Polymerization process

Details Polymerization process Polymerization process

2000-12-18

2003-03-25

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S133000, C526S134000, C526S153000, C526S901000, C264S464000

Reexamination Certificate

active

06538081

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a polymerization process. In particular, the invention relates to a process for improving the processability of bulky ligand metallocene catalyzed polymers by reducing the oligomer content. More specifically, the process of the invention utilizes an organometallic compound to reduce low molecular weight species which may cause the polymer to smoke during processing operations.
BACKGROUND OF THE INVENTION
Bulky ligand metallocene catalyst systems are utilized to produce a diverse array of new polymers for use in a wide variety of applications and products. Typical bulky ligand metallocene compounds are generally described as containing one or more ligands, usually, cyclopentadienyl derived ligands or moieties, in combination with a transition metal selected from Group 4, 5 or 6 or from the lanthanide and actinide series of the Periodic Table of Elements. Exemplary of the development of these and other metallocene catalyst compounds and catalyst systems are described in U.S. Pat. Nos. 5,017,714, 5,055,438, 5,096,867, 5,198,401, 5,229,478, 5,264,405, 5,278,119, 5,324,800, 5,384,299, 5,408,017, 5,491,207 and 5,621,126 all of which are herein fully incorporated by reference
Experience has demonstrated that, for example, where such relatively high molecular weight catalysts are used to polymerize ethylene, relatively high volumes of hydrogen gas must be present in the gaseous reaction medium in order to control the molecular weight of the polymer product such that a processable polymer having good melt flow properties can be achieved. Generally, H
2
:ethylene mole ratios of from about 0.006 to 0.035 may be required to appropriately control molecular weight of the polymer product. At these relatively high hydrogen concentrations, chain termination during polymerization tends to give rise to a polymer product which contains from about 0.4 up to about 2 wt % of low molecular weight polymer species (oligomers) which generally exhibit a molecular weight (M
n
) of 200 up to about 1000. During thermoprocessing of the resulting polymer product, such as extrusion, the presence of these oligomers in the polymer gives rise to a phenomenon known as “extrusion smoking”, which smoke is believed to be caused by a combination of vaporization and thermal decomposition of these low molecular weight species.
Organometallic compounds, for example, aluminum alkyls such as triethyl aluminum, are used as “scavengers” in metallocene catalyzed polymerization processes. These compounds are often introduced into the polymerization reactor environment at the onset of polymerization, but their introduction is then terminated or markedly reduced as polymerization proceeds. Contrary to the findings of the present invention, it is suggested in U.S. Pat. No. 5,712,352 that the presence of such scavengers during polymerization at levels of greater than 10 ppm, based on the weight of the reactor recycle stream, actually encourages the formation of low molecular weight oligomers during polymerization, and thus it is the goal of that patent to provide a process where the polymerization medium is free or essentially free of scavenger.
Accordingly, it would be advantageous to provide a polymerization process for producing olefin polymers and copolymers using metallocene catalyst systems which are processable, of controlled molecular weight, and which also contain a minimum amount of low molecular weight oligomer species which species tend to give rise to the evolution of smoke when thermoprocessed.
SUMMARY OF THE INVENTION
This invention provides a polymerization process for polymerizing olefin(s) in the presence of a bulky ligand metallocene catalyst system in utilizing at least one organometallic compound represented by the formula R
1
n
A wherein A is a Periodic Table Group 12 or 13 element. R
1
is the same or different, substituted or unsubstituted, straight or branched chain alkyl radical, cyclic hydrocarbyl radical, alkyl-cyclohydrocarbyl radical, aromatic radical or alkoxide radical and n is 2 or 3.
It has been found that the continuous introduction of the organometallic compound during the polymerization process significantly reduces the content of low molecular weight oligomer species (M
n
of about 200-1000) which are formed in the polymer product, thereby reducing or eliminating the evolution of smoke from thermoprocessing equipment when the polymer is processed.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to the use of an organometallic compound to reduce the presence of low molecular weight species in bulky ligand metallocene catalyzed polymerization processes. The presence of these oligomers in the polymer gives rise to a phenomenon known as “extrusion smoking” during thermoprocessing, which smoke is believed to be caused by a combination of vaporization and thermal decomposition of these low molecular weight species.
Bulky Ligand Metallocene Catalyst Compounds
The process of the invention provides polymers of enhanced processability by the addition of an organometallic compound during polymerization. Specifically the process of the invention enhances the processability of polyethylene polymers, produced in polymerization processes catalyzed by bulky ligand metallocene catalyst compounds. Generally, these 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 compounds are described as containing one or more bulky ligand(s) and one or more leaving group(s) bonded to at least one 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. The ring(s) or ring system(s) of these bulky ligands 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, germanium, 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 Groups 4, 5 and 6, and most preferably the transition metal is from Group 4.
In one embodiment, the polymerization process of the invention utilizes a bulky ligand metallocene catalyst compounds 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 zirconium, hafnium or titanium. The bulky ligands, L
A
and L
B
, are open, acyclic or fused ring(s) or ring system(s) and are any ancillary ligand system, including 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, cyclopentaphenanthreneyl ligands, indenyl ligands, benzindenyl ligands, fluorenyl ligands, octahydrofluorenyl ligands, cyclooctatetraendiyl ligands, cyclopentacyclododecene ligands, azenyl ligands, azulene ligands, pentalene ligands, phosphoyl ligands, phosphinimine (WO 99/40125), pyrrolyl ligands, pyrozolyl ligands, carbazolyl ligands, borabenzene ligands and the like, including hydrogenated versions thereof, for example tetrahydroindenyl ligands. In one embodiment, L
A
and L
B
may be any other ligand structure capable of &eegr;-bonding to M, preferably &eegr;
3
-bonding to M and most preferabl

Affiliated with

Also associated with

Rating

Polymerization process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Polymerization process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymerization process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3079297