| 摘要 |
<p>A two-step polymerization process for producing a polyolefin having a bimodal molecular weight distribution is provided. In step one, under polymerization conditions, at least two different alpha-olefins are contacted with a catalyst system which comprises an aluminoxane and a metallocene, selected from the group consisting of mono, di, and tri-cyclopentadienyls and substituted cyclopentadienyls, of a metal selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, provided however if said metal is titanium then a metallocene of at least one other of said metals is present such that a first polymerization mixture is formed which comprises a low crystallinity, high molecular weight, copolymer, unreacted monomer, unreacted comonomer, and catalyst. This is followed by contacting, under polymerization conditions, hydrogen (and optionally additional alpha-olefin), with said first polymerization mixture which comprises copolymer, unreacted monomer, unreacted comonomer, and catalyst, such that a second polymerization mixture is formed which comprises a low crystallinity, high molecular weight copolymer, and a high crystallinity, low molecular weight homopolymer.</p> |
