In contrast, Oppenlander and Xu  obtained different results using a flow photoreactor with UV irradiation at 172 nm, in which the HO* radicals were produced by water homolysis
. They obtained a rate of reaction that was essentially independent of the temperature for the decolorisation of RhB; that is, basically the activation energy was zero.
(36) present a study on light aging properties of PVC by the carboxylic ester rare earth salt and the organotin, which reveals that radicals S--R generated from homolysis
of Sn-S are combined to form R-S-S-R, which is an effective decomposer of hydroperoxides.
The thermal homolysis
of the initiator leads to the formation of the primary radicals.
A model study in hexadecane showed that the mechanism involves the selectivity of TEMPO for radical termination with carbon-centered radicals formed after peroxide homolysis
and propagation steps before peroxide-initiated crosslinking.
Peroxide yields, defined as the moles of VTEOS grafted per mole of cumyloxy radicals generated by DCP homolysis, varied from a low of 22 grafts per radical at a peroxide loading of 0.15 wt%, to a high of 66 when just 0.015 wt% of initiator was employed.
Simplified treatments of the initiation process attribute macroradical formation to hydrogen atom abstraction by the oxygen-centred radicals derived from peroxide homolysis. These electrophilic species  prefer hydrogen atom abstraction to addition to electron deficient olefins, whereas the opposite tendencies are observed for the nucleophilic methyl radicals derived from cumyloxy radical fragmentation [20, 21].
Since the rate constant for DCP homolysis is known, the application of this expression to VTEOS conversion profiles requires estimates of three parameters ([k.sub.tr], [k.sub.g], and f/[k.sub.t]).
The mechanism for metal cluster formation probably involves the homolysis
of Me-S bonds, with formation of zero-valence metal atoms and sulfur radicals, SR.
According to Grassie and Farish (14), mechanism of the thermal degradation of polystyrene consists of chain homolysis
and disproportionation below 300 [degrees] C.