The Application Research Of TiCl₄/MgCl₂ Catalytic System In The Polymerization Process Of Butene And Hexene

Polyolefin has been widely used in many fields due to its excellent performance.For the polyolefin industry,the research and development of polyolefin catalysts is the key to the development of high-performance polyolefin materials.Electron donor property plays a significant role in the Ziegler-Natta catalytic system.Based on the research of catalytic systems for 1-butene polymerization,the influence of carrier structure,internal and external electron donors,loading process and polymerization parameters on catalyst performance and resulted polymer microstructure was systematically investigated in this thesis.Meanwhile,this novel Ziegler-Natta catalyst was also used to catalyze 1-hexene polymerization.Based on polymer characterizations,the relationship between catalyst structure and polymer properties was further discussed.Spherical MgCl₂/ID/TiCl₄ catalyst was prepared,and the effects of carrier structure,the amount and type of internal electron donor(ID),and loading temperature on the catalytic performance were studied.The catalyst was characterized by inductively coupled plasma emission spectrometer(ICP)and specific surface area tester(BET),Fourier transform infrared spectrometer(FT-IR),scanning electron microscope(SEM).The optimal preparation process of the catalyst was determined as following:spherical carrier MgCl₂?2.14C₂H₅OH,the internal electron donor of diisobutyl phthalate(DIBP),the molar ratio of DIBP to Mg:0.1,and the load temperature of tetrachloro titanium:110°C.Four novel aminosilane external electron donors,dipiperidinyl dimethoxy silane(DPPDMS),dipyrrolidinyl dimethoxysilane(DPRDMS),and dipiperidinyl diethoxy-silane(DPPDES)and dipyrrolidinyl diethoxysilane(DPRDES)were synthesized,respectively.The relationship between the structure of the external electron donors and the performance of the catalyst was studied.Thereafter,the polymerization activity and polymer isotacticity under different polymerization conditions were investigated with DPPDMS as the external donor.The results showed that,compared with methyl cyclohexyl dimethoxysilane(CHMMS),the both conventional external electron donor DPPDMS and DPRDMS can increase the catalytic activity and polymer isotacticity.Furthermore,the amount of hydrogen had effect on the catalytic efficiency of the polymerization of butene-1,as well as on the polymer molecule weight and melt flow rate of polymerization products.The spherical TiCl₄/MgCl₂ catalyst described above was used to prepare a novel polybutene-1 alloy material by an in-situ pre-polymerization method.The poor morphology and stick-to-autoclave problems during the 1-butene polymerization were solved.Based on the characterization with differential scanning calorimetry(DSC),nuclear magnetic resonance carbon spectroscopy(¹³C NMR),polarizing microscope(POM),FT-IR,X-ray diffraction(XRD),the polymer structure was analyzed in detail,and the relationship between the different polybutene-1 content and product performance was investigated.Compared with bulk polymerization of butene-1,the in-situ pre-polymerization method can lead to improved morphology of polybutene-1 product,effectively reduced adhesion between polymer particles,and eliminate stick-to-autoclave phenomenon.The highest catalytic activity was as high as 10700gPB/gCat,the bulk density of the polymerized product was 0.44g/cm³,the particle size of the product was around 500?m.The transition period of polybutene-1 product from unstable crystalline form II to stable form I was effectively shortened by means of pre-polymerization method.The mechanical property test showed that the tensile strength and flexural modulus of thepolybutene-1 alloy increased with the propylene content,but the density,impact strength and elongation-at-breakage of the polymer decreased.At the same time,the mechanical performance of the polymer were close to those of imported products.In order to explore the adaptability of this new TiCl₄/MgCl₂ catalyst system,the polymerization of hexene-1 catalyzed by this system was studied.The process conditions such as reaction temperature,reaction time,catalytic system,monomer concentration,the type and the amount of solvent were determined based on the solution polymerization of hexene-1 at atmospheric pressure.The results showed that the catalyst activity reached 1268gPHe/gCat,the weight average molecular weight of the polymer was as high as 2.2×10⁵g/mol,and the glass transition temperature was-41.4°C.Microstructure of the polymer was analyzed by means of(FT-IR),¹³CNMR,Gel permeation chromatography GPC,DSC,XRD,and the isotacticity of the polymer was calculated based on NMR data.In the end,the resulting polyhexene-1(PHe)was blended with low density polyethylene to explore its application.Preliminary investigation was carried out on the morphology,crystallization behavior and mechanical properties of the blend.The results showed that the melt temperature of LDPE could be reduced and the crystallization rate of the system could be accelerated with the content of PHe reaching 10%,under this condition,elongation at break of blend was 186.4%.