Preparation and Characterization of Highly Water-Soluble Pendant Fullerene Polymers

Pendant fullerene polymers were prepared by attaching methano[60]fullerene carboxylic acid (MFCA) and methano[60]fullerene phenylpropyl carboxylic acid (MFPCA) to linear poly(propionylethylenimine-co-ethylenimine) (PPEI−EI) via amide linkages in carbodiimide-catalyzed coupling reactions. The pendant MFCA−PPEI and MFPCA-PPEI polymers, which were characterized using NMR, gel permeation chromatography, FT-IR, and other instrumental methods, most likely have a “charm bracelet” type structure without significant cross-linking. MFCA and MFPCA were also coupled with diethylamine in the same carbodiimide-catalyzed reactions, and the methano[60]fullerene amides thus obtained were used as monomeric model compounds for the pendant polymers. UV−vis absorption spectra of the polymer-bound fullerenes, though broader, retain the characteristic features observed in monomeric methano[60]fullerene derivatives. The pendant MFCA−PPEI and MFPCA−PPEI are highly water-soluble, with the equivalent aqueous solubilities of the polymer-bound fullerene cages significantly higher than that of the parent [60]fullerene in room-temperature toluene. Thus, the preparation of pendant fullerene polymers represents an effective approach for introducing fullerene cages into an aqueous solution or hydrophilic environment.