Vanadium carbonates

All the proposed models for syndiotactic propagation suppose that the active center is a vanadium-carbon bond and that the monomer first coordinates to the metal. Moreover, all of them attribute the stereospecificity to steric factors. However, different driving forces for the syndiospecificity have been proposed. 

The authors believe that the results are more readily explainable on the basis of a two-point absorption involving the vanadium-carbon-sulphur complex, the formation of which may be effected with little distortion of the tetrahedral valence angles. 

The reactivity ratio rQ is almost independent of the catalyst used, whereas r, is strongly dependent upon the catalyst and lowers with a decrease in the syndiotactic-specificity of catalyst. Thus, the regioselectivity of secondary insertion of propylene into a secondary vanadium-carbon bond (rj = ku/k10) correlates closely with the syndiotac-... 

As will be described in Section 5.3, the living polypropylene can be terminated with iodine to give an iodine-bonded monodisperse polypropylene. The analysis of the iodine-terminated polypropylene gives us an information on the structure of the active vanadium-carbon bond because a vanadium is replaced by an iodine atom. The following structure (4) of end groups has been observed in the H NMR spectrum of iodine-terminated polypropylene 98). 

The radical end (7) may be formed via homolytic decomposition of the vanadium-carbon bond in the presence of MMA and be stabilized by the vanadium ion. This stabilization is likely to cause a living radical polymerization of MMA. A similar conclusion has been reached by Lee et al. 113) who found that a mixture of chromium acetate with benzoyl peroxide initiated a living radical polymerization of MMA at low temperatures below 30 °C. 

Figure 3 Section of phase diagrams of the group 5 transition metal-carbon systems, (a) vanadium-carbon (b) niobium-carbon (c) tantalum-carbon. (Reprinted from Ref. 22. 1998, with permission from Elsevier)...

The dinuclear enolate complex (105) is then formed by treatment of (104) with carbon monoxide, which inserts into the vanadium-carbon bonds. 

V(CO)6 and [V(CO)6] are both octahedral. Which has the shorter carbon-oxygen distance The shorter vanadium-carbon distance ... 

The laser-induced plasma reactor initially used by Castleman s group to produce titanium-carbon and vanadium-carbon cluster cations has been described in de-... 

Figure 14. Partial phase diagrams of the systems titanium-carbon [51] and vanadium-carbon [52]. In the latter diagram, regions with short-range (SRO) and long-range order (LRO) ate indicated.

Fle] Flender, H., Wever, H., Activity of Carbon in the Iron-Vanadium-Carbon and Iron-Chromium-Carbon Systems (in German), Arch. Eisenhuettenwes., 34(10), 727-723 (1963) (Thermodyn., Experimental, 23)... 

Oya2] Oya, M., On the Equilibrium Diagram of the Iron-Vanadium-Carbon System , Sci. Rep. 

Wev] Wever, F., Rose, A., Eggers, H., Contribution to the Iron Comer of the Iron-Vanadium-Carbon Ternary System (in German), Mitt. Kaiser Wilhelm Institute Eisenforsch., 18, 239-246 (1936) (Phase Diagram, Phase Relations, Experimental,, 7)... 

Sut] Sutton, H.C., Whiteman, J.A., Structure and Mechanical Properties of Isothermally Transformed Iron-Vanadium-Carbon Alloys , J. Iron Steel Inst., 209(March), 220-225 (1971) (Crys. Structure, Morphology, Experimental, Meehan. Prop., 10)... 

A Catka, JS Williams. NanocrystaUine to microcrystalline transformation of ball milled vanadium carbon mixtures The effect of temperature and pressure. Spectra Metall Mater 27 999, 1992. 

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