Copolymers early transition metal catalysts

Early transition metal catalysts such as vanadium complexes and zirconocenes effectively copolymerize ethene with norbornene [81]. This capabihty eventually led to the commercial development of the APEL and TOPAS line of cyclic olefin copolymers by Mitsui and Ticona (formerly Hoechst), respectively [82]. Interest in this class of polymers is due to its high glass transition temperatures and transparency that is imparted by the norbornene component. 

Finally, the ethylene/norbornene copolymers obtained using the nickel catalysts are essentially indistinguishable from those obtained using metaUocene-based early transition metal catalysts, both in terms of the microstructure and such physical properties as Tg and tensile modulus. For the ethylene/norbornene polymers synthesized, the glass transition temperature (Tg) increases smoothly with increasing norbornene content. 

The high oxophilicity of early transition metal catalysts (titanium, zirconium, or chromium) causes them to be poisoned by most functionalized olefins, particularly the commercially available polar comonomers. However, there are examples of copolymerizations with special substrates or with very high levels of a Lewis acid incorporated into the polymerization system to protect the polar functionality through complexation. " Alternative routes to polar copolymers involving metathesis of cyclic olefins and functionalization of the resulting unsaturated polymer or metathesis of polar cycloolefins followed by hydrogenation to remove the resulting unsaturation have been published.The cost of these multistep... 

While the copolymerization of norbornene and ethylene by vanadium and titanium catalysts had been investigated in the 1970s, it was not until the invention of metallocene/MAO catalysts and their application to the homopolymerization of norbornene and other cycloolefins by Kaminsky et ai.8,15,19 that the use of early transition metal catalysts for the addition polymerization of norbornene drew new attention. Nevertheless, the industrial relevance of E/NB copolymers, and the nature of the homopolymers, described in the first reports as insoluble in organic solvents, crystalline, and extremely high melting, focused further investigations on copolymers rather than on norbornene homopolymers. 

Various copolymers, which differ with regard to their compositions, micro-structures, and properties, have been prepared by using several types of early transition metal catalysts, and these unique characteristics are dependent upon the nature of the complex catalysts used. The resultant copolymers possess unique properties as new polyolefin materials. The development of other new polyolefin materials (e.g., amphiphilic) may follow the use of this synthetic technique, which can be applied not only to styrene but also to styrene containing reactive functionalities (in combination with other polymerization techniques such as ATRP, RAFT, and ROP). 

E-N copolymers made by single-site catalysts are characterized by narrow molecular weight distributions, which make technical processing easier. The first commercial E-N copolymer products by early transition metal catalysts are already available. In contrast, late transition metal catalysts, which are more tolerant to polar functional groups, need further developments to be efficiently used in olefin-cycloolefin copolymerizations. 

W. Kaminsky and M. Amdt-Rosenau, "Tactic norbomene homo- and copolymers made with early and late transition metal catalysts," in L.S. Baugh and J.A.M. Canich, eds., Stereoselective Polymerization with Single-Site Catalysts, chapter 16, pp. 413-444. CRC Press, Boca Raton, FL, 2008. 

I C Cyclopentene Homo- and Copolymers Made with Early and Late Transition Metal Catalysts... 

Metallocene/methylaluminoxane (MAO) and other single site catalysts for olefin polymerization have opened a new field of synlhesis in polymer chemistry. Strained cyclic olefins such as cyclobutene, cyclopentene, norbornene (NB), and their substituted compounds can be used as monomers and comonomers in a wide variety of polymers." Much interest is focused on norbornene homo- and copolymers because of the easy availability of norbornene and the special properties of their polymers. Norbornene can be polymerized by ring opening metathesis polymerization (ROMP), giving elastomeric materials, or by double bond opening (addition polymerization). Homopolymerization of norbornene by double bond opening can be achieved by early and late transition metal catalysts, namely Ti, Zr, Hf, Ni, - ° and Pd (Scheme 16.1). 

Norbomene can be copolymerized with olefins such as ethylene, propylene, 1-butene, and longer-chain a-olefins using early and late transition metal catalysts. The resultant copolymer properties depend on different parameters, such as comonomer content and distribution throughout the polymer chain, as well as the conformational orientation of the comonomer units. The microstmcture of the copolymer can be controlled by the appropriate choice of reaction conditions and catalyst stmcture. The most powerful method to determine copolymer microstmcture is NMR spectroscopy. In the past years, much progress has been achieved in making peak assignments for olefin-norbornene copolymers. - ... 

Broadening this comparison to include copolymers prepared by both early and late transition metal catalysts, the results discussed immediately above show that Ci-symmetric zirconocenes such as 9/MAO produce only copolymers with isolated norbornene units or alternating structures (at 30 C), mainly with isotactic (meso) configurations. C2-symmetric zirconocenes such as 2/MAO readily produce norbornene dyads that are exclusively meso-linkcd (isotactic). In accordance with their catalyst structures, Q-symmetric zirconocenes such as 8/MAO produce norbornene dyads with a rac-linkage (syndiotactic), although with a generally lower stereoselectivity. Palladium a-diimine catalysts, despite the homotopic nature of their coordination sides (that would be expected to give a mixture of meso and racemic blocks), produce norbornene dyads that are solely rac-connected. This behavior can be attributed to a chain-end control type polymerization mechanism. 

High density polyethylene (HDPE) is defined by ASTM D1248-84 as a product of ethylene polymerisation with a density of 0.940 g/cm or higher. This range includes both homopolymers of ethylene and its copolymers with small amounts of a-olefins. The first commercial processes for HDPE manufacture were developed in the early 1950s and utilised a variety of transition-metal polymerisation catalysts based on molybdenum (1), chromium (2,3), and titanium (4). Commercial production of HDPE was started in 1956 in the United States by Phillips Petroleum Company and in Europe by Hoechst (5). HDPE is one of the largest volume commodity plastics produced in the world, with a worldwide capacity in 1994 of over 14 x 10 t/yr and a 32% share of the total polyethylene production. 

Only recently (2002) have the very first examples of the transition metal-catalyzed incorporation of acrylate monomers into linear polyethylene been demonstrated. In our opinion the most notable report is that of Drent and coworkers [48] who describe the use of a neutral palladium catalyst with a chelating P-O ligand to generate linear copolymers that included the incorporation of acrylate monomers (Drent s catalyst and proposed catalytic cycle are shown in Scheme 2). In these early results, there was only minor acrylate incorporation (limited to some 3-17 mol%) and the resulting polymers were of very low molecular weight (Mn 4000-15,000). 

The homo- and copolymerization of methacrylates and acrylates and the synthesis of block copolymers is also reported [108], Recently, it is reported that new organometallic compounds (late metals) also produce ethylene/MMA copolymers [54, 55]. The development of polymerization catalysts incorporating late transition metals is a promising area of research, since late metals are typically less oxophilic, and thus more functional group tolerant, than early metals. Examples of the functional group tolerance of late metals in insertion-type reactions include reports on Ru, Rh, Ni, and Pd catalysts. 

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