Study On The Preparation Of Branched Polyolefin Using ?-diimine Complexes As Catalysts And Its Properties

Polyolefin materials have been widely used in daily life because of their excellent properties.There is no doubt that the olefin polymerization catalysts have a significant effect on the properties of resultant polyolefin.Among various catalysts,a-diimine-based complexes have received extensive attention due to their excellent catalytic performance recently.The low glass transition temperature,high branching density and variable chain structure endow the polyolefin obtained by this kind of catalysts a broader prospect.The study on the performance of a-diimine-based complexes for olefin polymerization can help to further understand the effect of the ligand structure and reaction conditions on the performance of catalytic system and polyolefin obtained.This paper took ?-diimine-based complexes as research objects and explored their catalytic performance in ethylene homopolymerization and ethylene/1-hexene copolymerization through ligand structures,reaction conditions,oxidant and reductant.Besides,the gas storage and separation performance of porous liquid prepared by using the obtained hyperbranched polyethylene as steric solvent was investigated.(1)The effect of ligand structures and reaction conditions on the performance of ethylene homopolymerization and ethylene/1-hexene copolymerization were explored by using ?-diimine nickel(C28H48N2NiBr2(Cat.A),C36H48N2NiBr2(Cat.B)and C78H60N2O2NiBr2(Cat.C))as catalysts,methylaluminoxane(MAO)as cocatalyst.Differential calorimetric scanner(DSC),gel permeation chromatography(GPC)and nuclear magnetic resonance(NMR)were adopted to analyze the properties and branch structure of polyolefin obtained.The interaction between Cat.B and MAO was characterized by electron paramagnetic resonance(EPR).The results showed that the activities of the above three catalysts differ when encounting different temperature.The branching density of prepared polyolefin would increase while the phase transition temperature reduced in response to a higher ratio of Al/Ni or concentration of 1-hexene.With the increase of temperature from 25? to 75?,the proportion of methyl in the branch structures of the poly(ethylene-co-1-hexene)catalyzed by the three catalysts decreased,while the proportion of ethyl group and long-chain branches increased to a certain extent,Furthermore,the increased Al/Ni ratio made the cocatalyst MAO as a reductant and could reduce Ni(II)into Ni(I).(2)The performance of ethylene homopolymerization and ethylene/1-hexene copolymerization in the presence of CoCp2 and AgOTf was expored by using ?-diimine nickel C36H4aN2NiBr2(Cat.B)as catalyst,MAO as cocatalyst,cobaltocene(CoCp2)as reductant and silver trifluoromethanesulfonate(AgOTf)as oxidant,respectively.DSC,GPC and NMR were used to investigate the properties and chain structures of polyolefin.The tensile property was obtained through the strain-stress curves.UV-Vis and EPR were used to explore the interaction between the Cat.B and CoCp2.The results illustrated that the addition of CoCp2 would decrease the branching density but increase the melting temperature of products.However,AgOTf had no significant effect on it.The time when AgOTf was added to the reaction system and the ratio of Co:Ni:Ag had obvious impact on the catalytic systems and products.In addition,the increase of CoCp2 would increase the proportion of methyl,while the proportion of long-chain branches decreased.It was worth noting that CoCp2 can reduce Ni(?)into Ni(?)through the research of UV-Vis and EPR spectra.(3)Using acetic acid/caproic acid/capric acid as modulator to prepare Zr-Fc MOF-2/6/10 porous materials.The morphology,structure and dispersibility of Zr-Fc MOF were investigated through scanning electron microscope(SEM),transmission electron microscope(TEM),atomic force microscope(AFM),infrared diffraction spectroscopy(FT-IR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),solid-state NMR(SSNMR)and dynamic light scatterometer(DLS),respectively.Hyperbranched polyethylene(HBPE)with molecular weight of 2×103 g/mol was prepared by taking ?-diimine palladium C44H49N2PdCl as catalyst and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate(NaBAF)as cocatalyst.Zr-Fc MOF-2/6/10 with different additon amounts were respectively dispersed in HBPE to prepare a series of porous liquids.The adsorption performance of porous liquids to Ar,CH2=CH2,H2,N2 and CO2 was studied.A porous liquid-based mixed matrix membrane was prepared by using polycarbonate(PC)as support layer and the gas separation property was explored.The results demonstrated that the gas uptake increased with larger amount of Zr-Fc MOF in porous liquids,which indicated that the cavity in the porous liquid was preserved.The gas flux of membrane was not high due to the high viscosity and few proportions of Zr-Fc MOF.The membrane showed good gas selectivity for CO2/N2.The photothermal response study illustrated that the separation ratio of CO2/N2 decreased with the increase of membrane temperature,but theoretical gas flux increased.