Polymerization process

Details Polymerization process Polymerization process

2002-03-28

2004-04-20

Wu, David W. (Department: 1713)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S106000, C525S391000, C428S331000

Reexamination Certificate

active

06723769

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method for the production and treatment of stereoregular propylene polymers and more particularly to the treatment of isotactic propylene polymers involving the incorporation of ethoxylated amines as processing aids.
BACKGROUND OF THE INVENTION
Thermoplastic olefin polymers, such as linear polyethylene, polypropylene, and olefin copolymers, such as propylene/ethylene copolymer, are conveniently formed in continuous loop-type polymerization reactors and thermoformed to arrive at granules or pellets of the polymers. For example, polypropylene and/or propylene/ethylene copolymers are polymerized in continuous polymerization reactors in which the monomer stream is introduced into a reactor and circulated with an appropriate catalyst to produce the olefin homopolymer or copolymer. The polymer is withdrawn from the catalyst reactor and subjected to appropriate processing steps and then extruded as a thermoplastic mass through an extruder and die mechanism to produce the polymer as a raw material in particulate form, usually as pellets or granules. The polymer particles are ultimately heated and processed in the formation of the desired end products.
Polypropylene and propylene copolymers, as used in various applications involving production of films, fibers, and similar products in the polymers, are thermo-processed and shaped or oriented by one uni-directional or bi-directional stresses. Such polymers are thermoplastic crystalline polymers. Polymers of this nature are subject to degradation due to high temperatures and photochemical action induced by electromagnetic radiation in the visible light range and in the ultraviolet region. In order to retard the degradation of such polymeric objects, the base polymer system, which is molded or extruded to form the desired object, e.g. fiber or film, may be treated with hindered amine light stabilizers, identified by the acronym “HALS (hindered amine light stabilizers)” which function to protect the film, fiber, or other object against degradation due to electromagnetic radiation by radiation in the visible light spectrum.
Isotactic polypropylene is conventionally used in the production of films in which the polypropylene is heated and then extruded through one or more dies to produce a film or tape. The film thus produced can then be oriented in at least one direction. Typically, the polypropylene is heated and extruded and then subjected to biaxial orientation by stressing the film in both a longitudinal direction (referred to as the machine direction) and in a transverse or lateral direction sometimes referred to as the “tenter” direction. The structure of isotactic polypropylene is characterized in terms of the methyl group attached to the tertiary carbon atoms of the successive propylene monomer units lying on the same side of the main chain of the polymer. That is, the methyl groups are characterized as being all above or below the polymer chain. Isotactic polypropylene can be illustrated by the following chemical formula:
Stereoregular polymers, such as isotactic and syndiotactic polypropylene, can be characterized in terms of the Fisher projection formula. Using the Fisher projection formula, the stereochemical sequence of isotactic polypropylene, as shown by Formula (2), is described as follows:
Another way of describing the structure is through the use of NMR. Bovey's NMR nomenclature for an isotactic pentad is . . . mmmm . . . with each “m” representing a “meso” dyad, or successive methyl groups on the same side of the plane of the polymer chain. As is known in the art, any deviation or inversion in the structure of the chain lowers the degree of isotacticity and crystallinity of the polymer.
In contrast to the isotactic structure, syndiotactic propylene polymers are those in which the methyl groups attached to the tertiary carbon atoms of successive monomeric units in the polymer chain lie on alternate sides of the plane of the polymer. Using the Fisher projection formula, the structure of syndiotactic polypropylene can be shown as follows:
The corresponding syndiotactic pentad is rrrr with each r representing a racemic diad. Syndiotactic polymers are semi-crystalline and, like the isotactic polymers, are insoluble in xylene. This crystallinity distinguishes both syndiotactic and isotactic polymers from an atactic polymer, which is non-crystalline and highly soluble in xylene. An atactic polymer exhibits no regular order of repeating unit configurations in the polymer chain and forms essentially a waxy product. Catalysts that produce syndiotactic polypropylene are disclosed in U.S. Pat. No. 4,892,851. As disclosed there, the syndiospecific metallocene catalysts are characterized as bridged structures in which one Cp group is sterically different from the others. Specifically disclosed in the '851 patent as a syndiospecific metallocene is isopropylidene(cyclopentadienyl-1-fluorenyl) zirconium dichloride.
In most cases, the preferred polymer configuration will be a predominantly isotactic or syndiotactic polymer with very little atactic polymer. Catalysts that produce isotactic polyolefins can be characterized as falling in two general classes, metallocene catalysts and so-called “conventional” Ziegler-Natta catalysts. The conventional Ziegler-Natta catalysts are stereospecific complexes formed from a transition metal halide and a metal alkyl or hydride. Metallocene catalysts are coordination compounds or cyclopentadienyl groups coordinated with transitional metals through &pgr; bonding.
The polymerization catalysts may be characterized as supported catalysts or as unsupported catalysts, sometimes referred to as homogeneous catalysts. Metallocene catalysts are often employed as unsupported or homogeneous catalysts, although, as described below, they also may be employed in supported catalyst components. Traditional supported catalysts are the so-called “conventional” Ziegler-Natta catalysts, such as titanium tetrachloride supported on an active magnesium dichloride, as disclosed, for example, in U.S. Pat. Nos. 4,298,718 and 4,544,717, both to Myar et al. A supported catalyst component, as disclosed in the Myar '718 patent, includes titanium tetrachloride supported on an “active” anhydrous magnesium dihalide, such as magnesium dichloride or magnesium dibromide. The supported catalyst component in Myar '718 is employed in conjunction with a co-catalyst such and an alkylaluminum compound, for example, triethylaluminum (TEAL). The Myar '717 patent discloses a similar compound which may also incorporate an electron donor compound which may take the form of various amines, phosphenes, esters, aldehydes, and alcohols.
Stereospecific metallocenes are disclosed in U.S. Pat. Nos. 4,794,096 and 4,975,403, both to Ewen. These patents disclose chiral, stereorigid metallocene catalysts that polymerize olefins to form isotactic polymers and are especially useful in the polymerization of highly isotactic polypropylene. As disclosed, for example, in the aforementioned U.S. Pat. No. 4,794,096, stereorigidity in a metallocene ligand is imparted by means of a structural bridge extending between cyclopentadienyl groups. Specifically disclosed in this patent are stereoregular hafnium metallocenes which may be characterized by the following formula:
 R″(C
5
(R′)
4
)
2
HfQp  (4)
In Formula (4), (C
5
(R′)
4
) is a cyclopentadienyl or substituted cyclopentadienyl group, R′ is independently hydrogen or a hydrocarbyl radical having 1-20 carbon atoms, and R″ is a structural bridge extending between the cyclopentadienyl rings. Q is a halogen or a hydrocarbon radical, such as an alkyl, aryl, alkenyl, alkylaryl, or arylalkyl, having 1-20 carbon atoms and p is 2.
Metallocene catalysts, such as those described above, can be used either as so-called “neutral metallocenes” in which case an alumoxane, such as methylalumoxane, is used as a co-catalyst, or they can be employed as so-called “cationic metallocenes” which incorporate a stable non-c

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