Silica Modification On The Surface Of Silica Particles And In Situ Loading Of Metallocenes On Organic Chains

In recent years,the market share of metallocene catalysts in polyolefins has been increasingly.However,metallocene catalysts must be supported on a carrier for industrial application because homogeneous catalyzed olefin polymerization of the catalyst is prone to the phenomenon of polyolefin sticking.Spherical silica is currently the main carrier of metallocene catalysts in olefin polymerization reaction systems.With the use of silica carrier,its disadvantages are gradually revealed.It is mainly manifested in that the organic components of metallocene do not match the polarity of the inorganic surface of silica and the metallocene easily falls off the surface of silica,which reduces the content of metallocene in the supported catalyst and affects the catalytic efficiency of the composite catalyst to a certain extent.In order to solve this problem,this thesis carried out the organic modification of silica surface and effectively loaded metallocene dichlorozirconocene on the modified carrier surface,and achieved certain research results.details as follows:In this thesis（Chapter 2）,Zirconocene catalyst was synthesized and connected on modified silica with N¹,N²-bis（2-（triethoxysilyl）ethyl）oxalamide（OBA）by the reaction between the active hydrogen on the chain of OBA,Zr Cl₄ and cyclopentadienyl sodium.The composited catalyst was found to have high catalytic activities in ethylene polymerization（8.46×10⁶g PE/Mol（Zr）·h）and in ethylene-octene copolymerization（9.08×10⁵g PE/Mol（Zr）·h）by using methylaluminoxane as cocatalyst.The product of polyethylene was found to have a narrow molecular weight distribution（Mw/Mn=3.33）and higher molecular weight than those of product catalyzed by the composited catalyst that the metallocene was supported on the surface of silica unmodified.This result offers an important theoretical and practical value in solving low catalytic efficiency of the catalyst that was caused by falling off from support.In Chapter 3,three kinds of silica sesquimers with different micro morphologies and structures were prepared by the reaction between3-（triethoxysilyl）propyl isocyanate and cyclohexanediamine or ethylenediamine,the reaction between aminopropyl triethoxysilane and oxalyl chloride.The raw products were hydrolyzed in slightly acidic environment.Zirconium dichloride（Cp₂Zr Cl₂）was loaded on surface of the three silica sesquimers respectively to prepare three kinds of supported metallocene catalysts.Research results indicate that the three supported catalysts had high catalytic activity for olefin homopolymerization and copolymerization,especially Cp₂Zr Cl₂ supported on the surface of helical siloxane hemipolymer（product from the addition and hydrolysis of cyclohexanediamine）,and the melting point of ethylene polymerization product（polyethylene）was 139.2℃,higher than most of polyethylene catalyzed by other Cp₂Zr Cl₂ supported catalysts.The composite catalyst shows excellent industrial application value.