Mixed metallocene catalyst systems containing a poor comonomer incorporator and a good comonomer incorporator
The present invention provides polymerization catalyst compounds, catalyst systems including these catalyst compounds, and to their use in the polymerization of ethylene and at least one comonomer. In particular, the invention provides a catalyst system comprising a poor comonomer incorporating catalyst compound and a good comonomer incorporating catalyst compound. Preferably, the low comonomer incorporating catalyst compound is a metallocene containing at least one substituted or unsubstituted fused ring cyclopentadienyl based ligand which is substantially directed to the front of the molecule, contains a long bridging group, or which contains a methyl substitution pattern which correlates to poor comonomer incorporation. The invention also provides methods of selecting the poor comonomer incorporating metallocene to pair with the good comonomer incorporating metallocene to produce polymers that are easy to process into a variety of articles, especially polyethylene based film, having enhanced properties.
1. A process for polymerizing olefin(s) to produce a polymer product, the process comprising contacting ethylene and at least one comonomer with a catalyst system, wherein the catalyst system comprises a poor comonomer incorporating catalyst compound comprising a metallocene structure comprising at least one fused ring cyclopentadienyl ligand bridged to another cyclopentadienyl ligand, where the bridge is a long bridge defined as a bridge containing an Si-O-Si group, and a good comonomer incorporating catalyst compound; wherein the poor incorporator metallocene is a polymerization catalyst which when run under process conditions wherein (Ind) 2 ZrCl 2 would produce a 0.920 g/cm 3 density polyethylene, produces a polymer with a density greater than 0.920 g/cm 3 ; further comprising isolating a polymer product having a density of from 0.910 to 0.940 g/cm 3 , an Mw/Mn value of from 2 to less than 10 and an I 2 value of from 0.1 to 100 dg/min.
2. The process of claim 1 , wherein the poor comonomer incorporating catalyst compound comprises at least one fused ring cyclopentadienyl based ligand directed to the front of the molecule by an angle α which is greater than 30 degrees.
3. The process of claim 2 , wherein α is greater than 60°.
4. The process of claim 2 , wherein the poor comonomer incorporating catalyst compound comprises two fused ring cyclopentadienyl based ligands, wherein the angle α of one of the two ligands is about 70° to about 90° and wherein angle α of the second of the two ligands is greater than 15°.
5. The process of claim 4 , wherein the angle α of one of the two ligands is about 70° to about 90° and wherein angle α of the second of the two ligands is greater than 45°.
6. The process of claim 1 , wherein the polymer product is formed into a film.
7. The process of claim 1 , wherein the process is a gas phase process.
8. The process of claim 1 , wherein the poor comonomer incorporating catalyst compound requires a comonomer to monomer mole ratio at least two times that of the good comonomer incorporating catalyst compound to prepare the same density polymer.
9. The process of claim 8 , wherein the poor comonomer incorporating catalyst compound requires a comonomer to monomer mole ratio of at least three times that of the good comonomer incorporating catalyst compound.
10. The process of claims 8 or 9 , wherein the density of the polymer is 0.920 g/cm 3 .
11. The process of claim 1 , wherein the at least one comonomer is selected from alpha-olefins having from 4 to 15 carbon atoms.
12. The process of claim 11 , wherein the polymer product possesses a CDBI of from 55% to 85%.