Development And QSAR Study Of Pentane Heterocyclic Uranium Transition Metal Polyolefin Catalyst

Because of the extensive application of polyolefin materials,the research on catalysts in olefin polymerization was increasing continuously.More and more high-performance,low-cost polyolefin catalysts were introduced to the market.Brookhart’s Pyridine diimine post-transition metal olefin polymerization catalyst attracted extensive attention due to its high catalytic activity.On this basis,this paper modified and improved the structure of the ligands from different aspects such as electron effect and steric hindrance,obtaining a series of novel five-membered heterocyclic ligands.Corresponding olefin polymerization catalysts were synthesized from Pd,Ni coordination with ligands aforementioned.The influence of ligand structure,metal center,and experimental conditions on catalyst activity,polyethylene structure,molecular weight,and molecular weight distribution was analyzed.Finally the computer simulations were introduced to study the quantitative structure-activity relationship（QSAR）of those catalysts.The catalysts,intermediates and transition states in process of ethylene polymerization were optimized for energy calculation,proposing the possible reaction mechanism and speculating the catalyst structure with optimal performance.The specific content was as follows:1.Synthesis of ligands:A series of novel mon（minor）proles were synthesized from the HOAc catalyzed Schiff base condensation of 2-acetylpyrrole as precursor with aromatic amines by microwave-assisted.It was showed that the electron donating group on aromatic amine resulted in reactivity stronger than that of electron withdrawing group.The steric hindrance effect would be strengthened with the increase of substituents which could increase resistance to reaction.2.Synthesis of complexes:The metal complexes were obtained from mono（imino）pyrrolyl ligands and PdCl₂ by liquid reflux and hydrothermal synthesis.It was found that pyrrole monoimine ligand reacted with PdCl₂ according to the experimental phenomenon and characterization of the products by M.p,FT-IR,elemental analysis,UV-vis and TGA.It was found that this kind of complexes was composed of a single ligand and metal（PdCl₂L）structure,the ligand L and PdCl₂ were coordinated with 1:1,in which the Pd²⁺coordinated with two nitrogen atoms on the ligand and two Cl^-from PdCl₂ forming four-coordinate structure.3.Test of catalyst activity:The effects of steric hindrance and electronic properties of complexes on the catalytic activity of ethylene polymerization were investigated.The results indicated that the catalytic activity were higher when the alkyl were substituted for the aromatic amino ortho position than meta,para positions.And the activity was increased with the number of substituted methyl groups increasing.Next,the effect of different metal centers on catalytic activity was tested.For Ni（II）and Pd（II）complexes with the same ligand,the activity of the Ni-based catalyst was generally higher than that of the corresponding Pd catalyst.But the Pd-based catalysts would produce higher molecular weight oligomer compared with Ni-based.Finally the effect of reaction time,temperature,pressure,n（Al）/n（M）on the catalytic performance of ethylene polymerization were studied.It was found that the best condition was T=40℃,P=2MPa,t=1.5h,n（Al）/n（Pd）=1000,and the activity was 3.6×10⁴g（PE）·mol^-1·h^-1·MPa^-1.4.Study on QSAR:The complexes and ethylene polymerization processes were calculated by density functional theory（DFT）/UB3LYP/3-21G quantification package of Gaussian 09W/GaussView 5.0.The complexes structure was optimized and energy calculated.On this basis,energy of the reactants,transition states,and intermediates involved in the reaction were calculated,obtaining the activation energy of the reaction.The catalyst with the best performance was inferred from the relationship between catalytic activity and structure.The lower the energy barrier of the transition state was in the decisive step of the polymerization,the higher the activity of the catalyst would be.It was indicated the presence of an electron-withdrawing group on the catalyst promoted the olefin polymerization reaction,resulting in a higher activity.It was beneficial for polymerization reaction that the more substituents and the greater the steric hindrance was on catalyst,and its activity was higher.All these conclusions were basically consistent with the experimental results.