Process for the preparation of polyethylene or polypropylene

Details Process for the preparation of polyethylene or polypropylene Process for the preparation of polyethylene or polypropylene

1998-09-08

2001-01-23

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...

C526S160000, C526S352000, C526S351000, C526S348600, C526S348400, C526S348200

Reexamination Certificate

active

06177527

ABSTRACT:

TECHNICAL FIELD
This invention relates to the preparation of polyethylene or polypropylene using stereoisomeric mixtures of metallocene catalysts containing cycloalkadienyl ligands.
BACKGROUND INFORMATION
Single site catalysts such as metallocenes have received wide attention for their ability to make polyethylene and polypropylene having relatively narrow molecular weight distributions and uniform comonomer distributions at excellent polymerization rates. Recently, the narrow molecular weight distributions have been addressed and broadened out improving processability.
It is known that particular bridged metallocene catalysts containing cycloalkadienyl ligands epimerize into their racemic and meso forms in the presence of, for instance, light or amines with heating. The racemic form generates isotactic polypropylene, while the meso form produces atactic polypropylene. When bridged metallocene catalysts having cycloalkadienyl ligands are commercially used to make polypropylene, the meso stereoisomer is generally separated out, normally at great cost, to avoid the formation of atactic polypropylene to provide resin for applications in which atactic polypropylene is not desired.
U.S. Pat. No. 5,304,614 and Spaleck et al, “The Influence of Aromatic Substituents on the Polymerization Behavior of Bridged Zirconocene Catalysts”,
Organomet.,
1994, Vol. 13, p. 954, disclose the use of bridged metallocene catalysts having cycloalkadienyl ligands in the production of polypropylene and polyethylene. Each of these references emphasizes the importance of separating out undesirable meso stereoisomers from the catalyst composition. Further, as described by Bercaw et al “Racemo-Meso Isomerization for Ansa-scandocene and Ansa-yttrocene Derivatives”, 215th ACS Meeting, held in Dallas, Tex. between Mar. 29 and April 2, 1998, presentation # 059, the interconversion can occur more rapidly at higher temperatures due to more favorable energetics available such that systems which interconvert very slowly at room temperature, equilibrate rapidly above 55 degrees C. Since many of the industrial processes for polymerization are conducted at higher temperatures, there is a real possibility that interconversion can occur during polymerization, further producing the meso epimer and subsequently the atactic polymer this isomer is known to generate.
While there is an industrial need for a process utilizing a metallocene catalyst, which produces resins, which do not have an atactic component, there is a greater need for a process which gives the operator control over the atactic/isotactic components of polypropylene and polyethylene. This can be accomplished by selecting the cocatalyst, which selectively activates only the desired epimer or, alternatively, both epimers; thus, the resin properties (either polyethylene or polypropylene or other) can be varied when a mixture of epimers is present in the catalyst precursor by the correct selection of cocatalyst.
DISCLOSURE OF THE INVENTION
An object of this invention, therefore, is to provide a process for the preparation of polyethylene or polypropylene in which the operator has control over the atactic/isotactic components of polypropylene and polyethylene. Other objects and advantages will become apparent hereinafter.
According to the present invention, such a process has been discovered, i.e., a process for the preparation of (i) polyethylene or (ii) polypropylene, which is essentially isotactic or a mixture of atactic and isotactic polypropylenes comprising contacting ethylene or propylene per se, or in admixture with one or more alpha-olefins, under polymerization conditions, with a catalyst system comprising:
(a) a precatalyst comprising a mixture of racemic and meso stereoisomers of a metallocene catalyst containing two cycloalkadienyl ligands joined by a bridging linkage, said ligands complexed to a metal atom; and
(b) (1) to obtain polyethylene from the rac epimer only, a cocatalyst selected from the group consisting of tris(perfluorophenyl)borane and preheated isobutyl alumoxane;
 (2) to obtain polyethylene from both epimers, a cocatalyst selected from the group consisting of dimethylanilinium tetrakis(perfluorophenyl)borate and triphenylmethyl tetrakis(perfluorophenyl)borate;
 (3) to obtain polypropylene, which is essentially isotactic, a cocatalyst selected from the group consisting of tris(perfluorophenyl)borane and preheated isobutyl alumoxane;
 (4) to obtain polypropylene, which is a mixture of atactic and isotactic polypropylenes in a weight ratio of atactic to isotactic polypropylenes of about 0.01:1 to about 1:1, a cocatalyst selected from the group consisting of dimethylanilinium tetrakis(perfluorophenyl)borate and triphenylmethyl tetrakis(perfluorophenyl)borate
wherein, in the catalyst system, the atomic ratio of aluminum, if present, to the metal atom in the precatalyst is in the range of about 1:1 to about 1000:1 and the atomic ratio of boron, if present, to the metal atom in the precatalyst is about 1:1 to about 3:1, and when isobutyl alumoxane is used, a mixture of isobutyl alumoxane and the precatalyst is heated to a temperature of at least about 90 degrees C for at least about one hour prior to use.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Polyethylene and polypropylene produced according to the invention include homopolymers, and copolymers with alpha-olefins containing up to about 20 carbon atoms, with densities ranging from 0.860 to 0.950 gram per cubic centimeter. Suitable alpha-olefins include, for example, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and 3, 5, 5-trimethyl-1-hexene. Dienes, particularly non-conjugated dienes, can also be included as a comonomer, e.g., to prepare ethylene/propylene rubbers (EPRs) and ethylene/propylene/diene terpolymers (EPDMs) Suitable non-conjugated dienes are linear, branched, or cyclic hydrocarbon dienes having from about 5 to about 20 carbon atoms. Examples of dienes include 1,5-hexadiene, 5-vinyl-2-norbornene, 1,7-octadiene, 2-methyl-pentadiene, 7-methyl-1,6-octadiene, vinyl cyclohexene, dicyclopentadiene, butadiene, isobutylene, isoprene, and ethylidene norbornene. Aromatic compounds having vinyl unsaturation, such as styrene and substituted styrenes, can be included as comonomers as well.
Component (a) of the catalyst system, the precatalyst, is comprised of racemic and meso stereoisomers of a metallocene catalyst containing two cycloalkadienyl ligands joined by a bridging linkage, said ligands complexed to a metal atom. Preferably the metal atom is titanium, zirconium, or hafnium. More preferably, the metal atom is zirconium.
The following compounds are examples of bridged metallocene precatalysts containing two cycloalkadienyl ligands: dimethylsilylbis(indenyl)zirconium dimethide, ethylenebis(indenyl)zirconium dimethide, dimethylsilylbis(4,5,6,7-tetrahydroindenyl)zirconium dimethide, ethylenebis(4, 5,6, 7-tetrahydroindenyl)zirconium dimethide, dimethylsilylbis(2-methylindenyl)zirconium dimethide, dimethylsilylbis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dimethide, methylphenylsilylbis(2-methylindenyl)zirconium dimethide, dimethylsilylbis(2,4,7-trimethylindenyl)zirconium dimethide, ethylenebis(2-methylindenyl)zirconium dimethide, ethylenebis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dimethide, dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dimethide, dimethylsilylbis(2-methyl-4-isopropylindenyl)zirconium dimethide, dimethylsilylbis(2-methyl-4-naphthylindenyl)zirconium dimethide, dimethylsilylbis(2,4-dimethylcyclopentadienyl)zirconium dimethide, dimethylsilylbis(2-methyl-4-t-butylcyclopentadienyl)zirconium dimethide, and ethylenebis(2,4-dimethylcyclopentadienyl)zirconium dimethide.
The precatalyst is further exemplified by the following structural formula:
wherein R
1
to R
8
are the same or different monovalent substituents selected from the group consisting of alkyl, aryl, alkylaryl, arylalkyl, hydrogen, halogen, and hydrocarboxy, and any two of R
1
to R
8
can be connected to form a ring of 4 to 8 atoms such that

Affiliated with

Also associated with

Rating

Process for the preparation of polyethylene or polypropylene does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for the preparation of polyethylene or polypropylene, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of polyethylene or polypropylene will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2519347