Catalytic Performance Of Pyridyl Metallocene Catalysts For Ethylene Polymerzation

Polyethylene resin(PE)is a common production of synthetic resin in the largest varieties,including low density polyethylene,linear low density polyethylene,high density polyethylene etc.It is widely used in industry,agriculture and packaging.The catalysts of ethylene polymerization include Ziegler-Natta,Phillips,metallocene,and late-transition metal catalysts.Metallocene catalysts have attracted more and more attention from academia and industry.Highly active metallocene catalysts show only one type of active site(single site catalysts),which produces polymers with a narrow molar mass distribution(Mw/Mn=2),and their structure can be easily changed.It attracts wide attention from academia and Industry.The synthesis and characterization of three pyridyl cyclopentadienyl ligands:2-(2,3,4,5-tetramethylcyclopentadienyl)pyridine(L1),2-methyl-6-(2,3,4,5-tetramethylcyclopentadienyl)pyridine(L2),2-methyl-6-((2,3,4,5-tetramethylcyclopentadienyl)methyl)pyridine(L3),Catalyst(C1-C9)formed by the ligands(L1,L2,L3)respectively with CrCl3(THF)3,ZrCl4(THF)2 and TiCl4(THF)2 catalyze the polymerization of ethylene.The effects of cocatalyst types,reaction temperature,catalyst concentration,reaction time,Al/Cr and solvents on the performance of ethylene polymerization were studied.The main research work of this paper is as follows:(1)when chromium complexes(C1,C2,C3)are used as catalysts,The order of catalytic ethylene polymerization was DMAO>MAO>MMAO.Under the reaction condition that the reaction temperature was 450C,the reaction pressure was 1.0 MPa and n(Al)/n(Cr)was 500,the catalytic activity of C3 could reach 7.99×103kg(PE)·(molcr·h)-1,Mw was 999.8kg·mol-1,PDI was 2.4,Tm was 139.2℃.Comparing three kinds of chromium complex catalyst system,it was found that the activity of catalyst increases with the introduction of bridged carbon between cyclopentadienyl and the activity of catalyst decrease with increasing the steric hindrance of pyridine ring substituent.(2)The effects of reaction temperature,catalyst concentration,reaction time,n(Al)/n(Cr)and solvent on the performance of ethylene polymerization was studied by using chromium complex C3 as catalyst and MAO as cocatalysts.Under the reaction condition that the reaction temperature was 30℃,toluene as solvent,molar mass of catalyst was 1.2 μmol,the reaction time was 10min and n(Al)/n(Cr)was 500,the catalytic activity of C3/MAO could reach 19.03×103kg(PE)·(molCr·h)-1。(3)When titanium complexes(C4,C5,C6)and zirconium complexes(C7,C8,C9)were used as catalysts,the activity of ethylene polymerization is the highest when DMAO was used as a cocatalyst.In zirconium complex catalyst system,it was found that the activity of catalyst increases with the introduction of bridged carbon between cyclopentadienyl and the activity of catalyst increases with increasing the steric hindrance of pyridine ring substituent.The molecular weight distribution of polyethylene(PDI)formed by titanium/zirconium catalyst was less than 4.8.