Alkoxyamines, thermolysis

TMDBIO for the alkyl radicals formed by initiator (hydroperoxide) thermolysis. The further quantitation of this reaction is difficult without assuming a kinetic model or obtaining further analytical information such as the actual concentration of nitroxide that has reacted during the retardation reaction. In the special case of the pro-fluorescent nitroxide, this can be achieved by fluorescence analysis of the formed alkoxyamine R2NOP. 

Alkoxyamine chain ends have also heen removed hy reaction with maleic anhydride and maleimide derivatives. Pyrene-functionalized polystyrene was prepared by reaction of an alkoxyamine-terminated PS with a pyrene-suhstituted maleimide. The functionality of the polymer was determined by a combination of GPC, TGA, and UV-vis spertroscopy. This technique requires the synthesis of a new functionalized maleic anhydtide/maleimide for each functional group desired. Thermolysis of the alkoxyamine chain end in the presence of an enol ether such as a-benzyloxystyrene results in a phenyl ketone-functionalized polymer in low yield (34%). ... 

An important side reaction which complicates the thermolysis of alkoxyamines and particularly the NMP of methacrylates, is the intermolecular jS-hydrogen transfer (kn ) from the propagating radicals to the nitroxide, also called disproportionation (path (a), Scheme 4.7 or reaction (4.8), Scheme 4.5). 

Consequently, all the alkene 12 detected under such conditions was formed by the Cope-type elimination (b). On the other hand, alkene formed in the absence of thiophenol was generated by both paths. Recently, Marque et al showed that thermolysis of alkoxyamines in the presence of the scavenger PhSH induces chemically induced dynamic nuclear polarization (CIDNP). The CIDNP effect, detected by H-NMR, indicates that the intermolecular H-transfer occurs, in contrast to earlier reports,already in the spin correlated geminate (cage) radical pair, formed immediately after the cleavage of the NO C bond. 

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