Micelle formation induced by disproportionation of stable nitroxyl radicals supported on a diblock copolymer

Micelle formation induced by disproportionation was attained for a diblock copolymer containing 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO). Poly(4-vinylbenzyloxy-TEMPO)-block-polystyrene (PVTEMPO-b-PSt) showed no self-assembly in 1,4-dioxane, a nonselective solvent. Light scattering studies demonstrated that the copolymer self-assembled into micelles in this solvent with the addition of hydrochloric acid (HCl). The hydrodynamic diameter of the copolymer was estimated to be ca. 55 nm based on the cumulant analysis of the complete micellization. A UV analysis confirmed that the micellizarion proceeded through the disproportionation of the TEMPO into the oxoaminium chloride and the hydroxylamine by the reaction with HCl, because the absorption based on the oxoaminium chloride increased with an increase in the amount of HCl. ESR verified that the radical concentration of the TEMPO decreased with an increase in the HCl. Before the addition of HCl, the PVTEMPO-b-PSt copolymer showed broad signals based on the random orientation. As the amount of HCl increased, the broad signals changed to the typical triplet of TEMPO, accompanied by a decrease in the signal intensity. The g values had a negligible change throughout the micellization. Finally, 40% of the TEMPO remained unreacted when the micellization was completed. The micellization prevented the dispropotionation of the TEMPO, because the PVTEMPO blocks formed the micellar cores which were covered with the micellar coronas of the PSt blocks. TEM observations demonstrated that PVTEMPO-b-PSt formed spherical micelles through the dispropotionation-induced micellization.