In this communication, by means of stress relaxation experiments, the viscous stress at various strains during tensile deformation of oriented polyolefin samples including high density polyethylene （HDPE）, linear lo...In this communication, by means of stress relaxation experiments, the viscous stress at various strains during tensile deformation of oriented polyolefin samples including high density polyethylene （HDPE）, linear low density polyethylene （LLDPE） and isotactic polypropylene （iPP）, has been determined. The viscous stress in the oriented samples takes up to 50%-70% of the total stress, which is unusually high compared with their isotropic counterparts. The unusual high viscous stress was discussed based on mainly the existence of shish structure in oriented polyolefins, which could enhance the inter-lamella coupling significantly.展开更多
Recent successful examples for synthesis of new polyolefins containing (polar) functionalities by adopting the approaches by controlled incorporation of reactive functionalities (and the subsequent introduction of pol...Recent successful examples for synthesis of new polyolefins containing (polar) functionalities by adopting the approaches by controlled incorporation of reactive functionalities (and the subsequent introduction of polar functionalities under mild conditions) by coordination polymerization in the presence of transition metal complex catalysts have been described. Related methods (such as direct copolymerization of olefin with polar monomer using living radical or coordination insertion methods) have also been demonstrated for comparison. Our recent efforts for precise synthesis of polyolefins containing polar functionalities by efficient incorporation of reactive functionality by copolymerization of ethylene with nonconjugateddiene (1,7-octadiene, vinylcyclohexene etc.) or divinyl-biphenyl using nonbridged half-titanocene [ex. Cp’TiCl2(O-2,6-iPr2C6H3), Cp’ = C5Me5, tBuC5H4 etc.] catalysts have been introduced.展开更多
The cracking of polyolefins, especially polyethylene in the molten state was effectively catalyzed by the powdery spent FCC （Fluid Catalytic Cracking） catalyst which was dispersed in it. The activation energy of the...The cracking of polyolefins, especially polyethylene in the molten state was effectively catalyzed by the powdery spent FCC （Fluid Catalytic Cracking） catalyst which was dispersed in it. The activation energy of the catalytic cracking of polyethylene was about 74 kJ/mol. The cracked product was naphtha and middle distillate as the major product and gaseous hydrocarbon （C1-C4） as the minor product while little heavy oil was produced. The chemical compositions of the product were： aromatic hydrocarbons, isoparaffins and branched olefins, whereas that of the non-catalyzed products were： n-olefins and n-paraffins with minor amount of dienes with increasing the process time. Additionally, the product pattern shifted from naphtha rich product to kerosene and gas-oil rich product. However, any catalytic product showed low fluid point （〈 -10 ℃）, while that of the non-catalyzed product was as high as 40 ℃. Catalyst could process, more than 100 times by weight of polyethylene with fairly small amount （- 30 wt%） of coke deposition. Spent catalyst gave higher hydrocarbons while fresh catalyst gave gaseous product as the major product. Other polyolefins such as polypropylene and polystyrene were tested on same catalyst to show that their reactivity is higher than that of polyethylene and gave the aliphatic products, alkyl benzenes and C6-C9 iso-paraffins as the major product. Product pattern of the cracked product suggested that the reaction proceeded via the primary reactions making paraffins and olefins which were followed by the isomerization, secondary cracking, aromatization and hydrogen transfer which based on the carbenium ion mechanism.展开更多
In the quest for low-temperature polyolefins upcycling,overcoming the decomposition temperature limitations caused by chemically inert carbon-hydrogen(C(sp3)-H)bonds remains a challenge.Here we report a tandem endothe...In the quest for low-temperature polyolefins upcycling,overcoming the decomposition temperature limitations caused by chemically inert carbon-hydrogen(C(sp3)-H)bonds remains a challenge.Here we report a tandem endothermicexothermic magnetocatalytic(EEM)strategy for upcycling of polypropylene(PP)and polyethylene(PE)below their decomposition temperature(typically 300°C).A series of commodity polyolefins(PP,PE,and their mixtures(PP+PE))can be deconstructed magnetocatalytically at 290°C,for which a high H2 selectivity up to 86%can be achieved.Magnetothermal coupling simulations revealed that the interfacial temperature gap was the key to upcycling of polyolefins at low temperature.Overall,EEM method potentially provides a sustainable approach for end-of-life plastics upcycling.展开更多
Since Ziegler,Hogan and Banks’seminal discoveries for the catalytic polymerization of olefins,many generations of catalysts have been reported[1–5].These include the transition from the original heterogeneous cataly...Since Ziegler,Hogan and Banks’seminal discoveries for the catalytic polymerization of olefins,many generations of catalysts have been reported[1–5].These include the transition from the original heterogeneous catalysts(Ziegler and Phillips)to homogeneous catalysts combining metallocene.展开更多
Compared with non-cross-linked and dynamically covalent polymers,covalently cross-linked networks are irreplaceableinmany areas;however,they aredifficult to repair once fractured,due to limited polymer chain diffusion...Compared with non-cross-linked and dynamically covalent polymers,covalently cross-linked networks are irreplaceableinmany areas;however,they aredifficult to repair once fractured,due to limited polymer chain diffusion after cross-linking.Herein,the authors have reported a newkind of permanently cross-linked polyolefin,which when attached with amide side groups,yieldmechanically robust yet readily repairablematerials.A key is to use low cross-linking density,which enables satisfactory elasticity and chain mobility for thermodynamically favored healing.Another key is to incorporate dense hydrogen bonds that can undergo reversible associations.These factors jointly promise polyolefin networks with good mechanical properties and self-healing performance(recovered spontaneously up to 96%of its original tensile strength).More importantly,by means of mechanochemiluminescence from 1,2-dioxetane,which serves as the cross-linker and built-in self-reporting stress probe,a microscopic evaluation of how the chain entanglement proceeds upon healing and how failure occurs in the network can be obtained.展开更多
Under optimal process conditions,pyrolysis of polyolefins can yield ca.90 wt%of liquid product,i.e.,combination of light oil fraction and heavier wax.In this work,the experimental findings reported in a selected group...Under optimal process conditions,pyrolysis of polyolefins can yield ca.90 wt%of liquid product,i.e.,combination of light oil fraction and heavier wax.In this work,the experimental findings reported in a selected group of publications concerning the non-catalytic pyrolysis of polyolefins were collected,reviewed,and compared with the ones obtained in a continuously operated bench-scale pyrolysis reactor.Optimized process parameters were used for the pyrolysis of waste and virgin counterparts of high-density polyethylene,low-density polyethylene,polypropylene and a defined mixture of those(i.e.,25:25:50 wt%,respectively).To mitigate temperature drops and enhance heat transfer,an increased feed intake is employed to create a hot melt plastic pool.With 1.5 g·min^(-1) feed intake,1.1 L·min^(-1) nitrogen flow rate,and a moderate pyrolysis temperature of 450℃,the formation of light hydrocarbons was favored,while wax formation was limited for polypropylene-rich mixtures.Pyrolysis of virgin plastics yielded more liquid(maximum 73.3 wt%)than that of waste plastics(maximum 66 wt%).Blending polyethylenes with polypropylene favored the production of liquids and increased the formation of gasoline-range hydrocarbons.Gas products were mainly composed of C3 hydrocarbons,and no hydrogen production was detected due to moderate pyrolysis temperature.展开更多
Catalysts are key for olefin polymerization reactions and are also ubiquitous in catalysis science.Multinuclear metal catalysts have witnessed enhanced performances in catalytic reactions relative to mononuclear catal...Catalysts are key for olefin polymerization reactions and are also ubiquitous in catalysis science.Multinuclear metal catalysts have witnessed enhanced performances in catalytic reactions relative to mononuclear catalysts,but which substantially involve multi-step,tedious,and difficult synthesis.Herein,this study reports an intriguing approach to construct multi-nuclear catalysts for the milestoneα-diimine nickel catalysts using an oligomeric strategy.A polymerizable norbornene unit is incorporated into theα-diimine ligand backbone,leading to the formation of the monomeric nickel catalyst Ni_(1)and its corresponding oligomeric nickel catalysts(Ni_(3)and Ni_(5))with varying degrees of polymerization(DP=3 and 5).Notably,the oligomeric catalyst Ni_(5)was facilely scaled up(50 g-level),showed enhanced thermal stability,exhibited 4.6 times higher activity,and yielded polyethylene elastomer with a 379%increased molecular weight in ethylene polymerization,compared to the monomeric catalyst Ni_(1).Catalytic performance enhancements of oligomeric catalysts were found to be DP-dependent.The kilogram-scale polyethylene,produced using Ni_(5)in a 20 L reactor,presented a highly branched all-hydrocarbon structure,which demonstrated typical elastic properties(tensile strength:4 MPa,elastic recovery:SR=72%)along with great processability(MFI=3.0 g/10 min),insulating characteristics(volume resistivity=2×10^(16)Ω/m),and hydrophobicity(water vapor permeability:0.03 g/m^(2)/day),suggesting potentially practical applications.展开更多
Converting waste plastics directly into valuable aromatic chemicals is a promising,cost-effective recycling strategy.Traditional zeolite-catalyzed cracking of polyolefins to produce aromatics often needs high temperat...Converting waste plastics directly into valuable aromatic chemicals is a promising,cost-effective recycling strategy.Traditional zeolite-catalyzed cracking of polyolefins to produce aromatics often needs high temperatures and faces issues like low selectivity for liquid aromatics,separation difficulties,and rapid catalyst deactivation due to coking.To address this,a multifunctional Ni/HZSM-5 catalyst was developed to efficiently upgrade various polyolefins—including polyvinyl chloride—into gaseous alkanes(C_(1)–C_(5))and easily separable liquid aromatics(C_(6)–C_(12))at 400°C,without added solvents or hydrogen.Aromatic products make up 57.1 wt%of total output,with more than 97.8%selectivity for the liquid phase and a BTX(benzene,toluene,and xylene)selectivity of 76.1%.The high activity and selectivity for aromatics stem from synergistic interactions between Ni nanoparticles(NPs)and acid sites in the zeolite,which promote selective C–C bond breaking and control hydrogenolysis and aromatization pathways.This synergy allows precise control over the distribution of products by carbon number and favors the formation of separable aromatics.Notably,the catalyst also prevents coking by hydrogenolyzing and hydrogenating reactive intermediates before they form stable graphite-like deposits.Consequently,Ni/ZSM-5 catalyst demonstrates excellent stability,maintaining consistent aromatics yield over 13 consecutive cycles and processing over 30 times its weight in plastics without regeneration.After regeneration,the activity of the catalyst was fully restored,highlighting its potential for industrial use.This work offers valuable insights for designing durable,high-activity catalysts,providing a practical route to improve plastic recycling technologies.展开更多
The mass production of disposable polyolefin products has led to serious plastic pollution and an imbalance between manufacturing and recycling.Given these challenges,the chemical upcycling of waste polyolefins has at...The mass production of disposable polyolefin products has led to serious plastic pollution and an imbalance between manufacturing and recycling.Given these challenges,the chemical upcycling of waste polyolefins has attracted extensive attention due to its high efficiency and economic benefits.Herein,we review the development of polyolefin chemical upcycling in heterogeneous catalysis.The status quo of polyolefin recycling is first discussed.We then introduce the advanced strategies for chemical upcycling in the view of different value-added products and discuss their challenges and prospects.Our in-depth analysis centers on the catalytic mechanism and the design principle of heterogeneous catalysts.Finally,we outlook the promising directions to facilitate the degradation process via polymer and catalyst design and optimized catalytic engineering.Innovative strategies are expected to promote the chemical upcycling of polyolefins,bringing great promise for the sustainable development of society.展开更多
A nickel catalyst was modeled with ligand L^2, [NH = CH-CH = CH-O]^-, whichshould have potential use as a syndiotactic polyolefin catalyst, and the reaction mechanim wasstudied by theoretical calculations using the de...A nickel catalyst was modeled with ligand L^2, [NH = CH-CH = CH-O]^-, whichshould have potential use as a syndiotactic polyolefin catalyst, and the reaction mechanim wasstudied by theoretical calculations using the density functional method at the B3LYP/LANL2MB level.The mechanism involves the formation of the intermediate [NiL^2Me]^+, in which the metal occupies aT-shaped geometry. This intermediate has two possible structures with the methyl group trans eitherto the oxygen or to the nitrogen atom of L^2. The results show that both structures can lead to thedesired product via similar reaction paths, A and B. Thus, the polymerization could be considered astaking place either with the alkyl group occupying the position trans to the Ni-O or trans to theNi-N bond in the catalyst. The polymerization process thus favors the catalysis of syndiotacticpolyolefins. The syndiotactic synthesis effects could also be enhanced by variations in the ligandsubstituents. From energy considerations, we can conclude that it is more favorable for the methylgroup to occupy the trans-O position to form a complex than to occupy the trans-N position. Frombond length considerations, it is also more favoured for ethene to occupy the trans-O position thanto occupy the trans-N position.展开更多
Polyolefins are synthetic plastics that exist on the largest scale and are ubiquitous in human life.They are also the most frequently discarded plastics.Consequently,the ability to either upgrade polyethylene(PE)plast...Polyolefins are synthetic plastics that exist on the largest scale and are ubiquitous in human life.They are also the most frequently discarded plastics.Consequently,the ability to either upgrade polyethylene(PE)plastic for value-added applications or to degrade PE plastic for value-added chemicals and monomers is highly desirable and sought after to mitigate the plastic waste problem.Herein,we report an advanced strategy for tackling the issue of PE plastics,first through a sequential upgrading and then through a degrading pathway.The optimal Diels–Alder-type polar comonomer diester-substituted norbornadiene is copolymerized with ethylene to produce the desired polar-functionalized PEs with both high comonomer incorporations of 42.4 mol%(-COOMe:as high to 59.6 mol%)and high molecular weights of up to 224 kg mol^(−1)in high catalytic activities of>100 kg mol^(−1)h^(−1).By means of a decisive retro-Diels–Alder reaction,this upgraded PE,namely polar-functionalized PE,can completely switch to a clean and soluble vinylene PE with a high content(28.7 mol%)of dispersed internal double bonds,which are degradable.Ethenolysis of the highmolecular–weight(∼30 kg mol^(−1))vinylene PE with ethylene yields industrially relevant telechelic oligomers(∼360 g mol^(−1))of long-chainα,ω-dienes and C9/C9+hydrocarbon products.This chemical upgrading and recycling method makes polyolefin plastic more sustainable.展开更多
Cold plasma-assisted catalytic upcycling of polyolefin wastes integrated with CO_(2)into value-added chemicals is a promising solution for mitigating the global carbon emissions and fossil energy crisis,but still chal...Cold plasma-assisted catalytic upcycling of polyolefin wastes integrated with CO_(2)into value-added chemicals is a promising solution for mitigating the global carbon emissions and fossil energy crisis,but still challenging due to the complexity of products and low energy efficiency.Given this,a novel one-stage process of cold plasma coupled with Ga-modified hierarchical H-ZSM-5(Ga/Hie-ZSM-5)catalyst for polyolefins upgrading was designed with polyolefins followed by the catalysts within the plasma region,which facilitated the upcycling of polyolefins to light olefins and CO_(2)activation by plasma,and thereby the enhanced synergy between cold plasma and catalysts for aromatics production.At an input power of ca.45 W without external heating,the low-density polyethylene(LDPE)waste was completely converted with the assistance of CO_(2)and the yield of oil products over the Ga/Hie-ZSM-5 catalyst was highly up to 62.2 wt%,with nearly 100% selectivity of aromatics.Meanwhile,the degradation efficiency of LDPE and the energy efficiency could reach 2.5 g_(LDPE)·g_(cat)^(-1)·h^(-1)and 55.56 g_(LDPE)·g_(cat)^(-1)·kW^(-1)h^(-1),respectively.Mechanism investigation revealed that the plasma and CO_(2)synergistically affect the primary cracking of LDPE,forming a primary product enriched in olefins and a small amount of CO.Subsequently,the produced olefins intermediates were further aromatized via cyclizationdehydrogenation route on the Ga/Hie-ZSM-5 catalyst with assistance of CO_(2)under the synergistic effect of plasma-catalysis.This work offers a feasible strategy to improve the yield of aromatic products for the plasma-catalytic upcycling of polyolefins and CO_(2)at ambient pressure without any external heating.展开更多
A series of imido-vanadium(Ⅴ)complexes bearing bidentate phenoxy-phosphine ligands were synthesized and characterized by NMR,elemental analysis,and single-crystal X-ray diffraction.These complexes demonstrated excell...A series of imido-vanadium(Ⅴ)complexes bearing bidentate phenoxy-phosphine ligands were synthesized and characterized by NMR,elemental analysis,and single-crystal X-ray diffraction.These complexes demonstrated excellent catalytic performance in ethylene/1-hexene copolymerization,achieving high activities of 12.0×10~6–49.0×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1)and affording random copolymers with tunable 1-hexene incorporations.These catalysts also exhibited ultrahigh activity,up to 112.2×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1),in ethylene/norbornene(NB)copolymerization,yielding cyclic olefin copolymers with adjustable NB incorporations.Remarkably,these catalysts demonstrated exceptional tolerance toward polar functional groups,enabling efficient copolymerization of ethylene with both 10-undecen-1-ol(U-OH)and 5-norbornene-2-methanol(NB-OH),incorporating about 2 mol%polar comonomers with high efficiency.Different with the catalytic behaviors in copolymerization of ethylene with nonpolar comonomers,the catalytic activities in E/U-OH copolymerization(25.7×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1))were much higher than those in E/NB-OH copolymerization(8.6×10^(6) g_(polymer)·(mol_(V))^(-1)·h^(-1)).DFT calculations revealed that the catalytic performance is governed by synergistic electronic and steric effects.For E/NB copolymerization,strong preference for cyclic olefins was attributed to favorable transition state stabilization.In polar comonomer systems,steric effects were predominant,with NB-OH exhibiting a larger buried volume around vanadium center upon coordination compared to U-OH.Overall,this work provides fundamental insights into vanadium-catalyzed(co)polymerization and offers new strategies for tailored polyolefin design.展开更多
Although Ziegler-Natta(Z-N)polyolefins have been widely used as raw materials to produce pharmaceutical or food packaging,the migration of acid scavengers,an additive usually introduced in Z-N polyolefins,from the pac...Although Ziegler-Natta(Z-N)polyolefins have been widely used as raw materials to produce pharmaceutical or food packaging,the migration of acid scavengers,an additive usually introduced in Z-N polyolefins,from the packaging to its contents has not been reported.In this work,the migration of the two most used acid scavengers,calcium stearate(CaSt_(2))and zinc stearate(ZnSt_(2)),from a Z-N polypropylene random copolymer(PPR)into water during autoclaving at 121℃ were comparatively investigated.It was found that,for PPR plates containing 0.1 wt%CaSt_(2)or ZnSt_(2)(PPR-0.1CaSt_(2),PPR-0.1ZnSt_(2),respectively),the concentration of migrated calcium ion into water increased with autoclaving time,while that of zinc ion was much lower at same treatment durations and did not show a significant increase with treatment time.Interestingly,after removing all plates and acidification treatment,a considerable amount of stearic acid was detected in sterilized water for PPR-0.1ZnSt_(2),but no such significant stearic acid was detected in sterilized water for PPR-0.1CaSt_(2).Based on the structural evolution of the two soaps upon heating,possible mechanisms for the different migration behavior of CaSt_(2)and ZnSt_(2)from PPR into water during autoclaving treatment were proposed.Our results suggest that the migration issue of acid scavengers is worthy of attention in pharmaceutical packaging materials produced from Z-N polyolefins.展开更多
Mechanochromic polyolefins represent a novel class of functionalized polyolefins,which still remains significant challenges.Pd(II)-catalyzed coordination-insertion copolymerization is a feasible method for achieving t...Mechanochromic polyolefins represent a novel class of functionalized polyolefins,which still remains significant challenges.Pd(II)-catalyzed coordination-insertion copolymerization is a feasible method for achieving this kind of polymers,yet with linear microstructures.Ringopening metathesis polymerization(ROMP)offers another promising avenue for affording functionalized polyolefins.This method exhibits high polar group tolerance and the ability to precisely regulate polymer branches.In this study,we report the method for producing mechanochromic branched polyethylenes via ROMP.By employing the terpolymerization of a well-designed monomer containing the mechanochromic group,NB-ABF,with cyclooctene(COE)and long-chain 5-hexylcyclooctene(COE-C6),following by hydrogenation process,we synthesized a range of functionalized branched polyethylenes characterized by varied branching density and polar monomer incorporation.These polymers bear a structural resemblance to functionalized ethylene-octene copolymers.After crosslinking,mechanochromophores are generated,and mechanochromism is achieved in uniaxial tensile testing.A comprehensive assessment reveals that both the incorporation of polar monomers and variations in branching density significantly influence their mechanical properties.Notably,upon stretching,these materials display pronounced visible color change,confirming the successful development of mechanochromic branched polyethylenes.展开更多
The crystallization behavior of two commercial polyolefin elastomer(POE)samples was investigated using the fast scanning chip calorimetry(FSC)technique.Non-isothermal crystallization of the POE samples during cooling ...The crystallization behavior of two commercial polyolefin elastomer(POE)samples was investigated using the fast scanning chip calorimetry(FSC)technique.Non-isothermal crystallization of the POE samples during cooling to low temperatures cannot be inhibited under the largest efficient cooling rate employed in the current work.Thus,the isothermal crystallization of POE samples was limited to a narrow temperature range.When the POE samples were cooled to a certain temperature below the non-isothermal crystallization temperature for crystallization,a crystallization time dependent melting peak appeared in the low temperature region besides the high temperature melting peak originated from the non-isothermal crystallization.This low temperature melting peak was arisen from the melting of crystals isothermally crystallized at the selected crystallization temperature.At each crystallization temperature,the lengths of crystallizable segments were different,thus,the low melting peak increased with increasing the crystallization temperature.In terms of the high melting peak attributed to the non-isothermally crystallized crystals,it somehow decreased with increasing crystallization time and then became constant with further increasing crystallization time at the selected crystallization temperature.This could be explained by the fact that the crystallizable sequences with longer length would nucleate and crystallize first to form thicker crystals during cooling.The subsequent crystallization contributed by the shorter crystallizable sequences will result in the formation of thinner crystals,causing the melting peak to shift to the lower temperature.展开更多
To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements o...To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements on ethylene(co)polymerizations. The N-bridged phosphinecarbonyl Pd catalysts(Pd1-Pd5) and Ni catalysts(Ni1-Ni5) bearing five-to eight-membered-ring structures were designed and synthesized.Catalytic performance for ethylene(co)polymerization became better as the size of N-containing bridge increased. The seven-membered-ring bridged catalysts Pd4 and Ni4 exhibited the best performance in terms of catalytic activity, polymer molecular weight and incorporation of acrylates and acrylic acid. The better performance of these catalysts bearing larger-size bridges was tentatively attributed to the methyleneinduced higher electron density around nitrogen, which strenghtens the coordination of carbonyl group to metal center, and also to the steric effect offered by this cyclization. This work provides a new strategy to enhance hemilabile polymerization catalysts.展开更多
A neutral nickel(Ⅱ)catalyst D,{[O-(3-cyclohexyl)(5-Cl)C_6H_2-ortho-C(H)=N-2,6-C_6H_3(i-Pr)_2]Ni(Ph_3P)(Ph)}hasbeen synthesized and characterized by IH-NMR,FTIR and elemental analysis.The results indicate that Al(i-Bu...A neutral nickel(Ⅱ)catalyst D,{[O-(3-cyclohexyl)(5-Cl)C_6H_2-ortho-C(H)=N-2,6-C_6H_3(i-Pr)_2]Ni(Ph_3P)(Ph)}hasbeen synthesized and characterized by IH-NMR,FTIR and elemental analysis.The results indicate that Al(i-Bu)_3 is aneffective cocatalyst for the neutral nickel catalyst.With bis(1,5-cyclooctadiene)nickel(0)[Ni(COD)_2]or Al(i-Bu)_3 as a co-catalyst,the neutral nickel catalyst D is active for ethylene polymerisation and copolymerisation with polar monomers(tert-butyl 10-undecenoate(BU),methyl 10-undecenoate(MU),allyl alcohol(AA)and 4-penten-1-ol(PO))under mild conditions.The resulting polymers were characterized by (?)H-NMR,FTIR,DSC,and GPC.From the comparative studies,Ni(COD)_2 ismore active than Al(i-Bu)_3 for ethylene homopolymerization,while Al(i-Bu)_3 is more effective than Ni(COD)_2 for ethylenecopolymerisation with polar monomers.The polymerization parameters which affect both the catalytic activity and propertiesof the resulting polyethylene were investigated in detail.Under the conditions of 20 μmol catalyst D and Ni(COD)_2/D=3(molar ratio) in 30 mL toluene solution at 45℃,12×105 Pa ethylene for 20 min,the polymerization activity reaches ashigh as 7.29×105 gPE.(mol.Ni.h)^(-1) and M_η,is 7.16×104 g.mol^(-1).For ethylene copolymerization with polar monomers,theeffect of comonomer concentrations was examined.As high as 0.97 mol% of MU,1.06 mol% of BU,1.04 mol% of AA and1.37 mol% of PO were incorporated into the polymer,respectively,catalyzed by D/Al(i-Bu)_3 system.展开更多
Polyolefins that bear a chiral side chain(typically an isobutyl group)experience a so-called macromolecularamplification of chirality:the chiral side-chain induces a slight preference for either tg or tg(?) main chain...Polyolefins that bear a chiral side chain(typically an isobutyl group)experience a so-called macromolecularamplification of chirality:the chiral side-chain induces a slight preference for either tg or tg(?) main chain conformation.Thisslight conformational bias is amplified cooperatively along the chain,and results in preferred chirality of the main chainhelical conformations.As a result,these polymers display a liquid-crystal(LC)phase both in solution and,in the melt as atransient phase on the way to crystallization.The existence of two processes(melt-LC and LC-crystal transitions)results inunconventional behaviors that were first analyzed by Pino and collaborators back in 1975.These polymers also offer a meansto test the structural consequences of recently introduced crystallization schemes.These schemes postulate the formation of atransient liquid-crystal phase as a general scheme for polymer crystallization.展开更多
基金This work was financially supported by the National Natural Science Foundation of China (Nos. 20404008, 50533050 and 20490220)This work was subsidized by the Special Funds for Major State Basic Research Projects of China (No. 2003CB615600).
文摘In this communication, by means of stress relaxation experiments, the viscous stress at various strains during tensile deformation of oriented polyolefin samples including high density polyethylene （HDPE）, linear low density polyethylene （LLDPE） and isotactic polypropylene （iPP）, has been determined. The viscous stress in the oriented samples takes up to 50%-70% of the total stress, which is unusually high compared with their isotropic counterparts. The unusual high viscous stress was discussed based on mainly the existence of shish structure in oriented polyolefins, which could enhance the inter-lamella coupling significantly.
文摘Recent successful examples for synthesis of new polyolefins containing (polar) functionalities by adopting the approaches by controlled incorporation of reactive functionalities (and the subsequent introduction of polar functionalities under mild conditions) by coordination polymerization in the presence of transition metal complex catalysts have been described. Related methods (such as direct copolymerization of olefin with polar monomer using living radical or coordination insertion methods) have also been demonstrated for comparison. Our recent efforts for precise synthesis of polyolefins containing polar functionalities by efficient incorporation of reactive functionality by copolymerization of ethylene with nonconjugateddiene (1,7-octadiene, vinylcyclohexene etc.) or divinyl-biphenyl using nonbridged half-titanocene [ex. Cp’TiCl2(O-2,6-iPr2C6H3), Cp’ = C5Me5, tBuC5H4 etc.] catalysts have been introduced.
文摘The cracking of polyolefins, especially polyethylene in the molten state was effectively catalyzed by the powdery spent FCC （Fluid Catalytic Cracking） catalyst which was dispersed in it. The activation energy of the catalytic cracking of polyethylene was about 74 kJ/mol. The cracked product was naphtha and middle distillate as the major product and gaseous hydrocarbon （C1-C4） as the minor product while little heavy oil was produced. The chemical compositions of the product were： aromatic hydrocarbons, isoparaffins and branched olefins, whereas that of the non-catalyzed products were： n-olefins and n-paraffins with minor amount of dienes with increasing the process time. Additionally, the product pattern shifted from naphtha rich product to kerosene and gas-oil rich product. However, any catalytic product showed low fluid point （〈 -10 ℃）, while that of the non-catalyzed product was as high as 40 ℃. Catalyst could process, more than 100 times by weight of polyethylene with fairly small amount （- 30 wt%） of coke deposition. Spent catalyst gave higher hydrocarbons while fresh catalyst gave gaseous product as the major product. Other polyolefins such as polypropylene and polystyrene were tested on same catalyst to show that their reactivity is higher than that of polyethylene and gave the aliphatic products, alkyl benzenes and C6-C9 iso-paraffins as the major product. Product pattern of the cracked product suggested that the reaction proceeded via the primary reactions making paraffins and olefins which were followed by the isomerization, secondary cracking, aromatization and hydrogen transfer which based on the carbenium ion mechanism.
基金the National Key R&D Program of China(No.2018YFB1501404)the National Natural Science Foundation of China(No.52306293)+2 种基金Shenzhen Science and Technology Program(No.JCYJ20240813151118024)post-doctoral research grants for post-doctoral fellows to stay(come)to Shenzhen(szbo202318)the extended help from the Instruments Center for Physical Science of University of Science and Technology of China.
文摘In the quest for low-temperature polyolefins upcycling,overcoming the decomposition temperature limitations caused by chemically inert carbon-hydrogen(C(sp3)-H)bonds remains a challenge.Here we report a tandem endothermicexothermic magnetocatalytic(EEM)strategy for upcycling of polypropylene(PP)and polyethylene(PE)below their decomposition temperature(typically 300°C).A series of commodity polyolefins(PP,PE,and their mixtures(PP+PE))can be deconstructed magnetocatalytically at 290°C,for which a high H2 selectivity up to 86%can be achieved.Magnetothermal coupling simulations revealed that the interfacial temperature gap was the key to upcycling of polyolefins at low temperature.Overall,EEM method potentially provides a sustainable approach for end-of-life plastics upcycling.
基金supported by the National Science Foundation of the United States(NSF CBET 17-06911)。
文摘Since Ziegler,Hogan and Banks’seminal discoveries for the catalytic polymerization of olefins,many generations of catalysts have been reported[1–5].These include the transition from the original heterogeneous catalysts(Ziegler and Phillips)to homogeneous catalysts combining metallocene.
基金This research was made possible as a result of a generous grant from the National Key Research and Development Program of China(grant nos.2017YFA0207800 and 2017YFA0204503)the National Natural Science Foundation of China(grant nos.21975178 and 21734006).
文摘Compared with non-cross-linked and dynamically covalent polymers,covalently cross-linked networks are irreplaceableinmany areas;however,they aredifficult to repair once fractured,due to limited polymer chain diffusion after cross-linking.Herein,the authors have reported a newkind of permanently cross-linked polyolefin,which when attached with amide side groups,yieldmechanically robust yet readily repairablematerials.A key is to use low cross-linking density,which enables satisfactory elasticity and chain mobility for thermodynamically favored healing.Another key is to incorporate dense hydrogen bonds that can undergo reversible associations.These factors jointly promise polyolefin networks with good mechanical properties and self-healing performance(recovered spontaneously up to 96%of its original tensile strength).More importantly,by means of mechanochemiluminescence from 1,2-dioxetane,which serves as the cross-linker and built-in self-reporting stress probe,a microscopic evaluation of how the chain entanglement proceeds upon healing and how failure occurs in the network can be obtained.
基金supported by an Institutional Links (Grant No.527641843)under the Türkiye partnershipfunded by the UK Department for Business,Energy and Industrial Strategy together with the Scientific and Technological Research Council of Türkiye (TÜBİTAK,Project No.119N302)and delivered by the British Council.
文摘Under optimal process conditions,pyrolysis of polyolefins can yield ca.90 wt%of liquid product,i.e.,combination of light oil fraction and heavier wax.In this work,the experimental findings reported in a selected group of publications concerning the non-catalytic pyrolysis of polyolefins were collected,reviewed,and compared with the ones obtained in a continuously operated bench-scale pyrolysis reactor.Optimized process parameters were used for the pyrolysis of waste and virgin counterparts of high-density polyethylene,low-density polyethylene,polypropylene and a defined mixture of those(i.e.,25:25:50 wt%,respectively).To mitigate temperature drops and enhance heat transfer,an increased feed intake is employed to create a hot melt plastic pool.With 1.5 g·min^(-1) feed intake,1.1 L·min^(-1) nitrogen flow rate,and a moderate pyrolysis temperature of 450℃,the formation of light hydrocarbons was favored,while wax formation was limited for polypropylene-rich mixtures.Pyrolysis of virgin plastics yielded more liquid(maximum 73.3 wt%)than that of waste plastics(maximum 66 wt%).Blending polyethylenes with polypropylene favored the production of liquids and increased the formation of gasoline-range hydrocarbons.Gas products were mainly composed of C3 hydrocarbons,and no hydrogen production was detected due to moderate pyrolysis temperature.
基金financial support from the National Natural Science Foundation of China(Nos.22401274,U23B6011)the Jilin Provincial Science and Technology Department Program(No.20250102070JC)。
文摘Catalysts are key for olefin polymerization reactions and are also ubiquitous in catalysis science.Multinuclear metal catalysts have witnessed enhanced performances in catalytic reactions relative to mononuclear catalysts,but which substantially involve multi-step,tedious,and difficult synthesis.Herein,this study reports an intriguing approach to construct multi-nuclear catalysts for the milestoneα-diimine nickel catalysts using an oligomeric strategy.A polymerizable norbornene unit is incorporated into theα-diimine ligand backbone,leading to the formation of the monomeric nickel catalyst Ni_(1)and its corresponding oligomeric nickel catalysts(Ni_(3)and Ni_(5))with varying degrees of polymerization(DP=3 and 5).Notably,the oligomeric catalyst Ni_(5)was facilely scaled up(50 g-level),showed enhanced thermal stability,exhibited 4.6 times higher activity,and yielded polyethylene elastomer with a 379%increased molecular weight in ethylene polymerization,compared to the monomeric catalyst Ni_(1).Catalytic performance enhancements of oligomeric catalysts were found to be DP-dependent.The kilogram-scale polyethylene,produced using Ni_(5)in a 20 L reactor,presented a highly branched all-hydrocarbon structure,which demonstrated typical elastic properties(tensile strength:4 MPa,elastic recovery:SR=72%)along with great processability(MFI=3.0 g/10 min),insulating characteristics(volume resistivity=2×10^(16)Ω/m),and hydrophobicity(water vapor permeability:0.03 g/m^(2)/day),suggesting potentially practical applications.
基金supported by the National Key R&D Program of China(2021YFA1501700)the National Natural Science Foundation of China(22272114)+2 种基金the Funding for Hundred Talent Program(20822041E4079)the Fundamental Research Funds from Sichuan University(2022SCUNL103)This work has also been supported by SINOPEC Research Institute of Petroleum Processing Co.,Ltd.via collaborative project No.36800000-24-ZC0607-0175.
文摘Converting waste plastics directly into valuable aromatic chemicals is a promising,cost-effective recycling strategy.Traditional zeolite-catalyzed cracking of polyolefins to produce aromatics often needs high temperatures and faces issues like low selectivity for liquid aromatics,separation difficulties,and rapid catalyst deactivation due to coking.To address this,a multifunctional Ni/HZSM-5 catalyst was developed to efficiently upgrade various polyolefins—including polyvinyl chloride—into gaseous alkanes(C_(1)–C_(5))and easily separable liquid aromatics(C_(6)–C_(12))at 400°C,without added solvents or hydrogen.Aromatic products make up 57.1 wt%of total output,with more than 97.8%selectivity for the liquid phase and a BTX(benzene,toluene,and xylene)selectivity of 76.1%.The high activity and selectivity for aromatics stem from synergistic interactions between Ni nanoparticles(NPs)and acid sites in the zeolite,which promote selective C–C bond breaking and control hydrogenolysis and aromatization pathways.This synergy allows precise control over the distribution of products by carbon number and favors the formation of separable aromatics.Notably,the catalyst also prevents coking by hydrogenolyzing and hydrogenating reactive intermediates before they form stable graphite-like deposits.Consequently,Ni/ZSM-5 catalyst demonstrates excellent stability,maintaining consistent aromatics yield over 13 consecutive cycles and processing over 30 times its weight in plastics without regeneration.After regeneration,the activity of the catalyst was fully restored,highlighting its potential for industrial use.This work offers valuable insights for designing durable,high-activity catalysts,providing a practical route to improve plastic recycling technologies.
基金National Natural Science Foundation of China,Grant/Award Number:51901147Suzhou Key Laboratory of Functional Nano&Soft Materials,Collaborative Innovation Center of Suzhou Nano Science&Technology。
文摘The mass production of disposable polyolefin products has led to serious plastic pollution and an imbalance between manufacturing and recycling.Given these challenges,the chemical upcycling of waste polyolefins has attracted extensive attention due to its high efficiency and economic benefits.Herein,we review the development of polyolefin chemical upcycling in heterogeneous catalysis.The status quo of polyolefin recycling is first discussed.We then introduce the advanced strategies for chemical upcycling in the view of different value-added products and discuss their challenges and prospects.Our in-depth analysis centers on the catalytic mechanism and the design principle of heterogeneous catalysts.Finally,we outlook the promising directions to facilitate the degradation process via polymer and catalyst design and optimized catalytic engineering.Innovative strategies are expected to promote the chemical upcycling of polyolefins,bringing great promise for the sustainable development of society.
文摘A nickel catalyst was modeled with ligand L^2, [NH = CH-CH = CH-O]^-, whichshould have potential use as a syndiotactic polyolefin catalyst, and the reaction mechanim wasstudied by theoretical calculations using the density functional method at the B3LYP/LANL2MB level.The mechanism involves the formation of the intermediate [NiL^2Me]^+, in which the metal occupies aT-shaped geometry. This intermediate has two possible structures with the methyl group trans eitherto the oxygen or to the nitrogen atom of L^2. The results show that both structures can lead to thedesired product via similar reaction paths, A and B. Thus, the polymerization could be considered astaking place either with the alkyl group occupying the position trans to the Ni-O or trans to theNi-N bond in the catalyst. The polymerization process thus favors the catalysis of syndiotacticpolyolefins. The syndiotactic synthesis effects could also be enhanced by variations in the ligandsubstituents. From energy considerations, we can conclude that it is more favorable for the methylgroup to occupy the trans-O position to form a complex than to occupy the trans-N position. Frombond length considerations, it is also more favoured for ethene to occupy the trans-O position thanto occupy the trans-N position.
基金the National Natural Science Foundation of China(grant no.22122110)the Jilin Provincial Science and Technology Department Program(grant no.20230101347JC).
文摘Polyolefins are synthetic plastics that exist on the largest scale and are ubiquitous in human life.They are also the most frequently discarded plastics.Consequently,the ability to either upgrade polyethylene(PE)plastic for value-added applications or to degrade PE plastic for value-added chemicals and monomers is highly desirable and sought after to mitigate the plastic waste problem.Herein,we report an advanced strategy for tackling the issue of PE plastics,first through a sequential upgrading and then through a degrading pathway.The optimal Diels–Alder-type polar comonomer diester-substituted norbornadiene is copolymerized with ethylene to produce the desired polar-functionalized PEs with both high comonomer incorporations of 42.4 mol%(-COOMe:as high to 59.6 mol%)and high molecular weights of up to 224 kg mol^(−1)in high catalytic activities of>100 kg mol^(−1)h^(−1).By means of a decisive retro-Diels–Alder reaction,this upgraded PE,namely polar-functionalized PE,can completely switch to a clean and soluble vinylene PE with a high content(28.7 mol%)of dispersed internal double bonds,which are degradable.Ethenolysis of the highmolecular–weight(∼30 kg mol^(−1))vinylene PE with ethylene yields industrially relevant telechelic oligomers(∼360 g mol^(−1))of long-chainα,ω-dienes and C9/C9+hydrocarbon products.This chemical upgrading and recycling method makes polyolefin plastic more sustainable.
基金financially supported by the National Key R&D Program of China(2023YFA1506602 and 2021YFA1501102)the National Natural Science Foundation of China(21932002,22276023,22402019)+1 种基金the Fundamental Research Funds for the Central Universities(DUT22LAB602)Liaoning Binhai Laboratory Project(LBLF-202306)。
文摘Cold plasma-assisted catalytic upcycling of polyolefin wastes integrated with CO_(2)into value-added chemicals is a promising solution for mitigating the global carbon emissions and fossil energy crisis,but still challenging due to the complexity of products and low energy efficiency.Given this,a novel one-stage process of cold plasma coupled with Ga-modified hierarchical H-ZSM-5(Ga/Hie-ZSM-5)catalyst for polyolefins upgrading was designed with polyolefins followed by the catalysts within the plasma region,which facilitated the upcycling of polyolefins to light olefins and CO_(2)activation by plasma,and thereby the enhanced synergy between cold plasma and catalysts for aromatics production.At an input power of ca.45 W without external heating,the low-density polyethylene(LDPE)waste was completely converted with the assistance of CO_(2)and the yield of oil products over the Ga/Hie-ZSM-5 catalyst was highly up to 62.2 wt%,with nearly 100% selectivity of aromatics.Meanwhile,the degradation efficiency of LDPE and the energy efficiency could reach 2.5 g_(LDPE)·g_(cat)^(-1)·h^(-1)and 55.56 g_(LDPE)·g_(cat)^(-1)·kW^(-1)h^(-1),respectively.Mechanism investigation revealed that the plasma and CO_(2)synergistically affect the primary cracking of LDPE,forming a primary product enriched in olefins and a small amount of CO.Subsequently,the produced olefins intermediates were further aromatized via cyclizationdehydrogenation route on the Ga/Hie-ZSM-5 catalyst with assistance of CO_(2)under the synergistic effect of plasma-catalysis.This work offers a feasible strategy to improve the yield of aromatic products for the plasma-catalytic upcycling of polyolefins and CO_(2)at ambient pressure without any external heating.
基金financially supported by the National Natural Science Foundation of China(No.52130307)。
文摘A series of imido-vanadium(Ⅴ)complexes bearing bidentate phenoxy-phosphine ligands were synthesized and characterized by NMR,elemental analysis,and single-crystal X-ray diffraction.These complexes demonstrated excellent catalytic performance in ethylene/1-hexene copolymerization,achieving high activities of 12.0×10~6–49.0×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1)and affording random copolymers with tunable 1-hexene incorporations.These catalysts also exhibited ultrahigh activity,up to 112.2×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1),in ethylene/norbornene(NB)copolymerization,yielding cyclic olefin copolymers with adjustable NB incorporations.Remarkably,these catalysts demonstrated exceptional tolerance toward polar functional groups,enabling efficient copolymerization of ethylene with both 10-undecen-1-ol(U-OH)and 5-norbornene-2-methanol(NB-OH),incorporating about 2 mol%polar comonomers with high efficiency.Different with the catalytic behaviors in copolymerization of ethylene with nonpolar comonomers,the catalytic activities in E/U-OH copolymerization(25.7×10~6 g_(polymer)·(mol_(V))^(-1)·h^(-1))were much higher than those in E/NB-OH copolymerization(8.6×10^(6) g_(polymer)·(mol_(V))^(-1)·h^(-1)).DFT calculations revealed that the catalytic performance is governed by synergistic electronic and steric effects.For E/NB copolymerization,strong preference for cyclic olefins was attributed to favorable transition state stabilization.In polar comonomer systems,steric effects were predominant,with NB-OH exhibiting a larger buried volume around vanadium center upon coordination compared to U-OH.Overall,this work provides fundamental insights into vanadium-catalyzed(co)polymerization and offers new strategies for tailored polyolefin design.
基金supported by the National Natural Science Foundation of China(No.52173056)the Science and Technology Program of Gansu Province,China(No.23ZDGA001).
文摘Although Ziegler-Natta(Z-N)polyolefins have been widely used as raw materials to produce pharmaceutical or food packaging,the migration of acid scavengers,an additive usually introduced in Z-N polyolefins,from the packaging to its contents has not been reported.In this work,the migration of the two most used acid scavengers,calcium stearate(CaSt_(2))and zinc stearate(ZnSt_(2)),from a Z-N polypropylene random copolymer(PPR)into water during autoclaving at 121℃ were comparatively investigated.It was found that,for PPR plates containing 0.1 wt%CaSt_(2)or ZnSt_(2)(PPR-0.1CaSt_(2),PPR-0.1ZnSt_(2),respectively),the concentration of migrated calcium ion into water increased with autoclaving time,while that of zinc ion was much lower at same treatment durations and did not show a significant increase with treatment time.Interestingly,after removing all plates and acidification treatment,a considerable amount of stearic acid was detected in sterilized water for PPR-0.1ZnSt_(2),but no such significant stearic acid was detected in sterilized water for PPR-0.1CaSt_(2).Based on the structural evolution of the two soaps upon heating,possible mechanisms for the different migration behavior of CaSt_(2)and ZnSt_(2)from PPR into water during autoclaving treatment were proposed.Our results suggest that the migration issue of acid scavengers is worthy of attention in pharmaceutical packaging materials produced from Z-N polyolefins.
基金supported by the National Natural Science Foundation of China(No.U23B6011)the Jilin Provincial Science and Technology Department Program(No.20230101347JC)。
文摘Mechanochromic polyolefins represent a novel class of functionalized polyolefins,which still remains significant challenges.Pd(II)-catalyzed coordination-insertion copolymerization is a feasible method for achieving this kind of polymers,yet with linear microstructures.Ringopening metathesis polymerization(ROMP)offers another promising avenue for affording functionalized polyolefins.This method exhibits high polar group tolerance and the ability to precisely regulate polymer branches.In this study,we report the method for producing mechanochromic branched polyethylenes via ROMP.By employing the terpolymerization of a well-designed monomer containing the mechanochromic group,NB-ABF,with cyclooctene(COE)and long-chain 5-hexylcyclooctene(COE-C6),following by hydrogenation process,we synthesized a range of functionalized branched polyethylenes characterized by varied branching density and polar monomer incorporation.These polymers bear a structural resemblance to functionalized ethylene-octene copolymers.After crosslinking,mechanochromophores are generated,and mechanochromism is achieved in uniaxial tensile testing.A comprehensive assessment reveals that both the incorporation of polar monomers and variations in branching density significantly influence their mechanical properties.Notably,upon stretching,these materials display pronounced visible color change,confirming the successful development of mechanochromic branched polyethylenes.
基金financially supported by the National Natural Science Foundation of China(No.52422301)Natural Science Foundation of Jilin Province(No.SKL202302033)。
文摘The crystallization behavior of two commercial polyolefin elastomer(POE)samples was investigated using the fast scanning chip calorimetry(FSC)technique.Non-isothermal crystallization of the POE samples during cooling to low temperatures cannot be inhibited under the largest efficient cooling rate employed in the current work.Thus,the isothermal crystallization of POE samples was limited to a narrow temperature range.When the POE samples were cooled to a certain temperature below the non-isothermal crystallization temperature for crystallization,a crystallization time dependent melting peak appeared in the low temperature region besides the high temperature melting peak originated from the non-isothermal crystallization.This low temperature melting peak was arisen from the melting of crystals isothermally crystallized at the selected crystallization temperature.At each crystallization temperature,the lengths of crystallizable segments were different,thus,the low melting peak increased with increasing the crystallization temperature.In terms of the high melting peak attributed to the non-isothermally crystallized crystals,it somehow decreased with increasing crystallization time and then became constant with further increasing crystallization time at the selected crystallization temperature.This could be explained by the fact that the crystallizable sequences with longer length would nucleate and crystallize first to form thicker crystals during cooling.The subsequent crystallization contributed by the shorter crystallizable sequences will result in the formation of thinner crystals,causing the melting peak to shift to the lower temperature.
基金financial support from the National Natural Science Foundation of China (Nos. 22122110 ad 21871250)the Jilin Provincial Science and Technology Department Program (No. 20200801009GH)Shaanxi Provincial Natural Science Basic Research Program-Shaanxi Coal and Chemical Industry Group Co., Ltd. Joint Fund (No. 2019JLZ-02)。
文摘To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements on ethylene(co)polymerizations. The N-bridged phosphinecarbonyl Pd catalysts(Pd1-Pd5) and Ni catalysts(Ni1-Ni5) bearing five-to eight-membered-ring structures were designed and synthesized.Catalytic performance for ethylene(co)polymerization became better as the size of N-containing bridge increased. The seven-membered-ring bridged catalysts Pd4 and Ni4 exhibited the best performance in terms of catalytic activity, polymer molecular weight and incorporation of acrylates and acrylic acid. The better performance of these catalysts bearing larger-size bridges was tentatively attributed to the methyleneinduced higher electron density around nitrogen, which strenghtens the coordination of carbonyl group to metal center, and also to the steric effect offered by this cyclization. This work provides a new strategy to enhance hemilabile polymerization catalysts.
基金This work was supported by the NSFC(No.2007402820374043)SINOPEC(X500030).
文摘A neutral nickel(Ⅱ)catalyst D,{[O-(3-cyclohexyl)(5-Cl)C_6H_2-ortho-C(H)=N-2,6-C_6H_3(i-Pr)_2]Ni(Ph_3P)(Ph)}hasbeen synthesized and characterized by IH-NMR,FTIR and elemental analysis.The results indicate that Al(i-Bu)_3 is aneffective cocatalyst for the neutral nickel catalyst.With bis(1,5-cyclooctadiene)nickel(0)[Ni(COD)_2]or Al(i-Bu)_3 as a co-catalyst,the neutral nickel catalyst D is active for ethylene polymerisation and copolymerisation with polar monomers(tert-butyl 10-undecenoate(BU),methyl 10-undecenoate(MU),allyl alcohol(AA)and 4-penten-1-ol(PO))under mild conditions.The resulting polymers were characterized by (?)H-NMR,FTIR,DSC,and GPC.From the comparative studies,Ni(COD)_2 ismore active than Al(i-Bu)_3 for ethylene homopolymerization,while Al(i-Bu)_3 is more effective than Ni(COD)_2 for ethylenecopolymerisation with polar monomers.The polymerization parameters which affect both the catalytic activity and propertiesof the resulting polyethylene were investigated in detail.Under the conditions of 20 μmol catalyst D and Ni(COD)_2/D=3(molar ratio) in 30 mL toluene solution at 45℃,12×105 Pa ethylene for 20 min,the polymerization activity reaches ashigh as 7.29×105 gPE.(mol.Ni.h)^(-1) and M_η,is 7.16×104 g.mol^(-1).For ethylene copolymerization with polar monomers,theeffect of comonomer concentrations was examined.As high as 0.97 mol% of MU,1.06 mol% of BU,1.04 mol% of AA and1.37 mol% of PO were incorporated into the polymer,respectively,catalyzed by D/Al(i-Bu)_3 system.
文摘Polyolefins that bear a chiral side chain(typically an isobutyl group)experience a so-called macromolecularamplification of chirality:the chiral side-chain induces a slight preference for either tg or tg(?) main chain conformation.Thisslight conformational bias is amplified cooperatively along the chain,and results in preferred chirality of the main chainhelical conformations.As a result,these polymers display a liquid-crystal(LC)phase both in solution and,in the melt as atransient phase on the way to crystallization.The existence of two processes(melt-LC and LC-crystal transitions)results inunconventional behaviors that were first analyzed by Pino and collaborators back in 1975.These polymers also offer a meansto test the structural consequences of recently introduced crystallization schemes.These schemes postulate the formation of atransient liquid-crystal phase as a general scheme for polymer crystallization.
