Primary radical termination cyanoisopropyl radicals

Primary Radical Termination. Primary radical termination refers to the bimolecular reaction between a propagating radical and a primary, initiator-derived radical. This process leads to lower rates of initiation and propagation, thus causing a deviation from the predictions of classical kinetics (377). In analogy with the termination reactions between propagating radicals, primary radical termination can also occur by either combination or disproportionation. It has been shown that primary radical termination between cyanoisopropyl radicals and polystyryl radicals occurs mainly via combination at 98°C with extremely... 

Barton et al.1X7 have reported that primary radical termination between PBMA and cyanoisopropyl radicals (7) involves largely disproportionation. 

Primary radical termination may involve combination or disproportionation with the propagating radical, it is often assumed that small radicals give mainly combination even though direct evidence for this is lacking. Both pathways are observed for reaction of cyanoisopropyl radicals with PS (Scheme 3.14) (Section... 

The secondary benzoate (4) is labile below 300°C whereas the primary benzoate (3) is stable. Both the model compounds were found to be labile at 300°C. Hence it can be concluded that the stability of the polymers is direcdy related to the stability of the respective benzoates. Tliis study clearly shows the effect of one weak link per chain on the polymer properties. An additional route to secondary benzoates is discussed below under termination. In related studies on styrene we have established that both the cyanoisopropyl radicals (from AIBN) and t-butoxy radicals are much more selective in this system and add virtually exclusively to the tail to give polymers tliat are thermally stable. 

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