Addition polymers transition metal catalysis

In the first part of this section the elucidation of the mechanism will be presented, while the second part will be devoted to a discussion of the effect of cations on the viscoelastic properties. Both of these topics are grouped together because, as will be shown below, the relaxation mechanism of all the polymers discussed here is perfectly normal, i.e., simple molecular flow, [or the a mechanism according to the nomenclature of Ferry (27, 28, 29) and Hoff 37a), and the materials can thus be called chemically inactive. Finally, the work on viscoelasticity of bulk organic polyelectrol5des will be mentioned. The next section will be devoted to a discussion of the viscoelastic properties of materials in which, in addition to the a mechanism, bond interchange (the x mechanism) is also encoimtered, the chemical (hence x) activity being due to catalysis by transition metal ions. 

Metallocene catalysis is an alternative to the traditional Ziegler-Natta vanadium-based catalysis for commercial polyolefin production, e.g. the use of metallocene-catalyzed ethylene alpha-olefin copolymers as viscosity index modifiers for lubricating oil compositions [23]. The catalyst is an activated metallocene transition metal, usually Ti, Zr or Hf, attached to one or two cyclopentadienyl rings and typically activated by methylaluminoxane. Metallocene catalysis achieves more stereo-regularity and also enables incorporation of higher alpha-olefins and/or other monomers into the polymer backbone. In addition, the low catalyst concentration does not require a cleanup step to remove ash. 

Effects of a series of transition metal stearates, the concentration of the copper stearate, the solvent, various additives, and other factors on the thermal oxidation of polypropylene were studied in trichlorobenzene solution. The mechanism of copper catalysis is discussed. The order of decreasing catalytic activity of the metal stearates was Cu > Mn > Fe > Cr > Al Ni Co control Ti >> Zn >> V. The addition of propionic acid to the solvent accelerated the oxidation of the polymer. The presence of the copper leveled off oxygen uptake of the polymer after a certain time. The amount of oxygen absorbed decreased with increasing concentration of the copper, and at higher concentration (7.9 X 10 3M) the polymer oxidation was inhibited. 

A review on the industrial applications of homogeneous catalysts is particularly welcome. The proceedings of recent symposia and a general text have been published in addition to reviews on metal cluster catalysts, activation of saturated hydrocarbons by metal complexes in solution, catalysis by arene Group-VIB tricarbonyls, titanocene-catalysed reactions ofalkenes, transition-metal hydrides in catalysis, the mechanisms of the catalytic cyclization of aliphatic, hydrocarbons, asymmetric hydrosilylation and asymmetric synthesis. A n.m.r. study of the conformations of chelated Diop and a MO study of organo-metallic migration reactions are also of interest. Polymer supported catalysts have been reviewed and the relationship between cross-linking of the polymer and catalytic activity has been discussed. ... 

Vinylphosphines are a valuable class of compounds with a myriad of applications in organic synthesis and catalysis. Vinylphosphines also have a rich history in coordination chemistry due to the geometry and reactivity of this fragment with transition metal centers [414-420]. The proximity and flexibility of the alkene have been used to generate a host of coordination compounds in which the vinylphosphine is coordinated to the metal center through the phosphorus as well as through the alkene. In addition to providing a unique architecture for disCTCte coordination compounds, vinylphosphines are also valuable linkers in the formation of 3D arrays and coordination polymers [421-424],... 

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