Ligand Design Based On Substituent Effects For Metal-catalyzed Polymer Synthesis

Metal complex catalyzed polymerization has a very important application in the preparation of polyolefin,polyester and other synthetic polymer materials.The rational design of metal complexes not only can achieve high activity,but also realize precise control of the microstructure and material properties of the polymer.Thus,polymer that meet different application scope can be prepared.The structure of ligands has a crucial influence on the performance of metal complexes.On the one hand,electronic effect and steric hindrance effect of metal complexes can be flexibly adjusted by introducing different substituents into the ligand structure.On the other hand,the performance of metal complexes in other aspects can be changed.In this paper,a series of highperformance metal complexes have been synthesized by ligand structure design based on substituent effect.Those catalysts have been applied to catalytic polymerization to prepare polyolefin,polyester and other synthetic polymer materials.In the aspect of ligand design,this paper not only studied the influence of substituents on the electronic effect and steric hindrance effect of catalysts,but also studied their influence on other comprehensive properties of catalysts.The main research contents are as follows:1.The realization of high-temperature solution polymerization is an important strategy for the efficient preparation of polyolefin elastomers.Based on the remote substituent effect and solubility improvement of tert-butyl,this section designed,synthesized and characterized a series of tert-butyl α-diimine ligands and the corresponding nickel catalysts.Those catalysts were used to prepare the branched polyethylene materials by high-temperature solution polymerization process.It was found that the above catalysts can achieve highly active solution polymerization in the saturated hydrocarbon solvents at temperatures over 120℃.The prepared branched polyethylene had not only ultra-high molecular weight(Mn up to 3.3 × 106 g/mol),but also showed excellent elastic properties.On this basis,this section further studied the influence of electronic effect on the performance of the catalysts.Among them,the catalyst with electron donor group had higher activity and thermal stability,and the molecular weight of the polymer was higher.2.The substituent effect at different positions often has an important impact on the performance of the catalyst.In this section,a series of PNCO-type phosphine-oxygen ligands with different substituents and corresponding palladium and nickel catalysts were designed,synthesized and characterized,which used for ethylene polymerization and ethylene-polar monomer copolymerization.Through introducing electron-donating groups on the carbonyl side,the chain transfer reaction by β-H eliminated was controlled,and the increase of polymer molecular weight could be achieved.The cyclic structure of the skeleton made the reduction of the steric hindrance effect,which led to the increase of the activity and the decrease of polymer molecular weight.For the catalyst with pyridine side group,the complexation of Lewis acid B(C6F5)3 with pyridine group can reduce the complexation toxicity of the latter to the catalytic metal center,the activity of ethylene polymerization was greatly improved.3.Heterogeneous catalysts are of great significance in the route of ethylene slurry polymerization to prepare polyethylene.In this section,a series of heterogeneous catalysts were prepared by introducing hydroxy-anchored groups into the ligand structure,which can achieve the loading of nickel-based olefin polymerization catalysts on inorganic supports.Compared with the unsupported nickel catalyst,the introduction of support can significantly improve the activity of ethylene polymerization,realize the copolymerization of ethylene and polar monomers.Thus,the copolymer with higher polar monomer incorporation ratio were able to obtain.More than,the thermal stability of the catalyst was improved,and the polymer morphology can be well controlled to prevent sticking.4.Metal-organic bifunctional co-catalytic polymerization can be achieved through bifunctional ligands.In this section,a series of(thio)ureas were synthesized based on 2-,3-and 4-pyridyl groups,furthermore which were used to catalyze the ring-opening polymerization of lactone.Among them,intramolecular coordination were found between 2-pyridyl with alkali metal ions,result in producing an organic Br?nsted base/metal Lewis acid dual-functional synergistic catalytic system with high catalytic activity.In addition,the 2-pyridyl group in the side arm of the catalytic system can be used as the stimulus-response site in Lewis acid/base to regulate ring-opening polymerization.The ring-opening polymerization can be terminated,which can be explained that Lewis acid BEt3 formed coordination with the nitrogen atom on the side arm group.Subsequently,the addition of DABCO in the catalytic system can crack the coordination,and then achieve the reactivation of the catalyst.