HIGH VISCOUS STRESS OF ORIENTED POLYOLEFINS UNDER UNIAXIAL TENSILE DEFORMATION

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.

A Greener Approach for Synthesis of Functionalized Polyolefins by Introducing Reactive Functionality into Ethylene Copolymers

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.

Catalytic Cracking of Polyolefins in the Molten Phase——Basic Study for the Process Development of Waste Plastics Liquefaction

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.

Continuous flow pyrolysis of virgin and waste polyolefins:a comparative study,process optimization and product characterization

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.

Switchable Polyolefins from Polar Functionalization to Degradability

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.

Combination of olefin insertion polymerization and olefin metathesis to extend the topology and composition of polyolefins

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.

Covalently Cross-Linked and Mechanochemiluminescent Polyolefins Capable of Self-Healing and Self-Reporting

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.

Sustainable chemical upcycling of waste polyolefins by heterogeneous catalysis

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.

Design and Theoretical Study of Nickel Catalysts for Syndiotactic Polyolefins

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.

Separator Dependency on Cycling Stability of Lithium Metal Batteries Under Practical Conditions

Development of practical lithium(Li)metal batteries(LMBs)remains challenging despite promises of Li metal anodes(LMAs),owing to Li dendrite formation and highly reactive surface nature.Polyolefin separators used in LMBs may undergo severe mechanical and chemical deterioration when contacting with LMAs.To identify the best polyolefin separator for LMBs,this study investigated the separator-deterministic cycling stability of LMBs under practical conditions,and redefined the key influencing factors,including pore structure,mechanical stability,and chemical affinity,using 12 different commercial separators,including polyethylene(PE),polypropylene(PP),and coated separators.At extreme compression triggered by LMA swelling,isotropic stress release by balancing the machine direction and transverse direction tensile strengths was found to be crucial for mitigating cell short-circuiting.Instead of PP separators,a PE separator that possesses a high elastic modulus and a highly connected pore structure can uniformly regulate LMA swelling.The ceramic coating reinforced short-circuiting resistance,while the cycling efficiency degraded rapidly owing to the detrimental interactions between ceramics and LMAs.This study identified the design principle of separators for practical LMBs with respect to mechanical stability and chemical affinity toward LMAs by elucidating the impacts of separator modification on the cycling performance.

Ni-catalyzed carbon–carbon bonds cleavage of mixed polyolefin plastics waste

The inert carbon–carbon(C–C) bonds cleavage is a main bottleneck in the chemical upcycling of recalcitrant polyolefin plastics waste. Here we develop an efficient strategy to catalyze the complete cleavage of C–C bonds in mixed polyolefin plastics over non-noble metal catalysts under mild conditions. The nickelbased catalyst involving Ni_(2)Al_(3) phase enables the direct transformation of mixed polyolefin plastics into natural gas, and the gas carbon yield reaches up to 89.6%. Reaction pathway investigation reveals that natural gas comes from the stepwise catalytic cleavage of C–C bonds in polypropylene, and the catalyst prefers catalytic cleavage of terminal C–C bond in the side-chain with the low energy barrier.Additionally, our developed approach is evaluated by the technical economic analysis for an economically competitive production process.

Dependence of lithium metal battery performances on inherent separator porous structure regulation

Boosting of rechargeable lithium metal batteries(LMBs) holds challenges because of lithium dendrites germination and high-reactive surface feature.Separators may experience structure-determined chemical deterioration and worsen Li plating-stripping behaviors when smoothly shifting from lithium-ion batteries(LIBs) to LMBs.This study precisely regulations the crystal structure of β-polypropylene and separator porous construction to investigate the intrinsic porous structure and mechanical properties determined electrochemical performances and cycling durability of LMBs.Crystal structure characterizations,porous structure analyses,and electrochemical cycling tests uncover appropriate annealing thermal stimulation concentrates β-lamellae thickness and enhances lamellae thermal stability by rearranging molecular chain in inferior β-lamellae,maximally homogenizing biaxial tensile deformation and resultant porous constructions.These even pores with high connectivity lower ion migration barriers,alleviate heterogeneous Li^(+) flux dispersion,stabilize reversible Li plating-stripping behaviors,and hinder coursing and branching of Li dendrites,endowing steady cell cycling durability,especially at higher currents due to the highlighted uncontrollable cumulation of dead Li,which offers new insights for the current pursuit of high-power density battery and fast charging technology.The suggested separator structure-chemical nature functions in ensuring cyclic cell stability and builds reliable relationships between separator structure design and practical LMBs applications.

Determination of the Henry’s Law Constant of Hexane in High-Viscosity Polymer Systems

The Henry’s law constant of volatiles in polymer systems is a crucial parameter reflecting the gas-liquid equilibrium,which is very important for devolatilization.In this research,polyolefin elastomer(POE)-cyclohexane and polydimethylsiloxane(PDMS)-hexane systems were studied,and the Henry’s law constant was obtained by measuring the gas phase equilibrium partial pressure when polymer solutions containing different mass fractions of volatiles reached a saturated state.The effects of temperature,type of volatiles,and polymer viscosity on the gas phase equilibrium partial pressure and Henry’s law constant of the volatiles were investigated.The results indicate that,with the increase of temperature and polymer viscosity,the gas phase equilibrium partial pressure and Henry’s law constant of volatiles increase.As temperature increases,the solubility of gas in liquid decreases.The relationship between the Henry’s law constant and temperature is consistent with the Arrhenius law.In the PDMS-hexane system,the gas phase equilibrium partial pressure and Henry’s law constant of n-hexane are higher than those of cyclohexane.The obtained Henry’s law constants can be used as a reference for perfecting the devolatilization process and improving the devolatilization effect.

ETHYLENE POLYMERIZATION AND COPOLYMERIZATION WITH POLAR MONOMERS BY A NEUTRAL NICKEL CATALYST COMBINED WITH CO-CATALYST OF Ni(COD)_2 OR AL(i-Bu)_3

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.

UNUSUAL CRYSTALLIZATION AND MELTING PROCESSES OF AN OPTICALLY ACTIVE POLYOLEFIN:ISOTACTIC POLY((S)-4-METHYL-HEXENE-1)

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.

Functionalization of Polypropylene with High Dielectric Properties: Applications in Electric Energy Storage

Biaxial-oriented polypropylene (BOPP) thin films are currently used as dielectrics in state-of-the-art capacitors that show many advantages, such as low energy loss and high breakdown strength, but a limited energy density ( 600 MV/m. The PP-OH dielectric demonstrates a linear reversible charge storage behavior with high releasing energy density > 7 J/cm3 (2 - 3 times of BOPP) after an applied electric field at E = 600 MV/m, without showing any significant increase of energy loss and remnant polarization at zero electric field. On the other hand, a cross-linked polypropylene (x-PP) exhibits an ε ~ 3, which is independent of a wide range of temperatures and frequencies, slim polarization loops, high breakdown strength (E = 650 MV/m), narrow breakdown distribution, and reliable energy storage capacity > 5 J/cm3 (double that of state-of-the-art BOPP capacitors), without showing any increase in energy loss.

SUPER POLYOLEFIN BLENDS ACHIEVED VIA DYNAMIC PACKING INJECTION MOLDING:MORPHOLOGY AND PROPERTIES

As a long-term project aimed at developing super polyolefin blends, in this paper we summarize our work on themechanical reinforcement and phase morphology of polyolefin blends achieved by dynamic packing injection molding(DPIM). The main feature of this technology is that the specimen is forced to move repeatedly in the model by two pistonsthat move reversibly with the same frequency during cooling, which results in preferential orientation of the dispersed phaseas well as the matrix. The typical morphology of samples obtained via DPIM is a shear-induced morphology with a core inthe center, an oriented zone surrounding the core and a skin layer in the cross-section areas. Shear-induced phase dissolutionat a higher shear rate but phase separation at low shear rates is evident from AFM examination of LLDPE/PP (50/50) blends.The super polyolefin blends having high modulus (1.9-2.2 GPa), high tensile strength (100-120 MPa) and high impactstrength (6 times as that of pure HDPE) have been prepared by controlling the phase separation, molecular orientation andcrystal morphology.

Ionomer Toughened Polyolefine

The morphology and properties of HDPE blends with Zn-SEPDM and GR were studied through SEM and mechanical property test. The results show that as Zn-SEPDM/GR content amounts to 20%, the blend becomes an IPN in structure, and that a rather high impact and tensile strength of HDPE may be obtained after blending. The antistatic effect, the softening point,and HDT of the blend are higher as compared to HDPE/Zn-SEPDM/ZnSt (zinc stearate).The effect of Zn-SEPDM on the compatibility the morphology and properties of IPP blends were studied by DSC, TEM and mechanical properties test. The results show that as Zn-SEPDM content exceeds 20%. Zn-SEPDM in the blend becomes continuous and an abrupt change in impact strength is incurred there from. Owing to the incorporation of ionic groups into EPDM.the strong interactions betWeen the chains make both the impact and the tensile strength of IPP remarkably higher

Application of prodigiosin as a colorant for polyolefines

Serratia marcescens strain 9986 is a producer of prodigiosin used as a dye of polyolefines (polyethylene, ultratene). The biosynthesis of pigment was closely connected with controlled growth parameters. A prodigiosin yield 0.2 - 0.4 mg per l of culture medium in the batch culture under aerobic conditions was obtained. Prodigiosin was extracted from crude biomass treated by 0.1% of sodium dodecyl sulfate (SDS). This novel elaborated stage is necessary for thermostability a dye in polymer. The consumption of prodigiosin preparation is more economical in the technology of the coloration of polyolefines. The elaborated method has been manufactured for dyeing polyethylene by biological pigment-articles of the common use corresponding to the technological standard.

Diffusion Characteristics and Removal of Cyclohexane in Polyolefin Elastomer Melt

The diffusion coefficient of volatiles in polymer solutions is a crucial parameter to describe the mass transfer efficiency and ability of volatiles.In this research,polyolefin elastomer(POE)was used as a polymer,and cyclohexane was used as a volatile.A gravimetric analysis was applied to measure the diffusion coefficient of cyclohexane in POE.The devolatilization rate of the POE-cyclohexane system under different conditions was measured.The effects of temperature,film sample thickness,and initial concentration of volatiles on the devolatilization rate were discussed.Based on the devolatilization rate data,the average diffusion coefficient of cyclohexane in POE was obtained by fitting with a mathematical model.The experimental results indicate that the devolatilization rate increased with increasing temperature and initial concentration of volatiles,but it decreased with increasing sample thickness.As the thickness increased,the overall diffusion resistance increased.As the temperature increased,the molecular movement increased,resulting in the increase of average diffusion coefficient.The relationship between the diffusion coefficient of the POE-cyclohexane system and temperature follows the Arrhenius law.The diffusion activation energy E=6201.73 J/mol,and the pre-exponential factor of the diffusion coefficient D0=2.64×10^(-10) m^(2)/s.This work can provide basic data for exploring the devolatilization of POE polymers and serves as a useful reference for enhancing the effect of devolatilization.