The application of chromophoric radical spin traps for highly sensitive UV-vis monitoring of conversion of radical enhanced spin capturing polymerizations (ESCP) is presented. In ESCP the growing macroradical is reacting with a nitrone providing the corresponding polymeric nitroxide radical spin trap which will react irreversibly with a second macroradical to eventually give a polymeric alkoxyamine. The progress of styrene and n-butyl acrylate ESC polymerizations in the presence of pi-conjugated nitrones is successfully visualized via a significant change of absorbance of the nitrone chromophore in the 200-500 nm range due to the nitrone transformation into an alkoxyamine moiety upon incorporation into the polymer. Moreover, related studies on UV-vis monitoring of photochemical rearrangement of nitrones to their corresponding oxaziridines are discussed.