Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-09-25
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...
C526S160000
Reexamination Certificate
active
06559262
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to processes for production of &agr;-olefin polymers using unbridged fluxional metallocenes, primarily substituted aryl indenyl metallocenes, and more particularly to use of unbridged, fluxional, cyclopentadienyl or indenyl metallocene catalysts and catalyst systems in methods of production of high melting point olefin homo- and co-polymers, particularly elastomeric crystalline and amorphous block homo- and co-polymers of alpha olefins. More specifically, the invention is directed to: (1) the discovery and catalytic process use of a Polymerization Rate-Enhancement effect (PRE effect) in polymerization processes which involve the addition of minor amounts of ethylene to the polymerization system to produce polymers having properties ranging from crystalline thermoplastics to high melting point thermoplastic elastomers to amorphous gum elastomers, and methods for increasing polymerization production rates and polymer molecular weight; (2) the discovery and catalytic process use of an Elastomeric Property-Enhancement effect (EPE effect) in which small quantities of ethylene added to the polymerization system activates selected metallocene catalyst systems, which otherwise do not produce elastomeric polymers, to produce elastomeric polymers; and (3) novel substituted aryl indenyl metallocene catalysts.
BACKGROUND
Crystalline, amorphous, and elastic polypropylenes are known. Crystalline polypropylenes are generally regarded as comprising of predominantly isotactic or syndiotactic structures and amorphous polypropylene is regarded as comprising predominantly of an atactic structure. U.S. Pat. Nos. 3,112,300 and 3,112,301 both of Natta, et. al. describe isotactic and prevailingly isotactic polypropylene.
U.S. Pat. No. 3,175,199 to Natta et al. describes an elastomeric polypropylene which can be fractioned out of a polymer mixture containing prevailingly isotactic and atactic polypropylenes. When separated from the polymer mixture, a fraction of this polymer showed elastomeric properties which were attributed to a stereoblock structure comprising alternating blocks of isotactic and atactic stereosequences. U.S. Pat. No. 4,335,225 discloses a fractionable elastomeric polypropylene with a broad molecular weight distribution.
Elastomeric polypropylenes with narrow molecular weight distributions are also known which are produced in the presence of bridged metallocene catalysts. Polymers of this type were described by Chien et. al. in (J. Am. Chem. Soc. 1991, 113, 8569-8570), but their low melting point renders them unsuitable for certain applications. In addition, the activities of these catalyst systems are low.
U.S. Pat. No. 5,594,080 discloses an unbridged, fluxional metallocene catalyst system useful for the production of elastomeric polyolefins. These fluxional, unbridged catalysts can interconvert between geometric states on the time scale of the growth of a single polymer chain in order to produce isotactic, atactic stereoblock polyalphaolefins with useful elastomeric properties. Polyolefins produced with these fluxional catalysts systems can have a range of properties, from amorphous gum elastomers to useful thermoplastic elastomers to non-elastomeric thermoplastics.
The commercial utility of a catalyst system is closely tied to the polymerization activity. Processes that lead to an increase in activity of a polymerization system are of considerable practical utility. The activity of a polymerization system can in some cases be influenced by additives to the polymerization system. For example for both classical Ziegler-Natta systems as well as metallocene systems, the addition of hydrogen can result in an increase in propylene polymerization activity, see Pasquet, V., et al., Makromol. Chem. 1993, 194, 451-461 and references cited therein. One of the explanations for the hydrogen effect is the reactivation of the dormant sites resulting from 2,1-propylene misinsertions, see Corradini, P., et al., Makromol. Chem., Rapid Commun. 1992, 13, 15-20; Corradini, P., et al., Makromol. Chem., Rapid Commun. 1992, 13, 21-24; and Busico, V., et al., Makromol. Chem., Rapid Commun. 1993, 14, 97-103. Since hydrogen is also a chain transfer agent, the addition of hydrogen decreases the molecular weight, which limits the practical utility of the hydrogen effect where high molecular weight polymers are desired.
Activation of ethylene polymerization systems by the addition of small amounts of an alpha olefin is also known, see for example Brintzinger, H., et. al. Angew. Chemie, Int. Ed. Engl. 1995, 34, 1143-1170. This so-called “comonomer effect” (see Spitz, R., et al. Makromol. Chem. 1988, 189, 1043-1050) is useful in a process for the synthesis of ethylene polymers, but not for alpha olefin polymers. Hefert, N., et. al. Makromol. Chem. 1993 194, 3167-3182 report no effect of hexene on the rate of propene polymerization with a metallocene catalyst. Several explanations have been forwarded to explain this “comonomer effect” including a “trigger mechanism” (Ystenes, M., Makromol. Chem. “Macromolecular Symposia” 1993, 66, 71-81) and improved rates of diffusion due to the solubilization of active centers by incorporation of comonomer (see Koivumaki, J., et al. Macromolecules 1993, 26, 5535-5538).
Activation of propylene polymerization systems in the presence of 5% ethylene have been previously reported for magnesium chloride supported Ti-based catalysts by Spitz, R., et al. in Makromol. Chem. 1988, 189, 1043-1050 and in Spitz, R., et al. in “Transition Metal Catalyzed Polymerization”, Quirk, R. P., Ed., Cambridge Univ. Press 1988, pp. 719-728, and with V-based Ziegler catalysts by Valvassori, A., et al. in Makromol. Chem. 1963, 61, 46-62. While such “synergistic effects” have been observed with classical Ziegler-Natta catalyst systems, Koivurnaki et. al. point out that such synergistic effects do not work for homogeneous metallocene systems (see Koivumaki, J., et al. Macromolecules 1993, 26, 5535-5538).
Accordingly, there is a need for processes to improve the activity of metallocene catalysts systems capable of producing elastomeric polypropylenes of high molecular weight with high melting points.
THE INVENTION
SUMMARY, OBJECTS AND ADVANTAGES
We have discovered that the activity of fluxional unbridged metallocene polymerization catalysts containing at least one 2-arylindene ligand may be increased by the addition of small (typically 0.1-10 wt. %) amounts of ethylene to the polymerization system. In particular, the addition of ethylene to a propylene polymerization system derived from unbridged metallocene catalysts containing at least one 2-arylindene ligand results in a significant increase (up to ten-fold or above) in catalyst activity. We term this increase in activity the Polymerization Rate Enhancement effect (PRE), which can be measured in terms of an Ethylene Enhancement Factor (EEF) as a dimensionless ratio. Also, the molecular weight of the produced polymers may increase in the presence of ethylene. The amount of ethylene included in the reaction system can be selected and controlled to be so small as to result in essentially minimal (<2 mole %) incorporation of ethylene units into the polymer, yet surprisingly results in a significant, disproportionately large increase in polymerization activity. More specifically, by addition of small amounts of ethylene into polypropylene reaction systems, an unexpectedly large (order of magnitude or more) increase in activity is achieved to produce elastomeric products.
Thus, in a first aspect of this invention, elastomeric olefin polymers are formed using unbridged fluxional, metallocene-based, catalyst systems in a polymerization process in which an activity-enhancing amount of ethylene is incorporated into the polymerization feed. This effect is herein termed the PRE effect, for Polymerization Rate-Enhancement effect, and is quantified as a dimensionless number in the range of from about 1.1 to about 10 or above, called the EEF for Ethylene Enhancement Factor. Typically, useful PRE (activity-enhancing
Bendig Larry L.
Ernst Andreas B.
Kravchenko Raisa
Moore Eric J.
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Dulin, Esq. Jacques M.
Innovation Law Group, Ltd.
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The Board of Trustees of the Leland Stanford Jr. University
Wu David W.
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