The Copolymerization Of Ethylene And Polymerization Of Cycloolefin Catalyzed By Single-Site Catalysts

In this dissertation, we supposed that the presence of oligomerization active species and copolymerization active species was the key feature in tandem catalysis of ethylene. In order to prove our assumption, we attempted the tandem catalytic systems, consisting of one catalyst with two different cocatalysts, to prepare the branched polyethylene.For non-metallocene catalysts, the combination of dichlorobis(β-diketonato)zirconium and AlEt₂Cl could form the oligomerization active species, and oligomerized ethylene to produceα-olefins. The oligomers were composed by C4-C12, and the selectivity ofα-olefins was above 70%. The catalyst combined with MAO (or Al(i-Bu)₃, AlEt₃) to form copolymerization active species, which was responsible for copolymerizing the ethylene andα-olefins to prepare branched polyethylene. The tandem catalytic systems, dichlorobis(β-diketonato)zirconium /AlEt₂Cl/MAO (or Al(i-Bu)₃, AlEt₃), were able to produce branched polyethylene from ethylene as the sole monomer. The activity was up to 6.76×104g/(molZr?h), the branching degree of resulting polymer was not higher. The molar ratio between two cocatalysts, molar ratio of catalyst and cocatalyst, concentration of catalyst and polymerization temperature had effects on the catalytic activity and the properties of copolymer.In the Et(Ind)₂ZrCl₂ catalytic system, the Et(Ind)₂ZrCl₂/AlEt₂Cl system gave higher selectivity to C4-C16α-olefins (91%) at the relatively high pressure. The polymerization conditions influenced the activity and distribution ofα-olefins. The catalytic system of Et(Ind)₂ZrCl₂/AlEt₂Cl/MAO exhibited high activity (above 7×105g/molZr?h) and incorporation (above 20/1000C). The polymerization conditions also had effects on the result of copolymerization. In our tandem catalytic system, the catalyst precursor could be selected from commercial metallocene to easily synthesized non-metallocene, which makes this method possess general application value for preparing branched polyethylene. The catalytic systems (dbm)₂ZrCl₂/AlEt₂Cl (or MAO) were investigated by UV/visible absorption spectroscopy. For low molar ratios of Al/Zr, a hypsochromic shift of the initial catalyst absorption band, corresponding to the monomethylation of the catalyst, was observed. Further addition of AlEt2Cl (or MAO) was accompanied by a continuous bathochromic shift of the maximal wavelength corresponding to the formation of more dissociated ionic active species. Then, there would be a coordination of monomer to the ionic active species.Three ansa-metallocenes (Me₂C)(Me₂Si)Cp₂TiCl₂, [(CH₂)₅C](Me₂Si)Cp₂TiCl₂ and (Me₂C)(Me₂Si)Cp₂ZrCl₂ were used as catalysts for ethylene polymerization. Only in trace polymer was obtained using zirconocene complex. The copolymerizations of ethylene withα-olefins, catalyzed by titanocene catalysts, were investigated. The structural characteristics, such as short bridges, more rigid ligand, larger dihedral angle and different bridging groups, had significant effects on the stability, catalytic activity and polymerization behavior.The polymerizations of cycloolefin (norbornene) were carried out by catalystsβ-diketonate titanium (zirconium, nickel), respectively. The norbornene polymerization occurred via addition mechanism inβ-diketonate nickel catalyst system. The polynorbornenes, synthesized by titanium or zirconium complexes, contained both ring-opening metathesis and addition polymer chain structures. The polymerization activity and portions of double bonds in polynorbornene increased when the polymerization temperature and Al/Ti molar ratio increased. The copolymers of norbornene with 1-hexene, 1-octene, dicyclopentadiene and 5-ethylidene-2-norbornene were prepared usingβ-diketonate nickel, respectively. Theα-olefin content in the copolymers was lower. The copolymers of norbornene with dicyclopentadiene or 5-ethylidene-2-norbornene were also vinyl-addition polymers, and the content of comonomer was close to the ratio in reaction. The homopolymer and copolymer of norbornene exhibited good thermal stability.