Process for producing ethylene/olefin interpolymers

Details Process for producing ethylene/olefin interpolymers Process for producing ethylene/olefin interpolymers

1999-08-31

2002-07-09

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...

C526S348100, C526S348000, C526S209000, C526S213000, C526S217000, C526S154000, C526S157000, C526S158000

Reexamination Certificate

active

06417301

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a process utilizing a Ziegler-Natta catalyst for producing ethylene/olefin interpolymers, which for a given melt index (MI) and density, have reduced melting peak temperatures (T
m
). Melting peak temperature (T
m
) is alternatively referred to as melt transition temperature or melting point. The present invention also relates to a process for reducing the melting peak temperature (T
m
) of ethylene/olefin interpolymers having a given melt index and density. Additionally, this invention relates to novel ethylene/olefin interpolymers, and films and articles of manufacture produced therefrom.
BACKGROUND OF INVENTION
Polyethylene and interpolymers of ethylene are well known and are useful in many applications. In particular linear interpolymers of ethylene, also known as copolymers, terpolymers, and the like of ethylene, possess properties which distinguish them from other polyethylene polymers, such as branched ethylene homopolymers commonly referred to as LDPE (low density polyethylene). Certain of these properties are described by Anderson et al, U.S. Pat. No. 4,076,698.
A particularly useful polymerization medium for producing polymers and nterpolymers of ethylene is a gas phase process. Examples of such are given in U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,302,566; 4,543,399; 4,882,400; 5,352,749 and 5,541,270 and Canadian Patent No. 991,798 and Belgian Patent No. 839,380.
Ziegler-Natta catalysts 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 Ziegler-Natta polymerization catalysts in the production of polyethylene is disclosed in U.S. Pat. No. 3,354,139 and European Patent Nos. EP 0 529 977 B1 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 substituted 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 when employed during the catalyst preparation step are referred to as internal electron donors. Electron donors when utilized other than during the catalyst preparation step are referred to as external electron donor. For example, the external electron donor may be added to the preformed catalyst, to the prepolymer, and/or to the polymerization medium.
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 isotactic polymers. The use of electron donors generally improves the productivity of the catalyst in the production of isotactic polypropylene. This is shown generally in U.S. Pat. No. 4,981,930. It is also known to utilize electron donors to control molecular weight and molecular weight distribution of polypropylene. The result of increasing the stereoregularity, either the isotactic or syndiotactic content, of polypropylene is to increase the crystallinity of the polymer which generally correlates to an increase in the melting peak temperature (T
m
). This is shown generally in U.S. Pat. Nos. 5,710,222 and 5,688,735.
The concept of stereoregularity is not relevant in the field of ethylene interpolymerization where ethylene constitutes at least about 50% by weight of the total monomers present in the polymer. See for example U.S. Pat. No. 5,055,535. In ethylene polymerization 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. Exemplary patents describing the use of external electron donors in producing polyethylene are U.S. Pat. Nos. 4,234,710; 4,287,328; 5,055,535 and 5,192,729.
U.S. Pat. No. 5,399,638 discloses the use of a morphology protector obtained by reacting alkylaluminum with an electron donor during a prepolymerization step to maintain the morphology of the support and the catalytic component on the prepolymerized support. Also disclosed is the use of the alkylaluminum electron donor complex to increase the effectiveness of the comonomer in reducing the density of the interpolymer in the case of interpolymerization.
U.S. Pat. No. 5,055,535 discloses the use of an external monoether electron donor, such as tetrahydrofuran (THF), to control molecular weight distribution.
U.S. Pat. No. 5,244,987 and 5,410,002 disclose the use of external electron donors to control the reactivity of catalyst particles in the polymerization reactor.
U.S. Pat. No. 4,652,540 discloses the use of carbonyl sulfide to reduce the adverse effect on polymerization activity resulting from poison impurities contained in the olefin feed streams.
Illustrative examples of electron donors include carboxylic acid esters, anhydrides, acid halides, ethers, thioethers, aldehydes, ketones, imines, amines, amides, nitriles, isonitriles, cyanates, isocyanates, thiocyanates, isothiocyanates, thioesters, dithioesters, carbonic esters, hydrocarbyl carbamates, hydrocarbyl thiocarbamates, hydrocarbyl dithiocarbamates, urethanes, sulfoxides, sulfones, sulfonamides, organosilicon compounds containing at least one oxygen atom, and nitrogen, phosphorus, arsenic or antimony compounds connected to an organic group through a carbon or oxygen atom.
SUMMARY OF THE INVENTION
Applicants have unexpectedly found that the addition of at least one compound comprising at least one element from Group 15 and/or Group16 of the Periodic Table of Elements, herein referred to as a modifier, in a process for preparing ethylene/olefin interpolymers, having a given melt index and density, reduces the melting peak temperature (T
m
) of the ethylene/olefin interpolymer. The melting peak temperature (T
m
) values herein were obtained by Differential Scanning Calorimetry in accordance with ASTM D 3418-97.
The polymerization process of the present invention for producing an ethylene/olefin interpolymer having, at a given melt index and density, a reduced melting peak temperature (T
m
) comprises the introduction into a polymerization medium comprising ethylene and at least one or more other olefin(s), at least one Ziegler-Natta cata

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