Synthesis Of Supported Nickel Catalyst And Its Application In Preparation Of Brnched Polyethylene

Polyethylene is one of the most widely used polymer materials.Branched polyethylene,as an important branch of polyethylene,is widely used in films,tougheners,compatibilizers,dispersants,and rheology modifiers.The catalyst system is the key of the development of polyolefin preparation technology.The late-transition-metal?-diimine nickel(II)catalyst can catalyze the polymerization of the only monomer ethylene to produce branched polyethylene,and has high catalytic activity.However,the homogeneous?-diimide nickel(II)catalyst has the problem of polymer sticking,which is limited in industry.Supporting the homogeneous catalyst is an effective way to solve these problems.In this paper,supported catalysts were prepared by supporting?-diimide nickel(II)on carrier to catalyze the polymerization of ethylene.In addition,supported?-diimine nickel(II)catalyst and supported vanadium catalyst were compounded,study the situation of they catalyze the polymerization of ethylene at higher temperature.The specific researches are as follows:Firstly,the homogeneous?-diimide nickel(II)catalysts CatA,CatB,and CatC were respectively supported on a carrier to prepare supported catalysts S-CatA,S-CatB,and S-CatC.The loading rate and surface morphology of supported catalysts were characterized by ICP,SEM,EDX,etc.S-CatA,S-CatB,and S-CatD were used as the main catalysts for the polymerization of ethylene.The effects of different cocatalysts,different supports,polymerization temperature,ethylene pressure,and catalyst structure on the polymerization activity were investigated.The polymerization kinetics of S-CatB catalyst at different temperatures was studied.It was found that the supported catalysts showed good thermal stability.At 90^oC,the activity of S-CatA and S-CatB catalysts can reach 10⁶ g PE/mol Ni·h.It was found that both the melting point and molecular weight of the polymer decrease,and the degree of branching increases with increasing temperature.The polymer had a good morphology when polymerized below 50^oC.The?-diimine nickel catalyst CatD with asymmetric structure was further designed and synthesized,and its structure was characterized by ¹H NMR,FT-IR,and EA tests.The CatD catalyst was supported on Si O₂ carrier to obtain a supported catalyst S-CatD,and its morphology and structure were characterized.CatD and S-CatD catalysts were used for high-pressure polymerization of ethylene.The effects of polymerization temperature,molar ratio of Al to Ni and polymerization time on the polymerization activity were investigated.Polymerization kinetics of homogeneous catalyst and supported catalyst were comparative studied.S-CatD catalyst with large steric hindrance was more resistant to high temperature than S-CatA catalyst with similar structure.The polymer morphology prepared by the supported catalyst at 30^oC had a better improvement than the homogeneous catalyst.Supported vanadium-based catalysts S-CatM and S-CatN were prepared,and they were combined with S-CatD catalyst to form nickel-vanadium composite supported catalytic systems S-CatD/S-CatM and S-CatD/S-CatN,respectively.The high-pressure polymerization of ethylene was carried out use them.Investigate the situation of further improving the polymer morphology and solving the problem of sticky kettle at industrial temperature.The study found that the Ni/V composite supported catalytic systems can further improve the scale of the reaction kettle to a certain extent.DSC of polymer showed that the polyethylene prepared by the two catalysts in this catalytic system is only an in situ blend of linear polyethylene and branched polyethylene.