Polymerization behavior of α-olefins with rac- and meso-type ansa-metallocene catalysts: Effects of cocatalyst and metallocene ligand

✍ Scribed by Naofumi Naga; Takeshi Shiono; Tomiki Ikeda

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 101 KB
• Volume: 200
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/(sici)1521-3935(19990701)200:7<1587::aid-macp1587>3.0.co;2-5

✦ Synopsis

Polymerizations of propene, 1-butene and 1-hexene were conducted with a mixture of rac-and meso- [dimethylsilylenebis(2-methylindenyl)]zirconium dichloride (1) combined with methylaluminoxane (MAO), triethylaluminium (AlEt 3 )/triphenylcarbenium tetrakis(pentafluorophenyl)borate (2) or triisobutylaluminium (AliBu 3 )/2 as a cocatalyst. The polymerization profiles of propene with rac-1 and meso-1 were determined from the rate of overall propene consumption and the fractions of isotactic and atactic polymers which were sampled during polymerization. An induction time to reach the maximum R p (rate of polymerization) followed by gradual decay was observed in the case of using the systems rac-, meso-1 -MAO and rac-1 -AliBu 3 /2. Besides, a rapid drop of R p from the initial value was found when using AlEt 3 /2. Molecular weights of the isotactic and atactic polymers sampled do not change during polymerization, and it is suggested that the change of [C*] (number of active centers) is reflected in the profiles of R p . The rate ratio of rac-1 to meso-1 (R p (rac)/R p (meso)) in propene and 1-butene polymerizations decreases in the following order: AlEt 3 /2 A AliBu 3 /2 A MAO. In the case of 1-hexene polymerization, the highest R p (rac)/R p (meso) value was obtained. This result indicates that the coordination of 1-hexene to the sterically hindered site of meso-1 is difficult compared with propene and 1-butene.