Design And Synthesis Of Novel Dichromium Complexes Bearing Cycle Single NP Ligand For Ethylene Oligomerization/polymerization

Ethylene was one of the largest production of chemical products around the world.It was used to produce linear alpha olefin and polyethylene with its derivatives.Linear alpha olefin has been mainly used as polyethylene copolymer monomer,surfactant intermediates,plasticizers,oil additives and so on.According to the different structures of polyethylene,it could be divided into low density polyethylene,linear low density polyethylene,high density polyethylene and special functional polyethylene.The Cr-based catalysts have been the hot research topic because of their high activity and selectivity for ethylene oligomerization or polymerization.Among these,chroumium complexes with NP ligand peformed excellent propertities.Nowadays,most research work focused on exploring the structure of NP ligand in order to change the ligated environment of Cr(Ⅲ)and improve the catalytic activity and selectivity.In this paper,five novel cycle NP ligand were designed,synthesized and characterized.Complexes were formed by the above ligands and CrCl3(THF)3 in situ to catalytic ethylene oligomerization and polymerization with aluminoxane(MAO)and triethylaluminum(TEA)as cocatalyst.The main research work was as follows.(1)We designed,synthesized and characterized five novel cycle NP ligand,1,5,9,13-tetra(diphenylphosphanyl)cyclohexadecane ligand(L-C12Ph),1,5,9,13-tetra(dicy-clohexyl-phosphanyl)cyclohexadecane ligand(L-C12Cy),1,5,9,13-tetra(diisopropylphosp-hanyl)-cyclohexadecane ligand(L-C12iPr),1,4,8,11-tetra(diisopropylphosphanyl)cyclotetr-adecane ligand(L-C10iPr)and 1,4,7,10-tetra(diisopropylphosphanyl)cyclododecane ligand(L-C8iPr).(2)For ligands L-C8iPr and L-C10iPr,the effects of reaction temperature,n(Al)/n(Cr)and n(MAO)/n(TEA)on oligomerization performance of ligand/Cr(Ⅲ)/MAO were investigated in toluene.The effects of n(DMAO)/n(TEA)on oligomerization performance of ligand/Cr(Ⅲ)/DMAO/TEA were investigated in methylcyclohexane.(3)For ligands L-C12Ph,the effects of reaction temperature,n(Al)/n(Cr)and n(MAO)/n(TEA)on oligomerization performance of ligand/Cr(Ⅲ)/MAO were investigated in toluene.The effects of reaction temperature,catalyst concentration,n(DMAO)/n(TEA),chromium resource and n(L-C12Ph)/n(Cr)on polymerization performance of ligand/Cr(Ⅲ)/DMAO/TEA were investigated in methylcyclohexane.Besides,the effects of different solvents on oligomerization or polymerization performance of L-C12Ph/Cr(Ⅲ)/DMAO were also investigated.(4)The effects of ligands L-C12iPr and L-C12Cy with different substituents on oligomerization or polymerization performance of ligand/Cr(Ⅲ)/cocatalyst were investigated in toluene and methylcyclohexane respectively.The experiment results showed that:(1)L-C8iPr catalyst and L-C10iPr catalyst could catalytic ethylene oligomerization in toluene and the products performed wide range.L-C8iPr catalyst and L-C10iPr catalyst could also catalytic ethylene oligomerization in methylcyclohexane,although the catalytic activity was lower than that in toluene.(2)L-C12Ph catalyst could catalytic ethylene oligomerization in toluene and the products performed wide range.The L-C12iPr/Cr(Ⅲ)/MAO catalyst’s catalytic activity could reach 2.23×106 g/(molcr·h)under the reaction conditions that the reaction temperature was 80℃,the reaction pressure was 1.0 MPa,n(Al)/n(Cr)was 500 and the catalyst mole was 7.2 μmol.While in methylcyclohexane,L-Cl2Ph catalyst could catalytic ethylene polymerization and produced a large amount of low-molecular-weight PE wax.The L-Cl2Ph/Cr(Ⅲ)/MAO catalyst’s catalytic activity reached 8.75×105 g/(molcr·h)and the selectivity towards PE wax was 80.4%under the reaction conditions that the reaction temperature was 60℃,the reaction pressure was 1.0 MPa,n(DMAO):n(TEA):n(Cr)was 400:100:1 and the catalyst mole was 4.8 μmol.(3)L-Cl2iPr catalyst and L-Cl2Cy catalyst could catalytic ethylene oligomerization in toluene and the products performed wide range.L-C12iPr catalyst and L-C12Cy catalyst could also catalytic ethylene polymerization and produced a large amount of PE in methylcyclohexane.(4)When L-C12Ph:Cr(Ⅲ)was 1:2,the catalytic activity was almost twice than the activity of that L-C12Ph:Cr(Ⅲ)was 1:1,and maybe there were dichromium complexes which were favor for ethylene polymerization.