Organometallic radical anions preparation

Polymerization initiated by electron transfer from a metal, or by an aromatic radical anion, represents only one of the anionic mechanisms. It is, of course, possible to consider separately those polymerizations initiated directly by organometallic compounds. Of the latter, the organohthium compounds are probably the best examples, since they are soluble in a wider variety of solvents and are relatively stable. Furthermore, it is these organometallic compounds which are used commercially for the preparation of synthetic elastomers [161,162]. The mechanism of these polymerizations is somewhat simpler than in the case of sodium napththalene, since there is no electron transfer step thus... 

The first tin-centered radical has been isolated, though it is not strictly organometallic in the C-Sn bonded sense. It is prepared by the reaction shown in Equation (173), in which the SnCl2 acts both as a substrate for forming the stannyl anion and as a one-electron oxidizing agent. 

The core first method starts from multifunctional initiators and simultaneously grows all the polymer arms from the central core. The method is not useful in the preparation of model star polymers by anionic polymerization. This is due to the difficulties in preparing pure multifunctional organometallic compounds and because of their limited solubility. Nevertheless, considerable effort has been expended in the preparation of controlled divinyl- and diisopropenylbenzene living cores for anionic initiation. The core first method has recently been used successfully in both cationic and living radical polymerization reactions. Also, multiple initiation sites can be easily created along linear and branched polymers, where site isolation avoids many problems. 

Another possible precursor to conduct free radical reactions is the glycosyl-cobait(III) dimethylglyoximato complex 33 [22,23], These organometallic compounds can readily be prepared by the displacement of the halide atom in 17 with the highly nucleophilic cobalt(I) anion 32. The latter can be generated from the dimeric Co(II) complex 31 under reducing conditions. 

Addition polymerization of ferrocene-containing vinyl monomers is probably the earliest preparation method that has been widely studied. Vinylferrocene 1 [5], the first organometallic monomer, was synthesized in 1955 and its polymerization behavior has been extensively studied under radical [5, 6], cationic [7], and Ziegler-Natta conditions [7] it is inert to anionic initiation [8]. 

One of the primary factors slowing the growth of functional polymers has been the relative complexity and cost of their preparation. The synthesis of functional polymers is often made difficult because of chemical or phase incompatibilities or antagonisms. This chapter surveys the general methods for functional polj er syntheses. It reviews the scope and limtations of functionalization by direct polymerization (e.g. anionic, cationic, free radical and organometallic methods), as weU as post-polymerization bulk and surface modification of preformed backbones. 

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