MULTIMODAL POLYETHYLENE POLYMERS AND PROCESS PREPARING SAID POLYMER

摘要

The present invention provides a process for the preparation of a polyethylene comprising: (i) 20-70% wt of a lower molecular weight ethylene polymer; (ii) 20-70% wt of a first higher molecular weight ethylene polymer; and (iii) 0.5-30% wt of a second higher molecular weight ethylene polymer,
wherein said second higher molecular weight ethylene copolymer has a greater weight average molecular weight than said first higher molecular weight ethylene copolymer and wherein said process comprises the sequential steps (a)-(c):
(a) polymerising ethylene and optionally an ±-olefin comonomer in a first reactor to produce a lower molecular weight ethylene polymer;
(b) polymerising ethylene and an ±-olefin comonomer in a second reactor to produce a second higher molecular weight ethylene copolymer; and
(c) polymerising ethylene and an ±-olefin comonomer in a third reactor to produce a first higher molecular weight ethylene copolymer,
wherein each polymerisation is catalysed by a Ziegler Natta catalyst.