Y. Yamaguchi et al., Stereospecific polymerization of 1-hexene catalyzed by ansa-metallocene/methylaluminoxane systems under high pressures, J POL SC PC, 37(3), 1999, pp. 283-292
Citations number
42
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY
Stereospecific polymerization of 1-hexene under high pressures (up to 1,000
MPa = ca. 10,000 atm) using metallocene/methylaluminoxane (MAO) catalysts
was investigated. Several C-2-symmetric ansa-metallocenes, their meso-isome
rs, and two C-s-symmetric ansa-metallocenes were employed as catalyst precu
rsors. In the course of this study, novel C-2-symmetric germylene-bridged a
nsa-metallocenes, (rac-[Me2Ge(eta(5)-C5H-2,3,5-Me-3)(2)MCl2] (M = Zr, rac-4
a; M = Hf, rac-4b), have been prepared. High pressures induced enhancement
of the catalytic activity and the molecular weight of the polymers in most
of the catalysts. The maximum of both the catalytic activity and the molecu
lar weight of the polymers was mostly observed at 100-500 MPa in each catal
yst, although the enhanced ratio was smaller than that observed for nonbrid
ged metallocenes. Isospecificity of the C-2-symmetric ansa-metallocene cata
lysts was essentially maintained even under high pressure. Highly isotactic
polyhexene ([mmmm] = 91.6%) with very high molecular weight (M-w = 2,360,0
00) was achieved by rac-4b under 250 MPa. High pressures slightly decreased
syndiotacticity when the C-s-symmetric ansa-metallocene, isopropylidene(1-
eta(5)-cyclopentadienyl)(9-eta(5)-fluorenyl)zirconium dichloride 5, was emp
loyed. (C) 1999 John Wiley & Sons, Inc.