Process for the polymerisation of ethylene in the presence of a transitional metal catalyst (Zr, Ti, Hf)

摘要

A process for polymerizing ethylene or copolymerising and one or more alpha-olefins in the gas phase. The process involves: (a) in a first stage polymerizing ethylene or ethylene and one or more alpha-olefins in the gas phase at a temperature in the range of 20 to 70oC in the presence of a catalyst system comprising (1) a supported constrained geometry complex and (2) an activator; (b) optionally, recovering the prepolymerised catalyst; and (c) in a second stage polymerizing ethylene or ethylene and one or more alpha-olefins in the gas phase at a temperature in the range 65 to 100oC in the presence of the prepolymerised catalyst. The constrained geometry complex preferably has the formula (I) wherein; R' in each occurrence is independently selected from hydrogen, hydrocarbyl, silyl, germyl, halo, cyano, and combinations thereof, the R' having up to 20 non-hydrogen atoms, and optionally, two R' groups (where R' is not hydrogen, halo or cyano) together form a divalent derivative thereof connected to adjacent positions of the cyclopentadienyl ring to form a fused ring structure; X is a neutral h4-bonded diene group having up to 30 non-hydrogen atoms, which forms a p-complex with M; Y is O, S, NR*, PR*; M is titanium or zirconium in the +2 formal oxidation state; Z* is SiR*2, CR*2, SiR*2SiR*2, CR*2CR*2, CR*=CR*, CR2SiR*2, or GeR*2; wherein R* in each occurrence is independently hydrogen or a member selected from hydrocarbyl, silyl, halogenated alkyl, halogenated aryl, and combination thereof, the R* having up to 10 non-hydrogen atoms, and optionally, two R* group from Z* (where R* is not hydrogen), or an R* group from Z* and an R* group from Y form a ring system.