Ethylene and propylene polymerization by the new substituted bridged (cyclopentadienyl)(fluorenyl) zirconocenes

Abstract

AbstractEight Cs‐symmetric complexes, R1R2C(Cp)(Flu)MCl2 [R1 = R2 = CH3CH2CH2, M = Zr (1), Hf (2); R1 = R2 = pCH3OC6H4, M = Zr (3), Hf (4); R1 = ptBuC6H4, R2 = Ph, M = Zr (5), Hf (6); R1 = R2 = ptBuC6H4, M = Zr (7); R1 = R2 = PhCH2, M = Zr (8)] have been synthesized and characterized. Zirconocenes all showed the same high catalytic activities in ethylene polymerization as complex Ph2C(Cp)(Flu)ZrCl2 (9). However, in the propylene polymerization, the catalytic activities decreased in the order 5 ≈ 9 > 7 > 8. Introduction of tBu decreased the activities, probably due to the bulk steric hindrance. The polypropylene produced by 5 and 7 with tBu substituent showed a higher molecular weight (Mη) than that produced by 9. The 13C NMR spectrum revealed the polymers from 7 and 8 to have shorter average syndiotactic block length than polymer produced by 9. It was noted that [mm] stereodefect of polypropylene by 8 could not be observed from 13C NMR, which showed that the benzyl on bridge carbon 8 prevented chain epimerization and enatiofacial misinsertion in polymerization. Copyright © 2005 John Wiley & Sons, Ltd.