Preparation Of Bimodal Polyethylene By Brush-like Polymer Supported FI Catalyst

Higher performance are required in polyethylene products with the development of technology.Bimodal polyethylene,combined high molecular weight part and low molecular weight part,is excellent polyethylene material.The processes for producing bimodal polyethylene mainly include melt blending method,series reactor method and single-reactor method.The single-reactor method for producing bimodal polyethylene can realize the blending of two molecular weight polyethylene from the molecular level.Owing to its low cost and simple production process,single-reactor method has become a popular research topic.The catalysts must be supported in the existing industrial system.This paper designed a brush-like polymer as a supporter for FI catalyst.First,polymer brush having a uniform side chain was synthesized by the method of ATRP and ROMP.Then the phenoxyimine ligand was modified at the end of side chain by azidation reaction,click reaction and aldehyde amine condensation.Final metal catalyst was supported by brush-like polymer to carry out polymerization of ethylene.In this paper,six different ligands coped with central metal are designed by phenoxy-imine functionalization of brush side chain.And then,we used these six supported catalysts for ethylene polymerization in different pressures.We compared the homogeneous FI catalysts with the supported catalysts.By comparing the activities of catalysts,different ligands were modified at a certain ratio in the end of brush side chain and then coordinated with metal catalyst.Two kind of FI catalysts were supported at the end of same brush to prepare bimodal polyethylene.The results showed that the activity of catalysts and the molecular weight of polyethylene are related to the steric hindrance of the R₂ group of the phenoxyimine ligand.The activity of the supported catalyst is not lower than homogeneous catalyst,and the molecular weight of polyethylene decreased as the steric hindrance of R₁ group of phenoxyimine ligand increased at high pressure?1MPa?.The molecular weight of Ti-Cat-1 and Ti-Cat-3 appeared to decrease with increasing pressure.The molecular weight distribution of the mixed-ligand supported FI catalyst at low pressure is significantly broadened,and there is a tendency for bimodal polyethylene to appear.A special fish scale-like layer structure emerged by observing the polyethylene sample by SEM.In this paper,the FI catalysts was successfully loaded onto the brush-like topological supports,and the activity of the supported catalysts were greatly improved under the pressure of 1 MPa,which paved the way for the processing performance of polyethylene.