Process for the polymerization of olefins

Details Process for the polymerization of olefins Process for the polymerization of olefins

1999-08-31

2001-09-18

Teskin, Fred (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S125800, C526S142000, C526S144000, C526S147000, C526S236000, C526S901000

Reexamination Certificate

active

06291613

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a process for the polymerization of olefins and narrowing molecular weight distribution (MWD) of polyolefins. Polyethylenes produced in accordance with the process of the present invention are generally characterized further by having a reduced n-hexane soluble polymeric fraction.
BACKGROUND OF INVENTION
Catalyst systems for the polymerization of olefins are well known in the art and have been known at least since the issuance of U.S. Pat. No. 3,113,115. Thereafter, many patents have been issued relating to new or improved Ziegler-Natta catalysts. Exemplary of such patents are U.S. Pat. Nos. 3,594,330; 3,676,415; 3,644,318; 3,917,575; 4,105,847; 4,148,754; 4,256,866; 4,298,713; 4,311,752; 4,363,904; 4,481,301 and Reissue 33,683.
These patents disclose Ziegler-Natta catalysts that are well known as typically consisting of a transition metal component and a co-catalyst that is typically an organoaluminum compound. Optionally, used with the catalyst are activators such as halogenated hydrocarbons and activity modifiers such as electron donors.
The use of halogenated hydrocarbons with titanium-based Ziegler-Natta polymerization catalysts in the production of polyethylene is disclosed in European Patent Applications EP A 0 529 977 A1 and EP 0 703 246 A1. As disclosed, the halogenated hydrocarbons may reduce the rate of ethane formation, improve catalyst efficiency, or provide other effects. Typical of such halogenated hydrocarbons are monohalogen and polyhalogen substitutes of saturated or unsaturated aliphatic, alicyclic, or aromatic hydrocarbons having 1 to 12 carbon atoms. Exemplary aliphatic compounds include methyl chloride, methyl bromide, methyl iodide, methylene chloride, methylene bromide, methylene iodide, chloroform, bromoform, iodoform, carbon tetrachloride, carbon tetrabromide, carbon tetraiodide, ethyl chloride, ethyl bromide, 1,2-dichloroethane, 1,2-dibromoethane, methylchloroform, perchloroethylene and the like. Exemplary alicyclic compounds include chlorocyclopropane, tetrachlorocyclopentane and the like. Exemplary aromatic compounds include chlorobenzene, hexabromobenzene, benzotrichloride and the like. These compounds may be used individually or as mixtures thereof.
It is also well known, in the polymerization of olefins, particularly where Ziegler-Natta catalysts are employed, to utilize, optionally, electron donors. Such electron donors often aid in increasing the efficiency of the catalyst and/or in controlling the stereospecificity of the polymer when an olefin, other than ethylene, is polymerized. Electron donors, typically known as Lewis Bases, can be employed during the catalyst preparation step, referred to as internal electron donors, or during the polymerization reaction when the catalyst comes into contact with the olefin or olefins, referred to as external electron donors.
The use of electron donors in the field of propylene polymerization is well known and is primarily used to reduce the atactic form of the polymer and increase the production of the iosotactic polymers. However, while improving the production of isotactic polypropylene, electron donors tend, generally, to reduce the productivity of the Ziegler-Natta catalyst.
In the field of ethylene polymerization, where ethylene constitutes at least about 50% by weight of the total monomers present in the polymer, electron donors are utilized to control the molecular weight distribution (MWD) of the polymer and the activity of the catalyst in the polymerization medium. Exemplary patents describing the use of internal electron donors in producing polyethylene are U.S. Pat. Nos. 3,917,575; 4,187,385, 4,256,866; 4,293,673; 4,296,223; Reissue 33,683; 4,302,565; 4,302,566; and 5,470,812. The use of an external electron donor to control molecular weight distribution is shown in U.S. Pat. No. 5,055,535; and the use of external electron donors to control the reactivity of catalyst particles is described in U.S. Pat. No. 5,410,002.
Illustrative examples of electron donors include carboxylic acids, carboxylic acid esters, alcohols, ethers, ketones, amines, amides, nitrites, aldehydes, alcoholates, thioethers, thioesters, carbonic esters, organosilicon compounds containing oxygen atoms, and phosphorus, arsenic or antimony compounds connected to an organic group through a carbon or oxygen atom.
SUMMARY OF THE INVENTION
The process of the present invention comprises polymerizing at least one olefin in the presence of at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and a sufficient amount of dinitrogen monoxide (N
2
O) to obtain an olefin homopolymer or interpolymer having a narrower molecular weight distribution than would be obtained in the absence of dinitrogen monoxide.
Also provided is a process for narrowing molecular weight distribution of a polymer comprising at least one or more olefin(s) comprising contacting under polymerization conditions, at least one or more olefin(s) with at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and dinitrogen monoxide (N
2
O), wherein the dinitrogen monoxide is present in an amount sufficient that the molecular weight distribution of the resulting polymeric product is narrower than would be obtained in the absence of the dinitrogen monoxide.
All mention herein to elements of Groups of the Periodic Table are made in reference to the Periodic Table of the Elements, as published in “Chemical and Engineering News”, 63(5), 27, 1985. In this format, the Groups are numbered 1 to 18.
In carrying out the novel polymerization process of the present invention, there may optionally be added any electron donor(s) and/or any halogenated hydrocarbon compound(s).
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention comprises polymerizing at least one olefin in the presence of at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and a sufficient amount of dinitrogen monoxide (N
2
O) to obtain an olefin homopolymer or interpolymer having a narrower molecular weight distribution than would be obtained in the absence of dinitrogen monoxide.
Also provided is a process for narrowing molecular weight distribution of a polymer comprising at least one or more olefin(s) comprising contacting under polymerization conditions, at least one or more olefin(s) with at least one Ziegler-Natta catalyst comprised of a component comprising at least one transition metal and a co-catalyst comprising at least one organometallic compound, and dinitrogen monoxide (N
2
O), wherein the dinitrogen monoxide is present in an amount sufficient that the molecular weight distribution of the resulting polymeric product is narrower than would be obtained in the absence of the dinitrogen monoxide.
The polymerization of the at least one olefin herein may be carried out using any suitable process. For example, there may be utilized polymerization in suspension, in solution or in the gas phase media. All of these polymerization processes are well known in the art.
A particularly desirable method for producing polyethylene polymers according to the present invention is a gas phase polymerization process. This type process and means for operating the polymerization reactor are well known and completely described in U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,012,573; 4,302,566; 4,543,399; 4,882,400; 5,352,749; 5,541,270; Canadian Patent No. 991,798 and Belgian Patent No. 839,380. These patents disclose gas phase polymerization processes wherein the polymerization zone is either mechanically agitated or fluidized by the continuous flow of the gaseous monomer and diluent. The entire contents of these patents are incorporated herein by reference.
In general, the polymerization process of the present i

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