Process for making low-density polyolefins

Details Process for making low-density polyolefins Process for making low-density polyolefins

2002-08-02

2003-05-06

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...

C526S129000, C526S161000, C526S172000, C526S943000, C526S348200, C526S348500, C526S348600, C502S103000, C502S117000, C502S120000, C502S155000

Reexamination Certificate

active

06559251

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a process for making polyolefins. The process, which uses catalysts having a bridged indenoindolyl ligand with “open architecture,” is valuable for making polyolefins with exceptionally low densities.
BACKGROUND OF THE INVENTION
While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry's future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of &agr;-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics.
Single-site olefin polymerization catalysts having “open architecture” are generally known. Examples include the so-called “constrained geometry” catalysts developed by scientists at Dow Chemical Company (see, e.g., U.S. Pat. No. 5,064,802), which have been used to produce a variety of polyolefins. “Open architecture” catalysts differ structurally from ordinary bridged metallocenes, which have a bridged pair of pi-electron donors. In open architecture catalysts, only one group of the bridged ligand donates pi electrons to the metal; the other group is sigma bonded to the metal. An advantage of this type of bridging is thought to be a more open or exposed locus for olefin complexation and chain propagation when the complex becomes catalytically active. Simple examples of complexes with open architecture are tert-butylamido(cyclopentadienyl)dimethyl-silylzirconium dichloride and methylamido(cyclopentadienyl)-1,2-ethanediyltitanium dimethyl:
Organometallic complexes that incorporate “indenoindolyl” ligands are known (see U.S. Pat. No. 6,232,260 and PCT Int. Appl. WO 99/24446 (“Nifant'ev”)). The '260 patent demonstrates the use of non-bridged bis(indenoindolyl) complexes for making HDPE in a slurry polymerization. Versatility is an advantage of the complexes; by modifying the starting materials, a wide variety of indenoindolyl complexes can be prepared. “Open architecture” complexes are neither prepared nor specifically discussed. Nifant'ev teaches the use of bridged indenoindolyl complexes as catalysts for making polyolefins, including polypropylene, HDPE and LLDPE. The complexes disclosed by Nifant'ev do not have open architecture.
PCT Int. Appl. WO 01/53360 (Resconi et al.) discloses bridged indenoindolyl complexes having open architecture and their use to produce substantially amorphous propylene-based polymers. Resconi teaches many open architecture complexes but none that are bridged through the indolyl nitrogen. Moreover, all of the complexes are used only to make propylene polymers; their use to produce low-density ethylene polymers is not disclosed.
As noted earlier, the indenoindolyl framework is versatile. The need continues, however, for new ways to make polyolefins—especially ethylene copolymers—with very low densities. In particular, it is difficult to make ethylene polymers having densities less than about 0.915 g/cm
3
using known indenoindolyl complexes. On the other hand, ethylene polymers having such low densities are valuable for special applications requiring elastomeric properties. The industry would also benefit from the availability of new catalysts that capitalize on the inherent flexibility of the indenoindolyl framework.
SUMMARY OF THE INVENTION
The invention is a process for making ethylene copolymers. The process comprises copolymerizing ethylene with an &agr;-olefin in the presence of a catalyst system comprising an activator and a silica-supported organometallic complex. The complex, which has “open architecture,” includes a Group 4 to 6 transition metal and a bridged indenoindolyl ligand. Because the supported complex incorporates comonomers with exceptional efficiency, the process enables the production of ethylene copolymers having high molecular weights (Mw>100K) and very low densities (<0.910 g/cm
3
). The invention includes new open architecture catalysts that take advantage of bridging through the indolyl nitrogen of the indenoindolyl framework.
DETAILED DESCRIPTION OF THE INVENTION
In the process of the invention, ethylene polymerizes with one or more &agr;-olefins to give a copolymer having very low density. Suitable &agr;-olefins are 1-butene, 1-hexene, 1-octene, and mixtures thereof. 1-Hexene is particularly preferred.
Catalyst systems useful for the process comprise an activator and a silica-supported, indenoindolyl Group 4-6 transition metal complex having open architecture. More preferred complexes include a Group 4 transition metal such as titanium or zirconium.
“Indenoindolyl” ligands are generated by deprotonating an indenoindole compound using a potent base. By “indenoindole compound,” we mean an organic compound that has both indole and indene rings. The five-membered rings from each are fused, i.e., they share two carbon atoms. Preferably, the rings are fused such that the indole nitrogen and the only sp
3
-hybridized carbon on the indenyl ring are “trans” to each other. Such is the case in an indeno[1,2-b] ring system such as:
Suitable ring systems also include those in which the indole nitrogen and the sp
3
-hybridized carbon of the indene are beta to each other, i.e., they are on the same side of the molecule. This is an indeno[2,1-b]indole ring system:
The ring atoms can be unsubstituted or substituted with one or more groups such as alkyl, aryl, aralkyl, halogen, silyl, nitro, dialkylamino, diarylamino, alkoxy, aryloxy, thioether, or the like. Additional fused rings can be present, as long as an indenoindole moiety is present.
Numbering of indenoindoles follows IUPAC Rule A-22. The molecule is oriented as shown below, and numbering is done clockwise beginning with the ring at the uppermost right of the structure in a manner effective to give the lowest possible number to the heteroatom. Thus, 5,10-dihydroindeno[1,2-b]indole is numbered as follows:
while 5,6-dihydroindeno[2,1-b]indole has the numbering:
For correct nomenclature and numbering of these ring systems, see the
Ring Systems Handbook
(1998), a publication of Chemical Abstracts Service, Ring Systems File II: RF 33986-RF 66391 at RF 58952 and 58955. (Other examples of correct numbering appear in PCT Int. Appl. WO 99/24446.)
Methods for making indenoindole compounds are well known. Suitable methods and compounds are disclosed, for example, in U.S. Pat. No. 6,232,260, the teachings of which are incorporated herein by reference, and references cited therein, including the method of Buu-Hoi and Xuong,
J. Chem. Soc.
(1952) 2225. Suitable procedures also appear in PCT Int. Appls. WO 99/24446 and WO 01/53360.
Indenoindolyl complexes useful for the process of the invention have open architecture. By “open architecture,” we mean a complex having a fixed geometry that enables generation of a highly exposed active site when the catalyst is combined with an activator. The metal of the complex is pi-bonded to the indenyl Cp ring and is also sigma-bonded through two or more atoms to the indolyl nitrogen or the indenyl methylene carbon. (In contrast, many of the bridged indenoindolyl complexes described in the literature have a transition metal that is pi-bonded to the indenyl Cp ring and pi-bonded to another Cp-like group. See, e.g., U.S. Pat. No. 6,232,260 or WO 99/24446). Preferably, the metal is sigma-bonded to a heteroatom, i.e., oxygen, nitrogen, phosphorus, or sulfur; most preferably, the metal is sigma-bonded to nitrogen. The heteroatom is linked to the indenoindolyl group through a bridging group, which is preferably dialkylsilyl, diarylsilyl, methylene, ethylene, isopropylidene, diphenylmethylene, or the like. Particularly preferred bridging groups are dimethylsilyl, methylene, ethylene, and isopropylidene. The bridging group is cova

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