A-diimine Nickel Catalyzed Ethylene Polymerization And Preparation Of Graphene Foam Composites

Polyethylene is the most widely used polymer material,which completely changed people's production and life style.The key to the development of polyethylene lies in the development of olefin catalysts.At present,most academic researches are about late transition metal a-diimine catalyst,compared with previous generations of catalysts,it has a single activity center,high activity,well stability.However,such catalysts have poor thermal stability under industrial gas phase polymerization of 70-100 ?,which hinders the commercialization and industrialization of the a-diimine catalyst system.In this paper,after the condensation and other reactions successfully prepared N,N-bis(2,6-bis(bis(4-fluorophenyl)methyl)-4-(2-hydroxyethyl)phenyl)bis(methyl)-1,2-diimine nickel catalyst(Catl),N-2,4,6-trimethylphenyl-N-2,6-bis(bis(4-fluorophenyl)methyl)-4-(2-hydroxyethyl)-1,2-diimine nickel catalyst(Cat2)and N-2,6-diisopropylphenyl-N-2,6-bis(bis(4-fluorophenyl)methyl)-4-(2-hydroxyethyl)1,2-diimine nickel catalyst(Cat3).Through ethylene polymerization experiment,it was found that Catl had the best heat resistance,the activity at 90 ? has a decrease of 8.05%relative to its highest activity,Cat3 was the second,the activity at 70 ? has a decrease of 14.8%relative to its highest activity,polymerization activity of Cat2 decreased significantly at 70 ?,relative to its highest activity decreased by 52.4%.It indicates that the larger the steric hindrance of the substituents on the imine,the more difficult the aryl group of the ligand is to rotate,and the more excellent heat resistance of the catalyst,which indicates the direction for preparing the heat-resistant polyethylene catalyst later.Graphene has good mechanical,thermal and electrical properties,but it is easy to agglomerate in practical applications.The three-dimensional grapheme which consists of two-dimensional graphene not only retains the characteristics of nano-materials,but also has the advantages of macro-porous materials,and solve the problem of graphene difficult to use.In this paper,large size three-dimensional graphene foam(GF)was prepared by the improved Hummers method and solvothermal reaction.Then three-dimensional graphene foam/ethylene propylene rubber(GF/EPR)composites with different mass fraction was prepared by cold pressing and twin screw extruder.The structure of GF and composite were characterized by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).In addition,the effects of GF addition and different processing methods on the mechanical properties of the composite was investigated.Results indicated that GF can improve the tensile strength and the creep resistance of the composites.When the content of GF is less than I wt%,the materials prepared by the cold press have excellent elongation at break and yield strength.This is because the three-dimensional network structure in the GF can enhance the elasticity of the composite material.When the amount of GF is more than 3 wt%,the composites prepared by twin screw extruder have the highest breaking strength due to the fact that high shearing force improves the agglomeration of GF.