Ethylene In-situ Polymerization Catalyzed By Salicylaldiminato Non-metallocene Binuclear Titanium Complexes

Linear low density polyethylene?LLDPE?can be obtained by catalytic copolymerization of ethylene and?-olefin.Because of the branched structure,the performance of LLDPE is more excellent than that of common polyethylene.There are two methods for producing LLDPE.One is the traditional step copolymerization,and the other is in-situ copolymerization.In-situ copolymerization uses ethylene as the sole feed,during which oligomers are produced first,and copolymerization is followed without the need to separate the products.This approach has attracted a great deal of attention due to the high efficiency and simpleness of the process,low costs,as well as its capability to produce high-performance polyolefin materials with novel structures.This paper proposed the idea of constructing two different coordination environments in the same ligand at the same time and obtaining a bifunctional catalyst with both oligomerization and copolymerization activity centers through one-step coordination.A new method for preparing non-metallocene asymmetric dinuclear titanium complexes by two-step Sonogashiracouplingreactionwasdeveloped.Twonovelacetylene-bridged salicylaldimine-type asymmetric dinuclear titanium complexes were successfully synthesized.The tridentate dinuclear titanium complex was successfully used as a bifunctional catalyst to catalyze the in-situ copolymerization of ethylene to prepare branched polyethylene under the action of the same cocatalyst-MMAO.The main contents are as follows:1.Methylene bridged salicylaldimine[ONS]tridentate dinuclear titanium complexes with three different sidearm substituents 10a-10c and a fluorine-containing pyridine diimine iron complex 17 were linked together to constitute a bifunctional catalyst system.Under the action of cocatalyst MMAO,in-situ polymerization of ethylene to prepare LLDPE was realized.This bifunctional catalyst was found to have the following characteristics:good compatibility of the oligomerization and copolymerization centers,high catalytic activity,positive comonomer effect and bimetal synergy.The molecular weight and branching degree was also easily adjustable.To the best of our knowledge,this is the first report of non-metallocene bifunctional catalyst on in-situ copolymerization of ethylene.2.Using tert-butylphenol as raw material,3-tert-butyl-5-iodosalicylaldehyde was first obtained by formylation and iodination,and then reacted with methylthioaniline and methoxyphenylaniline to give iodine-containing salicylaldimine[ONS]and[ONO]tridentate ligands.Through the Sonogashira cross-coupling reaction co-catalyzed by Cu/Pd,an acetylene-bridged asymmetrical salicylaldimine[ONO-ONS]tridentate ligand 24 was successfully synthesized.Finally,titanium tetrachloride was directly coordinated in one step to obtain an asymmetric dinuclear titanium complex 25 with tert-butyl substitution at the ortho position of phenolic oxygen.The structure of the compound was characterized by¹H NMR,¹³C NMR,infrared spectroscopy,mass spectrometry,and elemental analysis.It was found that complex 25 was highly active for ethylene polymerization,with activity up to4.18×10⁶ g/mol?Ti?h.The resulting polyethylene was of ultra high molecular weight of more than one million D.3.Using p-bromophenol and o-tert-butylphenol as raw materials,[ONO]-type aryl terminal alkynes and[ONS]-type aryl iodides were synthesized successively.Then through Sonogashira cross-coupling reaction,an asymmetric tridentate ligand 31 was obtained.Titanium tetrachloride was finally coordinated in one step to obtain an asymmetric dinuclear titanium complex 32 with adamantyl substitution at the ortho position of phenolic oxygen.Under the action of MAO,complex 32 can catalyze the polymerization of ethylene to obtain polyethylene with ultra-high molecular weight of 2000195 g/mol,and activity up to 1.11×10⁶g/mol?Ti?h.The molecular weight of the PE produced by complex 32 bearing the adamantyl structure is much higher than that produced by the tert-butyl bearing complex 25.