Magnetocaloric and colossal magnetoresistance effects of the layered perovskite La 1.4 Sr 1.6 Mn 2 O 7 compound have been studied.A broad peak of magnetic entropy change （-△S M） is found above the Curie temperature...Magnetocaloric and colossal magnetoresistance effects of the layered perovskite La 1.4 Sr 1.6 Mn 2 O 7 compound have been studied.A broad peak of magnetic entropy change （-△S M） is found above the Curie temperature （T C =120 K）,which can be associated with the existence of two-dimensional short range ferromagnetic order.Additionally,the curvilinear shape of-△S M for layered perovskite is quite different from that of the Ln 1-x A x MnO 3 probably arising from magnetocrystalline anisotropy.At the same time,a wide peak of colossal magnetoresitance effect near T C is found in the layered provskite La 1.4 Sr 1.6 Mn 2 O 7.展开更多
Durable and efficient bi-functional catalyst,that is capable of both oxygen evolution reaction and hydrogen evolution reaction under acidic condition,are highly desired for the commercialization of proton exchange mem...Durable and efficient bi-functional catalyst,that is capable of both oxygen evolution reaction and hydrogen evolution reaction under acidic condition,are highly desired for the commercialization of proton exchange membrane water electrolysis.Herein,we report a robust L-Ru/HfO_(2)heterostructure constructed via confining crystalline Ru nanodomains by HfO_(2)matrix.When assembled with a proton exchange membrane,the bi-functional L-Ru/HfO_(2)catalyst-based electrolyzer presents a voltage of 1.57 and 1.67 V to reach 100 and 300 mA cm^(-2)current density,prevailing most of previously reported Ru-based materials as well as commercial Pt/C||RuO_(2)electrolyzer.It is revealed that the synergistic effect of HfO_(2)modification and small crystalline domain formation significantly alleviates the over-oxidation of Ru.More importantly,this synergistic effect facilitates a dual-site oxide path during the oxygen evolution procedure via optimization of the binding configurations of oxygenated adsorbates.As a result,the Ru active sites maintain the metallic state along with reduced energy barrier for the rate-determining step(^(*)O→^(*)OOH).Both of water adsorption and dissociation(Volmer step)are strengthened,while a moderate hydrogen binding is achieved to accelerate the hydrogen desorption procedure(Tafel step).Consequently,the activity and stability of acidic overall water splitting are simultaneously enhanced.展开更多
Brookhart-typeα-diimine nickel and palladium catalysts have been extensively studied over the past several decades;however,the heterogenization of these metal complexes has received much less attention.In this contri...Brookhart-typeα-diimine nickel and palladium catalysts have been extensively studied over the past several decades;however,the heterogenization of these metal complexes has received much less attention.In this contribution,we installed a trifluoroborate potassium substituent on anα-diimine framework.The ionic nature of trifluoroborate potassium endowed theα-diimine nickel complex with a strong affinity for the SiO_(2)support,while its electron-donating nature enhanced the catalyst stability and polyethylene molecular weight.In the presence of only 100 equiv.of Et2AlCl cocatalyst,the SiO_(2)-supported catalyst demonstrated significantly better performance than its homogeneous analog during ethylene polymerization,with extremely high activity(1.42–6.53×10^(7)g mol^(−1)h^(−1))and high thermal stability.The heterogeneous system led to the formation of high-molecular-weight polyethylenes(Mn 142,500–732,800 g/mol),narrow polydispersities(2.18–3.00),tunable branching densities(21–64 per 1000 carbon atoms),and great mechanical properties.Moreover,the efficient copolymerization of ethylene with comonomers such as methyl 10-undecenoate,6-chloro-1-hexene or 5-hexenylacetate was achieved.These superior properties enabled by the trifluoroborate potassium moiety may inspire its applications in other polymerization catalyst systems.展开更多
The tuning of olefin-polymerization catalyst properties through ligand modifications is efficient but requires complicated and costly syntheses.In this contribution,a simple Bu_(2)Mg-based cocatalyst strategy is desig...The tuning of olefin-polymerization catalyst properties through ligand modifications is efficient but requires complicated and costly syntheses.In this contribution,a simple Bu_(2)Mg-based cocatalyst strategy is designed that can simultaneously enhance the catalytic properties(activity,thermal stability,polymer molecular weight,branching density,melting point,etc.)of various nickel catalysts(α-diimine nickel,pyridine imine nickel and iminopyridine-N-oxide nickel)in ethylene polymerization,and enable great product morphology control.For example,a simpleα-diimine nickel catalyst can demonstrate polymerization activity of up to 1.29×10^(7)g mol^(−1)h^(−1)and molecular weight of up to 1.90×10^(6)g/mol in the presence of Bu_(2)Mg cocatalyst.The resulting polyethylenes exhibit excellent mechanical properties,with tensile stress of up to 47.4 MPa and strain of up to 1020%.This cocatalyst strategy is generally applicable to different nickel catalysts,and can lead to property enhancement in ethylene copolymerization with a series of polar comonomers such as methyl 10-undecylenate,10-undecylenic acid and 10-undecenol.展开更多
Objective: To study the effect of practicing Jianshenqigong-wuqinxi on subhealth problems including depression, anxiety, and memory loss. Methods: 1) 80 cases with subhealth problem were randomly divided into two grou...Objective: To study the effect of practicing Jianshenqigong-wuqinxi on subhealth problems including depression, anxiety, and memory loss. Methods: 1) 80 cases with subhealth problem were randomly divided into two groups. 40 cases practicing Jianshenqigong-wuqinxi were used as test group, and the other 40 unpracticing cases were used as control group. 2) The test group was practising Jianshenqigong-wuqinxi one hour in the morning five times per week for three months. 3) Scores of subhealth status such as depression and anxiety were evaluated once every two weeks, while the memory test was performed once a month. 4) Data analysis: SPSS11.0 software was used for statistical analyses. Data were shown in mean ± SEM. Difference was considered significant if the t-test P value is less than 0.05. Results: 1) Scores of subhealth state and depression were significantly lower in test group than those of control group. The beneficial effects of practicing Jianshenqigong-wuqinxi were more obvious for the subjects in the test group who had practiced Jianshenqigong-wuqinxi for two to twelve weeks (P < 0.05). 2) Scores of anxiety test were significantly lower in test group than those of control group after practicing Jianshenqigong-wuqinxi for six to twelve weeks (P < 0.05). 3) Scores of memory were significantly higher in test group than those of control group (P < 0.05). Conclusions: 1) Practicing Jianshenqigong-wuqinxi could promote health in people who have subhealth mental problems. 2) Practicing Jianshenqigong-wuqinxi could relieve depression, anxiety while enhance memory.展开更多
Orthorhombic YFeO_3 thin film was prepared on La_(0.67)Sr_(0.33)MnO_3/LaAlO_3 substrate by a sol-gel spin-coating method. The structures of the YFeO_3/La_(0.67)Sr_(0.33)MnO_3/LaAlO_3(YFO/LSMO/LAO) sample were detected...Orthorhombic YFeO_3 thin film was prepared on La_(0.67)Sr_(0.33)MnO_3/LaAlO_3 substrate by a sol-gel spin-coating method. The structures of the YFeO_3/La_(0.67)Sr_(0.33)MnO_3/LaAlO_3(YFO/LSMO/LAO) sample were detected by x-ray diffraction pattern, Raman spectrometer, scanning electron microscopy, and atomic force microscope. The local ferroelectric polarization switching properties of the orthorhombic YFO film were confirmed by piezoresponse force microscopy(PFM) for the first time. The results show that the YFO film deposited on LSMO/LAO possesses orthorhombic structure,with ultra-fine crystal grains and flat surface. The leakage current of the YFO film is 8.39 × 10^(-4) A·cm^(-2) at 2 V,with its leakage mechanism found to be an ohmic behavior. PFM measurements indicate that the YFO film reveals weak ferroelectricity at room temperature and the local switching behavior of ferroelectric domains has been identified. By local poling experiment, polarization reversal in the orthorhombic YFO film at room temperature was further observed.展开更多
The La0.85Sr0.015MnO3/Fe heterostructure deposited on Si （100） substrate was prepared by the magnetron sputtering. The laser-induced voltage in the sample and the difference in the voltage signals between the curre...The La0.85Sr0.015MnO3/Fe heterostructure deposited on Si （100） substrate was prepared by the magnetron sputtering. The laser-induced voltage in the sample and the difference in the voltage signals between the current-in-plane geometry and current-perpendicular-to-plane geometry at 77 K were investigated. This difference can be attributed to the different transport mechanisms.展开更多
The transport properties in the La2/3（Ca（1-x）Sr（x））1/3MnO3 （x=0.1/3, 2/3） films prepared using the RF magnetron sputtering method were investigated, The effect of the Ca, Sr double-doping at the A position in ...The transport properties in the La2/3（Ca（1-x）Sr（x））1/3MnO3 （x=0.1/3, 2/3） films prepared using the RF magnetron sputtering method were investigated, The effect of the Ca, Sr double-doping at the A position in the La（2/3）A（1/3）MnO3 on the structure of the targets and transport of the films has been studied. With the increase of x, the structures of the targets transform from the rhombohedral phase to the cubic phase; the metal-insulator phase transition temperature （Tp） of the films increases; and the corresponding peak resistivity decreases. All the phenomena can be qualitatively explained by the lattice effect.展开更多
The magneto-electric effect in magnetic materials has been widely investigated, but obtaining an enhanced magnetoelectric effect is challenging. In this study, tricolor superlattices composed of manganese oxides-Pr（...The magneto-electric effect in magnetic materials has been widely investigated, but obtaining an enhanced magnetoelectric effect is challenging. In this study, tricolor superlattices composed of manganese oxides-Pr（0.9）Ca（0.1）MnO3,La（0.9）Sr（0.1）MnO3, and La（0.9）Sb（0.1）MnO3-on（001）-oriented Nb：SrTiO3 substrates with broken space-inversion and timereversal symmetries are designed. Regarding the electric polarization in the hysteresis loops of the superlattices at different external magnetic fields, both coercive electric field Ec and remnant polarization intensity Pr clearly show strong magneticfield dependences. At low temperatures（〈 120 K）, a considerable magneto-electric effect in the well-defined tricolor superlattice is observed that is absent in the single compounds. Both maxima of the magneto-electric coupling coefficients ？Ec and ？Pr appear at 30 K. The magnetic dependence of the dielectric constant further supports the magneto-electric effect. Moreover, a dependence of the magneto-electric effect on the periodicity of the superlattices with various structures is observed, which indicates the importance of interfaces. Our experimental results verify previous theoretical results regarding magneto-electric interactions, thereby paving the way for the design and development of novel magneto-electric devices based on manganite ferromagnets.展开更多
Compared with the conventional strategies of electronic and/or steric perturbation,catalytic olefin polymerization modulated by light irradiation or metal-metal cooperativity effect is a fascinating challenge that att...Compared with the conventional strategies of electronic and/or steric perturbation,catalytic olefin polymerization modulated by light irradiation or metal-metal cooperativity effect is a fascinating challenge that attracts considerable attention in the academic community.In this context,we design a strategy that could employ both effects to influence the polymerization process.Some dinuclear salicylaldimine andα-imino-ketone nickel complexes bearing a stiff-stilbene bridge were prepared,which could transfer between(E)-isomers and(Z)-isomers under ultraviolet irradiation.This isomerization can tune the electronic,steric and metal-metal cooperativity effects of the nickel catalysts.In this way,the catalytic activity,as well as polymer microstructures including molecular weight and branching density can be modulated in ethylene polymerization and copolymerization reactions.This strategy is generally applicable to other olefin polymerization catalytic systems and other types of transition metal mediated catalysis.展开更多
A significant challenge in the recycling of plastics is the separation of various polymers. Mechanical recycling represents one of the most straightforward and cost-effective approaches to mitigate the escalating issu...A significant challenge in the recycling of plastics is the separation of various polymers. Mechanical recycling represents one of the most straightforward and cost-effective approaches to mitigate the escalating issue of plastic pollution. Unfortunately, the inevitable presence of mixed plastics in the waste stream and their phase separation always result in suboptimal properties for mechanically recycled materials. Multi-block copolymers(MBCPs) compatibilization represents an efficient strategy to address this issue and for upcycling of mixed plastics. The key to the implementation of this strategy lies in the efficient syntheses and structural modifications of diverse MBCPs. Especially, very few synthetic routes have been reported for the synthesis of MBCPs containing polyolefin blocks. In this contribution, we present a cyclic-acyclic monomers metathesis polymerization(CAMMP)mediated strategy for the preparation of polyolefin containing MBCPs using commercially available or easily accessible telechelic diol polymers. These polyolefins containing MBCPs can efficiently serve as compatibilizer additives for the upcycling of mixtures of polyolefins and other plastics. The combination of great variety of telechelic diol polymers with the ease of microstructure modification during CAMMP synthesis makes this strategy attractive for future investigations and potential practical applications.展开更多
The development of degradable polymers represents an appealing strategy to address ever-growing concerns for treating waste plastics.Olefin metathesis polymerization has been extensively explored for the synthesis of ...The development of degradable polymers represents an appealing strategy to address ever-growing concerns for treating waste plastics.Olefin metathesis polymerization has been extensively explored for the synthesis of various degradable polymers.Cyclic–acyclic monomers metathesis polymerization(CAMMP)has recently been reported to produce degradable polymers via copolymerization of cyclic monomers with acyclic diene comonomers.Unfortunately,this strategy suffers from poor product material properties,especially at high contents of diene comonomers.To address this issue,we have designed a tandem olefin metathesis polymerization(TOMP)system that combines olefin ringclosing metathesis(RCM)of diene comonomers,followed by ring-opening metathesis copolymerization(ROMCP)with cyclic olefin monomers(dicyclopentadiene,cyclooctene,or alkyl-substituted cyclooctene).This strategy overcame the intrinsic limitations of diene-induced chain-transfer reactions during olefin metathesis,leading to degradable polymers with high molecular weights and excellent material properties.The selection of different cyclic olefin monomers provided access to degradable and recyclable cross-linked thermosets,linear thermoplastics,and elastomers.Notably,this one-pot,two-step process was highly efficient and required the addition of only one metathesis catalyst.展开更多
The synthesis and design of transition metal catalysts have attracted extensive attention in ethylene polymer-ization.In this work,a series of α-diimine nickel catalysts(Ni1-Ni4)bearing ether substituents were design...The synthesis and design of transition metal catalysts have attracted extensive attention in ethylene polymer-ization.In this work,a series of α-diimine nickel catalysts(Ni1-Ni4)bearing ether substituents were designed and synthesized.The steric hindrance of these catalysts was systematically modulated by varying the ether groups,which directly influenced their ethylene(co)polymerization performances.These catalysts showed exceptionally high activities(up to 10^(7) g·mol^(-1)·h^(-1)).The resulting polyethylene displayed a broad range of branching densities(22 to 92/1000C)and high polymer molecular weights(up to 59.8×10^(4) g·mol^(-1)).Polyethylene produced by Ni1 and Ni2 exhibited outstanding mechanical properties and elastic recovery performance.Furthermore,these catalysts efficiently catalyzed ethylene copolymerization with diverse polar monomers,yielding copolymers with incorporation ratios ranging from 0.24%to 1.43%.展开更多
For transition metal-based olefin polymerization catalysts, ligand steric and electronic effects can strongly influence important catalytic properties. However, the simultaneous tuning of both steric and electronic ef...For transition metal-based olefin polymerization catalysts, ligand steric and electronic effects can strongly influence important catalytic properties. However, the simultaneous tuning of both steric and electronic effects has not been explored in most of the previous studies. In this contribution, a strategy to tune the ligand electronic and steric effects in a concerted fashion is reported. In such a system, both dibenzhydryl groups and multiple methoxy/fluoro groups were installed in α-diimine ligands. In addition to strongly influencing ligand electronics, the methoxy/fluoro groups can interact with the dibenzhydryl groups and efficiently increase ligand sterics. In ethylene polymerization, this concurrent tuning of electronic and steric effects can lead to simultaneous enhancement of several parameters(activity, stability, polymer molecular weight, melting point, branching density) for both the nickel and palladium catalysts. The effectiveness of this strategy is highly attractive for future studies in other catalytic systems.展开更多
In this review, a recent development of cationic ?-diimine palladium(II) complexes for ethylene polymerization and copolymerization with polar functionalized comonomers was briefly described. First, the polymerization...In this review, a recent development of cationic ?-diimine palladium(II) complexes for ethylene polymerization and copolymerization with polar functionalized comonomers was briefly described. First, the polymerization mechanism for this type of catalysts was discussed. Next, recent advances in ligand design were provided with special focus on the influence of ligand structures on the catalytic polymerization properties. Last, the ethylene homopolymerization and copolymerization with various polar comonomers, especially acrylate and vinyl ethers were summarized.展开更多
In the past few decades,the development of high-performance catalysts has been a key driving force and a center of research efforts in the field of olefin polymerization.However,a major discrepa ncy exists between in ...In the past few decades,the development of high-performance catalysts has been a key driving force and a center of research efforts in the field of olefin polymerization.However,a major discrepa ncy exists between in dustrial researches which utilize aliphatic hydrocarb on solventsz and academic researches which predominantly focus the catalytic properties in aromatic solvents.In this con-tribution,a novel diaryl-methyl aniline bearing eight tert-butyl groups was prepared and subsequently transformed to four different kinds of imine-type ligands.The corresponding nickel complexes as well as their counterparts derived from diphenyl-methyl aniline without the tert-butyl groups were prepared and investigated in ethylene polymerization.展开更多
The transition-metal-catalyzed copolymerization of olefins with polar comonomers is a direct strategy to access polar-functionalized polyolefins in an economical manner.Due to the intrinsic poisoning effect of polar g...The transition-metal-catalyzed copolymerization of olefins with polar comonomers is a direct strategy to access polar-functionalized polyolefins in an economical manner.Due to the intrinsic poisoning effect of polar groups towards Lewis acidic metal centers and the drastic reactivity differences of polar comonomers versus non-polar olefins,it is challenging to develop catalysts that provide the desired polymer molecular weight,comonomer incorporation,and activity.In this contribution,we tackle this issue from a comonomer perspective using 5,6-disubstituted norbornenes,which are highly versatile,easily accessible,inexpensive,and capable of introducing two functional groups in a single insertion.More importantly,they are only mildly poisoning due to the presence of long spacers between double bonds and polar groups,and are not prone to b-hydride elimination due to their cyclic structures.As strong pdonors,they can competitively bind to metal centers versus olefins.Indeed,phosphine-sulfonate palladium catalysts can catalyze the copolymerization of ethylene with 5,6-disubstituted norbornenes and simultaneously achieve a high polymerization activity,copolymer molecular weight,and comonomer incorporation.The practicality of this system was demonstrated by studying the properties of the resulting polymers,copolymerization in hydrocarbon solvents or in bulk,recovery/utilization of unreacted comonomer,molecular weight modulation,and large-scale synthesis.展开更多
Ziegler and Natta won the Nobel Prize in 1963 due to their contributions in olefin polymerization catalysis.Subsequent studies into related catalysts have led to a multibillion-dollar polyolefin industry.Currently,mor...Ziegler and Natta won the Nobel Prize in 1963 due to their contributions in olefin polymerization catalysis.Subsequent studies into related catalysts have led to a multibillion-dollar polyolefin industry.Currently,more than 178 million tons of polyolefin materials are produced annually,which constitute more than half of global plastics production.Interestingly,the metal nickel was initially recognized as a“poison”for olefin polymerization.Alkyl aluminum species can oligomerize ethylene(degree of polymerization up to 100)at high temperature and pressure;while the addition of nickel salt to the system led to the exclusive formation of 1-butene.This famous“nickel effect”marks the starting point of the era of Ziegler catalysts[1].After decades of research,the situation of nickel has changed dramatically,and a large number of nickelbased catalysts have been shown with the capabilities of producing high-molecular-weight polyethylene.As an exceptional demonstration,some groups have recently developed nickel catalysts that are able to produce ultra-high molecular weight polyethylene(UHMWPE).UHMWPE,with molecular weight of above one-million,is a special class of advanced engineering plastics with superior properties and wide applications.展开更多
A series of dibenzhydryl-based iminopyridine-N-oxide ligands bearing a range of electron-donating or-withdrawing substituents(OMe,H;and NO_(2))and corresponding nickel pre-catalysts are prepared and characterized.The ...A series of dibenzhydryl-based iminopyridine-N-oxide ligands bearing a range of electron-donating or-withdrawing substituents(OMe,H;and NO_(2))and corresponding nickel pre-catalysts are prepared and characterized.The substituents are installed at different positions on the ligand structure,including 4-position of the pyridine-N-oxide moiety(position X)and 4-position of the aniline moiety(position Y).These nickel pre-catalysts are highly active in ethylene polymerization with the addition of very little amount of aluminum cocatalysts,leading to the formation of polyethylenes with molecular weights of well above one million.Electron-donating substituents make the catalysts sensitive to polymerization temperature.In contrast,the catalysts bearing electron-withdrawing NO_(2) substituents show relatively steady performances at different temperatures.Most importantly,we demonstrate that different substituents and different positions both play important roles in determining the properties of nickel catalysts.This provides an alternative strategy for the future design of high-performance polymerization catalyst.展开更多
Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization.This type of catalyst features six-membered chelate ring size,and can enable the copolymerizations o...Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization.This type of catalyst features six-membered chelate ring size,and can enable the copolymerizations of ethylene with a wide variety of polar monomers.In this contribution,we decide to investigate the influence of chelate ring size on the properties of phosphinesulfonate palladium catalysts.As such,a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II)complexes[κ~2-(P,O)-2-(CH_2-PR_1R_2)-4-methylphenyl-sulfonato]Pd(Me)(DMSO)(Pd1,R_1=R_2=Cy,Pd2,R_1=R_2=o-Me O-C_6H_4;Pd3,R_1=Ph,R_2=2-[2,6-(Me O)_2C_6H_3]C_6H_4;DMSO=dimethyl sulfoxide)were designed,prepared and characterized.These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether.However,their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2′.The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50331040 and 60171043)
文摘Magnetocaloric and colossal magnetoresistance effects of the layered perovskite La 1.4 Sr 1.6 Mn 2 O 7 compound have been studied.A broad peak of magnetic entropy change （-△S M） is found above the Curie temperature （T C =120 K）,which can be associated with the existence of two-dimensional short range ferromagnetic order.Additionally,the curvilinear shape of-△S M for layered perovskite is quite different from that of the Ln 1-x A x MnO 3 probably arising from magnetocrystalline anisotropy.At the same time,a wide peak of colossal magnetoresitance effect near T C is found in the layered provskite La 1.4 Sr 1.6 Mn 2 O 7.
基金supported by the National Natural Science Foundation of China(Grant No.22279162,22261142664)Natural Science Fund for Colleges and Universities in Anhui Province(2022AH030057)CAS Project for Young Scientists in Basic Research(No.YSBR-094).
文摘Durable and efficient bi-functional catalyst,that is capable of both oxygen evolution reaction and hydrogen evolution reaction under acidic condition,are highly desired for the commercialization of proton exchange membrane water electrolysis.Herein,we report a robust L-Ru/HfO_(2)heterostructure constructed via confining crystalline Ru nanodomains by HfO_(2)matrix.When assembled with a proton exchange membrane,the bi-functional L-Ru/HfO_(2)catalyst-based electrolyzer presents a voltage of 1.57 and 1.67 V to reach 100 and 300 mA cm^(-2)current density,prevailing most of previously reported Ru-based materials as well as commercial Pt/C||RuO_(2)electrolyzer.It is revealed that the synergistic effect of HfO_(2)modification and small crystalline domain formation significantly alleviates the over-oxidation of Ru.More importantly,this synergistic effect facilitates a dual-site oxide path during the oxygen evolution procedure via optimization of the binding configurations of oxygenated adsorbates.As a result,the Ru active sites maintain the metallic state along with reduced energy barrier for the rate-determining step(^(*)O→^(*)OOH).Both of water adsorption and dissociation(Volmer step)are strengthened,while a moderate hydrogen binding is achieved to accelerate the hydrogen desorption procedure(Tafel step).Consequently,the activity and stability of acidic overall water splitting are simultaneously enhanced.
基金supported by National Key R&D Program of China(No.2021YFA1501700)National Natural Science Foundation of China(Nos.52025031,U19B6001 and U1904212)K.C.Wong Education Foundation.
文摘Brookhart-typeα-diimine nickel and palladium catalysts have been extensively studied over the past several decades;however,the heterogenization of these metal complexes has received much less attention.In this contribution,we installed a trifluoroborate potassium substituent on anα-diimine framework.The ionic nature of trifluoroborate potassium endowed theα-diimine nickel complex with a strong affinity for the SiO_(2)support,while its electron-donating nature enhanced the catalyst stability and polyethylene molecular weight.In the presence of only 100 equiv.of Et2AlCl cocatalyst,the SiO_(2)-supported catalyst demonstrated significantly better performance than its homogeneous analog during ethylene polymerization,with extremely high activity(1.42–6.53×10^(7)g mol^(−1)h^(−1))and high thermal stability.The heterogeneous system led to the formation of high-molecular-weight polyethylenes(Mn 142,500–732,800 g/mol),narrow polydispersities(2.18–3.00),tunable branching densities(21–64 per 1000 carbon atoms),and great mechanical properties.Moreover,the efficient copolymerization of ethylene with comonomers such as methyl 10-undecenoate,6-chloro-1-hexene or 5-hexenylacetate was achieved.These superior properties enabled by the trifluoroborate potassium moiety may inspire its applications in other polymerization catalyst systems.
基金supported by National Key R&D Program of China(No.2021 YFA 1501700)National Natural Science Foundation of China(Nos.52025031,U19B6001 and U1904212)K.C.Wong Education Foundation.
文摘The tuning of olefin-polymerization catalyst properties through ligand modifications is efficient but requires complicated and costly syntheses.In this contribution,a simple Bu_(2)Mg-based cocatalyst strategy is designed that can simultaneously enhance the catalytic properties(activity,thermal stability,polymer molecular weight,branching density,melting point,etc.)of various nickel catalysts(α-diimine nickel,pyridine imine nickel and iminopyridine-N-oxide nickel)in ethylene polymerization,and enable great product morphology control.For example,a simpleα-diimine nickel catalyst can demonstrate polymerization activity of up to 1.29×10^(7)g mol^(−1)h^(−1)and molecular weight of up to 1.90×10^(6)g/mol in the presence of Bu_(2)Mg cocatalyst.The resulting polyethylenes exhibit excellent mechanical properties,with tensile stress of up to 47.4 MPa and strain of up to 1020%.This cocatalyst strategy is generally applicable to different nickel catalysts,and can lead to property enhancement in ethylene copolymerization with a series of polar comonomers such as methyl 10-undecylenate,10-undecylenic acid and 10-undecenol.
文摘Objective: To study the effect of practicing Jianshenqigong-wuqinxi on subhealth problems including depression, anxiety, and memory loss. Methods: 1) 80 cases with subhealth problem were randomly divided into two groups. 40 cases practicing Jianshenqigong-wuqinxi were used as test group, and the other 40 unpracticing cases were used as control group. 2) The test group was practising Jianshenqigong-wuqinxi one hour in the morning five times per week for three months. 3) Scores of subhealth status such as depression and anxiety were evaluated once every two weeks, while the memory test was performed once a month. 4) Data analysis: SPSS11.0 software was used for statistical analyses. Data were shown in mean ± SEM. Difference was considered significant if the t-test P value is less than 0.05. Results: 1) Scores of subhealth state and depression were significantly lower in test group than those of control group. The beneficial effects of practicing Jianshenqigong-wuqinxi were more obvious for the subjects in the test group who had practiced Jianshenqigong-wuqinxi for two to twelve weeks (P < 0.05). 2) Scores of anxiety test were significantly lower in test group than those of control group after practicing Jianshenqigong-wuqinxi for six to twelve weeks (P < 0.05). 3) Scores of memory were significantly higher in test group than those of control group (P < 0.05). Conclusions: 1) Practicing Jianshenqigong-wuqinxi could promote health in people who have subhealth mental problems. 2) Practicing Jianshenqigong-wuqinxi could relieve depression, anxiety while enhance memory.
基金supported by the National Natural Science Foundation of China(Grant No.61471301)Natural Science Basic Research Program of Shaanxi,China(Grant No.2017JQ5083)PhD Research Startup Foundation of Xi’an University of Science and Technology,China(Grant No.2017QDJ044)
文摘Orthorhombic YFeO_3 thin film was prepared on La_(0.67)Sr_(0.33)MnO_3/LaAlO_3 substrate by a sol-gel spin-coating method. The structures of the YFeO_3/La_(0.67)Sr_(0.33)MnO_3/LaAlO_3(YFO/LSMO/LAO) sample were detected by x-ray diffraction pattern, Raman spectrometer, scanning electron microscopy, and atomic force microscope. The local ferroelectric polarization switching properties of the orthorhombic YFO film were confirmed by piezoresponse force microscopy(PFM) for the first time. The results show that the YFO film deposited on LSMO/LAO possesses orthorhombic structure,with ultra-fine crystal grains and flat surface. The leakage current of the YFO film is 8.39 × 10^(-4) A·cm^(-2) at 2 V,with its leakage mechanism found to be an ohmic behavior. PFM measurements indicate that the YFO film reveals weak ferroelectricity at room temperature and the local switching behavior of ferroelectric domains has been identified. By local poling experiment, polarization reversal in the orthorhombic YFO film at room temperature was further observed.
基金The authors are thankful to the National Natural Science Foundation of China （Grant No. 50331040）NWPU Doctor Foundation for supporting this work.
文摘The La0.85Sr0.015MnO3/Fe heterostructure deposited on Si （100） substrate was prepared by the magnetron sputtering. The laser-induced voltage in the sample and the difference in the voltage signals between the current-in-plane geometry and current-perpendicular-to-plane geometry at 77 K were investigated. This difference can be attributed to the different transport mechanisms.
基金supported by the National Natural Science Foundation of China(No.50331040)the National Natural Science Foundation of Shaanxi Provice(No.2001C21)NWPU Doctor Foundation(cx200323)
文摘The transport properties in the La2/3（Ca（1-x）Sr（x））1/3MnO3 （x=0.1/3, 2/3） films prepared using the RF magnetron sputtering method were investigated, The effect of the Ca, Sr double-doping at the A position in the La（2/3）A（1/3）MnO3 on the structure of the targets and transport of the films has been studied. With the increase of x, the structures of the targets transform from the rhombohedral phase to the cubic phase; the metal-insulator phase transition temperature （Tp） of the films increases; and the corresponding peak resistivity decreases. All the phenomena can be qualitatively explained by the lattice effect.
基金Project supported by the National Natural Science Foundation of China(Grant No.61471301)
文摘The magneto-electric effect in magnetic materials has been widely investigated, but obtaining an enhanced magnetoelectric effect is challenging. In this study, tricolor superlattices composed of manganese oxides-Pr（0.9）Ca（0.1）MnO3,La（0.9）Sr（0.1）MnO3, and La（0.9）Sb（0.1）MnO3-on（001）-oriented Nb：SrTiO3 substrates with broken space-inversion and timereversal symmetries are designed. Regarding the electric polarization in the hysteresis loops of the superlattices at different external magnetic fields, both coercive electric field Ec and remnant polarization intensity Pr clearly show strong magneticfield dependences. At low temperatures（〈 120 K）, a considerable magneto-electric effect in the well-defined tricolor superlattice is observed that is absent in the single compounds. Both maxima of the magneto-electric coupling coefficients ？Ec and ？Pr appear at 30 K. The magnetic dependence of the dielectric constant further supports the magneto-electric effect. Moreover, a dependence of the magneto-electric effect on the periodicity of the superlattices with various structures is observed, which indicates the importance of interfaces. Our experimental results verify previous theoretical results regarding magneto-electric interactions, thereby paving the way for the design and development of novel magneto-electric devices based on manganite ferromagnets.
基金supported by the National Natural Science Foundation of China(22471247,U1904212 and U2004191)the Natural Science Foundation of Henan Province(202300410477 and 222300420294)the China Postdoctoral Science Foundation(2020 M672260).
文摘Compared with the conventional strategies of electronic and/or steric perturbation,catalytic olefin polymerization modulated by light irradiation or metal-metal cooperativity effect is a fascinating challenge that attracts considerable attention in the academic community.In this context,we design a strategy that could employ both effects to influence the polymerization process.Some dinuclear salicylaldimine andα-imino-ketone nickel complexes bearing a stiff-stilbene bridge were prepared,which could transfer between(E)-isomers and(Z)-isomers under ultraviolet irradiation.This isomerization can tune the electronic,steric and metal-metal cooperativity effects of the nickel catalysts.In this way,the catalytic activity,as well as polymer microstructures including molecular weight and branching density can be modulated in ethylene polymerization and copolymerization reactions.This strategy is generally applicable to other olefin polymerization catalytic systems and other types of transition metal mediated catalysis.
基金supported by the National Key R&D Program of China (2021YFA1501700)the National Natural Science Foundation of China (22301294, 52025031, 22261142664)+1 种基金the Chinese Academy of Sciences (CAS) Project for Young Scientists in Basic Research (YSBR-094)USTC Research Funds of the Double First-Class Initiative (YD9990002030)。
文摘A significant challenge in the recycling of plastics is the separation of various polymers. Mechanical recycling represents one of the most straightforward and cost-effective approaches to mitigate the escalating issue of plastic pollution. Unfortunately, the inevitable presence of mixed plastics in the waste stream and their phase separation always result in suboptimal properties for mechanically recycled materials. Multi-block copolymers(MBCPs) compatibilization represents an efficient strategy to address this issue and for upcycling of mixed plastics. The key to the implementation of this strategy lies in the efficient syntheses and structural modifications of diverse MBCPs. Especially, very few synthetic routes have been reported for the synthesis of MBCPs containing polyolefin blocks. In this contribution, we present a cyclic-acyclic monomers metathesis polymerization(CAMMP)mediated strategy for the preparation of polyolefin containing MBCPs using commercially available or easily accessible telechelic diol polymers. These polyolefins containing MBCPs can efficiently serve as compatibilizer additives for the upcycling of mixtures of polyolefins and other plastics. The combination of great variety of telechelic diol polymers with the ease of microstructure modification during CAMMP synthesis makes this strategy attractive for future investigations and potential practical applications.
基金supported by National Key R&D Program of China(grant no.2021YFA1501700)National Natural Science Foundation of China(NSFC+3 种基金grant nos.22301294,52025031,and 22261142664)the Chinese Academy of Sciences(CAS)Project for Young Scientists in Basic Research(grant no.YSBR-094)China Postdoctoral Science Foundation(grant nos.BX20230339 and 2023M743352)the University of Science and Technology of China(USTC)Research Funds of the Double First-Class Initiative(grant no.YD9990002030).
文摘The development of degradable polymers represents an appealing strategy to address ever-growing concerns for treating waste plastics.Olefin metathesis polymerization has been extensively explored for the synthesis of various degradable polymers.Cyclic–acyclic monomers metathesis polymerization(CAMMP)has recently been reported to produce degradable polymers via copolymerization of cyclic monomers with acyclic diene comonomers.Unfortunately,this strategy suffers from poor product material properties,especially at high contents of diene comonomers.To address this issue,we have designed a tandem olefin metathesis polymerization(TOMP)system that combines olefin ringclosing metathesis(RCM)of diene comonomers,followed by ring-opening metathesis copolymerization(ROMCP)with cyclic olefin monomers(dicyclopentadiene,cyclooctene,or alkyl-substituted cyclooctene).This strategy overcame the intrinsic limitations of diene-induced chain-transfer reactions during olefin metathesis,leading to degradable polymers with high molecular weights and excellent material properties.The selection of different cyclic olefin monomers provided access to degradable and recyclable cross-linked thermosets,linear thermoplastics,and elastomers.Notably,this one-pot,two-step process was highly efficient and required the addition of only one metathesis catalyst.
基金supported by National Key R&D Program of China(No.2021YFA1501700)National Natural Science Foundation of China(No.52025031,22261142664,52403016)+1 种基金Fundamental Research Funds for the Central Universities(No.WK2060000074)CAS Project for Young Scientists in Basic Research(No.YSBR-094).
文摘The synthesis and design of transition metal catalysts have attracted extensive attention in ethylene polymer-ization.In this work,a series of α-diimine nickel catalysts(Ni1-Ni4)bearing ether substituents were designed and synthesized.The steric hindrance of these catalysts was systematically modulated by varying the ether groups,which directly influenced their ethylene(co)polymerization performances.These catalysts showed exceptionally high activities(up to 10^(7) g·mol^(-1)·h^(-1)).The resulting polyethylene displayed a broad range of branching densities(22 to 92/1000C)and high polymer molecular weights(up to 59.8×10^(4) g·mol^(-1)).Polyethylene produced by Ni1 and Ni2 exhibited outstanding mechanical properties and elastic recovery performance.Furthermore,these catalysts efficiently catalyzed ethylene copolymerization with diverse polar monomers,yielding copolymers with incorporation ratios ranging from 0.24%to 1.43%.
基金supported by the National Natural Science Foundation of China (21690071 and 21871242)the Fundamental Research Funds for the Central Universities.
文摘For transition metal-based olefin polymerization catalysts, ligand steric and electronic effects can strongly influence important catalytic properties. However, the simultaneous tuning of both steric and electronic effects has not been explored in most of the previous studies. In this contribution, a strategy to tune the ligand electronic and steric effects in a concerted fashion is reported. In such a system, both dibenzhydryl groups and multiple methoxy/fluoro groups were installed in α-diimine ligands. In addition to strongly influencing ligand electronics, the methoxy/fluoro groups can interact with the dibenzhydryl groups and efficiently increase ligand sterics. In ethylene polymerization, this concurrent tuning of electronic and steric effects can lead to simultaneous enhancement of several parameters(activity, stability, polymer molecular weight, melting point, branching density) for both the nickel and palladium catalysts. The effectiveness of this strategy is highly attractive for future studies in other catalytic systems.
基金supported by the National Natural Science Foundation of China(21374108,21304054)the Promotive Research Fund for the Young and Middle-aged Scientists of Shandong Province(BS2012CL018)+2 种基金the Foundation of Qufu Normal University(XJ201212)the Fundamental Research Funds for the Central Universities(WK3450000001)the State Key Laboratory for Modification of Chemical Fibers and Polymer Materials,Donghua University(LK1424)
文摘In this review, a recent development of cationic ?-diimine palladium(II) complexes for ethylene polymerization and copolymerization with polar functionalized comonomers was briefly described. First, the polymerization mechanism for this type of catalysts was discussed. Next, recent advances in ligand design were provided with special focus on the influence of ligand structures on the catalytic polymerization properties. Last, the ethylene homopolymerization and copolymerization with various polar comonomers, especially acrylate and vinyl ethers were summarized.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.52025031,21871242,U19B6001 and U1904212)and K.C.Wong Education Foundation.
文摘In the past few decades,the development of high-performance catalysts has been a key driving force and a center of research efforts in the field of olefin polymerization.However,a major discrepa ncy exists between in dustrial researches which utilize aliphatic hydrocarb on solventsz and academic researches which predominantly focus the catalytic properties in aromatic solvents.In this con-tribution,a novel diaryl-methyl aniline bearing eight tert-butyl groups was prepared and subsequently transformed to four different kinds of imine-type ligands.The corresponding nickel complexes as well as their counterparts derived from diphenyl-methyl aniline without the tert-butyl groups were prepared and investigated in ethylene polymerization.
基金the National Natural Science Foundation of China(52025031,21690071,U19B6001,and U1904212)K.C.Wong Education Foundation。
文摘The transition-metal-catalyzed copolymerization of olefins with polar comonomers is a direct strategy to access polar-functionalized polyolefins in an economical manner.Due to the intrinsic poisoning effect of polar groups towards Lewis acidic metal centers and the drastic reactivity differences of polar comonomers versus non-polar olefins,it is challenging to develop catalysts that provide the desired polymer molecular weight,comonomer incorporation,and activity.In this contribution,we tackle this issue from a comonomer perspective using 5,6-disubstituted norbornenes,which are highly versatile,easily accessible,inexpensive,and capable of introducing two functional groups in a single insertion.More importantly,they are only mildly poisoning due to the presence of long spacers between double bonds and polar groups,and are not prone to b-hydride elimination due to their cyclic structures.As strong pdonors,they can competitively bind to metal centers versus olefins.Indeed,phosphine-sulfonate palladium catalysts can catalyze the copolymerization of ethylene with 5,6-disubstituted norbornenes and simultaneously achieve a high polymerization activity,copolymer molecular weight,and comonomer incorporation.The practicality of this system was demonstrated by studying the properties of the resulting polymers,copolymerization in hydrocarbon solvents or in bulk,recovery/utilization of unreacted comonomer,molecular weight modulation,and large-scale synthesis.
基金This work was supported by the National Natural Science Foundation of China(21690071,U19B6001 and U1904212).
文摘Ziegler and Natta won the Nobel Prize in 1963 due to their contributions in olefin polymerization catalysis.Subsequent studies into related catalysts have led to a multibillion-dollar polyolefin industry.Currently,more than 178 million tons of polyolefin materials are produced annually,which constitute more than half of global plastics production.Interestingly,the metal nickel was initially recognized as a“poison”for olefin polymerization.Alkyl aluminum species can oligomerize ethylene(degree of polymerization up to 100)at high temperature and pressure;while the addition of nickel salt to the system led to the exclusive formation of 1-butene.This famous“nickel effect”marks the starting point of the era of Ziegler catalysts[1].After decades of research,the situation of nickel has changed dramatically,and a large number of nickelbased catalysts have been shown with the capabilities of producing high-molecular-weight polyethylene.As an exceptional demonstration,some groups have recently developed nickel catalysts that are able to produce ultra-high molecular weight polyethylene(UHMWPE).UHMWPE,with molecular weight of above one-million,is a special class of advanced engineering plastics with superior properties and wide applications.
基金the National Natural Science Foundation of China(Grant Nos.52025031,21690071,22001004,U19B6001 and U1904212)K.C.Wong Education Foundation。
文摘A series of dibenzhydryl-based iminopyridine-N-oxide ligands bearing a range of electron-donating or-withdrawing substituents(OMe,H;and NO_(2))and corresponding nickel pre-catalysts are prepared and characterized.The substituents are installed at different positions on the ligand structure,including 4-position of the pyridine-N-oxide moiety(position X)and 4-position of the aniline moiety(position Y).These nickel pre-catalysts are highly active in ethylene polymerization with the addition of very little amount of aluminum cocatalysts,leading to the formation of polyethylenes with molecular weights of well above one million.Electron-donating substituents make the catalysts sensitive to polymerization temperature.In contrast,the catalysts bearing electron-withdrawing NO_(2) substituents show relatively steady performances at different temperatures.Most importantly,we demonstrate that different substituents and different positions both play important roles in determining the properties of nickel catalysts.This provides an alternative strategy for the future design of high-performance polymerization catalyst.
基金supported by the National Natural Science Foundation of China (21690071, 51522306)
文摘Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization.This type of catalyst features six-membered chelate ring size,and can enable the copolymerizations of ethylene with a wide variety of polar monomers.In this contribution,we decide to investigate the influence of chelate ring size on the properties of phosphinesulfonate palladium catalysts.As such,a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II)complexes[κ~2-(P,O)-2-(CH_2-PR_1R_2)-4-methylphenyl-sulfonato]Pd(Me)(DMSO)(Pd1,R_1=R_2=Cy,Pd2,R_1=R_2=o-Me O-C_6H_4;Pd3,R_1=Ph,R_2=2-[2,6-(Me O)_2C_6H_3]C_6H_4;DMSO=dimethyl sulfoxide)were designed,prepared and characterized.These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether.However,their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2′.The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.
