Polymerization process
View Patent ↗A process for the polymerisation of olefins is described involving the use of a catalyst system comprising a supported transition metal compound and an activator based on an organoborane and an aluminoxane. Preferably the transition metal compound is a metallocene complex. The support is pretreated with an organoaluminium compound and the process is particularly suitable for the gas phase preparation of copolymers of ethylene and alpha-olefins having a molecular weight distribution in the range 2.5-7.0 and a melt strength in the range 3-12 cN.
1. A process for the preparation of copolymers of ethylene and alpha-olefins having
(a) a melt strength in the range 3-12 cN, and
(b) a molecular weight distribution (Mw/Mn) in the range 3.0-7.0,
said process comprising polymerizing ethylene and one or more alpha-olefins in the gas phase in the presence of a supported metallocene complex that was prepared by the following steps:
a) adding an aluminoxane to a support to form a supported aluminoxane mixture;
b) adding to the supported aluminoxane mixture from step a) a monocyclopentadienyl metallocene complex to form a mixture; and
c) adding to the mixture from step b) an organoborane compound.
2. The process according to claim 1 , wherein the copolymers have
(a) a melt strength in the range 6-9 cN, and
(b) a molecular weight distribution (Mw/Mn) in the range 3.0-5.0.
3. The process according to claim 1 , wherein the monocyclopentadienyl metallocene complex has the formula
wherein:
R′ each occurrence is independently selected from the group consisting of hydrogen, hydrocarbyl, silyl, germyl, halo, cyano, and combinations thereof, said R′ having up to 20 nonhydrogen 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→ 4 bonded diene group having up to 30 non-hydrogen atoms, which forms a π 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* 2 SIR* 2 , CR* 2 CR* 2 , CR*═CR*, CR* 2 SIR* 2 , or
GeR*2, wherein:
R* each occurrence is independently hydrogen, or a member selected from the group consisting of hydrocarbyl, silyl, halogenated alkyl, halogenated aryl, and combinations thereof, said R* having up to 10 non-hydrogen atoms, and optionally, two R* groups from Z* (when R* is not hydrogen), or an R* group from Z* and an R* group from Y form a ring system.
4. The process according to claim 3 , wherein the complex is a titanium complex.
5. The process according to claim 4 , wherein the complex is (t-butylamido)(tetramethyl-→ 5 -cyclopentadienyl)dimethyl silanetitanium-→ 4 -1,3-pentadiene.
6. The process according to claim 1 , wherein the support is silica.