Radical polymerizations and copolymerizations were carried out in the presence of phenyl tert-butyl nitrone(PBN) and tert-nitrosobutane (t-BuNO), and the structure of the spin adduct formed was investigated by ESR spectroscopy. The polymerization mixture of representative monomers showed ESR patterns that are indicative of the propagating radical being trapped. These trapped radicals were not necessarily very stable and, in most cases, disappeared after long reaction periods. Simultaneous trapping of different propagating radicals was attempted in several copolymerization systems. However, this was generally unsuccessful, because of the large difference in reactivities of the propagating radical with t-BuNO.
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