Living polymers, catalytic production

Consequently, a crucial goal that still remains to be realized is the catalytic production of living polymers that increase the polymer/catalyst ratio and thus enhance catalyst productivity. The catalytic production of living polymers is feasible if we develop FI catalysts that incorporate monomers without termination, even in the presence of a chain transfer agent, and which only undergo chain transfer in the absence of a reacting monomer. 

As far as the fate of 6.6 is concerned, there is a third possibility. The polymer chain may remain attached to the metal atom that is, the metal-alkyl bond remains intact. The product of the overall reaction in this case is 6.6. Polymerization of this type is often called living polymerization. Note that in this case there is no polymer chain termination step, and the catalytic cycle is not completed. In other words, although a single Ti4+ ion may be responsible for the polymerization of thousands of ethylene molecules, in the strictest sense of the term it is not a true catalytic reaction. In the event 6.6 is converted to 6.7 either by reaction with H2 or by /8-elimination, 6.7 further reacts with ethylene. Insertion of ethylene into the Ti-H bond regenerates 6.2 and completes the catalytic cycle. 

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