Dispersion of Fullerenes in Water and Organic Solvents by Cyclized Pluronic and PEG

Fullerene attracts much interest due to its potential in optoelectronic and biomedical applications. However, its insolubility in water and in many common organic solvents hinders further development. Herein, cyclized Pluronic L64 and 17R4 and cyclized poly(ethylene glycol) (PEG), namely, c-L64, c-17R4, and c-PEG, respectively, were used to disperse C60 and C70 in water as well as in ethanol and acetone, and the dispersion was shown to be governed by the polymer topology. Through simple ultrasonication in the presence of the cyclized polymers followed by centrifugation, C60 and C70 were dispersed without covalent modification of the fullerene structure. Under identical dispersion conditions, the cyclized polymers consistently outperformed their linear counterparts bearing either hydroxy or methoxy end groups: 1 g of c-L64 dispersed 0.53 g of C60, whereas HO-L64-OH and MeO-L64-OMe dispersed only 0.14 and 0.05 g, respectively, corresponding to a roughly 4-fold enhancement upon cyclization. The same topology-dependent trend was observed for the Pluronic 17R4 and PEG series and for C70, and it was accompanied by a smaller cluster size for every cyclized dispersant, as determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Notably, this is the first dispersion of fullerene by a cyclized PEG homopolymer without any chemical modification, achieved solely by the topological transformation. Moreover, the complexes of fullerene and the cyclized polymers were redispersed in ethanol and acetone. Finally, because the fullerene structure remained intact, the dispersions exhibited a superior •OH radical scavenging ability compared with water-soluble polyhydroxylated fullerene, in which a substantial proportion of the π-conjugation was lost. This research proposes a facile dispersion method for intact fullerene based on the polymer topology effect, with potential biological applications such as photodynamic therapy and drug delivery systems.