PRODUCTION OF MULTIMODAL POLYETHYLENE

摘要

A process for the preparation of polyethylene resins having a multimodal molecular weight distribution which comprises: (i) contacting ethylene monomer and a comonomer comprising an alpha-olefin having from 3 to 10 carbon atoms with a first catalyst system in a first reactor under first polymerisation conditions in a slurry process to produce a first polyethylene having a first molecular weight an HLMI of not more than 0.5g/10min and a first density of not more than 0.925g/ml and the first catalyst system comprising (a) a first metallocene catalyst of general formula R''(CpRm)(Cp'R'n)MQ2, wherein Cp is a cyclopentadienyl moeity, Cp' is a substituted or unsubstituted fluorenyl ring; each R is independently hydrogen or hydrocarbyl having 1 to 20 carbon atoms in which O ≤ m ≤ 4; each R' is independently hydrocarbyl having 1 to 20 carbon atoms in which O ≤ n ≤ 8, R'' is a bridge which comprises a C1-C20 alkylene radical, a dialkyl germanium or silicon or siloxane, or an alkyl phosphine or amine radical, which bridge is substituted or unsubstituted, M is a Group IVB transition metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen, the metallocene catalyst a centroid-M-centroid angle in the range 105° to 125°; and (b) a cocatalyst which activates the catalyst component; (ii) providing a second polyethylene having a second lower molecular weight and higher density than the first polyethylene; and (iii) mixing together the first and second polyethylenes to form a polyethylene resin having a multimodal molecular weight distribution.