Studies On The Influence Of Initiating Goups And Ligand Substituents On The Nickel Catalysts Polymerization Performance

Polyolefin is the polymer material with the largest annual output and the most versatile utility.However,due to the non-polar characteristics of polyolefin,the application of polyolefin is greatly restricted.Introducing a small amount of polar functional groups is an efficient method to modify polyolefin,which can significantly improve their properties,broaden their uses,and increase their commercial value.For example,the introduction of vinyl acetate into polyethylene,which is a copolymer of ethylene and vinyl acetate（EVA）,improves the toughness,impact resistance,heat sealing performance and filler compatibility of polymer materials,and is then widely used in hair Foam shoe materials,packaging molds,wires and cables,toys and other fields.However,it is very challenging to synthesize functionalized polyolefin materials.Transition metal catalysts can effectively realize the copolymerization of olefins and polar monomers,among which the late transition metal catalysts have the advantage of low oxygen affinity,high tolerance of polar groups,and wide application range of polar monomers.How to design and synthesize high-efficient catalysts to introduce polar functional groups into polyolefin has become a key research content of chemists.With the goal of increasing the content of polar monomers in polyolefin,this thesis mainly studied the factors that affect the performance of the catalyst,looking for the best reaction conditions to realize the high molecular weight polyolefin.（1）The influence of different initiating groups on phenol-phosphine catalystIn transition metal catalysts,ligands and initiating groups are both key components that affect the polymerization performance of catalysts.Previous studies have mostly focused on regulating the electronic effects and steric effects of ligands,while there is no comprehensive study on the effects of initiating groups.This work designed five different initiating groups,namely"Ni Me","Ni Ph","Ni（allyl）","Ni（COD）"and"Ni（acac）",which are installed in the phenol-phosphine nickel complexes with huge steric hindrance,and the ethylene（co）polymerization properties of these five nickel complexes with different initiating groups were studied.The research results show that the large sterically hindered initiating group is beneficial to the polymerization activity of the catalyst at high temperature.（2）The influence of different functional groups onα-diiminoketone catalystImine-derived ligands have become an attractive platform for olefin polymerization due to their ease of synthesis and modification.In this work,six ligands with different functional groups based onα-iminoketone were designed,namely"^tBu","Ph","Cy","NPh₂","Nap"and"Ada".The corresponding nickel complexes were synthesized by reacting the ligands with the same nickel precursor,and the performance toward ethylene（co）polymerization was studied.The results of the study show that rigid substituents are conducive to the molecular weight of the polymer;flexible substituents are conducive to the activity of the catalyst.In summary,the initiator group and the functional group of the ligand have different effects on the activity of the catalyst and the molecular weight of the polymer.In order to design and synthesize a catalyst with excellent polymerization performance,the combination of initiator group and ligand should be considered comprehensively.It is an effective method that combining different initiating groups with ligands with different steric hindrance and electronic effects to optimize the polymerization behavior of the catalyst.