Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-01-27
2003-11-25
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...
C526S161000, C526S172000, C526S351000, C502S117000, C502S155000
Reexamination Certificate
active
06653413
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to (i) the use of octahedral transition metal complexes as precatalysts for the polymerization of alpha-olefins; (ii) the use of homogeneous catalyst systems comprising these complexes and (iii) a novel class of such complexes. More particularly, the invention relates to the use of cationic chiral, racemic or non-chiral catalysts of the above-mentioned type for the polymerization of alpha-olefins to produce highly stereoregular polymers or poly alpha-olefin elastomers.
The polymerization of alpha-olefins with Ziegler-Natta catalysts is well-known in the chemical industry and it is used to a large extent. The various polymers that are derived from the polymerization of such olefins show differences in their chemical and physical properties, as a result of differences in molecular structure and molecular weights. Polymers of alpha-olefins having three or more carbon atoms as the monomeric unit will have pendant hydrocarbyl groups attached to the polymer backbone chain. The arrangement of these hydrocarbyl groups along the polymer backbone will determine, to a large extent, the physical properties of a particular polymer. For example, strong polymers tend to be stereochemically regular meaning that the adjacent pendant hydrocarbyl groups reside on the same side of the polymer backbone.
Three major types of stereoregularity, or tacticity have been characterized: atactic, isotactic and syndiotactic configurations. Atactic polyolefins are those wherein the pendant hydrocarbyl groups have no regular order in space with reference to the backbone and to other pendant groups. These are amorphous materials and are generally unsuitable for applications where high strength is required. Isotactic polyolefins are those wherein the pendant hydrocarbyl groups are ordered in space on the same side or plane of the polymer backbone chain. Polyolefins that are highly isotactic exhibit a high degree of crystallinity and high melting points, and accordingly are particularly suited to high strength applications.
The degree of stereoregularity may be determined from the pentad analysis using carbon-NMR techniques. A purely isotactic polyolefin will have a degree of crystallinity (mmmm) value of close to 100, whereas atactic poly alpha-olefins will have a theoretical statistical value of 6.5.
Syndiotactic polyolefins are those wherein the pendant hydrocarbyl groups of the polymer backbone alternate sequentially from one side or plane to the opposite side or plane relative to the polymer backbone. Although syndiotactic polymers, as compared with the corresponding isotactic polymers, are characterized by lower melting points, they are generally suitable for high strength applications, provided that their molecular weight exceeds 100,000 daltons.
Another category of high polymers with special stereosequencing is elastic polymers, or elastomers. As taught by
Textbook of Polymer Science
(edited by Fred W. Billmeyer, Jr., 3rd edition, Wiley Interscience: New York, 1984), page 507, the unique properties of elastomers include their ability to stretch and retract rapidly. Elastomers exhibit high strength and modulus while stretched, and recover fully on release of the stress. To obtain these properties, certain requirements are placed upon the molecular structure of the compounds: they must be high polymers, be above their glass transition temperatures, be amorphous in the unstretched state, but preferably develop crystallinity on stretching, and contain a network of crosslinks to restrain gross mobility of the chains.
In addition to the above-mentioned form of elastic polymers, polymers that contain crystalline areas (domains) and amorphous areas also exhibit elastomeric properties. This can be achieved in different ways, leading to (at least) two different microstructures, both of which are germane to the instant invention:
(a) a polymer containing domains of stereoregular and atactic sections, consecutively arranged in each polymer chain; and
(b) a stereoregular polymer in which the inclusion of numerous stereoregular mistakes provides the material with atactic parts.
The polymer described in (b) has elastomeric properties because the crystalline, stereoregular parts of the chains form lamellae, and the mistakes, incorporated into the otherwise stereoregular sequences, and when present in sufficient quantity, form the amorphous domains that provide the material with elastomeric properties.
One of the most important parameters to measure the elasticity is the modulus (for elongation of 300-400%). For example, natural rubber and SBR polymers have a modulus of 2500 psi; neoprene, which is not very elastic, has a modulus of about 1000 psi; isotactic polypropylene has a modulus of 91 psi.
Conventional titanium and zirconium based Ziegler-Natta catalysts for the preparation of isotactic polymers are well known in the art. The systems are, however, limited in terms of molecular weight, molecular weight distribution and tacticity control. Additional methods of producing isotactic polymers from an alumoxane cocatalyzed metallocene were reported by Ewen, J. Am. Chem. Soc., 106, 6355 (1984) and Kaminsky et al., Angew. Chem. Int. Ed. Eng., 24, 507 (1985).
The use of cocatalyzed catalyst systems for the production of highly crystalline polyolefins is disclosed in U.S. Pat. No. 5,318,935. The catalyst systems described therein comprise a complex formed upon admixture of the amido group IVb transition metal component with an alumoxane component.
According to a recent review (M. S. Eisen et al., J. Organometallic Chem., 503, 307 (1995)), a series of bis(trimethylsilyl)benzamidinate zirconium dichlorides are described as active catalysts for ethylene polymerization. As taught therein, the polymerization activity increases drastically with increasing pressure. However, these catalyst systems are generally characterized by a pronounced moisture-sensitivity due to the inherent hydrolytic instability imposed by the presence of several Si—N bonds in the molecules.
Homogeneous catalysts for stereoregular olefin polymerization are further disclosed in U.S. Pat. No. 5,330,948. According to this patent, by using a metallocene catalyst having a chiral substituent selected from neomenthyl, menthyl and phenylmenthyl with a cocatalyst, better control over the desired properties of the resulting polymer is achieved.
U.S. Pat. No. 5,594,080 describes metallocene catalysts bearing cyclopentadienyl-type ligands, which are used in the production of elastomeric polyolefins. The structure and therefore the properties of the obtained products depend on several factors, inter alia the olefin monomer pressure during the polymerization and the nature of the cyclopentadienyl-based ligands.
The synthesis of stereoregular polymers has been reported (M. Bochmann, J. Chem. Soc., Dalton Trans. 225, (1996); H. H. Brintzinger, D. Fischer, R. Müllhaupt, B. Rieger and R. M. Waymouth, Angew. Chem., Int. Ed. Engl. 34, 1143 (1995)) by using chiral organo-group IV (Ti, Zr, Hf) catalysts having approximate C
2
symmetry. Most of the ligands for these “C
2
” catalysts are based upon indenyl or related cyclopentadienyl components and are difficult and expensive to synthesize.
Octahedral transition-metal complexes for use in homogeneous catalyst systems for the polymerization of alpha-olefins are known. EP-A-0 675138 discloses the use of a catalyst comprising the cationic form of benzamidinato octahedral transition metal complexes and an anion of a Lewis acid or Brönsted acid for the polymerization of alpha-olefins including propylene. The polymerization reaction can be carried out at a pressure in the range from atmospheric pressure to 200 kg/cm
2
G. Although the polymerization catalyst disclosed is a cationic form of an octahedral transition metal complex, and the homopolymerization of propylene is specifically disclosed, there is no mention of the tacticity of the polymer, and more specifically, there is no teaching of the tacticity characteristics of the polymer as a function of the olefin mo
Averbuj Claudia
Eisen Moris
Shmulinson Michal
Tish Edith
Volkis Victoria
Ehrlich Ltd. G. E.
Harlan R.
Technion Research and Development Foundation Ltd.
Wu David W.
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