The Olefin Polymerization Catalyzed By Ansa-Metallocene Catalysts

In this dissertation the performance was investigated using two kinds of cycloalkylidene-bridged metallocenes and four kinds of asymmetric-doubly bridged metallocenes used in ethylene polymerization and copolymerization with a-olefin. The temperature sensibility of the metallocenes, "the comonomer effect" in the copolymerization with a-olefin and properties of the polymer produced were especially studied. Furthermore, the performance of these catalysts used in propylene polymerization was evaluated. The microstructure of polypropylene was characterized briefly. The relationship between structure of metallocene and performance was discussed.1. The ethylene polymerization and copolymerization by two cyclohexylidene-bridged metallocenes were studied in detail. The results indicated that the maximal activity could reach 6.13×l0~6g/mol·h and 2.57×10~6g/mol·h respectively at 70℃. In copolymerization, the temperature sensibility of metallocene II was lower than metallocene I while the selectivity of metallocene II was better due to the larger reaction space of the metal center in metallocene II.2. The ethylene homo-and copolymerization by four asymmetric-doubly bridged metallocenes were studied in detail. The results indicated that for metallocene IIIand IV, the maximal activity could reach 1.97×10~6g/mol·h and 2.65×10~6g/mol·h respectively at 40℃. However, there was no activity for metallocene V and VI, in that the short bridge matched up badly to the coordination requirement of the large zirconium atom. In copolymerization, the temperature sensibility and the selectivity of metallocene IV were higher than those of metallocene III. The nonbonded interactions between the cyclohexylidene bridge and cyclopentadienyl groups could be the reason.3. The propylene polymerization by asymmetric-doubly bridged metallocene was studied. The atactic polypropylene was produced at 0℃ by metallocene III and IV. The activity could reach 10~6g/mol·h, the molecular weight (M_w) of polypropylene produced was more than 10~5g/mol. The difference of bridges had no influence on stereoselectivity of polypropylene.