Tests for Living Radical Polymerization

Following on from the above, various methods have been described to test and/or rank the livingness of polymerization processes. All of these tests have limitations.. The following list paraphrases a set of criteria for living polymerization set out by Quirk and Lee who also critically assessed their applicability primarily in the context of living anionic polymerization. 

The better living radical systems produce X / X in the range 1.05-1,2. Errors associated with measuring the dispersity can be significant and most cause an underestimate of the actual value. A low dispersity alone does not imply the absence of side reactions. 

Quirk and Lee concluded there is no single criterion which is satisfactory for determination of whether a given polymerization is living or not, Most of the radical polymerizations discussed in this chapter meet one or more of these criteria. 

The kinetics and mechanism of living radical polymerization have been reviewed by Fischer, Fukuda et a(. and Goto and Fukuda. In eonventional radical polymerization, new chains are continually formed through initiation while existing chains are destroyed by radical-radical termination. The steady state concentration of propagating radicals is -lO M and an individual chain will have a lifetime of only 1-10 s before termination within a total reaction lime that is 

It is not necessary that living radical polymerizations be slow. However, it follows from the above discussion that, for a high fraction of living chains, either the final degree of polymerization must be significantly lower than that in an otherwise similar conventional process or that conditions must be chosen such that the rate of polymerization is substantially lower. 

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One might also anticipate that the influence of bootstrap effects (Section 8.3.1.2) would be quite different in living and non-living processes. 68 A comprehensive study of reactivity ratios in living and conventional radical polymerization may provide a test of the various hypotheses for the origin of this effect. 

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