Cyanoalkyl radicals, rate

Absolute rate constants for addition reactions of cyanoalkyl radicals are significantly lower than for unsubstituted alkyl radicals falling in the range 103-104 M V1.341 The relative reactivity data demonstrate that they possess some electrophilic character. The more electron-rich VAc is very much less reactive than the electron-deficient AN or MA. The relative reactivity of styrene and acrylonitrile towards cyanoisopropyl radicals would seem to show a remarkable temperature dependence that must, from the data shown (Table 3.6), be attributed to a variation in the reactivity of acrylonitrile with temperature and/or other conditions. 

A number of reportsindicate that primary radical termination can be important during polymerizations initiated by azonitriles. However, for the case of S polymerization initiated by AIBN, NMR end group determination shows that primary radical termination is of little importance except when very high rates of initiation are employed (e.g. with high initiator concentrations at high temperatures). Cyanoalkyl radicals give a mixture of combination and disproportionation in their reactions with other radicals (see also Sections 2.5,... 

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