In Situ Preparation Of Single Component Immobilized Phenoxv-imine Catalysts For Ethylene Polymerization

Three species of functional ligands and catalysts bearing ?-alkenyl group weredesigned and synthesized due to the desire of in-situ immobilization of phenoxy-imine SSCs.These ligands and catalysts contain the ones bearing 4-vinylphenyl groupon the para position of aniline ring?SFI series?,the one beaing allyl group ortho to thephenoxy-oxygen atom?AFI catalyst?and the one bearing allyloxy group para to thephenoxy-oxygen atom?AOFI catalyst?.When implementing ethylene polymerizationwith these catalysts,some unusal polymerization behavior would be observed.TheSFI catalysts show a decreased catalytic activity and an increased molecular weight ofthe obtained polyethylene(Mw>1×10⁶ g·mol^-1)compared with the ones just bearing Hatom on the para position of the aniline ring.The same effect occurred,that is,increased catalytic activity and decreased polymer molecular weight are observedwhen transforming vinyl terminated catalyst-4F-BSFI to ethyl terminated catalyst-4F-BSFI-E.However,the catalyst 4F-AFI exhibits both increased catalytic activityand the ability to synthesize polymer with higher molecular weight compared to allthe other C3 groups?propenyl,n-propyl and isopropyl?substituted catalysts 4F-iAFI,4F-nPFI and 4F-iPFI.To our surprise,the excellent situation and steric hindrance ofthe allyl group endow 4F-AFI with the ability to synthesized higher molecular weightPE(Mw>3×10⁶g·mol^-1)than the SFI series.Furthermore,the catalyst 5F-BAOFI wasdesigned according to the catalytic performance of both the SFI series and 4F-AFIcatalyst.This one exhibits higher catalytic activity than SFIs and 4F-AFI andUHMWPE(Mw<7.12×10⁶g·mol^-1)can be prepared in mild condition.Both of thetert-butyl and allyloxy groups have a positive effect on the catalytic performance of5F-BAOFI.After imaging the resultant polyethylene morphology,some sphere orsphere like particles with different size were found distributed in the polymer matrix,the polymer morphologies were improved to some extent,that is,these catalysts with?-alkenyl substituents are self-immobilized in ethylene polymerization.However,¹³CNMR spectra show the presence of small amount of short chain branches and theabsence of double bonds as well as aromatic rings on polymer chains,that is,the main chain termination mode of these catalysts is chain transfer to aluminum rather than?-H elimination,and the vinyl groups of the catalysts can not be incorporated in thepolymer chains.So,the "self-immobilization" effect of these catalysts is closelyrelated to the coordination of double bonds,the steric hindrance of metal center andmolecular movement.Furthermore,the obtained UHMWPEs are highly crystalline,nearly disentangled ones,which take an advantage of polymer melting processingover the Z-N based ones.The functional ligands,AFIL and AOFIL,were hydrosilylated withtriethoxysilane?TES?catalyzed by Pt-PMVS or PtO₂ to afford the bulkily substitutedsilane agents?ATESFIL or 5F-BAOTESFIL?.By coordination of these ligands withTi metal,the catalysts were synthesized for ethylene polymerization,we found thatthe catalyst 2F-ATESFI shows a moderate activity(?5×10⁵gPE·mol^-1Ti·h^-1)tosynthesize moderate molecular weight PEs with narrow MWDs.However,due to thegood solubility of 4F-ATESFI and 5F-ATESFI in weak polar solvent-hexane,thesetwo catalysts are hard to precipitate,so,the synthesis of hybrid catalysts usingATESFIL ligands has to be done.We synthesize four kinds of hybrid catalysts4F-A-ATESFI,5F-A-ATESFI,5F-M-ATESFI and 5F-B-ATESFI,which also showmoderate catalytic activity comparable to 2F-A-ATESFI and the ability to synthesizepolyethylene with adjustable molecular weight.Why are the activities of these fourcatalysts not improved compared to 2F-A-ATESFI?The huge steric hindrancearound metal center imposed by-?CH₂?₃Si?OCH₂CH₃?₃ group is the key factor,whichimpedes monomer insertion,causing a decreased chain propagation rate,thus,theactivity of these catalysts and molecular weight of the obtained PEs are lower than thedouble bond terminated catalysts?SFI,AFI and AOFI?.Furthermore,the homo-ligated catalyst 5F-BAOTESF1 exhibits a poor solubilityin toluene.When dispersing the catalyst in CH₂Cl2 rather toluene,5F-BAOTESFIshow an increased but still moderate catalytic activity from 1.2×10⁵gPE·mol^-1Ti·h^-1 to3.8×10⁵gPE·mol^-1Ti·h^-1 however,there are still insoluble solid powder precipitatingin the bottom.The poor insolubility of 5F-BAOTESFI can be attributed to the bigsize of complex molecule which results in a strong molecule rigidity which affects the solubility of catalyst in the solvent.So,it is unwise to directly immobilize 5F-BAOTESFI on the silica surface to get covalently bound catalyst.However,it is suitable for modifying silica surface with 5F-BAOTESFIL ligand at first and then constructing a covalently bound catalyst.The thermo-treated silica were modified with 5F-BAOTESFIL ligand,and then coordinated with the mono-ligated complex 4' to obtain the covalently bound catalyst 22,which has a titanium content of 0.198mmol·g^-1 determined by ICP test.By FT-IR,TGA,EA,LS and BET analysis,the variation of surface or bulk chemical composition,specific surface area and pore structure of the silica was followed,thus,whether the modification and ligation reactions happened or not and the degree of the reactions can be confirmed.When implementing ethylene polymerization under atmospheric pressure,catalyst 22 show a moderate activity,which is one order of magnitude lower than 5F-BAOTESFI and two order of magnitude lower than 5F-BAOFI.Increasing ethylene pressure would bring an increased activity.The PEs obtained by catalyst 22 possess ultra high molecular weight with narrow MWDs,that is,catalyst 22 is a heterogeneous single site catalyst.In the ethylene polymerization process,the polymer grows by replicating the morphology of catalyst 22 which has a strong control over the polyethylene morphology.