Polymerization process for producing easier processing polymers

Details Polymerization process for producing easier processing polymers Polymerization process for producing easier processing polymers

2001-08-17

2002-05-14

Nazario-Gonzalez, Porfirio (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heavy metal containing

C556S012000, C556S053000, C502S103000, C502S117000, C526S160000, C526S943000

Reexamination Certificate

active

06388115

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for polymerizing olefin(s) to produce polymers having improved processability. Also, the invention is directed to a bulky ligand metallocene-type catalyst compound and catalyst system for use in the polymerization of olefin(s) to produce polymers that are easier to process into various articles of manufacture. In particular, the invention is directed to cyclic bridged bulky ligand metallocene-type catalyst systems, their use in a polymerization process, and products produced therefrom.
BACKGROUND OF THE INVENTION
Processability is the ability to economically process and shape a polymer uniformly. Processability involves such elements as how easily the polymer flows, melt strength, and whether or not the extrudate is distortion free. Typical bulky ligand metallocene-type catalyzed polyethylenes (mPE) are somewhat more difficult to process than low density polyethylenes (LDPE) made in a high pressure polymerization process. Generally, mPE's require more motor power and produce higher extruder pressures to match the extrusion rate of LDPE's. Typical mPE's also have lower melt strength which, for example, adversely affects bubble stability during blown film extrusion, and they are prone to melt fracture at commercial shear rates. On the other hand, however, mPE's exhibit superior physical properties as compared to LDPE's.
It is now common practice in the industry to add various levels of an LDPE to an mPE to increase melt strength, to increase shear sensitivity, i.e., to increase flow at commercial shear rates; and to reduce the tendency to melt fracture. However, these blends generally have poor mechanical properties as compared with neat mPE.
Traditionally, metallocene catalysts produce polymers having a narrow molecular weight distribution. Narrow molecular weight distribution polymers tend to be more difficult to process. The broader the polymer molecular weight distribution the easier the polymer is to process. A technique to improve the processability of mPE's is to broaden the products' molecular weight distribution (MWD) by blending two or more mPE's with significantly different molecular weights, or by changing to a polymerization catalyst or mixture of catalysts that produce broad MWD polymers.
In the art specific bulky ligand metallocene-type catalyst compound characteristics have been shown to produce polymers that are easier to process. For example, U.S. Pat. No. 5,281,679 discusses bulky ligand metallocene-type catalyst compounds where the bulky ligand is substituted with a substituent having a secondary or tertiary carbon atom for the producing of broader molecular weight distribution polymers. U.S. Pat. No. 5,470,811 describes the use of a mixture of bulky ligand metallocene-type catalysts for producing easy processing polymers. Also, U.S. Pat. No. 5,798,427 addresses the production of polymers having enhanced processability using a bulky ligand metallocene-type catalyst compound where the bulky ligands are specifically substituted indenyl ligands.
A need exists in the industry for a process using a bulky ligand metallocene-type catalyst to produce more easily processable polymers.
SUMMARY OF THE INVENTION
This invention relates to a polymerization process utilizing a bridged bulky ligand metallocene-type catalyst system for producing polymer products that have excellent processability and enhanced physical properties. Also, the invention is directed to improved bridged bulky ligand metallocene-type catalyst compounds having a cyclic bridge, catalyst systems comprising these compounds, and polymerizing processes utilizing these compounds.
The preferred polymerization processes are a gas phase or a slurry phase process, most preferably a gas phase process.
In an embodiment, the invention provides for a process for polymerizing ethylene alone or in combination with one or more other olefin(s) in the presence of a cyclic bridged metallocene-type catalyst compound, preferably an achiral cyclic bridged metallocene-type catalyst compound, even more preferably an achiral cyclic bridged metallocene-type catalyst compound having two substituted bulky ligands and an activator. In a most preferred embodiment, the cyclic bridged metallocene-type catalyst compound has two bulky ligands only one of which is a substituted bulky ligand.
In another embodiment, the invention relates to a gas phase or slurry phase process for polymerizing olefin(s) using a cyclic bridged metallocene-type catalyst system to produce a polymer product having a M
z
/M
w
greater than or equal to 3 and an I
21
/I
2
of greater than 35. In this embodiment, it is particularly preferred that a supported cyclic bridged metallocene-type catalyst system is used.
DETAILED DESCRIPTION OF THE INVENTION
Introduction
The invention relates to a polymerization process for producing easy processing polymers using a cyclic bridged bulky ligand metallocene-type catalyst system. It has been suprisingly discovered that using the cyclic bridged metallocene-type catalysts of the invention, particularly in a slurry or gas phase polymerization process, produces polymers that have a high Melt Index Ratio (MIR). MIR is simply the ratio of I
21
/I
2
, where I
21
is measured by ASTM-D-1238-F and I
2
known as Melt Index (MI) is measured by ASTM-D-1238-E.
Bulky Ligand Metallocene-Type Catalyst Compounds
Generally, bulky ligand metallocene-type catalyst compounds include half and full sandwich compounds having one or more bulky ligands bonded to at least one metal atom. Typical bulky ligand metallocene-type compounds are generally described as containing one or more bulky ligand(s) and one or more leaving group(s) bonded to at least one metal atom. In one preferred embodiment, at least one bulky ligand is &eegr;-bonded to a metal atom, most preferably &eegr;
5
-bonded to the metal atom.
The bulky ligands are generally represented by one or more open, acyclic, or fused ring(s) or ring system(s) or a combination thereof. These bulky ligands, preferably ring(s) or ring system(s) are typically composed of atoms selected from Groups 13 to 16 atoms of the Periodic Table of Elements, preferably the atoms are selected from the group consisting of carbon, nitrogen, oxygen, silicon, sulfur, phosphorous, boron and aluminum or a combination thereof. Most preferably the ring(s) or ring system(s) are composed of carbon atoms such as but not limited to those cyclopentadienyl ligands or cyclopentadienyl-type ligand structures or other similar functioning ligand structure such as a pentadiene, a cyclooctatetraendiyl or an imide ligand. The metal atom is preferably selected from Groups 3 through 15 and the lanthanide or actinide series of the Periodic Table of Elements. Preferably the metal is a transition metal from Groups 4 through 12, more preferably 4, 5 and 6, and most preferably the metal is from Group 4.
In one embodiment, the bulky ligand metallocene-type catalyst compounds of the invention are represented by the formula:
L
A
L
B
MQ
n
  (I)
where M is a metal atom from the Periodic Table of the Elements and may be a Group 3 to 12 metal or from the lanthanide or actinide series of the Periodic Table of Elements, preferably M is a Group 4, 5 or 6 transition metal, more preferably M is a Group 4 transition metal, even more preferably M is zirconium, hafnium or titanium. The bulky ligands, L
A
and L
B
, are open, acyclic, or fused ring(s) or ring system(s) such as unsubstituted or substituted, cyclopentadienyl ligands or cyclopentadienyl-type ligands, heteroatom substituted and/or heteroatom containing cyclopentadienyl-type ligands. Non-limiting examples of bulky ligands include cyclopentadienyl ligands, indenyl ligands, benzindenyl ligands, fluorenyl ligands, octahydrofluorenyl ligands, cyclooctatetraendiyl ligands, azenyl ligands, azulene ligands, pentalene ligands, phosphoyl ligands, pyrrolyl ligands, pyrozolyl ligands, carbazolyl ligands, borabenzene ligands and the like, including hydrogenated versions thereof, for example t

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