Ethylene-a-olefin copolymerization

Copolymerization Parameters for Ethylene/a-Olefin Copolymerization with Various Metallocene/MAO Catalysts 1... 

Alexander KdppI was born in Vilseck, Germany, in 1970. He received his chemical education and his Ph.D. degree at the University of Bayreuth. His dissertation in the research group of Professor H. G. Alt dealt with new support materials for the immobilization of cocatalytically active alumoxanes and their application in ethylene homopolymerization and ethylene/a-olefin copolymerization. He is currently a chemist for BASF AG in Ludwigshafen, Germany. 

Jang Y-J, Nenov N, Klapper M, Mullen K (2003) Organic nanoparticles with polypropy-leneoxide chains as support for metallocene catalysts ethylene homopolymerization and ethylene/a-olefin copolymerization. Polym Bull 50 343-350... 

The standard kinetic scheme for ethylene/a-olefin copolymerization reactions usually includes several chain initiation reactions, chain propagation reactions, and chain termination reactions as shown below. In this scheme, C represents an active center and m is the number of ethylene and/or comonomer units in a polymer chain. 

In ethylene/a-olefin copolymerization reactions, those centers that incorporate an a-olefin into the polymer chain poorly (Centers IV and V) retain this high reaction order (n > 1), while the reaction order changes to first order for those centers that incorporate an a-olefin into the polymer chain well (Centers I, II, and III). 

A very wide variety of catalysts and comonomers has been investigated in metallocene-mediated ethylene/a-olefin copolymerization. Table 6 catalogs several of these, along with their... 

Table 6 Comparison of reactivity ratios for ethylene/a-olefin copolymerizations between heterogeneous ZN systems (entries 1-2) and several metallocene/MAO catalyst systems (3-13)... 

Most Kaminsky catalysts contain only one type of active center. They produce ethylene—a-olefin copolymers with uniform compositional distributions and quite narrow MWDs which, at their limit, can be characterized by M.Jratios of about 2.0 and MFR of about 15. These features of the catalysts determine their first appHcations in the specialty resin area, to be used in the synthesis of either uniformly branched VLDPE resins or completely amorphous PE plastomers. Kaminsky catalysts have been gradually replacing Ziegler catalysts in the manufacture of certain commodity LLDPE products. They also faciUtate the copolymerization of ethylene with cycHc dienes such as cyclopentene and norhornene (33,34). These copolymers are compositionaHy uniform and can be used as LLDPE resins with special properties. Ethylene—norhornene copolymers are resistant to chemicals and heat, have high glass transitions, and very high transparency which makes them suitable for polymer optical fibers (34). 

The selective orientation may indicate a steric hindrance from the branch. Internal olefins like 2-butene tend to be poisons. They adsorb strongly but do not copolymerize to any significant extent. 2-Methylpropene is not very reactive either. In the absence of ethylene, a-olefins can be polymerized over Cr/silica but their reactivity is much lower than that of ethylene. Sometimes adding a-olefins to the reactor will improve activity, not because they are more reactive monomers, but because they are better reducing agents. 

Michelotti, M., Altomare, A. and Ciardelli, F., Ethylene/a-Olefins Cooligomerization versus Copolymerization by Zirconocene Catalysts , Polymer, 37, 5011-5016 (1996). 

Ethylene has been co-polymerized with virtually any conceivable a-olefin, from propylene to vinyl-terminated PE and PP macromonomers. Ethylene/propylene (E/P) copolymerization to produce saturated rubbers and ethylene/propylene/diene (EPD) terpolymerization to produce unsaturated, vulcanizable rubbers will be discussed in Section 4.09.4.1.3. 1-Butene, 1-hexene, and 1-octene are the most commonly used co-monomers for the production of LLDPE. Ethylene/octene co-polymers, developed by Dow and marketed under the Engage tradename, have been shown to have improved thermal properties compared to ethylene/butene and ethylene/hexene co-polymers.503 In ethylene/a-olefin (E/O) co-polymeriza-tions, the critical parameters are co-monomer reactivity and co-monomer distribution . The former is most conveniently described by the relative reactivity parameter, R, defined as the ratio between polymer composition and reactor medium composition. 

Each monomer addition step interconverts the two organometallic components. The poly(methyl methacrylate) (PMMA) obtained is predominantly syndio-tactic, although isotactic PMMA has been obtained by using chiral indenyl zirconocenes in combination with non-zirconocene Lewis acids. No reports of attempted ethylene or a-olefin copolymerizations have been described. 

The area of ethylene polymerization with late metal catalysts was rejuvenated when Brookhart and his group reported a family of new cationic Pd (II) and Ni(II) a-diimine catalysts (trademarked the Versipol catalyst system by DuPont) for the polymerization of ethylene, a-olefins, and cyclic olefins and the copolymerization of nonpolar olefins with a variety of functionalized olefins. These catalysts are now the focus of a joint development effort between the University of North Carolina at Chapel Hill and DuPont, and as can be seen from the scope of this review, they are being pursued at many other companies and universities. 

R. Furuyama, M. Mitani, J.-L Mobii, R. Mori, H. Tanaka, T. Fujita, Ethylene/higher a olefin copolymerization behavior of fluminated bis(phenoxy- imine) titanium complexes with methylalumoxane synthesis of new polyethylene-based block copolymers. Macromolecules 38(5), 1546-1552 (2005)... 

This section reviews copolymerization studies and aims to give an overview of research on ethylene-1-olefin copolymerization, the role of ligand substitution in copolymerization and the polymerization mechanisms involved. The copolymerization behavior of a group of siloxy-substituted complexes is discussed because they have the ability to be activated at low MAO ratios and some of them provide excellent comonomer respraise. 

The first metallocene-mediated ethylene/propylene copolymerizations were reported by Kaminsky in 1983 and employed the Cp2TiMe2/MAO catalyst system. Advantages of metallocenes over dassical heterogeneous ZN systems for ethylene/ a-olefin copolymetizations indude a more random distribution of comonomer, a narrower MWD, and a decreased fraaion of oligomers, which tend to compromise tensile strength and other mechanical properties. ... 

Mortazavi SMM, Arabi H, Zohuri G, et al Copolymerization of ethylene/a-olefins using bis(2-phenylindenyl)zirconium dichloride metallocene catalyst structural study of comonomer distribution, Polym Int 59(9) 1258—1265, 2010. 

Fig. 2. Dependence of olefin reactivity on its carbon atom number when linear a-olefins are copolymerized with ethylene.

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