ABSTRACT
The value of PMv is higher than in the unimolecular case, but of the same order. Relatively fast mass loss has been observed at relatively low temperature; for
instance, in the photooxidation at 400 e (68), or in thermal oxidation at 500 e (39) for PP. This indicates that volatile products have a relatively low molar mass; thus, Pis not far from unity. Thus, we have to imagine very efficient mechanisms of volatile formation to explain the predominance of mass loss, for instance sequential back-biting reactions (68). A possible alternative could be, for instance, acetone release from Pscission (69) (Fig. 18). The efficiency of such a hypothetical process depends on the efficiency of the 1-2 hydrogen migration. This latter is thermodynamically favored because tertiary radicals are considerably more stable than primary ones, but indeed, the oxidation of primary radicals could be competitive.
