| 摘要 |
Multi-stage polymerization process for the production of a multi-modal linear low density polyethylene in at least two staged reactors connected in series comprising at least (i) polymerizing in a first slurry phase stage ethylene monomers and optionally one or more alpha-olefin comonomers, in the presence of a Ziegler-Natta polymerization catalyst system to obtain a first polyethylene fraction component (A) (ii) polymerizing in a second gas or slurry phase stage ethylene monomers and one or more alpha-olefin comonomers, in the presence of a Ziegler-Natta polymerization catalyst system to obtain a second polyethylene fraction component (B), whereby the Ziegler-Natta polymerization catalyst system comprises 1) a solid procatalyst formed by contacting at least: a) a Mg-alcoholate complex of the formula (I): Mg(OR1)2-n(R1)n, wherein each R1 independently represents a C1-C20 hydrocarbyl group and 0≦̸n<2 and may or may not be an integer; b) an aluminium compound of the formula (II) Al(R2)mX3-m, wherein each R2 independently represents an alkyl of up to 6 carbon atoms; each X is independently a halogen; 0≦̸m<3 and m and may or may not be an integer, c) a vanadium compound and a titanium compound in portions such as to provide a molar ratio of V:Ti from 10:90 to 90:10 in order to yield the solid procatalyst and 2) one or more organometallic cocatalyst(s) of the formula (III), wherein each R is independently a C1-C20-alkyl group, 0≦̸x≦̸2; 1≦̸y≦̸3; 0≦̸z≦̸2 and x+y+z=3; x, y and z may or may not be an integer, yielding a multi-modal polyethylene, whereby the process shows a reduced change of comonomer response with polymerization time and a more stable comonomer conversion with polymerization time compared to multistage processes using Ziegler-Natta catalysts with 100% Ti. |
