A New Type Of Iron(?) And Cobalt(?) Complexes Bistertbutylated Bis(imino)pyridine For Olefin Polymerization

Polyethylene is widely used in building materials,blow molding,packaging,textile and other industrial field.The catalysts of iron and cobalt complexes as a class of late transition metal complexes have shown high catalytic activity in the polymerization of monomers such as ethylene and propene,long lifetime,and high activity in copolymerization of olefin and polar monomer.Thus,they have received intensive research focus.Among them,the complexes of bis?imino?pyridine ligands exhibit best efficiency.The further modification of bis?imino?pyridine ligands mainly focus on the imine part of skeleton and the research on the central pyridine ring is few.among the modification of central pyridine ring,the aromaticity is mostly retained and most of them have much lower catalytic activity.Current thesis is trying to destroy the aromaticity of central ring of bis?imino?pyridine accompanying the increase of its steric hindrance in hope of getting a highly efficient catalyst.Thus,in this dissertation,a new type of bistertbutylated bis?imino?pyridine ligand L3 and its CoCl₂ complex?3a?and FeCl₂ complex?3b?were synthesized and characterized by NMR,IR and single-crystal X-ray diffraction,and the olefin polymerization activities of 3a and 3b were studied.The experimental results show that,when ethylene pressure is 10 atm,3a has high ethylene polymerization activity?8.78×10⁶ gPE/?mol[Co]×h??and oligomerization activity?6.77×10⁶ gPE/?mol[Co]×h?,and selectivity to C6?.When ethylene pressure is set at 1 atm,only high polymerization activity is observed,and the oligomerization activity is not observed.For ethylene polymerization at 0.1 MPa of ethylene pressure,the reaction conditions including alkyl aluminium activators,Al/Metal ratio,catalyst loading,reaction temperatures and the lifetime of the catalytic active species were screened.Experimental results showed that,for 3a,the optimium activator is Et₃Al and the optimium ratio of Et₃Al/Co is 100?3a load 2?mol?at 0.1 MPa ethylene pressure and 25 ^oC,and the maximium activity of 3a can reach 2.47×10⁶gPE/?mol[Co]×h?.The lifetime of active species was estimated to be around 60 minutes;The maximum reaction conditions for 3b are 2?mol 3b loading,Et₃Al,and the ratio of Et₃Al/Fe=100,at 0.1 MPa ethylene pressure,25 ^oC,45 min.The best activity of 3b is6.8×10⁶gPE/?mol[Fe]×h?and the lifetime of active species was estimated to be around45 minutes.Under the same conditions,the catalytic activity of 3b is higher than that of3a.The thermal stabilities of both 3a and 3b are low.In addition,3a has higher catalytic activity than the cobalt complex of the original ligand L1,indicating that tertbutyl groups showed stabilizing effect on the active site at certain degree.For polyethylene products,the average molecular weight and appearance of polyethylene products usng both 3a and 3b catalysts are different.In the case of 3a,the average molecular mass of corresponding polyethylene can reach more than 2 million g/mol when reaction is carried out at low temperature.For complex 3a,its catalytic activity in 1,3-butadiene polymerization was also investigated.The results showed that 3a had moderate butadiene polymerization activity and high selectivity towards cis-1,2 polymerization?96%?.The average molecular mass and molecular mass distribution of the products were related to the types of aluminum activators used.