NOVEL POLYMERS

摘要

Copolymers of ethylene and a-olefins are provided having (a) a density (D) in the range 0.900 - 0.940 g/cm3, (b) a melt index MI2 (2.16 kg, 190°C) in the range of 0.01 - 50 g/10 min, (c) a melt index MI2 (2.16 kg, 190°C) and Dow Rheology Index (DRI) satisfying the equation [DRI/MI2] > 2.65, and (d) a Dart Drop Impact (DDI) in g of a blown film having a thickness of 25 µm produced from the copolymer satisfying the equation DDI = 19000 x {1 - Exp [-750(D - 0.908)2] } x {Exp [(0.919 - D)/0.0045] } The copolymers may suitably be prepared by use of metallocene catalysts and are preferably prepared in multistage processes earned out in loop reactors in the slurry phase. The copolymers exhibit long chain branching as defined by Dow Rheology Index (DRI) and exhibit unexpected improvements in mechanical properties, in particular dart drop impact, when extruded into blown films.