Vanadium catalysts ethylene

In syndiospecific polymerization using soluble vanadium catalysts, defects of the chemical addition are noticeable, their number being consistent with the Markoff first — order distribution 59-6i.63> jjj jjjjg regioselectivity as well as stereospecificity are greatly influenced by the possibility of the secondary insertion of monomer The chiratity of the last monomeric unit of the growing polymer determines the stereocontrol of syndiotactic polymerization. The introduction of an achiral (ethylene) unit results in the loss of stereocontrol As active center of syndio-... 

A limited kinetic investigation has been carried out on promotors for vanadium catalysts (VO(Ot-Bu)3/Al2Et3Cl3) in ethylene polymerization [234]. It was shown that esters of trichloroacetic acid, added continuously during the polymerization, reactivated the catalyst and permitted polymerization to be carried out at 120°C. Under these circumstances over 250 polymer chains were produced per vanadium atom and the polymers had /Mn ratios close to 2.0, which would be anticipated for a single catalytic entity. 

With the VCl4/Al(Hex)3 catalyst the ratio of the rates of polymerization of ethylene and propene is ca. 1800, considerably larger than that found for more active catalysts for propene polymerization, such as TiCl4 /AIR3. The lai e ratio for the vanadium catalysts is because most of the catalyst sites cannot initiate the polymerization of propene, although once they have added a molecule of ethylene they can subsequently add either ethylene or propene. In conformity with this view it is found that the soluble portion of the catalyst will polymerize ethylene but not propene. The overall activation energy for copolymerization with VCI4 /Al(Hex)3 was found to be 6.5 kcal mole and to be the same as for the two individual monomers [194]. 

In addition to titanium-based Ziegler-Natta catalysts, vanadium-based systems have also been developed for PE and ethylene-based co-polymers, particularly ethylene-propylene-diene rubbers (EPDM). Homogeneous (soluble) vanadium catalysts produce relatively narrow molecular mass distribution PE, whereas supported V catalysts give broad molecular mass distribution.422 Polymerization activity is strongly enhanced by the use of a halogenated hydrocarbon as promoter in combination with a vanadium catalyst and aluminum alkyl co-catalyst.422,423... 

Derivation (1) Condensation of ethylene oxide with hydrocyanic acid followed by reaction with sulfuric acid at 320F (2) acetylene, carbon monoxide, and water, with nickel catalyst (3) propylene is vapor oxidized to acrolein, which is oxidized to acrylic acid at 300C with molybdenum-vanadium catalyst (4) hydrolysis of acrylonitrile. 

This synthesis has been adapted to make the natural (5 -isomer of 114, reducing the initially formed aldehyde to (S)-114 with baker s yeast. [This same synthesis has been adapted to make (S)-callosobruchic acid (115), see below]. Julia s synthesis of a-geraniol (73) was also extended to make 114 by hydro-boration. Hydroboration of 73 with diisopinocampheylborane (made from (- )-a-pinene [(-)-116]) gave only a small ee however. A synthesis of ( )-114 started with the reaction of 2-methylpropiolactone and the ethylene acetal of 3-oxobutylmagnesium bromide. The methyl ester of the acid 117 thus prepared was chain-lengthened by reaction with acetylene and rearrangement with a vanadium catalyst of the ynol thereby obtained. The aldehyde 118 was then reduced with lithium aluminum hydride to 114. ... 

As opposed to the problems associated with the formation of sequential block copolymers, the preparation of relatively random copolymers is much easier and the provision of polyethylenes having a controlled degree of branching by copolymerization with propylene and butene is now a well-established commercial operation. When ethylene and propylene are employed in approximately equal proportions the ethylene-propylene rubbers are obtained. For this purpose strictly random copolymers are desirable, for which soluble vanadium catalysts are often preferred (20). With TiCls-based catalyst the propylene monomer molecule prefers to add to a propylene end unit rather than to an ethylene end unit (and vice versa). This tends to produce nonrandom blocky copolymers. Thus a recent paper by Coover ef al. (21) selects as catalysts formulations which maximize this tendency and achieve the preparation of block copolymers in a TiCl3/AlEt2Cl catalyst system in the presence of butene and propylene together. 

Another use of vanadium is as a catalyst in a variety of reactions. Vanadium pentoxide, ivhen placed on an inert support material, is the principal catalyst used in the oxidation of SO2 to SO3 in the production of sulfuric acid, and for the conversion of naphthalene into phthalic anhydride during the formation of plastics. In addition, vanadium oxychloride, tetrachloride and triacetylacetonate are used as polymerization catalysts in the production of soluble copolymers of ethylene and propylene. In the reaction vessels, these polymers are viscous liquids, which can trap the vanadium catalysts and result in a vanadium content of up to 500 mgkg in products used for the packaging of food and pharmaceuticals. The disposal of spent catalysts could also be a point source for a contamination of the biosphere and of food with vanadium (Byerrum 1991). Furthermore, vanadium is used for the production of yellow pigments and ceramics. 

Recently, efforts have been made to expand the number of homogeneous vanadium catalysts using ancillary, nonreactive ligands. These catalysts may be in the -e5, +4 or q-3 oxidation states. The dianionic imido ligand is isolobal with cyclopentadienide and has been used to prepare diamagnetic, formally d° metal compounds like (10) (Figure 13) which, when activated by MAO, display modest activity for ethylene polymerization. VCI3 complexes of Q -diimines... 

With respect to titanium catalysts for polymerization of ethylene or propylene, Ziegler synthesized the first high-density polyethylene and Natta prepared isotactic polypropylene by means of coordination catalysts about 50 years ago. The preparation methods of catalysts have been studied extensively. These TiCL3 catalysts have very high activity for homopolymerization of ethylene and propylene, whereas, they exhibit low activity for random copolymerization of ethylene with propylene when compared to vanadium catalysts. Refer to Ziegler-Nata Catalyst, Vanadium Catalysts, and EP Terpolymer, (Source Elastomer Technology Handbook, N. P. Cheremisinoff - editor, CRC Press, Boca Raton, Florida, 1993). 

I. Jaber, S.J. Brown, Mixed titanium-vanadium catalysts for solution ethylene polymerization, U.S. Patent 6084042 of 04 July 2000 (filed 29 June 1998) CA 2271680 of 24 Nov 2009 ... 

Reinking and co-workers have raised the possibility that at least some of the LCB seen in metallocene-based polymers may arise from an unusual aliphatic C—H activation of dissociated ( dead ) polymer molecules (eq. 25) (As part of a study of non-metallocene vanadium catalysts, see Ref 164). In this study, abridged bis(indenyl) zirconocene was found to incorporate ethylene units into the heptane solvent, while an unbridged version, (n-C4H9Cp)2ZrCl2, did not. 

The mechanical properties of these branched polymers are assumed to differ from those of metallocene/MAO-based COCs. " Other amorphous copolymers of norbornene and ethylene are also available using less active vanadium catalysts. ... 

Early attempts to produce E/NB copolymers utilized heterogeneous TiCl4/AlEt2Cl or vanadium catalysts, but real progress was achieved utilizing metallocene catalysts for this purpose. Metallocenes are about ten times more active than vanadium systems, and by choosing the metallocene, the norbornene/ethylene comonomer sequence distribution in the copolymer may be varied from statistical (random) to alternating. 

Copolymerization of these cyclic olefins with ethylene or a-olefins cycloolefin copolymers (COC) can be produced, representing a new class of thermoplastic amorphous materials [217-220]. Early attempts to produce such copolymers were made using heterogeneous TiCl4/VAlEt2Cl or vanadium catalysts, but first significant progress was... 

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