Olefin polymerization process with improved operability and polymer properties
Ethylene and optional comonomers are polymerized in the presence of an organozinc compound and a catalyst system to produce an ethylene polymer. The catalyst system comprises a bridged indenoindolyl Group 3-10 transition metal complex and an activator. The organozinc compound is used in an amount effective to increase the polymer bulk density compared with that observed in the absence of the organozinc compound. The organozinc compound can also narrow the particle size distribution of the polymer and the wt. % of polyolefin chunks produced. The operability of processes utilizing bridged indenoindolyl metal complexes is enhanced while maintaining desirably high polyolefin molecular weights.
1. A process which comprises polymerizing ethylene in the presence of an organozinc compound and a catalyst system comprising a bridged indenoindolyl Group 3-10 transition metal complex and an activator to produce an ethylene polymer having a weight average molecular weight, M w , within the range of 150,000 to 400,000, wherein the organozinc compound is present in an amount effective to increase the polymer bulk density compared with that observed in the absence of the organozinc compound.
2. The process of claim 1 wherein the organozinc compound is present in an amount effective to reduce the wt. % of agglomerated polyolefin particles produced compared with the wt. % of agglomerated polyolefin particles produced in the absence of the organozinc compound.
3. The process of claim 1 wherein the organozinc compound is present in an amount effective to narrow the particle size distribution of the polymer compared with the particle size distribution obtained in the absence of the organozinc compound.
4. The process of claim 1 wherein the organozinc compound is present in an amount within the range of about 0.1 to about 5,000 mmoles per mmol of Group 3-10 transition metal.
5. The process of claim 1 wherein the organozinc compound is a C 2 –C 20 dialkylzinc or a C, 12 –C 20 diarylzinc compound.
6. The process of claim 1 wherein the organozinc compound is diethylzinc.
7. The process of claim 1 wherein the catalyst system comprises a Group 4 transition metal.
8. The process of claim 1 wherein the complex is a dimethylsilyl-bridged cyclopentadienyl(indeno[1 ,2-b]indolyl)zirconium complex.
9. The process of claim 1 wherein the activator is selected from the group consisting of alkyl alumoxanes, alkylaluminum compounds, aluminoboronates, organoboranes, ionic borates, ionic aluminates, and mixtures thereof.
10. The process of claim 1 wherein the activator is a mixture of an alkyl alumoxane and an ionic borate.
11. The process of claim 10 wherein the activator is a mixture of MAO and trityl tetrakis(pentafluorophenyl)borate.
12. The process of claim 1 wherein the polymerization is performed in the presence of at least one α-olefin to produce an ethylene copolymer.
13. The process of claim 12 wherein the ethylene copolymer is LLDPE.
14. The process of claim 12 wherein the ethylene copolymer is MDPE.
15. The process of claim 12 wherein the α-olefin is selected from the group consisting of propylene, 1-butene, 1-hexene, 1-octene, and mixtures thereof.