Synthesis Of Palladium And Nickel Metal Catalysts And Their Application On Olefin Polymerization And Copolymerization

Since Brookhart discovered cationic?-diimine palladium and nickel catalysts in 1995,olefin polymerization and copolymerization catalyzed by late transition metals have attracted more and more attention.Since then,researchers have developed a large number of catalysts based on late transition metals and polymerization methods,including many excellent catalytic systems,such as?-diimine palladium and nickel systems,salicylaldiminato nickel systems,phosphinesulfonate palladium and nickel systems and phosphino-phenolate nickel systems.However,the existing palladium and nickel catalysts still have some problems,such as low activity,poor thermal stability,low molecular weight and low comonomer incorporation rates of obtained polymer et al.These problems seriously limit the application prospect of palladium and nickel catalysts.Therefore,it is of great significance to develop high-performance palladium and nickel catalysts.In this paper,a series of palladium and nickel catalysts with excellent properties were synthesized and applied to olefin polymerization and copolymerization to prepare polyolefin materials with different microstructures.The specific research work and the results achieved are as follows:(1)By use of a concerted double-layer steric strategy,a new conceptual?-diimine nickel catalyst was prepared.The nickel catalyst featured highly thermally robust(0-150°C),was ultrahighly active(up to 1.03×10⁹ g mol^-1 h^-1)toward ethylene polymerization,which is unprecedented among late transition metal catalysts.And,it simultaneously produced ultrahigh molecular weight polyethylenes(M_w=4.2×10⁶ g mol^-1).Additionally,these obtained polyethylenes featured linear branched(2/1000C)to lightly branched(32/1000C)and could also be incorporated with a small amount of methyl 10-undecenoate.(2)By combining the concerted double-layer steric strategy with the rotation-restricted strategy,a series of?-diimine nickel catalysts with the flexible restraint and the rigid restraint were prepared.These nickel catalysts exhibited enhanced molecular weight than the freely rotated one in ethylene polymerization.More strikingly,the preferred nickel catalyst had the ability to produce virtually linear polyethylene(0.8/1000C,T_m=130.2°C)with both ultrahigh molecular weight(M_w=7.10×10⁶ g mol^-1)and ultrahigh catalytic activity.Even at high temperature of 90°C,ultrahigh molecular weight polyethylenes(1.10×10⁶ g mol^-1)was accessible.(3)By the combination of 4-(diphenylamino)phenyl moiety with different substituents including H,Me,CHPh₂,and Ph groups,a family of unsymmetrical?-diimine nickel catalysts Ni1-Ni4 has been prepared.Under the activation of co-catalyst,these catalysts are highly active(10⁷ g mol^-1 h^-1)for ethylene polymerization,giving polymers with different microstructures(from branched ethylene oligomers to linear ultrahigh molecular weight polyethylenes)over a wide temperature range of 30°C to 70°C.Notably,the preferred Ni4even enables a slow-chain-walking process and thus is capable of producing linear,semicrystalline ultrahigh molecular weight polyethylenes(M_n=1056 kg mol^-1,brs=9.1/1000C,T_m=123.5°C)at low ethylene pressure of 1 bar.Additionally,in 1-hexene polymerization Ni4 is highly selective(88.1%)for uncommon 2,1-insertion followed by complete chain-walking.Thus,the chain-straightening polymerization of 1-hexene efficiently yields semicrystalline poly(1-hexene)with a high T_m(102.1°C)that resembles low-density polyethylene.(4)A series of triphenylamine-based?-diimine nickel catalysts bearing groups with different electronic effects(F,H,Me)were synthesized and applied to ethylene polymerization and copolymerization with polar monomer.Under the activation of cocatalyst,these nickel complexes displayed very high activities(1.44-2.93×10⁷ g mol^-1 h^-1)toward ethylene polymerization ranging from 0°C to 90°C.The molecular weight(M_n)of polymer obtained by nickel catalyst bearing electron-donating Me group is 2.4 times higher than that by nickel catalyst bearing electron-withdrawing F group at 0°C(1807 k Da vs 758 k Da),and the branching density of the obtained polymer is slightly different(4.3-28.2/1000C vs2.3-26.4/1000C)ranging from 0°C to 90°C.In addition,stronger electron regulation was observed in the copolymerization of ethylene and methyl 10-undecenoate.Nickel catalyst bearing electron-donating Me group showed higher activity(5.52×10⁵ g mol^-1 h^-1 vs 4.32×10⁵ g mol^-1 h^-1),and generated copolymer with higher molecular weight(17.7 k Da vs 5.5 k Da)and higher incorporation rates of the polar comonomer(0.21%vs 0%)compared with nickel catalyst bearing electron-withdrawing F group.(5)A family of flexible cyclohexyl/rigid aromatic phosphine-sulfonate palladium and nickel catalysts was designed,synthesized,and comprehensively identified by varying number,position,and size of alkoxy groups on aromatic substituents of phosphine.In ethylene polymerization,the steric effect of alkoxy substituents in palladium and nickel catalysts plays an important role on tuning polymer molecular weight,which gives the high molecular weight of 380 kg mol^-1 at 80°C in the palladium system and also provides very high catalytic activity of 16000 kg mol^-1 h^-1 at 70°C in the nickel system.In ethylene copolymerization with polar monomers,the decrease of steric bulk leads to an increase on the co-monomer incorporation in the obtained copolymers.As a result,the copolymerization of ethylene with methyl acrylate,and acrylic acid using palladium catalysts affords the high incorporation of 9.5 mol%and 8.3mol%,respectively;and the nickel promoted ethylene copolymerization with vinyl trimethoxysilane,and 6-chloro-1-hexene gives the incorporation of 3.7 mol%and 5.0 mol%,respectively.