Solubility and Micellization Behavior of C₆₀ Fullerenes with Two Well-Defined Polymer Arms

Abstract

1,4-Disubstituted, low-polydispersity C60 derivatives of the types C60−(PS)2, C60−(PVP)2, and C60−(PS−PVP)2, where PS is polystyrene, PVP is poly(p-vinylphenol), and PS−PVP is a diblock copolymer of this sequence, were prepared by applying the nitroxide-controlled free radical polymerization technique and studied with their solubility behaviors in some organic solvents. The first clear experimental evidence was obtained for the formation of multimolecular micelles of C60-bearing polymers under certain conditions: for example, light-scattering measurements showed that the C60−(PVP)2, C60−(PS−PVP)2, and C60−(PS)2 samples with a number-average molecular weight of a polymer arm roughly about 10 000 formed stable micelles in dilute tetrahydrofuran (THF) solution with association numbers of about 20, 6, and 1 (no micellization), respectively. The solvent power of THF for the mother polymers increases in this order. The saturation solubilities SC60 of the C60 moiety in C60−(PS)2 and C60−(PVP)2 were determined as a function of the PS and PVP chain lengths, showing that, in THF, the SC60 in the PS adduct is exceptionally large, much larger than that in the PVP adduct of the same chain length, in accord with the mentioned micellization tendency in dilute solution. On the other hand, C60−(PVP)2 showed a reasonable solubility in a polar solvent (methanol), in which C60−(PS)2 was little soluble. The micellization was found to be accompanied by characteristic changes in the UV−vis spectra, depending on micelle size.