to99.9%) for the polymerization of butadiene. The microstructures, yield, molecular weight, and molecular weight distribution of the resulting polymer are well controlled by adjusting electronegativity/steric hindrance of the complexes. In addition, the kinetics, active species, and the possible process of polymerization are also discussed in this article.展开更多
To reveal the steric sea level change in 20th century historical climate simulations and future climate change projections under the IPCC＇s Representative Concentration Pathway 8.5 （RCP8.5） scenario, the results of...To reveal the steric sea level change in 20th century historical climate simulations and future climate change projections under the IPCC＇s Representative Concentration Pathway 8.5 （RCP8.5） scenario, the results of two versions of LASG/IAP＇s Flexible Global Ocean-Atmosphere-Land System model （FGOALS） are analyzed. Both models reasonably reproduce the mean dynamic sea level features, with a spatial pattern correlation coefficient of 0.97 with the observation. Characteristics of steric sea level changes in the 20th century historical climate simulations and RCPS.5 scenario projections are investigated. The results show that, in the 20th century, negative trends covered most parts of the global ocean. Under the RCPS.5 scenario, global-averaged steric sea level exhibits a pronounced rising trend throughout the 21st century and the general rising trend appears in most parts of the global ocean. The magnitude of the changes in the 21st century is much larger than that in the 20th century. By the year 2100, the global-averaged steric sea level anomaly is 18 cm and 10 cm relative to the year 1850 in the second spectral version of FGOALS （FGOALS-s2） and the second grid-point version of FGOALS （FGOALS-g2）, respectively. The separate contribution of the thermosteric and halosteric components from various ocean layers is further evaluated. In the 20th century, the steric sea level changes in FGOALS-s2 （FGOALS-g2） are largely attributed to the thermosteric （halosteric） component relative to the pre-industrial control run. In contrast, in the 21st century, the thermosteric component, mainly from the upper 1000 m, dominates the steric sea level change in both models under the RCPS.5 scenario. In addition, the steric sea level change in the marginal sea of China is attributed to the thermosteric component.展开更多
A diamine monomer 4,4′-methylenedianiline（MDA） was introduced to modify the polyimide of pyromellitic dianhydride（PMDA） and 4,4′-oxydianiline（ODA） by polycondensation. A series of polyamic acids was synthesize...A diamine monomer 4,4′-methylenedianiline（MDA） was introduced to modify the polyimide of pyromellitic dianhydride（PMDA） and 4,4′-oxydianiline（ODA） by polycondensation. A series of polyamic acids was synthesized from MDA and ODA of different molar ratios with PMDA of sum mole of moles of MDA and ODA, and polyimide films were obtained by thermal imidization. Polyimide（PI） films were characterized by tensile testing, dynamic mechanical analysis（DMA）, thermal gravimetry analysis（TGA）, Fourier transform infrared spectroscopy （FTIR）, wide X-ray diffraction（WAXD） and molecular simulation. With the increase of MDA content, the tensile strength and thermal decomposition temperature remained generally stable compared with those of PMDA/ODA polyimide. Unexpectedly, the glass transition temperature（Tg） and Young＇s modulus increased from 388.7 °C and 2.37 GPa to 408.3 °C and 5.74 GPa, respectively. The results of WAXD and molecular simulation indicate the steric hindrance among hydrogen atoms of the linkage groups and adjacent phenyls enhanced the properties of the polyimide modified with MDA.展开更多
Norbornene derivatives exo,endo-2-[2-(3,5-di-tert-butyl-4-hydroxyphenoxy)-acetoxy]methyl-5-norbornene(M1) and 3,3,5,5-tetramethyl-4-piperidinyl 5-norbornene-exo,endo-2-carboxylate(M2)were synthesized and polymerized b...Norbornene derivatives exo,endo-2-[2-(3,5-di-tert-butyl-4-hydroxyphenoxy)-acetoxy]methyl-5-norbornene(M1) and 3,3,5,5-tetramethyl-4-piperidinyl 5-norbornene-exo,endo-2-carboxylate(M2)were synthesized and polymerized by RuCl_2(=CHPh)(PCy_3)_2 to prepare a novel kind of bi-functional polymer bearing sterically hindered phenol(SHP)and hindered amine(HLAS)groups via ring-opening metathesis polymerization(ROMP).The resulting copolymers were characterized by gel permeation chromatography(GPC),~1H-NMR and differen...展开更多
A series of brominated polynorbornene derivatives,including bulky steric hydrophobic groups and highly physical and chemical stable backbones,were synthesized via ring-opening metathesis polymerization and post-functi...A series of brominated polynorbornene derivatives,including bulky steric hydrophobic groups and highly physical and chemical stable backbones,were synthesized via ring-opening metathesis polymerization and post-functionalized with trimethylammonium(QA),N-methylimidazole(Im),N-methylpyrrolidinium(Pyr)or N-methylpiperidinium(Pip)to construct the entire anion exchange membranes(AEMs).Benefited from prominent phase-separated morphology,PBO-x%-y(x=66,68,70;y=QA,Im,Pyr,Pip)AEMs with ion exchange capacity(IEC)approaching 2.0 meq·g^(−1)exhibited super high hydroxide conductivities.Thereinto,PBO-70%-Pip possessed the highest hydroxide conductivity of 137.3 mS·cm^(−1)at 80℃Moreover,all membranes exhibit low swelling ratio(SR)(the SR of PBO-66%-QA was just 8.6%at 80℃).That is,bulky steric hydrophobic groups play a crucial role in balancing the high hydroxide conductivity and low SR in AEMs.Furthermore,three AEMs(PBO-66%-QA,PBO-68%-Pyr,PBO-70%-Pip)showed good alkaline stability after immersion into 1.0 mol/L NaOH aqueous solution at 80℃for 480 h without any degradation.展开更多
基金funded by the National Key Research and Development Program of China(2022YFB2404500)the Shenzhen Outstanding Talents Training Fund(01090100002)the National Natural Science Foundation of China(52201280)。
文摘The practical application of emerging rechargeable aqueous zinc(Zn)batteries is challenged by the poor reversibility and cycling stability of Zn anodes,primarily due to parasitic side reactions.While numerous strategies have been proposed,balancing the suppression of side reactions with the maintenance of fast Zn plating/stripping kinetics remains a significant challenge.In this study,sucrose,a sterically-hindered organic molecule with abundant hydroxyl groups,is employed to suppress the side reactions and maintain the moderate kinetics of Zn plating/stripping by modulating the hydrogen bond network without altering the Zn^(2+)solvation structure.Its steric hindrance effect further impedes the lateral diffusion of Zn atoms on the electrode surface within the electric double layer,effectively mitigating dendrite growth and stabilizing the electrodeposition process.Consequently,the formulated Suc/ZnSO_(4)electrolyte achieves a remarkably Coulombic efficiency of 99.90% over 2600 cycles at 3 mA cm^(-2)for 1 mAh cm^(-2)in Zn‖Cu cells.The enhanced Zn anode reversibility leads to excellent cycling stability in Zn‖LiFePO_(4)cells and Zn‖β-MnO_(2)cells.This study underscores the potential of sterically-hindered organic molecule strategies to enhance Zn anode stability while maintaining favorable Zn deposition/stripping dynamics in aqueous Zn batteries.
基金financially supported by the National Key Research and Development Program of China (No. 2023YFB3608902)the National Natural Science Foundation of China (Nos. 22275003, 12404460)+3 种基金Key-Area Research and Development Program of Guangdong Province (No. 2019B010924003)Development and Reform Commission of Shenzhen Municipality (No. XMHT20220106002)Guangdong Key Laboratory of Flexible Optoelectronic Materials and Devices, the Foundation for Youth Innovative Talents in Higher Education of Guangdong Province (No. 2023KQNCX094)the Guangdong Basic and Applied Basic Research Foundation (No. 2023A1515111072)。
文摘Multiple donor-acceptor(D-A) combinations represent a promising category of thermally activated delayed fiuorescence(TADF) materials, offering potential for superior efficiency and stability. However, current systems are predominantly composed of limited donor groups, primarily carbazole-based derivatives. In this work, we developed a series of D-A type materials incorporating helical π-expanded carbazole(Cz Naph) and 7H-dinaphtho[1,8-bc:1,8-ef]azepine(Az Naph), alongside traditional carbazole, ranging from mono-to tetra-substituted configurations(D_(n)-A). Through systematic investigation of geometric and electronic structures, the number and positioning of multiple donors are confirmed with significant manipulations on charge transfer characteristics and the S_(1) state via steric effects. Density functional theory(DFT) calculations reveal that varying the number of π-extended donors within the acceptor framework produces emission colors from ultraviolet to red, providing a diverse range of emitters. Furthermore, the reduced reorganization energy of S1observed in tetra-substituted Cz and Cz Naph, as well as Mono Az N, indicates lower structural relaxation, highlighting these materials' potential as stable luminescent candidates. This study underscores the importance of diverse composing units in achieving efficient and stable TADF emitters with multiple and hetero-donor configurations.
基金supported by the State Key Research Development Program of China(No.2021YFB3800701)National Natural Science Foundation of China(NSFC,No.52173016)+2 种基金Guangdong Basic and Applied Basic Research Foundation(Nos.2024A1515012784,2024A1515011102,and 2023A1515110549)Fundamental Research Funds for the Central Universities,Sun Yat-sen University(No.24qnpy047)PetroChina Scientific and Technological Projects(No.2022DJ6308).
文摘A series of“half-sandwich”bis(imino)pyridyl iron complexes with a substituted 8-(p-Xphenyl)naphthylamine(X=OMe,Me,CF3)was designed and synthesized by combining weakπ-πinteraction with steric and electronic tunings.The weak noncovalentπ-πinteraction as well as the steric and electronic effects of bis(imino)pyridyl iron complexes were identified by experimental analyses and calculations.The roles of weakπ-πinteraction,steric bulk,and electronic tuning on the ethylene polymerization performance of bis(imino)pyridyl iron catalysts were studied in detail.The combination ofπ-πinteraction with steric and electronic tunings can access to thermally stable bis(imino)pyridyl iron at 130°C.
基金supported by the Key Technologies R&D Program of Xiamen(No.3502Z20231057)Industry Leading Key Projects of Fujian Province(No.2022H0057)+2 种基金the National Natural Science Foundation of China(No.21975212)High-Level Talent Start-Up Foundation of Xiamen Institute of Technology for financial support(No.YKJ23017R)Graduate Science and Technology Innovation Program of Xiamen University of Technology(No.YKJCX2023194).
文摘LiMnxFe1-xPO_(4) is a promising cathode candidate due to its high security and the availability of a high 4.1 V operating voltage and high energy density.However,the poor electrochemical kinetics and structural instability currently hinder its broader application.Herein,inspired by the hydrogen-bonded cross-linking and steric hindrance effect between short-chain polymer molecules(polyethylene glycol-400,PEG-400),the pomegranate-type LiMn_(0.5)Fe_(0.5)PO_(4)-0.5@C(P-LMFP@C)cathode materials with 3D ion/electron dual-conductive network structure were constructed through ball mill-assisted spray-drying method.The intermolecular effects of PEG-400 promote the spheroidization and uniform PEG coating of LMFP precursor,which prevents agglomeration during sintering.The 3D ion/electron dual-conductive network structure in P-LMFP@C accelerates the Li^(+)transport kinetics,improving the rate performance and cycling stability.As a result,the designed P-LMFP@C has remarkable electrochemical behavior,boasting excellent capacity retention(98%after 100 cycles at the 1C rate)and rate capability(91 mAh·g^(-1)at 20C).Such strategy introduces a novel window for designing high-performance olivine cathodes and offers compatibility with a range of energy storage materials for diverse applications.
基金supported by the National Natural Science Foundation of China(Grant nos.92372118,52072224)the Youth Innovation Team Project of Shandong Provincial Education Department(2021KJ093)+3 种基金the Natural Science Foundation of Shandong Province(ZR2020YQ35)the Qilu Young Scholar Funding of Shandong Universitythe Young Elite Scientists Sponsorship Program by CAST(YESS,2019QNRC001)the Natural Science Foundation of Shandong Provincial(ZR2023ZD52)。
文摘Li metal batteries(LMBs)offer signifi-cant potential as high energy density alternatives;nev-ertheless,their performance is hindered by the slow desolvation process of electrolytes,particularly at low temperatures(LT),leading to low coulombic efficiency and limited cycle stability.Thus,it is essential to opti-mize the solvation structure thereby achieving a rapid desolvation process in LMBs at LT.Herein,we introduce branch chain-rich diisopropyl ether(DIPE)into a 2.5 M Li bis(fluorosulfonyl)imide dipropyl ether(DPE)elec-trolyte as a co-solvent for high-performance LMBs at-20℃.The incorporation of DIPE not only enhances the disorder within the electrolyte,but also induces a steric hindrance effect form DIPE’s branch chain,excluding other solvent molecules from Li+solvation sheath.Both of these factors contribute to the weak interactions between Li^(+)and solvent molecules,effectively reducing the desolvation energy of the electrolyte.Consequently,Li(50μm)||LFP(mass loading~10 mg cm^(-2))cells in DPE/DIPE based electrolyte demonstrate stable performance over 650 cycles at-20℃,delivering 87.2 mAh g^(-1),and over 255 cycles at 25℃ with 124.8 mAh g^(-1).DIPE broadens the electrolyte design from molecular structure considera-tions,offering a promising avenue for highly stable LMBs at LT.
基金jointly supported by the Guangdong Major Project of Basic and Applied Basic Research (2023B0303000002)National Natural Science Foundation of China (22178126,22325802,U22A20417,22208110)+3 种基金Guangdong Basic and Applied Basic Research Foundation (2023B1515120005)Science and Technology Program of Guangzhou (2023B03J1281,2023A04J1357)China Postdoctoral Science Foundation (2023T160223)the State Key Laboratory of Pulp and Paper Engineering (2023ZD03)。
文摘Viologens known as a kind of promising negolyte materials for aqueous organic redox flow batteries,face a critical stability challenge due to the S_N2 nucleophilic attack by hydroxide ions(OH-)during the battery cycling.In this work,a N-cyclic quaternary ammonium-grafted viologen molecule,viz.1,1'-bis(4,4'-dime thylpiperidiniumyl)-4,4'-bipyridinium tetrachloride((DBPPy)Cl_(4)),is developed by the molecular engineering strategy.The obtained(DBPPy)Cl_(4) molecule shows a decent solubility of 1.84 M and a redox potential of-0.52 V vs.Ag/AgCl,Experimental and theoretical results reveal that the grafted N-cyclic quaternary ammonium groups act as the steric hindrance to prevent nucleophilic attack by OH~-,increasing the alkali resistance of the electroactive molecule.The symmetrical battery with 0.50 M(DBPPy)Cl4shows negligible decay during the 13-day cycling test.As demonstration,the flow battery utilizing 1.0 M(DBPPy)Cl_(4) as the negolyte and 1-(1-oxyl-2,2',6,6'-tetramethylpiperidin-4-yl)-1'-(3-(trimethylammonio)propyl)-4,4'-bipyridinium trichloride as the posolyte exhibits a high capacity retention rate of 99.99%per cycle at 60 mA cm^(-2).
基金supported by the National Natural Science Foundation of China(52203016)the USTC Research Funds of the Double First-Class Initiative(YD9990002018)+3 种基金the Overseas Students Innovation and Entrepreneurship Support Program Project of Anhui Province(2021LCX022)the Key R&D Projects in Anhui Province(2022i01020012)the Natural Science Foundation of Hefei(2022039)the Excellent Research and Innovation Team Project of Anhui Province(2022AH010001).
文摘α-Diimide catalysts have attracted widespread attention due to their unique chain walking characteristics.A series ofα-diimide nickel/palladium catalysts with different electronic effects and steric hindrances were designed and synthesized for olefin polymerization.In this work,we synthesized a series of asymmetricα-diimide nickel complexes with different steric hindrances and used them for ethylene polymerization.These nickel catalysts have high ethylene polymerization activity,up to 6.51×10^(6)g·mol^(−1)·h^(−1),and the prepared polyethylene has a moderate melting point and high molecular weight(up to 38.2×10^(4)g·mol^(−1)),with a branching density distribution between 7 and 94 branches per 1000 carbons.More importantly,the polyethylene prepared by these catalysts exhibits excellent tensile properties,with strain and stress reaching 800%and 30 MPa,respectively.
基金Supported by the National Key R&D Program of China(No.2016YFC1401008)the National Natural Science Foundation of China(No.41706203)。
文摘The relative contributions of surface temperature and salinity to steric sea-level variations are investigated using satellite observations and reanalysis datasets.By defi ning a contribution factor,the relative roles of thermal and haline steric height variations are quantifi ed over the South China Sea(SCS).The thermosteric height dominates the steric sea level variation in the northern SCS deep basin,while the contribution of the halosteric height increases southward.Further investigation reveals that this transition is related to the meridional imbalance of surface heat flux and precipitation variations.The revealed steric constitution distribution is not confi ned to the surface but extends within the upper layer to approximately 50m depth,and then the thermosteric component dominates from the depth underneath.The results of this study clarify the steric sea level constitution over the SCS,benefit the understanding of sea-level variations at the regional scale,and may further facilitate multisensor remote sensing data mining studies.
基金financially supported by the Fundamental Research Funds for the Central Universities (WK2060200025)Advanced Catalysis and Green Manufacturing Collaborative Innovation Center (ACGM2016-06-01)Yixing Taodu Ying Cai Program
文摘Naphthyl-α-diimine nickel complexes with systematically varied ligand sterics, activated by modified methylaluminoxane（MMAO）, were tested in the polymerization of higher α-olefin（1-hexene, 1-decene and 1-hexadecene） under suitable conditions. The polymerization results indicated the possibility of precise microstructure control, depending on catalyst structure, polymerization temperature, monomer concentration and types of monomers, which in turn strongly affects the resultant polymer properties. Naphthyl-α-diimine nickel complex bearing chiral bulky sec-phenethyl groups in the o-naphthyl position showed good catalytic activity, and resulted in branched polymers（42-88/1000 C） with high molecular weights（Mn：（4.3-15.2） × 10^4 g·mol^-1） and narrow molecular weight distribution（Mw/Mn = 1.13-1.29, RT）, which suggested a living polymerization. The increasing steric hindrance of catalyst leads to enhance insertion for 2,1-insertion of α-olefin and the chain-walking reaction.
基金Project supported by the National Natural Science Foundation of China (50973003)Anhui Science and Technology Program (090518026)+1 种基金Natural Science Foundation of Fuyang Normal College (2011CXY04,2009FSKJ04,2011HJJC02ZD,2011HJJC01ZD,2011HJJC05YB,2011HJJC04YB,2011HJJC03YB,2010FSKJ01ZD)Open fund of State Key Laboratory of Rare Earth Materials Chemistry and Applications (RE201101)
文摘The rare earth complexes Tb（o-BrBA）3,Tb（m-BrBA）3 and Tb（p-BrBA）3 were synthesized using o-,m-,p-bromo benzoic acids（2-bromo benzoic acid,3-bromo benzoic acid and 4-bromo benzoic acid） as ligand,respectively.The UV spectra showed that the absorption ability of Tb（m-BrBA）3 was the strongest.However,the fluorescent intensity of Tb（o-BrBA）3 was the weakest.The effect of the molecular structure,the energy level of Tb3＋ and energy transfer efficiency from ligands to Tb3＋ were discussed to explain the experimental results.The results indicated that,due to the large atomic radius of bromine,the steric effect caused by the different substitution bromine on the benzene ring might strongly affect the bond length formed by the coordination atoms and Tb3＋.The longer the bond length was,the lower the efficiency of energy transfer was,and the weaker the fluorescent intensity was.
基金Project supported by the National Natural Science Fund. (Nos. E 85111 and 4890275)
文摘The exchange action of six types of organic phenols on clay surfaces in seawater is systematically studied in this work. The following significant conclusions are drawn from the experiments. (1) The interaction of organic phenols with montmorillonite, illite and kaolinite in seawater is monovalent anion exchage.(2) Their isotherms of stepwise exchage on clay surfaces belong to the Langmuir type or stepwise type.(3) The discovery of the"steric hindrance effects of stepwise exchange of organic phenols on clays surfaces", and revelation of an exchange mechanisrn diffeient from that in references are the greatest achieverments in this work.
基金financially supported by the National Natural Science Foundation of China(No.51673193)Key Project for Frontier Research(2016)Youth Innovation Promotion Association Chinese Academy of Sciences
文摘Aluminum porphyrin complexes are heavy-metal-free and soil-tolerant green catalysts for the copolymerization of CO2 and propylene oxide（PO）, but they suffer from relatively poor poly（propylene carbonate）（PPC） selectivity. Herein, steric hindrance porphyrin ligand was used to enhance the PPC selectivity. Typically, a bulky anthracene-like group was incorporated into the porphyrin ring to form 5,10,15,20-tetra（1,2,3,4,5,6,7,8-octahydro-1,4：5,8-dimethanoanthracen-9-yl）porphyrin, the aluminum porphyrin complex with this ligand, in combination with bis（triphenylphosphine）iminium chloride as a co-catalyst, produced completely alternate PPC. Additionally, the obtained PPC showed high regioselectivity, with a head-to-tail linkage content（HT） of 92%. Therefore, we demonstrated that introduction of bulky steric ligand into the porphyrin ring could reduce the propylene oxide homopolymerization activity leading to excellent PPC selectivity, and improve regioselectivity for the PO ring-opening during the copolymerization.
基金financially supported by the National Natural Science Funds for Excellent Young Scholar(No.21322402)the National Natural Science Foundation of China(Nos.21274064,61475074,21504041 and 61136003)+3 种基金University of Jiangsu Province Natural Science Foundation Project(No.14KJB510027)Natural Science Foundation of Jiangsu Province(No.BM2012010)Excellent Science and Technology Innovation Team of Jiangsu Higher Education Institutions,Synergetic Innovation Center for Organic Electronics and Information Displays,Natural Science of the Education Committee of Jiangsu Province(No.15KJB430019)Jiangsu Planned Projects for Postdoctoral Research Funds(No.1501019B)
文摘Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we present our progress in the design of fluorene-based bulky semiconductors with a fractal four-element pattern. Firstly, we established one-pot methods to spirofluorenes, especially spiro[fluorene-9,9＇-xanthene] （SFX） serving as the next-generation spiro-based semiconductors. Secondly, we observed the supramolecular forces at the bulky groups and discovered the supramolecular steric hindrance （SSH） effect on polymorphisms, nanocrystals as well as device performance. Thus, a synergistically molecular attractor-repulsor theory （SMART） was proposed for the control of nanocrystal morphology, thin film phase and morphology. Thirdly, the third possible type of defects has been identified to generate green band （g-band） emission in wide- bandgap semiconductors by the introduction of molecular strain design of cyclofluorene. Finally, the first bulky polydiarylfluorene with highly crystalline and β conformation was achieved by an attractor-repulsor design of tadpole-shape monomer, which offered an effective platform to fabricate stable wide-bandgap semiconducting devices. All the discoveries offer the solid basis to break through bottlenecks of organic/polymer wide-bandgap semiconductors by the improvements of overall performances.
基金Project supported by National Natural Science Foundation of China (21601143)Natural Science Foundation of Shaanxi Province (2021JM309)+2 种基金Open Funds of the State Key Laboratory of Rare Earth Resource of Changchun Institute of Applied Chemistry (RERU2021012)Science and Technology Innovation Team Program of Shaanxi Province (2022TD-32) and DST/SERB (CRG/2018/000430,DST/SJF/CSA03/2018-10SB/SJF/2019-20/12)。
文摘The self-assembly reactions between mixed-ligand and tetrahydrate dysprosium acetate in the presence of mixed organic solvents lead to two structural similar dinuclear dysprosium complexes with composition formulas of Dy_(2)(L_1)_(2)(L_(2))_(2)(CH_(3)OH)_(2)·CH_(2)Cl_(2)·CH_(3)OH(1) and Dy_(2)(L_1)_(2)(L_(3))_(2)(CH_(3)OH)_(2)·CH_(3)CN(2),where L_1,L_(2) and L_(3) represent the deprotonated form of 4-tert-butyl-2-(7-methoxybenzo[d]oxazol-2-yl)phenol,(E)-1-(((3,5-di-tert-butyI-2-hydroxyphenyI)imino)methyl)naphthalen-2-ol and(E)-2,4-di-tertbutyl-6-((2-hydroxybenzylidene)amino)phenol.The tiny difference of the core structure of 1 and 2 is derived from the steric hindrance of Schiff base ligands L_(2) and L_(3).Dynamic magnetic measurements reveal that 1 and 2 show frequency-dependent out-of-phase alternating-current susceptibility signal peaks at different temperatures under zero dc field,diagnostic of single-molecule magnet behavior.The experimental derived energy barrier to magnetization reversal for 1 and 2 is 108(1),47(2) and 33(3) K.Ab initio CASSCF calculations performed on 1 and 2 suggest that the origin of the difference in magnetic properties originates from the variation in the single-ion anisotropy that arises due to minor structural variation.Further,the equation to calculate the effective energy barrier for Dy_(2) proposed earlier is found to yield an excellent agreement with the experimental results.Solid state fluorescence measurements performed on 1 and 2 demonstrate that both exhibit two ligands centered components of fluorescent emissive,in addition,with different emitting colors and chromaticity coordinates.The discrepancy of fluorescence and single molecule magnet behavior showed by 1 and 2 can be attributed to the steric hindrance effect of Schiff base ligands.
基金The Key Project of Chinese Natural Science Foundation under contract No.41330960the Chinese Polar Environment Comprehensive Investigation and Assessment Programs under contract No.CHINARE2014-04-03-01
文摘In this study the steric height anomaly which is calculated from the hydrological data （EN3） is compared with the sea level anomaly derived from satellite altimetry in the Nordic Seas. The overall pattern of steric height is that it is higher in the margin area and lower in the middle area. The extreme values of steric height linear change from 1993 to 2010 occur in the Lofoten Basin and off the Norwegian coast, respectively. Such a distribution may be partly attributed to the freshening trend of the Nordic Seas. The correlation between SLA （sea level anomaly） and SHA （steric height anomaly） is not uniform over the Nordic Seas. The time series of SLA and SHA agree well in the Lofoten Basin and northern Norwegian Basin, and worse in the northern Norwegian Sea, implying that the baroclinic effect plays a dominant role in most areas in the Norwegian Sea and the barotropic effect plays a dominant role in the northern Norwegian Sea. The weaker correlations between SLA and SHA in the Greenland and Iceland Seas lead a conclusion that the barotropic contribution is significant in these areas. The area-mean SHA over the entire Nordic Seas has similar amplitudes compared with the SLA during 1996-2002, but SHA has become lower than SLA, being less than half of SLA since 2006.
基金the National Natural Science Foundation of China(Nos.51473156 and 51873203)Key Projects of Jilin Province Science and Technology Development Plan(Nos.2018020108GX and 20160204028GX)
文摘Rare earth catalysts possessing characteristics of cation-anion ion pair show advantages of adjusting electronegativity and steric hindrance of metal active sites, which can control the catalytic performance and stereoselectivity better than those of traditional metallocene and Ziegler-Natta catalysts in diene polymerization. In this work, a series of neodymium organic sulfonate complexes,Nd(CF_3SO_3)_3·x H_2O·y L(x, y: the coordination number; L refers to an organic electron donating ligand, such as acetylacetone(acac), isooctyl alcohol(IAOH), tributyl phosphate(TBP), etc.), have been synthesized to form the cationic active species in the presence of alkylaluminum such as Al(i-Bu)_3, AlEt_3, and Al(i-Bu)_2H, which display high activities and distinguishing cis-1,4 selectivities(up to99.9%) for the polymerization of butadiene. The microstructures, yield, molecular weight, and molecular weight distribution of the resulting polymer are well controlled by adjusting electronegativity/steric hindrance of the complexes. In addition, the kinetics, active species, and the possible process of polymerization are also discussed in this article.
基金supported by the National High Technology Research and Development Program of China(863 Program)under Grant No.2010AA012304the"Strategic Priority Research Program-Climate Change:Carbon Budget and Related Issues"of the Chinese Academy of Sciences(Grant No.XDA05110301)the National Natural Science Foundation of China(Grant Nos.41125017 and 40890054)
文摘To reveal the steric sea level change in 20th century historical climate simulations and future climate change projections under the IPCC＇s Representative Concentration Pathway 8.5 （RCP8.5） scenario, the results of two versions of LASG/IAP＇s Flexible Global Ocean-Atmosphere-Land System model （FGOALS） are analyzed. Both models reasonably reproduce the mean dynamic sea level features, with a spatial pattern correlation coefficient of 0.97 with the observation. Characteristics of steric sea level changes in the 20th century historical climate simulations and RCPS.5 scenario projections are investigated. The results show that, in the 20th century, negative trends covered most parts of the global ocean. Under the RCPS.5 scenario, global-averaged steric sea level exhibits a pronounced rising trend throughout the 21st century and the general rising trend appears in most parts of the global ocean. The magnitude of the changes in the 21st century is much larger than that in the 20th century. By the year 2100, the global-averaged steric sea level anomaly is 18 cm and 10 cm relative to the year 1850 in the second spectral version of FGOALS （FGOALS-s2） and the second grid-point version of FGOALS （FGOALS-g2）, respectively. The separate contribution of the thermosteric and halosteric components from various ocean layers is further evaluated. In the 20th century, the steric sea level changes in FGOALS-s2 （FGOALS-g2） are largely attributed to the thermosteric （halosteric） component relative to the pre-industrial control run. In contrast, in the 21st century, the thermosteric component, mainly from the upper 1000 m, dominates the steric sea level change in both models under the RCPS.5 scenario. In addition, the steric sea level change in the marginal sea of China is attributed to the thermosteric component.
基金Supported by the National Natural Science Foundation of China(No.50973073)the Science and Technology Projects of Chengdu City, China(No.10GGYB114GX-182)
文摘A diamine monomer 4,4′-methylenedianiline（MDA） was introduced to modify the polyimide of pyromellitic dianhydride（PMDA） and 4,4′-oxydianiline（ODA） by polycondensation. A series of polyamic acids was synthesized from MDA and ODA of different molar ratios with PMDA of sum mole of moles of MDA and ODA, and polyimide films were obtained by thermal imidization. Polyimide（PI） films were characterized by tensile testing, dynamic mechanical analysis（DMA）, thermal gravimetry analysis（TGA）, Fourier transform infrared spectroscopy （FTIR）, wide X-ray diffraction（WAXD） and molecular simulation. With the increase of MDA content, the tensile strength and thermal decomposition temperature remained generally stable compared with those of PMDA/ODA polyimide. Unexpectedly, the glass transition temperature（Tg） and Young＇s modulus increased from 388.7 °C and 2.37 GPa to 408.3 °C and 5.74 GPa, respectively. The results of WAXD and molecular simulation indicate the steric hindrance among hydrogen atoms of the linkage groups and adjacent phenyls enhanced the properties of the polyimide modified with MDA.
基金Sasakawa Scientific Research Grant from the Japan Science Society.
文摘Norbornene derivatives exo,endo-2-[2-(3,5-di-tert-butyl-4-hydroxyphenoxy)-acetoxy]methyl-5-norbornene(M1) and 3,3,5,5-tetramethyl-4-piperidinyl 5-norbornene-exo,endo-2-carboxylate(M2)were synthesized and polymerized by RuCl_2(=CHPh)(PCy_3)_2 to prepare a novel kind of bi-functional polymer bearing sterically hindered phenol(SHP)and hindered amine(HLAS)groups via ring-opening metathesis polymerization(ROMP).The resulting copolymers were characterized by gel permeation chromatography(GPC),~1H-NMR and differen...
基金the National Natural Science Foundation of China(No.52130307)Foundation of State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering(No.2018-K05).
文摘A series of brominated polynorbornene derivatives,including bulky steric hydrophobic groups and highly physical and chemical stable backbones,were synthesized via ring-opening metathesis polymerization and post-functionalized with trimethylammonium(QA),N-methylimidazole(Im),N-methylpyrrolidinium(Pyr)or N-methylpiperidinium(Pip)to construct the entire anion exchange membranes(AEMs).Benefited from prominent phase-separated morphology,PBO-x%-y(x=66,68,70;y=QA,Im,Pyr,Pip)AEMs with ion exchange capacity(IEC)approaching 2.0 meq·g^(−1)exhibited super high hydroxide conductivities.Thereinto,PBO-70%-Pip possessed the highest hydroxide conductivity of 137.3 mS·cm^(−1)at 80℃Moreover,all membranes exhibit low swelling ratio(SR)(the SR of PBO-66%-QA was just 8.6%at 80℃).That is,bulky steric hydrophobic groups play a crucial role in balancing the high hydroxide conductivity and low SR in AEMs.Furthermore,three AEMs(PBO-66%-QA,PBO-68%-Pyr,PBO-70%-Pip)showed good alkaline stability after immersion into 1.0 mol/L NaOH aqueous solution at 80℃for 480 h without any degradation.
